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Emery and other abrasives
June, I894..]
Emery and other Abrasives.
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without any rims whatever, are r e c o m m e n d e d by all dealers in advanced gas light fixtures. Lastly, the position of the glass globe in reference to the gas flame is of a good deal of importance where it is desired t o secure a steady, bright light. It has been found long ago, by experiment, that by arranging a shadowless globe holder on the burner in such a m a n n e r as to place the level of the bottom of the flame in line with the bottom edge of the globe, the flame will burn very quietly and steadily, and will not be affected much, if any, by the ascending air current, whereas if the flame is set higher it is apt to flicker. This correct position and shape of a glass globe has been pointed out repeatedly by such gas engineers as Wilder, Peebles, Sugg, Broenner, Silber and others, in connection with their gas burning appliances; but on the whole, in practice, little attention has been paid to this simple yet efficient rule. [ To be concluded.]
E M E R Y AND O T H E R A B R A S I V E S . ~ BY T. DUNKIN PARET, President of t h e Tanite Company.
[ Concluded from p. 372.]
While small specimens of corundum, in the form of imperfect sapphires, have come from Montana, where the existence of this mineral has long been known, no other locality has yielded corundum except that well-known belt which reaches from Massachusetts to Georgia, and which seems to have its center in the corner where North and South Carolina, Georgia and Tennessee come together. In this belt the localities where corundum occurs are innumerable, but the prevalence of the mineral is a poor indication of its quantity. Corundum occurs in pockets, seams, sand veins, narrow streaks and detached crystals, seldom in large mass. Chester County, Pa., is, apparently, the only locality where large solid masses have been found. The
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[J. F. I.,
l a r g e s t a n n u a l p r o d u c t of A m e r i c a n c o r u n d u m has been 645 tons, and, t h o u g h c o r u n d u m m i n i n g companies h a v e multiplied r a p i d l y d u r i n g the last few years, the c o m m e r c i a l s u p p l y has never been more precarious. Unlike c o r u n d u m , e m e r y consolidates i n large m a s s e s . It does not, indeed, forth c o n t i n u o u s beds of g r e a t extent, like coal or iron, b u t its d i s c o n t i n u o u s masses and veins sometimes contain h u n d r e d s of tons. T h e e m e r y - b e a r i n g locality in W e s t c h e s t e r County, N. Y., is a strip from one-half to three-fourths of a mile in width, a n d from five to six miles in length. T h e g e o l o g y of this district and the occurrence of e m e r y in i~ m i g h t be described in a l m o s t the same l a n g u a g e as t h a t w h i c h Dr. S m i t h applies to the celebrated e m e r y district near E p h e s u s in A s i a Minor. Dr. S m i t h ~ says " a l l t h e rocks of the s u r r o u n d i n g c o u n t r y a p p e a r to belong to the old series ; the l i m e s t o n e is e n t i r e l y devoid of fossils and m e t a m o r p h i c in c h a r a c t e r ; i t rests on the older schists of w h i c h mica schist appears t h e m o s t a b u n d a n t ; and this a g a i n f a r t h e r to the n o r t h was traced in contact w i t h gneiss. T h e l i m e s t o n e is of a l i g h t blue p a s s i n g into coarse-grained m a r b l e . " " T h e place, however, to which it is traced in g r e a t e s t a b u n d a n c e , is on a p a r t of the s u m m i t a b o u t three miles from the village of G u m u c h , and some 1,5oo to 2,00o feet above the level of the v a l l e y ; it overlooks the m a g n i f i c e n t plain of the Miandre, whose curiously t o r t u o u s course is seen as if traced on a map. T h e e m e r y lies s c a t t e r e d on t h e surface ~ ~ ~ in a n g u l a r f r a g m e n t s of a dark color, a n d large masses of several tons w e i g h t are seen p r o j e c t i n g above the surface ; in p e n e t r a t i n g the soil, the e m e r y is f o u n d e m b e d d e d in it and a little f u r t h e r down i t is come to in the rock." " S o m e times the e m e r y forms a solid mass several y a r d s in l e n g t h and b r e a d t h . " In d e s c r i b i n g the W e s t c h e s t e r C o u n t y e m e r y beds, we would say t h a t the place in w h i c h the l a r g e s t n u m b e r of openings have .been made, and w h i c h has excited the m o s t interest, is on a p a r t of the s u m m i t a b o u t t h r e e miles f r o m A~n. Jour. Sci. and A r l s .
2, x, 356.
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the t o w n of Peekskill, and a b o u t 700 to 8o0 feet above tide level. It overlooks on the one side, the valley of the Croton, whose Stream is invisible, a n d on the other side, the H u d s o n , whose d i s t a n t waters look like some lake in a painting. On t h e n o r t h and n o r t h e a s t of the e m e r y belt a r e outcrops of granite. S o u t h of it lies the c o m m o n marble of Sing S i n g - - s t i l l f u r t h e r south, at S p u y t e n Duyvil, occur t h e oldest of t h e L a u r e n t i a n gneisses, and still f u r t h e r south, on M a n h a t t a n I.sland, t h e mica schist. T h e e m e r y is, however, all i m m e d i a t e l y associated w i t h a h o r n b l e n d e rock. L a r g e masses of e m e r y are seen p r o j e c t i n g above the sur•face. T h e s e are delusive, and those which hold out a large promise are s o m e t i m e s f o u n d to e x t e n d only one or two feet u n d e r g r o u n d a n d to yield only five to t w e n t y tons. Such masses are u s u a l l y s u r r o u n d e d by soft, reddish earth. 'Dr. S m i t h says of the T u r k i s h locality, " t h e earth in t h e n e i g h b o r h o o d of the blocks of e m e r y is a l m o s t always of a red color, and serves as an i n d i c a t i o n to those who are in search of the mineral." In W e s t c h e s t e r , the red e a r t h is not an indication, for there is w i t h i n the e m e r y belt an iron-beari n g rock w h i c h decomposes v e r y r a p i d l y and forms a red earth, while t h e r e is no emerv associated w i t h it. T h e r e is no sign of f r a c t u r e in these d i s c o n t i n u o u s masses of moderate size, and t h e y occur on the very tops of hills and u n d e r such c i r c u m s t a n c e s as to indicate t h a t t h e y are not boulders and have not broken down from h i g h e r cliffs. As in T u r k e y , so also here, " i n p e n e t r a t i n g the soil, the e m e r y is f o u n d e m b e d d e d in it, and a little f u r t h e r down it is come to in the rock." Small f r a g m e n t s t u r n e d up by the plow in c u l t i v a t e d melds are s o m e t i m e s the first indications. Search in their n e i g h b o r h o o d reveals o t h e r f r a g m e n t s e m b e d d e d in t h e earth, and near these and lower is f o u n d the rock. Somet i m e s this o n l y approaches the surface and forms such a small point t h a t it m i g h t lie u n d i s c o v e r e d for years. In one place discovery on the surface of a very fine grained, pure block, w e i g h i n g a b o u t 200 pounds, s t i m u l a t e d search which was c o n t i n u e d at intervals, fruitlessly, for several years. O t h e r varieties were discovered, b u t no sample like the original. Several blasts were m a d e Within a few feet of the nat-
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[J. F. I..
r o w p o i n t w h i c h j u s t fell s h o r t of r e a c h i n g the surface, and y e t did n o t disclose it. A l u c k y b l a s t u n c o v e r e d it, and over Ioo tons of u n i f o r m q u a l i t y w e r e taken out, l e a v i n g it far from exhausted. A s in T u r k e y , so also here, " t h e e m e r y lies s c a t t e r e d on t h e surface ~ ~ ~ in a n g u l a r fragm e n t s of a dark color," b u t a t this p o i n t m y description m u s t differ from t h a t of Dr. Smith. H e says : " i n no place does it p r e s e n t a n y t h i n g like a vein, nor has it signs of stratification." I find, in W e s t c h e s t e r , t h a t the a n g u l a r pieces g e n e r a l l y indicate veins. S u c h veins are distinct and n u m e r o u s . T h e r e g u l a r i t y w i t h w h i c h t h e y thin o u t at t h e e d g e s and thicken at t h e centre s u g g e s t s true lenticular beds, t h o u g h there are, of course, e x c e p t i o n s to the rule. T h e q u i t e r e g u l a r recurrence of s e a m s separated, b u t parallel, s t r o n g l y s u g g e s t s stratification. T h e s e s e a m s occur in t h e solid rock and the e m e r y b r e a k s freely from it, it b e i n g a m o s t u n u s u a l t h i n g to find a n y a d h e r e n c e of t h e top o r b e d rock. E m e r y from veins breaks easily, w i t h flat sides and sharp angles. T h e s e sides, when dry, often s e e m painted, so b r i g h t are t h e y w i t h yellow and red, and s o m e t i m e s t h e y take on an a l m o s t iridescent tint, w i t h s h e e n of pink and green. S t r a n g e l y e n o u g h , large a m o r p h o u s m a s s e s are s o m e t i m e s found, d i s c o n n e c t e d from rock, a n d l y i n g b e t w e e n t h e r e g u l a r veins. T h e s e a m o r p h o u s masses, w h e t h e r t h e y be small or large, p r e s e n t no a n g u l a r outlines, and do n o t b r e a k up in such flat-sided pieces as do t h e seams. It s h o u l d b e n o t e d t h a t t h e a n g u l a r i t y of t h e vein e m e r y is n o t due to its b e i n g freshly mined. T h e b r o k e n - d o w n e d g e s of veins, f o u n d in f r a g m e n t s on the hill-sides far b e l o w the veins, and w h i c h h a v e w e a t h e r e d for h u n d r e d s or t h o u s a n d s of years, s e e m as sharp and u n a l t e r e d as t h o s e freshly broken. T h e a m o r p h o u s masses, on the o t h e r hand, are so d e s t i t u t e of cleavage t h a t c o n t i n u e d u s e of a h e a v y sledge h a m m e r only b a t t e r s t h e m into shapeless pieces. The e m e r y in each vein is of c o m p a r a t i v e l y u n i f o r m q u a l i t y t h o u g h differences can s o m e t i m e s b e d e t e c t e d in blocks l y i n g side b y side. T h a t in the a m o r p h o u s m a s s e s varies far more. One such mass, of y e t u n a s c e r t a i n e d quality, I
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estimate, b y a r o u g h calculation of its cubic contents, to contain from 5oo to 7oo tons. T h i s m a s s was j o k i n g l y christened b y the miners as " K n i g h t ' s bonanza." It was of a light g r a y i s h color, not m a r k e d l y different from the top and b e d rock, from w h i c h it stood o u t almost s e p a r a t e l y on all sides, a n d like those rocks, was covered with gray moss. T h e o w n e r decided t h a t all t h e rock was alike and e s t i m a t e d t h a t there were h u n d r e d s of t h o u s a n d s of tons. T h e e m e r y of this district p r e s e n t s easily discernible differences. S o m e is coarse grained, some fine, some black and shiny, s o m e gray. Some is u n i f o r m in color, s o m e d i s t i n c t l y streaked. T h i s d e p o s i t was d e s c r i b e d a b o u t t w e n t y years ago b y Dr. J. P. Kimball, and his classification agrees with m y own. H e describes t w o classes as " g r a n u l a r , massive, resinous," g i v i n g a slightly different analysis for each. I should s a y one coarse and one fine. A third he describes as a " b a n d e d variety, g r a y in g e n e r a l color, and sparkling, from t h e presence of a m i c a c e o u s mineral." A fourth, as a " q u a r t z o s e variety, g r a y and sparkling, like n u m b e r three b u t w i t h o u t a b a n d e d or gneissic structure." I n a s m u c h as t h e " E m e r y M a n u f a c t u r e r s ' A s s o c i a t i o n " has issued a circular referring to t h e p r o d u c t of these m i n e s as " a spurious article of emery," and referring to its ore as " i n f e r i o r or c o m p a r a t i v e l y w o r t h l e s s stone," the opinion of Dr. K i m b a l l is w o r t h consideration. It deserves additional w e i g h t b e c a u s e his i n v e s t i g a t i o n h a d no reference w h a t e v e r to t h e use o f this ore as an abrasive. It was solely with t h e view of its u s e in iron m e t a l l u r g y t h a t his s t u d y was made. T h e analyses he refers to were m a d e by Dr. C. F. Chandler and Mr. F. A. Cairns. Dr. K i m b a l l says, " T h e a b o v e analyses, t o g e t h e r w i t h the physical and mineralogical f e a t u r e s of this material, serve to identify its c h a r a c t e r as a m i x t u r e of c o r u n d u m with m a g n e t i t e , slightly titaniferous, as usual, w h e n t h u s associated, analogous to t h e e m e r y of Chester, Mass., and its proportions b e a r i n g a still closer r e s e m b l a n c e to s p e c i m e n s o b t a i n e d b y Dr. Genth, from t h e Goldboro ore b e l t of N o r t h Carolina in I87I, and analyzed b y t h a t chemist." Dr. K i m b a l l ' s article is entitled
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[ 1. F. I.,
" E m e r y and its Uses in I r o n Metallurgy," and t h r o u g h o u t this lengthened essay he always refers to the W e s t e h e s t e r ores as emery. I t is an admitted fact that the Percentage of alumina in these" ores is less than that in the Greek and Turkish samples analyzed by Dr. Smith, b u t I have' already shown that the effective hardness of Dr. Smith's samples w a s not proportioned to the percentage of alumina. I have also shown that American corundum has been sold at the highest price commanded by a genuine article, though its percentage of alumina was much less than that Contained in the W e s t e h e s t e r ores, and though it contained no insoluble corundum at all. In fact, Dr. Chatard* says of it that " the sample contained in all probability no CorunThe six analyses of Dr. Chatard referred to in this lecture were made at m y request, a n d were from samples o f commercial material. These samples were reduced to such fine powder t h a t t h e i r i d e n t i t y was destroyed. W i t h t h e i r origin u n k n o w n a n d t h e i r superficial characteristics obscured, Dr. Chatard, from chemical analysis alone, p r o n o u n c e s one sample of commercial c o r u n d u m (southern) t o b e from a n o n - c o r u n d u m - b e a r i n g rock a n d h a v i n g no insoluble c o r u n d u m at all. T h e sample of W e s t c h e s t e r emery, which contained lO"I4 of insoluble corundum, h e classed as spinel. As bearing s t r o n g l y o n popular beliefs as to the differences between i m p o r t e d a n d domestic emery, it is w o r t h while to sum up the opinions of distinguished scientific m e n as tO the i d e n t i t y and characters of various emeries. Dr. Charles T. J a c k s o n * gives analyses ` showing t h a t the proportions o f alumina a n d iron in Chester, Mass., e m e r y agree closely with those of Naxos emery, a n d states t h a t practical trial in armories a n d m a c h i n e shops proved the Chester e m e r y f u l l y equal to the Naxos. Dr. J. Lawrence S m i t h ~ states t h a t he considers " t h e Chester mineral as true an emery as t h a t of N a x o s . " Dr. J. P. Kimball:~ states t h a t t h e analyses of W e s t c h e s t e r e m e r y i d e n t i f y it " a s a m i x t u r e of c o r u n d u m with m a g n e t i t e analogous to t h e emery of Chester." Dr. Smithll confirms Dr. C h a t a r d ' s recent identification of Westchester e m e r y with spinel by p r o n o u n c i n g all emery Spinel. In c o m m e n t i n g on t h e discussion of Professors J a c k s o n and Shepard, as to w h e t h e r emery was a g r a n u l a r variety of c o r u n d u m or a separate species, Dr. S m i t h says : " t h e question as to t h e mineralogical position of e m e r y can be easily settled w i t h o u t resorting to a n y new mineral species. I t is simply a massive iron spinel (hercynite) with the a n o m a l y of h a v i n g a h a r d n e s s equal to corundum.
'
* A m . J o u r . ScL a n d A r l s . ~, xxxlx, 90. t A m . J o u r . Sci. ~ndArgs. :~, xlii, 89. A m. Chemisl, date unknown ; republished in T~e E m e r y Grinder. [FAm.Jour. Sci. and Arts. 2, xlii, 83.
April, I874.
June, r894 ]
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alum at all, b e i n g o n l y an o r d i n a r y si!icate." It was so m u c h of a silicate t h a t it c o n t a i n e d 44"64 per cent. o f Silica, while t h e l a r g e s t p e r c e n t a g e in a n y sample of e m e r y a n a l y z e d by Drs, S m i t h and C h a t a r d was only 9"63 per cent. H a v i n g s h o w n t h a t the chemical proportions of e m e r y a n d c o r u n d u m bear no direct ratio to price or effective hardness, we have now to consider w h e t h e r t h e r e is~a direct r e l a t i o n b e t w e e n effective h a r d n e s s and abrasive value. In h i s article on "Mineralogy " in the EncyclopwdiaBritannica, Prof. M. F. H e d d l e d i s t i n g u i s h e s two forms of hardness. He e x p l a i n s the established scale of h a r d n e s s which c u l m i n a t e s in the diamond, and shows how the file test is applied. But he t h e n goes o n to show t h a t m i n e r a l s m a y appear soft u n d e r t h e file test while t h e y scratch o t h e r m i n e r a l s on w h i c h the file has no effect. Tl~is h e says is because the particles are h a r d b u t loosely a g g r e g a t e d . Dr. Smith, also, dwells u p o n this point. H e says t h a t his glass and a g a t e t e s t for abrasive effect does not f u r n i s h the m i n e r a l o g i c a l hardness, ~ "two m i n e r a l s possessing the same h a r d n e s s b u t differing in s t r u c t u r e , one b e i n g f r i a b l e , and the other resisting, will be f o u n d v e r y different in their abrasive effects." T h e inference w h i c h Dr. S m i t h draws i s a g a i n s t t h e friable and in f a v o r of the r e s i s t i n g material. T h i s inference is perfectly correct so far a s it relates to the exact m e t h o d b y w h i c h Dr. S m i t h secured his result, or in so far as it m a y relate to practical processes w h i c h ' r e p r o d u c e Dr. S m i t h ' s conditions. It is u t t e r l y i n a c c u r a t e and m i s l e a d i n g so far as it refers to the larger proportion of m o d e r n processes in w h i c h abrasives are used. I am inclined to t h i n k t h a t Dr. S m i t h ' s test for effective h a r d n e s s by use of glass and a g a t e is responsible for the a l m o s t hopeless confusion w h i c h exists to-day r e g a r d i n g the requisites of a good abrasive. T h e g e n e r a l inference is t h a t h a r d n e s s is the prime requisite. P r a c t i c a l operations i n e m e r y m i n i n g prove t h a t this i n f e r e n c e is a m i s t a k e n one. It is no u n c o m m o n t h i n g to find the rock o v e r l y i n g an e m e r y vein h a r d e r t h a n the Amer. Jour. Sci. and Arts.
2, x, 363.
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[I. F. I.,
emery. T h a t is to say, it is more resisting to the action of a drill, dulling the tool more rapidly and d e m a n d i n g more time to drill an equal distance. If the class of hardness shown by this rock were the right kind,, it ought to make a good abrasive, but actual trial shows that it does not do so. Its hardness is probably due to its compact aggregation. In Dr. Smith's famous test, which has been copied by all his followers, separate grains of emery, not bound to each other or to a n y t h i n g else, but rolling and moving freely, are rubbed between two pieces of glass or between glass and agate. If these grains are loosely aggregated or if they are of bad shape (for instance, fiat and thin, with splintery edges)~ they will, being unsupported, crush down rapidly between the hard opposing surfaces, while fragments of diamond or sapphire would stand up larger and do m o r e work. The practical question, however, is, how m a n y modern processes reproduce Dr. Smith's test conditions. E m e r y is principally used on wood and leather wheels, in solid wheels and in the form of e m e r y cloth or paper. It is also used on the lapidary's wheel. If the latter is a lead wheel the e m e r y becomes embedded in the lead, the lead being selected because it is soft enough to allow of the e m e r y grains sinking into it, and so being supported and backed up. W h e n used on the wood and leather wheel emery is attached to the leather band by a coat of the strongest, toughest glue. The e m e r y is forced into the hot, plastic glue, which fills all interstices in the grain, adapts itself to every peculiarity of shape, and then hardens into a perfectly fitted bed or backing which supports and braces the grain. W h e n used in solid wheels e m e r y is still more thoroughly braced and backed up, for it is first mixed with a base and then united with such base by gums, glues or cements, aided by the processes of slow drying, baking heat, vitrifaction, tamping and hydraulic pressure. W h e n emery is used to make e m e r y cloth and paper it is also bedded in and backed up by glue. In not one of these cases do the e m e r y grains have any free motion of their own. T h e y do not change place in
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relation to each other, and are n o t worn-out b y the friction of e m e r y w i t h emery. T h e y do n o t b r e a k d o w n and crush to pieces, for t h e y are n o t only b a c k e d b u t s u r r o u n d e d b y t h e i r p r o t e c t i n g matrix, and so cannot flatten, spread and s q u e e z e a p a r t as does a free, u n s u p p o r t e d grain of which o n l y a small p a r t comes in c o n t a c t w i t h t h e opposing surfaces. Still a n o t h e r vital condition of Dr. Smith's test is" l a c k i n g in t h e cases of t h e lead wheel, the leather-covered wheel, and the e m e r y cloth and paper. In t h e s e cases the e m e r y is not r u b b e d b e t w e e n two u n y i e l d i n g surfaces, such as glass and agate, b u t b e t w e e n one yielding and one unyielding. Before the grain can cr~sh, the leather, generally chosen for its s p o n g i n e s s and compres*sibility, will y i e l d - - t h e lead will allow the grain to sink deeper in its surface, t h e cloth and p a p e r will do the same. T h e s e latter, so thin as to possess little compressibility, are often backed u p b y t h e h u m a n hand, which affords the s a m e cushion as does the s p o n g y walrus or sea-horse. Of these differences in t h e conditions of use the ordinary b u y e r takes no m o r e note than does the professional expert. .He applies, in a r o u g h way, the s a m e sort of test as does the e x p e r t - - a test w h i c h only s h o w s w h a t the e m e r y will do u n d e r conditions entirely different from those in which it will be used. H e placed s o m e of the e m e r y on a smooth, solid piece of metal, and presses it as hard as he can, affd w i t h a sliding motion, w i t h a n o t h e r piece of metal. If the grains are loosely a g g r e g a t e d or b a d l y shaped t h e y crush to pieces and the e m e r y is c o n d e m n e d . A n o t h e r test is to place the e m e r y in the p a l m of the h a n d and r u b it together with the t h u m b or finger. H e r e the e m e r y is used as an a b r a s i v e a g e n t to d e s t r o y itself. T h e thin edges and sharp corners are g r o u n d off and the e m e r y is c o n d e m n e d as soft and dirtyj It appears, therefore, that looseness of aggregation, or friability,and also the shape of grain, m a y be of importance. It is in the larger grains that friabilityshows most markedly, a n d it is q u i t e p r o b a b l e t h a t this friability differs very g r e a t l y in grains of different size. If e m e r y is a varied m e c h a n i c a l m i x t u r e m i n u t e subdivision m a y lessen the
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."
[J. F. I.,
v a r i e t y of m a t e r i a l s in each g r a i n and so alter the s t a a d a r d of cohesion and a g g r e g a t i o n . W h e r e the grain, in c r u s h i n g down, sets free particles of p u r e sapphire, it s e e m s clear t h a t these will not c r u s h to pieces as the more h e t e r o g e n e o u s g r a i n did. Even if a coarse g r a i n were proved too friable for some special work it w o u l d not follow t h a t finer e m e r y from the same ore was also too friable. It is an i m p o r t a n t fact t h a t the proportion of coarse g r a i n in use h a s g r e a t l y d i m i n i s h e d and t h a t f e w processes really d e m a n d a v e r y coarse and a v e r y r e s i s t i n g grain. T h e m a n u f a c t u r e r s of plows and of fire-proof safes, a n d the workers in g r a n i t e are those who seem m o s t inclined to coarse e m e r y . . T h e coarser it is the more }esistant m u s t be the grain, for the more it projects b e y o n d its glue bed the more easily will it b r e a k off or crush down. It is an i n t e r e s t i n g fact t h a t e m e r y w h i c h is p r o n o u n c e d too soft for such use m a y be a d a p t e d to i t b y special processes. W h a t e v e r m a c h i n e or process m a y be used to accomplish this, the principle of its o.peration is to abrade the e m e r y by friction a g a i n s t itself till sharp points, brittle corners and loosely a d h e r i n g particles are removed. C o n c e r n i n g t h e c o m p a r a t i v e v a l u e s of r o u n d - g r a i n e d e m e r y a n d t h a t of o t h e r shapes m u c h difference of opinion exists. T h e r o u n d e d or cubical g r a i n of large size will cert a i n l y be m o s t resistant, and, in all processes w h i c h reproduce the conditions of Dr. S m i t h ' s test, will p r o b a b l y be m o s t v a l u a b l e ; b u t it does not s e e m e v i d e n t t h a t a n y a d v a n t a g e will a t t a c h to such shapes w h e n t h e y are e m b e d d e d in a solid mass. A_r o u n d e d or cubical g r a i n of the finest g r a i n e d , h a r d e s t and m o s t c o m p a c t ore would p r o b a b l y be the best for g r a n i t e workers, b e c a u s e their processes are such as to crush a friable grain. I t is this fact w h i c h has led .to t h e g r o w t h of a new i n d u s t r y in the m a n u f a c t u r e of artificial abrasives. Chilled s h o t a n d c r u s h e d steel have a l r e a d y won a position a m o n g stone workers a n d will p r o b a b l y h a v e lasting and i n c r e a s i n g sale. ~ * T h e makers of crushed steel report that in 189o, their first business year, they sold 230,ooo pounds, which sale increased in 1892 to 460,00o pounds. I have not been able to learn the annual product of chilled shot.
June, 1894. ]
Emery and other Abrasives.
43I
A chilled shot and a g r a i n of W e s t c h e s t e r emery, loosely a g g r e g a t e d and b r i s t l i n g w i t h points, afford e x t r e m e contrasts. Our facts lead to the belief that loose a g g r e g a t i o n is not a serious defect, provided, as Dr. H e d d l e shows, that t h e particles are hard e n o u g h . T h e inference from his s t a t e m e n t is t h a t abrasive effect is p r o p o r t i o n e d to the h a r d n e s s of the particles. B u t Dr. H e d d l e ' s file test, like t h e giass and a g a t e test of Dr. Smith, lacks the principal condition in the m o d e r n use of abrasives. T h a t condition is hig h speed. P e n e t r a t i o n is effected b y velocity, and abrasion is effeeted b y the points of one s u b s t a n c e penet r a t i n g the s u b s t a n c e of another. A b o a r d is h a r d e r than a candle, y e t it is said t h a t a candle can b e shot t h r o u g h a board. Glass is harder t h a n lead, y e t a bullet of lead will m a k e a d e a n hole t h r o u g h a window. It s e e m s possible t h a t a like rule m a y hold good as to abrasives, and that mineral grains may, if used at t h e right velocity, p e n e t r a t e s u b s t a n c e s h a r d e r than t h e m s e l v e s and prove satisfactory a g e n t s of abrasion. On still a n o t h e r i m p o r t a n t point does Dr. Smith's test fail to m e e t the r e q u i r e m e n t s of practical use. It takes n o note of t h e p r e s s u r e required. If a grain of c r u s h e d steel or a d i a m o n d g e m be e m b e d d e d in the face of a solid e m e r y wheel t h e s e two articles w o u l d a b r a d e t h r o u g h the use of w h a t e v e r p r o j e c t i n g points t h e y m i g h t present. As the points wear off fiat faces w o u l d appear, d e s t i t u t e of c u t t i n g power, and no f u r t h e r abrasion w o u l d take place until p r e s s u r e e n o u g h h a d b e e n applied to crush the grains of d i a m o n d and steel and m a n u f a c t u r e n e w points for them. T h e h a r d e r and m o r e r e s i s t a n t the grains were the g r e a t e r w o u l d b e the pressure n e e d e d to effect this. T h e criterion which d e m a n d s the e x t r e m e of hardness, fineness, p u r i t y , c o m p a c t n e s s and resistance in a b r a d i n g minerals, is one w h i c h calls on the m a n u f a c t u r e r for a w a s t e f u l e x p e n d i t u r e of power, which forces on the l a b o r e r u n d u e physical strain, w h i c h p r e v e n t s his a t t a i n m e n t of m a n u a l skill, and which exposes h i m to u n n e c e s s a r y danger. T h i s criterion has m a d e d u r a b i l i t y the prime requisite in a b r a d i n g materials and t o o l s - - a d u r a b i l i t y w h i c h the b u y e r d e m a n d s w i t h o u t
432
P a r e t ."
[~. F. I.,
reference to t h e cost of his product, or to the welfare and s a f e t y of his men. R e s i s t a n c e of m a t e r i a l calls for resistance of worker, and t h a t a b r a d i n g m a t e r i a l is b e s t w h i c h does equal w o r k in equal time with the least possible p o w e r and pressure. S u c h a d a p t a t i o n to its work is n o t likely to b e f o u n d in a n y mineral of e x t r e m e p u r i t y or oneness of composition, w h o s e t e x t u r e is dense, w h o s e grain is fine, w h o s e cohesion is great. It is m o r e likely to be f o u n d in a mineral of such friability and such varied c o m p o s i t i o n as c a u s e s it to b r e a k up into c h a n g i n g and irregular f o r m s u n d e r m o d e r a t e pressure. W h i l e I consider the facts t h u s far s t a t e d u n q u e s t i o n a b l e and the inferences from t h e m correct, I h a v e to a v o w regard. ing e m e r y and o t h e r abrasives, w h a t I a v o w e d as to e m e r y wheels s o m e f o u r y e a r s a g o , b e f o r e the m e m b e r s of this Institute, namely, t h a t there are few exact data to demon. strate m y inferences. T h e g r e a t e r the c o n s u m p t i o n of a b r a s i v e s and the more varied their use, t h e g r e a t e r is t h e d i v e r g e n c e of o p i n i o n s - - t h e m o r e hopeless t h e c o n f u s i o n - the deeper the d i s t r u s t as to a n y scientific basis in the g r i n d i n g industry. T h e m e n w h o e m p l o y licensed firemen to run a s t e a m boiler, and still f u r t h e r p r o t e c t t h e m s e l v e s b y the periodical test of their boilers, give no t h o u g h t to the latent explosibility of solid e m e r y wheels in charge of common laborers. T h e railroad, which sends in to the f o u n d e r its own chemical f o r m u l a for car brasses, pays no h e e d to the i n h e r e n t s a f e t y of a vulcanized e m e r y wheel or the inherent d a n g e r of a vitrified one. T h e m a n u f a c t u r e r w h o insists on h a v i n g the candle-power of his electric light g u a r a n t e e d , and t h e horse-power of his t u r b i n e or e n g i n e m e a s u r e d b y a d y n a m o m e t e r , b u y s the lowest-priced e m e r y wheel he can find, b u t n e v e r discovers the cost of t h a t wheel's product. This d e g r a d a t i o n of the g r i n d i n g i n d u s t r y is d u e in part to that criterion of hardness in a b r a s i v e material which has m a d e w e i g h t and s t r e n g t h the criterion of the h u m a n grinder. It is due in part to the fact that g r i n d i n g p r o b l e m s are so o b s c u r e and difficult to the skilled m e c h a n i c t h a t he r e m i t s t h e m u n s o l v e d to the u n l e a r n e d w o r k m a n . This
Jane, t894.]
Emery and other Abrasives.
433
d e g r a d a t i o n of the g r i n d i n g i n d u s t r y goes back to early times. In the R o y a l M u s e u m at Berlin is a p a i n t i n g b y G e r a r d T e r Botch, of Deventer, p r o b a b l y e x e c u t e d a b o u t I65 o, which is m a r k e d b y all t h a t detail which generally characterizes p a i n t i n g of the H o l l a n d school. T h i s picture r e p r e s e n t s " T h e Grinder's Family." T h e work-room is a tumble-down, w r e t c h e d shed, a t t a c h e d to the dwelling-house. Only one m e m b e r of the family is at work, unless t h a t operation can be called w o r k in w h i c h the m o t h e r is engaged. She s e e m s to be s e a r c h i n g in t h e hair of her y o u n g d a u g h t e r for s o m e t h i n g that o u g h t n o t to be there. T h e g r o w n son, with almost a simpleton's face, and w i t h t a t t e r e d g a r m e n t s , ieans idly a g a i n s t a post. T h e old father has a wide shelf, j u s t level with the top of the grindstone, and lies upon it at full length upon his stomach, while he presses a scythe u p o n the grindstone. T h e o t h e r s c y t h e s lie o u t of reach on the floor. T h e mandril of the stone revolves in an uncovered groove in a beam, and a notch in that b e a m holds a w o o d e n w e d g e to keep the mandril in its place. E v e r y t h i n g indicates that activity is at a b i g d i s c o u n t - - a r t at a low e b b and w a g e s lower still. It is unfair, y o u will say, to steal this q u a r t e r - c e n t u r y old example from a pastoral c o u n t r y like Holland. Why not go to a m a n u f a c t u r i n g c o u n t r y in m o d e r n times ? W h y not visit Sheffield, for instance ? I did visit Sheffield in 1892. I asked a m a s t e r cutler to s h o w me the latest thing in grinding. H e said there was no late thing. I asked him a b o u t abrasives and he said'each individual grinder supplied his own, bu.ying a few p e n n y s w o r t h of e m e r y at the n e a r e s t chemist's and h a v i n g it chalked up a g a i n s t him j u s t as he h a d his b e e r chalked up at the tavern. H e said the grinders could generally be f o u n d at work when tfiey had no m o n e y to spend, a l w a y s p r o v i d i n g there w a s n ' t a football m a t c h on hand. H e told me to visit R o d g e r s ' and see w h a t t h e y did and then he w o u l d take m e outside the town to mills h u n d r e d s of years old and t h a t I w o u l d find the tools, the processes, the conditions identical. T h e factory b u i l d i n g he called " a wheel," and the v a u l t e d dungeons, w h o s e w i n d o w s had all t h e i r glass s h a t t e r e d to let in the VOL. CXXXVII. 28
434
Parer :
[ J. F. I.,
light which the splash and slop of the wet stone obscured, hc called "troughs." A strap (belt), a stone, a razor and a grinder were what constituted the grinding industry. I ignorantly spoke of the grinders as " men," but he said it was a c o m m o n Sheffield saying, "he's not a man; hc's only a grinder." I did go to the main establishment of Rodgers and then to a "wheel " in a valley some miles out of the city. T h e "wheel" was a long, dull building of cut stone. T h e newer part was about ioo or I5O years old, while one wing was m u c h older--too old for the date of its founding to be remembered. T h e grinder was a m a n over sixty, and he assured m c that his father and his father's farther had also ground razors there. "As I talked with him two younger m e n examined a pile of apparently worn-out grindstones, which they said were bought second-hand, w h e n too small for other use, and, selecting one of the quality desired, split it in two pieces because it was too thick. F r o m this dilapidated building, from these scant tools and crude processes, were evolved by grinders not thought worthy to be called men, those b' ~des which have m a d e the n a m e of Rodgers famous. Inherited skill and restriction to one narrow branch of work take the place of modern improvements. A s I r e m e m b e r this'initiation into the art of Sheffield, I smile at the London merchant w h o wrote to America that he could get a big order for Japan if I could supply a complete plant for razor grinding. In our o w n freer and more versatile country the tyranny of the trades-union has not gone so far as to insist that only the sons and grandsons of razor grinders shall learn to grind razors. Instead of old processes, perpetuated unchanged for hundreds of years, w e have all the newest wrinkles. Automatic grinding machines, almost h u m a n in their complication, and which render brains almost unnecessary to the w o r k m a n ; and others which look beautifully on paper, and either go to the waste pile or swell the maker's account of " returned goods." W e have the newest wrinkles, but no rulesnthe most ingenious devices, but no accepted standards--the most varied opinions, but no authorities.
June, x894.]
Emery and other Abrasives.
435
W h i l e g r i n d i n g processes are complicated and solid e m e r y wheels high-class tools, and while economical g r i n d i n g d e m a n d s conditions based on t h e careful s t u d y of e d u c a t e d mechanics, no one e s t a b l i s h m e n t uses e n o u g h to enlist the i n t e r e s t of the e d u c a t e d man. A b r a s i v e s are c o m m i t t e d to the lowest class of labor, and reports as to results drift t h r o u g h circuitous c h a n n e l s to the buyer, whose next purchase is based on the latest a n d m o s t distorted report. T h e n a m e of " W e l l i n g t o n " is so p o t e n t t h a t often the g r i n d e r will use no o t h e r b r a n d of emery, t h o u g h he will take a n y a n d all kinds of m a t e r i a l w i t h o u t discovering a n y difference, provided t h e y are poured out of a " W e l l i n g t o n " keg and have a coloi not found in the original material. T h r o u g h o u t the a p p a r e n t discussiveness of this lecture I h a v e carried on a s u s t a i n e d a r g u m e n t , b u t t h a t a r g u m e n t has been so l e n g t h y and so involved as to d e m a n d a summ a r y of conclusions. It seems clear to me t h a t c u r r e n t opinions about abrasives h a v e been based too m u c h on cabinet specimens and labo~'atory experiments, a n d too little on the average prod u c t s of the m i n e and on the conditions of m o d e r n work. It seems d e m o n s t r a t e d t h a t chemical analysis does not g a u g e a c c u r a t e l y the abrasive c a p a c i t y of a n y m i n e r a l - t h a t t h e h a r d n e s s of such m a t e r i a l does not bear a definite relation to its p u r i t y ( m e a n i n g t h e r e b y a h i g h p e r c e n t a g e of alumina), and equally clear t h a t mere h a r d n e s s is not the prime requisite. It seems clear t h a t abrasive capacity d e p e n d s l a r g e l y on some u n e x p l a i n e d p e c u l i a r i t y of structure. It seems e v i d e n t t h a t speed, time and pressure are factors too little considered in connection w i t h the problem of safe and economical g r i n d i n g . It seems settled t h a t e x t e r n a l appearance is a poor g u i d e to g r i n d i n g c a p a c i t y ; t h a t colors, shape of g r a i n and a t t r a c t a b i l i t y b y the m a g n e t are not t r u s t w o r t h y indications. It seems clear t h a t commercial abrasives v a r y in quality, a n d t h a t their acceptance or c o n d e m n a t i o n depends on prejudices and notions r a t h e r t h a n on ascertained facts as to cost of product. Some of the causes which" lead to variable and contradict o r y results w i t h abrasives are those c o m m o n to shop prac-
436
Parer:
[ J. F. I.,
flee, b u t which p r o d u c e far g r e a t e r effects w i t h the e m e r y wheel t h a n w i t h the l a t h e or planer. T h e effective work of an e m e r y wheel is based on its speed of a mile a m i n u t e . T h e correct speed is less likely to be m a i n t a i n e d , because the pressure a g a i n s t t h e wheel is h e a v i e r and more variable t h a n t h a t in a lathe. T h e l a t h e tool presses w i t h a sharp point only a g a i n s t the r e v o l v i n g work, and is so set that, after the first cut, the pressure scarcely changes. T h e grinder, however, forces his work a g a i n s t the wheel with g r e a t l y v a r y i n g s t r e n g t h , a n d s o m e t i m e s adds to direct pressure a h e a v y leverage. I have often seen wheels slowed down till t h e y almost stopped. Pulleys of too small diameters are used, and belts which are too narrow. Slip of belt and d i m i n u t i o n of speed are p o t e n t factors in the problem. A n o t h e r e q u a l l y p o t e n t one is d i s c o n t i n u i t y of contact. A w h e e l m a y r u n a mile a m i n u t e and y e t be so o u t of r o u n d or m o u n t e d on such a l i g h t m a c h i n e or s h a k y floor t h a t v i b r a t i o n and c h a t t e r interfere w i t h c o n t i n u o u s contact. I n s t e a d of a mile l o n g file passing over the work in a m i n u t e , it is s o m e t i m e s only an e i g h t h or a q u a r t e r mile file. I h a v e e x a m i n e d wheels whose c o n t i n u o u s s t r e a m of sparks s u g g e s t e d c o n t i n u o u s contact, a n d f o u n d t h a t only two or three inches of the surface h a d come in c o n t a c t w i t h the metal. T h e c u s t o m of i m p u t i n g all v a r i a b i l i t y of result to defect in the wheel and the overlooking of v a r i a b i l i t y in the m e t a l operated on is a n o t h e r cause of c o n t r a d i c t o r y result. A class of wheels w h i c h h a d l o n g s u i t e d a plow m a n u f a c t u r e r was at last r e p e a t e d l y c o n d e m n e d and t h e wheel declared worthless. A f t e r a v e r y l o n g i n t e r v a l it a p p e a r e d t h a t the plows h a d been c h a n g e d from one h o m o g e n e ous thickness to three sheets of v a r y i n g temper. A class of wheels was c o n d e m n e d which h a d long s u i t e d for car brasses, and only a f t e r l o n g delay was it m a d e k n o w n t h a t the first m e t a l was yellow brass and the last phosphor-bronze. I have lately discovered by use of an imp r o v e d t e s t i n g m a c h i n e t h a t the q u a l i t y of the test bars of east iron is more variable t h a n the q u a l i t y of t a n i t e wheels. W h a t , then, is needed, to clear up this confusion ?
June, x894.]
Emery and other Abrasives.
437
It s e e m s to me t h a t the t h i n g m o s t needed is a practical t e s t i n g machine, which shall take the place of the laboratory test m a d e p o p u l a r b y Dr. J. L a w r e n c e Smith. Such a m a c h i n e should be run b y an i n d e p e n d e n t engine to secure u n i f o r m speed. P u l l e y s and belts should be so proportioned t h a t no slip shall occur. Floor and m a c h i n e should be so solid as to do a w a y with vibration. T e s t bars should be e m p l o y e d of the m o s t u n i f o r m quality. A n d then a series of e x p e r i m e n t s should b e carried out so as to establish definite standards. It should b e ascertained w h a t is the least p r e s s u r e per square i n c h at w h i c h a cubic inch of test m e t a l can be g r o u n d off in the least time with the least c o n s u m p t i o n of w h e e l m a t e r i a l In other words, the final e c o n o m y of t h e process should be d e m o n s t r a t e d , taking into strict a c c o u n t the c o n s u m p t i o n of w h e e l material, the a m o u n t of m e t a l ground, the time occupied, the speed employed, the horse-power e x p e n d e d and the pressure exerted. T h u s will g r a d u a l l y arise a fixed s t a n d a r d as to w h a t c o n s t i t u t e s a g o o d e m e r y wheeI, and the b u y e r will d e m a n d an article of k n o w n and certified p r o d u c t i v e effect w h o s e cost of p r o d u c t is also known. T h u s will arise on the grinder's side a d e m a n d for t h o s e wheels and those a b r a s i v e s which entail the least b o d i l y fatigue. T h u s will arise a p u b l i c opinion w h i c h shall hold to strict account those reckless b u y e r s w h o p u t wheels of known d a n g e r o u s q u a l i t y in the h a n d s of their employds. F o r this m a c h i n e should riot only be used to ascertain the economic value of abrasives, b u t also to d e m o n s t r a t e the relative safety of solid e m e r y wheels. In closing this lecture, I desire to point o u t that it is not so m u c h a s t a t e m e n t of w h a t is k n o w n a b o u t abrasives as a confession of h o w little is known. T h i s confession i m p u t e s no special i g n o r a n c e to the user, b u t pleads the g r e a t o b s c u r i t y of the problem. I believe the difference b e t w e e n the p o o r e s t and the b e s t of the abrasives in c o m m o n use is so m o d e r a t e t h a t g r e a t expertness is r e q u i r e d to discover it. My o b j e c t will be a c c o m p l i s h e d if, b y pointing o u t the fallacies w h i c h attach to old-time tests and superficial indi-
438
G i l m a n ."
[ I. F. I..
cations, the w a y is cleared for a more a s c e r t a i n i n g abrasive q u a l i t y - - a more g e t t i n g at t h e economic r e s u l t - - a n d sideration of the laborer's d a n g e r a n d APPLICATION SQUARES
scientific m e t h o d of business-like w a y of a more h u m a n e confatigue.
OF THE METHOD TO THE DEVELOPMENT OF FUNCTIONS.
OF
LEAST
BY F. GILMAN.
T h e u s u a l m e t h o d s of d e v e l o p i n g a f u n c t i o n are b y the b i n o m i a l series and by the t h e o r e m s of Maclaurin and Taylor. In g e n e r a l practice, however, only a l i m i t e d number of t e r m s of t h e d e v e l o p m e n t can be calculated, and for such cases these t h e o r e m s do n o t give the best values o b t a i n a b l e for the co6fficients. L e t us take, for example, t h e f u n c t i o n I
l,/I + x T h e b i n o m i a l t h e o r e m gives i
= i--½x
1/i+x
+~}~--¢~+
(~)
W e will now a s s u m e I
--I
+ax
+bx2
+cx
3
1/i + x
and t r e a t i n g I
] / / I -~ X
as an observed q u a n t i t y , we will d e t e r m i n e the values of t h e c o n s t a n t s a, b and c from the condition t h a t the s u m of t h e squares of the residual errors shall be a m i n i m u m . S u p p o s i n g x to v a r y from o to I, the following table gives the values of I
1/i + x
Emery and other Abrasives.
42!
without any rims whatever, are r e c o m m e n d e d by all dealers in advanced gas light fixtures. Lastly, the position of the glass globe in reference to the gas flame is of a good deal of importance where it is desired t o secure a steady, bright light. It has been found long ago, by experiment, that by arranging a shadowless globe holder on the burner in such a m a n n e r as to place the level of the bottom of the flame in line with the bottom edge of the globe, the flame will burn very quietly and steadily, and will not be affected much, if any, by the ascending air current, whereas if the flame is set higher it is apt to flicker. This correct position and shape of a glass globe has been pointed out repeatedly by such gas engineers as Wilder, Peebles, Sugg, Broenner, Silber and others, in connection with their gas burning appliances; but on the whole, in practice, little attention has been paid to this simple yet efficient rule. [ To be concluded.]
E M E R Y AND O T H E R A B R A S I V E S . ~ BY T. DUNKIN PARET, President of t h e Tanite Company.
[ Concluded from p. 372.]
While small specimens of corundum, in the form of imperfect sapphires, have come from Montana, where the existence of this mineral has long been known, no other locality has yielded corundum except that well-known belt which reaches from Massachusetts to Georgia, and which seems to have its center in the corner where North and South Carolina, Georgia and Tennessee come together. In this belt the localities where corundum occurs are innumerable, but the prevalence of the mineral is a poor indication of its quantity. Corundum occurs in pockets, seams, sand veins, narrow streaks and detached crystals, seldom in large mass. Chester County, Pa., is, apparently, the only locality where large solid masses have been found. The
422
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[J. F. I.,
l a r g e s t a n n u a l p r o d u c t of A m e r i c a n c o r u n d u m has been 645 tons, and, t h o u g h c o r u n d u m m i n i n g companies h a v e multiplied r a p i d l y d u r i n g the last few years, the c o m m e r c i a l s u p p l y has never been more precarious. Unlike c o r u n d u m , e m e r y consolidates i n large m a s s e s . It does not, indeed, forth c o n t i n u o u s beds of g r e a t extent, like coal or iron, b u t its d i s c o n t i n u o u s masses and veins sometimes contain h u n d r e d s of tons. T h e e m e r y - b e a r i n g locality in W e s t c h e s t e r County, N. Y., is a strip from one-half to three-fourths of a mile in width, a n d from five to six miles in length. T h e g e o l o g y of this district and the occurrence of e m e r y in i~ m i g h t be described in a l m o s t the same l a n g u a g e as t h a t w h i c h Dr. S m i t h applies to the celebrated e m e r y district near E p h e s u s in A s i a Minor. Dr. S m i t h ~ says " a l l t h e rocks of the s u r r o u n d i n g c o u n t r y a p p e a r to belong to the old series ; the l i m e s t o n e is e n t i r e l y devoid of fossils and m e t a m o r p h i c in c h a r a c t e r ; i t rests on the older schists of w h i c h mica schist appears t h e m o s t a b u n d a n t ; and this a g a i n f a r t h e r to the n o r t h was traced in contact w i t h gneiss. T h e l i m e s t o n e is of a l i g h t blue p a s s i n g into coarse-grained m a r b l e . " " T h e place, however, to which it is traced in g r e a t e s t a b u n d a n c e , is on a p a r t of the s u m m i t a b o u t three miles from the village of G u m u c h , and some 1,5oo to 2,00o feet above the level of the v a l l e y ; it overlooks the m a g n i f i c e n t plain of the Miandre, whose curiously t o r t u o u s course is seen as if traced on a map. T h e e m e r y lies s c a t t e r e d on t h e surface ~ ~ ~ in a n g u l a r f r a g m e n t s of a dark color, a n d large masses of several tons w e i g h t are seen p r o j e c t i n g above the surface ; in p e n e t r a t i n g the soil, the e m e r y is f o u n d e m b e d d e d in it and a little f u r t h e r down i t is come to in the rock." " S o m e times the e m e r y forms a solid mass several y a r d s in l e n g t h and b r e a d t h . " In d e s c r i b i n g the W e s t c h e s t e r C o u n t y e m e r y beds, we would say t h a t the place in w h i c h the l a r g e s t n u m b e r of openings have .been made, and w h i c h has excited the m o s t interest, is on a p a r t of the s u m m i t a b o u t t h r e e miles f r o m A~n. Jour. Sci. and A r l s .
2, x, 356.
June, t894.]
Emery and otker Abrasi~'es.
423
the t o w n of Peekskill, and a b o u t 700 to 8o0 feet above tide level. It overlooks on the one side, the valley of the Croton, whose Stream is invisible, a n d on the other side, the H u d s o n , whose d i s t a n t waters look like some lake in a painting. On t h e n o r t h and n o r t h e a s t of the e m e r y belt a r e outcrops of granite. S o u t h of it lies the c o m m o n marble of Sing S i n g - - s t i l l f u r t h e r south, at S p u y t e n Duyvil, occur t h e oldest of t h e L a u r e n t i a n gneisses, and still f u r t h e r south, on M a n h a t t a n I.sland, t h e mica schist. T h e e m e r y is, however, all i m m e d i a t e l y associated w i t h a h o r n b l e n d e rock. L a r g e masses of e m e r y are seen p r o j e c t i n g above the sur•face. T h e s e are delusive, and those which hold out a large promise are s o m e t i m e s f o u n d to e x t e n d only one or two feet u n d e r g r o u n d a n d to yield only five to t w e n t y tons. Such masses are u s u a l l y s u r r o u n d e d by soft, reddish earth. 'Dr. S m i t h says of the T u r k i s h locality, " t h e earth in t h e n e i g h b o r h o o d of the blocks of e m e r y is a l m o s t always of a red color, and serves as an i n d i c a t i o n to those who are in search of the mineral." In W e s t c h e s t e r , the red e a r t h is not an indication, for there is w i t h i n the e m e r y belt an iron-beari n g rock w h i c h decomposes v e r y r a p i d l y and forms a red earth, while t h e r e is no emerv associated w i t h it. T h e r e is no sign of f r a c t u r e in these d i s c o n t i n u o u s masses of moderate size, and t h e y occur on the very tops of hills and u n d e r such c i r c u m s t a n c e s as to indicate t h a t t h e y are not boulders and have not broken down from h i g h e r cliffs. As in T u r k e y , so also here, " i n p e n e t r a t i n g the soil, the e m e r y is f o u n d e m b e d d e d in it, and a little f u r t h e r down it is come to in the rock." Small f r a g m e n t s t u r n e d up by the plow in c u l t i v a t e d melds are s o m e t i m e s the first indications. Search in their n e i g h b o r h o o d reveals o t h e r f r a g m e n t s e m b e d d e d in t h e earth, and near these and lower is f o u n d the rock. Somet i m e s this o n l y approaches the surface and forms such a small point t h a t it m i g h t lie u n d i s c o v e r e d for years. In one place discovery on the surface of a very fine grained, pure block, w e i g h i n g a b o u t 200 pounds, s t i m u l a t e d search which was c o n t i n u e d at intervals, fruitlessly, for several years. O t h e r varieties were discovered, b u t no sample like the original. Several blasts were m a d e Within a few feet of the nat-
424
_ P a r e t ."
[J. F. I..
r o w p o i n t w h i c h j u s t fell s h o r t of r e a c h i n g the surface, and y e t did n o t disclose it. A l u c k y b l a s t u n c o v e r e d it, and over Ioo tons of u n i f o r m q u a l i t y w e r e taken out, l e a v i n g it far from exhausted. A s in T u r k e y , so also here, " t h e e m e r y lies s c a t t e r e d on t h e surface ~ ~ ~ in a n g u l a r fragm e n t s of a dark color," b u t a t this p o i n t m y description m u s t differ from t h a t of Dr. Smith. H e says : " i n no place does it p r e s e n t a n y t h i n g like a vein, nor has it signs of stratification." I find, in W e s t c h e s t e r , t h a t the a n g u l a r pieces g e n e r a l l y indicate veins. S u c h veins are distinct and n u m e r o u s . T h e r e g u l a r i t y w i t h w h i c h t h e y thin o u t at t h e e d g e s and thicken at t h e centre s u g g e s t s true lenticular beds, t h o u g h there are, of course, e x c e p t i o n s to the rule. T h e q u i t e r e g u l a r recurrence of s e a m s separated, b u t parallel, s t r o n g l y s u g g e s t s stratification. T h e s e s e a m s occur in t h e solid rock and the e m e r y b r e a k s freely from it, it b e i n g a m o s t u n u s u a l t h i n g to find a n y a d h e r e n c e of t h e top o r b e d rock. E m e r y from veins breaks easily, w i t h flat sides and sharp angles. T h e s e sides, when dry, often s e e m painted, so b r i g h t are t h e y w i t h yellow and red, and s o m e t i m e s t h e y take on an a l m o s t iridescent tint, w i t h s h e e n of pink and green. S t r a n g e l y e n o u g h , large a m o r p h o u s m a s s e s are s o m e t i m e s found, d i s c o n n e c t e d from rock, a n d l y i n g b e t w e e n t h e r e g u l a r veins. T h e s e a m o r p h o u s masses, w h e t h e r t h e y be small or large, p r e s e n t no a n g u l a r outlines, and do n o t b r e a k up in such flat-sided pieces as do t h e seams. It s h o u l d b e n o t e d t h a t t h e a n g u l a r i t y of t h e vein e m e r y is n o t due to its b e i n g freshly mined. T h e b r o k e n - d o w n e d g e s of veins, f o u n d in f r a g m e n t s on the hill-sides far b e l o w the veins, and w h i c h h a v e w e a t h e r e d for h u n d r e d s or t h o u s a n d s of years, s e e m as sharp and u n a l t e r e d as t h o s e freshly broken. T h e a m o r p h o u s masses, on the o t h e r hand, are so d e s t i t u t e of cleavage t h a t c o n t i n u e d u s e of a h e a v y sledge h a m m e r only b a t t e r s t h e m into shapeless pieces. The e m e r y in each vein is of c o m p a r a t i v e l y u n i f o r m q u a l i t y t h o u g h differences can s o m e t i m e s b e d e t e c t e d in blocks l y i n g side b y side. T h a t in the a m o r p h o u s m a s s e s varies far more. One such mass, of y e t u n a s c e r t a i n e d quality, I
June, I894.]
Emery and otlter Abrasives.
425
estimate, b y a r o u g h calculation of its cubic contents, to contain from 5oo to 7oo tons. T h i s m a s s was j o k i n g l y christened b y the miners as " K n i g h t ' s bonanza." It was of a light g r a y i s h color, not m a r k e d l y different from the top and b e d rock, from w h i c h it stood o u t almost s e p a r a t e l y on all sides, a n d like those rocks, was covered with gray moss. T h e o w n e r decided t h a t all t h e rock was alike and e s t i m a t e d t h a t there were h u n d r e d s of t h o u s a n d s of tons. T h e e m e r y of this district p r e s e n t s easily discernible differences. S o m e is coarse grained, some fine, some black and shiny, s o m e gray. Some is u n i f o r m in color, s o m e d i s t i n c t l y streaked. T h i s d e p o s i t was d e s c r i b e d a b o u t t w e n t y years ago b y Dr. J. P. Kimball, and his classification agrees with m y own. H e describes t w o classes as " g r a n u l a r , massive, resinous," g i v i n g a slightly different analysis for each. I should s a y one coarse and one fine. A third he describes as a " b a n d e d variety, g r a y in g e n e r a l color, and sparkling, from t h e presence of a m i c a c e o u s mineral." A fourth, as a " q u a r t z o s e variety, g r a y and sparkling, like n u m b e r three b u t w i t h o u t a b a n d e d or gneissic structure." I n a s m u c h as t h e " E m e r y M a n u f a c t u r e r s ' A s s o c i a t i o n " has issued a circular referring to t h e p r o d u c t of these m i n e s as " a spurious article of emery," and referring to its ore as " i n f e r i o r or c o m p a r a t i v e l y w o r t h l e s s stone," the opinion of Dr. K i m b a l l is w o r t h consideration. It deserves additional w e i g h t b e c a u s e his i n v e s t i g a t i o n h a d no reference w h a t e v e r to t h e use o f this ore as an abrasive. It was solely with t h e view of its u s e in iron m e t a l l u r g y t h a t his s t u d y was made. T h e analyses he refers to were m a d e by Dr. C. F. Chandler and Mr. F. A. Cairns. Dr. K i m b a l l says, " T h e a b o v e analyses, t o g e t h e r w i t h the physical and mineralogical f e a t u r e s of this material, serve to identify its c h a r a c t e r as a m i x t u r e of c o r u n d u m with m a g n e t i t e , slightly titaniferous, as usual, w h e n t h u s associated, analogous to t h e e m e r y of Chester, Mass., and its proportions b e a r i n g a still closer r e s e m b l a n c e to s p e c i m e n s o b t a i n e d b y Dr. Genth, from t h e Goldboro ore b e l t of N o r t h Carolina in I87I, and analyzed b y t h a t chemist." Dr. K i m b a l l ' s article is entitled
426
Paret :
[ 1. F. I.,
" E m e r y and its Uses in I r o n Metallurgy," and t h r o u g h o u t this lengthened essay he always refers to the W e s t e h e s t e r ores as emery. I t is an admitted fact that the Percentage of alumina in these" ores is less than that in the Greek and Turkish samples analyzed by Dr. Smith, b u t I have' already shown that the effective hardness of Dr. Smith's samples w a s not proportioned to the percentage of alumina. I have also shown that American corundum has been sold at the highest price commanded by a genuine article, though its percentage of alumina was much less than that Contained in the W e s t e h e s t e r ores, and though it contained no insoluble corundum at all. In fact, Dr. Chatard* says of it that " the sample contained in all probability no CorunThe six analyses of Dr. Chatard referred to in this lecture were made at m y request, a n d were from samples o f commercial material. These samples were reduced to such fine powder t h a t t h e i r i d e n t i t y was destroyed. W i t h t h e i r origin u n k n o w n a n d t h e i r superficial characteristics obscured, Dr. Chatard, from chemical analysis alone, p r o n o u n c e s one sample of commercial c o r u n d u m (southern) t o b e from a n o n - c o r u n d u m - b e a r i n g rock a n d h a v i n g no insoluble c o r u n d u m at all. T h e sample of W e s t c h e s t e r emery, which contained lO"I4 of insoluble corundum, h e classed as spinel. As bearing s t r o n g l y o n popular beliefs as to the differences between i m p o r t e d a n d domestic emery, it is w o r t h while to sum up the opinions of distinguished scientific m e n as tO the i d e n t i t y and characters of various emeries. Dr. Charles T. J a c k s o n * gives analyses ` showing t h a t the proportions o f alumina a n d iron in Chester, Mass., e m e r y agree closely with those of Naxos emery, a n d states t h a t practical trial in armories a n d m a c h i n e shops proved the Chester e m e r y f u l l y equal to the Naxos. Dr. J. Lawrence S m i t h ~ states t h a t he considers " t h e Chester mineral as true an emery as t h a t of N a x o s . " Dr. J. P. Kimball:~ states t h a t t h e analyses of W e s t c h e s t e r e m e r y i d e n t i f y it " a s a m i x t u r e of c o r u n d u m with m a g n e t i t e analogous to t h e emery of Chester." Dr. Smithll confirms Dr. C h a t a r d ' s recent identification of Westchester e m e r y with spinel by p r o n o u n c i n g all emery Spinel. In c o m m e n t i n g on t h e discussion of Professors J a c k s o n and Shepard, as to w h e t h e r emery was a g r a n u l a r variety of c o r u n d u m or a separate species, Dr. S m i t h says : " t h e question as to t h e mineralogical position of e m e r y can be easily settled w i t h o u t resorting to a n y new mineral species. I t is simply a massive iron spinel (hercynite) with the a n o m a l y of h a v i n g a h a r d n e s s equal to corundum.
'
* A m . J o u r . ScL a n d A r l s . ~, xxxlx, 90. t A m . J o u r . Sci. ~ndArgs. :~, xlii, 89. A m. Chemisl, date unknown ; republished in T~e E m e r y Grinder. [FAm.Jour. Sci. and Arts. 2, xlii, 83.
April, I874.
June, r894 ]
F~mery a n d other Abrasives.
427
alum at all, b e i n g o n l y an o r d i n a r y si!icate." It was so m u c h of a silicate t h a t it c o n t a i n e d 44"64 per cent. o f Silica, while t h e l a r g e s t p e r c e n t a g e in a n y sample of e m e r y a n a l y z e d by Drs, S m i t h and C h a t a r d was only 9"63 per cent. H a v i n g s h o w n t h a t the chemical proportions of e m e r y a n d c o r u n d u m bear no direct ratio to price or effective hardness, we have now to consider w h e t h e r t h e r e is~a direct r e l a t i o n b e t w e e n effective h a r d n e s s and abrasive value. In h i s article on "Mineralogy " in the EncyclopwdiaBritannica, Prof. M. F. H e d d l e d i s t i n g u i s h e s two forms of hardness. He e x p l a i n s the established scale of h a r d n e s s which c u l m i n a t e s in the diamond, and shows how the file test is applied. But he t h e n goes o n to show t h a t m i n e r a l s m a y appear soft u n d e r t h e file test while t h e y scratch o t h e r m i n e r a l s on w h i c h the file has no effect. Tl~is h e says is because the particles are h a r d b u t loosely a g g r e g a t e d . Dr. Smith, also, dwells u p o n this point. H e says t h a t his glass and a g a t e t e s t for abrasive effect does not f u r n i s h the m i n e r a l o g i c a l hardness, ~ "two m i n e r a l s possessing the same h a r d n e s s b u t differing in s t r u c t u r e , one b e i n g f r i a b l e , and the other resisting, will be f o u n d v e r y different in their abrasive effects." T h e inference w h i c h Dr. S m i t h draws i s a g a i n s t t h e friable and in f a v o r of the r e s i s t i n g material. T h i s inference is perfectly correct so far a s it relates to the exact m e t h o d b y w h i c h Dr. S m i t h secured his result, or in so far as it m a y relate to practical processes w h i c h ' r e p r o d u c e Dr. S m i t h ' s conditions. It is u t t e r l y i n a c c u r a t e and m i s l e a d i n g so far as it refers to the larger proportion of m o d e r n processes in w h i c h abrasives are used. I am inclined to t h i n k t h a t Dr. S m i t h ' s test for effective h a r d n e s s by use of glass and a g a t e is responsible for the a l m o s t hopeless confusion w h i c h exists to-day r e g a r d i n g the requisites of a good abrasive. T h e g e n e r a l inference is t h a t h a r d n e s s is the prime requisite. P r a c t i c a l operations i n e m e r y m i n i n g prove t h a t this i n f e r e n c e is a m i s t a k e n one. It is no u n c o m m o n t h i n g to find the rock o v e r l y i n g an e m e r y vein h a r d e r t h a n the Amer. Jour. Sci. and Arts.
2, x, 363.
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[I. F. I.,
emery. T h a t is to say, it is more resisting to the action of a drill, dulling the tool more rapidly and d e m a n d i n g more time to drill an equal distance. If the class of hardness shown by this rock were the right kind,, it ought to make a good abrasive, but actual trial shows that it does not do so. Its hardness is probably due to its compact aggregation. In Dr. Smith's famous test, which has been copied by all his followers, separate grains of emery, not bound to each other or to a n y t h i n g else, but rolling and moving freely, are rubbed between two pieces of glass or between glass and agate. If these grains are loosely aggregated or if they are of bad shape (for instance, fiat and thin, with splintery edges)~ they will, being unsupported, crush down rapidly between the hard opposing surfaces, while fragments of diamond or sapphire would stand up larger and do m o r e work. The practical question, however, is, how m a n y modern processes reproduce Dr. Smith's test conditions. E m e r y is principally used on wood and leather wheels, in solid wheels and in the form of e m e r y cloth or paper. It is also used on the lapidary's wheel. If the latter is a lead wheel the e m e r y becomes embedded in the lead, the lead being selected because it is soft enough to allow of the e m e r y grains sinking into it, and so being supported and backed up. W h e n used on the wood and leather wheel emery is attached to the leather band by a coat of the strongest, toughest glue. The e m e r y is forced into the hot, plastic glue, which fills all interstices in the grain, adapts itself to every peculiarity of shape, and then hardens into a perfectly fitted bed or backing which supports and braces the grain. W h e n used in solid wheels e m e r y is still more thoroughly braced and backed up, for it is first mixed with a base and then united with such base by gums, glues or cements, aided by the processes of slow drying, baking heat, vitrifaction, tamping and hydraulic pressure. W h e n emery is used to make e m e r y cloth and paper it is also bedded in and backed up by glue. In not one of these cases do the e m e r y grains have any free motion of their own. T h e y do not change place in
June, I894.]
Emery and other Abrasives.
429
relation to each other, and are n o t worn-out b y the friction of e m e r y w i t h emery. T h e y do n o t b r e a k d o w n and crush to pieces, for t h e y are n o t only b a c k e d b u t s u r r o u n d e d b y t h e i r p r o t e c t i n g matrix, and so cannot flatten, spread and s q u e e z e a p a r t as does a free, u n s u p p o r t e d grain of which o n l y a small p a r t comes in c o n t a c t w i t h t h e opposing surfaces. Still a n o t h e r vital condition of Dr. Smith's test is" l a c k i n g in t h e cases of t h e lead wheel, the leather-covered wheel, and the e m e r y cloth and paper. In t h e s e cases the e m e r y is not r u b b e d b e t w e e n two u n y i e l d i n g surfaces, such as glass and agate, b u t b e t w e e n one yielding and one unyielding. Before the grain can cr~sh, the leather, generally chosen for its s p o n g i n e s s and compres*sibility, will y i e l d - - t h e lead will allow the grain to sink deeper in its surface, t h e cloth and p a p e r will do the same. T h e s e latter, so thin as to possess little compressibility, are often backed u p b y t h e h u m a n hand, which affords the s a m e cushion as does the s p o n g y walrus or sea-horse. Of these differences in t h e conditions of use the ordinary b u y e r takes no m o r e note than does the professional expert. .He applies, in a r o u g h way, the s a m e sort of test as does the e x p e r t - - a test w h i c h only s h o w s w h a t the e m e r y will do u n d e r conditions entirely different from those in which it will be used. H e placed s o m e of the e m e r y on a smooth, solid piece of metal, and presses it as hard as he can, affd w i t h a sliding motion, w i t h a n o t h e r piece of metal. If the grains are loosely a g g r e g a t e d or b a d l y shaped t h e y crush to pieces and the e m e r y is c o n d e m n e d . A n o t h e r test is to place the e m e r y in the p a l m of the h a n d and r u b it together with the t h u m b or finger. H e r e the e m e r y is used as an a b r a s i v e a g e n t to d e s t r o y itself. T h e thin edges and sharp corners are g r o u n d off and the e m e r y is c o n d e m n e d as soft and dirtyj It appears, therefore, that looseness of aggregation, or friability,and also the shape of grain, m a y be of importance. It is in the larger grains that friabilityshows most markedly, a n d it is q u i t e p r o b a b l e t h a t this friability differs very g r e a t l y in grains of different size. If e m e r y is a varied m e c h a n i c a l m i x t u r e m i n u t e subdivision m a y lessen the
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."
[J. F. I.,
v a r i e t y of m a t e r i a l s in each g r a i n and so alter the s t a a d a r d of cohesion and a g g r e g a t i o n . W h e r e the grain, in c r u s h i n g down, sets free particles of p u r e sapphire, it s e e m s clear t h a t these will not c r u s h to pieces as the more h e t e r o g e n e o u s g r a i n did. Even if a coarse g r a i n were proved too friable for some special work it w o u l d not follow t h a t finer e m e r y from the same ore was also too friable. It is an i m p o r t a n t fact t h a t the proportion of coarse g r a i n in use h a s g r e a t l y d i m i n i s h e d and t h a t f e w processes really d e m a n d a v e r y coarse and a v e r y r e s i s t i n g grain. T h e m a n u f a c t u r e r s of plows and of fire-proof safes, a n d the workers in g r a n i t e are those who seem m o s t inclined to coarse e m e r y . . T h e coarser it is the more }esistant m u s t be the grain, for the more it projects b e y o n d its glue bed the more easily will it b r e a k off or crush down. It is an i n t e r e s t i n g fact t h a t e m e r y w h i c h is p r o n o u n c e d too soft for such use m a y be a d a p t e d to i t b y special processes. W h a t e v e r m a c h i n e or process m a y be used to accomplish this, the principle of its o.peration is to abrade the e m e r y by friction a g a i n s t itself till sharp points, brittle corners and loosely a d h e r i n g particles are removed. C o n c e r n i n g t h e c o m p a r a t i v e v a l u e s of r o u n d - g r a i n e d e m e r y a n d t h a t of o t h e r shapes m u c h difference of opinion exists. T h e r o u n d e d or cubical g r a i n of large size will cert a i n l y be m o s t resistant, and, in all processes w h i c h reproduce the conditions of Dr. S m i t h ' s test, will p r o b a b l y be m o s t v a l u a b l e ; b u t it does not s e e m e v i d e n t t h a t a n y a d v a n t a g e will a t t a c h to such shapes w h e n t h e y are e m b e d d e d in a solid mass. A_r o u n d e d or cubical g r a i n of the finest g r a i n e d , h a r d e s t and m o s t c o m p a c t ore would p r o b a b l y be the best for g r a n i t e workers, b e c a u s e their processes are such as to crush a friable grain. I t is this fact w h i c h has led .to t h e g r o w t h of a new i n d u s t r y in the m a n u f a c t u r e of artificial abrasives. Chilled s h o t a n d c r u s h e d steel have a l r e a d y won a position a m o n g stone workers a n d will p r o b a b l y h a v e lasting and i n c r e a s i n g sale. ~ * T h e makers of crushed steel report that in 189o, their first business year, they sold 230,ooo pounds, which sale increased in 1892 to 460,00o pounds. I have not been able to learn the annual product of chilled shot.
June, 1894. ]
Emery and other Abrasives.
43I
A chilled shot and a g r a i n of W e s t c h e s t e r emery, loosely a g g r e g a t e d and b r i s t l i n g w i t h points, afford e x t r e m e contrasts. Our facts lead to the belief that loose a g g r e g a t i o n is not a serious defect, provided, as Dr. H e d d l e shows, that t h e particles are hard e n o u g h . T h e inference from his s t a t e m e n t is t h a t abrasive effect is p r o p o r t i o n e d to the h a r d n e s s of the particles. B u t Dr. H e d d l e ' s file test, like t h e giass and a g a t e test of Dr. Smith, lacks the principal condition in the m o d e r n use of abrasives. T h a t condition is hig h speed. P e n e t r a t i o n is effected b y velocity, and abrasion is effeeted b y the points of one s u b s t a n c e penet r a t i n g the s u b s t a n c e of another. A b o a r d is h a r d e r than a candle, y e t it is said t h a t a candle can b e shot t h r o u g h a board. Glass is harder t h a n lead, y e t a bullet of lead will m a k e a d e a n hole t h r o u g h a window. It s e e m s possible t h a t a like rule m a y hold good as to abrasives, and that mineral grains may, if used at t h e right velocity, p e n e t r a t e s u b s t a n c e s h a r d e r than t h e m s e l v e s and prove satisfactory a g e n t s of abrasion. On still a n o t h e r i m p o r t a n t point does Dr. Smith's test fail to m e e t the r e q u i r e m e n t s of practical use. It takes n o note of t h e p r e s s u r e required. If a grain of c r u s h e d steel or a d i a m o n d g e m be e m b e d d e d in the face of a solid e m e r y wheel t h e s e two articles w o u l d a b r a d e t h r o u g h the use of w h a t e v e r p r o j e c t i n g points t h e y m i g h t present. As the points wear off fiat faces w o u l d appear, d e s t i t u t e of c u t t i n g power, and no f u r t h e r abrasion w o u l d take place until p r e s s u r e e n o u g h h a d b e e n applied to crush the grains of d i a m o n d and steel and m a n u f a c t u r e n e w points for them. T h e h a r d e r and m o r e r e s i s t a n t the grains were the g r e a t e r w o u l d b e the pressure n e e d e d to effect this. T h e criterion which d e m a n d s the e x t r e m e of hardness, fineness, p u r i t y , c o m p a c t n e s s and resistance in a b r a d i n g minerals, is one w h i c h calls on the m a n u f a c t u r e r for a w a s t e f u l e x p e n d i t u r e of power, which forces on the l a b o r e r u n d u e physical strain, w h i c h p r e v e n t s his a t t a i n m e n t of m a n u a l skill, and which exposes h i m to u n n e c e s s a r y danger. T h i s criterion has m a d e d u r a b i l i t y the prime requisite in a b r a d i n g materials and t o o l s - - a d u r a b i l i t y w h i c h the b u y e r d e m a n d s w i t h o u t
432
P a r e t ."
[~. F. I.,
reference to t h e cost of his product, or to the welfare and s a f e t y of his men. R e s i s t a n c e of m a t e r i a l calls for resistance of worker, and t h a t a b r a d i n g m a t e r i a l is b e s t w h i c h does equal w o r k in equal time with the least possible p o w e r and pressure. S u c h a d a p t a t i o n to its work is n o t likely to b e f o u n d in a n y mineral of e x t r e m e p u r i t y or oneness of composition, w h o s e t e x t u r e is dense, w h o s e grain is fine, w h o s e cohesion is great. It is m o r e likely to be f o u n d in a mineral of such friability and such varied c o m p o s i t i o n as c a u s e s it to b r e a k up into c h a n g i n g and irregular f o r m s u n d e r m o d e r a t e pressure. W h i l e I consider the facts t h u s far s t a t e d u n q u e s t i o n a b l e and the inferences from t h e m correct, I h a v e to a v o w regard. ing e m e r y and o t h e r abrasives, w h a t I a v o w e d as to e m e r y wheels s o m e f o u r y e a r s a g o , b e f o r e the m e m b e r s of this Institute, namely, t h a t there are few exact data to demon. strate m y inferences. T h e g r e a t e r the c o n s u m p t i o n of a b r a s i v e s and the more varied their use, t h e g r e a t e r is t h e d i v e r g e n c e of o p i n i o n s - - t h e m o r e hopeless t h e c o n f u s i o n - the deeper the d i s t r u s t as to a n y scientific basis in the g r i n d i n g industry. T h e m e n w h o e m p l o y licensed firemen to run a s t e a m boiler, and still f u r t h e r p r o t e c t t h e m s e l v e s b y the periodical test of their boilers, give no t h o u g h t to the latent explosibility of solid e m e r y wheels in charge of common laborers. T h e railroad, which sends in to the f o u n d e r its own chemical f o r m u l a for car brasses, pays no h e e d to the i n h e r e n t s a f e t y of a vulcanized e m e r y wheel or the inherent d a n g e r of a vitrified one. T h e m a n u f a c t u r e r w h o insists on h a v i n g the candle-power of his electric light g u a r a n t e e d , and t h e horse-power of his t u r b i n e or e n g i n e m e a s u r e d b y a d y n a m o m e t e r , b u y s the lowest-priced e m e r y wheel he can find, b u t n e v e r discovers the cost of t h a t wheel's product. This d e g r a d a t i o n of the g r i n d i n g i n d u s t r y is d u e in part to that criterion of hardness in a b r a s i v e material which has m a d e w e i g h t and s t r e n g t h the criterion of the h u m a n grinder. It is due in part to the fact that g r i n d i n g p r o b l e m s are so o b s c u r e and difficult to the skilled m e c h a n i c t h a t he r e m i t s t h e m u n s o l v e d to the u n l e a r n e d w o r k m a n . This
Jane, t894.]
Emery and other Abrasives.
433
d e g r a d a t i o n of the g r i n d i n g i n d u s t r y goes back to early times. In the R o y a l M u s e u m at Berlin is a p a i n t i n g b y G e r a r d T e r Botch, of Deventer, p r o b a b l y e x e c u t e d a b o u t I65 o, which is m a r k e d b y all t h a t detail which generally characterizes p a i n t i n g of the H o l l a n d school. T h i s picture r e p r e s e n t s " T h e Grinder's Family." T h e work-room is a tumble-down, w r e t c h e d shed, a t t a c h e d to the dwelling-house. Only one m e m b e r of the family is at work, unless t h a t operation can be called w o r k in w h i c h the m o t h e r is engaged. She s e e m s to be s e a r c h i n g in t h e hair of her y o u n g d a u g h t e r for s o m e t h i n g that o u g h t n o t to be there. T h e g r o w n son, with almost a simpleton's face, and w i t h t a t t e r e d g a r m e n t s , ieans idly a g a i n s t a post. T h e old father has a wide shelf, j u s t level with the top of the grindstone, and lies upon it at full length upon his stomach, while he presses a scythe u p o n the grindstone. T h e o t h e r s c y t h e s lie o u t of reach on the floor. T h e mandril of the stone revolves in an uncovered groove in a beam, and a notch in that b e a m holds a w o o d e n w e d g e to keep the mandril in its place. E v e r y t h i n g indicates that activity is at a b i g d i s c o u n t - - a r t at a low e b b and w a g e s lower still. It is unfair, y o u will say, to steal this q u a r t e r - c e n t u r y old example from a pastoral c o u n t r y like Holland. Why not go to a m a n u f a c t u r i n g c o u n t r y in m o d e r n times ? W h y not visit Sheffield, for instance ? I did visit Sheffield in 1892. I asked a m a s t e r cutler to s h o w me the latest thing in grinding. H e said there was no late thing. I asked him a b o u t abrasives and he said'each individual grinder supplied his own, bu.ying a few p e n n y s w o r t h of e m e r y at the n e a r e s t chemist's and h a v i n g it chalked up a g a i n s t him j u s t as he h a d his b e e r chalked up at the tavern. H e said the grinders could generally be f o u n d at work when tfiey had no m o n e y to spend, a l w a y s p r o v i d i n g there w a s n ' t a football m a t c h on hand. H e told me to visit R o d g e r s ' and see w h a t t h e y did and then he w o u l d take m e outside the town to mills h u n d r e d s of years old and t h a t I w o u l d find the tools, the processes, the conditions identical. T h e factory b u i l d i n g he called " a wheel," and the v a u l t e d dungeons, w h o s e w i n d o w s had all t h e i r glass s h a t t e r e d to let in the VOL. CXXXVII. 28
434
Parer :
[ J. F. I.,
light which the splash and slop of the wet stone obscured, hc called "troughs." A strap (belt), a stone, a razor and a grinder were what constituted the grinding industry. I ignorantly spoke of the grinders as " men," but he said it was a c o m m o n Sheffield saying, "he's not a man; hc's only a grinder." I did go to the main establishment of Rodgers and then to a "wheel " in a valley some miles out of the city. T h e "wheel" was a long, dull building of cut stone. T h e newer part was about ioo or I5O years old, while one wing was m u c h older--too old for the date of its founding to be remembered. T h e grinder was a m a n over sixty, and he assured m c that his father and his father's farther had also ground razors there. "As I talked with him two younger m e n examined a pile of apparently worn-out grindstones, which they said were bought second-hand, w h e n too small for other use, and, selecting one of the quality desired, split it in two pieces because it was too thick. F r o m this dilapidated building, from these scant tools and crude processes, were evolved by grinders not thought worthy to be called men, those b' ~des which have m a d e the n a m e of Rodgers famous. Inherited skill and restriction to one narrow branch of work take the place of modern improvements. A s I r e m e m b e r this'initiation into the art of Sheffield, I smile at the London merchant w h o wrote to America that he could get a big order for Japan if I could supply a complete plant for razor grinding. In our o w n freer and more versatile country the tyranny of the trades-union has not gone so far as to insist that only the sons and grandsons of razor grinders shall learn to grind razors. Instead of old processes, perpetuated unchanged for hundreds of years, w e have all the newest wrinkles. Automatic grinding machines, almost h u m a n in their complication, and which render brains almost unnecessary to the w o r k m a n ; and others which look beautifully on paper, and either go to the waste pile or swell the maker's account of " returned goods." W e have the newest wrinkles, but no rulesnthe most ingenious devices, but no accepted standards--the most varied opinions, but no authorities.
June, x894.]
Emery and other Abrasives.
435
W h i l e g r i n d i n g processes are complicated and solid e m e r y wheels high-class tools, and while economical g r i n d i n g d e m a n d s conditions based on t h e careful s t u d y of e d u c a t e d mechanics, no one e s t a b l i s h m e n t uses e n o u g h to enlist the i n t e r e s t of the e d u c a t e d man. A b r a s i v e s are c o m m i t t e d to the lowest class of labor, and reports as to results drift t h r o u g h circuitous c h a n n e l s to the buyer, whose next purchase is based on the latest a n d m o s t distorted report. T h e n a m e of " W e l l i n g t o n " is so p o t e n t t h a t often the g r i n d e r will use no o t h e r b r a n d of emery, t h o u g h he will take a n y a n d all kinds of m a t e r i a l w i t h o u t discovering a n y difference, provided t h e y are poured out of a " W e l l i n g t o n " keg and have a coloi not found in the original material. T h r o u g h o u t the a p p a r e n t discussiveness of this lecture I h a v e carried on a s u s t a i n e d a r g u m e n t , b u t t h a t a r g u m e n t has been so l e n g t h y and so involved as to d e m a n d a summ a r y of conclusions. It seems clear to me t h a t c u r r e n t opinions about abrasives h a v e been based too m u c h on cabinet specimens and labo~'atory experiments, a n d too little on the average prod u c t s of the m i n e and on the conditions of m o d e r n work. It seems d e m o n s t r a t e d t h a t chemical analysis does not g a u g e a c c u r a t e l y the abrasive c a p a c i t y of a n y m i n e r a l - t h a t t h e h a r d n e s s of such m a t e r i a l does not bear a definite relation to its p u r i t y ( m e a n i n g t h e r e b y a h i g h p e r c e n t a g e of alumina), and equally clear t h a t mere h a r d n e s s is not the prime requisite. It seems clear t h a t abrasive capacity d e p e n d s l a r g e l y on some u n e x p l a i n e d p e c u l i a r i t y of structure. It seems e v i d e n t t h a t speed, time and pressure are factors too little considered in connection w i t h the problem of safe and economical g r i n d i n g . It seems settled t h a t e x t e r n a l appearance is a poor g u i d e to g r i n d i n g c a p a c i t y ; t h a t colors, shape of g r a i n and a t t r a c t a b i l i t y b y the m a g n e t are not t r u s t w o r t h y indications. It seems clear t h a t commercial abrasives v a r y in quality, a n d t h a t their acceptance or c o n d e m n a t i o n depends on prejudices and notions r a t h e r t h a n on ascertained facts as to cost of product. Some of the causes which" lead to variable and contradict o r y results w i t h abrasives are those c o m m o n to shop prac-
436
Parer:
[ J. F. I.,
flee, b u t which p r o d u c e far g r e a t e r effects w i t h the e m e r y wheel t h a n w i t h the l a t h e or planer. T h e effective work of an e m e r y wheel is based on its speed of a mile a m i n u t e . T h e correct speed is less likely to be m a i n t a i n e d , because the pressure a g a i n s t t h e wheel is h e a v i e r and more variable t h a n t h a t in a lathe. T h e l a t h e tool presses w i t h a sharp point only a g a i n s t the r e v o l v i n g work, and is so set that, after the first cut, the pressure scarcely changes. T h e grinder, however, forces his work a g a i n s t the wheel with g r e a t l y v a r y i n g s t r e n g t h , a n d s o m e t i m e s adds to direct pressure a h e a v y leverage. I have often seen wheels slowed down till t h e y almost stopped. Pulleys of too small diameters are used, and belts which are too narrow. Slip of belt and d i m i n u t i o n of speed are p o t e n t factors in the problem. A n o t h e r e q u a l l y p o t e n t one is d i s c o n t i n u i t y of contact. A w h e e l m a y r u n a mile a m i n u t e and y e t be so o u t of r o u n d or m o u n t e d on such a l i g h t m a c h i n e or s h a k y floor t h a t v i b r a t i o n and c h a t t e r interfere w i t h c o n t i n u o u s contact. I n s t e a d of a mile l o n g file passing over the work in a m i n u t e , it is s o m e t i m e s only an e i g h t h or a q u a r t e r mile file. I h a v e e x a m i n e d wheels whose c o n t i n u o u s s t r e a m of sparks s u g g e s t e d c o n t i n u o u s contact, a n d f o u n d t h a t only two or three inches of the surface h a d come in c o n t a c t w i t h the metal. T h e c u s t o m of i m p u t i n g all v a r i a b i l i t y of result to defect in the wheel and the overlooking of v a r i a b i l i t y in the m e t a l operated on is a n o t h e r cause of c o n t r a d i c t o r y result. A class of wheels w h i c h h a d l o n g s u i t e d a plow m a n u f a c t u r e r was at last r e p e a t e d l y c o n d e m n e d and t h e wheel declared worthless. A f t e r a v e r y l o n g i n t e r v a l it a p p e a r e d t h a t the plows h a d been c h a n g e d from one h o m o g e n e ous thickness to three sheets of v a r y i n g temper. A class of wheels was c o n d e m n e d which h a d long s u i t e d for car brasses, and only a f t e r l o n g delay was it m a d e k n o w n t h a t the first m e t a l was yellow brass and the last phosphor-bronze. I have lately discovered by use of an imp r o v e d t e s t i n g m a c h i n e t h a t the q u a l i t y of the test bars of east iron is more variable t h a n the q u a l i t y of t a n i t e wheels. W h a t , then, is needed, to clear up this confusion ?
June, x894.]
Emery and other Abrasives.
437
It s e e m s to me t h a t the t h i n g m o s t needed is a practical t e s t i n g machine, which shall take the place of the laboratory test m a d e p o p u l a r b y Dr. J. L a w r e n c e Smith. Such a m a c h i n e should be run b y an i n d e p e n d e n t engine to secure u n i f o r m speed. P u l l e y s and belts should be so proportioned t h a t no slip shall occur. Floor and m a c h i n e should be so solid as to do a w a y with vibration. T e s t bars should be e m p l o y e d of the m o s t u n i f o r m quality. A n d then a series of e x p e r i m e n t s should b e carried out so as to establish definite standards. It should b e ascertained w h a t is the least p r e s s u r e per square i n c h at w h i c h a cubic inch of test m e t a l can be g r o u n d off in the least time with the least c o n s u m p t i o n of w h e e l m a t e r i a l In other words, the final e c o n o m y of t h e process should be d e m o n s t r a t e d , taking into strict a c c o u n t the c o n s u m p t i o n of w h e e l material, the a m o u n t of m e t a l ground, the time occupied, the speed employed, the horse-power e x p e n d e d and the pressure exerted. T h u s will g r a d u a l l y arise a fixed s t a n d a r d as to w h a t c o n s t i t u t e s a g o o d e m e r y wheeI, and the b u y e r will d e m a n d an article of k n o w n and certified p r o d u c t i v e effect w h o s e cost of p r o d u c t is also known. T h u s will arise on the grinder's side a d e m a n d for t h o s e wheels and those a b r a s i v e s which entail the least b o d i l y fatigue. T h u s will arise a p u b l i c opinion w h i c h shall hold to strict account those reckless b u y e r s w h o p u t wheels of known d a n g e r o u s q u a l i t y in the h a n d s of their employds. F o r this m a c h i n e should riot only be used to ascertain the economic value of abrasives, b u t also to d e m o n s t r a t e the relative safety of solid e m e r y wheels. In closing this lecture, I desire to point o u t that it is not so m u c h a s t a t e m e n t of w h a t is k n o w n a b o u t abrasives as a confession of h o w little is known. T h i s confession i m p u t e s no special i g n o r a n c e to the user, b u t pleads the g r e a t o b s c u r i t y of the problem. I believe the difference b e t w e e n the p o o r e s t and the b e s t of the abrasives in c o m m o n use is so m o d e r a t e t h a t g r e a t expertness is r e q u i r e d to discover it. My o b j e c t will be a c c o m p l i s h e d if, b y pointing o u t the fallacies w h i c h attach to old-time tests and superficial indi-
438
G i l m a n ."
[ I. F. I..
cations, the w a y is cleared for a more a s c e r t a i n i n g abrasive q u a l i t y - - a more g e t t i n g at t h e economic r e s u l t - - a n d sideration of the laborer's d a n g e r a n d APPLICATION SQUARES
scientific m e t h o d of business-like w a y of a more h u m a n e confatigue.
OF THE METHOD TO THE DEVELOPMENT OF FUNCTIONS.
OF
LEAST
BY F. GILMAN.
T h e u s u a l m e t h o d s of d e v e l o p i n g a f u n c t i o n are b y the b i n o m i a l series and by the t h e o r e m s of Maclaurin and Taylor. In g e n e r a l practice, however, only a l i m i t e d number of t e r m s of t h e d e v e l o p m e n t can be calculated, and for such cases these t h e o r e m s do n o t give the best values o b t a i n a b l e for the co6fficients. L e t us take, for example, t h e f u n c t i o n I
l,/I + x T h e b i n o m i a l t h e o r e m gives i
= i--½x
1/i+x
+~}~--¢~+
(~)
W e will now a s s u m e I
--I
+ax
+bx2
+cx
3
1/i + x
and t r e a t i n g I
] / / I -~ X
as an observed q u a n t i t y , we will d e t e r m i n e the values of t h e c o n s t a n t s a, b and c from the condition t h a t the s u m of t h e squares of the residual errors shall be a m i n i m u m . S u p p o s i n g x to v a r y from o to I, the following table gives the values of I
1/i + x