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Engineering practice and education
44
[l' ~a{~
Zanza:
Each m a y sell his rights, or assign his interests, with~'~ti~ t h e consent of the other parties in interest. Many nice questions of law have arisen upon the q u e s t i o n of assignment, license and grant, and, in n u m e r o u s recent eases, {ine hair.splitting distinctions have been elaboramly discussed in the decisions, especially in eases where instruments purporting to be assignments were contended not to be such, but mere licenses for lack of proper phraseology, and, in n u m e r o u s cases, have been so held. T i m e forbids further discussion of the subject, and deeper invasions upon your indulgence in the consideration of t h e " Law of Invention." If these brief papers should be the means of giving the layman some insight into this particular branch of jurisprudence the object of their author has been accomplished.
ENGINEERING
PRACTICE
AND E D U C A T I O N .
BY GARTANO LANZA, S. B., C. & M. E., Professor of Theoretical and Applied Mechanics, Massachusetts Institute of • T~-chnology.
[Continued from vol. cxxxviii, t9. 478.]
T h e foregoing shows that the engineer who has to perform responsible work m u s t not trust to guesswork, b u t m u s t know the principles by means of which to determine the stresses in all parts of the machine or structure, and make his calculations in accordance with these principles. He should know the character of the experiments from which are deduced the constants he proposes to use, and he should also know enough about the tests to have an opinion as to w h e t h e r they were made u n d e r such conditions as to render them applicable to the work he has in hand. Besides this, he m u s t see, by careful inspection and tests, that the materials used are up to standard in quality. He must draw up such specifications as will secure suitable
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Engineering l"t'aclicc and Education.
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material, and t h e n he m u s t a p p l y the n e c e s s a r y tests to d e t e r m i n e w h e t h e r it fulfils the specifications. In order to do this properly he must, of course, k n o w w h a t tests s t r u c t u r a l m a t e r i a l of s u i t a b l e q u a l i t y can b e r e a s o n a b l y e x p e c t e d to fulfil, and w h a t kinds of tests are n e c e s s a r y in o r d e r to be able to d e t e r m i n e w h e t h e r the material possesses t h e good qualities desired, and w h e t h e r it is free from defects. In order to k n o w w h a t conditions to insist u p o n as to tensile strength, ductility, c a p a b i l i t y of bending, etc., he m u s t b e c o m e familiar with the b e h a v i o r of the m a t e r i a l s u n d e r stress and strain, and h e n c e he n e e d s to m a k e a careful s t u d y of the e x p e r i m e n t s t h a t h a v e been p e r f o r m e d especially those m a d e u n d e r such conditions as occur in practice. In addition to this he m u s t k n o w w h a t c o n s t i t u t e s good w o r k m a n s h i p , and he m u s t take t h e p r e c a u t i o n s n e c e s s a r y to secure it. U n l e s s t h e s e details are faithfully a t t e n d e d to, the result will not b e w h a t it should, even t h o u g h his calculation of the stresses m a y h a v e been ail right, and his constants correct for good m a t e r i a l s and w o r k m a n s h i p . In v i e w of w h a t I h a v e said, one m i g h t be inclined to ask w h y disasters are not of m o r e f r e q u e n t occurrence, and w h y o u r s t r u c t u r e s and m a c h i n e s g e n e r a l l y are as safe as t h e y are. F i r s t of all, we m a y o b s e r v e that, once in a while, s o m e disaster h a p p e n s w h i c h cannot be p r e v e n t e d from attracting public a t t e n t i o n ; such as the b r e a k a g e of t h e B u s s e y bridge, or t h e b u r s t i n g of t h e A m o s k e a g fly-wheel; but, f r e q u e n t l y w h e n b r e a k a g e s h a p p e n i'c is n o t considered b y the m a n a g e m e n t to b e c o n d u c i v e to their b e s t i n t e r e s t s to p u b l i s h an a c c o u n t of them. T h e n t h e r e are cases w h e r e p r o s p e c t i v e failure m a k e s itself e v i d e n t b e f o r e h a n d ; in o t h e r words, the piece g i v e s w a r n i n g of s t r u c t u r a l weakness, and, before an accident happens, it is e i t h e r replaced b y a s t r o n g e r one or else it is reinforced in s o m e way. Naturally, such cases as these are n o t p u b l i s h e d and are k n o w n to b u t a few; for the mana g e m e n t w o u l d not c o n s i d e r it to be to t h e a d v a n t a g e of their firm to have t h e r e p o r t s p r e a d a m o n g their employ6s
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[J. F. I,
or the o u t s i d e p u b l i c t h a t t h e s t r u c t u r a l w e a k n e s s e x i s t e d . Cases of t h i s k i n d h a v e c o m e to m y n o t i c e . A g a i n , t h e r e a r e o t h e r c a s e s w h e r e t h e s t r u c t u r e or m a c h i n e is n o t on t h e v e r g e of collapse, b u t w h e r e t h e marg i n of s a f e t y is less t h a n g o o d e n g i n e e r i n g r e q u i r e s , a n d w h e r e t h e s t r u c t u r a l w e a k n e s s s h o w s i t s e l f in a l a c k of stiffness, a n d c o n s e q u e n t l y in p o o r work, in t h e c a s e of a m a c h i n e ; or in v i b r a t i o n or y i e l d i n g in t h e case of a s t r u c t u r e , as a b u i l d i n g , or a b r i d g e . W e m u s t r e m e m b e r t h a t t h e s t r e n g t h of a s t r u c t u r e is t h e s t r e n g t h of its w e a k e s t p a r t , a n d t h a t a d d i n g to t h e s t r e n g t h of o t h e r p a r t s is o n l y a w a s t e of m a t e r i a l ; a l s o t h a t a d d i n g m a t e r i a l w h e r e it d o e s n o t i n c r e a s e t h e s t r e n g t h is also a w a s t e of m a t e r i a l ; so t h a t a d e s i g n w h i c h d o e s n o t p r o p e r l y c o n s i d e r t h e n e c e s s a r y s t r e n g t h a n d s t i f f n e s s of all t h e p a r t s is n o t m e r e l y u n s a f e b u t is also u n e c o n o m i c a l , a n d r e s u l t s in a w a s t e of m o n e y . E n o u g h h a s b e e n said to s h o w t h e i m p o r t a n c e to t h e e n g i n e e r of a t h o r o u g h k n o w l e d g e of t h e s t r e n g t h of m a t e r i a l s w h e n e v e r it c o m e s i n t o p l a y i n t h e d e s i g n a n d c o n s t r u c t i o n of e i t h e r s t r u c t u r e s or m a c h i n e s , a n d it o n l y r e m a i n s to s h o w t h a t t h e s e are m a t t e r s t h a t t h e e n g i n e e r has to c o n s i d e r a n d act u p o n a t e v e r y t u r n , w h e t h e r h e is w h a t is c o m m o n l y c a l l e d a civil e n g i n e e r , a m e c h a n i c a l e n g i n e e r , a m i n i n g e n g i n e e r , a m e t a l l u r g i c a l e n g i n e e r or a. c h e m i c a l e n g i n e e r . T o b e c o n v i n c e d of this, w e n e e d o n l y c o n s i d e r the c h a r a c t e r of s o m e of t h e d u t i e s t h a t d e v o l v e ~pon tb.c e n g i n e e r , in t h e d i f f e r e n t k i n d s of w o r k s w h i c h w , : ~ r c d~,scribed in t h e first t h r e e l e c t u r e s . Re, fcrrh~ g n e x t to s o m e o t h e r m a t t e r s in c o n n e c t i o n w,t!, a p p l i e d "mechanics, I m u s t e m p h a s i z e t h e i m p o r t a n c e ~t" t.d
Jan., I895.]
E~iffi~zeeringPractice an~ZEdztcaffan.
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variety of tests of the s t r e n g t h and stiffness of iron, steM, wood, cement, etc., we are c o n s t a n t l y t e s t i n g t h e s t r e n g t h of full-size t i m b e r beams. E v e r y once in a while one will break by s h e a r i n g along the n e u t r a l axis or center of the depth, i n s t e a d of t e a r i n g at the b o t t o m or c r u s h i n g at the top. I r e m e m b e r , on a certain occasion, w h e n I called attention to this fact, t h a t a g e n t l e m a n proceeded to argue trom it t h a t t h e r e was a s h e a r i n g force a c t i n g in the case of a beam which the c o m m o n t h e o r y of b e a m s did n o t take into account. E v i d e n t l y to h i m the c o m m o n t h e o r y of beams was only the set of formulze most c o m m o n l y recorded in the books, for he a p p a r e n t l y was not aware t h a t it does include a c o n s i d e r a t i o n of the s h e a r i n g stresses. A n o t h e r i l l u s t r a t i o n m i g h t be taken in the fact t h a t the ordinary formulae for the deflections of b e a m s are deduced from an a p p r o x i m a t e equation, where one term has been neglected, w h i c h is small in all o r d i n a r y cases of b e a m s in structures. By u s i n g this a p p r o x i m a t e e q u a t i o n in a case where the n e g l e c t e d term was very large, some one m a d e out an i m a g i n e d m a t h e m a t i c a l d e m o n s t r a t i o n t h a t an unbalanced r o t a t i n g body g o i n g at a h i g h speed p o u n d s towards the light i n s t e a d of the h e a v y side, a r e s u l t m a n i f e s t l y absurd. Again, if the s t u d e n t clearly u n d e r s t a n d s all the assumptions made in d e d u c i n g the formulae, he will u n d e r s t a n d that the Gordon f o r m u l a for columns is not d e m o n s t r a t e d , depending as it does on a s s u m p t i o n s t h a t c a n n o t be proved ; and he will be in a more judicial f r a m e of m i n d in tryil~<~r to d e t e r m i n e how to make use of the experimenta! k n o w l e d g e on the subject t h a t we possess up to date. Next, in r e g a r d to the t h e o r y of e l a s t i c i t y ; this is necessary in c o n s i d e r i n g certain eases of complicated stresses, and while we use it now to some extent, as in d e t e r m i n i n g the . s t r e n g t h of flat plates and of shafting, it will, I do not doubt, come more into use w h e n we g e t more light e x p e r i m e n t a l l y on some m a t t e r s c o n n e c t e d with it. I need ¢,~,., n o t h i n g upon the i m p o r t a n c e of h a v i n g a knowledge of the principles of friction and lubrication, and of the e x p e r i m e n t a l k n o w l e d g e on the s u b j e c t up to date,
48
Lanaa
."
[ 1. F. I.,
b e y o n d calling to y o u r n o t i c e , t h a t the c h a n g e from a poor to a good l u b r i c a n t m a y often m a k e a decided difference in the size of the dividends received b y t h e stock-. holders of a large concern. T h e n e x t course to receive our a t t e n t i o n is t h a t of Then> m o d y n a m i e s a n d S t e a m E n g i n e e r i n g . It m i g h t be a s s u m e d by some t h a t this was peculiarly the province of the so. called m e c h a n i c a l e n g i n e e r ; b u t if y o u will consider again the a c c o u n t of the different works of w h i c h the first three lectures treated, y o u will realize that, in every work of any m a g n i t u d e , power is needed, and in a l m o s t all cases the power used is steam. T h e exceptions are those eases where tile works are favorably s i t u a t e d for the use of water-power, and even t h e n s t e a m is a l m o s t always used in a d d i t i o n ; and p e r h a p s I o u g h t to m a k e a n o t h e r exception in the case of sailing vessels, where the w i n d is used. O t h e r sources of power, or w a t e r or wind in eases other t h a n those mentioned, are only e m p l o y e d for small a m o u n t s of power. W i t h o u t power all the works would h a v e to s h u t down ; the b r i d g e works could n o t b u i l d bridges, the m a c h i n e shop or m a n u f a c t o r y or mill would have to stop, t h e m i n e could not be operated, the rolling mill could not run, the dynamos a n d electric motors w o u l d be idle, the p a p e r mill, the s u g a r refinery, etc., would h a v e to d i s e o n t i n n e operations. Moreover, the expenses for power in a n y large concern form a very large i t e m ; t h e y i n c l u d e the first cost of m a c h i n e r y , of n e c e s s a r y buildings, of coal bunkers, etc., the expenses of m a i n t e n a n c e , i n c l u d i n g coal, water and a t t e n d a n c e , and the expenses for repairs. It behooves the engineer, therefore, to try to realize the g r e a t e s t possible economy. One of the l a r g e s t i t e m s of expense, after t h e p l a n t is once in operation, is coal, and a n y m e t h o d b y w h i c h he can save coal will increase the profits of the concern. In order to accomplish this, the e n g i n e e r m u s t unden> s t a n d the principles of s t e a m e n g i n e e r i n g , a n d the l a r g e r the works w i t h which he is connected, a n d hence, the g r e a t e r the q u a n t i t y of m o n e y involved, the m o r e i m p o r t a n t is it t h a t he s h o u l d h a v e all t h e l i g h t possible, b o t h from theory~ and from e x p e r i m e n t , t h a t will aid h i m in d e t e r m i n i n g how
Jan., 1895.]
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his engines should be d e s i g n e d and built, h o w his boilers should be d e s i g n e d and built, w h a t d e g r e e of efficiency he has reason to expect with a n y given a r r a n g e m e n t which he m a y propose to adopt. Hence, it is plain that our prospective e n g i n e e r needs a t h o r o u g h course in s t e a m engineering, of w h i c h t h e r m o d y n a m i c s is m e r e l y the theoretical part; and he n e e d s this, w h a t e v e r be t h e kind of engineering works he m a y expeet to be e o n n e c t e d with, if they are to be of considerable m a g n i t u d e . In d e c i d i n g upon the question as to h o w such a course s h o u l d b e laid out, we sha!.l a s s u m e t h a t he is a l r e a d y familiar with v a l v e gears, and with the rest of the m e c h a n i s m of t h e s t e a m e n g i n e ; also assume that he has had a course on heat in his physics, and that, in this course, he has been taught the subjects of ~hermometry, calorimetry, and the laws of the transference of heat. H e should be taught the nature and construction of the steam engine indicator; h o w it is to be used; h o w the indicator card is taken, and what it means, and he should acquire some familiarity with interpreting the characteristlc and also/ some of the peculiar features of indicator cards; and then he Should be m a d e familiar with the general characteristics, i. e., outward characteristics, of the different types of steam engines. Next, he should receive a t h o r o u g h drill in the principles of t h e r m o d y n a m i c s . W h a t is t h e r m o d y n a m i c s , and w h a t kind of a course should our p r o s p e c t i v e e n g i n e e r have in the s u b j e c t ? T h e r m o - d y n a m i c s is simply the mechanical theory of heat, or, in o t h e r words, the science of heat with special reference to p r o d u c i n g motion and power. T h e s u b j e c t was originally d e v e l o p e d f r c m the standpoint of the m a t h e m a t i c a l physicist, and we have a number of treatises w r i t t e n from this point of view, such as that of Clausius and others. Besides the f u n d a m e n t a l principles of t h e science, t h e y take up e l a b o r a t e discussions of the n a t u r e of heat, and also a large mass of applications and d e v e l o p m e n t s in the direction, a n d .from the point of view, of pure science, r a t h e r than in t h e direction of w h a t we need to use in the consideration and the s t u d y of the VOL. CXXXIX. 4
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." •
•
action of the s t e a m engine, or of other h e a t engines, as the gas engine, t h e h o t air engine, etc. I n s t e a d of this, in the course to be g i v e n to our prospeetive engineer, we s h o u l d include a t h o r o u g h t r e a t m e n t of the f u n d a m e n t a l principles o f the subject, a s t u d y of the laws of t h e r m o - d y n a m i e s , Carnot's function, and the whole set of f u n d a m e n t a l equations, and t h e i r i n t e r p r e t a t i o n s . T h e n should come the applications of these f u n d a m e n t a l principles to the gases and vapors used in practice for prod u c i n g power, espeeially steam, and also gas and air. T h e n a s t u d y of the e x p e r i m e n t s t h a t h a v e been made, and the results of the e x p e r i m e n t s on the properties of vapors and gases; the e x p e r i m e n t a l d e t e r m i n a t i o n s of the m e c h a n i c a l equivalent of h e a t ; the tables of the properties of s'aturated steam, as pressure, t e m p e r a t u r e , density, specific heat, l a t e n t heat, entropy, etc.; also the same for other vapors. Then a st~idy of the laws g o v e r n i n g t h e flow of fluids, both gases and vapors, t h r o u g h orifices and in pipes, i n c l u d i n g a consideration of the resistances and a s t u d y of t h e steam injector. T h e n the s t u d e n t is prepared for a s t u d y of the bel~vi,,~' ~,f ,~team in the cylinder of a s t e a m engine• A t this point he should be t a u g h t the m o d e r n m e t h o d s of :m:!l\-zing and s e p a r a t i n g the various actions of the steam timt passes t h r o u g h the engine, and of g i v i n g to each {t~ pr<,per c o n s i d e r a t i o n ; as, for example, t h e h e a t used up in work, t h a t used up in cylinder condensation, t h a t H~-~ ~,? il~ ('onden,~ation in the jackets, if there are any, the heat rejected by the engine, radiation ; also the m e t h o d s of bttid) itig the effects of s u p e r h e a t e d steam, etc.: all these for both single and multiple expansion engines, and, in the cases ,,f tl,c latter, the effects of different sizes and a r r a n g e m e n t s of receivers, the m e t h o d s of p r o p o r t i o n i n g the cylinders, etc. Next, he should learn w h a t are the r e q u i r e m e n t s for a proper engine test, both w h e n it is m a d e for o r d i n a r y commercial purposes, and also when it is to be m a d e in a t h o r o u g h l y complete and scientific m a n n e r for the purpose of o b t a i n i n g definite k n o w l e d g e as to how to produce the
Jan., I895]
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best and m o s t economical results by m e a n s of a steam engine. T h e day w h e n the ~aking of a few i n d i c a t o r cards from an engine, or the m a k i n g of tests in which scientific principles and scientific accuracy are neglected, a n d c l a i m i n g t h a t such tests can f u r n i s h i n f o r m a t i o n as to w h a t the real effects of different a r r a n g e m e n t s are, is r a p i d l y p a s s i n g away, the advocates of such a course c o n f o u n d i n g t h e m s e l v e s and each other by r e a c h i n g too m a n y Contradictory conclusions by their tests. Now, from the e x p e r i m e n t a l point of view, the s t u d e n t should have p r e s e n t e d to him, in a c a r e f u l l y s y s t e m a t i z e d form, an a c c o u n t of sudh e x p e r i m e n t s as have been made, with such a degb"ee of a c c u r a c y and such r e g a r d for scientific principles as t6 r e n d e r t h e m w o r t h y of study. Of course, there will be a n u m b e r of tests in this list which are not up to the scientific s t a n d a r d s of to-day ; b u t such a s t u d y will make the s t u d e n t f a m i l i a r with w h a t is the e x t e n t of our l:nowledge of the subject up to date, and he will be.all the b e t t e r able to m a k e this s t u d y effective, b y being relieved of the n e c e s s i t y of r e a d i n g a c c o u n t s of a lot of worthless tests for the sake of finding out those t h a t are worth considering. T h e n he should have a good course on s t e a m boilers, including the c o n s t r u c t i o n and action of the various types in use ; on the laws controlling the c o m b u s t i o n of fuel, and the evaporation of w a t e r ; on questions of h e a t i n g surface, gra~e area, t u b e section, horse-power, capacity, evaporative ethciency, e v a p o r a t i o n from and at 212 °, p r i m i n g or superheating, d r a u g h t , q u a n t i t y of air r e q u i r e d for combustion, t e m p e r a t u r e of flue gases, size of c h i m n e y , m e t h o d s of feed ing, m e t h o d s of d e t e r m i n i n g q u a l i t y of the s t e a m ; and on boile: accessories, such as gauges, w a t e r glasses, grates, stokers, feed pumps, injectors, feed w a t e r heaters, economizers, d a m p e r regulators, etc. T h i s i n s t r u c t i o n should embrace also the r e q u i r e m e n t s for a reliable a n d accurate evaporative t e s t ; w h a t arc the possible m a x i m u m evaporative efficiencies, and w h a t are usual e v a p o r a t i v e efficiencies attainable u n d e r o r d i n a r y conditions.
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Lanza :
[ J. F. I.,
He s h o u l d also s t u d y the more recent applications of t h e r m o - d y n a m i c s , such as air compressoR, gas engines and r e f r i g e r a t i n g m a c h i n e s . In these cases a lack of f a m i l i a r i t y w i t h the laws of t h e r m o - d y n a m i c s on the part of the m a k e r s is very likely to m a k e itself a p p a r e n t to the u s e r t h r o u g h the m e d i u m of his pocket-book, and in no case will this be more likely to be true t h a n in the case of the r e f r i g e r a t i n g machine, e i t h e r for cold storage or for the m a k i n g of artificial ice, a n d those w h o are e n g a g e d in this business are very r a p i d l y realizing this fact. Now, w h e n the s t u d e n t has finished the work referred to on the s t e a m e n g i n e indicator, and has a c q u i r e d t h e fundam e n t a l principles of therm-odynanZxics, and is s t u d y i n g the action of t h e s t e a m in an engine, it is a pr6per time for him to begin work in the laboratory, b y m a k i n g s t e a m e n g i n e tests, a l t e r n a t i n g his duties at each successive test u n t i l he has been drilled in p e r f o r m i n g all the different parts of the work, and in m a k i n g all the necessary calculations. For this purpose a small engine is, of course, b e t t e r t h a n none, b u t it is m u c h b e t t e r for the e d u c a t i o n of t h e s t u d e n t if his work can be done u p o n an e n g i n e sufficiently large to work w i t h an e c o n o m y comparable w i t h t h a t f o u n d in such e n g i n e s as are used in large and well-designed m o d e r n plants. S u c h tests m a d e by the s t u d e n t himself, u n d e r the direction a n d g u i d a n c e of the instructor, will leave a l a s t i n g impression upon his mind, and will c o n v e y i n f o r m a t i o n which he c a n n o t acquire as wel! in any o t h e r way. Hence, it is far b e t t e r to use a triple, or at least a c o m p o u n d engine, of sufficient size to secure a s t e a m c o n s u m p t i o n of a b o u t f o u r t e e n or fifteen p o u n d s of w a t e r per horse-power per hour, t h a n to use a small single engine, w h e r e the steam c o n s u m p t i o n per h o r s e p o w e r per h o u r is as h i g h as thirty, f o r t y or m o r e pounds. In m a k i n g the tests no loose work s h o u l d be allowed, b u t the s t u d e n t should be r e q u i r e d to p e r f o r m all the work w i t h the g r e a t e s t a c c u r a c y possible, a n d this a c c u r a c y s h o u l d be such as to r e n d e r the test t h o r o u g h l y reliable from a scientific standpoint. T h i s can be accomplished provided the i n s t r u c t o r exercises the necessary supervision over the work.
Jan. 1895.]
~11~[izc~'ri71o?Prclc[l'cc
~n~ E~llcctg~'ol~.
~3
Later in the course the s t u d e n t should m a k e a c c u r a t e and carefully c o n d u c t e d boiler tests on some large boilers. By these m e t h o d s , he will be m a d e to appreciate b e t t e r the work w h i c h he is doing in the class-room and will see t h a t it finds its application in j u s t s u c h work as an engineer has to do in the course of his profession. Of course, he s h o u l d h a v e to perform other sorts of experimental work with s t e a m in the l a b o r a t o r y besides e n g i n e and boiler tests, b u t of these will be referred to later. The whole idea of such a course as I have o u t l i n e d is, as you will see, to give the s t u d e n t a t h o r o u g h drill in the fundamental principles of' the subject, and t h e n to t e a c h h i m how these principles apply to the work of t h e engineer, by means of b o t h class-room and l a b o r a t o r y work, t h e deductions and d e v e l o p m e n t s from t h e f u n d a m e n t a l principles being made in the direction of e n g i n e e r i n g work, i n s t e a d of in the direction of "pure science ; and then, by m e a n s of this work, and also by s h o w i n g h i m where we s t a n d to-day in regard to t h e m a t t e r of reliable e x p e r i m e n t a l results, to equip him as fully as possible to appreeiate a n d to take p a r t in the best and m o s t scientific e n g i n e e r i n g work of the present times, a n d t h u s to be r e a d y in the f u t u r e , ever to take a d v a n t a g e of, and to take his part in developing, whatever progress the f u t u r e m a y h a v e in store for us. A n o t h e r f u n d a m e n t a l s u b j e c t is hydraulics. Our prospective e n g i n e e r should u n d e r s t a n d the principles of hydrostatics and h y d r o d y n a m i c s ; in o t h e r words, the laws governing the pressure of water, and the flow of water, w h e t h e r in pipes, in open channels, t h r o u g h orifices or over weirs. He should also be f a m i l i a r w i t h the c h a r a c t e r a n d the results of such e x p e r i m e n t s as h a v e been m a d e u p o n t h e s e subjects, a n d should know how to conduct such experimental work. W h a t e v e r m a y be the special line of e n g i n e e r i n g in which he is engaged, he is liable to have to establish a water supply, with all the necessary works, such as reservoirs, p u m p i n g engines, piping, etc.; or to b u i l d a s y s t e m of sewerage, or he m a y find his m a n u f a c t o r y so s i t u a t e d t h a t it is advisable to take a d v a n t a g e of a water-power, a n d to
54
L a m i n a ."
,[J. F. I.,
b u i l d all the necessary works, such as dams, canals, locks, sluice-ways, etc. H e m a y have to establish river or h a r b o r works, or, even if not these, he m a y h a v e to b u i l d a wharf, a quay, or even a dock, if his works are on the water's edge. Unless he is to m a k e a specialty of h y d r a u l i c work, he cannot, in a four years' course of engineering, afford t h e time to make h i m s e l f m a s t e r of the details of all these k i n d s of works, but he s h o u l d become f a m i l i a r with the principles stated above, and t h e n he can a f t e r w a r d m a k e a special s t u d y of p a r t or all of these subjects. N e x t comes t h e q u e s t i o n as to h o w far electricity s h o u l d be a c c o u n t e d a f u n d a m e n t a l subject, and c o n s e q u e n t l y one to be required of all e n g i n e e r i n g s t u d e n t s , w h a t e v e r their special lines. It is now u s u a l l y c u s t o m a r y to require t h e m to learn some electricity in connection w i t h general physics, and s o m e t i m e s a little more ; the rest b e i n g g i v e n to s t u d e n t s of electrical e n g i n e e r i n g only. W h e t h e r or not a considerably larger a m o u n t s h o u l d be p u t in the list of f u n d a m e n t a l studies, will d e p e n d u p o n h o w far a n d how i n t i m a t e l y electrical appliances come to associate t h e m s e l v e s with the every-day work of the engineer, w h a t e v e r his specialty. T h e p r o b a b i l i t i e s are, it seems to me, t h a t it will not be m a n y years before we shall have to insert a m u c h larger a m o u n t of electricity t h a n we now do in our list of f u n d a m e n t a l studies. T h e subjects t h u s far e n u m e r a t e d are f u n d a m e n t a l , and are necessary for our prospective engineer, w h a t e v e r be the special line of e n g i n e e r i n g to which he is to d e v o t e himself. He cannot afford to do w i t h o u t a n y one of t h e m . In l a y i n g out, therefore, a n y e n g i n e e r i n g course, of whatever name, w h e t h e r civil, mechanical, m i n i n g , metallurgical, electrical, or chemical engineering, we s h o u l d arrange, first of all, the t i m e n e c e s s a r y to give good courses in mathematics, g e n e r a l physics, d r a w i n g (including descriptive geometry), m e c h a n i s m , applied m e c h a n i c s (including, of course, s t r e n g t h of materials), t h e r m o - d y n a m i c s a n d steam, and the g e n e r a l principles of hydraulics. Moreover, thoro u g h i n s t r u c t i o n in these should not be sacrificed to a n y
Jan., ~895.]
E~zgim'crinff Fractice and Edztcatwn.
55
other subjects, w h e t h e r of an e n g i n e e r i n g or of a general character. In o t h e r words, the work in these s u b j e c t s should be thorouffhly performed, w h a t e v e r else is or is not accomplished. W h e n this has b e e n done, we can then, and not till then, begin to consider w h a t other s u b j e c t s s h o u l d be added, and these m a y be classified as follows: (x) s u b j e c t s of a professional n a t u r e b e a r i n g on the work of an e n g i n e e r in general, w h a t e v e r his specialty; (2) s u b j e c t s of a professional nature, w h i c h bear directly on the special line of engineering which the course is intended to t e a c h ; (3) subjects of a non-professional character i n t e n d e d to b r o a d e n the field of k n o w l e d g e and to i m p a r t general i n f o r m a t i o n ; (4) s u b j e c t s w h i c h fulfil partly one of these functions, and partly another. In the first class, t h o u g h respectively of v e r y different degrees of importance, I should place (a) m a c h i n e design, (b) dynamics of machinery, (c) m e t a l l u r g y of iron, (d) heating and ventilation, (e) stereotomy, ( f ) surveying, (g) shopwork. H o w m a n y , and which of these s u b j e c t s can be added will d e p e n d u p o n circumstances. R e v i e w i n g in detail the kind, of course, I h a v e in mind under each of these heads, I will make t h e following remarks : (a) dgac/zhze Dcs@/z.--This course, to be of the g r e a t e s t value, should take up problems of real e n g i n e e r i n g design, and should deal especially w i t h the details. T h u s the student should be m a d e to s t u d y each s e p a r a t e piece, and its connection with the other pieces, to d e t e r m i n e the forces acting upon it, and the stresses to which t h e piece is subject in c o n s e q u e n c e of the action of these forces, and to design the separate details in such a m a n n e r t h a t they shall have the r e q u i s i t e s t r e n g t h and stiffness. Of course, it is desirable, also, to have some w o r k done on mechanism design, where the s t u d e n t s h a l l have practice in a d a p t i n g m e c h a n i s m s to the special o b j e c t s that are to be accomplished, b u t it is also i m p o r t a n t t h a t he shouhl learn that in m a k i n g any such design, he m u s t s t u d y the s t r e n g t h and stiffness of each separate piece of which the m a c h i n e is
56
Chemical Section.
[ J. F. I ,
composed, and m u s t be fully i m p r e s s e d with the facts t h a t any one of these that is not properly designed, m e a n s a m a c h i n e that is not properly c o n s t r u c t e d and m a y m e a n the total failure of the r e s u l t i n g mechanism. (b) U n d e r the t e r m d y n a m i c s of machinery, I include such s u b j e c t s as governors, fly-wheels, d y n a m o m e t e r s , the action of the r e c i p r o c a t i n g p a r t s of a s t e a m engine, etc. I need only m e n t i o n these topics to m a k e plain their i m p o r t a n c e to a n y engineer. M e t a l l u r g y of iron and h e a t i n g and ventilation will, I think, also m a k e plain their i m p o r t a n c e b y a m e r e m e n t i o n of their names. [ To be canc/ucled.] A REVIEW
oF S T E R E O - C H E M I S T R Y . ~
BY STEWART WOODFORD YOUNG.
T h e old s t r u c t u r a l formula for m e t h a n e r e p r e s e n t e d t h e molecule of t h a t s u b s t a n c e as b e i n g c o n s t r u c t e d by p l a c i n g the carbon a t o m at the point of intersection of t h e t w o diagonals of a square, t h e four corners of the square b e i n g the positions occupied b y the four h y d r o g e n s . T h i s form u l a (Fig~. z) however, conflicts w i t h the facts w h e n we consider the di-derivatives of m e t h a n e . As is well known,
H2 H1
C ,-
Ha
I
H~ FIG. T.
m e t h a n e allows of the formation of b u t one series of di-derivatives. One and only one d i c h l o r m e t h a n e is known. Now, this f o r m u l a allows of the existence of two series of isomeric all-derivatives, (Yz~. 2) (a) r e p r e s e n t i n g a di-derivaRead before the C h e m i c a l Section.
[l' ~a{~
Zanza:
Each m a y sell his rights, or assign his interests, with~'~ti~ t h e consent of the other parties in interest. Many nice questions of law have arisen upon the q u e s t i o n of assignment, license and grant, and, in n u m e r o u s recent eases, {ine hair.splitting distinctions have been elaboramly discussed in the decisions, especially in eases where instruments purporting to be assignments were contended not to be such, but mere licenses for lack of proper phraseology, and, in n u m e r o u s cases, have been so held. T i m e forbids further discussion of the subject, and deeper invasions upon your indulgence in the consideration of t h e " Law of Invention." If these brief papers should be the means of giving the layman some insight into this particular branch of jurisprudence the object of their author has been accomplished.
ENGINEERING
PRACTICE
AND E D U C A T I O N .
BY GARTANO LANZA, S. B., C. & M. E., Professor of Theoretical and Applied Mechanics, Massachusetts Institute of • T~-chnology.
[Continued from vol. cxxxviii, t9. 478.]
T h e foregoing shows that the engineer who has to perform responsible work m u s t not trust to guesswork, b u t m u s t know the principles by means of which to determine the stresses in all parts of the machine or structure, and make his calculations in accordance with these principles. He should know the character of the experiments from which are deduced the constants he proposes to use, and he should also know enough about the tests to have an opinion as to w h e t h e r they were made u n d e r such conditions as to render them applicable to the work he has in hand. Besides this, he m u s t see, by careful inspection and tests, that the materials used are up to standard in quality. He must draw up such specifications as will secure suitable
Jan., x895 ]
Engineering l"t'aclicc and Education.
45
material, and t h e n he m u s t a p p l y the n e c e s s a r y tests to d e t e r m i n e w h e t h e r it fulfils the specifications. In order to do this properly he must, of course, k n o w w h a t tests s t r u c t u r a l m a t e r i a l of s u i t a b l e q u a l i t y can b e r e a s o n a b l y e x p e c t e d to fulfil, and w h a t kinds of tests are n e c e s s a r y in o r d e r to be able to d e t e r m i n e w h e t h e r the material possesses t h e good qualities desired, and w h e t h e r it is free from defects. In order to k n o w w h a t conditions to insist u p o n as to tensile strength, ductility, c a p a b i l i t y of bending, etc., he m u s t b e c o m e familiar with the b e h a v i o r of the m a t e r i a l s u n d e r stress and strain, and h e n c e he n e e d s to m a k e a careful s t u d y of the e x p e r i m e n t s t h a t h a v e been p e r f o r m e d especially those m a d e u n d e r such conditions as occur in practice. In addition to this he m u s t k n o w w h a t c o n s t i t u t e s good w o r k m a n s h i p , and he m u s t take t h e p r e c a u t i o n s n e c e s s a r y to secure it. U n l e s s t h e s e details are faithfully a t t e n d e d to, the result will not b e w h a t it should, even t h o u g h his calculation of the stresses m a y h a v e been ail right, and his constants correct for good m a t e r i a l s and w o r k m a n s h i p . In v i e w of w h a t I h a v e said, one m i g h t be inclined to ask w h y disasters are not of m o r e f r e q u e n t occurrence, and w h y o u r s t r u c t u r e s and m a c h i n e s g e n e r a l l y are as safe as t h e y are. F i r s t of all, we m a y o b s e r v e that, once in a while, s o m e disaster h a p p e n s w h i c h cannot be p r e v e n t e d from attracting public a t t e n t i o n ; such as the b r e a k a g e of t h e B u s s e y bridge, or t h e b u r s t i n g of t h e A m o s k e a g fly-wheel; but, f r e q u e n t l y w h e n b r e a k a g e s h a p p e n i'c is n o t considered b y the m a n a g e m e n t to b e c o n d u c i v e to their b e s t i n t e r e s t s to p u b l i s h an a c c o u n t of them. T h e n t h e r e are cases w h e r e p r o s p e c t i v e failure m a k e s itself e v i d e n t b e f o r e h a n d ; in o t h e r words, the piece g i v e s w a r n i n g of s t r u c t u r a l weakness, and, before an accident happens, it is e i t h e r replaced b y a s t r o n g e r one or else it is reinforced in s o m e way. Naturally, such cases as these are n o t p u b l i s h e d and are k n o w n to b u t a few; for the mana g e m e n t w o u l d not c o n s i d e r it to be to t h e a d v a n t a g e of their firm to have t h e r e p o r t s p r e a d a m o n g their employ6s
46
Lanza
."
[J. F. I,
or the o u t s i d e p u b l i c t h a t t h e s t r u c t u r a l w e a k n e s s e x i s t e d . Cases of t h i s k i n d h a v e c o m e to m y n o t i c e . A g a i n , t h e r e a r e o t h e r c a s e s w h e r e t h e s t r u c t u r e or m a c h i n e is n o t on t h e v e r g e of collapse, b u t w h e r e t h e marg i n of s a f e t y is less t h a n g o o d e n g i n e e r i n g r e q u i r e s , a n d w h e r e t h e s t r u c t u r a l w e a k n e s s s h o w s i t s e l f in a l a c k of stiffness, a n d c o n s e q u e n t l y in p o o r work, in t h e c a s e of a m a c h i n e ; or in v i b r a t i o n or y i e l d i n g in t h e case of a s t r u c t u r e , as a b u i l d i n g , or a b r i d g e . W e m u s t r e m e m b e r t h a t t h e s t r e n g t h of a s t r u c t u r e is t h e s t r e n g t h of its w e a k e s t p a r t , a n d t h a t a d d i n g to t h e s t r e n g t h of o t h e r p a r t s is o n l y a w a s t e of m a t e r i a l ; a l s o t h a t a d d i n g m a t e r i a l w h e r e it d o e s n o t i n c r e a s e t h e s t r e n g t h is also a w a s t e of m a t e r i a l ; so t h a t a d e s i g n w h i c h d o e s n o t p r o p e r l y c o n s i d e r t h e n e c e s s a r y s t r e n g t h a n d s t i f f n e s s of all t h e p a r t s is n o t m e r e l y u n s a f e b u t is also u n e c o n o m i c a l , a n d r e s u l t s in a w a s t e of m o n e y . E n o u g h h a s b e e n said to s h o w t h e i m p o r t a n c e to t h e e n g i n e e r of a t h o r o u g h k n o w l e d g e of t h e s t r e n g t h of m a t e r i a l s w h e n e v e r it c o m e s i n t o p l a y i n t h e d e s i g n a n d c o n s t r u c t i o n of e i t h e r s t r u c t u r e s or m a c h i n e s , a n d it o n l y r e m a i n s to s h o w t h a t t h e s e are m a t t e r s t h a t t h e e n g i n e e r has to c o n s i d e r a n d act u p o n a t e v e r y t u r n , w h e t h e r h e is w h a t is c o m m o n l y c a l l e d a civil e n g i n e e r , a m e c h a n i c a l e n g i n e e r , a m i n i n g e n g i n e e r , a m e t a l l u r g i c a l e n g i n e e r or a. c h e m i c a l e n g i n e e r . T o b e c o n v i n c e d of this, w e n e e d o n l y c o n s i d e r the c h a r a c t e r of s o m e of t h e d u t i e s t h a t d e v o l v e ~pon tb.c e n g i n e e r , in t h e d i f f e r e n t k i n d s of w o r k s w h i c h w , : ~ r c d~,scribed in t h e first t h r e e l e c t u r e s . Re, fcrrh~ g n e x t to s o m e o t h e r m a t t e r s in c o n n e c t i o n w,t!, a p p l i e d "mechanics, I m u s t e m p h a s i z e t h e i m p o r t a n c e ~t" t.d
Jan., I895.]
E~iffi~zeeringPractice an~ZEdztcaffan.
47
variety of tests of the s t r e n g t h and stiffness of iron, steM, wood, cement, etc., we are c o n s t a n t l y t e s t i n g t h e s t r e n g t h of full-size t i m b e r beams. E v e r y once in a while one will break by s h e a r i n g along the n e u t r a l axis or center of the depth, i n s t e a d of t e a r i n g at the b o t t o m or c r u s h i n g at the top. I r e m e m b e r , on a certain occasion, w h e n I called attention to this fact, t h a t a g e n t l e m a n proceeded to argue trom it t h a t t h e r e was a s h e a r i n g force a c t i n g in the case of a beam which the c o m m o n t h e o r y of b e a m s did n o t take into account. E v i d e n t l y to h i m the c o m m o n t h e o r y of beams was only the set of formulze most c o m m o n l y recorded in the books, for he a p p a r e n t l y was not aware t h a t it does include a c o n s i d e r a t i o n of the s h e a r i n g stresses. A n o t h e r i l l u s t r a t i o n m i g h t be taken in the fact t h a t the ordinary formulae for the deflections of b e a m s are deduced from an a p p r o x i m a t e equation, where one term has been neglected, w h i c h is small in all o r d i n a r y cases of b e a m s in structures. By u s i n g this a p p r o x i m a t e e q u a t i o n in a case where the n e g l e c t e d term was very large, some one m a d e out an i m a g i n e d m a t h e m a t i c a l d e m o n s t r a t i o n t h a t an unbalanced r o t a t i n g body g o i n g at a h i g h speed p o u n d s towards the light i n s t e a d of the h e a v y side, a r e s u l t m a n i f e s t l y absurd. Again, if the s t u d e n t clearly u n d e r s t a n d s all the assumptions made in d e d u c i n g the formulae, he will u n d e r s t a n d that the Gordon f o r m u l a for columns is not d e m o n s t r a t e d , depending as it does on a s s u m p t i o n s t h a t c a n n o t be proved ; and he will be in a more judicial f r a m e of m i n d in tryil~<~r to d e t e r m i n e how to make use of the experimenta! k n o w l e d g e on the subject t h a t we possess up to date. Next, in r e g a r d to the t h e o r y of e l a s t i c i t y ; this is necessary in c o n s i d e r i n g certain eases of complicated stresses, and while we use it now to some extent, as in d e t e r m i n i n g the . s t r e n g t h of flat plates and of shafting, it will, I do not doubt, come more into use w h e n we g e t more light e x p e r i m e n t a l l y on some m a t t e r s c o n n e c t e d with it. I need ¢,~,., n o t h i n g upon the i m p o r t a n c e of h a v i n g a knowledge of the principles of friction and lubrication, and of the e x p e r i m e n t a l k n o w l e d g e on the s u b j e c t up to date,
48
Lanaa
."
[ 1. F. I.,
b e y o n d calling to y o u r n o t i c e , t h a t the c h a n g e from a poor to a good l u b r i c a n t m a y often m a k e a decided difference in the size of the dividends received b y t h e stock-. holders of a large concern. T h e n e x t course to receive our a t t e n t i o n is t h a t of Then> m o d y n a m i e s a n d S t e a m E n g i n e e r i n g . It m i g h t be a s s u m e d by some t h a t this was peculiarly the province of the so. called m e c h a n i c a l e n g i n e e r ; b u t if y o u will consider again the a c c o u n t of the different works of w h i c h the first three lectures treated, y o u will realize that, in every work of any m a g n i t u d e , power is needed, and in a l m o s t all cases the power used is steam. T h e exceptions are those eases where tile works are favorably s i t u a t e d for the use of water-power, and even t h e n s t e a m is a l m o s t always used in a d d i t i o n ; and p e r h a p s I o u g h t to m a k e a n o t h e r exception in the case of sailing vessels, where the w i n d is used. O t h e r sources of power, or w a t e r or wind in eases other t h a n those mentioned, are only e m p l o y e d for small a m o u n t s of power. W i t h o u t power all the works would h a v e to s h u t down ; the b r i d g e works could n o t b u i l d bridges, the m a c h i n e shop or m a n u f a c t o r y or mill would have to stop, t h e m i n e could not be operated, the rolling mill could not run, the dynamos a n d electric motors w o u l d be idle, the p a p e r mill, the s u g a r refinery, etc., would h a v e to d i s e o n t i n n e operations. Moreover, the expenses for power in a n y large concern form a very large i t e m ; t h e y i n c l u d e the first cost of m a c h i n e r y , of n e c e s s a r y buildings, of coal bunkers, etc., the expenses of m a i n t e n a n c e , i n c l u d i n g coal, water and a t t e n d a n c e , and the expenses for repairs. It behooves the engineer, therefore, to try to realize the g r e a t e s t possible economy. One of the l a r g e s t i t e m s of expense, after t h e p l a n t is once in operation, is coal, and a n y m e t h o d b y w h i c h he can save coal will increase the profits of the concern. In order to accomplish this, the e n g i n e e r m u s t unden> s t a n d the principles of s t e a m e n g i n e e r i n g , a n d the l a r g e r the works w i t h which he is connected, a n d hence, the g r e a t e r the q u a n t i t y of m o n e y involved, the m o r e i m p o r t a n t is it t h a t he s h o u l d h a v e all t h e l i g h t possible, b o t h from theory~ and from e x p e r i m e n t , t h a t will aid h i m in d e t e r m i n i n g how
Jan., 1895.]
Enffipzeerilz~ Practice attd Edzlcatiolt.
49
his engines should be d e s i g n e d and built, h o w his boilers should be d e s i g n e d and built, w h a t d e g r e e of efficiency he has reason to expect with a n y given a r r a n g e m e n t which he m a y propose to adopt. Hence, it is plain that our prospective e n g i n e e r needs a t h o r o u g h course in s t e a m engineering, of w h i c h t h e r m o d y n a m i c s is m e r e l y the theoretical part; and he n e e d s this, w h a t e v e r be t h e kind of engineering works he m a y expeet to be e o n n e c t e d with, if they are to be of considerable m a g n i t u d e . In d e c i d i n g upon the question as to h o w such a course s h o u l d b e laid out, we sha!.l a s s u m e t h a t he is a l r e a d y familiar with v a l v e gears, and with the rest of the m e c h a n i s m of t h e s t e a m e n g i n e ; also assume that he has had a course on heat in his physics, and that, in this course, he has been taught the subjects of ~hermometry, calorimetry, and the laws of the transference of heat. H e should be taught the nature and construction of the steam engine indicator; h o w it is to be used; h o w the indicator card is taken, and what it means, and he should acquire some familiarity with interpreting the characteristlc and also/ some of the peculiar features of indicator cards; and then he Should be m a d e familiar with the general characteristics, i. e., outward characteristics, of the different types of steam engines. Next, he should receive a t h o r o u g h drill in the principles of t h e r m o d y n a m i c s . W h a t is t h e r m o d y n a m i c s , and w h a t kind of a course should our p r o s p e c t i v e e n g i n e e r have in the s u b j e c t ? T h e r m o - d y n a m i c s is simply the mechanical theory of heat, or, in o t h e r words, the science of heat with special reference to p r o d u c i n g motion and power. T h e s u b j e c t was originally d e v e l o p e d f r c m the standpoint of the m a t h e m a t i c a l physicist, and we have a number of treatises w r i t t e n from this point of view, such as that of Clausius and others. Besides the f u n d a m e n t a l principles of t h e science, t h e y take up e l a b o r a t e discussions of the n a t u r e of heat, and also a large mass of applications and d e v e l o p m e n t s in the direction, a n d .from the point of view, of pure science, r a t h e r than in t h e direction of w h a t we need to use in the consideration and the s t u d y of the VOL. CXXXIX. 4
5o
Zanza
[J. F. I.,
." •
•
action of the s t e a m engine, or of other h e a t engines, as the gas engine, t h e h o t air engine, etc. I n s t e a d of this, in the course to be g i v e n to our prospeetive engineer, we s h o u l d include a t h o r o u g h t r e a t m e n t of the f u n d a m e n t a l principles o f the subject, a s t u d y of the laws of t h e r m o - d y n a m i e s , Carnot's function, and the whole set of f u n d a m e n t a l equations, and t h e i r i n t e r p r e t a t i o n s . T h e n should come the applications of these f u n d a m e n t a l principles to the gases and vapors used in practice for prod u c i n g power, espeeially steam, and also gas and air. T h e n a s t u d y of the e x p e r i m e n t s t h a t h a v e been made, and the results of the e x p e r i m e n t s on the properties of vapors and gases; the e x p e r i m e n t a l d e t e r m i n a t i o n s of the m e c h a n i c a l equivalent of h e a t ; the tables of the properties of s'aturated steam, as pressure, t e m p e r a t u r e , density, specific heat, l a t e n t heat, entropy, etc.; also the same for other vapors. Then a st~idy of the laws g o v e r n i n g t h e flow of fluids, both gases and vapors, t h r o u g h orifices and in pipes, i n c l u d i n g a consideration of the resistances and a s t u d y of t h e steam injector. T h e n the s t u d e n t is prepared for a s t u d y of the bel~vi,,~' ~,f ,~team in the cylinder of a s t e a m engine• A t this point he should be t a u g h t the m o d e r n m e t h o d s of :m:!l\-zing and s e p a r a t i n g the various actions of the steam timt passes t h r o u g h the engine, and of g i v i n g to each {t~ pr<,per c o n s i d e r a t i o n ; as, for example, t h e h e a t used up in work, t h a t used up in cylinder condensation, t h a t H~-~ ~,? il~ ('onden,~ation in the jackets, if there are any, the heat rejected by the engine, radiation ; also the m e t h o d s of bttid) itig the effects of s u p e r h e a t e d steam, etc.: all these for both single and multiple expansion engines, and, in the cases ,,f tl,c latter, the effects of different sizes and a r r a n g e m e n t s of receivers, the m e t h o d s of p r o p o r t i o n i n g the cylinders, etc. Next, he should learn w h a t are the r e q u i r e m e n t s for a proper engine test, both w h e n it is m a d e for o r d i n a r y commercial purposes, and also when it is to be m a d e in a t h o r o u g h l y complete and scientific m a n n e r for the purpose of o b t a i n i n g definite k n o w l e d g e as to how to produce the
Jan., I895]
-Engi,ieering Practice and Educatian.
5
best and m o s t economical results by m e a n s of a steam engine. T h e day w h e n the ~aking of a few i n d i c a t o r cards from an engine, or the m a k i n g of tests in which scientific principles and scientific accuracy are neglected, a n d c l a i m i n g t h a t such tests can f u r n i s h i n f o r m a t i o n as to w h a t the real effects of different a r r a n g e m e n t s are, is r a p i d l y p a s s i n g away, the advocates of such a course c o n f o u n d i n g t h e m s e l v e s and each other by r e a c h i n g too m a n y Contradictory conclusions by their tests. Now, from the e x p e r i m e n t a l point of view, the s t u d e n t should have p r e s e n t e d to him, in a c a r e f u l l y s y s t e m a t i z e d form, an a c c o u n t of sudh e x p e r i m e n t s as have been made, with such a degb"ee of a c c u r a c y and such r e g a r d for scientific principles as t6 r e n d e r t h e m w o r t h y of study. Of course, there will be a n u m b e r of tests in this list which are not up to the scientific s t a n d a r d s of to-day ; b u t such a s t u d y will make the s t u d e n t f a m i l i a r with w h a t is the e x t e n t of our l:nowledge of the subject up to date, and he will be.all the b e t t e r able to m a k e this s t u d y effective, b y being relieved of the n e c e s s i t y of r e a d i n g a c c o u n t s of a lot of worthless tests for the sake of finding out those t h a t are worth considering. T h e n he should have a good course on s t e a m boilers, including the c o n s t r u c t i o n and action of the various types in use ; on the laws controlling the c o m b u s t i o n of fuel, and the evaporation of w a t e r ; on questions of h e a t i n g surface, gra~e area, t u b e section, horse-power, capacity, evaporative ethciency, e v a p o r a t i o n from and at 212 °, p r i m i n g or superheating, d r a u g h t , q u a n t i t y of air r e q u i r e d for combustion, t e m p e r a t u r e of flue gases, size of c h i m n e y , m e t h o d s of feed ing, m e t h o d s of d e t e r m i n i n g q u a l i t y of the s t e a m ; and on boile: accessories, such as gauges, w a t e r glasses, grates, stokers, feed pumps, injectors, feed w a t e r heaters, economizers, d a m p e r regulators, etc. T h i s i n s t r u c t i o n should embrace also the r e q u i r e m e n t s for a reliable a n d accurate evaporative t e s t ; w h a t arc the possible m a x i m u m evaporative efficiencies, and w h a t are usual e v a p o r a t i v e efficiencies attainable u n d e r o r d i n a r y conditions.
52
Lanza :
[ J. F. I.,
He s h o u l d also s t u d y the more recent applications of t h e r m o - d y n a m i c s , such as air compressoR, gas engines and r e f r i g e r a t i n g m a c h i n e s . In these cases a lack of f a m i l i a r i t y w i t h the laws of t h e r m o - d y n a m i c s on the part of the m a k e r s is very likely to m a k e itself a p p a r e n t to the u s e r t h r o u g h the m e d i u m of his pocket-book, and in no case will this be more likely to be true t h a n in the case of the r e f r i g e r a t i n g machine, e i t h e r for cold storage or for the m a k i n g of artificial ice, a n d those w h o are e n g a g e d in this business are very r a p i d l y realizing this fact. Now, w h e n the s t u d e n t has finished the work referred to on the s t e a m e n g i n e indicator, and has a c q u i r e d t h e fundam e n t a l principles of therm-odynanZxics, and is s t u d y i n g the action of t h e s t e a m in an engine, it is a pr6per time for him to begin work in the laboratory, b y m a k i n g s t e a m e n g i n e tests, a l t e r n a t i n g his duties at each successive test u n t i l he has been drilled in p e r f o r m i n g all the different parts of the work, and in m a k i n g all the necessary calculations. For this purpose a small engine is, of course, b e t t e r t h a n none, b u t it is m u c h b e t t e r for the e d u c a t i o n of t h e s t u d e n t if his work can be done u p o n an e n g i n e sufficiently large to work w i t h an e c o n o m y comparable w i t h t h a t f o u n d in such e n g i n e s as are used in large and well-designed m o d e r n plants. S u c h tests m a d e by the s t u d e n t himself, u n d e r the direction a n d g u i d a n c e of the instructor, will leave a l a s t i n g impression upon his mind, and will c o n v e y i n f o r m a t i o n which he c a n n o t acquire as wel! in any o t h e r way. Hence, it is far b e t t e r to use a triple, or at least a c o m p o u n d engine, of sufficient size to secure a s t e a m c o n s u m p t i o n of a b o u t f o u r t e e n or fifteen p o u n d s of w a t e r per horse-power per hour, t h a n to use a small single engine, w h e r e the steam c o n s u m p t i o n per h o r s e p o w e r per h o u r is as h i g h as thirty, f o r t y or m o r e pounds. In m a k i n g the tests no loose work s h o u l d be allowed, b u t the s t u d e n t should be r e q u i r e d to p e r f o r m all the work w i t h the g r e a t e s t a c c u r a c y possible, a n d this a c c u r a c y s h o u l d be such as to r e n d e r the test t h o r o u g h l y reliable from a scientific standpoint. T h i s can be accomplished provided the i n s t r u c t o r exercises the necessary supervision over the work.
Jan. 1895.]
~11~[izc~'ri71o?Prclc[l'cc
~n~ E~llcctg~'ol~.
~3
Later in the course the s t u d e n t should m a k e a c c u r a t e and carefully c o n d u c t e d boiler tests on some large boilers. By these m e t h o d s , he will be m a d e to appreciate b e t t e r the work w h i c h he is doing in the class-room and will see t h a t it finds its application in j u s t s u c h work as an engineer has to do in the course of his profession. Of course, he s h o u l d h a v e to perform other sorts of experimental work with s t e a m in the l a b o r a t o r y besides e n g i n e and boiler tests, b u t of these will be referred to later. The whole idea of such a course as I have o u t l i n e d is, as you will see, to give the s t u d e n t a t h o r o u g h drill in the fundamental principles of' the subject, and t h e n to t e a c h h i m how these principles apply to the work of t h e engineer, by means of b o t h class-room and l a b o r a t o r y work, t h e deductions and d e v e l o p m e n t s from t h e f u n d a m e n t a l principles being made in the direction of e n g i n e e r i n g work, i n s t e a d of in the direction of "pure science ; and then, by m e a n s of this work, and also by s h o w i n g h i m where we s t a n d to-day in regard to t h e m a t t e r of reliable e x p e r i m e n t a l results, to equip him as fully as possible to appreeiate a n d to take p a r t in the best and m o s t scientific e n g i n e e r i n g work of the present times, a n d t h u s to be r e a d y in the f u t u r e , ever to take a d v a n t a g e of, and to take his part in developing, whatever progress the f u t u r e m a y h a v e in store for us. A n o t h e r f u n d a m e n t a l s u b j e c t is hydraulics. Our prospective e n g i n e e r should u n d e r s t a n d the principles of hydrostatics and h y d r o d y n a m i c s ; in o t h e r words, the laws governing the pressure of water, and the flow of water, w h e t h e r in pipes, in open channels, t h r o u g h orifices or over weirs. He should also be f a m i l i a r w i t h the c h a r a c t e r a n d the results of such e x p e r i m e n t s as h a v e been m a d e u p o n t h e s e subjects, a n d should know how to conduct such experimental work. W h a t e v e r m a y be the special line of e n g i n e e r i n g in which he is engaged, he is liable to have to establish a water supply, with all the necessary works, such as reservoirs, p u m p i n g engines, piping, etc.; or to b u i l d a s y s t e m of sewerage, or he m a y find his m a n u f a c t o r y so s i t u a t e d t h a t it is advisable to take a d v a n t a g e of a water-power, a n d to
54
L a m i n a ."
,[J. F. I.,
b u i l d all the necessary works, such as dams, canals, locks, sluice-ways, etc. H e m a y have to establish river or h a r b o r works, or, even if not these, he m a y h a v e to b u i l d a wharf, a quay, or even a dock, if his works are on the water's edge. Unless he is to m a k e a specialty of h y d r a u l i c work, he cannot, in a four years' course of engineering, afford t h e time to make h i m s e l f m a s t e r of the details of all these k i n d s of works, but he s h o u l d become f a m i l i a r with the principles stated above, and t h e n he can a f t e r w a r d m a k e a special s t u d y of p a r t or all of these subjects. N e x t comes t h e q u e s t i o n as to h o w far electricity s h o u l d be a c c o u n t e d a f u n d a m e n t a l subject, and c o n s e q u e n t l y one to be required of all e n g i n e e r i n g s t u d e n t s , w h a t e v e r their special lines. It is now u s u a l l y c u s t o m a r y to require t h e m to learn some electricity in connection w i t h general physics, and s o m e t i m e s a little more ; the rest b e i n g g i v e n to s t u d e n t s of electrical e n g i n e e r i n g only. W h e t h e r or not a considerably larger a m o u n t s h o u l d be p u t in the list of f u n d a m e n t a l studies, will d e p e n d u p o n h o w far a n d how i n t i m a t e l y electrical appliances come to associate t h e m s e l v e s with the every-day work of the engineer, w h a t e v e r his specialty. T h e p r o b a b i l i t i e s are, it seems to me, t h a t it will not be m a n y years before we shall have to insert a m u c h larger a m o u n t of electricity t h a n we now do in our list of f u n d a m e n t a l studies. T h e subjects t h u s far e n u m e r a t e d are f u n d a m e n t a l , and are necessary for our prospective engineer, w h a t e v e r be the special line of e n g i n e e r i n g to which he is to d e v o t e himself. He cannot afford to do w i t h o u t a n y one of t h e m . In l a y i n g out, therefore, a n y e n g i n e e r i n g course, of whatever name, w h e t h e r civil, mechanical, m i n i n g , metallurgical, electrical, or chemical engineering, we s h o u l d arrange, first of all, the t i m e n e c e s s a r y to give good courses in mathematics, g e n e r a l physics, d r a w i n g (including descriptive geometry), m e c h a n i s m , applied m e c h a n i c s (including, of course, s t r e n g t h of materials), t h e r m o - d y n a m i c s a n d steam, and the g e n e r a l principles of hydraulics. Moreover, thoro u g h i n s t r u c t i o n in these should not be sacrificed to a n y
Jan., ~895.]
E~zgim'crinff Fractice and Edztcatwn.
55
other subjects, w h e t h e r of an e n g i n e e r i n g or of a general character. In o t h e r words, the work in these s u b j e c t s should be thorouffhly performed, w h a t e v e r else is or is not accomplished. W h e n this has b e e n done, we can then, and not till then, begin to consider w h a t other s u b j e c t s s h o u l d be added, and these m a y be classified as follows: (x) s u b j e c t s of a professional n a t u r e b e a r i n g on the work of an e n g i n e e r in general, w h a t e v e r his specialty; (2) s u b j e c t s of a professional nature, w h i c h bear directly on the special line of engineering which the course is intended to t e a c h ; (3) subjects of a non-professional character i n t e n d e d to b r o a d e n the field of k n o w l e d g e and to i m p a r t general i n f o r m a t i o n ; (4) s u b j e c t s w h i c h fulfil partly one of these functions, and partly another. In the first class, t h o u g h respectively of v e r y different degrees of importance, I should place (a) m a c h i n e design, (b) dynamics of machinery, (c) m e t a l l u r g y of iron, (d) heating and ventilation, (e) stereotomy, ( f ) surveying, (g) shopwork. H o w m a n y , and which of these s u b j e c t s can be added will d e p e n d u p o n circumstances. R e v i e w i n g in detail the kind, of course, I h a v e in mind under each of these heads, I will make t h e following remarks : (a) dgac/zhze Dcs@/z.--This course, to be of the g r e a t e s t value, should take up problems of real e n g i n e e r i n g design, and should deal especially w i t h the details. T h u s the student should be m a d e to s t u d y each s e p a r a t e piece, and its connection with the other pieces, to d e t e r m i n e the forces acting upon it, and the stresses to which t h e piece is subject in c o n s e q u e n c e of the action of these forces, and to design the separate details in such a m a n n e r t h a t they shall have the r e q u i s i t e s t r e n g t h and stiffness. Of course, it is desirable, also, to have some w o r k done on mechanism design, where the s t u d e n t s h a l l have practice in a d a p t i n g m e c h a n i s m s to the special o b j e c t s that are to be accomplished, b u t it is also i m p o r t a n t t h a t he shouhl learn that in m a k i n g any such design, he m u s t s t u d y the s t r e n g t h and stiffness of each separate piece of which the m a c h i n e is
56
Chemical Section.
[ J. F. I ,
composed, and m u s t be fully i m p r e s s e d with the facts t h a t any one of these that is not properly designed, m e a n s a m a c h i n e that is not properly c o n s t r u c t e d and m a y m e a n the total failure of the r e s u l t i n g mechanism. (b) U n d e r the t e r m d y n a m i c s of machinery, I include such s u b j e c t s as governors, fly-wheels, d y n a m o m e t e r s , the action of the r e c i p r o c a t i n g p a r t s of a s t e a m engine, etc. I need only m e n t i o n these topics to m a k e plain their i m p o r t a n c e to a n y engineer. M e t a l l u r g y of iron and h e a t i n g and ventilation will, I think, also m a k e plain their i m p o r t a n c e b y a m e r e m e n t i o n of their names. [ To be canc/ucled.] A REVIEW
oF S T E R E O - C H E M I S T R Y . ~
BY STEWART WOODFORD YOUNG.
T h e old s t r u c t u r a l formula for m e t h a n e r e p r e s e n t e d t h e molecule of t h a t s u b s t a n c e as b e i n g c o n s t r u c t e d by p l a c i n g the carbon a t o m at the point of intersection of t h e t w o diagonals of a square, t h e four corners of the square b e i n g the positions occupied b y the four h y d r o g e n s . T h i s form u l a (Fig~. z) however, conflicts w i t h the facts w h e n we consider the di-derivatives of m e t h a n e . As is well known,
H2 H1
C ,-
Ha
I
H~ FIG. T.
m e t h a n e allows of the formation of b u t one series of di-derivatives. One and only one d i c h l o r m e t h a n e is known. Now, this f o r m u l a allows of the existence of two series of isomeric all-derivatives, (Yz~. 2) (a) r e p r e s e n t i n g a di-derivaRead before the C h e m i c a l Section.