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Essays on bleaching
MR. R~NNH,:'S I'L~says on Bleaching.
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ratus squeezes the dried clay, to save tile expensive operatior~ o} s upping, described at pa,,e l.)l ; alter which xt passes to an iron cylinder, full of knives, where it is cut into pieces with great expc(ii tion~ which saves the expense of cutting it by hand with brass wire~, as before mentioned. This receptacle is not properly a cylindc~ ~, but a large hollow inverted cone of Don, and the knives at'e fixed h~ an upright shaft which revolves within it and passes through its ceu tre. These knives are so contrived that the clay, as it is cut, is forced lower and lower by every revolution, until at last it is pressed by the power of the machinery through a square hole near the bottom of the apparatus, from whence it is removed as it falls, and is carried in blocks to the odmr parts of the manufactory. The clay havln/under,,,Zmlc those varied operations, it is now lit for being lbrmed into any shap% or emph)yed for any purpose, for which it is designed. Accordingly, it is faslfi0ned into various to :ms by meatis of a variety of moulds madc of plaster of" Paris; or put into as great a diversity of shapes by the potter's wheel. ]'EO BE ('0NTINUED.]
ESSA ~i5; ()N B 13EAC H I N G . By James lgennic~ .7. J!:L, /.ect~,,'er o~ l;hilos'o)~hy, (?c. 6"c. ! omh'~,. ~O.
I ~ I t . ~ 0 1 4 E M t C A L .~,NI) I'HYS[CAL NATtII~::
(11': S T U b ' F ' , , .
2. HTool.~For our knowledt~e of the texture and compo.~itio~ ')[ this important material of t lc clod~ mauufacturc~ we are greatly indebied to Detube~ton, The qualifies of wool as to length anti tenuity ot'iil)re, vary according to the Darts of tl'e anhnal whence it ma.v have I:wm.~ taken; to the'bt'eed v.f'sh'.:cp from which it is pvoduced;'the d?matc where they ti~e: ihc p'.>~'~u,'cwhere they feed; and accovdi~?; a',~ tt,e animals a~:e lma!tbx cr disc~c,3. TMt which grows (m the ~lcck, the sld¢s, and tl~e t ~:~ <.ri< , i * t I~t' ~ ~~(>S~: l~:U't 0~" fl{e fleet% and fortunately lhe trust: af~u~davt. The !v.~>tbreeds arc foam[ t¢~degenerate in cm~ail~ cilmatc::;, aw,', ccrtah, r~as:tuvcs, of which we have 'an illustrative ins/a~ce i~; i.,,e Eu"~q)ean brecd~ in some t:!aces of America, which now prod,.',ce hah'~i>~tead of wool. This seem:,; to depend on tim same general prineil)!e with the effects produced on wool by the diseases of the animals, tim m,~st healthy always affiwdiug the best~ for change of climate% and food. may alter the constitutional secretions, as muci, as diseus.'e. Great: at'ten(ion has lately been paid in l.iritaii~ to those ch'cum.~tatmes which aiD.or the qualities of wool~ and great im)rovements have h~en made b j the sheep farmers. This is of much ~mportance, as we are indebted to Spare for all our finest wools. Ks the fineness of wool cannot be accurately ascertained by simple ins ection, the manufacturer ought to comi)are by means of'a microscope, the ddferent specimens wluch may be offered to h~s purclmse. When the wool is in its ~atura state, it" s protected from moistm by a substance of a soapy nalure, called yolk by the English, and eeli 4
MJ, R~.~r~:'~ Ess~lgs o~ Bleaching.
15;~
m Scothnd. TMs, according to M. Vauquelin, (Ann. de Chim. xlvii. ~276,) consists of a basis of potash combined with m~ animal oil, together with lime united to tile carbonic, acetic, and muriati¢ acids. This nutritions matter is ahvays most abundant on the wool of healthy sheep. . . . Mr. Mushet tbtlnd, that after (hstdhng m the dry way 180 grains of pure white wool, there remained a residuum coal, of a dark shin. ing gray colour, welded, or caked, into one mass, adhering in part to tire sides of the retort. It weighed only 49 grains, hawng lost in distillation 197 grains. In 100 parts, therefore, are contained 76 volatile matter, and ~23.89 oxide of carbon. The mechanical structure of wool is worthy of attention, both as an object of curiosity, and as, probably, of some impm'tance in explaining the rationale of bleaching it. This structure was first described by the abbe Monge, (Ann. tie Chim. vi. $O0;~see also Nich. quarto Journ. i.) he having discovered it when examining the process of fnlhng. Accorthn= to tlus philosopher, the fibres of wool consist, either of laminz lying in a slanting mariner upon one another, fi'om fln~. root to the extremity, somewhat like the scales of a fish, or of a series of rings zrad!mlly decreasing in diameter fi'om the.root to the point, and overlapping one another, as in the ho,'ns of ammals. M. Monge states, and his statement is ,'epeated by Bancroft, and in the Edinburzh Encyclopedia, that this structure may be perceived by drawing~a fibre between the thumb and finzer, from the point towards thotroot, in which case a tremuhms motion, it is said, will be distinctly li;lt, accompanied wiih a sensible grating noise. Now I am disposed to co~trovert this; fi~r upon repeated trials, with tibres of every degree of fineness~ I couht neithe," feel the motion n o r hear the grating. This cannot even be perceived in the coarse hairs of cows and horses, though th~,se have a similar structure. The only way by which it can be made sensible, is with a microscope, or by putting a hair between the linger and thumb, and moving ~hem gently one upon another, when the fibre will move forward, or backward, according as the point, or the root, is placed anterior, or posterior, to the part by which it is held. This property of hairs has been lon~ known to some of our peasants, who take advantage of it to excit'~, the wonder of the ignorant, by telling the root, or the point, of any hair, although it be cut into ever so many pieces. It is on tiffs structure that fulling and felting,~ depend; it is to smooth the asperities caused by it, tllat spinners ~rease their wooll and it is in the inter. stices of these lamin~, that the colouring matter, which it is our object to find a method of removing, is lodged. The laminae seem to be elastic, and~ consequently, the pores must be dilatable by heat. This it may be useful to remember. 3. Cotton.~This substance is a down contained in the pods of the gossypia of Linnams. This down is different in the ditt~rent spe. cies, both in fineness a.nd colour. In most it is white, of different shades; but that from which the nankin is made, is what Werner would call Sienna yellow, or bofforauge: a sort is mentioned as growing in Dahomy of a bright yellow; and several kinds, having YoL. I V . ~ N o . 9.--SI,:P'rE~I~'.II, 189.7. 20 .
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31 f~, P,.~:,~,~l ~:'.~ E~'.~a?/.~ o~ B l e a c h i n g .
different shades of red, have been described. The coloured sort~, h o w e v e r , are not common, and the chief diflhrence between one sort and another, seems to consist ill the length, tenuity, and strength o[" the filaments. Naturalists do not seem to have ascertained with accuracy, the structure t)l' these tilaments The microscoue, accordin,, to Lewenhoeck, shows that they have two sharp sides. It certainly possesses some kind of asperities, or how can we account for the irritation which it i)r.duces when used in dressing wounds? In this it is totally di|re,.cm f,',)m lint. Perhaps this irr~tating action may be account ed for [rom the filaments being shorter than those of fla w and consequently prescl,ting d greater number o[" points on the surface of the cloth, l)r. Zhtmlso~t found the specitio heatofcotton to be 0.53, that of water hein,g 1, but [vonx the diiliculty of ascertaining this, he does not slat(; it ~;;ith confidence. (Ann. of Phil. II. ~7.) W e learn somethin~ of the composition of cotton from Mr. Mushet's expcrlments ond@ distillation. (Phil. Mag.XXXIll. 9.) lie distilled 263 l~t'aillS of-the cloth which had been previously bleached. It emitted, dm, in~ the operation, a quantity of.pale blue flame, anti left, as a rcsidm,~, a ligh~ fl'iable coal, possessing the original shape antl texture of the cloth'; wl:icll weighed 39 grains~loss, 1~4 grains. It appears, (hcj~, th:tt a hundred parts consisted of 85.16 volatile matte,', and 14.84 of carbon; being 16.16 less carbon tharx is conrained in as much silk, and 9.05 less than exists in pure wool. The fibres ()["cotton, according to Nicholson, (Dict. of Cheml art. vegetables,) are insoluble in water, in alcohol, or in ether; but soluble in alkalies. It tbllows, of coarse, that strong alkaline leys will injure the texture of cotton goods in tile process of bleaching. When treated with the nitric acid, cotton yields the oxalic. There seems to be in cotton, holm of dmt particular resinous kind of matter which constitules or c(,ntai~,s the colouring matter of ut~bleached linen.* 4. L i n e n . - - T h e mode of preparing flax, tbr the linen manufacture, has already been cursorily mentioned, when treating of water, and I shall not ~'epeat what was then stated. The llax, when taken from the field, is put into ponds of standing water to steep, and stones are laid above it, to keep it fi-om floating. When no such ponds are to be had, it is pu~ into those parts of running water where there is little curren't, or little streams are banked up for the purpose. None of these, however, answer so we|l as ponds, for the process is both more tedious and more uncertain. The intention of steeping is to dissolve the oily or mucilaginous substance which makes the bark adhere to the woody part of the tlax, and thusto effect a separation of the latter. This intention is answered by the putrefactive fermentation~ * Des Charmes, however, (p. 106,) ascribes to such a resin, or to an oil ors gum, existing' in cotton, tbe. difficulty with which it imbibes water. Des. Ch~a'mesl remarks also, that though it may not appear foul, yet it never fails to render, by its impurities, the water in which it may be macerated, of a darkish ¢olour. As it imbibes water with difficulty, it also retains it with some obstinacy, amt be. fore bleaching, is found to be long' in drying. This may be countenanced by an ot)servatinn of Mr. T. Henry's, (Man. Mere. iii.) that it imbibes water much tnore reamer alter ~ has been bleached than before,
MR. RENm,,:'S L'ssa3ts on Bleaching.
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which steeping induces, tbr it renders tile oil and tile mucilage soluble in water. It requit:es some nicety, however, to know w~en the putrefactive process has accomplished its purpose, for tl!e flax will be equal Iv useless if it has been steeped too much, or too little, tn the onecase'the fibres will not be separable, or black bat's in the linen will be the consequence, whose numbers increase with the deficiency in steeping, and which, in bleaching, are very difficult to remove. In the.other,'~hey will be destroyed, or very much weakened, by !osing. theu- tenacity. Now, the length of time which flax has been m the pond, can give no criterion of this, for the putrefactive fermentation depends much on other circumstances, such as the naf'ure of the flax~ its quantity, the heat of the weather, the length of the nights, the pressure o'f t ae stones laid upon it, and the-quality of tile water. The quickness or slowness of the fermentation~ then, must be the measure of the time of steeping. On the second or third day, when t le weather is warm~ a ~reat many air bubbles arise to the sm~faee of the water, and a scum, o~-pellicle,-is gradually fro'reed. The temperature of the water increases, and it acquires a corrupted smell. ]Phe tlax ought to be inspected every six hours, after tim fourth day# and as soon as a Klutinous or oily matter is perceived on the outer bark, and when this separates easily fi'om the woody part, it ought to be taken out. But it ouzht not to lie till this separation becomes too easy, as this will be ~etter cmnpleted by exposing it to the dew. Steeping ought always to be peribrmed m a place much sheltered li'om the wi~ds, as (he process is checked by nothing so much as by agitation and cold, ~hilc it is vreatly promoted by quietness and heat. l~'orthis reason also, the ponds ought not to be too shallow, as in that case they are more liable to be aflhcted by changes of temperature. The flax ought not to touch the bottom of the pond, otherwise. what is below will perhaps be rotten, in consequence of the superincumbent pressure, before that at the surface is nearly watered. This process appears, then, to be extremely difficult in management; and by it is produced a great deal of that brown colouring matter, which it is the object of tim bleacher to l'emove.*" Mr. Lee's nmfliod of preparing flax, which has been before staled, is not liable either to difficulty of management, nor to its injurious etIhcts, and bids fair to supersede the proccss of steeping, altogether. The nature of the colouring matter of brown linen, whether it exist naturally in the flax, or be acquired by steeping, has been accurately mveshgated I)v lh', ~xlt'~ an, m the Fransacttons ot the Royal h'ish Academy, VolJIIL lie made his experiments upon ley, satue
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• With regard to colours so produced, Chaptal basmade a g'eneral remark Of some ~mportance, namely, that all eolouring'matter, arisi~g fi'om fermentation, are less soluble in water than in alkalies. He illustrates this by referring"to the well-known dye-stuffs, indigo, woad,and annotta. Boilin~water dissolves 0,!ly a ninth part of its weig'ht of indig'o; woad communicates very little colour to waterl and annotta can scarely be dissolved in it .at all without the aid of an alkall. Water, then, it will tbliow by analogy, confirmed, as we shall immediately see, by experiment, will have but little effect o1~the colour acquired by tlax iu the putrid li~rmcutatio, iuduecd hy ~tcel,b~g..
156
Ma. RaNM~:'s Essays on 131caehing~
rated with this matter, which he procured from thebleachers. This liquor was turbid, of a reddish brown colour, having a strong smell and exhibiting no indication of aeidity~ or alkalescence. It did not effervesce with the muriatic acid, but aflbrded with it a copious precipitate, leaving a supernatant liquor of a red amber eolour. W h e n this is drawn off by a syphon, and the precipitate treated pretty co~ piously with water, a~itatinz the whole, andauain allowing it to subside, the floating liqu°or exhC]bits evident sign~ of acidity, and con. tinues reddish, glving room to suppose that it contains.a peculiar acid. After copious effusions of cold water~ and when the precipitate is thrown on a filter and suffered to dry partially, it is of a dark greenish colour, and nearly of the consistence of moist clay. This was not dissolved when treated with sixty times its own weight of boiling water. If dried in a sand beat, it assumes a shining black colour, but when broken, shows a greenish yellow fracture, and becomes more brittle. On this the following experiments were made: 1, ltaving digested a portion of it in rectified spirit of wine, it communicated to it a reddish huc, and was in a great measure dissolved; but by the effusion of distilled water, the solution became milky, anti a white deposite was gradually formed: the black matter dissolved m the same manner, o Neither the green nor the black matter was soluble in oil of turpentine, or lit~seed oil, by a long continued digestion. 3, The black matter being placed on a red hot iron, bur|rod with a yellow flame and a black smoke, leaving a carbonaceous residuum. 4, The green matter being put into the sulphuric, muriatic, and nitric acids, communicated a brownish tinge to the two former~ and a greenish to the latter, but did not seem in tile least to be diminished. W e infer fi'om this, that the matter extracted by the alkalies from brown linen, is a peculiar sort of resin, ditI?ring from the pure resins only by its insolubility in essential oils, and agreein,~, in this. res, l~ect, with .lacs'" In..examinin,,, . ~ the action, of. alkalies, on tins matter, 8 grams of tt were digested m a solutmn ot crystals of soda, saturated to the temperature of 60 °, which instantly commu~ nicated to the solution a d a r k brown colour; two measures, each of wliich would contain 11 dwts. of water, did not entirely dissolve this substauce. Two measures of mild vegetable alkali, dissolved the wixole.• Olle mc':tsurc~. of caustic •soda,. of tlie~ s,pecific. ~ravity. of 1.05~3,,. d~ssolved nearly the whole, leaving only a white residuum. One measure of caustic potash~ of the specific gravity of 1.0,39, dissolved the whole. One measure of liver of sulphur, (sulphuret of potash or soda,) whose specitic gravity was 1.070, dissolved the whole. ()he nteasure of caustic ~olatile alkali~ dissolved also a portion of this matter. Three ounces of the solution of Windsor soap, dissolved 8 grains of the colouring matter. It was found also that 4.~2 grains of the saline substance o}~"kelp, produced the same effect as 75 of that from Dantzic pearl ash, 58 of that from barilla, 15 of that fi'om cashup, and ~1S of soap. The sulphuret 0[; lime was found to act very IL'ebly on it. It follows li'om these experiments, that sulphuret of potash, or soda, is of all the alkaline compounds the strongest solvent of the ,.olou" n~ matter; next to th s the faust c vegetable.and •
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MR. RENNIE'S EssttJ/s olt Bleaching.
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after this the caustic mineral alkali; the mild alkalies occupy the least nlaee. Hence, tile solutions of kelp, cashup, and markoff, are advan'tageously used in the first processes of bleaching, for which 1)autzic ashes and sweet barilla are less fit. Tile experiments, how. ever, show that six tons of kelp will be necessary to produce the same effect as one ton of cashup. It was ibund by Mr. Mushet, that flax contained more carbonaceous matter than cotton. His experiments were made by dry distillation. When he treated 397 grains of flax in this way, after a copious discharge of white flame, a soft inflammable coal was left as a residuum in the retort. 5Fileoriginal vegetable fibre remained entire, and equally compact as to form and bulk, as when introduced. It weiehed 65 era, us, havin~ lost by the process 332grains. A hundred parts are t]lerefore composed of 85.62 volatile matter, and 1638 of carbon. (Phil. Mag. XXIII. 8.) ~To. V . ~ P R O C E S S E S
FOLLOWED IN BLEACHING.
SECTION I,
By the arrangement which I have adopted, many of the detail~ which, in most of the treatises on Bleaching are given under tile present head, have beet, anticipated, a circumstance which, I hope, will render our account of the processes more perspicuous than it couhl otherwise have been madej it will~ at least, make it shorter. An outline of the processes of bleaching fidlowed about halfa century ago will be fmmd in the history~ p. ~07, vol. it. by comparing which with the l\~llowing, au idea may be lornied of the rapid march of improvement. I begin with the processes for bleaching piece goods and heavy cotton cloth% which do not materially differ, except in the repetition of immersions, the cottons requiring fewer than tile linens. 1. Steeping.~'l'his process is intended to remove, without the expense of fi'esh alkaline ley, the impurities which the goods may have contracted it, passing through the previous stages of manufacture f:'om the spinner and tile weave,', and which the subsequent maua~,ement mi~,ht tend to fix. Flax is mostly spun by hand, and tile spinuer constantly moistens it with saliva to make it draw out more readily to the proper grist. Now as saliva is known to be a more universal soN,cut tha(l even water, we may infer that many impurities may, by this means, be fixed in the yarn. It will also~ fi'om its nature, fi~rm, when dry; a pelliele of tenacious matter on the surface of the threads, and may thus l;,'event the solvents from coming into contact with the colouring matters which are lodged in the body of by the oil which is used for the machinery. Both are also filled with impurities by the weaver, who finds that he cannot make good wo,'k, unless he previously dress tile yarn with some gelatinous matter that may give it a stronger adhesion. The linen weaver cot,monly uses~t'or this purpose a sour paste, made from the seeds of oatmeal; which is applied with a brush to the yarn; and then tho-
Ms. R ~ m ~ ' s Essays on Bleachi~g.
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roughly dried in~ by passing a hot iron over the web. IIe then take,~ a brush~ on which he has rubbed a small quantity of tallow~ and Izoes over the whole. The cotton weaverseldom usesthe flummery pa'~ste, but prefers one made of flour, or of mashed potatoes in a state of fermentation, and ~ometimes a mixture of both: and the combustibility of the cotton will not permit him to use so expeditious a mode of drying, as the hot iron aflords. He dues h~s web with a large tan, and afterwards lzoes over it with the grease brush, in the same way as the linen weaver~. I was astonished to read in Mr. Parkes ~ Essays on Bleaching, (Vol. IV. p. lol.) that the weaver "melts a quantity of grease over hi~ warp, which he afterwards spreads with a brush:" a thing which I am persuaded no weaver would ever be so foolish as to. try, ,as the, l,.,vn'ts where.the g;,rease fell. would do away all tl e ~q-, teets ol tit(,, prevmus dressing. I~or tins reason, weavers are always very carelul not to rub too much grease on their brushes. Mr. Parkes must therefore lind some more likely account of tile origin of copper ~tains. The small quantity of grease in the cloth, is fixed by the subse~ quent operatio, of singeing, when this is had recourse to; and if this as not taken (,vt in the previous processes of bleaching, it will not yield afterwa,'ds t~) the usual processes of ashing and souring. For the removal ()f these impurities, the th'st thingto be done is to have the cloth thoroughly washrxt, (with soap if necessary,) by the dash wheel~ to get rid of \vhat may be loosely attached to it. I(time can be spared, it would render this washing more effectual to have t[te goods (lisl)(~sed in very open tblds, to prevent unequal eompresstun, and soaked in water, either in a trough, or in a running stream. (Des Charmes, p. 95.) They are next pIaced in similar tohfings ill a kieve which is filled with waler, or waste alkaline, or soap levs, at a •
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the water~ aml from its previous acidity induces the acetous t'ermenteflon. An intestine motion becomes perceptible, the temperature increases, and air bubbles are entitled, which by carrying up to the surfitce some of the light oleaginous particles, produce a thick scum. These ett~cts, however, are geutle, and slow9 as the dressing is i~ small quantity, in proportion to the water. The acid salts, according to I)r. Ilome, are no sooner sel)arated by the acetous fermentatim~, fi'om the absorbent earth which made them not perceptible t(~ the tongue in their tbrmer state, t lan they are united to the oily particles of tile tallow, which likewise adhere superficially, dissolve them and rm~der them iu some degree miscible with water. In this state they are soon washed oit'by the intestine motion of the liquor. This fermentation continues ti'om twelve to eighteen hour% according to the state of tile weather; but even in summer may he allowed, if
Ma. RE~mE'~ Essays on Bleaching.
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we may trust Des Charmes, to go on without inconvenience for fortyeight hours. It is known to have continued the proper time, when an infinity of white bubbles are seen on the surface, and a foetid smell is perceived; or when the goods have assumed a clear yellowish colour, Instead of ~rav or brown. When no more air bubbles rise to support the scum, it separates, is precipitated, and wou d again become attached to the cloth, if not timeously removed. But greater dan~er may be apprehended from the putrid fermentation taking pla~, whic'h woul~fboth weaken the texture of the cloth, perhaps rot it, and also generate and fix a dark colouring matter, that it might be difficult afterwards to remove. Attention to the indications now given will prevent such serious accidents. There has been some discussion and difference of opinion respecting the liquid most proper for steeping. Waste alkaline leys are most commonly used, fi'om our idea that they produce the strongest fermentation; -but this, if it be the ease, may arise from the impurities with which they are loaded. For fine calico bleaching they certainly ought not to be used, as indelible stains may be the conse' luence- The alkaline salts ma attract the. acid. salts, generated by the fermentation, and prevent t~eir combination with the oleaginous impurities. On the contrary, if the alkaline salts are not previously saturated they may be of use in combining with, and carrying offthe tallow. Dr. Home tried to come to some decision on this subject, but his experiments proved unsatisfactory. Des Charmes used milk ~f lime with advantaze. He allowed the goods to remain in this liquid not longer thai~'five or six hours, when they were found sufficiently prepared tbr the subseqvent processes. "~Vater,however, when 'time can be spared, is as efficacious as either this or an infusion of bran, which has also been recommended--to this a decided preference is given in [reland.~(1)ub. Reiot. 1791.) When the goods are found to be sufficiently steeped, the steW is ~o be drawn off and the goods taken to the squeezers, in order that all the loosened impurities may be pressed out. They are then taken to the dash wheel and washed titl the water come off clear, when they are either wrung to such a degree that they ma~ remain only moist, or are left to drain, on a proper stage' After rinsing or clearing piece goods subsequent to steeping, particular attention oug'ht to be paid to rubbing them well with black soap, especially along-their selvages, for this part being closer wrought than the rest requires to be particularly cleared to open it to the action of the succeeding detergents. Vehen this is not attended to, it may probably be necessary, after the several operations, to rub them separately by hand, and the bleaching would be retarded by requiring several extraordinary immersions, to prevent these parts from bein_~ less nerfeetlv white than the rest. "Cottons which have received ~tains o'f oil are best cleared by a hot solution of black soap. ~
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ratus squeezes the dried clay, to save tile expensive operatior~ o} s upping, described at pa,,e l.)l ; alter which xt passes to an iron cylinder, full of knives, where it is cut into pieces with great expc(ii tion~ which saves the expense of cutting it by hand with brass wire~, as before mentioned. This receptacle is not properly a cylindc~ ~, but a large hollow inverted cone of Don, and the knives at'e fixed h~ an upright shaft which revolves within it and passes through its ceu tre. These knives are so contrived that the clay, as it is cut, is forced lower and lower by every revolution, until at last it is pressed by the power of the machinery through a square hole near the bottom of the apparatus, from whence it is removed as it falls, and is carried in blocks to the odmr parts of the manufactory. The clay havln/under,,,Zmlc those varied operations, it is now lit for being lbrmed into any shap% or emph)yed for any purpose, for which it is designed. Accordingly, it is faslfi0ned into various to :ms by meatis of a variety of moulds madc of plaster of" Paris; or put into as great a diversity of shapes by the potter's wheel. ]'EO BE ('0NTINUED.]
ESSA ~i5; ()N B 13EAC H I N G . By James lgennic~ .7. J!:L, /.ect~,,'er o~ l;hilos'o)~hy, (?c. 6"c. ! omh'~,. ~O.
I ~ I t . ~ 0 1 4 E M t C A L .~,NI) I'HYS[CAL NATtII~::
(11': S T U b ' F ' , , .
2. HTool.~For our knowledt~e of the texture and compo.~itio~ ')[ this important material of t lc clod~ mauufacturc~ we are greatly indebied to Detube~ton, The qualifies of wool as to length anti tenuity ot'iil)re, vary according to the Darts of tl'e anhnal whence it ma.v have I:wm.~ taken; to the'bt'eed v.f'sh'.:cp from which it is pvoduced;'the d?matc where they ti~e: ihc p'.>~'~u,'cwhere they feed; and accovdi~?; a',~ tt,e animals a~:e lma!tbx cr disc~c,3. TMt which grows (m the ~lcck, the sld¢s, and tl~e t ~:~ <.ri< , i * t I~t' ~ ~~(>S~: l~:U't 0~" fl{e fleet% and fortunately lhe trust: af~u~davt. The !v.~>tbreeds arc foam[ t¢~degenerate in cm~ail~ cilmatc::;, aw,', ccrtah, r~as:tuvcs, of which we have 'an illustrative ins/a~ce i~; i.,,e Eu"~q)ean brecd~ in some t:!aces of America, which now prod,.',ce hah'~i>~tead of wool. This seem:,; to depend on tim same general prineil)!e with the effects produced on wool by the diseases of the animals, tim m,~st healthy always affiwdiug the best~ for change of climate% and food. may alter the constitutional secretions, as muci, as diseus.'e. Great: at'ten(ion has lately been paid in l.iritaii~ to those ch'cum.~tatmes which aiD.or the qualities of wool~ and great im)rovements have h~en made b j the sheep farmers. This is of much ~mportance, as we are indebted to Spare for all our finest wools. Ks the fineness of wool cannot be accurately ascertained by simple ins ection, the manufacturer ought to comi)are by means of'a microscope, the ddferent specimens wluch may be offered to h~s purclmse. When the wool is in its ~atura state, it" s protected from moistm by a substance of a soapy nalure, called yolk by the English, and eeli 4
MJ, R~.~r~:'~ Ess~lgs o~ Bleaching.
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m Scothnd. TMs, according to M. Vauquelin, (Ann. de Chim. xlvii. ~276,) consists of a basis of potash combined with m~ animal oil, together with lime united to tile carbonic, acetic, and muriati¢ acids. This nutritions matter is ahvays most abundant on the wool of healthy sheep. . . . Mr. Mushet tbtlnd, that after (hstdhng m the dry way 180 grains of pure white wool, there remained a residuum coal, of a dark shin. ing gray colour, welded, or caked, into one mass, adhering in part to tire sides of the retort. It weighed only 49 grains, hawng lost in distillation 197 grains. In 100 parts, therefore, are contained 76 volatile matter, and ~23.89 oxide of carbon. The mechanical structure of wool is worthy of attention, both as an object of curiosity, and as, probably, of some impm'tance in explaining the rationale of bleaching it. This structure was first described by the abbe Monge, (Ann. tie Chim. vi. $O0;~see also Nich. quarto Journ. i.) he having discovered it when examining the process of fnlhng. Accorthn= to tlus philosopher, the fibres of wool consist, either of laminz lying in a slanting mariner upon one another, fi'om fln~. root to the extremity, somewhat like the scales of a fish, or of a series of rings zrad!mlly decreasing in diameter fi'om the.root to the point, and overlapping one another, as in the ho,'ns of ammals. M. Monge states, and his statement is ,'epeated by Bancroft, and in the Edinburzh Encyclopedia, that this structure may be perceived by drawing~a fibre between the thumb and finzer, from the point towards thotroot, in which case a tremuhms motion, it is said, will be distinctly li;lt, accompanied wiih a sensible grating noise. Now I am disposed to co~trovert this; fi~r upon repeated trials, with tibres of every degree of fineness~ I couht neithe," feel the motion n o r hear the grating. This cannot even be perceived in the coarse hairs of cows and horses, though th~,se have a similar structure. The only way by which it can be made sensible, is with a microscope, or by putting a hair between the linger and thumb, and moving ~hem gently one upon another, when the fibre will move forward, or backward, according as the point, or the root, is placed anterior, or posterior, to the part by which it is held. This property of hairs has been lon~ known to some of our peasants, who take advantage of it to excit'~, the wonder of the ignorant, by telling the root, or the point, of any hair, although it be cut into ever so many pieces. It is on tiffs structure that fulling and felting,~ depend; it is to smooth the asperities caused by it, tllat spinners ~rease their wooll and it is in the inter. stices of these lamin~, that the colouring matter, which it is our object to find a method of removing, is lodged. The laminae seem to be elastic, and~ consequently, the pores must be dilatable by heat. This it may be useful to remember. 3. Cotton.~This substance is a down contained in the pods of the gossypia of Linnams. This down is different in the ditt~rent spe. cies, both in fineness a.nd colour. In most it is white, of different shades; but that from which the nankin is made, is what Werner would call Sienna yellow, or bofforauge: a sort is mentioned as growing in Dahomy of a bright yellow; and several kinds, having YoL. I V . ~ N o . 9.--SI,:P'rE~I~'.II, 189.7. 20 .
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different shades of red, have been described. The coloured sort~, h o w e v e r , are not common, and the chief diflhrence between one sort and another, seems to consist ill the length, tenuity, and strength o[" the filaments. Naturalists do not seem to have ascertained with accuracy, the structure t)l' these tilaments The microscoue, accordin,, to Lewenhoeck, shows that they have two sharp sides. It certainly possesses some kind of asperities, or how can we account for the irritation which it i)r.duces when used in dressing wounds? In this it is totally di|re,.cm f,',)m lint. Perhaps this irr~tating action may be account ed for [rom the filaments being shorter than those of fla w and consequently prescl,ting d greater number o[" points on the surface of the cloth, l)r. Zhtmlso~t found the specitio heatofcotton to be 0.53, that of water hein,g 1, but [vonx the diiliculty of ascertaining this, he does not slat(; it ~;;ith confidence. (Ann. of Phil. II. ~7.) W e learn somethin~ of the composition of cotton from Mr. Mushet's expcrlments ond@ distillation. (Phil. Mag.XXXIll. 9.) lie distilled 263 l~t'aillS of-the cloth which had been previously bleached. It emitted, dm, in~ the operation, a quantity of.pale blue flame, anti left, as a rcsidm,~, a ligh~ fl'iable coal, possessing the original shape antl texture of the cloth'; wl:icll weighed 39 grains~loss, 1~4 grains. It appears, (hcj~, th:tt a hundred parts consisted of 85.16 volatile matte,', and 14.84 of carbon; being 16.16 less carbon tharx is conrained in as much silk, and 9.05 less than exists in pure wool. The fibres ()["cotton, according to Nicholson, (Dict. of Cheml art. vegetables,) are insoluble in water, in alcohol, or in ether; but soluble in alkalies. It tbllows, of coarse, that strong alkaline leys will injure the texture of cotton goods in tile process of bleaching. When treated with the nitric acid, cotton yields the oxalic. There seems to be in cotton, holm of dmt particular resinous kind of matter which constitules or c(,ntai~,s the colouring matter of ut~bleached linen.* 4. L i n e n . - - T h e mode of preparing flax, tbr the linen manufacture, has already been cursorily mentioned, when treating of water, and I shall not ~'epeat what was then stated. The llax, when taken from the field, is put into ponds of standing water to steep, and stones are laid above it, to keep it fi-om floating. When no such ponds are to be had, it is pu~ into those parts of running water where there is little curren't, or little streams are banked up for the purpose. None of these, however, answer so we|l as ponds, for the process is both more tedious and more uncertain. The intention of steeping is to dissolve the oily or mucilaginous substance which makes the bark adhere to the woody part of the tlax, and thusto effect a separation of the latter. This intention is answered by the putrefactive fermentation~ * Des Charmes, however, (p. 106,) ascribes to such a resin, or to an oil ors gum, existing' in cotton, tbe. difficulty with which it imbibes water. Des. Ch~a'mesl remarks also, that though it may not appear foul, yet it never fails to render, by its impurities, the water in which it may be macerated, of a darkish ¢olour. As it imbibes water with difficulty, it also retains it with some obstinacy, amt be. fore bleaching, is found to be long' in drying. This may be countenanced by an ot)servatinn of Mr. T. Henry's, (Man. Mere. iii.) that it imbibes water much tnore reamer alter ~ has been bleached than before,
MR. RENm,,:'S L'ssa3ts on Bleaching.
155
which steeping induces, tbr it renders tile oil and tile mucilage soluble in water. It requit:es some nicety, however, to know w~en the putrefactive process has accomplished its purpose, for tl!e flax will be equal Iv useless if it has been steeped too much, or too little, tn the onecase'the fibres will not be separable, or black bat's in the linen will be the consequence, whose numbers increase with the deficiency in steeping, and which, in bleaching, are very difficult to remove. In the.other,'~hey will be destroyed, or very much weakened, by !osing. theu- tenacity. Now, the length of time which flax has been m the pond, can give no criterion of this, for the putrefactive fermentation depends much on other circumstances, such as the naf'ure of the flax~ its quantity, the heat of the weather, the length of the nights, the pressure o'f t ae stones laid upon it, and the-quality of tile water. The quickness or slowness of the fermentation~ then, must be the measure of the time of steeping. On the second or third day, when t le weather is warm~ a ~reat many air bubbles arise to the sm~faee of the water, and a scum, o~-pellicle,-is gradually fro'reed. The temperature of the water increases, and it acquires a corrupted smell. ]Phe tlax ought to be inspected every six hours, after tim fourth day# and as soon as a Klutinous or oily matter is perceived on the outer bark, and when this separates easily fi'om the woody part, it ought to be taken out. But it ouzht not to lie till this separation becomes too easy, as this will be ~etter cmnpleted by exposing it to the dew. Steeping ought always to be peribrmed m a place much sheltered li'om the wi~ds, as (he process is checked by nothing so much as by agitation and cold, ~hilc it is vreatly promoted by quietness and heat. l~'orthis reason also, the ponds ought not to be too shallow, as in that case they are more liable to be aflhcted by changes of temperature. The flax ought not to touch the bottom of the pond, otherwise. what is below will perhaps be rotten, in consequence of the superincumbent pressure, before that at the surface is nearly watered. This process appears, then, to be extremely difficult in management; and by it is produced a great deal of that brown colouring matter, which it is the object of tim bleacher to l'emove.*" Mr. Lee's nmfliod of preparing flax, which has been before staled, is not liable either to difficulty of management, nor to its injurious etIhcts, and bids fair to supersede the proccss of steeping, altogether. The nature of the colouring matter of brown linen, whether it exist naturally in the flax, or be acquired by steeping, has been accurately mveshgated I)v lh', ~xlt'~ an, m the Fransacttons ot the Royal h'ish Academy, VolJIIL lie made his experiments upon ley, satue
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• With regard to colours so produced, Chaptal basmade a g'eneral remark Of some ~mportance, namely, that all eolouring'matter, arisi~g fi'om fermentation, are less soluble in water than in alkalies. He illustrates this by referring"to the well-known dye-stuffs, indigo, woad,and annotta. Boilin~water dissolves 0,!ly a ninth part of its weig'ht of indig'o; woad communicates very little colour to waterl and annotta can scarely be dissolved in it .at all without the aid of an alkall. Water, then, it will tbliow by analogy, confirmed, as we shall immediately see, by experiment, will have but little effect o1~the colour acquired by tlax iu the putrid li~rmcutatio, iuduecd hy ~tcel,b~g..
156
Ma. RaNM~:'s Essays on 131caehing~
rated with this matter, which he procured from thebleachers. This liquor was turbid, of a reddish brown colour, having a strong smell and exhibiting no indication of aeidity~ or alkalescence. It did not effervesce with the muriatic acid, but aflbrded with it a copious precipitate, leaving a supernatant liquor of a red amber eolour. W h e n this is drawn off by a syphon, and the precipitate treated pretty co~ piously with water, a~itatinz the whole, andauain allowing it to subside, the floating liqu°or exhC]bits evident sign~ of acidity, and con. tinues reddish, glving room to suppose that it contains.a peculiar acid. After copious effusions of cold water~ and when the precipitate is thrown on a filter and suffered to dry partially, it is of a dark greenish colour, and nearly of the consistence of moist clay. This was not dissolved when treated with sixty times its own weight of boiling water. If dried in a sand beat, it assumes a shining black colour, but when broken, shows a greenish yellow fracture, and becomes more brittle. On this the following experiments were made: 1, ltaving digested a portion of it in rectified spirit of wine, it communicated to it a reddish huc, and was in a great measure dissolved; but by the effusion of distilled water, the solution became milky, anti a white deposite was gradually formed: the black matter dissolved m the same manner, o Neither the green nor the black matter was soluble in oil of turpentine, or lit~seed oil, by a long continued digestion. 3, The black matter being placed on a red hot iron, bur|rod with a yellow flame and a black smoke, leaving a carbonaceous residuum. 4, The green matter being put into the sulphuric, muriatic, and nitric acids, communicated a brownish tinge to the two former~ and a greenish to the latter, but did not seem in tile least to be diminished. W e infer fi'om this, that the matter extracted by the alkalies from brown linen, is a peculiar sort of resin, ditI?ring from the pure resins only by its insolubility in essential oils, and agreein,~, in this. res, l~ect, with .lacs'" In..examinin,,, . ~ the action, of. alkalies, on tins matter, 8 grams of tt were digested m a solutmn ot crystals of soda, saturated to the temperature of 60 °, which instantly commu~ nicated to the solution a d a r k brown colour; two measures, each of wliich would contain 11 dwts. of water, did not entirely dissolve this substauce. Two measures of mild vegetable alkali, dissolved the wixole.• Olle mc':tsurc~. of caustic •soda,. of tlie~ s,pecific. ~ravity. of 1.05~3,,. d~ssolved nearly the whole, leaving only a white residuum. One measure of caustic potash~ of the specific gravity of 1.0,39, dissolved the whole. One measure of liver of sulphur, (sulphuret of potash or soda,) whose specitic gravity was 1.070, dissolved the whole. ()he nteasure of caustic ~olatile alkali~ dissolved also a portion of this matter. Three ounces of the solution of Windsor soap, dissolved 8 grains of the colouring matter. It was found also that 4.~2 grains of the saline substance o}~"kelp, produced the same effect as 75 of that from Dantzic pearl ash, 58 of that from barilla, 15 of that fi'om cashup, and ~1S of soap. The sulphuret 0[; lime was found to act very IL'ebly on it. It follows li'om these experiments, that sulphuret of potash, or soda, is of all the alkaline compounds the strongest solvent of the ,.olou" n~ matter; next to th s the faust c vegetable.and •
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MR. RENNIE'S EssttJ/s olt Bleaching.
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after this the caustic mineral alkali; the mild alkalies occupy the least nlaee. Hence, tile solutions of kelp, cashup, and markoff, are advan'tageously used in the first processes of bleaching, for which 1)autzic ashes and sweet barilla are less fit. Tile experiments, how. ever, show that six tons of kelp will be necessary to produce the same effect as one ton of cashup. It was ibund by Mr. Mushet, that flax contained more carbonaceous matter than cotton. His experiments were made by dry distillation. When he treated 397 grains of flax in this way, after a copious discharge of white flame, a soft inflammable coal was left as a residuum in the retort. 5Fileoriginal vegetable fibre remained entire, and equally compact as to form and bulk, as when introduced. It weiehed 65 era, us, havin~ lost by the process 332grains. A hundred parts are t]lerefore composed of 85.62 volatile matter, and 1638 of carbon. (Phil. Mag. XXIII. 8.) ~To. V . ~ P R O C E S S E S
FOLLOWED IN BLEACHING.
SECTION I,
By the arrangement which I have adopted, many of the detail~ which, in most of the treatises on Bleaching are given under tile present head, have beet, anticipated, a circumstance which, I hope, will render our account of the processes more perspicuous than it couhl otherwise have been madej it will~ at least, make it shorter. An outline of the processes of bleaching fidlowed about halfa century ago will be fmmd in the history~ p. ~07, vol. it. by comparing which with the l\~llowing, au idea may be lornied of the rapid march of improvement. I begin with the processes for bleaching piece goods and heavy cotton cloth% which do not materially differ, except in the repetition of immersions, the cottons requiring fewer than tile linens. 1. Steeping.~'l'his process is intended to remove, without the expense of fi'esh alkaline ley, the impurities which the goods may have contracted it, passing through the previous stages of manufacture f:'om the spinner and tile weave,', and which the subsequent maua~,ement mi~,ht tend to fix. Flax is mostly spun by hand, and tile spinuer constantly moistens it with saliva to make it draw out more readily to the proper grist. Now as saliva is known to be a more universal soN,cut tha(l even water, we may infer that many impurities may, by this means, be fixed in the yarn. It will also~ fi'om its nature, fi~rm, when dry; a pelliele of tenacious matter on the surface of the threads, and may thus l;,'event the solvents from coming into contact with the colouring matters which are lodged in the body of by the oil which is used for the machinery. Both are also filled with impurities by the weaver, who finds that he cannot make good wo,'k, unless he previously dress tile yarn with some gelatinous matter that may give it a stronger adhesion. The linen weaver cot,monly uses~t'or this purpose a sour paste, made from the seeds of oatmeal; which is applied with a brush to the yarn; and then tho-
Ms. R ~ m ~ ' s Essays on Bleachi~g.
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roughly dried in~ by passing a hot iron over the web. IIe then take,~ a brush~ on which he has rubbed a small quantity of tallow~ and Izoes over the whole. The cotton weaverseldom usesthe flummery pa'~ste, but prefers one made of flour, or of mashed potatoes in a state of fermentation, and ~ometimes a mixture of both: and the combustibility of the cotton will not permit him to use so expeditious a mode of drying, as the hot iron aflords. He dues h~s web with a large tan, and afterwards lzoes over it with the grease brush, in the same way as the linen weaver~. I was astonished to read in Mr. Parkes ~ Essays on Bleaching, (Vol. IV. p. lol.) that the weaver "melts a quantity of grease over hi~ warp, which he afterwards spreads with a brush:" a thing which I am persuaded no weaver would ever be so foolish as to. try, ,as the, l,.,vn'ts where.the g;,rease fell. would do away all tl e ~q-, teets ol tit(,, prevmus dressing. I~or tins reason, weavers are always very carelul not to rub too much grease on their brushes. Mr. Parkes must therefore lind some more likely account of tile origin of copper ~tains. The small quantity of grease in the cloth, is fixed by the subse~ quent operatio, of singeing, when this is had recourse to; and if this as not taken (,vt in the previous processes of bleaching, it will not yield afterwa,'ds t~) the usual processes of ashing and souring. For the removal ()f these impurities, the th'st thingto be done is to have the cloth thoroughly washrxt, (with soap if necessary,) by the dash wheel~ to get rid of \vhat may be loosely attached to it. I(time can be spared, it would render this washing more effectual to have t[te goods (lisl)(~sed in very open tblds, to prevent unequal eompresstun, and soaked in water, either in a trough, or in a running stream. (Des Charmes, p. 95.) They are next pIaced in similar tohfings ill a kieve which is filled with waler, or waste alkaline, or soap levs, at a •
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the water~ aml from its previous acidity induces the acetous t'ermenteflon. An intestine motion becomes perceptible, the temperature increases, and air bubbles are entitled, which by carrying up to the surfitce some of the light oleaginous particles, produce a thick scum. These ett~cts, however, are geutle, and slow9 as the dressing is i~ small quantity, in proportion to the water. The acid salts, according to I)r. Ilome, are no sooner sel)arated by the acetous fermentatim~, fi'om the absorbent earth which made them not perceptible t(~ the tongue in their tbrmer state, t lan they are united to the oily particles of tile tallow, which likewise adhere superficially, dissolve them and rm~der them iu some degree miscible with water. In this state they are soon washed oit'by the intestine motion of the liquor. This fermentation continues ti'om twelve to eighteen hour% according to the state of tile weather; but even in summer may he allowed, if
Ma. RE~mE'~ Essays on Bleaching.
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we may trust Des Charmes, to go on without inconvenience for fortyeight hours. It is known to have continued the proper time, when an infinity of white bubbles are seen on the surface, and a foetid smell is perceived; or when the goods have assumed a clear yellowish colour, Instead of ~rav or brown. When no more air bubbles rise to support the scum, it separates, is precipitated, and wou d again become attached to the cloth, if not timeously removed. But greater dan~er may be apprehended from the putrid fermentation taking pla~, whic'h woul~fboth weaken the texture of the cloth, perhaps rot it, and also generate and fix a dark colouring matter, that it might be difficult afterwards to remove. Attention to the indications now given will prevent such serious accidents. There has been some discussion and difference of opinion respecting the liquid most proper for steeping. Waste alkaline leys are most commonly used, fi'om our idea that they produce the strongest fermentation; -but this, if it be the ease, may arise from the impurities with which they are loaded. For fine calico bleaching they certainly ought not to be used, as indelible stains may be the conse' luence- The alkaline salts ma attract the. acid. salts, generated by the fermentation, and prevent t~eir combination with the oleaginous impurities. On the contrary, if the alkaline salts are not previously saturated they may be of use in combining with, and carrying offthe tallow. Dr. Home tried to come to some decision on this subject, but his experiments proved unsatisfactory. Des Charmes used milk ~f lime with advantaze. He allowed the goods to remain in this liquid not longer thai~'five or six hours, when they were found sufficiently prepared tbr the subseqvent processes. "~Vater,however, when 'time can be spared, is as efficacious as either this or an infusion of bran, which has also been recommended--to this a decided preference is given in [reland.~(1)ub. Reiot. 1791.) When the goods are found to be sufficiently steeped, the steW is ~o be drawn off and the goods taken to the squeezers, in order that all the loosened impurities may be pressed out. They are then taken to the dash wheel and washed titl the water come off clear, when they are either wrung to such a degree that they ma~ remain only moist, or are left to drain, on a proper stage' After rinsing or clearing piece goods subsequent to steeping, particular attention oug'ht to be paid to rubbing them well with black soap, especially along-their selvages, for this part being closer wrought than the rest requires to be particularly cleared to open it to the action of the succeeding detergents. Vehen this is not attended to, it may probably be necessary, after the several operations, to rub them separately by hand, and the bleaching would be retarded by requiring several extraordinary immersions, to prevent these parts from bein_~ less nerfeetlv white than the rest. "Cottons which have received ~tains o'f oil are best cleared by a hot solution of black soap. ~
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