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Essays on bleaching
Essctjs on Bleaching.
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two-thirds of its length next the base, and terminated by shining, reddish, brown poiut~, giving the general colour to the pelage; tim other is short, very fine, thick, tufted and soft, being of differ¢nt shades of silver gray or light lead colour. On the head and feet the hair is shorter than elsewhere. The tail, which is ten or eleven inches long, is covered with hair similar to that of the back, for about one-third of its length nearest the base, tile rest of it is covered by hexagonal scales, which are not imbricated. The only species of beaver, known, is the one we have described; all the others-which have been noticed, are varieties of this species. During the first year of their lives, the beavers are termed pappooses, by the hunters; when two years old, small meddlers; at three years of age, large meddlers; in their fourth year tlmy are called beavers, and after that, old, or great beavers.
ESSAYS ON B L E A C H I N G . By JAMES RENNIn, A. M. Lecturer on Philosophy, &c. &e. London. No. V.--Processes followed in Bleaching. SECTION
II.
~. J~ucking.--This is one of the processes which has lately received important improvcme~lts t'~'omthe invention of an apparatus called the whale boiler, whose ope,'ation has ah'cady been described. But w rather this b e , sod, (a,~d it is not yet general,) oF the okI apparatus, the goods are treated precisely in the same way, and it is a very important part of the whole operations. The first thing to be attended to in bucking is the preparation of an alkaline ley of a proper strength. For this purpose the crude alkali is to be broken into small pieces not exceeding the bigness of a hazel nut, or bruised by means of a horse mill, and put into .the. boiler with a proper. _quantityof water. It would be an economizing of fuel to put tMs ln~:o the boiler immediately on drawing oit" old leys, when the heat of the •
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liquor ought not to be permitted to boil, for Dr. Home, (p. 105,) proves by experiment that salts h'om ashes by boiling are not so strono_ly alkaline as the ashes themselves. If pearl ashes are added to a l~y made from the other crude alkalies, they need not be put in till the solution is nearly completed, as their greater quantity of carbonic acid renders them much easier to dissolve. Those who pursue the older modes of bleaching, put the goods into the alkaline solution which is thus prepared; but as its strength can be, accordinz to Kirwan's experiments, increased one-half'by the addition of socheap an article as quick-lime, this ought never to be neglected, particularly also as chemistry informs us, that no alkali will combine with any oleaginous matter (unless it be in a state of causticity). It
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Essa3ts on Bleaching.
is of great importance to attend to this when American pearl a ~ l is used, as it always contains a large nroportion of carbonic a m d . i J e s Charmes advises to take of quick°-lime the whitest which can be l)ao, a third or a fourth part in weight of the solution, and heat u p ~!l a bag or cloth to prevent it from rendering the ley turbid. A p e t t e r method is to add one part of welbburned fresh-slaked and finely pu verized quick-lime, to two parts of the alkali dissolved as a b o v e . When the lime has been added, the mixture is to be brought to boil,
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supernatant liquor, now in a state of causticity fi'om the loss o f its carbmfic acid, may be run oiF fin" use. The lime which has s u b s i d e d is to be washed with water till it comes off d e a r without a l k a l i n e taste, and the washings are to be kept fur making, fresh leys. T h e bleachers i,,norant~ of chemistry, erroneousl, y imagine that the...lime irnl)arts some of" its ro )erties to the le but as the precipitated lltne allinity abstracted the acid fiom the~carbonated alkali. Des C h a r m e s sa~-s that it is not necessary to add lime to American and R u s s i a n asnes, as they contain a large proportion of it when imported, b u t he surely forgot that this lime is commonly in the state of a c a r b o n a t e , and therefore cannot take up the carbonic acid which r e n d e r s the ashes mild. I have stated~ that in rendering alkalies, caustic quickdime is to be added in the proportion of two to one by weight, but this is s o m e what vague, anti will not apply where there is much difference of quality in the alkalies. It will consequently be of importance to ascertain some test by which to determine when a proper q u a n t i t y of lime has been used. For this imrpose, when the boiling of the l'{~ixtm'e has heen stopped~ take a little of the supernatant liquor in a wine glass, and breathe into it through a small glass tube, or a d d to it a few drops of clear solution of subcarbonat~ of pot-ash.: if t h e r e be a redundancy of lime, the dissolved earth will absorb the c a r b o n i c add from the human breath, or from the pot-ash, and will r e n d e r the liquor turbid. If it does not become turbid, add a little l i m e water, and if this occasions turbidness, it shows, that the liquor contained carbonated alkali, and has not had a sufficient q u a n t i t y of lime. If the lime be in due proportion, the ley will neither s h o w turbidness from these tests nor will it effervesce with acids. It is of the greatest importance to the bleacher to be able to d e t e r mine readily, the specific gravity of his leys, as they must be u s e d as nearly as possible, of the usual strength: ley of 1.01~7, or 1 . 0 1 5 6 speciiic gravity is what is commonly employed. To ascertairt this, the hydrometer is generally used. A new instrmnent of this sort was, some time ago, proposed by Professor Leslie, (Ph M a ~ x - v l ~00,) but I have not heard whether at has ever come into u s e . I t was to be constructed on the principle which he has flllly d e m o n -
Essays o~ Bleachin~.
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strafed~(hat capillary attraction is nothing more than the specific relative attraction of solids and fluids, and the purity of the liquid ex,'uuined, would be indicated by its ascent in a capillary tube graduated with enamel coIours. The instrument in common use is not so simple, not" so elegant. Those w.hich were formerly employed were not constructed on a fixed principle, so that when one of th*m was broken, another could not be made to the same scale. This inconvenience, however, has been removed by the ingenuity of Mr. 1 weedale of Glasvow, whose hydrometers are now universally used. The method which he adopts is to commence the scale at 1, and to make every degree indicate .005 of specific gravity. Hence, supposing tile alkaline ley to indicate ~0 ° on the Scale, its specific gravity would be 1.-[-~o0x.005=l.100, the specific gravity of water being unity. A complete series of these numbers from 1 to 6, indicates tile specific gravity of fluids~ fi'om distilled water, as 0. to ~sul])huric acid, ~. the-heavlest liquid known. In using such inSh'uments it is necessary to attend to the temperature of the atmosphere~ as~ll bodies are greatly intluenced by tli&r sensible caloric, an'd tlie~r bulk increased or diminished accordin_,z to the quantity wllich they con* tain. In water, the fifth decimal figure changes with every degree of Fahrenheit's thermometer, other fluids obser~:e diffhrent rates. Some bleachers guess at the strength of their leys by the taste, but this musE, at best, be an uncel:tain criterion. Des Charmes tells us that the laundresses of France ascertain the quality of leys fi'om their lubricity when rubbed between the fin_~er and thumb, or fi'om the readiness with which they absorb the co~lourina• matter of the goods. ~Vhen leys are made caustic by means of (l'uick-lime, and drawn oit' fbr use, they will commonly be of the same strength at the top and bottom of the vessel; but when they are not removed from the boiler, and the goods are put in as soon as the solution has been effected, the liquor will-be often three-fourths stronger at the botto]n, than at the top, fi'om the undissolved alkali continuing to melt. ~lais duaht to be carefully attended to, as it is contrary to-the general lhw wh'i'ch obtains in solutions, namely, that they are of eqUal-strength tln-oughout. Dr.. H o m e . psup oses the. anomal, y t o dependon the-presence of hme m a state of mechamcal mtxture. It is of iml)ortance flint the ley should be always as clear and limpid as possible, for if the lime remain either in solution or suspension in the smallest proportion, it is apt to be precipitated into the fabric of the cloth, and' will be fixed by the sulphuric acid sour, which will produce an insoluble selenite. This, however~ is not of so much consequence lot' the two or three first immersions, as it is when tile goods have once acquired an even colour, and require only to be brightened, it is then essential for the savin~ of time and lat)oUr, to have them as colourless as possible. Des_ Charmes directs the ~,,~oodsto be. 1)ut into the buckin~ apparatus in a,, moist state; 1)r. IIome, that. fl~ey should be. dry, 11 !" order, hc sa~'s, that the salts may enter into lhe body of the cloth, along with the water, as (hey ~11 not (:n(er in such q~antitv if i( l)e wet', VoL. I V . - - N o . 4,~()O,,T01"~EI~., 1~;~7. :;() F •
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E s s a y s o,n
I~leaching.
and by 'tcth,g t~o powerfully m~ the extermd threads may endanger in tim kieve it, ~p~'a l\flds, as in tile steeping process, and a qua~tity of the caustic h'v (h~:ah~d to tile temperature of the blood), is poured over them, sufli~;iCnt fi)r their thorou~zh immersion. The heat is increased, very ~radm~.ily~ tiff it reach the boiling point, when it is thrown up aNaim~t the mlfimqla, and spread, by it, over the surface of the g~¢,ds, thron ::h which it t ercoiatcs into [he boiler ag'fin, and so on iLL succession till it b~'~.~aturated with impuriLies. This is knowu from its l,si~g its cau~,ticity, and ae(luiving an offensive smell, or lio,n tile deepness of the coI~)tu"both of the Icy and the cloth. T h e succ(~s of the l)r()ct~ss indeed is commonly estimated in proportion to the de~qmess of the c~[our, which the cloth has acquired. (lh)me~ p. 72.) Particular attentiol~ ought to be ~iveu to the gradual increase of lempcrztiure now directed. F(n' the resinous or oleaahaous colourH~;Xmatter ot the cloth, tile twist ng of the threads, and closeness of texture, must hin(leL• the liquid from T)enetratin~ it, particularly at tirst, so that if tim Icy were poured o~L at ~lOflthe'cloth might be liable in several parts to a dry heat. This is usu'dl'f illustrated by the general ett'ccts which heat produces on coloured'veNetable matter. Thus if any ve~:etable is to be softened, or to have its juices extracted, it is tbund that this can be better done by b%innin~ witk moderate degrees of heat~ titan by olun£1no' it all at once in l~oiling water, winch would rather harden it and tix its colours. Cooks are well aware of this, and always when they wish to preserve the green colour of v%etables after boiling, never put them in till the water has acquired its highest temperature. 'rhe same reasoning applies to the process of b~{cking: anti here also it is confirmed by experienee~ as gomls which have n6ibrtunately been put into boiling Icy in the lh-s-t instance, can never be brought to a good white, llr. Home is so much impressed with the importance of this, that he deems it adviseable to keep the Icy under the boili~g point liar the two first buckings; but this is surely can'vina; the precaution too far. Des Charmes' metl[od exclu(led boiling as unnecessary, it beinsutlicient, he thin,;s, that the Icy be hot a~d sutliclently abundant. tie takes out his goo;ls when the liquid under the cover in the middie of the heap is too hot to admit of" the hand being held in it, or ~vhen it simmers round the circumference of the boi]er~ and throws up white bubbles, which circulate towards the centre. Frequently he only.plunged tile goods, tbr a few minutes, into ley of a "~ery gentle heat, and he found that by this treatment, both cotton and piece g~ods, bleached perfectly well. The leys, when the above circumstances are indicated, are to be drawn oil,; and warm water poured over the cloth in the kieve, which by cmnbi'ning with part of the remainin~ impurities which have beert loosened, se':'ves to carry them oil: When this has been don% a stream of cold water is allowed to play on the goods till it run off nearly limpid, after which they are taken to tile dash wheel; the reason for this process, which is not always properly attended to, •
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is, that were the cloth carried firm the kleve to file dash wheal, while hot, a certain portion of the eolouring matter would be agaitt ftxed in it, which wouhl not easily be again removed. The process of bucking is successivelv repeated, even as often as 10 thne~,befoce the operations are finished, and with leys of dift;~.rent strength. I find that with respect to the wu'iation of the strength of the leys, there are two modes recommended, directly opposed to one another. Des Cha,'mes says it is adviseable to keep the leys at the same degree of force, durhlo- the first two or three immersions of the sume goods, diminishine thee strength one third o~"one fourth, as soon as the pieces have acqu~'ed a uniform colour. In this pe,'iod, weaker leys may be advantageously used, because there remains scarcely any thing more of impurity to be carried oil'; and the Subsequent process . ma J~ be conside,'ed. merci as . a brMjtenin ..Y . g of the. eolour b. Y d e tachmg the small portmn ot mqmnty w~lch may remain fixed m the texture of the thread, (p. 81.) With this, agree the experiments of Mr. l{oe and of ]ging~, (Report on Experiments, &c. Dublin, 1791;) The practice of our bleachers in Scotland and Ireland is directly the reverse of this. They use the weakest levs at the commencement, and increase them in Strength as they prorated. Dr. Home's reasoning on this ,.seems to, be conclusive. " The leys," he sa)~s, "should be weakest m the In'st buckmgs, because then they act only on the more external parts, but when the clo~h is more opened, and the tield of action increased, the chemical agent ought hkewtse to be in.
this point. In repeating the bucking process, most bleachers occasionally use leys which have formerly bee.a used Nr a similar purpose, even mQre than once. This practice we have already reprobated, when treating of steeping, and in the present case it is of no less importance to avoid it, part{cularly in bucking fine goods. They seem ?to haye been led to this bad practice ti'om its apparent econoiny, b/tlwii~n it is coaside,'ed that it is only the unsaturated portion which can act, pure ley must evidently be cheaper. Besides, cloth bucked with foul lej;, becomes heavier instead of lighter, and consequently must receive impurity fi'om it:. Des (3harlnes directs a l?~ixture to be made of foul with new Icy, adding a third or fourth of tat latter; but these added portions of fi'csh le~' iliust bQ,greatly impah'ed in strength, by taking up the imput'it.ies ~xrith whicb~the old Icy is loaded, and this is found to agree with experience. It is of some consequence to remark, that little advantage can arise fi'om several buckings, immedialelq] succeeding one another: even the second immersion in the le,y will'fre(luentiy leave it (luite, limpid. Des: Chavmes.. tbund .it of more advantage to use t ~e Icy rein ere( caushc by hme at the Coinmencement of the buckings than afterwards, when it might impair t!~e texture of the go~ds.
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Essays on Bleaching.
s~e'rmx m. 3 H/a.~'hing.--It is never to be forgotten, that between each of the several processes~ of steeping, buckmg, souring, &c.~ the goods a "c to be thoroughly washed by the dash wheel in pure waker, so that all the loosene~i impurities, as well as the detergent which has been em I ~1o) 'ed, may be. eit'ectually removed. When any of these are left . • ,~ defect , , - ot waslnn~, o. t 11ey not onl y prevent the propex" opma~" tlnou,,h tion (it' the agents afterwards supplied, but often leave in the cloth indelible sta{as. Besides, as it may, through ne~leet~ become dry after buckling or souring, the salts will be conden~sed in i)roportion to the dryn&s of the c[otlb and acting with greater force will. de. stroy its texture. Soap ~s not employed except in the tirst washing' and in tinishing. Black, or soft soap is found to be the best tor these purl)oSes, brown soap leaving a yellowish tin,_,'e ou the cloth. If these precautions are not attended t% the goods~which are imperfectly washed will be in danger of becominlx yellow instead of white, by immersion in preparations of chlorine; al~d even of acquiring a tenacious and disagreeably ruddy tinge, either partially, if the washing has been partLal~ or totally, ff tt has been entirely neglected. The bleacher should be on his gilard, not to soap clea:ed g'~mds in the soapy solution which has been used for pieces taken (mr of a strong chlorine preparation, even though they have lirst passed flirough a suur of sulphuric acid; for this soapy solution does not fiuI to aequtre the property of dlseolourm~ other uoods~ unless the °'oods which, were soap,ed, aRer bein~ tak~u out fr~om~the chlorine preparatton, have been immersed for a Iona time in clear water. Washing should always if possible be performed immediately aRer bucking', while the goods a?e ;yet warm, as the filth and refu'se will then bd easier removed than after they become cold. 4. Croflin¢, or ezy)osure on the F i e l d . ~ I t has been accounted a great deside~'atum in bleaching to find a method of finishing goods ~vithmtt exposing them on the bleach-~.reen, as it consumes a ~reat deal ot mac and labour, and keeps out of eulttvatmn lare,e tracts of good arable hind. It was thought, at one time, that the introduction of chlorine bleaching, would supersede croffing; and it would do so, in a great measure, were it practicable to apply it in a proper manner. But, however great may be its facility in bteachino~-, it is scarcely possible to adopt it in anextensive maimfitctory to ti~e exclusion of trotting, without very heavy charges in work-shops and apparatus. This naturally follows fi'om what has already been remarked with regard to finishing the bucking process; and it is useful to take notice of it. as bleachers often let their goods lie in heaps lbr a considerable thne belbre washing. The washing of goods after souring, ts sometnnes admitted on the erroneous notmn that the acid which adheres to the elott b is useful in giving activity to the oxymuriatie salts. Evils of which they are unaware, arise from this mode of managementl for when the sulphuric acid thus left in the cloth, meets with lime, it forms a sulphate, which becomes tixed in the pores of the eloth~ and produces stains that crofting ca.nnot remove. O
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The ::prevalence~of this may.. be seen. b}r examining. . the kiers which. are ottcn covered on the lnstde with tills permclous sulphate; it can therefore only be economically adopted with such goods as are intended to receivewhat is called a half, or three-quarter white. It has certainly very much diminished tile period which crofting was wont to require, and in this seems to consist the chief diflbrence between the ohl and the new modes of" bleaching. The first thing which claims attention~ is the soil and situation of the. bleach-green. A gravelly or sandy soil seems to be the best, as the water will pass quickly through a soil of this kind, and will increase the rellection of the heat, for the tn'ocess depends on the, cva|)oration which may thus be caused. For tlie same reason if; ought to have a southern exposure, and if possible sli0tdd rather he sloping than level. To prevent the water becoming muddy it should run in a channel paved witli sand-stone. When the cloth has been steeped and bueked~ it is spread onion the field, and fi-equently watered ibr the first six hours, to prevent tile condensation of anyalkali which the washing may not likve ~ 2 moved. Dry spots are then allowed to appear before any a(iditional watering. Dr. Home thinks that it profits most by this exposure when near drying~ as the evaporatin_~ particles come rather fi'om the more internal parts, than the surface; and that it is chietty evaporation. which, operates, is inferred from. the thct, that. the upper, is. uni-. tormly wluter than the under surface. That ~t loses together with its grayish tinge the remainder of the acids and alkalies, with which it t;as bceri tl:eated, apl)ears ti'om the safety with which it may be afterwards dried. Soap when sliced down and exposed to the sun and air, with fl'equent waterings, will lose half its weight in a fortnight; the inference is obvious and need not be stated. From some experilnents it appears that the sulphur of the leys is one of tlie substances which is evaporated in croffing, and we know that this always has a tendency to produce a yellow tinge. (See Trans. R, T. Acad' IIL p. 45.) Berthollet seems to have taken a view of this prodels not quite so scientific as might have been expected, when he tells us (Ann. de Chim. II.) that crofting only prepares the colouring particles for being afterwards dissolved and separated by the ley. He surely never had observed the peasants bleach, by croffing alone, or by crofting tfler boilino~ in alkaline or soap leys. It is supposed by bleaclmrs, that exp6sure on the field has more eli?el in the months of March, April, anti May, than in any of the other months. As this idea is universal, it is likely well-fbunded, although Dr. Ilome has endeavoured to account for it by the greater attention which is usually paid to goods at the beginning Of tlie bleachin~ season. He states also that Mr. Christie, an experienced and enlightened bleacher, found the summer and autumnal months to be more efficacious than those of sprin~. But may not the drought prevalent in March, produce such an elt~ct, if evaporation i s t h e a,,'ent~ And if li,ht, as seems indubitable, is requisitc~ wilInot the want tlf clouds at this tmle be ot consequencer l'he effect of hght on colours is often very striking. When 1 was in lreland, I observed
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that the bed curtains in the reruns of Shane's castle, which are ex~ posed to the retlection of lij4ht t'roin loch Neath, were changed from fast and bt'illiant colc)urs, to pure white. Baume (Journ. de Physique 179S) fimnd that yelh~w raw silk, loses its colour in a short time, by exposure to the sun, (see a memoir on this subject, Ann. de Chim. Vl. 80.) Be.rthollct ira'@ned that there might be something ill dew, which was efficacious in crofting, and he accordingly examined the dcws which t)ll at ditt'erent periods of the night. Ire found them (Aim. de China. 11.) so strongly impregnated with the ]n'iuciph: of acidity, that lbey reddened paper tinged with turiisole. .From this lie at:c:mmts tbr'the greater "etliciency of spring dews, on the erroneous d~)ctrm¢,s that dew is transpired fi'om plants, and lllat plants transl)ir(~ oxv~(m and dew mr)st copiously in spt'in~. That the sun has a cm~sii'lerablc effect in whitening, independent of evaporation, aI~lmars fmln Ibis. lhat in dry windy weather the eva•ali~ l is me "e a ~eed',, [ it tllt, ble'tehin~ is slower than in cahn ~,Ul]Shllle, which seellls ~o [)(? the best weather for croftin~, lh-. 11o it thil ks Imwcve" that i ~ consequence of the slowness of tae evaporation, the m~istur~ c~nm'~s mm'e li'mn the internal parts of the go~ds~ this he thinks mu.~ , ~ the case, in consequence of tile heat tending to open the pores, whih; tim wind will rather ch~se them. The same iutelligmat cheinist rmnark~., that it is in conse~luence of its completing the bucking process, by e~ap~rating the salts which are combined with the lo~sening ilnlmriti~,.s~ that trolling l~roves beneticial~ no sort ~1' washing which he tried as a substitute, was found capable of superse..: . . lirJ~ . . ihe t~r°cess;", crof~in--,~ .ahvay s tbllows every buckin,,.~, and boihn~. There are, strictly speakmT/, two modes of croftmg: the goods' are artiticially watered from tr~oughs or little eanalsj or, they ~;l'e exposed to all tim vicissitudes of the atmosphere, without artilicial watering. Tile latter is called dry erofting. 5. Boiling.~('~oarse lineTl calmer aftbrd the time and labour, but particularly the quantities el" alkali, necessary tbr bucking, and must tmdergu the shot'ier and m(~t'c active operation of boiling. Although, howex,er, it may seem t~) be the more active process, it by no means follows that it is the most ell]tacit)us; on the contrary, the ley is much thicker amt darker af'ter bucking, than after boiling. As the heat continues longer at the degree of boiling, the leys used for the coarse cloth must be weaker than those used for the fine. There is not so much danger lYm~ heat in tim coarse as in the fine clotlb because the Nrmer is of ~t more open texture and' will allow the ley to penetrate more speedil)~; but in coarse cloths of a more close texture, the heat slmuld be l'ai~cd gra(hlally to the boiling p()int. The ettt~et of boiling raw colmn ~r linen in a diluted solution ~f ,.;tlistic alkali, is to give the li~lum' a deep brown colour and to &.stl'o~" its causticity; and t"es~ pm'iious of clear ley applied a s,~cmit[ or third time'wi/I i~roducc ;imilar ea;~cts, but in an inferior degree, (ll.ees' Cy¢l. ]lleacliing.) I n bleachlng fine goods, boiling is among the flniahhlg operations, and is rally Cmllloyed when the g~mds are nearly white, in order to remove the disagreeable smell of the prel~arations. The Icy in this
3ff. lYrl,:ins's new Steam Engine.
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case is composed of pearl ashes, or of pearl ashes and white soap. The boilin,.ou~bt not to be urged with a brisk fire, but kept barely at the boiling point, lhe ~,oods must be completely covered with the Icy, and kept ti'om rising by a cross similar to that used ill steeping, in order that they may be exposed equally to the action of the alk~ili or soap. In bleaching fine cottons, such as lawn grounds~ books, and light jaconets, no pearl ashes are used, the Icy being made wholly of soap. 6. l'mmersion 5, the preyarations of Chlorlne.~When the oxymuriates of lime, potash, soda, or magnesia have been prepared in the way ah'cady diree(ed, they are to be diluted to the spec-ific-gravityof 1005-, or 5 or 8 quarts of the solutions may be mixed with ~0 gallon~ Of water, and put into the immersing apparatus of Rupp or any Other Inch may be thought best. The test hquors already sofully desmbed are then to be had recourse to, to check the indication Of the speei' tic gt'avity. Mr. Dalton's certainl.¢ seems to be the best, .but ~h~re tins ~s not at hand, solutmns of nad~,_,'%cochineal, or turnsol~l~ay be used; even red wine is no despicab°le test, when the others can, not be had. It may be useful to take notice of the several eolours which these test liquors acquire when the chlorine preparations are of sufficient strenzth. Dalton's tests ]lave ah-eadv been copiously explained. Ihe md~zo test becomes yellowish, passm~ into wood', and of a deeper or l~inter tint, in proportion to the°dm'kuess of the blues: the tinctm'e of cochineal, becol/~es Dutch orange; red-wine becomes wine yellow; aud inlhsion of turnst)le, becomes amber brown. The gm~ds are to be immersed in the liquor immediately on being removed from the bleach-green, and particular care ought to be taken that they be all equally exposed to its action, otherwise stains and spots may be produced, which subsequent treatment may not be able to remove. Twelve hours is the usual period allotted for the immersion of linens; but less time will sometimes be sufficient. The bleaching liquors, according to Mr. Roe's expkriments, may be repeatedly used without detrimeat, till their wli.01c strehgth be exhausted. (1)ublin ReTort ~1791.) ~'9
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MR. PERKINS'S N E W STEAM ENGINE. We are anxious to satisfy public curiosity, which has been considerably excited by what we have already published, oll the subject of Mr. Perkins's new steam elegiac. The letter addressed to us by that gentleman, promised a specification with drawines, and enquiries have been repeatedly made, whether these had arrive~l: but as the en, rolment of his last patent in England, which embraces his recent improvements, was not to take place until September, we appreh}nd that at least a month must yet elapse, betbre the expected papers arrive; we however publish, fi'om the London jou,'na]s,'such i~formalion as they contain, and are particularly pleased :with having it in our power to present some engravings which will suffice to give a
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two-thirds of its length next the base, and terminated by shining, reddish, brown poiut~, giving the general colour to the pelage; tim other is short, very fine, thick, tufted and soft, being of differ¢nt shades of silver gray or light lead colour. On the head and feet the hair is shorter than elsewhere. The tail, which is ten or eleven inches long, is covered with hair similar to that of the back, for about one-third of its length nearest the base, tile rest of it is covered by hexagonal scales, which are not imbricated. The only species of beaver, known, is the one we have described; all the others-which have been noticed, are varieties of this species. During the first year of their lives, the beavers are termed pappooses, by the hunters; when two years old, small meddlers; at three years of age, large meddlers; in their fourth year tlmy are called beavers, and after that, old, or great beavers.
ESSAYS ON B L E A C H I N G . By JAMES RENNIn, A. M. Lecturer on Philosophy, &c. &e. London. No. V.--Processes followed in Bleaching. SECTION
II.
~. J~ucking.--This is one of the processes which has lately received important improvcme~lts t'~'omthe invention of an apparatus called the whale boiler, whose ope,'ation has ah'cady been described. But w rather this b e , sod, (a,~d it is not yet general,) oF the okI apparatus, the goods are treated precisely in the same way, and it is a very important part of the whole operations. The first thing to be attended to in bucking is the preparation of an alkaline ley of a proper strength. For this purpose the crude alkali is to be broken into small pieces not exceeding the bigness of a hazel nut, or bruised by means of a horse mill, and put into .the. boiler with a proper. _quantityof water. It would be an economizing of fuel to put tMs ln~:o the boiler immediately on drawing oit" old leys, when the heat of the •
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liquor ought not to be permitted to boil, for Dr. Home, (p. 105,) proves by experiment that salts h'om ashes by boiling are not so strono_ly alkaline as the ashes themselves. If pearl ashes are added to a l~y made from the other crude alkalies, they need not be put in till the solution is nearly completed, as their greater quantity of carbonic acid renders them much easier to dissolve. Those who pursue the older modes of bleaching, put the goods into the alkaline solution which is thus prepared; but as its strength can be, accordinz to Kirwan's experiments, increased one-half'by the addition of socheap an article as quick-lime, this ought never to be neglected, particularly also as chemistry informs us, that no alkali will combine with any oleaginous matter (unless it be in a state of causticity). It
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Essa3ts on Bleaching.
is of great importance to attend to this when American pearl a ~ l is used, as it always contains a large nroportion of carbonic a m d . i J e s Charmes advises to take of quick°-lime the whitest which can be l)ao, a third or a fourth part in weight of the solution, and heat u p ~!l a bag or cloth to prevent it from rendering the ley turbid. A p e t t e r method is to add one part of welbburned fresh-slaked and finely pu verized quick-lime, to two parts of the alkali dissolved as a b o v e . When the lime has been added, the mixture is to be brought to boil,
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supernatant liquor, now in a state of causticity fi'om the loss o f its carbmfic acid, may be run oiF fin" use. The lime which has s u b s i d e d is to be washed with water till it comes off d e a r without a l k a l i n e taste, and the washings are to be kept fur making, fresh leys. T h e bleachers i,,norant~ of chemistry, erroneousl, y imagine that the...lime irnl)arts some of" its ro )erties to the le but as the precipitated lltne allinity abstracted the acid fiom the~carbonated alkali. Des C h a r m e s sa~-s that it is not necessary to add lime to American and R u s s i a n asnes, as they contain a large proportion of it when imported, b u t he surely forgot that this lime is commonly in the state of a c a r b o n a t e , and therefore cannot take up the carbonic acid which r e n d e r s the ashes mild. I have stated~ that in rendering alkalies, caustic quickdime is to be added in the proportion of two to one by weight, but this is s o m e what vague, anti will not apply where there is much difference of quality in the alkalies. It will consequently be of importance to ascertain some test by which to determine when a proper q u a n t i t y of lime has been used. For this imrpose, when the boiling of the l'{~ixtm'e has heen stopped~ take a little of the supernatant liquor in a wine glass, and breathe into it through a small glass tube, or a d d to it a few drops of clear solution of subcarbonat~ of pot-ash.: if t h e r e be a redundancy of lime, the dissolved earth will absorb the c a r b o n i c add from the human breath, or from the pot-ash, and will r e n d e r the liquor turbid. If it does not become turbid, add a little l i m e water, and if this occasions turbidness, it shows, that the liquor contained carbonated alkali, and has not had a sufficient q u a n t i t y of lime. If the lime be in due proportion, the ley will neither s h o w turbidness from these tests nor will it effervesce with acids. It is of the greatest importance to the bleacher to be able to d e t e r mine readily, the specific gravity of his leys, as they must be u s e d as nearly as possible, of the usual strength: ley of 1.01~7, or 1 . 0 1 5 6 speciiic gravity is what is commonly employed. To ascertairt this, the hydrometer is generally used. A new instrmnent of this sort was, some time ago, proposed by Professor Leslie, (Ph M a ~ x - v l ~00,) but I have not heard whether at has ever come into u s e . I t was to be constructed on the principle which he has flllly d e m o n -
Essays o~ Bleachin~.
9S8
strafed~(hat capillary attraction is nothing more than the specific relative attraction of solids and fluids, and the purity of the liquid ex,'uuined, would be indicated by its ascent in a capillary tube graduated with enamel coIours. The instrument in common use is not so simple, not" so elegant. Those w.hich were formerly employed were not constructed on a fixed principle, so that when one of th*m was broken, another could not be made to the same scale. This inconvenience, however, has been removed by the ingenuity of Mr. 1 weedale of Glasvow, whose hydrometers are now universally used. The method which he adopts is to commence the scale at 1, and to make every degree indicate .005 of specific gravity. Hence, supposing tile alkaline ley to indicate ~0 ° on the Scale, its specific gravity would be 1.-[-~o0x.005=l.100, the specific gravity of water being unity. A complete series of these numbers from 1 to 6, indicates tile specific gravity of fluids~ fi'om distilled water, as 0. to ~sul])huric acid, ~. the-heavlest liquid known. In using such inSh'uments it is necessary to attend to the temperature of the atmosphere~ as~ll bodies are greatly intluenced by tli&r sensible caloric, an'd tlie~r bulk increased or diminished accordin_,z to the quantity wllich they con* tain. In water, the fifth decimal figure changes with every degree of Fahrenheit's thermometer, other fluids obser~:e diffhrent rates. Some bleachers guess at the strength of their leys by the taste, but this musE, at best, be an uncel:tain criterion. Des Charmes tells us that the laundresses of France ascertain the quality of leys fi'om their lubricity when rubbed between the fin_~er and thumb, or fi'om the readiness with which they absorb the co~lourina• matter of the goods. ~Vhen leys are made caustic by means of (l'uick-lime, and drawn oit' fbr use, they will commonly be of the same strength at the top and bottom of the vessel; but when they are not removed from the boiler, and the goods are put in as soon as the solution has been effected, the liquor will-be often three-fourths stronger at the botto]n, than at the top, fi'om the undissolved alkali continuing to melt. ~lais duaht to be carefully attended to, as it is contrary to-the general lhw wh'i'ch obtains in solutions, namely, that they are of eqUal-strength tln-oughout. Dr.. H o m e . psup oses the. anomal, y t o dependon the-presence of hme m a state of mechamcal mtxture. It is of iml)ortance flint the ley should be always as clear and limpid as possible, for if the lime remain either in solution or suspension in the smallest proportion, it is apt to be precipitated into the fabric of the cloth, and' will be fixed by the sulphuric acid sour, which will produce an insoluble selenite. This, however~ is not of so much consequence lot' the two or three first immersions, as it is when tile goods have once acquired an even colour, and require only to be brightened, it is then essential for the savin~ of time and lat)oUr, to have them as colourless as possible. Des_ Charmes directs the ~,,~oodsto be. 1)ut into the buckin~ apparatus in a,, moist state; 1)r. IIome, that. fl~ey should be. dry, 11 !" order, hc sa~'s, that the salts may enter into lhe body of the cloth, along with the water, as (hey ~11 not (:n(er in such q~antitv if i( l)e wet', VoL. I V . - - N o . 4,~()O,,T01"~EI~., 1~;~7. :;() F •
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I~leaching.
and by 'tcth,g t~o powerfully m~ the extermd threads may endanger in tim kieve it, ~p~'a l\flds, as in tile steeping process, and a qua~tity of the caustic h'v (h~:ah~d to tile temperature of the blood), is poured over them, sufli~;iCnt fi)r their thorou~zh immersion. The heat is increased, very ~radm~.ily~ tiff it reach the boiling point, when it is thrown up aNaim~t the mlfimqla, and spread, by it, over the surface of the g~¢,ds, thron ::h which it t ercoiatcs into [he boiler ag'fin, and so on iLL succession till it b~'~.~aturated with impuriLies. This is knowu from its l,si~g its cau~,ticity, and ae(luiving an offensive smell, or lio,n tile deepness of the coI~)tu"both of the Icy and the cloth. T h e succ(~s of the l)r()ct~ss indeed is commonly estimated in proportion to the de~qmess of the c~[our, which the cloth has acquired. (lh)me~ p. 72.) Particular attentiol~ ought to be ~iveu to the gradual increase of lempcrztiure now directed. F(n' the resinous or oleaahaous colourH~;Xmatter ot the cloth, tile twist ng of the threads, and closeness of texture, must hin(leL• the liquid from T)enetratin~ it, particularly at tirst, so that if tim Icy were poured o~L at ~lOflthe'cloth might be liable in several parts to a dry heat. This is usu'dl'f illustrated by the general ett'ccts which heat produces on coloured'veNetable matter. Thus if any ve~:etable is to be softened, or to have its juices extracted, it is tbund that this can be better done by b%innin~ witk moderate degrees of heat~ titan by olun£1no' it all at once in l~oiling water, winch would rather harden it and tix its colours. Cooks are well aware of this, and always when they wish to preserve the green colour of v%etables after boiling, never put them in till the water has acquired its highest temperature. 'rhe same reasoning applies to the process of b~{cking: anti here also it is confirmed by experienee~ as gomls which have n6ibrtunately been put into boiling Icy in the lh-s-t instance, can never be brought to a good white, llr. Home is so much impressed with the importance of this, that he deems it adviseable to keep the Icy under the boili~g point liar the two first buckings; but this is surely can'vina; the precaution too far. Des Charmes' metl[od exclu(led boiling as unnecessary, it beinsutlicient, he thin,;s, that the Icy be hot a~d sutliclently abundant. tie takes out his goo;ls when the liquid under the cover in the middie of the heap is too hot to admit of" the hand being held in it, or ~vhen it simmers round the circumference of the boi]er~ and throws up white bubbles, which circulate towards the centre. Frequently he only.plunged tile goods, tbr a few minutes, into ley of a "~ery gentle heat, and he found that by this treatment, both cotton and piece g~ods, bleached perfectly well. The leys, when the above circumstances are indicated, are to be drawn oil,; and warm water poured over the cloth in the kieve, which by cmnbi'ning with part of the remainin~ impurities which have beert loosened, se':'ves to carry them oil: When this has been don% a stream of cold water is allowed to play on the goods till it run off nearly limpid, after which they are taken to tile dash wheel; the reason for this process, which is not always properly attended to, •
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is, that were the cloth carried firm the kleve to file dash wheal, while hot, a certain portion of the eolouring matter would be agaitt ftxed in it, which wouhl not easily be again removed. The process of bucking is successivelv repeated, even as often as 10 thne~,befoce the operations are finished, and with leys of dift;~.rent strength. I find that with respect to the wu'iation of the strength of the leys, there are two modes recommended, directly opposed to one another. Des Cha,'mes says it is adviseable to keep the leys at the same degree of force, durhlo- the first two or three immersions of the sume goods, diminishine thee strength one third o~"one fourth, as soon as the pieces have acqu~'ed a uniform colour. In this pe,'iod, weaker leys may be advantageously used, because there remains scarcely any thing more of impurity to be carried oil'; and the Subsequent process . ma J~ be conside,'ed. merci as . a brMjtenin ..Y . g of the. eolour b. Y d e tachmg the small portmn ot mqmnty w~lch may remain fixed m the texture of the thread, (p. 81.) With this, agree the experiments of Mr. l{oe and of ]ging~, (Report on Experiments, &c. Dublin, 1791;) The practice of our bleachers in Scotland and Ireland is directly the reverse of this. They use the weakest levs at the commencement, and increase them in Strength as they prorated. Dr. Home's reasoning on this ,.seems to, be conclusive. " The leys," he sa)~s, "should be weakest m the In'st buckmgs, because then they act only on the more external parts, but when the clo~h is more opened, and the tield of action increased, the chemical agent ought hkewtse to be in.
this point. In repeating the bucking process, most bleachers occasionally use leys which have formerly bee.a used Nr a similar purpose, even mQre than once. This practice we have already reprobated, when treating of steeping, and in the present case it is of no less importance to avoid it, part{cularly in bucking fine goods. They seem ?to haye been led to this bad practice ti'om its apparent econoiny, b/tlwii~n it is coaside,'ed that it is only the unsaturated portion which can act, pure ley must evidently be cheaper. Besides, cloth bucked with foul lej;, becomes heavier instead of lighter, and consequently must receive impurity fi'om it:. Des (3harlnes directs a l?~ixture to be made of foul with new Icy, adding a third or fourth of tat latter; but these added portions of fi'csh le~' iliust bQ,greatly impah'ed in strength, by taking up the imput'it.ies ~xrith whicb~the old Icy is loaded, and this is found to agree with experience. It is of some consequence to remark, that little advantage can arise fi'om several buckings, immedialelq] succeeding one another: even the second immersion in the le,y will'fre(luentiy leave it (luite, limpid. Des: Chavmes.. tbund .it of more advantage to use t ~e Icy rein ere( caushc by hme at the Coinmencement of the buckings than afterwards, when it might impair t!~e texture of the go~ds.
2 31,
Essays on Bleaching.
s~e'rmx m. 3 H/a.~'hing.--It is never to be forgotten, that between each of the several processes~ of steeping, buckmg, souring, &c.~ the goods a "c to be thoroughly washed by the dash wheel in pure waker, so that all the loosene~i impurities, as well as the detergent which has been em I ~1o) 'ed, may be. eit'ectually removed. When any of these are left . • ,~ defect , , - ot waslnn~, o. t 11ey not onl y prevent the propex" opma~" tlnou,,h tion (it' the agents afterwards supplied, but often leave in the cloth indelible sta{as. Besides, as it may, through ne~leet~ become dry after buckling or souring, the salts will be conden~sed in i)roportion to the dryn&s of the c[otlb and acting with greater force will. de. stroy its texture. Soap ~s not employed except in the tirst washing' and in tinishing. Black, or soft soap is found to be the best tor these purl)oSes, brown soap leaving a yellowish tin,_,'e ou the cloth. If these precautions are not attended t% the goods~which are imperfectly washed will be in danger of becominlx yellow instead of white, by immersion in preparations of chlorine; al~d even of acquiring a tenacious and disagreeably ruddy tinge, either partially, if the washing has been partLal~ or totally, ff tt has been entirely neglected. The bleacher should be on his gilard, not to soap clea:ed g'~mds in the soapy solution which has been used for pieces taken (mr of a strong chlorine preparation, even though they have lirst passed flirough a suur of sulphuric acid; for this soapy solution does not fiuI to aequtre the property of dlseolourm~ other uoods~ unless the °'oods which, were soap,ed, aRer bein~ tak~u out fr~om~the chlorine preparatton, have been immersed for a Iona time in clear water. Washing should always if possible be performed immediately aRer bucking', while the goods a?e ;yet warm, as the filth and refu'se will then bd easier removed than after they become cold. 4. Croflin¢, or ezy)osure on the F i e l d . ~ I t has been accounted a great deside~'atum in bleaching to find a method of finishing goods ~vithmtt exposing them on the bleach-~.reen, as it consumes a ~reat deal ot mac and labour, and keeps out of eulttvatmn lare,e tracts of good arable hind. It was thought, at one time, that the introduction of chlorine bleaching, would supersede croffing; and it would do so, in a great measure, were it practicable to apply it in a proper manner. But, however great may be its facility in bteachino~-, it is scarcely possible to adopt it in anextensive maimfitctory to ti~e exclusion of trotting, without very heavy charges in work-shops and apparatus. This naturally follows fi'om what has already been remarked with regard to finishing the bucking process; and it is useful to take notice of it. as bleachers often let their goods lie in heaps lbr a considerable thne belbre washing. The washing of goods after souring, ts sometnnes admitted on the erroneous notmn that the acid which adheres to the elott b is useful in giving activity to the oxymuriatie salts. Evils of which they are unaware, arise from this mode of managementl for when the sulphuric acid thus left in the cloth, meets with lime, it forms a sulphate, which becomes tixed in the pores of the eloth~ and produces stains that crofting ca.nnot remove. O
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The ::prevalence~of this may.. be seen. b}r examining. . the kiers which. are ottcn covered on the lnstde with tills permclous sulphate; it can therefore only be economically adopted with such goods as are intended to receivewhat is called a half, or three-quarter white. It has certainly very much diminished tile period which crofting was wont to require, and in this seems to consist the chief diflbrence between the ohl and the new modes of" bleaching. The first thing which claims attention~ is the soil and situation of the. bleach-green. A gravelly or sandy soil seems to be the best, as the water will pass quickly through a soil of this kind, and will increase the rellection of the heat, for the tn'ocess depends on the, cva|)oration which may thus be caused. For tlie same reason if; ought to have a southern exposure, and if possible sli0tdd rather he sloping than level. To prevent the water becoming muddy it should run in a channel paved witli sand-stone. When the cloth has been steeped and bueked~ it is spread onion the field, and fi-equently watered ibr the first six hours, to prevent tile condensation of anyalkali which the washing may not likve ~ 2 moved. Dry spots are then allowed to appear before any a(iditional watering. Dr. Home thinks that it profits most by this exposure when near drying~ as the evaporatin_~ particles come rather fi'om the more internal parts, than the surface; and that it is chietty evaporation. which, operates, is inferred from. the thct, that. the upper, is. uni-. tormly wluter than the under surface. That ~t loses together with its grayish tinge the remainder of the acids and alkalies, with which it t;as bceri tl:eated, apl)ears ti'om the safety with which it may be afterwards dried. Soap when sliced down and exposed to the sun and air, with fl'equent waterings, will lose half its weight in a fortnight; the inference is obvious and need not be stated. From some experilnents it appears that the sulphur of the leys is one of tlie substances which is evaporated in croffing, and we know that this always has a tendency to produce a yellow tinge. (See Trans. R, T. Acad' IIL p. 45.) Berthollet seems to have taken a view of this prodels not quite so scientific as might have been expected, when he tells us (Ann. de Chim. II.) that crofting only prepares the colouring particles for being afterwards dissolved and separated by the ley. He surely never had observed the peasants bleach, by croffing alone, or by crofting tfler boilino~ in alkaline or soap leys. It is supposed by bleaclmrs, that exp6sure on the field has more eli?el in the months of March, April, anti May, than in any of the other months. As this idea is universal, it is likely well-fbunded, although Dr. Ilome has endeavoured to account for it by the greater attention which is usually paid to goods at the beginning Of tlie bleachin~ season. He states also that Mr. Christie, an experienced and enlightened bleacher, found the summer and autumnal months to be more efficacious than those of sprin~. But may not the drought prevalent in March, produce such an elt~ct, if evaporation i s t h e a,,'ent~ And if li,ht, as seems indubitable, is requisitc~ wilInot the want tlf clouds at this tmle be ot consequencer l'he effect of hght on colours is often very striking. When 1 was in lreland, I observed
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Ess(ljs o~ Blcachin~.
that the bed curtains in the reruns of Shane's castle, which are ex~ posed to the retlection of lij4ht t'roin loch Neath, were changed from fast and bt'illiant colc)urs, to pure white. Baume (Journ. de Physique 179S) fimnd that yelh~w raw silk, loses its colour in a short time, by exposure to the sun, (see a memoir on this subject, Ann. de Chim. Vl. 80.) Be.rthollct ira'@ned that there might be something ill dew, which was efficacious in crofting, and he accordingly examined the dcws which t)ll at ditt'erent periods of the night. Ire found them (Aim. de China. 11.) so strongly impregnated with the ]n'iuciph: of acidity, that lbey reddened paper tinged with turiisole. .From this lie at:c:mmts tbr'the greater "etliciency of spring dews, on the erroneous d~)ctrm¢,s that dew is transpired fi'om plants, and lllat plants transl)ir(~ oxv~(m and dew mr)st copiously in spt'in~. That the sun has a cm~sii'lerablc effect in whitening, independent of evaporation, aI~lmars fmln Ibis. lhat in dry windy weather the eva•ali~ l is me "e a ~eed',, [ it tllt, ble'tehin~ is slower than in cahn ~,Ul]Shllle, which seellls ~o [)(? the best weather for croftin~, lh-. 11o it thil ks Imwcve" that i ~ consequence of the slowness of tae evaporation, the m~istur~ c~nm'~s mm'e li'mn the internal parts of the go~ds~ this he thinks mu.~ , ~ the case, in consequence of tile heat tending to open the pores, whih; tim wind will rather ch~se them. The same iutelligmat cheinist rmnark~., that it is in conse~luence of its completing the bucking process, by e~ap~rating the salts which are combined with the lo~sening ilnlmriti~,.s~ that trolling l~roves beneticial~ no sort ~1' washing which he tried as a substitute, was found capable of superse..: . . lirJ~ . . ihe t~r°cess;", crof~in--,~ .ahvay s tbllows every buckin,,.~, and boihn~. There are, strictly speakmT/, two modes of croftmg: the goods' are artiticially watered from tr~oughs or little eanalsj or, they ~;l'e exposed to all tim vicissitudes of the atmosphere, without artilicial watering. Tile latter is called dry erofting. 5. Boiling.~('~oarse lineTl calmer aftbrd the time and labour, but particularly the quantities el" alkali, necessary tbr bucking, and must tmdergu the shot'ier and m(~t'c active operation of boiling. Although, howex,er, it may seem t~) be the more active process, it by no means follows that it is the most ell]tacit)us; on the contrary, the ley is much thicker amt darker af'ter bucking, than after boiling. As the heat continues longer at the degree of boiling, the leys used for the coarse cloth must be weaker than those used for the fine. There is not so much danger lYm~ heat in tim coarse as in the fine clotlb because the Nrmer is of ~t more open texture and' will allow the ley to penetrate more speedil)~; but in coarse cloths of a more close texture, the heat slmuld be l'ai~cd gra(hlally to the boiling p()int. The ettt~et of boiling raw colmn ~r linen in a diluted solution ~f ,.;tlistic alkali, is to give the li~lum' a deep brown colour and to &.stl'o~" its causticity; and t"es~ pm'iious of clear ley applied a s,~cmit[ or third time'wi/I i~roducc ;imilar ea;~cts, but in an inferior degree, (ll.ees' Cy¢l. ]lleacliing.) I n bleachlng fine goods, boiling is among the flniahhlg operations, and is rally Cmllloyed when the g~mds are nearly white, in order to remove the disagreeable smell of the prel~arations. The Icy in this
3ff. lYrl,:ins's new Steam Engine.
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case is composed of pearl ashes, or of pearl ashes and white soap. The boilin,.ou~bt not to be urged with a brisk fire, but kept barely at the boiling point, lhe ~,oods must be completely covered with the Icy, and kept ti'om rising by a cross similar to that used ill steeping, in order that they may be exposed equally to the action of the alk~ili or soap. In bleaching fine cottons, such as lawn grounds~ books, and light jaconets, no pearl ashes are used, the Icy being made wholly of soap. 6. l'mmersion 5, the preyarations of Chlorlne.~When the oxymuriates of lime, potash, soda, or magnesia have been prepared in the way ah'cady diree(ed, they are to be diluted to the spec-ific-gravityof 1005-, or 5 or 8 quarts of the solutions may be mixed with ~0 gallon~ Of water, and put into the immersing apparatus of Rupp or any Other Inch may be thought best. The test hquors already sofully desmbed are then to be had recourse to, to check the indication Of the speei' tic gt'avity. Mr. Dalton's certainl.¢ seems to be the best, .but ~h~re tins ~s not at hand, solutmns of nad~,_,'%cochineal, or turnsol~l~ay be used; even red wine is no despicab°le test, when the others can, not be had. It may be useful to take notice of the several eolours which these test liquors acquire when the chlorine preparations are of sufficient strenzth. Dalton's tests ]lave ah-eadv been copiously explained. Ihe md~zo test becomes yellowish, passm~ into wood', and of a deeper or l~inter tint, in proportion to the°dm'kuess of the blues: the tinctm'e of cochineal, becol/~es Dutch orange; red-wine becomes wine yellow; aud inlhsion of turnst)le, becomes amber brown. The gm~ds are to be immersed in the liquor immediately on being removed from the bleach-green, and particular care ought to be taken that they be all equally exposed to its action, otherwise stains and spots may be produced, which subsequent treatment may not be able to remove. Twelve hours is the usual period allotted for the immersion of linens; but less time will sometimes be sufficient. The bleaching liquors, according to Mr. Roe's expkriments, may be repeatedly used without detrimeat, till their wli.01c strehgth be exhausted. (1)ublin ReTort ~1791.) ~'9
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MR. PERKINS'S N E W STEAM ENGINE. We are anxious to satisfy public curiosity, which has been considerably excited by what we have already published, oll the subject of Mr. Perkins's new steam elegiac. The letter addressed to us by that gentleman, promised a specification with drawines, and enquiries have been repeatedly made, whether these had arrive~l: but as the en, rolment of his last patent in England, which embraces his recent improvements, was not to take place until September, we appreh}nd that at least a month must yet elapse, betbre the expected papers arrive; we however publish, fi'om the London jou,'na]s,'such i~formalion as they contain, and are particularly pleased :with having it in our power to present some engravings which will suffice to give a