Bleaching. fufpecting that this rule, tho' it may be pretty general, does not take place here; at least it is worth the purfuit of experiment.

"I weighed at the bleachfield a piece of glafs in fome cold lye, after it had been boiled, ftood for two days, and about the fourth part of it had been used. The glafs weighed 3 drams 1 grains in the lye, and 3 drains 7 grains in river-water. The fame glafs weighed in the fame lye, when almost all used, 2 grains lefs than it had done before. This thows, that the last of the lye contained a third more of the diffolved body; and, confequently, was a third ftronger than the first of the lye.

"As this might, perhaps, be owing to a continuation of the folution of the falts, I repeated the experiment in a different way.

I took from the furface fome of the lye, after the falts were diffolved, and the liquor was become clear. At the fame time I immerfed a bottle, fixed to a long ftick, fo near the bottom, as not to raise the afhes there, and, by pulling out the cork by a ftring, filled the bottle full of the lye near the bottom. The glafs weighed in river-water 3 drams 38 grains; in the lye taken from the furface 3 drams 34 grains; and in the lye taken from the bottom 3 drams 31 grains. This experiment fhows, that the lye at the bottom was, in this cafe, 4ths ftronger than the lye at the furface.

"At other times when I tried the fame experiment, I found no difference in the fpecific gravity; and therefore, I leave it as a queftion yet doubtful, though deferving to be ascertained by thofe who have an opportunity of doing it. As the lye ftands continually on the ashes, there can be no doubt but what is ufed laft must be stronger than the firft. I would therefore recommend, to general practice, the method used by Mr John Christie, who draws off the lye, after it has fettled into a fecond receptacle, and leaves the ashes behind. By this means it never can turn ftronger; and he has it in his power to mix the top and bottom, which cannot be done fo long as it ftands on the afheз." Having considered the lye, let us next inquire how it acts. On this inquiry depends almoft the whole theory of bleaching, as its action on cloth is, at leaft in this country, abfolutely neceffary. It is found by experiment, that one effect they have on cloth is the diminishing of its weight; and that their whitening power is, generally, in proportion to their weakening power. Hence arifes a probability, that these lyes act by removing fomewhat from the cloth, and that the lofs of this fubftance is the caufe of whitenefs. This appears yet plainer, when the bucking, which lafts from Saturday night to Monday morning, is at. tended to.

There are various and different opinions with regard to the operations of thefe falts: that they act by alter ing the external texture of the cloth, or by feparating the mucilaginous parts from the reit, or by extracting the oil which is laid up in the cells of the plant. The laft is the general opinion, or rather conjecture, for none of them deferves any better name; but we may venture to affirm, that it is fo without any better title to pre-eminence than what the others have. Alkaline falts diffolve oils, therefore these falts diffolve the cellular oil of the cloth, is all the foundation which this

theory has to reft on; too flight, when unfupported Bleaching. by experiment, to be relied on.

Dr Home endeavours to fettle this queftion by the following experiments and obfervations.

"Wax (fays he) is whitened by being expofed to the influence of the fun, air, and moisture. A difcovery of the change made on it by bleaching may throw a light upon the queftion.

"Six drams of wax were fliced down, expofed on a fouth window, September 10. and watered. That day being clear and warm, bleached the wax more than all the following. It feemed to me to whiten quicker when it had no water thrown on it than when it had. September 15. it was very white, and 1 dram 3 grains lighter. 3 drams of this bleached wax, and as much of unbleached, taken from the fame piece, were made into two candles of the fame length and thickness, having cotton wicks of the fame kind. The bleached candle burnt 1 hour 33 minutes; the unbleached 3 minutes longer. The former run down four times, the latter never. The former had an obfcure light and dull flame; the latter had a clear pleasant one, of a blue colour at the bottom. The former when burning feemed to have its wick thicker, and its flame nearer the wax, than the latter. The former was brittle, the latter not. It plainly appears from thefe facts, that the unbleached wax was more inflammable than the bleached; and that the latter had loft so much of an inflammable fubftance as it had loft in weight; and confequently the fubitance loft in bleaching of wax is the oily part.

"As I had not an opportunity of repeating the former experiment, I do not look on it as entirely conclufive; for it is poffible that fome of the duft, flying about in the air, might have mixed with the bleached wax, and fo have redered it lefs inflammable. Nor do I think the analogical reafoning from wax to linen without objections. Let us try then if we cannot procure the fubftance extracted from the cloth, fhow it to the eye, and examine its different properties. The proper place to find it, is in a lye already ufed, and fully impregnated with these colouring particles.

"I got in the bleachfield fome lye, which had been ufed all that day for boiling coarse linen, which was tolerably white, and had been twice boiled before. There could be no dreffing remaining in these webs. No foap had ever touched that parcel; nor do they mix foap with the lye ufed for coarfe cloth. Some of this impregnated lye was evaporated, and left a dark coloured matter behind. This fubftance felt oily betwixt the fingers, but would not lather in water as foap does. It deflagrated with nitre in fufion, and afforded a tincture to spirit of wine. By this experiment the falts feem to have an oily inflammable fubftance joined with them.

"Could we separate this colouring substance from thefe falts, and exhibit it by itself, fo that it might become the object of experiment, the question would be foon decided. Here chemistry lends us its affiftance. Whatever has a stronger affinity or attraction to the falts with which it is joined than this fubftance has, must fet it at liberty, and make it visible. Acids attract alkaline falt from all other bodies; and therefore will ferve our purpose.

"Into

foft. Boiling water has the fame effect on animal fub- Bleaching, ftances; for if falt beef is put into it, the water is kept from getting at the falts from the outfide of the beef being hardened.

"Into a quantity of the impregnated lye mentioned in the former experiment, I poured in oil of vitriol. Some bubbles of oil arose, an intestine motion was to be perceived, and the liquor changed its colour from a dark to a turbid white. It curdled like a folution of foap, and a fcum foon gathered on the furface, about half an inch in thickness, the deepnefs of the liquor not being above fix inches. What was below was now pretty clear. A great deal of the fame matter lay in the bottom; and I obferved that the fubftance on the furface was precipitated, and showed itself heavier than water, when the particles of air, attached to it in great plenty, were difpelled by heat. This fubftance was in colour darker than the cloth which had been boiled in it.

"I procured a confiderable quantity of it by fkimming it off. When I tried to mix it with water, it always fell to the bottom. When dried by the air, it diminished very much in its fize, and turned as black as a coal. In this ftate it deflagrated ftrongly with nitre in fufion; gave a ftrong tincture to fpirit of wine; and when put on a red-hot iron, burnt very flowly, as if it contained a heavy ponderous oil; and left fome earth behind.

"From the inflammability of this fubftance, its rejecting of water, and diffolving in fpirit of wine, we difcover its oleaginous nature; but from its great fpecific gravity we fee that it differs very much from the expreffed or cellular oil of vegetables; and yet more from their mucilage. That it diffolves in fpirit of wine, is not a certain argument of its differing from expreffed oils; because thefe, when joined to alkaline falts, and recovered again by acide, become foluble in fpirit of wine. The quantity of earthy powder left behind after burning, fhows that it contains many of the folid particles of the flax. The fubftance extracted from cloth by alkaline lyes appears then to be a compofition of a heavy oil, and the folid earthy particles of the flax.

"In what manner thefe falts act fo as to diffolve the oils, and detach the folid particles, is uncertain; but we fee evidently how much cloth must be weakened by an improper ufe of them, as we find the folid particles themfelves are feparated."

It is neceffary that cloth fhould be dry before bucking, that the falts may enter into the body of the cloth along with the water; for they will not enter in fuch quantity if it be wet; and by acting too powerfully on the external threads, may endanger them.

The degree of heat is a very material circumflance in this operation. As the action of the falts is always in proportion to the heat, it would appear more proper to begin with a boiling heat, by which a great deal of time and labour might be faved. The reafon why this method is not followed appears to be this. If any vegetable or vegetable substance is to be foftened and to have its juices extracted, it is found more proper to give it gentle degrees of heat at firft, and to advance gradually, than to plunge it all at once in boiling water. This laft degree of heat is fo ftrong, that when applied at once to a vegetable it hardens inftead of foftening its texture. Dried vegetables are immediately put into boiling water by cooks, that thefe fubftances may preferve their green colour, which is only to be done by hindering them from turning too VOL. III. Part I.

But when we confider how much of an oily fubftance there is in the cloth, especially at first, which will for fome time keep off the water, and how the twilling of the threads, and clofenefs of the texture, hinders the water from penetrating, we shall find, that if boiling water were put on it at once, the cloth might be liable, ir. several parts, to a dry heat, which would be much worse than a wet one. That the lyes have not accefs to all parts of the cloth, at firft, appears plainly from this, that when it has lain, after the firit bucking, till all the lyes are washed out, it is as black, in fome parts, as when it was fterped. This must be owing to the difcharge of the colouring particles from thofe places to which the lye has accefs, and to their remaining where it has not. It would feem advisable then, in the first bucking or two, when the cloth is foul, to ufe the lye confiderably below the boiling point; that by this foaking or maceration, the foulnefs may be entirely difcharged, and the cloth quite opened for the fpeedy reception of the boiling lye in the buckings which follow.

The lyes fhould likewife be weakest in the first buckings, because then they act only on the more external parts; whereas, when the cloth is more opened, and the field of action is increased, the active powers ought to be fo too. For this reafon they are at the ftrongest after fome fourings.

The only thing that now remains to be confidered, is,,the management of the coarfe cloth, where boiling is fubftituted in place of bucking. This fpecies of linen cannot afford the time and labour neceffary for the latter operation; and therefore they must undergo a fhorter and more active method. As the heat continues longer at the degree of boiling, the lyes ufed

to the coaife cloth muft be weaker than those used to the fine. There is not fo much danger from heat in the coarse as in the fine cloth, because the former is of a more open texture, and will allow the lye to penetrate more speedily. In the clofer kinds, however, the first application of the falts fhould be made without a boiling heat.

Alternate watering and drying. After the cloth has been bucked, it is carried out to the field, and fre quently watered for the first fix hours. For if, during that time, when it is ftrongly impregnated with falts, it is allowed to dry, the falts approaching clofer toge ther, and affifted by a greater degree of heat, increafing always in proportion to the drynefs of the cloth, act with greater force, and deftroy its very texture. After this time, dry fpots are allowed to appear before it gets any water. In this ftate it profits. moft, as the latter part of the evaporation comes from the more internal parts of the cloth, and will carry away moft from thofe parts. The bleaching of the wax, in a preceding experiment, helps to confirm this; for it feemed to whiten moft when the laft particles of water were going off.

This continual evaporation from the furface of the cloth fhows, that the defign of the operation is to carry off fomewhat remaining after the former procefs of bucking. This appears likewife from a fact known to M m

all

Bleaching, all bleachers, that the upper fide of cloth, where the evaporation is ftrongeft, attains to a greater degree of whiteness than the under fide. But it is placed beyond all doubt by experiment, which shows, that cloth turns much lighter by being expofed to the influence of the fun, air, and winds, even though the falts have been wathed out of it.

What, then, is this fubftance? As we have difcovered in the former section, that the whitening, in the operation of bucking, depends on the extracting or loofening the heavy oil, and folid particles of the flax; it appears highly probable, that the effects of watering, and expofition to the fun, air, and winds, are produced by the evaporation of the fame fubftance, joined to the falts, with which compofite body the cloth is impregnated when expofed on the field. That thefe falts are in a great measure carried off or destroyed, appears from the cloth's being allowed to dry without any danger after the evaporation has gone on for fome time. "If we can fhow (fays Dr Home) that oils and falts, when joined together, are capable of being exhaled, in this manner, by the heat of the atmofphere, we shall reduce this question to a very great degree of certainty.

"September 10. I expofed in a fouth-welt window half an oz. of Caftile foap, fliced down and watered. September 14. when well dried, it weighed but 3 dr. 6 gr. September 22. it weighed 2 dr. 2 gr. September 24. it weighed 1 dr. 50 gr. It then feemed a very little whiter; but was much more mucilaginous in its tafte, and had no degree of faltness which it had before.

"It appears from this experiment, that foap is fo volatile, when watered, and expofed to air not very warm, that it lofes above half its weight in 14 days. The fame muft happen to the faponaceous fubitance, formed from the conjunction of the alkaline falts, heavy oil, and earthy particles of the flax. The whole defign, then, of this operation, which by way of pre-eminence, gets the name of bleaching, is to carry off, by the evaporation of water, whatever has been loosened by the former procefs of bucking.

Against this doctrine there may be brought two objections, feemingly of great weight. It is a geneIt is a general opinion amongft bleachers, that linen whitens quicker in March and April than in any other months: but as the evaporation cannot be fo great at that time as when the fun has a greater heat; hence the whitening of cloth is not in proportion to the degree of evaporation; and therefore the former cannot be owing to the latter. This objection vanishes, when we confider, that the cloth that comes firft into the bleachfield, in the fpring, is closely attended, having no other to interfere with it for fome time; and as it is the whiteft, gets, in the after-buckings, the firft of the lye; while the fecond parcel is often bucked with what has been used to the first. Were the fact true, on which the objection is founded, this would be a fufficient answer to the objection. But it appears not to be true, from an obfervation of Mr John Chriftie, That cloth laid down in the beginning of June, and finished in September, takes generally lefs work, and undergoes fewer operations, than what is laid down in March, and finished in June.

"The other objection is, That cloth dries much faster in windy weather than in calm fun-fhine; but it

does not bleach fo faft. This would feem to show, that Bleaching. the fun has fome parricular influence independent on evaporation. In answer to this objection, let it be confidered, that it is not the evaporation from the surface, but from the more internal parts, that is of benefit to the cloth. Now, this latter evaporation must be much ftronger in funfhine than in windy weather, on account of the heat of the fun, which will make the cloth more open; while the coldnefs of windy weather muft fhut it up, fo that the evaporation will all be from the furface. Clear fun-fhine, with a very little wind, is obferved to be the beft weather for bleaching; a convincing proof that this reafoning is juft.

"It would feem to follow as a corollary from this reafoning, that the number of waterings fhould in general be in proportion to the ftrength of the lye; for the fronger the lye is, the more there is to be evaporated; and the greater the danger, in cafe the cloth fhould be allowed to dry. But there is an exception to this general rule, arifing from the confideration of another circumftance. It is obferved, that cloth when brown, dries fooner than when it becomes whiter, ariling from the clofenefs and oilinefs which it then has not allowing the water a free paffage. Perhaps that colour may retain a greater degree of heat, and in that way affift a very little. Cloth therefore, after the first buckings, muft be more carefully watered than after the laft.

"It follows likewife from this reafoning, that the foil of the bleachfield fhould be gravelly or fandy, that the water may pafs quickly through it, and that the heat may be increased by the reflection of the foil, for the fuccefs of this operation depends on the mutual action of heat and evaporation. It is likewife neceffary that the water fhould be light, foft, and free from mud or dirt, which not being able to rife along with the water, muft remain behind. When there is much of this, it becomes neceffary to rinfe the cloth in water, and then give it a milling, to take out the dirt; elfe it would be fixed in the cloth by the following bucking, as it is not foluble by the lye.

"This operation has more attributed to it by bleachers than it can justly claim. The cloth appears, even to the eye, to whiten under thefe alternate waterings and dryings; and thefe naturally get the honour of it, when it more properly belongs to the former operation. Here lies the fallacy. Alcaline falts give a very high colour to the decoctions or infufion of vegetables. This is probably owing to the folution of the oleaginous colouring particles of the plant; which particles, being opened and separated by the falts, occupy a greater fpace, and give a deep colour to the liquor. The cloth participates of the liquor and colour. Hence bleachers always judge of the goodnefs of the bucking by the deepnefs of its colour. The rule, in general, is good. I obferve that in thofe buckings which continue from the Saturday night to the Monday morning, the cloth has always the deepeft colour. When that cloth has been expofed fome hours to the influence of the air, these colouring particles which are but loofely attached to it, are evaporated, and the linen appears of a brighter colour. This operation does no more than complete what the former had almost finished. If its own merit were thoroughly known, there would be no occafion to attribute that of another operation to it. Thread, and open cloths, fuch as diaper, may be reduced to a great

degree

"Since the only advantage of watering is the removal of the falts, and what they have diffolved, might we not effectuate this by fome cheaper and more certain method? For it occupies many hands; and muft depend altogether on the uncertainty of the weather; fo that in the beginning of the feason, the bleacher is often obliged to repeat his buckings without bleaching. We might take out the alkaline falts by acids; but then the other fubftance would be left alone in the cloth, nor would any washing be able to remove it. Millwashing appears a more probable method of taking out both falts and oils; and it would feem that this might in a great measure fupply the place of watering; but upon trial it does not fucceed. Two parcels of linen were managed equally in every other refpect, except in this, that one was watered, and expofed to the influence of the air, and the other was only mill-wafhed. This method was followed until they were fit for fouring. The cloth which had been mill-washed had a remarkable green colour, and did not recover the bright colour of the pieces managed in the common way, until it had been treated like them for a fortnight. The green colour was certainly owing to a precipitation of the fulphureous particles, with which the lye is impregnated, upon the furface of the cloth; owing to the falta being washed off more speedily than the fulphur, to which they are united in the lye. The attachment betwixt these two bodies we know is very loofe, and the feparation eafily made. Evaporation then alone is Evaporation then alone is fufficient to carry off these fulphureous particles."

Souring. It is well known to all chymifts, that alkaline falts are convertible, by different methods, into abforbent earths. Frequent folution in water, and eva. poration of it again, is one of these. This tranfmutation then of thefe falts, which are not volatilised or washed away, must be continually going on in the cloth under these alternate waterings and dryings of the former procefs: not much indeed after the first two or three buckings; because the falts, not having entered deep into the cloth, are easily washed off, or evaporated. But when they penetrate into the very compofition of the laft and mineteft fibres, of which the firft veffels are made, they find greater difficulty of efcaping again, and must be more fubject to this tranfmutation. But if we confider the bleaching ashes as a compofition of lime and alkaline falts, we must discover a fresh fund for the depofition of this absorbent earth. The common caustic, a compofition of this very kind, foon con.. verts itself, if expofed to the open air, into a harmless earthy powder.

Frequent buckings and bleachings load the cloth with this fubftance. It becomes then neceffary to take it out. No washing can do that, because earth is not foluble in water. Nothing but acids can remove it. These are attracted by the abforbent earth, join themfelves to it, and compofe a kind of neutral imperfect falt, which is foluble in water, and therefore eafily washed out of the cloth. The acid liquors commonly ufed are butter-milk, which is reckoned the beft, fourmilk, infufion of bran, rye-meal, &c. kept for fome day's till they four. Sour whey is thought to give the cloth a yellow colour.

May 25. I put a thermometer of Fahrenheit's into fome butter-milk, of which the bleachers were compofing their fours, and which flood in a vat adjoining to another, where the milk was the fame, and the fouring procefs had been going on for two days. After the thermometer had been 20 minutes in the buttermilk, the mercury ftood at 64 degrees. In the fouring vat it rofe to 68 degrees. An increase of four de grees fhows a pretty brifk inteftine motion.

"To what are all thefe effects owing? To the acetous fermentation going on in those vegetable li quors, whofe acids, extricating themfelves, produce heat, intestine motion, and air-bubbles. As the change is flow, the process takes five or fix days before it is finished. During this time the acid particles are continually uniting themfelves to the absorbent earth in the cloth. That this fermentation goes on in the liquor alone, appears from this confideration, that the fame effects, viz. air-bubbles, and scum, are to be feen in the butter-milk alone. The only effect then it has is, by the fmall degree of heat, and inteftine motion, which attend it, to affift the junction of the acid and abforbent particles. We fhall presently fee that this procefs may be carried on to as great advantage, without any fermentation; and therefore it appears not abfolutely neceffary.

"When these abforbent particles are fully faturated, the remaining acids may unite with, and have fome fmall effect in extracting the colouring particles. This appears from the two following experiments.

"Sept. 20. A piece of cloth which had been steeped, weighing 41 gr. was put into a half-pound of butter-milk, whigged, and well foured, by a mixture of water, and by boiling. of water, and by boiling. Sept. 24. When taken out, and washed in water, it appeared a very little whiter. The mineral acids, as will appear afterwards, whiten cloth, even though they are very much diluted.

"Juft before the acetous fermentation is finished, the cloth fhould be taken out; otherwise the fcum will fall down and lodge in the cloth, and the putrefaction which then begins will weaken it. This appears from the following experiment.

66

Sept. 16. A piece of cloth weighing 42 gr. was laid in butter-milk unwhigged. Novem. 15. The milk had a putrefied fmell. The cloth was a little whiter, but very tender; and weighed, when well washed in warm water and dried, 40 gr."

All the fours made of bran, rye-meal, &c. ought to be prepared before ufe; for by this means fo much time will be faved. Befides, when the water is poured upon the cloth and bran, as is done in the management of coarse cloth, the linen is not in a better fituation than if it had been taken up wet from the field; and by this means the acid particles cannot penetrate fo deep. Again, this method of mixing the bran with the cloth, may be attended with yet worse confequences. All vegetable fubftances, when much prefM m 2

fed,

Bleaching. fed, fall into the putrefcent, and not the acetous fermentation. This often happens to the bran preffed betwixt the different layers on the linen, which muft weaken the cloth. Hence, all fours fhould be prepared before the cloth is fteeped in them; and none of the bran or meal fhould be mixed with the cloth.

The fours are ufed ftrongest at firft, and gradually weakened till the cloth has attained to its whitenefs. In the first fourings, there is more of the earthy matter in the cloth, from the many buckings it has undergone, than what there can be afterwards. As the quantity of this matter decreases, so fhould the ftrength of the four. There is not, however, the leait danger, at any time, from too strong a four.

What is most wanted in this operation is a more expeditious and cheaper method of obtaining the fame end. As it takes five or fix days, it retards the whitening of the cloth confiderably; and as bleachers are obliged to fend for milk to a great diftance, it becomes very dear. This latt confideration makes them keep it fo long, that, when used, it can have no good effect; perhaps it may have a bad one.

There is one confideration that may lead us to fhorten the time. It is obferved, that the fouring procefs is fooner finished in warm than in cold weather. Heat quickens the fermentation, by aiding the inteftine motion. The vats therefore fhould not be buried in the ground, as they alway are, which muft keep them cold; there fhould rather be pipes along the walls of the room, to give it that degree of heat which, on trial, may be found to anfwer beft. There are few days in fummer fo hot as is neceffary; and the begin. ning and end of the feafon is by much too cold. That this is no ideal fcheme, the following fact is a fufficient proof. There are too vats in Salton bleachfield, adjoining to a partition wall, at the back of which there is a kitchen fire. In thefe vats the fouring procefs is finifted in three days, whereas it lafts five or fix days in the other placed round the fame room.

This improvement, tho' it fhortens the time of fouring a very little, yet is no remedy against the scarcity and dearness of milk fours. Such a liquor as would ferve our purpose, muft be be found either among the vegetable acids, which have no further fermentation to undergo, or among the mineral acids. The former are a large clafs, and contain within themfelves many different fpecies; fuch as the acid juice of feveral plants, vinegars made of fermented liquors, and acid falts, called tartars. But there is one objection against thefe vegetable acids: they all contain, along with the acid, a great quantity of oily particles, which would not fail to difcolour the cloth. Befides, the demand of the bleachfields would raife their price too high.

The mineral acids have neither of these objections. They are exceedingly cheap, and contain no oil. "I will freely own (fays Dr Home), that at firft I had no great opinion of fuccefs from the mineral, from two reafons; their want of all fermentation, which I then looked on as neceflary; and their extreme corrofiveness. But the experience of two different fummers, in two different bleachfields, has convinced me, that they will anfwer all the purposes of the milk and bran fours; nay, in feveral refpects be much preferable to them. I have feen many pieces of fine cloth, which had no

other fours but those of vitriol, and were as white and Bleaching, ftrong as those bleached in the common way. I have cut feveral webs through the middle, and bleached one half with milk and the other with vitriol; gave both the fame number of operations, and the latter were as white and ftrong as the former."

The method in which it has been hitherto used is this. The proportion of the oil of vitriol to the water, with which it is diluted, is half an ounce or at most three quarters, to a gallon of water. As the milkfours are diminished in ftrength, so ought the vitriolfours. The whole quantity of the oil of vitriol to be ufed, may be firft mixed with a fmall quantity of water, then added to the whole quantity of water, and well mixed together. The water fhould be milk-warm; by which means the acid particles will penetrate further, and operate fooner. The cloth should then be put dry into the liquor.

It is obferved, that this four performs its task much fooner than thofe of milk and bran; so that Mr John Chriftie, in making the trial, ufed to lay the milk. fours 24 hours before the vitriol. Five hours will do as much with this four as five days with the common fort. But the cloth can receive no harm in allowing it to remain for fome days in the four; but rather, on the contrary, an advantage. The cloth is then taken out, well rinfed, and mill-washed in the ordinary way.

The liquor, while the cloth lies in this four, is lefs acid the fecond day than the firtt, lefs the third than the fecond, and fo diminishes by degrees. At first it is clear, but by degrees a mucilaginous fubftance is obferved to float in it, when put into a glafs. This foulnefs increafes every day. 1 his fubftance, extracted by the acid, is the fame with what is extracted by the alkaline falts; and blunts the acidity of the former, as it does the alkalefcency of the latter. Hence the liquor lofes by degrees its acidity. But as the acid falts do not unite fo equally with oily fubitance as the alkaline do, the liquor is not fo uniformly tinged in the former as in the latter cafe, and the mucous fubftance prefents itfelf floating in it.

It is obferved, that in the first fouring, which is the ftrongeft, the liquor, which was a pretty firong acid before the cloth was put in, immediately afterwards becomes quite vapid; a proof how very foon it performs its talk. But in the following operations, as the linen advances in whitenefs, the acidity continues much longer; fo that in the last operations the liquor lofes very little of its acidity. This happens although the firft buckings after the first fourings are increased in ftrength, while the fours are diminished. There are two caufes to which this is owing. The texture of the cloth is now fo opened, that although the lyes are strong, the alkaline falts and absorbent earth are easily washed out; and the oily particles are in a great measure removed which help to blunt the acidity of the liquor.

Two objections are made againft the ufe of vitriolfours. One is, that the process of fouring with milk is performed by a fermentation; and as there is no fermentation in the vitriol fours, they cannot serve the purpose fo well: the other, that they may hurt the texture of the cloth. The anfwer to the former objection is very fhort; that the vitriol-fours operate fuccefsfully without a fermentation, as experience fhows; and therefore in them a fermentation is not necessary.

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