(56.) "The other objection is, That cloth dries much faster in windy weather than in calm funfhine; but it does not bleach fo faft. This would feem to show, that the fun has fome particular influence independent on evaporation. In answer to this objection, let it be confidered, that it is not the evaporation from the furface, but from the more internal parts, that is of benefit to the cloth. Now, this latter evaporation must be much stronger in funshine than in windy weather, on account of the heat of the fun, which will make the cloth more open; while the coldness of windy weather muft fhut it up, fo that the eva poration will all be from the furface. Clear funitine, with a very little wind, is obferved to be the best weather for bleaching; a convincing proof that this reasoning is juft.

(57.) It would seem to follow as a corollary from this reafoning, that the number of waterings should in general be in proportion to the ftrength of the ley; for the stronger the ley 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, ariling from the confideration of another circumftance. It is obferved, that eloth when brown dries fooner than when it becomes whiter, arifing from the clofeness 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, must be more careSully watered than after the last.

(8.) It follows likewife from this reafoning, that the foil of the bleach-field should be gravelly er fandy, that the water may pafs quick's 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 neceflary that the water thould 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; elle it would be fixed in the cloth by the following bucking, as it is not foluble by the ley. (9.) This operation has more attributed to it by the bleachers than it can juftly claim. The cloth appears, to the eye, to whiten under thefe ternate waterings and dryings; and thefe naturally get the honour of it, when it more properly bags to the former operation. Here lies the falbey. Alkaline Salts give a very high colour to the decoctions or infufion of vegetables. This is probaby owing to the folution of the oleaginous cobining particles of the plant; which particles, being opened and feparated by the falts, occupy a greater space, and give a deep colour to the licor. The cloth participates of the liquor and colour. Hence bleachers always judge of the goodness of the bucking by the deepnefs of its colour. This 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 deepest colour. When that cloth has been expofed fome hours to the influcace of the air, these colouring particles, which

are but loosely attached to it, are evaporated, and the linen appears of a brighter colour. This o peration 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 of whitenefs, after one bucking, by it alone. No cloth, as would appear, can attain to a bright whitenefs without it.

(60.) "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 begin ning 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 fubitance would be left alone in the cloth, nor would any washing be able to remove it. Mill-washing 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 millwashed. This method was followed until they were fit for fouring. The cloth which had been mill-wathed 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 ley is impregnated, upon the furface of the cloth; owing to the falts being wathed off more speedily than the fulphur, to which they are united in the ley. The attachment betwixt thefe two bodies we know is very loofe, and the feparation eafily made. Evapora→ tion then alone is fufficient to carry off thefe fulphureous particles.'

SECT. V. OF SOURING.

(61.) That alkaline falts are convertible, by different methods, into abforbent earths, is a fact well known in chemistry. Frequent folution in water, and evaporation of it again, is one of thefe.. The tranfmutation then of thefe falts, which are not volatilifed or wathed away, must be continually going on in the eloth under these alternate waterings and dryings of the former process: not much indeed after the first two or three buckings; because the falts, not having entered deep into the cloth, are eafily wathed off, or evaporated. But when they penetrate into the very compofition of the cloth and minutest fibres, of which the first veffels are made, they have great difficulty of efcaping again, and must be more fubject to this tranfmutation. But if we confider the bleaching afhes as a compofition of lime and alkaline falts, we muft difcover a frefu fund for the depofition of this abforbent earth. The common cauftic, a compolition of this very kind, is foon converted if exposed to the open air, into a harmlefs earthy kind of powder.

(62.) Fre

(62.) Frequent buckings and bleachings load cload with this fubftance. It becomes then necef fary to take it out. No wafhing can do that, becaufe earth is not foluble in water. Nothing but acids can remove it. Thefe are attracted by the abforbent earth, join themfelves to it, and com pofe a kind of neutral imperfect falt, which is foluble in water, and therefore easily washed out of the cloth. The acid liquors commonly used, are butter-milk, which is reckoned the beft, four milk, infufion of bran, rye-meal, &c. kept for fome days till they four. Sour why is thought to give the cloth a yellow tinge.

(63.) Before the linen is put in the four, it fhould be dried, that the acid particles may penetrate, along with the watery, through the whole. A few hours after it has been there, air-bubbles arife, the liquor fwells, and a thick feum is formed; manifeft figns of a fermentation. The following experiment, fays Dr Home, fhows the degree of heat which attends it. "May 25, I put a thermometer of Fahrenheit's into fome butter milk, of which the bleachers were compoting their fours, and which stood in a vat adjoining to another, where the milk was the fame, and the fouring process had gone on for two days. After the thermometer had been 20 minutes in the butter milk, the mercury stood at 64 degrees. In the fouring vat it rofe to 68 degrees. An increafe of four degrees fhows a pretty brifk inteftine motion.

(64.) To what are all these effects owing? To the acetous fermentation going on in thofe vegetable liquors, whofe acids, extricating them felves, produce heat, inteftine motion, and airbubbles. As the change is flow, the procefs takes five or fix days before it is finished. During this time the acid particles are continually uniting themfelves to the abforbent 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 icum, 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 affist the junction of the acid and abforbent particles. We shall prefently fee that this procefs may be carried on to as great advantage, without any fermentation; and therefore it appears not abfolutely neceffary. (65.)" When thefe abforbent particles are fully faturated, the remaining acids may unite with, and have fome finall effect in extracting the colouring particles. This appears from the two following experiments. Sept. 30, a piece of cloth which had been fteeped, weighing 414 gr. was put into a half-pound of butter milk, whigged, and well foured, by a mixture 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.

(66.) "Just before the acetous fermentation is finithed, the cloth fhould be taken out; otherwife the feum will fall down and lodge in the cloth, and the putrefaction which then begins will weaken it. This appears from the following experiSept. 16, a piece of cloth weighing 42 gr. d in butter milk unwhigged. Novem. 15,

pt.

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."

(67.) Sours made of bran, rye-meal, &c. ought to be prepared before use, to fave time. Befides, when the water is poured upon the cloth, the linen is not in a better fituation than if it had been taken up wet from the field; and thus the acid particles cannot penetrate fo deep. Again, this method of mixing the bran with the cloth, may be attended with ftill worie confequences. All vegetable fubftances, when much prefied, 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 should be prepared before the cloth is fteeped in them; and none of the bran or meal fhould be mixed with the cloth.

(68.) The fours are used strongest at first, 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 there can be afterwards. As the quantity of this matter decrea fes, fo fhould the ftrength of the four. There is not, however, the least danger, at any time, from too ftrong a four. What is most wanted in this operation is a more expeditious and cheap 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 laft confideration makes them keep it fo long, that, when ufed, it can have no good effect; perhaps it may have a bad one.

(69.) One confideration may lead us to fhorten the time. The fouring process 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 always are, and which keeps them cold: there thould be pipes along the walls of the room, to give it that degree of heat which, on trial, aufwers beft. There are few days in fummer fo hot as is necessary; and the beginning and end of the feafon are by much too cold. That this is no ideal scheme, the following fact proves. There are two 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 finished in three days, whereas it latts five or fix days in those that are placed round the fame

room.

(70.) This improvement, though 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 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 these vegetable acids: they all contain, along the acid, a great quantity of oily mat

ter,

ter, which would not fail to difcolour the cloth. Befides, the demand of the bleachfields would raise their price too high. But the mineral acids have neither of these objections. They are exceedingly cheap, and contain no oil.

(71.) "I will freely own (fays Dr Home,) that at first I had no great opinion of fuccefs from the mineral acids, from two reafons; their want of all fermentation, which I then looked on as neceffary; and their extreme corrofiveness. But the experience of two different fummers, in two different bleachields, 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 thofe of vitriol, and were as white and ftrong as thofe 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 strong as the former."

(72.) The following is the method in which it has been hitherto ufed: The proportion of the oil of vitriol to the water, with which it is diluted, is half an ounce, or at moft three quarters, to a gallon of water. As the milk fours are diminished in itrength, fo ought the vitriol fours. The whole quantity of the oil of vitriol to be used, may be Art mixed with a fmall quantity of water, then added to the whole quantity of water, and well xed together. The water thould be milk-warm; by which means the acid particles will penetrate further, and operate fooner. The cloth fhould then be put dry into the liquor; as this four performs its talk much fooner than that compofed of mak and bran, fome, in making the trial, have been used 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 by allowing it to remain for fone days in the four; but rather an advantage. The cloth is then taken out, well rinfed, and mill-washed in the ordinary way.

(73.) While the cloth lies in this four, the liquor is lefs acid the fecond day than the firft, lefs the third than the fecond, and fo diminishes by degrees. At firft it is clear, but by degrees a muciugnous substance is observed to float in it, when put into a glass. This foulness increases every day. This fubstance 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 a by degrees its acidity. But as the acid falts dont unite fo equally with oily substances as the alkaline, the liquor is not fo uniformly tinged in the former as in the latter cafe, and the mucous biance prefents itself floating in it.

(74.) In the first fouring, which is the ftrongeft, the liquor, which was a pretty strong 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 laft operations the liquor lofes very little of its acidity. This Lappens although the first buckings after the first VOL. IV. PART I.

fourings are increased in ftrength, while the fours are diminished. There are two caufes for this. The texture of the cloth is now fo opened, that although the leys are ftrong, the alkaline falts and abforbent earth are easily washed out; and the oily particles are in a great measure removed which help to blunt the acidity of the liquor.

(75.) There are two objections however, against the ufe of vitriolic fours. One is, that the procefs of fouring with milk is performed by a fermentation; and as there is no fermentation in the vitriol fours, they cannot ferve the purpose so 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 fuccesfully without a fermentation, as experience thows; and therefore in them a fermentation is unnecellary. As to the latter objection, that oil of vitriol, being a very corrofive body, may hurt the cloth; that will vanish likewife, when it is confidered how much the vitriol is diluted with water, that the liquor is not stronger than vinegar, and that it may be fafely taken into the human body. Indeed that it may be fafely used much stronger than what is neceffary in the bleachfield, appears from the following experiment with regard to the stamping of linen.

(76.) After the linen is boiled in a ley of afhes, it is bleached for fome time; after which, to make it receive the colour, it is steeped in a four of water and oil of vitriol, about 15 times ftronger than that made ufe of in the bleachfield; for to 100 gal. lons of water are added 24 of oil of vitriol. Into this quantity of liquor, made fo warm as the hand can just be held in it, is put 7 pieces, of 28 yards each. The linen remains in it about two hours, and comes out remarkably whiter. The fine cloth often undergoes this operation twice; nor is there any danger if the oil of vitriol is well mixed with the water. But if the two are not well mixed together, and the vitriolic acid remains in fome parts undiluted, the cloth will be corroded.

(77.) The vitriolic fours have various advantages over thofe of milk. The latter is full of oily particles, fome of which must be left in the cloth, but the cafe is worfe when the feum is allowed to precipitate upon the cloth. The former is liable to neither of thefe objections. The common fours haften very fast to corruption; and if, from want of proper care, they ever arrive at that ftate, muft damage the cloth very much. As the milk is kept very long, it is often putrid before it is ufed and, without acting as a four, has confiderable bad effects, whilft the vitriol fours are not fubje&t to putrefaction at all. Milk fours are very dear, and often difficult to be got; those of vitriol are cheap, and may be easily procured at any time. The milk takes 5 days to perform its tafk; but the vitrol fours do it in as many hours; nay, perhaps in as many minutes. Their junction with the abforbent particles in the cloth must be immediate, whenever these acid particles enter with the water.

(78) An unanfwerable proof, that the fact is fo, arifes from the circumftances which happen when the cloth is firft fteeped in the vitriol four; the cloth has no fooner imbibed the acid liquor, than it lofes all acidity, and becomes immediately vapid. This

effect

that alkaline falts added to lime, diminish its power of weakening and corroding cloth, in proportion to the quantity of the falts. The compoEition, as it is not fo dangerous as lime alone, fo it is not fo expeditious in whitening. When equal parts of each are ufed, the whitening power is trong, and the weakening power not very confiderable; fo that they might be used with fafety to bleach cloth, in the proportion of one part of fine to four of pure alkaline falts. This is agreeable to an obfervation made by all bleachers, That the bleaching falts, when mixed together, operate fafer and better, than when ufed feparately. For the corrofive power of the Mufcovy, Marcoft, and Calhub ashes, is corrected by the pearl afhes, and the whitening quality of the latter is increased by that of the former.

(8) No fubftance is more cauftic, when appied to animal bodies, than alkaline falts and lime joined together, efpecially when fufed in the fire. But lime alone, or lime-water will preferve animal matter in a found ftate. It appears then furprifing, that falts and lime fhould be found fo little defructive of linen cloth, when lime, or lime-water alone, destroys it fo remarkably. But chemiftry affords many facts equally unaccountable; and that this is a fact, is evident from many experiments. It has been practifed with fuccefs and facty, by a bleacher, who gives the following account of his method of employing lime.

(88.) "First, (says he) I fteep the cloth in warm water for 24 hours; then clean it in a washing mill, of all the drefling, or fowen, as the vulgar term it. Afterwards I buck cloth with cow-dung and water, and bleach it with this for 3 days; then clean it again, and boil it with a ley made of Cathub athes. A pound to each piece of 18 or 20 yards is fufficient. This I do twice, as no lime ought to be given to cloth before it is a full third whitened; as it by no means advances the whitening of the cloth, but, on the contrary, protracts : for, instead of loofening the oil and dirt in the eluth, when brown, it rather fixes them; juft as when fine cloth is bucked with over-warm leys in the Erft buckings. Lime is by no means fit for dicharging the oil in the cloth, but for cleaning it of the dead part, commonly called fprat.

(9.) "The cloth, being cleaned, is laid upon a dreeper. It must not be drier before bucking with lime, otherwise it will take in more than can be got out again before the next application: for as I have obferved already, that lime is only fit far difcharging the dead part, bucking thus wet es it reft on the outfide of the cloth. I take. ppy of the fineft and richeft powdered lime that can be got, of the brightest white colour, as poor lime does more hurt than good, to 30 pieces of the above length; and make a cold ley of it, by furring and pouring water off the lime, until all be diffolved but the drofs, which is thrown away: then I add a little foap, which makes the key have the nearest resemblance to milk that breaks in boiling, of any thing I can think of: for this foap blunts the hotnefs of the lime. Then I take the cloth and dip it in the lime-ley, and that moment out again, and lay it on a dreeper until it be bucked: then put it on the field, watering it carefully; for if allowed to dry, it is much da

maged. This is done always in the morning; as it cannot be done at night, in regard of the hot quality of the lime, which foon heats the cloth and tenders it. If a hot fun-thine follows, it has great effect; for lime is just like all other materials for bleaching, that have more or less effect, according as the weather is good or bad.

(90.) "I take it up the 2d day after bucking, and give it a little milling, or hand-rubbing, or bittling, commonly called knocking; and lay it on the field again, watering it carefully as before. The effect is more vifible the 2d than the first day. As all cloth when limed fhould have a great deal of work, otherwife more than half the effect is loft; and not only that, but a great deal of labour and pains is requifite to take the lime out of the cloth again; it muft never be exposed on the Sabbath day, but carefully kept wet always while used in this way. Thus bucking for 3 or 4 times at moft, is fufficient for any cloth except that made of flax pulled either over-green, or which grows in a droughty season, or perhaps not fo well heckled as it fhould be. This fort occafions great trouble and expence to the bleacher. But the moft effectual and expeditious way I ever found for this kind was, after boiling, to take a little of the warm ley, and mix a very fmall quantity of lime with it, and draw the cloth through that as hot as poffible, and put it on the field directly, watering it carefully. This will clean it of the fprat furprisingly. Then I boil it with pearl afhes, and give it the laft boil with foap.

(91.) There are innumerable mistakes in the ufe of lime committed by the vulgar, who are ig norant of its quality and effects. They know only this in general, that it is a thing which whitens cloth cheap, and is eafy purchased; therefore they will ufe it. Some of them begin whitening of their cloth with it, which I have already observed to be wrong, and given reafons for it, and continue it until the cloth is bleached; give it a boil or two at moft, and then wash it up while the grofs body of the lime is in the fubftance of the cloth. This makes limed cloth eafily distinguishable from unlimed, as the former has a yellowish colour, and is full of a powder. Befides, as lime is of a very hot corroding nature, it must by degrees weaken the cloth. The bad effects of this fubstance do not end here. When the cloth is put on board, it contracts a dampnefs, which not only makes it yellow, and lofe any thing of colour it has, but directly rots it. And although it fhould efcape this, which it is poffible it may, by a quick and fpeedy paffage; yet whenever it is t in any warehoufe, it will meet with moisture there, especially if the winter feafon fhould come on before it is difpofed or made ufe of. Thefe I take to be the principal reafons for fo much complaint in bleaching with this material."

(92.) It is evident, the whole art and safety in ufing lime, according to this method, depends on the junction of the alkaline falts, during the bucking, to the particles of lime which were on the furface of the cloth. As bleaching depends on the extraction of a certain quantity of phlogistic matter from the cloth, it is natural to fuppofe that it might be accelerated by rendering the alkali very cauftic. Thus the falt would be entirely B 2

freed