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 569 B L E A C H I N G. table acids, which have no further fermentation to under* It is obferved, that, in the firft fouring, which is the go, or among the mineral acids. The former are a ftrongeft, the liquor, which was a pretty ftrong acid belarge clafs, and contain within themfelves many different fore the cloth was put in, immediately afterwards befpecies; fuch as th& acid juice of feveral plants, vinegars comes quite vapid; a proof how very foon it performs made of fermented liquors, and acid falts, called tartan. its talk. But in the following operations, as the linen But there is one objedion agaiijft thefe vegetable acids : advances in whitenefs, the acidity continues much longThey all contain, along with the acid, a great quantity er ; i fo that in the laft operations the liquor lofes very of oily particles, which would not fail to difcolour the little of its acidity. This happens although the firft cloth. Befides, the demand of the bleachfields would buckings, after the firft fourings, are increafed in ftrength, while, the fours are diminilhed. There are two caufes to raife their price too high. The mineral acids have neither of thefe objedions. which this is owing. The texture of the cloth is now They are exceedingly cheap, and contain no oil. “ I fo opened, that although the lyes are ftrong, the alkawill freely own, fays Dr Home, that at firft I had no line falts and abforbent earth are eafily walhed out; and great opinion of fuccefs from the mineral, from two rea- the oily particles are, in a great meafure, removed whicfl fons ; their want of all fermentation, which I then look- help to blunt the acidity of the liquor. ed on as neceflary ; and their extreme eo^rofivenefs. Two objedions are made againft the ufe of vitriolBut the experience of two different fummers, in two fours. One is, that the procefs of fouring with milk is different bleachfields, has convinced me, that they will performed by a fermentation; and, as there is no feranfwer all the purpofes of the milk and bran fours ; nay, mentation in the vitriol-fours, they cannot ferve the purin feveral refpeds, be much preferable to them. I have pofe fo well: The other, that they may hurt the texture feen many pieces of fine cloth, which had no other fours of the cloth. The anfwer to the former objedion is very but thofe of vitriol, and weje as white and flrong as thofe Ihort; that the vitriol-fours operate fuccefsfully without bleached in the common way. I have cut feveral webs a fermentation, as experience ftiews ; and therefore in through the middle, and bleached one half with milk, them a fermentation is not neceflary. and the Other with vitriol; gave both the fame number As to the latter objedion, that oil of vitriol, being a of operations, and the latter were as white and ftrong as very corrofive body, may hurt the cloth ; that will vathe former.” nifh likewife, when it is confidered how much the vitriol The method in which it has been hitherto ufed is this. is diluted with water, that the liquor is not ftronger than The proportion of the oil of vitriol to the water, with vinegar, and that it may be fafely taken into the human which it is diluted, is naif an ounce, or at mofl three body. quarters, to a gallon of water. As the milk-fours are That it may be ufed with fafety, much ftronger than diminifhed in ftrength, fo ought the vjtriol-fours. The what is neceflary in the bleachfield, appears from the whole quantity of the oil of vitriol to be ufed, may be following experiment with regard to the ftamping of lifirft mixed with a fmall quantity of water, then added to nen. After the linen is boiled in a lye of allies, it is the whole quantity of watbr, and well mixed together. bleached for fome time. After this, in order to make it The water ftiould be milk-warm ; by which means the receive the colour, it is fteeped in a four of water and acid particles will penetrate further, and operate fooner. oil of vitriol, about fifteen times ftronger than that made The cloth fhould then be put dry into the liquor. life of in the bleachfield; for, to 100 gallons of water It is obferved, that this four performs its talk much are added two and a half of oil of vitriol. Into this fooner than thofe of milk and bran; fo that Mr John quantity of liquor, made fo warm as the hand can juft Chryftie, in making the trial, ufed to lay the milk-fours be held in it, is put feven pieces of 28 yards each. The twenty-four hours before the vitriol. Five hours will linen remains in it about two hours, and comes out redo as much with this four, as five days with the common markably whiter. The fine cloth often undergoes this fort. But the cloth can receive no harm in allowing it operation twice. Nor is there any danger if the oil of to remain for fome days in the four ; but rather, on the vitriol is well mixed with the water. But if the two are contrary, an advant age. The cloth is then taken out, not well mixed together, and the oil of vitriol remains well rinfed, and mill-walhed in the ordinary way. in fome parts undiluted, the cloth is corroded into holes. The liquor, while the cloth lies in this four, is lefs Let' us now take a view of the advantages which the acid the fecond day than the firft, lefs the third than the vitriol-fours muft have over the milk. The latter is full fecond, and fo diminilhes by degrees. At fixft it is clear, of oily particles, fome of which muft be left in the cloth : but oy degrees a mucilaginous fubftance is obferved to 'But the cafe is worfe when the fcum is- allowed to prefloat in it, when put into a glafs. This foulnefs increa- cipitate upon the cloth. The former is liable to neither fes every day. This fubftance, extracted by the acid, is of thele objections. the fame with what is extracted by the alkaline falts, The common fours haften very fall to corruption ; and and blunts the acidity of the former, as it does the alka- if, from want of proper care, they ever arrive at that ftate, lefcency of the latter. Hence the liquor lofes by de- muft damage the ck>th very much. As the milk is kept grees its acidity. But as the acid falts do not unite fo very long, it is often corrupted before it is ufied ; and, equally with oily fubftances as the alkaline do, the liquor without aCting as a four, has all the bad effeCts of putreis not fo uniformly tinged in the former as in the latter The vitriol-fours are not fubjeCt to putrefaccafe, and the mucous fubftance prefents itfelf floating faCtion. tion. in it. The milk takes five days to perform its talk, but the Vpl. I. No. 24. 7E • vitriol3