An BJfay on Bleaching, 25 1 



this fulphate, when the temperature of the atmofphere is 

 6^ F,, while one part is fufficient to diflblve a like weight 

 of potafh; one needs only boil together an equal weight of 

 common potafh and river water for fome minutes, leave it to 

 reft twenty-four hours, and then decant the clear ley ; if the 

 refiduum be then warned with a fourth of the quantity of the 

 water employed, and the clear liquor be poured off, the re- 

 maining depofit will be compofed of foreign falts or hetero- 

 geneous matters, found there accidentally, or which have 

 been employed in adulterating the potafh. 



We have mentioned the avidity with which potafh abforbs 

 the carbonic acid. As this principle diminishes its deterfive 

 force, it muft be deprived of it by mixing it with twice its 

 weight of lime; then lixiviating it, or, what is ftill better, 

 pouring faturated lime water into a folution of potafh alfo 

 faturated, and until the lime water ceafes to give a precipi- 

 tate. It is on this property poflefied by alkalies, of uniting 

 with oils and fat matters, of rendering them foluble in water, 

 and difengaging them from the fubltances with which they 

 are mixed, that the theory of bleaching with foaps and alka- 

 line mixtures is founded. This deterfive force, however, 

 muft be moderated. Potafh, even in the ftate of carbonate, 

 attacks not only the colouring matter, but the fubftance, alfo, 

 of flax, hemp, and cotton : being rendered cauftic, its refolv- 

 jng force is increafed ; it is a dangerous enemy when it3 

 agency is abufed, but a powerful auxiliary when employed 

 with moderation. 



It is by a prudent ufe of this matter that we propofe to 

 employ an alkalino-cauftic lixivium in a fteam-apparatus for 

 bleaching the linen of public inftitutions : the afhes alone of 

 their fire-places, where the fuel is wood, lixiviated and ren- 

 dered cauftie, will be fufficient for this operation, which will 

 be attended with a degree of ceconomy that no other procefs 

 can counterbalance. 



Though I recommend the ufe of cauftic leys, I am far 

 from recommending lime applied alone or mixed with alka- 

 lies. Ignorant manufacturers, imagining that it bleaches the 

 cloth, make ufe of it imprudently, to the detriment of their 

 manufactures, and excufe themfelves by the example of en- 

 lightened men, who add lime to render the alkalies cauftic; 

 but every chemift knows that, notwithftanding this addition, 

 there does not remain a Jingle atom of pure lime in the alka- 

 lino-caultic liquor when it has been made with the neceflary 

 precautions. 



Of 



