l$l An Ef r ay on Bleaching.. 



Of Soda. 



Nature prefents us with foda in ftill greater abundance than 

 potafh ; and it is even found in a pretty pure ftate in Egypt, 

 where it is collected at the bottom of the lakes. The com- 

 bullion of plants, and the different kinds of falt-zvort or foda 

 which grow on the fea-fhore, furnifh it in great abundance : 

 it is from this plant that it takes its name. But modern che- 

 •miftry has taught us how to obtain it in ftill greater pronation 

 by the decompofhion of fea fait (muriate of foda). 



Its properties in regard to bleaching are nearly the fame 

 as thofe of potafh, with this exception, that it does not unite 

 itfelf to the, oxygenated muriatic acid; in general, the adtion 

 of foda, even when cauftic, is much weaker ; and it attacks 

 cloth and fluffs much lefs than potafh. We {hall therefore 

 make choice of it in preference for our procefs of bleaching 

 with it earn. 



Soda is generally more mixed with heterogeneous matters 

 than potam, and the fraud is more difficult to be detected. 

 In this cafe, recourfe mult be had to repeated cryftallizations. 

 Kirwan, in his excellent memoir, recommends boiling the 

 foda in three times its weight of water ; fuffering the iblution 

 to remain at reft; then filtering it, and boiling the refiduum 

 left on the filter with half the quantity of water, and making 

 it again pafs through the filter. Soda, being cauftic, requires 

 iome days expofure to the air before it crvftallizes. If it be 

 of a bad quality, it will not form cryftals in five or fix davs: 

 if the contrary be the cafe, the fait is extracted, the mother 

 water is reduced to one half, and it is again fuffered to cryftal- 

 Jize. This refiduum is once more expofed, and this procefs is 

 repeated till the whole of the cryltallizable foda has been ex- 

 tracted. If the foda has been adulterated by a great deal of 

 lime, it will befoon detected by diffolving an ounce of common 

 foda in boiling water, and letting fall into it a drop of corrofive 

 muriate of mercury : if the liquor aflumcs a brick colour, it 

 contains a little lime : the quantity of this fubftance mav be 

 appreciated, in fome meafure, by the intenfity of the yellow 

 ihades which its prefetice produces. 



Of Soap. 



The property I have already mentioned as inherent in al- 

 kalies,. of combining with oils and fat animal matters, forms 

 the balls of the procefs for making that deterfive fubftance 

 called /bap. There is a very prominent line of demarcation 

 between foap obtained by means of foda and that furnifhed 



by 



