SOAP-MAKING. 207 



liant, and nearly equal to wax : tlie acid, however, 

 has a great tendency to crystallize, ,which interferes 

 with its use for the manufacture of candles. At one 

 time a small quantity of arsenic was added to the 

 stearic acid, as it was found to counteract this tend- 

 ency. It has since then been found that other sub- 

 stances will produce the same effect, and thus the 

 addition of this very objectionable substance is ob- 

 viated. A great number of different mixtures of 

 stearine, stearic acid, wax, spermaceti, and other 

 solid fatty substances, in various proportions, are 

 used in the manufacture of candles. 



520. Soap may be stated to be a salt, or rather a 

 mixture of several different salts ; namely, the mar- 

 garate, stearate, and oleate of potash and soda. Soap 

 is either hard or soft ; the former is made with soda 

 alone, or a mixture of soda and potash, whilst the 

 latter is made exclusively with potash. 



521. In making soap, all that is necessary is to 

 boil together caustic alkali with the oil or fat to be 

 saponified ; carbonated alkali will not combine with 

 the fat acids. The first thing, therefore, is to prepare 

 a strong caustic alkaline lye ; for this purpose the 

 kelp, barilla, or other crude alkali, is mixed with 

 lime, which decomposes the alkaline carbonates, and 

 sets free the caustic alkali ; the mixture is then lix- 

 iviated with water, and a strong alkaline lye is ob- 

 tained. 



522. The oil, fat, or tallow, is next heated in a 

 suitable boiler, and the alkaline lye is then gradually 



