146 Chemistry. [Lecture 29. 



from the hard and horny parts of animal sub- 

 stances. The horns of deer were formerly used, 

 hence it obtained the name of salt of hartshorn ; 

 when obtained from soot, it was called spirit of 

 soot. The volatile alkali is easily separated from 

 the other salts in sal ammoniacs; hence the 

 purest volatile salt is produced from sal ammo- 

 niac, and hence it was called volatile sal am- 

 moniac. 



The alkalies are of a very extensive use in the 

 arts, particularly in bleaching and soap-making, 

 from their detergent or cleansing quality, which 

 is the result of their attraction for oily matter, 

 for dirt or foulness is generally some matter 

 united with grease or oil of some kind or other. 

 Soap consists of ail alkali, almost always one 

 of the fixed alkalies, united with oil or fat. If 

 either of these substances be boiled with a strong 

 lye of potass, the oil or grease, which commonly 

 repels water, now, by the intervention of the 

 alkali, mixes readily with it. Potass alone, how- 

 ever, only produces a soft soap. In order to 

 obtain hard soap, the compound is boiled in 

 water with a quantity of muriat of soda, (coir- 

 mon salt). The explanation of this process de- 

 pends on the doctrine of affinities. The mu- 

 riatic acid has a stronger affinity for potass ; it 

 therefore takes a part of that substance from the 

 oil, and gives it in exchange the soda with which 

 it was before combined. This consolidation of 

 the soap enables the manufacturerto get it easily 



