70 ORGANIC CONSTITUENTS. 



Some of these fats possess the property of being decomposed 

 by strong bases, especially by the alkalies, and by oxide of lead ; 

 in this case one of the two principal constituents separates 

 itself, while the other (an acid) combines with the base, forming 

 a soap Avith the alkalies and a plaster with oxide of lead. 

 Hence it follows that those fats which, on account of this pro- 

 perty, are termed saponifiable, are, like the salts, formed of an 

 acid and of a base ; these acids and their bases being themselves 

 the oxides of compound radicals, probably of hydro-carburets. 



There are other fats which cannot be decomposed in this 

 manner : they are termed non-saponifiable fats. 



We shall commence with the consideration of the former 

 class, the saponifiable or true fats. 



a. Fatty Bases. We are acquainted with three bodies, oxides 

 of different radicals, which act the part of bases in the animal 

 fats. These are fflyceiin, the oxide of cetyl, and cerain : the 

 first of these three is the most widely distributed, and forms 

 the base of the fats of the human body ; the oxide of cetyl exists 

 in spermaceti, and cerain in bees^ wax. We shall restrict oui* 

 remarks to glycerin. 



Glycerin^ is separated from the fats by the act of saponifica- 

 tion, when the acid with which it was combined enters into 

 combination with the new base. The best method of obtaining 

 it in a state of purity is to boil an animal fat with oxide of 

 lead. The salt of lead which is formed is insoluble in water, 

 (it is, in fact, a plaster,) while the glycerin remains in solution. 

 After remo\-ing any excess of lead by a current of sulphuretted 

 hydrogen, we must evaporate the fluid i7i vacuo over sulphuric 

 acid. 



The glycerin, prepared in this manner, is a clear uncrystal- 

 lizable fluid, of spec. grav. 1*28, of a yellowish colour, devoid 

 of odour, of a marked sweet taste, very soluble in Avater and 

 alcohol, but insoluble in ether. It burns with a clear blue 

 flame. It is considered as the hydrate of an oxide of a radical, 

 glyceryl (Cg H.), which has not yet been isolated. Its compo- 

 sition is expressed by the formula- C^ H^ O^ + HO. Stenhouse 



' This substance, glycerin, is united in each fat with a ditferent acid, and hence the 

 fats may he considered as salts of glycerin. 

 ■-' See Appendix 1, Note 23. 



