72 ORGANIC CONSTITUENTS. 



separates first, mixed with a small quantity of the margarate. 

 The more frequently the solution is repeated the more certain 

 are we that ultimately the whole of the margarate will be re- 

 tained in solution. 



The pure stearate of potash is decomposed by warm dilute 

 hydi'ochloric acid ; and the stearic acid which precipitates is to 

 be washed in water and dissolved in boiling alcohol, from which 

 it crystallizes, on cooling, in white brilhant scales. By the 

 same process the margaric acid is separated from the pure mar- 

 garate of potash. Margaric acid is obtained most easily from 

 human fat, which contains a very large amount of margarin. 

 Stearic acid mehs at 158^^. The specific gravity of the acid in 

 its sohd state is I'Ol. It is perfectly insoluble in water, but 

 dissolves readily in ether as well as in boihng alcohol, in which, 

 on cooling to 122'', crystals begin to form. Its solution exhibits 

 a mild acid reaction towards litmus ; in the solid form it bui-ns 

 with a clear flame, like wax. 



The leading difference bet^veen margaric and stearic acids 

 is the greater fusibility of the former, which becomes liquid at 

 140°. Its crystals assume an acicular form, and are smaller 

 and less brilliant than those of stearic acid. 



Stearic acid is represented by the formula' Cg^ H^^ O,. In 

 its crystalline state it is combined with 2 atoms of water (forming 

 the hydrate of stearic acid), which it gives up on uniting with 

 a base. 



Margaric acid is represented by the formula Cg^ H33 O3. The 

 hydrate contains only 1 atom of water. 



The radical of these two acids, marganjl, is represented by 

 the formula C.^^ H33 (M) 



Hence, margaric acid = M + O3 

 and stearic acid r= 2 M + O^ 

 If we treat stearic acid for some time with nitric acid at a 

 temperature of 212°, it becomes completely converted into 

 margaric acid. 



A similar, although not so perfect an effect is produced by 

 sulphuric and chromic acids. 



The stearic and margaric are very weak acids ; at an elevated 

 temperature they have the power of expelling carbonic acid 



' Sec Appendix 1, Note 24. 



