STFARIC ACID. 959 



potash or soda, such as that of olive oil, when dissolved in about 

 eight times its weight of hot water, and the solution afterwards 

 diluted by fifty times its bulk of water, allows an acid margarate 

 of potash or soda to precipitate, which may be purified from a 

 little oleate with which it is contaminated by repeated crystalli- 

 zation from alcohol. This salt contains 1 atom of water, and i 

 atom of potash as base. Both the acid and neutral margarates 

 of potash crystallize from an alcoholic solution in plates, which 

 have less lustre than the corresponding stearates. Margarine, 

 or the margarate of glyceryl, has not been analysed in a state of 

 purity. The solid matter which is formed in olive oil when 

 cold, is a combination of margarate and oleate of glyceryl, ac- 

 cording to Pelouze and Boudet. 



Stearic acid, hypomargarylic acid, 2HO + C 68 H 66 O 5 =2HO 

 + 2(C 34 H 33 ) +O 5 . This acid was discovered by Chevreul, com- 

 bined with oxide of glyceryl in animal and vegetable fats and 

 in the bile of many animals. It may be obtained pure by 

 crystallizing the stearic acid of commerce from alcohol, till its 

 point of fusion is between 158 and 167. The latter substance, 

 which forms the stearine candles of commerce, is obtained by 

 saponifying tallow with hydrate of lime, to get rid of its oxide 

 of glyceryl which being set free dissolves in water, and de- 

 composing the insoluble soap of lime with dilute and boiling 

 sulphuric acid. The oleic acid is separated from the stearic 

 acid by submitting the latter to pressure between hot metallic 

 plates. The cake thus obtained is said to contain not more 

 than traces of margaric and oleic acids. Mixed stearic and 

 oleic acids may also be separated by solution in boiling alcohol, 

 from which the stearic acid crystallizes out, and may be 

 purified by successive crystallizations from alcohol. 



Stearic acid crystallizes by cooling in white brilliant needles, 

 soft to the touch, pulverisable and insoluble in water. When 

 fused and cast in a mould its surface is rough from crystalline 

 granulation, but if a minute quantity of finely pulverised talc 

 (French white) be mixed with the melted acid, it then soli- 

 difies with a perfectly smooth and glossy surface like that of 

 wax. Arsenious acid was improperly used at one time to 

 produce the effect described in stearine candles. Stearic acid 

 fuses at 167, and solidifies at 158 (Chevreul) ; its density 

 when solid is 1.01, in the liquid condition 0.854. It is tasteless 



