1272 BENZOIC ACID. 



consumption of theobromine and caffeine in some form or other by 

 practically the whole human race less surprising than it might at 

 first sight appear. Their universal use also indicates that they 

 supply some distinct want of the economy which cannot as yet be 

 explained purely with reference to their relationship to the nitro- 

 genous extractives of animal tissues, but rather to the physiological 

 effect their ingestion produces. In moderate doses they exert an 

 agreeable stimulating action whereby the sensations of fatigue and 

 drowsiness are removed, the body being thus enabled to exert itself 

 with less sense of effort and less initial stimulus, and the mind is 

 more active, clear-sighted and resistent to the depressing effects of 

 unpleasant influences. There is no evidence, as was at one time 

 assumed, that they act in any way by reducing the activity of nitro- 

 genous metabolism. In the case of cocoa and chocolate we have to 

 deal not merely with the stimulating effects of the theobromine they 

 contain, but also with the fact that they are of extreme nutrient 

 value owing to the large amount of fats (50 p.c.), proteids (12 p.c.), 

 and carbohydrates which enter into their composition. 



THE AROMATIC SERIES. 

 1. Benzoic acid. C 6 H 5 . COOH. 



This is not found as a normal constituent of the body. 

 When it occurs in (chiefly herbivorous) urine its presence is 

 usually due to a fermentative decomposition of hippuric acid 

 whereby benzoic acid and glycine (glycocoll) are formed. 



C 6 H 5 . CO . NH . CH 2 . COOH . +H 2 O 



= C 6 H 5 . COOH . + CH 2 (NH 2 ) . COOH. 



The acid is usually prepared by the above decomposition of 

 hippuric acid, which is readily effected by a short boiling with 

 mineral acids or, less readily, with caustic alkalis. It is also 

 obtained by the dry distillation of gum-benzoin, from which the 

 acid separates by sublimation. The sublimed acid generally 

 crystallizes in fine needles which are light and glistening. It 

 is soluble in about 200 parts of cold or 25 of boiling water and 

 very soluble in alcohol, ether and petroleum-ether, 1 in which 

 latter hippuric acid is insoluble. When precipitated from solu- 

 tions, either by cooling or the addition of acids to its salts in 

 the cold, the crystalline form is usually much less distinct. 



Apart from the crystalline form benzoic acid is characterized 

 by its property of readily subliming, even at 100, thus resem- 

 bling leucine and differing markedly from hippuric acid. As a 

 result of this it passes off freely in the vapours arising from its 



1 Petroleum-ether consists ordinarily of a mixture of the more volatile 

 hydrocarbons obtained by distillation during the fractionating of crude petro- 

 leum and boils up to about 120. The most volatile petroleum-ether boils up 

 to about 80. 



