AROMATIC ACIDS AND THEIR DERIVATIVES 299 



matters (silk, wool, indigo, Peruvian balsam, etc.), and is manu- 

 factured on a large scale by slowly dropping carbolic acid into 

 fuming nitric acid; it is used as a yellow dye for silk and wool, 

 and as a reagent for albumen; most picrates are explosives. 



Benzoic acid, Acidum benzoicum, HC_H 5 2 or C 6 H 5 C0 2 H = 122. 

 Found in gurn-benzoin and some other gums; it is obtained 

 from benzoin by heating it carefully, when the volatile benzoic 

 acid sublimes. It forms white, lustrous scales or friable needles, 

 having a slight aromatic odor of benzoin, and an acid reaction; 

 it is but slightly soluble in cold water, but easily soluble in 

 alcohol, ether, oils, etc. 



Benzoic acid, when neutralized with an alkali, gives a flesh- 

 colored or reddish precipitate of ferric benzoate on the addition 

 of a neutral solution of ferric chloride. 



By neutralizing benzoic acid with either ammonium hydrate 

 or sodium hydrate, the two officinal salts ammonium benzoate, 

 NH 4 C 7 H 5 2 , and sodium benzoate, NaC 7 H 5 2 .H 2 O, are obtained. 

 Both salts are white, soluble in water, and have a slight odor of 

 benzoin. 



Oil of bitter almond, Oleum amygdalae amarae, C 7 H 6 or C 6 H 5 COH 



(Benzaldehyde). As shown by the formula, oil of bitter almond 

 differs from benzoic acid in containing one atom less of oxygen ; 

 in all its reactions it behaves like a true aldehyde, being, for in- 

 stance, easily converted into benzoic acid by oxidation. 



It does not occur in a free state in nature, but is formed by a 

 peculiar fermentation of a glucoside, amygdaline, existing in bitter 

 almonds, in cherry-laurel, and in the kernels of peaches, cherries, 

 etc., but not in sweet almonds. The ferment causing the de- 

 composition of amygdaline is a substance termed emulsine, 

 which is found both in bitter and sweet almonds. As water is 

 required for the decomposition, the emulsine does not act upon 

 the amygdaline contained in the same seed until water is added, 

 when the decomposition takes place as follows : 



C 20 H 2 .NO U + 2H 2 : 2C 6 H 12 6 . + HCN + C 7 H 6 O. 



Amygdaline. Water. Glucose. Hydrocyanic Oil of bitter 



acid. almond. 



The oil is obtained by distilling bitter almonds with water, 



