850 BENZOYL. 



To prepare benzole acid from the resin. Dr. Mohr directs 1 

 pound of it to be broken and spread uniformly in a cast iron 

 bason, 8 or 9 inches in diameter and 2 inches deep, the mouth 

 of which is then covered, like a drum, by unsized paper pasted 

 down at the edges. A cylindrical vessel of paper of the size 

 and ordinary form of a man's hat is pulled over this, and bound 

 about the bason by a thread. The bason is then placed on a 

 sand-bath for three or four hours, attention being paid to the 

 management of the heat, for the beauty and purity of the pro- 

 duct depend entirely upon the slowness and regularity with 

 which the sublimation is effected. The paper cylinder is found 

 completely filled with superb crystals of benzoic acid of splendid 

 whiteness and perfectly free from the black empyreumatic oil 

 which they are generally soiled with ; but having on the contrary 

 a strong and very agreeable odour of benzoin. This process 

 yields about 4 per cent of benzoic acid. 



Benzoic acid is also prepared in the humid way ; the resin 

 is finely pulverised and care taken to mix it intimately with an 

 equal weight of hydrate of lime ; the mixture is then boiled with 

 twenty times its weight of water by which the benzoate of lime 

 is dissolved ; the solution is filtered, antl after being concen- 

 trated to about one-fifth of its bulk hydrochloric acid is added, 

 by which the benzoic acid is liberated, and crystallizes on cool- 

 ing. The chief point to be attended to in this process is the 

 mixing of the resin and hydrate of lime, which must be inti- 

 mate, otherwise the mass agglomerates in boiling water, and the 

 benzoic acid can only be obtained by reducing the mass to 

 powder and mixing it again with hydrate of lime. 



The benzoic acid may be purified by a second sublimation, 

 or by sending a stream of chlorine through its solution in 

 boiling water (Liebig's Traite.) 



Benzoic acid crystallizes when sublimed in long hexagonal 

 silky needles ; when pure it is colourless and inodorous ; but 

 it acquires by heat an odour, analogous to that of benzoin. Its 

 taste is sweet and hot, but quite peculiar. It reddens litmus 

 feebly ; water dissolves TV of its weight of benzoic acid at 212, 

 and Tf^v only at the ordinary temperature. It is soluble in two 

 parts of alcohol and the same quantity of ether, and dissolves also 

 in oil of turpentine. Benzoic acid fuses at 248, and sublimes at 

 293, phosphorescing in the dark; it boils at 462.2 (239 



