BENZOIC ACID. 83 



rectangular tablets, which, for the most part, are arrayed in rows, 

 being linked together by their opposite angles. Its slight solubility 

 in water, the facility with which it sublimes (as may be seen 

 with a minute quantity between two pieces of flat glass or shallow 

 watch-glasses), together with its crystalline form, afford strong pre- 

 sumption of its presence. Since the remaining acids of this group, 

 which in other respects are very similar to benzoic acid, are not 

 found in the animal body, they cannot give rise to any confusion 

 or mistake in testing for this acid. We have already explained in 

 p. 77> how it may be distinguished from succinic acid, and from 

 sebacic acid, which, however, can scarcely be regarded as existing 

 preformed in the animal body. The mode of distinguishing it 

 from hippuric acid, which closely resembles it in physical pro- 

 perties, will be given in a future page. If we can obtain a 

 sufficient quantity, an elementary analysis and a determination of 

 the atomic weight are by no means superfluous. 



Physiological Relations. 



Occurrence. In a physiological point of view, benzoic acid 

 deserves a full consideration, although numerous experiments 

 render it probable that it does not exist preformed in any animal 

 fluid. No one has suspected its presence in any animal fluid but 

 the urine ; and in this, both in the case of herbivora and carnivora, 

 it occurs very often in the place of hippuric acid. Liebig*, in his 

 classical essay on Fermentation, Putrefaction, and Decay, attributed 

 the occasional occurrence of benzoic acid, in place of hippuric 

 acid, in the urine of horses, solely to a process of fermentation 

 which the latter acid underwent when the urine began to decom- 

 pose; benzoic acid being formed from it, together with other 

 products. Subsequently,! however, he changed his opinion, 

 believing that he had ascertained that horses, when very hardly 

 worked, and living on insufficient fodder, discharged urine contain- 

 ing benzoic acid, while, under the opposite conditions, the urine 

 contained hippuric acid. In order to ascertain which, or whether 

 either of these views were correct, 1 1 analysed the urine of a large 

 number of horses, both well-fed and half-starved, and healthy and 

 diseased ; but invariably found hippuric acid and no benzoic acid, 

 unless when the urine had been a good deal exposed to the air at 

 an ordinary temperature. But, on the other hand, when it had 

 stood for some time in the stable, and began to be ammoniacal, it 



* Ann. d. Ch. u. Pharm. Bd. 30, S. 261 ff. 



f Ibid. Bd. 41, S. 272. 



t Handworterbuch d. Physiol. Bd, 2, S. 14. 



G 2 



