S82 Chemical Society, 



water, vapour or air being contained in a glass globe of about fif- 

 teen cubic inches capacity, having a narrow neck, through which 

 the thermometer was admitted. The globe was supported in the 

 bath by a wire -cage in the same manner as is done in the operation 

 of taking the density of vapours. 



It would hence appear from the proximity of the temperature of 

 the substance heated and the bath, that if the experiments were con- 

 tinued a sufficient length of time, and every chance of error avoided, 

 the substance might be heated to an equal degree, and the law of 

 equilibrium of temperature maintain its universality. 



I could never, however, raise the temperature of aether vapour 

 nearer than one degree below the temperature of the bath, and to 

 effect this required at least half an hour. I would therefore recom- 

 mend, in taking the density of vapours, that the temperature of the 

 globe be considered as one degree less than that of the bath, in 

 making the calculations. Notwithstanding, with this correction 

 the weight of the vapour can scarcely be effected to a greater extent 

 than '04 grain. 



" On the Preparation of Hippuric Acid," by Geo. Fownes, Esq.* 



Being very desirous of possessing a specimen of a very interesting 

 substance, hippuric acid, namely, and failing to obtain it in any 

 quantity from the horse-urine collected in London stables, I was 

 induced to make trial of that of cows, and speedily found it to be a 

 substance highly advantageous for the purpose. 



Perfectly fresh cow-urine presents the aspect of a transparent 

 amber-coloured liquid of peculiar but not disagreeable odour, and 

 quite neutral to test-paper. When this is evaporated down in a 

 water-bath to about one-tenth, and mixed with hydrochloric acid, a 

 very large quantity of a brown crystalline substance separates, 

 which is hippuric acid. It is very easy in this way to operate upon 

 whole gallons of the liquid, and thus procure many ounces of hip- 

 puric acid. 



To purify this substance, I find the following method very ad- 

 vantageous. The brown rough acid is dissolved in boiling water, 

 of which, by the way, it requires a much larger quantity than from 

 the descriptions given would be imagined, and through the solution 

 a stream of chlorine gas is transmitted, until the odour of that gas 

 becomes perceptible in the liquid, and its brown colour passes into 

 a sort of deep amber-yellow. The hot solution is then filtered 

 through cloth, and upon cooling, the acid, still very impure, crystal- 

 lizes out. The acid is next dissolved in a dilute hot solution of 

 carbonate of soda, taking care to have a little excess of the alkali, 

 digested for a few minutes with a little animal charcoal, filtered, and 

 lastly, the solution strongly acidified by hydrochloric acid, which 

 removes the base and sets free the hippuric acid. Should that 

 substance not be by such treatment rendered perfectly white, it 



[* A paper on the conversion of benzoic into hippuric acid, by Mr. 

 Garrod, read before the Chemical Society, January 18, will be found in 

 Phil. Mag., S. 3. vol. xx. p. 501.] 



