150 THE ROYAL SOCIETY OF CANADA 



added and the insoluble ferric benzoate after filtration is decomposed 

 by hydrochloric acid. 



(3). The fresh urine is evaporated to about one third its original 

 volume, filtered, acidified with hydrochloric acid and allowed to 

 cool. Hippuric acid crystallizes out and may be hydrolyzed to 

 benzoic acid and glycocoll by boiling with concentrated hydrochloric 

 acid or sodium hydrate. 



All three methods present certain difficulties, especially when 

 considered as processes for use on the farm. Methods (1) and (2) 

 involve expensive and disagreeable evaporation and (3) requires the 

 necessary apparatus for the preparation of carbonic acid gas and in- 

 cludes the troublesome filtration of a fine, voluminous precipitate. 



From a consideration of the change of solubility of benzoic acid 

 with the temperature, the possibility suggested itself of separating 

 benzoic acid from putrefied urine and also hippuric acid from fresh 

 urine by precipitation, at low temperatures. 



Solubility of Benzoic Acid in Water 



Grams Benzoic acid 

 Temperature per 100 grams solution 



C. 



0-170 



10 0-209 



20 0-289. 



25 0-343 



From these data it may be shown that by cooling a solution of 

 benzoic acid to 0°C an amount of acid will separate out equivalent 

 to an amount obtained by concentration of the solution to one half 

 its volume and cooling to 25°C.^ Thus, from a solution of benzoic 

 acid containing -5 grams per 100 cc -330 grams will separate out 

 on cooling to 0°C, leaving in solution • 170 grams. The same solution 

 (-5 grams per 100 cc.) concentrated to one half its volume, i.e. 50 cc, 

 precipitates -329 grams on cooling to 25°Ci leaving in solution -171 

 grams. 



No table of solubilities for hippuric acid could be found, but 

 conjecturing that its curve of solubility would approximately parallel 

 that of benzoic acid, the work about to be described in this paper was 

 undertaken, the method used for determining the benzoic acid content 

 i.e. the total amount of benzoic acid after hydrolization of the hip- 



^To- avoid loss of benzoic acid by volatilization during evaporation it would 

 be necessary to first convert into the sodium salt by addition of caustic soda. 



