118 THE SECRETIONS: 



"In its pure state the hippuric acid produced from human urine 

 presents the same long, shining, transparent, four-sided ob- 

 liquely-truncated prisms, by which the hippuric acid produced 

 from the urine of animals is so easily detected and distinguished 

 from benzoic acid. (See fig. 23.) The hippuric acid of human 

 urine is not volatile at the subliming temperature of benzoic 

 acid ; at a higher temperature it undergoes fusion, forming a 

 brown-red liquid, and yielding upon dry distillation the same 

 products which common hippuric acid forms under the same 

 circumstances, viz., a red-coloured oil smelling like tonka-beans, 

 ammonia, benzoic acid, and a copious residue of carbon. It 

 dissolves in nitric acid at a high temperature, and yields, upon 

 cooling, crystals of benzoic acid, owing to the decomposition 

 which it undergoes. 



"From 0-499 of hippuric acid produced from urine, 1-0791 

 of carbonic acid and 0-2317 of water were obtained. This gives 

 for 100 parts 



Found. Calculated . 



Carbon . . . 59'47 . . 60-89 

 Hydrogen . 5-15 .. 4-45 



This analysis corresponds sufficiently with the calculated results 

 to remove all doubt as to the nature of the acid ; it will be per- 

 ceived that it contains lOg less carbon than benzoic acid."] 



3. Extractive matters. The exhibition of the divisions of ex- 

 tractive matter, namely, the water- extract, the spirit-extract, 

 and the alcohol-extract, can only be effected by evaporating the 

 urine, and treating it with alcohol, as we shall presently show 

 in speaking of the quantitative analysis of this fluid. Little 

 has yet been done in this department of chemistry, but the 

 presence of the extractive matters can generally be easily re- 

 cognized by the addition of certain tests : for instance, acetate of 

 copper, chloride of tin, perchloride of iron, and sulphate of prot- 

 oxide of iron, throw down precipitates from freshly-passed urine; ' 

 and bichloride of mercury, nitrate of tin, and tannic acid, cause 

 a degree of turbidity. There is, however, no certain proof, al- 

 though there is every probability that normal urine in all cases 

 behaves in this way with the above tests. The extractive mat- 



