ON HIPPURIC ACID AND ITS TESTS. 
339 
to dissolve it, it will be found expedient to give it along with 
phosphate of biborat of soda ; since they enhance its solubili- 
ty without abating its specific power. Thus, four parts, by 
weight, of the former, or one part and a half of the latter salt, 
will enable a comparatively small proportion of distilled wa- 
ter to take up one of the acid. This difficulty, as is ob- 
vious, does not apply to the benzoate of ammonia or of 
potash. 
Phosphate of soda not only serves to hold benzoic acid, 
but likewise hippuric acid, in solution; and this is a point of 
some consequence, seeing that any excess of the latter acid, 
accidentally present in the urine, will remain dissolved by 
means of the neutral phosphate of soda, or the triple phos- 
phate of soda and ammonia (microcosmic salt) naturally ex- 
isting in that secretion. These phosphates, however, produce 
a very different effect upon the uric acid, inasmuch as they 
promptly convert it into urate of soda, by depriving the salt 
of one half of its base, and thereby transforming it into bi- 
phosphate. This fact, which recently presented itself to me 
in the course of some experiments, and which has not been 
heretofore noticed by any chemical authority, seems to furnish 
a simple and rational explanation of the mode of formation of 
urate of soda, the basis of chalk-stones. Hence, whenever the 
oxidizing processof the kidney is proceeding with such energy 
as to supply a superabundance of soluble phosphates on the 
one hand, and of uric acid on the other, there must inevitably 
result an excess of urate of soda. 
Having premised the above observations with the mere 
view of pointing out what appears to cast some new light up- 
on the importance of benzoic acid and its compounds, as 
therapeutical agents in virtue of their power of generating 
hippuric acid, it has appeared to me proper to indicate the 
distinguishing features of these two acids, as some objections 
have been started touching the difficulty of discriminating the 
one from the other. For convenience sake the leading pecu- 
liarities have been arranged in collateral order, as follows : 
