CONVERSION OF BENZOIC INTO HIPPURIC ACID. 11 
added. After the lapse of twenty-four hours it had de- 
posited a precipitate of a granular appearance and of a 
very dark-red nearly black color, which dissolved with 
effervescence in nitric acid, and on evaporation yielded the 
beautiful purple color of purpuric acid. It therefore con- 
sisted of uric acid. Twenty minutes after the first, another 
portion was obtained, which, treated in the same way, 
yielded a precipitate in all respects similar to the above. 
Its quantity also had not diminished ; but besides this pre- 
cipitate there appeared a moderate quantity of needle- 
shaped crystals of hippuric acid. 
These experiments evidently show that the formation of 
hippuric acid does not diminish the quantity of the uric 
acid, and that the formation of the former seems entirely 
independent and disconnected with that of the latter. 
The urine voided in the morning had a sp. gr. of 1.0112. 
That voided three or four hours after dinner, and therefore 
containing most of the hippuric acid, had a sp. gr. of 1.024. 
Its color was but slightly more yellow than the former. 
Distinction is generally made between the urine secreted 
after fluids have been taken, especially on an empty 
stomach, and that secreted subsequently to the digestion of 
food. The former is much more limpid and tasteless, and 
contains much less of the solid ingredients. It has been 
found, that if any substance be taken under the first cir- 
cumstances, dissolved in the water, it passes much more 
rapidly into the urine, where some substances have been 
detected in the short time of from two to ten minutes after 
their introduction into the stomach ; while, when taken 
with the food, they generally require a much longer time 
for their reappearance in the urine. In regard to the time 
which elapses before the benzoic acid reappears as hippu- 
ric, it will be seen that in the above experiments it had not 
yet appeared there in twenty minutes, and that forty 
minutes after being taken its appearance had but fairly 
commenced. In another experiment, where the benzoic 
