188 ON THE CONVERSION OF 
added. After the lapse of twenty-four hours it had deposited a precipitate of a oranular 
appearance and of a very dark-red nearly black colour, which dissolved with effervescence 
in nitric acid, and on evaporation yielded the beautiful purple colour of purpuric acid. It 
therefore consisted of uric acid. ‘Twenty minutes after the first, another portion was ob- 
tained, 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 precipitate there appeared 
a moderate quantity of needle-shaped crystals of hippuric acid. 
These experiments evidently show that the formation of hippuric acid does not dimi- 
nish 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 con- 
taining most of the hippuric acid, had a sp. gr. of 1.024. Its colour 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 ingre- 
dients. It has been found, that if any substance be taken under the first circumstances, 
dissolved in the water, if 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 hippuric, 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 
acid was taken immediately before dinner, a portion of urine, obtained immediately after 
the meal, and about thirty minutes after the introduction of the acid yielded, when treated 
as above, an abundant crop of crystals. It was interesting to ascertain how long the hip- 
puric acid would continue to appear in the urine from the time the benzoic acid was 
taken. In an experiment, where two grammes were taken before and two grammes more 
immediately after dinner, the urine secreted (from seven to eleven o’clock in the evening 
or) from four to eight hours after its introduction, contained an abundance of hippuric 
acid, while none could be detected in the urine voided after that time the next morning. 
The quantity of hippuric acid obtained exceeds that of the benzoic acid taken; six 
grammes taken, two grammes after breakfast, two before and two after dinner yielded in 
two experiments about eight grammes of crude hippuric acid, or about one-third more 
than its own weight. 
It was a matter of considerable interest to ascertain with what base the hippuric acid 
occurred combined in the urine, whereby it was held in solution till liberated by an acid. 
The bases occurring in the urine are potassa, soda, lime, magnesia, and ammonia. Besides 
these, urea Seems in some instances to have a basic nature: thus, in the compounds which 
it forms with nitric and oxalic acids it evidently acts the part of a base. Cap and Henry 
have asserted that a portion of it occurs combined with lactic acid in human urine and 
with hippuric acid in urine of the horse, and they prescribed a method of forming these 
two compounds by double decomposition of lactate or hippurate of lime and oxalate of 
