12 CONVERSION OF BENZOIC INTO HIPPURIC ACID. 
acid a 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 hippuric 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 imme- 
diately 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 com- 
pounds which it forms with nitric and oxalic acids it evi- 
dently acts the part of a base. Cap and Henry have as- 
serted 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 hippu- 
rate of lime and oxalate of urea, and they also described 
the methods by which they had extracted the lactate of urea 
from human urine, and the hippurate of urea from the urine 
of the horse. The former was repeated by Lecanu, who 
could obtain no lactate of urea. Cap and Henry replied, 
and gave a new method of obtaining it in crystals by 
