BENZOIC INTO HIPPURIC ACID. 187 
lows, that we may be able to perform the same transformation out of the body. It was 
with a view of determining this point that our experiments were undertaken, and we still 
look for success, although they have not hitherto afforded a satisfactory result. 
Wocehler was the first to observe that benzoic acid, when administered internally to a 
dog, and again separated from the urine, reappeared as prismatic crystals, unlike benzoic 
acid; and he conjectured correctly, from their resemblance to hippuric acid, that the former 
by passing through the system was converted into the latter. He also suggested, that 
this might be the source of the hippuric acid in the urine of herbivorous animals, since 
the benzoic acid might be supposed to occur in their food, and by the digestion be con- 
verted into hippuric. Ure subsequently stated, that he had found hippuric acid in the 
urine of a patient who had taken benzoic acid; he also supposed that the uric acid had 
been employed in this conversion, and recommended it as a remedy for calculous conere- 
tions of uric or lithic acid. ‘This induced Keller, at the instigation of Woehler, to make 
some experiments on this point, which he published in Liebig’s Annals of Chemistry and 
Pharmacy. He took, in the evening before bed-time, two grammes or about thirty-one 
grains of benzoic acid, and found the next morning, on examining the urine, that by the 
addition of chlorohydric acid it deposited long prismatic crystals, which it continued to 
do as long as he continued the use of benzoic acid. By re-dissolving these crystals in 
hot water and treating them with animal charcoal, he obtained them perfectly colourless. 
The crystals thus obtained behaved in all respects like pure hippuric acid. They fused 
easily, and by a stronger heat they charred with a smell of oil of bitter almonds and sub- 
limation of benzoic acid. He also determined the quantity of carbon, which he found 
to agree with that of hippuric acid, namely, 60.7 per cent., while benzoic acid contains 
69.1 per cent. of carbon. 
Keller furthermore ascertained that the urine from which hippuric acid had been se- 
parated, deposited a large amount of nitrate of urea, on the addition of nitric acid. It 
had also previously deposited uric acid. It therefore contained these two usual ingredi- 
ents of urine. He also inferred, that since the urine could be inspissated without depo- 
siting hippuric acid before the addition of chlorohydric acid, it was evident that the 
hippuric acid existed in combination with a base. 
As hippuric acid may be said, to a certain extent, to replace uric acid in the herbivorous 
mammalia, this probably led Ure to the supposition that the uric acid was employed in the 
conversion of the benzoic acid; but Keller’s experiment showed that the urine deposited 
uric acid, and that therefore this latter assertion could not be correct. 
We have repeated Keller's experiments, and with the same results. We have in gene- 
ral found that after the use of benzoic acid the urine makes a copious deposite of uric 
acid, both in the red or dark-coloured variety and in that of a clay-coloured or muddy 
appearance. 
In one experiment the urine was examined in the morning when no benzoic acid had 
been taken. It deposited no sediment on cooling, and when tested for uric acid by the 
addition of nitric acid, the latter effected after twenty-four hours a deposite of only a few 
isolated colourless crystals scattered over the inside of the vessel. The same day two 
grammes of benzoic acid were taken immediately after dinner. ‘Twenty minutes after- 
wards the urine was voided, evaporated to one-fourth its volume, and chlorohydric acid 
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