120 THE SECRETIONS: 



ammonia, to the former of which it appears to enact the part 

 of a mild base, imparting to it a more or less deep red colour. 

 This constituent can therefore be detected by the addition of 

 hydrochloric acid to the urine, in the manner already described 

 in speaking of uric acid. In some few diseased states, we find 

 a gray or yellow precipitate of uric acid, as if this constituent 

 was present in large quantity, while the uroerythrin was defi- 

 cient : on the addition, however, of hydrochloric acid, dark 

 coloured uric acid is soon precipitated. 



7. Carbonic acid is probably a constituent of healthy urine, 

 existing in a state of solution : in order to detect it, fresh urine 

 must be warmed in a retort, the neck of which rests a few lines 

 under the surface of lime-water. The presence of carbonic 

 acid renders the lime-water turbid. In order to guard against 

 the production of carbonate of ammonia, we must take care 

 that the urine is not submitted to too powerful a heat, and 

 that the distillation is not carried too far. 



[The following method is far less liable to give erroneous re- 

 sults. It is founded on the principle that one gas passed through 

 a solution of another will displace it, so that hydrogen or ni- 

 trogen will liberate carbonic acid and dissolve in its place. A 

 series of Wolfe's bottles must be arranged, so that hydrogen 

 gas evolved in the ordinary manner from the first shall pass 

 through a strong solution of caustic potash to free it from any 

 carbonic acid that may be mixed with it, and then through an- 

 other bottle containing lime-water, in order to certify its purity; 

 in the next bottle through the urine to displace the gas dis- 

 solved in it, and, finally, through lime-water a second time, to 

 show if the displace^ gas were carbonic acid or contained it.] 



8. Lactic acid is always present in the urine, imparting to 

 it an acid reaction. It may be presumed that the carbonates 

 which are left upon the incineration of the solid residue of the 

 urine correspond to the lactates, because lactates with fixed 

 bases are transformed into carbonates by incineration, and 

 because the other salts which occur in the urine, the sulphates, 

 phosphates, and hydrochlorates, are not similarly changed. It 

 may, however, happen that no carbonic acid is found in the 



