COMPOUND ANIMAL SUBSTANCES. 95 



reciystallization, and dissolved in water, cannot be precipitated 

 by acetate of lead, nitrate of silver, or nitrate of the black 

 oxide of mercury. 



If the fluid, during evaporation, gives off an urinous odour 

 some hydrochloric acid must be added, and it must be allowed 

 to stand for some time. If acicular crystals are formed, which, 

 after being purified by recrystallization, and dissolved in water 

 containing enough alkali to neutralize the acid of the crj^stals, 

 give a white precipitate with the above-named tests, an orange 

 with the perchloride of iron, and when moistened with nitric 

 acid, and warmed, do not assume a purple-red colour, they 

 consist of hippuric acid. 



If however the crystals are very minute, are not readily 

 dissolved in water, and give, Avhen moistened with nitric acid 

 and warmed, a purple-red stain, they are uric acid crystals. 



4. If the fluid which we are examining is of a brownish 

 yelloAv colour, and if on treating a little of it with an excess 

 of nitric acid, the colour successively changes to green, blue 

 and red, then biliphsein is present. 



5. On evaporating a portion of the fluid to dryness, pulver- 

 ising it, and boiling it with ether, we obtain, by the evaporation 

 of the ethereal solution, a fatty residue. If it be fluid, it is 

 composed of olein, if it have a tendency to be solid, either 

 stearin or margarin, or both are also present. The fatty 

 acids, and probably free lactic acid, with traces of other sub- 

 stances may be present, especially if the ether contained any 

 alcohol or w\ater. These substances remain in solution, on 

 washing the fatty residue with water. The lactic acid may be 

 easily recognized by its acid reaction ; and the fatty acids may 

 be detected by the addition of acetate of lead or acetate of 

 copper to their alcoholic solutions. They are completely pre- 

 cipitated in this manner, and a residue of pure fat is left, which 

 must be again washed and the water removed by evaporation. 

 The fat must then be saponified ; if a portion of it resists this 

 process, cholesterin or serolin, or both, must constitute a por- 

 tion of the fatty residue. They must be taken up by ether, 

 after the saponified portion has been evaporated to dryness. 

 Serolin is less soluble in alcohol, and melts at a lower tem- 

 perature than cholesterin,' by which means the two fats may 



' [Serolin melts at 95°, cholesterin at about 275°.] 



