468 SOLID PARTS OF ANIMALS. 



ceptible smell. .It slightly reddened litmus-paper. It was 

 mixed with carbonate of soda, till it became slightly alkaline. 

 Being now evaporated to dryness, and a drop of sulphuric acid 

 let fall upon the small saline residue, a smell was emitted strong- 

 ly urinous, but mixed with a sensible odour of vinegar. Hence 

 it was obvious that acetic acid existed in the residue. But it 

 might have been formed from lactic acid during the process. For 

 Scheele showed long ago that lactic acid is very easily converted 

 into acetic acid. 



Urine contains always some uric acid, as was first observed by 

 Scheele. It separates in minute crystals when the urine is 

 mixed with nitric acid, and set aside for some time in an open 

 glass vessel. Berzelius states the average quantity of uric acid 

 in urine at j o l oothof its weight.' Lecanu states the uric acid in 

 100 urine to be 0-75. A copious table of the quantity of uric 

 acid in many different specimens of urine, as determined by Le- 

 canu, will be given in a subsequent part of the present chapter. 

 I found that 1000 parts of urine of the specific gravity 10*185 

 let fall 0*242 of uric acid when mixed with nitric acid. Now, 

 according to the experiments of Prout, uric acid does not dis- 

 solve in 10,000 times its weight of water, while urate of ammonia 

 is soluble in about 500 times its weight of that fluid. Hence it 

 is natural to infer that uric acid in urine is in the state of urate 

 of ammonia. And, as urate of ammonia reddens vegetable blues, 

 the acidity of the urine may be partly owing to the presence of 

 urate of ammonia. 



The most remarkable substance in urine is urea. According 

 to Berzelius, it exists in urine to the amount of 3 per cent. But 

 he does not give us the specific gravity of the urine tried. Le- 

 canu found that urine of sp. gr. 1-030 contained 2*94 per cent. 

 I obtained from urine of specific gravity 1-0185 2*364 per cent, 

 of urea. A copious table of the quantity contained in different 

 urines will be given at the end of this chapter. 



Besides these substances, and the colouring matter, which has 

 not hitherto been obtained in a separate state, urine contains always 

 phosphoric and sulphuric acids, together with lime, magnesia, po- 

 tash, and ammonia, and a notable quantity of common salt. 



The first analysis of urine was published by Berzelius in 1813. 

 He does not give the specific gravity of the urine examined by 

 him. But he states that it became turbid on standing. Hence 



