254 MANURES THE PUTREFACTIVE FERMENTATIOIf . 



upon herbage contained only 2 per cent, of uric acid. That of a 

 pheasant fed upon barley contained, on the contrary, 14 per cent. ; 

 and that of a falcon which fed upon flesh alone, yielded scarcely any 

 thing but uric acid. The urine of an ostrich was found by Fourcroy 

 and Vauquelin to contain uric acid in the proportion of about one six- 

 teenth of its mass. 



I have already given the composition of urea. Hippuric acid is 

 an azotized acid which is readily obtained by adding a little hydro- 

 chloric acid to the fresh urine of the horse reduced by evaporation to 

 about one tenth of its original volume, when a granular crystalline 

 mass is precipitated. If the urine have been stale instead of fresh, 

 benzoic acid and not hippuric acid is obtained ; benzoic acid was, in 

 fact, long admitted as one of the elements of the urine of herbivorous 

 animals ; but it is derived from the transformation of hippuric acid 

 into benzoic acid and ammonia, the change being produced by con- 

 tact with the organic matters which putrefy so quickly in urine. 

 Liebig was the author of this observation; it was in operating upon 

 unchanged urine that he discovered hippuric acid. The following is 

 its composition : — 



Carbon 60.7 



Hydrogen .5.0 



Oxygen 26.3 



Azote 8-0 



100.0 



Uric acid has not yet been met with in the urine of mammiferous 

 herbivora ; but it exists in that of man, having been first discovered 

 in calculi from the bladder ; whence it received the name of lithic 

 acid. Liebig's analysis shows it to be composed of : — 



Carbon 36.1 



Hydrogen 2.4 



Oxygen 28.2 



Azole 33.4^ 



lOO.O 



The litter most commonly used to absorb the urine of stall-kept 

 animals is wheat straw, which consists in principal part of lignine 

 or woody fibre : like all vegetable tissues, however, it contains an 

 azotized principle, and substances that are soluble in caustic alkalies. 

 In the ashes of straw, we have indicated silica as abundant, and va- 

 rious alkaline and earthy salts. The proportion of azote appears to 

 vary in t|ie ratio of from 3 to 6 per 1000. An analysis which I made 

 of dry wheat straw gave the following elements : — 



Carbon 48.4 



Hyilrogen 5.3 



Oxygen 38.9 



Azote 00.4to0.6 



Ashes 07.0 



100 



Agriculturists have, in all ages, admitted that the most powerfu. 

 manures are derived from animal substances, an opinion or rather a 

 fact, which, expressed in scientific language, anounts to this, that 



