38 ANIMAL ACIDS CONTAINING AZOTE. 



composition of urea, if we admit with Wohler and Liebig, that 

 urea is one of the constituents of uric acid. 



SECTION III. OF PYRURIC ACID. 



It has been stated in the last section, that when Scheele sub- 

 jected uric acid to distillation, a substance sublimed which he 

 took for succinic acid ; that Dr Pearson considered it to be ben- 

 zoic acid ; that Dr Henry examined it more in detail, and was 

 of opinion that it constituted a new and peculiar acid; and, finally, 

 that Chevallier and Lassaigne subjected it to a rigorous examina- 

 tion, and gave it the name of pyruric acid. 



It may be obtained either by heating uric acid, or uric acid 

 calculi in a retort : the calculi must be pulverized and washed 

 with boiling water before being put intt) the retort. The acid 

 sublimes in plates, which attach themselves to the upper part of 

 the retort. Besides this there is a good deal of acid, combined 

 with ammonia, dissolved in the water which comes over into the 

 receiver. There comes over at the same time cyanuric acid, and, 

 in general, carbonate of ammonia, and an empyreumatic oil. 



The acid may be obtained from the matter which has passed 

 into the receiver, and which speedily assumes a solid form. This 

 matter is to be treated with boiling water, and filtered. The 

 filtered liquor lets fall a brown bituminous-looking substance- 

 When saturated with ammonia and evaporated, small crystals 

 are formed, consisting of super-pyrurate of ammonia, but disco- 

 loured by an empyreumatic oil. Being, dissolved in water, and 

 the solution mixed with diacetate of lead, a precipitate falls, 

 which, being washed with water, and decomposed by sulphuret- 

 ted hydrogen gas, filtered and evaporated, yields crystals of pyruric 

 acid. The colour is still yellow, but they may be purified by re- 

 peated solutions and crystallizations. 



Pyruric acid is white. It crystallizes in small needles. When 

 heated it melts and sublimes entirely in white needles. When 

 passed through a red-hot glass-tube it is decomposed into char- 

 coal, oil, carburetted hydrogen, and carbonate of ammonia. It 

 dissolves in about forty times its weight of cold water. The so- 

 lution reddens vegetable blues. It dissolves in boiling alcohol 

 (of 0*843) and when the solution cools is deposited in small white 

 grains. 



It dissolves in concentrated nitric acid. When the solu- 



