26 Historical Sketch of Improvements in [July, 



Pyro-urate of barytes is a white powder scarcely soluble in 

 cold water. Potash, soda, and ammonia, form with it soluble 

 salts, the two former of which are crystallizable. 



The only metals precipitated by pyro-urate of potash are the per- 

 oxides of iron and copper, and the oxides of silver and mercury, 

 and the subtritacetate of lead. The perpyro-urate of iron is 

 chamois-yellow ; that of copper, bluish-white ; those of silver, 

 mercury, and lead, perfectly white. 



The subpyro-urate of lead obtained by decomposing pyro-urate 

 of soda by means of subtritacetate of lead is composed of 



Acid 28-5 5-58 



Protoxide of lead 71-5 14-00 



100-0 



The equivalents for the pyro-uric acid derived from these two 

 different analyses cannot easily be reconciled with each other, 

 unless we suppose the subpyro-urate of lead to be a compound 

 of one atom acid + seven atoms protoxide of lead, a supposition 

 not very likely to be true. 



ChevaUier and Lassaigne analyzed pyro-uric acid by heating 

 it with 20 times its weight of peroxide of copper in a glass tube. 

 The onl)"^ gases obtained were carbonic acid, and azotic in the 

 proportion of four volumes of the former to one volume of the 

 latter. They state the composition of pyro-uric acid as follows : 



Oxygen 44 32 



Carbon 28-29 



Azote 16-84 



Hydrogen 10-00 



99-45 



This is equivalent to the following volumes of these respective 

 bodies, supposing them in the gaseous state : 



Volumes. 



Oxygen 7 



Carbon 12 



Azote 3 



Hydrogen 25^ 



Now this is equivalent to 



14 atoms oxygen = ] 4-0000 



12 atoms carbon = 9-0000 



3 atoms azote = 5-2500 



25-1 atoms hydrogen = 2-1875 



30-4375 



According to this analysis, the equivalent number for an atom 

 of pyro-uric acid is 30'4375 — a number which neither agrees 



