202 CONJUGATED ACIDS. 



That such hypotheses are not always to be rejected in the natural 

 sciences, is shown by Newton's hypothesis of emanating rays 

 of light, which now, indeed, is entirely displaced by the undu- 

 latory theory. In this light we must consider the view re- 

 garding the composition of uric acid, put forth some years 

 ago by Liebig and Wohler. From the decomposition of uric 

 acid by peroxide of lead, they deduced, for uric acid, the hypo- 

 thetical formula, C 2 H 4 N 2 O 2 + 2C 4 NO 2 ; that is to say, they 

 regarded urea as existing preformed in it, together with an acid 

 incapable of isolation in an undecomposed state, to which they 

 applied the name of urilic acid. Now that the substratum of this 

 hypothesis has been more than shaken by the discovery of the 

 true atomic weight of uric acid, we may yet make use of this 

 fiction in order to be able to represent the formation of the pro- 

 ducts enumerated by Liebig and Wohler in their classical investi- 

 gations regarding uric acid. Thus we may conceive, that on the 

 decomposition by peroxide of lead, 2 equivalents of hydrated uric 

 acid contain 1 equivalent of urea, which is isolated, while the 2 

 equivalents of urilic acid are, in the first place, decomposed into 

 C 4 O 4 and C 4 N 2 , of which the former assimilates 2 atoms of oxygen, 

 and forms oxalic acid, while the latter assimilates 3 atoms of water, 

 and produces allantoine. In a similar way we can elucidate the 

 mode of formation of those numerous products which result from 

 the action of nitric acid on uric acid. 



Combinations. It is only with the fixed alkalies that uric acid 

 forms salts which possess even a moderate degree of solubility ; 

 the lithia-salt is especially soluble, while urate of ammonia is 

 almost insoluble. Potash and soda are the only bases with which 

 uric acid forms neutral salts ; with ammonia and all other bases it 

 forms only acid and insoluble salts. On passing carbonic acid 

 into a potash-solution of uric acid, an acid potash-salt is precipi- 

 tated. 



Neutral urate of potash, KO.C 5 HN 2 O 2 , is obtained on mixing 

 alcohol with a solution of uric acid in potash (free from the car- 

 bonate) and concentrating the solution. It crystallises in needles 

 free from water, dissolves in 30 or 40 parts of boiling water, slightly 

 in alcohol, and not at all in ether, has a strong alkaline reaction, and 

 attracts carbonic acid -from the atmosphere. 



Bi-urate of potash, KO.C 5 HN 2 O 2 + HO.C 5 HN 2 O,y is precipi- 

 tated by carbonic acid from the solution of the neutral salt ; it 

 crystallises in needles, dissolves in 70 or 80 parts of boiling water, 

 and in 700 or 800 parts of water at 20. The solution does not 



