Dr. Gregory on the Decomposition of Uric Acid. 187 



the alloxantine is dissolved, which requires from a quarter to 

 half an hour, even when enough water is present for the final 

 solution of the whole. The solution is filtered while hot, 

 which takes place very rapidly, and deposits on cooling an 

 abundant crop of crystals of alloxantine. The quantity reaches 

 its maximum in twenty-four hours, and the amount retained 

 in the acidulous mother-liquor is but small. It may however 

 be obtained by concentration. By this method the mother- 

 liquid of the alloxan above mentioned, although some part of 

 it was used for other experiments, yielded upwards of 8 oz. of 

 pure alloxantine. 



2. Dialurate of Ammonia. 



This salt may be also obtained in abundance from the 

 mother-liquid of alloxan, as well as from that of alloxantine. 

 Ammonia is to be cautiously added in the cold, so as to leave 

 a slight excess of acid, and hydrosulphuret of ammonia is to 

 be then added in excess, so as to redissolve any sulphur that 

 may be at first thrown down. The dialurate is formed in the 

 cold so abundantly as to cause the whole to become thick. It 

 may be dissolved in the liquid by the aid of heat, and it is 

 then deposited on cooling in crystals. We ought to see that 

 nothing is left undissolved by the hot liquid ; should this oc- 

 cur it is probably owing to sulphur, and in that case a little 

 hydrosulphuret of ammonia clears all up. The crystallized 

 dialurate of ammonia is collected on a filter and washed, at 

 first with a weak solution of hydrosulphuret of ammonia, then 

 with alcohol, to which enough hydrosulphuret has been added 

 to give it a pale yellow colour, and finally with pure alcohol 

 till the latter passes through quite colourless and pure. The 

 salt is quickly submitted, while still on the filter, to pressure 

 between folds of bibulous paper, and is finally dried in vacuo 

 over sulphuric acid. Should it not appear pure, the process 

 of dissolving it in water with the addition of hydrosulphuret 

 of ammonia, of crystallizing, and washing as above, is to be 

 repeated. By this method I have prepared this salt in large 

 quantity, and have obtained it dry and quite pure, with only 

 a faint tinge of flesh colour, in fact almost colourless. If dried 

 in the air, without the use of the alcohol and hydrosulphuret 

 in washing, and with the aid even of a gentle heat, it becomes 

 blood-red. 



The pure dialurate forms minute prismatic crystals, which 

 are united together when dried in light bulky masses of a 

 faint silky lustre. I took advantage of the possession of a 

 large stock of this salt to repeat the analysis of it, determining 

 the nitrogen by the process of Varrentrapp and Will. Se- 

 veral analyses made by myself, and one made by Mr. Keller, 



