XANTHIC OR URIC OXIDE. 103 



SECTION I. OF XANTHIC OR URIC OXIDE. 



Dr Marcet gave the name of xanthic oxide to the constituent 

 portion of a small calculus, which Dr Babington having receiv- 

 ed from one of his patients gave to Marcet for examination. Its 

 texture was compact, hard, and laminated. The surface was 

 smooth, and it had a reddish cinnamon colour, which was much 

 heightened by adding caustic alkali to the calculus in powder. 

 Before the blow-pipe, it crackled, split in pieces, became black, 

 and was ultimately consumed, leaving only a minute particle of 

 wliite ash. The smell which it emitted was that of an animal 

 substance, and was peculiar, though feeble and not easily defined. 



When exposed to destructive distillation, it crackled, split into 

 scaly fragments, blackened, and emitted a fetid ammoniacal li- 

 quor, from which carbonate of ammonia crystallized, leaving a 

 heavy yellowish oil. 



When reduced to an impalpable powder, the greatest part of 

 it dissolved in boiling water, and the solution reddened litmus pa- 

 per. When the liquid was allowed to cool, it became covered 

 with a white flocculent film, which gradually subsided and con- 

 stituted a white crust. 



Caustic potash dissolved this calculus very readily, and the so- 

 lution was precipitated by acetic acid, provided the acid was not 

 added in great excess. The mineral acids also dissolved it, though 

 not nearly so readily as the alkalies. Concentrated sulphuric 

 acid did not blacken it 



When the solution of the calculus in nitric acid was evaporat- 

 ed to dryness, the residue assumed a bright lemon colour. This 

 yellow residue was partly soluble in water, to which it commu- 

 nicated its colour. The addition of an acid destroyed the yel- 

 low colour, but caustic potash turned it red, and upon evapora- 

 tion, it assumed a brilliant crimson hue. This colour disappear- 

 ed on adding water, the yellow tint being reproduced, while the 

 liquid remained transparent. The previous action of nitric acid 

 is necessary for these changes of colour : for if potash be added 

 to the pure xanthie oxide, no change of colour takes place. 



Xanthic oxide is insoluble in alcohol and ether, very sparing- 

 ly soluble in acetic, and not at all in oxalic acid. It is insoluble 

 in bicarbonate of potash and bicarbonate of ammonia.* 



Such are the properties of this uncommon substance as deter- 



* Marcel's Essay on Calculous Disorders, p. 96. 



