Siliceous Deposits from the Urine. 261' 



the tube. Nitrogen gas was now introduced from a capillary 

 pipe connected with a bladder of this gas into the tube, till the 

 whole of the mercury and the muriatic solution were expelled. 

 A longer tube being filled with and inverted over, mercury, 

 about two drachms of lime-water was passed into it, and rose 

 to the top of the quicksilver. The gas of the first tube was 

 now passed into the second : the lime-water became muddy, 

 and a diminution in volume succeeded from the absorption of 

 the carbonic acid, the nitrogen remaining behind*. The re- 

 cently formed carbonate being acted on by diluted hydrochloric 

 acid, dissolved again with effervescence. The muriatic solu- 

 tion being collected by a pipette, was precipitated by oxalate 

 of ammonia in the usual way, thus proving the composition 

 to be carbonic acid united to lime. 



The little nucleus which, it has been noticed, was placed in 

 a capsule and subjected to the action of nitric acid, next at- 

 tracted my attention. The capsule had been left at rest for 

 several days under a glass, and on examining it there was 

 found a very minute residue of an indistinctly crystalline ap- 

 pearance, but of high refractive density. The capsule was 

 heated and the acid boiled, but the boiling effected no solu- 

 tion. After subsidence, the acid was removed as carefully as 

 possible ; it was then evaporated till the whole of the acid was 

 driven off. The insoluble residue was now ignited by the 

 flame of the lamp enlivened by the blow-pipe directed upon 

 the mass in the capsule: it effectually resisted the heat, under- 

 going no alteration whatever ; but, on adding a little soda, it 

 melted with effervescence into a transparent convex button, 

 flattened at the bottom by the shape of the capsule, thus prov- 

 ing the siliceous character of the residue. 



Hence, then, it appears that, in this specimen of gravel, 

 there were distinct traces of silex in two separate fragments. 

 In the one, the silex was in a crystallized form and in- 

 termixed with carbonate of lime: in the other, it was in 

 an amorphous or pulverulent form, and mixed with lithic 

 acid combined with ah alkaline and earthy basef . If I had 



This was the most easy and ready process with so minute a quantity. 



f From the nitric solution carbonate of potass precipitated carbonate of lime in 

 large proportion, soluble with effervescence in hydrochloric acid, and reprecipitable 

 by oxalate of ammonia. 



