Chemical Science. 405 



the study of a skilful analysis ; it is matter of regret therefore that 

 Mr. Cooper has not given the details of his experiments on the 

 brown mamillated blende, which is the subject of his communi- 

 cation. 



9. Preparation of Nitrate of Silver. — M. Brandenbourg has 

 an economical method of separating silver from copper, in the 

 preparation of nitrate of silver from the alloys of silver. He 

 dissolves the alloy in nitric acid, and having evaporated the ni- 

 trates to dryness, places them in an iron spoon, and fuses them 

 until ebullition ceases. The fused mass is then poured on an 

 oiled slab. A small portion of it is tested for copper, by solution 

 in water, filtration, and ammonia. If it is found, by the blue tint, 

 still to contain copper, the fusion is continued a few seconds 

 longer. The mass is now a mixture of nitrate of silver and black 

 oxide of copper. It is to be dissolved in water, filtered, evapo- 

 rated, and crystallized, and the pure nitrate of silver is ob- 

 tained. 



10. Urate of Ammonia Calculi. — -Dr. Prout has met with one 

 of those rare calculi which are formed of the urate of ammonia. 

 It weighed, when entire, about 50 grains. Its general shape 

 was ovoid, a little flattened, its external surface was smooth, 

 and of a greenish clay colour. It was composed of thin concen- 

 tric layers, easily separable from one another, and readily break- 

 ing into sharp angular pieces, with a compact earthy fracture. 

 Its general colour internally differed, both in shade and inten- 

 sity, from that of its external surface ; it might be denominated 

 a pale reddish clay colour. The different layers differed, how- 

 ever, somewhat in intensity, which caused the laminated struc- 

 ture to be visible to the eye. Between some of the layers also 

 there were minute depositions of the earthy phosphates, whicli 

 rendered the structure still more visible. The nucleus exhi- 

 bited the same general appearance as the rest of the calculus, 

 except that it appeared to be made up of a fine powder, and a 

 few larger grains loosely agglutinated together. It was spar- 

 ingly soluble in cold water, but it dissolved readily iu boiling 



