400 SILVER COINS. 



Clean polished Almost the whole of the copper may be precipitated from 

 tates'ahnostall '^^ solutions by means of a plate of iron, provided the iron 

 the copper, &c. be well polished and pure. If it be rough, a portion of the 

 copper get? into the interstices, and cannot be separated. I 

 dissolved 50 grains of pure granular copper (sp. gr. 8.6233) 

 in sulphuric acid, evaporated to dryness, redissolved in water, 

 and put into the solution a polished plate of iron. The 

 copper precipitated weighed 49-5 gr., not reckoning a little 

 which adhered to one side of the iron plate. Here the loss 

 was only 1 per cent. 100 grains of copper dissolved in mu- 

 riatic acid, were recovered with rather less loss ; but when I 

 employed a rough plate of iron, there was a loss of more than 

 6 per cent. ; for 68 grains of copper, dissolved in muriatic acid, 

 gave only 65.43 grains. 



When copper is held in solution by nitric acid, it is thrown 

 down partly in the metallic state, and partly oxidized. If 

 mujiatic acid be poured upon the precipitate, the whole is dis- 

 solved almost immediately, and converted into colourless mu- 

 riate of copper. But if common salt be poured into the nitric 

 acid solution, and the whole be evaporated to dryness, to dis- 

 sipate any excess of acid, and redissolved in water, acidulated, 

 if necessary, with muriatic acid, then iron throws down the 

 copper in the metallic state. 



I did not succeed so well in my attempts to precipitate cop- 

 per by means of a cylinder of zinc. That metal usually be- 

 came porous, and it was difficult to separate the c(ipper from 

 it. Besides, part of the copper was thrown down in the state 

 of an alloy, for it effervesced when washed with muriatic acid. 

 Curious fact. A curious phenomenon repeatedly occured when diluted muri- 

 atic acid was poured upon copper precipitated in this manner 

 by zinc. The effervescence w£ts sudden and strong, and the gas 

 separated was 7iitrovs gas, as became evident by the red fumes 

 generated. 



The specific gravity of the fine powder of copper separated 

 from acid solutions by iron, I found only 7.056 in the tempe- 

 rature of 63° ; but, by simply fusing it with black flax, the spe- 

 cific gravity became 8.535. 

 Coins which Sect. II. — The follov.'iiig Table exhibits a list of the different 

 were analysed, ^^^^^ which I have analysed, placed in the order of analysis; 

 together with the products obtained. 



An 



