On the Oxydation of Tin and other Metals. 5 1 7 



degree of expofure to light. It is fufible by heat, and affumes the appearance of a muriate- 

 of filver, in which ftate Proufl propofcs to keep it. 



The fulphuric acid has no aftion on this fubftance, but the muriatic acid immediately dif- 

 folves it, and it cryftallizes in tetrahedrons. The nitric acid alfo diflblves it, during which 

 it pafll;s through various fliades of colour ; but at lad it retains the appearance of a folution 

 of nitrate of copper, in which the prefcncc of muriatic acid may be eafily detcdled. But the 

 difengagement of nitrous gas which 'takes place during the folution, proves that it is not 

 faturated with oxygen. 



Prouft, obferving that this muriate was without colour, and that it was alfo foluble in am- 

 moniac without colouring it, thought at firft that he might conclude, contrary to the prin- 

 ciple eftabliflied by Lavoifier, that the copper was abfolutely clear of oxygen ; but the ana- 

 lyfiS which he made foon undeceived him. 



He diffolved 100 grains of this white fufed muriate in very pure nitric acid, which he 

 afterwards precipitated by the nitrate of filver, and obtained 142 grains of muriate of filver, 

 which reprefent 24 4: grains of marine acid. On the other hand, 100 grains of very white 

 muriate of filver treated with nitric acid, and carbonate of pot-afh, afforded him 113 grains 

 of carbonate of copper, which, according to experiment, anfwer to 62-J, or 63 of copper, fo 

 that from his analyfis he found thefe produ£ts: — marine acid 24^; oxyde of tin i ; copper 63 j 

 and the i\\ deficiency remain for oxygen. 



Whereas he was fatisfied, that in the green muriate, in the fulphate, in the nitrate, and in 

 the acitite of copper, the metal which is at the maximum of oxygenation, contains about 26 

 of oxygen in the centenary. 



Laftly, it is proved that while the copper is oxyded no farther than 1 7 or 18, its folutions 

 are white, and it cannot then give colour either to its muriate, or to ammoniac. 



The following, as Proufb informs us, is another proof of the prefence of oxygen in this 

 white powder. If a fmall quantity be put into water with iron filings, the copper' foon fepa- 

 rates, and the iron becomes oxyded to the minimum, fo that when diflblved the alcalies pre- 

 cipitate it of a green colour. 



If it be demanded whence the oxygen comes in the white folution of copper in the muri- 

 atic acid, Prouft replies, that it is from the water. The water is decompofed, as Berthollet 

 had before fhewn. The oxygen combines, and oxydes the copper. Prouft even relates an 

 experiment in which the hydrogene of the water was rendered perceptible to the fmell, by 

 the affiftance of a fmall quantity of fulphur which was formed, and was diflblved and volati- 

 lized with the hydrogene. This experiment confifts in boiling the blue fulphate of copper 

 in muriatic acid. A folution is obtained, which is precipitated by water, during which the 

 hydrogene becomes perceptible to the fmell. 



When a green muriate is diftiiled, it may eafily be brought to the point of cryftallization j 

 but if the diftillation be carried further, it is. decompofed, and lofes the portion of oxygen, 

 which makes the difference between the oxyde containing 25 parts, and that containing only 

 1 8 ; but the diftillation then affords oxygenated muriatic gas. At length tliis gas ceafes, 

 and there remains at the bottom of the retort a grey, well-fufed mafc, which is the white 

 muriate of copper. This is an eafy method of procuring the white muriate. Prouft adds. 

 Vol. II— Feb. 1799. h, X that 



