Improvements in Science. 445 



solution ; quite colourless in a dilute solution, the copper 

 being wholly thrown down. A solution of acetate of 

 copper becomes pale coloured, and gradually becomes a 

 whitish powder by the action of phosphorus. This powder 

 is phosphate of copper, which is not re-dissolved by the 

 free acetic acid.''^ 



Reduction of Mercurial Salts by Copper. — If we plunge a 

 plate of polished copper into an aqueous solution of corro- 

 sive sublimate, the copper becomes blackish gray, the 

 solution milky, and shortly afterwards a white powder is 

 deposited, which is sub-chloride of mercury, or calomel 

 mixed with some globules of mercury. This was observed 

 by Fischer of Breslaw. But Vogel has since noticed, that 

 the copper plate, instead of presenting a silvery appearance, 

 is covered with a black layer destitute of all metallic lustre. 

 He left a plate of copper for 24 hours in a concentrated 

 solution of corrosive sublimate ; the liquid had become 

 green, and a quantity of calomel had been formed which 

 rendered the liquid milky; the greater part was, however, 

 deposited at the bottom of the vessel. The surface of the 

 copper was covered with a very thin black coating, and 

 with small globules of mercury which did not adhere, but 

 fell on the slightest touch. The plate of copper was washed 

 with water and dried. The black layer adhered so strongly 

 to the copper, that it was difficult to remove it by friction 

 with paper. This black matter dissolved in muriatic acid 

 without effervescence, and the liquid decanted from the 

 copper contained deuto-chloride of copper, in which some 

 flocks of calomel were observed to swim. The copper, 

 after digestion in the acid, was white, and acquired the 

 lustre of mercury by friction. Solutions of sublimate in 

 alcohol and ether, act upon copper in the same way. 

 Calomel, though almost insoluble in water, may be de- 

 composed by copper. If, when suspended in water, a plate 

 of copper be immersed in the liquid, copper soon begins to 

 be dissolved, and the plate becomes black. The decom- 

 position of calomel is still more rapid, if the water in 

 which it is suspended be kept in a boiling state. The 

 copper is soon covered with a black coating, beneath which 

 there is a metallic layer. 



• Phann. Central blatt, Oct., 18S6, p. 628. 



2 G 2 



