Chemical Science, 155 



the tank is sank partly into the ground, and it is upon its internal 

 surface, and always where two staves meet, that the mushrooms 

 of metallic copper form ; tliey appear as small masses, enlarge by 

 degrees, and ultimately are of considerable size ; one weighed 

 75 grammes (1158 grains). 



When detached from the wood, they are found on one side to 

 be marked by the stries of the wood, whilst the other surface is 

 mamillated, and present%ery small, but brilliant crystalline facets. 

 They are formed, in consequence of the presence of sulphate of 

 protoxide of copper, in solution, which, in passing to the state of 

 per-sulphate, deposits one portion of copper in the metallic state, 

 Avhilst the other is peroxidized. The effect does not require access 

 of air. M. Clement was particularly struck with the cohesion 

 acquired by the copper thus vprecipitated from a solution ; it was 

 such as to allow of the metal being forged at common temperatures, 

 and being reduced to thin leaves. Its specific gravity, also, was 

 8.78 being equal to that of fused copper. When filed, the 

 surface produced was as brilliant and as close as that of an ingot 

 of common copper. — Ann. de Chim. xxvii. 440. 



At some of the Anglesea copper-mines,' the solution of sulphate 

 of copper pumped up by the engines is decomposed by the intro- 

 duction of iron, and the copper is precipitated. Jt frequently 

 happens there, that the circumstances are such as to produce 

 copper as compact and dense as fused copper, and there is no 

 difficulty in selecting such specimens from the pits in which the 

 precipitation is usually performed. — Ed. 



14. Ammoniacal Chromate of Copper. — M. Vuaflart has observed, 

 that chromate of copper prepared by precipitating sulphate of cop- 

 per by chromate of potash, and which is of a reddish brown colour, 

 is soluble in diluted ammonia, producing a clear solution of a 

 beautiful and deep green colour. When the solution is evapo- 

 rated, the reddisli chromate of copper appears as the ammonia 

 flies off. 



This solution was made for the purpose of decorating the front 

 of a druggist's shop. The green is finer than most of those ob- 

 tained in the usual manner, and undergoes no change by length 

 of time or exposure to bright light. It is readily prepared by 

 adding solution of chromate of potash to ammoniacal sulphate of 

 copper. — Joiir. de Phar. 1824. p. 607. 



15. Artificial Crystals of Chromate of Lead. — A diluted solution of 

 nitrate of lead being added to a very alkaline solution of chromate 

 of potash, and left at rest for some time ; there was found in the 

 mixed solution small red crystals, which, upon examination, proved 

 to resemble, in all their characters, the native chromate of lead 

 from Siberia. — M. F. 



