320 Scientific Proceedings, Royal Dublin Society. 



coherent form, while the iron in the cell passes into solution; when 

 the sulphate of iron solution becomes too concentrated it is 

 diluted and fresh iron added. The copper deposited is the exact 

 equivalent for the iron dissolved, viz., 63'5 copper for 56 of iron. 

 The cost of extraction is about one cent, per pound. 



Dynamo-electricity has been tried at Ocker in Germany, where 

 a Siemens- Alteneck machine supplies the current to ten or twelve 

 precipitatino' cells, which deposit about fifty pounds of copper in 

 twenty-four hours, that contains only about O'o per cent, of 

 impurity. (See note added in press.) 



The liquors from which the copper has been extracted generally 

 contain large quantities of sulphates of iron and alumina, besides 

 small quantities of zinc and manganese. Much of the iron, present 

 as ferrous sulphate, separates out by natural oxidation if the 

 solution is exposed for a time with constant agitation, basic salts 

 being deposited and the acid liberated. ( Wagner). 



Cementation at Agordo. 



At Agordo,* the copper solution is obtained from a poor pyrites 

 containing one and a-half per cent, of copper, which is first sub- 

 jected to a process of kernal roasting, which results in the forma- 

 tion of a rich kernal of sulphide of copper, containing from twenty 

 to fifty per cent, of copper, surrounded by an envelope of oxides 

 and sulphates of iron and copper ; this is broken ofi", the kernals 

 are smelted for copper, but the shells are treated with water, the 

 lixivium run to the precipitating vats containing cast-iron, heat 

 is applied for the double purpose of concentrating the liquors and 

 accelerating the precipitation, this is effected in two different 

 forms of arrangement, the one is a large wooden vat containing a 

 leaden vessel (" chambre de plomb "), in which a fire is lighted ; 

 the other is an ordinary re verberatory furnace, the bed of which is 

 converted into the precipitating tank, the flame passing along 

 the surface of the liquors. 



Cast-iron is piled in these vessels and the liquors run in, heat 

 is then applied, and the temperature maintained at 62° or 63° C. 



* For detaHs of these workings, see " Annales des Mines," 1855, 5th Series, Vol. viii,, 

 pp. 407-498. " Annales des l\Iines," 1876, 7ih Series, Vol. ix., pp. 190-200- 



