220 THE CANADIAN NATURALIST. [June 



2. Closely allied to this process is the one still followed at Fol- 

 dal in Narway, where an artificial oxidation takes the place of the 

 natural oxidation of similar ores. They are roasted in heaps, and 

 then lixiviated. 



3. At Stadtbergen in Westphalia, and at Linz on the Rhine, the 

 vapors evolved in roasting various sulphurets are brought into con- 

 tact with poor ores containing malachite, and with oxidized ores 

 containing cupric oxide. After these have been acted on for sev- 

 eral weeks, they are lixiviated in the usual manner. 



4. Dilute muriatic and sulphuric acids, hyposulphite of soda, 

 and even ammonia, have been proposed and occasionally used for 

 dissolving out the copper of oxidized ores. 



5. Much resembling the process mentioned under 2, is the 

 method in which the oxidation is performed by calcining in rever- 

 beratory furnaces. At various Russian smelting works and in 

 Mansfeldt this process is applied, but in no case does the extrac- 

 tion appear to be at all complete. A large quantity of the copper 

 is removed in the soluble form, l»ut fully as much remains in the 

 residue, which is subject to further metallurgical treatment. 



6. The first stage of Bankart's process is the same as the fore- 

 going ones. Rich Cuban sulphurets are first calcined by them- 

 selves in reverberatory furnaces, and then lixiviated ; the residues 

 are mixed with a fresh portion of raw ore and again calcined. 

 The peroxide of iron contained in the calcined ore causes the con- 

 version into sulphuric acid of a portion of sulphur which would 

 otherwise escape as sulphurous acid. The additional amount of 

 sulphuric acid thus formed contributes of course to rendering the 

 copper soluble. This principle is doubtless correct, but there 

 appear to have been other circumstances which interfered with the 

 practical application of the process. 



7. Longmaid calcines pyritous ores with common salt, and then 

 lixiviates. In his process there is doubtless a larger amount of 

 copper rendered soluble than when the sulphurets are calcined 

 alone ; but the residues, even when abundance of sulphur is present, 

 are far from being free from copper. The process which I have 

 adopted in the experiments about to be described may be said 

 to be a combination of the two last mentioned methods,— Bank- 

 art's and Longmaid's. 



8. Henderson's process differs from Longmaid's merely in this 

 particular, that the calcination is performed at such a temperature 

 as to cause the volatilization of the copper in the form of a sub- 



