JRecovery of Gopper froin its Solution in Mine Drainage. 305 



The settling pits or hutches and the launders, where the inclina- 

 tion is slight, are cleared out about once a quarter, and the 

 copper precipitate so obtained is passed through a perforated 

 copper sieve, of about eight or ten holes per linear inch, the 

 small pieces of iron and scales of copper are retained on the sieve, 

 the latter being carefully picked out and added to the sifted pre- 

 cipitate. This, when it has properly settled in the sifting hutch 

 becomes a stiff mass, which is extracted and taken to the drying 

 kiln, when slabs of fire-clay or cast-iron are placed across flues 

 and heated from underneath, when the water is driven off and 

 the most of the copper converted to oxide, the greater the heat the 

 more effectually the latter is accomplished. At some mines the 

 precipitate is sundried, and in others it is packed in the raw 

 state, containing five or six per cent, of water, which keeps 

 the copper bright and fresh, and allows of its being barrelled 

 with little loss or injury. In either case, after packing in barrels, 

 the precipitate is despatched to Swansea. 



MeTnarJcs on this Method of Procedure. 



In practice the foregoing general method of procedure has 

 several serious objections, some of these it may be well to 

 point out as concisely as possible. 



As regards the disposition of the launders it has been found that, 

 with moderately rich copper solutions, very little inclination is 

 required ; in fact, that the less agitated the waters are, under 

 these circumstances, provided a steady continuous flow is main- 

 tained, the richer will be the resultant precipitate, which, at the 

 same time, will be more abundant for a given quantity of iron 

 consumed. When agitation takes place, not only is the con- 

 sumption of iron excessive, but owing to aeration of the water, 

 oxidation of the iron salts takes place and ochre is deposited, 

 which, covering the metals, prevents the further action of the 

 copper solution upon them. 



Eegarding the cleansing of the metals, in some mines they are 

 brushed twice in twelve hours, being violently agitated with 

 rakes and vigorously scrubbed with the brooms ; as a consequence, 

 the softer parts of the iron and graphite are carried away with 

 the copper to the settling hutch, when, not only do they largely 

 contaminate the precipitate but are also rendered useless for 

 precipitating a further quantity of copper, as, being buried in 



