276 Scientific Intelligence. 



of pyrol igneous acid and other volatile substances, given off by the 



process of charring. 



21. Reducing Copper Ores by Electricity, (London Mining Jour- 

 nal.) — Having published several communications on this subject, in- 

 quiring the nature of the process, and also descriptive particulars from 

 our respected correspondent, Mr. John Mitchell, of Napier's patent, we 

 now give the general particulars of the French invention, mentioned by 

 " J. H.'-' of Cornhill— that of MM. Dechaud and Gualtier de Claubry. 

 These gentlemen have long been engaged on the effect of weak elec- 

 trical currents on copper ores; and the following is an account ot the 

 results at which they had arrived before taking out their patent. The 



process consists of two operations — viz : roasting the ore, and the pre- 

 cipation of the copper. The roasting is effected in a reverberatory fur- 

 nace, either by the conversion of the sulphuret into sulphate by the ac- 

 tion of the air; or in the transformation of the oxyd of copper into sul- 

 phate, by calcining it with sulphate of iron, at a dull red heat in a cur- 

 rent of air — the iron being left in a state of peroxyd. Washing, then, 

 extracts the sulphate of copper — so that the most impure minerals will 

 afford copper equally pure with the carbonates or oxyds. In the precipi- 

 tation by galvanism, batteries would be far too costly ; and they have ob- 

 tained the same results without the use of exterior batteries. The prin- 

 ciple is as follows : — If two solutions are placed one over the other, one 

 of sulphate of copper very dense, and the other sulphate of iron less 

 dense, and in the first is placed a plate of copper, and in the second a 

 fragment of cast iron, and then these two metals are united by a conduc- 

 tor, the precipitation of copper commences at once, and is completed in 

 a long or short period, according to the temperature, the concentration ot 

 the liquids, and the extent of metallic surfaces — the state of the copper 

 becomes greatly changed as the liquor becomes weaker. To obviate 

 this, they take advantage of the following phenomena : After some min- 

 utes' action, there exist four strata in the liquids; at the bottom is a 

 dense solution of sulphate of copper, then a less dense solution of the 

 same salt ; next, a sulphate of iron, and on the surface a less dense so- 

 lution of the same. If, therefore, we arrange at the level of each o 

 these liquids, suitable apertures for the addition or removal of the liqui 

 they can be kept at a uniform state of density, and thus the copper is a 

 ways pure, and in the same physical condition. t , c 



For convenience, the liquids are now arranged in vertical, instea 

 horizontal, layers; they are then to be separated by a diaphragm ve y 

 permeable to electricity, but not to liquids — pasteboard answers per ec^ 

 ly well for this, and lasts for months. The apparatus is then arratl ^ c 

 as follows : A chest of wood, lined with lead or some suitable m as ' 



le solution of sulphate of iron; into this chest a numpe 



al- 



contains the 



cases are plunged, made of a frame having its ends and bottoms lor 

 of iron plates coated with lead, the sides being of pasteboard, 

 strong solution of sulphate of copper enters through a pipe near t 

 torn, and escapes in its weak state through an opening at the top ; in ^ ^ 

 case is placed a sheet of leaded iron, and between each are pa 

 cast-iron ; separate rods connect each plate with the common con ^ 

 which is supported over the apparatus, and the copper is P rec, P lta - f0fll e. 



both sides of the sheets of metal, the pasteboard preventing the I 



