318 Scientific Proceedings, Royal Dublin Society. 



surface.* Spongey iron has been strongly recommended {Bischof 

 Aas, &c.) It may be prepared from the roasted residues after 

 lixiviating, or directly from pyrites ; much impurit}^ however, is 

 often introduced by it,+ but it might be very advantageously ap- 

 plied for weak liquors. 



Heating the liquors has been found very advantageous in 

 accelerating the precipitation ; it is usually effected by a steam 

 jet, at Oker-Hiitte the copper is all precipitated in two or three 

 hours, the precipitate containing 77'55 per cent, of copper and O'lO 

 of silver. 



Sulphuretted Hydrogen. — The application of sulphuretted 

 hydrogen for precipitating the copper is attended with the very 

 serious objection that a very bulky precipitation is produced in a 

 moist state generally requiring a filter-press. The presence of 

 free acid is necessary in the solution, and for this reason, but more 

 especially on account of the large volume of water to be treated, 

 this precipitant seems ill adapted for treating mine drainage. We 

 may, however, notice some of the methods proposed for its pre- 

 paration, as it may be applied when iron is too costly. 



At Foldal, Norway, where metal is expensive, Sinding prepared 

 sulphuretted hydrogen by distilling fuels yielding hydrocarbons, 

 and passing these over red hot pyrites when sulphuretted hydro- 

 gen is produced, and finely divided carbon deposited. 



At the Bede Metal Works, Jarrow-on-Tyne, sulphuretted 

 hydrogen was prepared from sulphate of soda (recovered, by 

 evaporation, from the lixivium after the copper had been ex- 



* If the tin be left on the plates half of it remains, as thin scales, -which are separated 

 on sifting the precipitate, leaving about 1"5 per cent, tin in the precipitate ; this hardens 

 the copper produced from it subsequently, and lowers the value of the precipitate. 



The removal of the tin from the tin plate cuttings was effected at Alderbj' Edge by- 

 treating them with caustic soda. A process has been patented by Mr. E. A. Parnell to 

 effect the same ; this consists in treating the cuttings with a solution of black ash (sul- 

 phide of soda), and about three per cent, of sulphur. This heated and concentrated to 

 25° Twaddle removes the tin almost immediately in solution, from which it is recovered as 

 oxide on calcining, the sulphide of soda being converted to sulphate, is removed on 

 -washing and crystallized out as glauber salts. The cuttings contain a small quantity of 

 tin re-ndering the iron very brittle when worked up into blooms or bars, but this may be 

 completely removed by a solution of calcic chloride. 



t If the ochre were recovered from solution after the removal of the copper, a very pure 

 form of this reagent might be obtained. 



