TRANSACTIONS OF SECTION B. 545 



are now profitably treated, all the metals being extracted in a marketable foi*m, 

 including zinc, which was previously entirely lost whenever the working of such 

 ores was attempted. 



The process is briefly the following : The ore, ha-ving been ground, is calcined 

 in a muffle furnace, so as to convert the sidphides of the various metals into sul- 

 phates and oxides. The sidphurous acid produced in this operation is conveyed to 

 leaden chambers for conversion to sulphuric acid in the usual manner. The cal- 

 cined ore is then agitated with weak sulphuric acid, which dissolves the zinc and 

 most of the copper, while all the lead, silver, and gold remain undissolved in the 

 residue. Sufficient hydrochloric acid is generally present in the sidphuric acid to 

 convert all the sulphated silver into insoluble chloride. Separation of the zinc 

 being then effected by lixiviation, the insoluble portion is smelted for the extrac- 

 tion of its metals in the usual way. The sulpliate of zinc liquor thus obtained 

 contains very little iron, provided the ore had been calcined sufficiently to convert 

 all the iron to peroxide. All the copper contained in the liquor is next 

 precipitated by metallic iron or zinc, after which tlie liquor is concentrated by 

 evaporation and mixed, when it begins to thicken, with a small quantity of finely 

 ground blende (1 eq. of sidphide of zinc to 3 eqs. of sulphate of zinc). After 

 further desiccation this mixture is heated to redness in a muffle furnace when 

 the sulphide and sidphate by mutual reaction become changed to oxide of zinc 

 and sulphurous acid gas (3 ZnSO^ + ZnS = 4ZnO and 4SO2). The former is in 

 a condition well adapted for the manufacture of spelter by distillation in the 

 usual way ; the latter is conveyed to leaden chambers for reproduction of sulphuric 

 acid. 



The conversion of sulphate of zinc into oxide of zinc may be effected by other- 

 reducing agents than blende. Coal and charcoal may be used for that purpose, 

 but as the sulphurous acid is then mixed with carbonic acid, it is not so well 

 adapted for conversion to sidphuric acid in the chamber process, as the gas de- 

 rived from the mixture of sidphate of zinc with blende. 



The operations here described are now being extensively carried on at the 

 works of the Swansea Zinc Ore Company, near Swansea. 



Another sulphate which is easily convertible into oxide in an analogous manner 

 is that of magnesia. Pure wood charcoal should be used as the reducing agent, 

 and the mixture heated to dull redness. The magnesia thus prepared corresponds 

 in density to the variety known as ' hea%^ ' calcined magnesia. 



8. On a New Process for the Production., from Aluminous Minerals contain- 

 ing Iron, of Sulphate of Alumina free from Iron. By J. W. Kynaston, 

 F.C.8., FJ.G. 



In this paper the author gives an account of an investigation undertaken for 

 the purpose of devising a means for the production, on a large scale, of sulphate 

 of alumina so pure that it may be used in the arts for all purposes for which pure 

 soluble alumina is required, and so to prevent the loss of the large quantities of 

 potassa or ammonia and sulphiu-ic acid requii-ed in the manufacture of the crys- 

 tallised alums. 



He gives a historical statement of the methods in actual use to produce alum 

 substitutes, and of the attempts that have been made to utilise for this purpose the 

 newly-discovered rich aluminous mineral. Bauxite. The great difficidty in the 

 production of pure alumina salts from this mineral arises from the presence in the 

 ore of a comparatively large proportion of peroxide and some protoxide of iron, 

 which dissolves with the alumina when the ore is attacked with acids. 



The author states that he has found that a solution of oxalic acid possesses the 

 power of dissolving the oxides of iron contained in Bauxite without materially 

 attacking the alumina, and gives in detail the mode of carrying out the operations, 

 together with the process adopted for recovering the oxalic acid employed for re- 

 peated use for the same purpose. He then states the difficidties in the practical 

 working of any process of purifying Bauxite from iron which involves the repeated 



1880. N N 



