546 REPOBT — 1880. 



"washing of the ore, and goes on to describe some reactions which permit of the 

 separation of dissolved iron from aluminous solutions. 



In a solution of alumina obtained by treating Bauxite with sulphuric acid, 

 there is contained iron to the extent of 0'80 to I'OO per cent., about three-fourths 

 of which exists as peroxide and the remaining one-fourth as protoxide. The iron 

 existing as peroxide is rendered insoluble, and precipitated from the solution by 

 converting it into arsenite by the addition of arsenious acid, and then, by means 

 of carbonate of lime, neutralising any free acid, and at the same time producing 

 in the solution a little tetrabasic sidpliate of aliunina. Under such circumstances, 

 the whole of the iron existing as peroxide falls out of the solution. 



The remaining ferrous iron is then removed by the addition of ferrocyanide of 

 calcium, a reaction which, though so well known, has not hitherto been successfidly 

 appUed for the purpose, hj reason of the difficidty of separating the impalpable 

 precipitate of Prussian blue from the solution. 



The author has found that the addition to the blue mixture of a mere trace of 

 either the sulphate of copper or of zinc, induces an aggregation of the previously 

 imponderable particles of Prussian blue, which then rapidly fall out of the solution. 

 This precipitate is collected and washed, and by treatment with lime the ferro- 

 cyanide of calcium is regenerated and again used to remove more iron. 



The solution of sulphate of alumina now freed from iron is lastly treated with 

 sulphide of calciiun to remove the excess of arsenic, and then boiled down until of 

 such a density that it solidifies on cooling. The residt is a sulphate of alumina, 

 neutral, practicall}^ free from iron, and containing about 16 per cent, of alumina, 

 as compared with 10'83 per cent, contained in the ordinary crystallised potash 

 alum. 



A description is then given of tlie mode of cari-ying out these reactions in the 

 actual process of manufacture as carried on at St. Helens, and, finally, attention is 

 drawn to the probabilitj' of an extensive consumption of sulphate of alumina, in 

 the future, in the process of refining beetroot sugar. A large quantity of potash is 

 contained in sugar from this source, and it prevents the crystallisation of much of the 

 sugar. It has been known for some jears that by means of sidphate of alumina 

 potash might be removed from the syrup, but the process has not been extensively 

 adopted by reason of the difficulty of obtaining sulphate of alimiina sufficiently 

 pure for the purpose. 



9. Oh a New Process for separating Silver from Copper contained in 

 Copper Ores and Begnluses. By "William Henderson. 



The latest literature on this subject seems to award the palm of accuracy and 

 cheapness to Zeir-vogel, who proposes by calcidation of reguluses to form in the 

 first place sulphates of iron and copper which are gradually decomposed by further 

 calcination into the state of oxides, lea\"ing argentic sulphate, which stands a much 

 higher temperature undecomposed, and wliich is soluble in pure water. 



The difficulty always remains, in calcining reguluses or ores, to do it in such a 

 way as to convert the whole of the silver into sulphates. To ensure the result 

 with certainty I have called in the aid of a bisulphate, and I have taken bisulphate 

 of soda as the cheapest and as carrying a large proportion of available sidphuric 

 acid. The theory of the process is, that bisidphate of soda cannot be reduced to 

 sulphate by simple fusion, but parts with its second equivalent of sulphuric acid to 

 several metals at a comparatively low temperature. I thus ensure at once, and 

 early in the process, sufficient imprisoned sulphuric acid to make sure that the 

 whole of the .silver will be converted into sulphate at the end of the process after 

 the other metallic sulphates are decomposed. 



If the reguluses are comparatively free from arsenic and antimony the bi- 

 .sulphate may be at once mixed ^^'it'\l them, and the calcination proceed at once, as 

 in the Zeir-vogel process. 



For several years I have again and again taken up this subject viathout suc- 

 cessful results ; at aU events the results were, as a rule, imperfect and no improve- 

 ment upon those at present in use. In the early part of 1879 my attention was 



