116 president's address— section b. 



ditions, does not present very strong attractions from the point of 

 view of efficiency since tlie days of Bessemer, wlien he demonstrated 

 the perfect action of a thin column of blast forced through a bath of 

 molten material, with portion of which it may combine. Nor does 

 the necessity of a certain amount of separate firing, which these innova- 

 tions impose, commend itself to modern demands on pneumatic self- 

 smelting processes. 



However, to round off this review of medium- forced oxidation 

 methods, and as a pendant to the more genuine pneumatic type from 

 a direction in which the latter has failed through excessive metal 

 losses, a brief statement of the most important of these methods which 

 have been used may be in order. The observation that a blast is 

 more efficacious in purifying very dirty, leady, arsenical, or antimonial 

 mattes than oft-repeated calcinations is centuries old. The work was 

 done in high-roofed, square (latterly circular), reverberatory furnaces, 

 with a hearth of about 100 square feet in size, fired on the long side, 

 and the blast was strong and copious for the historical period impli- 

 cated. Modernised examples of about 40 years ago are the following.(?) 

 At St. Andreasberg, in the Hartz Mountains, leady matte from the 

 matte concentration operation (fourth smelting), was subjected, in 2-ton 

 charges, to an air-blast oxidising smelting for eight to 10 hours, skimmed 

 and tapped. A small amount of metallic lead liquated out. The 

 partly purified matte product was sent through a low blast-furnace 

 with leady materials to effect a desilverisation and a further purifica- 

 tion of the copper, portion of the antimony and arsenic joining the 

 resultant lead-bullion. The matte was then repeated in the rever- 

 beratory furnace in charges of 2J tons, with a blast pressure of 20ozs., 

 and an air consumption of 25-5 cubic feet per minute ; this 

 second exposure lasting 12 to 16 hours, and resulting in slags, lead- 

 bullion, and lOcwts. to 16cwts. of matte, carrying 20 per cent, to 25 

 per cent, copper, and deprived of an essential proportion of the worst 

 impurities. The further concentration and refining of this matte was 

 conducted in the ordinary way. At Altenau, in the same district, 

 desilverised coppers, with about 76 per cent, copper and 24 per cent. 

 lead, from the liquation process, were treated in a similar furnace in 

 charges of 40cwts. to 44cwts. at a time, under a strong blast, the 

 exposure lasting about 20 hours, and yielding a slag with 61 per cent, 

 lead and an improved copper product, which was then further refined 

 into black copper under a blast. In fact, the oxidising smelting of 

 copper middle-products with a strong blast was an important link in 

 the lengthy chain of operations practised in the olden days. 



Examples of modern applications of a medium-forced oxidation 

 are those at Oker, in the Hartz Mountains district, and at Brixlegg, 

 in the Tyrol. They represent the nearest approximations to actual 

 Bessemerising which present-day metallurgists can devise for the 

 treatment of difficult materials, which, possibly, are permanently 

 beyond the pale of more energetic pneumatic work. At Oker.(m) 



{I) Kerl, " Obei'harzer Hiittenprocesse," Clausthal, 1860. 

 (m) Huhn, Gliickauf, 1905, vol. XLI., No. 37. 



