Mr. J. Napier on Copper Smelting. 183 



Sulphurous acid in a dry atmosphere is not converted into 

 sulphuric acid by taking more oxygen from the air ; but when 

 moisture is present, small quantities are formed ; and in the pre- 

 sence of peroxide of iron the formation of sulphuric acid is rapid ; 

 hence at the early part of the calcination sulphates are abundant. 

 The peroxide of iron is convei'ted into the magnetic oxide, the acid 

 combining with a portion of the protoxide of iron, and the quan- 

 tity of sulphate of iron is always large before the heat of the 

 furnace becomes high, and often before any sulphate of copper 

 exists. When sulphate of iron is decomposed by the intensity 

 of the heat, there is always a simultaneous formation of sulphate 

 of copper, probably from a mere transfer of the acid, the iron 

 being converted into the state of peroxide. When the heat of 

 the furnace is too high for the existence of sulphate of iron, and 

 no moisture present, we nevertheless think that the oxygen of 

 the peroxide of iron converts the sulphurous acid into sul- 

 phuric acid, which simultaneously combines with the oxide of 

 copper. 



These experiments point to the conclusion, that to obtain rapid 

 and complete calcination, the stuff must be in powder, and sub- 

 jected to a free current of air with a regular and increasing heat, 

 and that it might be effected in not more than five or six hours. 

 Various plans have been proposed to effect such a rapid calcina- 

 tion, such as a jet of steam blown over the surface of the matters 

 calcining, and a current of hot air blown over the chamber by a 

 blast, &c. ; all have their merits as to the principle required, 

 but there are practical considerations that have to be borne in 

 mind in these applications. Whether calcining ore, coarse metal 

 or powder, a quantity of the stuff is in the state of fine dust, 

 which even under the mildest draft is carried away into the flue 

 or culvert, which must be avoided as much as possible. Every 

 attempt to increase the draft, either by more open fires, air-holes 

 or blast, is followed by a greater loss of calcining matters. We 

 have seen an increased draft lessen the time of calcination to 

 one half, but the increase in the loss of stuffwas more than com- 

 pensated for the saving of time ; so that improved drafts and 

 steam-jets or blast must be kept within certain limits, or accom- 

 panied with some invention to prevent escape of light particles, 

 which we believe within reach of practice. 



The following are analyses of stuff obtained from flues and 

 culverts leading from the calcining furnaces. 



The first is from the culvert leading from a coarse metal cal- 

 ciner : sample taken about 20 feet from the furnace. The sub- 

 stance was in the state of powder. 



