Mr. J. Napier on Copper Smelting. 457 



Here there is more iron than is requisite to fuse the silica ; but 

 were this ore put into a fusing-furnace it could not be melted ; the 

 iron, copper^ and sulphur would fuse together^ leaving the unfused 

 silica or quartz mixed up with it, forming an agglomeration, as 

 silica will not combine with sulphurets of metals. In the combi- 

 nation of matters in fusion we have often to be guided by the cir- 

 cumstances regulating affinity, as for example, — 



Iron requires a heat of about 3000° F. to melt it, 

 Copper ... 1900 



Sulphur is separated from these metals at a temperature of about 

 700° or 800°; but at a temperature of about 1200° the sulphur 

 and these metals melt together, and their affinity for each other 

 at this heat is increased. Oxide of iron and quartz combine and 

 fuse at about 1800°. Bearing these conditions and relations in 

 mind, it will be obvious that calcination is a primary and essen- 

 tial operation, the object of which is twofold. The ore contains 

 a great quantity of silica that must be got rid of by fusion ; the 

 best means for doing so is by oxide of iron. The ore contains 

 sufficient iron to effect this, which must also be got rid of; but 

 the sulphur both retains and prevents it from combining with 

 the silica ; hence the operation of calcination is to drive away the 

 sulphur and oxidate the iron, which is effected by exposing the 

 ore to a temperature of from 700° to 1200°, so that the sulphur 

 is separated from the metals and sublimed. It is evident, there- 

 fore, that in mixing the ores for smelting, it is as necessary to 

 mix them in relation to the iron they contain as to the earths. 



Other circumstances have to be considered in mixing ores, 

 namelj', the presence of metals that would be injurious to the 

 copper if not removed. These are generally tin, antimony and 

 arsenic ; the latter does not deteriorate copper much, but it mate- 

 rially affects the operations of calcination and fusion. Arsenic 

 has a peculiaji' property over other metals in not having any fluid 

 range; it remains solid until heated to about 3o6° F., when it 

 passes off in a gaseous state, absorbing and carrying along with 

 it a great quantity of heat which retards the operation of calci- 

 nation ; so that ores containing much arsenic should be sparingly 

 mixed with other ores ; or what is preferable, should be treated 

 separately in the calcining operation, and mixed with other ores 

 afterwards. A large admixture of highly arscnious ores is a great 

 drawback to the fusion, if the greater portion of the arsenic be 

 not previously driven off. We have known an extra expense of at 

 least £20 per week for time, fuel and flux, to have been incurred 

 during the smelting of a few hundred tons of ores containing 

 much arsenic, under the impression that they were stiff and re- 

 quired flux, when an analysis would have shown that fluxes were 



