458 Mr. J. Napier on Copper Smelting. 



not required. But move money is spent in a year uselessly in the 

 copper- works tlian would pay the salary of an efficient chemist, 

 who could define the character of every ore before mixing, besides 

 making other necessary inquiries which would be useful. 



The mixture of ores being selected according to the rule 

 adopted by the manager, it is carried to the large hoppers 

 on the top of the calcining fm-nace and then let down into the 

 hearth, where, after diying a little, it is spread equally over the 

 bottom, covering it to a depth of from six to eight inches. The 

 quantity of ore put in varies, according to the size of the furnace, 

 from three tons to six tons. The fire of the furnace is kept low at 

 first ; after two or three hours the ore on the surface becomes 

 visibly red, the heat is gradually increased to a yellow red ; but 

 this heat only penetrates to the depth of about an inch, conse- 

 quently the ore has to be stirred and turned over by means of long 

 ii'ou paddles every hour, so as to expose a new siu'face to the action 

 of the air and fire. This calcination lasts generally nine hom's ; 

 but when ores are known to be stifi^, containing much silica and 

 sulphm'et of iron, twelve hours are allowed. The following 

 changes and chemical actions take place : the sulphur is partly 

 burned ofi" by combining with oxygen and forming sulphurous 

 and sulphm-ic acids, and partly volatilized as sulphur uncom- 

 bined ; arsenic is volatilized either as metal or oxide ; the copper 

 and iron lose sulphur and combine with oxygen, which changes 

 are subject to variations according to circumstances occurring in 

 the operation. 



In order to judge of the time necessaiy to calcine an ore, 

 the nature and richness of the mat or coarse metal it will pro- 

 duce when fused has to be considered; and this does not depend 

 upon the richness of the ore in copper Avhen it goes into the 

 calciner, but upon the quantity of sulphur and ii-on it contains. 

 For instance, if we take the following ore and fuse it, adding 

 flux to combine w'ith the silica, — 



Copper . . 22 



Iron 31 



Sulphur ... 32 



Silica .... 15 



100 

 we should obtain a coarse metal or mat haxdng only 26 per cent, 

 of copper ; and if we take another ore, having the following com- 

 position, — 



Copper . . . . 11-2 



Iron 18-4 



Sulphur .... 12-4 



Silica .... 58-0 



1000 



