Mr. J. Napier on Copper Smelting. 



179 



We observe in the above table the same kind of reaction as 

 was noticed in the calcination of the ore^-a sudden evolution of 

 sulphur, and then a gradual absorption continuing for several 

 hours. The change of sulphates into sulphurets, and again into 

 sulphates, &c., is also worthy of remark ; and this action takes 

 place to a certain extent even in the lowest bed. The peroxide of 

 iron at one time gives off a portion of its oxygen and is con- 

 verted into the magnetic oxide, as we have often ascertained ; at 

 other times it takes up oxygen and is converted into the red 

 oxide. We have repeatedly found that, in the samples taken out 

 when the testing showed the decomposition of the sulphates into 

 sulphurets, the powder was full of granules, which when broken 

 had a vitreous appearance, and a yellow bronze colour resem- 

 bling rich copper pyrites. 



The next table shows the changes and reactions in the powder 

 when calcined in a three-bed calciner, the fire entering directly 

 into each bed, as described for the ore at page 46'^ of the last 

 volume ; so that the fumes from the one bed do not pass over the 

 other, in order to avoid the sulphur in the fumes from the lower 

 beds being absorbed by the powder in the upper beds. 



