[ 175 ] 



XXVIII. On Copper Smelting. By James Napier, F,C.B,^ 



[Continued from p. 39.] 

 Calcination of the granulated coarse Metal. 



THE next operation is the calcination of the granulated 

 coarse metal ; this is done in the same manner as the cal- 

 cination of the ore, but the furnaces used are always single-bedded, 

 and measure inside about 21 feet in length and 14 feet in width. 

 The charge of metal covers the bottom of the hearth to the depth 

 of about 4 inches, making about 4 tons, and is put in through 

 the hoppers fitted upon the top of the furnace as described for 

 the ore. 



The coarse metal being easily fused, great care is required not 

 to raise the heat of the furnace too high, otherwise the metal 

 will cake, and by adhering to the bricks will prove prejudicial to 

 both the calcination and the furnace. When . the charge is let 

 into the furnace, it is slowly brought to a visible red, the fire is 

 gradually and cautiously increased until the metal acquires a 

 bright red heat, which should take about fourteen hours. This 

 temperature is continued until the charge has been altogether 

 twenty-four hours in the furnace, when it is let down through 

 the bottom into the cubs or vaults beneath. 



Fineness of granulation ensures a more perfect calcination, 

 a more extensive surface being exposed. As the heat requisite 

 to drive off the sulphur does not penetrate deep into the solid 

 granules, rendering the calcination of coarse metal tedious, the 

 mass is turned over by means of iron paddles every two hours 

 during the operation. At some works it is done every hour, 

 which we consider preferable ; but there is a far greater loss of 

 heat, owing to the doors of the furnace being kept longer open 

 in stirring every hour than every two hours, which neutralizes 

 the advantage of the extra turning over. 



After the charge has laid a little in the cubs a quantity of water 

 is thrown upon it, and it is then allowed to cool. The addition 

 of the water prevents dust, which flies ofi^ readily when dry, 

 causing loss ; and also effects a certain amount of oxidation, as a 

 great quantity of sulphuretted hydrogen is given off, the metal 

 assuming a black colour. When cold, the metal is removed from 

 the cubs to a heap, from which it is taken to the fusing furnaces. 



The chemical changes which take place during the calcination 

 of the coarse metal are somewhat similar to those described in 

 the case of the ore, but are not fully developed owing to the solid 

 state of the granules. That sulphates are formed, we have had 

 sufficient evidence by taking out small portions during the ope- 

 ration and testing ; but the quantities are small. 



* Communicated by the Author, who reserves to himself the copyright, 

 my infriugewejil; w^jereof will invpke legal procefdiugss,— Eps, 



