Mr. J. Napier on Copper Smelting. 347 



operation. We have seen moss upon blue metal from the most 

 impure ores equally as good as that from the best. ;j_^ 



When blue metal is put into water immediately after setting, 

 it assumes a red-brown colour. When this is examined with 

 a lens, the colour is seen to be caused by the reduction of copper 

 in fine grains, not only over the surface but through the mass, 

 bearing out the supposition that the copper moss may be pro- 

 duced by moisture. 



Copper moss occasionally occurs in some of the other opera- 

 tions, but it is most common in the blue metal. 



The sharp slags obtained with the blue metal are also of varied 

 composition. The following three analyses give a fair average 

 of their qualities : — 



Copper 1-5 1*9 2*0 



Silica 40-2 35-8 36-6 



Protoxide of iron .... 54*4 56*4 57*5 



Lime . , 1-3 1-6 9 



Oxides of tin, antimony, &c. '7 1*3 I'O 



98-1 97-0 98-0 ^ 



Some of the iron in these analyses was in a higher state of 

 oxidation than protoxide. 



By referring to the table of equivalents of flux for silica, 

 p. 455, vol. iv., the value of these sharp slags will be apparent, 

 and also the proper proportions in which they should be added 

 to an ore. Taking the mean of these analyses, we have — 



Silica 37-5 



Y« Oxide of iron . . . 56*1 



^^^ », . Lime 1'3 



'..,.,-. Other oxides ... 1*0 



95-9 

 not including the copper. Then, as 46 silica requires 36 oxide 

 of iron, the 37'5 will take 30 of the oxide of iron, leaving upwards 

 of 27 per cent, of these sharp slags available^ as flux. 



Several modifications have been introduced at this stage of the 

 operation. Some smelters, instead of tapping the mat into 

 sand-beds to make blue metal, tap it into deep pits of water in 

 the same manner as we have described for coarse metal, granu- 

 lating it for the purpose of giving it another calcination. When 

 this is done, the granulated mat is termed fine metal, in contra- 

 distinction to coarse metal. 



The calcination of the fine metal is conducted in the same 

 manner as that of the coarse metal, and the chemical changes 

 which take place in the furnace are the same. When the cal- 

 ^ipgd fijae flaptal i^ fused, some refinery slags rich ijj popper are 



2A2 



