Mr. J. Napier on Copper Smelting. 349 



calcining, but is distinct both in its mode and objects. The 

 roasting furnace has ah'eady been described, page 346_, vol. iv. 

 The charge for an ordinary-sized furnace is about three tons. 

 When the metal is brought to fusion, the air-holes of the furnace 

 are all opened and a free current allowed to pass over the surface 

 of the fused mass ; the heat of the fire is then regulated so as 

 to keep the charge in a sort of semifluid state. When blue metal 

 is roasted, the action which occurs between the air and charge 

 is similar to that which takes place in the calciner — the sulphur 

 is oxidized and passes off as sulphurous acid ; the iron with a little 

 copper also oxidizes, forming scoria, which from time to time is 

 skimmed off. These slags vary in composition according to the 

 stage of the operation at which they are skimmed. At the be- 

 ginning of the operation their average composition is — 

 , Oxide of copper . . 8 



...f>ii^ao Oxide of iron ... 49 



'3kUiwm ^^fl ' ^l 



• " Sulphur ..... 3 



Other oxides . , ' , V 3 



100 

 Those produced at the end of this process, j ust previous to the 

 commencement of the true chemical reactions which occur in the 



grocess of roasting, furnished the following result : — 



Xdfcsnmlcfo'. Oxide of copper . . 15 



■iio.o.fBi, Oxide of iron • • • 43 



fv^A.fF ...: .,( Silica 33 



Sulphur 2 



.,,, , Oxygen and oxides . . 7 



100 

 This operation is termed the first roasting ; the quantity of 

 scoria from it amounts to about one-third of the weight of the 

 metal put in. As this operation is usually continued twenty-four 

 hours, the quality of the metal obtained varies exceedingly, and 

 is distinguished by some peculiarity of appearance, as pimpled 

 metal, white metal, or regulus, &c. The following analyses of a 

 few of these varieties will illustrate our remarks : — 



By Le Play. 



1000 100 100 100 99-8 



It will be observed that these compounds have the same 

 general character, the principal differences consisting in the 



