88 Mr. J. Napier on Copper Smelting. 



and tin in solution if any of these metals were present in the 

 ore. 



The sulphate of soda used in the above process should be of 

 the best sort ; that obtained in the manufacture of nitric acid 

 from nitrate of soda is better than that procured from common 

 salt in making soda ash. The former contains on an average 

 about 99 per cent, of sulphate, while the latter does not contain 

 more than 70 per cent., the remainder being common salt, the 

 presence of which is deleterious. 



The slag obtained from the fusion of the ores is an important 

 consideration in a smelting establishment : by referring to the 

 average composition of the ore, in connexion with the fact that 

 all the iron and silica goes to form slag, it will be seen that 

 upwards of one-half of the weight of the ores remains in the 

 form of refuse ; so that a small work, producing 30 tons metalhc 

 copper weekly, will yield not less than 120 tons of slag in that 

 time, being 7000 tons annually ; an important item, and costing 

 a considerable sum to put out of the way. 



Many plans have been suggested for applying these slags to 

 useful purposes, but few of them have been acted upon. They 

 are extensively used in the neighbourhood of Swansea for repair- 

 ing roads ; an application not the most suitable, as they produce 

 uncomfortable dark roads at night, from the almost entire absence 

 of reflected light. 



Propositions have been made to use the scoria for building 

 materials, which, however, requires two conditions : first, the 

 moulding it into a shape suitable for building purposes ; and 

 secondly, annealing: being a kind of glass, unless annealed 

 it is brittle. To mould the slag as it is skimmed, prevents its 

 examination for copper and induces carelessness in skimming ; 

 risking a loss of copper, which is so much more important than 

 a common building article : the moulding of the slags is there- 

 fore seldom practised. We have seen an old slag wall, three feet 

 high, having in it copper sufficient to give the wall a value of 20^. 

 a lineal yard for the copper alone. 



Whatever proposition is made for using the slags, it should 

 not interfere or have any connexion with the smelting opera- 

 tions, or the thorough examination of the slags for copper. 



From the fact that the slags contain on an average 30 per 

 cent, of iron, it has been suggested, and trials have been made, 

 to manufacture iron from it. The great quantity of silica pre- 

 sent, and the necessity of adding flux sufficient to combine with 

 it before the iron can be obtained, is a commercial drawback to 

 any such scheme; and even were this not the case, the iron 

 obtained from the slags is vciy impure and generally contains 

 other metals, and always copper. A sample of iron made from 



