Mr. J. Napier on Copper Smelting. 197 



slacks are red, the heat has been too high ; but if brown, the proof 

 is good." 



"How hard-ftoiving Copper Ores are jyroved. 

 " Hard-flowing ores are not to be proved as the smooth, but 

 in another manner. Thus, take the ore, beat it as small as the 

 seeds of hemp, weigh two centners and put into a crucible, and 

 give it a very gentle heat that it begin to roast itself, stirring it 

 with an iron rod, else the ore will turn to ashes (cake) and not 

 roast. When it is stirred the first time, give it a little stronger 

 fire that it may glow well, then lift out the crucible and let it 

 cool ; it is then i)ut back into the fire, and kept there until it 

 has done smoking and smells not of sulplmr. It is now ground 

 a little finer, but not so fine as flour ; roast it again until it 

 stinks no more of sulphur, stirring it with the iron rod to pre- 

 vent caking. AYhen cool, it is again ground as fine as can be, 

 and roast once more until quite dead, that is, till it has no sul- 

 phurous smell, when it is ready for the proof. Divide the Avhole 

 into two parts, so that should the first fail, another can be done, 

 or two may be done to have a surer proof. One part is put into 

 a crucible, with three times as much of the before-mentioned ^ 

 flux and some flowing glass gall (a flux mostly oxide of iron) 

 well mixed, and cover it with common salt, as before mentioned ; 

 lute it over with clay, and fuse for a considerable time ; take out 

 the crucible and break it, when a button of copper of quality 

 according to the nature of the ore will be got, from which a 

 right proof of the ore will be obtained." 



These short extracts upon copper ores will verify the above 

 remarks. 



From the fact of the manufacturers of copper obtaining a 

 greater quantity of copper from the ore on the large scale than is 

 indicated by the assay, the source of this has been sought for in 

 the above method of assaying not giving accurate results. We 

 have tested the slag of the Cornish assayer, and have almost 

 invariably found it to contain copper, but not more than the 

 slag obtained from the smelting operations ; the cause of the 

 discrepancy between the assayer and smelter will be noticed in 

 another paper. In the mean time it has been suggested to be 

 owing to the assayers using liuor-sjjar as a flux ; but this sub- 

 Btauce the smelters also use as a flux. 



The flux we use for fusing, when assaying sulphurets, and 

 which gives us slags without a trace of copper, is composed of — 



1 part dried borax. 



1 ])art slaked lime. 



1 part oxide of iron, 



I part nitre. 



^ part common salt. 



■j^ part of charcoal dust. 



