182 Mr. J. Napier on Copper Smelting/. 



In all these experiments the powder was moist when put into 

 the furnace, which greatly facilitated the formation of sulphuric 

 acid. A furnace was constructed with a close chamber on the 

 top, in which the powder was dried previous to being let into 

 the calcining chamber. The first trial made was with regulus 

 crushed into powder ; it contained when lowered into the calci- 

 ning bed 16*5 per cent, of sulphur. Samples were taken out 

 every four hours and tested for sulphur and sulphuric acid, with 

 the following results : — 



There was no sulphuric acid formed. It will be observed that 

 eight hours were as effective as the twenty -four hours. We have 

 often met with similar results, no doubt arising from the want 

 of a proper heat and a regular current of air. The next trial 

 was with powder made as described, in the water- tanks ; it con- 

 tained when dry 22*6 per cent, of sulphur. Samples taken out 

 every four hours and tested for sulphuric acid and sulphur gave — 



Here we observe a regular evolution of sulphur; and the 

 results of many trials besides those now given, have shown that, 

 when the calcination was done with care, twenty hours were often 

 as effective as the twenty-eight in the above table. 



We are now in a condition to offer a few remarks upon the 

 nature of the action going on during calcination. When the 

 powder is put into the furnace moist, there is little change in 

 the first and second hour but the evaporation of water, after 

 which sulphur is rapidly disengaged, mostly in an uncombined 

 state. The flame or current from the fire travels circuit- 

 ously within the hearth, carrying in its course the sulphurous 

 vapours, which are deposited as it passes over cooler portions of 

 the bed, and sulphates of iron and copper are there formed ; hence 

 the slowness and irregularity of the evolution of sulphur. Samples 

 taken from different parts of the hearth previous to stirring, have 

 often given a difference of more than double the amount of 

 sulphur. 



