COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 99 



and sometimes two or more staj^es will be more or less combiued. Fre- 

 (lueutly the first operations will be carried ou at or near the mines and 

 the product of matte or pig coi)i)er shipped away to be refined. This 

 is ji'enerally the case if the copper contains silver. These stage;;^ are : 



First. The preparation of the ore. 



Second. The smelting for matte. 



Third. The smelting for pig copper. 



Fourth. The refining of pig copper for the production of ingot. 



Since nearly all copper ores are sulphureted, the most universal pre- 

 paration is roasting to remove sulphur. In the older works this roast- 

 ing was generally accomplished by making a pile of the coarsely 

 crushed ore with a small amount of fuel, setting fire to it, and allow- 

 ing it to burn as long as it would. This operation but imperfectly 

 removed the sulphur, and a portion of each pile had generally to be re- 

 roasted. It was also very long and tedious. Sometimes the coarsely 

 crushed ore is roasted in brick stalls, where the combustion is more un- 

 der control, more complete, satisfactory, and expeditious. Fine ore, 

 such as results from concentrating operations, is generally roasted in 

 reverberatory furnaces. In all these processes the only object sought 

 is the removal of the sulphur, but ores consisting largely of pyrite are 

 sometimes roasted in specially constructed furnaces, arranged to save 

 the products of combustion and convert the sulphur into sulphuric 

 acid. 



The smelting for matte is simply a concentrating operation by fusion. 

 A mixture of the ore is made up with the necessary fluxes, so as to 

 yield a matte consisting of sulphides of copper and iron and a slag con- 

 taining the earthy impurities of the ore and too little copper to be of 

 any value. This fusion is carried on in either cupola or reverberatory 

 furnaces. This matte is roasted and then smelted again, generally with 

 the addition of rich slags, i)roducing a matte containing more copper 

 and less iron and sulphur and a slag containing sufficient copper to be 

 reworked. This process of roasting and fusing for matte is repeated 

 several times, according to circumstances, until pig copper is produced. 



Pig copper contains a small amount of sulphur, together with some 

 other impurities, and has to be refined in a reverberatory furnace to 

 produce ingot copper. 



THE VERMONT COPPER MINING COMPANY. 



These works represent a condition of affairs not often met with in 

 recent works. They were established for the production of ingot coi)per 

 from the ores from a single region, and as an adjunct to the mining oi)era- 

 tions. In more modern practice, the mining company undertakes only 

 the first stages of the smiiltingor concentrating operations. The refin- 

 ing and production of ingot cot)per is carried on at indei)ondent works, 

 where material can be drawn from a large number of sources. The ores 

 were first roasted in heaps to remove the sulphur. The roasted ore 



