COPPER 933 



c, a wooden chimney, which stands in the centre of the mound, with a small pile of 

 charcoal at its bottom ; b b are largo lumps of ore surrounded by smaller pieces ; 

 ./'./", are rubbish and earth to form a covering. A current of air is admitted under the 

 billets by an opening in the middle of each of the four sides of the base, a a, so that 

 two principal currents of air cross under the vertical axis, c, of the truncated pyramid, 

 as indicated in the figure. 



The fire is applied, through the chimney, c, to the charcoal at its bottom ; the 

 pile, b b, is kindled, and the sulphurous ores are raised to such a high temperature as 

 to expel the sulphur in the state of vapour. 



In the Lower Harz a roasting mound continues burning during four months. Some 

 days after it is kindled the sulphur begins to exhale, and is condensed by the air at 

 the upper surface of the pyramid. When this seems impregnated with it, small 

 basins are excavated, in which some liquid sulphur collects ; it is removed from 

 time to time with iron ladles, and thrown into water, where it solidifies. It is then 

 refined and cast into roll brimstone. 



A similar roasting mound contains, in the Lower Harz, from 100 to 110 tons of 

 ore and 730 cubic feet of wood. It yields in four months about one ton and a half 

 of sulphur from copper pyrites. Lead ore is treated in the same way, but it furnishes 

 less sulphur. 



There are usually from 4 to 5 roasting heaps in action at once for each smelting 

 works of the Lower Harz. After the first roasting two heaps are united to form a 

 third, which is calcined anew, under a shed ; the ores are then stirred up and roasted 

 for the third time, whence a crude mixture is procured for the smel ting-house. 



The most favourable seasons for roasting in the open air are spring and autumn ; 

 the best weather is a light wind accompanied with gentle rain. When the wind or 

 rain obstruct the operation, this inconvenience is remedied by planks distributed round 

 the upper surface of the truncated pyramid over the sulphur basins. 



WET METHODS OF EXTRACTING COPPBE. 



The Process of extracting Copper from Ores, at the Mines in the Rio Tinto District, 

 Province of Huelva, Spain, by what is termed ' Artificial Cementation.' This method, 

 which was first applied here by Don Felipe Prieto, a mine proprietor of Seville, in the 

 year 1845, is the only one employed in the present day in the copper-mines of that 

 district. 



The operation begins with the calcination of the ores, previously reduced to small 

 pieces ; piles or heaps of these ores (sometimes in the form of cones) are made on 

 beds of stubble fire-wood of about a yard thick ; each pile is made up with from 400 

 to 500 tons of mineral, and allowed to burn for six months ; the smoke destroying 

 all vegetation within its reach. 



The ores, after being thus burnt or calcined, are thrown into wooden troughs let 

 into the ground, about 6 yards long, 4 wide, and 1 deep, called ' dissolvers.' In 

 each of these troughs, or cisterns, are placed about twelve tons of calcined ore, and 

 the trough is then filled with water ; which water is, after remaining in contact with 

 the ores for forty-eight hours, drained off into a similar trough placed at a lower level, 

 and called a ' depositor.' The ores remaining in the dissolver are covered by a second 

 quantity of water, left on, this time, for three days ; and the process repeated four 

 times successively, the water being always drained off into the same depositor. 



From the depositors the water flows on to another set of troughs called ' pilones,' 

 into which is placed a quantity of pig iron, broken into, pieces of about the size of bricks, 

 and piled loosely together so that the vitriol in the water may better act on its whole sur- 

 face. Each of these troughs (jrilones) will hold from 12 to 18 tons of pig iron (wrought 

 iron answers the purpose as well, but it is much more expensive) ; and, as experience 

 has demonstrated that a slow continuous movement in the water hastens the process, 

 a man is employed for the purpose of agitating it, until all the copper suspended in 

 the vitriol-water is deposited, which, in summer, is effected in about 2 days, and in 

 from 3 to 5 days in winter. After the water has been renewed four or five times, and 

 the agitation process repeated, the scales of copper deposited on the iron, as well as 

 that in the form of coarse grains of sand found in the bottom of the trough, are col- 

 lected together, washed, and melted, when it is found to prodiice from 65 to 70 per cent. 

 of pure copper. 



From the remains of the first washings of the above copper-scales, &c., another 

 quality is obtained, worth about 50 per cent, for copper, which is mixed with the 

 after- washings, yielding about 10 per cent, of copper, and passed on to the smelting 

 furnace. 



The method is very defective. Minerals containing 5 per cent, of copper, treated 

 by this system of reduction, will scarcely give a produce of 2 per cent, of that metal, 



