54 ECONOMIC GEOLOGY. 
Practical workings. This process was first worked continuously for a year at the 
Davidson mine in North Carolina. The ore, a pyritous copper ina slaty gangue, was 
dressed up to 5 or 6 per cent., crushed, roasted so as to contain about one fourth of its 
copper as sulphate, and treated in stirring-vats in charges of 3,000 pounds. The loss 
of copper was from .3 to .5 per cent.; and the bath maintained its strength in chloride 
of iron without the use of copperas or sulphurous acid. The amount of iron consumed 
was equal to 70 per cent., and the salt to 25 per cent., of the copper produced. The 
entire cost of producing cement copper from the dressed ore of 53 per cent. was esti- 
mated at 33 cents per pound. 
Next, six calcining furnaces for the treatment of twelve tons of pryitous ore daily 
were erected by the same proprietors at the Ore Knob mine in the same state. Up to 
January 1, 1875, over 200 tons of copper had been made there by this process. The 
cost of mining, making the copper, and all expenses, amounted to 8 cents per pound. 
These works were soon after enlarged to nearly three times their former capacity; but, 
in sinking below the water-line in the mine, the ore, hitherto free from lime, was found 
to contain 30 per cent. of carbonate of lime. This rendered it necessary to concen- 
trate the ore by crushing and washing,—works for which have been erected. 
At Phenixville, Penn., two sorts of copper ores are being treated by this process,— 
the one a magnetic iron containing about 3 per cent. of copper, the other a hydrated 
silicate. One ton of the first and four fifths of a ton of the second are now daily suc- 
cessfully treated at this locality. 
The cost of the plant, or buildings and machinery required for the 
working of the process, is from $12,000 to $15,000. The details are 
given in the annexed letter from Dr. Hunt: 
LETTER FROM Dr. Hunt. 
As you desired, I write you some notes as to our copper process, its cost and its ad- 
vantages, compared with smelting or shipping ores, considered from the point of view 
of New Hampshire copper mines. I give, first, the cost of treating in a small work 12 
tons of 2,000 pounds daily, and suppose the ore to yield 8 per cent. of copper, labor to 
be $1.25 a day, and wood $4 a cord: 
For grinding (steam power), 14 cords, . - $6.00 
Labor of 3 men, at $1.25, . : i » 3.75 
For roasting, 4 cords, ‘ ‘ ® < - 16.00 
Labor of 12 men, . a 5 é ‘ + 15.00 
Tank-house, 2 men, ‘ : : ‘ « 2.50 
Superintendent and chemist, . “ ‘ + 5.00 
Scrap-iron, 1,300 pounds, at 14. cents, . - 19.60 
Three hundred pounds salt, and sundries, “A625 
$72.00—=$6 for 2,000 lbs. ore. 
