The apparatus used for separating the graphite from the impurities, when the mine was first opened, consisted of a wooden barrel, perforated with small holes, an iron rod passing through it lengthwise. The ends of the rod formed journals, which rested on two upright posts, the machine by hand, by means of a crank, precisely like a barrel churn. The dirt to be washed being put into the barrel by means of an opening at the side, a small stream of water was led through a pipe to the top of the machine. After a few minutes' turniug, all the graphite, sand, and fine grit were washed through the holes ; the stones and lumps remaining in the barrel were thrown out at every charge. The water containing the finer materials was caught iu a tank, about 5 ft. deep, placed immediately under the barrel, the only outlet from the tank being a shallow spout a few inches from the top. The graphite in exceedingly fine particles floated off in the water which passed over this spout, while nearly all the sand and other materials remained in the tank. The water holding the graphite in suspension was then passed through a series of shallow tanks made of board. After a " run " of several days, the water was let out of the shallow tanks, and the sediment they contained was left exposed to the sun for a few hours, when it became blackened ready for the market. That obtained from the last of the tanks was finer than that from the first, though all was extremely fine. An analysis made of some from the last tank gave 97.9 per cent, carbon. Nearly 200 tons were prepared iu this way, and sold readily in New York, Philadelphia, &c., at 201. per ton.
As operations increased, improvements were made. Iron cylinders worked by water-power were substituted for the barrel, the water and sediment leaving them being conveyed by pipes to a large tank made of planks and stout framing, and capable of holding 1000 tons. When this tank was filled (in about three days), its contents were allowed to settle for 24 hours, after which the dirty water was let off from the surface, and a powerful stream of clean water was let on, which forced the sediment through spout's into 18 shallow tanks, each 20 ft. wide, 25 ft. long, and 1 ft. deep. After remaining in these tanks about 3 days, the water was let off, and the sediment was exposed to the sun. In 24 hours it becomes hard enough to be taken out in blocks, which,- after lying for another 24 hours on plank platforms, are ready for market. About 25-30 tons per week were treated by this method ; but the demand still growing, arrangements had to be made for turning out 20-25 tons per day.
These consist of a sort of arrastra, or puddling-machine, to replace the cylinders, comprised in a circular bed 20 ft. in diameter, with water-tight sides 3 ft. high, in the centre of which is an upright post with 4 arms, to which are attached stirrers instead of grinders, as in an arrctstra, it being desirable not to grind the mineral, only to separate the particles. It is driven by a water-wheel, and 15
Chinamen are employed to feed in the mineral. A small stream of water passing constantly through it carries all the lighter particles away. The rocks and sand are let out by a sluice-gate every 3-4 hours. The water carrying the graphite is conveyed by a flume to an enormous tank built in the ground, measuring 200 ft. long, 150 ft. wide, and 7 ft. deep, and capable of holding 30 days' collec tion. This was very expensive to construct, its entire inner surface being coated with a specially prepared cement, sufficiently smooth to prevent the graphite adhering, and so porous as to preclude its retaining moisture after the water had been let off. When the tank contains 3-4 in. of sediment, it is considered full, and, after standing for a few days, the water is run out, and the sediment is exposed to the sun. In two days, with fine warm weather, it is sufficiently dry to be taken out and laid on the drying-platforms, and in 24 hours is ready for market.
The cost per ton of the pure graphite needing no preparation, employing Chinese labour at 8 dol. a week, without hoard, is thus stated :—Extraction, 4s. 2d.; sacks, 8s. 4d.; land carriage to Stockton, 65 miles, 11. 17s. 6d. ; rail to San Francisco, 6s. 3d. ; ship to Liverpool, 21. 18s. 4d. ; commissions, insurances, &c., 21. 12s. ld. ; total, 8l. 6s. 8d. Its market value in Liverpool is about 201. per ton, The output is about 500 tons per annum, nearly all of which is exported to Europe.
The second considerable American deposit is worked on the eastern slope of the "Black-lead Mountain " of the old maps of Essex County, New York State. The mountain lies just behind the village of Ticonderoga. The ore is mainly of the foliated variety, interspersed in veins among gneiss and quartz, with a dip of about 45°. Two analyses yielded and 97.422 per cent. of carbon respectively. Some of the veins are much richer than others ; one has been worked to a depth of about 350 ft., and found to be of varying thickness and with occasional pockets. After leaving the mine, the mineral is first crushed in an ordinary stamp battery to a fine powder, and the constituents are separated by Cornish huddles and settling-tanks. The graphite is then washed, dried in an oven, and bolted like flour, after which it is ground in water in a Bogardus mill, and again bolted. The grade thus produced is called " crucible stock " ; for finer grades, additional processes are necessary. The miners are paid at the rate of about 251. per ton of prepared graphite. The five grades of manufactured graphite are estimated to be worth about 21d. per lb. for stove polish ; Md. for powder polish ; 2s. ld. for pencils ; and 4s. 2d. for stereotype powder.