cooling pipe would radiate 0.025 B. t. u. from the gases. A rough sketch of the plant necessary (not drawn to scale) is shown in figure 13. The itemized costs of construction are as follows:

Cost of a 25-ton plant for igneous concentration of zinc ores.

The furnace chosen could easily handle twice the estimated amount of ore by increasing the blowing equipment and the facilities for handling the slag. The crushing equipment is ample for 50 tons daily, and the only feature that would have to be altered much for increasing the plant to this capacity would be the length or size of the cooling flue and the bag house. The difference in cost for a 50ton plant would probably not exceed $5,000. However, all the calculations have been for a 25-ton plant, in order that a rough idea could be obtained of the cost of producing a ton of zinc-oxide concentrate.

On the assumptions that only 80 per cent of the zinc will be recovered, that the product will contain 75 per cent zinc, that 25 per cent of coke on the weight of the ore will be necessary, and that lime rock can be quarried in the vicinity of the plant and delivered for $1.50 per ton, the cost per ton of ore of treatment in the 25-ton plant will be as shown in Table 39 and plotted in figures 14 and 15. The daily cost of operating the plant will be as follows:

TABLE 39.-Costs and profits of a 25-ton zinc oxide plant.

[Cost per ton of ore, based on 80 per cent recovery, 75 per cent zinc in product, $7.50 per ton of zinc oxide, and freight to "gas belt."]

FIGURE 14.-Curves showing cost per ton of ore of operating a 25-ton igneous concentration plant, and returns as calculated from "ore" contract. Curves a, b, and c show value of zinc oxide product and d, e, and the net profit per ton with spelter at 5, 7, and 9 cents per pound, respectively. Metallurgical cost estimated at $6.05 and mining cost at $2.50 per ton; freight on zinc oxide product variable.

For a similar plant treating 50 tons daily the expenses per ton of ore would be less. The original cost of the plant would not be much greater than for a 25-ton plant, and the amount of labor would be only slightly greater than for the 25-ton plant. Likewise the power bill would not be much larger, and the only item that is rela

FIGURE 15.-Curves showing cost per ton of ore of operating a 25-ton igneous concentration plant, and returns as calculated from "zinc oxide" contract. Curves a, b, and c show value of zinc oxide product and d, e, and ƒ the net profit with spelter at 5, 7, and 9 cents a pound, respectively. Metallurgical cost is estimated at $6.05 and mining cost at $2.50 per ton of ore; freight on zinc oxide product variable.

tively fixed per ton of ore is that of fuel. This makes a probable metallurgical cost of $4.80 per ton of ore. Mining on this scale could probably be done for $2 per ton in oxidized deposits near the surface, whereas freight on the zinc-oxide product would be the same as in the former calculations. Thus the returns from a 50-ton plant would be larger, as shown in Table 40 and figures 16 and 17.

TABLE 40.-Costs and profits of a 50-ton zinc oxide plant.

[Cost per ton of ore, based on 80 per cent recovery, 75 per cent zinc in product, $7.50 per ton of zinc oxide, and freight to "gas belt."]

FIGURE 16.-Curves showing cost per ton of ore of operating a 50-ton igneous concentration plant, and returns based on "ore" contract. Curves a, b, and c show value of zinc oxide product, and d, e, and f the net profit with spelter at 5, 7, and 9 cents, respectively. Metallurgical cost is estimated at $6.05 and mining cost at $2.50 per ton; freight on product variable.