Variations in the cost occur from time to time, and are due to several causes, principally the irregularity of the bullion supply and its consequent effect on the work of the plant. When the amount of bullion available for treatment is small, the plant cannot be run to its maximum capacity, and the cost per ton will naturally be increased. To illustrate this variation, the average cost per ton of base bullion refined during nine months in 1893 was:
January, $4.864; February, $5.789; March, $5.024; April, $3.915; May, $5.094; June, $4.168; July, $4.231; August, $4.216; September, $5.299.
The yearly variation shows but little change, as the average cost per ton was for 1893, $4.75; for 1894, $3.99; for 1895, $4.21; for 1896, $3.90. In considering the total cost of refining, the additional factors of interest, expressage, parting, brokerage, and reworking of by-products must be considered. As the doré silver is treated at the works or elsewhere, so will the total cost be less or greater. The following table gives the cost in detail, when the parting is done at the same works:
AVERAGE MONTHLY COST OF REFINING PER TON OF BULLION TREATED
| Items | 1895Jan. to July | 1895July to Dec. | 1896Jan. to July | Average |
|---|---|---|---|---|
| Labor | $2.351 | $1.718 | $1.836 | $1.968 |
| Spelter | 0.757 | 0.840 | 0.987 | 0.861 |
| Coal | 0.585 | 0.442 | 0.461 | 0.496 |
| Coke | 0.634 | 0.418 | 0.511 | 0.521 |
| Supplies, repairs and general expenses | 0.343 | 0.273 | 0.252 | 0.289 |
| Interest | 1.808 | 1.075 | 1.070 | 1.317 |
| Expressage | 1.360 | 1.015 | 0.882 | 1.085 |
| Parting and brokerage | 2.483 | 2.084 | 1.796 | 2.121 |
| Reworking by-products | 1.567 | 1.286 | 1.625 | 1.492 |
| Totals | $11.888 | $9.151 | $9.420 | $10.151 |
| Tons bullion refined 5,511.58 | 9,249.07 | 10,103.43 | 8,287.99 |
An analysis of the different items of cost is important, and a brief summary is given below.
Labor and Attendance.—The cost for this item varies but little from year to year, and its reduction depends, for the most part, on a larger yield per man rather than on a reduction of wages. If a man at the same or slightly increased cost can give a larger output, so will the labor cost per ton be diminished. This result is accomplished by enlarging the furnace capacity and by using appliances which will handle the bullion and its products in an easier and quicker manner. The small size of the furnaces, settlers and retorts used at modern refineries is open to criticism; I believe that great improvement can be made in this direction.
Spelter.—The cost of this item varies with the market conditions, and will probably be changed but little in the future, as the amount necessary per ton of bullion seems to be fixed.
Coal.—The amount required per ton of bullion is fairly constant, and while lessened cost for fuel may be attained by the substitution of oil or gaseous fuel, the fuel cost in comparison with the aggregate cost is very small, and leaves little opportunity for improvement in this line.
Supplies.—This item includes brooms, shovels, wheelbarrows, etc., and the amount is small and fairly constant from year to year.