| (a) | 40 cwt. at | 4 | 1⁄4 | ounces of silver per ton; | in whole | 9 | oz. | - | 30 oz. | |
| (b) | 20 cwt. at | 21 | — | — | 21 |
Each of these alloys (a) and (b) will be joined to alloys of like quality obtained in the treatment of one or several other portions of three tons of the primitive alloy. Again, three tons of each of these rich alloys are subjected to the crystallization process, and thus in succession. Thus poorer and poorer lead is got on the one hand, and richer and richer alloys on the other. Sometimes the mother metal is parted from a great body of poor crystals, by opening the discharge-pipe, and running off the liquid, while the workman keeps stirring, to facilitate the separation of the two.
25 fodders, 15 cwts., 49 lbs. = 540 cwts., 49 lbs. of alloy, holding 5 oz. of silver per fodder, in the whole 130 oz., afforded, after three successive crystallizations—
| oz. | |||||
|---|---|---|---|---|---|
| 440 | cwts. of | poor lead, | holding 1⁄2 oz. of silver per fodder; in all | 10 | 1⁄2 |
| 15 | cwt. 49 | — | holding the original quantity, nearly | 3 | 1⁄2 |
| 84 | cwts. of | lead for the cupel, holding 29 oz. | 116 | ||
| Total | 130 | ||||
| 1 cwt. of loss, principally in the reduction of dross. | |||||
The expenses of the new method altogether, including 3s. per fodder of patent dues are about one-third of the old; being 17l. 13s. and 54l. 16s. respectively, upon 84 cwts. of lead, at 29 oz. per fodder.
In the conditions above stated, the treatment of argentiferous lead occasions the following expenses:—
| FOR ONE FODDER. | £ | s. | d. | |
|---|---|---|---|---|
| By the | new process | 0 | 13 | 7 |
| old process | 2 | 2 | 2 | |
Admitting that the treatment of silver holding lead is economically possible only when the profit is equal to one-tenth of the gross expenses of the process, we may easily calculate, with the preceding data, that it is sufficient for the lead to have the following contents in silver:—
| With the new process, 3 ounces per fodder; or, | 0·000078 |
| With the old process, 84⁄10 ounces per fodder; or, | 0·000218 |