| Drop charge | 7 a.m. |
| Begin firing down | 12 a.m. |
| Begin tapping | 1 p.m. |
| Rake out slag | 2 p.m. |
| Begin tapping | 2.30 p.m. |
| Drop charge | 3 p.m. |
| Begin firing down | 8 p.m. |
| Begin tapping | 9 p.m. |
| Rake out slag | 10 p.m. |
| Begin tapping | 10.30 p.m. |
| Drop charge | 11.00 p.m. |
| Begin firing down | 4 a.m. |
| Begin tapping | 5 a.m. |
| Rake out slag | 6 a.m. |
| Begin tapping | 6.30 a.m. |
The hearths were composed of about 8 in. of gray slag beaten down solidly on a basin of brick, which rested on a filling of clay, rammed solid. The hearth was patched if necessary after the drawing of each charge.
The system of smelting was analogous to that which was practiced in Wales rather than to the Silesian, the charges being worked off quickly, and with the aim of making a high extraction of lead directly and a gray slag of comparatively low content in lead. The average furnace charge was 3500 lb. At the beginning of the reaction period about 85 to 100 lb. of crushed fluorspar was thrown into the furnace and mixed well with the charge. The furnace doors were then closed tightly and the temperature raised, the grate having previously been cleaned. At the first tapping about 1200 lb. of lead would be obtained. A small quantity of chips and bark was thrown into the lead in the kettle, which was then poled for a few minutes, skimmed, and ladled into molds, the pigs weighing 80 lb. The skimmings and dross were put back into the furnace. The pig lead was sold as “ordinary soft Missouri.” The gray slag was raked out of the furnace, at the end of the operation, into a barrow, by which it was wheeled to a pile outside of the building. Shipments of the slag were made to other smelters from time to time, 95 per cent. of its lead content being paid for when its assay was over 40 per cent., and 90 per cent. when lower.
Each furnace was manned by one smelter ($1.75) and one helper ($1.55) per shift, when two shifts per 24 hours were run. They had to get their own coal, ore and flux, and wheel away their gray slag and ashes. In winter, when three shifts were run, the men were paid only $1.65 and $1.50 respectively. There was a foreman on the day shift, but none at night. The total coal consumption was ordinarily about 0.8 to 0.9 per ton of ore. Run-of-mine coal was used, which cost about $2 per ton delivered. The coal was of inferior quality, and it was wastefully burned, as previously referred to, wherefore the consumption was high in comparison with the average at Tarnowitz, where it used to be about 0.5 per ton of ore.
The chief features of the practice at Desloge are compared with those at Tarnowitz, Silesia and Holywell (Flintshire), and Stiperstones (Shropshire), Wales, in the following table, the data for Silesia and Wales being taken from Hofman’s “Metallurgy of Lead,” fifth edition, pp. 112, 113.
| Detail | Holywell | Stiper-stones | Tarnowitz | Tarnowitz | Desloge |
|---|---|---|---|---|---|
| Hearth length, ft. | 12.00 | 9.75 | 11.75 | 16.00 | 16.00 |
| Hearth width, ft. | 9.50 | 9.50 | 10.83 | 8.83 | 11.00 |
| Grate length, ft. | 4.50 | 4.50 | 8.00 | 8.00 | 8.00 |
| Grate width, ft. | 2.50 | 2.50 | 1.67 | 1.67 | 3.00 |
| Grate area: hearth area | 1:8 | 1:6⅔ | 1:10 | 1:10 | 1:7-1/3 |
| Charges per 24 hr., | 3 | 3 | 2 | 2 | 3 |
| Ore smelted per 24 hr., lb. | 7,050 | 7,050 | 8,800 | 16,500 | 10,500 |
| Assay of ore, % Pb | 75-80 | 77.5 | 70-74 | 70-74 | 70 |
| Gray slag, % of charge | 12 | 15 | 30 | 27 | |
| Gray slag, % Pb | 55 | 38.8 | 56 | 38 | |
| Men per 24 hr. | 6 | 4 | 4 | 6 | 6 |
| Coal used per ton ore | 0.57-0.76 | 0.56 | 0.46 | 0.50 | 0.90 |
The regular furnace charge at Desloge was 3500 lb. The working of three charges per 24 hours gave a daily capacity of 10,500 lb. per furnace. These figures refer to the wet weight of the concentrate, which was smelted just as delivered from the mill. Its size was 9 mm. and finer. Assuming its average moisture content to be 5 per cent., the daily capacity per furnace was about 10,000 lb. (5 tons) of dry ore.
The metallurgical result is indicated by the figures for two months of operation in 1900. The quantity of ore smelted was 1012 tons, equivalent to approximately 962 tons dry weight. The pig lead produced was 523.3 tons, or 54.4 per cent. of the weight of the ore. The gray slag produced was 262.25 tons, or about 27 per cent. of the weight of the ore. The assay of the ore was approximately 70 per cent. lead, giving a content of 673.4 tons in the ore smelted. The gray slag assayed approximately 38 per cent. lead, giving a content of 99.66 tons. Assuming that 90 per cent. of the lead in the gray slag be recoverable in the subsequent smelting in the blast furnace, or 89.7 tons, the total extraction of lead in the process was 523.3 + 89.7 ÷ 673.4 = 91 per cent. The metallurgical efficiency of the process was, therefore, reasonably high, especially in view of the absence of dust chambers.