as he walks over and over the torta, much after the manner that seed is sown with us. The tester determines when the silver has all been collected and amalgamated with the mercury. Whether the tramping process and the turning by shovels shall continue for six weeks or for only three, is decided by him. When he decides that it is prepared for washing, the mass is transported to an immense washing machine, which is propelled by water, where the base substances are all washed from the amalgam, and then the amalgam is resolved into its original elements of silver and quicksilver by fire, as already explained, with the loss of about seventy-five to one hundred pounds of mercury upon each torta.
Let us now run over the many chemical processes that have been resorted to in order to separate the silver from the ore. The roll-brimstone, that has been procured in Durango, or in the volcano of Popocatapetl, is bought up at the mint in the city of Mexico, where it is burned in a room lined with lead, and into which water is jetted until the smoke of the burning brimstone is condensed. This water of sulphur is then carefully collected, and distilled in a boiler of platinum, on which sulphur can not act. The sulphuric acid obtained by this distillation is used to separate the gold that is found in the silver bars from silver. This sometimes amounts to ten per cent. The acid dissolves the silver, but does not act upon the gold, which is thus separated from the silver.