CHANGES IN PRACTICE
The quicksilver industry is less likely to be modified by changes in mining methods than by improvements in metallurgy. Although very simple in principle, the treatment of quicksilver ores, owing to the mobility and elusiveness of the metal both in the liquid and vaporized condition, is beset with many practical difficulties.
Coarsely broken ore is generally treated in various types of simple shaft furnaces, the fuel being either mixed with the charge or burned in a firebox. Finely broken or pulverulent ore, however, such as forms the larger part of the material from most quicksilver mines, requires different treatment. In Europe the common type of furnace for fine ore is the Spirek and in the United States the Scott-Hütner, or, as more commonly called, the Scott furnace. In both, the ore descends by gravity over tiles of fire-clay so shaped and placed as to permit the flame to pass back and forth through passages under tiles, the passageways or flues being formed partly by the tiles and partly by the ore itself. From the furnace the mercury-laden vapors are conducted through a series of condensing chambers of brick, iron, wood, or other material, in which the metal collects.
When intelligently operated, the Scott furnace is remarkably economical and efficient; but its construction is expensive and requires specially skilled masons. Moreover the furnace is difficult to repair, and once erected can not be moved. These are serious disadvantages to the man of small capital who is developing a new mine, and he usually has to fall back on retorts which are expensive to operate and are unsatisfactory except for relatively small quantities of rich ore.
Of late years attempts have been made in California and Texas to use slightly modified rotary cement-kilns for treating quicksilver ores. This innovation is promising and seems likely to prove successful. Such a furnace, although it may not displace the Scott under some conditions, does not require elaborate masonry structure, and its use may lead to a considerably increased production from the smaller mines.
The condensing systems used with quicksilver furnaces differ greatly and at no two mines in the United States are they identical. The brick condensing chambers formerly so extensively used with the Scott furnace are expensive to build; also the bricks are poor conductors of heat and absorb large quantities of quicksilver. The recent tendency in California has been to replace the brick chambers with large boxes or cylindrical tanks of wood. European practice, followed by one mine in Oregon and one in Texas, favors condensers constructed of vitrified earthenware pipe. The whole question of quicksilver condensation calls for study and skillful experiment. The establishment of a standard of practice would increase production by elimination of much of the loss and discouragement that come from inefficient individual efforts to collect the mercury from the furnace vapors and gases in the most complete and economical way.