I took a small ball of amalgam, placed it in a double fold of new fine-grained calico, and after soaking in hot water put it under a powerful press. The weight of the ball before pressing was 1583 gr. From this 383 gr. of mercury were expressed and five-eighths of a grain of gold was retorted from this expressed mercury. The residue, in the form of a dark, grey, and very friable cake, was powdered up between the fingers and retorted, when it became a brown powder; it was afterwards calcined on a flat sheet in the open air; result, 510 gr. of russet-coloured powder. Smelted with borax, the iron oxide readily separated with the slag; result, 311 gr. gold 871-1000 fine; a second smelting brought this up to 914-1000 fine. Proportion of smelted gold to amalgam, one-fifth.
The principal point about this mode of treatment is the squeezing out of the mercury, whereby the amalgam goes into the retort in the form of powder, thus preventing the slagging of the iron and enclosure of the gold. The second point of importance is thorough calcining before smelting.
Of course it would be practicable, if desired, to treat the powder with hydrochloric acid, and thus remove all the iron, but in a large way this would be too expensive, and my laboratory treatment, though necessarily on a small scale, was intended to be on a practical basis.
The amalgam at this mine was in this way afterwards treated with great success.
For the information of readers who do not understand the chemical symbols it may be said that
| FeCO₃ | is carbonate of iron; |
| CaCO₃ | is carbonate of calcium; |
| CaSO₄ | is sulphate of calcium; |
| CaCl₂ | is chloride of calcium; |
| MgCl₂ | is chloride of magnesium; |
| NaCl | is chloride of sodium, or common salt |