Note (return) — Chapter XII · VOYAGE ROUND THE WORLD, BY CAPTAIN GEORGE SHELVOCKE, IN 1719-1722.

The whole being thoroughly washed in these basins, which are lined with leather, till the water runs clear off, the amalgam of mercury and silver is found at the bottom, and is termed la pella. This is put into a woollen bag and hung up, from whence some of the mercury runs out. The bag is then beaten and pressed as much as they can, laying upon it a flat piece of wood loaded with a heavy weight, to get out as much of the mercury as they can. The paste is then put into a mould of wooden planks bound together, generally in the form of an octagon pyramid cut short, its bottoms being a plate of copper, full of small holes, into which the paste is stirred and pressed down, in order to fasten it. When they design to make many pinnas, or spongy lumps of various weights, these are divided from each other by thin beds or layers of earth, which hinder them from uniting. For this purpose, the pella, or mass of amalgam, must be weighed out in separate portions, deducting two-thirds for the contained mercury, by which they know to a small matter the quantity of silver contained in each. They then take off the mould, and place the pella or mass with its copper base on a trivet, or such like instrument, standing over a great earthen vessel full of water, and cover it with an earthen cap, which again is covered by lighted coals. This fire is fed and kept up for some hours, by which the mass of pella below becomes violently heated, the contained mercury being thereby raised into vapour: But, having no means of escape through the cap or cover, it is forced down to the water underneath, where it condenses into quicksilver and sinks to the bottom. By this contrivance, little of the mercury is lost, and the same serves over again. But the quantity must be increased, because it grows weak.2 At Potosi, as Acosta relates, they formerly consumed six or seven thousand quintals of mercury every year, by which Some idea may be formed of the silver there procured.