Page:The Overland Monthly Volume 5 Issue 3.djvu/18



the thumb and fingers of either hand; the pressure detecting any foreign substance. Every substance of this kind is closely examined before being placed with the lesser dééris, the test employed being that of biting the article, and the miner usually telling instantly whether or not it be gold. Sometimes, however, he is cheated or unable to determine, and the dééris of this second cleaning is kept for a still more complicated process.

Many very curious incrustations are common to the lesser débris, as dimes, quarters, and half-dollars that have lost all semblance of their moneyed relationship; pins and needles, buttons and buckles, of all sizes and shapes; shot, bullets, tacks, shingle-nails—a conglomerate, indeed, of such queer substances that a chemist alone can classify them.

Retorting—or the process to which the amalgam is next subjected, is that operation by which the quicksilver is separated from the gold by the application of heat to the amalgam, the heat being sufficiently powerful to vaporize the quicksilver.

The retort for this purpose is usually made of brick, having a small chamber and a fire-place under the same. In the centre of this chamber, a half-cylinder is placed in a horizontal position, running lengthwise of the chamber, made of iron, having a smooth inner surface, about four feet in length by three feet in diameter. Corresponding to this is an upper half, which serves as a cover after the amalgam has been placed in the lower one. A pipe from this passes through the wall of the retort to a condenser outside of it which receives the vapor—the condenser further communicating with an outside vessel fitted for the reception of the quicksilver.

The amalgam is now placed in a number of small half-cylinders about ten inches in length, each having a central partition running lengthwise of it, and

all closely fitting into the lower halfcylinder of the chamber. With these cylinders in place, the cover securely fastened, and a fire built in the furnace below, retorting commences.

Great care is taken that the heat applied to the amalgam be regular, also of a low degree: otherwise there is danger of an explosion, usually destructive, and sometimes fatal in its results. A case in question is duly recorded in the annals of the Blue Gravel; but, further than opening the wall of the retort in several places, and routing the men from the room by the escaping vapor, it did no serious damage. This process generally takes about eight hours, and is one of the most disagreeable in the whole range of mining. No matter how great the precaution taken, some of the vapor escapes, and is breathed in by the workmen. Thus it is that salivation often occurs. Men are troubled, too, with throat or lung difficulties for weeks after the operation, and diseases may be contracted of mercurial origin, and therefore almost incurable.

When retorted, the gold is in small, porous loaves of a dull, metallic lustre, and very firmly cohesive—so much so that it can only be fitted for "smelting" by means of a cold-chisel, which, under the stroke of a heavy hammer, breaks and cuts it in pieces.

For the purpose of smelting, a furnace is sometimes arranged with two compartments, as is the case in the Blue Gravel Mine. This furnace is built of brick, with two cavities about eighteen inches in diameter by the same in depth, being separated from each other by a strong brick partition, and are circular in form, to give a more even heat, which is obtained from a coke-fire built in the bottom of the furnace.

The broken loaves are then placed in crucibles about ten inches in height and five inches in diameter, having the form of a common bowl, and made of black