History of the big bonanza

by Dan De Quille

While in the strainers a great quantity of the superfluous quicksilver mingled with the amalgam drains off, and flowing through pipes, is conducted to a large receiving-tank under the floor of the room. After it has thus drained till no more quicksilver will flow from it, the amalgam is removed from the ordinary strainers and is taken to the hydraulic strainer.

It is now a pasty mass of fine particles of silver, held together by quicksilver, and when pressed between the fingers gives out a peculiar squeaking sound. Although we may be unable to start a single globule of quicksilver from a lump of this amalgam by pressing it beneath our fingers, yet it is far from being as dry as it may be made by pressure. In this state it is placed in the hydraulic strainer, a heavy cylindrical cast-iron vessel, a good deal resembling a mortar—such as bombs are fired from. Over the “muzzle” of the “mortar” is fastened, by means of bolts and screws, a lid of iron through which enters an iron pipe. This pipe is then connected with a water-pipe, and water under several hundred feet of pressure is turned into the strainer. The pressure exerted upon the amalgam in this strainer amounts to 150 pounds to the square inch.

When taken out the amalgam has changed color and looks much less bright than before; one would think that but little quicksilver now remained in it, yet three-fourths of the mass is still quicksilver. Though strained and pressed as thoroughly as possible by ordinary methods, amalgam yields but one-sixth or one-seventh in silver bullion when retorted, whereas by the hydraulic strainer the yield is one-fourth.

The quicksilver pressed out by the hydraulic strainer is also conducted to the large receiving tank under the floor of the room. From this tank it is pumped up by powerful patent machinery—a pump having valves which are india-rubber balls [Toy balls of india-rubber, such as children play with may be used when those furnished with the pump are not at hand]—and goes to the distributing tanks. There are two of these tanks, one standing above each row of pans. Each distributing tank feeds eight quicksilver bowls, and each bowl supplies two pans, all by means of pipes. Thus, it will be seen, the quicksilver is in constant circulation. It passes through the pans, settlers, and strainers to the main receiving tank, from which it is pumped up into the distributing[distributing] tanks, from these flows into the quicksilver bowls, thence passing into the pans again. So it goes on constantly circulating until it is worn out and lost.

The loss in quicksilver by grinding the “life” out of it in the pans is very great. In the eight mills of the Consolidated Virginia Mining Company—mostly mills of from ten to twenty stamps each—the loss in quicksilver amounts to between $60,000 and $70,000 per month. Much of this loss is occasioned by grinding quicksilver in the pans five hours, when it should only be subjected to this destructive process two and a half hours. The intention is to have quicksilver in the pans but the length of time last mentioned, but in drawing off their contents into the settlers a considerable quantity remains behind in the interstices of the dies in the bottom of the pans, and is thus subjected to the two and a half hours of grinding given the first charge of pulp, previous to the putting in of the usual dose of 300 pounds of quicksilver. Many millmen and amalgamators are experimenting for the purpose of, if possible, devising means by which this extra grinding of quicksilver may be obviated.

Through the whole length of the amalgamating-room, between the two rows of strainers, a car-track is laid upon the floor and on this runs the amalgam car, made wholly of iron, and capable of holding two tons of amalgam. When told that this car, so insignificant in size, holds two tons, we get some idea of the great weight of the amalgam. The car takes the amalgam from the hydraulic strainer and conveys it to the retort-house, standing about 30 feet from the main mill building.

The floor of the amalgamating-room is eight or ten feet above the level of that of the retort-house, and when the car, with its load, has reached the end of the car-track in the amalgamating room, it is run upon a hydraulic elevator by means of which it is quickly lowered to the level of the track running to the retorts.

The retort-house is built of brick and is 24×60 feet in size. It contains six retorts, capable of retorting five tons of amalgam per day, but the amount retorted daily is but from two to two and a half tons. The retorts are cast-iron cylinders about six feet in length and eighteen inches in diameter, placed horizontally in brickwork, each having under it a small furnace. The row of retorts closely resembles a row of little steam boilers.

In charging the retorts they are about half filled with the amalgam, which looks more like grey mud than silver or any other metal. It is very cheap-looking stuff. Although one cannot see a single globule of quicksilver in it, yet it is about three-fourths quicksilver. You can squeeze no quicksilver out.