Surface arrangements, Ore dressing and milling, Sampling ores, Roasting and calcining ores, the Cyanide process

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1902 Excerpt: ...works somewhat better on the plates than silver amalgam, but is seldom used, on account of the great expense. To prepare plates for amalgamation, they are first scoured with sand or emery paper until they are clean and bright. They are then washed with a strong soda or lye solution to remove all traces of grease. Dilute nitric acid--a 10-percent. solution--or a comparatively strong solution (about 2fr Per cent.) of potassium cyanide may be used instead of lye or soda. After washing with the chemicals, the plate is well washed with water and then a mixture of equal parts of sand and sal ammoniac and a little mercury is rubbed on with a scrubbing brush. The sand and sal ammoniac are used to keep the plate clean while the mercury is being rubbed in. Enough water is used to make a thick mud. More mercury is sprinkled upon the plate from a flask with a piece of cloth tied over the top, and the rubbing is kept up until the surface of the plate has absorbed all the mercury it will hold. The plate is allowed to stand for about an hour and is then washed clean with water or with cyanide of potassium and water, and more mercury is added if the plate will hold it. If the plates are plain copper, they are next given a coating of gold or silver amalgam and are then ready for use. The amalgam is rubbed in with a piece of rubber belting or cloth, the plate meanwhile being kept wet with sal ammoniac. When rubber belting is employed, a piece is fastened between two blocks of wood, so as to leave about 1 inch of the belting projecting from the wood. The entire block, belting and all, is sometimes called the rubber. If old mercury is used in preparing the plates, the use of special amalgam is unnecessary, as mercury strained, or even distilled, from amalgam retains enough gol...