PRECIPITATION,
and is then conducted through a system of boxes filled with scrap iron, thus precipitating the copper.
The richer copper liquors which have been drawn from the tanks fire not allowed to run in with that which comes from the dump heaps. This liquor is also run into settling tanks, and from them pumped into four large barrels, mounted horizontally on friction rollers, to which a very slow motion is given. These barrels are 18 feet long and six feet six inches deep outside measure. They are built very strongly, and are water-tight. Ten tons of scrap iron are always kept in each of these barrels, which are refilled six times daily, complete precipitation being effected in less than four hours. Each barrel is provided with two safety valves, inserted in the heads, which open automatically to allow the escape of gas and steam. The precipitation of the copper in the barrels forms copper cement. This cement is discharged from the barrels on to screens which hold any lumps of scrap iron which may be discharged with the cement. It is then dried by steam, after which it is conveyed into another tank, left to cool, and then placed in bags ready for shipment, as copper cement. The building in which the liquor is treated is the mill part of the property, from which they send out 42 tons monthly of an average of 85 per cent, of copper cement, this being the average yield of the mine.
There are 23 white men and 40 Chinamen employed at the mine and the mill. There are also several wood choppers, etc., on the company's pay-roll. Eight months' supply of ore is always kept on hand, there now being 12,000 tons roasting. The mine is now paying regular monthly dividends, and everything argues well for the continuance of the same.
SIR WILLIAM THOMSON'S PILE.
The Thomson pile, which is employed with success for putting in action the siphon recorder, and which is utilized in a certain number of cases in which an energetic and constant current is needed, is made in two forms. We shall describe first the one used for demonstration. Each element of this (Fig. 1) consists of a disk of copper placed at the bottom of a cylindrical glass vessel, and of a piece of zinc in the form of a grating placed at the upper part, near the surface of the solution. A glass tube is placed vertically in the solution, its lower extremity resting on the copper. Into this tube are thrown some crystals of sulphate of copper, which dissolve in the liquid, and form a solution of a greater density than that of the zinc alone, and which, consequently, cannot reach the zinc by diffusion. In order to retard the phenomenon of diffusion, a glass siphon containing a cotton wick is placed with one of its extremities midway between the copper and zinc, and the other in a vessel outside the element, so that the liquid is sucked up slowly nearly to its center. The liquid is replaced by adding from the top either water or a weak solution of sulphate of zinc.
FIG. 1.--THE THOMSON PILE.(Type for demonstration.)