~The electrodes~ consist of a platinum spiral and cylinder. The spiral should have the shape shown in A, fig. 54. When in work it is passed through one of the holes fitted with glass tubes and connected with the copper end of the battery. The thickness of the wire of which it is made is unimportant, provided it is stout enough to keep its form and does not easily bend. The spiral will weigh about 8 grams. The cylinder (C, fig. 54) will weigh about 12 grams. It should have the shape shown in the figure. In working it is clamped to one of the terminals, and on it the copper is deposited. A cylinder will serve for the deposition of from 1 to 1.5 gram of copper. It is made by rivetting a square piece of foil on to a stiff piece of wire, and then bending into shape over a glass tube or piece of rounded wood. Each cylinder carries a distinctive number, and is marked by impressing Roman numerals on the foil with the blade of a knife. The weight of each is carefully taken and recorded. They lose slightly in weight when in use, but the loss is uniform, and averages half a milligram per month when in daily use. The cylinders are cleaned from deposited copper by dissolving off with nitric acid and washing with water; and from grease by igniting. The ~beakers~, to contain the solution of copper to be electrolysed, are ordinary tall beakers of about 200 c.c. capacity, and are marked off at 100 c.c. and 150 c.c. They are supported on movable stands, consisting of wooden blocks about six inches high and three inches across. The bar of wood which carries the connecting wires and electrodes is permanently fixed over the working bench, at such a height that, with the beakers resting on these blocks, the electrodes shall be in position for working. To fix the electrodes to the rod, remove the stand and beaker and pass the long limb of the spiral up through one of the glass tubes. Connect it with the free end of the copper spiral by means of a connecting screw (fig. 52), and then draw out and bend the copper spiral so that the platinum one may hang freely. Screw the wire of the cylinder to the terminal, and, if necessary, bend it so that the cylinder itself may be brought to encircle the rod of the spiral in the manner shown in fig. 53. The ~general method of working~ is as follows:--The quantity of ore to be taken for an assay varies with the richness of the ore, as is shown in the following table:-- Percentage of Copper Quantity of Ore in the Ore. to be taken. 1 to 5 5 grams 5 to 10 3 " 10 to 30 2 " 30 to 50 1.5 " 50 to 100 1 "