Obtain a clear plank twelve inches wide, well seasoned, and free from knots or sappy places. Cut two sides twenty inches long and two ends eight inches long. With chisel, saw, and plane shape the ends of the side planks as shown at Fig. 2; or if there is a mill at hand it would be well to have the ends cut with a buzz-saw, thus insuring that they will be accurate and fit snugly. Screw-holes are bored with a gimlet-bit, and countersunk, so that screws will pass freely through them and take hold in the edges of the boards. Screws and plenty of white-lead, or asphaltum varnish, should be used on these points to make them water-tight; then the lower edge of the frame is prepared for the bottom board. Turn the tank bottom up, and, with a fat steel-wire nail and a hammer, dent a groove at the middle of the edge of the planks all around, as shown in Fig. 3. It will not do to cut this out with a gouge-chisel, because it is intended that the wood should swell out again if necessary. The object of driving the wood down is to form a valley into which a line of cotton string-wicking, soaked in asphaltum varnish or imbedded in white-lead, may be laid. This should be done (as shown in Fig. 4) before the bottom is screwed on, so that afterwards (in the event of the joint leaking) the wood will swell and force the wicking out, and thus properly close the fissure. The bottom board should be provided with holes all around the edge, not more than two inches apart, through which screws can be driven into the lower edge of the tank. Treat the wood, both in and outside, to several successive coats of asphaltum varnish, and as a result you will have a tank resembling Fig. 1. Two shallow grooves are to be cut in the top of each end board of the tank, for the cross-bars to fit in immovably. These bars should be about three inches apart; and the ones holding the anodes, or flat copper plates, should be close to one side, leaving plenty of room for objects of various sizes to be properly immersed. Another manner in which the bottom of the tank can be attached is shown in Fig. 5, which is a view of the tank sides turned bottom up. A rabbet is cut from the lower edges of the sides and ends, before they are screwed together, and a bottom is fashioned of such shape as to accurately fit in the lap formed by the rabbet. This rabbet and the outer edge of the bottom plank should be well smeared with white-lead, and all put together at the same time, driving the screws into the edge of the bottom plank, through the lower edges of the sides and bottom, and also through the bottom board into the lower edges of the sides and ends (Fig. 6).