Page:The fundamental laws of electrolytic conduction.djvu/71

 of the cylinder, together with the vessel, c, is first filled with the solution. The same is done with the upper part in which the cathode is placed, care being taken that no air-bubbles remain in the inside. By means of a glass plate, g, which is ground on the open end of this cylinder, a definite quantity of liquid can be measured off. When this has been done the cylinder is inverted and, together with the glass plate, placed in the vessel c beside the cylinder a. For convenience of manipulation, a silver wire, h, passes through four holes in the corners of the plate, thereby forming two handles. The vessel c is just large enough to permit the cylinder a and the glass plate g to rest side by side on the bottom. The cylinder a, moreover, is so cemented in, that its upper edge projects above the bottom by just the thickness of the glass plate, so that it lies in the same plane with the upper surface of the latter. The smaller cylinder filled with solution can, therefore, be easily slid along from the plate on to the lower cylinder, thus forming a single cylinder. In this position its contents are supported by the atmospheric pressure.

The solution contained in the cylinder undergoes a change only at the electrodes during electrolysis. The liquid around the anode becomes more concentrated and, therefore, remains in the lower part; the solution around the cathode becomes diluter and collects on the cover. When the current has decomposed a sufficient quantity, the upper cylinder is slid back again onto the glass plate, and taken out. The outside is cleaned from adhering liquid, and the contents carefully poured into another vessel for analysis. If the upper cylinder be now filled with the original solution and this quantity likewise analyzed, one has, with the quantity of metal deposited, all data necessary for computing the transference.

The cathode projects, intentionally, only to the centre of the upper cylinder in order that the liquid at the opening shall remain unchanged, and the mixing with the liquid in the vessel c, which occurs at this place on sliding the cylinder back on to the glass plate, shall occasion no error. To prevent the liquid in c from becoming concentrated by evaporation during electrolysis, the apparatus is set into a ground-glass plate, i, and covered with a bell-glass during the experiment. Fig. 5 represents in cross-section the apparatus completely set up. The dimensions of my apparatus are as follows: The inside