Page:The fundamental laws of electrolytic conduction.djvu/70

 and contains the anode d. This has the form of a circular perforated plate, and is made of metal, the salt of which is to be electrolyzed. The support fastened to its centre passes through a small cork in a glass plate and permits connection with the galvanic cell. This plate forms the base of the cylinder, and is held in place by a cover which screws on. The anode is not permitted to lie on the bottom, but is placed a little higher up, so that the concentrated solution, which forms at its surface during electrolysis, can flow down through the holes. The smaller part of the cylinder b is closed above by a similar perforated glass plate, provided with a cork, and contains the cathode e, likewise fastened to a support which projects outward. The cathode must be given a different form from the anode. If it consists of a horizontal plate, the metal deposited by the current on the under surface cannot hold. It falls down and sets the liquid in motion. In order to prevent this, a metal cone is used as cathode, which is fixed with its apex at the centre of a horizontal circular glass plate. The glass plate is much smaller than the cross-section of the cylinder, and so chosen that points in its circumference are approximately equally distant from the base and from the apex of the cone. By this device all parts of the surface of the cone are nearly the same distance from the anode, and the deposited metal distributes itself nearly uniformly over the whole. The base of the cone presses closely against the plate forming the cover. Its height is so chosen that the glass plate f comes about in the middle of the cylinder. The cone and support are made preferably of platinum or gold. Failing these, silver may be used, which is what I was obliged to use.

Fig. 4

When an experiment is to be made, the lower cemented part