A CONDUCTIVITY APPARATUS JESSE B. DAYAND FORDC. DAVIS.THEOHIO STATE UUNIVERS~TV, COLUMBUS, Orno Several models of conductivity apparatus for first-course chemistry students have been described in either laboratory manuals or the literature. Some of these are constructed so that they may be used a t the desk of any student and some of them are for fixed laboratory locations. All of them possess the merit of inexpensiveness. Three years ago the authors built the apparatus shown in the drawing. A General Electric No. 36537 porcelain 30 ampere, double pole covered main-line cut-out is the receptacle, B, for the 10-watt, S 14 clear lamp, E, and the Bryant No. 699 split attachment plug, A. One pole of the attachment receptacle is wired to the open binding post, D, and the other to the roundhead wood screw, L; one pole of the lamp receptacle is connected to the post, C, and the other to the screw, F. The contact strip, G, is a radio bus strip and the button, H, the insulated nut of a radio binding post, the latter being attached to the former by means of a machine saew and the whole (excepting the contact points) covered with liquid Bakelite. The enclosing box is of soft wood treated with oil stain and the attaching clamp, M, is from a funnel support. For safety from a "short" a piece of rubber tubing, K, is placed on the rod of the ring stand opposite the contact bar. The electrodes are of #6 soft copper wire. The apparatus is more expensive than any referred to in the introduction but has several offsetting points in its favor, particularly when needed in fairly large numbers by large classes. (1) The feed wires are enclosed which eliminates the "blowing" of fuses. (2) The electrodes are well outside the apparatus which lessens the likelihood of solution "shorts" resulting from spillage. (3) Current flows only when the key is closed. (4) The apparatus can be attached to the "plug-in" box on the student's
desk. ( 5 ) Being portable, each student may thus be held responsible for the condition of the apparatus. (6) The apparatus may be raised or lowered (to the extent of the height of the support rod) to accommodate the conductivity vessel. . (7) When the lamp and attachment cord (with the upper part of the split plug) are removed and the electrodes folded up and pushed back, the apparatus may without risk of damage be stored in a small space.
