INEXPENSIVE CONDUCTIVITY APPARATUS A. J. CURRIER
AND
J. S. BUSER
The Pennsylvania State College, State College, Pennsylvania
A
T THE present time, when appropriations for the purchase of apparatus have been seriously curtailed or canceled entirely, instructors are faced with the necessity of remodeling old apparatus or devising simple types from materials a t hand. Equipment for the experimental demonstration of the electrical conductivity of solutions is indispensable for the study of ionization which is now a fundamental topic in all high-school and college courses in general chemistry. A number of diierent types of conductivity apparatus, designed for lecture demonstration or for the use of the individual student, are described in the literatUre,1.2.3.4
rials are used in the construction of the apparatus
viz., a ring-stand, two clamps, two clamp fasteners, one number 7, 2-hole rubber stopper, two pieces of number 7 insulated copper wire (such as is used for house wir-
ing), electrical insulation tape for wrapping the connections between the electrode wires and the four-foot length of extension cord with an attached plug, an ordinary porcelain lamp socket, and a 15-watt electric bulb. The rubber insulation was stripped off the ends of the electrode wires and the bare wire was carefully scraped forming copper electrodes about 8 an.in length. The number 7 wire fits snugly into the holes of the rubber stopper. (Either alternating or direct current is, of course, suitable for demonstrating conductivity whereas in experiments on electrolysis of water or salt solutions only direct current should be used.) Incidentally, it is desirable to paint the laboratory hardware (used in demonstration work) with ordinary aluminum paint to prevent corrosion and to make the apparatus more neat and attractive in appearance. k In demonstrating the conductivity (or non-conductivity) of various solutions the two clamps holding the electrodes and the lamp may be placed in any position desired. Our procedure is to place the parts in the position indicated in the photograph and to raise the beaker containing the solution to be treated under the electrodes so that they are well immersed in the solution. The electrodes should be immersed in a beaker of water after testing each solution to remove any adhering electrolyte. Differences in conductivity of such weak electrolytes as tap water, acetic acid, ammonium hydroxide, and strong electrolytes such as The conductivity apparatus illustrated by the ac- sodium hydroxide and hydrochloric acid can easily be companying photograph was constructed by one of the shown by the difference in intensity of the light. The authors (A. J. C.) about two years ago and has been effect of dilution on conductivity can also be shown found to be very effective in lecture demonstrations effectively by placing a beaker of distilled water on the of electrical conductivity of solutious in the usual table, lowering the electrodes into the water, and adding qualitative manner. By reference to the photograph, glacial acetic acid by means of a funnel or thistle tube it will be observed that only common laboratory mate- placed so that the acid flows to the bottom of the beaker. DAY AND DAVIS,"A conductivity apparatus;' J. CnEM. When the acid is stirred into the water the light changes from a faint to a distinct glow. When non-electrolytes Eouc.. 5, 1121 (Sept., 1928). AND PEASE,"An improved lecture-table demonG~LBERT are being studied, the electrodes may he short-circuited stration of ionization and conductivity," ibid., 4, 1297 (Oct., by placing a screw driver (with a wooden handle) across 1927). a GORDON. "Simple cell for study of conductance," iw., 10, them just above the solution showing that the electric 440 (July, 1933). current is still available a t the electrodes. The screw 4 PETERSON, "A device for measuring the comparative condriver is also useful in testing the apparatus before use. ductivity of electrolytes," ibid., 9, 923 (May, 1932).
