VOL. 4, No. 10
DEMONSTRAT~ON OF IONIZATION AND CONDUCTIVITY
1297
AN IMPROVED LECTURE-TABLE DEMONSTRATION OF IONIZATION AND CONDUCTIVITY E. C. GILBERTAND CHARLES S. PEASE, OREGONAGRICULTURAL COLLEGE, CORVALLIS, OREGON
Many textbooks describe lecture demonstrations to show the effect of dilution on the conductivity of electrolytes, most of them using a layer of sulfuric or acetic acid below a layer of water in a glass trough provided with electrodes. By a very simple modification, we achieved a considerable improve-
ment in this important demonstration, at least as evidenced by student interest and ability to answer questions concerning it. Using glacial acetic acid, we colored it a brilliant red with fuchsin. With the common set-up shown, the colored acid was allowed to run beneath the water. The students were fascinated to see the brilliant red layer approach and touch the electrodes. All but a few now expected the light to glow. This emphasized the idea that electrolytes must commonly be in solution before they ionize. Bringing the acid into solution by stirring the mixture caused the light to glow visibly. The addition of another liter of water, of course, caused a brighter glow, leading to a discussion of the maximum conductivity to be expected and the expression of ionization in terms of the conductivity ratio. The demonstration catches the eye of the student, with the brilliant color. With a white towel beneath the trough, a large class can follow the spread of the acid to the electrodes; furthermore, the use of an elec-
trolyte for which the law of mass action holds obviates any hesitation on the part of the instructor in speaking of the presence of unionized molecules of the acid in solution, and he may follow the classical theory of Arrhenius, ad lib.
