Minas Ensanian Bell Aerorystems Company'

Buffalo, New York 14240 I The Bequerel Effect

In practice, a thermogalvanic cell or thermocell is the simplest battery that can he made, consisting merely of a glass tube filled with a solution of a metal salt at whose opposite ends are electrodes of the same metal but a t different temperatures.=

It is possible to convert a thermogalvanic cell into a photogalvanic cell, e.g., if a copper thermocell with coiled wire electrodes is left alone for a period of 5 or 10 days a t ambient temperature (0.005 M cupric sulfate) it will exhibit both thermo and photogalvanic behavior. In contrast to the platinum electrode, thionine, ferrous sulfate aqueous system3 for demon- strating the Becquerel Effect, the above system is very inexpensive and easy to construct. Voltages in excess of 100 mv can readily be obtained.

On the other hand if it is desired to demonstrate the effect in a single laboratory period, this can be nc- complished by the addition of some glucose to the 0.005 M electrolyte, and if the cell is in the form of a vertical Pyrex tube (the ends of which are Tygon tubing and the electrodes held in place by means of pinch clamps) the repeated heating of the region (glass wall)

of the upper electrode with a hot air gun (78°C) for durations of about 5 min will promote both thermo and photogalvanic action. It is not necessary that the lower electrode be kept in the dark.

If the upper electrode region is illuminated while it is still warm there will be a sharp decrease in the output voltage of the cell, and conversely, under this condition illumination of the lower electrode will produce a greater increase in the cell voltage. If the room is darkened the photogalvanic effect can be demonstrated with a match.

A Textron Company. ' ENSANIAN, M., J . Eledmchem. Soe., 112, 6 (196.5). Newly

constructed cells will generally exhihit a voltage in the absence of a temperatore differential. This is an interesting and important phenomena which is associated with the relative information content of the electrodes e.g., surface conditions, strain energy etc. m d it! urinciule offen a method to determine the stored energy of a solid. -

RABINOWITCH, E., in Solar Energy Research, F. DANIELS and J . A. DUFPIE. EditOm. Universitv of Wisconsin Press. 1955. DD. 195-201; H E ~ T , L. J:, et al., in""~hotochemistr~ in the id and Solid States," John Wiley & Sons, Inc., New York, 1960, p. 84.

240 / Journol of Chemiml Education