Effect of Chemical Reagents.
I shall now give photographic records of a few typical cases which will graphically illustrate the influence of chemical reagents. The mode of procedure is as follows. The cell is filled with water, and photographic records are taken of responses to single vibrations of constant amplitude, applied to one of the two wires at intervals of 1 minute. The responses will be found uniform. Chemical reagent is now added, and similar vibrations applied as before. The responses will exhibit either an increase or diminution, depending on the exciting or depressing power of the reagent. It is also quite easy to obtain duplicated results by alternately vibrating the A and B wires. Uniform responses, alternately positive or negative, will be first obtained; after the addition of reagent both will exhibit either an increase or a diminution. As has been said before a very high external resistance, varying from 1 to 5 megohms, is interposed in the external circuit, the slight variation of internal resistance of the cell due to the addition of the reagent being then quite negligible compared with the total resistance of the circuit. That there is no appreciable variation in the total resistance can be independently verified by applying a known electromotive force before and after the addition of the reagent, when the resulting deflection will be found to be the same in the two cases. The responsive deflections are thus simply proportional to the electromotive variations produced.
Chemical Excitants. The following record (fig. 11) exhibits the
Fig. 11.—Enhanced response by the action of Na2CO3 solution on platinum. The intensity of stimulus is kept constant throughout. The curves to the left show the responses before, and those to the right after, the application of Na2CO3.
