1902.] accompanying Mechanical Disturbance in Metals. 289 



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 photo- 

 graphic 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 depress- 

 ing 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 addi- 

 tion 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 varia- 

 tion 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 deflec- 

 tion 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 NaoC0 3 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 ]S"a 2 C0 3 . 



Before 



i 



1 



After 



VOL. LXX. 



X 



