Page:On Electromotive Wave accompanying Mechanical Disturbance in Metals in Contact with Electrolyte.djvu/19

1902.] enhancement of response thereby produced. A further quantity of KHO was now added so as to increase the strength to 3 parts in a hundred. This caused (c) a complete abolition of response. (Refer to fig. 2, c, d.)

I shall now briefly mention some of the interesting points in connection with the action of chemical reagents. The effect of reagent is not only to increase or diminish the height of response, but also to modify the time relations. By the action of some the quickness with which the maximum effect is reached is enhanced, others produce a prolongation of the period of recovery. Curious effects of this in producing diphasie variation have already been mentioned. In a sensitive annealed wire the further enhancement of response by Na$2$CO$3$ is not so great as in a fresh wire. The effect produced by a reagent is thus seen to depend to some extent on the previous condition of the wire. A certain time is required for the full development of this effect. With some the maximum effect takes place almost instantaneously, while with others it takes place gradually. Again, the effect may with some reach a maximum, after which there is a slight decline. The after-effect of some reagents is transitory while that of others is very persistent.

It is difficult to say how much of this modiﬁcation of responsiveness by various reagents is due to "physical" and how much to "chemical" cause. It has been shown that the responsive power does not depend on the chemical activity of the substance. Ti11 is more responsive than zinc. Pt i11 distilled water shows response. Strong acids and alkalies abolish response, but very dilute KHO enhances response. Oxalic acid, even in minute quantities, abolishes it. Neutral Na$2$CO$3$ enhances it, but dilute NaCl produces no change in the normal response. The responses of the same wire under different physical modiﬁcations are different, and under certain molecular modiﬁcation the sign of response is even reversed. But continued vibration makes the response normal. Again, the enhancement of response produced by Na$2$CO$3$ can be closely imitated by the effect of continued vibration. The stimulating effect of this reagent gradually attains a maximum. The after—effects of some chemical reagents persist even after all traces have been removed. For example, in a certain experiment the A and B wires gave each a response of 23.5 divisions. The wires were lifted from the cell, and the A wire touched with dilute oxalic acid. It was then rubbed under tap—water with a piece of cloth, so as to remove all traces of the acid. On replacing the wire on the cell, the responsiveness of the untouched B was found unchanged, but that of A had undergone an abolition. The depressing action is often so persistent and deep that I have on many occasions failed to revive the response even after the surface layers had been removed by rubbing the wire