INORGANIC RESPONSE 97 



*> 



The amplitude of a given vibration can thus be pre- 

 determined by the adjustment of the sliding stop. In 

 this way we can obtain either uniform or definitely 

 graduated stimuli. 



Considerations showing that electric response is due 

 to molecular disturbance. The electromotive variation 

 varies with the substance. With superposition of 

 stimuli, a relatively high value is obtained in tin, 

 amounting sometimes to nearly half a volt, whereas 

 in silver the electromotive variation is only about *01 of 

 this value. The intensity of the response, however, 

 does not depend on the chemical activity of the sub- 

 stance, for the electromotive variation in the relatively 

 chemically inactive tin is greater than that of zinc. 

 Again, the sign of response, positive or negative, is 

 sometimes modified by the molecular condition of the 

 wire (see Chap. XII). 



As regards the electrolyte, dilute Nad solution, 

 dilute solution of bichromate of potash &c. are normal 

 in their action, that is to say, the electric response in 

 such electrolytes is practically the same as with water. 

 Ordinarily I use tap-water as the electrolyte. Zinc 

 wires in ZnS0 4 solution give responses similar in 

 character to those given by, for example, Pt or Sn in 

 water. 



Test experiment. It may be urged that the E.M. 

 effect is due in some way (1) to the friction of the 

 vibrating wire against the liquid ; or (2) to some 

 unknown surface action, at the point in the wire of 

 the contact of liquid and air surfaces. This second 

 objection has already been completely met in experi- 



H 



