Page:On Electromotive Wave accompanying Mechanical Disturbance in Metals in Contact with Electrolyte.djvu/7

	Permanent current.	Current of response.
A treated with sodium carbonate ..............	$\leftarrow$	$\leftarrow$
,,,,,,oxalic acid .............	$\leftarrow$	$\to$
,,,,,, very dilute potash .............	$\leftarrow$	$\leftarrow$
,,,,,,strong potash..................	$\leftarrow$	$\to$

Current of response is always towards the more excitable point.

Deflection of Traces of Physio-chemical Change.

I will now describe an experiment which will show in a striking manner how exceedingly delicate is the method of electric response to stimulation, and how by its means we can detect and measure traces of physico-chemical changes in different parts of the same solid. Take a wire and touch two points, one with Na₂CO₃ solution the other with oxalic acid. Wash the wire. There is no trace left of the previous treatment. Let one contact be permanently made at a normal or previously unacted point N. Let the other exploring contact be moved

Fig. 3.—Electro-molecular Explorer.