METHODS OF ELECTRICAL STIMULATION 27 



carbon. Touch the ends of the wires together. 

 An electric current passes, as evidenced by the 

 spark when the contact is made or broken, but 

 no material change can be observed in the me- 

 tallic conductor. 



2. Place two pieces of platinum foil in a solu- 

 tion of copper sulphate and connect them to the 

 terminal zinc and carbon as before. Copper will 

 be deposited on the platinum connected with the 

 zinc, and oxygen will be deposited on the plati- 

 num connected with the carbon. Thus the 

 passage of the current through the conducting 

 solution or electrolyte has caused a change in 

 the solution, evidenced by a movement of pon- 

 derable matter. 



Faraday discovered that the quantity of matter 

 moved by the current was always proportional 

 to the quantity of the current, independent of 

 its strength or speed. In the electrolysis of 

 hydrochloric acid 96,500 coulombs 1 will set free 

 1 gm. of hydrogen. Faraday also discovered 

 that the same quantity of current (96,500 cou- 

 lombs) which carries 1 gm. of hydrogen will 

 carry the chemical equivalent of any other sub- 



1 A coulomb (ampere) of electricity is the quantity of cur- 

 rent which, when passed through a solution of silver nitrate in 

 water, deposits silver on the cathode, or negative pole, at the 

 rate of 0.001118 gram per second. 



