INORGANIC RESPONSE 141 
be produced in the internal resistance of the cell. The 
effect of this on the deflection is eliminated by inter- 
posing a very high external resistance (from one to five 
megohms) in comparison with which the internal re- 
sistance of the cell is negligible. The fact that the 
introduction of the reagent did not produce any varia- 
tion in the total resistance of the circuit was demonstrated 

Before 4 After 
Fic. 89.—Srimuiatine Action oF Na,CO, on T1x 
by takine two deflections, due to a definite fraction of 
a volt, before and after the introduction of the re- 
agent. These deflections were found equal. 
I first give a record of the stimulating action of 
sodium carbonate on tin, which will become evident by 
a comparison of the responses before and after the 
introduction of Na,CO, (fig. 89). The next record 
