"Transfer -resistance" in Electrolytic Cells. 133 



With the dilute sulphuric acid the expansion was =3*0 mm. 

 in two seconds, and on then stopping the current the contrac- 

 tion was 1*0 mm. in three seconds. Hydrogen was freely 

 evolved. Increasing the density of the current by raising 

 the bottle partly out of the liquid, increased the rate of ex- 

 pansion and decreased that of contraction. 



With the strong nitric acid the expansion was I/O mm. in 

 three seconds, and on then stopping the current a contraction 

 occurred of about *2 mm. in three seconds. No gas was 

 evolved at the cathode. Increasing the density of the current 

 in the above manner had but little effect. By passing the 

 same strength of current up through the flask, by means of 

 a platinum wire in contact with the bottom of the bottle, an 

 expansion of only *5 mm. was produced in ten seconds. 



The larger expansion with the dilute sulphuric acid than 

 with the strong nitric acid, notwithstanding the cooling in- 

 fluence of the evolved and gaseous hydrogen in the former 

 case, was probably due to greater resistance of some kind at 

 the surface of the bottle in the former than in the latter liquid. 

 If this conclusion is correct the heat produced by such re- 

 sistance at the platinum cathode in dilute sulphuric acid was 

 greater than that absorbed by the liberation and assumption 

 of the gaseous state of the hydrogen in that liquid, and also 

 greater than that evolved by such resistance in strong nitric 

 acid. The small amount and slowness of expansion occurring 

 when the current was passed up the flask, showed that the 

 sudden expansion was not due to heat of conduction-resistance 

 of that vessel. 



In another experiment with dilute sulphuric acid one volume 

 of strong acid to ten of water, and a current of "336 ampere, 

 the expansion was 3 mm. in two seconds ; and on then stop- 

 ping the current the contraction was 1*0 mm. in thirty seconds. 

 And with nearly concentrated nitric acid, and a current of 

 •084 ampere, the expansion was 1*0 mm. in three seconds, 

 and by then stopping the current, a trace of contraction in 

 thirty seconds. Of course, in every one of the experiments, 

 the amount of expansion shown by the index was less than 

 the total, because the bottle itself expanded as well as the 

 air in it. 



If the sudden expansion in these cases was really due to 

 some " resistance " at the surface of the bottle, it ought to 

 vary directly with it. In order to test this point the amounts 

 of such " resistance " at the surface of the bottle when used 

 as a cathode were carefully measured whilst a current of "454 

 ampere was passing. That in the dilute sulphuric acid (one 

 to ten) equalled 3*41 ohms ; whilst that in the strong nitric 



