170 



Prof J. Dewar. 



[Feb. 12.. 



II. " Note on Electrolytic Experiments." By JAMES Dewar, 

 M.A., F.R.S., Jacksonian Professor, University of Cam- 

 bridge. Received February 10, 1880. 



Having had occasion to employ the intermittent current of the 

 de Meritens magneto- electric machine arranged for intensity in con- 

 nexion with spectroscopic work, the following notes of electrolytic 

 experiments made by means of it may not be without some interest. 



The number of intermittent currents taking place in the circuit 

 during the course of the following experiments may be taken as 

 about 300 per second, and as the amount of energy in circulation is 

 very considerable, an examination of its action on electrolytes 

 was of some interest. 



Dilute sulphuric acid, of about 1 of acid to 6 of water, used as the 

 electrolyte in a large circular glass vessel, gave the following results : — 



On placing two rather large platinum poles, each exposing a sur- 

 face of about 32 square centims., no decomposition took place, a few 

 bubbles of gas came off: at one pole for a short time, which soon 

 ceased. The current was proved to be passing by placing a telephone 

 near the side of the glass vessel, and also by the rapid increase in 

 the temperature of the acid, which very soon reached the boiling 

 point. The absence of decomposition was due to the rapidity with 

 which the current in the de Meritens machine is alternated, the gases 

 given off at each pole being rapidly superposed and combining imme- 

 diately to form water. 



Decomposition was immediately produced by making and breaking 

 the current rapidly with the hand, or better still, by placing a large 

 tuning fork in the circuit, to which was attached a copper rod which 

 dipped in and out of mercury at every vibration of the fork. 



When two poles were used, consisting of platinum wire, decom- 

 position went on without intermission at both poles, but on the other 

 hand, when one pole was a plate of platinum and the other a platinum 

 wire, the mixed gases were given off at the wire pole only. 



The spectrum of the platinum poles, viewed with a small direct 

 vision spectroscope, was very complicated, showing the H and air 

 lines. 



Platinum wire of about '5 millim. in diameter used as one pole, 

 readily fused when held close to the surface of the liquid, and re- 

 mained white hot when immersed below the surface, with a continual 

 ejection of the particles of the fluid, and successive small explosions 

 of the mixed gases. 



Aluminium wire behaved in a remarkable way when used as one 

 of the poles, the other pole consisting of a large surface of platinum. 



