Density of the Electrolyte at the Electrodes. 277 



is necessary in order to see the streaks, which, like the sur- 

 rounding electrolyte, are colourless, and are only visible on 

 account of the difference between their index of refraction 

 and that of the main bulk of the electrolyte. A vessel with 

 parallel sides of good plate-glass was employed, and a mirror 

 used to reflect light obliquely into the cell. The arrangement 

 which has been found to be most convenient is shown in the 

 figure, and consists of a cell made of two pieces of plate-glass 

 about 15 centim. square. A piece of india-rubber, 25 centim. 

 long and 3 centim. square section, is bent in a semicircular 

 form and clamped between the two glass plates by means of 

 four iron screw-clamps. In this way a water-tight cell, about 

 1*5 centim. broad, is obtained which may readily be taken to 



pieces for the purpose of cleaning. The electrodes have 

 usually consisted of two pieces of palladium, about *05 centim. 

 thick and with a surface of "5 square centim., fastened to 

 platinum wires and supported by means of a convenient 

 electrode-holder. 



Streaks obtained in dilute pure Sulphuric Acid. 



The electrodes were first heated to redness in order to drive 

 out any occluded gas, and then cleaned by means of glass- 

 paper. They were then placed, by means of the electrode- 

 holder H, in the electrolytic cell containing dilute pure 

 sulphuric acid. The current was sent from one electrode (A) 

 to the other (B) , which is thus the kathode, for a certain time 

 and then reversed. On reversal no gas appears at first from 

 B, which is now the anode, but streaks resembling a dense 

 liquid are with careful observation seen flowing downwards 

 from this electrode. After a time, depending on the size of 

 the electrodes, the strength of the current, and its duration in 



Phil. Mag. S. 5. Vol. 25. No. 155. April 1888. U 



