1891.] 



On Electrical Evaporation. 



tube, and touching the poles B and C, were two pieces of cadmium 

 of the same size and shape. The tube was exhausted to the 

 phosphorescent point, and the current was turned on, C being made 

 negative and D positive. No heat was applied. The current was 

 kept on for about half an hour, until a good deposit of metal had 

 been deposited on the glass, the appearance being as shown in fig. 4, 



Fm. 4. 



the glass near the pole C being coated with metal, while the glass 

 round the pole D was clean. The outer boundary of the dark space 

 during the experiment is shown by the dotted line ef. 



The pole B was now made positive and the pole A negative, the 

 current being kept on for another half hour. At the end of the time 

 the only additional effect was a slight darkening round the lump of 

 cadmium, in the same place as, but very much fainter than, the deposit 

 shown in fig. 5. This is probably due to a little leakage of negative 



FIG. 5. 



discharge from the positive pole. The experiment shows that 

 positive electrification does not cause the metal sensibly to vola- 

 tilise. 



In these experiments no estimation was made of the weight of 

 metal removed, and the cadmium only rested by its own weight upon 

 the platinum wires that had been sealed through the glass. To 

 render the experiment quantitative, and at the same time to remove 

 any disturbing effect that might be caused by heating at the point of 

 indifferent contact, the following experiments were made: 



A U-shaped tube, shown in fig. 6, had a platinum pole sealed in 

 each end. 6 grains of pure cadmium were put into each limb and 

 fused round the platinum wire. The ends of the tube were then put 

 into an air-bath, and kept at a temperature of 200 C. during the 



