189 l.J On Electrical Evaporation, 91 



FIG. 1. 



with the pole B, which in the experiment was always kept negative, 

 the pole A being positive. When the exhaustion was such that the 

 passage of the current gave green phosphorescence over the glass, 

 heat was applied simultaneously to both ends of the U-shaped tube 

 by means of a gas-burner and air-bath, so that one piece of cadmium 

 was at the same temperature as the other. The current was then 

 applied and was kept on for about an hour, and it was remarkable 

 that no metal was deposited in the neighbourhood of the positive pole, 

 the surrounding portion of the tube being quite clean, while the 

 corresponding part of the other limb of the tube, having no electrodes, 

 was thickly coated, the appearance being shown in the drawing. 



As the temperature was high, metal had distilled off from both 

 lumps ; hence there was no visible difference in the amount of the 

 deposit in the two sides. It is evident that, to render the electrical 

 action most visible, the temperature should be kept short of the 

 normal volatilising point. 



In the next experiment an exactly similar tube was used ; the 

 vacuum was such that the green phosphorescence of the glass was 

 well seen, the temperature was kept just below the melting point of 

 cadmium, and the current was kept on for an hour. On examining 

 the tube at the end of this time, the appearance was as seen in fig. 2. 

 A considerable deposit had taken place on the end of the tube near 

 the negative pole, the space round the positive pole was clear, while 

 in the limb of the tube where no electricity had been passing only 

 a very little deposit of metal was seen, as shown in the figure. 



The temperature in this experiment having been kept below the 

 melting point, had no electricity been applied, there would have been 

 very little, if any, evaporation. The amplitude of the molecular 

 oscillations was increased by the rise of temperature, but not suffi- 



