90 Mr. W. Crookes. [June 11, 



Hitherto I have spoken of a liquid evaporating into a gas ; but the 

 same reasoning applies equally to a solid body. But whilst a solid 

 body like platinum requires an intense heat to enable its upper 

 stratum of molecules to pass beyond the sphere of attraction of the 

 neighbouring molecules, experiment shows that a very moderate 

 amount of negativ^ electrification superadds sufficient energy to 

 enable the upper stratum of metallic molecules to fly beyond the 

 attractive power of the rest of the metal. 



If a gaseous medium exists above the liquid or solid, it prevents to 

 some degree the molecules from flying off. Thus both ordinary and 

 electrical evaporation are more rapid in a vacuum than at the ordinary 

 atmospheric pressure. 



I have recently made some experiments upon the evaporation of 

 different substances under the electric stress. 



Evaporation of Water. A delicate balance was taken, and two very 

 shallow porcelain dishes were filled with acidulated water and 

 balanced on the pans. Dipping into each dish touching the liquid, 

 but not the dish was a platinum wire, one connected with the in- 

 duction coil and the other insulated. The balance was left free to 

 move, but was not swinging, the pointer resting at the centre of the 

 scale. The water in connection with the coil was first made positive. 

 After If hours there was scarcely any difference between the weight 

 of the insulated water and that which had been exposed to the 

 positive current. Equilibrium being restored, the current was re- 

 versed, the negative current being kept 011 the dish for tw T o hours. 

 At the end of this time the electrified water was decidedly lighter. 

 After having again restored equilibrium, the electrification of the 

 dishes was reversed, i.e., the one that had before been insulated was 

 made negative and the other one was insulated. In an hour the 

 electrified water had become decidedly lighter than the insulated 

 water. The experiment was performed in a room of uniform tempera- 

 ture, and any draught was prevented by the glass case of the 

 balance. In a subsequent experiment in which the quantities were 

 weighed, it was found that negatively electrified water lost in 1^ hours 

 l/1000th part of its weight more than did insulated water. 



This experiment shows that the disturbing influence which assists 

 evaporation is peculiar to the negative pole even at atmospheric 

 pressures. 



The metal cadmium was next experimented upon. 



Evaporation of Cadmium. If the flying-off of the metal of the 

 negative pole is similar to evaporation or volatilisation, the operation 

 should be accelerated by heat. 



A tube was made as shown in fig. 1. A and B are the platinum 

 poles sealed through the glass. C and D are two blocks of metallic 

 cadmium of the same size and weight. The piece C is in contact 



