EESEAECHES ON EVAPOKATION AND DISSOCIATION. 303 



J 



Fig. 1. 



It appears from these experiments that the evaporation 

 at the surface of a solid is capable of indefinite increase 

 however much heat the solid receives ; and that the vola- 

 tilizing-point of a solid rises with rise of pressure and falls 

 with fall of pressure, as is tlie case witli the boiling-point 

 of a liquid; and moreover, that these temperatures are 

 sensibly coincident with those corresponding to their vapour- 

 pressures, a'hat they cannot bo absolutely identical is evi- 

 dent ; for there must be a certain excess of ju'essure to 

 produce a flow of vapour from the evaporating substance to 

 the surrounding space, and consequently tho evaporating 

 substance must have a higher temperature, correspondino' 

 to the higher pressure in its immediate neiglibourhood. 



(2) The pressure of the vapour in contact with a sub- 

 stance in the solid state is lower than tliat of the vajiour in 

 contact with the liquid, at the same temperature for both 

 provided that temperature lies below the melting-point of 

 the solid {Phil. Trans. ^ 1884, part ii., p. 4fJl). This question 

 was experimentally investigated by Eegnault, with negative 

 results {Memoires, xxvi., p. 751-759). Regnault says : " J'ai 



c c 



