

By Prof. WILLIAM RAMSAY, Ph.D., P.R.S., and 

 Pbof. SYDNEY YOUNG, D.Sc. 



THE investigations, a description of whicli is given in the 

 following pages, were Tindortaken in order to arrive 

 at a more accurate knowledge of the relations between the 

 phenomena of the evaporation of stable solids and liquids, on 

 the one hand, and of dissociating bodies, on the other. But 

 as the relations of stable bodies as regards volume, tempera- 

 ture, and pressure had not boon fully investigated, our 

 experiments have beon largely directed towards the elucida- 

 tion of such relations. The question we have endeavoured to 

 solve is: — Wliat processes are actually in operation during 

 the evaporation or volatilization of a liquid or solid? 



(1) It was necessary first to prove that the dynamical 

 method of measuring the vapour-pressures of solids gives 

 results identical with the statical method. This has long 

 been known to be the case with liquids. This led — 



(2) To a proof of theoretical deductions by Kirchhoff, and 

 subsequently a,Tul independently by James Thomson, that, 

 at the same temperature, the pressure of vapour in contact 

 with a substance in the solid state is lower than that of 



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