46 
DRS. W. RAMSAY AND S. YOUNG ON THE INFLUENCE OF 
The tension was observed three times when the camphor solidified in the barometer- 
tube. The readings differed only by 3"5 millims., and as a mean gave 350 millims. 
The tension at which solidification took place in the bulb-apparatus was observed 
to he 358 millims. The mean of both determinations is 354 millims. 
The annexed figure (fig. 4) shows the curve obtained from both sets of results; the 
pressures corresponding to temperatures of vaporization being indicated by a cross ; 
the vapour-tensions by a dot surrounded by a circle. 
Fig. 4. 
16. It is thus proved that in the case of camphor the pressures corresponding to 
the temperatures of volatilization coincide with the vapour-tensions of solid camphor 
at these temperatures ; and it appears that this assertion can also be made of ice. 
It may be advisable here to point out the difference between the evaporation of a 
liquid and of a solid. When the bottom of a vessel containing a liquid is heated, the 
whole of the liquid becomes hot owing chiefly to convection currents, and evaporation 
takes place only at its surface. When the temperature has reached the boiling point, 
either superheating or ebullition must take place. It would thus seem that the sur¬ 
face is not large enough to afford escape for the gaseous molecules, and in the former 
case the temperature of the liquid rises indefinitely, whereas in the latter the liquid 
