ello a 
IV. 
ON THE CONTINUITY OF ISOTHERMAL TRANSFORMATION FROM THE 
LIQUID TO THE GASEOUS STATE. By THOMAS PRESTON, M.A., F.R.U.I. 
[Read Frsrvary 19, 1896. } 
WueENn any substance passes from the liquid to the gaseous state by isothermal 
transformation, the relation between pressure and volume is represented diagra- 
matically by a curve such as that shown in fig. 1. In this curve, the part AB 
refers to the condition of the substance in which it is altogether liquid, and 
along this part the volume alters only slightly as the pressure is varied. When 
Ere: 1. Fie. 2. 
the pressure is gradually reduced, however (the temperature being maintained 
constant), a point B is reached at which the liquid begins to boil, and the whole 
mass may be transformed into the gaseous state under constant pressure, if heat 
be supplied to keep the temperature constant while the volume is allowed to 
increase from B to D. The part BD of the isothermal is consequently a right 
line parallel to the axis of volume, and at D the whole mass is in the condition 
of saturated vapour. Beyond D the curve D E is approximately a rectangular 
hyperbola as it represents the isothermal of a gaseous substance which approxi- 
mately obeys Boyle’s law. 
Very shortly after Andrews’ celebrated experiments on the isothermals of 
carbon dioxide, and on the continuous transformation of matter from the gaseous 
TRANS. ROY. DUB. SOC., N.S. VOL. VI., PART IY. U 
