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Thermal Properties of Ethyl Alcohol. [May 7, 



the dissociation of a compound, observations regarding its vapour- 

 density, which would apparently lead to a correct estimate of the 

 amount of dissociation under any given constant temperature and 

 pressure, are complicated by the phenomena exhibited by liquids as 

 such ; and it still admits of question whether bodies with such 

 abnormal vapour-densities as are displayed by acetic and homologous 

 acids, should have their abnormality ascribed to dissociation ; or, less 

 exclusively, it may be asked, how much of this abnormality is to be 

 attributed to the one cause and how much to the other ? 



To reach a conclusion on this point, it was necessary to study and 

 compare the behaviour of substances belonging to the four types : — 

 (a) liquids, the vapours of which are not known to dissociate under 

 the conditions of temperature of the experiment ; (b) liquids, the 

 vapours of which probably dissociate into like molecules ; (c) bodies 

 which dissociate gradually in the gaseous state into unlike mole- 

 cules ; (d) bodies which dissociate completely on passage into the 

 gaseous state. 



The liquid ethyl alcohol has been chosen as a typical representa- 

 tive of the first class, and its behaviour has been fully studied. 

 Numerous measurements have been made which establish relations : 

 — (a) between volume of liquid alcohol and temperature at various 

 pressures ; (6) between volume of liquid alcohol and pressure (com- 

 pressibility) at various temperatures ; (c) between volume of un- 

 saturated and of saturated vapour, temperature, and pressure ; and 

 (d) the heats of volatilisation have been calculated from these data. 

 The limits of temperature extended from 13° to 246° ; and the limits 

 of pressure from 10 mm. to 60,000 mm. 



The point of chemical importance deduced from this research is 

 that alcohol vapour in contact with liquid acquires its normal density, 

 23, at about 50° ; and that at lower temperatures no tendency 

 towards a rise in vapour-density could be detected; as it will be 

 shown in a subsequent memoir that the vapour of acetic acid, in 

 contact with its liquid, acquires increased density on lowering tempe- 

 rature and pressure, the probable conclusion may be drawn that 

 complex molecular groups are produced in larger number, or exhi- 

 biting greater complexity with decrease of temperature. The vapour 

 of alcohol, on the other hand, shows no such tendency. 



This research has also shown that the critical point of ethyl alcohol 

 lies at a temperature differing not more than 0'5° from 243*6°, and at 

 a pressure of nearly 48,900 mm., while the volume of 1 gram of the 

 critical fluid is approximately 3 -5 c.c. 



