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TIT. On Evaporation and Dissociation .—Part II. A Study of the Thermal Properties 
of Alcohol. 
By William Ramsay, Ph.D., and Sydney Young, D.Sc. 
Communicated hy Professor G. G. Stokes, Sec.R.S. 
Received April 18,—Read May 7, 1885. 
[Plates 3-7.] 
1. The density of gases is found to increase as the temperature falls towards their 
condensing point. This may be explained by one of two theories :— 
(1) That complex gaseous molecules are formed in increasing numbers as the tem¬ 
perature falls; these complex molecules consisting of congeries of the simpler molecules 
known to exist in gases (see Playfair and Wanklyn, Trans. Roy. Soc. Edin., xxii., 
(3), p. 441, and ‘ Annalen,’ 122, p. 245 ; also Naumann, ‘ Annaien,’ 155, p. 325, and 
‘ Thermochemie,’ pp. 86 et seq.). 
(2) That mutual attraction of the molecules, caused by their greater proximity, 
comes into play, and reduces their mean distance from each other. 
The second of these hypotheses involves a deviation from Avogadro’s law; while 
the first does not. 
Similarly, with those substances in which dissociation takes place in the gaseous 
state, the density of the mixture of gases increases with fall of temperature, and 
this is doubtless caused by the increase in number of compound molecules. That this 
is the case with nitrogen peroxide can hardly be questioned, from the different 
physical properties of the gas under different conditions of temperature ; and the 
phenomenon is also well seen in the case of tertiary amyl bromide. 
It may be pointed out that both these causes may operate at the same time. It has 
occurred to us that light may be thrown on this question by a study of the thermal 
properties of three representative compounds :— 
(1) What may be called a normal substance; i.e., a substance in which no chemical 
dissociation is generally supposed to occur. Ethyl alcohol has been chosen as a 
representative of such a type. 
(2) A substance the vapour-density of which shows marked abnormality, and 
which is suspected by many chemists of forming complex molecular groups. It is 
generally supposed that acetic acid, tends to form double molecules of the 
formula C 4 H 8 0 4 , and that its abnormal vapour-density is to be explained on this 
hypothesis. Hence we have chosen it as a subject of experiment. 
(3) It is hoped that it may be possible to effect a similar investigation of a sub- 
r 2 
