120 On the Critical Point of Liquefiable Gases. 
gas to have a density greater than that of the liquid anhydride. 
Again M. Jamin has been anticipated. " But I venture to 
think that the possession of surface-tension is not a criterion 
of the existence of a liquid. And a most striking argument 
in support of this theory has lately been furnished by M. 
Cailletet (Compt. Rend. xc. 210). He found that carbonic 
anhydride at a temperature of 5 0, 5, when the lower portion 
of his experimental tube was filled with liquid, the upper 
portion being filled with a mixture of gaseous carbonic 
anhydride with air, mixed with the air when a pressure 
of 130 atmospheres was applied. The question is a simple 
one, Does the gas become liquid, or the liquid become gas ? 
Or do they both enter a state to be called neither liquid nor 
gas?" For the theory brought forward I must refer to the 
original memoirs in the Royal Society's Proceedings ; but if 
I have not already trespassed on your space, let me finish 
with the last paragraph of my second memoir. 
"The views expressed in this paper are : — (1) That a gas 
may be defined as a body whose molecules are composed of a 
small number of atoms ; (2) a liquid may be regarded as 
formed of aggregates of gaseous molecules forming a more 
complex molecule ; and (3) that above the critical point the 
matter may consist wholly of gas, if a sufficient volume be 
allowed ; wholly of liquid, if that volume be diminished suffi- 
ciently; or of a mixture of both at intermediate volumes 
When prevented from mixing by interposing a capillary 
tube between the two. the liquid and gas retain their several 
properties." 
I am much interested to find that the further experiments 
made by M. Cailletet at the instance of M. Jamin appear to 
substantiate these views; and I cannot refrain from expressing 
my gratification that they are shared by such a distinguished 
physicist as M. Jamin. 
It may be of interest to add that, in one or two experiments, 
I have noticed that amyl alcohol near its critical point forms 
globules which rise comparatively slowly in the tube in which 
it is confined and then disappear. These globules appear to 
float, and would present the phenomenon of a liquid lighter 
than a gas. 
I am, Gentlemen, 
Your obedient servant, 
William Ramsay. 
