1891.] Professor W. Uamsay on Liquids and Gases. 365 



WEEKLY EVENING MEETING, 



Friday, May 8, 1891. 



Sir Frederick Bramwell, Bart. D.C.L. F.R.S. Honorary Secretary 

 and Vice-President, in the Chair. 



Professor W. Ramsay, Ph.D. F.R.S. M.B.L 



Liquids and Gases. 



Almost exactly twenty years ago, on June 2nd, 1871, Dr. Andrews, 

 of Belfast, delivered a lecture to the Members of the Royal Institution 

 in this Hall, on " The Continuity of the Gaseous and the Liquid 

 states of Matter." He showed in that lecture an experiment which 

 I had best describe in his own words : — 



" Take, for example, a given volume of carbonic acid at 50^ 

 Centigrade, or at a higher temperature, and expose it to increasing 

 pressure till 150 atmospheres have been reached. In the process its 

 volume will steadily diminish as the pressure augments ; and no 

 sudden diminution of volume, without the application of external 

 pressure, will occur at any stage of it. When the full pressure Las 

 been applied, let the temperature be allowed to fall until the carbonic 

 acid has reached the ordinary temperature of the atmosphere. 

 During the whole of this operation no break of continuity has 

 occurred. It begins with a gas, and by a series, of gradual changes, 

 presenting nowhere any abrupt alteration of volume or sudden 

 evolution of heat, it ends with a liquid. 



" For convenience, the process has been divided into two stages, 

 the compression of the carbonic acid and its subsequent cooling. 

 But these operaticms might have been performed simultaneously if 

 care were taken so to arrange the application of the pressure and the 

 rate of cooling that the pressure should not be less than seventy-six 

 atmospheres when the carbonic acid has cooled to 31°." 



I am able, through the kindness of Dr. Letts, Dr. Andrews* 

 successor at Belfast, to show you this experiment, with the identical 

 piece of apparatus used on the occasion of the lecture twenty years 

 ago. 



I must ask you to spend some time to-night in ctmsidering this 

 remarkable behaviour ; and in order to obtain a correct idea of what 

 occurs, it is well to begin with a study of gases, not, as in the case 

 you have just seen, exposed to high pressures, but under pressures 

 not differing greatly from that of the atmosphere, and at temperatures 

 which can be exactly regulated and measured. To many here to-night 

 such a study is unnecessary, owing to its familiarity, but I will ask 

 such of my audience to excuse me, in order that I may tell my story 

 from the beginning. 



