LIQUIDS AND GASES.* 

 By ]*r()f. William Ramsay, F. R. S. 



Almost exactly twenty years ago, on June 2, IcSTl, Dr. Andrews, of 

 Belfast, delivered a lecture to the members of tlie Jfoyal Institution 

 in this hall, on ^<The Continuity of the Gaseous and the Liquid States 

 of Matter."'' lie showed in that lecture an experiment which 1 had best 

 describe in liis own words: 



"Take, for exam]ile, a i;iven volume of carbonic acid at HOOC, or af 

 a hijiher temperature, and expose it to increasing- i)ressure till 150 

 atmosidicrcs have been reached. In the process, its vohini<' will steadily 

 diminish as the pressure auji'ments; and no sudden dimunition of 

 volume, without the application of external ])ressure, will occur at any 

 stage of it. Wlien the full ])ressure has been applied, let tlie tempera- 

 ture be allowed to fall, until the carl)onic acid has reached rlie 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 gi-adual changes, presenting nowhere any abrupt alterations 

 of volume, or sudden evolution of heat, it ends with a liquid. I^'or con- 

 \<'nience, the i)rocess lias been devided into two stages — the compress- 

 ion of the carbonic a('i<l, and its subsequent cooling. But these opera- 

 tions might have been performed sinuiltaneously, if care Avere taken so 

 to arrange the ap]»li<'ation of the pressure and the rate of cooling that 

 the ju'essure should not be less than 70 atmospheres when the carbonic 

 acid had cooled to-'HoC." 



1 am able, through the kindness of Dr. Letts, Dr. Andrews's succes- 

 sor at Belfast, to show you this exi)erimcnt, with the identical piece of 

 api»aratus used on the o(;casion of the lecture twenty years ago. 



1 must ask you to spend some time to-night in consideiing this 

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

 occurs, it is well to begin with the 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, an<l at tem])eratures 

 M'hich can be exactlx' legulated and measure<l. 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 1 may tell my story 

 from the beginning. 



* IjCf'tnre deliv<Me<l iit tlu^ Koy;il Institution, on Fiidii.v, May S. (From Xiiture, 

 July 23, 1891; vol. xuv, j)p. 274-277.) 



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