1871.] Abrupt Change at Boiling or Condensing fyc. 3 



some real and true significance. This theoretical continuity, from the 

 ordinary liquid state to the ordinary gaseous state, must be supposed to 

 be such as to have its various courses passing through conditions of pres- 

 sure, temperature, and volume in unstable equilibrium for any fluid matter 

 theoretically conceived as homogeneously distributed while passing through 

 the intermediate conditions. Such courses of transition, passing through 

 unstable conditions, must be regarded as being impossible to be brought 

 about throughout entire masses of fluids dealt with in any physical opera- 

 tions. Whether in an extremely thin lamina of gradual transition from a 

 liquid to its own gas, in which it is to be noticed the substance would not 

 be homogeneously distributed, conditions may exist in a stable state having 

 some kind of correspondence with the unstable conditions here theoreti- 

 cally conceived, will be a question suggested at the close of this paper in 

 connexion with some allied considerations. 



It is first to be observed that the ordinary liquid state does not neces- 

 sarily cease abruptly at the line of boiling-points, as it is well known that 

 liquids may, with due precautions, be heated considerably beyond the 

 boiling temperature for the pressure to which they are exposed. This 

 condition is commonly manifested in the boiling of water in a glass vessel by 

 a lamp placed below, when the temperature of the internal parts of the 

 water, or, in other words, of the parts not exposed to contact with gaseous 

 matter, rises considerably above the boiling-point for the pressure, and the 

 water boils with bumping *. At this stage it becomes desirable to refer to 

 Dr. Andrews's diagram of curves showing his principal results for carbonic 

 acid, and to consider carefully some of the remarkable features presented 

 by those curves. In doing so, we have first, in the case of the two curves 

 for 13°'l and 21°*5, which pass through the boiling interruption of con- 

 tinuity, to guard against being led, by the gradually bending transition 

 from the curve representing obviously the liquid state into the line seen 

 rapidly ascending towards the curve representing obviously the gaseous 

 state, to suppose that this curved transition is in any way indicative of a 

 gradual transition from the liquid towards the gaseous state. Dr. Andrews 

 has clearly pointed out, in describing those experimental curves, that the 

 slight bend at about the commencement of the rapid ascent from the 

 liquid state is to be ascribed to a trace of air unavoidably present in the 

 carbonic acid ; and that if the carbonic acid had been absolutely pure, the 

 ascent from the liquid to the gaseous state would doubtless have been quite 

 abrupt, and would have shown itself in his diagram by a vertical straight 



* It has even been found by Dufour (Bibliotbeque Universelle, Archives, year 1861, 

 vol. xii., " Eecbercbes sur 1' ebullition des Liquides) that globules of water floating im- 

 mersed in oil, so as neither to be in contact with any solid nor with any gaseous body 

 may, under atmospheric pressure, be raised to various temperatures far above the ordi- 

 nary boiling-point, and occasionally to so bigh a temperature as 178° C, without boilinc. 



On tbis subject inference may also be made to tbe important researches of Donuy, 

 "Sur la cohesion des Liquides et sur leur adherence aux Corps solides," Ann.de 

 Chimie, year 1846, 3rd ser. vol. xvi. p. 167.— Jul 28, 1871. 



B 2 



