EXPERIMENTAL KNOWLEDGE OF THE PROPERTIES OF MATTER. 4P9 



The authors, by showing that the specific heats of the so-called per- 

 fect gases obey the law applicable to all other gases and vapours — that 

 the specific heat increases as the temperature rises — have shown that one 

 supposed distinction between these and the rest does not exist ; and 

 draw this distinction between specific heats of gases and Boyle's and 

 Gay-Lnssac's volume relations, that whereas the latter are concerned 

 with intermolecular actions mostly and with the motions of the centres 

 of mass of the molecules, tlie former are concerned also until the viature 

 of the molecule itself and of the relations of its component parts to each 

 other. 



So far as specific heats are concerned it would seem then that the 

 general results gained by these experiments at very high temperatures 

 were two : that the specific heat in all cases of bodies in the state of gas 

 or vapour increases with the temperature, and that when a gas at high 

 tempei'atnres obeys Boyle's law its specific heat is independent of the 

 pressure ; but this is not quite all, for that the laws of specific heats of 

 bodies in the gaseous state are to be looked for in the very molecules 

 themselves is a very important guide for any future investigations. 



Papers on portions of the above subject have appeared from time to 

 time in the ' C. R.'; as in ' C. R.' 91, pp. 125-828; 93, pp. 145-148; 

 pp. 1014-1016; pp. 1076-1079; 95, pp. 599, 1352; 97, pp. 102,157; 

 also in the ' Bull, de la Soc. Chim.' ; ' Bull.' 2, 39, pp. 268, 369, 572 ; 

 48, p. 122. 



In the last-named communication ' Le Chatelier, noticing that the 

 curves of specific heats of CO2 and HgO vapour converge to a point 

 below the absolute zero, infers that probably the specific heats of all 

 gases tend to the same limit as the temperature ajaproaches absolute 

 zero. He proposes a formula for the molecular heat- capacities of gases, 

 C=68 + aT, at constant pressure, 6*8 being the value for 'perfect ' gases, 

 T the absolute temperature, and a a constant for each gas depending on the 

 nature of the molecule of the gas, and being greater the more complex 

 the molecule. Applying this formula to CO2 and vapour of water, the 

 results for different temperatures agree well with those given by the 

 experiments of Mallard and Le Chatelier. If this result is accepted the 

 problem of specific heats of bodies in the state of gas or vapour reduces 

 itself to that of finding the general relation which connects a with the 

 molecule. 



Specific Heats of Gases and Vapours at Hir/h Temperatures — 

 Berthelot and Vieille. 



The investigations of Berthelot and Vieille on explosions of gaseous 

 mixtures led to similar conclusions to those deduced by Mallard and Le 

 Chatelier as to the specific heats of bodies in the state of gas at very high 

 temperatures. 



In the ' C. R.' 94, pp. 101-108 Berthelot and Vieille give an account 

 of the phenomena accompanying the detonation in a long narrow tube of 

 explosive mixtures of hydrogen and oxygen and of carbon monoxide and 

 oxygen, and find the velocities of the explosive wave for the two cases, 

 their experiments giving 2,810 metres per second, and 1,089 metres per 

 second for the two explosive mixtures ; the theoretical bearing of these 

 results are discussed by Berthelot.- Experiments were made by these 



' C. S. J. Abs. March 1888, p. 21.3. - C. B. 94, 1882^ pp. 149-152. 



K K 2 



