82 Royal Society : — Dr. Andrews on the Physical 



seen, either as liquids or solids, till much lower temperatures even 

 than those produced by liquid uitrous oxide are reached. 



Law of Gay-Lnssac. — That the law of Gay-Lussac in the case 

 of the so-called permanent gases, or in general terms of gases 

 greatly above their critical points, holds good at least at ordinary 

 pressures, within the limits of experimental error, is highly probable 

 from the experiments of Eegnault ; but the results I have obtained 

 with carbonic acid will show that this law, like that of Boyle, is 

 true only in certain limiting conditions of gaseous matter, and 

 that it wholly fails in others. It will be shown that not only does 

 the coefficient of expansion change rapidly with the pressure, but 

 that, the pressure or volume remaining constant, the coefficient changes 

 with the temperature. The latter result was first obtained from 

 a set of preliminary experiments, in which the expansion of carbonic 

 acid under a pressure of 17 atmospheres was observed at 4°, 20°, 

 and 54°; and it has since been fully confirmed by a large number 

 of experiments made at different pressures and well-defined tem- 

 peratures. These experiments were conducted by the two methods 

 commonly known as the method of constant pressure and the 

 method of constant volume. The two methods, except in the 

 limiting conditions, do not give the same values for the coefficient 

 of expansion ; but they agree in this respect, that at high pressures 

 the value of that coefficient changes with the temperature. While 

 I haA e confined this statement to the actual results of experiment, 

 I have no doubt that future observations will discover, in the case, 

 at least, of such gases as carbonic acid, a similar but smaller change 

 in the value of the coefficient for heat at low pressures. The 

 numerous experiments I have made on this subject will shortly be 

 communicated in detail to the Society ; and for the present I will 

 only give the following results : — 



Expansion of Heat of Carbonic Acid Gas under high pressures. 



(A) 



Pressure. 



at. 

 22-26 . 



Vol. C0 2 at 0° & 

 760 milLims. = 1. 



Vol. C0 2 at 6°-05 

 & 22-26 at. = 1. 



Temperature. 



. . . 0-03934 . 



. . 1-0000 . . . 



6-051 



22-26 . 



. . . 0-05183 . 



. . 1-3175 . . . 



63-79 \ . 



22-26 . 



. . . 0-05909 . 



. . 1-5020 . . . 



100-10 J 



Pressure. 



at. 

 31-06 . 



Vol.CO 2 at0°& 

 760 milfims. = l. 



Vol. CO/at 6°'62 

 & 31-06 at. = 1. 



Temperature. 



. . . 0-02589 . 



. . 1-0000 . . . 



6-62) 



31-06 . 



. . . 0-03600 . 



. . 1-3905 . . . 



63-83 [ . 



31-06 . 



. . . 0-04160 . 



. . 1-6068 . . . 



100-64 J 



Pressure. 



at. 

 40-06 . 



Vol. C0 2 at 0° & 

 760millims. = l. 



Vol. C0 2 at 6°-01 

 & 40-06 at. = 1. 



Temperature. 



. . . 0-01744 . 



. . 1-0000 



6-on 



40-06 . 



. . . 0-02697 . 



. . 1-5464 



63-64 1 . 



40-06 . 



. . . 0-03161 . . 



. . 1-8123 



100-60 



(B) 



(C) 



Taking as unit 1 vol. of carbonic acid at 6°-05 and 22-26 atmo- 

 spheres, we obtain from series A the following values for the 

 coefficient of heat for different ranges of temperature : — 



