224 Intelligence and Miscellaneous Articles. 



interesting paper by Berthelot and Ogier in the Annates de Chimie 

 et de Physique for 1883, in which the authors set forth the result of 

 their careful experiments on the Specific Heats of the Vapours of 

 Acetic Acid and Xitrogen Tetroxide. The quantities of heat absorbed 

 at different temperatures are compared with the percentage disso- 

 ciation, as deduced from the vapour-density experiments, of INTau- 

 mann, Soret, and other experimenters. The experiment is very 

 close (as may easily be seen by placiug the several series of num- 

 bers on curves), and well within the limits of experimental error. 

 In spite of the valued opiuion of M. Berthelot, I therefore venture 

 to consider that the experiments referred to do afford additional 

 evidence in favour of the hypothesis of the dissociation of these 

 gases ; the alternative theory involving j so far as I can see, the 

 relinquishiug of Avogadro's law as far as these gases are con- 

 cerned. 



Assuming therefore, for the moment, that dissociation does take 

 place, and that the thermal changes measured by Berthelot and 

 Ogier are the natural expression of this effect, some information, 

 it seems to me not altogether devoid of interest, may be gained by 

 a comparison of these results with those obtained by Eegnault for 

 the specific heats of those gases which undergo a condensation in 

 the course of their formation from their elements. As is well 

 known, the specific heats of nitrous oxide and carbonic acid have, 

 according to Regnault, a small temperature-ccefficient, showing 

 that, as the temperature rises, the specific heats increase, at all 

 events up to 200° Centigrade. This, however, is precisely w T hat 

 has been found to hold true in a more complicated form for 

 nitrogen tetroxide aud acetic-acid vapour, where the temperature- 

 coefficient is much greater and reaches a maximum. If, however, 

 we decide to attribute this to a molecular change tending from 

 greater to less molecular complexity in the case of acetic-acid vapour 

 and nitrogen tetroxide, why should we not apply the same argu- 

 ment to the gases examined by Begnault, and regard the tempera- 

 ture-coefficient of the specific heats of nitrous oxide and carbonic 

 acid &c. as evidencing a similar molecular change ? Might we not 

 argue, in fact, that at low temperatures the molecular composition, 

 as expressed by the ordinary formulas for carbonic acid and nitrous 

 oxide, only refers to the vast majority of the molecules ; and that 

 the number of molecules of a higher degree of complexity, as well 

 as of a lower (i. e. dissociated), is not negligibly small. On raising 

 the temperature, those of higher than normal complexity might 

 decompose and account for the extra absorption by heat, evidenced 

 by Eegnault's temperature-coefficient. Such a view seems to me 

 to be in harmony with the views set forth by Clausius and TVil- 

 liamson, which are daily gaining ground among physical chemists. 

 I am, Gentlemen, 



Tour obedient servant, 



ElCHAED THEELFALL. 



University of Svdney, 

 November 8/1886. 



