48 Notices respecting New Books. 



dilatations of atmospheric air and carbonic acid gas is much more 

 considerable when the pressure is the same at 0° and at 100°, than 

 in those in which the dilatations are calculated according to the 

 changes of elastic force. 



Hydrogen is the only gas of which the coefficient does not alter 

 with the pressure, at least up to that of four atmospheres, while that 

 of air continually increases from the point of ordinary barometric 

 pressure, under which the two gases have sensibly the same dilata- 

 tion. 



In general, the more considerable the pressure under which the 

 gases are examined, the greater difference is found between their 

 coefficients of dilatation. Inversely, the coefficients of dilatation of 

 the different gases approach to an equality in proportion as their 

 pressures become weaker, so that the law which says that gases 

 liave all the same coefficient of dilatation, may be considered as a 

 limited law, which applies only to gases in an extreme condition of 

 dilatation, but which departs from the reality in proportion as the 

 gases are more compressed, in other terms, as their atoms are more 

 closely approximated. 



The first task of M. Regnault, which we have just rapidly sur- 

 veyed, confirms us in that opinion which we announced at the out- 

 set, namely, that a great error is committed in supposing the gaseous 

 condition to be a state in which the physical properties of the body, 

 with the exception of the density, are independent of its peculiar 

 nature, and connected solely with its general constitution. We see, 

 in fact, that the coefficient of dilatation of the gas varies with its 

 nature, with its density, and with the mode in which it is operated 

 on. Hydrogen alone appears to present more general relations in 

 this respect. 



The direct determination of the densities which forms the object 

 of M. Regnault's second memoir, conducts to consequences in every 

 respect analogous. This determination, effected by a method much 

 more simple than those hitherto employed, and at the same time 

 very exact, gives the densities at 0° and 100° of the different gases 

 in proportion to air, which allows of the deduction from it of the 

 coefficients of dilatation by the method of weighing. The values of 

 these coefficients are nearly the same as those which had been ob- 

 tained by the direct methods. 



The densities at 0° and under the pressure of 760 millims., found 

 by M. Regnault for nitrogen, hydrogen, oxygen and carbonic acid, 

 differ very little from those to which MM. Dumas and Boussingault 

 arrived ; they are each the mean of very slightly differing numbers, 

 furnished by a great number of experiments. But if they are taken 

 at other temperatures, and under other pressures, the results are no 

 longer the same, and they furnish curious consequences. Thus 

 by taking the density of carbonic acid at 0° under different press- 

 ures, but all lower than the atmospheric pressure, it is ascertained 

 that this gas departs from Mariotte's law in a very marked manner, 

 whilst at the temperature of 100° it sensibly follows this law. It is 

 evident, therefore, that according to the temperature and pressure 



