Notices respecting New Books. it 



It remained to determine the influence exercised on the coeffi- 

 cient of dilatation by the pressure to which the gas is subject. 

 M. Regnault studied this influence on various gases, by subjecting 

 them to both a less and a greater pressure than that of the atmo- 

 sphere. The apparatus employed for researches of this kind were 

 the same as for the preceding ; the balloon which contained the gas 

 was successively surrounded with boiling water and melting ice. 

 The pressure was measured in the cases both of a high and low 

 pressure, by a column of mercury, the level of which was given by 

 the cathetometer. In the first case, as the pressure was carried up 

 to four atmospheres, the column was sometimes very long, and 

 much care was required to measure it very accurately. It was re- 

 quisite also, among other precautions, to protect the column of 

 mercury from the heat coming by radiation from the source which 

 maintained the balloon at the temperature of boiling water, and to 

 take account by direct appreciation, of the increase of volume which 

 the balloon acquired from the effect of a high pressure, which was 

 done by filling it with water instead of gas. 



The experiments showed that, setting out from the atmospheric 

 pressure, the coefficient of dilatation of air diminishes and increases 

 with the pressure in a very marked manner. Thus, under a pressure 

 of 109-72 millims. at 0°, and of 149-31 millims. at 100°, it is 1-36482, 

 and under a pressure of ri655'56 millims., at 0°, and 4992*09 millims. 

 at 100°, it is 1-37091. The densities of gas at the temperature of 

 melting ice, varied between the same limits of pressure, that is 

 to say, from 109*72 millims. to S655'56 millims., from 0*1444 up 

 to 4-8100 (that of air at 0° under the pressure of 760 millims. 

 being=l), that is to say, in the proportion of 1 to 33. Hence it 

 results, therefore, that the law admitted by physicists, that air di- 

 lates by the same fraction of its volume at 0°, whatever may be its 

 density, is inexact, and that, on the contrary, it dilates between the 

 same limits of temperature, by quantities which are the more con- 

 siderable in proportion as the density of the gas is greater, or in 

 other terms, as its molecules are more closely approximated. 



The same is the case with carbonic acid, the dilatation of which 

 increases progressively with the pressure, much more rapidly than 

 that of atmospheric air. 



Other experiments, made equally under different pressures, but 

 executed by the method of constant pressure, led to the same result, 

 namely, an increase of the coefficient of dilatation growing with the 

 pressure. The increase is even more rapid when this method is 

 used, than when the coefficient of dilatation is determined by means 

 of the variation of the elastic forces. Carbonic acid, above all sul- 

 phurous acid, present a dilatation increasing very rapidly with the 

 density ; thus for a change of pressure so slight as that from 760 

 millims. to 980 millims., the coefficient of dilatation of sulphurous 

 acid changed from 0*3902 to 0*3960 ; and nevertheless, the gas 

 under a pressure of 980 millims. is not yet near to theO° of its point 

 of liquefaction. 



A somewhat remarkable thing is, that the difference between the 



