EXPEEIMENTAL KNOWLEDGE OF THE PKOPEETIES OF MATTER. 



107 



The above ai'e described in the first part of the first memoire of 

 Regnault in t. xxi. of the 'Memoires de I'Academie.' Similar experi- 

 ments were made (described in the second part of the same memoire) 

 with the following gases : — 



This difi'erence in all cases between the expansion of volume at con- 

 stant pressure, and the increase of pressure in constant volume, from 

 0° to 100°, is due to the fact that in none of the cases is Boyle's law 

 accurately true. But the numbers for constant volume and for constant 

 pressure are very nearly equal for hydrogen, air, and carbon monoxide. 



In this memoire it is shown for air at constant pressure (p. 99) that — 



100a=-3657 for 511 mm. 

 •3648 „ 149 mm., 



thus diminishing with diminishing pressure ; also that the rate of expan- 

 sion of air at increased pressures increases ; thus (p. 110) for air at 

 pressure 3655 mm. — 



100a=-3709. 



From these and from results for gases other than air, given in this 

 memoire, Regnault infers that the differences in the coefficient of dila- 

 tation of diff'erent gases are most striking for great pressures, and espe- 

 cially if these are not far removed from those under which the gases can 

 be liquefied, and that the deviations from the coefficient for air are 

 smaller the smaller the pressures under which the gases are examined. 

 The coefficient a for such gases as sulphurous and carbonic acid gases, 

 for instance, diminishes very much more rapidly with diminishing 

 pressure than the coefficient for air. 



Gay-Lussac's law of the equal dilatation of gases with equal rise of 

 temperature is therefore considered by Regnault as a 'loi limite,' which 

 is approaclied more and more nearly by each gas the smaller the density 

 and pressure at which its dilatation is observed. 



Voluvie and Temperature — Amagat. 

 Amagat' tests air and hydrogen for compressibility at temperatures 



up to 320°, and finds that the ratio -^~i where v is very nearly 2 xv, 



p V 



is for air, 



at 0° . . =1-0015, 



„ 100° . . =1-00011, 



250° 



=100025, 

 =1-00018, 



„ 320° 



' Annales de CMmie et de Physique, 1873 (4), xxviii. p. 274. 



