EXrERIMENTAL KNOWLEDGE OF THE PHOPERTIES OF MATTER. 109 



drawn expressing the results in reference to this relation for tempera- 

 tures from 16° to 100° ; and the pressures for each curve for each substance 

 ranging from about 20 metres to 320 metres. The gases treated in this 

 exhaustive manner are nitrogen, hydrogen, ethylene, carbon dioxide 

 and marsh -oas. 



With the exception of the curves for hydrogen, each curve vt^as irre- 

 gular, the relation of ]}V to p becoming regular only after the pi'essure 

 was about 120 metres, or about 160 atmos, after which the result for any 

 substance was expressed very approximately by the equation p (y — a) = & • 

 where li was difi'erent for different temperatures for any substance, and a 

 was nearly constant for all the temperatures employed. In studyino' the 

 effect of Amagat's results in this paper in extending our knowledge of 

 Boyle's and Gay-Lussac's laws, it must be remembei-ed that the tempera- 

 tures were necessarily very restricted, being not over 100°, while the 

 pressures were very great. But the facts brought into notice by com- 

 paring curves for the same substance for different temperatures are im- 

 portant ; we will be content with indicating one or two of these. 



At high pressures, for all the gases studied, the values of piv at any- 

 given temperature increase continiially with the pressure, and are repre- 

 sented by an almost absolutely sti-aight line for the increasing abscissse p, 

 so that if p' and v' are higher pressure and corresponding volume 



«- — >1; that is, the gas in this condition is less compressible than if 



pv ^ 



Boyle's law were exact. The question arises, does this deviation increase 

 or diminish as temperature rises ? The case of any gas will do to try 

 this. Taking the case of hydrogen, we extract the following data 



(p. 378 loc. cit.) : if ^(<1) is the ratio for hydrogen at 100m. and 



pv 



320m. pressures, this ratio is 



at 177° 

 „ 40-4 



0-830 

 0-838 



at 60 '4° 

 „ 100-1 



0-853 

 0-856 



whence we see that for higher and higher temperatures the ratio 

 approaches more and more nearly to 1, or the gas deviates less and less 

 from Boyle's law. But this approximation does not imply that Boyle's 

 law is even a theoretical condition for these very high pressures at much 

 higher temperatures ; for a may approximate more and more, as tempera- 

 ture rises, to some value, for. each gas, less than 1. 



Dilatation of Gases at very High Pressures. 

 To find for high pressures the dilatation of gases, we must find v' — v 



by finding -^ and ^— , or the ratio of the ordinate to the abscissa at two 

 p p 



temperatures t and t', the pressure being the same in both cases, so that 



we have the dilatation at constant pressure. We give an extract from a 



table ' which illustrates this for hydrogen, and therefore, for other gases, 



at very high pressures ; the table gives the whole dilatation for the 



temperature-range stated ; the coefficient may be deduced by dividino- 



by the temperature-range in each case. 



' Annales de Chimie et de Physiqve [.■;], 1881, xxii. p. 382. 



