Laws of Molecular Force* 



233 



The approximate equality of the values of the constant b is 

 worth noting. I have also reproduced here the values of k at 

 the side of those for ft, in order to point out that ft is nearly 

 Jc/S in each case. Amagat has not published data for methane 

 at volumes below the critical region, but the numbers given 

 in brackets for methane were obtained indirectly as explained 

 below. These relations of /3 and b give our equation such a 

 degree of simplicity as largely to establish the soundness of its 

 form. The next Table shows the degree of accuracy with which 

 it represents the experimental facts. 



Table XX.- 



—Oxygen at hi 



gh pressures. 





Volume 



1-277. 



1-097. 



1-008. 



•949. 



•905. 





iron / Pressure, exp 



10 U \ „ calc. ... 



760 

 739 



1140 

 1141 



1520 

 1512 



1900 

 1893 



2280 

 2296 



The agreement is quite as good for hydrogen and nitrogen. 



By means of this equation we can calculate the volumes of 

 a gramme of liquid nitrogen and oxygen at their boiling- 

 points under a pressure of *76 metre, for comparison with 

 Wroblewski and Olszewski's determinations of the same 

 (Compt. Rend, ch.; Wied. Beibl.it.; and ' Nature,' April 

 1887). 



Volume 

 at -184 c 



{Wroblewski 

 Olszewski 

 Equation 



Oxygen. 



•85 

 •89 

 •90 



at 



Nitrogen. 

 1 1-20 

 194°U-13 

 1-26 



The equation is seen to give the volumes of these two bodies 

 at these low temperatures within the present limits of experi- 

 mental accuracy, and accordingly it covers a range of 2000- 

 metres pressure and almost the whole experimental range of 

 temperature. In the case of methane, if we take Olszewski's 

 value 2*41 for its volume at — 164°, and assume b is the mean 

 of b for H 2 , N 2 , and 2 , then we can calculate the value of /3 

 which is tabulated above. 



To ethylene above the critical region we had to assign a 

 special form intermediate between that for ordinary compounds 

 and that for elements ; so that Ave had better do likewise for 

 its infracritical equation, which I have cast in the form 



f ,= (1+ i>ET( 1+ -i^)-i.^, 

 Phil. Mag. B, 5. Vol. 35. No. 214. March 1893. 



R 



