Laws of Molecular Force. 219 



taken account of when we come to Natanson's results. From 

 Regnault's data we have, in dynamical measure 



K„ = 424(-187 + -000270. 



Table V . 



(Cooling effect of C0 2 escaping through a porous plug under 

 a pressure excess of 2'54 metres of mercury.) 



Temperature 0.... 



7°4. 



4-4 



4 4 



-25° 



8°. 



19°-1. 



35° -6. 



54°. 



91°5. 



2-35 



27 



93°-5 



97° 5 



213 



2-6 



Tli. and Joule ... 

 Calculated 



4-2 

 4-4 



3-9 

 41 



34 



3-7 



295 

 34 



2-16 



27 





Temperature 0. 



3°. 



100°. 













Regnault 



6-3 

 55 



41 



45 



26 



2-6 







The agreement is as good as possible if both sets of experi- 

 ments are taken into consideration. But Natanson's result 

 affords a more delicate test ; he found that at 20° up to 25 

 atmospheres the cooling effect for a pressure excess of one 

 atmosphere could be represented by 



^=l-18 + -0126p; 



while the theoretical equation above gives 



| = l-23 + -01^, 



which is practically identical with Natanson's. On account 

 of the closeness of this agreement we obtain as an indirect 

 conclusion, that the experimental work on C0 2 taken as a 

 whole makes the absolute thermodynamic zero —273°, the 

 same result as Sir W. Thomson has obtained for air and H 

 in the article "Heat" {Encyc. Brit.), while for C0 2 , using 

 only Regnault's coefficient of expansion and Joule and his 

 own cooling effects, he found — 273 0, 9. Now that C0 2 is 

 seen to be in harmony with the other two more perfect gases, 

 the number 273 may be accepted definitely as the absolute 

 temperature of melting ice. 



The equation therefore applies accurately at high volumes, 

 a fact which we can prove by another test, seeing that Amagat 

 carried out a special research ( Compt.Reud. xciii.) to determine 

 the ratios of pv top'v 1 at different temperatures and up to values 

 of p' about 8 atmospheres, v being double v'. 



Q2 



