Correction of the Gas- Thermometer. 77 



diatomic gases, and that the variations with pressure may 

 estimated by the formulae already given. 



be 



J iD 



15. Constants for C0 2 corrected for Variation of S. 



In order to correct the values of <? and b for C0 2 calculated 

 in Table II. from the observed values of Q on the assumption 

 that S was constant and equal to 8*4 x 10 u C.G.S., we may take 

 Regnault's values of S at 0° and 100° at a pressure of 1 atmo, 

 since the final pressure in Joule and Thomson's experiments 

 was always approximately atmospheric. The values of S 

 required may be taken as 



S =7*85x 10 6 c.G.s., and S 100 = 8'95 x 10 6 c.g.s.; 



but the absolute values, as well as the rate of variation, are 

 necessarily a little uncertain on account of the defects of 

 Regnault's thermometry, and of the error of his formula for 

 the variation of the specific heat of water. 



Adopting the values of Q and Q 100 given in Table II., and 

 assuming SQ = 3c — b, we obtain the following values of the 

 constants, 



c = 3*76 c. c, £> = 0'58c.c. 



This would reduce all the values of the corrections for C0 2 

 given in Table V. nearly in the proportion of 5 to 6, since 

 they depend only on c . The agreement with ChappmV 

 observations * plotted in fig. 1 would be slightly impaired, 

 but the Joule-Thomson curve would coincide more nearly 

 with Chappuis' empirical formula. The value of the absolute 

 zero correction for the constant-pressure thermometer is 

 scarcely altered ; so that the value deduced from Chappuis' 

 expansion coefficient is still correct. But on the other hand 

 the zero correction for the constant-volume thermometer 

 (Table IV.) by formula (40) is reduced in the proportion 

 376/456 from 5°'55 to 4 a 60, which gives 6/ = 273 o, 05 ? thus 

 agreeing with the direct method of calculation given in 

 Section 5, formula (22). 



If we compare the values of the compressibility deduced 

 from the corrected values of the constants, with the values 

 observed by Amagat, we find again the agreement much im- 

 proved, which confirms the importance of the correction for 

 the variation of the specific heat. It should be remarked. 

 however, that the values of c—b deduced from Amagat'- 

 observations are a little uncertain, as the observations Jo 



* More recent observations by Chappuis ('Int. Bureau Reports,' 1902) 

 make the scale- correction for CO., at^ = 100 cms., -f— 089° both at 20° and 

 40° C. instead of -043° and -059°". 



