Correction of the Gas-Thermometer. 83 



metre cubic centimetres approximately, whereas molecular 

 weights of the other gases appear to conform to the limit 

 17,710 rn.c.c, which is given as the ideal value for a perfect 

 gas. At the higher temperature, the order of the gases is 

 inverted. Helium and neon appear to be more imperfect 

 than at the lower temperature, and their curves lie below 

 krypton and argon. It seems to be impossible to offer any 

 theoretical explanation of these anomalies ; but if we admit 

 that the limiting values for krypton at zero pressure should 

 be 18,510 rn.c.c. at 11°2 C, and 33,210 rn.c.c. (the corre- 

 sponding value for the same mass of gas) at 237 c, 3 0., the 

 limiting values of the slope (c — b) may be estimated as 0*84 c.c. 

 and 0'43 c.c. respectively per gramme of gas. In the case 

 of the other gases the slope is too small, or its initial value 

 too uncertain, to afford a comparison. If we assume as above 

 that the coaggregation c should vary inversely as the square 

 root of the temperature (>i = l/2), we find c = l'61 c.c. at 

 284°-2 Abs. and c = l'20 c.c. at 510°-3 Abs., whence 

 b—0'77 c.c. If on the other hand we assumed n = l, we 

 should find c = 0*52 c.c. at 510°-3 Abs., and 6 = 0-09 c.c. 

 A higher value such as n = 2 would make b large and negative, 

 which would be impossible, or at least incapable of rational 

 interpretation. The volume of liquid krypton at its boiling- 

 point was found to be 46 c. c. per gramme, so that the value 

 of b deduced on the assumption ?i=l/2 is perhaps the most 

 probable. The fact that helium appears to be less perfect 

 than hydrogen, and neon nearly as imperfect as nitrogen at 

 11°*2 C, also supports the hypothesis of a very low value ot 

 a for monatomic gases. 



Adopting provisionally the basis n = l/2, I have calculated 

 the following tables of corrections for argon and helium in 

 addition to krypton, since, as 1 have previously explained 

 (Phil. Mag. Dec. 1899_, p. 541), the inert monatomic gases 

 are peculiarly suitable for thermometric purposes. I have 

 assumed the values of b for helium and argon to be equal 

 to the volumes of the liquids (which are estimated at 3*3 c. c, 

 and 0'83 c. c. respectively) multiplied by the ratio 0*77/0 - 4(.) 

 found above in the case of krypton. The values of c are 

 deduced from the observed compressibilities at 11°*2 C. For 

 helium I have assumed c = b, since the pv line for helium is 

 practically horizontal up to a pressure of 50 metres. It 

 must be admitted that these data are somewhat uncertain, 

 but they afford at least a reasonable basis for comparison with 

 -experiment, 



G2 



