6 Capt. A. C. Egerton on the 



published a series of accurate measurements at relatively 

 low pressures and discussed his results in connexion with 

 those of Hertz, Ramsay and Young, Pfaundler and others. 

 He finally arrives at the formula which agrees with that of 

 Hertz in the value of the 2nd term, and holds up to 270° C: 



logp = 10-5724-0-847 logT 



3342-26 



T 



Smith and Menzies (J. Am. (/hem. Soc. xxxii. p. 1434, 

 1910) have carried out accurate measurements of the vapour 

 pressure of mercury from 250° 0. upwards and arrive at 

 the expression : 



logp = 9-9073436-0-6519904 log T- '* 2 '^' 628 . 



The value for the boiling-point obtained from these vapour- 

 pressure measurements 356*95 ;+0 o 'l C. agrees very closely 

 with that obtained by Callender & Griffiths 35705 ; whereas 

 Knudsen's formula leads to a boiling-point 355 0, 1 C. The 

 following table gives a few points calculated from these 

 formulae : — 





Table I. 





T° abs. 



Laby. Knudsen. 



Smith & Menzies 



630 B.Pt. 



760-4 (ii) 787 



760 



473 



17-81 (i) 



17-41 



17-22 



373 



0-276 (1) 



0-2715 



02794 



273-4 



0-00016(1) 



0-0001846 



0-0002073 



234-2 M.Pt. 



— 



0000001970 



0-000002354 



Above 250° G. the values obtained by Smith and Menzies 

 are probably correct within 0*2 per cent. : between 250° 

 and 150° C. the data somewhat conflict, and the nearest value 

 probably lies between that of Knudsen and that of Smith and 

 Menzies, while at the lower temperature it seems probable 

 (taking into consideration also Hertz and Pfaundler's 

 results) that Knudsen's figures are within at least 0*5 per- 

 cent. 



The extrapolation to the melting-point is reasonable, 

 as there is no sufficient change in the specific heat of the 

 liquid between 0° 0. and the melting-point as would lead to 

 an appreciable change in the value of the constant of the 

 formula. 



