92 Journal of the Mitchell Society. [Nov. 



typical of a low vapor pressure (that it is typical will be seen 



5 P 



if other substances are examined), we have ^-7=- = 0.329, 



6 1 



T = 273, P = 4.600, V = 211131, v = 1, and the equation 

 takes the form 0.329 X 273 - 4.600 = ^^TlMVf 



Since 0.329 X 273 = 89.80, the influence upon the constant of 

 an error in the vapor pressure is relatively very small. T 

 may be assumed correct, and the determining- error therefore 



SP 



rests with the y^r- It is exceedingly important to note that 



while an error of 0.01 millimeter in the vapor pressure is an 

 error of only two-tenths of one per cent, in that observation, 



SP 

 yet if the same error exists in the -^=- the error so caused 



o 1 



in the constant is three per cent. 



For high vapor pressure considering- water at 270° C (also 



SP 

 a typical case) we have j^ = 614, T = 543, P = 40570 



(from Biot's formula as given by Regnault), and the 

 equation takes the form 614 X 543 — 40570 = etc. And since 

 614 X 573 = 351800, it again appears that an error in the 

 pressure produces only a very greatly diminished proportional 

 error in the constant. It is again important to note that 

 while an error of 20 millimetres in the pressure means an 

 error of only o.oj of one per cent, in that measurement, yet 



this error occurring in the -^-=; would produce an error of 



more than three per cent in that constant. 



SP 

 The function ^7=- was obtained from Biot's formula (see 



equation 5). Biot's formula has stood the most severe tests, 

 and I do not believe the accuracy of that formula per se can 



