470 Mr. W. Sutherland on the 



We can study this dissociation from a slightly different 

 point of view. Amagat's data {Ann. de Ch. et de Ph. [6] 

 xxix.) enable us to assign the temperature of maximum 

 density of water under 150 atmos as "5°. Although his 

 pressures go up to 3000 atmos the maximum density has not 

 been ascertained by him at a higher pressure than 150 atmos. 

 Accordingly I have found the equation like Mendeleeff's 

 which will represent the expansion of water under 150 atmos. 

 With the volume of a gramme of water at 4° and under 

 1 atmo as unity it is 



i aa7^/i , ,,ori -087724 -67584 \ , n . 



P = l-00747(l + -76354- 1 + , 00837 . t - 1 _, 001()77i ). (C) 



The volumes of a gramme of water as given by this formula 

 and by Amagat, when we have changed his unit of volume to 

 that just mentioned, are : — 



Table V. 



t 0° 20° 40° 60° 80° 100° 198° 



p formula... 1-00745 '99489 1-00104 1-01013 1-02175 1-03568 1-1389 

 pexper 1-00745 -99489 1-00102 101012 1-02177 103568 1-1443 



Up to 100° the equation represents the actual data with a 

 maximum error of 2 parts in 100,000, the comparison for 

 198° being added to show how far the form fails when applied 

 much beyond the ordinary boiling-point. 



On comparing this last equation with Mendeleeff's for one 

 atmo (A) and with (B), we see how the terms expressing ex- 

 pansion of the two ingredients and dissociation have got 

 mixed up; a result always to be feared with empirical equa- 

 tions, which fact indeed makes it appear a happy accident 

 that Mendeleeff's formula (A) is capable of such easy inter- 

 pretation. We have now to disentangle the mixed up parts 

 of the last equation. It relates to p of 1 mixed with 1 — p parts 

 of a mixture which we shall denote by S' (different from S). 

 The density of S' is 1*00747, and therefore its volume is 

 "99259, and the volume of 1 (dihydrol) as a liquid, being 

 1/1-08942 at 0° under 1 atmo, is -91572 under 150 atmos 

 when the compressibility '000016 is taken into account. 

 Now S' also contains 2 under 150 atmos ; under 1 atmo at 

 it was taken to have a volume l/'88, and the compressibility 

 '00001 was conceded to it, so that its volume at 0° under 

 150 atmos is 1*13466; and applying the mixture formula to 

 the density of S' we have 



•99259 = -91572 + (l-13466--91572)_p 2 , 

 .-. p 2 = '351 at 0° under 150 atmos. . . . (18) 



