towards a Dynamical Theory of Solutions. 43 



From the measurements of Drude and Heerwagen we 

 know that at 20° C, K for water is 80, so that in the limit 

 with pure water (K 2 — l)/p 2 is 79. So it appears that 

 50 per cent, of alcohol in a mixture reduces (K 2 — l)/p 2 from 

 79 to 72, while 90 per cent, of alcohol reduces it to 61. 

 Since (K — 1)1 p for ice and for water at 0° 0. are nearly 

 equal, they are nearly equal for trihydrol and dihydrol. 

 Hence as the change caused by nlcchol as it is increased 

 from to 50 per cent, is chiefly that of trihydrol into 

 dihydrol, the value 72 for (K 2 — l)/p 2 when p l = 0'5 is but 

 little different from 79, a result confirming our general 

 conclusion as to the first process when alcohol is mixed with 

 water. As p x is increased from 0*5, the second process of 

 changing dihydrol into hydrol goes on. It appears that 

 (K— 1)1 p for hydrol must be less than for dihydrol, since 

 (K 2 — 1)1 p2 in the above table diminishes with increase in the 

 amount of hydrol. 



Th wing's values at 15° C. are : — 



100p l 



100 90 



80 70 60 



50 



40 



30 



20 



10 



K 



25-02 2571 



28-15 33-66 36-31 



4411 



48-40 



59-55 



6179 



67-95 



(K 2 -l)/p 2 . 



... 28 



39 54-7 53-2 



63-8 



64 



74-3 



70-7 



745 



Thwing found K for water to be 75*5 at 15° C, so that with 

 his data the limiting value of (K 2 — l)/p 2 for pure water 

 is 74*5. Mixtures containing 10 per cent, of alcohol and 

 30 per cent, give practically the same result with a fall to 

 about G4 whenp 1 = 0"5. The conclusion to be drawn agrees 

 with that from Nernst's datum for p 1 =0*5. For larger 

 values of pi the value of (K 2 — l)/p2 diminishes as it did 

 before, but in a more pronounced manner. The chief dif- 

 ferences between Nernst's and Thwing's results might be 

 explained on the supposition that under the conditions of 

 the experiments hydrol had a much smaller K in Thwing's 

 than in Nernst's. In Nernst's experiments with 79 for the 

 limit of (K 2 — l)!p2 for pure water 79 — (K 2 — l)//? 2 is nearly 

 proportional to A/p 2 the corresponding contraction of unit 

 mass of water, obtainable from Table I., thus : — 



100^ 90 80 70 60 50 



79-(K 2 -l)/p 2 ... 18 13-5 10-3 8-8 7 



10 4 A/^ 2 1815 1437 1181 986 820 



We have nearly 



79-(K 2 -l)/p i! =92A/p 2 , 



and more roughly for Thwing's results 



74-5-(K 2 -l)/ / . 2 = 214A/ / ^ 



