﻿Constitution of Aqueous Solutions. 9 



\BU\/i> = 280 shown in "Ionization &c." (Joe. cit.) to hold 

 for the majority o£ ions. For H the product, even with the 

 too small value of B used in that paper, is 980 instead of 

 280, while for OH it is 765. It will now be shown that the 

 ionic velocities hitherto assigned to H and OH are not the 

 real velocities of these ions, but the real velocities increased 

 by velocities belonging to ions derived from water. The 

 exceptional properties of H and OH ions can be traced back 

 to the single property, that of being able to ionize H 2 0. 



From the data for NaOH solutions with 2*13 for the 

 density of NaOH, the contraction in forming a gramme of 

 solution can be written 0'49 Pi(J--~p^), whence from (7) r for 

 NaOH is 1*66. But for Na r is 1-96, so for OH t is -0*30. 

 From the data for KOH the value — 0'28 is obtained, the 

 mean being —-0*29. 



To determine r for the H ion of acids we may take HN0 3 

 as a convenient typical acid, free from the exceptional relations 

 of H 2 S0 4 towards water, and having a definite liquid density 

 at ordinary temperature and pressure unlike HC1, HBr, and 

 HI. The data of Lunge and Rey show a contraction 

 0'26/> 4 (l — p^ on mixing 1 — p 4 grm. of water with p± grm. of 

 HN0 3 fOT a11 valu es of p 4 . From this r = 1/39 lor HN0 3 . 

 But for N0 3 t is —1*27 ; so for H the value of t is 2*66. 

 If we treat the data for H 2 S0 4 in the same way, they yield a 

 value 1*88 for t for H. With this acid some other action 

 accompanies that we are now investigating. 



The data for the halogen acids show a remarkable departure 

 from (7) which makes the contraction proportional to jt? 4 (l — £> 4 ). 

 With these the factor 1 — p± falls out over a considerable 

 range of p±. The difference of the volume of a gramme of 

 solution and of the original volume of the water in it for HC1 

 at 15° is very nearly 0*5p 4 up to p 4 = 0T. For HF the same 

 difference is nearly 0'6p± up to p 4 = 0*2 ; for HBr 0"3/? 4 up 

 to pi = 0*2, and for HI 0"27/? 4 up to j9 4 = 0'67. It appears 

 then that in the dissolving of halogen acids in water there is 

 an additional contraction of amount p 4 /(l— p^) times the 

 normal one which w T e are investigating. As this fraction 

 vanishes with jt? 4 we can obtain the contraction for HC1 for 

 instance in the form (b — 0*5)p 4 for small values of p 4 , where b 

 is the volume of the molecules in a gramme of HC1 at 15°. 

 The difficulty is to determine this rather fictitious volume. 

 A gramme of liquid HC1 under its vapour-pressure at 15° # 85 

 occupies 1*2 c.c. This would probably be too large a value 

 to take. The best way to proceed then is to use the limiting 

 volume of the molecules in a gramme as corresponding to 

 the volumes used for solid salts coing into solution. This 



