236 



PRINCIPLES OF GENERAL PHYSIOLOGY 



and, in this latter compound, we may consistently use the termination ol. The activity <>t 

 Imlnmul" corresponds, on the "association" theory of chemical change, to the H> and 

 Oil ions of water on the electrolytic dissociation theory. In the former view, which cannot 

 be discussed further in this place, the electrical conductivity of concentrated solutions, say 



/H 

 of hydrochloric acid, is conditioned mainly by hydrolyxed solute, H 2 O , and in dilute 



Cl 

 /H 

 solution by hydrolated solute, HClC ; so that, in strong solutions, it is chiefly the solute 



which is active, in \veak solutions, the solvent. It follows further that "hydration" may be 

 of two types, " hydrolation " and " hydronation. " For more details the reader is referred to 

 the paper qu"oted. 



With regard to the actual existence of these two isomeric forms of the associated molecules 

 of water, it is clear that they can be represented by structural formulae ; but, as previously 

 remarked, this does not in itself prove their existence. I cannot pretend to be able to give 

 an opinion on the evidence for this, about which there is much contention. I would merely 

 point out that the phenomena whose explanation requires their assumption can, apparently, 

 be explained as satisfactorily on the electrolytic dissociation theory. 



In any case, the arguments of Bousfield. and Lowry (1910, p. 18) are not affected, since, as 

 they indicate, dihydrol, and perhaps trihydrol, would only have to be thought of as mixtures 

 of hydrone and hydronol with a given average density, instead of simple substances. 



It is important to note that Philippe A. Guye (1910), approaching the problem 

 from the chemical point of view, also comes to the same conclusion as Bousfield 

 and Lowry do, with regard to the ternary nature of water. 



HYDRATTON OF IONS 



The behaviour of ions as regards combination with water is similar to that 

 of solutes in general. The fact has been referred to in previous pages in various 

 connections, so that it is unnecessary to discuss the question further, except to 

 call attention to an interesting paper by Kohlrausch (1902). This investigator 

 found that the rates of migration of different ions approached nearer to the 

 same value as the temperature was raised. Above the normal boiling point of 

 water the effect is still more obvious, as appears from the following table of 

 Noyes and Coolidge (1907, p. 47) : 



RATES OF MIGRATION OP IONS AT DIFFERENT TEMPERATURES. 



If drawn in curves, these results show that the mobilities would be identical at 

 360 C., that is practically at the critical temperature of water. At low 

 temperatures, therefore, the sodium ion is the more bulky and for that reason 

 the slower in movement, on account of the fact that it has more water molecules 

 associated with it than the potassium ion has. But at high temperatures, owing 

 to the loss of water, the two approximate to equal size and mobility. 



OSMOTIC PRESSURE, HYDRATION AND THE CONSTITUTION 



OF WATER 



It might perhaps be supposed that the considerations of the previous pages 

 would invalidate conclusions with regard to osmotic pressure, since the concen- 

 tration of the solvent is diminished by the amount of it which is taken up by 

 the solute, so that the effective concentration of the solute would be increased. 

 It is pointed out by Nernst (1911, p. 271) that it is not found experimentally 

 that any anomalies result from this cause. 



