ELECTROLYTES AND THEIR ACTION 183 



Arrhenius himself (1914, p. 1424) points out that the dielectric constant of the solvent is 

 increased by the presence of strong electrolytes of higher dielectric constants than itself. 

 This would increase its dissociating power. 



It must be admitted that some intemperate partisans of the electrolytic 

 dissociation theory may have claimed too much; at any rate, the sweeping 

 statement that all chemical reactions are between ions must not be made without 

 the qualification that no absolute proof of the absence of the intervention of 

 electrical forces has been given in any particular reaction. 



THE ACTION OF IONS IN PHYSIOLOGICAL PROCESSES 



When we come to consider the part which electrolytes play in the processes of 

 the living organism, we have to note that there are three modes in which they may 

 act. In the discussion of the colloidal state, we saw that, in the intervention of 

 neutral salts in such phenomena, we may distinguish, in the first place, an effect 

 connected with the electrical charge on the ions, specially marked with ions of 

 valencies above one, and not in relation to the chemical nature of the ions ; so that 

 the effect, say, of Ca* * is not to be distinguished from that of Ba' '. Especially in 

 the case of multivalent ions, this action is manifested by very small concentration. 

 It may be illustrated by the effect of simple trivalent ions on tlie heart, an action 

 which does not seem to be associated with the chemical nature of these ions, since 

 it is shown by a large number of them, and in extraordinarily low concentrations 

 (Mines, 1911). 



In the second place, there is an action shown by salts usually in somewhat high 

 concentration, which is not directly connected with their electrical charges as such, 

 and is most satisfactorily explained as being an action of some kind on the solvent, 

 " lyotropic," as it is called by Freundlich. This is shown in the " salting out " of 

 proteins, and in the various effects of anions and cations on such processes as 

 imbibition, in which the " Hofmeister series " is followed. 



In the third place, there are the actions in which differences of a more chemical 

 kind come into play. Such cases are those of potassium and sodium salts on the 

 heart muscle. In these, we know that it is the ions which are concerned, and not 

 the molecules of the salts, by the facts that the action is shown by solutions so 

 dilute that undissociated molecules are nearly absent, and that it does not matter 

 what particular salts of these metals are used. 



Other instances that may be given are the effect of calcium ions on the clotting of blood, 

 in which even closely related elements, such as barium, are unable to replace calcium ; and 

 the powerful action of barium in producing contraction of smooth muscle. 



The great activity of acids and bases in various ways is a familiar fact, so that, 

 in our consideration of the various ions of physiological importance, it is natural to 

 take these first. 



It is also a matter of common experience that the properties associated with 

 them are much more strongly marked in the case of certain chemical individuals 

 than in others. Some acids will turn out others from combination ; their solutions, 

 in equal strength, taste much sourer, and some invert solutions of cane-sugar more 

 rapidly than others, in the same molar concentration, do. 



It is here that the electrolytic dissociation theory has shown itself to be of 

 especial value, in that it is able to give precise numerical values to express the 

 acid or alkaline properties of a solution. Now what, according to this doctrine, 

 is the character common to all acids and what to all bases'? Obviously, the 

 hydrogen ion in the first case and the hydroxyl ion in the second. Hydrochloric 

 and acetic acids in solution are dissociated into H' and Cl' and into H' and acetic 

 anion respectively ; the only chemical substance common to both is the H' ion. 

 But why is hydrochloric acid the stronger of the two, as is so obvious in many 

 ways'? The answer is given by measurements of the electrical conductivity of the 

 two. Hydrochloric acid is a much better conductor ; it is therefore more highly 

 dissociated and contains a much higher concentration of hydrogen ions. Here we 



