CARRIERS IN ELECTROLYTIC SOLUTIONS 209 



ductance of a typical salt in pyridine differs but little from that of a 

 salt of the solvent itself. 



While, therefore, there are cases in which the ions common to the 

 solvent exhibit an abnormally high conducting power, as they do in 

 water at ordinary temperatures, there are other cases in which the con- 

 ducting power of these ions is entirely normal. In this connection it is 

 to be borne in mind that with rising temperature the speed of the hydro- 

 gen and hydroxyl ions in water approaches that of the more slowly 

 moving ions. At 306 the conductance of the hydrogen ion differs from 

 that of the potassium ion less than the conductance of the potassium ion 

 differs from that of the acetate ion at ordinary temperatures. As has 

 been pointed out, the relative decrease in the speed of the more rapidly 

 moving ions at higher temperatures is due to the increase in the size 

 of the more rapidly moving ions. It seems more rational, therefore, to 

 ascribe the abnormally high speed of the hydrogen and hydroxyl ions in 

 water to the low value of their hydration, which moreover is in accord 

 with the experimentally determined values of the relative hydration of 

 the different ions in water at ordinary temperatures. 



While it cannot be definitely stated that all hydrogen ions in water 

 are associated with at least one molecule of water, it nevertheless appears 

 probable that such is the case. Were the hydrogen ion unhydrated, we 

 should expect a much greater value for the conductance of the hydrogen 

 ion. In the case of liquid ammonia solutions, it has been shown that the 

 speed of the negative electron, which at low concentrations is associated 

 with at least one ammonia molecule, is approximately seven times that of 

 the sodium ion. It seems not unlikely that the negative electron in dilute 

 solutions is actually associated with a greater number of ammonia mole- 

 cules. Taking all these facts into consideration, it appears probable that 

 the hydrogen ion is associated with at least one molecule of water. 



It is evident that our conception as to the nature of the ions has 

 undergone a great amplification during the past twenty years. Prior to 

 that time the ion of an element was looked upon merely as an atom of 

 the element associated with a charge. Now, however, we know that the 

 ions consist of more or less definite complexes containing the solvent, and 

 the nature and dimensions of these complexes depend, not alone upon 

 the properties of the electrolyte and of the solvent, but also upon the 

 condition under which the solution exists, such as concentration, tempera- 

 ture, pressure, etc. 



6. The Complex Metal- Ammonia Salts. A number of salts of the 

 heavy metals, particularly those of cobalt, chromium and the platinum 

 metals, form series of compounds with ammonia in which there appears 



