| Formic acid HCO2 | 51.2 | .. |
| Acetic " H3C2O2 | 38.3 | -12.9 |
| Propionic " H5C3O2 | 34.3 | - 4.0 |
| Butyric " H7C4O2 | 30.8 | - 3.5 |
| Valeric " H9C5O2 | 28.8 | - 2.0 |
| Caprionic " H11C6O2 | 27.4 | - 1.4 |
+----------------------+----------+---------------------+

_Nature of Electrolytes._--We have as yet said nothing about the
fundamental cause of electrolytic activity, nor considered why, for
example, a solution of potassium chloride is a good conductor, while a
solution of sugar allows practically no current to pass.

All the preceding account of the subject is, then, independent of any
view we may take of the nature of electrolytes, and stands on the basis
of direct experiment. Nevertheless, the facts considered point to a very
definite conclusion. The specific velocity of an ion is independent of
the nature of the opposite ion present, and this suggests that the ions
themselves, while travelling through the liquid, are dissociated from
each other. Further evidence, pointing in the same direction, is
furnished by the fact that since the conductivity is proportional to the
concentration at great dilution, the equivalent-conductivity, and
therefore the ionic velocity, is independent of it. The importance of
this relation will be seen by considering the alternative to the
dissociation hypothesis. If the ions are not permanently free from each
other their mobility as parts of the dissolved molecules must be secured
by continual interchanges. The velocity with which they work their way
through the liquid must then increase as such molecular rearrangements
become more frequent, and will therefore depend on the number of solute
molecules, i.e. on the concentration. On this supposition the observed
constancy of velocity would be impossible. We shall therefore adopt as a
wording hypothesis the theory, confirmed by other phenomena (see
ELECTROLYSIS), that an electrolyte consists of dissociated ions.

It will be noticed that neither the evidence in favour of the
dissociation theory which is here considered, nor that described in the
article ELECTROLYSIS, requires more than the effective dissociation of
the ions from each other. They may well be connected in some way with
solvent molecules, and there are several indications that an ion
consists of an electrified