electricity and the other with negative electricity;
moreover the sum of all the positive charges is always equal to the sum
of all the negative charges. The solution as a whole is therefore
electrically neutral. If we represent dissociation by the usual chemical
equations, with the electrical charges indicated by + and - signs
following the symbols, the dissociation of sodium chloride molecules is
represented thus:

NaCl --> Na^{+}, Cl^{-}.

The positive charge on each sodium ion exactly equals the negative
charge on each chlorine ion. Sodium sulphate dissociates, as shown in
the equation

Na_{2}SO_{4} --> 2Na^{+}, SO_{4}^{--}.

Here the positive charge on the two sodium ions equals the double
negative charge on the SO_{4} ion.

4. _Not all compounds dissociate._ Only those compounds dissociate whose
solutions form electrolytes. Thus salt dissociates when dissolved in
water, the resulting solution being an electrolyte. Sugar, on the other
hand, does not dissociate and its solution is not a conductor of the
electric current.

5. _Extent of dissociation differs in different liquids._ While
compounds most readily undergo dissociation in water, yet dissociation
often occurs to a limited extent when solution takes place in liquids
other than water. In the discussion of solutions it will be understood
that the solvent is water unless otherwise noted.

~The theory of electrolytic dissociation and the properties of solutions.~
In order to be of value, this theory must give a reasonable explanation
of the properties of solutions. Let us now see if the theory is in
harmony with certain of these properties.

~The theory of electrolytic dissociation and the boiling and freezing
points of solutions.~ We have seen that the boiling point of a solution
of a substance is raised in proportion to the concentration of the
dissolved substance. This is but another way of saying that the change
in the boiling point of the solution is proportional to the number of
molecules of the dissolved substance present in the solution.

It has been found, however, that in the case of electrolytes the boiling
point is raised more than it should be to conform to this law. If the
solute dissociates into ions, the reason for this becomes clear. Each
ion has the same effect on the boiling point as a molecule, and since
their number is greater than the number of molecules from which they
were formed, the effect on the boiling point is abno