3. _The positive charges equal the negative charges._ The ions formed by the dissociation of any molecule are of two kinds. One kind is charged with positive 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 abnormally great. In a similar way, the theory furnishes an explanation of the abnormal lowering of the freezing point of electrolytes. ~The theory of electrolytic dissociation and electrolysis.~ The changes taking place during electrolysis harmonize very completely with the theory of dissociation. This will become clear from a study of the following examples. [Illustration: Fig. 32]