that the Oh^{-} ions remain as such in the solution.  The union of the H^{+} ions with the CN^{-} ions to form the undissociated HCN diminishes the concentration of the H^{+} ions, and more water dissociates (H_{2}O <—­> H^{+} + Oh^{-}) to restore the equilibrium.  It is clear, however, that there must be a gradual accumulation of Oh^{-} ions in the solution as a result of these changes, causing the solution to exhibit an alkaline reaction, and also that ultimately the further dissociation of the water will be checked by the presence of these ions, just as the dissociation of the H_{2}S was lessened by the addition of HCl.

An exactly opposite result follows the solution of such a salt as Al_{2}(so_{4})_{3} in water.  In this case the acid is strong and the base weak, and the Oh^{-} ions form the little dissociated Al(Oh)_{3}, while the H^{+} ions remain as such in the solution, sulphuric acid being extensively dissociated.  The solution exhibits an acid reaction.

Such hydrolytic processes as the above are of great importance in analytical chemistry, especially in the understanding of the action of indicators in volumetric analysis. (See page 32.)

The impelling force which causes an element to pass from the atomic to the ionic condition is termed !electrolytic solution pressure!, or ionization tension.  This force may be measured in terms of electrical potential, and the table below shows the relative values for a number of elements.

In general, an element with a greater solution pressure tends to cause the deposition of an element of less solution pressure when placed in a solution of its salt, as, for instance, when a strip of zinc or iron is placed in a solution of a copper salt, with the resulting precipitation of metallic copper.

Hydrogen is included in the table, and its position should be noted with reference to the other common elements.  For a more extended discussion of this topic the student should refer to other treatises.

Potentialseries of the metals

_______________________________________________________

___________
|           |                    |
| Potential |                    | potential
| in volts  |                    | in volts
_____________________|___________|____________________|_____

______
|           |                    |
Sodium      Na^{+}   | +2.44     | Lead       Pb^{++} | -0.13
Calcium     Ca^{++}  |           | Hydrogen    H^{+}  | -0.28
Magnesium   Mg^{++}  |           | Bismuth    Bi^{+++}|
Aluminum    A1^{+++} | +1.00     | Antimony           | -0.75
Manganese   Mn^{++}  |           | Arsenic            |
Zinc        Zn^{++}  | +0.49     | Copper     Cu^{++} | -0.61
Cadmium     Cd^{++}  | +0.14     | Mercury    Hg^{+}  | -1.03
Iron        Fe^{++}  | +0.063    | Silver     Ag^{+}  | -1.05
Cobalt      Co^{++}  | -0.045    | Platinum           |
Nickel      Ni^{++}  | -0.049    | Gold               |
Tin         Sn^{++}  | -0.085(?) |                    |
_____________________|___________|____________________|__________

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