By such methods W. Ostwald, G. Bredig and other observers have found the specific velocities of many ions both of inorganic and organic compounds, and examined the relation between constitution and ionic velocity. The velocity of elementary ions is found to be a periodic function of the atomic weight, similar elements lying on corresponding portions of a curve drawn to express the relation between these two properties. Such a curve much resembles that giving the relation between atomic weight and viscosity in solution. For complex ions the velocity is largely an additive property; to a continuous additive change in the composition of the ion corresponds a continuous but decreasing change in the velocity. The following table gives Ostwald's results for the formic acid series:-- Table XII. +----------------------+----------+---------------------+ | | Velocity.| Difference for CH2. | +----------------------+----------+---------------------+ | 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.