When the potential gradient is one volt (10^8 C.G.S. units) per centimetre this becomes u + v = 1.036 × 10^-7 × k/m. Thus by measuring the value of k/m, which is known as the equivalent conductivity of the solution, we can find u + v, the velocity of the ions relative to each other. For instance, the equivalent conductivity of a solution of potassium chloride containing one-tenth of a gram-equivalent per litre is 1119 × 10^-13 C.G.S. units at 18° C. Therefore u + v = 1.036 × 10^7 × 1119 × 10^-13 = 1.159 × 10^-3 = 0.001159 cm. per sec. In order to obtain the absolute velocities u and v, we must find some other relation between them. Let us resolve u into ½(u + v) in one direction, say to the right, and ½(u - v) to the left. Similarly v can be resolved into ½(v+u) to the left and ½(v-u) to the right. On pairing these velocities we have a combined movement of the ions to the right, with a speed of ½(u - v) and a drift right and left, past each other, each ion travelling with a speed of ½(u + v), constituting the electrolytic separation. If u is greater than v, the combined movement involves a concentration of salt at the cathode, and a corresponding dilution at the anode, and _vice versa_. The rate at which salt is electrolysed, and thus removed from the solution at each electrode, is ½(u + v). Thus the total loss of salt at the cathode is ½(u + v) - ½(u - v) or v, and at the anode, ½(v + u) - ½(v - u), or u. Therefore, as is explained in the article ELECTROLYSIS, by measuring the dilution of the liquid round the electrodes when a current passed, W. Hittorf (_Pogg. Ann._, 1853-1859, 89, p. 177; 98, p. 1; 103, p. 1; 106, pp. 337 and 513) was able to deduce the ratio of the two velocities, for simple salts when no complex ions are present, and many further experiments have been made on the subject (see _Das Leitvermögen der Elektrolyte_). By combining the results thus obtained with the sum of the velocities, as determined from the conductivities, Kohlrausch calculated the absolute velocities of different ions under stated conditions. Thus, in the case of the solution of potassium chloride considered above, Hittorf's experiments show us that the ratio of the velocity of the anion to that of the cation in this solution is .51 : .49. The absolute velocity of the potassium ion under unit potential gradient is therefore 0.000567 cm. per sec., and that of the chlorine ion 0.000592 cm. per sec. Similar calculations can be made for solutions of other concentrations, and of different substances. Table IX. shows Kohlrausch's values for the ionic velocities of three chlorides of alkali metals at 18° C, calculated for a potential gradient of 1 volt per cm.; the numbers are in terms of a unit equal to 10^-6 cm. per sec.:-- TABLE IX.