Page:Text-book of Electrochemistry.djvu/131

 ii6 ELECTROLYTES. chap.

the ordinary temperature (20°) must therefore be decomposed (dissociated) into hydrogen and oxygen molecules. According to the method of Helmholtz {3) it can be calculated that, taking 3 X 10^ water molecules, two are dissociated into 2Ha and O2.

In the same way it can be shown that all possible com- binations of hydrogen and oxygen, e,g, 0, H, OH, O2H, must

occur in water. In a solution of potassium chloride, there-

+ -

fore, we must have the free ions K and CI, but Clausius

suggested that the quantity is so small as not to be recog- nisable by chemical methods. Nevertheless, the quantity was supposed to be sufficient to give an electric conductivity to the solution. When Clausius admitted that the number of free ions is so small, this proof lost much of its meaning when we consider that by the same reasoning we can show that even the compound O2H occurs in the water in small quantity. For, although the correctness of the development cannot be doubted, it must yet be admitted that the substance O2H does not really exist ; if, for instance, 10^^ water molecules give rise to only one such molecule, then that has no practical significance. Furthermore, Clausius was not able to prove that the extremely small quantity of ions present in the salt solution was sufficient for the transportation of the electricity. Charging Current. — If electricity be conducted through a trough containing an electrolytic solution, the

surface of the liquid receives a Y T z small charge during the first

moment. After this has occun^ed,

no further accumulation of elec- 1 j tricity takes place either in the

Fig. 25. solution or at the surface. If we

imagine two cross sections, Y and Yi, of the solution (Fig. 25), then as much electricity must pass out from the liquid between these sections through Yi as enters it through Y, In this way it can be proved that in 6iny closed circuit the same quantity of electricity passes through every section after the charging current has ceased.

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