Littell's Living Age/Volume 135/Issue 1743/The Electric Conductivity of Water
THE ELECTRIC CONDUCTIVITY OF WATER.
It seems at first sight curious that in the case of so common a substance as water there should be any doubt among physicists as to the power which the liquid possesses of conducting electricity. Not that the subject has by any means been neglected, as the labors of Magnus, Pouillet, Becquerel, Oberbeck, Rossetti, and Quincke abundantly testify. But the results obtained by these several investigators differ so widely among themselves that it is not easy to know which are to be accepted. The figures brought out by Pouillet, for example, are sixty times greater than those deduced by Magnus. Professor Kohlrausch has, therefore, thought it high time that the subject was settled; and after a most carefully conducted investigation, he has published the results of his inquiry in Poggendorf's "Annalen" (Ergänzungsb. iii. 1877, p. 1). Many substances have their electric conductivity affected to a remarkable extent by the presence of impurities, even when these are present in only minute proportion. Matthiessen showed that copper, for instance, has its conductivity lowered forty per cent., by presence of a mere trace of arsenic. In like manner Kohlrausch has found it necessary to pay scrupulous attention to the purity of the water which he examined, and indeed the discrepancies among the results of previous inquirers may probably be explained by inattention to this point. Having prepared the liquid in as pure a state as the resources of the laboratory can permit, Kohlrausch tested the conductivity by examining a shell of this water enclosed between two hemispherical vessels of platinum nearly fitting one into the other, and serving as electrodes. On passing a current of electricity through this arrangement, it was found that the pure water offered remarkable resistance; in fact its conductivity was only one one-hundred-and-twentieth of that assigned to it by Pouillet. Rain, which is, of course, the purest natural form of water, conducted electricity twenty-five times better than the artificially purified liquid which served as a standard.