Page:Text-book of Electrochemistry.djvu/40

 following abstract of the address may serve to indicate what were the best-foiinded electrochemical views of that period : —

Since the quantity of electricity on any atom is equal to, or is a whole multiple of, that on a hydrogen atom, Helm- holtz proposed a unit for this — the atomic charge. Electricity is assumed to exist in matter in distinct homogeneous par- ticles which correspond to the atoms. An atom can occur charged either i>ositively or negatively — for example, in hydrogen sulphide the sulphur is negative, in sulphuric anhydride (SOg) it is positive.

According to Helmholtz, all substances are electrolytes, and better or worse conductors of electricity. After electro- lysing the " non-conductor " turpentine for twenty-four hours, it was found that an electrometer placed between the two elec- trodes indicated a potential difference— that is, polarisation had taken place, proving that there had been some electrolysis (8 dll. ccmsed a polarisation of 0*3 dll. in ether, oil, and turpentine, and of 08 dll. in benzene). Similarly, Helm- holtz found a potential difference between metals, such as copper and zinc, which were separated by the best known insulators — glass, resin, shellac, paraffin, or sulphur — and proved that this result was not due to hygroscopic moisture. He called attention to the extraordinarily high values of the electric forces binding hydrogen and oxygen in water, which forces are able to completely change the proj^rties of these elements on combination.

Helmholtz explained the capability of one element of separating another from its compound as due to the greater affinity for positive electricity. The Berzelius series is to be understood in this sense. This, too, is the cause of the Volta eflTect.

Each valence corresponds with a single charge, con- sequently the atoms combine in multiple proportions. In the case of unsaturated compounds with two free valencies, it is to be assumed that one of these corresponds with a positive, the other with a negative charge. Unsaturated compounds with an odd number of free valencies were assumed to exist

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