Page:Text-book of Electrochemistry.djvu/133

 1 1 8 ELECTROLYTES. chap.

law is that the gram-equivalent of every ion carries a charge of 96,500 coulombs, and consequently all equivalents have the same charge. When the electricity passes through a liquid it is transported by the ions, the positive electricity being carried by the positive ions, and the negative by the negative ions. The electricity is firmly bound to the ions, and can only be given up at the electrodes, and the ions then cease to exist as such. It is easy to understand that equiva- lent quantities of different substances are charged with the same amount of electricity; for when we mix solutions of two electrolytes — for instance, calcium chloride (CaCla) and sodium nitrate (NaNOs), partial exchange takes place, and there are formed sodium chloride (NaCl) and calcium nitrate (Ca(N08)2). Now, if one atom of calcium (=2 equivalents) were not charged with the same quantity of electricity as two NOa radicles, or th« two sodium atoms originally com- bined with these, but had a greater positive charge, the molecules of calcium nitrate (Ca(N03)2) would be positively charged, and the sodium chloride molecules would be negatively charged, since the original solutions were electri- cally neutral. By evaporation or by some chemical means, one Idnd of molecule, e.g, the sodium chloride molecules, can be precipitated from the solution, or the two substances can be separated by diffusion. After this separation the solutions should be electrically charged. As not the slightest charge can be found on the solutions, we must assume that equivalent quantities of the various substances have the same charge.

Composition of the Ions — Berzelius found that in the electrolysis of a solution of sodium sulphate (NaaS04), or, as he wrote it, Na20S08, the base NaOH collected at the negative pole, and the acid HaS04 collected at the positive pole. He therefore regarded NaaO and SOa as the ions which, with water, formed 2N'aOH and H2SO4. Others were of the opinion that the decomposition of Na3S04 takes place in the same way as that of copper sulphate, CUSO4, namely, into the metal Na, which, with water, forms XaOH with evolution

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