Page:Text-book of Electrochemistry.djvu/34

 lower end of the tube, which dipped into a basin of water. When the sparks struck through the water, bubbles of gas were disengaged from the metal wires, and, rising in the tube, gradually displaced the water. As soon as the column of water sank below the upper electrode, the gas, which was a mixture of hydrogen and oxygen, exploded. This experiment was later repeated by Eitter, using silver wires and a solution of a silver salt, and he observed that the negative pole became coated with precipitated silver. On changing the poles, silver was dissolved from one and deposited on the other (now the negative pole). In Deimann's experiment, oxygen and hydrogen were simultaneously formed, both at the positive and at the n^ative poles, so that the process was not a true electrolytic one like that of Eitter.

Galvani and Voita. — The whole state of the science was changed in a great degree by the discoveries of Gralvani, and particularly by those of Volta. In 1795 Volta arranged the metals in a series according to their behaviour in galvanic experiments, and in 1798 Eitter showed that the same series is obtained when the properties of the metals to separate other metals from their salt solutions are compared.

After the introduction of Volta's pile (in 1800) the physiological and optical phenomena were less studied, and more attention was paid to the chemical actions. As opposed to the electrical machines, these piles gave large qucmtities of electricity at a comparatively low potential. Nicholson and Carlisle, in 1800, studied the evolution of oxygen and hydrogen in salt solutions at immersed gold electrodes which were connected with the poles of a Voltaic pile, and observed that litmus in the neighbourhood of the positive pole was turned red by the acid produced there.

Some years later Davy made his brilliant electrochemical discoveries. He succeeded in decomposing the oxides of the alkali and alkaline earth metals, which had previously been regarded as elementary substances, and in preparing the pure metals. Further progress in obtaining the more difl&cultly

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