Page:Outlines of Physical Chemistry - 1899.djvu/206

 ��OUTLINES OF PHYSICAL CHEMISTRY

��quantity of the N0 3 ion goes in the reverse direction, and these changes take place until the two solutions are of uniform concentration. It is to be noted that neither the quantity of metal nor of silver salt suffers any change.

In the other two cases mentioned the action is due to the tendency of the two amalgams to equalise their con- centrations.

A theory of the action of these cells has been proposed by Nernst, and is to be found in M. Le Blanc's ' Elements of Electro-chemistry,' English translation by Whitney.

��Apparatus and Methods

Having given these general statements we shall now pass on to some of the practical methods in which electro-chemical principles are involved. It cannot be expected that we should here enter into a detailed descrip- tion of all the apparatus of any importance, and so we

shall confine ourselves only to the most essential operations.

Perhaps the most important auxiliary apparatus of the electro-chemical labora- tory are the Standard Cells, such as the Daniell-Fleming, the Gouy, and the Latimer-Clark.

This last is of the form shown in fig. 88. Two tubes, into the bottoms of which are fused two platinum wires, are connected by a lateral tube. Into one of the tubes an amalgam of nine parts of mercury and one part of zinc is poured (in the molten condition), and into the other some mercury is placed, and this is covered with a mixture, in the form of a paste, of mercurous sulphate, mercury, and zinc sulphate made up with a concentrated solution of zinc sulphate. The whole of the apparatus is then filled with this same solution. The tubes are then hermetically

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