Page:Text-book of Electrochemistry.djvu/226

 A case of this nature was studied by G. Meyer (9). The arrangement of the element used by him was—

Concentrated amal- gam of a metal, M.

��Aqueous solution of Dilute amalgam

��a salt of metal, M.

��of a metal, M.

��He examined the metals— zinc, cadmium, lead, tin, copper, and sodium. Now, if one mol of one of these metals passes from the concentrated amalgam of concentration Ci to the dilute amalgam of concentration C2, the work done will be (see Chap. VI. p. 77)—

A =IiTln^\

If the work is measured in gram-calories, B = 1-99. An element of this kind, which depends for its action on dififerences of concentration, is called a concentration dement.

If, now, the circuit of a combination of two amalgams be closed by a metal wire, a current passes through the solution in the direction indicated by the arrow, so that metal is dissolved from the concentrated amalgam, and just as much is deposited at the dilute amalgam. The total result of the process is that, simultaneously with the transportation of 96,500 coulombs, one gram-equivalent of metal passes from one amalgam to the other, and the concentration of the solution between the two remains unaltered.

If a gram-molecule contains n equivalents, the same

work will be done by the motion of jrram-molecule. The

work obtainable is, therefore, in general —

A =23,070P = -i?rin J\

n 6a

By measuring the electromotive force P, Meyer verified this result. From this he determined the value of w, and found numbers which agree well with those arrived at by

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