Page:Text-book of Electrochemistry.djvu/235

 220 ELECTROMOTIVE FORCE. chap.

of the remainder of the deviation has not yet been found. For some silver salts the disagreement was still greater; the observed values were 00214 and 00146 volt, whilst calculation gives 0*0109 and 0*008 respectively.

If the above combination consists of n-valent ions, then for each mol w..96,500 coulombs must be passed through the element, and we obtain for the electric work —

7i23,0707r = 1-997-7-'' In ?'.

Consequently n passes into the denominator of the final formula, and we have —

Nerast's Calculation of the Electromotive Forces of Concentration Elements (14) — Let us again consider the Helmholtz combination —

��Cu I dilute CuSO* | concentrated CUSO4 | Cu. Pi Pi

When a current passes through this element in the direction indicated by the arrow, the following changes

occur : —

(1) A gram-ion (63*6 grams) of copper is dissolved from the copper electrode in contact \iith the dilute copper sulphate solution, and is transformed from the metallic to the ionic condition ;

(2) At the surface of separation of the two solutions the same process takes place as described in the previous case ;

and

(3) A gram-ion (636 grams) of copper is deposited from the concentrated solution on the copper electrode in contact with it, the copper passing from the ionic to the metallic condition.

The final result of processes (1) and (3) is that a gram-ion of copper passes from the concentrated to the dilute solution.

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