Page:Text-book of Electrochemistry.djvu/252

 XIV.

��EXPERIMENTAL DETERMINATIONS.

��Results of Experimental Determinations. By means of these various methods the difference of potential between mercury and electrolyte can be determined. The starting- point chosen by Ostwald {10) was —

��or-

��Hg I HgCl in Ti-HCl = - 0560 volt, Hg I HgaS04 in n-HaSO^ = -099 volt.

��If one potential difiference is known, then all the others can be measured by a suitable combination of galvanic elements. Thus, if it be required to ascertain the tension between zinc and normal zinc sulphate solution, we should form the element —

Hg I HgaSO^ in BSO^{n) \ ZnS04(n) | Zn.

The electromotive force of this element has been found to be 1*514 volts. If we subtract from this 0*99 volt for Hg I 7i-HaS04, we obtain as remainder 0*524 volt for Zn I ZnSOi. (For a correction, see p. 240.)

The potential differences given below between metals and normal solutions of their salts have been determined in this way.

From the values so obtained the electrolytic solution pressure P for metals in normal solutions of their salts can be calculated by means of the formula —

��RT ^ P TT = — ^ In -

��nE

��The values for w and P contained in the following tables have been obtained by Ostwald : —

��Potential Differexce, », between Metals and theiu Salts in

Normal Solution.

��Volt-.

��Volts.

Silver -I'Ol

�� �