Page:Text-book of Electrochemistry.djvu/169

 154 CONDUCTIVITY OF ELECTROLYTES. chap.

According to the table on p. 149, the value of Pi for Na is 2180 X l(fi kUograms, and that of Pa for CI, 1450 x 10« = 3630 X 10* kilograms. If we take the day instead of the second as the unit of time, the number given has to be = 8-64 X 10*). We then obtain for sodium chloride at 18°— 3,630 xlO« ~

Nemst (26),^ who first developed this theory, showed that the calculated numbers agree well with those found by experiment, as can be gathered from the next table. The difference between the observed and calculated values is mainly due to the fact that solutions of such concentration were used that the dissociation was not complete, and so the osmotic pressure was actually smaller than the value employed in the calculation; it will be observed that the calculated values are generally higher than those found from experiment.

DiFFi'siox Coefficients at 18^. (Unit of time, the day.)

Obe. Calc. Obs.

HNO3 2-22 2-32 ' NaCgHjO,. ..

KOH 1-86 2-07 NaCHO, ....

NaOH 1-40 1-56 NaCeH^SO^. ..

NaCl 1-08 1-17 KCl

NaBr MO M3, KBr

Nal 105 M2 ' KI

KNOg 1-22 1-42 LiBr

NH,C1 1-30 1-44 I Lil

It is easy to see that the temperature coefficient of the diffusion must be the sum of the temperature coefficients of

^ In bis calculation Nernst used other figures than here employed, and obtained for N 1*12 instead of 1*17.

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