IX.

��ABSOLUTE VELOCITY OF THE IONS.

��Cation.

�rxio'.

�H

�K

�Na

�Li

�NH,

�Ag

��Anion.

�F X 10».

�OH

�CI

�I

�CH,CO» C^HftCOjj

��From these data we can calculate the mechanical force

necessary to drive a gram-ion through the water with a

certain velocity. The volt is so defined that the work

Iff' ergs is required to transport 1 coulomb agfidnst this

potential difference. Inversely, if the fall of potential is

1 volt per centimetre, then W dyne-cms. (ergs) are

required to transport 1 coulomb through 1 cm. against this

kilograms. The force required for a gram-ion charged with

96,500 coulombs against this same fall of potential is therefore

96,500 X 1018 = 983,000 kilograms. This force drives a

gram-ion of hydrogen with the velocity 325 x 10 "'^ cms. per

second. The force required in order that the velocity may be

10* 1 cm. per second must be ^r^ times greater, i.e. it must be

^^^'^325^ ^^' = ^^^ ^ ^^* kilograms. The following table gram-ion through water at 18° with a velocity of 1 cm. per second : —

��K .

�NH, .

�CI .

�Na,

�H . .

�I .

�Li .

�Ag. .

From these numbers it can be seen what enormous mechanical forces are required to move the ions through the solvent with an appreciable velocity. As the tempera- ture rises, these values, which are a measure of the friction, decrease in about the same ratio as that in which the mobilities

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