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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