Their mass can be calculated when we
know, through experiments of this kind, the speed of the ions in a
given field, and on the other hand--as we can now estimate their
electric charge--the force which moves them. They evidently progress
more slowly the larger they are; and in the viscous medium constituted
by the gas, the displacement is effected at a speed sensibly
proportional to the motive power.
At the ordinary temperature these masses are relatively considerable,
and are greater for the positive than for the negative ions, that is
to say, they are about the order of some ten molecules. The ions,
therefore, seem to be formed by an agglomeration of neutral molecules
maintained round an electrified centre by electrostatic attraction. If
the temperature rises, the thermal agitation will become great enough
to prevent the molecules from remaining linked to the centre. By
measurements effected on the gases of flames, we arrive at very
different values of the masses from those found for ordinary ions, and
above all, very different ones for ions of contrary sign.
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