APPENDIX 357tide) or a helium nucleus (alpha particle) and leaving as a residue
the nucleus of a simpler element. The beta or alpha particles are
ejected with enormous velocity, and streams of these particles
constitute the so-called beta and alpha rays. For each radio
element there is a definite probability as to the length of time an
atom will maintain its identity before the radioactive disintegra-
tion occurs. The radioactivity of uranium, for example, is very
weak, and if we start with a definite mass today it will take eight
billion years (8 X 10^9 ) before one-half of its atoms have disinte-
grated. On the other hand, the much more strongly radioactive
radium disintegrates more rapidly, and it takes but two thousand
years before one-half of its atoms have changed.
Without doubt somewhere in the universe nuclei of all elements
are being both built up and disintegrated. Such processes are
perhaps going on in the interior of the sun and the hot stars where
temperatures of 40,000,000 degrees prevail, perhaps also out in
infinite space, but such ideas are highly speculative.
Law of Electrostatic Attraction and Repulsion. This law, which
is known as Coulomb's law, has the same mathematical form
as Newton's law of gravitation: The force repelling two like
charges is equal to the product of the charges divided by the
square of the distance between. The force attracting unlike
charges is of the same magnitude. If the charges are of 1 electro-
static unit each and the distance is 1 cm. the force is 1 dyne.
The total net charge on one electrochemical equivalent of ions,* say
on 35.45 grams of chlorine ions, is 6.06 X 10^23 X 4.774 X lO"^10 or
29 X 10^13 electrostatic units. Therefore, if this charge is concen-
trated at a point and the total net charge on 23 grams of sodium
ions is concentrated at a point 1 cm. away, the attraction between
these charges will be 84 X 10^27 dynes, or 10^20 metric tons.
If these charges are a meter apart the attraction will be 10^16
metric tons. If they are as far apart as the north and south poles
of our earth the attraction will still be 60 metric tons.
Structural Forces within the Atom. Coulomb's law holds ac-
curately for all distances outside of atomic dimensions (10~^8 cm.),
- The total charge on one gram equivalent of ions, expressed in the common
unit, is 96,500 coulombs. This quantity of electricity is known as the faraday,
and it is constantly used by electrochemists. One coulomb consists of 3 X 10^9
electrostatic units, and the faraday therefore contains 29 X 10^13 electrostatic
units.