of the numbers and the
minuteness of the quantities dealt with.

Electric charge carried by each H atom in
electrolysis 4.65 x 10^{-10} e.s.[1]
Electric charge carried by each [alpha]
particle 9.3 x 10^{-10} e.s.
Number of atoms in 1 gram of H 6.2 x 10^{23}
Mass of 1 atom of H 1.6 x 10^{-24} gram
Number of molecules per cc. of any gas at
standard pressure and temperature 2.72 x 10^{19}
Number of [alpha] particles expelled per
second per gram of radium itself 3.6 x 10^{10}
Number of [alpha] particles expelled per
second per gram of radium in
equilibrium with its products 14.3 x 10^{10}

[1] The expression 10^{-10} means multiplying by .000,000,000,1;
10^{10} means multiplying by 10,000,000,000.

CHAPTER V

THE STRUCTURE OF THE ATOM

Properties of Radium

A study of the properties of radium will aid in throwing light upon
the question as to the building up of the atom. First to be considered
are the usual properties which distinguish an elementary body.
Metallic radium has been prepared by a method similar to that used in
the preparation of barium. It is a pure white metal, melting at 700 deg.,
and far more volatile than barium. It rapidly alters on exposure to
the air, probably forming a nitride. It energetically decomposes water
and the product dissolves in the water. Its atomic weight is 226.

Radium forms a series of salts analogous in appearance and chemical
action to those of barium. In the course of time they become colored,
especially if mixed barium salts. The radiations from radium produce
marked chemical effects in a number of substances. Carbon dioxide is
changed into carbon, oxygen, and carbon monoxide, and the latter is
changed into carbon and oxygen. Ammonia is dissociated into nitrogen
and hydrogen; hydrochloric acid into chlorine and hydrogen. Oxygen is
condensed into ozone. In general, the action upon gases appears to be
similar to that of the silent electric discharge. Water is decomposed
into hydrogen and oxygen. If moist radium chloride or a salt of radium
containing water of crystallization is sealed in a glass tube, the
gradual accumulation of hydrogen and oxygen will burst the tube.

The radiations rapidly decompose organic matter with the evolution of
gases. Thus grease from stopcocks of apparatus use