presents the resultant activity of all the
matter present at a given moment, and the process of disentangling the
component effects consists in finding a number of curves, which express
the rise and fall of activity of each kind of matter as it is produced
and decays, and, fitted together, give the curve of the experiments.

Other methods of investigation also are open. They have enabled
Rutherford to complete the life-history of radium and its products, and
to clear up doubtful points left by the analysis of the curves. By the
removal of the emanation, the activity of radium itself has been shown
to consist solely of alpha-rays. This removal can be effected by passing
air through the solution of a radium salt. The emanation comes away, and
the activity of the deposit which it leaves behind decays rapidly to a
small fraction of its initial value. Again, some of the active deposits
of the emanation are more volatile than others, and can be separated
from them by the agency of heat.

From such evidence Rutherford has traced a long series of disintegration
products of radium, all but the first of which exist in much too minute
quantities to be detected otherwise than by their radio-activities.
Moreover, two of these products are not themselves appreciably
radio-active, though they are born from radio-active parents, and give
rise to a series of radio-active descendants. Their presence is inferred
from such evidence as the rise of beta and gamma radio-activity in the
solid newly deposited by the emanation; this rise measuring the growth
of the first radio-active offspring of one of the non-active bodies.
Some of the radium products give out alpha-rays only, one beta- and
gamma-rays, while one yields all three types of radiation. The pedigree
of the radium family may be expressed in the following table, the time
noted in the second column being the time required for a given quantity
to be half transformed into its next derivative.

Time of half Radio- Properties
decay activity

Radium About 2600 years alpha rays Element chemically analogous
to barium.

Emanation 3.8 days alpha rays Chemically inert gas;
condenses at -150 deg C.

Radium-A 3 minutes alpha rays Behaves as a solid deposited on
surfaces; co