The second column gives the observed activity (measured by means of an electroscope) for a long exposure of 24 hours in the presence of the emanation.
In cases where a steady current of air is drawn over the active body, the observed values are slightly lower than the theoretical. This is probably due to a slight volatility of the product radium B at ordinary temperatures.
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Fig. 90.
223. Analysis of the α-ray curves. The analysis of the
decay curves of the excited activity of radium, measured by the α
rays, will now be discussed. The following table shows the variation
of the intensity of the radiation after a long exposure in the
presence of the radium emanation. A platinum plate was made
active by exposure for several days in a glass tube containing
a large quantity of emanation. The active platinum after removal
was placed on the lower of two parallel insulated lead plates, and
a saturating electromotive force of 600 volts was applied. The
ionization current was sufficiently large to be measured by means
of a sensitive high-resistance galvanometer, and readings were
taken as quickly as possible after removal of the platinum from
the emanation vessel. The initial value of the current (taken
