458 
Rad. Em., 29.1%, Rad. A, 31.4%, Rad. (B) and C, 39.5%. Total, 100%. 
The line marked Rad. Em. starts initially at 30.% and in four hours has 
diminished to 29.1% according to the half period of 3.85 days. Rad. A. 
initially is zero, because initially emanation alone is placed in the chamber. 
Curve A rises to half value in three minutes and in 20 or 30 minutes becomes 
in equilibrium, that is, it disintegrates into Rad. B as fast as it is formed 
from the emanation. The latter part of the curve is practically a straight 
line parallel to the curve for emanation. 
Rad. B does not give off a particles. The ionization due to the @ 
radiation can be neglected. Rad. B changes into Rad. C whose half period 
is 19.5 minutes. Thus the curve (B) and C depends upon the amount of Rad. 
C present. This initially depends upon the formation of Rad. A and B. The 
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» 
S 
Fic. 3. 
curve starts from zero and reaches its equilibrium in about four hours. The 
total ionization depends upon all three, so the current in the chamber, assum- 
ing that all ions capable of being produced by the « particles are used, 
increases according to the curve Em.+A+B-+C, which is formed by summing 
the ordinates of the three curves. This reaches 100% in about three hours. 
In a chamber of smaller dimensions the effect of the slower electrons will be 
greater than the above, since a greater number of the high velocity ones 
will be absorbed by the walls of the chamber before they have produced 
their maximum number of ions. 
The quantity of emanation gas associated with or occluded in, or in 
equilibrium with, a quantity of radium has been found to be directly pro- 
portional to the mass of radium. This is so true that the amount of emana- 
tion in equilibrium with one gram of radium has been measured very exactly 
and is called the curie. Thus one gram of old radium contains or is in equi- 
librium with one curie of radium emanation gas. The volume of this gas 
under standard conditions is .62 cu. mm. 
To collect this ga the radium is put into solution, boiled and the gas 
diluted with air is collected over mercury and then introduced into the elec- 
troscope. The radium solution after standing one month is again in equi- 
