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 p 

 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 



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 a. 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 gas 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- 



