Transformation Products of Radium. 647 
Variation of the Activity of Radium with Time. 
It has long been known that the activity of freshly prepared 
radium increases at first with the time and reaches a maximum 
value after an interval of about one month. The results 
already considered show that there is a further slow increase 
of activity with the time. This is the case whether the 
activity is measured by the a or Brays. After a lapse of 
about 200 years the amount of the products radium D 
and E will have practically reached a maximum value. The 
same number of atoms of each of the products C and D will 
then break up per second. If each atom of these products 
in disintegrating throws off an equal number (probably one) 
of $8 particles, the number of £8 particles thrown off per 
second will be twice as great as from radium a few months 
old. The number wiil increase at first at the rate of about 
2 per cent. a year. 
Similar considerations apply to the @ ray activity. Since, 
however, there are four other products of radium besides 
radium itself which expel a particles, the number of a2 
particles emitted per second from old radium will not be 
more than 25 percent. greater than the number from radium 
a few months old. The activity measured by the @ rays will 
thus not increase more than 25 per cent., and probably still 
less, as the @ particles from radium E probably produce less 
ionization than the « particles expelled from the other radium 
products. It is probable that half of the radium itself is 
transformed in about 1000 years. The activity of radium 
will consequently rise to a maximum after 200 years and 
then slowly die away with the time. 
Products in Pitchblende. 
The products radium D and E must be present in pitch- 
blende in amounts proportional to the quantity of radium 
present, and should be capable of separation from the mineral 
by suitable chemical methods. The radioactive properties of 
these substances, if obtained in the pure state, is summarized 
below. 
Radium D).—The product immediately after separation 
should emit only 8 (and probably y) rays. The B ray 
activity should decay to halt value in about forty years. In 
consequence of the change of D into E, the latter of which 
gives out a rays, the a ray activity will increase for a few 
years, pass through a maximum, and then decrease with the 
time and fall to half value in about forty years. Since the 
rate of change of D is about 25 times as fast as radium itself, 
