x] RADIO-ACTIVE PROCESSES 311 
Similar results have also been found to hold for the y rays. 
This was tested by the writer in the followmg way. The emana- 
tion from some solid radium bromide was released by heat, 
and condensed m a small glass tube which was then sealed off. 
The radium so treated, and the emanation tube, were placed 
together under an electroscope, with a screen of lead 1 cm. thick 
interposed in order to let through only the y rays. The experi- 
ments were continued over three weeks, but the sum total of the 
y rays from the radium and the emanation tube was, over the 
whole interval, equal to that of the original radium. During this 
period the amount of y rays from the radium at first decreased to 
only a few per cent. of the original value, and then slowly increased 
again, until at the end of the three weeks it had nearly regained 
its original value, before the emanation was removed. At the same 
time the amount of y rays from the emanation tube rose from zero 
to a maximum and then slowly decreased again at the same rate 
as the decay of the activity of the emanation in the tube. This 
result shows that the amount of y rays from radium was a constant 
quantity over the interval of observation, although the amount of 
y rays from the radium and emanation tube had passed through a 
cycle of changes. 
197. Résumé of results. Before discussing the general 
theory advanced to account for the processes occurring in the radio- 
element, a brief réswmé will be given of the more important results 
already described in detail in previous chapters. 
The radio-activity of uranium, thorium, and radium has been 
shown to be maintained by the production at a constant rate of new 
kinds of matter, which possess temporary activity. The constant 
activity of the radio-elements is due to a state of equilibrium where 
the rate of production of new active matter compensates for the 
change in that already produced. In some cases, the active products 
possess well-defined chemical properties different from those of the 
parent elements and can be separated from them by chemical 
means. The separation of Ur X and Th X from uranium and 
thorium are good examples of this process. In other cases, the 
new products, as in the case of the thorium and radium emana- 
tions, are gaseous in character and are released from the radio- 
