220 RADIO-ACTIVE EMANATIONS [CH. 
In that time the accumulation of the emanation again attained a 
practical maximum and again represented a steady state. The 
stream of air was blown through, as before, for 25 seconds, stopped 
and the current again measured. In both cases, the electrometer 
recorded a movement of 14°6 divisions per second. By blowing 
the same stream of air continuously through the solution the final 
current corresponded to 79 divisions per second or about one-half 
of that observed after the first rush. 
Thus the rate of production of emanation is the same in the 
solid nitrate as in the solution, although the emanating power, we. 
the rate of escape of the emanation, is over 600 times greater in 
the solution than in the solid. 
It seems probable that the rate of production of emanation 
by thorium, like the rate of production of Ur X and Th X, is inde- 
pendent of conditions. The changes of emanating power of the 
various compounds by moisture, heat, and solution must therefore 
be ascribed solely to an alteration in the rate of escape of the 
emanation into the surrounding gas and not to an alteration in 
the rate of its production in the compound. 
On this view, it is easy to see that slight changes in the mode 
of preparation of a thorium compound may produce large changes 
in emanating power. Such effects have been often observed, and 
must be ascribed to slight physical changes in the precipitate. 
The fact that the rate of production of the emanation is indepen- 
dent of the physical or chemical conditions of the thorium, m which 
it is produced, is thus in harmony with what had previously been 
observed for the radio-active products Ur X and Th X. 
Source of the Thorium HEmanation. 
145. Some experiments of Rutherford and Soddy? will now 
be considered, which show that the thorium emanation 1s pro- 
duced, not directly by the thorium itself, but by the active 
product Th X. 
When the Th X, by precipitation with ammonia, is removed from 
a quantity of thorium nitrate, the precipitated thorium hydroxide 
1 Phil. Mag. Noy. 1902. 
