Vit] RADIO-ACTIVE EMANATIONS 245 
occurs in tubes of lead or glass at about the same temperature as 
in tubes of copper. 
160. In experiments that were made by the static method 
with a very large quantity of radium emanation, a slight amount 
of escape of the condensed emanation was observed several degrees 
below the temperature at which most of the emanation was released. 
This is to be expected, since under such conditions the electrometer 
is able to detect a very minute proportion of the whole quantity of 
the emanation condensed. 
Special experiments, with a large quantity of emanation, that 
were made with the spiral immersed in a bath of rapidly boiling 
nitric oxide, showed this effect very clearly. For example, the con- 
densed emanation began to volatilize at — 155°C. In 4 minutes 
the temperature had risen to — 153°5°, and the amount volatilized 
was four times as great as at — 155°. In the next 54 minutes the 
temperature had increased to 152°3° and practically the whole 
quantity, which was at least fifty times the amount at the 
temperature of — 153°5°, had volatilized. 
It thus seems probable that, if the temperature were kept 
steady at the point at which volatilization was first observed, 
and the released emanation removed at intervals, the whole of 
the emanation would in course of time be liberated at that tem- | 
perature. These results also point to the probability that the 
condensed emanation possesses a true vapour pressure, but great 
refinements in experimental methods would be necessary before 
such a conclusion could be definitely established. 
The true temperature of condensation of the thorium emana- 
tion is probably about —120°C., and that of radium about 
—150°C. Thus there is no doubt that the two emanations are 
quite distinct from each other in this respect, and also with regard 
to their radio-activity, although they both possess the property 
of chemical inertness. These results on the temperatures of 
condensation do not allow us to make any comparison of the 
condensation points of the emanations with those of known gases, 
since the lowering of the condensation point of gases with diminu- 
tion of pressure has not been studied at such extremely minute 
pressures. 
