208 Profs. EK. Rutherford and H. T. Barnes on the 
proportional to the emanation present. If no emanation had 
been lost, the y rays from the radium and the emanation-tube 
together should, at any time, be equal to that from the original 
radium. If this were not the case, it showed that a portion 
of the emanation had escaped into the pump, and the amount 
so lost would be calculated from the difference in the rates of 
discharge of the electroscope. These measurements could be 
made with rapidity and accuracy, and served as a guide to 
the amount of emanation present in a vessel. It must be 
borne in mind that the y rays emitted only serve as a measure 
of the amount of emanation present, when sufficient time has 
elapsed (3 to 4 hours is enough) for the emanation and its 
product emanation X to reach a state of approximate radio- 
active equilibrium. Immediately after the introduction of 
the emanation into a vessel no @ or y rays are observed, but 
the intensity of the @ rays and ¥ rays reaches about half their 
maximum value 45 minutes later. 
Description of Experiments. 
The heating effect of 30 milligrams of radium bromide, 
inclosed in a-narrow glass tube, was first determined in the 
air-calorimeter. The radium tube R (fig. 3) was then con- 
nected through a phosphorus-pentoxide tube A to a short 
narrow glass tube T, about 3 cms. long, connected to a 
mercury pump P. The tube T passed through a small 
liquid-air vessel, made of ebonite, in order to condense any 
emanation passing through it. 
Liquid air was placed in the vessel, and the tubes partially 
exhausted. The radium was then heated* with a spirit-lamp 
to drive off the emanation. The water-vapour given off was 
absorbed in the tube P and the emanation was condensed in 
the tube T, andthe whole emanation given off was condensed 
in the tube T by slowly working the pump. ‘The tube T and 
the radium tube were then sealed off, and the heating effect 
of each tested as soon as possible afterwards in the air- 
calorimeter. The results obtained are shown in fig. 4 (p. 210). 
The heating effect of the radium, when first tested, had fallen 
considerably, and continued to do so for about three hours, 
when it reached a minimum corresponding to about 30 per 
cent. of the original value. At the same time the emanation- 
tube, when first tested, showed considerable heating effect. 
* When the radium was heated to about a red heat a very bright — 
phosphorescence was produced in the radium compound. The luminosity 
was bright enough to observe in ordinary daylight and persisted for 
several days. Its spectrum was kindly photographed for us by Dr. Schenck 
and was found to be continuous. 

