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Mr. A. Fleck on the Condensation of 



require to be known. It is only necessary to keep the time 

 employed in making the initial measurements always constant. 

 Results. — The curve obtained is shown in curve A, fig. 8. 

 It exhibits no points that require detailed reference, but it 

 will be observed that the shape of the curve is similar to that 

 obtained by Rutherford and Soddy for thorium emanation 

 mixed with air at atmospheric pressure. The greater part 

 of the emanation is condensed between — 165° C. and 

 -170° C. 



Fig. 8. 



-(,0° "So" -ioo° -/2.o° -lUo° ~/60 v -/£o° 



Curve A. Thorium emanation in exhausted straight tube (fig. 7). 

 Curve B. Thorium emanation in exhausted bent tube (fig. 9). 



As the net activity for the amount of emanation condensed 

 at liquid air temperature was only 11 d.p.m., the curve was 

 not prolonged to high temperatures. 



Experiments at Low Pressure with Mixed Thorium and 

 Radium Emanations. 



Apparatus and Method of Experiment. — Experiments were 

 now started on the mixed emanations in a sealed tube at 

 low pressure. A new type of tube, as shown in fig. 9, was 

 constructed of glass permeable to /3 rays and was filled with 

 O07 millicurie of emanation. The thorium preparation was 

 slightly stronger than that used in the previous experiment, 

 and was, as before, in a filter-paper drum which was fixed 



