1909] on Prohlems of Helium and Radium. 731 



out to which these objections did not apply. In this experiment 

 the gauge as well as the connecting tubes were well cleaned out 

 with nitric acid, and all thoroughly dried. The radium, after the 

 1100 hours in which it was under high exhaustion with frequent 

 heating, was certainly in a more satisfactory condition. Further, 

 to prevent the unchecked action of tlie emanation throughout the 

 apparatus, the little charcoal condenser was maintained at a degree 

 or two below that of the boiling point of oxygen by the use of old 

 liquid air for a period of about six weeks. A larger quantity of char- 

 coal was used, viz., 1 grm., the more effectively to condense out 

 extraneous gases while leaving any helium substantially unaffected. 

 This charcoal had been treated with chlorine at a red heat, and 

 subsequently with hydrogen. 



Beyond this the conduct of the experiment followed the lines of 

 the former one. The mercury pump exhaust was continued for 

 several hours — the charcoal being well heated meanwhile — and was 

 carried to 0'002 mm. The large charcoal bulb was then cooled 

 for several hours in Hquid air while continuing the heating of 

 the 1 grm. of charcoal and the radium salt. A pressure as low as 

 0*00005 mm. was thus obtained when the charcoal was sealed off. 

 On now placing the U tube containing the 1 grm. of charcoal in 

 liquid air the pressure registered was * 000044 mm. 



These conditions were maintained for five days, during which a 

 steady growth of pressure was observed corresponding to an incre- 

 ment of approximately • 3 c.mm. per grm. of radium per day. The 

 radium was then heated with a small Bunsen flame as before to below 

 a red heat, when the pressure was increased by about 40 per cent. 

 This increase showed no sign of disappearing, but during the next 

 week a decided but somewhat irregular growth of pressure was 

 recorded. The radium was again heated, when a further increase of 

 pressure was observed. In the succeeding five days it remained 

 steady, only to be again increased on heating the radium. This 

 treatment was repeated in all ten times at varying intervals during 

 1100 hours, and in each case the pressure rose on heating and 

 remained fairly steady on standing. All the observations of the 

 second set of experiments are graphically represented in Fig. 4. A 

 mean line is drawn through the observations taken with the radium 

 heated, giving a steadily maintained helium increment of approxi- 

 mately 0"37 c.mm. per grm. of radium per day. 



In order to ascertain if any helium was occluded in the cooled char- 

 coal and the surrounding glass, the latter was raised to near a low red 

 heat while the tube containing the radium chloride was temporarily 

 cooled in liquid air, with the object of condensing out and localising 

 the emanation coming from the heated charcoal and preventing its 

 access to the gauge. The temperature was maintained for an hour, 

 and the charcoal was then allowed to cool, and finally replaced in the 

 liquid air. The radium chloride was then allowed to warm up, and 



