206 EXPERIMENTS IN RADIO-ACTIVITY. 



Oil two .subsequent oecu.sion.s the gase.s evolved fi'oiii both solutions 

 of radium bromide were mixed, after four days' accumulation, which 

 amounted to about 2.5 cubic centimeters in each case, and were exam- 

 ined in a similar way. The D3 line of helium could not be detected. 

 It may l)e well to state the composition found for the gases continu- 

 ously generated by a solution of radium, for it seemed likely that the 

 large excess of hydrogen over the composition required to form water, 

 shown in the analysis given by Bodliinder (Ber., loc. cit.), might be 

 due to the greater solubility of the ox3^gen. In our analyses the gases 

 were extracted with the pump, and the first gave 28.6, the second 29.2, 

 per cent of oxygen. The slight excess of hydrogen is doubtless due 

 to the action of the oxygen on the grease of the stopcocks, which has 

 been already mentioned. The rate of production of these gases is 

 about 0..5 cubic centimeter per day for .50 milligrams of radium bro- 

 mide, which is more than tsvice as great as that found l)y Bodliinder. 



(4) PRODUCTION OF HKLIUM BY THK KADUTM EMANATION. 



The maxinuun amount of the emanation obtained from 50 milligrams 

 of radium bromide was conveyed by means of oxygen into a U-tube 

 cooled in liipiid air, and the latter was then extracted by the pump. 

 It was then washed out with a little fresh oxygen, which was again 

 pumped ofl'. The vacuum tube sealed onto the U-tu))e, after remov- 

 ing the litjuid air, showed no trace of helium. The s})ectrum was 

 apparently a new one, probably that of the emanation, ])ut this has 

 not yet been completely examined, and we hope to publish further 

 details shortly. AiUn- standing from July IT to 21; the helium spec- 

 trum appeai-ed, and the characteristic lines were observed identical in 

 position with those of a helium tube thrown into the field of vision at 

 the same time. On July 22 the yellow, the green, the two blues, and 

 the violet were seen, and in addition the three new lines also present 

 in the helium obtained from radium. A confirmatory experiment 

 gave identical results. 



We wish to express our indebtedness to the research fund of the 

 chemical society for a part of the radium used in this investigation. 



