468 Perkins — Molecular Weight of Radium Emanation. 



and sample 2. Plot leak in div. per min. as ordinates and 

 time of decay of the active deposit as abscissae, time to begin 

 at the moment the water pump is turned on. The ratios of 

 the two ordinates at any given time after the first few minutes ■ 

 are proportional to the relative amounts of emanation in 

 sample 1 and sample 2. 



In order that any slight changes in the porosity of the plug 

 might be eliminated, experiments with the emanation were 

 alternated with those for mercury vapor, using the two methods 

 already described. Diffusion under constant supply (method 

 1) furnished a ready means of revealing any systematic change 

 in porosity. 



Results. 



The earlier trials made under constant supply gave about 1*2 

 grs. of mercury diffusing per hour, showing that diffusion 

 probably took place about as rapidly as the vapor was formed. 

 In order, therefore, to materially lessen the amount diffusing, 

 the inner tube C was removed and all but one of the original 

 porous plugs were closed with a drop of water glass. About 

 one sixth as much diffusion took place through this one plug 

 as through the forty originally made. 



The position of this plug with respect to the mercury 

 supply made no difference in the amount of vapor diffusing 

 per min., showing the density of the vapor in the diffusion 

 chamber to be pretty uniform. 



The following tables give the results in full of diffusion with 

 the emanation for Jan. 23, at 250° C. ; and the observed values 

 for h only, for experiments made on succeeding days : 



Time after Le 

 pump began in 



15 min. 



ak of Sample 1 

 div. per min. 



36-5 



Leak of Sample 



corrected for 



4 hrs. decay 



18-6 



2 



k 

 •0336 



20 



a 





34-5 







17-8 





•0331 



25 



a 





32-4 







16-8 





•0328 



30 



a 





30-4 







15-6 





•0333 



35 



it 





2S-7 







14-4 





•0344 



40 



a 





26-5 







13-3 





•0344 



Jan. 24 



, at 2 



50° C. 



Jan. 25, at 250° C. 



Jan. 27, at 250° C 



Time after 



pump began 



in min. 



15 



k 

 ■0337 



Time after 



pump began 



in min. 



15 



k 

 •0346 



Time after 



pump began 



in min. 



15 



A; 

 •0334 



20 





•0339 





20 



•0353 





20 



•0334 



25 





•0340 





25 



•0349 





25 



•0334 



30 





•0339 





30 



•0348 





30 



•0329 



35 





•0335 





35 



•0346 





35 



•0321 



40 





•0337 





40 



•0346 





40 



■0324 



45 





•0339 





45 



•0344 





45 

 50 



•0329 



•0329 



