594 



SCIENCE 



[N. S. Vol. XL VI. No. 1198 



distances, the difference between observed and 

 calculated times was negligible; for greater 

 distances at slow velocities, the calculated 

 times were considerably greater. In Fig. 3 

 curves are given, using rates of flow in cu. ft. 

 per min. as ordinates and time in sees, as ab- 

 scisssB. 



radiation from uranium is so easily absorbed 

 ■ by air that the recombination constant ob- 

 tained for this cylinder when placed in the 

 tube of 2.95 diameter was .0099, a value evi- 

 dently too large owing to the diffusion of the 

 ions which were largely produced near the 

 surface of the tube. 



Curves A and A^ are plotted, using the cal- 

 culated and observed times, respectively, for 

 ions to pass 121.4 cm. through a brass tube of 

 5.4 cm. diameter. Curves B, B^j C, G^; D, D^ 

 are plotted, using calculated and observed 

 times for ions to pass 246 cm., 109 cm., and 

 25.4 cm., respectively, through a brass tube 

 2.95 cm. in diameter. For a brass tube 1.12 

 cm. in diameter, with the spark gap placed 

 226. cm. from the electroscope, for rates of 

 flow greater than .25 cu. ft. per min. the dif- 

 ference between the calculated and observed 

 times was less than .1 see. 



Sample decay curves are shown in Fig. 4. 

 Observed times of passage of the ions through 

 the tube were used as abscissae rather than 

 the times calculated by means of the meter 

 from the rate of flow. Experimental condi- 

 tions under which these curves were obtained 

 are recorded in Table II. 



The radium salt used in these experiments 

 was contained in tiny aluminum tubes .7 mm. 

 thick and approximately 2 em. long. These 

 were sealed into thin glass tubes to prevent 

 leakage of radium emanation, and when used 

 inside the brass tube were suspended at its 

 axis by silk threads. The uranium cylinder 

 referred to under E in Table II. was a hollow 

 paper tvibe 5 cm. long and 2.9 cm. in diameter, 

 with a coating of black oxide of uranium 

 glued on the inside. This cylinder was sus- 

 pended in the middle of the tube. The a 



McClung^ has shown that the recombination 

 constant does not change with the pressure 

 of the gas. Under the experimental arrange- 

 ment of Fig. 2 the number of ions produced 

 would change with the gas pressure and intro- 

 duce a small correction for large capacities. 

 Investigation showed that this change, if 

 assumed to be linear, would be negligible for 

 all capacities used. 



a/r current in cu- f t. per.mii)l 

 Fig. 5. 



Fig. 5 shows the pressures in tube B for 

 various air currents. The barometer reading 

 was 75.35 cm. At 1.6 cu. ft. per min. the 

 curve shows the correction to be .2 per cent. 



Table III. contains the observed ionizations 

 in divisions per minute for the above curves 

 of Fig. 4, also the calculated values obtained 



6 Loc. cit. 



