12 Duane — Emission of Electricity. 



having been deposited on A, the currents were measured first 

 in the small tube and then in the large condenser, etc. One set 

 of measurements is given in Table V. Making the correction 

 for the decay of the activity, the ratio of the two currents at 

 62 minutes is 52*4. (The currents in the table are already cor- 

 rected for a small ionization in the condenser before A was 

 inserted.) 



22. Combining this with the ratio previously determined, 

 69, we find that the saturation current in air when the a rays 

 produce all the ions they can produce is 3,600 times as large 

 as the positive current in the tube B in a liquid air vacuum, 

 produced by the same activity. In these experiments the pre- 

 caution was taken of sand -papering the end of electrode A, so 

 as to remove all the activity deposited there. 



Time 



55 



.62 

 63 

 TO 

 71 



23. The total quantity of negative electricity emitted per 

 second in vacuum from the electrode A is at least as great as 

 the \ algebraic sum of the positive and negative currents, and 

 probably is greater than the positive current itself. The ratio 

 of the positive current to this -J algebraic sum is (for 2*2 volts) 

 2*5 for brass. Hence the negative electricity discharged per 



second from the electrode is at least as ffreat as the == 



& 3600X25 



-th part of the ionization current the a rays from its radio- 



Table V. 



4- Current 



Electrode 



9-45 



in tube 



425* ) 

 425* \ 



in condenser 



7-00 ) 

 6*95 X 



in tube 



9000 



activity are capable of producing. Rutherford* has found 

 that each a particle projected from radium produces 86,000 

 ions. Assuming that each a particle from radium C produces 

 a number of ions proportional to the length of its path and to 

 the excess of its energy over the critical value, namely, 180,000 

 ions, it follows that for every a particle projected by radium C 

 there are at least 20, and probably more than 50, electrons 

 expelled from the active surface. 



24. Conclusions, (a) A piece of metal made radio-active 

 by immersion in radium emanation emits considerable quanti- 

 ties of negative electricity ; and the rate of discharge decays 

 with the time in such a way as to indicate that radium B when 



* Rutherford, Radio-activity, p. 434. 



