60 



73 



80 



92 



120 



40 



71 



44 



63 



36 



Ionization "produced by Healed Salts. 377 



equal values at the lower temperatures, but vary with the 

 temperatures at different rates. 



The maximum positive currents in the salted tube increased 

 in the ratio of 20 : 1 in passing from a temperature of 

 350° C. to 415° C. at a pressure of 1*3 cm., the same 

 quantity of salt being used in the two cases. 



The ionization in tube B exhibited several maxima during 

 the period of slow decay or steady valued currents in 

 tube A. Points D, E, and F in curve 2 of figure 3 indicate 

 such maxima. Also, at 415° C. it was found that the 

 currents in A decayed asymptotically with the time from a 

 value of 105xl0 -10 ampere at the thirty-minute point, to- 

 a steady value of 22xl0 -10 ampere after an hour's further 

 heating. In the same interval of time the maxima and 

 minima given below occurred in B : — 



Time (min.) 50 



Current 88 



1 div. = 10~ 10 ampere. 



These secondary maxima appeared under different conditions 

 of pressure and temperature. It is not likely that they were 

 due to salt which had condensed on the cooler portions of 

 the tube and fallen back, for these maxima did not occur in 

 tube A which carried the salt and, moreover, they did not 

 occur in the emission from the original salt, but were found 

 in the ionization effects from the first distillate as tested by 

 the air-cooled electrode method (see page 386). Professor 

 Richardson * has recently reported work in which he was 

 unable to obtain with cadmium iodide the specific charge 

 characteristic of the cadmium atom. Values were obtained, 

 however, showing the presence of sodium, potassium, and 

 zinc. Complex chemical changes may, then, have taken 

 place, causing these maxima and minima in the positive 

 ionization, or else several substances present as impurities 

 and having different decay constants may have been the 

 sources. 



A rapid fall in current values is shown in curves 3 and 4, 

 figure 6, at the points M and N, followed immediately by a 

 practically steady current condition of 5-10 X 10~ n ampere 

 covering a period of over an hour. These end effects indicate 

 the disappearance of the salt and the rapid ionization of the 

 salt vapour present in the tubes. The steady current stage 

 may be attributed to the ionization from the platinum alone, 

 or to the ionization from the products formed at the elec- 

 trodes due to the interaction of the vapour and the platinum. 



* Physical Review, xxxiv. p. 386 (1912). 



