Specific Charge of the Ions emitted by Hot Bodies. 559 



of sodium (23*1), and it seems most probable that these 

 positive ions which seem common to so many different sub- 

 stances are due to sodium or its compounds which are present 

 as an impurity. It seems unlikely that they are due to a 

 common constituent of the different substances carrying a 

 fraction of the ionic charge, since Dr. F. C. Brown* has 

 shown that the positive ions emitted by most of the substances 

 examined have approximately the value of the kinetic energy 

 proper to the temperature of the metal from which they are 

 emitted, on the assumption that they carry the normal charge. 

 The fact that the value of m/H tends to run a little higher 

 than the atomic weight of sodium, may mean that in most 

 cases there is a small amount of potassium or its compounds 

 present. 



Additional evidence in favour of the view that the 

 positive ionization emitted by metals at low pressure is 

 due to the presence of alkaline impurities will shortly 

 be presented in a paper by one of the authors, dealing 

 with the positive ions emitted by the various alkali 

 sulphates. 



Whatever the cause of the positive ionization may be, it is 

 clear that it is very intimately associated with the metal. 

 For a platinum wire which has been boiled in pure nitric 

 acid for hours and afterwards had oxygen deposited on it by 

 electrolysis in the same medium, when mounted and tested, 

 after washing with distilled water, is found to give a large 

 initial positive ionization which decays with time. In fact 

 it behaves very like a wire which has not been specially 

 treated. This shows that the " impurities " must be very 

 deep-seated. 



In conclusion we desire to thank Mr. Irving B. Grandall, 

 A.B., graduate student in physics, and Mr. Cornelius Bol, 

 research assistant, for their help during part of the investi- 

 gation. 



Palmer Physical Laboratory, 

 Princeton, N. J. 



* Phil. Mag. [6] vol. xviii. p. 649 (1909). 



