672 Multiply-charged Atoms. 



All the elements I have examined give multiply-charged' 

 positive atoms with the exception of hydrogen. On which I 

 have never ohserved more than one charge : in no other 

 case, however, have I observed charges approaching that 

 possessed by mercury. The majority of the elements seem 

 to acquire only two charges ; this is the number acquired by 

 helium, and this case is interesting since in the vacuum* 

 tube the helium atom occurs with both single and double 

 charges, whilst as an a particle it alwaj^s seems to have two 

 charges, suggesting that the process by which the a particle 

 acquires its charge is analogous to the process by which 

 multiply-charged atoms are produced in the discharge-tube. 



I have observed nitrogen atoms with three charges* but 

 the parabola due to the triply-charged atom is exceedingly 

 faint. Argon shows triply-charged atoms very distinctly 

 as can be seen from fig. 2, where the parabolas I, II, in due 

 to Arg + , Arg ++ , Arg + + + are all very distinct ; the Arg + + 

 parabola has probably a parabola due to neon superposed 

 on it. 



This plate shows the helium line, and thus incidently gives 

 us an estimate of the sensitiveness of this method of detecting 

 small quantities of a gas. The volume of the discharge-tube 

 was about two litres, the pressure 1/300 of a mm. of mercury J 

 there was thus in the discbarge-tube about 1/100 c.c. of 

 argon at atmospheric pressure. This is about the amount in 

 1 c.c. of air at this pressure, and as the helium line was 

 visible along with the argon, we see that this method can 

 detect the amount of helium in 1 c.c. of air, which, according 

 to Sir William Ramsa} r , is about 4x 10~ 6 c.c, even though 

 this is mixed with an enormous excess of argon. The tube 

 used for this photograph was not at all well adapted for 

 detecting small quantities of an impurity, as the cathode 

 had been in use for several weeks and the tube through it 

 was almost silted up by the sand-blast action of the positive 

 rays, and was just about to be replaced by a new tube. 



An interesting result, which is now being investigated, is 

 that when very pure nitrogen is in the discharge-tube the 

 mercury line corresponding to the atom with five charges 

 becomes abnormally bright, brighter than those for the atom 

 with four or even three charges, though in other gases the 

 greater the charge on the atom the fainter the line. 



I have much pleasure in thanking Mr. F. W. Aston, B.A., 

 Trinity College, for the great assistance he has given me in 

 these investigations. 



