﻿428 Sir E. Rutherford and Dr. J. Chadwick on the 



carried out. A glass apparatus, similar in design to the 

 standard apparatus, was used. The details will be clear from 

 the diagram (fig. 4). 



In order to avoid the bombardment of the glass walls and 

 consequent liberation of H particles the inside of the tube 

 was lined with platinum foil. The surfaces of the brass 

 plate B and of the rod carrying the source were protected 

 from the action of the chlorine by a coating of hard pitch. 

 The stopcocks and grouod-joint were lubricated with a 

 brominated grease. The source of a rays was a platinum foil 

 coated with radium active deposit. Pure dry chlorine was 

 prepared by heating gold chloride, AuCl 3 , contained in the tube 

 A, and was passed over P 2 5 before entering the vessel T. 

 As an additional precaution a little P 2 0$ was placed in the 

 vessel itself. 



When the source was placed in position the air was 

 removed by pumping and washing with dry carbon dioxide. 

 Carbon dioxide was then let in to atmospheric pressure and 

 the natural H particles were counted at absorptions varying 

 from 16 cm. to 30 cm. The carbon dioxide was then 

 replaced by chlorine, and the scintillations at similar absorp- 

 tions were observed. The chlorine was then allowed to be 

 reabsorbed by the gold chloride and carbon dioxide let in 

 again. In this way counts on the chlorine were included 

 between counts of the natural particles, and any traces of 

 adventitious hydrogen could be allowed for. The results 

 showed no evidence of the liberation of H particles from 

 chlorine in the range examined, i. e. at absorptions more than 

 16 cm. of air. 



Discussion of Results. 



For convenience of discussion the atomic numbers and the 

 masses of the isotopes of the elements from hydrogen to 

 potassium are given in the following table. Of these 

 elements aluminium is the only one which has not yet been 

 examined for isotopes, but it appears likely that it is a pure 

 element of atomic mass 27. With the exception of helium, 

 neon, and argon, all the elements in the table have been 

 tested to see whether H nuclei are ejected by the action, of a 

 particles. The six active elements, as they may be termed 

 for convenience, are underlined. 



