Dixon & Wigham — Radiations from Radium Bromide. 187 



It is possible that with a feeble basic indicator more marked 

 results would be obtained. 1 



In connexion with the hypothesis just described, it will be 

 interesting to compare the action of diastase on starch, and that of 

 trypsin on gelatin when exposed to the influence of the radiations. 



1 [Note added in Press. — The experiment was carried out as follows : — On a 

 mica plate, supported over a surface of caustic potash in solution, some neutral agar 

 containing phenolphthalein was spread. The radium was supported over the agar, and 

 at a distance of 1 mm. ahove it ; and the whole was shut in from the surrounding 

 atmosphere in a receiver. At the end of twenty-four hours the phenolphthalein had 

 become pink. The receiver was then opened, and the indicator decolorized by contact 

 with the air. "When it had become colourless, it was again shut up. On the following- 

 day, it had become pink a second time. The receiver was again opened, and the 

 phenolphthalein decolorised. Before closing for the third time, the radium was 

 removed. The pink coloration now failed to re-appear. 



Although the experiment seemed at the time quite conclusive, on repeating it sub- 

 sequently with variations, it has been found that a neutral solution of phenolphthalein, 

 either in pure water or in agar, though not exposed to radium, becomes pink when 

 supported over a solution of caustic potash in a closed chamber. The indicator in 

 this case, too, may be decolorised and coloured again three or four times ; but it finally 

 loses its power of regaining colour, although under the same conditions which previously 

 caused it to become pink. This unexpected behaviour 'of the indicator renders the 

 detection of the electrons by its means very uncertain.] 



