810 



Mr. A. B. Wood on the 



Case I. Thorium D collected by Recoil from Ordinary 



Active Deposit. 

 Before exposure to the emanation or active deposit, as the 

 case may be, the platinum foil was heated, to remove traces 

 of grease, &c, for a few minutes to a white heat. The highly 

 polished platinum foil was then exposed for about 30 minutes 

 at a negative potential to thorium active deposit, and a very 

 active source of pure Th D was obtained. This was treated 

 in the following ways: — 



(i.) Thorium D undissolved in Acid. 



The pure Th D obtained by recoil was at once transferred 

 to the /3-ray electroscope, and three or four observations of its 



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T/ME f/N MINUTES) — f 



activity quickly made, the exact times of these measurements 

 being noted. The foil was then placed in the furnace, heated 



