[ s ATTERLY-EL WORTHY] CANADIAN MINERAL SPRINGS 21 



the activity due to radium emanation and its products rises for the 

 first ten minutes, remains constant for some time and then rises until 

 a maximum is reached three hours after the gas enters the can. 



Steady readings can therefore be obtained from 10 to 20 minutes 

 after the active air has been passed into the vessel. This procedure 

 is much better than waiting for the three hour maximum. In 20 

 minutes only a small activity is deposited on the walls of the vessel 

 and if, after the leak has been taken, the vessel is exhausted and air 

 drawn through, the apparatus is practically at once ready for a new test. 

 Occasionally samples of air to be tested were left in the can for three 

 hours and readings all along up to the maximum were taken to see 

 whether it was really radium emanation that was being dealt with. 

 In every case the 3-hour leak was found to be 50% greater than the 

 ten minute leak showing that the ionization was due to radium 

 emanation.^ 



Measurement of the Dissolved Radium Salts. 



For the measurement of dissolved radium salts large quantities 

 of each water (5 to 10 gallons) were sent to Ottawa and there evapor- 

 ated down to smaller bulk taking great precautions to keep every 

 substance present in the water in solution. The following treatment 

 ensured that all the mineral matter present was got into solution. A 

 volume of water from 10 to 20 litres was evaporated down to 4 or 5 

 litres in large porcelain evaporating basins. The liquid remaining was 

 filtered ofif and the residue dissolved up as much as possible in hot 

 dilute hydrochloric acid solution (distilled water and redistilled acid). 

 The insoluble portion was transferred to the filter, the whole well 

 washed, dried, and then heated in a platinum crucible till all the 

 organic matter was thoroughly ignited. Hydrofluoric acid and re- 

 distilled hydrochloric acid were added to the residue, evaporated 

 to dryness and the crucible again ignited. A treatment with hot 

 dilute hydrochloric acid dissolved most of the residue; the solution 

 was filtered off and the residue treated in a similar manner. These 

 operations were repeated until the last trace of residue was com- 

 pletely dissolved. All the filtrates were added to the original filtrate. 

 The concentrates so obtained were bottled in large glass flasks (5 litre 

 capacity) and sealed up with well cleaned rubber stoppers. 



After keeping for sufficient time to ensure an equilibrium con- 

 dition between any radium salts and emanation these were boiled 

 out as described on page 20, passing air through the solutions and 

 then into the ionisation vessel. 



1 Satterly, Proc. Camb. Phil. Soc. Vol. XVI, part 6, 1912, p. 514. 



