Boltwood — Radio-activity of Uranium Minerals. 283 



dishes, a further experiment was made in which 10 cc of the 

 radium solution were evaporated to dryness in a shallow platinum 

 tray 5 0m square with edges having a height of only l mm . The 

 activity of the film obtained (the film extended to, but did not 

 touch the edges) was 1*401 div. per min. This gave the value 

 of the ratio as 0*451. 



It has been shown* that for the electroscope used in these 

 experiments, the activity of radium containing equilibrium 

 amounts of the emanation and the products radium A, radium 

 B and radium C, is about 5*64 times the activity of the radium 

 itself. Taking the activity of the radium in the minerals as 

 0*45 of that of the uranium present, the activity of the radium 

 and its immediate products is found to be 5*64x0*45 = 2*54 

 times the activity of the uranium present. The activity of 

 the equilibrium amounts of the products radium emanation, 

 radium A, radium B and radium C is therefore equal to 

 4*64x0*45 = 2*09 times the activity of the uranium. This is 

 the factor used in Table IV in correcting the activity of each 

 mineral for the radium emanation lost by the powdered material. 



An attempt was made to determine the activity of the pro- 

 ducts A, B and C by direct experiment. The radium eman- 

 ation from exactly 0*200 gram of uraninite No. 4 (Table IT) 

 was collected and introduced into an air-tight, glass vessel 

 having a capacity of about 250 0c . One end of the vessel con- 

 sisted of a copper plate 8 cm in diameter, and 5*5 cm from this and 

 near the opposite side was a spiral of copper wire. The cop- 

 per plate was attached to the negative pole of a battery giving 

 a potential of 400 volts and the wire spiral was connected 

 with the positive terminal. At the end of about four hours 

 the copper plate was removed and quickly placed in the elec- 

 troscope. Its activity was followed for the course of about 

 sixty minutes. As was to be expected, it was found that the 

 amount of active deposit collected by the plate varied with the 

 character of the field, and was greatest when the inner side of 

 the glass vessel was entirely covered with a conducting coating 

 to within about one millimeter of the copper plate and the 

 coating was connected with the positive terminal. 



The data obtained from the decay curve for the active 

 deposit were used for calculating the maximum value for the 

 activity of radium A and radium C by means of the equations 

 given by Ruth erf or d.f 



The data furnished by measurements of the most active 

 deposit are shown graphically in figure 3. The ordinates are 



*This Journal, xxi, 409, 1906. 



f Radio-activity, 2d edition, p. 834. The values taken for the constants 

 were : "l, (radium A) = 0*231 (min.)- 1 ; A 2 (radium B) = 0*0266 (min.)- 1 ; 'A z 

 (radium C) = 0*0365 (min.)- 1 . Bronson, Phil. Mag., xi, 73, 1906. 



