Boltwood — Radio-activity of Uranium Minerals. 285 



the same as the ratio of ranges of the a particles emitted by 

 these substances, namely, 



5-7 : 9-5 = 4-23 : 7-06. 



This is an important confirmation of the suggestion made 

 in an earlier paper* that the ionization produced by an a par- 

 ticle is proportional to its range. f 



The value found for the activity of radium A and C in the 

 active deposit on the copper plate is only about 60 per cent of 

 the activity to be expected. It is probable that under more 

 favorable conditions the entire equilibrium amount of these 

 products could be obtained. 



The results obtained indicate that if the activity of the 

 uranium in a mineral be taken as unity, the activities of radium 

 and its immediate products are approximately the following : 



Radium 



= 



0-45, 



Emanation 



= 



0-62, 



Kadium A 



.— 



0-54, 



Radium B 



— 



0'04? 



Radium C 



— 



0-91, 



(Uranium 



= 



l -oo). 



Activity of Polonium (Ha F). 



About four years ago I carried out some experiments on the 

 separation of the polonium from known amounts of certain 

 uranium minerals. About 10 grams each of uraninite and 

 gummite were taken, the former containing 75 per cent and 

 the latter 63 per cent of uranium. The minerals were dis- 

 solved in dilute hydrochloric acid, the solutions evaporated to 

 dryness to remove silica, and the filtrate from the silica, after 

 the addition of a little bismuth nitrate, was treated with an 

 excess of hydrogen sulphide. The sulphides were decomposed 

 with nitric acid, the lead was removed as sulphate, and the 

 bismuth and other substances were precipitated with ammonia. 



* Boltwood, this Journal, xxi, 414, 1906. 



f Professor Bumstead has pointed out to me that this assumption is in no 

 way contradictory to the evidence furnished by the ionization curves 

 obtained by the Bragg method. A typical Bragg curve for radium C has 

 been given by McClung (Phil. Mag., xi, 135. 1906). On the assumption 

 that the ionization is proportional to the range, the total ionization is con- 

 sidered as proportional to the area of the rectangle measured by the range 

 and the ionization per centimeter for the first centimeter or so of the range. 

 In the Bragg curves the ionization is proportional to the area included within 

 the curve, and the range is taken as the point where the first, upper, well- 

 defined break occurs in the curve. It will be found that the area of that 

 portion of the rectangle which lies without the curve is approximately equal 

 to the area included by the curve which lies without the rectangle This 

 equality will hold for a particles having a range of 3 cm or more ; when 

 the range of the a particle is less than about three centimeters the propor- 

 tionality between range and ionization will be less exact. 



Am. Jour. Sci. — Fourth Series, Vol. XXV, No. 148. — April, 1908. 

 20 



