A. S. Eve — Radium in Minerals ~by the ^-Radiation. 5 



present applies to ores which contain only uranium or only 

 thorium. If the ore consists of a mixture of these two ele- 

 ments, the method cannot be applied except to obtain their 

 joint amount. With these limitations, the method is capable 

 of giving exact results, but when the amount of substance 

 employed is large, a correction may be necessary for the absorp- 

 tion of the rays in the substance itself. 



Specimens of uraninite from Joachimstahl were obtained, 

 weighing a kilogram, and it was found that radium E, assum- 

 ing it to be present, either does not emit 7-rays, or, more prob- 

 ably, it emits 7-rays which, like those of uranium, are of a 

 feeble penetrating nature. The very penetrating radiation 

 from pitchblende can therefore be wholly attributed to the 

 presence of radium C. 



In the course of this work the amount of radium present in 

 the kilogram of uraninite was found to be of the order of the 

 amount contained in a quarter of a milligram of pure radium 

 bromide. Consequently it was possible to estimate the amount 

 of uranium contained in the ore, using as a basis of calculation 

 the result of Rutherford and Boltwood that 1 gram of uranium 

 contains 7'4:XlO~ 7 grams of radium. The amount of uranium 

 thus determined was surprisingly small, and in consequence 

 part of the pitchblende was sent to Dr. Boltwood at New 

 Haven in order to check the results in the two laboratories, 

 and to get at the bottom of the divergence in results. 



Dr. Boltwood found that the radium present was about 

 twice as great as in the determination by the writer at Mon- 

 treal. As both Dr. Boltwood and myself were confident of 

 the accuracy of our measurements, and as both methods 

 appeared to be above suspicion, an examination was made of 

 the standards on which the measurements depended. 



It is, therefore, necessary to give some account of the stand- 

 ard solutions employed by Dr. Boltwood. In March, 1905, a 

 crystal of radium bromide was taken from a supply which 

 Professor Rutherford found gave a heating effect of 110 gram- 

 calories per hour per gram, and which was presumably pure. 

 This was compared by Professor Rutherford, using the 7-ray 

 test, with a larger known quantity of radium bromide, and it 

 was also weighed carefully by the writer. The results were in 

 excellent agreement, and the weight determined was- '95 mg . 

 The crystal was placed in 95 cc of distilled water, and fractions 

 of the solution were then drawn off, and w T ater was again 

 added so that three glass flasks were filled, containing 10" 2 , 

 10"*, 10~ 6mg of radium bromide per c. c. of water. Portions 

 of these were evaporated to dryness in small zinc trays, the 

 resulting activities were measured and their ratios were found 

 to be satisfactory. The standards were sealed and put aside 



