6 A. S. Em — Radium in Minerals by the ^-Radiation. 



for permanent use. Unfortunately, no acid was added to the 

 solution, and, in the light of subsequent events, this omission 

 was serious, although the step did not appear necessary at the 

 time. Some time later, Professor Rutherford supplied part 

 of the medium (10~ 4 mg per c.c.) solution to Dr. Boltwood, and 

 on this standard their joint results depended. The advantage 

 of using this standard was obvious, as it would presumably 

 place in agreement the results obtained at Montreal and New 

 Haven. 



In January, 1906, when the discrepancy before mentioned, 

 concerning the amount of radium in uraninite, was discovered, 

 the writer examined the standard solutions which had been 

 prepared ten months previously. On drawing off one-half of 

 the strongest solution, placing it in a clean bottle, sealing it, 

 and testing it when in equilibrium, it was found that the 

 activity in the new bottle was only about one-half that remain- 

 ing in the old. It was proved beyond doubt that the total 

 amount of radium in the bottle was correct, but that the 

 radium was not all in solution, the water containing only fifty 

 per cent of the total radium present. 



As soon as it was ascertained that the standards were no 

 longer correct, Dr. Levin and the writer weighed, with dif- 

 ferent weights and balances, 3*69 mg of radium bromide, from 

 the supply which Professor Putherford found gave a heating 

 effect of 110 gram-calories per gram per hour. The results of 

 the two weighings were in excellent agreement, and the crys- 

 tals were then sealed in a test tube in the solid state to serve 

 as a standard for future use. A smaller crystal was also sealed 

 in a phial and compared with the new standard by the 7-ray 

 test. The activity rose slightly during the ensuing month, 

 and was finally found to be that due to -27 mg of radium bro- 

 mide. This was verified with various electroscopes, and under 

 diverse conditions as regards screens and distances. It was 

 now possible to redetermine the amount of radium in the kilo- 

 gram of pitchblende, and the correct value was equivalent to 

 •32 mg of radium bromide per kilogram of uraninite. 



On receipt of the small crystal Dr. Boltwood found that his 

 original solution was one hundred per cent too weak, and on 

 redetermining the amount of radium present in the pitch- 

 blende his result, using the emanation method, was -31 mg of 

 radium bromide per kilogram of the sample of uraninite tested. 

 The results obtained by these two distinct methods are thus in 

 close agreement. 



From first to last, the methods used and the measurements 

 made by all concerned appear to be correct, but errors arose 

 because the radium bromide in the original solutions was in 

 some way deposited on the sides and bottom of the vessels 



