OBSERVATIONS ON RADIO-ACTIVITY. 383 



American uranium bearing minerals were examined by 

 B. B. Boltwood 1 for radium, and it was found that in 

 uraninite, gummite, uranophane, and samarskite, the radium 

 present as indicated by the emanation method was propor- 

 tional to the uranium content. This does not appear to 

 hold, for the uraninite and samarskite examined by Strutt, 

 for the former was only half as active as the latter, and 

 this would scarcely be the ratio of the uranium in the two 

 minerals. More recently 2 he has studied the radio-activity 

 of natural waters. Radium has been found by Obalski 3 to 

 occur in a cleveite and in a bituminous substance from 

 Quebec, containing uranium as an impurity. Elster and 

 Geitel 4 have detected radio-activity in fine mud from the 

 Italian watering place Battaglia. Radio-activity was 

 detected in natural gas by E. F. Burton. 5 An examination 

 of the radio-activity of Russian mads was made by J. 

 Borgmann. 6 A radio-active gas was found in the soil and 

 water near New Haven, U.S.A., by H. A. Blumstead and 

 L. P. Wheeler. 7 Later Mr. Blumstead 8 published an account 

 of atmospheric radio-activity. 



M. F. Pisani 9 has recently examined by photographic 

 methods a large number of diverse types of minerals, in all 

 about 77, and found that in every case those containing 

 uranium or thorium were active ; exceptional cases were 

 certain specimens of fluorspar, which from his results 

 appear to act comparatively strongly on the photographic 

 plate. Specimens of fluorspar from the same districts 

 were tested in our apparatus and gave negative results. 



1 Amer. Journ. Sci., 18, p. 97, 1904. * Loc. cit., p. 378. 



3 Eng. and Min. Journ., March 17, 1904. 



4 Phys. Zeitschr., v., p. 11, 1903, 



J University of Toronto Studies — Physical Science Studies. 



« Nature, 70, p. 80, 1904. 



7 Amer. Journ. Sci., 16, p. 328, 1903, and 17, p. 97, 1904. 8 Loc. cit., 18, p. 1. 



9 Bull. Soc. Franc, de Mineralogie, part 1, 27, p. 58, 1904. 



