2S0 Bolt wood — Radio-acli/oity of Uranium Minerals. 



in a feldspar matrix from which they could be readily separated- 

 The large specimen was crushed and about three grams of the 

 pure uraninite was picked out. This was divided into two 

 portions consisting- of larger and smaller fragments respectively. 

 Examined with a lens, the portion consisting of smaller frag- 

 ments appeared to carry a slight admixture of the matrix. 

 The appearance of all of the material indicated the complete 

 absence of secondary alteration. The smaller fragments were 

 taken for the preparation of this sample, which was found to 

 contain O50 per cent of silica and matter insoluble in dilute 

 nitric acid. 



No. 2. This was prepared from the larger fragments men- 

 tioned above. It was found to contain - 34 per cent of silica 

 and matter insoluble in dilute nitric acid. 



Wo. 3. Uraninite from Spruce Pine, 1ST. C. This was a por- 

 tion of a lot of about 50 grams of very pure material obtained 

 from the centers of a number of good-sized lumps which had 

 l)een externally altered into gunmrite and uranophane. The 

 material selected showed only the slightest traces of secondary 

 alteration and was found to contain only 0*03 per cent of mate- 

 rial other than silica which was insoluble in dilute nitric acid. 

 The silica present was equal to 0'14 per cent. 



No. 4. Material similar to No. 3, but containing a slightly 

 greater proportion of secondary alteration products. It con- 

 tained - 37 per cent of silica and 0-04 per cent of insoluble 

 matter other than silica. 



No. 5. Uraninite from Joachimsthal. Carefully selected 

 material of fair purity, but containing small amounts of sul- 

 phides. 



No. 6. Uraninite from Saxony. An inferior variety con- 

 taining various impurities. 



No. 7. Uraninite from Colorado. This material was very 

 kindly sent to me by Professor McCoy, who stated that it was 

 similar to the No. 1 Pitchblende from Colorado described in 

 his paper in the Philosophical Magazine for January, 1906. 



No. 8. Carnotite from Colorado. This was also obtained 

 from Professor McCoy and was a sample of the No. 5 Carno- 

 tite mentioned in his paper. Both this specimen and No. 7 

 above were tested in the powdered form in which they were 

 received. 



No. 9. Carnotite from Colorado. Obtained through the 

 kindness of Mr. William Zowe of Uranium, Colorado. It 

 gave a residue insoluble in nitric acid amounting to 16*7 per 

 cent of the total. 



No. 10. Thorianite, Sabaragamuwa Province, Ceylon. A 

 portion of some very fine material kindly supplied by Mr. 

 H. S. Miner of the Welsbach Company. 



The result of the measurements made with these minerals 

 are ffiven in Table IV. 



