424 Boltwood — Thorium Jinx rote and Salts. 



The data given in this paper has also a direct bearing on 

 the claim made by Hofmann and Zerban* that the activity of 

 thorium in a mineral is dependent on the amount of uranium 

 contained in the mineral. There is a great variation in the 

 uranium content of the two minerals thorianite and thorite, in 

 fact the former contains nearly 18 times as much uranium per 

 gram of thoria as the latter, but as shown in the table the 

 specific activity of the thorium in both minerals is the same. 

 This is also true for the thorium in the orangite and thorite. 

 It is interesting to n>ote that Dr. Zerban was so kind as to send 

 the writer a specimen of 100 grams of gadolinite from Soters- 

 dalen, Norway, supposed to be similar to that examined by 

 Hofmann and Zerban. The mineral was slightly but quite 

 measurably radio-active, was found to give off small quanti- 

 ties of radium emanation (corresponding to about - 0l per' 

 cent U) on solution in acids, and on being worked up fur- 

 nished a small quantity of thorium oxide of approximately 

 normal activity. The same results were obtained with gado- 

 linite from Llano County, Texas, and the same species of 

 mineral from Ytterby, Sweden. In the published writings of 

 Hofmann and Zerban there is nothing to indicate that any 

 account was taken of the actinium in the minerals with which 

 they worked. This radio-active element invariably accompanies 

 the separated thorium, and in the thorium oxide separated 

 from minerals containing much uranium and little thorium 

 the activity due to the actinium may be much greater than the 

 activity due to the thorium present. Thus, for example, the 

 thoria separated from a sample of North Carolina uraninite, 

 containing 1*5 per cent of Th0 2 and 68 per cent of uranium, 

 was found 40 days after separation to have an activity 

 measured in the smaller electroscope equal to over 550 divi- 

 sions per minute, or nearly ten times the normal activity. A 

 solution of ten grams of this mineral was, however, examined 

 by Mr. Dadourian, using the excited activity method (see p. 427 

 of this number), for determining the activity of the thorium 

 in solution, and the activity of the thorium as determined in 

 this manner was found to be normal. All the data available 

 at present point to the conclusion that the amount of actinium 

 in a radio-active mineral is proportional to the amount of 

 uranium in the mineral, and it is the opinion of the writer 

 that the results obtained by Hofmann and Zerban are merely 

 in support of this conclusion and have no direct bearing on 

 the question of the activity of thorium and thorium com- 

 pounds. In the table on page 422 of this paper (Table II), 

 the high result obtained for the activity of the thorium oxide 

 separated from thorianite (No. 5) is without doubt to be attri- 



* Loc. cit. 



