82 B. B. Boltwood — Ultimate Disintegration Products 



ful analysis of which presents so many difficult problems. 

 The writer had the good fortune to meet Professor Warren at 

 the time that this analysis was in progress and the latter kindly 

 consented to take special precautions in the determination of 

 the lead and uranium. 



In Group IV the analyses of three samples of a mineral 

 closely resembling samarskite give values for the ratio show- 

 ing a good agreement, although the different specimens were, 

 according to Hillebrand, quite different in general appearance. 



In Group V, the agreement is again very good, while in 

 Group V 2 , including Nos. 34 and 35, the agreement is excel- 

 lent, for the difference in the case of the xenotime from 

 Naresto, near Arendal, is no more than is to be expected 

 when the relatively small amounts of both uranium and lead 

 are taken into consideration. 



In Group YI the ratios given by the two species from dif- 

 ferent Swedish localities are of little value for the present 

 purposes of comparison, and are significant only as indicating 

 a ratio of the same general order as that found in Group V x . 



It is unfortunate for the purpose of the present calculation 

 that the analyses of thorianite from Ceylon by Dunstan and 

 Blake and by Dunstan and Jones have been published in so 

 incomplete a form. This interesting mineral, containing a 

 relatively high proportion of both thorium and helium, affords 

 an exceptional material for the study of radio-active changes, 

 and an accurate knowledge of its general composition would 

 be of much assistance in settling some of the doubtful ques- 

 tions. The published analyses are defective however in the 

 following particulars : — In analyses Nos. I and II* (Nos. 38 

 and 39 in Table I) the results as given indicate that all of the 

 uranium is present in the form of uranous oxide (UO a ), while 

 in analysis No. Ill (I. c.) (No. 40 in Table I) a greater propor- 

 tion of uranic oxide (U0 3 ) than of uranous oxide is shown. 

 Such an extreme variation in composition is not only highly 

 improbable, but (in the light of a more recent analysis of 

 thorianite of a similar variety f in which the uranium is given 

 as U0 2 +U0 3 = 13'4 per cent) is probably quite misleading as 

 to the actual composition. Out of the seven analyses given 

 in the paper by Dunstan and. Jones, in only one (No. 43 in 

 Table I) are the separate amounts of uranous and uranic 

 oxides shown, while in the other six a number representing 

 the sum of the percentages of the two oxides is inserted, 

 which affords no reliable clue as to the amount of either oxide 

 or the amount of uranium itself contained in the mineral. 



The following table containing the values given in the paper 

 by Dunstan and Jones would not appear to be contradictory to 



*Proc. Eoy. Soe. Lond., Ixxvi (A), 253, 1905. f Dunstan and Jones, I. c. 



