Hidden and Warren — Yttrocrasite. 519 



amount of niobium and tantalum. As will be pointed out in 

 the accompanying note ou the estimation of niobium and tanta- 

 lum in the presence of titanium, it is entirely possible for 

 seyeral per cent of niobium and tantalum to be present and 

 still leave practically no residue when fused with bisulphate 

 and leached with water. At present there appears to be no 

 way of accurately determining the small amount of niobium 

 present. Tantalum was found to be present only as a trace. 



Assuming that the amount of niobium is too small to affect 

 the molecular ratio materially, we have on combining the acid 

 and basic radicals, as shown in table above, the following 

 approximate ratios: 



H o : R n O : R 2 m 3 : R IV 2 : Ti0 2 etc. 

 6:1:3 : 1 : 16 



Where R IT is chiefly lime, R 2 m 3 chiefly yttrium earths, 

 R0 2 IT chiefly thorium. The mineral is therefore essentially a 

 hydrous titan ate of the yttrium earths and thorium. The 

 above ratios may, of course, be no more than a coincidence 

 but they are sufficiently sharp to argue in favor of the correct- 

 ness of our assumptions. In view of the necessary incomplete- 

 ness of the analysis and also of the small amount of exact 

 knowledge which we possess regarding the true molecular 

 relations existing between the so-called "rare-earths" and acid 

 radicals, a further discussion here of the constitution of this 

 mineral is hardly worth while. In fact it may be remarked 

 that before a satisfactory understanding of the entire group 

 of the so-called " titano-niobates " can be had, we must have, 

 not only better analytical methods but also much clearer ideas 

 of the capacity of these elements, and their compounds, to 

 form isomorphous mixtures and solid solutions. 



Radio-active properties. — Some fragments of the mineral 

 were examined for radio-activity by Professor B. B. Boltwood 

 of ^sew Haven, to whom we wish to express our thanks for 

 his kindness. The total activity of the mineral was found to 

 correspond to 10 per cent of thorium and 2*08 per cent of 

 uranium. The amount of uranium found by analysis was 2'29 

 per cent and of thoria 8*75 per cent, which are in very satis- 

 factory agreement with Dr. Boltwood's figures. 



The mineral is evidently a new species and the authors would 

 suggest the name Yttrocrasite for it. 



