100 Hidden and Ilillebrand — MacJcintoshite, a 



for analysis after careful hand-picking under the lens. It was 

 almost entirely free from recognizable impurity and had a density 

 of 5*43 at 21-4° C. 



In powder the mineral is not entirely decomposed by any one 

 acid so far as the necessarily restricted tests indicated. Sul- 

 phuric acid attacks it quite strongly, but the gelatinous silica set 

 free protects a portion from further action. The addition of 

 nitric acid then, however, causes speedy and complete solution. 

 This behavior is perhaps susceptible of a different explanation, 

 namely, that the mineral is not homogeneous, but consists of two 

 different substances the predominant one of which is decompos- 

 able by sulphuric acid, the other much less affected by it but 

 when once it has been opened up by removal of the former is 

 readily dissolved by nitric acid. Nitro-hydrochloric acid like- 

 wise dissolves it completely. 



Considering that the limited sample had to be divided into 

 three portions in order to estimate the constituents tabulated 

 below, it is not perhaps surprising that the analysis should present 

 a loss of three and one-half per cent. The presence of even the 

 little phosphoric acid shown renders the analytical operations by 

 which the silica and bases are determined extremely complicated, 

 particularly when zirconia and yttria are present. Precipitates 

 are then obtained which under similar conditions the other earth 

 bases do not give, and thus separations and identifications are 

 rendered more difficult and losses are almost inevitable. It is 

 therefore not at all certain that the very considerable loss is to be 

 sought in some constituent not enumerated ; it is more probable 

 that it should be distributed somewhat unevenly over a number 

 of those given, silica and lead oxide excepted, they being with- 

 out doubt nearly correct. The following observations, however, 

 may be of importance in this connection. After sealing the tube 

 in which was the sample serving for the estimation of the oxidiz- 

 able constituents a slow but long continued evolution of gas was 

 observed, just as in the case of most uraninites when similarly 

 treated, but owing to the very small quantity of powder in the 

 tube — only '15 gram — it could not be proven that the gas was 

 nitrogen and not 00 2 . The latter it should not be, for thoro- 

 gummite, the direct alteration product of the mineral, is free 

 from it according to Hidden and Mackintosh's analysis. In any 

 event its amount is probably very small. 



With respect to the oxidizable constituents it was found to be 

 impossible to secure complete solution of the powder in the tube 

 even after several days' heating with dilute sulphuric acid, owing 

 presumably to the above mentioned protective action of silica set 

 free and ot thorium sulphate thrown out. The amount of oxygen 

 consumed indicated 16 per cent of oxidizable bases counted as 

 U0 2 ; it may be, therefore, that all the uranium exists in that form 

 and the iron in the ferrous state, as they are given in the analyses 

 which follow. Of these b was made on a small sample selected 

 grain by grain with the utmost care, but it was evidently not 



