102 Hidden and Ilillebrand — MacJcintoshite, a 



water was possibly absent. It is to be hoped that opportunity 

 may yet be afforded for a more thorough examination of this 

 mineral, which though apparently allied to thorite and urano- 

 thorite, is distinguished from them chiefly by greater content in 

 uranium and by a higher degree of basicity." 



Discussion of Composition. — It may be of interest to add a 

 few words as to the relation of this mineral to thoro-gummite, 

 although in view of the loss of 3*5 per cent in the analysis 

 there is an unavoidable element of doubt attached to any for- 

 mulae w T hich may be deduced. However, if the larger pro- 

 portion of the loss is considered as due to general losses, due 

 to the small quantity of material used, the following sugges- 

 tions as to the true composition of mackintoshite, may be 

 made. 



A comparison of the two analyses with that of thoro-gum- 

 mite shows at once that the change has essentially been the 

 further oxidation of the uranium (from U0 2 to U0 3 ) and the 

 assumption of one molecule more of water. Thus, as 3Si0 2 , 

 U0 3 , 3Th0 2 , 6H 2 expresses well the composition of thoro- 

 gummite, so 3$i0 2 , IJ0 2 , 3Th0 2 , 3H 2 is very probably the 

 formula of the new mineral. In both minerals about one 

 fourth of the thoria is replaced by its equivalent in RO, R0 2 , 

 K 2 3 which, if later proved to be a constant factor, should be 

 expressed in the formula. Both the analyses seem to show 

 that 3Si0 2 , L T 2 , 3(f Th0 2 , iRO)3H 2 expresses best the min- 

 eral analyzed. 



That an anhydrous form occurs in nature, as is thought true 

 of thorite, seems indeed most probable, this would then be 

 3Si0 2 , IJ0 2 , 3Th0 2 ; which requires: Thoria 63'67 per cent, 

 silica 1447 per cent, uranous-oxide 21 86 per cent = 100. As 

 a basic silicate, in condensed form, it could be expressed thus : 

 3Si, 4(U, 3Th)0 I4 . 



In the calculations of the molecular ratios the alkalies and 

 magnesia have been neglected as non-essential and the phos- 

 phoric acid has been considered as combined with the excess of 



uranium ; this 



gives the 



follow 



Mol. 



mg resuli 



ts. 





Per cent. 



wt. 





Molec. ratios. 



Si0. 2 



= 13-90 - 



f- 60 . 



= 23-167 



= 3-048 = 3 



TJ0 2 



22-40 



272 



8-231 



1-083 1 



Th0 2 



45-30 



264 



17159 



2-256 1 



(Yt, La) 2 3 



1-86 



288 



•645^1 



5 700 0-750 j 



ZrO, 



0-88 



122 



•721 | 



Pt>0 



3-74 



222 



1-684 [ r 



FeO 



1-15 



72 



1 597 j 





CaO 



0-59 



56 



1-053J 





H 2 



4-31 



18 



23-944 



3150 3 



