Products of the liadio-active Elements. 265 



waters, etc., with the removal of certain constituents and the 

 substitution of others originally dissolved in the waters, the 

 resulting hydrated residue will in some cases consist of a mix- 

 ture of several different chemical compounds and its general 

 composition will not correspond to any definite formula, but 

 will depend on chance and the accidental local conditions. An 

 excellent example of a secondary product of this character is 

 afforded by the mineral known as gummite, which occurs as 

 an alteration product of the North Carolina uraninites. Sam- 

 ples of this mineral from the Flat Rock mine have been exam- 

 ined by the writer, in which great variations in the proportions 

 of lead, thorium and uranium present were observed in samples 

 removed from different parts of the same comparatively small 

 specimen. The mineral known as uranophane from the same 

 locality shows corresponding variations in composition. Both 

 these substances are amorphous in structure but very frequently 

 occur with a crystalline form as pseudomorphs after the origi- 

 nal uraninite. It is obvious that these facts must be considered 

 in attempting to arrive at any conclusions from a chemical 

 examination of these materials. 



In other cases the percolating waters undoubtedly dissolve 

 the more readily soluble components of the primary minerals 

 and deposit them again as definite, crystalline compounds of a 

 relatively high degree of purity. Examples of this sort are 

 afforded by such minerals as torbernite [Cu(IT0 2 ) 2 P 2 Q 8 • 8H 0], 

 autunite [Ca(U0 2 \P 2 8 • 8H 2 0,], uranocircite [Ba(U0 2 ) 2 P 2 8 • 

 81I 2 O], zeanerite [Cu (U0 2 ) 2 As 2 8 * 8H 2 O], uranosphaerite 

 [(BiO) 2 U 2 (V 3H 2 0], and a considerable number of others. 

 The examination of minerals of this character will probably 

 afford data of considerable value on the nature of the ultimate 

 disintegration products of uranium. 



The mineral mackintoshite is quite possibly of secondary 

 origin, but owing to some doubt in the matter it has been 

 placed among the primary minerals. It may represent a 

 variety of thorite, containing originally a considerable propor- 

 tion of uranium, which has undergone alteration owing to the 

 radio-active processes which have taken place within it. The 

 evidence is strongly in favor of the view that the thorogum- 

 mite has been formed from the alteration of the mackintoshite 

 through external causes. 



Any definite conclusions at present as to the formation of 

 carnotite are quite impossible. Its composition and occurrence 

 are both so unique that little or no analogy with other known 

 uranium compounds can be detected. It seems highly probable, 

 however, that its age is not relatively very great and its general 

 composition, e. g. the low amount of lead present and the 

 practical absence of thorium and helium, is quite in accord 

 with such a conclusion. 



