110 



the atoms of oxygen connected with the acids are always very 

 predominant over those of the basic ingredients, the ratio 

 varying from a Httle over 2 in wøhlerite to about 4 in lewisite. 

 These ratios cannot, of course, as for inst. in the mere sili- 

 cates, be used directly for the classification of the minerals; 

 here it is also necessary to pay regard to the ratio between 

 the two different kinds of acids , and then this latter ratio 

 proves also to be nearly connected with the oxygen ratio 

 mentioned above. 



This accordance is owing to the rather peculiar circum- 

 stance that almost all the combinations treated of here may be 

 interpreted, and have also been interpreted, as combinations of 

 metatitanates etc. with metaniobates etc. This feature, of 

 course, is most distinct in the minerals containing neither 

 fluorine nor water; for these minerals the following formulae 

 have been calculated ^) : 



Wöhlerite : 12 R {Si, Zr) 0^ • RNb._ 0^ 



Dysanalyte: ЬЕТгО.^ • ÉNb^O^ 



Aeschynite: Éo_[TiTh)^0^^ - 'Е.,Ш^О^.^ 



Polymignite: ЪЕПО^ . 5 ÈZrO.^ • É[m^Ta).^0^ 



Derbyhte: bFeTiO.^ - FeSb^ß^ 



Lewisite : 5 CaO • 2 TiOo • 3 Sb,_0^ = 2 Ca ТгО., • ZCa Sb,, 0^ 



As will be seen , the aeschynite is the only one of these 

 minerals that has not the common combination. The deviation, 

 however, is only slight; if, for the sake of clearness, we put 

 J?2 instead of ^3 the formula may be expressed É^(Ti, Th)^^^. 

 2RNb^0Q, so that it will be seen that the amount of acid is 

 only a trifle too large. 



if we now pass to an examination of the minerals con- 

 taining fluorine or water or both, the features become con- 



') Here, as everywhere in the following, the statements are taken from 

 Dana, where no other source is mentioned. 



