195 



«The water was determined by ignition with sodium 

 carbonate, collected and weighed in calcium chloride tubes.» 

 The composition was found to be: 



per cent 

 found 



SiO^ 16-77 



P^O, 6-48 



{Ce,La,Di)^0^ 60-54 | 



Fe^ O3 0-43 j 



CaO 11-28 \ 



MgO 0-13 / 



Na^O 1-85 



H^O 1-27 



F 1-33 



100-08 



60-97 



11-41 





per cent 





calculated 



27-95 



16-70 



4-56 



6-59 



18-46 \ 

 0-27 / 



60-90 



2014 1 

 0-32 / 



11-18 



2-98 



2-06 



7-06 



1-25 



7-00 



1-32 



100-00 



The proportion between acid and basic atoms of oxygen 

 are, when phosphoric acid is included 78:83-4. 



Of the diiferent, possible combinations the one must cer- 

 tainly be preferred, where the phosphoric acid is supposed to 

 be combined with the cerium (or lanthanum or didymium) as 

 in monacite. 



If now the fluorine is supposed to be combined with sodium, 

 the following formula is arrived at: 



\ [4 Si O2 • 2 (Ce, La, Di, Fe)^0^ • 3 [Ca, Mg) 0'H^0-NaF]2 [P^ Or, - Ce,_ O3]. 



From this formula the percentages are calculated, which are 

 quoted in the last column of the above table. 



Occurrence. The pegmatitic rock , in which the britholite 

 is found, contains as principal components: arfvedsonite, 

 eudialyte, white feldspar, steenstrupite , nephelite, sodalite and 

 aegyrite. The britholite crystals , which on an average are 

 one centimeter in length, are foimd with a fully developed crystal 



13* 



