194 



The crystals are optically negative. The acute bisectrix is ф^ 

 the vertical axis. The angle of the optic axes is small, but 

 could not be measured exactly , as the plates had to be made 

 very thin to be transparent. The optic orientation is: 



ä = Ь 

 Ъ = с 

 с = а 



The hardness is 5V2. The fracture is uneven. There is 

 no traceable cleavage. 



The specific gravity by means of a Pyknometer was found 

 to be 4-446. 



Chemical properties. The chemical analysis was made by 

 cand. polyt. Chr. Christensen, who stales as follows: 



«The mineral was evaporated in a water-bath with nitric 

 acid. After treatment with warm water the silica was filtrated, 

 evaporated with hydrofluoric and sulphuric acid and the 

 residue was then added to the filtrate. Phosphoric acid 

 was then precipitated with ammonium molybdate. To the 

 filtrate ammonia and ammonium sulphide were added. The 

 precipitated hydroxides and sulphides were dissolved in 

 hydrochloric acid, then evaporated to expel hydrochloric 

 acid, diluted and precipitated with oxalic acid. The oxalate 

 of cerium was ignited and weighed. The oxide was dissolved 

 in hydrochloric acid together with a fixed quantity of ferrous 

 salt and the remainder which was not oxidized was titrated 

 with potassium permanganate. By these experiments an 

 excess of oxygen (over Ce^O^) Avas found.» 



«Ferric oxide, manganous oxide, and the oxides of 

 magnesium , calcium and sodium were determined in the 

 usual manner after the molybdenum had been precipitated 

 with hydrochloric acid.» 



«The fluorine was determined by Berzelius & Rose's 

 method.» 



