326 



Prof. W. Ramsay and Mr. W. M. Travers. 



The oxides of niobium and tantalum were converted into double 

 fluorides of these metals with potassium fluoride ; and on examination 

 of the crystals under the microscope, they were seen to be almost 

 entirely of one form. They were easily soluble in water, and, from 

 previous experience with these compounds, we were able to recognise 

 them as potassium niobium oxy-fluoride. There appears to be 

 hardly any tantalo -fluoride present in the possible mixture. The 

 uranium dioxide was estimated by heating the mineral with dilute 

 sulphuric acid in a sealed tube, and titrating the dioxide with potas- 

 sium permanganate. The trioxide was calculated by difference from 

 the total uranium. The cerium metals were separated, as usual, by 

 means of a saturated solution of potassium sulphate. 



It is thus seen that fergusonite is mainly a niobate of yttrium, 

 containing oxides of uranium, but in no great quantity. 



The gases evolved by the incandescence of nearly 5 grams (4 - 852) 

 of the mineral, heated in a vacuous tube, had the following compo- 



sition : — 



Per grain of 



Total gas. mineral. Per cent, 



c.c. c.c. 



Helium 5"24 1-080 75'50 



Hydrogen 0*38 0-078 5'47 



Carbon dioxide .... 1-19 0"245 17*14 



Nitrogen 0*13 0-027 T88 



6-94 1-430 99-99 



The remaining mineral was mixed with hydrogen potassium 

 sulphate, and heated to redness. More gas was evolved; oxygen, 

 resulting from the decomposition of the sulphuric anhydride, was 

 present in considerable quantity. The sulphur dioxide and the 

 carbonic anhydride were removed by passing the gases through soda- 

 lime, before it entered the pump ; hence they do not appear in the 

 analysis. 



Per gram of 

 Total gas. mineral. Per cent. 



c.c. c.c. 



Helium 3-48 0-733 60'3 



Nitrogen 0*42 0-088 73 



Oxygen T87 0'394 32-4 



5-77 1-215 100-0 



The mineral taken weighed 4' 744 grams. 



The density was determined before and after heating. Great care 

 was taken to make sure of the absence of air-bells, by warming the 

 powdered mineral under water in a vacuum, before weighing it. 



