271 



A weighed portion of the prepared mica was decomposed 

 by hydrofluoric and sulphuric acids in a closed platinum 

 crucible in an atmosphere of carbon dioxide, and then titrated 

 by standard permanganate solution for ferrous iron. Then 

 the solution was reduced by sulphuretted hydrogen, boiled in 

 an atmosphere of carbon dioxide, and again titrated for total 

 iron. Finally,. the same solution was used for the determina- 

 tion of titanium chemically combined in the mica. By 

 taking some of the pure powdered rutile and treating it with 

 hydrofluoric and sulphuric acids for some time in a platinum 

 crucible, there was no indication of any colour when hydrogen 

 peroxide was added, consequently these acids have little, if 

 any, action upon rutile under the conditions. Hence the 

 titanium estimated by this method is present chemically com- 

 bined in the mica itself, and not as inclusions. 



Microscopic examination revealed the presence of many 

 needle-like inclusions of rutile, but apart from these the mica 

 itself contains over 0'60 per cent, of Ti0 2 . 



The total titanium was estimated from another portion 

 by fusing with alkali carbonates. From this portion also the 

 silica, total 'iron, magnesia, lime, and manganese were 

 estimated by the usual methods. 



Having obtained total Ti0 2 , the combined Ti0 2 previously 

 estimated was subtracted, indicating over 1*30 per cent, of 

 rutile included in the mica. Id calculating the corrected 

 compositions of the mica, allowance was made for the included 

 rutile. 



Geological Department, 



University, Adelaide. 



