Dr Turner on Lithion-Mica. 263 



added, to remove any manganese or iron which might be pre- 

 sent. This was in general unnecessary ; for the manganese is 

 separated completely in the former parts of the process ; and 

 though a little iron always escaped, it was rendered insoluble 

 by the ignition alone. 



In the former analysis of the brown Cornwall-mica already 

 alluded to, I did not succeed in separating the lithia from the 

 potash completely. I there followed Professor Gmelin's me- 

 thod of removing the baryta by sulphuric acid, adding muri- 

 ate of platinum to the mixed sulphates of potash and lithia, and 

 dissolving away the sulphate of lithia from the double salt of 

 platinum and potash by the aid of water. With whatever care 

 this process was performed, the water always took up more or 

 less of the double salt in addition to the sulphate of lithia, 

 and on this account I adopted the process which has just been 

 described. 



Analysis of the Zinmcald Mica. — This mica is of a silver- 

 white colour, mixed with grey, as described by Klaproth. It 

 occurs in crystalline groups, the laminae of which are flexible, 

 elastic, and of considerable size. The specific gravity of some 

 crystals, which had been boiled in distilled water to expel air, 

 was 2.985. 



Heated to redness, it suffers no appreciable loss of weight, 

 and undergoes little change of aspect. Before the blow-pipe 

 flame it fuses readily, and at the same time tinges the flame 

 distinctly of a red colour. An appearance of boiling accom- 

 panies the fusion, and a black scorious mass is left. 



To determine the alkalies, 51.235 grains of the powder were 

 acted on by carbonate of baryta. The mass contracted great- 

 ly from the ignition, and became of a dark greenish black 

 colour. By the process already described, I obtained 7.35 

 grains of sulphate of lithia, equivalent to 2.281 grains, or 

 4.09 per cent., of pure lithia ; and 9-68 sulphate of potash, 

 equivalent to 5.28 grains, or 9-467 per cent., of pure potash. 



In making these calculations, it is presumed, that sulphate 

 of potash is composed of 40 sulphuric acid, and 48 potash ; 

 and sulphate of lithia, of 40 acid, and 18 lithia. (Dr Thomson.) 



The determination of the other constituents is somewhat 

 complicated, owing to the presence of fluoric acid, which oc- 



