Dr Turner's Analysis of a Mica from Cornwall. 139 



them. Its density is very considerable, being 3.066 when first 

 put into water, and 3.081 after being boiled in distilled water 

 to expel air from between its lamina?. 



When a thin layer of it is exposed to the blow-pipe flame it 

 fuses, an appearance of ebullition ensues, as if from the escape 

 of gaseous matter, and a black shining enamel is left. It com- 

 municates at the same time a red tinge to the flame, but 

 which is so slight as to escape observation unless considerable 

 care be taken. 



Analysis. — When heated to redness in a platinum crucible 

 it lost only i^ava of its weight, its lustre being rather improv- 

 ed than diminished by the operation. 47-39 grains, reduced 

 to fine powder by continued friction in an agate mortar, were 

 intimately mixed with six times their weight of carbonate of 

 baryta, and exposed to a white heat for one hour. The mass 

 had shrunk greatly, had a semi-vitrified appearance, did not 

 adhere to the sides of the crucible, and was of a dark green, 

 near black, colour. By digestion in water, a pink solution 

 formed, and on adding a small quantity of muriatic acid, 

 brown flocculi of manganese separated. The ignited mass 

 was readily attacked by diluted muriatic acid, being wholly 

 dissolved, except a small quantity of what appeared to be 

 silica in a gelatinous state. The solution was coloured strongly 

 by iron. It was carefully evaporated to dryness, and the 

 silica separated in the usual manner. It rather exceeded 42 

 per cent., but was obviously impure, since it was coherent 

 instead of being a light powder. I therefore resolved to de- 

 vote the present analysis solely to the determination of the 

 alkalies, and to examine a separate portion for fluoric acid. 



The baryta was precipitated by sulphuric acid, the iron, 

 alumina, and manganese, by ammonia, and after concentrating 

 the solution, hydrosulphuret of ammonia was added to separ- 

 ate the last traces of manganese. The salts were then heated 

 in a platinum crucible to expel the sulphate and muriate of 

 ammonia. After the addition of a little sulphuric acid, to de- 

 compose any muriate of potash, the alkaline sulphates were 

 fused. A colourless salt was obtained, a part of which was 

 of sparing solubility, and which, by the addition of oxalate 



