[ 149 ] 

 XX III. Intelligence and Miscellaneous Articles. 



ANALYSIS OF A HYDRATED SILICATE OF ALUMINA. 

 BY MM. DAMOUR AND SALVETAT. 



T^HIS mineral is found in the environs of Montmorillon (Vienne). 

 -* It occurs in cavities in a brownish argil ; it is very soft and sa- 

 ponaceous to the feel, perfectly amorphous, and may be readily broken 

 down between the fingers ; its colour is bright rose-red. Without 

 possessing the plastic properties of clay, it very readily diffuses 

 through water ; it is infusible by the blowpipe ; it is also infusible in 

 the high temperature of a porcelain furnace, but assumes the white- 

 ness and appearance of biscuit, and is hard enough to scratch glass. 



When heated in a tube, it j'ields much water, loses its rose colour, 

 and becomes grayish-white ; from 60° F. and upwards it loses water 

 gradually, and when heated to 212°, it still obstinately retains 0-1512 

 of combined water. With niicrocosmic salt it partially dissolves, 

 and leaves a bulky skeleton of silica ; solution of caustic soda sepa- 

 rates from it a small portion of gelatinous silica. 



Hydrochloric acid partially attacks it, without producing the 

 slightest effervescence, and dissolves some lime, magnesia, potash, 

 alumina, oxide of iron, and traces of manganese ; the greater part of 

 the mineral remains insoluble, and retains its rose colour. If, after 

 this treatment with acid, the insoluble portion be boiled in a so- 

 lution of caustic soda, a considerable quantity of silica is dissolved ; 

 the insoluble portion being again treated with hydrochloric acid, it 

 is completely decomposed ; the silica separates in a flocculent state, 

 and the solution contains the rest of the alumina. 



Sulphuric acid, when heated till it begins to vaporize, completely 

 decomposes the mineral, within about one-hundredth ; on pouring 

 water on the substance thus acted upon, the alkali and the other 

 bases are dissolved, and pure silica is deposited. The solution, se- 

 parated from the silica, gives with ammonia a precipitate coloured 

 with a little oxide of iron ; the solution, separated from the alumina, 

 is rendered turbid by oxalate of ammonia, and phosphate of soda 

 afterwards produces an appreciable degree of turbidness. 



Examination showed that the mineral contained no sulphuric acid ; 

 and the various tests indicated that the mineral is essentially com- 

 posed of silica, alumina and water, and also contained small quanti- 

 ties of lime, magnesia, potash, oxide of iron, and manganese ; the 

 peculiar rose colour appeared to be owing to combustible matter. 



The different analyses of this mineral were performed by various 

 processes ; and in all of them at least one gramme was used. 



A. The mineral was fused with four times its weight of very dry 

 carbonate of soda ; the residue was treated with water and hydro- 

 chloric acid ; the silica was separated by evaporation twice to dry- 

 ness ; heated to redness and weighed, it was totally soluble in a 

 solution of caustic soda. 



The solution, separated from tlie silica, was precipitated by am- 

 monia, and suffered to remain at rest during twenty-four hours. The 



