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above-mentioned genus. Dr. Babington, from its physical characters, 

 and from some experiments made on its solution in acids, ascertained 

 that it was a mineral substance not yet described, and that it con- 

 tained a considerable portion of aluminous earth. 



This mineral is generally found in small hemispherical groups of 

 crystals, composed of filaments radiating from a common centre, and 

 inserted on the surface of the schistus : sometimes, however, it forms 

 small veins of irregularly disposed prisms. It is of a white colour, 

 having sometimes a tinge of gray, or of green ; and, when beginning 

 to be decomposed, of yellow. Its lustre is silky ; it is generally al- 

 most opake, but sometimes semi-transparent. It is fragile ; but its 

 small fragments are so hard, as to be capable of scratching agate. It 

 has no smell when breathed upon ; it has not any taste, nor does it 

 adhere to the tongue till it has been strongly ignited. It does not 

 become electrical, or phosphorescent, by heat or friction ; nor does 

 it decrepitate before the blowpipe, but loses its hardness, and be- 

 comes quite opake. Its specific gravity, Mr. Davy thinks, does not 

 exceed 270, water being considered as 100. 



The white and semi-transparent specimens of this substance are 

 soluble in the mineral acids, and also in fixed alkaline lixivia, with- 

 out effervescence ; but when coloured or opake specimens are ex- 

 posed to alkaline lixivia, a small part remains undissolved. 



A small transparent piece, by being exposed to the greatest heat 

 of a forge, had its crystalline texture destroyed, and was rendered 

 opake, but was not fused. It now had lost more than one-fourth of 

 its weight, and adhered strongly to the tongue ; neither water nor 

 alcohol had any effect on this mineral. When exposed, in a glass 

 tube, to a heat of from 212 to 600, it gave out an elastic vapour, 

 which, when condensed, was a clear fluid, having a slightly empy- 

 reumatic smell, but not differing in taste from pure water. 



The solution of this substance in sulphuric acid produced crystals 

 in thin plates, which had the properties of sulphate of alumine, and 

 from which, when re-dissolved and mixed with potash, octahedral 

 crystals of alum were obtained. 



The solid matter precipitated from the solution of this substance 

 in muriatic acid, was not acted upon by carbonate of ammonia, con- 

 sequently it did not contain glucine or yttria. 



Several experiments were made on the opake and coloured varieties 

 of this mineral, from which it appears that the substances which 

 cause these varieties, are calcareous earth, manganese, and oxide of 

 iron. 



Mr. Davy then proceeded to the analysis of the mineral. For this 

 purpose he made use of the whitest and most transparent pieces he 

 could obtain. The particulars of this analysis we shall pass over ; 

 and shall merely state that, according to its general results, 100 parts 

 of the mineral contain, of alumine 70, of lime T4, of fluid 26'2, the 

 loss amounting to 2'4 ; which loss Mr. Davy is inclined to attribute 

 to some fluid remaining in the stone after the process of distillation, 



