1818.] some remarkable Minerals. 197 



ness of snow. Its most remarkable property remains now to be 

 stated ; namely, its partial solution and action in acids. Placed 

 in highly concentrated nitric acid of spec. gr. l - 45, its loses its 

 white colour and changes to a dingy hue ; the acid, at the same 

 time, becoming clouded. The same acid being boiled upon it, 

 and distilled water, previously boiled, added, there was no 

 appearance of effervescence, but a solution took place. From 

 this solution pi'ussiated alkali threw down a leaf-green precipitate ; 

 the supernatant fluid assuming afterwards a beautiful amethyst 

 colour, which by longer exposure to the air changed to 

 brownish red; afterwards becoming reddish brown and then 

 brownish black. These changes of colour leading us to suspect 

 the presence of manganese, we undertook the analysis in the 

 following manner : 



A. Ten grains of the powder were exposed to a red heat, in 

 a platinum crucible, during a quarter of an hour ; to expel the 

 water of absorption. The same powder being afterwards weighed, 

 had lost -Jg- of a grain. 



B. Boiled during 20 minutes in nitric acid diluted with an 

 equal bulk of distilled water, the insoluble part, washed, and 

 dried in a white heat, weighed 9^ grains. 



C. The supernatant fluid collected from B, added to the wash- 

 ings of the insoluble residue, being with moderate heat evapo- 

 rated to diyness, there remained a pale lemon-coloured salt; 

 which, after exposure to a smart red heat for 25 minutes in 

 platinum foil, left a black powder weighing i- of a grain ; this 

 powder before the blow-pipe gave a fine purple colour to borax, 

 and proved to be the black oxide of manganese. 



D. The insoluble substance left by the nitric acid in B being 

 mixed with five times its weight of the bicarbonate of potash, 

 was placed in a platinum crucible, and kept exposed, during 

 three quarters of an hour, nearly to a white heat the whole time. 

 Distilled water was then dropped upon the fused alkaline mass 

 (which appeared slightly tinged with a rosy hue), merely in suffi- 

 cient quantity to soften it ; muriatic acid being afterwards added, 

 the whole assumed a gelatinous appearance. Upon the addition 

 of more muriatic acid a white powder subsided ; which, being 

 carefully washed and dried in a white heat, weighed eight grains ; 

 it proved to be pure silica. 



E. To the supernatant solution and washings collected from 

 D, a sufficient quantity of alkali was added, barely sufficient to 

 neutralize the acid. Pure liquid ammonia was then poured in, 

 and a white flocculent precipitate slowly subsided, leaving the 

 fluid above it, beautifully transparent. This precipitate, care- 

 fully washed and dried as before weighed li grain, and proved 

 to be pure alumina. 



The constituents therefore of this mineral, according to the 

 preceding analysis, may be stated in the following manner : 



