VOL. LXXIV.J PHILOSOPHICAL TRANSACTIONS. 54() 



Variety, heavy gypsum. Ponderous spar. Marmor metallicum. Cronstedt 



Min. \ 18, 2, 10, c. 



From Kilpatrick hills near Glasgow. A sort, with smaller crystals, among 

 the iron ore about Ketley in Shropshire. In the lead mines at Alston-Moor. 

 It is white ; nearly transparent, but has not the property of double refraction ; 

 composed of laminae of rhomboidal crystals ; decrepitates in the fire. Specific 

 gravity from 4.402 to 4.440. 



Exper. a. 100 grs. exposed to a red heat for 1 hour, in a black lead crucible, 

 lost 5 grs. in weight ; but as a sulphureous smell was perceptible, I suspected 

 that a decomposition had taken place, and therefore exposed another portion to 

 a similar heat for the same space of time in a tobacco-pipe. This had no smell 

 of sulphur, nor was it diminished in weight. 2. It is barely fusible under the 

 blow-pipe ; but with borax fluxes readily into a white opaque glass. 



b. 100 grs. ground in a mortar, and washed over extremely fine by repeated 

 additions of water, were boiled in the same water, and after settling the water 

 was poured off. The powder, when dried, had not sensibly lost weight. 2. To 

 separate portions of the washing water, were added mild vegetable and mild 

 fossil alkali ; but without any appearance of precipitation. Nitre of mercury 

 gave a very slight brownish cloud, barely discernible ; and nitre of silver an ex- 

 tremely slight bluish appearance. 3. The same powder, boiled again in fresh 

 water, thd not affect the water at all ; for it stood the test of nitre of silver 

 without any change. 



c. Portions of the powder b were boiled in vitriolic, nitrous, and muriatic 

 acids, of the usual strength, for several minutes. The acids were then saturated 

 with vegetable fixed alkali, but without any appearance of precipitation, nor had 

 the portions of powder lost any weight. 2. But when boiled in vitriolic acid, 

 till that acid became very much concentrated and nearly red-hot, the whole of it 

 dissolved; but, separated again on the addition of water, was not altered in its 

 weight, was not acted on by acids of the usual strength, and under the blow- 

 pipe had the properties mentioned at a 2. 3. Some of the solution in the con- 

 centrated vitriolic acid was left exposed to the atmosphere, that the acid might 

 slowly attract water. After some days, beautiful crystals appeared in the shapes 

 of stars, fasciae, and other radiated forms. 4. To another portion of this solu- 

 tion mild fixed vegetable alkali was added ; but the precipitate appeared to be 

 the marmor metallicum unchanged. 



d. One ounce of this marmor metallicum in fine powder was fluxed in a cru- 

 cible with 2 oz. of salt of tartar, till it ran thin. This substance, boiled with 

 water in a Florence flask, left a residuum of 6 drams. 



e. This residuum was thrown into water, and pure nitrous acid added, till 

 there was no more effervescence. The undissolved part weighed 52 grs. 



f. This undissolved part appeared to be the original substance no ways 



