Volltext Seite (XML)
*3 6 ArgiUaceous Genua. The curved llaty argilütes have their crofs frac- ture hackly, and opake. » xft Variety. Angkfey Slate. Purple, or rcddifh purple. Internal Iuftre r. Opake. Hardnefs, from 7 to 8. 8p. gr. from 2,84102,876. It doesnot imbibe water, gives a rcddifh white flreak. Does not effervelce with acids, unleis powdered, and thcn weakly. Gives a greenifh colour to nitrous acid after ftanding fome days. Becomes brownifh red when heated. Slightly detonates with nitre. Melts intoa black fpongy mafs. Contains 0,38 filex, 0,26 argill o,c8 magnefia, 0,04 calx, 0,14 iron perhaps mixed wich nickel, or perhaps the green colour of the nitrous acid may proceed from the bitumi- nous fubflance contained within it, this feems inoft probable. 2d Variety. Wcßmoreland Slate. Many forts are found in that county; but tbat which paffes for the beft has its colour, bluilh grey; when moift, greenifh grey. Luftre, filky, 2, opake. Hardnels, 6. 8p, gr. 2,7325 gives a white flreak; does not imbibe water; flightly effervefces with acids; by heat becomes reddifh brown;