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' £lt> PITCHSTONE FAMILY. It is semi-hard in a high degree. It is rather easily frangible ; and Rather heavy, but in a very low decree Specific gravity, 2., 9(i t0 2.389,°.!/./. ^ ^ Ilf, Brisson. Chemical Characters. Before the blowpipe it is fusible without addition. 1 he black variety of Arran, at 21° 0 f Wedgwood’s py rometer, intumesced a little, its colour was slightly alter ed, the surface glazed, and internally porous; at 31° i„. tumesced considerably and softened ; at 65° the intu mescencewas more considerable; at 100°, it was still vesicular but more compact. The blackish-green va- nety of Arran becomes black, is much rent, and inter nally porous at 23°; at 55° formed a porous enamel; at 70 it became perfectly white, and still porous. The pitchstones of Meissen in Saxony, according to Mr Kir- wan, appear to be more infusible than those of Arran. f/JT! S ° me t0 mdt at 130 ° others at , 165 ° ; and a red variety remained nearly unal tered at 160°. Constituent Parts. Pilchstone of Meissen. Silica , - - 73.00 Alumina, . ]4, 50 Lime, . L00 Oxide of Iron, . i.oo Oxide of Manganese, 0.10 N atron, . _ j Water, . . 8 ' 50 99.85 Kla P- Beit. b. iii. s. 257. G cognostic
