I’LOMBGOMME. 525 pb 41° 35' pp 96 60 sa 68 26 SS' 63 8 mb 28 35 nb 47 28 ab 90 0 Combinations, bs, las', basn', bpm'n', bpa'm’n', bpsdri, bpamn's. Twins. Twin-face a. Cleavage, b, perfect. Frac ture conchoidal. Transparent... semi-transparent. Lustre vitre ous. e = 1*62. The optic axes are in a plane parallel to a, and, when seen in air through the faces M>, make angles of 29° 45' with a normal to b. Colourless, yellow, brown. Streak white. 11 = i 4 5...2’0. o = roo...i’76. Pyroelectric, the analogous pole being at the end on which the hemihedral face a occurs; the antilogous pole at the opposite end of the crystal. In the matrass yields water and ammonia. Before the blow pipe melts into a colourless glass which becomes opaque on cooling. Very slightly soluble in water. Soluble in hydro chloric acid. Mg’P + NIP + 13II, phosphoric acid 28 9, magnesia 167, ammonia 6'9, water 47‘5. Part of the magnesia is sometimes replaced by protoxide of iron. Struvite was found in crystals in 18-15, in digging the foun dations of the new' church of St. Nicholas at Hamburgh, where it had evidently been produced by the decomposition of animal matter; also in guano from the coast of Africa (guanite). It is deposited as a granular precipitate from neutral or alkaline solutions containing phosphoric acid, ammonia and magnesia. 359. PLOMBQOMME. —Plombgomme; Phillips. Plomb hydro-alumiueux ; llauy. Bleigummi; Mohs, llausmann, llai- dinger. lieniform, botryoidal. Fracture conchoidal. Translucent. Lustre resinous, inclining to vitreous. Yellow, browm. Streak White. II = 5. O = 4'88...6'421. In the matrass decrepitates and yields water. Before the blowpipe or charcoal melts with intumescence. AVith soda yields lead. With nitrate of cobalt becomes blue. Soluble in concentrated nitric acid. Analyses of plombgomme a from Iluelgoet by Damour, b from Beaujeu by Bufrenoy:— ta 67° so' tp 22 10 tb 46 9 ts 43 51 tm 22 10 mm" 122 60 tin" 85 4 FIG. 617 V 0