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272 HYDROUS EARTHS, OXIDES, AND ACIDS. A mixture of AL P il 8 with A1H 3 in various proportions. Analyses of gibbsite from Richmond by Hermann:— Alumina ... 26’66 38'29 60'20 53'92 Phosphoric acid . 37'62 26'30 1630 11'90 Water .... 35-72 35'41 34'50 34-18 Is found in botryoidal masses at Richmond in Massachusetts. The first analysis represents the composition of the precipi tate of hydrous phosphate of alumina, obtained by adding phos phate of soda to a solution of alum. tv 14 ! 7 ' Diaspore; Phillips, Ilauy. Eutomer JJisthen-Spath ; Mohs. Diaspor; Hausmann, Haidinger. Prismatic. 011,010=57° 38'; 101,001=30° 39'; 110,100=40°50'. a 100, c 001, e 101, d 120, k 320, I 210, p 111, s 122, 0 922. 0 truncates the edge pa. fig. 298. ca 90° o' oa 23° 56' ea 59 21 88 28 6 ee 61 18 ss" 62 36 ea 28 9 s's" 69 68 ka 35 30 pp’ 63 10 da 64 67 pp" pp" 00 67 14 dd’ 50 6 81 54 do 90 0 132 8 sa 75 67 00" 25 4 pa 63 25 00" 139 66 Combinations. akdc,akdso,alkdepg. The edges sd, ok rounded. Cleavage, a, very perfect; d, less perfect. Fracture con- choidal...uneven. Transparent...translucent. Lustre vitre ous; a, pearly ; on surfaces of fracture resinous. The minimum deviations of light refracted through dd" are 21° 54', 21° e' the least refracted ray being polarized in the plane of refraction. Colourless, greyish-white, yellowish-white, greenish-white, pale green, blue, dark violet, yellowish-brown from an admixture of hydrate of red oxide of iron. The variety from Sehemnitz appears of a reddish plum-blue colour when viewed in a direc tion perpendicular to c, violet inclining to blue when viewed in a direction perpendicular to a, and asparagus green when viewed in a direction parallel to the edge ae. Streak white, h = 6 - 6. a = 3-30... 3-43.
