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152 SE1ESTIDES. borax yields a globule of silver. Easily soluble in. fuming nitric acid; with great difficulty in dilute nitric acid. AgSe, silver 73'16, selenium 26'85. Analysis by G. Rose :— Silver .... 65’56 Eead .... 4-91 Selenium .... 25-93 In thin plates, having a crystalline structure. Is found at Tilkerode in the Harz, with clausthalite in narrow veins in diabase. 42. CLAUSTHALITE. — Seleniuret of lead ; Phillips. Clausthalie ; Beudant. Selenblei; Mohs, Hausmann. Claus- thalit; Haidinger. Cubic. a 100 cleavage. aa! 90° o', (fig. 137.) Cleavage, a. Opaque. Lustre metallic. Lead-grey. Streak grey. Sectile. n = 2-5...3-0. g == 8'2...8 - 8. In the matrass decrepitates violently. The varieties con taining cobalt yield a sublimate of selenium. In the open tube deposits a sublimate of selenium, partly red, partly grey. Before the blowpipe on charcoal fumes, emits a smell of se lenium, deposits a red, yellow, and white sublimate, and imparts a blue colour to the flame; does not melt, but becomes rounded and is gradually dissipated, leaving a black slag, which, with borax, affords the reactions of iron, copper, and sometimes of cobalt. Partially soluble in nitric acid, leaving a residue of selenium. PbSe, lead 72’3l, selenium 27.69. Some varieties contain selenide of silver, others solenide of cobalt. Analyses of Clausthalite a from Tilkerode, by II. Ro ae ; b from the Lorenz Gegentrum mine near Clausthal, by Stro- meyer; c from Clausthal, by Stromeyer; d from Tilkerode, by Itammelsberg:— Lead a b c d . 71-81 63-92 70-98 60-15 Silver — — 11'67 Cobalt 3‘It 0-83 Iron 0" 45 Selenium . 27-59 31-42 28-11 26-62 In granular masses, exhibiting cubic cleavages, compact and disseminated.