CHAPTER V 



SULPHIDES, ARSENIDES, ANTIMONIDES 

 REALGAR 



Realgar. Sulphide of arsenic, As 2 S 2 ; As =^70.1; S = 29.9; 

 Monoclinic ; Type, Digonal Equatorial ; & : b : c = 1.4403 : 1 : 

 '.9729 ; = 66 5 ' = 001 A 100 ; 100 A 110 = 52 47', 001 A 101 = 

 40 22', 110 A 110 =105 34', 001 A 011 = 41 39'; Common 

 forms, a (100), b (010), c (001), m (110), r (012) ; Cleavage, b per- 

 fect, c, a, and m less so ; Sectile ; Fracture, conchoidal ; H. = 1.5-2 ; 

 G. = 3.55 ; Color, a dark orange-red, streak somewhat lighter in 

 color; Luster, resinous; Transparent to translucent; Optically 

 (-); Plane of the optic axes, b (010) ; Bx aA c = +ll; 2V = 

 92 58'. 



B.B. On coal in O. F. burns, yielding an arsenic odor and when 

 pure leaves no residue. In the closed tube yields a cherry-red sub- 

 limate of arsenic sulphide, in the open tube yields a white subli- 

 mate of As 2 O 3 and an SO 2 odor. 



General description. Crystals prismatic, usually combina- 

 tions of (001), (110), (010) with the prism zone striated lengthwise ; 

 also occurs as compact masses, granular, or in crusts. Usually 

 coated with a yellow film of orpiment into which it changes on ex- 

 posure. Realgar is associated with antimony, arsenic, and silver 

 ores. It occurs as a sublimation product in the lavas of Vesuvius, 

 and at the present time it is being deposited associated with orpiment 

 from the water of the hot springs of Norris Geyser Basin, Yellow- 

 stone Park. In the United States it is mined at Monte Cristo, 

 Washington. 



Uses. Mixed with lime, realgar is used in tanning, to remove 

 the hair from the hides; it furnishes the white lights in pyro- 

 technics. It is also used as a pigment, but the commercial, or ruby, 

 arsenic is an artificial product. When realgar is dissolved in sodium 

 bicarbonate at 150 under pressure, upon cooling the solution, it 

 separates as crystals. 



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