Arsenic Vitreous

Steel-gray crystalline brittle metal hexagonal crystal system atomic volume 13.09 cc/g atom three allotropes are known namely, the a-metaUic form, a black amorphous vitreous solid known as P-arsenic, and also a yellow aUotrope. A few other allotropes may also exist but are not confirmed. Sublimes at 613°C when heated at normal atmospheric pressure melts at 817°C at 28 atm density 5.72 g/cc (P-metallic form) and 4.70 g/cm (p-amor-phous form) hardness 3.5 Mohs electrical resistivity (ohm-cm at 20°C) 33.3xlCh (B—metallic polycrystalline form) and 107 (p—amorphous form) insoluble in water. 

When heated with chlorine, bromine or iodine vapors arsenic forms the corresponding trihalides however, with fluorine, arsenic pentafluoride, AsFs is produced. With sulfur it forms mixtures of sulfides, AS2S3, AS2S2 and AS2S5 in vitreous forms and varying proportions depending on the conditions of reactions. 

That arsenic may exist in both crystalline and amorphous forms was observed by Berzelius,2 who designated them a- and /3-arsenic, respectively. Two crystalline allotropes, metallic arsenic (the a-form) and yellow arsenic, are now recognised, and three amorphous forms, vitreous arsenic (the /3-form), grey and brown amorphous arsenic, have been described. The majority of investigators, however, deny the existence of more than one amorphous form, and indeed, as will be seen, it is an open question whether any amorphous form is to be considered as a true allotrope. 

Unlike the octahedral form, vitreous white arsenic on heating melts before volatilisation begins.8 The density of the glass has been variously given 9 as 3-70 to 3-88 Winkler found the density under water to be 3-7165 at 12-5° C. but under petroleum 4-6815. The glass is brittle and its hardness is comparable with that of Iceland spar.10... 

Antimony Arsenite.—When powdered antimony is digested with a concentrated aqueous solution of arsenic acid, and the solution then diluted with water, a precipitate forms, which was described by Berzelius 6 as antimony arsenite. He obtained a similar product by heating a mixture of arsenic and antimony pentoxide it remained as a transparent vitreous mass. The exact composition of these products does not appear to have been investigated. 

SCORODITE. This hydrated arsenate of feme iron and aluminum (Fe . +, Mg3+)AsOz -2H20. crystallizing in the orthorhombic system, is the iron-rich isomorphous end member of a complete series extending to the aluminum-rich mineral Mansfieidite, Crystals usually occur as drusy crusts. Alsu occurs as massive, compact, ami earthy material. Hardness of 3.5 4, with specific gravity of 3.278. Vitreous to subadamantine luster, of pale green to liver-brown color. 

O Hare, P.A.G., Lewis, B.M., Susman, S. and Volin, K.J. (1990) Standard molar enthalpies of formation and transition at the temperature 298.15 K and other thermodynamic properties of the crystalline and vitreous forms of arsenic sesquiselenide (As2S3). Dissociation enthalpies of As-Se bonds. Journal of Chemical Thermodynamics, 22, 1191-206. 

Audrey S. Glebov, The Nature of the Current Instability in Chalcogenide Vitreous Semiconductors A. M. Andriesh, M. S. Iovu and S. D. Shutov, Optical and Photoelectrical Properties of Chalcogenide Glasses V. Val. Sobolev and V. V. Sobolev, Optical Spectra of Arsenic Chalcogenides in a Wide Energy Range of Fundamental Absorption... 

ZHD/MAL] Zhdanov, V. M., Mal tsev, A. K., Low-temperature heat capacity, enthalpy, and entropy of crystalline and vitreous arsenic sesquiselenide and of crystalline arsenic sesquitelluride, Russ. J. Phys. Chem., 42, (1968), 1078-1080. Cited on pages 190, 191. 

The taste of arsenic trioxid in solution is at first faintly sweety afterward very slightly metallic. The solid is almost tasteless. It is odorless. In aqueous solution (see below) it has a faintly acid reaction. The sp. gr. of the vitreous variety is 3.785 that of the crystalline, 3.089. 

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