﻿UAUSMANN ON ARSENIOUS ACID, ETC. 



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the specific gravity of the transparent 3*7385, and the opake 3* 695. 

 The hardness also is subject to change, the gloss sometimes becoming 

 pulverulent, so that its fracture is earthy and the lustre quite gone. 



Fuchs in his beautiful work on Amorphism has thrown out the con- 

 jecture that the glassy arsenious acid loses its transparency by virtue 

 of a gradual change into a crystalline mass. Again, in his ' Natural 

 History of the Mineral Kingdom,' he asserts it distinctly ; for he says 

 that the amorphous arsenious acid in time becomes white, opake, and 

 porcellanous, and also becomes pulverulent, so that it can scarcely be 

 recognized as crystalline. In order to ascertain whether the cry- 

 stalline structure could be detected in the altered arsenikglas, I have 

 examined the crumbling outer crust under a magnifying power of 400, 

 but could not perceive any trace of it. Though this experiment 

 seems opposed to this view, yet I have been lately satisfied of its 

 truth in the most convincing manner. In the year 1835, I received 

 from the silver furnaces of St. Andreasbeig, through the kindness of 

 the director Herr Seidensticker, (to whose management the arsenic 

 works there owe their excellence,) a specimen of the arsenikglas ma- 

 nufactured there, about two cubic inches in size, which he had broken 

 off with his own hands immediately on opening the still warm appa- 

 ratus, and had caused to be instantly packed up that it might arrive as 

 little injured as possible. The specimen, as I received it, had a distinct 

 conchoidal fracture, without a trace of crystallization ; it was trans- 

 parent and colourless, and altogether of a glassy appearance. I laid 

 it by in a drawer-of my mineralogical collection, in a dry situation 

 close to my dwelling-room. A long time passed before I had leisure 

 to lay my hands on it again ; when I did so some years after, its ap- 

 pearance was surprisingly changed. Not only was the principal mass 

 become porcellanous, but also on the opposite sides the parts next 

 the surface had lost their clean conchoidal fracture, and to a depth 

 of two lines had adopted an acicular structure, so that the surface 

 seemed rough and cracked. This change excited my surprise, which 

 was greatly increased when at the end of a few weeks I found that 

 not only had this acicular structure proceeded further, and reached a 

 depth of four French lines in some places, but also that the exposed 

 side of the acicular masses were studded with a great number of di- 

 stinct octohedral crystals (!) ; some of these crystals were half a French 

 line in diameter. They were collected in small clusters, so as to give 

 the whole surface a drusy, intumescent appearance. The acicular- 

 shaped parts of the crust which were at right angles to the surface 

 passed insensibly into crystals, the groups of which seemed, as it 

 were, to be pushed out beyond the surface. The crystals were white 

 like the rest of the mass, but more lustrous and more translucent. 



Such a transformation of arsenikglas into a mass of well-formed 

 crystals is a most remarkable instance of molecular change in a rigid 

 body, and is the more striking, since apparently it is not caused by 

 any exterior circumstance, nor is attended by any change of constitu- 

 tion. It would seem that the molecules are put in motion by a ten- 

 dency of the amorphous mass to pass from the condition of tension 

 to that of repose and equilibrium, which is the characteristic condition 



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