﻿HAUSMANN ON ARSENIOUS ACID, ETC. 



6 



cavities there are crystals, but these appear under the lens to be regular 

 octohedral crystals of arsenious acid coloured by sulphuret of arsenic. 

 This product when fused in the glass tube neither becomes crystallized 

 nor vitreous, the fracture is imperfectly conchoidal, or uneven, with 

 a slightly waxy lustre. The mass contracts and cracks, but shows no 

 sign of crystallizing. On the concave surface small white brilliant 

 crystals of arsenious acid show themselves. 



The red arsenikglas of commerce, which also passes by the name 

 of realgar, shows by its colours that the proportion of its arsenic to 

 the sulphur is small, as must necessarily be the case from the mode 

 of preparation. It has a very perfect, large-conchoidal fracture, a 

 vitreous lustre sometimes approaching the waxy, and is only transpa- 

 rent at the edges. Its specific gravity is always less than that of 

 native realgar. The latter as determined by Karsten is 3*5444, whilst 

 the former, according to experiments of my own made with distilled 

 water at a temperature of 1 5° R., ranges between 3*20 and 3*32 ; that 

 of a specimen from the silver-mines of St. Andreasberg being 3*318 ; 

 a dark red specimen purchased here being 3*258 ; and one of a beau- 

 tiful bright red colour from Ehrenfriedersdorf being 3*254. The 

 hardness of the arsenikglas on the other hand is much greater than 

 that of native realgar, that of the former being equal to calc-spar, 

 while the latter only reaches 1*5. The red arsenikglas when fused 

 still retains its vitreous character, and even when very slowly cooled 

 shows no trace of crystallization. The lower specific gravity seems 

 to indicate that when produced in large quantities it has usually a 

 greater proportion of sulphur than native realgar. This is confirmed 

 by the fact, that by fusing native, realgar with orpiment (Rauschgelb) 

 a substance is produced closely resembling the red arsenikglas of com- 

 merce. A large addition of orpiment to the arsenikglas while in 

 fusion destroys the tendency to crystallize. Moreover the mode of 

 preparing the red arsenikglas justifies a belief that a smaller propor- 

 tion of arsenious acid is present. At all events, the red arsenikglas 

 cannot be looked on as identical with the crystalline realgar composed 

 of definite proportions ; and the assertion that realgar is a vitreous 

 substance, which occurs in modern manuals of Chemistry, must in 

 future be rectified. 



Orpiment or Rauschgelb, which is so well marked a crystalline 

 substance by its very perfect foliated cleavage, differs strikingly from 

 realgar, with which it often occurs mixed in nature, in this respect, 

 that when fused it passes into an amorphous mass. The glass thus 

 produced has not its original yellow colour, but is more or less bright 

 red. Karsten has already remarked that the change of colour may 

 arise from a change in its flexibility. If the fusion is carried on in 

 close vessels, the result is a semi-transparent glass of a ruby or hya- 

 cinth-red colour, differing from arsenikglas both in greater transpa- 

 rency and in the deeper yellow of its powder. When melted in a 

 glass tube it shows with transmitted light a beautiful ruby colour, 

 and has a phosphorescent appearance, which is also observed in the 

 fusion of realgar and red arsenikglas. Herr Wohler had the good- 

 ness to send me from the laboratory of the Academy some orpiment 

 prepared there, which was perfectly vitreous, semi-transparent, of a 



