ON ORPIMENT AND REALGAR. 77 



*ill serve farther to establish the former fact, and will place 



the latter in a stronger light. 



It is very certain, that, if arsenic were in the state of ox- These &ulphu« 



itle in these compounds, they might easily be formed hy for ^ } nr ^ ar _ e 



employing arsenious acid and sulphur. But on heating senious acid & 



these substances together in a retort, &c, we obtain for a oxiglSgiveu 



long time nothing but sulphurous acid: it is not till this gas out. 



nearly ceases to come over, that orpiment or realgar is 



formed. It may be said indeed, that arsenic is les3 oxided 



in these sulphurets, than in arsenious acid. But the exist-> 



ence of such oxides has never been proved. When arseni- Nointerme- 



ous acid is reduced by any method whatever, even by means oxidation. 



of bidrogen gas, nothing is ever obtained but arsenious acid 



and arsenic, suspend the process at what period of it you 



please: and probably, if there were any fixed intermediate 



degrees of oxidation, they would be detected by proceeding 



in this way. Be this as it may, by combining sulphur with 



arsenic in different proportions in close vessels, we obtain at 



pleasure orpiment or realgar. 



Three parts of sulphur and four of arsenic form orpiment: Extinguishing- 



r properties of 



one of sulphur and three 'of arsenic form realgar. Realgar thetwosul- 



enters into fusion at a very low temperature, and continues L )llurets * 

 fluid long after the retort is withdrawn from the fire. Orpi- 

 ment requires a somewhat higher heat to fuse it. Both rise 

 by sublimation, and adhere to the neck of the retort. The 

 orpiment is transparent, and of a hyacinth colour, so that 

 at first it might he taken for a sort of realgar: but native 

 orpiment itself assumes this colour on being melted ; and 

 both, that is the native orpiment after its beautiful colour Los 

 been thus changed, and the artificial, become of a very pure 

 and lively yellow by pulverization. It is not the same with 

 the orpiment produced in the humid way. The colour of 

 this is similar to that of native orpiment that has never been 

 exposed to heat : and it is in every respect similar to it, whe- 

 ther it be the prod net of a mixture of arsenious acid and 

 sulphuretted hidiogen, or of a soluble arsenite, hidrosulphu 

 .ret, and an acid. 



Thus it appears demonstrated, that yellow orpiment in 

 shining scales, and even endued with a sort of elasticity, is 

 formed in some fluids; while realgar is produced by arsenic 



an<i 



