Us Oxides and Sulphurets, 319 



colour to blue, when previously reddened by an acid*. The cause 

 of these differences has not been examined with sufficient care, 

 and Guibourt leaves it unsettled. He says it takes place in 

 consequence of the contact of the air ; but the accuracy of this 

 opinion may be questioned. He has remarked, that it is brought 

 about very rapidly by treating the transparent variety with am- 

 monia ; but he draws no conclusions from the fact. 



As to the compounds of sulphur with arsenic, the latest mi- 

 nute researches, those of Berzelius and of Laugier, seemed to 

 show, that, contrary to the opinion of Proust, the native and ar- 

 tificial sulphurets differ in no essential particular from one ano- 

 ther, and that none of them contain oxigen. Whence does it 

 happen, then, says Guibourt, that, according to the observations 

 of Hoffmann, and the late experiments of Renault, the native 

 sulphurets, orpiment and realgar, as well as the sulphuret pro- 

 cured by transmitting sulphuretted hydrogen through a solu- 

 tion of oxide of arsenic, are not poisonous, while the sublimed 

 orpiment, and even the artificial realgar, prepared by melting 

 together metallic arsenic and an excess of sulphur, are exceed- 

 ingly deleterious ? It depends, he says, on the artificial sulphu- 

 rets always containing some oxide of arsenic intermingled. The 

 artificial realgar contains 14 per cent. ; the artificial orpiment so 

 much as 40 per cent. This last fact we can confirm by our own 

 experience ; in fact, we have seen fine tetrahedral pyramids of 

 the oxide on the inside of the cakes sometimes sold in the shops. 

 M . Guibourt is wrong, however, in supposing that the native sul- 

 phurets are not poisonous. Renault, it is true, found them 

 to be much inferior to the oxide and other soluble compounds 

 of arsenic, in their effects on the animal system. But instances 

 are to be found in the Acta Germanka, of poisoning with real- 

 gar, and M. Pelletan informed him, after the composition of his 

 paper, that he had known an instance of poisoning with natural 

 orpiment. In consequence of the opinion expressed by Guibourt, 

 Professor Orfila has related, in an ulterior number of the Journal 

 deChimie Medicale, some experiments he has made expressly with 

 the native sulphurets, and with that procured by transmitting sul- 

 phuretted hydrogen through a solution of the oxide ; and it ap- 



• Our experience is at variance with that of the author ; a solution of the 

 opaque oxide faintly reddens litmus, and restores reddened litmus very imper- 

 fectly. 



