360 Berzelitis's Experiments to determine the Composition {May, 



171*3 of sulphuret; that is to say, in 100 parts of metallic arse- 

 nic. Hence he concludes, agreeably to the conjecture of Haiiy, 

 that these native sulphurets were probably combinations of the 

 sulphuret obtained by fusion with difterent quantities of arsenious 

 acid. The want of correspondence between the composition of 

 the sulphuret of arsenic obtained by fusion in the experiments of 

 Laugier, and that of the acids of this metal, induced me to exa- 

 mine these native sulphurets with this object in view, and to 

 avoid all error from combustion, I exposed them to heat in vessels 

 previously freed from air. The sulphuret melted and formed a 

 brown transparent liquid, which required a very strong heat to 

 be distilled over. I left it a long time at a temperature little 

 lower than that at which it boils, without any trace of arsenious 

 acid subliming. Afterwards, on increasing the heat, the sulphu- 

 ret boiled, and distilled over in yellow drops. In these experi- 

 ments, no trace of arsenious acid could be perceived ; but on 

 making the same experiment in an open phial, the sulphuret 

 underwent a kind of roasting, in consequence of which sulphur- 

 ous acid gas and arsenious acid were disengaged, the former of 

 which made its escape, while the latter crystalhzed in the upper 

 part of the phial. 



Let us now examine the composition of the native sulphurets 

 of arsenic. In the first place, they contain only sulphur and 

 arsenic. Laugier found that the yellow sulphuret contains 38-14 

 per cent, of sulphur. In the yellow brilliant substance obtained 

 by precipitating a solution of arsenious acid by sulpliuretted 

 hydrogen gas, there are, according to experiments already 

 stated, 39 per cent, of sulphur; that is to say, that 100 parts of 

 arsenic are combined in it with 64-33 * of sulphur. We know 

 that orpiment is more or less sensibly mixed with realgar, which 

 probably is never wanting. This circumstance ought to diminish 

 the qu-antity of sulphur found in it by analysis. Hence the 

 reason why analysis gave 38-14 instead of 39 per cent, of this 

 last substance. Laugier and Klaproth found in realgar 100 

 arsenic united to 43-07 sulphur; but this quantity is very nearly 

 two-thirds of 6'4-33. The precise quantity should have been 

 42-9 ; but it is to be presumed that realgar contains a mixture of 

 orpiment, thereby containing a slight excess of sulphur ; just as 

 we have seen the reverse to be the case with orpiment. 1 think 

 then that we may admit it as established that orpiment and 

 realgar are two different sulphurets of arsenic in which the quan- 

 tity of sulphur is as 1 : li, or as 2 : 3, The yellow sulphuret is 

 proportional to the arsenious acid, and the red sulphuret to a 

 degree of oxidation, which contains two-thirds as much oxygen 

 as arsenious acid, and which may be the oxide which we have 

 seen combined with arsenious acid. 



The artificial sulphuret produced in the experiments of Laugier 



* 6J-9J.— T, 



