98 On the Cause of Chemical Proportions. [Feb. 



mixed 4 parts of sulphur with 1 part of arsenious acid ; and when 

 the disengagement of sulphurous acid gas was at an end, and a 

 portion of the sulphur sublimed, I allowed the retort to cool. I 

 found two different layers : the upper one was thin, yellow, and 

 opake, and was pure sulphur ; the lowtr one was pellucid, had a 

 hrownish yellow colour, and was exactly similar to Burgundy pitch. 

 To see whether it was any thing else than a mixture of sulphur and 

 sulphuret, I fused it again with sulphur, mixing them well toge- 

 ther ; but the two liquids again separated. The sulphuret being 

 the heaviest sank to the bottom, and the sulphur floated on the 

 surface. This substance was, then, a supersulphuret of arsenic at 

 the true maximum : 5 parts of this supersulphurel oxidated by 

 nitromuriatic acid yielded ■2G'J2 parts of sulphate of barytes, equi- 

 valent to S'G'JGJ of sulphur : so that this sulphuret is composed of 



Arsenic 26-47 100 



Sulphur 73-53 280 



100-00 



This sulphuret contains four times as much sulphur as realgar ; 

 for 7 1 '5 X 4 = 286 : and if realgar, as we shall see afterwards, is 

 composed of As + 3 S, the other sulphuret must be As + 12 S, 

 that is to say, the maximum of combination admitted by the 

 hypothesis of atoms. This supersulphuret gives a beautiful yellow 

 colour, which might be employed as a paint, and could be fabri- 

 cated at a moderate expense. 



This supersulphuret not being artificial realgar, as I had at first 

 supposed, 1 endeavoured to procure realgar from it by distilling it in 

 a retort. I obtained at first a little sulphur, then supersulphuret 

 very little coloured, and afterwards portions which became more 

 and more red as tlie distillation advanced When there remained 

 but very little sulphuret I allowed the retort to cool. I divided tl>e 

 sublimate according to its colour into four different portions, wliich 

 I oxidated by the nitiomuriatic acid. None of these portions was 

 composed as I expected. I found them all mixtures of different 

 degrees of sulphuration. The portion of sublimate nearest the 

 belly of the retort was composed of 100 arsenic and 84-S of sul- 

 phur. The ruby red and very brilliant drops which had condensed 

 in the retort itself contained 76 sulphur to 100 of metal : so that 

 the portions sublimed, in proportion as the distillation went on, 

 approached more and more to realgar. I now mixed one part of 

 the last sulphuret obtained with metallic arsenic, and sublimed the 

 mixture ui a long-necked phial. But I found the metal and sul- 

 phuret so nearly of the same volatiHty, that the sulphuret was 

 mechanically mixed with crystals of metallic arsenic. The sulphuret 

 did not appear altered. Hence it follows that there does not exist 

 a sulphuret containing less sulphur than realgar, at least it cannot 

 be formed by means of heat. These experiments are sufficient to 

 show that the analysis of realgar by Laugier must be exact. Of 



