1820.] of different inorganic Bodies. 361 



by the fusion of the natural sulphurets neither agrees with the 

 composition of the sulphurets examined, nor with the acids of 

 arsenic. From the theory of chemical proportions, it is obvious 

 that it cannot be a simple sulphuret. It is probably the result 

 of the combination of a higher degree of sulphuration with 

 realgar. We know that arsenic acid is decomposed by sulphu- 

 retted hydrogen gas. The resulting sulphuret must be composed 

 of 100 arsenic combined with 106'91 of sulphur. If we calculate 

 the composition of a combination of this sulphuret with realgar 

 in which the arsenic in each sulphuret is in equal quantity, 100 

 of arsenic in it will be combined with 74'6 of sulphur. If, on the 

 contrary, we admit a composition such that the sulphur of the 

 persulphuret is double that of the realgar, 100 of arsenic in it 

 will be combined with 71-26 of sulphur, which agrees perfectly 

 with the analysis of Laugier. 



On examining the maximum of sulphuration of which arsenic 

 is capable, I have found that this metal and sulphur may be 

 mixed in almost all proportions. The sulphur for some time 

 swims upon the surface of the fused sulphuret ; but by degrees 

 it mixes with it into a homogeneous yellow mass. I have in this 

 way united arsenic with more than seven times its weight of 

 sulphur. The sulphuret, when cool, was elastic, hke caoutchouc, 

 just as happens sometimes with sulphur itself, and some weeks 

 elapsed before it became quite solid and hard. The quantity of 

 sulphur was determined by dissolving it in nitromuriatic acid, 

 and precipitating the sulphuric acid by muriate of barytes. 

 When we distill this sulphuret, it gives at first sulphur, containing 

 little arsenic ; but as the process advances, the arsenic increases 

 in quantity in the product distilled, which becomes at the same 

 time more coloured ; so that the last drops sublimed into the 

 top of the retort have a fine ruby red. Hence it appears that 

 heat does not furnish a method of obtaining the sulphurets of 

 arsenic in the state of definite combinations. 



(To be continued.) 



Article X. 



Memoir relative to the Lead Mines of Sardinia. 

 (With a Plate. See CIV.) 



Th f. mines in Sardinia have, there is no doubt, been wrought 

 extensively at a very remote period. History relates, that both 

 the Romans and Carthagenians carried on mining operations 

 when they possessed the island. Zurita, in his histoiy of the 

 11th century, as also the Genoese historians, Frederici and 

 Giustiniano, state, that the silver which was on board the Pisau 

 fleet, captured in 1283 by the Genoese, and which the latter 



