DR T. THOMSON'S Analysis of some Minerals. 455 



I do not know to what the excess is to be ascribed in this 

 analysis. I repeated the analysis, and obtained similar results, and 

 an excess which amounted to 2.5 per cent. The silica is an ac- 

 cidental impurity. The ore is obviously a compound of 



Lead, . . .".,.' 86.175 or 78 or 156 

 Sulphur, . . . 14.405 . V 13.04 . 26.08 



The atom of lead being 13, and that of sulphur 2, it is obvious 

 that 156 lead is equal to 12 atoms; while 26.08 sulphur is al- 

 most exactly equal to 13 atoms. The supersulphuret of lead, 

 therefore, which 1 analyzed, is a compound of 



1 2 atoms lead, 



13 atoms sulphur. 



This is an unexpected combination, nothing similar to which 

 I have met with before. I have not made any experiments to 

 ascertain whether lead be susceptible of combining with sulphur 

 in various proportions. Analogy would lead us to suppose that 

 it is ; for we generally find, that oxygen and sulphur enter into 

 the same number of combinations with most of the metals. 

 There probably, then, exists a sesquisulphuret of lead ; if so, we 

 may consider the supersulphuret of lead just analyzed, as a com- 

 pound of 



5 atoms sulphuret of lead, 



1 atom sesquisulphuret of lead. 



This at least would accord with the results obtained. 



V. Chabasite. 



This mineral, as is well known to mineralogists, exists rather 

 abundantly in the neighbourhood of Glasgow. The finest spe- 



