206 Chemistry. [Lecture 31. 



nerally manifest their having suffered crystal- 

 lization. Most commonly it is met with in 

 masses which have no regular external form. 

 Those which are round have a fibrous structure, 

 radiated from the centre to the circumference. 

 Those used for the manufacture of brimstone are 

 so hard as to strike fire with steel. We discover 

 the composition of pyrites by heat : it burns like 

 brimstone ; and if a stronger heat is applied, it 

 rises in vapour, which when condensed is brim- 

 stone. 



The sulphur thus obtained is, however, sel- 

 dom pure, the steam of metals, earths, and other 

 substances condensing along with it. It may be 

 purified by being melted in an *iron vessel, and 

 kept in a melted state, and then the impurities 

 settle at the bottom, and the matter being skim- 

 med, is cast into moulds. 



If we wish sulphur still purer, we must use 

 the flowers of brimstone, which is sulphur pu- 

 rified by sublimation; but during this process 

 some of the sulphur is apt to take fire, which 

 gives an acidity to the rest. Hence we find in 

 some flowers a little sulphurous acid, which 

 prevents their gently laxative effects; but this 

 acid may.be removed by only pouring boil- 

 ing water upon the flowers, and drying them 

 again. 



Besides the pyrites, there are other substances 

 which contain more or less sulphur ; as all ores 

 of metals except gold. The ores of copper are 



