17? 



the form of pyrites or sulphurets. The sulphur, however, it must 

 be remembered, does not enter necessarily into the composition of 

 the coal, any more than the metal does, except that both are depo- 

 sited together in the numerous small intersections which every where 

 divide the substance of the coal ; and frequently they are deposited 

 in very splendid pyrites, on the surface next to the superior accom- 

 panying stratum. Thus at Whitehaven, where the coal pits are very 

 deep, the surface of the slate, which forms the roof to the coal, is 

 entirely covered with pyrites. 



As I shall have repeated occasion to refer to the pyrites, I will 

 here remark, that pyrites, marcasites, or metallic sulphurets, those 

 bodies which generally manifest a metallic lustre, and possess at 

 the same time a crystallized form, are compounds of sulphur and 

 metal ; the latter of which is sometimes copper, but most commonly 

 iron. By slow decomposition they derive oxygen from the air, 

 which, uniting with the sulphur, forms sulphuric acid, which then 

 acts on the metal, and forms with it a sulphate, or solution of the 

 metal in sulphuric acid. 



Besides these substances, analysis demonstrates that several of 

 the acids, in combination with some of the alkalies and of the 

 earths, but chiefly with the latter, are blended with the coal. These 

 acids are also found in the accompanying strata of coal pits, and 

 sometimes add to the pecuniary advantages derivable from those 

 real mines of wealth. 



Thus the earth, or stone, accompanying coal, is frequently em- 

 ployed for the formation of alum, it possessing almost all the princi- 

 ples of that salt. By long exposure to the air and moisture, or by a 

 judicious application of heat, and a subsequent use of moisture, the 

 sulphuret of iron undergoes the following change : the sulphur be- 

 comes oxygenized; and the acid thus formed, uniting with the 

 metal, forms a sulphate of iron. A second employment of heat, 



VOL. i. A A 



