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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 de- 
posited together in the numerous small intersections which every 
where divide the substance of the coal ; and frequently they are de- 
posited in very splendid pyrites, on the surface next to the superior 
accompanying 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 sulphui 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 prin- 
ciples 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 
