I RAW MATERIALS AND PRIMITIVE MANUFACTURES 9 



with water, a soluble substance is dissolved out and separates 

 in green crystals on allowing the washings to evaporate. 

 The glassy appearance of the crystals won for the substance the 

 name of viTRiOL(Latin vitrum, glass). It played a most impor- 

 tant part in the early development of chemistry on account of 



FIG. 7 NODULE OF MARCASITE AS DESCRIBED BY GLAUBER. 



FIG. 8 STRIATED CUBES OF PYRITES. 



Marcasite and iron pyrites both consist of disulphide of iron (FeSa), but they 



differ in crystalline form. The crystals of iron pyrites are cubic whilst those of 



marcasite belong to the orthorhombic system. 



the discovery of an oily product, OIL OF VITRIOL, to which it 

 gave rise when strongly heated (see Chapter II). The 

 following description of the way in which green vitriol was 

 prepared from nodules of marcasite was written by Glauber 

 about 1648 A.D., and translated into English in 1651 : 



