18 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



obtained by the weathering of different varieties of pyrites. 

 The blue vitriol was of special interest because iron dipped 

 into it became coated with copper, and seemed to have 

 been transmuted into that metal. These two vitriols were 

 prepared artificially by the action of oil of vitriol on plates 

 of iron or copper, by Glauber, who writes as follows : 



" Take of your heavy oil .... as much as you please, 

 put it into a glass body together with plates of copper or 

 iron, set it in a warm sand, and let it boil until that the oil 

 will dissolve no more of the metal, then pour off the liquor, 

 filter it through brown paper, and put it into a low gourd 

 glass and set it in sand, and let the phlegm evaporate until 

 there appear a skin at the top, then let the fire go out, and 

 the glass grow cold, then set it in a cold place, and within 

 some days there will shoot fair Crystals ; if of Iron, greenish ; 

 if of Copper, something bluish ; take them out and dry them 

 upon filtering paper, the remaining liquor, which will not 

 shoot into Vitriol, evaporate again in sand, and then let it 

 shoot as before ; continue this proceeding, until all the 

 solution (or filtered liquor) be turned to Vitriol" (Philoso- 

 phical Furnaces. Part IV; Works, I. 18). 



These two vitriols were described by Lavoisier and his 

 colleagues as SULPHATE OF IRON and SULPHATE OF COPPER, 

 after the acid and metals from which they were derived. 



GLAUBER'S SALT was prepared by the action of oil of 

 vitriol on common salt. When this action was carried out 

 in a glass retort, the salt was separated easily in a pure con- 

 dition by crystallisation. Its discoverer attributed to it 

 almost miraculous properties and called it " sal mirabile." 

 It was afterwards prepared from oil of vitriol and soda, and 

 was therefore called SULPHATE OF SODA. The corresponding 

 salt prepared by the action of oil of vitriol on potash was 

 known in Boyle's time as VITRIOLATED TARTAR, but in 

 Lavoisier's system became SULPHATE OF POTASH. 



GYPSUM or SELENITE (Fig. 10), which could be prepared 



