vitriols. 103 



2. Metallosalixes. 



These embrace the preparation of various metallic salts, 

 which are chiefly employed for dyes or making pigments. We 

 may most conveniently divide the subject into the vitriols, or 

 sulphates of iron, copper, zinc, and manganese, with the pig- 

 ments derived from them ; the salts and pigments of lead ; 

 the prussiates ; the chromates, and a few others. 



1. Vitriols. — Copperas, green vitriol, or protosulphate of 

 iron, is made directly from sulphuric acid and scrap-iron, or 

 from calcined pyrites, or is obtained in the kindred and con- 

 nected manufacture of alum. These two articles are made on 

 an extended scale in the United States, and but little can be 

 offered that is new in relation to them. 



Copperas. — It may be freed from lead and copper, and at 

 the same time all peroxide of iron reduced to protoxide, by 

 boiling its solution with good scrap-iron, nails, &c. until it 

 becomes light and green. By evaporating the solution, it 

 then yields bluish-green crystals. The precipitate will contain 

 the copper, lead, &c. (Encycl. Zeitschr. d. Gewerbehandl. 

 1846.) 



Preservation of Copperas. — According to Ruspini (Journ. 

 de Chim. Med. vi.) the protosulphate of iron, when in crystals, 

 may be preserved from oxidation, by pressure, desiccation 

 between the folds of bibulous paper, and, finally, efflorescence 

 in a drying chamber at 86°. It is to be kept in well-stoppered 

 bottles. 



Oxidation of Copperas. — According to Wittstein (Buchner's 

 Report, i.) a solution of 1 pt. protosulphate of iron in 4 pts. 

 water, after 11 months' exposure in a loosely covered vessel, 

 deposits 2Fe,03 + 3S03+8IIO, and not 2Fe,03-f SO^, as is ge- 

 nerally admitted. 



Sulphate of zinc, or white vitriol, is made directly from zinc 

 and sulphuric acid. 3Ianganese vitriol is made directly from 

 black oxide of manganese and oil of vitriol, or it is obtained 

 as a residue in making bleaching-salt from manganese, salt, 

 and oil of vitriol. Blue vitriol, or sulphate of copper, is made 



