LESSONS IN CHEMISTRY. 165 



Ferrous sulphate (FeS0 4 -f7H 2 0) is commonly known as 

 green vitriol or copperas. It is manufactured from iron pyrites, 

 so common in the coal measures. It is used in the manufacture 

 of ink and black dyes. There are ferrous and ferric oxides and 

 chlorides, sulphates, nitrates and silicates, and many other in- 

 teresting compounds of iron, but they are of little value in the 

 arts and need not be discussed. 



Iron oxides, hydrates and other compounds yield a large 

 variety of colors, and these compounds are so abundant every 

 where that iron has been called the pigment of nature. 



There are ferrous and ferric cyanides of iron. Common Prus- 

 sian blue seems to be a mixture of these cyanides, formula 

 (Fe 7 C 18 N 18 ). It is largely used in dyeing and calico printing. 

 Potassium ferrocyanide is a mordant of great value. 



NICKEL (Ni)is a metal sometimes found in meteoric iron, and is 

 found associated with cobalt arsenic and sulphur. It is chiefly 

 valuable from its property of imparting a white color to alloys 

 of copper and zinc, as German silver and the five-cent coins. The 

 salts of nickel form green solutions. 



COBALT (Co) is a metal somewhat similar to iron, but is not 

 abundant enough to be of great value, but some of its com- 

 pounds are important on account of their brilliant and perma- 

 nent colors. The salts of the oxides have a fine red color in the 

 hydrated state, while they are blue in the anhydrous. Cobalt 

 blue is the more common color. Chloride of cobalt is used as a 

 sympathetic ink. It has a slight pink color when cold and turns 

 blue when heated. 



MANGANESE (Mn) is a hard, grayish-white metal resembling iron 

 in some of its physical and chemical qualities, and is often asso- 

 ciated with iron in nature. The principal ore of Manganese is 

 the dioxide, Mn0 2 . The compounds of Manganese give up their 

 oxygen readily ; the use of the dioxide in preparing oxygen has 

 been noted. One of the most interesting and valuable com- 

 pounds of Manganese is potassium per manganate, KMn0 4 ; it 

 is soluble in water, forming a dark purple solution. It gives up 

 its oxygen easily, losing its color, and is much used in purifying 



