262 METALS. 



this gag is given up. As the ores are often impure, it Is important 

 to ascertain their value in this respect. This is most leadily done by 

 heating gently the pulverised ore with muriatic acid, and ascertaining 

 the amount of chlorine given off. The chlorine may be made to pass 

 into milk of lime, to form a chlorid, and the value of the chlorid then 

 tested according to the usual modes. The amount of chlorine derived 

 from a given quantity of muriatic acid depends not only on the amount 

 of oxygen in the ore, but also on the presence or absence of baryta and 

 such other earths as may combine with this acid. The binoxyd of man- 

 ganese when pure, affords 18 parts by weight of chlorine, to 22 parts 

 of the oxyd ; or 23£ cubic inches of gas from 22 grains of the oxyd. 

 The best ore should give about three-fourths its weight of chlorine, or 

 about 7000 cubic inches to the pound avoirdupois. 



The chlorine for bleaching is used commonly in combination with 

 lime. To make the chlorid of lime, the chlorine is generally obtained 

 either through the action of muriatic acid on the oie, (3 to 4 parts by 

 weight of the former, to 1£ of the 'latter,) or more commonly by mix- 

 ing 1 part of the ore with 1\ parts of common salt, 2 or 2\ parts of con- 

 centrated sulphuric acid, and as much water. As the chlorine passes 

 off, it is conveyed into chambers containing slaked lime, by which it ia 

 absorbed. 



Manganese is also employed to give a violet color to glass. The 

 sulphate and the chlorid of manganese are used in calico printing. The 

 sulphate gives a chocolate or bronze color. 



The best beds of manganese ores in the United States, which have 

 been opened, are at Brandon, Chittenden, and Irasburg, Vt. 



16. CHROMIUM. 



The ores of chromium are the chromates of lead and 

 chromic iron, which are described under Lead and Iron. 

 There is also a native chromic ochre, supposed to consist of 

 silica chromic acid, alumina, and iron. Wolchonskoite is an 

 allied mineral. Miloschine or Serbian is considered a chro- 

 miferous clay. 



17. NICKEL. 



The ores of nickel, excepting one or two, have a metallic 

 luster, and pale color ; their specific gravity is between 3 

 and 8, and hardness mostly between 5 and 6, (in one, aboul 

 3.) They resemble some cobalt ores, but do not like them 

 give a deep blue color with borax. 



How is manganese used? For what other purpose is mangane:-* 

 used 1 What is said of the ores of chromium 1 What if said of th 

 ores of nickel 1 



