CLASSIFICATION OF METALS. 251 



Barium, as sulphate. 



Calcium, \ 



Strontium, > As carbonates, sulphates, silicates. 



Magnesium, J 



Aluminum, in silicates. 



Iron, ^ 



Zinc, [ As oxides, carbonates, sulphide. 



Cadmium, J 



Arsenic, 



Antimony, 



Cotit, Chiefly as sulphides. 



Nickel, 



Molybdenum, J 



Chromium, ^ 



Manganese, > Chiefly as oxides. 



Tin, 



Classification of metals. 



For the purpose of study, metals may be differently arranged into 

 groups according to the selection of those properties which are made 

 the basis for comparison. Thus, the valence alone may serve for 

 classification, and in that case the arrangement will also largely cor- 

 respond to the periodic system. The scheme adopted below is based 

 more especially on the analytical behavior of the metals. While 

 this classification brings together in many cases those metals belong- 

 ing to one group of the periodic system, in a few cases the elements 

 of one periodic group are separated, as for instance in the case of 

 magnesium, zinc, and cadmium. These elements resemble one 

 another closely in many respects, and are found together in group 

 II. of the periodic system, while in a classification based chiefly on 

 analytical properties these metals are found in different groups. 



Light metals. Heavy metals. 



Sp. gr. from 6 to 4. Sp gr. from 6 to 22.4. 



Sulphides soluble in water. Sulphides insoluble in water. 



Light metals. 



Earth metals. Alkaline earth metals. Alkali-metal. 



Al, and many rare metals. Ba, Ca, Sr, (Mg). K, Na, Li, (NH 4 ). 



Oxides insoluble. Oxides soluble ; Oxides, carbonates, and 



Carbonates insoluble. most salts soluble. 



Heavy metals. 



Arsenic group. Lead group. Iron group. 



As, Sb, Sn, Au, Pt, Mo. Pb, Cu, Bi, Ag, Hg, Cd. Fe, Co, Ni, Mn, Zn, Cr. 



-v Sulphides soluble in 



Sulphides insoluble in dilute acids. dilute acids. 



Sulphides soluble in am- Sulphides insoluble in 

 monium sulphide. ammonium sulphide. 



