CHEMISTRY. 



oxides (manganese, MnO and Mn 2 O 3 ; chromium, 

 CrO and Cr 2 O 3 ; and Uranium, UO and U 2 O 3 ) ; 

 some have only the oxide corresponding to ferrous 

 oxide (magnesium, MgO ; zinc, ZnO ; cadmium, 

 CdO) ; while aluminium has only the oxide cor- 

 responding to ferric oxide, A1 2 O 3 . Nickel and 

 cobalt form both oxides, NiO and Ni 2 O 3 ,CoO 

 and Co 2 O 3 ; but the peroxide of cobalt has scarcely 

 any basic character, and the peroxide of nickel has 

 none. 



Magnesium occurs in nature in the carbonate 

 of magnesia (MgO,CO 2 ), the mineral magnesite, 

 and associated with carbonate of lime in magne- 

 sian limestone, or dolomite ; in the sulphate of 

 magnesia (Epsom salts, MgO,SO 3 ,7H 2 O), which 

 is found in many mineral waters. Chloride and 

 bromide of magnesium occur in small quantities 

 in sea-water. Steatite and meerschaum are sili- 

 cates of magnesia. The soluble salts of magnesia 

 have a peculiar bitter taste. The metal magne- 

 sium can be obtained by the electrolysis of fused 

 chloride of magnesium, or by the action of sodium 

 on chloride of magnesium (MgCl 2 -f- 2Na = 

 2NaCl + Mg). It is a bright white metal, of 

 specific gravity 175 ; when heated to redness in 

 air or oxygen, it takes fire, burning with an in- 

 tensely bright white light, and producing mag- 

 nesia. 



Zinc occurs in nature as zincblende (sulphide 

 of zinc, ZnS), carbonate of zinc (ZnOjCO^, and 

 silicate of zinc. The method of obtaining it from 

 its ores is described in the article METALS AND 

 METALLURGY. Its oxide (ZnO) is formed when 

 the metal is strongly heated in air or oxygen. 

 Sulphate of zinc (white vitriol) is formed when 

 the oxide is dissolved in sulphuric acid, or when 

 sulphuric acid (hydric sulphate) or cupric sulphate 

 acts on metallic zinc : Zn -f- H 2 SO 4 = H 2 + ZnSO 4 

 or Zn + CuSO 4 = Cu + ZnSO 4 . It crystallises 

 (like Epsom salts) with seven molecules of water, 

 of which one is water of halhydration, and can be 

 driven off only at a high temperature. Chloride 

 of zinc, ZnCl 2 , formed by dissolving oxide of zinc 

 or metallic zinc in hydrochloric acid (ZnO -f- 2HC1 

 = H 2 O + ZnCl 2 or Zn + 2HC1 = H 2 + ZnCl 2 ), is 

 a very soluble salt ; it is used in surgery as a 

 caustic, and a strong solution of it is sold under 

 the name ' Burnett's Disinfecting Solution.' 



Cadmium usually occurs in nature along with 

 zinc, which it greatly resembles. The sulphide of 

 cadmium (CdS) is yellow, and is used as a pig- 

 ment. 



Iron occurs in nature free as native iron, prob- 

 ably always in the form of meteoric masses which 

 have fallen upon the earth. We know nothing of 

 the origin of these meteoric stones ; they appear 

 to have been bodies moving through space, which, 

 coming into the earth's atmosphere, have been 

 attracted to the earth, and so have fallen upon its 

 surface. Iron occurs in combination with oxygen 

 as ferric oxide (red haematite, specular iron ore, 

 Fe 2 O 3 ) ; as hydrated ferric oxide (limonite, goethite, 

 brown haematite) ; as magnetic iron ore, or fer- 

 roso-ferric oxide (FeO,F 2 O 3 ). Ferrous carbonate 

 (FeO,CO 2 ) occurs pure in spathic iron ore, mixed 

 with clay in the clay iron ore, and mixed with coal 

 in the black-band iron-stone ; ferrous silicate occurs 

 in many minerals. The most abundant compound 

 of iron and sulphur is iron pyrites (FeS^. The 

 most important compounds of iron (not treated of 

 in the paper on METALS AND METALLURGY) are : 



i. The Ferrous Compounds : Ferrous Sulphide 

 (FeS), formed by the direct union of iron and 

 sulphur heated together, a black, fusible substance, 

 used as a source of sulphuretted hydrogen, which 

 is easily obtained from it by treating it with dilute 

 acids, thus : FeS + H 2 SO 4 = H 2 S + FeSO 4 . Fer- 

 rous Carbonate ; see above. Ferrous Sulphate 

 (green vitriol), formed by the action of dilute sul- 

 phuric acid on iron or on ferrous sulphide 

 (Fe + H 2 S0 4 + H 2 + FeS0 4 or FeS + H 2 SO 4 

 H 2 S + FeSO 4 ), also by the oxidation of iron 

 pyrites in the presence of water (FeS, + H,O 

 + 70 = FeS0 4 + H 2 S0 4 ), also by the action of 

 cupric sulphate on metallic iron (Fe -f CuSO 4 

 = Cu + FeSO 4 ) ; green vitriol crystallises (like 

 Epsom salts and white vitriol) with seven mole- 

 cules of water, six of which are water of crystal- 

 lisation, and one water of halhydration. 2. Ferric 

 Compounds : Ferric Oxide (Fe 2 O 3 ) occurs in 

 nature as red haematite. Ferric Chloride (FeClj) 

 is formed by dissolving ferric oxide in hydro- 

 chloric acid (Fe 2 O 3 + 6HC1 = 3H 2 O + 2FeC\^), 

 or by oxidising ferrous chloride in the presence of 

 hydrochloric acid (2FeCl 2 + 2HC1 -f- O = 2FeCl 3 

 + H 2 O). Ferric chloride is the substance often 

 called muriate of iron, and is used in medicine a 

 solution of it in weak alcohol is sold as 'steel drops.' 

 The 'rust' of iron is a ferric compound, being 

 a hydrate of ferric oxide, and having nearly the 

 same composition as the mineral limonite. Ferric 

 oxide is a comparatively weak base, and (see p. 

 308) acts also as a weak (anhydrous) acid. So we 

 have compounds of ferric oxide with stronger 

 bases as with magnesia in magnesic ferrite 

 (MgO,Fe 2 O 3 ) ; with ferrous oxide in magnetic 

 iron ore (FeO,Fe 2 O 3 ) ; with oxide of zinc in frank- 

 linite, &c. 3. We have a series of salts (of which 

 only a few are known), the Ferrates, as ferrate of 

 potash (K 2 O,FeO 3 ), in which iron appears to 

 play the part of sulphur K 2 O,FeO 3 correspond- 

 ing to sulphate of potash, K 2 O,SO 3 . 



Manganese. The most important compounds 

 of manganese are : i. Peroxide of Manganese 

 MnO 2 ), which has been already mentioned (p. 

 324) as used in making chlorine. 2. The Man- 

 ganous Salts, corresponding to the ferrous salts, 

 as MnO,SO 3 ; MnCl 2 ; &c. 3. Manganic Salts, 

 which easily lose oxygen, and are transformed 

 into manganous salts (as Mn 2 O 3 ,3SO 3 -f- H 2 O 

 = 2(MnO,SO 3 ) + H 2 O,SO 3 + O). 



Chromium occurs in nature chiefly as chrome 

 iron ore (FeOjCr-jO^, a compound in which 

 chromic oxide (Cr 2 O 3 ) acts as an acid. Its most 

 important compounds are the chromates, corre- 

 sponding to the ferrates or sulphates, as chromate 

 of potash (K 2 O,CrO 3 ), bichromate of potash 

 (K 2 O,2CrO 3 ). Chrome yellow is chromate of lead 

 (PbO,CrO 3 ). Chromic acid, a red crystalline sub- 

 stance (CrO 3 ), is a powerful oxidising agent, easily 

 giving up half of its oxygen to form chromic oxide 

 (Cr 2 3 ). 



Nickel and Cobalt have already been referred to 

 as forming compounds perfectly analogous to the 

 ferrous salts. Silicate of cobalt is remarkable for 

 its intense blue colour ; in the state of fine powder 

 it forms the pigment ' smalt.' 



Aluminium. The most important compounds 

 of this metal are its oxide alumina (Al^Os) and 

 the salts of this oxide. Alumina occurs in nature 

 pure as ' corundum ;' coloured by small quantities 

 of other oxides, as sapphire, topaz, ruby, and 



