CHAMBERS'S INFORMATION FOR THE PEOPLE. 



amethyst. Emery is corundum mixed with ferric 

 oxide. Combined with water, it forms the min- 

 erals diaspore and gibbsite. Clay is a silicate of 

 alumina, and is formed in nature by the decom- 

 position of felspar. There are three chief species 

 of felspar potash felspar, soda felspar, and lime 

 felspar silicates respectively ot alumina and pot- 

 ash, alumina and soda, and alumina and lime. 

 Sulphate of alumina (concentrated alum) is formed 

 by the action of sulphuric acid on clay. Common 

 alum is a double sulphate of alumina and potash 

 (K 2 0,S0 3 ,A1 2 3 ,3S0 3) 24H 2 0). 



Uranium occurs in the mineral pitchblende, 

 which is essentially an oxide corresponding to 

 magnetic oxide of iron (UOjUgOs). This oxide is 

 used for producing an intense and permanent 

 black colour on porcelain. Uranic oxide (U 2 O 3 ) 

 forms a silicate of a yellowish green colour, and 

 is used to give this colour to glass. 



4. Copper Group. Copper forms two basic 

 oxides cuprous oxide, red oxide of copper (Cu 2 O), 

 and cupric oxide, black oxide of copper (CuO). 

 There are two corresponding oxides of mercury 

 (Hg 2 O and HgO), but silver forms only one basic 

 oxide (Ag 2 O), peroxide of silver (AgO) not being a 

 base. The only basic oxide of lead is that corre- 

 sponding to cupric oxide namely, plumbic oxide 

 (PbO).* Copper occurs free, as 'native copper,' 

 in large quantities in North America, particularly 

 in the neighbourhood of Lake Superior ; in com- 

 bination with oxygen, as cuprous oxide (red copper 

 ore), in Siberia, in Cornwall, and in Australia ; as 

 cupric oxide (CuO), near Lake Superior ; as car- 

 bonate (malachite, lazurite) ; combined with sul- 

 phur as 'gray sulphide of copper' (Cu 2 S) in 

 Cornwall ; along with sulphide of iron as copper 

 pyrites (CuFeS 2 ), the most abundant of all the 

 copper ores, in Cornwall, Devonshire, Sweden, 

 and many parts of the United States ; along with 

 sulphide of antimony and sulphide of arsenic as 

 sulphantimonite and sulpharsenite of . copper, in 

 the so-called ' fahl ore.' 



The most important salts of copper are the 

 cupric salts : Cupric sulphate (CuO, SO 3 or CuSO 4 ), 

 formed by the oxidation of sulphide of copper, or 

 by the action of strong sulphuric acid at a high 

 temperature on metallic copper (Cu -f- 2H 2 SO 4 = 

 CuSO 4 + 2H 2 O + SO 2 ). It crystallises as blue 

 vitriol or blue stone with five molecules of water, 

 one of which is water of halhydration (p. 316). 

 Cupric nitrate (CuO,N 2 O 5 or Cu(NO 3 ) 2 ), formed 

 by the action of nitric acid on metallic copper 

 (p. 321), or on cupric oxide (3Cu-f4(H 2 O,N 2 O 5 )= 

 3(CuO,N 2 5 )+2NO+4H 2 ; CuO+H 2 O,N 2 O 5 = 

 H 2 O -f- CuO,N 2 O 5 ), is a blue salt, which, when 

 heated, gives cupric oxide, peroxide of nitrogen, 

 and oxygen (CuO,N 2 O 6 = CuO + 2NO 2 + O). 



Mercury occurs in nature free as native mer- 

 cury, but much more frequently as cinnabar, the 

 mercuric sulphide (HgS). The most important 

 compounds of mercury are : Mercuric sulphate 

 (HgO,SO 3 ), formed by the action of strong sul- 

 phuric acid at a high temperature on metallic 

 mercury (Hg+2H 2 SO 4 = HgSO 4 +2H 2 O+SO 2 ) ; 

 mercuric chloride (corrosive sublimate, HgCl 2 ), 

 formed by heating common salt with mercuric 

 sulphate(HgO,SO 3 +2NaCl=Na 2 O,SO 3 +HgCl 2 ); 

 the corrosive sublimate being volatile, rises in 



* It is with some hesitation that we place lead in this group ; the 

 characters of the lead salts would incline us to group it with 

 calcium, strontium, and barium. 

 330 



vapour, and is condensed in the cold parts of the 

 apparatus. It is soluble in water, and very 

 poisonous. The mercurous salts are formed by 

 adding metallic mercury to the mercuric salts ; 

 thus, calomel (mercurous chloride, HgCl) may be 

 formed by heating 271 parts of corrosive sub- 

 limate with 200 of mercury (HgCl 2 +Hg=2HgCl) r 

 or by heating mercuric sulphate with metallic 

 mercury and common salt (HgSO 4 +Hg+2NaCl= 

 Na 2 SO 4 + 2HgCl) ; the calomel is volatile, and 

 sublimes, collecting on the cold parts of the 

 apparatus. It is insoluble in water, and can r 

 therefore, be freed from any corrosive sublimate 

 which may be mixed with it by washing with 

 water. Vermilion is mercuric sulphide. 



Lead occurs chiefly as galena (plumbic sulphide, 

 PbS). It forms three oxides : I. Plumbic oxide 

 (litharge, massicot, PbO). This is produced when 

 lead is strongly heated in air or oxygen. When 

 fused, it forms brown scales (litharge) ; when 

 prepared at a lower temperature, so that it is not 

 fused, it is a yellow powder (massicot). It is the 

 only basic oxide of lead. 2. Red lead. This oxide 

 is formed when litharge is exposed at a tempera- 

 ture considerably below its fusing-point to the 

 action of air or oxygen ; its composition is some- 

 what variable, but corresponds pretty closely to 

 the formula Pb 3 O 4 . It may be regarded as a 

 compound of plumbic oxide and the third oxide 

 of lead, peroxide of lead. When treated with 

 nitric acid, it forms plumbic nitrate and per- 

 oxide of lead (2PbO,PbO 2 + 2(H 2 O,N 2 O 6 ) = 

 2(PbO,N 2 O 5 ) -f 2H 2 O + PbO 2 ). White-lead is a 

 compound of carbonate of lead and hydrated oxide 

 of lead. It is formed by exposing metallic lead 

 to air, carbonic acid, water-vapour, and the vapour 

 of vinegar. Sulphate of lead (PbO,SO 3 ) is in- 

 soluble in water ; for this reason, persons working 

 in lead are recommended to add a small quantity 

 of sulphuric acid to the water they drink, as the 

 insoluble sulphate is not poisonous. Sulphide of 

 lead is black, and all pigments containing lead are 

 blackened by sulphuretted hydrogen, on account 

 of the formation of the sulphide. Chrome yellow 

 is chromate of lead (PbO,CrO 3 ). 



Silver occurs in nature free as native silver, as 

 chloride in ' horn silver,' as sulphide (Ag 2 S) both 

 alone and mixed with other sulphides, most 

 specimens of galena (sulphide of lead) containing 

 some silver, also in fahl ore as sulphantimonite of 

 silver. The most important compounds of silver 

 are : Nitrate of silver (Ag 2 O,N 2 O 5 ), formed by the 

 action of nitric acid on silver (6Ag -f- 4H 2 O,N 2 O 5 

 = 3(Ag 2 O,N 2 Og) + 2NO + 4H 2 O). It is" soluble 

 in water, and is used in photography, and as a 

 mild caustic (lunar caustic) in surgery. Chloride 

 of silver (AgCl) is insoluble in water and acids, 

 soluble in ammonia. British 'standard silver,' of 

 which our silver coins are made, is an alloy of 

 silver and copper, containing in 100 parts, 92-5 of 

 silver and 7-5 of copper. It is harder than pure 

 silver. 



5. Of the Platinum group, we need only men- 

 tion gold and platinum. These metals occur 

 chiefly free, as native gold and native platinum. 

 They are not dissolved by either nitric or hydro- 

 chloric acid, but are converted into chlorides (AuCl 3 

 and PtClJ by the action of chlorine, or of a mix- 

 ture of nitric and hydrochloric acids (aqua regia). 

 These chlorides unite with the chlorides of the 

 metals of the alkalies, forming double salts, as,. 



