CHAMBERS'S INFORMATION FOR THE PEOPLE. 



large number of the anhydrous acids and anhy- 

 drous bases are oxides, and the anhydrous bases 

 which are oxides are all oxides of metals. 



This brings us to the consideration of the fourth 

 group or family of substances mentioned in 

 p. 307 namely, Metals. 



Like all the other groups which we have 

 examined, the metals possess certain characters 

 in common, by which they may be recognised as 

 belonging to the group ; some of these characters 

 are physical, some are chemical. The most 



metal as an element which forms in combination 

 with oxygen at least one base. There are two 

 general principles which may be mentioned here : 

 I. The more readily a metal unites with oxygen, 

 the more basic is the oxide ; thus, sodium is more 

 easily oxidised than magnesium, magnesium than 

 zinc, zinc than copper, copper than silver ; and 

 soda (oxide of sodium) is a stronger base than 

 magnesia (oxide of magnesium), magnesia than 

 oxide of zinc ; and so on. 2. When a metal 

 forms two basic oxides, we usually find that that 



marked physical characters of the metals are, j which contains the least oxygen is the stronger 

 the ' metallic lustre,' and the readiness with which base. Thus, two of the oxides of iron are bases ; 



they conduct heat and electricity. The metallic 

 lustre is the name given to the peculiar brilliancy 

 of a polished metallic surface. All metals, when 

 polished, shew this lustre ; but some substances 

 which are not metals shew it also. Thus, ' black- 

 lead,' or plumbago, which is not a metal, and is 

 in no way related to lead, but is a fonn of carbon, 

 has a brilliant metallic lustre ; and a considerable 

 number of compounds shew it also, such as iron 

 pyrites and galena. The power of conducting 

 heat and electricity is possessed to a greater or 

 less extent by all substances ; by some, however, 

 to such a small extent, that they are usually called 

 ' non-conductors ; ' as instances, we may mention 

 glass, resin, gutta-percha. The metals differ 

 greatly from one another in ' conductivity,' or the 

 power of conducting heat and electricity ; but they 

 are, as a rule, much better conductors than non- 

 metallic substances. In other physical properties, 

 metals shew great variety in fusibility, ranging 

 from mercury, which is liquid at ordinary tem- 

 peratures, and only freezes at about 40 Fahr. 

 to platinum, which requires the highest tempera- 

 ture we can produce for its fusion ; and osmium, 

 which has not yet been fused. Metals differ 

 greatly in density ; the lightest known simple 

 solid and the heaviest lithium and osmium 

 being both metals. Some metals are malleable 

 and ductile that is, they can be beaten into thin 

 plates or leaves, and drawn into wire, as is the 

 case with gold, silver, copper, and iron ; others 

 are brittle, and can be pounded into a powder in 

 a mortar. This is the case with antimony and 

 bismuth. Most metals are white or gray, but we 

 have yellow gold and red copper. Some are 

 very hard, others very soft. As examples among 

 common metals, we may compare the hard- 

 iron with that of silver, and that of 



ness of 

 lead. 



Let us now turn to the chemical characters of 

 metals. We have just mentioned that all the 

 anhydrous bases which are oxides are oxides of 

 metals. We may now add further, that every 

 metal has an oxide which is a base. It is possible, 

 directly or indirectly, to obtain a compound of 

 each metal with oxygen. Some metals, such as 

 zinc, aluminium, and magnesium, unite with oxy- 

 gen in only one proportion ; others, such as iron, 

 copper, lead, mercury, form each more than one 

 oxide, the various oxides containing the metal and 

 oxygen in different proportions. In the former 

 case, the oxide is a base; in the latter case, at 

 least one of the oxides is a base. Thus, the oxide 

 of zinc, the oxide of aluminium, and the oxide of 

 magnesium, are bases ; two of the three oxides of 

 iron, both of the oxides of copper, one of the 

 three oxides of lead, and both of the oxides of 

 mercury, are bases. We may therefore define a 



312 



one (ferrous oxide) contains iron and oxygen in 

 the proportion of 7 to 2 ; the other (ferric oxide) 

 in the proportion of 7 to 3 ; and the former is the 

 stronger base. 



We shall now examine the action of acids and 

 salts upon metals. The anhydrous acids, as a rule, 

 do not act at all upon metals. There are some 

 exceptions to this rule, which we may have occasion 

 to allude to farther on. The action of the hydrated 

 acids or hydric salts on metals is quite analogous 

 to that of other salts. We shall illustrate this 

 action by one or two examples. If we take a clear 

 colourless solution of nitrate of silver, and place in 

 it a piece of bright clean copper, we see in a few 

 minutes that the copper is covered over with a 

 growth of what looks like soft white moss; this 

 gradually increases, the liquid at the same time 

 becoming blue. The white covering on the copper 

 consists of small scales of silver, and the blue 

 colour of the liquid is due to nitrate of copper. If 

 we take enough copper, we can in this way decom- 

 pose the whole of the nitrate of silver, separating 

 the silver in the metallic state. Again, if we place 

 a piece of clean iron in a solution of nitrate (or 

 sulphate) of copper, metallic copper is deposited 

 on the iron, the blue colour of the solution dis- 

 appears, and we have a solution of nitrate (or 

 sulphate) of iron.* Again, if we place a piece of 

 iron in a solution of hydrated sulphuric acid (oil of 

 vitriol), that is, hydric sulphate, we have hydrogen 

 gas given off, and sulphate of iron remains in 

 solution. In each of these cases we have one 

 metal driving out another, and taking its place, f 

 Copper drives out silver, iron drives out copper, 

 and iron drives out hydrogen. In each such case, 

 the metal which drives the other out is said to be 

 ' positive ;' that which is driven out is said to be 

 ' negative.' Thus, silver is negative to copper ; 

 copper is positive to silver, but negative to iron ; 

 iron is positive to copper ; and so on. By means 

 of a number of experiments of this kind, we can 

 arrange the metals in a series, beginning with 

 the most negative, and ending with the most 

 positive. If we examine this series, we find that 

 the more ' positive ' a metal is, the more basic is 

 its most basic oxide. So that just as a strong 

 base drives out a weak one, so the metal of 

 a strong base drives out the metal of a weak 

 one. 



We have hitherto looked upon salts as com- 

 pounds of acids and bases, but the reader will now 

 see that they may also be represented in another 



* This action may be taken advantage of to detect copper in a 

 solution : thus, a steel fork is covered with a red deposit of copper 

 when it is dipped in a jar of picldes which have been coloured green 

 by means of copper. 



t We here speak of hydrogen as a metal. Chemically it is so, 

 for water (the oxide of hydrogen) acts as a base, and substances 

 have been obtained which may be regarded as alleys of hydrogen. 





