583 



METALS. 



METALS. 



CLASS 2 Metals which do not decompose water under 212, but far 

 below a red heat : 



Aluminium 

 Glucinum 



Thorinum 



Yttrium 



Zirconium 



Lantlianium 



Cerium 



Manganese 



Magnesium 



CLASS 3. Metals which do not decompose water except at a red 

 heat, or at common temperatures in contact with strong acids : 



Iron 



Kickel 



Cobalt 



Zinc 



Cadmium 



Tin 



Chromium 

 Vanadium 



CLASS 4. Metals which decompose water at a red heat, but not at 

 common temperatures, even in contact with strong acids: 

 Tunjfst n Tantalum Antimony 



Molybdenum Titanium Tellurium 



Osmium Arsenic Uranium 



CLASS 5 Metals which do not decompose water even at a red heat, 

 and whose oxides are not reduced by heat alone : 



Copper Lead Bismuth 



CLASS 6. Metals which do not decompose water under any circum- 

 stances, but whose oxides are reduced by heat : 



Silver Gold Flatinntn 



Mcicnry Palladium Rhodium 



Iridium 



The special characters of the metals ; their farther relation to, and 

 action upon, one another ; the action of metalloids, acids, &c , upon 

 them individually; and the formation, properties, use, 4c., of their 

 compounds, will be found described under their respective names, 

 with the exception of iron, which we shall now proceed to describe. 



Iron (Fe). In combination with other bodies, iron is perhaps more 

 widely diffused than any of the metals. It is found in the ashes of 

 nearly all plants, is a constant constituent of the blood of the vertebrate 

 animals, and although only a few of its ores are economically made use 

 of, they are more numerous th^n those of any other of the heavy 

 metals. [Inox, in NAT. HIST. Div.] The range of affinities of iron is so 

 great that it is very rarely met with in the uncombined state, and it is 

 only with considerable difficulty that it can be artificially obtained in 

 an absolutely pure condition. The process recommended by Berzelius 

 for preparing chemically pure iron consists in heating filings of the best 

 bar iron with pure oxide of iron under a layer of powdered green glass 

 in a Hessian crucible : the whole being subjected to the highest tempe- 

 rature of a smith's forge, the filings are deprived of their carbon and 

 silicon by the oxide, and fusing together collect at the bottom of the 

 crucible in a button possessing silver-like lustre and whiteness. Iron 

 thus prepared has a specific gravity of 7'8439, and is very tough and 

 much softer than the ordinary metal. Another method of procuring 

 perfectly pure iron is by passing a current of hydrogen gas over pure 

 peroxide of iron, heated carefully to redness : if the temperature is too 

 low the resulting product inflames spontaneously on coming in contact 

 with the air, but when prepared at a h.gher temperature may be kept 

 unaltered ; in this state it is sometimes used in medicine, under the 

 name of Quevenii'* //'></, /-' / /"/,/>, or Pulvisferri. 



1'i'i, cant, moll able, and rolled iron are the ordinary states of thi 

 metal met with in commerce ; their manufacture and properties have 

 already been described. [IiioN MAXCFACTI/UK AND TIIAOE ] In one 

 or more of these conditions iron has been known from the most remote 

 period. Cutting instruments made of this metal are mentioned in the 

 books of Moses. The method of reducing and forging iron is described 

 in Homer and Hesiod, and Pliny's '(Natural History' contains a long 

 article on the subject The alchymists considered it to be a compound 

 of gold and the hypothetical body acrimony, and symbolised it there- 

 fore by the sign & ; they gave it the name of Mars, probably because 

 weapons made of it were used in the service of the god of war. 



Iron has a white or grayish white colour. When tolerably pure, as 



in bar-iron, it is very difficult of fusion, but at a white heat possesses 



the valuable property of welding; that is, two pieces brought into 



contact at that temperature, and well pressed together by hammering, 



unite aa perfectly as if they had been joined by melting. The heat of 



the oxyhydn>gen blowpipe or of the voltaic arc, however, is sufficient to 



even volatilise iron. Iron can be beaten out into tolerably thin sheets, 



uot nearly so malleable as gold or silver. It is very ductile, 



being ca]>able of being drawn into thinner wire than that of any other 



In tenacity also it is unsurpassed, a wire of one thirty-sixth of 



an inch in diameter sustaining a weight of sixty pounds before breaking. 



readily conducts heat and electricity, but is inferior in these 



respects to some other metals. It is attracted by the magnet, and may 



be rendered permanently magnetic; the latter property is 



dfstrnyed on heating the metal to redness, but is recovered again on 



cooling. 



Under the influence of air and moisture iron rapidly attracts oxygen, 

 or null, especially after the first spot has been produced. The exact 

 action that goes on is not very well madu out ; it appears probable 

 that the peroxide first formed is reduced to the state of protoxide by 

 tip- pirticles of the metal with which it U immediately in contact, the 

 protoxide so produced absorbing oxygen from the air and being re-con- 



AUTS A.ND SCI. DIV. VOL. V. 



verted into peroxide ; in short, that the peroxide of iron protoxidises 

 the metal and that the air peroxidises the protoxide. The carbonic 

 acid present in the air also plays an important part in the rusting of 

 iron. This liability of iron to rust is perfectly prevented by keeping 

 it dry ; but the object is most commonly effected by constant removal 

 of the surface of oxide by polishing powders, such as emery or brick- 

 dust, or by enveloping the metal in a covering of plumbago, a mechanical 

 process known in domestic life as blackleading. 



Iron decomposes water at a red heat, hydrogen being evolved, and a 

 black oxide of iron produced. Diluted sulphuric, hydrochloric, nitric, 

 and other acids dissolve iron, with evolution of hydrogen or, in the 

 case of nitric acid, of binoxide of nitrogen. Strong nitric acid, how- 

 ever, does not act upon iron, the metal remaining in what is termed 

 the i"i-viri: c <d><tin;a condition that seems to be intimately connected 

 with the electrical relations of this metal. 



Wrought iron, steel, and cant irun differ from each other chemically 

 chiefly in the amount of carbon they contain. Thus wrought iron 

 contains only from about 0'2 to 0'4 per cent. ; steel, from 1'3 to 1'5; 

 while cast-iron sometimes contains as much as 5'0 per cent, of carbon. 

 From recent researches it appears that to the presence of a greater or 

 smaller quantity of titanium is owing the value of iron used for 

 making steel, and that titanium moreover confers other important 

 properties on iron. Iron also sometimes contains silicon, sulphur, 

 phosphorus, arsenic, and traces of other metals, such as aluminium, 

 calcium, potassium, manganese, &c., but these deteriorate its quality. 



The combining equivalent of iron is 28, and its symbol (Fe), (from 

 ferrum, Lat). It unites with other elements and compounds, chiefly 

 in two proportions, forming respectively protosal/s and permits. In the 

 former the constituents are equal in number; in the latter, two 

 equivalents of iron are associated with three of the other body, and for 

 that reason are sometimes called sesquisalts. 



Iron and oxygen form three definite compounds : 



1 . Protoxide of iron 



2. Peroxide of iron 



3. Ferric acid . 



FeO 



Fe.0 3 



FeO., 



A fourth is also sometimes described, it contains Fe 3 0,, and is termed 

 the black or magnetic oxide, but it does not form salts, and may be 

 viewed as a combination of one equivalent of protoxide with OUR of 

 peroxide (FeO + Fe 2 3 = Fe 3 04). It is in fact formed by precipitating 

 a solution of equivalent quantities of a proto and per-salt by an alkali . 

 The natural form of this oxide is the well-known mineral iuadstunc, 

 and is the valuable ore from which Swedish iron is smelted. 



1. Pr toxiile of iron (ferrous o.cide) (FeO). This body, though a very 

 powerful base, and forming, with acids, a well-marked class of com- 

 pounds called salts of protoxide of iron, is nevertheless not known in 

 the sep irate state, so readily does it take up oxygen and form peroxide. 

 In the hydrated state fFeO.HO) it is precipitated in white flocks on 

 adding an alkali to a solution of a protosalt of iron. If care is not 

 taken to exclude every trace of air from the liquid used in its pre- 

 paration it is contaminated with more or less peroxide, and then falls 

 down as a light green or blue precipitate. In contact with air it 

 gradually becomes entirely converted into red peroxide. 



2. Ptnendt of iron (sesqitiixide or ferric o.cide) (Fe,0.,). This 

 oxide occurs native as hrcmatite, specular iron ore, &c. [litox, in NAT. 

 HIST. L>iv.] It is artificially prepared by heating the hydrate, or by 

 igniting the protosulphate. Under the names of colcothnr, crocus of 

 Mars, roiiye, &c., it is largely used as a pigment, and for polishing glass 

 and jewellery. The hydruted oxide (Fe 2 O 3 i HO) is best prepared by 

 precipitating a solution of the perchloride or persulphate with 

 ammonia, well washing and gently heating. When first precipitated 

 this hydrate is very flocculent and bulky, but contracts remarkably on 

 drying. It hns a dull red colour, not nearly so bright as the anhydrous 

 oxide. It forms salts with acids, but is a weaker base than the 

 protoxide. 



Hydrated peroxide of iron is now largely used for the purification 

 of coal-gas. [GAS-LIGHTING.] 



'A. Ferric acid (FeO,) is not known in the free state. Combined 

 with potash it is obtained on heating to bright redness peroxide of 

 iron with four times its weight of nitrate of potash. It is very soluble 

 in water, forming a dark violet solution. Other ferrates are produced 

 by double decomposition ; they are all uncrystallisable and very 

 unstable, readily yielding up their oxygen, especially to organic 

 matter. 



Iron and sulphur combine in several proportions. The two most 

 important sulphides are : 



1. Protosulphide of iron ..... FeS 



2. Bisulphide of iron FcS,, 



1. Protoiu/.phidc of iron (FeS) is a bye-product in certain mctallurgio 

 operations with copper. It is of little value, being chiefly employed 

 in chemical laboratories for the generation of sulphuretted hydrogen. 

 For this purpose it is sometimes prepared by fusing together equivalent 

 proportions of iron (filings) and sulphur, or better, by rubbing rolls of 

 sulphur on a bar of iron heated to whiteness in a smith's forge, tho 

 liquid sulphide being allowed to flow down into cold water. 



2. Bimlplude of iron (FeS s ) (iron jiyri/ct) occurs native in beautiful 

 brass-yellow crystalline masses. It is valueless as a source of metal, 



QQ 



