Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/545

Rh INDIUM.] CHEMISTRY 533 nium hydroxide is converted into aluminium oxide or alumina, A1.,O 3 ; if it has been exposed only to a moderate red heat the alumina is a soft, white, light powder like magnesium oxide, and is soluble in acids ; but after strong ignition it becomes very hard and insoluble, or difficultly soluble, in acids. Alumina occurs native as corundum in crystals isomorphous with the corresponding oxides of chro mium andiron ; in the crystalline state it is the hardest sub stance known next to the diamond, and insoluble in all acids, but like silica it is dissolved on fusion with alkalies. The only reactions which, in the case of aluminium, have been submitted to thermochemical investigation are Reaction. Units of heat developed. A1 2, Clg 321,870 AloClj;, Aq 153,690 Al 2 ,6H01Aq 239,640 A1 2&amp;gt; 3, 3H 2 388,800 Al a, O fi ,H 6 593,880 A1 2 (OH) 6, GHClAq 55,920 Al 2 (OH) ti, 3S0 3 Aq 62,970 SiCl 4 ,Aq = 81,640 BCl 3 ,Aq = 79,200 A1 2 C1 6, Aq = 153,690 A.i= 35,920 I SiCl 4, Aq = 61,230 BC1 3, Aq = 79,200 I Al 2 Clg, Aq = 76,845 14 JlgCl 2, Aq = 53,780 It may be remarked also that magnesium and aluminium both form very soluble sulphates, which readily combine with other sulphates. Indium is easily reduced from its oxide by hydrogen, and is precipitated from solutions of its salts by cadmium and zinc. It is an extremely rare metal, and occurs always associated with zinc. It is a soft, ductile, white metal, destitute of crystalline structure, much resembling lead iu appearance. It rapidly dissolves in concentrated hydrochloric acid, slowly in dilute nitric and sulphuric acids. It melts at 176 C., but is much less volatile than cadmium, and may be melted in the air without oxidizing; at a bright red heat it burns with a violet flame form ing a yellow oxide, In 2 O 3. Indium chloride, In 2 Cl 6, sublimes without fusion at an incipient white heat, condensing in soft white laminae. Indium oxide, In 2 O 3, is not volatile even at a white heat ; it is readily soluble in acids. It is stated that by heating in a stream of hydrogen the oxides In 7 O 9, In 4 O 5 , and InO 2 are in succession formed from it, but their existence as definite compounds has not been satisfactorily established. Indium hydroxide separates as a white gelatinous precipitate on the addition of ammonia to cold solutions of indie salts ; it is soluble in alkalies, and on ignition is converted into the oxide In 2 O 3. Indium sulphate forms with ammonium sulphate a double sulphate In 2 (XH 4 ) 2 (SO 4 ) 4 ,24H. 2 O, iso- morphous with the alums; when heated only to 36 C., however, this salt is converted into one containing only 4 molecules of water of crystallization. On passing hydrogen sulphide into solutions of indium a yellow precipitate is obtained, which is decomposed by hydrochloric acid ; no precipitate is produced when alumi nium salts are similarly treated, aluminium sulphide being at once decomposed by water and converted into the hydroxide. CHROMIUM MANGANESE IKON COBALT XICKEL. The resemblance of aluminium to boron, silicon, and magnesium is most evident when the oxides and chlorides are compared. Thus, their oxides are all bodies of great stability, and, excepting magnesium oxide, possess marked acid properties ; and their chlorides behave similarly when added to water, boron and silicon chlorides being entirely decomposed, and aluminium and magnesium chlorides at least partially, the reaction in each case being attended by the development of a very considerable amount of heat ; thus, according as quantities are taken which are as the molecular weights of the chlorides, or which contain the same amount of chlorine, we have Name. Symbol. At. wt. Sp.gr. At. voL Electrical con ductivity. Chromium Cr 52-4 6-8 77 Manganese Mn 54-8 8-0 67 Iron Fe 55-9 7 8 7-1 16-81atOC. Cobalt Co 58-6 8 9 6-5 17-22 Nickel Ni 58-6 8 2 7-1 13-11 The general resemblance between these metals is very great, but each exhibits properties which serve to distinguish it readily from the others. They are also related to many other elements ; thus, chromium and iron are closely allied to aluminium; and chromium is also allied to sulphur and its congeners ; manganese manifests some analogy with the halogens ; nickel has properties in common with copper : and iron, cobalt, and nickel are closely related to the so-callccl platinum metals. The oxides of chromium and manganese are reduced by charcoal only at a white heat ; the oxides of the remaining metals are easily reduced on ignition with hydrogen 01 carbon. The properties of chromium appear to differ considerably according to the manner in which it is prepared. Thus, by heating its chloride with potassium it is obtained as a dark grey powder, which oxidizes readily, taking fire in the air. at a heat below redness, and dissolving in dilute sulphuric and hydrochloric acids. By heating its chloride with sodium, however, it is obtained in hard, shining crystals, insoluble in all acids. The metal prepared by reducing the oxide with charcoal is shining, has a steel-grey colour, and is hard enough to scratch glass. Manganese is a soft, brittle, greyish-white metal, which oxidizes quickly on exposure to the air, decomposes water slowly at ordinary temperatures, and dissolves easily in acids ; it is feebly magnetic. The properties of iron are too well known to need descrip tion. It dissolves readily in acids, and decomposes water rapidly at a red heat, it does not alter in dry air, but rapidly oxidizes in moist air; especially in presence of carbonic acid. Cobalt has a steel-grey colour ; nickel is silver-white. Both are hard, ductile, malleable metals, of great tenacity,, somewhat more fusible than iron; they decompose water at a red heat, and like iron dissolve without difficulty in acids. They are not altered by the combined action of air and 1 water at ordinary temperatures, but if previously heated burn in oxygen like iron. Nickel appears to be less oxidiz- able than cobalt. They are both magnetic metals. Each of these metals forms several oxides ; and hydrox ides and chlorides, or fluorides, corresponding to most of their oxides are known, as will be evident from the following list : Mn 2 2 Fe a 2 Co 2 a NLO, Cr 2 (OH) 4 Mn 2 (OH) 4 Fe 2 (OH) 4 Co 2 (OH) 4 Ni s (OH) 4 Cr 3 4 Mnj0 4 Fe 3 4 Co 3 4 Oxides. Cr 3 3 Mn.O, Fe 2 3 Co 2 3 Ni,0 3 Hydroxides. Cr s (OH). Mn,(OH) 6 Fe 2 (OH) 3 CrO, MnO. N&OH),