536 CHEMISTKY [IRON GROUP. r " Reaction. Units of heat de- Teloped. Remarks. Mn, C1 3 111,990 1 Formation of the anhyd- Mn 0, H 2 94,770 hydroxide, manganic Mn H,0 116,280
hydroxide MnO(OH)j ,
389,650 and potassium pertaaii- MnClj Aq 16,010 MnS0 4 +4H 2 O, Aq 1,770 Dissolution of the salts in MuS0 4 + 5H 2 0, Aq, 40 water. Mn 2 8 Kj , Aq -20,790 Mn(OH), , SO,Aq . 26,480 S f Mn(OH)., 2HClAq 22,950 ganous hydroxide. Mn O.SCXjAq 121,250 Mn C1 2 , Aq 128,000 solution. 2Mn(OH) s , 5 , 2KOHAq ... 2MnO(OH) 2 , 5 , 2KOHAq 14,760 - 28,260 (Formation of solution of permanganate from man- ganous and manganic hydroxide. Resetted. Units of heat de veloped. Remarks. Fe,Cl 3 82,050 ^ Fe CL 192,060 2FeCL, C1 2 27,960 Formation of the Fe, 0, H 2 68,280 (anhydrous com Fe 2 0,,3H 8 191,130 pounds. 2Fe(OH) 2 , O 54,570 FeCl 2 , Aq 17,900 Fe.CL , An . 63,360 Dissolution of the FeSO 4 + 7H 2 0, Aq -4,510 salts in water. Fe(OH) 2) SO. t Aq Fe(OH) 2 , 2HClAq 24,920 21,390 ] Fe 2 (OH) 6 , 3SO.,Aq 33,750 Neutralization of Fe 2 (OH) 6 , 6HClAq 33,450 > ferrous and feme Fe.{OH). . SN.O.Aq . 33,600 hydroxide. Fe 2 (OH) 6 , 6C 2 H 4 2 Aq Fe, C1 2 , Aq 23,970 99,950 J Fo , CL , An . 255,420 r ormation of the 2FeCl 2 Aq, C1 2 55,520 chlorides and sul- Fe , 0,S() 3 Aq 93,200 pnatea m aqueous Fe 2 , 3 , 3S0 3 Aq 224,880 solution. The only two compounds of the metals of the iron group of which the vapour density has been determined are ferric chloride and chromium oxychloride ; the density of the former corresponds to the formula Fe 2 Cl 6 , and that of the latter to the formula Cr0 2 Cl 2 . Hence the composition of ferric chloride is similar to that of aluminic chloride, the density of which corresponds to the formula A1 2 CL, and it is therefore probable that chromic chloride, which is in all respects analogous to aluminic and ferric chlorides, is similarly constituted, and that its formula is Cr 2 Cl 6 . The majority of the formulae employed to represent chemical compounds which cannot be converted into gas are merely the simplest expressions of their composition in terms of the atomic weights of their constituent elements. Thus it is usual to express the composition of the lower chlorides of chromium, iron, manganese, <tc., by the simple formulae CrCl. 2 , MnCl 2 , FeCl 2 , and the correspond ing oxides by the similar formulae CrO, MnO, FeO ; there are reasons, however, which lead us to suppose that in many cases the less simple formulae, such as Cr 2 Cl 4 , Cr 2 O 2 , are to be preferred, and that the lower chlorides and oxides of iron, &c., like the higher chlorides and oxides, contain at least two atoms of the metal in the molecule. For example, the lower chlorides of chromium and iron are readily con verted into the higher chlorides by the action of chlorine ; now if the formula of ferrous chloride is FeCl 2> that of ferric chloride being Fe 2 Cl , the conversion of the former into the latter by the action of chlorine involves the extremely improbable assumption that a molecule of the ferric compound is formed from two molecules of the ferrous compound : Chlorine is not known ever to produce an effect of this kind, that is to say, directly to cause the formation of a more complex from a less complex molecule ; but its action is frequently to produce an effect the very reverse of this, many instances of simplification of the molecule by the action of chlorine being known. By adopting the for mula Fe 2 Cl 4 for ferrous chloride a natural interpretation of its conversion into ferric chloride is at once possible, how- FeCl 2 II FeCL Ferrous chloride. + CL = FeCl 3 FeClg Ferric chloride. Corresponding formula} may be assigned to the lower chlorides of chromium, manganese, cobalt, and nickel, on account of their resemblance to ferrous chloride; and from the general resemblance which the nickel compounds bear to the cupric compounds it appears probable that, if nickel chloride has the formula Ni 2 Cl 4 , cupric chloride has the formula Cu 2 Cl 4 . The argument may be extended much further, and from the more or less perfect resemblance of silver chloride to cuprous chloride, mercurous chloride, and other chlorides which certainly contain at least two atoms of chlorine in their molecules, we may infer that the formula Ag 2 Cl 2 is probably a more correct expression than that commonly employed. The existence of a subchloride and a suboxide of silver indicates that silver is not uniformly a monad element, and if we regard copper, silver, and gold as triad elements (although the last mentioned is undoubtedly capable of assuming pentad functions) we may represent their lower chlorides by similar formulae, and thus, in a measure, account for the similarity in their properties : CuCl AgCl AuCl CuCl Cuprous chloride. AgCl Argentic chloride. AuCl Aurous chloride. But it has been pointed out that certain of the silver compounds are isoinorphous with the corresponding sodium and potassium compounds, and as there is no reason to suppose that the argentic compounds generally are not of similar constitution to argentic chloride, the conclusion that there are. two atoms of silver in the molecule of argentic chloride would appear to necessitate the assump tion that the compounds of the alkali metals also contain at least two atoms of the metal in their molecules ; that the formula of sodium nitrate, for example, is Na 2 (N0 3 ) 2 , and not NaNO 3 . The existence of a compound of sodium ethyl with zinc ethyl, NaZn(C 2 H 6 ) 3 , from which the former cannot even be separated, appears to show that sodium does not invariably function as a monad. Speculations of this kind are extremely hazardous, but, as 110 method is known enabling us to ascertain the molecular composition of compounds which cannot be volatilized, they possess a certain interest and, moreover, point to the necessity of investigation in this direction. RUTHENIUM RHODIUM PALLADIUM OSMIUM IRIDIUM PLATINUM. Name. Symbol. At. wt. Sp.gr. At. vol. Ruthenium Ru 103-5 11-4 9-1 Rhodium Rh 104-1 12-1 8 6 Palladium Pd 106-2 12-0 8-8 Osmium ()s 198-6 22-4 8-8 ] ridium Ir 196-7 22-4 8-7 Platinum Ft 196-7 21-5 9-7 These metals always occur in the native state, and
are usually associated together. The relation between
