Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/550

Rh 538 CHEMISTRY [TIN GROUP. properties, dissolving in alkalies. Rhodium and iridium are precipitated from solutions of their salts by most metals, but not by silver or gold. In many cf their properties palladium and platinum more nearly resemble silver and gold than the preceding metals, just as nickel is more closely allied to copper than to cobalt and iron. Palladium is superficially oxidized at a lower temperature than silver, but its oxide is decomposed at a red heat ; platinum is not in the least affected when heated in air or oxygen. The most stable compounds of palladium are the palladious compounds, a solution of palladic chloride, PdCl 4, being decomposed when heated, with evolution of chlorine, Pd. 2 Cl 4 being produced ; the most stable compounds of platinum, however, are those which correspond in composition to platinic chloride. Palladium, like silver, is stained by iodine, which is with out action on platinum, owing to the formation of palladious iodide, which is also obtained on adding potassium iodide to a solution of a palladious salt; it is a black powder insoluble in, water but soluble in ammonia, and also, like silver iodide, in a solution of potassium iodide. Both platinous and platinic chlorides, like auric chloride, readily unite with hydrochloric acid, forming chloroplatinous and chloroplatinic acids, H 2 PtCl 4 and H 2 PtCl 6 ; salts of these acids are produced by the combination of platinous and platinic chlorides with the chlorides of other metals. Fulladious and palladic chlorides, and the corresponding chlorides of the other platinum metals, as already pointed out, form similar compounds, thoser which correspond in composition being in all cases isomorphous. Although platinum and palladium do not furnish compounds analog ous to the ferro- or ferri-cyanides, they form a distinct series of very beautiful and highlystable salts termed [latino- cyanides and palladiocyanides, which are analogous in com position to the chloroplatinites, and from which the corre sponding acids may be obtained by decomposing the silver salts, for example, with hydrogen sulphide ; thus : K 2 PtCl 4 K 2 Pt(CN) 4 K 2 Pd(CN) 4 Potassium platinochloride. Potassium platinocyanide. Potassium palladiocyanide. The palladiocyanides are isomorphous with the corre sponding platinocyanides. These salts combine with the halogens, forming compounds such as potassium platini- chlorocyanide, K 2 PtCl 2 (CN) 4, which are analogous to the chloroplatinates such as K 2 PtCl G. A somewhat similar series of .bodies may be obtained from gold, e.g., potassium auricyanide, KAu(CN) 4, and potassium aurichlorocyanide, KAuCl 2 (CN) 2. The oxides and hydroxides of platinum and palladium are somewhat more stable than the silver and gold compounds, but are entirely decomposed on ignition ; they dissolve in acids, but the resulting salts have little stability, although they are considerably more stable than those of gold. The hydroxides appear all to possess acid properties, platinic hydroxide dissolving readily in solutions of alkalies, form ing metallic derivatives which may be obtained in crystals. Platiuic hydroxide, like auric hydroxide, is converted into a fulminating compound by the action of ammonia. Cobalt and the platinum metak are especially character ized by the readiness with which they enter into reaction with ammonia, forming salts of cobalt and platinum bases, which are often extremely complex in composition. Thus, a solution of platinous chloride in warm, moderately strong ammonia, concentrated by evaporation, on cooling deposits yellow crystals of platinodiammomum chloride, PtN 4 H 12 Cl 2 , H 2 O ; by treating a solution of this salt with silver sul phate it is converted into the sulphate PtN 4 H 12 (S0 4 ), from which the corresponding hydroxide PtN 4 H 12 (OH) 2 may be procured by adding to the solution the equivalent quantity of barium hydroxide. Platinodiammonium hydroxide may be obtained in crystals ; it is a powerfully alkaline, caustic substance, and, according to Thomson, its heat of neutral ization is as great as that of the alkalies and the hydroxides of barium, strontium, and calcium. When platinodiam monium hydroxide is heated as long as it gives off am monia and water, it is converted into platinoammonium oxide PtN 2 H 6 O, from which salts such as platinoammonium chloride, PtN 2 H Cl 2, may be prepared by the action of acids; on passing chlorine into water in which the latter is suspended it is converted into chloroplatinoammonium chloride, PtCl 2 N 2 H 6 Cl 2. The relation of these compounds to platinous chloride and to one another may be expressed by the following for- muke : rtt l 2 Pt[NH 2 Cl(NH 4 )] 2 II II PtCl, Pt[NH,Cl(NH 4 )], Platinous Platinodlamtnonluui chloride. chloride. Pt(XII 3 Cl) 2 PtCl(NH 3 Cl) 2 rt(NH 3 Cl) 2 Platinoammonium chloride. rtCl(NH 3 Cl) t Chloroplatinoam monium chloride Similarly, when a solution of cobaltous chloride in ammonia is exposed to the air, the liquid assumes first a brown and then a red colour, and if the reddened liquid is mixed with hydrochloric acid a brick-red precipitate is pro duced ; by recrystallizing this from hot water containing hydrochloric acid it is obtained in beautiful ruby-red crys tals of the composition Co 2 N 10 H 30 Cl c. The relation of this compound, which is termed purpureocobaltic chloride, to cobaltous and cobaltic chlorides may be expressed as follows : f^pi C* PI P j -*^a ^OLJ 2 coui 3 &amp;lt;^o &amp;lt; r^,, PifNTI ^1 cld a dci 8 c oj^g&amp;lt; NH ^ Cobaltous Cobaltic chloride. Purpureocobaltic chloride. chloride. Nickel and copper appear to form similar compounds, but they are mostly very soluble and far less complex, these elements having little or no tendency to function as hexads. TITANIUM ZIRCONIUM TIN. N.ime. Symbol. At. wt. Sp. gr. At. voL Titanium T 48 Zirconium Zr DO 4-1 21-9 Tin Sn 117-8 7 3 16-1 Titanium and zirconium are closely related to silicon and, therefore, to carbon, and occupy an intermediate position between these elements and the true metals. Titanium and tin, however, are more nearly related than either titanium and zirconium or tin and zirconium, zirconium more closely resembling silicon, especially in tho properties of its oxide. Titanium and zirconium apparently resemble silicon closely in their physical properties, and exist both in the amorphous and crystalline state. In the amorphous state they burn with great brilliancy when heated to redness in oxygen, and they take fire when heated to redness in chlorine; titanium also unites directly with nitrogen ab high temperatures, and it is stated forms the three nitrides Ti 3 N 2, Ti 3 N 4 , TiN 2. Titanium is said to be soluble in warm hydrochloric acid, but zirconium is only slowly attacked by ordinary acids, although it readily dissolves even in cold hydrofluoric acid. Crystalline zirconium is very hard, and resembles antimony in colour, lustre, and brittleness ; it is less fusible than silicon. Tin is a soft, very malleable, white metal, with a tinge of yellow, and is a tolerably good conductor of electricity, titanium and zirconium being non-conductors of electricity. It fuses at about 230 C. It scarcely tarnishes at ordinary temperatures, but at a red heat it rapidly oxidizes, and readily decomposes water. It is only slowly dissolved by
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