THE PLATINUM MEf ALS 888 



the types of combination, all the platinum metals, under certain circun> 

 stances, give compounds of the type RX 4 for instance, HQ 2 , RC1 4 , &o, 



give crystalline salts with bases, and their alkaline solutions partially deposit them 

 again when boiled (an excess of water decomposes the salts). The formulae Os0 4 and 

 Eu04 correspond with the vapour density of these oxides, Thus Deville found the 

 vapour density of osmic anhydride to be 128 (by the formula 127*6) referred to hydrogen. 

 Tennant and Vauquelin discovered this. con\pound, and Berzelius, Wb*hler, Fritzsche, 

 Struve*, Deville, Claus, Joiy,and others, helped in its investigation; nevertheless there 

 are still many questions concerning it which remain unsolved. It should be observed 

 (hat BO* is the highest known form for an oxygen compound, and BH4 is the highest 

 known form for a compound of hydrogen; whilst the highest forms of acid hydrates 

 contain SLE^O*, PH 3 4 , SH 2 4 , .ClHOf-oll with four atoms of oxygen, and therefore in 

 this number there is apparently the limit for the simple forms of combination of hydrogen 

 dad oxygen. In combination with several atoms of an element, or several elements, 

 there may be more than O 4 or EE^ but a molecule never contains more than four atoms 

 of either or H to one atom of another element. Thus the simplest forms of combina* 

 tion of hydrogen and oxygen are exhausted by the list BB^, BH$, BH 2 , BH, BO, B0 fl , 

 BOsj B0 4 . The extreme members are BH 4 and B0 4 , and are' only met with for such 

 elements as carbon, silicon, osmium, ruthenium, which also give BtJla w ^h chlorine. 

 In these extreme forms, BH4 and BO^ the compounds are the least stable (com. 

 pare SiH^, PH 5 , SH 2 , C1H, or BuO^ MoOj, Zr0 8 >.SrO), and easily give up part, or even 

 all, their oxygen or hydrogen. 



The primary source from which the compounds of ruthenium and osmium are 

 obtained is^either osmiridium (the osmium predominates, from IrOs to IrOs 4 , sp.gr. 

 from 16 to 2*1), which occurs tn platinum ores (it is distinguished from the grains of 

 platinum by its crystalline structure, hardness, and insolubility in aqua regia), or else 

 those insoluble residues which -are obtained, as we saw above, after treating platinum 

 with aqua regia. Osmium predominates in these materials, which sometimes 'contain 

 from 80 p.o. to 40 p.c. of it, and rarely more than 4 p.o. to 5 p.c. of ruthenium. The 

 process for their treatment is as follows : they are -first fused with 6 parts of zinc, %nd 

 the zinc is then extracted with dilute hydrochloric acid* The osmiridium thus treated 

 is, according to Fritzsche and Struv^s method, then added to a fused mixture of 

 potassium hydroxide and chlorate in an iron crucible ; the mass as it begins to evolve 

 oxygen acts on the- metal, and the reaction afterwards proceeds spontaneously. The 

 dark product is treated with water,, and gives a solution of osmium and ruthenium in 

 the form of soluble salts, BjOs0 4 and B^BuO^ whilst the ins&luble residue contains a 

 mixture of oxides of iridium fancl pome osmium, rhodium, and ruthenium), and grains 

 of metallic iridium still unactefl on. According to Fre*my's method the lumps of 

 osmiridium are straightway heated to whiteness in a porcelain tube in a stream of air or 

 oxygen, when the very volatile osmio anhydride is obtained directly, and is collected in 

 a well-cooled receiver, whilst the ruthenium gives a -crystalline sublimate ci the dioxide, 

 Bu0 2 , which is, however, very difficultly volatile (it volatilises together with osmio 

 anhydride), and therefore remains in the cooler portions of the tube j this method does 

 not give volatile ruthenic anhydride, and thevirldium and other metals are not oxidised 

 or give non-volatile products, This method $s simple, and at once gives dry, pure osmio 

 anhydride in the receiver, and ruthenium dioxide in the sublimate. The air which 

 passes through the tube should be previously passed through sulphuric acid, not only in 

 order to dry R, but also to remove the organic and reducing dust. The vapour of osmio 

 anhydride must be powerfully cooled, and ultimately passed over caustic potash. A 

 third mode of treatment, which is most frequently employed, was proposed by Wohler, 

 and consists in slightly heating (in order that the sodium chloride, should not melt) an 

 intimate mixture of osmiridium and common salt in a stream of moist chlorine. The 

 metals then form compounds with chlorine and sodium chloride, whilst the osmium 

 forms the chloride, OsCl^ which reacts with the moisture, and gives osmic anhydride, 

 which is condensed. The ruthenium in this, as in the other processes, does not* directly 



