884 PRINCIPLES OF CHEMISTRY 



But this is the highest form for only platinum and palladiuraY 

 The remaining platinum metals further, like iron, give acids of the type 



give ruthenic anhydride, but is always extracted as the soluble ruthenium salt, K 2 Ru04, 

 obtained by fusion with potassium, hydroxide and chlorate or nitrate. When the orange- 

 coloured ruthenate, K 2 RuO 4 , is mixed with acids, the liberated ruthenic acid immediately 

 decomposes into the volatile ruthenio anhydride and the insoluble ruthenic oxide: 

 2K 2 Ru0 4 + 4HN0 5 =Ru0 4 +Ru0 2 ,2H 2 O + 4KN0 5 . When once one of the above com- 

 pounds of ruthenium or osmium is procured it is easy to obtain all the remaining 

 compounds, and by reduction (by metals, hydrogen, formic acid, &c.) the metals 

 themselves. 



Osmic anhydride, Os0 4 , is 'very easily deoxidised by many methods. It 1 blackens 

 organic substances, owing to reduction, and is therefore used in investigating vegetable 

 and animal, and especially nerve, preparations under the microscope. Although osmic 

 anhydride may be distilled in hydrogen, still complete reduction is accomplished when a 

 mixture of hydrogen and osmic anhydride is slightly ignited (just before it inflames). If 

 osmium be placed in the flame it is oxidised, and gives vapours of osmic anhydride, which 

 become reduced, and the flame gives a brilliant light. Osmio anhydride deflagrates 

 like nitre on red-hot charcoal ; zinc, and even mercury and silver, reduce osmic anhydride 

 from its aqueous solutions into the lower oxides or metal ; such reducing agents as 

 hydrogen sulphide, ferrous sulphate, or sulphurous anhydride, alcohol, &c., act in the 

 same manner with great ease. 



The lower oxides of osmium, ruthenium, and of the other elements of the platinum 

 series are not volatile, and it is noteworthy that the other elements behave differently. 

 On comparing S0 2 , S0 3 ; As 2 3 , As 2 O 5 ; P 2 3 , P 2 O 5 ; CO, C0 2 , Ac., we observe a 

 converse phenomenon ; the higher oxides are less volatile than the lower. In the case 

 of osmium all the oxides, with the exception of the highest, are non-volatile, and it may 

 therefore be thought that this higher form is more simply constituted than the lower. 

 It is possible that osmic oxide, OsO^ stands in the same relation to the anhydride as 

 C 2 H 4 to CH 4 i.e. the lower oxide is perhaps Os 2 O 4 , or is still more polymerised, which 

 would explain why the lower oxides, having a greater molecular weight, are less volatile 

 than the higher oxides, just as we saw in the case of the nitrogen oxides, N 2 and NO. 



Buthenium and osmium, obtained by the ignition or reduction of their compounds 

 in the form of powder, have a density considerably less than in the fused form, and differ 

 in this condition in their capacity for reaction ; they are much more difficultly fused than 

 platinum and iridium, although ruthenium is more fusible than osmium. Ruthenium 

 in powder has a specific gravity of Q'5, the fused metal of 12 - 2 ; osmium in powder has a 

 specific gravity of 20'0, and when semi-fused or, more strictly speaking, agglomerated 

 in the oxy -hydrogen flame, of 21'4, and fused 22'5. The powder of slightly-heated osmium 

 oxidises very easily in the air, and when ignited burns like tinder, directly forming the 

 odoriferous osmic anhydride (hence its name, from the Greek word signifying odour) ; 

 ruthenium also oxidises when heated in air, but with more difficulty, forming the oxide 

 Bu0 2 . The oxides of the types RO, R 2 3 , and RO 2 (and their hydrates) obtained by 

 reduction from the higher oxides, and also from the chlorides, are analogous to those 

 given by the other platinum metals, in which respect osmium and ruthenium closely 

 resemble them. We may also remark that ruthenium has been found rn the platinum 

 deposits of Borneo in the form of laurite, Ru 2 S 3 , in grey octahedra of sp. gr. 7'0. 



For osmium, Moraht ' and Wischin (1893) obtained free osmic acid, H 2 OsO 4 , by 

 decomposing K 2 OsO 4 with water, and precipitating with alcohol in a current of hydrogen 

 (because in air volatile Os0 4 is formed) ; with H 2 S, osmic acid gives Os0 3 (HS) 2 at the 

 ordinary temperature. 



Debray and Joly showed that ruthenic anhydride, RuO 4 , fuses at 25, boils at 100, 

 and evolves oxygen when dissolved in potash, forming the salt KRu0 4 (not isomorphous 

 with potassium permanganate). 



Joly (1891), who studied the ruthenium compounds in greater detail, showed that the 

 easily-formed KRu0 4 gives RuK0 4 Ru0 3 when ignited, but it resembles KMn04 in many 



