S69 



CHAPTER 



THE PLATINUM METALS 



THE six metals : ruthenium, Ru, rhodium, Rh, palladium, Pd, osmium, 

 Os, iridium, Ir, and platinum, Pt, are met with associated together in 

 nature. Platinum always predominates over the others, and hence 

 they are known as the platinum metals. By their chemical character 

 their position in the periodic system is in the eighth group, correspond- 

 ing with iron, cobalt, and nickel. 



The natural transition from titanium and vanadium, to copper and 

 einc by means of the elements of the iron group is demonstrated by all 

 the properties of these elements, and in exactly the same manner a 

 transition from zirconium, niobium, and molybdenum to silver, cadmium, 

 and indium, through ruthenium, rhodium, and palladium, is in perfect 

 accordance with fact and with the magnitude of the atomic weights, as 

 also is the position of osmium, iridium, and platinum between tantalum 

 and tungsten on the one side, and gold and mercury on the other. la 

 all these three cases the elements of smaller atomic weight (chromium, 

 molybdenum, and tungsten) are able, in their higher grades of 

 oxidation, to give acid oxides having the properties of distinct but 

 feebly energetic acids (in the lower oxides they give bases), whilst the 

 elements of greater atomic weight (zinc, cadmium, mercury \ even in 

 their higher grades of oxidation, only give bases, although with feebly 

 developed basic properties. The platinum metals present the same 

 intermediate properties such as we have already seen in iron and the 

 elements of the eighth group. 



In the platinum metals the intermediate properties qf feebly acid 

 and feebly basic metals are developed with great clearness, so tbat 

 there is not one sharply-defined acid anhydride among their oxides, 

 although there is a great diversity in the grades of oxidation from the 

 type R0 4 to R 2 (X The feebleness of the chemical forces observed in 

 the platinum metals is connected with the ready decomposability of 

 their compounds, with the small atomic volume of the metals them? 



