18 Mr. Cock on Palladium. 



are first precipitated and then redissolved, while those of iron, 

 lead, &c, remain insoluble. To the clear ammoniacal solu- 

 tion, muriatic acid is then added in excess, which occasions 

 a copious precipitation of the yellow ammonio-chloride of pal- 

 ladium, from which, after sufficiently washing it with cold 

 water and ignition, pure metallic palladium is obtained. The 

 mother liquor and washings contain all the copper and some 

 palladium, which are recovered by precipitation with iron. 



Pure palladium is of a greyish-white colour, rather darker 

 than that of platinum ; it is both malleable and ductile, though 

 inferior in those qualities to pure platinum ; its specific gra- 

 vity is 11*3, which may be raised by hammering or rolling to 

 11*8. When perfectly pure it cannot be fused even in small 

 quantities in an ordinary blast furnace, but may be brought 

 into such a state of agglutination as to bear laminating or 

 drawing into wire. 



It may be completely fused by means of oxygen gas, and 

 being kept some time fused, is said to burn with the production 

 of brilliant sparks ; it is not tarnished by exposure to sulphu- 

 retted hydrogen, nor oxidated by the air at the ordinary tem- 

 perature, or at a bright red heat ; but it has the singular 

 property of becoming oxidated by exposure to air at a dull 

 red heat, the surface becoming coloured in the same manner 

 as iron or steel ; and by continuing the process cautiously for 

 some time, the metal becomes coated with a brittle crust of 

 oxide of a brown colour; this oxide is, however, reduced by 

 a temperature very little higher than that necessary for its 

 formation ; and the surface of the metal regains its original 

 colour upon being heated to a bright red, and cooled out of 

 contact with the air. 



It is with difficulty soluble in nitric acid when pure and 

 fused, or in a state of aggregation, but is readily so when al- 

 loyed to some extent with silver or copper, and still more so 

 when in the form of the black powder above referred to, in 

 which state it is also soluble with the aid of heat in sulphuric 

 and muriatic acids; but its proper solvent is nitro-muriatic 

 acid, which, if it be not very much alloyed with silver, dis- 

 solves it readily. 



It is of all the metals that which has the greatest affinity for 

 cyanogen ; and by means of cyanide of mercury, it may be 

 separated from all its solutions. 



It may be alloyed so as to be malleable with gold, silver 

 and copper, several of its alloys with the two latter metals 

 being of great use in the arts from their hardness and elasti- 

 city, and non-liability to rust or tarnish. When added to 

 gold or copper, it whitens both those metals in a very great 



