of the Elements. 495 



The not uafrequent isomorphism of unequal numbers of 

 atoms of different elements has been before alluded to*. 



Group XIII. 

 Palladium, Platinum, — Gold. 



The propriety of associating gold with the platinum group is 

 very questionable. Palladium appears to present a relation of 

 parity with rhodium and ruthenium, — platinum with iridium 

 and possibly with osmium, though indeed many osmic reactions 

 are altogether special. The double chlorides of platinum, iri- 

 dium, and osmium are isomorphous. 



The atomic weight of palladium, or 53-2, is rather more than 

 half that of platinum, or 98*6 ; or the two metals may be looked 

 upon as members of an uncompleted triad, the increment of 

 atomic weight being 45 '4. 



Palladium and platinum are both white, hard, ductile, tena- 

 cious, scarcely fusible, and veiy unoxidizable metals. They both 

 crystallize in octahedra. The two protoxides are of a black 

 colour ; the two binoxides are brownish, substances which dis- 

 solve in alkaline solutions forming ill-defined salts. 



The sulphides and chlorides are analogous. Each of the bi- 

 chlorides becomes converted into a protochloride at a tempera- 

 ture considerably below the boiling-point of mercury. Each 

 metal gives rise to numerous analogous double chlorides, with 

 the chlorides of ammonium and the basylous metals, &c. The 

 platinum bases are very numerous, but several corresponding 

 palladium bases have been also obtained. Platinum and palla- 

 dium have the same atomic volume, 57, and sensibly the same 

 atomic heat, namely 3-15 and 3-19. 



Gold differs from the other two members of this group in 

 its colour, softness and fusibility. The protoxide and protochlo- 

 ride of gold correspond with the proto-compounds of palladium 

 and platinum ; the bisulphide of gold with the bisulphide of 

 platinum ; and the teroxide and terchloride of gold with the 



manifested by quadroxides as well as by teroxides, is shown in the following 

 examples : — 



T<«mnr«t,m,. r MN03 . . Na NO^ Nitiatc of soda. 



terxTdes V^I=CO^ . Ca^CO^ Calc-spar.| 



teroxwes. [^sSbOs . Ag^SbSs Red silver. 



I«n«,nrnl,n.,c { ^010^ . KCIO" Peichlorate of potash. 

 qrdrxlr{^:|0^, • Ba^SO^ SmphateofbaJyta. 



Again, in the hydrated salts, — 

 MCIO^ . 7W0 



M-SO' . 7H'0 . Fe^S0^.7H-0 sulphate of iron. 

 M^AsO'. 7IP0 . IINVAsO". 711-0 Aiseuiate of soda. 

 These last two salts both crystallize iu the oblique prismatic system, in 

 closely approximating, if not in identical forni.s. 

 * Laurent's ' Chemical Method,' Cavendish Society's translation, p. 140. 



