852 PRINCIPLES OF CHEMISTS? 



iron, 56 ; they are metals of a more basic character, they do not fonn 

 stable acids or higher degrees of oxidation, and are a transition to 

 copper, 63, and zind, 65. On the other hand, manganese, 55, and 

 chromium, 52, are the nearest to iron ; they form both basic and acid 

 oxides, and- are a transition to the metals possessing acid properties. 

 In addition to having atomic weights approximately alike, chromium, 

 manganese, iron, cobalt, nickel, and .copper have also nearly the same 

 specific gravity, so. that the atomic volumes and the molecules of their 

 analogous compounds are also near to one another (see table at the 

 beginning- of -this volume). Besides this, the likeness between the 

 *above-mentioned elements is also seen from the following : 



They form suboxides, RO, fairly energetic bases, isornorphous with 

 magnesia for instance, the salt RS0 4 ,7H 2 0, akin to MgS0 4 ,7H 2 O, 

 And FeS0 4 ,7H 2 0, or to sulphates containing less water j with alkali 

 ^sulphates all form double salts crystallising with 6H 2 ; all are capable 

 of forming ammonium salts, &c. The lower oxides, in the cases of 

 nickel and cobalt, .are tolerably stable, are not easily oxidised (the 

 nickel compound with more difficulty than cobalt, a transition to 

 copper); with manganese, and .especially with chromium, they are 

 more easily oxidised than with iron and pass into higher oxides. 

 They also form oxides of the form R 2 3 , and with nickel, cobalt, 

 .and manganese this oxide is veify unstable, and is more easily reduced 

 than ferric oxide ; but, in the case of chromium, it is very stable, and 

 forms the ordinary kind of salts. It is_isomorphous with ferric oxide, 

 forms alums, is a feeble base, &c. Chromium, manganese, and iron are 

 oxidised by alkali and oxidising agents, forming salts like Na 2 S0 4 j 

 but cobalt and nickel are difficult to oxidise ; their acids are not known 

 with any certainty, and are, in all probability, still less stable than the 

 ferrates. Cr.Mn and Fe form compounds R 2 C1 G which are like Fe 2 Cl 3 

 in many respects ; in Co this faculty is weaker and in Ni it has almost 

 disappeared. The cyanogen compounds, especially of manganese and 

 cobalt, are very near akin to the corresponding ferrocyanides. The 

 oxides of nickel and cobalt are more easily reduced to metal than those 

 of iron, but those of manganese and chromium are not reduced so 

 easily as iron, and the metals themselves are not easily obtained in a 

 pure state j they are capable of forming varieties resembling cast iron. 

 The metals Cr,Mn,Fe,Co, and Ni have a grey iron colour and are very 

 -difficult to melt, but nickel and cobalt can be melted in the reverbera- 

 'tory furnace and are more fusible than iron, whilst chromium is more 

 -difficult to melt than platinum (Deville). 'These metals decompose 

 water, but with greater difficulty as the atomic weight rises, forming a 

 transition to copper, which does not decompose water. All the com- 



