of the Elements, 487 



atomic volume of manganese and cobalt, and of no other metal 



whatever. The calculated specific gravities form the sequence, 



Fe = 7'95, Ni = 8-39, Gu = 9-0, that of nickel being exactly inter- 



,. , ^.. 7-95 + 8-39 + 9-0 25-34 o i^ rru 



mediate, — Ni = —- ■ = — ^ = 8-44. The experi- 



o o 



mental specific granties correspond very closely with the calcu- 

 lated numbers, re = 7-84, Ni = 8'6, Cu = 8-96. Iron is strongly 

 magnetic, nickel feebly magnetic, copper diamagnetic. Iron is 

 the most infusible, then nickel, then copper. Metallic nickel, 

 when viewed in some lights, manifests a reddish tinge, inter- 

 mediate between the blue of iron and the red of copper. Iron 

 and copper are both known to be weldable metals. The three 

 metals are soluble in hydrochloric acid with evolution of hydro- 

 gen, — iron most readily, then nickel, then copper*. All three 

 metals precipitate the highly basylous metals tin and cadmium 

 from their solutions. All three metals form protosalts of a 

 marked green colour. The hydrates are all insoluble in potash, 

 but soluble in solutions of sal-ammoniac and ammonia, — iron to 

 a slight extent only, then nickel, copper most of all. All three 

 metals form definite disulphides, Fe"* S, Ni"* S, Cu"* S. Copper 

 alone forms a dinoxide, Cu"* O, and disalts. The hydrosulphates 

 are all soluble in chlorhydric acid with evolution of sulphydric 

 acid. The precipitation of hydi'osulphate of iron is prevented 

 by a slight acidulation, of nickel by a stronger acidulation, while 

 for copper the liquid must be very powerfully acid. The sul- 

 phates of iron and nickel crystallize with seven atoms of water 

 and are isomorphous. Sulphate of copper usually crystallizes 

 with five atoms of water, and is then isomorphous with the cor- 

 responding sulphate of manganese. The sulphates of iron and 

 copper crystallize together in all proportions. When the iron 

 predominates, the mixed salt crystallizes with seven atoms of 

 water, and has the form of sulphate of iron ; when the copper 

 predominates, the mixed salt crystallizes with five atoms of 

 water, and has the form of sulphate of copper. The double 

 sulphates of the three metals with potassium, crystallize with 

 six atoms of water and are isomorphous. The dinoxide and the 

 disalts of copper are imperfectly repi-esented by the disulphides 

 of nickel and iron. Ii'on forms a sesquioxide and sesquisalts ; 

 nickel a sesquioxide but no definite sesquisalts ; copper no definite 

 sesquioxide or sesquisalt, though, indeed, the probable existence 

 of a sesquioxide has been pointed out by Crumf- Iron and 

 nickel also form bisulphides, and an ill-defined bisulphide of 

 copper has been alluded to by Berzelius. Iron gives origin to 



* Odling, QHarterly Journal of Chemical Society, ix. 291. 

 f I have endeavoured unsuccessfully, by variously contrived experiments, 

 to prepare disalts of nickel and sesquisalts of copper. — W. O. 



