132 



Prof. T.Carnelley on the Colour 



increase in the quantity of the electronegative element pro- 

 duces a colour-change towards the red end of the spectrum, 

 in accordance with the above chromatic scale, for example: — 



Bi 2 8 , 



yellow. 



Bi 2 5 , brown. 



Sb 2 3 , 



white. 



Sb 2 5 , yellow. 



Cr 2 Cl 4 , 



white. 



Cr 2 Cl 6 , violet. 



PtCl 2 , 



olive. 



PtCl 4 , orange. 



Cu 2 0, 



red. 



CuO, black. 



NiO, 



green. 



Ni 2 3 , black. 



Au 2 0, 



green. 



Au 2 3 , brown. 



Hgl, 



green. 



Hgl 2 , red. 



Cr 2 3 , 



green. 



Cr0 3 , red. 



FeO, 



yellowish. 



Fe 2 3 , red. 



PbO, 



yellow. 



Pb 3 4 , red; Pb0 2 , brown. 



MnO, 



green. 



( Mn 3 4 , red-brown; Mn 2 3 , 

 \ brown-black; Mn0 2 , black 



We have also a -well-known case of this in the colour- 

 changes which the green colouring-matter of plants undergoes 

 during autumn ; this green colouring-matter, as oxidation 

 proceeds, passing through the colours green, yellow, orange, 

 brown, dark brown. 



III. Influence of Atomic Weight. — The influence of atomic 

 weight on the colour of compounds may be stated thus : — In 

 any series of compounds A^ R^, B^ R y , C^ R^,, &c, in which R 

 is any element or group of elements, whilst A, B, C, &c. are 

 elements belonging to the same subgroup of Mendeljeff 's 

 Table of the Natural Classification of the Elements, given 

 below, the colour passes either wholly or partially through the 



White or Colourless. 



Violet. 



Indigo. 



Blue. 



Green. 



Yellow. 



Orange. 



With increase of the 

 Atomic Weight of the 

 elements A, B, C, &c. 



Red. 



Brown, 

 t Black. 



Or, in other words, as the atomic weight of the elements A 

 B, C, &c. increases, the more does the colour of the compound 

 pass towards the red end of the spectrum, and thence (in 

 many cases) to brown and black. 



The following Table of the Classification is given for com- 

 parison, elements belonging to even series being printed in 

 ordinary type and those belonging to odd series in thick type. 



