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COLOUR AND CHEMICAL CONSTITUTION. 
Part YIL — Spectra of Solid Compounds of Cobalt, Nickel, 
Manganese, and Uranium. 
By James Moir, M.A., D.Sc, F.LC. 
The main result of the earlier part of this work is the demonstration of 
the fact that simple coloured substances can have their colour altered by 
"loading" the molecule either internally or by combination with a non- 
ionising solvent. This phenomenon being very regular in the organic field, 
it became of interest to see whether it could be traced in the coloured 
compounds of such metals as give derivatives possessing a definite spectrum. 
Cobalt was first chosen because the striking spectrum of cobalt-glass sug- 
gested that non-ionised cobalt compounds would all have characteristic 
spectra. 
I. Spectra of the Compounds of Cobalt. 
The spectrum of cobalt salts dissolved in water is not striking ; it is the 
same for all salts when a dilute solution is examined in a thick layer, and 
consists of a single very broad indefinite band with its centre near \ 495, 
this being due to the hydrated cobalt ion. Examination of partly non- 
ionised cobalt solutions in thin layers of strong solutions show small 
differences due to partial combination with the salt ion, this leading to a 
higher molecular weight or volume and therefore to a " loaded " vibration 
with higher wave-length. The centre of the broad band is near \ 505 
for both the chloride and nitrate and near X 510 for the acetate when a 
strong solution is examined in a thin layer. When the nitrate is fused 
without the addition of water the band-centre is raised to X 510, which thus 
appears to be the wave-length of Co(N03)3 . 6Aq in the non-ionised 
condition. 
Solution of CoSO^ in hot cone. II2SO4 is blue, with the band-centre 
raised as high as X 575 ; on cooling this turns pink and has the band at 
X 545. On the loading hypothesis the latter is probably due to Co(HSO^)2 
and the blue form to a compound of this with HoSO^. The change of 
pink cobalt compound to blue by heat is a general phenomenon (whether 
