Colour and Chemical Constitution. 
47 
d. Cohalt-glass and its aiialogues. — This blue glass has three marked 
absorption-bands with centres at XX 641, 589 and 652. The spectrum of 
the cobalt horax-head is similar, but the bands are lower down (mol. wt. of 
cobalt borate less than that of cobalt silicate), the centres being at XX 527, 
577 and 641. A third spectrum of this class is given by cobalt dissolved 
in hot fused metaphosphoric acid (Co(P03)2 in HPO3) which has band- 
centres at XX 533, 582, and about 640. This turns pink on cooling and loses 
the spectrum just describod. The middle band is much stronger than the 
others in all cases. The blue solution of cobalt in very strong potash, 
containing Co(OK)o, gives a fourth spectrum of this class, the centres being 
at XX 530, 579 and 638. The purple solution from cobalt, potash and sugar 
contains only two bands, the chief one being at X 592, the other, at x 490, 
being probably only that of cobalt hydrate. If glycerol be used instead of 
sugar the solution is blue and the bands are at XX 585 and 640, i. e. very like 
the glass. Cobalt ammonium phosphate in ammonia is purple and the bands 
are at XX 598 and 629. 
Another and more remarkable blue cobalt solution is the double 
potassium sulphocyanide K2CoScyj^. This, when extracted into alcoholic 
ether, has sharp bands at XX 579 and 621, and when in amyl alcohol or 
amylacetate has the bands at XX 581 and 626. 
The cobaltammines with trivalent cobalt have no characteristic spectra. 
II. Spectra of the Nickel Compounds. 
Although nickel chloride gives a characteristic spectrum, none of the 
other compounds show anything definite. This is probably because the 
effect of loading the molecule is to shift the absorption-bands right off 
the spectrum. ]SriCl2 . Aq has two absorption-bands with centres at about 
XX 652 and 690 and a strong narrow transmission between them (at about 
^ 675). This transmission survives in strong solutions in which the bands 
have broadened so as to cut off nearly all the rest of the red. 
III. The SpECTurM or the Permanganates. 
Dilute solutions of permanganates, it is well known, give an absorption- 
spectrum containing five bands which appear to be equally spaced. Two of 
these, the second and third, are much stronger than the others, and by using 
stronger solutions the author has been able to observe two more farther 
down in the violet, making seven bands in all. The author has also 
succeeded in expressing their rhythmic character by a mathematical formula, 
10' 
VIZ. X = ]^75Q _[_ ]v^ > which, by taking N to be successively 0, 1, 2, 3, 4, 5, 
and 6, gives seven values of x agreeing within experimental error with the 
