1876.] 
8i 
Colouring of the Shells of Birds* Eggs . 
to explain the more obvious peculiarities of the colours of 
eggs, since those examined were carefully selected for this 
purpose. 
1. Oorkodeine .— This is perhaps the most important and 
interesting of all the colouring-matters, not only because it 
gives a number of most interesting spedfra, of such a well- 
marked character that a very minute quantity can be 
recognised without any difficulty, even when mixed with a 
relatively large quantity of coloured impurities, but because 
it occurs, in large or small amount, in the shells of such a 
great number of eggs that its entire absence is exceptional. 
When in a perfectly neutral condition it is almost insoluble 
in alcohol ; so that when the washed shell-residue is digested 
in cold absolute alcohol very little is dissolved, until a small 
quantity of hydrochloric acid is added. On evaporating this 
solution to dryness at a gentle heat, and treating it at once 
Fig. 1. 
Strongly acid 
solution. 
Nearly neutral 
solution. 
In a solid neutral 
state. 
Spedtra of Oorhodeine. 
with absolute alcohol, a considerable part dissolves, probably 
because a small quantity of acid clings to it ; but if a small 
excess of ammonia be added, and the solution again eva- 
porated to dryness, the neutral residue is all but insoluble in 
alcohol. These peculiarities enable us to separate oorho- 
deine from most of the other colouring-matters, and to obtain 
it approximately pure. It gives spedtra with extremely 
well-marked absorption-bands, which differ in number, cha- 
racter, and position according to the conditions in which it 
occurs. The more important of these spedtra are shown by 
fig. 1, in which, as well as in all the other figures, they are 
given, not as seen with a prism , but as they would appear 
in an interference spectroscope, since in that case alone do we 
see the true relations of the different parts.* To any one 
* We are indebted to the kindness of the Zoological Society for the use of 
the woodcuts illustrating this paper. 
VOL. VI. (N.S.) 
M 
