82 
Colouring of the Shells of Birds' Eggs. [January, 
accustomed only to an ordinary spectroscope the blue end 
will therefore appear abnormally contracted and the red end 
expanded unusually. The numbers given at the top represent 
millionths of a millimetre of wave-lengths of the light. 
As will be seen, the strongly acid solution gives a spectrum 
with three bands, two of which are so well marked that a 
most minute quantity of the substance serves to show them 
in a satisfactory manner. When as small a quantity of free 
acid is present as will enable the alcohol to dissolve oorho- 
deine, the spectrum shows the five absorption-bands given 
in fig. i, and the general colour is brownish-red. This in the 
spectrum of the almost neutral modification when in a state 
of solution. When in a free solid form, as in the shell, or as 
found in the washed dry skin-like residue after removing the 
carbonate of lime by an acid, the spectrum is most materially 
different, as will be seen from the woodcut. Only three 
Fig. 2. 
700 400 
bands are distinctly visible, and they lie nearer to the red 
end, whilst there is far more of general absorption at the blue 
end. The result of this is that the general colour is a peculiar 
brown- red. 
Oorhodeine is of such a very permanent character that it 
resists the action of very powerful reagents. I have been 
able to destroy it, but have not yet succeeded in changing 
it into any other coloured substance. 
2. Oocyan . — In most cases this is readily soluble in neutral 
alcohol, and can thus be separated from oorhodeine. It is ? 
however, often associated with yellow substances that cannot 
easily be removed ; very commonly, therefore, the solution 
is of a somewhat green-blue colour, but in many cases the 
yellow impurity is far more easily decomposed by the adtion 
of light or by weak oxidising reagents, and can be removed 
by this means, so as to enable us to determine the true 
