1876.] Colouring of the Shells of Birds' Eggs . 83 
colour and speCtrum of the oocyan itself. When dissolved 
in alcohol it is of a very fine blue colour. The speCtrum 
shows no detached bands, but a strong general absorption 
of the entire red end and of a small portion of the extreme 
blue, as shown in fig. 2. 
3. Banded Oocyan . — This also is of fine blue colour, but 
differs from the former species in givingaspefftrum with a well- 
marked detached absorption-band near the red end, as shown 
in fig. 2. It is also far less soluble in neutral alcohol, so 
that it is left in the shell-residue after having been digested 
for some time in cold neutral alcohol, and can subsequently 
be dissolved out by alcohol, to which a minute quantity of 
hydrochloric acid has been added. The solution must, how- 
ever, be examined at once, since banded oocyan is rapidly 
decomposed by strong acids. 
Both these different kinds of blue colouring-matter are 
evidently in a state of very unstable equilibrium. Sometimes 
the greater part of the colour is lost by merely evaporating 
their solutions to dryness at a gentle heat ; and several 
very interesting products can easily be obtained by aCting 
on them with reagents. 
On adding a moderate excess of hydrochloric acid to a 
solution of oocyan, no other immediate change occurs than 
the destruction of some of the yellow substances that may 
be present ; but in the case of banded oocyan, two new 
faint bands are developed in the orange and yellow end 
of the green, and it is gradually changed into a new modi- 
fication, or perhaps even into a new substance, characterised 
by giving a speCtrum with two bands, quite unlike that of 
the original. On adding to the solution of banded oocyan 
a little hydrochloric acid and potassic nitrite, it is rapidly 
decomposed into an orange-coloured substance, giving a 
speCtrum with a simple well-marked absorption-band between 
the green and blue, as shown in the figure. In the case of 
oocyan this same substance is also produced : but there is 
an intermediate red compound formed, characterised by 
giving a speCtrum with two bands (one in the orange, and 
the other at the yellow end of the green), which, however, 
do not correspond to those of the product of the aCtion of 
acid on the banded oocyan. 
It will thus be seen that these two blue colouring-matters 
(oocyan and banded oocyan) differ in very important par- 
ticulars, but are obviously closely related, since they both 
yield the same well-marked produCt when oxidised. 
4. Yellow Ooxanthine. — This substance may be best ob- 
tained from moderately fresh Emu-eggs. These are of a 
