356 MR. H. C. SORBY ON THE [May 4, 
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 
modification, or perhaps even into a new substance, characterized 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 nitrite of potash, 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 fig. 
In the case of oocyan this same substance is also produced ; but there 
is an intermediate red compound formed, characterized 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 particulars, but are 
obviously closely related, since they both yield the same well-marked 
product when oxidized. 
4, Yellow Oowanthine.—This substance may be best obtained 
from moderately fresh Emu-eggs. These are of a fine malachite 
green colour, due to a mixture of yellow ooxanthine with oocyan. 
On completely dissolving out the carbonate of lime with moderately 
strong hydrochloric acid, the residue is of deep green-blue colour, 
and a large part of the ooxanthine is decomposed by the action of 
the acid. On the contrary, if the carbonate of lime be dissolved 
out by acetic acid, nearly all the oocyan is lost, and a yellow residue 
is obtained, coloured by yellow ooxanthine, which, however, is so 
‘firmly associated with the thick tough membrane, that it is almost 
impossible to dissolve it out in alcohol. If, however, the shell be 
partially dissolved in dilute hydrochloric acid, a yellow layer is 
formed on the surface, which may be detached from the greener 
part below, not yet free from the earthy matter; and this yellow 
layer easily gives up part of its colour to neutral alcohol, and a 
further quantity to alcohol containing a little acetic acid. These 
solutions are of a clear yellow colour, giving a spectrum with no de- 
tached bands, absorbing the whole of the blue light, and strongly 
transmitting nearly all the green and the whole of the red end of the 
spectrum ; that is to say, light of less wave-length than 500 millionths 
of a millimeter is absorbed, and of greater wave-length transmitted. 
In a solid state, in the egg-shell, the absorption extends down to 
wave-length 508. Alkali and weak acids produce no immediate 
change in the solution; but a strong acid like hydrochloric rapidly 
decomposes yellow ooxanthine, and leaves only a pale, almost colour- 
