1875.] COLOURING OF BIRDS’ EGGS. 357 
less residue of another substance, which will be described in the 
sequel. This change takes place immediately if a minute portion of 
nitrite of potash be added to the acid solution. The alcoholic neu- 
tral or acetic solution is also rapidly decolorized by exposure to direct 
sunlight. Hence it will be seen that this yellow substance is in a 
state of very unstable equilibrium, and is rapidly decomposed by 
oxidization, when a strong acid is present in a free state, or when 
exposed to bright light. 
5. Ltufous Ooxanthine.—Hitherto I have not met with this sub- 
stance in any other eggs but those of the different species of Tina- 
mou, and have studied it more especially in those of Rhynchotis 
rufescens, in which it occurs associated with much oocyan. It 
agrees with yellow ooxanthine in being rapidly decomposed by a 
strong free acid, and immediately when a little nitrite of potash is 
added ; but it is not so easily, if indeed at all, destroyed by the action 
of a moderately dilute aqueous solution of hydrochloric acid; and its 
presence does not seem to have any effect m decomposing the oocyan ; 
whereas yellow ooxanthine has a most remarkable influence, since, as 
will be apparent from what I have already said, when the carbonate 
of lime is dissolved out by a weak acid the whole of the oocyan dis- 
appears if the amount of yellow ooxanthine is considerable, whereas 
no such decomposition occurs when it is absent. Rufous ooxanthine 
also differs from yellow ooxanthine in absorbing light to a very con- 
siderably greater distance from the blue end. Even when dissolved 
in alcohol it absorbs not only all the blue, but also at least one half 
of the green; that is to say, all light of less wave-length than 550 
millionths of a millimetre is absorbed, and all of greater wave-length 
transmitted, which, of course, is a very well-marked difference, as 
will be seen on comparing the spectra given in fig. 3. 
Fig. 3. 
700 4009 
Yellow ooxan- 
thine. 
Rufous ooxan- 
thine in so- 
lution. 
Rufous ooxan- 
thine in a 
solid state. 
a 
Spectra of the ooxanthines. 
When in a solid state in the egg the absorption extends consider- 
ably further towards the red end, down to wave-length 590 or there- 
abouts ; so that the tint is decidedly red, and not the orange-colour 
of the solution or the bright yellow of yellow ooxanthine. When 
mixed with oocyan, it therefore gives rise to the peculiar lead-colour 
