84 Colouring of the Shells of Birds' Eggs . [January, 
line 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 adtion 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 hydro- 
chloric 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 spedtrum with no 
detached bands, absorbing the whole of the blue light, and 
strongly transmitting nearly all the green and the whole of 
the red end of the spedtrum ; that is to say, light of less 
wave-length than 500 millionths of a millimetre is absorbed, 
and of greater wave-length transmitted. In a solid state, in 
the egg-shell, the absorption extends down to wave-length 
508. Alkalies 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 colourless residue of another substance, which will 
be described in the sequel. This change takes place im- 
mediately if a minute portion of potassic nitrite be added 
to the acid solution. The alcoholic neutral or acetic solu- 
tion is also rapidly decolorised by exposure to diredfc sun- 
light. Hence it will be seen that this yellow substance is 
in a state of very unstable equilibrium, and is rapidly de- 
composed by oxidisation, when a strong acid is present in a 
free state, or when exposed to bright light. 
5. Rufous Ooxanthine . — Hitherto I have not met with this 
substance in any other eggs but those of the different species 
of Tinamou, 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 potassic nitrite is added : but it is not so easily, if 
indeed at all, destroyed by the adtion of a moderately dilute 
aqueous solution of hydrochloric acid ; and its presence does 
not seem to have any effedt in decomposing the oocyan ; 
whereas yellow ooxanthine has a most remarkable influence, 
