OCR Text |
Show 1875.] COLOURING O F BIRDS' E G G S . 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 neutral 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. 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 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 in 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 disappears 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 considerably 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. 4 00 Yellow ooxan thine. Rufous ooxan thine in so lution. Rufous ooxan thine in a solid state. Spectra of the ooxanthines. When in a solid state in the egg the absorption extends considerably further towards the red end, down to wave-length 590 or thereabouts ; 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 |