OCR Text |
Show 356 MR, H. c SORBY O N T H E [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 Ooxanthine.-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 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 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- |