Proceedings of the Scientific Meetings of the Zoological Society of London 1875

Page 418

354 MR. H. C SORBY ON T H E [May 4, suffice to explain the more obvious peculiarities of the colours of eggs. 1. Oorhodeine.-This is perhaps the most important and inter­esting of all the colouring-matters, not only because it gives a number of most interesting spectra, of such a well-marked character that a very minute quantity can be recognized without any difficulty, even when mixed with a relatively large quantity of coloured im­purities, but because it occurs, in large or smaller amount, in the shells of such a great number of eggs that its entire absence is exceptional. W h e n in a perfectly neutral condition it is almost insoluble in alcohol; so that when the washed shell-residue is digested in cold absolute alcohol very little is dissolved, until a small quantity of hydrochloric acid is added. On evaporating this solution to dryness at a gentle heat, and treating it at once with absolute alcohol, a considerable part dissolves, probably because a small quantity of acid clings to it; but if a small excess of ammonia be added, and the solution again evaporated to dryness, the neutral residue is all but insoluble in alcohol. These peculiarities enable us to separate oorhodeine from most of the other colouring-matters, and to obtain it approximately pure. It gives spectra with ex­tremely well-marked absorption-bands, which differ in number, cha­racter, and position according to the conditions in which it occurs. The more important of these spectra are shown by fig. 1, in which, as well as in all the other figs., they are given, not as seen with a prism, but as they would appear in an interference spectroscope, since in that case alone do we see the true relations of the different parts. To any one accustomed only to an ordinary spectroscope the blue end will therefore appear abnormally contracted and the red end expanded unusually. The numbers given at the top represent millionths of a millimetre of wave-lengths of the light. Strongly acid solution. Nearly neu-i tral solu­tion. In a solid neu tral state. As will be seen, the strongly acid solution gives a spectrum with three bands, two of which are so well marked that a most minute quantity of the substance serves to show them in a satisfactory manner. When as small a quantity of free acid is present as will Fig. 1. Spectra of oorhodeine.