354 MR. H. C. SORBY ON THE [May 4, 
suffice to explain the more obvious peculiarities of the colours 
of eggs. 
1. Oorhodeine.—This is perhaps the most important and inter- 
esting 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 vim- 
purities, 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. When 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 ex- 
tremely well-marked absorption-bands, which differ in number, cha- 
racter, 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 witha 
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. 
700 400 
Strongly acid 
solution, 
Nearly neu- 
tral solu- 
tion. 
Inasolid neu- | 
tral state. 
palette of oorhodeine. 
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 
