204 Transactions of the Royal Microscopical Society. 
shows three absorption bands, and on adding an extremely small 
quantity of ammonia these bands are slightly and unequally de- 
pressed towards the red end, so that the interval is a little increased, 
and a new band is developed in the red, at a wave-length interval 
equal to that between the others. The addition of a little more 
ammonia entirely removes the two bands which lie towards the 
blue end, so that the spectrum contains only two at nearly the same 
wave-length ratio as when the solution is neutral ; but on adding 
large excess of ammonia they are unequally depressed towards the 
red end, the interval becomes less, and the colouring matter is 
rapidly decomposed, the change in the wave-length ratio being 
perhaps in some way connected with the decomposition. All these 
changes will be more easily understood by means of Fig. 3. 
Fig. 3. — Spectra of the Colouring Matter of Alkanet Root. 
700 400 
Neutral or acid . 
With very little 
ammonia .. 
With more ammo- 
nia 
Much excess ol 
ammonia 
Another excellent illustration of the effect of acids is furnished 
by the alcoholic solution of the red colouring matter found in the 
shells of birds’ eggs, for which I have proposed the name oorhodeine. 
When neutral, or containing only some such weak acid as acetic, 
the spectrum exhibits five bands, whereas when the solution con- 
tains excess of some such strong acid as hydrochloric, there are only 
three bands, and these two spectra have such a different character 
that at first sight they would not be thought to be related to one 
another. However, on more careful examination it will be found 
that they have two bands in common, whose centres are of nearly 
the same wave-length, but the band which is very faint in the case of 
the neutral solution is dark in that of the acid, and that which is 
dark in the neutral is faint in the acid. The three other bands 
are destroyed by the strong acid, and a new very dark band 
