Microscope Spectrum Apparatus. By H. C. Sorby. 203 
following table. Along with them I give the spectrum of deoxi- 
dized hoematin, to show how spectra of very similar character may 
be completely distinguished by a great difference in the ratio be- 
tween the wave-lengths, whilst the spectra of the same substance in 
two different conditions may vary far more in general appearance, 
and yet the ratio be the same. 
Fig. 2. — Spectra op Turacine. 
700 
400 
In a solid state, or\ 
as in the feathers/ 
Dissolved in water 
with a little am- 
monia 
Deoxidized hsema- 
tin for compari- 
son 
Condition. 
Centre of 
Bands. 
Ratio. 
In a solid state, or as in the feathers . . 
Dissolved in water with a little ammonia 
Deoxidized hsematin for comparison . . 
582 541 
564 524 
586 522 
1 : -9294 
1 : -9290 
I : -8908 
One band of the deoxidized haematin is thus nearly in the same 
place as one of the solid turacine, and another nearly in that of the 
other of the solution. 
As will be seen from the above figures, there is not only a 
change in the position of the bands, but also in their intensity and 
width, according to the nature of the solvent, and these changes 
may produce a certain amount of departure from the general law. 
The cause of this will be more apparent when we have considered 
the effect produced by the presence of free acids and alkalies. 
Many vegetable colouring-matters give spectra with a single 
broad absorption band, whose position and character vary con- 
siderably, according as the solution is made acid or alkaline. 
Usually acids raise the centre of the band towards the blue end, 
whilst alkalies lower it towards the red end. The red colouring 
matter of Alkanet root ( Aucliusa tinctoria) is a good example of 
another kind of change, when the spectrum shows several bands. 
When dissolved in alcohol containing some water, the spectrum 
