Microscope Spectrum Apparatus. By H. C. Sorhy. 203 
following table. Along with them I give the spectrum of deoxi- 
dized haematin, to show how spectra of very similar character may 
be completely distinguished by a great difierence 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. 
Condition. 
Centre of 
Bands. 
Ratio. 
In a solid state, or as in the feathers , . 
582 541 
1 : -9294 
Dissolved in water with a little ammonia 
564 524 
1 : -9290 
Deoxidized hsematin for comparison . . 
586 522 
1 : -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 (Auchusa tinctoria) is a good example of 
another kind of change, when the spectrum shows several bands. 
When dissolved iii 9,lcohoi containing some water, the spectrum 
