142 VEGETABLE PHYSIOLOGY 
benzol, and a few other liquids can extract the chlorophyll 
from the plastids and leave them colourless. The pigment 
can be obtained from them also by treatment with dilute 
alkalis, such as potash and soda. By whatever solvent it 
is extracted, however, it appears to undergo decomposition, 
so that the solution does not yield it up in the form in 
which it exists in the vegetable cell. 
A solution of chlorophyll in alcohol or chloroform shows 
the curious property of fluorescence ; if regarded by trans- 
mitted light it appears green, whatever may be the degree 
of concentration of the solution; if a strong solution is 
looked at by reflected light, it has a blood-red coloration. 
When a beam of white light is allowed to pass through 
a prism, and is then made to impinge upon a screen of 
white paper, it gives the appearance of a band in which all 
the colours are represented in the following order :—red, 
orange, yellow, green, blue, indigo, and violet. This is due 
to the different degrees in which the rays which produce 
the sensations of those colours are bent or deflected by 
the prism. This coloured band is called the spectrum of 
white light. In order to get it exhibited to the greatest 
advantage, it is best to admit the beam of light to the 
prism through a narrow slit. The spectrum may then be 
regarded as a succession of images of the slit, each ray 
giving its own image of the aperture and producing that 
image in its appropriate colour. Ifa solution of chlorophyll 
is placed in the path of the beam before it reaches the slit, 
the resulting.spectrum is found to be considerably modified. 
Instead of showing a continuous band in which all the 
colours are represented, it is interrupted by seven vertical 
dark spaces. The rays which would have occupied these 
spaces in the absence of the solution of chlorophyll have no 
power to pass through the latter, and consequently their 
images of the slit are represented by dark lines, which 
together constitute the black bands. In other words, 
chlorophyll absorbs these particular rays:of light which are 
missing. 
