Carbon Assimilation. 
2 1 
blue to violet parts of the spectrum. 
b. Phceophytin. By adding a drop of strong hydrochloric 
acid to the extract used in a, the magnesium is removed from the 
complex containing it and phaeophytin formed. 
There is now an intense absorption in the green just before 
the line E. 
c. Copper compound with phceophytin (see Experiment 9). 
The intense absorption in the green disappears and the spectrum 
is very similar to the chlorophyll spectrum. 
d. Carotin and xanthophyll. The absorption spectra of the 
yellow pigments has been described in section C. There is one 
band in the blue, another in the indigo blue and the end absorption 
in the violet. Unless the correct concentration is used there will 
either be complete absorption or none. By altering the concentra¬ 
tion it should be possible to obtain the correct strength of solutions 
for observing the bands. 
Spectroscopic analysis is, of course, very useful in work with 
chlorophyll and its derivatives, as most of the pure substances 
have characteristic spectra. But in class work where it is difficult 
to obtain even moderately pure substances, it will scarcely be 
possible to go much further in this matter than we have indicated 
in the preceding experiment. It should however be noted that one 
of the crucial tests for chlorophyll is its spectrum, as the breaking 
down of the magnesium-containing complex alters this. 
Experiments on the state of aggregation of chlorophyll. 
Experiment 16. Formation of a colloidal solution of chlorophyll. 
Evaporate down 10 c.c. of the acetone extract as obtained in 
Experiment 1 to about 2 c.c. A colloidal solution of chlorophyll is 
then made by pouring this acetone solution into a large volume of 
distilled water (20 to 100 c.c.) the liquid being continually stirred. 
This operation can be most conveniently done by taking the acetone 
solution in a pipette and allowing it to run out of the pipette while 
the latter is used as a stirring rod in the water. Note the change 
in colour to a purer green, and the disappearance of fluorescence. 
The principle involved in this method of preparation of colloidal 
chlorophyll consists in the replacement of the solvent (acetone) by 
a medium (water) in which the solute (chlorophyll) is insoluble. 
Thus a colloidal solution of sulphur can be similarly made. 
Sulphur is slightly soluble in warm alsohol, but insoluble in water. 
