36 Carbon Assimilation. 



blue to violet parts of the spectrum. 



b. PhcBophytin. By adding a drop of strong hydrochloric 

 acid to the extract used in a, the magnesium is removed from the 

 complex containing it and ph^ophytin 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. 



Experivients 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 alcohol, but insoluble in water, 



