PHO TOS YN THESIS. 



EXPEKI.MKXT 26. This may be settled by examining the effect 

 produced upon a ray of light by its passage through chlorophyll in 

 comparison with one not passed through the chlorophyll. This ex- 

 amination must be made with an instrument designed for light 

 analysis, namely, the spectroscope (see page 331, while the chloro- 

 phyll is best examined in solution. Prepare a solution of chlorophyll 

 from clear green leaves as yielded by Experiment 24; it should not 

 be over a few hours old, and, to prevent its alteration in light, must 

 be kept in darkness while not in use. Place the solution in three 

 flat-sided Soyka flasks, which may be supported one, two, or three at 

 a time before the spectroscope (see the arrangement in Fig. 1 7) ; ex- 

 amine these, one, two, and three at a time, with the spectroscope, 

 and compare the solar spectrum pure and as affected by the chloro- 

 phyll. Try to interpret the result, and record the spectra as nearly 

 natural as possible. 



FIG. 17. ARRANGEMENT OE SPECTROSCOPE FOR STUDY OF ABSORPTION 



SPECTRUM OF CHLOROPHYLL. 



The light in the middle supplies both the scale and the comparison prism. One- 

 fourth the true size. 



Practically it is just as instructive, and certainly it is much more 

 convenient, to use instead of the sunlight the incandescent electric light. 

 A good arrangement is shown by Fig. 17. A comparison should of 

 course be made between electric light and sunlight, but the principal 

 study may then be carried on with the former. 



Incidentally the other leading characteristics of chlorophyll should be 

 noted, particularly its fluorescence, which may be heightened by focusing 

 sunlight upon it with a hand-lens. 



