22 PHYSIOLOGY OF NUTRITION. 



7. The Absorption Spectrum and the Fluorescence of 

 Chlorophyll. 



To investigate the absorption spectrum of chlorophyll, we 

 require a suitable spectroscope. According to circumstances we 

 may use Bunsen's spectral apparatus, a direct vision spectroscope, 

 a pocket spectroscope, or a micro-spectral apparatus, to be used in 

 combination with a microscope. The micro-spectral apparatus, 

 with scale tube and comparison prism, is to be obtained of excel- 

 lent quality from Zeiss, of Jena, or from Seibert & Krafft, Wetzlar. 

 The other instruments named are supplied, e.g., by B. Muencke, 

 Berlin, Luissenstrasse 58, and Geissler Nachf, in Bonn. An exact 

 description of all the instruments would carry us too far. Detailed 

 information maybe found, e.g., in Miiller's Lehrbuch der Physik und 

 Meteorologie, 1879, Bd. II., First pt., p. 206. 



According to my own experience, it is most convenient to work 

 with direct- vision spectroscopes. In investigations intended to 

 determine exactly the position of the absorption bands, it is best 

 to select instruments provided with scales, not graduated arbi- 

 trarily, but according to wave lengths. The exact focussing of 

 the scale can then be effected in the simplest manner by means of 

 the Frauenhofer's lines. 



Considering first the micro- spectral apparatus represented in 

 Fig. 6 as supplied by Seibert & Kraift, Wetzlar it is to be noted 

 that t represents the drum containing the slit and comparison 

 prism. The screw d serves to narrow the slit, and the screw li 

 to shorten it ; / is the ocular tube, o the screw for focussing the 

 slit to the eye of the observer ; in the tube rr are the prisms, 

 s is a mirror for conveying light to the comparison prism when 

 it is inserted ; pp is a perforated plate fixed at the side of the 

 drum t, and provided with spring clamps. To obtain a com- 

 parison spectrum, the requisite substance is placed immediately in 

 front of the hole in the plate pp. We shall not here describe 

 the adjustment of the measuring apparatus, which may be attached 

 laterally to the top of the spectroscope. The student is referred 

 to Behren's Hilfsbuch bei mikroscopischen Untersuchungen, 1883, 

 p. 121. 



If we desire to investigate chlorophyll solutions, we prepare 

 them in the manner described in 6. Here again we shall only 

 experiment with the ordinary alcoholic crude chlorophyll solution, 

 leaving out of account other chlorophyll preparations, which are 



