4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



mined that additions to the standard chlorophyll solutions of carotene 

 or xanthophyll in amounts up to a hundred times that of the 

 chlorophyll, do not influence the transmission in the spectral region 

 employed. 



1 1 1 1 1 r 



MO. CHLOROPHYLL PER LITER 



Fig. 2. — Calibration curve showing percentage transmission plotted against 

 milligrams of chlorophyll per liter. 



Once this curve has been established the continued use of standard 

 chlorophyll solutions is eliminated. The transmission data obtained 

 from unknown chlorophyll solutions are compared with the calibration 

 curve and the concentrations read directly. The calibration curve 

 used is an empirical one for the particular filters, absorption cell, and 

 solvent employed. 



