THE DETERMINATION OF SMALL AMOUNTS OF CHLO- 

 ROPHYLL—APPARATUS AND METHOD 1 



By EARL S. JOHNSTON and ROBERT L. WEINTRAUB 2 

 Division of Radiation and Organisms, Smithsonian Institution 



(With Two Plates) 



INTRODUCTION 



The present paper describes a photometric method for the determi- 

 nation of small amounts of total chlorophyll present in plant tissue, 

 and the apparatus employed. The method is based on the fact that 

 chlorophyll has an absorption band in a certain region of the spectrum 

 that does not overlap the absorption bands of other soluble pigments 

 such as carotenoids. Although it is fully realized that other methods 

 have been employed and described, it is nevertheless felt worth while 

 to point out some advantages of this method which is adapted very 

 nicely to certain problems under investigation in this laboratory. 



APPARATUS 



The apparatus is illustrated in plate I and figure I. Essentially it 

 consists of a light source properly shielded in a housing and a hori- 

 zontal optical path in which the chlorophyll solution may be interposed. 



A single-filament street-series lamp ( 1,000 lumens and 6.6 amperes) 

 serves admirably as the light source. This is connected to 10 storage 

 batteries in such a manner as to give 12 volts. A battery source of 

 current is more desirable than the commercial city supply because of 

 its steadiness. Inside the lamp housing is a metal cylinder which may 

 be raised or lowered so as to transmit or intercept the light in its 

 passage through the optical system. From a condensing lens 3 inches 

 in diameter (shown in fig. 1) the light is passed through a Corning 

 heat-resistant, heat-absorbing light shade glass filter 2.66 mm. thick 

 (F]), a Corning heat-resistant pyrometer red, number 241, 48 percent 

 filter, 4.85 mm. thick (F 2 ), and a glass cell 2 cm. thick containing 



1 Presented before the Division of Biological Chemistry of the American 

 Chemical Society, Baltimore, Md., Apr. 3-7, 1939. 



2 The authors wish to acknowledge the assistance of L. A. Fillmen in the 

 construction of the apparatus, and of E. R. Brydon in carrying out the 

 determinations. 



Smithsonian Miscellaneous Collections, Vol. 98, No. 19 



