SIGNIFICANCE OF CHLOROPLAST PIGMENTS AND OF METHODS 

 FOR THEIR SEPARATION 



PHOTOSYNTHESIS REVEALED BY ANALYSIS 



Priestley' s Contributions 



These annual Priestley lectures, sponsored jointly by the Pennsyl- 

 vania State University and by the Mu Chapter of Phi Lambda Upsilon pro- 

 vide a dynamic memorial to an outstanding chemist in America, They also 

 provide a unique opportunity for the presentation of scientific accom- 

 plishments in specialized fields. They permit the elaboration of many 

 aspects of these accomplishments that are frequently unsuited for the 

 specialized publications of this day. 



It is not surprising that many of the preceding lecturers in this 

 series have traced the beginnings of their science to the work of Joseph 

 Priestley and his contemporaries. The discovery of dephlogisticated air 

 by Priestley and by Scheele in 177U marked a key point in chemical pro- 

 gress. The recognition of dephlogisticated air as a chemical element, 

 named oxygen by Lavoisier in 1776, helped clarify the nature of air, the 

 nature of combustion and oxidation, the characteristics of respiration, 

 and the features of photosynthesis (the assimilation of carbon dioxide 

 or fixed air by green plants with the concomitant production of dephlogis- 

 ticated air) . 



Priestley is famous not only for the basic nature of his scientific 

 experiments but also for his defense of an erroneous concept. His keen 

 observations on the properties of gases and on the nature of gaseous ex- 

 change stand in sharp contrast to his stout support of the phlogiston 

 theory. Nonconformist as a minister, Priestley ironically championed 

 the phlogiston theory in the face of increasing contrary evidence, much 



