provide the grist for the mill of scientific progress-^. 



At Priestley's time, the controversies about the chemical nature 

 of combustion, respiration, fermentation and photosynthesis resulted 

 largely from the lack of methods for the separation of gaseous mixtures. 

 For example, the physiologists, the observant physicians of that day, 

 soon recognized that animals consumed dephlogisticated air leaving spent 

 air or phlogisticated air, our nitrogen, and fixed air^. Fixed air, 

 obtainable from carbonates and from fermentation, was only gradually 

 recognized as a product of combustion and an oxide of carbon . 



The early difficulties in the elucidation of gaseous reactions 

 may be ascribed not only to the lack of analytical techniques for the 

 separation and identification of gases but also to the deficiency of 

 methods for the establishment of their chemical composition. Even 

 today chemists and graduate students do not have a ready answer to the 

 question, "How may one determine the chemical composition of carbon 

 dioxide?" 



Gradual progress in the chemical analysis of gaseous mixtiires 

 led, eventually, to a sound chemical understanding of gaseous exchange 

 in combustion, respiration, fermentation, and photosynthesis. Through 

 analysis by quantitative chemical methods, combustion (particularly of 

 organic substances) and respiration were characterized as processes in- 

 volving the cons\unption of oxygen. Combustion was oxidation accompanied 

 by the liberation of heat or energy. Respiration was controlled, bio- 

 chemical oxidation accompanied by the production of work and heat. As 

 the carbon compounds of plant material have an average composition 

 roughly equivalent to carbohydrate, the over-all processes of respira- 

 tion may be written as a chemical equation, namely. 



