- 3 = 



atoirdo weight of oxygen iwas due to the fact that oxygen as it occurs in 

 nature, either free or combined, is a mixture. It is a mixture of iso- 

 topes that differ in atomic weight and that are not readily detectable 

 or separable by chemical methods. 



With the development of the mass spectroscope during I9I8-I920, 

 oxygen was found to be a mixture of three isotopes , ', and , 

 the comprising about 99.759 P©r cent of the mixture. Natural oxygen 

 is, therefore, just a little heavier than the isotope, which is the 

 reference standard of the physicists. For this reason, the atomic 

 weights employed by the chemist are a little heavier than the atomic 

 weights employed particularly by the nuclear physicists and nuclear 

 cheraistSo Specifically these chemical atomic weights are heavier than 

 the physical isotopic weights by a factor of 1«000272 ± 0,000005 or 272 

 units in 1,000,000 or about 5 in 10,000. 



This difference between the basic physical and chemical atomic 

 weights arose primarily because of the limitations of the analytical 

 techniques that were available to the chemist. It is but one of many 

 illustrations showing that analysis is an indispensable step in the 

 resolution of mixtures and in the description of the components^'-'. 



Analysis and the Interpretation of Photosynthesis 



From the academic standpoint of correlation, interpretation, and 

 instruction, the role of analysis in the physical, chemical and biologi- 

 cal sciences is frequently overlooked. But from the technical stand- 

 point of investigation and discovery, analysis often plays a critical 

 role. It defines and establishes the progress that has been made. It 

 brings to light new observations and new materials that continually 



