APPENDIX 



345 



fOOO 



the expense of rays absorbed by the chlorophyll. In order to 

 do so we had only to perform Priestley's experiment simul- 

 taneously in different parts of the spectrum. The experiment 

 was performed in the following way : a series of glass tubes 

 (fig. 83 II, I, 2, 3, 4, 5) 

 were filled with a mix- 

 ture of air together 

 with a certain per- 

 centage of carbonic 

 • acid. Green leaves 

 from the very same 

 plant and of similar 

 size were introduced 

 into each of them. 

 Then the vessels were 

 exposed to the spec- 

 trum of the sun ob- 

 tained in a perfectly | 

 dark room. After a 

 few hoiurs it was de- 

 termined, by analys- 

 ing the gas, in which 

 tubes the carbonic acid 

 had decomposed and 

 in which not — ^those in 

 which it had decom- 

 posed more, and those 

 in which less. 



This experiment en- 

 tirely proved the hy- 

 pothesis. It turned 

 out that the decom- 

 position of carbonic 

 acid took place exclu- 

 sively in rays which 

 corresponded to the black band in the spectrum of chlorophyll 

 (fig. 83, I Red. — and fig. 82 between B and D), which means 

 that rays which do not get absorbed by the chlorophyll do 

 not decompose carbonic acid; whereas rays which become 

 absorbed decompose it the more, the more they themselves 



Fig. 83. 



