PHYSICS. 241 



light is reducing. Between D and E the photo-chemical 

 action is zero. (2) That on organic substances the action is 

 an oxidizing one, continually increasing from red to violet, 

 being represented by 2 in the former and 3 in the latter, if 

 that in darkness be taken as 1. (3) That fluorescent rays 

 do chemical work within the substance, transforming qui- 

 nine, for example, into quinicine. The heat accompanying 

 the light does not affect the result. 



Timiriazeff has studied with great experimental precision 

 the question of the decomposition of carbon dioxide by light 

 in the leaves of plants, with a view to establish the connec- 

 tion of the rays of the spectrum active in this decomposition 

 with the results. Since to obtain reliable results a pure 

 spectrum is necessary, and in that case the light is much en- 

 feebled, and the amount of decomposition proportionately 

 small, the author contrived an exceedingly convenient ap- 

 paratus for working on and measuring small quantities of 

 gas. The solar light was received by a lens from the helio- 

 stat, nearly at the focus of which was a slit one millimeter 

 wide. Beyond this was a second lens and a carbon disul- 

 phide prism. The purity of the spectrum was such that 

 when a solution of chlorophyll was interposed, all its ab- 

 sorption bands were sharply defined. The leaves used were 

 bamboo, the surface of each piece being a square decimeter. 

 These pieces were placed in test-tubes of ten to twelve mil- 

 limeters diameter, which were then filled with mercury, in- 

 verted, and a mixture of air with five per cent, carbon diox- 

 ide allowed to enter from a gasometer, filling the tube to a 

 mark on the glass. Six tubes were thus prepared, one being 

 used as a check, containing no leaf, and the other five being 

 placed in the spectrum, the first in the ultra red, the second 

 in the red between B and C, the third in the orange, the 

 fourth in the yellow, the fifth in the green. They w r ere ex- 

 posed to the light for six hours, and the gas was then ana- 

 lyzed. The results were uniformly the same, and showed a 

 maximum of decomposition in the second tube correspond- 

 ing to the space between B and C. But this is exactly the 

 position of the principal absorption band of chlorophyll. 

 Hence the author concludes that his experiments prove the 

 position that the identical energy absorbed by chlorophyll is 

 the energy active in decomposing carbon dioxide in leaves. 



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