THE CHEMISTRY OF PHOTOSYNTHESIS 313 



absorbed carbon dioxide. All of these alcoholic precipitates had a high 

 ash content, varying from 20 to 50 per cent according to the species of 

 leaves used. 



By employing the apparatus which Van Slyke '^•' designed for deter- 

 mining the carbon dioxide in blood, it was possible to demonstrate that 

 the larger part of the absorption of carbon dioxide by the dried leaf 

 material and the alcoholic precipitates obtained therefrom could be 

 ascribed to bicarbonate formation. I'y the use of this apparatus the 

 amount of carbon dioxide liberated from a solution of the alcoholic 

 precipitates or from susi:)ensions of the finely powdered leaf material, 

 in a TorriceUian vacuum, and after the addition of sulphuric acid could 

 be determined. It is a noteworthy fact that the two species of leaves 

 with which Willstatter and Stoll studied the absorption of carbon dioxide 

 were the sunflower and nettle. With these leaves Spoehr and Newton 

 also observed highest absorption. Moreover, with the exception of these 

 two leaf materials, others, including spinach, hydrangea, turnip, lettuce, 

 alfalfa, rhubarb, grass and Ramilina reticulata showed no absorption by 

 the leaf material and only slight absorption by the alcoholic precipitates 

 in some cases, and in most cases none at all. Also, with the exception 

 of sunflower and nettle, after saturation of the leaf material with car- 

 bon dioxide, the evolution of this gas, on addition of sulfuric acid, was 

 exceedingly small. When this leaf material (excepting sunflower and 

 nettle) was saturated with carbon dioxide the amount of this gas which 

 was liberated in vacuo was equivalent to the amount which could be dis- 

 solved in the quantity of water present. Hence if there is an absorption 

 factor in this leaf material, it is too smaU to be detected by this method. 

 The sunflower and nettle material is noteworthy because both the 

 dried leaf material and the alcoholic precipitates absorb more carbon 

 dioxide than can be accounted for by the solubility of this gas in the water 

 added to the dried or precipitated material. When preparations of this 

 sort (e.g. dried and powdered leaves to which a quantity of water 

 equivalent to that originally present in the fresh leaves was added) were 

 exposed to an atmosphere free of carbon dioxide for several hours, and 

 then acidified, considerable carbon dioxide was liberated. When similar 

 material was saturated with carbon dioxide and then acidified, the amount 

 of this gas which was liberated was approximately double the quantity 

 evolved in the case just described. These facts would indicate that the 

 absorption of carbon dioxide is due to a carbonate : bicarbonate reaction. 

 The values for the material that was saturated with carbon dioxide were 

 obtained by acidifying the suspension after removing the carbon dioxide 

 which came ofif under a Torricellian vacuum. The alcoholic precipitates 

 behaved in a similar manner. For instance, a precipitate obtained from 

 sunflower after being in an atmosphere free of carbon dioxide for 4 

 hours evolved 8.6 mg. carbon dioxide on acidification, and after having 



"* Van Slyke and Stadie, Jour. Bio. Cheni., 49, 1 (1921). Van Slyke and Cullen, 

 ibid., 30, 289 (1917). 



