Carbon and Plants ¹

Abstract

IN a paper recently laid before the Royal Society, dealing with the physical processes which regulate the entry of atmospheric carbon dioxide into the leaves of plants,² the authors incidentally described a series of experiments relating to the rate of absorption of dilute gaseous carbon dioxide by surfaces of solutions of caustic alkali, when air containing definite small amounts of this gas is drawn over the liquid. Contrary to what might be expected from the perfect absorbing nature of the solution, and the known laws of gaseous diffusion, the amount of CO₂ absorbed by unit area of the liquid surface in unit time ceases sensibly to increase when a comparatively low velocity of the moving air current has been reached. This, however, only holds good when the proportion of CO₂ in the air stream is. maintained quite constant, any slight variation in the amount at once affecting the rate of absorption. On investigation, it was found that for dilutions of carbon dioxide lying between 0.6 part and 6 parts per 10,000 of air, the rate of absorption of the carbon dioxide is strictly proportional to its partial pressure.