204 THE ATMOSPHERE 



The whole of the carbon of the living world, of the vast 

 forests and myriad animal forms, comes from the -03 per cent. 

 C0 2 in the atmosphere. 1 The amount of this C0 2 is estimated 

 at 2 - 4 x 10 12 tons. Brown and Enscombe have contrasted the 

 rate of absorption of a solution of potash with that of the 

 stomata of the leaves of Catalfa Ugnonioides, and found that 

 the latter absorb C0 2 from a current of air no less than fifty 

 times quicker than the potash. One square metre of leaf surface 

 laid on 1 grm. of dry substance per hour corresponding to 784 c.c. 

 C0 2 , and the stomata occupied only 1 per cent, of the surface. 

 The chloroplasts of the plant cells act as an " activator," con- 

 verting by the fluorescence of the chlorophyll pigment a large 

 part of the highly refractile rays of sunlight into red rays, and 

 activating the chemical reactions of the protoplasm which result 

 in the condensation of C0 2 and H 2 to hexose. It has been 

 suggested that the formation of formaldehyde, H . CHO, is the 

 first stage in the reduction of C0 2 . This substance in the 

 presence of weak alkali readily undergoes polymerisation into 

 formose (CH 2 0) G , a mixture of substances some of which 

 have the composition of the sugars. Huxley has calculated 

 that the atmosphere, superincumbent on one square mile of 

 country, continually holds 13,800 tons of C0 2 enough carbon 

 to supply 7400 tons of trees. Bunge suggests that in the early 

 and more volcanic periods of the earth's history the percentage 

 of C0 2 stood at a higher figure, and the luscious growth of 

 vegetation in the Carboniferous period abstracted this excess. 

 This, buried as coal, is now being rapidly returned to the 

 atmosphere by fire. Bunge also suggests that the percentage 

 of C0 2 in the atmosphere is being reduced by its union with 

 the bases of the earth's crust. The chief rocks of the crust 

 are carbonates and silicates of calcium, magnesium, ferrous 

 oxide, &c. In the presence of water and in the cold C0 2 has 

 a greater affinity than silicic acid for the bases. Rain and 

 waves containing traces of C0 2 ceaselessly corrode the silicic 

 rocks, and from their solution the carbonates of chalk and 

 magnesia, and the silicates clay and sand are thrown down. 

 In the deeper strata heat arises from the mechanical effects 

 of compression, and under the influence of heat silicic acid 



1 Bacteria are known which assimilate the minute trace of hydrocarbon in 

 the atmosphere and cannot utilise C0 2 . 



