526 THE AIR AND LIFE. 



With this formidable aniouiit of production in view, we may well be 

 astonished that the proportion of carbonic aci<l in the atmosphere 

 remains so slii;ht, for we can easily calculate what proportions it would 

 reach in ten, twenty, or a hundred years, and how fatal such i)ropor- 

 tions would be to life, were there not some cause constantly at work 

 destroying? this gas. We are sure therefore that some powerful means 

 eliminates this gas from tlie atmospliere in about the proportion in 

 whicli it is produced. Three of these means Ave know, viz, an.mals, 

 plants, and the sea. 



Although plants by their respiratory function are exhalers of car- 

 bonic acid, they absorb a much larger quantity of it for their nutrition. 

 They absorb this gas and decompose it into its elements, carbon, which 

 becomes part of their tissues, and oxygen, which they restore to the 

 air. Plants are great producers of oxygen. 



Next in order of carbonic-acid destroyers are animals having skele- 

 tons or calcareous carapaces, such as shellfish, corals, nearly all marine 

 and terrestrial animals which form carbonate of lime. Van Dechen 

 has estimated that the calcareous strata of the carboniferous rocks 

 alone contain six times more carbon than the atmosphere now has, a fact 

 which suggested to Sterry Hunt, the American geologist, that there 

 must be some other source of carbonic acid, namely, interstellar space. 

 Indeed, if the carbonifevous rocks should liberate into the atmosphere 

 all the carbonic acid they contain, the pressure upon that gas would 

 be so great that a large ])art of it Avould be soon liquified or even 

 solidified. (Stanislas Meunier.) 



Lastly, the sea has a most important part in the absorption and 

 regulation of the production of carbonic acid, and thus prevents its 

 accumulation in the air beyoiid certain limits. Experiments made by 

 Mr. Schloesing prove that sea-water holds in solution a nnich larger 

 quantity of carbonic acid than the air contains. When carbonic acid 

 increases in the air on account of a production in excess of the destruc- 

 tion, a portion of it becomes dissolved in the sea- water and unites 

 with the neutral insoluble carbonate of lime that that water always 

 contains to form a soluble bicarbonate. Inversely, when the quantity 

 of carbonic acid diminishes in the atmosi)here, the soluble bicarbo 

 nate decomposes into the neutral carbonate which remains in the 

 sea, and into carbonic acid, which penetrates into the atmosphere. 

 In short, when there is equilibrium of tension between the carbonic 

 acid of the atmosphere and the acid of the sea water, nothing is 

 produced, but the moment the equilibrium of tension is destroyed the 

 sea proceeds, by this simple chemical process, to restore it. This 

 adjustment, constantly going on, is made possible because the sea con- 

 tains a much greater amount of carbonic acid than the atmosphere — 

 ten times more according to a calculation of Mr. Schloesing. However 

 great, then, the production of carbonic acid may be on the surface of 

 the globe by all the agents we have enumerated, we are certain that 



