2 50 POPULAR SCIENCE MONTHLY. 



carbonate of lime separate from the water as a solid precipitate, the 

 second part of the carbon dioxide would be free to pass from the 

 water into the atmosphere. We are thus led to consider the agencies 

 which have caused the deposition of lime from dilute solution. 



Modern views of chemical combinations regard compounds in solu- 

 tion as going through a constant interchange of reactions, by which 

 ions pass continuously from one association to another, as in the grand 

 chain the dancers weave in and out with touch of hands. The dance 

 of the ions, more technically called dissociation, is most active in dilute 

 solutions, and is promoted by higher, retarded by lower temperatures. 

 It has been shown by experiment that bicarbonate of lime may be dis- 

 sociated by agitating the solution, and there are occurrences of calcare- 

 ous formations which indicate that the monocarbonate is deposited as 

 a result of such action. Thus it is probable that, through tliis process, 

 warm seas surrender to the air a notable amount of carbon dioxide, but 

 that the contribution becomes insignificant or ceases when the waters 

 are chilled. 



Under favorable conditions the ocean abounds in organisms which 

 secrete normal carbonate of lime as parts of their structures. They 

 swarm in the warm waters of tropical oceanic currents, they exist in 

 multitudes on the warm shallows where the sea spreads over the mar- 

 gins of continental masses with a depth not exceeding 100 fathoms, but 

 they are rare or are replaced by species without hard parts in cold 

 waters. The physiological reactions by which these organisms obtain 

 the normal carbonate from the water are not definitely known. They 

 may take it from bicarbonate in solution, or by reaction on sulphate of 

 lime setting free sulphuric acid, which attacks the bicarbonate. In any 

 case, the effect is to fix one ion of carbon dioxide in the solid normal 

 carbonate, and to free the second ion, which may pass into the air. The 

 enormous volume of organic calcareous deposits now forming, and the 

 massive limestone strata of past ages, largely or wholly of organic 

 origin, attest the importance of the process. Life may be considered 

 the most important of those agencies which restore carbon dioxide to 

 the atmosphere, but it is narrowly conditioned by limitations of habitat 

 and warmth. 



Carbon dioxide absorbed in sea-water is yielded to the atmosphere 

 and returned by it under varying conditions of tension of the gas, of 

 barometric pressure, and of temperature. At moderate temperature the 

 sea gives up the gas freely, and would supply a deficiency gradually 

 brought about in the atmosphere. But colder waters hold it faster, and 

 may even take carbon dioxide from an already depleted atmosphere. 



Thus the processes of dissociation by chemical and organic agencies 

 and of absorption depend upon temperature, and through this depend- 

 ence promote the prevailing tendency of climatic changes. If the 



