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XXVI. On the Formation and Decomposition of Carbonic Acid. 

 By J. B. Lawes, F.R.JS* 



IVj facts in science have been more clearly established 

 -L 1 than those which relate to the decomposition of carbonic 

 acid by the green parts of plants (resulting in the fixation of 

 the carbon and the return of the liberated oxygen to the atmo- 

 sphere) and the part played by animal life and combustion in 

 again uniting the carbon with the oxygen. 



The vast quantity of carbon locked up in coal and other 

 carbonaceous deposits leads to the conclusion that, at one 

 period of the earth's existence, the amount of carbonic acid 

 must have been larger than it is at the present time; but 

 since the period when accurate determinations of carbonic acid 

 were first made, no appreciable difference in the quantity has 

 been shown to exist, although it would appear probable that 

 the great increase of animal life, the destruction of forests, and 

 the combustion of coal would tend to increase the amount. 



The Rothamsted experiments which have heen carried on 

 for so long a period, while they clearly establish the fact that 

 the atmosphere is the main, if not the exclusive, source of the 

 carbon fixed by plants, at the same time point to conclusions 

 which differ somewhat from those generally received, with 

 regard to the action of man and animal life on one side, and 

 that of plants on the other, in maintaining the equilibrium of 

 the atmosphere. 



I propose to take stock of the soil and atmosphere resting 

 upon Great Britain, with the assumption (fortunately for us 

 not a true one) that our atmosphere is as much a fixture as 

 our soils, and is not constantly being exchanged with the 

 atmosphere coming from other parts of the globe. 



The sources of the carbon given off into the atmosphere as 

 carbonic acid are three : — 



(1^ Those derived from the consumption of coal ; 



(2) From the imported products used as food or for com- 



bustion ; 



(3) From the products of our own soil. 



The agricultural statistics make the area of Great Britain to 

 consist of between 56 and 57 million acres. In order to reduce 

 the amount of figures as much as possible, in adopting this 

 estimate as my basis, I have given in the table below the figures 

 which apply to each acre of the surface per annum. 



The figures relating to the consumption of coal, which con- 

 stitute far the largest item in the table, have been furnished 



* Communicated "by the Author, 



