9-4 Mr. J. Stevenson on the Chemical and 



is obvious that a considerable proportion of organic remains 

 escapes oxidation, and is preserved for a considerable time, at 

 any rate, in the form of peat or coal. It is not easy to form an 

 estimate of the proportion or percentage of vegetable remains 

 that is preserved in this way; but when it is observed that 

 about 6, 000,000 acres in the United Kingdom, or nearly 

 8 per cent, of the total surface of the country, are covered by 

 peat-bogs, it is obvious that the proportion must be of consi- 

 derable importance. No doubt the rate of growth of vegetation 

 in or on peat-bogs may be much less than the average rate 

 for the whole country, and the proportion of the earth-surface, 

 taken as a whole, which is covered by peat- bogs may be very 

 much less than 8 per cent. ; but still it is quite possible that 

 the amount of vegetable remains which escapes oxidation in 

 this and in other ways may be as much as 1 per cent, of the 

 total quantity of such remains, and probably it is at least 

 0'1 per cent. That is to say, there is more carbonic acid 

 annually removed from the atmosphere by the growth of 

 vegetation than is returned to it by the oxidation of vegetable 



O l 1 • . 



and animal remains, the difference being probably at least 

 0*1 per cent, of the amount removed, and possibly as much as 

 1 per cent, or even more. 



Of the other agencies which add carbonic acid to the atmo- 

 sphere, the most important is probably volcanic action, or 

 the heating of certain rocks under such conditions as to cause 

 the evolution of carbonic acid ; but still we have very little 

 quantitative information regarding it. Boussingault consi- 

 dered that the volcano Cotopaxi evolved annually more car- 

 bonic acid than a whole city like Paris (which he calculated 

 to evolve about 3,000,000 cubic metres of carbonic acid daily); 

 and Lecoq calculated that the mineral springs of Auvergne 

 gave off annually 7000 x 10 G cubic metres of carbonic acid 

 gas, an amount rather less than ^ of the volume produced 

 by the annual combustion of the coal employed throughout 

 the whole of Europe. Bischof estimated that the quantity of 

 carbonic acid evolved in the Brohl Thai in the Eifel district 

 of Rhenish Prussia amounted to 5,000,000 cubic feet, or 

 300 tons of gas per day. These are not perhaps very large 

 quantities in themselves ; but still there are many other 

 volcanoes and volcanic regions in the world, and the total 

 quantity of carbonic acid evolved from subterranean sources 

 may be very large indeed. It is also known from the 

 Report of the ' Challenger ' Expedition that carbonic acid is 

 evolved in some places at the bottom of the sea in very con- 

 siderable quantities. Further, it is even possible that carbonic 

 acid may be evolved from the ground in regions which are 



