as a Constituent of the Atmosphere. 389 



too high. Again, Eoscoe and Schorlemmer (' Chemistry,' 

 vol. i. p. 449) state that " the amount of C0 2 in the atmo- 

 sphere reaches to upwards of 3000 billions of kilogrammes," 

 which is about 33 per cent, in excess of the truth*. 



Sources whence the Air derives its Carbon Dioxide. 

 These are mostly natural ; but the progress of civilization 

 has added a large artificial supply to those already existing. 

 We may state them as follows: — 



(1) Combustion of carbonaceous bodies. 



(2) Respiration of animals. 



(3) Decomposition of vegetable and animal substances. 



(4) Yolcanos and other subterranean supplies. 



Under the first heading is included the amount produced 

 by the burning of coal, wood, peat, &c. From the most re- 

 cently issued statistics with regard to the amount of coal 

 raised in the world that I have been able to consultf, I find 

 that for the last three years at least 280 millions of tons have 

 been raised annually. This is probably a slight underestimate. 

 Assuming that 75 per cent, of this consists of pure carbon, 

 which if completely burnt in air would produce C0 2 , and 

 allowing a further 10 per cent, for the carbon thrown away 

 with the ash, we leave 182 millions of tons which are annually 

 converted into carbon dioxide. This will produce 1,800,000 

 tons per 'day, or very nearly 1800 millions of kilogrammes 

 per day. Assuming that by the combustion of wood, peat, 

 oil, &c. there is added one third more, we produce a total of 

 2400 millions of kilogrammes daily. 



In the case of the respiration of animals we can only form 

 an approximate estimate. The population of the world is at 

 present about 1500 millions; and it has been shown by experi- 

 ment that each individual produces on an average about a 

 kilogramme of C0 2 per day of 24 hours. Thus the human 

 race, in respiring, add to the air about 1500 millions of kilo- 

 grammes of carbon dioxide per day. Remembering the " 



* The above calculations are made on the figures deduced from the 

 results of the experimenters cited above. Recent investigations have, 

 however, thrown some doubt on the correctness of these numbers, the 

 general opinion being that 4 vols, in 10,000 is much too high. Thus, 

 Fittbogen and Hasselbarth (Chem. Centr. 1875, p. 694) give 3-4 vols, in 

 10,000 as the average; Farsky (Chem. Centr. 1877, p. 198) found 3-4, 

 while more recently Reiset (Comptes Rendus, lxsxviii. pp. 1007-1011) de- 

 duces 2-942. Taking the mean of these numbers, we have 



Weight of C0 2 in air .... 1545 billions of kilogrammes nearly. 



t Mineral Statistics for Great Britain for 1881 ; and Smyth's ' Coal 

 and Coal-Mining,' latest edition. 



