388 Mr. E. H. Cook on Carbon Dioxide 



Amount of Carbon Dioxide in the Atmosphere. 

 This question has been made the subject of experiment by 

 many of our leading chemists. In order to calculate the ab- 

 solute amount, we require to know two things — viz. the capa- 

 city or weight of the air, and the percentage of C0 2 which it 

 contains. Fortunately the data for doing this have been 

 determined with very great accuracy. The lengths of the 

 diameters of the earth have been determined to be very nearly 

 7899 miles for the polar and 7925^ for the equatorial ; " and 

 in these measures it is pretty certain that there is not an error 

 of a quarter of a mile " *. Applying the ordinary rule for the 

 cubic content of an oblate spheroid, we obtain 259,026,554,299 

 cubic miles as the capacity of the earth. .Now the height of 

 the homogeneous atmosphere is found to be 26,214 feetf, or 

 very nearly 5 miles ; calculating the capacity of the spheroid 

 formed by adding this distance to the lengths of the diameters 

 given above and subtracting the capacity of the earth, we 

 obtain the cubic content of the atmosphere supposed homo- 

 geneous: this is found to be 591,647,337 cubic miles. With 

 regard to the amount of carbon dioxide present in the air, 

 the older experimenters, Dumas and Boussingault (Ann. Ch. 

 Phys. iii. pp. 257, 288), Lowy and Saussure (Pogg. Ann. 

 xix. p. 391), have published results which yield a mean of 

 4 vols, in 10,000 of air, or 4£ parts in 10,000 by weight. 

 Thorpe (Journ. Chem. Soc. vol. xx. p. 189) has shown that 

 over the sea the average is 3 vols, in 10,000 ; while Saussure 

 states that at high altitudes the proportion of dioxide is greater 

 than at lower levels. Without deviating very far from the 

 truth we may take 4 vols, in 10,000 of air; and we thus find 

 (assuming capacity of air to be 592,000,000 cubic miles) 

 236,800 cubic miles as the amount of C0 2 in the atmosphere. 

 Finally, calculating from the specific gravity, we find the 

 weight to be 4287 billions of pounds. Expressed on the 

 metric system these figures become : — 



Cubic capacity of air... 2,439,987,200,000,000,000 kilolitres. 

 Weight of C0 2 in air... 1,913,685,908,480,000 kilogrammes. 



I have given these calculations somewhat in detail because 

 of the great difference between my numbers and those hitherto 

 published. Thus, Dumas and Boussingault (op. cit.) say that the 

 air is equal in weight to 581,000 cubes of copper each having 

 a side of 1 kilometre : this gives 4,200,000,000,000,000,000 

 kilolitres as the capacity of the air, or very nearly 40 per cent. 



* Herschell, ' Familiar Lectures,' p. 58. 

 t Maxwell, « Theory of Heat,' p. 228. 



