OXYGEN AND CARBON. 



carbon for fruit or grain, and for grass or 

 trees, are different. 



It is not denied that manure exercises an 

 influence upon the development of plants ; 

 but it may be affirmed with positive cer- 

 tainty, that it neither serves for the produc- 

 tion of the carbon, nor has any influence 

 upon it, because we find that the quantity 

 of carbon produced by manured lands is 

 not greater than that yielded by lands which 

 are not manured. The discussion as to the 

 manner in which manure acts has nothing 

 to do with the present question, which is, 

 the origin of the carbon. The carbon must 

 be derived from other sources ; and as the 

 soil does not yield it, it can only be ex- 

 tracted from the atmosphere. 



In attempting to explain the origin of 

 carbon in plants, it has never been con- 

 sidered that the question is intimately con- 

 nected with that of the origin of humus. It 

 is universally admitted that humas arises 

 from the decay of plants. No primitive 

 hurnus, therefore, can have existed for 

 plants must have preceded the humus. 



Now, whence did the first vegetables de- 

 rive their carbon ? and in what form is the 

 carbon contained in the atmosphere ? 



These two questions involve the conside- 

 ration of two most remarkable natural phe- 

 nomena, which by their reciprocal and un- 

 interrupted influence maintain the life of the 

 individual animals and vegetables, and the 

 continued existence of both kingdoms of or- 

 ganic nature. 



One of these questions is connected with 

 the invariable condition of the air with re- 

 spect to oxygen. One hundred volumes of 

 air have been found, at every period and in 

 every climate, to contain 21 volumes of 

 oxygen, with such small deviations that they 

 must be ascribed to errors of observation. 



Although the absolute quantity of oxygen 

 contained in the atmosphere appears very 

 great when represented by numbers, yet it 

 is not inexhaustible. One man consumes 

 by respiration 25 cubic feet of oxygen in 

 2 hours; 10 cwt. of charcoal consume 

 32,066 cubic feet of oxygen during its com- 

 bustion; and a small town, like Giessen, 

 (with about 7000 inhabitants) extracts yearly 

 from the air, by the wood employed as fuel, 

 more than 551 millions of cubic feet of this 

 gas. 



When we consider facts such as these, 

 our former statement, that the quantity of 

 oxygen in the atmosphere does not diminish 

 in the course of ages* that the air at the 

 present day, for example, does not contain 

 less oxygen than that found in jars buried 



* If the atmosphere possessed, in its whole ex- 

 tent, the same density as it does on the surface 

 of the sea, it would have a height of 24,555 

 Parisian feet ; but it contains the vapour of water, 

 BO that we may assume its height to be one geo- 

 graphical mile =22,843 Parisian feet. Now the 

 radius of the earth is equal to 860 geographical 

 miles ; hence the 



for 1800 years in Fompeii appears quite 

 incomprehensible, unless some source exists 

 whence the oxygen abstracted is replaced. 

 How does it happen, then, that the propor- 

 tion of oxygen in the atmosphere is thus 

 invariable ? 



The answer to this question depends upon 

 another; namely, what becomes of the car- 

 bonic acid, which is produced during the 

 respiration of animals, and by the process 

 of combustion! A cubic foot of oxygen 

 gas, by uniting wifn carbon so as to form 

 carbonic acid, does not change its volume. 

 The billions of cubic feet of oxygen ex- 

 tracted from the atmosphere, produce the 

 same number of billions of cubic feet of 

 carbonic acid, which immediately supply its 

 place. 



The most exact and most recent experi 

 meats of De Saussure, made in every sea- 

 son for a space of three years, have shown, 

 that the air contains on an average - 000415 

 of its own volume of carbonic acid gas ; so 

 that, allowing for the inaccuracies of the 

 experiments, which must diminish the 

 quantity obtained, the proportion of carbonic 

 acid in the atmosphere may be regarded as 

 nearly equal to 1-1000 part of its weight. 

 The quantity varies according to the sea 

 sons ; but the yearly average remains con- 

 tinually the same. 



We have no reason to believe that this 

 proportion was less in past ages ; and never- 

 theless, the immense masses of carbonic 

 acid which annually flow into the atmos- 

 phere from so many causes, ought percepti- 

 bly to increase its quantity from year to 

 year. But we find that all earlier observers 

 describe its volume as from one-half to ten 

 times greater than that which it has at the 

 present time ; so that we can hence at most 

 conclude that it has diminished. 



It is quite evident that the quantities of 

 carbonic acid and oxygen in the atmosphere, 

 which remain unchanged by lapse of lime, 

 must stand in some fixed relation to one 

 another; a cause must exist which prevents 

 the increase of carbonic acid by removing 

 that which is constantly forming; and there 



Volume of atmosphere =9, 307, 500 cubic miles. 



= cube of 210-4 miles. 

 Volume of oxygen =1,954,578 cubic miles. 



= cube of 125 miles. 



Vol. of carbonic acid =3,8627 cubic miles. 

 = cube of 15'7 miles. 



The maximum of the carbonic acid contained 

 in the atmosphere has not here been adopted, but 

 the mean, which is equal to 000415. 



A man daily consumes 45,000 cubic inches 

 (Parisian.) A man yearly consumes 9505'2 cubic 

 feet. 100 million men yearly consume 9,505,- 

 200,000,000 cubic feet. 



Hence a thousand million men yeaily consume 

 0'79745 cubic miles of oxygen. But the air is 

 rendered incapable of supporting the process of 

 respiration, when the quantity of its oxygen is 

 decreased 12 per cent. ; so that a thousand million 

 men would make the air unfit for respiration in a 

 million years. The consumption of oxygen by 

 animals, and by the process of combustion, is not 

 introduced into the calculation. 



