201 
OF GARDENING AS A SCIENCE. 
NO. IX. 
AIR. 
The air of the atmosphere must be considered as at least important to vege- 
tables, although it does not appear so vital to them as it is to the animal organiza- 
tion ; for, in point of fact, its direct operation cannot be decidedly traced. The 
composition, however, of the air must be understood, in order that the physiologist 
may be prepared to investigate its agency. Chemists are in the habit of stating 
that one hundred volumes of air consist of twenty-one volumes of oxygen gas, and 
seventy-nine volumes of nitrogen gas — in a condition of simple mixture, not of 
chemical union— -they therefore assert that " the composition of the atmosphere is 
extremely uniform in all parts of the world, and at all heights above its surface." 
But when they assert this, they admit and afford proof that air contains at all 
times varying proportions of aqueous vapour and of carbonic acid ; and therefore 
as an approximation we find that *' the ordinary constituents of the atmosphere 
appear to be the following — 
Nitrogen .... by measure 7 7 "5 or by weight 75 '55 
Oxygen .... „ 21- „ 23-32 
Aqueous vapour . . 1*42 1*03 
Carbonic acid ... ,, 0*08 ,, '10 
100 100 
Brande's Manual, p. 411.'" 
Let us now recur to Liebig (pp. 16, 17) in order to acquire insight into some 
remarkable phenomena, which, were they not of familiar occurrence, are of magni- 
tude sufficient to overwhelm the mind with awe. 
Presuming that one hundred volumes of air contain twenty-one volumes of 
oxygen, he observes, " Although the absolute quantity of oxygen contained in the 
atmosphere appears very great when represented by numbers, yet it is not inex- 
haustible. One man consumes by respiration about forty-five Hessian cubic 
feet (nearly twenty-five English) of oxygen in twenty-four hours; and a small town 
like Giessen, with about 7000 inhabitants, extracts yearly from the air, by the 
w^ood employed as fuel, more than 1000 millions of cubic feet of this gas." In a 
note, we find " The air contains in maximo l^-g- carbonic acid gas, and ■j-i-§Q-§^ 
oxygen gas. A man consumes in one year 166,075 cubic feet of oxygen, or forty- 
five cubic inches in one day, according to Lavoisier, Seguin, and Davy ; a 
thousand million men must accordingly consume 166 billion cubic feet in one 
year ; this is equal to -^-^ih. of the quantity which is contained in the air in the 
form of carbonic acid. The carbonic acid in the air would thus be doubled in 1 000 
years, and man alone would exhaust all the oxygen and convert it into carbonic 
VOL. VIII. NO. XCIII. D D 
