24 THE CULTURE OF FARM CROPS. 



ed in ajar of oxygen or consumed in an intensely heated 

 furnace. The heat and time, in both instances, multiplied 

 together, would produce precisely the same sum. Vegetable 

 matter decomposes or is consumed by the action of oxygen 

 in a similar way. The oxygen breaks up the organic sub- 

 stance into simpler compounds; separating the other ele- 

 ments previously mentioned (see chap. II) and uniting with 

 them ; forming carbonic acid with the carbon, water with 

 the hydrogen, nitric acid with the nitrogen, potash with the 

 potassium, soda with the sodium, lime with the calcium, 

 magnesia with the magnesium, phosphoric acid with the 

 phosphorus, silica with the silicon, and sulphuric acid with 

 the sulphur. All of these constituents of plants are thus 

 seen to be composed in part of this common element, which 

 pervades all nature. 



Oxygen is the universal supporter of respiration; and 

 plants perform this function in much the same manner as 

 animals. That is, they imbibe air through the pores in 

 their leaves and separate oxygen from it and utilize this in 

 their vital functions. Animals draw it into their lungs 

 where it comes in contact with the blood, then and there 

 loaded with impure matter brought through the veins from 

 the extremities of the system, and oxidizing it changes these 

 impurities, frees the blood from them, and sends the vital 

 fluid back through the arteries, bright, clear and fitted to 

 reinforce and build up the muscular tissue. And this oxi- 

 dizing effect of this "vital air" as it has been called, is ac- 

 companied by a certain elevation of temperature for it is 

 accompanied by a chemical process closely akin to com- 

 bustion. 



The air over every square inch of the earth's surface 

 weighs 15 pounds. Three pounds of this is oxygen. A 

 man consumes by respiration about 2 pounds of oxygen 

 daily. One pound of coal in burning consumes 21 pounds 

 of oxygen, so that the heat produced in a man's system by 

 the process of respiration is equal to that produced by the 

 combustion of one pound of coal. 



Oxygen not only contributes the vital element to the at- 



