36 SCIENCE AND SOIL 



stearin by having two less hydrogen atoms in each acid radicle. 

 By itself, olein is a liquid or oil. 



The oil of corn contains about 4 per cent of stearin, 45 per cent 

 of olein, and 48 per cent of linolin, which differs from olein by two 

 hydrogen atoms, and from stearin by four hydrogen atoms, in 

 each acid radicle. 



When these fats and oils are heated with a strong base (alkali) 

 such as potassium hydroxid, three potassium atoms displace 

 the glyceryl radicle (=C 3 H 5 ) and form potassium stearate 

 (C 17 H 35 COOK), potassium oleate (C 17 H 33 COOK), etc.; while 

 the three hydroxyl groups unite with glyceryl to form glycerin, 

 C 3 H 6 (OH) 3 . The salts formed by potassium or sodium with these 

 fatty acids are what we call soap, the potassium compounds being 

 soft soap, and the sodium, hard soap. 



While the fixation of carbon, oxygen, and hydrogen, resulting 

 ultimately in the formation of carbohydrates and fats, is properly 

 considered the most important process in plant growth, we may 

 well remember that no fixation and no growth occur in the absence 

 of the other seven essential elements of plant food. Indeed, from 

 the standpoint of possible control of crop production, another 

 tripod is more important than these three; namely, nitrogen, 

 phosphorus, and limestone. 



Nitrogen. This element has received more consideration as 

 plant food than any other essential element. In the free state (N 2 ) 

 it is a gas, and in this form it constitutes three fourths of the air. 

 The total supply of nitrogen over each acre of the earth's surface, 

 if available, would meet the needs of a hundred-bushel crop of 

 corn every year for 500,000 years; whereas the supply of carbon 

 is sufficient for such crops for only two years. Nevertheless, carbon 

 has no commercial value as plant food, while nitrogen in available 

 form is worth 15 to 20 cents a pound in the markets. These facts 

 only emphasize the need of science in agriculture. 



Nitrogen is not contained in the mineral matter of the earth, but 

 it is a constituent of common organic matter. It is an essential 

 part of the structure of every plant and animal, and is present in all 

 crops and crop residues and, consequently, in the organic matter, 

 vegetable matter, or humus, of the top soil; and it is from the 

 decomposition products of this organic matter that nitrogen is 



