120 THE SPIRIT OF THE SOIL 



ing have taught men something of electricity. 

 When the untaught man, however, finds himself 

 confronted with chemistry, he is apt to feel himself 

 in a strange world with no means of determining his 

 bearings. He has seldom been brought face to face 

 with the elements of which chemistry deals. The 

 air he breathes is not only a mixture of Oxygen, 

 Nitrogen, water vapour, and Carbon dioxide, but he 

 finds that it is a storehouse of half a dozen of the 

 so-called rare gases. Iron, the metal he is perhaps 

 most familiar with, he learns, has Carbon in com- 

 bination with it, and by the addition of traces of 

 other elements may change its properties and 

 develop astounding degrees of hardness. The gold, 

 silver, and copper coins that he has been wont to 

 regard as pure are each and all of them alloys. Nor 

 is this all. The first book that he opens on the 

 subject bristles with an apparently infinite number 

 of mysterious symbols. Figures are scattered about 

 among them, some on the line and some beneath it, 

 and if he chances to light on the simplest calcula- 

 tion he sees it at once stretching to four places of 

 decimals. 



For these reasons I am including in this volume a 

 short chapter on the chemistry of the soil so far as 

 we are concerned with it in connection with Nitrogen 

 fixation, in the hope that it may help those who have 

 no knowledge of the subject to get a clearer appre- 

 ciation of the problems involved. 



Despite the complexity of nature as we see it 

 around us, the world contains only a few elementary 

 substances, known as elements. They are some 



