INTRODUCTION 5 



which are formed in the soil at the expense of the nitrog- 

 enous matter contained in diluvium, which is the basis 

 of vegetable earth ; compounds in which nitrogen exists 

 in stable combination, only becoming fertilizing by the 

 effect of time." As to the absorption of the gaseous 

 nitrogen of the air by vegetable earth, he says : " I am 

 not acquainted with a single irreproachable observation 

 that establishes it ; not only does the earth not absorb 

 gaseous nitrogen, but it gives it off." 2 



The investigations of DeSaussure and Boussingault, 

 and the writings of Davy, Thaer, Sprengel, and Schiib- 

 ler prepared the way for the work and writings of Lie- 

 big. In 1840 he published " Organic Chemistry in its 

 Applications to Agriculture and Physiology." Liebig's 

 agricultural investigations were preceded by many valu- 

 able discoveries in organic chemistry, which he applied 

 directly in his interpretations of agricultural problems. 

 His writings were of a forceful character and were ex- 

 tremely argumentative. They provoked, as he intended, 

 vigorous discussions upon agricultural problems. He 

 assailed the humus theory of Thaer, and showed that 

 humus was not an adequate source of the plant's carbon. 

 In the first edition of his work he noted that farms 

 from which certain products were sold became less pro- 

 ductive, because of the loss of nitrogen. In a second 

 edition he considered that the combined nitrogen of 

 the air was sufficient for crop production. He overesti- 

 mated the amount of ammonia in the air, and underesti- 

 mated the value of the nitrogen in soils and manures. 



