XXll INTRODUCTION. 



Amongst the names of those who have contributed 

 to the. science of Agricultural Chemistry, that of 

 Liebig stands pre-eminent. The thanks of all are 

 due to him, both for the valuable and laborious ex- 

 periments he has performed, and likewise for the 

 exertions which he has made to remove the many 

 doubts and uncertainties that surrounded the very 

 elements of the subject. But little has been done 

 since the days of Priestley and Ingenhousz to prove 

 how plants obtained their food, what were the sources 

 whence they derived the elements of organic matter, 

 and the nature of the office performed by manures. 

 Chemists, and likewise physiologists, had formed 

 many ingenious speculations; but they had not em- 

 ployed the only real mode of getting at the truth, 

 namely, well-selected and carefully performed expe- 

 riments. Liebig, in his Organic Chemistry applied 

 to Agriculture and Physiology^ has strongly drawn 

 attention to these important questions ; he has exposed 

 the fallacy of many of the theories which had been 

 formed to explain them, and has established, on good 

 evidence, the simple chemical rules which regulate 

 the growth of plants. 



Although the experiments of Priestley and Ingen- 

 housz had shown that plants possess the power of 

 decomposing Carbonic Acid ; and, although they had 



