INTRODUCTION, XVll 



for the most part they were employed in examining 

 the innumerable substances which plants produce; 

 whilst the great questions as to the food of plants, 

 their growth, and nourishment, were left very nearly 

 in the same state which the experiments of Priestley 

 and Ingenhousz had brought them to. 



At the end of the last century, and in the com- 

 mencement of the present. Organic Chemistry made 

 rapid advances ; the labors of Hassenfratz, -Hum- 

 boldt, Berzelius, Saussure, Senebier, Einhof, and 

 Davy, contributed to throw light on many parts of 

 the subject ; whilst the investigations of Gay-Lussac, 

 Hatchett, Lampadius, Lavoisier, Marcet, Prout, 

 Thompson, Yauquelin, Th^nard, and others, in all 

 parts of Europe, led to a more complete and accurate 

 knowledge of the nature, composition, and properties 

 of organic matter. 



The first chemist who wrote on agriculture appears 

 to have been J. G. Wallerius, who, in 1754, published 

 a book on the Cause of Fertility. Even before this 

 time, however, several books had been written on 

 agriculture, in which attempts were made to explain 

 the operations of farming on chemical principles; 

 such, for example, were The Rational Fanner, 

 1743, a curious book, containing numerous accounts 

 of rude chemical experiments, together with a num- 



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