290 Agricultural Chemistry. 



permission to premise some historical notices, in order to define 

 accurately the point of view from which my book was written. 



"It must be remembered (see 2nd edition, p. vii.) that the 

 object of the author was not to write a system of agricultural 

 chemistry, but to furnish a treatise on the chemistry of agri- 

 culture." In all the subsequent editions the book has retained 

 this character ; the distinction above pointed out is self-evident. 



A system of agricultural chemistry contains the theory and its 

 application to practical agriculture ; in my book, on the con- 

 trary, the object of which was chemistry in its application to 

 agriculture, the principles of chemistry are laid down, and the 

 chemical conditions of cultivation, with the chemical processes 

 or changes concerned, are explained and developed. A system 

 of agricultural chemistry can only be written by a practical 

 agriculturist, who knows the universal experience of agricul- 

 turists. Such a work must contain the rules for the preparation 

 of the soil, for the manuring of the different crops, as of wheat, 

 or of turnips, with their succession ; but the chemistry of agricul- 

 ture endeavours to harmonize the" experience of farmers with 

 natural laws, or with known and established truths. " The pur- 

 pose of this work is to elucidate the chemical processes concerned 

 in the nutrition of vegetables." (p. 3.) 



Compared with a system of agricultural chemistry, my book 

 appears a work altogether deficient in arrangement and full of 

 the strangest contradictions : while on one page the advantage 

 derived from ammonia is proclaimed, and it is most urgently 

 recommended to the farmer to collect with the utmost care the 

 ammonia of his manure, and to apply it to his fields, the best 

 means being indicated for avoiding any loss of this substance ; it 

 is stated on another page, that plants obtain all their nitrogen 

 from the atmosphere, and that the nitrogen of the manure, con- 

 sidered by itself as a part of the food of plants, hardly contributes 

 to increase the produce of the crop. There is here no advice to 

 the farmer as to what he ought to do in order to obtain from his 

 soil a maximum of produce in the way most profitable for him- 

 self. No one can find here any statement as to whether ammonia 

 should or should not be given in the manure, to wheat, or to 

 what other crop soever ; for in the Vocabulary of Science the 

 word Profit does not exist. 



All these apparent contradictions are explained, when we 

 place ourselves, and this an author is entitled to insist upon, at 

 the point of view of the writer, and make up our minds to follow 

 him in his reasoning with some degree of attention. 



The most distinguished agriculturists (such as Schwerz and 

 Thaer), the greatest chemists and men of science (Berzelius, 

 Gay Lussac, Boussingault, Payen, De Saussure), believed, up to 



