INTRODUCTION. XXVll 



quentlj, guide him in the application of artil&cial 

 means to produce the most beneficial results. He 

 must, however, not expect too much from the aid of 

 Chemistry, nor give himself blindly up to specula- 

 tions or theories. Whilst he gives due credit and 

 belief to well-authenticated facts, he must always 

 receive theories with caution and doubt. 



Perhaps the most important advantage which a 

 practical man may at present derive from a know- 

 ledge of Agricultural Chemistry, is connected with 

 the use of manure. If he knows what it is that 

 gives the fertilizing powers to manure, and is aware 

 of the nature of those substances, he will soon learn 

 the best method of preserving and using them; he 

 will then understand how to make the most of the 

 various sources of manure at his disposal, and he 

 will be enabled readily to save much, that, for the 

 want of such knowledge, would otherwise be lost. 



