AGRICULTURAL CHEMISTRY. 



more difference of opinion has existed 

 than that of the state in Avhich manure 

 ought to be ploufj;hed into the land; whe- 

 ther recent, or when it has gone through 

 the process of fermentation ?' and this 

 question is still a subject of discussion; but 

 whoever will refer to the simplest princi- 

 ples of chemistry cannot entertain a doubt 

 on the subject. 



As soon as dung begins to decompose 

 it throws off its volatile parts, which are 

 the most volatile and most efficient. Dung 

 which has fermented, so as to become a 

 mere soft cohesive mass, has generally 

 lost from one third to one half of its most 

 useful constituent elements. It evidently 

 should be applied as soon as fermentation 

 begins, that it may exert its full action 

 upon the plant, and lose none of its nutri- 

 tive powers. 



It would be easy to adduce a multitude 

 of other instances of the same kind; but 

 sufficient I trust has been said to prove 

 that the connection of chemistry with 

 agriculture is not founded on mere vague 

 speculation, but that it offers principles 

 which ought to be understood and fol- 

 lowed, and which in their progression 

 and ultimate results, can hardly fail to be 

 highly beneficial to the community. 



A view of the objects in this course of 

 lectures, and of the manner in which they 

 are to be treated, will not, I hope, be con- 

 sidered as an imj^roper introduction. It 

 will inform you what you are to expect; 

 it will afford a general idea of the connec- 

 tion of the different parts of the subject, 

 and of their relative importance; it will 

 enable me to give som.e historical details 

 of the progress of this branch of know- 

 ledge, and to reasf)n from what has been 

 ascertained concerning what remains to be 

 investigated and discovered. 



The phenomena of vegetation must be 

 considered as an important branch of the 

 science of organized nature; but though 

 exalted above inorganic matter, vegetables 

 are yet in a great measure dependant for 

 their existence upon its^ laws. They i-e- 

 ceive their nourishment from the external 

 elements; they assimilate it by means of 

 peculiar organs: and it is by examining 

 their j:)hysical and chemical constitution, 

 and the substances and powers which act 

 upon them, and the modifications which 

 they undergo, that the sci 'utific princi- 



ples of agricultural chemistry are ob- 

 tained. 



According to these ideas, it is evident 

 that the study ought to be commenced by 

 some general inquiries into the composi- 

 tion and nature of material bodies, and the 

 laws of their changes. 



The surface of the earth, the atmo- 

 sphere, and the water deposited from it, 

 must, either together or separately, af- 

 ford all the principles concerned in vege- 

 tation; and it is only by examining the 

 chemical nature of these principles, that 

 we are capable of discovering what is the 

 food of plants, and the manner in which 

 this food is supplied and prepared for their 

 nourishment. 



The principles of the constitution of 

 bodies consequently, will form the first 

 object of our consideration. 



By methods of analysis dependent upon 

 chemical and electrical instruments dis- 

 covered in late times, it has been ascer- 

 tained, that all the varieties of material 

 substances may be resolved into a compa- 

 ratively small number of bodies, which, 

 as they are not capable of being decom- 

 pounded, are considered in^ the pre- 

 sent state of chemical knowledge as ele- 

 ments. 



The bodies incapable of decomposition 

 at present known, are forty-seven. Of 

 these, thirty-eight are metals; six are in- 

 flammable bodies; and three substances 

 which unite with metals and inflammable 

 bodies, and form with them acids, alka- 

 lies, earths, or other analagous compounds. 



The chemical elements acted upon by 

 attractive powers combine in different 

 aggregates. 



In their simpler combinations, they 

 produce various crystaline substances, dis- 

 tinguished b}' the regularity of their forms. 

 In more complicated arrangements they 

 constitute the varieties of vegetable and 

 animal substances, bear the higher charac- 

 ter of organization, and are rendered sub- 

 servient to the purposes of life. And by 

 the influence of heat, light, and electrical 

 jToweis, there is a constant series of 

 changes; matter assumes new forms; the 

 dcsliuction of one order of beings tends to 

 the conservation of another; solution and 

 consolidation, decay and renovation, are 

 connected; and wliilst the parts of the 

 svstem continue in a state of fluctuation 



