of vegetation, and to some important processes of 

 manufacture. 



All the varieties of substances found in plants, 

 are produced from the sap, and the sap of plants is 

 derived from water, or from the fluids in the soil, and 

 it is altered by, or combined with principles derived 

 from the atmosphere. The influence of the soil, of 

 water, and of air, will therefore be 'the next subject of 

 consideration. Soils in all cases consist of a mixture 

 of different finely divided earthy matters ; with ani- 

 mal or vegetable substances in a state of decomposi- 

 tion, and certain saline ingredients. The earthy mat- 

 ters are the true basis of the soil ; the other parts, 

 whether natural, or artificially introduced, operate in 

 the same manner as manures. Four earths generally 

 abound in soils, the aluminous, the siliceous, the cal- 

 careous, and the magnesian. These earths, as I have 

 discovered, consist of highly inflammable metals 

 united to pure air or oxygene ; and they are not, as 

 far as we know, decomposed or altered in vegetation. 

 The great use of the soil is to afford support to the 

 plant, to enable it to fix its roots, and to derive nour- 

 ishment by its tubes slowly and gradually, from the so- 

 luble and dissolved substances mixed with the earths. 

 That a particular mixture of the earths is con- 

 nected with fertility, cannot be doubted : and almost 

 all sterile soils are capable of being improved, by a 

 modification of their earthy constituent parts. I shall 

 describe the simplest method as yet discovered of 

 analysing soils, and of ascertaining the constitution 

 and chemical ingredients which appear to be connect- 



