224 MANUAL OF AGEICULTUPtE. 



the formatiou and nature of the Earth s crust, the forces which 

 have been at work in preparing it for its present condition, and 

 those at j)i'esent affecting its modification. In its relation to 

 agriculture, it reveals to the farmer the various compositions of 

 soils, and their derivation, and it gives him practical hints upon 

 drainage operations. Botany, in its bearing npon agriculture, 

 teaches the systematic classification of the various plants scat- 

 tered over the face of the globe, their native localities, the variety 

 of soil and climate best suited to the cultivation and growth of 

 individual plants, and their internal structure, and modes of re- 

 production and growth. Chemistry — the grammar, so to speak, 

 of all the physical sciences — acquaints us with the primary ori- 

 ginal materials of earth, air, and water, and consequently of all 

 animal and vegetable life. As being the most fundamental of all 

 the physical sciences bearing upon agriculture, its consideration 

 in that relation comes naturally first. 



Chapter II. — Of Clicmistry. 



Our earth, with its sea and atmosphere, and all whatsover 

 therein contained, is composed of about sixty-three original and 

 simple elements, whose substance cannot be further reduced. Of 

 these only four occur in the atmosphere ; upwards of thirty have 

 been found in sea water ; whilst in the solid structure of the 

 globe, the whole are to be found in varying proportions. They 

 can exist in three states, viz., solid, liquid, or gaseous ;* and that 

 either alone or in combination. And such changes of state take 

 place at fixed degrees of heat or temperature for each. The seve- 

 ral elements consist of an aggregation of atoms, those of each 

 particular elements being always alike in material weight and 

 volume. In the gaseous state, and whilst free from combination, 

 the atoms of all the elements are of equal volume; but they vary 

 in weight, and also, of course, in point of material. Although not 

 in au apparent manner, the elements can, under certain condi- 

 tions, be artificially reduced to their atomic state — i.e., isolation of 

 individual atoms — by the aid of heat or electricity. When 

 thus reduced to the' free, or as it is called, the nascent state, the 

 atoms of any element have a tendency to unite with those of one 

 or more different elements, when brouGjht into contact with the 

 latter. This is being continually effected through the agency 

 of natural means ; and, as will be seen, it is the cause of all phy- 

 sical change on our planet. The atoms of one element unite 

 with those of another in certain fixed invariable proportions, 

 and they have a greater tendency to unite with, or affinity for, 

 those of some elements than of others. What is known as chemi- 

 cal combination is this union of the atoms of different elements, 



^Liquids are tecliuically known as incompressible fluids, and gasses as compres- 

 sible fluids. 



