INTRODUCTION. XVll 



ilver are indeed occasionally discovered in minnte quantities, 

 iiiit the value attached to these substances is a proof that 

 they constitute but a small portion of the forms of matter 

 usually met with around us. 



There is a constant tendency In nature to produce com- 

 pounds. Expose a piece of bright iron to the air, and it is 

 gradually covered with a reddish brown coating; and if we 

 weigh it we find that it has increased in weight. It has in fact 

 united with another simple body,* which is one of the constitu- 

 ents or elements of the air. It is the disposition which the ele- 

 mentary bodies possess of uniting together, that presents us 

 with the apparently endless variety of forms of matter which 

 we everywhere observe. When the farmer spreads upon his 

 field the burned limestone which he has procured from the 

 kiln it, though already a compound substance, becomes stDl 

 more complicated in its composition. Like the iron, it unites 

 with one of the ingredients of the air,f and at the same time 

 increases in weight and experiences a material alteration in 

 its properties ; before its exposure to the air it was a hard, 

 causticj substance, but after that, it assumes the form of a 

 mild powder, which experience has taught the farmer contri- 

 butes to increase the fertility of his soils. 



In the following chapters, my object will be to make the 

 young farmer acquainted with so much of the characters of 

 the elementary and compound bodies which we meet with in 

 nature, as it is important for him to know, and also to point 

 out to him such applications of this knowledge as may be 

 useful to him in the practice of his profession. I trust that 

 he will be induced to accompany me from the beginning, and 

 diligently endeavour to obtain clear ideas of the various sub- 

 jects which may be brought before him. 



* Oxygen. (7.) f Carbonic acid. (20.) 



X Caustic, capable of producing a burn. 



