28 ON THE STUDY OK 



Upon this principle, all unorganized substances 

 have been divided into four classes, as forming 

 the basis or primary sources of which the earth 

 is composed namely, pure earths ; salines, in- 

 cluding the alkalies and acids ; inflammables or 

 combustible substances, and metals : of which, 

 several, according to the late experiments of Sir 

 Humphrey Davy, appear to be compounds ; but 

 as this subject is still in its infancy, our illustra- 

 tions will be better understood, by confining 

 ourselves to the simple arrangement we have now 

 adopted. We therefore beg to observe, that by 

 a varying combination of these substances with 

 each other, or with oxygen (the basis of vital air 

 which forms one of the constituent parts of the 

 atmosphere), most of the mineral substances are 

 formed. These have been divided into species 

 and sub-species, according to the leading article 

 of which they are composed ; or to the substance 

 which serves as the medium of union to the con- 

 stituent parts. 



To illustrate these combinations, we may men- 

 tion that chalk, a substance familiarly known to 

 us all, is composed of the earth lime in its simple 

 state, and of the gas produced from charcoal, 

 denominated carbonic acid gas or fixed air ; and 

 from thence it is called the carbonate of lime. 

 Granite, frequently used in architecture, which 

 forms the basis of all the other rocks, and makes 

 up the greatest portion of the highest mountains, 



