AGRICULTURAL CHEMISTRY. 21 



is a figure. These figures represent the atomic weight 

 of all substances. All matter is believed to exist in 

 atomSy or indivisible particles. The atom of hydro- 

 gen, which is the lightest of all bodies, is put down 

 at 1. The atom of oxygen is known to be 8 times as 

 heavy, and is therefore put down at 8 ; that of chlo- 

 rine, for a like reason, at 36 ; of sulphur, 16 ; phos- 

 phorus, 32, &c. Now when elements combine with 

 each other, they combine by atoms, one atom of one 

 to one atom of another, two atoms of one to one atom 

 of the other ; and so on, either 1, 2, 3, 4, 6, 6, or 7 of 

 one to one of the other ; or, as sometimes happens, 3 

 of one to 2 of the other. This enables the chemist to 

 tell beforehand precisely how much of one substance 

 will combine with a given quantity of another. If 

 you look at nitrogen in the table, you will perceive 

 that the number against it is 14. Now if you wished 

 to combine oxygen with 14 grs. of nitrogen, it would 

 take just 8 grs., or just twice 8 grs., or three, four, 

 five, six, seven times 8 grs. That is, oxygen will 

 ^mbine with nitrogen in the proportion of 8, 16, 24, 

 32, 40, 48, or 56 grs. of the former, to 14 grs. of the 

 latter, but in no other proportions. So it is with all 

 other substances ; they combine in the proportions of 

 their own atomic weight, as expressed by figures, or 

 in the proportion of even times these numbers. This 

 will be plainer as we proceed. 



37. The compounds of oxygen with the elements 

 arranged below it (so many of them as we shall no- 

 tice in this ^ork) are placed opposite those elements 

 respectively. (See Table I.) Other compounds^ of 



