46 CHEMlSTIiY OF SOIL. 



case, as the atoms are indivisible, combination can occur 

 only, by twice, thrice, &c., the quantity of that of the first 

 compound ; for instance, 1 carbon may be combined with 1 

 oxygen, forming oxide of carbon, or with 2 of oxygen, and 

 form carbonic acid. There is, and can be no intermediate 

 step. Having determined the combining atomic number uf 

 oxygen, that of all other bodies may be found by determin- 

 ing how much of each is necessary exactly to unite with 8 

 of oxygen. For instance, the iron used in the experiment 

 of decomposing water, increases in weight; if it is all 

 equally oxidated, it is found to increase 8 lbs. for every 28 

 lbs. of iron used. If, therefore, 28 lbs. of iron are used, and 

 9 lbs. of water, the iron may be wholly oxidated by the 8 

 lbs. of oxygen of the water. Deducting this from the total 

 weight of the oxide of iron, 36 lbs., the balance is the com- 

 bining or atomic weight of iron. The sum of 8 -f 28 = 36 is 

 therefore the atomic weight of oxide of iron. The atomic 

 weight of all compounds is the sum of the atomic weight of 

 their constituents. The number of atoms in any compound, 

 whose proportional constituents by weight are given, is 

 found by dividing each by its respective atomic weight. For 

 instance, the composition of carbonic acid above, gives in 22 

 parts, 6 of carbon, and 16 of oxygen. Each divided by its 

 atomic weight, gives 1 carbon, 2 of oxygen, = 22 of car- 

 bonic acid. So in a compound of several elements, having 

 their proportions per cent, given, each divided by its atomic 

 number, gives the relative proportion of the atoms. These 

 reduced to simplest terms, and affixed to the letters or sym- 

 bols of the elements, constitute what is called the chemical 

 formula of this compound. 



Three laws discovered by multiplied observation, con- 

 firmed by repeated experiments, govern all chemical science. 

 These laws are : 



