122 THE SPIRIT OF THE SOIL 



Experiment has proved that any given weight of 

 an elementary substance consists of a certain number 

 of ultimate particles or atoms of substance. One 

 may conceive, for instance, of a speck of Carbon 

 enormously magnified. In such a case one could 

 to assist the imagination regard it as consisting of 

 myriads and myriads of round black grains, each of 

 them the exact replica of the others. Each of these 

 grains would be an atom of Carbon. For the pur- 

 poses of general chemistry one may say that these 

 atoms are indivisible. 



The enormous majority of substances, all, in fact, 

 except the elements themselves, are either mixtures 

 or compounds. In a mixture the atoms would lie 

 more or less any way like a series of differently 

 coloured marbles jumbled together in a bag. In a 

 compound there would be no single atoms at all, but 

 groups of atoms, two, three, four, or even hundreds 

 and thousands firmly held together, each group being 

 the exact counterpart of each other group. In most 

 instances, too, the atoms of an element by itself 

 form little groupings or molecules. Thus, the gas 

 Oxygen does not exist in the air as single, but as 

 twin atoms. As will be seen, the chemist, therefore, 

 writes it as O 2 , and not 0^ 



In connection with chemical work figures are used 

 in two ways. Take such a substance as Sulphuric 

 Acid. This might be written H 2 S!O 4 (it is written 

 H 2 SO 4 ), and means that the unit or molecule of 

 Sulphuric Acid has, combined together, 2 units or 

 atoms of Hydrogen, i unit or atom of Sulphur, and 

 4 units or atoms of Oxygen. In other words, the 



