28 CHEMISTRY. 



solved out ; the microscope reveals a homogeneous mass, and 

 the whole is soluble in acids, evolving a very disagreeable 

 odor. The new substance, while containing iron and sul- 

 phur, is neither iron nor sulphur ; chemists call it sulphide 

 of iron. 



24. Two Kinds of Molecules. Molecules may be com- 

 pound or simple. Simple molecules are made up of atoms 

 of one and the same substance. By exposing the sulphide 

 of iron to the action of other substances, with the agency of 

 heat and chemical force it may be resolved into its constit- 

 uents, iron and sulphur ; sulphide of iron, then, is a com- 

 pound molecule composed of atoms of iron and atoms of 

 sulphur. Iron is not capable of being decomposed, nor is 

 sulphur that is, their molecules are simple, or compounded 

 only of like atoms. They are elementary bodies, as you 

 were told in the first chapter ; but you now learn to regard 

 the elements from another and peculiar point of view. 



25. Further Properties of Atoms. These atoms, it is sup- 

 posed, can not be destroyed or altered or divided, but have 

 remained precisely the same since their first creation. The 

 atoms of some elements have been continually uniting with 

 the atoms of others, changing from one kind of combination 

 to another, and yet, after myriads of such changes, they 

 have not altered in shape or character. Take oxygen for 

 example. When its atoms unite with those of hydrogen 

 to form water, it is not by any change in the atoms them- 

 selves that a fluid so different from each of these gases 

 is produced, but it is only by some arrangement of these 

 atoms. So when potassium is thrown upon water, and pro- 

 duces fire and smoke, amid all the commotion and burn- 

 ing not an atom of either the potassium or oxygen or hy- 

 drogen is lost or injured, but they simply form new associ- 

 ations. The disturbance is the mere result of the eagerness 

 of the atoms of oxygen and potassium to unite together. 



