12 v ..,,:; CHEMISTRY. 



3. Idea ^ of Elements among the Ancients. The ancients 

 <?uj0ae(! tjiit t thi-e were only four elements viz., air, wa- 

 ter, fire, and earth. But the science of chemistry has shown 

 us that these are not elements. We could see this to be 

 true of earth without any chemical experiments, for what 

 we commonly call earth is very different in different places. 

 Then water, simple as it appears to be, is composed of two 

 gases, one of which is the lightest of all substances. Air is 

 neither an element nor a compound, but a mere mixture of 

 gases. And what we call fire is merely a result of some 

 changes that take place in various substances under certain 

 circumstances. When wood or oil or gas, or any thing 

 burns, the result that we see we call fire. Fire, then, is not 

 only not an element, but it is not even a thing. It is not 

 a substance at all, but it is merely a phenomenon or ap- 

 pearance. 



4. Number of Elements. Chemists have discovered six- 

 ty-three elements. More may yet be discovered; and, on 

 the other hand, some which are now considered elements 

 may hereafter be found to be compounds. Seventy years ago 

 several substances were supposed to be elements that have 

 since been decomposed by chemists. Potash, for example, 

 formerly supposed to be an element, was discovered by Sir 

 Humphrey Davy to be a compound composed of a gas and 

 a metal. 



Here is a list of the Elementary Substances, with their 

 Symbols and Atomic Weights. What these symbols and 

 numbers mean we will explain in another chapter. The 

 most important elements in this table are printed in CAPI- 

 TALS, the next in importance in italics, and those which are 

 very rare in ordinary type. Do not try to commit these 

 long names to memory all at once; you will get familiar 

 with them by degrees. 



