LPJSSONS IN CHEMISTRY. 103 



a mathematical constitution as fixed as that of the solar system 

 itself. The stones and soil beneath our feet, and the ponderous 

 mountains, are not mere confused masses of matter; they are 

 pervaded throughout their innermost constitution by the har- 

 mony of numbers, The fuel we burn wastes away before us, dis- 

 solves in air, and passes beyond the reach of sight ; but the in- 

 visible changes among the unseen particles are definite, exact, 

 and harmonious. And so it is with all chemical mutations." It 

 was found that, however often matter might change its form, 

 nothing was either gained or lost that its quantity always re- 

 mained the same ; and it was likewise discovered that the con- 

 stituents of chemical compounds are always combined in the 

 same definite proportions. 



Chemistry deals with those phenomena of matter and energy 

 which involves some change in the composition of bodies. The 

 combination of two or more simple substances into one substance 

 possessing properties different from those of either of the compo- 

 nents is a chemical process. If we mix carefully powdered sulphur 

 and copper filings, they remain sulphur and copper and may be 

 separated ; but if they are heated strongly the sulphur combines 

 with the copper forming a compound which shows none of the 

 peculiar properties either of copper or sulphur. This illustrates 

 something of the difference between a physical mixture and a 

 chemical combination. The liquid, water, may be separated into 

 the gases oxygen and hydrogen. A piece of wood is composed 

 mainly of the gases, oxygen and hydrogen, and the solid, carbon. 

 When wood is burned, oxygen of the wood and of the air unites 

 with the hydrogen forming steam, which may be condensed into 

 water. Other portions of oxygen unite with some of the carbon 

 forming carbonic acid gas ; some of the carbon may be left as 

 charcoal; some, very finely divided, may be carried away with 

 the steam, making a black smoke from which the carbon may be 

 collected as soot; and in the ash are several mineral ingredients 

 which existed in small quantities in the wood. The various 

 reactions which take place in all kinds of combustion, whether 

 alow or rapid, are chemical changes. 



