1 8 CHEMISTRY. 



to form carbonic anhydride, in becoming invisible it must 

 be made exceedingly thin, and therefore occupy a very 

 large space. Many solid substances are formed by the union 

 of a large bulk of some gas with a comparatively small bulk 

 of some solid. Thus when iron rusts or any metal tarnishes, 

 it is by the union of the solid with a large volume of the 

 oxygen of the atmosphere. In a pound of iron rust there 

 have been nearly twenty-seven gallons of oxygen condensed 

 in the union of this gas with the iron. In quicklime we have 

 a union of this same gas with a metal. There is a great 

 number of these metallic compounds, called oxides, from the 

 oxygen that is in them. Animal and vegetable substances 

 generally are composed, to a great extent, of this and cer- 

 tain other gases ; and the gases that result from combustion 

 and decay fly off in the atmosphere only to appear again in 

 the living forms that we see around us. This agency of 

 gases in forming solid substances is always surprising to a 

 beginner in the study of chemistry, and he can hardly credit 

 the supposition of chemists that oxygen gas constitutes full 

 one third of the solid crust of the earth. 



1 2. Extent and Variety of Chemical Action. Some of the 

 elements are very busily at work producing changes every 

 where. When any thing burns we see an exhibition of the 

 chemical action of elements upon each other. The rusting 

 of a metal is the uniting of two elements. The effects of 

 manure, compost, lime, etc., in the soil come from chemic- 

 al action effecting compositions and decompositions. Air 

 and water are every where busy helping to produce these 

 changes in the soil. The operations of life, both in vegeta- 

 bles and in animals, are in part chemical, and those which 

 occur when death comes to either are wholly so. The sap 

 of vegetables and the blood of animals are made up of 

 chemical compounds of elements. Even the heat of the 

 body is produced by a chemical process, which is like com- 



