APPLIED ^ SCIENCE 



explains the changes that take place in a sub- 

 stance when its identity is destroyed. When iron, for 

 example, is exposed to damp air, it becomes covered with a 

 reddish brown substance called rust. This rust is due to 

 a combination of the oxygen and moisture of the air with 

 the iron. Copper or brass when exposed in this way becomes 

 greenish in color from the same cause. The science of 

 chemistry makes clear why such changes as these take 

 place. 



Other sciences explain the why and wherefore of other 

 classes of phenomena or physical changes. Thus, botany 

 treats of the growth and changes in plants. Bacteriology 

 explains how changes in substances are caused by germs. 

 An example of such a change is the rotting of wood. Geology 

 treats of the structure of the earth, especially of rocks. 

 Hygiene explains the principles underlying the care of 

 our bodies. It is desirable to understand the principles 

 of science as they relate to the different trades, so that we 

 may have an intelligent knowledge of the processes and 

 changes whereby raw substances or materials taken out of 

 the ground are transformed into useful and beautiful things. 



3. Properties of Matter. Materials used in industry 

 are generally defined and described according to their 

 physical and chemical properties or characteristics. For 

 most purposes the chemical properties are not so important 

 as the physical, although in some cases the composition of 

 the materials must be taken into account. The chief prop- 

 erties of materials are cohesion, adhesion, inertia, elasticity, 

 ductility, brittleness, toughness, malleability, compressibility, 

 porosity, durability, infusibility, hardness. Some of these 

 characteristics, such as inertia, porosity, cohesion, and 



