204 GENERAL SCIENCE 



but so elastic as to spring back at once into the original form. 

 The hairsprings of watches are good illustrations of steel 

 painstakingly tempered, their cost representing largely the 

 labor expended upon them. Spring balances of tempered 

 metal are used for weighing, and comfort in travel is made 

 greater by the steel springs under the wagon or auto body 

 and underneath the railway car. The character of the work 

 of "The Village Blacksmith" has materially changed during 

 the past fifty years, machine work in metals having now 

 largely replaced hand labor. However, the increase in 

 dependence of mankind upon the use of metals in that time 

 for comfort and well-being has been little short of marvelous. 

 In extent of use, and in the changes wrought by such uses 

 in the affairs of men and of the world at large, iron and steel 

 rank chief among the metals. 



SUMMARY 



The industrial activity and commercial supremacy of an enlightened 

 nation is intimately related to its national resources in metals, and in 

 coal supplies for the development of these resources. 



By reason of the enormous quantities of iron employed in the arts 

 and industries, and because of properties which adapt it to innumerable 

 uses, iron ranks first among the metals in usefulness. 



The metals are chemical elements. An ore is a mixture of rock or 

 other earthy material with some compound of a metal present in suffi- 

 cient quantity to make its extraction profitable. 



The "pig iron" of commerce is a product of the "blast" or "reduc- 

 tion" furnace where the iron ore as an oxide gives up its oxygen to 

 combine with the intensely heated carbon of coke or coal. 



Castings of iron and steel of excellent design are possible by reason 

 of their expansion as they solidify. Metals very generally shrink in 

 volume as they change from the molten to the solid state. Gold and 

 silver coins have designs and lettering stamped upon their surfaces 

 under pressure of powerful machinery. Mixtures of various metals in 

 a molten state and in certain proportions are known as alloys. Some 

 of these, such as type-metal and various kinds of "bronze", are suc- 

 cessfully moulded due to their expansion when solidifying. 



