PROPERTIES OF MATTER 13 



Articles made of soft iron may be hardened by heat- 

 ing to a high degree and plunging at once into water 

 or oil. Springs are tempered in this way, after being 

 bent. Hardened iron may be made soft by heating 

 and then slowly cooling ; this is called annealing. Try 

 each process. 



17. Brittleness. It may be noticed that certain sub- 

 stances, though they are hard, are easily broken by a 

 blow. Glass, for example, is easily broken to bits by 

 a blow from a hammer, by being dropped upon a hard 

 surface, or sometimes by mere pressure of the hand. 

 Some knife blades, though of very hard steel, may be 

 snapped in the fingers. Such substances as are thus 

 easily broken by a blow are said to be brittle. 



Experiment 12 Test the brittleness of various substances, by 



hammering lightly, by dropping them upon a hard surface, or 

 by trying to snap them in the fingers. Chalk, pasteboard, glass, 

 iron wire, a steel needle, copper wire, a cracker, a bit of china, 

 a watch spring, or a wafer may serve as examples. 



18. Malleability. A solid substance that may be 

 hammered into thin sheets is said to be malleable. 

 Several of the metals are very malleable and may be 

 rolled into sheets thinner than tissue paper. Gold is 

 the most malleable of substances ; it can be hammered 

 into sheets that are only ^nnnnr ^ an ^ nc ^ thick. We 

 are familiar with thin sheets of this metal under the 

 name " gold leaf." . 



Experiment 13. Hammer some bits of different substances 

 into the thinnest sheets you can make. Try lead, iron, tin, cop- 

 per, aluminium, and others 



