EXPANSION. 



757 



FIG. 379 



i real sizt 



the crucible tongs in the outer portion of the flame 

 of a spirit lamp or Bunsen's burner, so 

 that the piece b c may become as hot as 

 possible, while the piece ef is very little 

 heated ; then, as soon as b c is sufficiently 

 hot, the piece ef drops out of the frame, 

 although it was very firmly fixed pre- 

 vious to the heating. It follows that the 

 heated portion of the wire has expanded. 

 If j^he piece ef is held in its place between 

 a and d, allowing it to rest upon the end 

 d, an exceedingly small gap will be seen 

 between a and e; the expansion of brass 

 by heat must hence be very inconsider- 

 able. Finally, if the piece abed be again cooled by 

 immersing it in water, it will clasp the bar ef as firmly 

 as before the heating; it follows that the wire has 

 contracted again by being cooled. 



All solid bodies behave like the brass wire in the 

 preceding experiment: they expand when their tem- 

 perature is raised, and contract when their temperature 

 is lowered. Some substances expand more, many others 

 much less, than brass. 



If a test-tube, 15 or 18 cm long, be filled with paraffine 

 oil to about 3 cm from the edge and heated, the liquid 

 rises in the tube 1 or 2 cm ; when the tube is cooled the 

 liquid contracts again, just as the brass did in the pre- 

 ceding experiment. Most liquids do not expand so 

 much as paraffine oil ; but in all liquids the expansion 

 caused by heat is greater than in solid bodies. 



A retort or a flask is clamped in the fork of the 

 retort-stand, the mouth downwards, and dipping a 



