54 



HEAT. 



must be made against change of length by change of 

 weather. 



118. LIQUIDS EXPAND MORE THAN SOL- 



IDS. A column of water inclosed in a glass 

 sion of water tube, will expand aV in length on being 



heated from freezing to the boiling point 

 of water, while a column of iron will expand only ^l^. 



119. ILLUSTRATION. The overflow of 

 Illustrate the 



expansion of water from full vessels before boiling 

 liquids by heat. commenceSj so o f ten observed in the 



kitchen, is in consequence of expansion by heat. To 



illustrate the expansion of liquids, a 



test-tube full of water may be heated 



over a spirit lamp, as indicated in the 



figure. The water will be found to 



heap itself into a convex surface over 



the mouth of the tube, and even to run 



over, long before boiling commences. 



120. COLD WATER EX- 



What effect 



PANDS BY COLD. - There is 



an important exception to the general law 

 of expansion of liquids by heat and contraction by cold, 

 or withdrawal of heat. Very cold water (39 F. ) expands 

 by further cold before it freezes. Again, on conver- 

 sion into ice, it undergoes still further expansion. 



12 1 . ILLUSTRATION. Expansio n by these 



How may ex- 



pansionbycoid combined causes may be shown by bury- 



be illustrated? ing ft tegt . tube full of water m a mixtllre o f 



snow and salt. Before the water is completely frozen, 

 it will rise at least a quarter of an inch, and fill the 

 tube.. 



has cold on 



' 



