230 WELLS'S NATURAL PHILOSOPHY. 



allowed to cool. lu cooling thej gradually contract, and by their contrac- 

 tion draw up the waUs. 



On account of the expansion of metal by heat, the successive rails which 

 compose a hne of railway can not be placed end to end, but a small space is 

 left between their extremities for expansion. 



A stove snaps and crackles wlien a fire is first kindled in it, and also when 

 the fire in it is extinguished. This noise is occasioned by the expansion and 

 contraction of the several parts consequent on the increase and diminution of 

 heat. 



A glass or earthen vessel is Uable to break when hot water is poured 

 into it, on account of the unequal expansion of the inner and outer surfaces. 

 Glass and earthen ware being poor conductors of heat, the inner surfaces 

 m contact with the hot water become heated and expand before the outer aro 

 afiectod ; the tendency of this is to warp or bend the sides unequally, and as 

 the brittle material can not bend, it breaks. 



Nails in old houses are often loose and easily drawn out ; the iron expands 

 in summer and contracts in winter more than the wood into which it has 

 been driven, and thus in time the opening is enlarged. 



When the stopper of a decanter or smelling-bottle sticks, a cloth dipped in 

 hot water, and applied to the neck of the bottle will frequently loosen it, since 

 by the heat of the cloth its dimensions aro expanded and enlarged. 



The tone of a piano is higher in a cold than in a warm room, for the reason 

 that the strings, being contracted by cold, are drawn tighter. 



526. Liquids expand through the ao;ency of 



To what extent -■■ n i i 



do liquias ox- heat more unequally, and to a mucli cjreater 



pandbyheatr , i i-i 



degree than solids. 



A column of water contained in a cylindrical glass 

 vessel will expand aV in length on being heated from 

 the freezing to the boiling point, while a column of 

 iron, with t£e same increase of temperature, will expand 

 only -,h. 



A familiar illustration of the expansion of water by heat is seen in the over- 

 flow of full vessels before boiling connnences. Diflerent liquids expand very 

 unequally with an equal increase in temperature. Spirits of wine, on being 

 heated from 32° to 212°, increase one ninth in bulk; oil expands about one 

 twelfth ; water, as before stated, about one twenty-third. A person buying 

 oil, molasses and spirits in winter, will obtain a greater weight of the same 

 material in the same measure than in summer. Twenty gallons of alcohol 

 bought in January, will, with the ordinary increase of temperature, become, 

 by expansion, twenty-one gallons in July. 



What pccuii- 527. Water, as it decreases in temperature 

 paasion°^doe8 toward the freezing point, exhibits phenomena 

 water exhibit? yf\^[Q\^ q^j-q wholly at variauce with the general 



