50 HEAT OR CALORIC. 



8. Solids expand very unequally, and as far as has been discover- 

 ed,* follow no general law. 



9. There are partial exceptions to the law of expansion in certain 

 parts of the scale of heat, but none on the whole, for through a wide 

 range of temperature, all bodies expand by heat and contract by 

 cold. 



(a.) Solid iron, bismuth, and antimony, float on the surface of 

 their respective fluids, formed by melting. 



Such metals and their compounds are peculiarly fitted for taking 

 impressions from moulds, as by their expansion in cooling, they fill 

 every part, and copy the most delicate ramifications. 



(6.) The expansion in freezing is generally attributed to a kind 

 of crystallization but mercury, and nitric and sulphuric acids con- 

 tract, although they suffer a partial crystallization. 



(c.) Salts generally expand in crystallizing, and frequently break 

 the bottles containing them. 



(d.) Water is the most remarkable exception, but it exists only 

 within a limited number of degrees. 



In cooling, it attains its maximum of density at 40, when it be 

 gins to expand, and continues to do so as it cools below 40 ; its ex- 

 pansion is the same for any equal number of degrees above and 

 below 40 ; e. g. at 32 and 48. 



If water be cooled below 32 without freezing, it goes on expand- 

 ing, and the same relations of density are maintained. 



Pure ice floats on water, about one eighth or one ninth of its 

 volume being out, as is seen to a certain degree, in the icebergs.f 



(e.) The fact respecting water's being an exception from the 

 law of expansion, is well exhibited, by taking two thermometer balls 

 with tubes attached, and filling one ball with water and the other with 

 alcohol ; both may be immersed in melting snow, or in freezing 

 water, and the difference will be very manifest, if the experiment be 

 commenced above 40. The alcohol will sink regularly, but the 

 water at 40 will begin to rise in the tube, and will continue to rise 

 till it freezes. 



(/.) Water, in the act of freezing, expands more than it does 

 when heated from the freezing to the boiling point. { 



* It has however been ascertained by Petit and Dulong that at high temperatures, 

 solids dilate in an increasing ratio. Jinn, de Ch. and Phy. Vol. 7, and Turner's 

 Chem. p. 20. For a table of the expansion of various substances, see the latter 

 author same page. 



t Anchor-ice. Is it formed on the bottom of running streams, on account of the 

 conducting power of stones ? 



t This is beautifully illustrated, by immersing in a freezing mixture, a ball filled 

 with water, and having a tube attached to it ; as the fluid approaches freezing, and 

 especially when it begins to freeze, it will rise out of the top of the tube. 



