HEAT OR CALORIC. 51 



The sp. gr. of water at 60 being assumed at 1, that of ice at 32, 

 is only .92.* 



(g.) Were it not for the exception above described, water would 

 begin to freeze at the bottom of rivers and lakes. 



10. Cause of the expansion of water in freezing, and for eight 

 degrees above, f 



(a.) There can be little doubt that it is owing to crystallization, de- 

 pending on corpuscular attraction, which begins to operate even before 

 congelation. Water in freezing, assumes a linear arrangement : lines 

 of ice intersect each other at 60 and 120; this is seen distinctly in a 

 shallow freezing pond, or in a basin of water : also in snow flakes, which 

 are usually stars of six rays, or confused bundles of prismatic crys- 

 tals ; distinct crystals, prisms of six sides, are often seen on a cellar 

 wall in winter, or in a moist bank, and hoar frost is a collection of 

 crystals of ice. 



(6.) The particles of water are supposed to be endowed with a 

 kind of polarity, which causes the volume to expand, in consequence 

 of the attraction of certain points, edges or angles. 



(c.) An illustration is derived from magnetic needles thrust 

 through corks, and thrown upon water ; they would arrange them- 

 selves as the aqueous particles are supposed to do in crystallizing. 

 Dr. Black. 



11 When the freezing of water is examined by the microscope, this 

 peculiarity of arrangement can be observed, the lines shooting out 

 from each other at an angle either of 60 or of 120. "{ 



1 1 . Effects of unequal expansion of water, and of its expansion 

 infreezing. 



(a.) The bursting of domestic vessels in which water freezes ; the 

 flaking of the glazing from earthen vessels. 



(b.) The bursting of water pipes, of wood or metal, when not 

 adequately protected. 



* Webster, p. 25. 



t This expansion was denied by Mr. Dalton, who attributed it to the contraction of 

 the glass exceeding that of the water, and vice versa its expansion exceeding that 

 of the water, in the specified degrees between 32 and 40. 



This question was however fully settled by Dr. Hope, and Mr. Murray, and this 

 inequality is considered as well established. See the controversy ably stated in 

 Murray, Vol. I. p. 194, &c. 



Sir Charles Blagden ascertained that when water is prevented from freezing at 

 32, by being kept perfectly still, the water still continues to expand, even for ten 

 or more degrees below the ordinary freezing point, and this in even a greater ratio ; 

 and if the freezing point be reduced, by mixing salt with the water, the contraction 

 begins at about the same distance from the point at which the particular solution 

 does freeze. 



Mr. Dalton succeeded (Manchester Memoirs, v. 374,) in cooling water down so 

 far without freezing, that from expansion, it had risen as high as the point to 

 which it would have been raised had it been heated to 75. " Its real temperature 

 must then have been 10. On freezing, it darted suddenly up to 128." 



t Murray, 2d Ed. Vol. I. p. 182. 



