The Iron and steel magazine . ot fall belowB until the mass is all frozen because any attempt to do so wouldso accelerate the freezing and consequently the liberation oflatent heat as to raise the temperature to B again. On theother hand, it cannot rise above B, for then freezing would atonce cease and with it the liberation of latent heat, and thetemperature would at once drop back to B. Freezing keeps * Received January n, 1906. (ooling ( of Metallic Solution 97 pace with the abstraction of heat, the temperature remainconstant until it is completed. As a mat (cm- of fact the actual cu
The Iron and steel magazine . ot fall belowB until the mass is all frozen because any attempt to do so wouldso accelerate the freezing and consequently the liberation oflatent heat as to raise the temperature to B again. On theother hand, it cannot rise above B, for then freezing would atonce cease and with it the liberation of latent heat, and thetemperature would at once drop back to B. Freezing keeps * Received January n, 1906. (ooling ( of Metallic Solution 97 pace with the abstraction of heat, the temperature remainconstant until it is completed. As a mat (cm- of fact the actual curve obtained from coolingsuch a mass of tin is as shown in Fig. 2. Here we see that the molten tin cooled to E, somewhatbelow the freezing temperature of tin. The temperature thenquickly rose to B and remained constant until freezing was com-pleted at C. AB, as before, represents the cooling of molten tinand BC the freezing out of solid tin. The part of the curve BEBstill requires explanation. This phenomenon is known as sur-. Fig. 2. fusion and seems to be entirely analogous to undercooling orsupersaturation in liquid solutions. Kuster * has suggested anexplanation for the latter. He states that the solubility dependson the state of division of the dissolved body and suggests thatthere may exist particles which he terms primitive crystals,that are so small as to be invisible and that the solution maynot be saturated with respect to these when it is saturated withrespect to particles of appreciable size. The limit between theseis the range of supersaturation or surfusion. On cooling downa solution to the limit of solubility of the primitive crystals theseseparate out, and if particles of appreciable size are introducedwill grow on them. On cooling to the lower limit the normal * Zs. Inor. Ch., 33 (3), 363-369 (1903). 98 The Iron and Steel Magazine crystals begin to separate out. Such an explanation does notseem adequate, however, for if the primitive crystals are freez-ing out
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