. Popular science monthly. keor Monoclinic Solphur. When firstformed they are bright yellow. Afterstanding for a few hours they changeto a dull yellow color and become verybrittle. A microscopic examination ofa fragment shows that it is nowmade up of minute rhombic crystals(Fig. 7). a minute, while one thirty-second ofan inch a minute is the velocity ofcrystallization of betol. In naturecrystals often grow much moreslowly than this. The examples cited above dealwith undercooled liquids, but thephenomenon of undercooling is byno means restricted to this class ofsubstances. When molten sulphur i
. Popular science monthly. keor Monoclinic Solphur. When firstformed they are bright yellow. Afterstanding for a few hours they changeto a dull yellow color and become verybrittle. A microscopic examination ofa fragment shows that it is nowmade up of minute rhombic crystals(Fig. 7). a minute, while one thirty-second ofan inch a minute is the velocity ofcrystallization of betol. In naturecrystals often grow much moreslowly than this. The examples cited above dealwith undercooled liquids, but thephenomenon of undercooling is byno means restricted to this class ofsubstances. When molten sulphur is allowedto cool slowly, long lustrous needle-shaped (monoclinic) crystals sepa-rate from the liquid. On standingfor a few days the appearance of thecrystals changes; they lose their luster, and examination with the micro-scope shows that their crystalline form is no longer needle-like, but con-sists of so-called rhombic figures. The temperature at which the tran-sition from needles to the rhombic form takes place is 96°.. fig. 7. Crystals of RhojibicSulphur. 28 THE POPULAR SCIENCE MONTHLY The change by which water is transferred to ice and its reverse maybe represented as follows: At 0° ice ^ water. The arrows pointing in opposite directions indicate that the processis reversible. The significance may be expressed as follows: at 0° ice canbe changed to water or water to ice. Similarly in the case of the sulphur, At 96° sulphur (monoclinic) ?=± sulphur (rhombic).
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