▁the ▁same ▁temperature ; ▁however , ▁certain ▁subst ances ▁possess ▁differ ing ▁solid – liqu id ▁transition ▁temper atures . ▁For ▁example , ▁ag ar ▁displays ▁a ▁h yst er esis ▁in ▁its ▁mel ting ▁point ▁and ▁free zing ▁point . ▁It ▁mel ts ▁at ▁ 8 5 ° C ▁( 1 8 5 ° F ) ▁and ▁solid ifies ▁from ▁ 3 2 ° C ▁to ▁ 4 0 ° C ▁( 8 9 . 6 ° F ▁to ▁ 1 0 4 ° F ). ▁ ▁Cry st all ization ▁ ▁Most ▁liqu ids ▁free ze ▁by ▁cry st all ization , ▁formation ▁of ▁cry st all ine ▁solid ▁from ▁the ▁uniform ▁liquid . ▁This ▁is ▁a ▁first - order ▁therm od ynamic ▁phase ▁transition , ▁which ▁means ▁that ▁as ▁long ▁as ▁solid ▁and ▁liquid ▁co exist , ▁the ▁temperature ▁of ▁the ▁whole ▁system ▁remains ▁very ▁nearly ▁equal ▁to ▁the ▁mel ting ▁point ▁due ▁to ▁slow ▁removal ▁of ▁heat ▁when ▁in ▁contact ▁with ▁air , ▁which ▁is ▁a ▁poor ▁heat ▁conduct or . ▁Because ▁of ▁the ▁lat ent ▁heat ▁of ▁fusion , ▁the ▁free zing ▁is ▁greatly ▁slow ed ▁down ▁and ▁the ▁temperature ▁will ▁not ▁drop ▁anymore ▁once ▁the ▁free zing ▁starts ▁but ▁will ▁continue ▁dro pping ▁once ▁it ▁finish es . ▁Cry st all ization ▁consists ▁of ▁two ▁major ▁events , ▁nucle ation ▁and ▁cry stal ▁growth . ▁N uc le ation ▁is ▁the ▁step ▁where in ▁the ▁mole cules ▁start ▁to ▁gather ▁into ▁clusters , ▁on ▁the ▁nan ometer