I have a quick question: Suppose that you observed a solid melting at 150 degrees - 160 degrees Celsius. Once it is recrystallized, the observed melting point drops to 145-145.5 degrees Celsius. How can this be? At first, I thought it was due to an impurity, which would act to lower the melting point. However, the melting point of the recrystallized solid is very narrow, so it is probably quite pure. Then again, the recrystallized mixture might be eutectic, which would explain the sharp melting point. But then again... How is it possible to contaminate a sample that badly? Any help is appreciated.