A simple and quick way to demonstrate the general law of crystallization
Abstract
The general law referred to here is that a crystal precipitating from a solution tends to assume the smallest surface area. This law, which has a simple and well-known theoretical basis, is usually demonstrated by examples of crystallization, or rather recrystallization, requiring a long time, even months, or at least days. I came across a preparation in which this demonstration can last a few seconds; this preparation is Chilean saltpeter (sodium nitrate), the microscopic crystals of which dissolve from breathing in a few seconds and recrystallize in approximately the same time due to evaporation. Thanks to this rapidity, the aforementioned law is, of course, demonstrated just as quickly.
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