To prepare small and large crystals of different salts by cooling hot saturated solutions of the salts.
Prepare a saturated solution of each specimen of salt in four different beakers (250 ml.) such that solid particles of the salt settle at the bottom. Now heat the mixture to dissolve the solid particles, and obtain a hot saturated solution. Pour a portion of the hot solution from each beaker into separate test tubes, another portion into separate watch glasses, and leave the rest in the beaker. Cool the solutions in the test tubes rapidly under tap water, but leave the rest on the table to cool down slowly.
Observe the particles obtained from each of A, B and C with a hand lens. You will find that crystals are deposited in all four cases; while those that separate from the test tubes are tiny crystals, those from the beakers and the watch glasses are larger crystals. When observed through the hand lens, each crystal is found to have a definite geometrical shape, plane surfaces and a shiny appearance. Crystals of common salt are cubes; alum forms eight-sided or octahedral crystals, Epsom salt crystals are prismatic and blue copper sulphate crystals triclinic.
Crystals can be obtained by cooling a hot saturated solution of the substance. Rapid cooling, e.g. under the tap, produces small crystals, while slow cooling produces larger crystals.