PRACTICAL

I. Crystallization By Cooling:1. To about 5 ml. of water in a test tube, add an excess of the supplied solid. Dissolve as much as possible of the solid by the aid of both heating and vigorous shaking. Make sure that an excess of the solid still remains undissolved (saturation). 2. Separate the supernatant liquid, preferably by decantation rather than by filtration (nucleation). Put the test-tube under running tap water (supersaturation by cooling ).3. Observe that crystallization soon commences. II. Crystallization By evaporation:1. To about 5 ml. of water, contained in a testtube, add an excess of the supplied solid. Dissolve as much as possible of the solid by the aid of heating and vigorous shaking. Make that an excess of the solid still remains undissolved (saturation 1). 2. Separate the supernatant liquid, preferably by decantation rather than by filtration (nucleation 1).3. Try to induce supersaturation by cooling, as described before, and note that this is unsuccessful. Evaporate part of the solution by the aid of gentle heating (supersaturation by evaporation). Observe that crystallization gradually proceeds. III. Crystallization By Precipitation:1. To about 5 ml. of alcohol in a test-tube, add solid. If soluble, add more solid and shake vigorously till complete saturation. 2. Decant the supernatant in another tube and add gradually few ml. of water to the second tube. Make sure that an excess of the solid still remains undissolved (saturation). Observe that crystallization promptly takes place.