Growing of Alum Crystals

8 Experiments on Particle Model of Matter E4.1 Growing of Alum Crystals 

Material Crystallizing bowl, 2 beakers, funnel, filter paper, glass rod, thread alum salt (KA1 (S04)2 x 12 H20). 

Procedure Dissolve approximately 40 g of alum in 200 ml of warm water, and cool the solution. Filter the saturated solution and take a little portion of it into the crystallizing bowl. Let it stand for two days until some octahedronshaped crystals are formed. Attach the best crystal to a thread and hang it from the glass rod into the saturated solution filled into the beaker. The crystal is completely covered. After a few days remove new crystals from the thread, and filter the solution again. Occasionally add saturated solution of the same temperature. 

Observation The crystal grows to a fist size over weeks and months it has the form of an octahedron. Its edges are perfectly straight, the surfaces are smooth, and the angles between the surfaces are constant. 

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