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Crystal Growing

The idea of this is to grow crystals of coloured metal compounds in drops of water on glass slides, under a biological microscope. A drop of water will completely dry up and crystallize in 30 minutes, so if you start ’em 15 minutes before class, students can observe the progress of crystal growth They don’t quite grow visibly, but almost: have the students check them every 2 minutes or so
Biological (transmitting) microscopes. Stereoscopic mikes are no good for this. Glass slides (high school biology labs have lots of these). In dropper bottles, saturated solutions of Copper Sulphate and Nickel Chloride (my favourites; but any water- soluble transition metal compound is worth trying, because all you need are nice coloured crystals. Ask the storeroom techy for suggestions). Note: saturated solutions just mean that the water has taken up all the solute that it can. An easy way to guarantee this is to mix enough of the powder into the water so that some sits on the bottom of the bottle.
Not much. Put drops of the solutions on the slides and put them on the microscopes. The light from the tight sources on the scopes heats up the water and hastens the drying-up process. Atfirst the crystals will be really small and scattered. At mid- stage (20 minutes) you have the most beautiful array of large ones. In the latest stage, quench crystals with irregular tree-like shapes grow rapidly from the edges of the drop inwards. These are like hoar frost on a window pane. A few minutes after they start, the water is gone and crystallization is complete. Safety considerations: these compounds are poisonous: no one should drink them, lick the slides, or run them on their skin. No panic, but ensure responsible lab behaviour.
1. This experiment models the growth of natural crystals like quartz, only on a very compressed time scale. Quartz c

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