To produce a large crystal of potash alum.
Put some finely-powdered potash alum into some distilled water in a beaker until a saturated solution is obtained. Heat the mixture until the solid at the bottom dissolves. Then allow the mixture to settle for a few minutes and then transfer the clear liquid to another beaker. From the crystals deposited, remove a single crystal that is well formed and suspend it from a glass rod in the saturated solution with a piece of string attached as shown. In order to get a large crystal, examine the crystal each day and remove from the solution any other crystal that may be formed elsewhere in the solution. Add more of the saturated solution from time to time to enable the alum crystal to grow to a large size. Repeat the experiment with other salts like copper sulphate, potassium chlorate, and nitre.
It is possible to grow a crystal of about one inch diameter. It is recorded that crystals of potash alum of more than three feet across have been prepared.
This experiment shows that crystals may be made to grow in size.