Growing Crystals
In this section you will find condensed directions for making crystals
from a solution
,
from a melt
, and
from a vapor
. You will find it very helpful to obtain Elizabeth Wood’s book,
Crystals—A Handbook for School Teachers
, or the Alan Holden book,
Crystals and Crystal Growing
for trouble shooting or for more extensive examples and explanations. These books can be borrowed from the New Haven Teachers Institute office.
To grow crystals from an
alum solution
dissolve 4 teaspoons of alum powder in a half cup of hot water. Stir until all of the powder dissolves. Cover the beaker with paper or cloth to keep the dust out and slow evaporation. Crystals will begin to form on the bottom of the container. It is important to keep your solution free from drafts or temperature changes. If your room has a widely varying temperature range, set the beaker in a large bucket of water, being careful not to get extra water in the beaker. The water will help prevent any rapid temperature changes.
When some good size crystals have formed, pour off and save the solution and carefully pick out the best crystals with tweezers. Dry the crystals and the tweezers well. Now pour the solution back into the beaker with the remaining crystal masses and gently reheat and redissolve the solute.
The next step is a real test of your dexterity! You must fasten the crystal to a thread, either by means of a slip knot or with a minuscule spot of glue (Duco cement is good). Suspend your hanging crystal “seed” in the cooled solution and cover the top. It is important to be sure there are no extraneous crystal grains on the sides of your crystal seed, on the thread, or in the container. Growth of your seed will be impeded by them. Again place the beaker in the water bath to control temperature during the growing time. This process would result in a single, large, well-formed crystal.
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Other substances which can form nice crystals are borax, salt, sugar, copper sulfate, and Epsom salts. The amount of solute will vary, but you can determine the appropriate amount by trial and error or by checking one of the books given above.
To grow crystals
from a melt
, obtain some
salol
(phenyl salicylate, HOC6H4COOC6H5) from a drugstore. Put a small amount on a glass slide or sheet of aluminum pie plate, and heat it with a candle. Since it melts at 42 degrees Celsius, you will not need much flame. As it cools, put a tiny grain of salol powder on the melted salol; this will act as a seed for the crystal to grow around.
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To grow crystals from a vapor, obtain some naphthalene (moth-flakes, C10H8). CAUTION — NAPHTHALENE IS VERY FLAMMABLE AND MUST NOT BE HEATED NEAR AN OPEN FLAME! Woods suggests placing a few flakes in a tall glass jar and placing a loose cover (aluminum foil) on top. Place the base of the jar on a lighted 100 watt bulb, and soon you will see the rising vapor sublimating (changing from vapor to solid) onto the top sides of the container. This experiment should be done in a very well ventilated room, preferably within a vented hood.
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