Crystallization Shown on a Screen
The formation of chemical crystals can be shown in an interesting manner as follows: Spread a saturated solution of salt on a glass slide, or projection-lantern glass, and allow it to evaporate in the lantern's light or beneath a magnifying glass. The best substances to use are solutions of alum or sodium, alum being preferable. Ordinary table salt gives brilliant crystals which reflect the light to a marked degree. For regular formation, where the shape of the crystal is being studied, use a solution of hyposulphite of soda.
Many startling facts may be learned from the study of crystals in this manner, and watching them "grow" is great sport even to the chemist.—Contributed by L. T. Ward, Des Moines, Iowa.