Simple Crystals

Some crystals are rather pitiful without the use of polarized light, but that’s best left for another time. -K

Crystals are a fine object for the microscope and few are the beginners texts which do not direct the observations of one sort of crystal or an other. By far the most common directive is to create a saturated solution of salt (sodium chloride) and placing a drop on a clean slip observe the process of crystalization as the water evaporates. Interesting enough as an activity, but not as enlightening as it might be. Occasional one might be directed to try kosher or even rock salt and compare it to iodized table salt, but even then a salt crystal is a salt crystal and one is apt to find it dull.

If one has been diligently preparing insects via the maceration and pressure method one will have on hand a solution that makes a rather more interesting crystal. The sodium hydroxide or potassium hydroxide one has been using to macerate insects may be deposited in the center of a slide in a small drop and put aside under a cover to dry. There’s no need to prepare a saturated solution, yet, but in a short time the liquid will evaporate and one will have a delightful snow-flake like crystal to observe.

Naturally having created a fine crystal one will desire to keep it. The slide might be retained as it is, without a mountant or coverslip, indefinitely. It is much better to use a coverslip and create a more secure slide. One may think that upon application of a liquid mountant the crystal will immediately dissolve and be lost, occasionally this will be the case, but then there are always other mountants and methods one may employ. Try mounting a sodium hydroxide crystal under natural balsam; is the result different if xylol balsam is used? Is the result different for Euparal or Damar, for Nu-Mount or Hyrax? If the crystal proves to be soluble in all of the mountants one posses it may still be secured under a cover by a method that is becoming increasingly uncommon, the thin cell mount (to be covered in an upcoming post).

Once one has the hang of creating a simple crystal mount certain questions may come to mind concerning their form. Before running to the nearest chemical handbook, I would recommend trying to answer a few questions by practical experiment:

  1. Does a different concentration of chemical yield a different form of crystal? (10% vs. saturated for example.)
  2. Does a different temperature or speed of crystallization? (Place the slide upon a hot-plate, or in a freezer.)
  3. Does a different solvent? (There’s water, but what of the other solvents, isopropyl and ethyl alcohol are likely on hand.)

Afterwards run off and see if the results are congruent with what is shown in a chemical text, then wonder at the career you might have enjoyed in chemical analysis. This is of course the most basic sort of crystal mount one may make but the idea is to discover a new object for microscopy and many owners of the microscope will have never examined anything beyond the world in a drop of water.