Regular readers know that I love microscopy. Through my trusty Spencer I've spent many hours roaming majestic beds of microscopic algae and floating forests of phytoplankton. But until recently, I had never studied crystal growth. Doing so normally involves melting something under the lens and letting it solidify, which requires a way of warming the microscope slides. Over the years I'd tried a few schemes but was never able to get fine temperature control and uniform heating. So I was delighted to receive an innovative design from Ely Silk, an accomplished amateur scientist in Tamarac, Fla. With it, you can create your own startling images of crystals [see illustrations].
Silk constructed his heater from electroconductive glass of the kind used by automobile manufacturers for defrostable windows. The glass has a thin, transparent layer of either tin oxide or indium-tin oxide deposited on one side. An electric current flowing through this layer can heat the glass to temperatures greater than the boiling point of water. (Although Silk independently developed the idea of using conductive glass, Stephen A. Skirius described a similar project in a 1984 issue of the Microscope magazine.) The main drawback is that I have been unable to find an inexpensive source of the material. So I've purchased and cut up a large sheet of it and will make the pieces available through the Society for Amateur Scientists; details are at the end of this article.
Once you have secured the glass, you must prepare it to accept current. Silk used two thin strips of copper about 3 millimeters (about 0.1 inch) wide to form the electrodes. You can cut these strips from a sheet of copper foil, which is stocked by most sheet-metal dealers and art supply shops. Place the glass so that the oxide layer is up and affix the electrodes onto the left and right sides [see illustration above] using a metallized epoxy, which unlike most adhesives will let the electricity through. Resins filled with silver or aluminum powder are available at most hardware stores. If you can't find any, call Epoxies, Etc., in Greenville, R.I. (401-231-2930).
Next you'll need to protect the oxide layer from scratching while exposing specimens to the heat. Silk placed a drop of glycerin at the center of the oxide side of the glass stage and covered it with a large but thin coverslip. If you don't have any glycerin, any fluid with a high boiling point will work, such as radiator fluid, brake fluid or motor oil. For the coverslip, Silk recommended a No. 0 grade (the thinnest grade) that is 22 by 30 millimeters (0.9 by 1.2 inches), but just about any size will work. This arrangement lets your specimens respond quickly to any adjustments you may make in the amount of heating.
The object of study goes on top of the coverslip. Blanket it with an 18-millimeter square glass cover. For ease of handling, this topmost cover should be of a thicker grade, either No. 1 or No. 2. Fisher Science Education in Burr Ridge, Ill., sells a collection of various coverslips in boxes of 100 for $3 (call 800-955-1177; item number CQS17525A).
Finally, attach the electrodes to a power source that can deliver enough current. Silk used a variable 15-volt, 1-amp AC or DC supply. You can probably find such a source at most electronics surplus stores for about $20. Parts suppliers--such as Jameco (800-831-4242 or www. jameco.com)--can also provide lower-power sources, but you may need to wrap the stage partially in insulating material, such as newspaper. Or try picking through the wares of those small electronics suppliers who sell at local swap meets or flea markets. I once came across an entire bin of power supplies for $4 each. Silk reported that his easily heats the stage to 100 degrees Celsius (212 degrees Fahrenheit). Naturally, never leave the stage unattended with the power on
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