Exercise B Starch Grains

  1. I,KI turns blue-black in the presence of starch. To prepare UKl stain, dissolve 20 g of KI (potassium iodide) in 1,000 ml of distilled water. Using a magnetic stirrer, add 4.0 g of iodine to the potassium iodide solution. It will take some time for the iodine to dissolve. Store in brown bottles, as I2KI breaks down in light Dispense in dropper botdes.
  2. Polarizing filters, of course, can be bought for student microscopes but an inexpensive alternative is to purchase polarizing plastic sheets from Edmund Scientific (Tech Spcck Linear Polarizing Laminated Film). Cur into 10 cm x 10 cm squares. Two per microscope. This is a one-time purchase since these filters can be used over and over.

You may use the flours of potato (the usual soluble starch sold by supply houses), corn, and arrowroot to show the Maltese cross under polarizing light. Also, a sample of sweet potato root works well. Illuminate the field on high. Completely open the diaphragm and use highest lamp setting to get the best results.

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