Iodine crystals can be used for disinfecting water. Wilderness experts outline one way of achieving the desired effect. Place 4 g of iodine crystals, equivalent to about 0.141 oz., in a 2-oz. glass bottle filled with water. Shake the bottle for a few seconds then decant just the iodine-saturated water, leaving the crystals at the bottom, into another vessel containing a gallon of clear water. Wait 15 to 30 minutes before drinking. Do not drink the crystals because they are poisonous.
Police use iodine crystals during criminal investigations. You can reveal fingerprints on paper by exposing the surface to iodine crystals or fumes. The iodine crystals are often provided in ampules for use in breath-activated fuming guns. As a forensics expert blows the crystals across the paper, the crystals stick to the fatty acids left by the fingers, causing a stain. Electronically fired fuming guns are also used for larger surfaces.
Solutions of iodine crystals have been used as dental disclosing agents because they reveal the presence of plaque on teeth. The dentist "paints" the patient's teeth with a cotton swab containing the iodine solution, then asks the patient to rinse his mouth with the solution. As an alternative, the dentist can also give the patient an iodine tablet to chew. However, the solution has an unpleasant taste and can cause allergic reactions.
Iodine crystals can be used in the remediation of polluted soils, sediments and groundwater. Two other chemicals -- sodium ethylenediaminetetraacetic acid, otherwise known as Na-EDTA, and potassium iodide -- were also used in a test in which iodine crystals removed 99 percent of mercury from a sample of loam that had been spiked with the substance.