|"Sample of iodine" by LHcheM. |
Licensed under Creative Commons
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Prills are tiny balls of a substance, formed by letting droplets of the liquid fall from a height (in a prilling tower.) Surface tension has its way and the droplets become spheres, which then solidify. Many bulk industrial chemicals, particularly fertilizers and detergents, are prilled for easier handling.
Prilling has its roots in 18th century copper mining, referring to beads of high purity copper.
While I rarely buy chemicals, I have purchased iodine flakes for a teaching lab. The catalog does offer me the choice of "iodine, beads" — prills by another name.