This salt is used to give fireworks their orange colour, as a de-icer, desssicant and in heating pads. Not only is it hygroscopic, taking water from the atmosphere, but it is also deliquescent — absorbing so much water from the atmosphere as to form an aqueous solution.

I made this slide with a glass slide and the adhesive coverslip provided with my Foldscope kit. Standard glass slides did not work as well as within a few minutes the crystals would be in aqueous solution, the adhesive coverslides prevented this and provided a nice polarization + compensator plate too.