Dear Mr. Scientist,
Ever since I was a kid I’ve always wondered about this, how do scratch and sniff stickers work?
—Matt S.
The process for making these childhood favorites is relatively simple. Scented oil and a clear polymer are mixed together until the oil forms really small droplets (on the scale of millionths of a meter). The polymer coats each droplet, forming millions of microscopic capsules of the scented oil. These microcapsules are then mixed with an adhesive so they can be applied to the stickers. When you scratch one of the stickers, you break open some of the tiny capsules and release a small amount of the scented oil which you are then able to smell.
Dear Mr. Scientist,
During the winter, gloves can never keep my hands warm so I often use hand warmers. What exactly goes on inside those packets that makes them warm?
—Chris R.
The most common hand warmers use a mixture of iron, water, vermiculite (a mineral), activated carbon (charcoal that’s full of tiny holes) and salt. The oxygen in the air reacts with the iron causing it to oxidize (i.e. rust) which releases heat, and the salt acts as a catalyst to help speed up this reaction. The activated carbon helps spread the heat throughout the packet and the vermiculite acts as an insulator to retain the heat.
These hand warmers can only be used once though, since all of the iron eventually oxidizes and can no longer produces heat.
There are, however, hand warmers that are reusable. They contain a supersaturated solution of sodium acetate (the stuff that’s left after your vinegar and baking soda volcano erupts) and a metal strip. When you flex the metal strip, the solution crystallizes which releases heat. After the warmer has stopped giving off heat, placing the packet in boiling water will cause the crystals to go back into solution and it is ready to be used again and again.
Ask Mr. Scientist is written by Michael Leitch. If you have a burning science question you want him to answer, tweet it @DC_Science or email it to science@dailycardinal.com.
