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Stocking stuffer chemistry

Christmas, as everyone knows (except parents who insist on giving socks and underwear—you know who you are) is all about toys. But that doesn’t mean it can’t also be about science.

David A. Katz, a chemist, educator, science communicator and consultant from Tucson, Arizona, has a webpage called Chemistry in the Toy Store which describes in enormous detail the chemistry behind some well known toy and novelty items. I took a look at what he has to say about several items suitable for stocking stuffers, beginning with a favorite of mine when I was a kid: Silly Putty.

Silly Putty was the result of an unsuccessful effort by General Electric chemists to create a synthetic rubber based on silicon. They couldn’t find an industrial use for this “bouncing putty,” but a salesman thought it was fun stuff and began giving away samples, leading to it eventually being marketed as a toy.

Unlike most fluids, the viscosity of Silly Putty is not just dependent on temperature, but can be altered by stress. Under low stress, such as a slow pull, Silly Putty flows into thin strands. Under gentle pressure, it will flatten. But under high stress, such as a sharp pull, it snaps. Slap your hand on a ball of the stuff, and the ball will hardly change. Drop the ball, and it will bounce. But hit the ball with a hammer, and it will shatter.

Back in my day the thing to do with Silly Putty for big laughs (well, okay, smallish laughs) was to use it to pick up an image from a newspaper, then distort the image by stretching the putty. Older types of newspaper inks were composed of mineral oil and carbon black or colored pigments and did not dry well (which is why newspapers turned your hands black). The pigment transferred easily from the ink’s mineral oil to the excess silicone oil in the Silly Putty.

A related toy is Slime, which is made from the gum of the guar plant, a legume similar to a soybean plant. Guar gum is used as a stabilizing, thickening and film-forming agent in everything from cheese to salad dressing to ice cream to toothpaste to hand cream, but when you add borax (sodium borate) to it, it begins to act like Silly Putty, but, well, slimier. Pull it slowly, and it will flow and stretch and even form a thin film, but pull it sharply and it will break. If you pour a little of it from a container and then tip the container upward slightly, it will continue to flow out (this is called self-siphoning)—yet even though it looks like a liquid, you can cut the pouring stream with scissors. If you put a small piece of Slime on a table top and hit it with your hand, it won’t splash or splatter, though it looks like it should. Throw a small piece against a hard surface, and it will bounce.

Similar substances abound in the toy world, with fun names like “Gak,” “Living Nightmare Body Fluids,” “Teenage Mutant Ninja Turtles Retromutagen Ooze,” “Toxic Crusaders Toxic Waste” and “Dinosaur Ooze,” proving that nobody ever went broke appealing to children’s interest in grossing out other children (and grown-ups).

Another toy that was all the rage when I was a kid (Wham-O, the manufacturing company, sold 20 million of them) is the Super Ball, invented by accident by Norman Stingley, a chemical engineer. The Super Ball is very resilient (bouncy), loses very little kinetic energy to heat each time it bounces (which means it keeps bouncing for a very long time) and has a high-coefficient of friction (which means that even a slight spin to it will cause it to bounce off the floor, wall or ceiling in unpredictable fashion).

There’s also a Stupid Ball, which is just the opposite of a Super Ball: it’s made from an energy-absorbing material with a very low resiliency—in other words, it doesn’t bounce, though it looks like it should.

Another good old-fashioned stocking stuffer is a balloon. The long, stringy molecules in the rubber from which balloons are made are all folded in on themselves. When stressed—by the pressure building up inside the balloon as it’s inflated—they unfold and elongate, allowing the balloon to expand. Of course, stretch them too much and they break—and the balloon pops.

Whatever Santa stuffs your stocking with this year, be it non-Newtonian fluids, high-resiliency energy-conserving spheroids, thin bladders made of folded, stringy molecules, or none of the above, I hope you have very Merry—and scientifically fascinating!—Christmas.

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