Explorers

A new year, a new location, a brand-new school, and a new set of students—but the Explorers are again investigating the wonders of science and nature.

We started off this new season with several activities related to absorption. We looked at—and in one case looked through—three types of material that could be called “super absorbers” of water. Absorption, of course, occurs when a substance soaks up and holds a liquid—just think of a paper towel sopping up a watery mess. What is happening is that the water molecules are being “trapped” by the molecules of the paper towel fabric. In this case it is a fairly loose trap—you can still easily feel the water if you pick up the paper towel, and if you lay it out on a counter the water will escape through evaporation in just a few hours.

The materials the Explorers examined, however, trap the water molecules much more effectively, with each water molecule being surrounded in a sort of tight cage of other molecules. This has two main effects that can be observed: first, after absorbing the water the resulting material does not feel particularly wet; and second, it takes much, MUCH longer for the water molecules to escape through evaporation.

The first material starts off as an innocent-looking white powder. Mr. Ramsey and club assistant Lissa poured a small amount of this powder into three separate containers and then, as the club members gathered around, added a quart or so of water to each container. The powder rapidly (in only a few seconds) soaked up the water, puffed up, and became to all appearances an entirely new type of substance—one that remarkably looks and feels like fresh snowfall. Mr. Ramsey told the students that this material is in fact sold by science supply stores under the name “Instant Snow,” and that one of its uses is by the film industry for making movies with scenes of winter.

The club members agreed that this was a pretty cool (ha!) idea for the stuff, but they were considerably less enamored by the revelation of the OTHER main use of this material. The stuff inside disposable diapers is a close relative of the instant snow, which makes sense—after all, for a diaper you want a material that can soak up a large amount of liquid without leaking dampness.

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As interesting as the instant snow was, the Explorers seemed even more fascinated by the next goodies in line: jelly marbles. In fact, at first they weren’t even aware these little guys were right in front of them, bobbing invisibly in a bowl of water. These marble-sized squishy blobs start life off as tiny little clear beads, but when they are put in water they act similarly to the instant snow powder: they start sucking up water like they’re dying of thirst. After awhile they have puffed up to many times their original size. But why are they invisible in water? After all, as the Explorers noted, a transparent marble made of glass is clearly visible in water, so what makes the jelly marbles different?

The answer to this lies in the concept of refraction. Refraction is the bending of light rays. We learn in school that the speed of light is a constant 186,000 miles per second (enough to travel around the entire Earth over seven times in one second), but in fact this is only its speed in a vacuum, such as found in outer space. When light travels through any sort of material, even one that is transparent, its speed will be slowed down, and how much it is slowed down depends precisely on the material through which it is passing. Air slows it down just a slight bit, while water and glass slow it down considerably more. This makes the light rays bend as they pass from one substance to another—an effect you can easily observe by putting a fork into a clear glass of water. Depending on how you turn the glass, you can see how the fork appears to be bent or broken at the point where it enters the water—this is because of the refraction, or bending, of the light rays as they leave the air, pass through the glass and then the water, and then back through the glass and into the air again.

Being made of glass, a normal marble bends the light rays by a different amount from the water, so even though it and the water are both “clear,” the marble is clearly visible in a bowl of water. Jelly marbles, though, are made almost entirely of water itself—so a light ray passing through water and then through the jelly marbles barely bends at all. This makes them virtually invisible in the water, until an unsuspecting student reaches in and pulls out a handful of them. In the palm of a hand, they look exactly like little globes of water—which is essentially just what they are.

Finally, the Explorers checked out a close relative of the jelly marble, the jelly crystal. These are made of the exact same substance, but are just blobs rather than spheres when they grow. Also, the variety Mr. Ramsey gave to the students came colored (which the jelly marbles themselves can be if food coloring is added to their “growing water”). Each pair of students had a bowl full of yellow crystals, a bowl of red crystals, and a bowl of blue crystals.

To wrap up this first meeting, the students each used a half-liter drinking water bottle to fill with colored crystals. Mr. Ramsey told the students that if they made layers of colors in the bottles, the crystals would over time slowly share and mix their colors as the colored water trapped within managed to spread from one crystal to another. This should result in the three primary colors being joined by the secondary colors—red and yellow mixing as orange, for example, and red/blue resulting in purple and yellow/blue giving green. Many of the students took this layered approach, while others favored a tuity-fruity method of just tossing in a random mixture of crystals. Over time this will likely result in a uniform neutral (think brownish) shade throughout the bottle—but hey, it’s THEIR bottle, they can do as they please. One way or another, it’s an experiment to see what will happen, and really, that’s the whole point!

So everyone went home with a bottle of crystals and a baggie with a few jelly marbles. With luck none of them will get eaten by the family dog.

To read about an earlier session with the super absorbers, click the first link below. The second link is to the online science supply store where we got our snow, marbles, and crystals.

An Absorbing Activity

Jelly Marbles