This experiment shows how to make a play-doh/slime-like substance that's safe to handle.
Some Elmer®'s White Glue (be sure and use Elmer's only & NOT the type labeled 'Washable'), Borax (Sodium Tetraborate, available most larger supermarkets - Look for Borax in the laundry detergent section.), Water, some Ziploc® or other sealable plastic bags, some stirring items such as a spoon or craft sticks, a jar or large cup, and a bowl to mix all the ingredients together.
In the bowl, mix an equal quantity of the Elmer's glue and water.
Mix well with a spoon or left-over "popsicle" sticks.
In the jar or water cup, we'll make a saturated solution of borax. Combine a tablespoon of borax powder with a cup or so of water and stir. It's easier if you use a jar with a lid as you can then screw on the lid and shake the mixture well. If all of the borax powder dissolves, then you need to add a bit more. When you get to the point where no more borax will dissolve, then the solution is saturated.
Now, add about two tablespoons of the borax solution to the bowl with the glue and water mixture and stir quickly. The resulting mixture should be slimy or gooey. You can save your slime for a long time by putting the 'stuff' into sealable plastic bags. If your slime dries out, you can add a bit of water back into it. If it gets too dry, you'll have to start over.
When you mix Elmer's glue with a bit of water, you make a substance that
is known as a polymer, in this case a form of poly-vinyl acetate. The borax solution
(sodium tetraborate) is a 'cross-linking' substance that binds this polymer we just made into long chains
of molecules bound together to make the glue solution thicker. So, as the polymer chains get more
"bound", it gets harder for them to move around, and your slime starts
to be more like Silly-putty. Experiment with adding more borax solution to
see if this indeed makes the slime thicker or thinner.
Knowing just how much Borax solution to add is the trick to this experiment. If you add too little, your slime will contain excess glue (the polymer part) and it will be sticky. If you add too much, your slime will be very wet (too much 'cross-linking'). Touch your slime with your hands when it doesn't look like a liquid anymore. If your slime feels sticky, try adding a little Borax solution. If your slime feels very wet and slippery (but is not still runny), remove it from the container and kneed it in your hands. In a few minutes, any extra Borax solution will evaporate or be absorbed.
The substance known as 'Gak' is really a specialized form of a polymer known as poly-vinyl alcohol, but is not too dissimilar what we made with Elmer's glue in this experiment.
You might get some of the Elmer's glue on your clothes. If you do, just get some clean water and wet the area well to help remove the glue. The Slime that we made isn't really toxic, but I wouldn't eat it. Borax is used to clean clothes (it's a form of soap), so that won't be much of a bother. If you use food coloring, it'll stain your hands (for a while) and your clothes, so be careful with that.
The Slime we made is just a demonstration of how certain polymers are effected
by other chemicals, such as 'cross-linkers' . Polymers are used in nearly
everything these days, such as most kinds of plastics, nylon, and clothes.
You can sometimes spot a polymer by it's name: if it ends in -on, like nylon or rayon,
it can be a polymer.
See if you can find other polymers in and around the house. Some easy ones are: Fishing line and Eye glasses are made of polymers. See if you can find others...