I had put some Soil Moist granules in water in a plastic container the night before. I took them in and announced that they were "ghost brains". The kids didn't buy it, of course. I spooned some out into small plastic bags while explaining that it was a hydrophilic polymer I had used in the garden over the summer, it would dry back out into granules if left on a paper towel, and it was pretty much the same thing that they could find in a disposable diaper. This last bit of info really elicited some cries of "eeeewwwwww!"
Then we made Slime, using the directions in the old Girl Scout Junior Badge Book in the Making It Matter Badge; these are the best directions I've found for making Slime with a crowd of kids in 3rd through 5th grade. Of course, this badge book is no longer available because
Pass out cups to the kids, along with wooden popsicle sticks for stirring. Measure out 1 tablespoon of Elmer's Glue (or other glue -- there are lots of websites comparing the virtues of various glues in regards to Slime-making) into each cup (have kids help with this or not -- sort of depends on your crowd)to . Go down the row putting 3 tablespoons of water into each cup, and have them stir the water and glue together.
(For the record, all I had told them about what we were doing was that we were going to make a polymer by having using the Borax hook together the polyvinyl acetate [in the glue] sort of like paper clips hooking together lots of little chains. Some kids recognized what we were doing, most didn't. Several websites give nice explanations of the science of this demonstration, and thanks to Wikipedia I think I know the difference between polyvinyl acetate and polyvinyl alcohol.)
We then put a squirt of glow-in-the-dark paint in each cup.
Earlier I had mixed 2 tablespoons of Borax in a cup of warm water. Each cup of watery glue next got one tablespoon of the Borax solution, with directions to "keep stirring". Unfortunately as the water cooled a lot of the Borax precipitated out (I'd done this at home, and at least an hour had elapsed). So the first few cups had a few duds, as they didn't have enough Borax to start the reaction. But, wow, it was pretty cool when SURPRISE, Slime started to form in the cups that worked. Since we had plenty of cups, glue, and Borax solution, we started over on some of the duds.
We then discussed where we could go to see whether or not it would really glow in the dark -- I hadn't tried this out ahead of time and wasn't really sure. We all ran downstairs to a big room with no windows, and discovered, YES, we have glowing slime! I meant to give a quick lesson in how glow in the dark paint works, but it was lost in the excitement.
I had brought plastic bags for them to put there Slime in. So, take-home bags of Ghost Brains and Slime! Perfect Halloween science class!