Meeting in the middle

Time for more fun with food coloring. We had previously used two colors to see whether salt water was slower to diffuse than fresh water. This time we repeated the experiment with two containers of differently colored fresh water. To our surprise, although the colors eventually seemed to meet in the middle, the red took days longer than the yellow color. It seems that whatever makes the different colors causes them to diffuse at different rates. We'll have to play around with that some more.

Water race

To try to show that, even though water looks the same after you dissolve salt in it, it's changed, we decided to compare the speed of diffusion for salt water and fresh water. We filled one bottle with fresh water, dyed green, and a second bottle with water with Epsom salt dissolved into it, dyed red. Then we rolled up a paper towel and put an end in each bottle. The green fresh water started climbing the paper towel. At first it looked like the red salt water was just sitting there, but we checked and the un-dyed paper towel coming from the red was wet, while the paper towel from the fresh water was only wet where it was green. Eventually the red color started moving along the towel. It looks like the salt slowed the diffusion of the color, but not the diffusion of all the water.

Making water run upstream

We decided to try to make water run upstream, so to speak, using diffusion. We filled a bottle with colored water. Then we took a long piece of paper towel, rolled it up, and used string to keep it rolled up. We put one end of the paper towel in the water-filled bottle and the other end in an empty bottle that we put on a raised platform. Nearly instantly the colored water started creeping up the paper towel. We quickly learned that a paper towel saturated with water is much heavier than a dry paper towel and we had to add supports to hold the paper towel up. Throughout the evening we watched its slow progress. We checked on it in the morning and, to our surprise, the water hadn't made it all the way to the other bottle. Instead, it stopped part-way up, leaving a dark ring of color, followed by dry paper towel. I guess diffusion will only go so far.