What is that blue stuff all over the sidewalk?
I've been explaining to Younger Son for years that the blue crystals and stains on sidewalks in cold weather are salt that help melt the ice. But it’s taken lots of experimenting with salt for him to get how that could possibly be so. The other day he asked for some salt to take outside and was at it again. We used two types of salt to see if one melted faster (the sea salt did seem a wee bit faster). Next time we will test out sugar, which also lowers the freezing temperature of water.
What you need:
- ¼ cup of sea salt
- ¼ cup of table salt
- ¼ cup of sugar
- Let your child pick out some other things around the kitchen to test (Pepper? Cinnamon? Hot cocoa mix? Meat seasoning?)
- 4 or more ice blocks (made ahead of time by filling food storage containers with water and setting in freezer or outdoors overnight)
- Smooth surface for a work area (we used a sled)
1. Loosen the blocks of ice and let your child examine them. It’s okay to break them up into pieces.
2. When you are ready to start the activity, set each piece of ice on work surface with at least a few inches in between.
3. Sprinkle each substance on a different piece of ice.
4. Leave one piece of ice untouched as a control.
5. Go and play while you wait! Check back frequently.
6. Discuss your results. This activity is more for fun than scientific study, although it’s a little of both. Lots of things can affect the rate at which the ice melts – the size of the ice, the amount of salt or sugar added, the temperature of the substance put onto the ice, etc.