You will need to assemble the following:
- Milk (whole )
- Dinner plate
- Food coloring (red, yellow, green, blue)
- Dish-washing soap (Dawn brand works well)
- Cotton swabs
Here’s What to do:
1. Start with a plastic dinner sized plate. Pour enough milk in the dinner plate to completely cover the bottom and allow it to settle.
2. Add one drop of each of the four colors of food coloring-red, yellow, blue and green-to the milk. Keep the drops close together in the center of the plate of milk.
3. Get a cotton swab. Go ahead and predict what will happen when the tip of the cotton swab is touched at the center of the milk. Touch the tip of the cotton swab to the center of the milk. It is important not to stir, but just touch it with the tip of the cotton swab.
4. Place a drop of liquid soap on the tip of a cotton swab. Place the soapy end of the cotton swab in the middle of the milk and hold it there for 10-15 seconds. What happens?
How does it work?
Milk is full of protein. This is one of the reasons that your parents encourage you to drink it! Soap causes those protein molecules to bend, roll and twist in all sorts of directions. The soap also breaks the surface tension of the milk since milk contains mostly water. This allows the colors to zig zag through the milk.
But there is more for you to do!
Add another drop of soap to the tip of a cotton swab and try it again. Place the cotton swab in different places in the milk. Notice that the colors in the milk continue to move even when the cotton swab is removed. What makes the food coloring in the milk move?
Try these additional experiments!
- Repeat the experiment using water in place of milk. Will you get the same eruption of color? Why or why not?
- What kind of milk produces the best swirling of color: skim, 1%, 2%, whole milk, cream? Does the fat content of the milk affect the reaction?