While You're Waiting for the Food to Come by Eric Muller, Illustrated by Eldon Doty Hardcover version Paperback version To order or find out more about this book, click on the book cover above or on either cover version. Make liquids drip-up and down. Slowly pour some oil into the glass. Because oil is less dense than water, the oil will float. Next, generously sprinkle salt on top of the oil and watch what happens.
Oil is less dense than water, so it floats.
What makes things interesting in this trick is that the oil tends to cling to the salt temporarily. Together, the oil and salt blobs are denser than water, so they descend to the bottom of the cup. As the blobs go down, the oil coats and protects the salt from dissolving. However, after it sinks, the oil soon yanks free from the salt and floats up again.