Sometimes the classic science experiments / demonstrations are classic for a reason. They're just wonderful at grabbing the attention of students and getting them to think about their world. Such is the case with the delightful "Rising Raisins" and the awesome "Soda Pop Bottle Fountain". By combining the two, the kids will be begging for more.

First, the "Rising Raisins" have been in print forever, usually just as a diversion or bed time sleep inducement. For this activity it will be used to enhance observation skills as well as a spring board for a discussion of density. Feel free to adapt the activity and questions to suit the age of your students.

Though soda will work for this activity, I always use seltzer water. Soda has a tendency to get sticky upon drying while seltzer water will just evaporate with no mess. No mess, that's for me.

You will need a sealed two liter bottle of seltzer, a tall clear container, raisins, other testable items.

Ask the student to inspect the sealed bottle. What is seen? (Clear liquid) Are there any bubbles? (No) Now, open the bottle and ask what is seen and possible reasons for the occurrence. (Lots of bubbling, foaming over. Also, sound is heard. This could be caused by a reduction in pressure once the bottle is opened.) Where did the bubbles usually form? (On the bottle's walls) I wonder if bubbles need someting on which to form?

Now, pour the seltzer water into the tall clear container. No doubt, more bubbles will form on the container's wall. Show a raisin and have the student predict what will happen when it is placed in the container.

When added, the raisin will sink to the bottom. There, bubbles will form in its nooks and crannies. This will cause the raisin to float to the surface where the bubbles will pop. The raisin will sink again and the process will continue until little gas is left in the seltzer water.

At this point, the experiment can go in two ways. One is for the student to suggest other items that might sink and float like raisins. What are the characteristics of these items that allow the activity? (Lightweight, not really smooth, etc.) Objects may include pieces of broken spaghetti, macaroni, straws, penny, marble, etc. Students can categorize objects that move and those that don't, then create possible reasons for their activity or inactivity.

Older students may be engaged with a discussion of density once they understand it fundamentally. Why did the raisin float? (It had bubbles around it.) Why didn't the bubble surrounded penny float? (Too heavy) Is the raisin's mass more or less at the top? (Same - the mass of the raisin itself remains the same just as your mass remains the same if you are on the ground or jumping into the air.) Continue questioning and move to questions about density. If we were to find the mass of the raisin and the mass of the same volume of water, which would have more mass? (Raisin - it sinks in water). If we were to find the mass of the raisin and its bubbles and the same volume of water as the raisin and bubbles which would be greater? (Water - the raisin/bubbles float because they have less mass combined as the same volume of water). And so goes it... As an inquiry questioning device to check understanding of density, the "Rising Raisin" is a winner.

Next time, we'll take the bubble formation ideas and use them in creating the "Awesome Pop Bottle Fountain." Have fun!