Ultimate Cloud-Forming Apparatus
Publication No. 11839
An exquisitely simple demonstration that allows you to literally form a cloud with your own two hands. The thunder and lightning are up to you.
Boiling flask, flat bottom, 500 mL*
Bulb, 60 mL capacity*
Stopper, size 8*
*Materials included in kit.
Although the materials provided in this kit are considered nonhazardous, always follow laboratory safety guidelines.
The Cloud Forming Apparatus may be saved for future use.
To assemble the stopper apparatus, place the tubing connector in the hole of the wide end of the stopper. Now place the rubber bulb on the opposite end of the tubing connector (see Figure 1).
Student Worksheet PDF
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesPlanning and carrying out investigations
Disciplinary Core IdeasMS-ESS2.C: The Roles of Water in Earth’s Surface Processes
MS-ESS2.D: Weather and Climate
HS-ESS2.C: The Roles of Water in Earth’s Surface Processes
Crosscutting ConceptsCause and effect
MS-ESS2-5. Collect data to provide evidence for how the motions and complex interactions of air masses results in changes in weather conditions.
This demonstration is somewhat analogous to cloud formation in the atmosphere. Squeezing the bulb dramatically increases the pressure (and ever slightly increases the temperature) inside the flask. At this higher pressure some of the water that was in the vapor phase returns to the liquid phase until a new equilibrium state is reached. When the pressure on the bulb is released, the pressure (and temperature) within the bottle drops suddenly, creating a partial vacuum. To reattain equilibrium, water now goes from the liquid phase to the vapor phase. At this point, the area above the liquid becomes saturated with water vapor which condenses on the “airborne” smoke particles (condensation nuclei) to form the cloud. This saturation is caused by unequal pressures of the vapor phases upon expansion of the bulb. The inequality of pressure can be thought of as an instantaneous partial vacuum.
Adapted from an item written by Bruce Parks that appeared in Connect, January/February, 1995. Connect is a publication of the Teachers Laboratory, Inc., Brattleboro, VT.