EXPERIMENT: Swirling Milk
Operating Guide
Swirling Milk
Visitors create swirly, colorful patterns in milk with food color and
detergent.
OBJECTIVES: Visitors learn about how detergents react with the fats in .
SCIENCE TOPICS
PROCESS SKILLS
VOCABULARY
Fats/Oils
Chemical Reactions
Observing
Molecule
Measuring
Controlling Variables
Comparing
Surface Tension
UNIT 8 EVERYDAY CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
U8.1
EXPERIMENT: Swirling Milk
Operating Guide
Swirling Milk
Procedure:
1. Always wear safety goggles.
2. Rinse the graduated cylinders and the two petri
dishes in the sink.
3. Use graduated cylinder 1 to measure out 20 ml of
milk and pour it into the petri dish labeled “milk”.
4. Use graduated cylinder 2 to measure out 20 ml of
water and pour it into the petri dish labeled “water”.
5. Add 1-2 drops of each food color to each dish.
What happens?
Does the color act differently in the milk than the
water?
6. Now take a clean toothpick and dip its end into the
detergent in the "detergent" bottle.
7. Look at the milk dish, where the food color spots
have probably not moved. Now carefully touch the
center of each food color spot with the soapy
toothpick. Watch (do not stir).
What happened to the color?
8. Empty and rinse the graduated cylinders and the
petri dishes in the sink. Discard the toothpick into the
waste container.
U8.2
UNIT 8 EVERYDAY CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
EXPERIMENT: Swirling Milk
Operating Guide
How does milk
react with
detergent?
A Closer Look:
When you first place the drop of food coloring into the
liquids, it mixes more with the water than the milk. This is
because the food coloring is water-based, so it mixes well with
water, but not very well with the milk, which has both fats and
water inside.
Touching the milk with the detergent
causes the colors to swirl for several reasons.
The surface of the milk, like the surface of
water, is stretched tight across the dish by
surface tension. In milk, the surface tension
comes from the water and fat molecules pulling
on each other.
The spot of detergent stops helps the fat
mix with the water, and therefore it changes the
surface tension in the milk. But such a tiny spot of detergent
can only affect the milk in small spots and streams near its
origin. The food coloring moves to these spots and streams
where the fat, soap, and water have mixed.
and causing a kind of “tear” in the surface of the milk.
The food color moves out into the area of low surface
tension.
UNIT 8 EVERYDAY CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
U8.3
EXPERIMENT: Swirling Milk
Operating Guide
This causes the milk outside the soap spot to have a
higher surface tension, so it pulls away from that spot. The
food
coloring moves with the milk molecules, streaming away from
the soap drop. The water has a much lower surface tension,
so you might see the color spread the first time you touch the
detergent to it, but after that the water and food coloring are
fully mixed and do not react any more.
Detergent also has the ability to bind to both fat molecules
and water molecules, so it creates a bond between the milk and
the food coloring. As the detergent becomes evenly mixed with
the milk, the action slows down and eventually stops
MATERIALS
U8.4

(with amounts to have on hand)

Two 25-ml graduated cylinder

Two plastic Petri dishes

Four small dropper bottles of food coloring.

Two 250-ml squeeze bottles

Whole milk, keep 1 gallon on hand

Dish-washing soap (keep 8 oz on hand)

Food coloring (red, yellow, blue, green)

One 600 ml beaker

One small jar with lid with hole drilled in lid

Toothpicks, keep 100 on hand

Small plastic beaker

Medium plastic beaker
UNIT 8 EVERYDAY CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
EXPERIMENT: Swirling Milk
Operating Guide
Setup/Takedown Procedures
ORIGINAL SETUP

Color code and label the two graduated cylinders “1” and “2.” , and “20 ml”
Color code and label the lids to match the labels on the bottles.

Color code and label the two plastic squeeze bottles “milk” and “water.”
(The color of the labels should match those of the graduated cylinders
above.)

Color code and label the two Petri dishes “milk” and “water” to match the
labels on the bottles and jars.

Label the small plastic container “detergent.”

Label the small plastic beaker “Toothpicks”

Color code and label the four dropper bottles with food coloring.

Label the medium plastic beaker “Used Toothpicks”

Label the 600 ml beaker “Ice water”
WEEKLY SETUP

Make up new solutions as necessary

DAILY SETUP

Set out the visitor instructions in a Plexiglas holder.

Fill the “Milk” and “Water” squeeze bottles.

Put out two food coloring bottles


On a tray lined with a white mat, set out the following:
 Two color-coded, labeled graduated cylinders
 Two labeled plastic Petri dishes
 Two dropper bottles of food coloring
 Cup of toothpicks
 Detergent container
 Two 250-ml squeeze bottle labeled “Milk” and “Water”
 Used toothpicks container
DAILY TAKEDOWN
UNIT 8 EVERYDAY CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
U8.5
EXPERIMENT: Swirling Milk
Operating Guide
 Thoroughly clean graduated cylinders and Petri dishes.
 Return milk to refrigerator
 Return all materials to the experiment tub.
WEEKLY TAKEDOWN

Clean the Petri dishes and graduated cylinders.

Relabel and clean the materials as needed.

Return the tray and mat to general lab storage.

Pour any milk left in sqeeze bottle or stock bottle down drain and
clean both bottles.
RUNNING SUGGESTIONS

Make sure milk is kept in ice beaker, and that beaker is cold
enough.

EXTENSIONS
Try with different kinds of milk with varying fat contents, how
does the detergent react differently? Also try rice milk or soy
milk.
Safety & Disposal
MATERIALS PREP
To prepare milk solution:
 Combine one part whole milk with three parts water.
To prepare food coloring solutions:
 Combine one part food coloring with one part water.
To prepare detergent solution:
U8.6
UNIT 8 EVERYDAY CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
EXPERIMENT: Swirling Milk
Operating Guide
Combine one part dishsoap with three parts water.
UNIT 8 EVERYDAY CHEMISTRY
EXPERIENCING CHEMISTRY ©2006 OMSI
U8.7