began by melting large containers of cold animal fat. Many different
kinds of fat can be used to make soap, and we chose a combination of
leftover bacon grease and drippings from roasted chickens and
turkeys -- the smell reminded me of Thanksgiving dinner.
Numerous soap recipes can be found on the Internet, but we liked Snowdrift Farm's website in particular because it allows readers to specify the oil in use.
To the right is a photo of Chris explaining the importance of melting points as we melted the fat into oil on a hot plate.
STEP TWO: Combine the lye and water, and bring the mixture to the right temperature.
After melting the fat to the right temperature (we used a chemical thermometer from The Lemelson Center's Spark!Lab),
we determined the weight of the fat (this time, with the help of
Spark!Lab's digital scales). Next, we combined water and lye, and I was
surprised by how quickly the temperature rose upon combination.
According to Chris, nineteenth-century Americans had to be careful
when adding the lye: too much and the solution can become very caustic
and leave chemical burns on the skin.
Below, you can see Chris mixing the lye and water.
STEP THREE: Mix all the ingredients together, and let it set for a month.
Once the oil and water/lye combination were all set, Chris brought
them together in a bowl using a (decidedly non-period-appropriate)
electronic hand mixer. The solution quickly transformed into a thick,
light yellow liquid. I can only imagine how tiring the process must have
been without the help of a handy electric appliance. We then poured
the soap into a container, where it will rest for a few weeks before we
kick off our laundry program on the National Mall terrace.
The picture at the top of this page shows Chris combining the oil and water/lye solution.
Between melting the fat and working with a substance like lye,
saponification can be dangerous and cause serious burns if one does not
take the appropriate cautionary measures. If you decide to make soap on
your own, be sure to wear safety goggles and use heat-resistant gloves
like we did.
The saponification lesson made me feel like I was back in school:
hearing words like "melting point," "caustic" and "chemical reaction"
reminded me of the degree to which science can dictate our everyday
lives -- and even household chores. We hope you come visit the "Wash, Rinse, Wring, Repeat!" program at the museum this summer, and suds up!
Do you have any science lesson stories to share? Have you ever made
soap, or even done laundry without the help of modern machines? Share
your thoughts and comments below.
See more posts from and about the Smithsonian.
This post was originally published on the National Museum of American History's O Say Can You See?" blog and is republished here with permission.
Images: Smithsonian Institution.