Internet Version [Naruhodo no Mori] Vol.52

by Yumiko Mori

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Vol.52   July 15th, 2000

Extracting Sea Salt

What else can we obtain from sea water?

Home science experiments for mothers of elementary school children

Ren: "Look! A lot of crabs are walking around."
Satoshi: "There are a lot of small bugs as well."
Mom: "I wonder these are sea slaters?"
Satoshi and his friend, Ren, are so excited on the beach that they have almost forgotten the purpose for this trip.
Waves are coming to the beach one after another.
Satoshi: "Mom, how are we going to use this sea water?"
Mom: "We are going to boil the sea water to obtain sea salt."

Back to our home. We start working on sea salt making.
First we filter the sea water and then boil on the stove. After a while, we filter the sea water again in order to remove calcium compounds. We boil the sea water one more time.

Mom: "Look! Can you see something glittering in the pot?"
Tae: "Yes, I can see! Looks pretty!"
Mom: "Satoshi, what do you think this glittering thing is?"
Satoshi: "Is it sugar?"
Satoshi notices strange silence.
Satoshi: "This looks like snow!"
Tae: "Satoshi, this is sea salt."

We turn off heat and filter it again. Now, sea salt and bittern are ready.
We have tasted the sea salt.
Ren: "It's very salty."
Mom: "This is particularly tasty salt. We can make onigiri (rice balls) with this salt. It should taste very delicious."
Tae: "I really want to eat onigiri."
Mom: "The other one is bittern. We add bittern when we make tofu."
Tae: "I want to eat tofu, too."
Mom: "For the next experiment, we can use this bittern to make tofu."
Satoshi: "I want to make tofu. By the way, is tofu also made from sea water?"

Extra

Materials (for 50 grams of sea salt)

Clean sea water	(2 liter)
A plastic bottle	(2 liter bottle)
Coffee filter	3 filters
A funnel	(Or Coffee filter cone)
2 Pots	(a big pot and a small pot)
A tea cup
A paddle

How to extract sea salt

1. Filter sea water through a coffee filter to remove any debris.

2. Boil the filtered sea water in a big pot at high heat.
   When the volume is reduced to one tenth of the original volume and the sea water looks turbid, filter the sea water through a coffee filter.
   Cream-colored material left on the filter is calcium compounds.
   Also, remove calcium compounds from the bottom of the pot.

3. Transfer the filtered clear sea water into a small pot and boil at medium heat for 3-10 minutes.
   Once whitish salt crystals start to appear, turn off the heat.

4. Remove crystals from the bottom of the pot with the paddle and then separate remaining bittern from salt by filtering again.

Photo courtesy of Sankei Newspaper.

From left, salt, bittern, calcium compounds

Salt Extraction: 7 findings and questions

• We find many different animals around the beach.

• I had thought sea water would taste much saltier.

• Various chemical compounds are dissolved in sea water.
  We have isolated approximately 15 grams of calcium compounds and 20 mL of bittern.

• Bittern is literally bitter.

• Calcium compounds are relatively dry. Salt crystals have rough touch feeling. Calcium compounds tastes differently from salt.
  Salt dissolved quickly, but Calcium compounds didn't dissolve in the same amount of water.

• When we went to the beach at night, I felt the ocean was scary in the dark.

• When I went to the shop, I have found many different types of salts.

* You may want to taste the sea water before and during the experiment. But be careful, since it can be very hot.

Ocean and our life

Why don't you take a plastic bottle with you when you visit beach this summer? Then you should try to extract sea salt. Our body always needs salt. That may be the reason why many people live near the beach.