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Anne Marie Helmenstine, Ph.D.

How to Make Rochelle Salt

By March 18, 2014

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Rochelle salt or potassium sodium tartrate is an interesting chemical that is used to grow large single crystals, which are attractive and interesting, but also may be used as transducers in microphones and grammophone pickups. The chemical is used as a food additive to contribute a salty, cooling taste. It is an ingredient in useful chemistry reagents, such as as Fehling's solution and Biuret reagent. Unless you work in a lab, you probably don't have this chemical lying around, but you can make it yourself in your own kitchen.

Make Rochelle Salt

You will need:
  • Cream of Tartar
  • Washing Soda or Sodium Carbonate (which you can get by heating baking soda or sodium bicarbonate in a 275°F oven for an hour)
  1. Heat a mixture of about 80 grams cream of tartar in 100 milliliters of water to a boil in a saucepan.
  2. Slowly stir in sodium carbonate. The solution will bubble after each addition. Continue adding sodium carbonate until no more bubbles form.
  3. Chill this solution in the refrigerator. Crystalline Rochelle salt will form on the bottom of the pan.
  4. Remove the Rochelle salt. If you redissolve it in a small amount of clean water, you can use this material to grow single crystals.

Photo: Rochelle salt crystal grown on Skylab (NASA)


May 5, 2011 at 1:23 pm
(1) GoatRider says:

It has to be “real” cream of tartar, potassium bitartrate. There’s a cheap substitute that uses some other acid and corn starch to make it act like cream of tartar in cooking. But it does NOT work to make rochelle salt. I’ve bought Cream of Tarter from a lot of different sources, and haven’t been able to get this recipe to work. It stops fizzing after I’ve added about 1/4 of the Sodium Carbonate, and the solution is amber colored, probably from the corn starch. Apparently every cooking store is now selling the cheap substitute.

One possible reason for this is that Rochelle salt is might be an ingredient in some designer drugs, and the DEA has asked them to stop selling the real stuff. Or more likely, in today’s business climate where everybody is cutting costs, they’re just selling the cheap stuff because they can get away with it.

May 5, 2011 at 1:51 pm
(2) Anne says:

It’s possible to obtain potassium bitartrate or cream of tartar by collecting the crystals that precipitate from fresh grape juice that is chilled and undisturbed. The chemical crystallizes from wine also.

May 9, 2011 at 8:34 am
(3) John L says:

Try a homebrew shop. We use Potassium Bitartrate in winemaking to settle out excess tartaric acid. I know it’s available from Presque Isle Winery, piwine.com.

May 9, 2011 at 4:45 am
(4) Spotightman1234 says:

I know Mic cormick sells actual cream of tartar (Potassium bitartrate) as I’ve made KNaC4H4O6 from it in the past.

If you are using Sodium carbonate made from baking soda in the oven (anhydrous) you’ll need to add 22.529 grams to the 80 grams of Potassium bitartrate, but if you are using washing soda bought from the store (decahydrate) you’ll need to add 60.824 grams of Sodium carbonate.

May 23, 2011 at 2:18 pm
(5) PK says:

I have tried it two times and it didn’t work the solutions crystallized or hardened but didn’t formed into crystal. Is there online stores that sells the Crystal to buy for Science project instead of retrying????

October 19, 2012 at 9:47 pm
(6) austin says:

I believe Goatrider is talking about “Baking Powder”, which is by the cornstarch and baking soda or/and bread mix.

Cream of Tartar can be found in the McCormick spices.

Washing Soda can be found in the laundry detergent area next to the baking soda and borax or the bleach. Tip: The Baking Soda in this area can be found for cheaper in a greater quantity than in the baking area.

A pool supply store might supply even more quantity of baking soda for cheaper, or else at Walmart during pool season they sell a hefty container full for about $15 in their pool chemical area.

February 20, 2013 at 8:41 pm
(7) Chris says:

How many genes of Crem of Tartar do you need for this recipie? I tried it and got a milky white grainy substance. I think it was the wrong kind.

July 21, 2013 at 5:10 am
(8) Jim says:

Smart and final has a large container for $15 that works great.
Make solution as described.
Let it cool slowly in double boiler, then strain into Tupperware. In a few hours small cubes will be all along the bottom. Collect and dry them. Place them in ice cube trays with curved bottoms and sides, no flat surfaces. Reheat and strain through a coffee filter without a trace of crystal. Once it is barely warm gently pour into ice cube trays containing immaculately clean seeds. Large crystals will form is a few hours, grab them out before the shapes start to distort from space constraint. Flat surfaces cause false facets and cause improper structure for this type (rhombic). The best candidates from the trays can be tied with dental floss and suspended in a fresh batch of tepid solution for spectacular perfect single crystals. If you intend to harvest piezo electricity please note only working seed crystals produce working large crystals. Have fun, this met

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