Rochelle salt

Rochelle salt It is a water-soluble and slightly alcohol- soluble salt that has the property of double refraction (like Iceland spar). It is one of the components of Fehling’s liquor that is used to test the reducing power of sugars. It is also called the salt of Pierre Seignette, named after a pharmacist from Rochelle who synthesized it in 1675.


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  • 1 Chemical composition
  • 2 Physical properties
  • 3 Applications
  • 4 Storage
  • 5 Source

Chemical composition

  • The chemical composition is that of a sodium and potassium tartrate:

KNa (C 4 H 4 O 6) · 4H 2 O

  • Molecular Weight: 282.23
  • Description: colorless crystals, white powder
  • Merck Index Number: 6381-59-5


Physical properties

  • Melting Point: 70º-80ºC
  • Solubility in water: 73 g. Rochelle salt / 100g of water at 20ºC. Practically insoluble in alcohol.
  • Crystallization system: rhombus shaped prisms


The main fields of use of seignette salt are the following:

  • Electroplating
  • Food Industry (manufacture of pectins and jellies)
  • Pharmaceutical industry
  • Cigarette paper (combustion regulator)
  • Piezoelectricity
  • Metal treatment
  • Gas purification
  • Inks for graphic arts
  • Silver mirror
  • Laboratory reagent
  • Chelating agent to remove aluminum salts, among other metals


The tartaric acid must be kept in an airtight wrapping and stored in a dry place, protected from moisture and under normal temperature. It is a stable compound that does not change over time if these storage conditions are respected. However, according to the regulations, an expiration date of one year is assigned. The product has a tendency to panic; prolonged storage is not recommended, especially for the finest grain sizes.

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