Potassium sodium tartrate tetrahydrate, also known as Rochelle salt, is a double salt of

tartaric acid Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes, but also in bananas, tamarinds, and citrus. Its salt Salt is a mineral composed primarily of sodium chloride (NaCl), a c ...

first prepared (in about 1675) by an

apothecary ''Apothecary'' () is a mostly archaic term for a medical professional who formulates and dispenses '' materia medica'' (medicine) to physicians, surgeons, and patients. The modern chemist (British English) or pharmacist (British and North Amer ...

Pierre Seignette Pierre is a masculine given name. It is a French form of the name Peter. Pierre originally meant "rock" or "stone" in French (derived from the Greek word πέτρος (''petros'') meaning "stone, rock", via Latin "petra"). It is a translation ...

, of

La Rochelle La Rochelle (, , ; Poitevin-Saintongeais: ''La Rochéle''; oc, La Rochèla ) is a city on the west coast of France and a seaport on the Bay of Biscay, a part of the Atlantic Ocean. It is the capital of the Charente-Maritime department. Wit ...

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...

. Potassium sodium tartrate and

monopotassium phosphate Monopotassium phosphate (MKP) (also, potassium dihydrogenphosphate, KDP, or monobasic potassium phosphate) is the inorganic compound with the formula KH2PO4. Together with dipotassium phosphate (K2HPO4.(H2O)x) it is often used as a fertilizer, f ...

were the first materials discovered to exhibit

piezoelectricity Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ' ...

. This property led to its extensive use in "crystal" gramophone (phono) pick-ups, microphones and earpieces during the post-World War II consumer electronics boom of the mid-20th century. Such

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and cont ...

s had an exceptionally high output with typical pick-up cartridge outputs as much as 2 volts or more. Rochelle salt is

deliquescent Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substan ...

so any transducers based on the material deteriorated if stored in damp conditions. It has been used medicinally as a

laxative Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lub ...

. It has also been used in the process of

silvering Silvering is the chemical process of coating a non-conductive substrate such as glass with a reflective substance, to produce a mirror. While the metal is often silver, the term is used for the application of any reflective metal. Process ...

mirrors. It is an ingredient of Fehling's solution (reagent for reducing sugars). It is used in

electroplating Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric cur ...

, in

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

and

, and as a combustion accelerator in cigarette paper (similar to an

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

pyrotechnics Pyrotechnics is the science and craft of creating such things as fireworks, safety matches, oxygen candles, Pyrotechnic fastener, explosive bolts and other fasteners, parts of automotive airbags, as well as gas-pressure blasting in mining, quarry ...

). In organic synthesis, it is used in aqueous workups to break up

emulsion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althou ...

s, particularly for reactions in which an aluminium-based

hydride In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of ...

reagent was used. Sodium Potassium tartrate is also important in the food industry. It is a common precipitant in

protein crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

and is also an ingredient in the

Biuret reagent Biuret is a chemical compound with the chemical formula . It is a white solid that is soluble in hot water. A variety of organic derivatives are known. The term "biuret" also describes a family of organic compounds with the chemical formula , where ...

which is used to measure

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

concentration. This ingredient maintains cupric ions in solution at an alkaline pH.

Preparation

The starting material is

tartar Tartar may refer to: Places * Tartar (river), a river in Azerbaijan * Tartar, Switzerland, a village in the Grisons * Tərtər, capital of Tartar District, Azerbaijan * Tartar District, Azerbaijan * Tartar Island, South Shetland Islands, Ant ...

with a minimum

content 68 %. This is first dissolved in water or in the mother liquor of a previous batch. It is then basified with hot saturated

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkal ...

solution to pH 8, decolorized with

activated charcoal "Activated" is a song by English singer Cher Lloyd. It was released on 22 July 2016 through Vixen Records. The song was made available to stream exclusively on ''Rolling Stone'' a day before to release (on 21 July 2016). Background In an inter ...

, and chemically purified before being filtered. The filtrate is evaporated to 42 °Bé at 100 °C, and passed to granulators in which Seignette's salt crystallizes on slow cooling. The salt is separated from the mother liquor by centrifugation, accompanied by washing of the granules, and is dried in a rotary furnace and sieved before packaging. Commercially marketed grain sizes range from 2000 μm to < 250 μm (powder). Larger crystals of Rochelle salt have been grown under conditions of reduced gravity and convection on board

Skylab Skylab was the first United States space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three separate three-astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Major operation ...

. Rochelle salt crystals will begin to dehydrate when the relative humidity drops to about 30 per cent and will begin to dissolve at relative humidities above 84 per cent.

Piezoelectricity

In 1824, Sir David Brewster demonstrated

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ' ...

effects using Rochelle salts, which led to him naming the effect

pyroelectricity Pyroelectricity (from the two Greek words ''pyr'' meaning fire, and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the a ...

. In 1919, Alexander McLean Nicolson worked with Rochelle salt developing audio related inventions like microphones and speakers at Bell Labs.url = https://sites.google.com/view/rochellesalt/home

References

{{reflist Potassium compounds Organic sodium salts Piezoelectric materials Ferroelectric materials Tartrates Food acidity regulators Food antioxidants Double salts E-number additives