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

double salt A double salt is a salt that contains two or more different cations or anions. Examples of double salts include alums (with the general formula ) and Tutton's salts (with the general formula ). Other examples include potassium sodium tartrate, ammo ...

of tartaric acid first prepared (in about 1675) by an apothecary,

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, France. 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. This property led to its extensive use in "crystal"

gramophone A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogu ...

(phono) pick-ups, microphones and earpieces during the post-World War II consumer electronics boom of the mid-20th century. Such transducers had an exceptionally high output with typical pick-up cartridge outputs as much as 2 volts or more. Rochelle salt is deliquescent so any transducers based on the material deteriorated if stored in damp conditions. It has been used medicinally as a laxative. It has also been used in the process of silvering 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 reduction of cations of that metal by means of a direct electric current. The part to be ...

, in electronics and piezoelectricity, and as a

combustion accelerator Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...

cigarette paper Rolling paper is a specialty paper used for making cigarettes (commercially manufactured filter cigarettes and individually made roll-your-own cigarettes). Rolling papers are packs of several cigarette-size sheets, often folded inside a cardboard ...

(similar to an oxidizer in

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). In organic synthesis, it is used in aqueous workups to break up emulsions, particularly for reactions in which an aluminium-based hydride

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

was used. Sodium Potassium tartrate is also important in the food industry. It is a common precipitant in protein crystallography 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 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 tartaric acid content 68 %. This is first dissolved in water or in the

mother liquor The mother liquor (or spent liquor) is the solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approx ...

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 alkali ...

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 interv ...

, 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 . 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 Sir David Brewster KH PRSE FRS FSA Scot FSSA MICE (11 December 178110 February 1868) was a British scientist, inventor, author, and academic administrator. In science he is principally remembered for his experimental work in physical optics ...

demonstrated piezoelectric effects using Rochelle salts, which led to him naming the effect pyroelectricity. 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