Sodium sesquicarbonate (Systematic name trisodium hydrogendicarbonate) Na₃H(CO₃)₂, which is a double salt of sodium bicarbonate and sodium carbonate, and has a needle-like crystal structure. However, the term is also applied to an equimolar mixture of those two salts, with whatever water of hydration the sodium carbonate includes, supplied as a powder.

The dihydrate, Na₃H(CO₃)₂·2H₂O, occurs in nature as the evaporite mineral trona

[edit] Uses

Sodium sesquicarbonate is used in bath salts, swimming pools and as an alkalinity source for water treatment.

Sodium sesquicarbonate is used in the archaeological conservation of objects made of copper and copper alloys that have been corroded by salt water. Treatment with sodium sesquicarbonate removes copper chlorides from the corroded layer; if these were not removed the object would continue to corrode ("copper disease") while exposed to air.

It is also used as a precipitating water softener, which combines with hard water minerals (calcium- and magnesium-based minerals) to form an insoluble precipitate, removing these hardness minerals from the water. [1] It is the carbonate moiety which forms the precipitate, the bicarbonate being included to moderate the material's alkalinity.

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