Science Fair Project Encyclopedia
|Appearance||White or dirty gray solid|
|Formula weight||101.1 amu|
|Melting point||607 K (334 °C)|
|Boiling point||decomposes at 673 K (400 °C)|
|Density||2.1 ×103 kg/m3|
|Solubility||38 g in 100g water|
|S0gas, 1 bar||? J/mol·K|
|S0liquid, 1 bar||? J/mol·K|
|Ingestion||May cause GI irritation, nausea, vomiting, diarrhea.|
|Inhalation||Irritation, long term exposure may be fatal.|
Its common names include saltpetre (from Medieval Latin sal petrae: "stone salt" or possibly "salt of Petra"), American English saltpeter, Chilean saltpetre, Nitrate of potash and nitre. The name saltpeter is also applied to sodium nitrate.
It is the oxidising (oxygen-supplying) component of gunpowder. Prior to the large-scale industrial fixation of nitrogen (the Haber process), a major source of Potassium nitrate was the deposits crystallising from cave walls or the drainings of decomposing organic material. Dung-heaps were a particularly common source: ammonia from the decomposition of urea and other nitrogenous materials would undergo bacterial oxidation to produce nitrate.
Historically, nitre-beds were prepared by mixing manure with either mortar or wood ashes, common earth and organic material such as straw to give porosity to a compost pile typically 1.5 metres high by 2 metres wide by 5 metres long. The heap was usually under a cover from the rain, kept moist with urine, turned often to accelerate the decomposition and leached with water after approximately one year. The liquid containing various nitrates was then converted with wood ashes to potassium nitrates, crystallized and refined for use in gunpowder.
One of the most useful applications of potassium nitrate is in the production of nitric acid, by adding concentrated sulfuric acid to an aqueous solution of potassium nitrate, yielding nitric acid and potassium sulfate which are separated through fractional distillation.
Potassium nitrate is also used as a fertilizer, as a model rocket propellant, and in several fireworks such as smoke bombs, in which a mixture with sugar produces a smoke cloud of 600 times their own volume. In the process of food preservation, potassium nitrate is a common ingredient of salted meat.
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