Nitrates
<h2 >Occurrence</h2>
<p >Nitrate compounds are found naturally on earth as large deposits, particularly of <a href="http://en.wikipedia.org/wiki/Nitratine" title="Nitratine" >Chile saltpeter</a> a major source of sodium nitrate.</p>
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Nitrites are produced by a number of species of <a href="http://en.wikipedia.org/wiki/Nitrifying_bacteria" title="Nitrifying bacteria" >nitrifying bacteria</a>, and the nitrate compounds for <a href="http://en.wikipedia.org/wiki/Gunpowder" title="Gunpowder" >gunpowder</a> (see this topic for more) were historically produced, in the absence of mineral nitrate sources, by means of various <a href="http://en.wikipedia.org/wiki/Industrial_fermentation" title="Industrial fermentation" >fermentation</a> processes using urine and dung.
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<h2 >Uses</h2>
<p >Nitrates are mainly produced for use as <a href="http://en.wikipedia.org/wiki/Fertilizer" title="Fertilizer" >fertilizers</a> in <a href="http://en.wikipedia.org/wiki/Agriculture" title="Agriculture" >agriculture</a> because of their high solubility and biodegradability. The main nitrates are ammonium, sodium, potassium, and calcium salts. Several million kilograms are produced annually for this purpose.<sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-2" >[3]</a></sup>
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<h3 >Other uses</h3>
<p >The second major application of nitrates as oxidizing agents, most notably in explosives where the rapid oxidation of carbon compounds liberates large volumes of gases (see<a href="http://en.wikipedia.org/wiki/Gunpowder" title="Gunpowder" >Gunpowder</a> for an example). Sodium nitrate is used to remove air bubbles from molten glass and some ceramics. Mixtures of the molten salt are used to harden some metals.
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