What’s saltpetre, I don’t hear you asking. Potassium nitrate:

Potassium nitrate is a chemical compound with the formula KNO3. It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre (saltpeter in American English), from Medieval Latin sal petræ: “stone salt” or possibly “Salt of Petra” and nitrate of potash.

Sounds dull but you’re probably more familiar with it’s many uses than you thought. Apart from providing a natural source of nitrogen in fertilizers, it has the following uses also:

In the process of food preservation, potassium nitrate has been a common ingredient of salted meat since the Middle Ages, but its use has been mostly discontinued due to inconsistent results compared to more modern nitrate and nitrite compounds. Even so, saltpetre is still used in some food applications, such as charcuterie and the brine used to make corned beef. Sodium nitrate (and nitrite) have mostly supplanted potassium nitrate’s culinary usage, as they are more reliable in preventing bacterial infection than saltpetre. All three give cured salami and corned beef their characteristic pink hue.

Potassium nitrate is an efficient oxidizer, which produces a lilac flame upon burning due to the presence of potassium. It is therefore used in amateur rocket propellants and in several fireworks such as smoke bombs. It is also added to pre-rolled cigarettes to maintain an even burn of the tobacco.

Potassium nitrate is the main component (usually about 98%) of tree stump remover, as it accelerates the natural decomposition of the stump.

From wikipedia.