Given my preteen chemistry set experiments with smoke bombs, I had to look this up.
What is saltpeter (cooking curing salt)?
"In West African cuisine, potassium nitrate (salt petre) is widely used as a thickening agent in soups and stews such as Okra soup and Isi ewu. It is also used to soften food and reduce cooking time when boiling beans and tough meat." -- Cookipedia
"Potash includes various mined and manufactured salts that contain potassium in water-soluble form. The name derives from pot ash, plant ashes or wood ash soaked in water in a pot, the primary means of manufacturing potash before the Industrial Era. The word potassium is derived from potash." -- Wikipedia
potash - alkaline potassium compound, especially potassium carbonate or potassium hydroxide a caustic chemical like lye.
You don't want to cook with saltpeter containing potash.
Definitely don't cook with stump remover -- it is not food grade..