It is lead bromide and potassium nitrate
The reaction between nitric acid and potassium hydroxide will yield potassium nitrate (KNO3) in addition to water. Potassium nitrate is a colorless, crystalline salt that is commonly used in fertilizers, food preservation, and fireworks.
Add more water and stir.
Mixing potassium iodide with nitric acid will result in a chemical reaction that produces iodine gas and potassium nitrate. Nitric acid will oxidize the iodide ion to produce iodine gas, while the potassium will form a salt with the nitrate ion from the acid. It is important to handle nitric acid with care, as it is a strong oxidizing agent and can be corrosive.
Nitrogen gas which is created by mixing sodium azide with potassium nitrate which produces the nitrogen.
Gunpowder is not a pure substance. It is a mixture composed of potassium nitrate, charcoal, and sulfur in specific proportions. Each of these individual components maintains its chemical identity in the mixture.
The two solutions likely contained ions that reacted together to form a solid compound. In this case, mixing solutions of potassium sulfate (containing potassium and sulfate ions) and calcium nitrate (containing calcium and nitrate ions) led to a reaction where calcium ions from calcium nitrate bonded with sulfate ions from potassium sulfate to form calcium sulfate solid.
What exactly does "compatible" mean to you? Ammonium salts, and nitrates, are generally pretty soluble, so I wouldn't expect a precipitate to form from mixing ammonium nitrate with much of anything. If that's what you meant by "compatible," then yeah, probably.
Some examples of simple precipitation reactions include mixing silver nitrate with sodium chloride to form silver chloride precipitate, mixing lead nitrate with potassium iodide to form lead iodide precipitate, and mixing barium chloride with sodium sulfate to form barium sulfate precipitate.
When potassium nitrate dissolves in water, it absorbs heat from its surroundings to break the bonds between the ions, causing the solution to become colder. This process is called an endothermic reaction, which means it requires energy input to occur. This is why mixing potassium nitrate with water results in a cold sensation.
Mixing hydrochloric acid with sodium hydroxide to form salt and water. Combining sulfuric acid with calcium hydroxide to produce calcium sulfate and water. Reacting nitric acid with potassium hydroxide to yield potassium nitrate and water. Mixing acetic acid with ammonia to form ammonium acetate and water. Combining phosphoric acid with barium hydroxide to produce barium phosphate and water. Reacting citric acid with sodium bicarbonate to yield sodium citrate and water. Mixing hydrofluoric acid with sodium carbonate to form sodium fluoride and water. Combining carbonic acid with potassium hydroxide to produce potassium carbonate and water. Reacting oxalic acid with calcium hydroxide to yield calcium oxalate and water. Mixing hydrobromic acid with magnesium hydroxide to form magnesium bromide and water.
Dissolve each of the silver nitrate and potassium iodide separately in water, then mix the two solutions slowly with stirring. Silver iodide will precipitate and can be separated by filtering it from the liquid.
Mixing sodium hydroxide and calcium nitrate will not form a precipitate. Instead, it will form solutions of sodium nitrate and calcium hydroxide.