Sodium Nitrate can be combined with sulfuric acid to produce nitric acid, which is distilled off. At lower pressure the lower temperature needed results in less decomposition. The theoretical 2 moles of nitric acid per 1 mole of sulfuric acid results in a very high end temperature, much decomposition and a solid neutral sulfate that is difficult to remove. When this reaction was important industrially, it was common practice to operate with sulfuric acid in excess to end on a mostly bisulfate product poured molten out of the retort.
Hobbyist gold refiners use sodium nitrate to make a hybrid aqua regia that dissolves gold and other metals.Less common applications include as an oxidizer in fireworks, replacing potassium nitrate commonly found in black powder, and as a component in instant cold packs.
Sodium nitrate is used together with potassium nitrate and calcium nitrate for heat storage and, more recently, for heat transfer in solar power plants. A mixture of sodium nitrate, calcium nitrate and potassium nitrate is used as energy-storage material in prototype plants, such as Andasol Solar Power Station and the Archimedes project.