Nitric Acid: Chile Saltpetre Distilled with Oil of Vitriol in an Iron Retort

Nitric acid as commerce made it in 1912, from Thorpe's Dictionary: nearly equal weights of sulphuric acid and sodium nitrate (Chile saltpetre) distilled in a cast-iron retort. Keeping the condensed acid hot until it leaves the cooling worm keeps out nitrous acid; very strong sulphuric acid and melted nitrate give very strong nitric acid. The fused residue is sodium sulphate and disulphate. The vapour and fumes are poisonous: fume hood, respirator. The picture: our diagram.