The manufacture of gun-cotton and of nearly all nitro-com pounds consists essentially in immersing the prime material (cotton, glycerin, and similar materials) in a mixture of nitric and sulphuric acids and allowing the nitric acid to act upon it for a more or less prolonged time. The explosive body thus formed is then separated from the spent acid, and washed, with the addition of alkalies as a rule, until it has lost all traces of acidity.