The fungus is cut into slices and then steeped in a solution of nitre.
In the combined state nitrogen is fairly widely distributed, being found in nitre, Chile saltpetre, ammonium salts and in various animal and vegetable tissues and liquids.
It is mentioned in the De inventione veritatis ascribed to Geber, wherein it is obtained by calcining a mixture of nitre, alum and blue vitriol.
It is also beneficial, especially in the case of partially exhausted beds, to water with a dilute solution of nitre.
These are washed with ammonium chloride until the filtrate is colourless, ignited, fused with caustic potash and nitre, the melt dissolved in water and nitric acid added to the solution until the colour of potassium ruthenate disappears.