Encyclopædia Britannica, Ninth Edition/Saltpetre

SALTPETRE, or Nitrate of Potash (KNO₃), is a salt obtained as a commercial product in three different ways. (1) It occurs as an efflorescence on the surface or in the superficial stratum of the soil in many parts of the world, but specially to a great extent in the Ganges valley and other parts of India. (2) It is obtained in a semi-artificial manner in nitraries or saltpetre plantations. These consist of heaps of decomposing animal matter mixed with lime ashes, road scrapings, and other rubbish covered over from rain, and from time to time damped with the runnings from stables and other urine. Such heaps develop within them small proportions of the salt and other nitrates, and are, in effect, artificial imitations of the saltpetre-bearing soil of India. They were formerly very common in Switzerland, France, Germany, and Sweden. (3) A large quantity of saltpetre is now prepared from Chili saltpetre, the nitrate of soda, by double decomposition of the soda salt with another salt of potash. See Nitrogen, vol. xvii. p. 518, and Gunpowder, vol. xi. pp. 319, 323. Saltpetre is of importance in numerous industries, among the most prominent of which are gunpowder manufacture and pyrotechny. It is also used as an oxidizing agent in glass-making and in metallurgical operations. In the curing of meat it is extensively employed with common salt and sugar, and it also occupies an important place in pharmacy.

In the year 1884 337,708 cwt. of saltpetre was imported into the United Kingdom, the estimated value being £306,113. Of this amount 200,065 cwt. came from Bengal and British Burmah alone, and 78,545 cwt. of converted saltpetre came from Germany. During each of the two years 1883 and 1884 the imports of Chili saltpetre, under the name of cubic nitre, exceeded 2,000,000 cwt., nearly the whole supply coming from Bolivia and Peru.