Nitreoccurscrystallisedintwoforms

Nitre occurs crystallised in two forms: (1) prisms of the rhombic system, and (2) rhombohedral crystals. It is very soluble in water, the solubility increasing rapidly with the temperature, 100 parts of water dissolving about 25 parts of nitre at ordinary temperatures, and 247 parts at 100° C. It is employed extensively in medicine (known also as sal prunella;), in the chemical laboratory, for pickling purposes, for the production of touch-papers and fuses, and in pyrotecbny. Its chief use, however, is for the manufacture of gunpowder (q.v.), of which it forms about 75 per cent.