NITRATE OF POTASS ; NITRE ; SALTPETRE. KO, N06. This important salt is obtained in India in large quantities, but in an impure form, by lixiviating certain soils ; and in France, and other countries, it is obtained from old mortar rubbish, in which organic matter has supplied the nitrogen wherewith to form nitrate of lime, which is then decomposed by carbonate of potass.
Pure nitre is not rendered turbid, when in solution, either by nitrate of silver, or nitrate of baryta. It crystallizes in long six sided prisms, and is anhydrous, the moisture of the crystals being merely interstitial. They are permanent in the air. Nitre is soluble in about 4 parts of water at 60 and in equal parts of boiling water, but is nearly insoluble in alcohol ; it fuses at 600 without decom position, and at a red heat is slowly decomposed and yields oxygen, 11b. of nitre giving off about 12,000 cubic inches of gas.
Fulminating powder is made by mixing 3 parts of nitre, 2 of dry carbonate of potass, and 1 of sulphur. If a small quantity of this mixture be placed upon a shovel over the fire, it first melts and blackens, and then explodes with violence.
Gunpowder is made by mixing 1 part of charcoal, 1 of sulphur, and 6 of nitre, all in fine powder.
The principal impurities in nitre are the chlorides of sodium and potassium, sulphate of potass, and nitrate of soda.
Nitrate of potass added to protosulphate of iron forms a tolerably good developer for collodion positives, but nitrate of baryta is better, because sulphate of baryta is insoluble, and may be separated from the solution, which sulphate of potass cannot.
Pyroxylin is sometimes made by adding nitrate of potass to sulphuric acid, instead of mixing the sulphuric and nitric acids. The plan is not good, because it is extremely difficult to remove the whole of the bisulphate of potass which is formed from between the fibres of the pyroxylin with which it is entangled.
The nitrate of potass formed in the nitrate bath when iodide of potassium is used as an iodizer, is neutral, and appears to be inert in the process.