NITRATE OF POTASH, Nitre, Salt petre. This salt occurs native as an efflorescence upon limestones, sand stones, marls, chalk, and ealctuff ; it forms a saline crust in caverns, as also upon the surface of the ground in certain places, especially where animal matters have been decomposed. Such caverns exist in Germany near Homburg (Burk ardush); in Apulia upon the Adriatic sea (Polo di Mofettal, in France ; in the Fast Indies ; in Ceylon, where 22 nitri ferous caverns are mentioned; in North America, at Crooked river, Tennessee, Kentucky, and upon the Missouri ; in Brazil, Teneriffe, and Africa. Nitre oc curs as an efflorescence upon the ground in Arragon, Hungary, Podolia, Sicily, Egypt, Persia, Bengal, China, Arabia, North America, and South America. Several plants contain saltpetre • parti cularly borage, dill, tobacco, sunflowers, stalks of maize, beet-root, bugloss, park taria, &c. It has not hitherto been found in animal substances.
This salt consists of 54 nitric acid 48 potassa ; its equivalent, therefore, is 102. It is spontaneously generated in the soil, and crystallizes upon its surface in seve ral parts of the world, especially in In dia, whence nearly the whole of the nitre used in Britain is derived. It has occa sionally been produced artificially in nitre beds, formed of a mixture of calcareous soil with animal matter ; in these, nitrate of lime is slowly formed, which is ex tracted by lixiviation, and carbonate of potash added to the solution, which, by double decomposition, gives rise to the formation of nitrate of potash and car bonate of lime : the latter is precipitated: the former remains in solution, and is obtained in crystals by evaporation. Ni tre crystallizes in six-sided prisms, solu ble in seven parts of cold water, and in less than its weight of boiling water. It has a cooling saline taste, and is anhy drous. At 616° it fuses, and at a red heat is decomposed. Its great use is in the manufacture of gunpowder, and in the production of nitric acid. It is also em ployed in the preservation of meat. Dr. Ure, in his valuable Dictionary of Arts, discusses this interesting question —How is nitre annually reproduced upon the surface of limestones, and the ground, after it has been removed by washing? It has been said, in reply, that as secondary limestones contain re mains of animal matters, the oxygen of the atmosphere, absorbed in virtue of the porous structure, will combine with their azote to form nitric acid ; whence nitrate of lime will result. Where potash is present in the ground, a nitrate of that base will be next formed. The genera tion of nitre is in all cases limited to a very small distance from the surface of porous stones ; no further, indeed, than where atmospherical air and moisture can penetrate ; and none is ever pro duced upon the surface of compact stones, such as marble and quartz, or of argillaceous minerals. Dr. John Davy
and M. Longchamp have advanced an opinion, that the presence of azotized i matter is not necessary for the generation of nitric acid or nitrous salts, but that the oxygen and azote of the atmosphere, when condensed by capillarity, will com bine in such proportions as to form nitric acid, through the agency of moisture and of neutralizing bases, such as lime, mag nesia, potash, or soda. They conceive that as spongy platina serves to combine oxygen and hydrogen into water, or the vapor of alcohol and oxygen into acetic acid, and as the peroxyde, as well as the hydrate of iron and argillaceous minerals, serve to generate ammonia from the oxygen of the air and the hydrogen of water ; in like mariner, porous lime stones, through the agency of water, operate upon the constituents of the at mosphere to produce nitric acid, without the of animal matter. This opinion may certainly be maintained; for in India, Spain, and several other coun tries, at a distance from all habitations, immense quantities of saltpetre are re produced in soils which have been wash ed the year before. But, on the other hand, it is known that the production of this salt may be greatly facilitated and in creased by the admixture of animal offals with calcareous earths.
It is now known, that ammonia in the nascent state, or just in the moment of be ing generated by decomposition of ani mal matters, is converted into nitric acid, if a stronger base, such as lime or potash, be present : the oxygen of the air is brought into play, and, uniting with the ammonia just formed, alters that sub stance into nitric acid and water ; 8 equi valents of oxygen uniting with 1 equi valent of ammonia, to form 1 equivalent of nitric acid and 8 equivalents of water. The acid thus produced then seizes on the potash, and becomes neutralized. This explains why animal matter, and stirring the compost, hastens nitrifica tion.
Nitre is applied to many purposes :-1, to the manufacture of gunpowder ; 2, to that of sulphuric acid ; 8, to that of ni tric acid, though nitrate of soda or cubio nitre has lately superseded this use of it to a considerable extent ; 4, to that of flint-glass ; 5, it is used in medicine; 6, for, many chemical and pharmaceutical preparations ; 7, for procuring, by defla gration with charcoal or cream of .tartar, pure carbonate of potash, as also black and white fluxes; 8, for mixing with salt in curing butcher meat ; 9, in some countries for sprinkling in solution upon grain, to preserve it from insects ; 10, for making fireworks.
Nitre has sometimes been mistaken for Glauber's salt ; and, when taken in the quantity of half an ounce or an ounce, it acts as a powerful poison. In such cases the stomach should be evacuated as ra pidly as possible, and the symptoms of spasm relieved by opiates. In doses of 5 to 15 grains it is diuretic and diaphoretic.