Nitria

“ Hence nitric acid is always met with in the form of salts in nature. The soluble salts of nitric acid are called nitres. This name is derived from the Latin sal nitri. The potassium salt, KNO3, is common nitre, and the sodium salt, NaNO3, Chili saltpetre, or cubic nitre. Nitres are formed in the soil when a nitrogenous [269] substance is slowly oxidised in the presence of an alkali by means of the oxygen of the atmosphere. In nature there are very frequent instances of such oxidation. ”

“ All vegetable and animal material deposited in or on the soil contains more or less of these proteid or nitrogenous matters while the amount of nitric acid supplied in this way is probably represented entirely by the quantity in the organism of the plant or animal and unabsorbed at the time of its death. In other words it is not demonstrated that nitrates or nitrites are in any sense a special product of plant growth save in the case of nitrifying organisms themselves which are supposed to be of a vegetable nature. Animal organisms do not in any sense assimilate nitric nitrogen. ”

“ The nitrogen in decaying roots, in the dead stems and leaves of plants, and in humus generally is sooner or later changed into a nitrate, the change being effected by bacteria. That
the action of living organisms is the cause of the production of nitrates is supported by the fact that the change does not occur when the soil is heated nor when it is treated with disinfectants which destroy or check the growth and life of bacteria. The process resulting in the formation of nitrates in the soil is spoken of as nitrification. ”

“ It is afterwards ground into a fine powder and sifted as in the case of the charcoal.
Potassium nitrate is eminently suitable as an oxygen-provider, not being deliquescent. Nitrates are continually being produced in surface soils, &c., by the oxidation of nitrogenous substances. Nitric and nitrous acids are also produced by electric discharges through the atmosphere, and these are found eventually as nitrates in soils, &c. Nitre is soluble in water, and much more so in hot than in cold. Crude nitre, obtained from soils or other sources, is purified by recrystallization. ”

“ These nitrifying germs attack the humus, break it down, separate the nitrogen, cause it to unite with the oxygen of the air and thus build it into nitric acid which can be used by plant roots. This nitric acid if not immediately used will unite with lime or potash or soda or other similar substances and form nitrates, as nitrate of lime, nitrate of potash or common saltpetre. These nitrates are soluble in water and can be easily used by plant roots. If there are no plant roots to use them they are easily lost by being washed out of the soil. ”

“ The processes of nitrification and the isolation and determination of the nitrifying organisms will be considered in a special chapter of this manual. By reason of the great solubility of the nitrates, and the inability of the soil to retain them, there can never be a great accumulation of nitric acid in the soil save in localities deficient in rain-fall or in specially protected spots, such as caves. The nitric acid, therefore, produced in the soil passes at once into growing vegetation, or is found eventually in the drainage waters. ”

“ The nitrogen passes into the atmosphere, and is "lost"; the carbonic acid and water return to nature and are at once used by vegetation. The ammonia and nitrites await further changes. These further changes become necessary on account of the fact, already discussed, that plants require their nitrogen to be in the form of nitrates in order to use it. Nitrates obviously contain a considerable amount of oxygen, but ammonia contains no oxygen, and nitrites very much less than nitrates. Hence a process of oxidation is required to change the ammonia into nitrites and the nitrites into nitrates. ”

“ It is as nitrates that most plants absorb the nitrogen they require to build up their tissue. In nature the nitrogen, present in the soil as ammonia and different organic forms, is constantly being converted into nitric acid. This conversion of nitrogen into nitrates, known as nitrification, is a process of very great importance, and, as has been already pointed out in the Introductory Chapter, is effected through the agency of micro-organisms (ferments) . ”

“ The nitrated soils are very abundant in this region of South America, where they cover large surfaces. Their composition is variable, but in all of them calcium carbonate and phosphate are met with, and organic nitrogenous material. The nitric acid is found always combined with lime. In some of the soils as high as thirty per cent of calcium nitrate have been found. Nitrification of organic material takes place very rapidly the year round in this tropical region. ”

“ Nitre therefore is not dug out of a Mountain, or found in the Cavity of a Subterranean Den, or any where cover’d with Earth, but gather’d up a concrete Body from the surface of a Desart or solitary Place, and is to be ascrib’d more to the Earth than Water, by reason the Earth has there a kind of nitrous Substance. When Rain, Fountain or the Nile-Water has stood long in a Valley, it at length becomes nitrous, by exhaling up to its self a salt Matter or Substance from the bottom, which afterwards concretes, with the heat of the Sun, and becomes much harder than Salt. ”

“ All these explosives are made from nitric acid and this used to be made from nitrates such as potassium nitrate or saltpeter. But nitrates are rarely found in large quantities. Napoleon and Lee had a hard time to scrape up enough saltpeter from the compost heaps, cellars and caves for their gunpowder, and they did not use as much nitrogen in a whole campaign as was freed in a few days' cannonading on the Somme. Now there is one place in the world—and so far as we know one only—where nitrates are to be found abundantly. ”

“ Nerita is a purely marine genus, occurring on rocks in the littoral zone; one species, however, (N. lineata, [17] Chem.) ascends rivers as far as 25 miles from their mouth, and others haunt marshes of brackish water. Neritina is the fresh-water form, some species of which are found in brackish swamps or even creeping on wet mud between tide marks, while the great majority are fluviatile, one group (Neritodryas) actually occurring in the Philippines on trees of some height, at a distance of a quarter of a mile from any water. ”

“ The greater part of our nitre is derived from Bengal, where, as in Egypt, Persia, Spain, &c., it exists in the soil. It is separated by lixiviation and crystallization. In France, Sweden and some other countries it is prepared artificially in nitre-beds. These are formed of various animal matters, mixed with lime or mortar-rubbish; the mixture is watered and stirred occasionally, and allowed to remain for a considerable time. The whole is then lixiviated and decomposed by carbonate of potash. The nitre is then separated and purified by crystallization. ”

“ Nitric acid, however, is not only one of the most important fertilizers, but also the most expensive; hence the passing-off of nitrates in drainage-water is of such serious concern to the farmer, that the causes of its occurrence, and the means of preventing such loss, should be fully understood. ”

“ But that these fire-air particles exist also in nitre is evident, since this salt will support the combustion of sulphur in vacuo. Fill a tube with gunpowder slightly moistened, and it will burn out in vacuo, or with its mouth inverted over water. Hence the aereal part of nitre, is the same with the fire-air particles of the atmosphere, and is one component part of the acid spirit of nitre: the other being (like the fixed part) obtained from the earth, p. 17. 18. The fiery particles thus common to nitre and to the air, he denominates nitro-aereal. ”

“ It is found in efflorescences and incrustations frequently combined with nitrate of lime. Its colour is grayish or yellowish white. The manufacture of nitre, in the numerous caves in Kentucky, is conducted as follows: The earths containing the nitrates of lime and potash are lixiviated; the lixivium is afterwards passed through the ashes of wood, by the alkali of which the nitrate of lime is decomposed. If the earths, after having been lixiviated, are replaced in the caves, they again become impregnated with the same salts.
One bushel of earth commonly yields from one to four pounds of nitre. ”

“ Pliny, Lib. 31. cap. 10. says, The Nature of Nitre is not to be esteem’d very different from Salt, and this he the more diligently asserts, inasmuch as those Physicians who have written of it, were ignorant of its true Nature, altho’ none has written more carefully of it than Theophrastus. He says, moreover, some Nitre is made in Media, the Vallies growing white and hoary with dryness. After the Rain or Fountain-Water is exhal’d from it, it is condens’d by the Soil, and converted into Nitre. ”

“ Plant-life is unable to live upon the complex nitrogenous compounds of the organic matter of the soil, and were it not for bacteria these substances would remain unavailable. Attention will be drawn in the Chapter on Farmyard Manure to this question more in detail. Of these bacteria, among the most important are those which are the active agents in the process known as "nitrification"—i.e., the process whereby organic nitrogen and ammonia salts are converted into nitrites and nitrates. The presence of these organisms, it would appear, is indispensable to the fertility of any soil. ”

“ Although nitrate of potassa is generated in abundance, particularly in the East, yet in all countries, where the circumstances are favourable to its production, it is found. It never occurs, native, in very large masses. It is generally found in an efflorescence, on the surface of the soil, or in caverns. It never exists in the soil more than a few yards beneath the surface. We may remark, that native nitre has never been found in pure clay, or pure sand, except in the rock-ore, as it is called, of the western United States. ”

“ Peculiar Formation of Nitre.—The leaves and stems of beet root contain oxalate and malate of potash. Some leaves were tied together and hung up in a warm and slightly-humid place, where there was but little light, to dry. Being examined at the end of several months, they were found penetrated with, and covered by, an immense number of minute crystals of nitre. The oxalic and malic acids had been replaced by nitric acid; but whether from animalized matter naturally in the leaves of the plant, or from the action of the air, or in what manner, is not known.—M. HENRI BRACONNOT, Ann. ”

“ When the solution is boiled, and set aside in the troughs to crystallize, the nitre will form in a regular manner. The mother water, or the fluid which remains after the crystallization, may contain, from the circumstance before stated, either potash, or undecomposed nitrate of lime—hence it is thrown on the hopper in a subsequent operation.
The nitre, however, as made at the caves, is called rough or crude nitre. Before it is used for the manufacture of gunpowder, and other purposes, it is purified or refined. ”

“ Warington showed some time ago that many species are able to reduce nitrates to nitrites, and such reduction is now known to occur very widely in nature. The researches of Gayon and Dupetit, Giltay and Aberson and others have shown, moreover, that bacteria exist which carry such reduction still further, so that ammonia or even free nitrogen may escape. The importance of these results is evident in explaining an old puzzle in agriculture, viz. that it is a wasteful process to put nitrates and manure together on the land. ”

“ In the midst of this sandy waste, where uniformity is rarely interrupted by grass or shrubs, there are extensive districts where nitre springs from the earth like crystallized fruits. One thinks he sees a wild, overgrown with moss, weeds, and shrubs, thickly covered with hoar frost. And to imagine this winter scene beneath the fervid heat of an Egyptian sun, will give some idea of the strangeness of its aspect. ”

“ When the dead bodies are decomposed in the soil there are other bacteria, in addition, that have the power of further acting on the ammonia, causing its oxidation and producing nitrous and nitric acids and their salts. The unicellular plants that bring about these changes are the nitrifying bacteria. Conspicuous illustrations of the functional activity of these little naked pieces of protoplasm are seen in the immense saltpeter beds of Peru and Chili, where, from the enormous fecal accumulations of sea-fowls, the immense quantities of nitrates are produced that supply the commercial world. ”

“ One of these nitres—sodium nitrate—is extracted from the earth in large quantities in Chili, where it was probably formed by the oxidation of animal refuse. This kind of nitre is employed in practice for the manufacture of nitric acid and the other oxygen compounds of nitrogen. Nitric acid is obtained from Chili saltpetre by heating it with sulphuric acid. The hydrogen of the sulphuric acid replaces the sodium in the nitre. The sulphuric acid then forms either an acid salt, NaHSO4, or a normal salt, Na2SO4, whilst nitric acid is formed from the nitre and is volatilised. ”

“ Furthermore, owing to the low percentage of organic matter present and to the porous nature of desert soils the anaerobic dentrifying bacteria are not so active in changing nitrates into free nitrogen, while the lack of vegetation prevents their convertion into protein nitrogen. The nitrates which are formed are thus enabled to accumulate, and either remain in the soil or are transferred by underground waters to other localities where they may be concentrated by evaporation of the water at the surface of the ground. ”