Nitrates

“ The nitrates of the metals, on heating, leave the oxide of the metal. It is as yielders of oxygen that nitrates are so largely used in the manufacture of explosives. Gunpowder contains from 65 to 75 per cent. of potassium nitrate (nitre) .
Nitrates are best detected and determined by their yielding nitric oxide when treated with sulphuric acid and a suitable reducing agent, such as ferrous sulphate, mercury, or copper. Nitric oxide is a colourless gas very slightly soluble in water. ”

“ 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. ”

“ Another class, the nitro-celluloses, are formed from cellulose, C_{6}H_{10}O_{5}, which forms the groundwork of all vegetable tissues. Cellulose has some of the properties of the alcohols, and forms ethereal salts when treated with nitric and sulphuric acids. The hexa-nitrate, or gun-cotton, has the formula, C_{12}H_{14}O_{4} (ONO_{2}) _{6}; and collodion-cotton, pyroxylin, &c., form the lower nitrates, i.e., the tetra- and penta-nitrates. These last are soluble in various solvents, such as ether-alcohol and nitro-glycerine, in which the hexa-nitrate is insoluble. ”

“ II.—Calcium nitrate, ammonium nitrate, potassium sulphate, magnesium phosphate, iron chloride (or sulphate) (sodium silicate) .
It is well known that in nature nitrates are formed wherever decomposition of organic nitrogenous substances takes place in the air, the ammonia formed by the decomposition being oxidized to nitric acid. These conditions for the formation of nitrates are present in nearly every cornfield, and they are also the cause of the presence of nitrates in water that has its source near stables, etc. ”

“ THE production of nitrates during the decay of nitrogenous organic matter under suitable conditions of moisture, aëration, and temperature, is a reaction of no little importance both technically and agriculturally: technically, as the sole natural source of saltpeter; agriculturally, on account of the fact that the nitrates formed in the soil constitute the chief if not the only supply of nitrogen to the plant. But, while the conditions of nitrification have long been well known, it is only within the past eight or nine years that its true cause has been recognized. ”

“ Development of Nitric and Nitrous Acids in Soils.—Owing to the solubility of nitrates there can be but little accumulation of them in soils in those countries where there is any considerable amount of rain-fall. On the other hand in arid regions there may be found extensive deposits of nitrates. The occurrence of a certain quantity of nitrates in the soil, however, is essential to the growth of plants. Until within a few years little was known of the origin of nitric acid in the soil. ”

“ 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 nitrates are crystalline, deliquescent compounds, readily soluble in water and alcohol, but less easily in nitric acid, a fact which has been of considerable importance for purposes of separation. The solubility is greatest in the case of lanthanum nitrate, diminishing through the cerium group to a minimum in gadolinium nitrate, and then increasing again. They separate from aqueous solution in the form of crystalline hydrates; in the cerium group, these have commonly the formula R (NO3) 3,6H2O, whilst the nitrates of the yttrium elements usually crystallise with 3 or 5 molecules of water. ”

“ The Theory of Nitrification.—The production of nitrates in soils, and in waters contaminated with sewage, are facts thoroughly familiar to chemists. It is also well known that ammonia, and various nitrogenous organic matters, are the materials from which the nitric acid is produced. Till the commencement of 1877 it was generally supposed that this formation of nitrates from ammonia or nitrogenous organic matter was the result of simple oxidation by the atmosphere. ”

“ Crude sewage generally contains no nitrates. Nitrites as a rule indicate more recent contamination, and therefore greater danger than nitrates. The presence of more than a trace of phosphates is a strong indication of contamination with sewage matter.
To determine the amount of Nitrites and Nitrates the best known methods are by the indigo, the phenol-sulphuric, the aluminium, or the zinc-copper couple tests. For nitrites the metaphenylene-diamine test is employed (page 85) . The following qualitative tests will suffice for elementary work. ”

“ The nitrate of this base (known as nitron) is so insoluble that nitrates may be gravimetrically estimated with its help. These bases combine with the alkyl iodides triazolié to yield quaternary ammonium salts. ”

“ Schloesing’s Apparatus for Nitric Acid.
Another and more rapid method for dissolving the nitrate, may also be practiced. In a flask holding about one liter, place 220 grams of the soil and 660 cubic centimeters of distilled water and shake vigorously, or enough water to make 660 cubic centimeters together with the moisture remaining in the air-dried sample taken. All the nitrates pass into solution. Throw the contents of the flask into a filter and take 600 cubic centimeters of the filtrate which will contain all the nitrates in 200 grams of the sample taken. ”

“ Of the large number of double nitrates which have been prepared, the general types R ́2Th (NO3) 6, where R ́ = NH4,K,Rb,Cs, and R ́ ́Th (NO3) 6,8H2O, where R ́ ́ = Mg,Mn,Zn,Ni,Co, are the most important. ”

“ They all consist of the variety of nitro- cellulose known as collodion-cotton, i.e., a mixture of the penta- and tetra-nitrates dissolved in nitro-glycerine, and made up with various proportions of wood-pulp, and some nitrate, or other material of a similar nature. As the gun-cotton contains too little oxygen for complete combustion, and the nitro-glycerine an excess, a mixture of the two substances is very beneficial. ”

“ Of the various phenomena of oxidation due to bacteria, the formation of nitrites and nitrates has the greatest practical importance, since it is by this means that the ammonia which results from the decomposition of animal and vegetable tissue and waste products is again rendered available to green plants as food in the form of nitrates. Practically all the nitrates found in nature, sometimes in large quantities, are formed in this way. ”

“ A very much less technical, but so far as our knowledge at present goes, a more promising method of fixing atmospheric nitrogen in the form of nitrates, is through the agency of bacteria. While it is true that one group of bacteria has the power of breaking down nitrates with the production of nitrogen gas, there are other groups which are equally able to absorb elementary nitrogen with the production of nitrates. ”

“ 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. ”

“ Dinitro-benzol is formed, which is dissolved in alcohol, and the resulting solution subjected to the reducing action of ammonia and sulphuretted hydrogen, as described under aniline. Nitraniline forms yellow, acicular crystals, little soluble in cold water, but freely soluble in alcohol and ether. Its salts are crystallisable.
NI′TRATE. Syn. Nitras, L. A salt of nitric acid (e.g. AgNO3, nitrate of silver) . The nitrates are very easily prepared by the direct solution of the metal, or its oxide, or carbonate, in nitric acid, which, in most cases, should be previously diluted with water. ”

“ But nitrates contain considerable oxygen. Ammonia, which is one of the products of putrefactive de- composition, contains no oxygen, and nitrites, another factor, contains less oxygen than nitrates. These bodies are thus too simple for plants to make use of as a source of nitrogen. The chemical destruction of the food material which results from the action of the putrefactive bacteria is too thorough, and the nitrogen foods are not yet in condition to be used by plants. ”

“ Many theories have been advanced to account for the origin of the nitrates, but all appear to fall short of adequately accounting for all the conditions under which the nitrates are found in Chile. It is generally considered that an organic source is the most probable, but there have not been lacking explanations for the formation of these nitrates which have been based on inorganic agencies.
Thus one of the theories advanced is that the nitrates may have resulted from electric storms occuring in the Andes. ”

“ Sterilized soil has no power to generate the nitric from the nitrous ferment. The two organisms are, therefore, of different species.
After a few generations the power of producing nitrates seems to be lost although the nitrous ferment may still be active. This suppression of the power to oxidize the nitrites is not due to any pernicious influence of the culture-medium but to the condition of the successive solutions at the time of taking the seeding samples. ”

“ Yet there are many chemists who get good results, and place considerable faith in its accuracy. This can only be due to differences in the manner of working. It is generally understood that nitric acid or nitrates must be absent; and our experience fully confirms this. Precipitations in nitrate solutions are worthless, as the following experiments show. In each experiment the bulk of the solution was 150 c.c. The solutions contained 10 grams of nitre, were freely acid with hydrochloric acid, and were precipitated (while boiling) with slight excess of baric chloride. ”

“ Some nitrates being insoluble in nitric acid, form a protecting coat to the metal which hinders further action. Where the strong acid does act the action is very violent, so that generally it is better to use the dilute acid. When iron has been immersed in strong nitric acid it not only remains unacted on, but assumes a passive state; so that if, after being wiped, it is then placed in the dilute acid, it will not dissolve. Tin and antimony are converted into insoluble oxides, while the other metals (with the exception of those already mentioned) dissolve as nitrates. ”

“ Additional evidence is given to show that the concentration in nitrates in brown spots in which nothing will grow is not due to the accumulation of preexisting nitrates, but to the action of microorganisms which are able to bring about the fixation in the soil of atmospheric nitrogen, and that the dark-brown color which is characteristic of the spots is due, not to black alkali, but to the development of pigment by the organisms. ”

“ Small nitrate deposits are also to he found in various other parts of the world, as in the Sahara, in Russian Turkestan, and in Egypt, where nitrate earths occur which contain about 15 per cent, of calcium and sodium nitrates. The earth has long been used locally as a fertilizer, and its use is supposed to be increasing. The source of the nitrates in this region is not known. ”

“ We don’t put it on our fields in Iowa—not yet; but if it weren’t for those white specks on the clover-roots, we should be obliged to do so—as they do back east.”
“How do them white specks keep us from needin’ nitrates?”
“It’s a long story,” said Jim. “You see, before there were any plants big enough to be visible—if there had been any one to see them—the world was full of little plants so small that there may be billions of them in one of these little white specks. They knew how to take the nitrates from the air——”
“Air!” ejaculated Newton. “Nitrates in the air! You’re crazy!” ”

“ When the test is properly performed, there will be three layers—the uppermost being the nitrate solution, the middle ferrous sulphate, and the lowest sulphuric acid; the middle layer becomes of a smoky or black hue if a nitrate is present. Organic matter interferes much with the reaction.
(3.) Nitrates in solution, treated in the cold with a zinc copper couple, are decomposed first into nitrites, and then into ammonia. The nitrites may be detected by a solution of metaphenyldiamine, which strikes a red colour with an infinitesimal quantity. ”

“ It is found that a 50 per cent. solution of nitrates gives the best results, the impregnation requiring half an hour; a warm bath is usually employed. It is usual to add to the bath a quantity of thorium hydroxide, since the thorium nitrate of commerce generally contains nitric acid, which has a bad effect on the fabric. [537] The excess of solution is removed by means of a glass or porcelain centrifuge, not, as with cotton or ramie mantles, by use of a wringer; drying must be carried out very slowly. ”