Ammonia

'Whenever organic matter containing nitrogen is submitted to destructive distillation, more 01' less ammonia is formed. The chief sources of ammonia are: the distillation of coal for gas or coke, of uituminous shales, and of bones and other animal matter; putrid urine; the residues of the beet sugar industry and those left after the fermentation of molasses for alcohol; and the waste gases from blast furnaces. Ammonia can be made from the nitrogen of the ail'. The reactions involved are as follows: -

1) Ba(OH)2 +3 C +2:N + 0 = Ba(C:N)2 + H20 +CO2,
2) Ba(CX)2 +4 H20 = ~a (OH)2 +2 CO +2 XHs.

The first reaction is accomplished by passing air over barium hydroxide or oxide and carbon, heated to a white heat. Then the temperature is lowered to about '1;jO° C., and steam admitted to decompose the barium cyanide according to (2). The reactions are not quantitative, and the process is not economical and is unimportant. The chief source of ammonia is the "gas liquor" from the hydraulic main and scrubbers of the illuminating gas manufacture (p. 275). The nitrogen contained in coal is largely converted into ammonia and cyanogen compounds by destructive distillation. The principal ammonium salts are the carbonate, sulphide and sulphydrate, which are volatile with steam, and sulphate, thiosulphate, sulphite, sulphocyanide, and ferrocyanide, which are not volatile with steam. These salts, together with free ammonia, are found in the" gas liquor." Gas liquor is valued according to its percentage of ammonium salts, as determined by distilling with caustic soda, absorbing the vapors in normal sulphuric acid and titrating the uncombined acid. The liquor is gauged according to the number of ounces of concentrated oil of vitriol necessary to neutralize one gallon of it; e.g., an "eight ounce" liquor requires eight ounces of oil of vitriol to combine with the ammonia from one gallon. 1I10reor less tar is mixed with the gas liquor, but on standing this settles to the bottom of the tank. The clear liquor is then distilled to separate the ammonia. There are several forms of apparatus for this distillation. In the simplest form the gas liquor is heated in one still until all the volatile salts are expelled, and then it is drawn into another still, where" milk of lime" is added, and heat again applied until the fumd salts are decomposed and the ammonia driven off. The ammonia and volatile salts are condensed in a vessel containing suIphuric or hydrochloric acid. Some hydrogen sulphide and other foul-smelling gases pass out of the absorption vessel, and are led into the chimney or are decomposed in a Claus kiln . In England, a large part of the gas liquor is distilled in Coffey stills, but since it is inconvenient to use lime in these stills, most of the fixed salts are lost. The gas liquor, having been heated in the rectifier, passes into the analyzer, and there the volatile ammonia salts and free ammonia are chiven out and pass through the rectifier, on their way to the absorption vessel. The more modern apparatus of Feldmann and of Gri'meberg and Blum, are now much used on the continent of Europe and in America. Feldmann's apparatus (Fig. 54) is most used in this country. The gas liquor is drawn from the settling tank (F) into the economizer (E), which consists of a long, cylindrical shell, containing a number of narrow tubes, through which the gas liquor flows. In the absorption vessel (D) is sulphuric acid, to combine with the ammonia vapors passing from the still by the pipe (G). The hydrogen sulphide and carbon dioxide liberated ill (D) are collected under the bell. The heat of the reaction between the acid and the ammonia raises the temperature of these gases to a high degree. They pass through the outlet pipe into the outside jacket or shell surrounding the tubes in the economizer, where they heat the gas liquor which is flowing through the small tubes, so that it is hot when it arrives at the top of the towel' (AB) through the pipe (K). In the tower, the free ammonia. and its volatile salts are driven out by the steam which is passing up through it. The liquor containing the fixed ammonia salts then passes to the lower part of (A B), where it is mixed with "milk of lime " while steam is blown in. The mixture then overflows through the pipe (M) into the smaller still (C), where aU the ammonia set free by the lime, is driven out by a steam jet from S (S). This ammonia p passes through (0 N) into the first towel', where it mixes with the gas escaping from (AB), and is absorbed in (D). The waste liquors escape through the pipe (P), and the sludge of calcium salts formed in (B) is drawn off at regular intervals through (R). The still may be run for months without stopping.
The Grlineberg-Blum apparatus is rather more complicated in its details, but involves nearly the same principles as the above. All the stills mentioned here employ the principle of dephlegmation.
An appliance for distilling gas liquor is sometimes employed in which the vapors, set free by the action of the lime, are made to bubble through fresh gas liquor in a second vessel. Thus the volatile ammonia salts are expelled by the heat of these vapors, awl pass off with them to the acid absorption tanks, while the gas liquor is drawn into the first vessel and is there treated with lime. This Mallet. The ammonia gas set free in any of the above described stills is generally absorbed in sulphuric acid. If dilute acid (800 to 1000 Tw.) is used, there is no separation of ammonium sulphate crystals in the saturator, and the liquor is easily clarified from tar and suspended impurities before emporating to crystallize. This yields the lightest colored product. If more concentrated acid (1400 Tw.) is used, a separation of ammonium sulphate crystals takes place in the saturator, and these are" fished out." But they are often discolored, since the liquor has had no chance to clarify by settling. As fast as the crystals are removed, fresh acid is introduced in a small stream into the satmator. This is always covered with a lid, or hood, from which a pipe carries off the foul gases, consisting largely of hydrogen sulphide. These are often led to a Claus kiln (p. 85) and decomposed to recover the sulphur, thus avoiding contamination of the atmosphere. A recent patent'" involves the burning of this gas hi an atmosphere highly impregnated with sulphur dioxide, whereby the following reaction occurs:-

2 H"S + S02 = 2 H"O + 3 S.

Care is taken that no ammonia passes out with the gases, a slight excess of acid always being present. The ammonia gas is led into the saturator through a pipe perforated with small holes and submerged in the acid.
Gas liquor is not always distilled. Occasionally it is neutralized directly with mineral acid and evaporated to dryness, but this produces a salt which is contaminated with tar, while the escape of hydrogen sulphide and other foul-smelling gases during the neutralizating is liable to cause nuisance. :1\1oreover,the solutions thus obtained arc dilute, and much fuel is consumed in concentrating them ..
Ammonia has been made in this country by the destructive distillation of waste animal matter from slaughter houses and tanneries. Hair, "fleshings" from tanneries, scrap leather, etc., are the raw materials. These are dried and put into an upright iron cylinder, provided with a manhole at the top and at the bottom, and luwing a large perforated pipe running np through the centre, about threefomths of the (listance to the top. Hot chimney gases are forced by an air compressor through the pipes of a superheater (a furnace containing coils of pipe heated to a bright reel heat), and into the bottom of the cylinder, where they escape through the perforated pipe, and come into direct contact with, and char, the animal matter. * The volatile products of the heating pass out at the top of the retort into a hydraulic main, similar to those used in gas works. The tarry matter settles in the main, and the gases pass through condensers, which are cylinders containing 4-inch tubes. Both the condensed liquors and the gases pass into absorption tanks containing water. The unabsorbed gases pass through a "scrubber," the same as that usee1 for gas liquor, to remove the last traces of ammonia. The washed gases are burned under the retort. The liquor produced in the absorbers and scrubbers is distilled in an ammonia still, Feldmann's being generally used.
The coke remaining in the retort is porous, and contains a high percentage of nitrogen. It is generally used for fuel, but may perhaps be utilized for making cyanides.
Ammonium sulphate, as found in commerce, has a light gray or yellowish color, or, if carefully made and washed after crystallizing, is nearly white. when prepared by direct saturation the color may be brown or nearly black. COlllmon acid made from pyrites yields a salt which is yellow in color, owing to the iron or arsenic present. The crystals should be washed, and dried in a lead-lined centrifugal machine. It is sometimes sold damp, but is generally dried by warm air. When sold in large quantities it is lthmys valued according to its content of ammonia or nitrogen. Good samples contain from 23 to 25 per cent :NHs. It is largely used as a source of nitrogen in making fertilizers, but for this purpose must be free from sulphocyanide, which is very injurious to vegetation. When made by absorbing the gas in acid, little or no sulphocyanide is present, but by direct neutralization of the gas liquor the cyanide may separate with the sulphate. The salt is used as a source of other ammonium compounds, and to a slight extent in rendering fabrics and other tissues non-inflammable. By distilling with lime it yields a very pure ammonia gas, "IV hich lllay be absorbed directly in water for the" aqua ammonia" of trac1e; or the gas may be passed through towers filled with charcoal, to remove any trace of tar, before absorption. Any sulphuretted hydrogen may be removed by passing the gas over oxide of iron.
1\. considerable amount of liquid ammonia is now prepared and sent into the market for use in ice machines. This is compressed into steel cylinders, usually containing about 100 pounds of the liquid.
Ammonium chloride is made by absorbing ammonia gas in dilute hydrochloric acid, or by neutralizing gas liquor with the acid directly and evaporating the solution. During the evaporation much of the tarry matter separates, and is skimmed off. Some nuisance may result from the gases escaping during the neutralizing. Another method is to mix a saturated solution of ammonium sulphate with a strong solution of salt or potassium chloride. On evaporating somewhat, monohydrated sodium sulphate (X a2S04 . H20) separates from the hot liquor, leaving the ammonium chloride in solution. On cooling, the ammonium chloride crystallizes: -

(NH4)2S04 + 2 NaCl = Na2S04 + 2 NH4Cl.

The crystallized chloride is more or less discolored by tar, and is purified by sublimation in iron or earthen ware pots or retorts. The ammonium chloride collects on the cover of the pot as a thick, fibrous cake, in which form it comes in trade under the name of sal-conmoniac. This generally contains iron as an impurity. It was formerly made by subliming the soot obtained by buring dried camel's dung, but is now nearly all made from gas liquor. The crystallized salt is often sold under the name of "muriate of ammonia," and is usually less pure than sal-ammoniac: l\furiate of ammonia is much used in the arts for charging Leclanche electric batteries; in the process of " galvanizing" iron; in soldering liquors; for making" rust cement" for pipe joints; and in textile coloring. Ammonium carbonate as found in commerce is not a pure salt, but is a mixture of acid ammonium carbonate (NH4. HCOs) and a salt of carbamic acid (NH2· CO2, NH4). The commercial salt is made by heating a mixture of the sulphate and powdered calcium carbonate in iron retorts. The vapors are condensed in lead-linell chambers, and the impure product is generally sublimed in iron pots having lead caps. A little water is put into each pot along with the salt, this causing the sublimed product to be transparent instead of opaque white. The temperature of this second sublimation is not much above 70° C.
Ammonium carbonate is transparent when fresh and pure, but on exposure to the ail', becomes covered with a white layer of bicarbonate, owing to the loss of ammonia. It is entirely volatile when heatedl, and from this fact is derived its old name of sal-volatile. It is used considerably in wool scouring, in certain baking powders, in medicine, and for the preparation of "smelling salts," and to some extent, as an analytical reagent.