Spent Oxide Treatment and Byproducts

this means the iron sulphide is reconverted into hydrated iron oxide, sulphur separating out at the same time. When the oxidation is complete, the oxide can again be em- ployed for purification. After this process has been repeated a number of times the quantity of sulphur in the mass may rise to 40—50 per cent. Besides sulphur, however,ammonium compounds(sulphate and thiocyanate) are also deposited in quantities varying from §—Io per cent, and frequently also very consi- derable quantities (s—25 per cent) of Prussian blue. 8 Chemistry of Ammonia. Of late years, therefore, the spent-oxide has received a large amount of attention, not only asa source of ammonium compounds, but also of ferrocyanides, and thiocyanates. The ammoniacal liquors obtained from the prepara- tion of animal charcoal and potassium ferrocyanide have at the present time lost most of their importance, notwithstanding the fact that they are exceptionally rich in ammonia, chiefly in the form of carbonate. The liquor from bones is a brown nauseous-smelling liquid, having a density of 7—15° Tw. On distillation it always gives a yellow distillate, and cannot there- fore be employed for the manufacture of colourless salts, 2. AMMONIUM COMPOUNDS. (a.) Ammoniaand Water.—Whenammonia dissolves in water a considerable evolution of heat takes place, the volume of the solution increasing at the same time. The solubility of ammonia in water at various temperatures is given in the following table :— One volume of water absorbs : At 0° C.(32°F.) 4... 4. 1050 vols, ammonia. n 10°C. (50°F)... os 813 55 » » 15°C. (50°F)... P7 » ” 20°C. (68°F) bag, x 100 grams of water dissolve 507—60 grams of ammonia at the ordinary temperature. The aqueous solution of ammonia comes into commerce as caustic ammonia, or liquor ammonia. It has a sp, gr. of 0'°880—0'930 and contains from 35—20 per cent. of ammonia. Ifthe Ammonia and Acids. 9 solution be warmed, ammonia gas is evolved ; the more concentrated the solution, the lower the tempera- **ture at which the evolution begins. If, on the other hand, it be cooled to—40° white crystals separate out. When a rapid current of air is passed through a cold concentrated solution, the temperature of the liquid falls so low that mercury freezes if placed in it. The solution is decomposed by chlorine with form- ation of nitrogen and hydrochloric acid. If, how- ever, chlorine be in excess; chloride of nitrogen is formed. This is a yellow, extremely explosive oil which is also formed by the action of chlorine on ammonium salts. By the action of acids on ammonia solution, or by passing ammonia gas into aqueous solutions of acids, ammonium salts are obtained. If the acid be re- placed by its anhydride, we get instead of the salt of the corresponding acid, a so-called amido-salt. Thus, for example, by the action of ammonia on sulphuric anhydride, ammonium amidosulphonate is formed. SO, +2NH,= 80.{ ONE, From ammonia and carbon dioxide again we ob- tain ammonium carbamate. CO; + 2NH, = CO {OHk, All these compounds unite with water, forming salts of the acid corresponding to the anhydride employed. As has already been stated, the ammonium salts bear a remarkable resemblance to the corresponding 10 Chemistry of Ammonia. potassium and sodium compounds in their general character, such as solubility, crystalline form, &c. They are, however, distinguished from them by their insta- bility at high temperatures, no ammonium compound being known which is not decomposed at a red heat ; many of them indeed are volatile with steam, and some few evaporate even at the ordinary temperature. When heated with alkalies or alkaline earths, ammonia is at once set free, and may be easily recognized by its characteristic pungent smell. Further, allammonium salts are decomposed by alkaline hypobromites with evolution of nitrogen, (6.) Ammonium Sulphate—(NH,),SO, Thissaltis obtained by neutralizing sulphuric acid with ammonia. It separates from a hot saturated aqueous solution on cooling, in beautiful large rhombic tables, which are very readily soluble in water. According to Alluard, 100 parts of water dissolve at oC (328 F) 74 ooparts (NH'SO, 20°C. (68°F) ) 76) » ” oc (122° F) by" 25 ” ” ° C. (176° F.) 92'20 yy ” 100° C, (212° F.) 97°50 yy 2 It melts at 140° C, (284° F.), and decomposes at a higher temperature with evolution of ammonia, and sulphur dioxide. If its solution be boiled with one of common salt, a double decomposition takes place, sodium sulphate and ammonium chloride crystalling out on cooling. When heated with calcium carbo- nate (chalk), ammonia and ammonium carbonate pass off, and calcium sulphate (gypsum) remains behind. The chemically pure salt finds an application in Ammonium Sulphate. II analytical chemistry, being employed for standard- izing normal-acid solutions, The sulphate prepared on the large scale is used exclusively as manure. Ammonium sulphate combines also with other sulphates forming double salts. Of these, the most important is ammonium-alym, or aluminium ammo- nium sulphate, Al,(SO,),(NH,)SO, + 24 HO. ° It is obtained as a crystalline meal by mixing concentrated solutions of the two sulphates, and in all its properties closely resembles the common or potash alum. On ignition, it loses ammonia and sulphuric acid, whilst pure alumina remains behind. 100 parts of water dissolve only 12 parts of the double salt at the ordinary temperature, whereas at the boiling point, 422 parts are dissolved. At the present day, ammonium-alum is not manufactured ‘to the same extent as in former years, when the price of potassium salts was much higher. It is chiefly used in dyeing and calico-printing. Ferrous Ammonium Sulphate—FeSO, + (NH,): SO, + 6 H,0O is formed whena hot saturated solution of iron vitriol is added to a similar solution of ammo- nium sulphate ; on cooling, the double salt separates in bluish-green monoclinic crystals. It isused instead of iron vitriol in dyeing, calico-printing, and analytical chemistry, as it possesses over the latter the great advantage of undergoing no alteration in the air. Nickel Ammonium Sulphate—NiSO, + (NH,), SO, + 6 H,O can be obtained in a similar manner to the foregoing salt. It crystallizes in dark-blue monoclinic 12 Chemistry of Ammonia. prisms, which dissolve in sixteen parts of cold, and three parts of boiling water, and is employed in nickel- plating. Cuprammonium Sulphate-—CuSO,4 NH; + HO is not a true double salt. It may be regarded as copper vitriol in which four molecules of water of crystalliza- tion have been replaced by four of ammonia. A so- lution of copper vitriol gives with excess of ammonia a deep blue solution, which on addition of alcohol deposits the above compound in dark blue crystals. These dissolve in 1°5 parts of water, have an un- pleasant metallic taste and slight ammoniacal odour. The pure salt is employed in medicine in nervous diseases and affections of the eye, the crude substance being also employed in the preparation of coloured fireworks, and for the destruction of vermin. (c.) Ammonium Chloride (Sal-Ammoniac.)—NH,Cl. This, the first known ammonium salt, is obtained by neutralizing hydrochloric acid with ammonia. NH, + HCl = NH,CL It is very soluble in water, the solubility at different temperatures being given in the following table :— 100 parts of water dissolve ato®C. 20°C, 40°C. 60°C. 80°C. 100°C, 284 373 462 55:0 639 ©=— 728 parts NH,CL. The saturated solution boils at 115°—116° C. (239°—241° F.). It crystallizes from its hot solution in snow-white, feathery aggregates, which are built up of small regular octahedra. It dissolves also to some extent in alcohol. On boiling the solution, a small quantity Sal-ammoniac. 13 of ammonia is given off, and the solution becomes slightly acid, and therefore attacks iron. Sal-ammoniac has a sharp, saline taste, and is un- altered in the air, but can be sublimed at a higher temperature. The vapours evolved consist of a mixture of free ammonia and hydrochloric acid, which re- unite on cooling. If the cooling take place quickly, it forms a light, crystalline powder ; if, on the other hand, the vapours are slowly cooled, a semi-trans- parent, fibrous, crystalline mass is obtained. In the middle ages, sal-ammoniac was prepared from camel’s excrement. Even at the present time the dried excrement forms the sole available fuel in the desert. The soot deposited on burning it, contains considerable quantities of sal-ammoniac, which may be obtained by extracting with hot water and evaporating the solution thus obtained. It was brought into commerce by Armenian merchants, and hence obtained the name sal armentacum, Later on this name was changed to sal ammoniacum, a name which had been originally given to the common salt (sodium chloride) found near the ruins of the temple of Jupiter Ammon in the Libyan desert,and with which this sal armeniacum was confused. In the course of time, sal ammoniacum became contracted to sal- ammoniac, which name forms the source of the word ammonium, of which sal-ammoniac and the numerous analogous compounds are now regarded as derivatives, Sal-ammoniac is largely used in dyeing and calico- printing, and also in brazing and soldering. (a) Ammonium Carbonate.—Neutral ammonium carbonate (NH,),CO; is an extremely unstable body, 14 Chemistry of Ammonia. It forms fine silky crystals, which contain one mole- cule of water of crystallization, and smell strongly of ammonia, The ‘crystals lose ammenia on standing in the air, and become opaque, forming acid ammo- nium carbonate. Commercial ammonium carbonate (sal-volatile, or salt of hartshorn) is not a true carbonate. It is obtained by heating a mixture of ammonium sulphate with calcium carbonate, and consists of a mixture of acid ammonium carbonate with ammonium carbamate, NH,HCO, + CO {Onu, free ammonia being evolved during its preparation. It is also formed when neutral ammonium carbonate is distilled. When the salt is exposed to the air, it loses ammonia, leaving about 50 percent. of acid ammonium carbonate. It is readily soluble in water, 4 parts of water dissolving at the ordinary temperature 1 part of the salt; the solution contains both neutral and acid salt, and on heating gives off carbonic acid at 75° C. (167° F.), ammonia at 85° C. (185° F.) and at 100° C, (212° F.) the whole is volatilized, Ifsal-volatile be dissolved in concentrated ammonia solution, crystalline plates of normal ammonium car- bonate are obtained. On treating with alcohol, ammonium carbonate goés into solution, whilst the acid carbonate remains undissolved. Acid Ammonium Carbonate-—NH,HCO, is usually prepared from sal-volatile by allowing it to stand in the air, or by passing carbonic acid through its saturated aqueous solution, It forms smallcrystalline plates, which dissolve in 7—8 parts of water. It Ammonium Carbamate. 15 oceurs in crystalline and fairly pure condition in the lower layers of the guano deposits in South America. Ammonium Carbamate—CO{ ONis_ is deposited ’ as a white saline mass, when dry carbonic acid and ammonia are brought together. It: smells strongly of ammonia, and volatilizes at 60° C. (140° F.). It is converted by water into ammonium carbonate. (e.) Ammonium Sulphide —(NH,).S is obtained as a white crystalline mass when one volume of sulphuretted hydrogen and two volumes of ammonia gas are brought together. 2NH, + HS = Nyt tS. It is easily soluble in water, is somewhat volatile at the ordinary temperature and loses ammonia in the air, forming Ammonium Hydrosulphic NEY ii Tydvosulphide—" 55 5 S. This can also be prepared by saturating a solution of ammonia with sulphuretted hydrogen. Like the foregoing compound, it is easily soluble, and undergoes alteration in the air. It occurs in gas-liquor, often in consider- able quantity. & Higher ammonium sulphides, such as (NH,),S,and (NH,),S, are obtained by the action of sulphur on ammonium sulphide solution. A mixture of these bodies was formerly used in medicine under the name “volatile liver of sulphur.” Ammonium Hydrosulphide is largely used in analytical chemistry, but none of these compounds 16 Chemistry of Ammonia. have much technical importance. The hydrosulphide is occasionally used for the purpose of etching copper. (4) Ammonium Nitrate—NH,NO,. To prepare this salt, nitric acid is neutralized with ammonia or ammonium carbonate. It forms, colourless, rhombic crystals, which are somewhat hygroscopic, and dis- solve at the ordinary temperature in half their weight of water. By its solution a considerable absorption . of heat takes place, the temperature of the liquid being consequently lowered. It is also readily soluble in alcohol. It melts at 152° C. (305° F.), and when heated beyond this point, splits up into nitrous oxide and water. NH,NO, = N,0+2H,0. Nitrous oxide or “laughing-gas ” is largely used by dentists as an anzsthetic agent. (g:) Ammonium Phosphate—Common phosphoric acid forms three ammonium salts, viz :—Normal Ammonium Phosphate (NH,),PO, Hydrogen Ammonium Phosphate (NH,),HPO, and Dihydrogen Ammonium Phosphate (NH,)H,PO, The first two salts are rather unstable, losing ammonia in the air and leaving a residue of Dihydrogen ammonium phosphate. This salt can be easily prepared from phosphoric acid and ammonia in the ordinary manner. It crystallizes in colourless quadratic prisms, similar to those of the corresponding potassium salt. It dissolves easily in water, giving a solution which has an acid reaction. (4.) Ammonium Thiocyanate or Sulphocyanide.— Ammonium Thiocyanate. 17 NH,CNS has of late years assumed some technical importance. It is often contained in considerable quantities in spent-oxide, from which it is now recovered on the large scale, and also occurs in gas- liquor in varying quantities, English gas-liquors may contain as much as I per cent., but asa general rule the amount does not exceed 2—3 grm. per litre. Ammonium thiocyanate can also be obtained by heating ammonium thiocarbonate to 100 C, (212° F,) 'S {NEF _ CS {RMII=NHLCNS + IS. The latter body is obtained by the action of carbon- bisulphide on an alcoholic solution of ammonia. cs, + 2NH, = cs {MMe The yield is, however, by no means good. According to Gélis, ammonium sulphide and carbon bisulphide combine together to form am- monium thiocarbonate (NH,),CS,, which, on heat- ing, likewise splits up into ammonium thiocyanate and sulphuretted hydrogen. It may, moreover, be obtained by the action of hydrocyanic acid on yellow ammonium sulphide. The salt is very easily soluble in water and alcohol, and crystallizes in large colourless deliquescent plates which are somewhat volatile with steam, It melts at 159° C. (318° F.) and decomposes on further heating. P CO,NH. (2.) Ammonium Oxalate. Theneutral salt { CO.N H is obtained by saturating a solution of oxalic acid with ammonia, and crystallizes with one molecule of c 18 Chemistry of Ammonia. water in long rhombic prisms. It is easily soluble in water, insoluble in alcohol, and on heating loses cone. The acid salt [eon is obtained by adding to a solution of By oxalic acid one half the quantity of ammonia necessary for its complete saturation. It crystallizes in needles which also contain one molecule of water, and is less soluble than the normal salt. On heating it loses water and is converted into oxamic +a ( CO.NH; acid f CO.H. (&.) Ammonium Metavanadate—NH,VO, forms a white crystalline powder, which is very sparingly soluble in water, almost insoluble in sal-ammo- niac solution, and completely insoluble in alcohol. ° On heating, it loses ammonia, leaving a residue of vanadic anhydride. The solution of the salt gives with tincture of galls, a deep black ink, which is, however, according to Wéhler, not permanent. The vanadate is employed in the preparation of aniline black. (2) Ammonium Molybdatg-—(NH,),Mo.0, is obtained as a white powder by neutralizing molybdic acid with ammonia and precipitating the salt by addition of alcohol. If the solution be evaporated ammonium heptamolybdate (NH,)Mo,O,, + 4H,0O is obtained. The solution of this salt in nitric acid is employed for the detection and estimation of phos- phoric acid. (m.) Ammonium Chromate—(NH,).CrO is pre- water, forming oxamide {