Sulfuric Acid

SULFURIC ACID, H₂SO₄, Acidum sulfuricum. Chemically pure anhydrous sulfuric acid is a chemical compound of sulfur trioxide SO₃ (81.63%) and water H₂O (18.37%). It is a colorless, transparent, oily, non-volatile liquid, highly hygroscopic with a specific gravity of 1.841. Upon cooling below 0° it solidifies (unlike sulfuric acid containing even a negligible amount of water), and at 338° it boils, decomposing into sulfur trioxide and water. It dissolves almost all metals, except gold and platinum, and acts very weakly on lead. It mixes with water in all proportions, with a significant amount of heat being released, as a result of which dangerous splashing can occur (add the acid to the water, not the other way around). In industry, several grades of sulfuric acid are distinguished. The purest product, containing about 98% H₂SO₄, is known as monohydrate. Oleum is monohydrate saturated with sulfur trioxide (fuming sulfuric acid); the content of SO₃ in oleum can reach 44.95% by weight, and then a special, not very stable compound of the composition H₂SO₄SO₃ is formed, the so-called pyrosulfuric acid, which is solid at ordinary temperature with a melting point of 35°. Vitriol oil contains from 93% to 97% H₂SO₄ (the rest is water) and has a correspondingly lower specific gravity. Diluted sulfuric acid is obtained from the previous preparations by proper dilution. The official Acidum sulfuricum purum dilutum is prepared by mixing 1 part of pure sulfuric acid and 5 parts of water and has a specific gravity of 1.110–1.114. The so-called chamber and Glover sulfuric acid are diluted semi-finished products contaminated with foreign impurities (Pb, Hg, Cu, Zn, Fe, Mn, As, P, etc.). BaCl₂ serves as a reagent for sulfuric acid, which precipitates white, acid-insoluble barium sulfate from dilute solutions. Sulfuric acid is of very great importance in the national economy and is one of the most important products of production and consumption in the basic chemical industry. The scale of sulfuric acid production serves in all countries as an indicator of the level of development of the chemical industry. In the USSR, the production of sulfuric acid during the first five-year plan increased two and a half times—from 199 to 510 thousand tons. The greater part of the produced sulfuric acid goes to the manufacture of artificial fertilizers, a significant amount to the manufacture of acids, salts, and the purification of petroleum products; other larger consumers are the textile, pharmaceutical industry, metallurgy, production of paints, explosives, various organic products, and a whole range of other industries. The starting material for the industrial production of sulfuric acid is mainly iron pyrites (pyrite), FeS₂ (see Acid Production). Sulfur has a much smaller significance for now. Arsenic, contained in pyrite as a constant impurity, easily passes into sulfuric acid and makes it extremely dangerous upon contact with metals (see Arseniuretted hydrogen). Despite thorough purification, arsenic can still be present in very small quantities in any sulfuric acid that has not undergone special purification by distillation. The purest grade of technical acid is sulfuric acid obtained by the contact process. The toxicodynamics of sulfuric acid are characterized mainly by local action. Coming into contact with the skin and especially with mucous membranes, concentrated sulfuric acid produces coagulation necrosis of the tissue, in the mechanism of which three factors play a role: chemical interaction with protoplasm proteins, dehydration of the tissue, and the heat release associated with this, which explains the significant destructive action of sulfuric acid. At the site of the defect formed in this way, a dense scab initially forms, preventing further penetration of the acid deep into the tissue, which is then sloughed off by demarcation inflammation, and the defect is filled with scar tissue, as a result of which, depending on the localization and extent of the damage, disfigurement or a more or less significant impairment of functions occurs, associated with partial loss of working capacity. If sulfuric acid enters the stomach, perforation of its wall is possible. Under industrial conditions, sulfuric acid can enter the respiratory tract and produce a local irritating effect there. This is possible where sulfuric acid turns into a droplet-liquid state due to rapid mechanical movement (spinning machines of viscose factories) or is carried in such a state into the air by evolving gases (charging of large storage batteries) or, finally, when SO₃ of fuming sulfuric acid, entering the respiratory tract, turns into H₂SO₄ on the moist mucous membrane. A case of the latter kind, ending in death, is mentioned in the literature. An increased incidence of respiratory tract diseases among battery workers has also been noted.—For preventive measures and therapy, see Acid Production. As a medicinal substance, sulfuric acid is currently little used. Internally in the form of diluted sulfuric acid, Ac. sulfuricum purum dilutum, 0.25–1.0 per dose with 100.0–200.0 of water as a drink, quenching thirst and partly lowering temperature; prophylactically, such a drink can be used to prevent chronic lead poisoning. Externally—for cauterization, Ricord proposed a paste of Ac. sulfuricum purum and charcoal; externally, a mixture of 1 part sulfuric acid with 3 parts alcohol—Mixtura sulfurica acida, s. Elixir acidum Halleri—is used for washing (0.5–1.0 per 100.0 of water) for the purpose of soothing skin itching in urticaria, and also for lubricating gums in scurvy. Salts of sulfuric acid have great medical significance: Na₂SO₄ and MgSO₄—as laxatives, ZnSO₄—as an astringent, CuSO₄—as a cauterizing agent and emetic, and some others.

N. Pravdin. Detection in forensic cases and determination in occupational poisonings. For the detection of sulfuric acid in cases of poisoning, stomach contents and vomitus are used. The examination is performed only when not only the acidic reaction to litmus changes color, but also Congo red paper, dimethylaminoazobenzene, tropaeolin 00, and methyl violet. A characteristic sign of concentrated sulfuric acid is the charring of carbohydrates. The detection of the sulfate ion with barium chloride provides a basis for the determination of free sulfuric acid; for this, it is reduced to sulfur dioxide, the latter is distilled off and absorbed by oxidizing agents, which convert it back into sulfuric acid, which is then confirmed. For this, an aqueous extract from the stomach contents, etc., is placed in a distillation flask, copper filings are added, and the flask is connected by a bent tube to a condenser equipped with an adapter. The end of the adapter is lowered into a solution of iodine in the presence of potassium iodide. The flask is heated on a 'cylinder' oil bath to a temperature at which the reaction of copper with sulfuric acid begins, which is visible by the absorption of iodine in the receiver. When the iodine solution no longer changes color, the distillation is stopped, the iodine is driven off by heating, and with the help of barium chloride, the sulfate ion is detected and quantitatively determined in the receiver liquid. For the determination of sulfuric acid vapors in the air, a certain volume of the latter is drawn through absorbers with distilled water. In the solution, after boiling to remove sulfur dioxide (often accompanying sulfuric acid vapors under factory conditions), the sulfate ion is detected with barium chloride and the amount of free acid is determined by titration (indicator—methyl orange).

A. Stepanov. Intentional poisoning with sulfuric acid, in view of its caustic properties, is almost always observed as suicide; accidental poisonings are rare; sometimes sulfuric acid is used for the purpose of murdering children and persons in a helpless state. Dousing with sulfuric acid is practiced as a means of causing disfigurement (see) of the face. The lethal dose of strong sulfuric acid is about 5 g. With the usual introduction of sulfuric acid through the mouth, symptoms of poisoning manifest immediately as pains along the digestive tract, vomiting, with the expulsion of acidic masses of a brown or black color (phenomena of toxic gastritis). In some cases, death occurs very quickly, in 2-3 hours, from shock or suffocation by vomited masses. Usually, the poisoning drags on for a day or more, with the general effect of the poison being revealed—protein in the urine, sometimes blood pigment. Recovery is incomplete; scars form (stricture of the esophagus), and digestive disorders and enteralgia are observed. It is also believed that in sulfuric acid poisoning, the depletion of alkalis, caused by the entry of sulfuric acid into the blood, significantly contributes to the onset of death. Upon autopsy, phenomena of a 'gray burn' are found in the mouth and esophagus—the mucous membrane separates in the form of dense, dark-gray films. The wall of the stomach is thickened, its inner surface is uneven, bumpy, and dark-brown or black in color due to the impregnation of the eschar with altered blood pigment—acid hematin. Perforations also occur, but they are not always of antemortem origin and more often depend on postmortem corrosion of the stomach walls. Organs adjacent to the stomach appear as if scalded, gray, and dense to the touch due to the seepage of sulfuric acid; the blood in the vessels of the stomach and nearby organs, due to the loss of water, thickens and turns into a brown, crumbling mass. In the kidneys, a picture of cloudy swelling is usually observed. In cases of chemical examination of organs, only the discovery of free sulfuric acid is conclusive.

V. Vladimirsky. The production of sulfuric acid is based on the oxidation of sulfurous gas (SO₂), obtained by burning iron pyrites, sulfur, zinc blende, flotation pyrites, etc. Gaseous waste from metallurgical plants can be used as raw material. There are two main methods for obtaining sulfuric acid: the chamber process and the contact process. A modification of the former is the so-called tower process. In both cases, sulfurous gas is obtained by burning sulfur-containing ore or sulfur. In the chamber process, sulfurous gas is oxidized by atmospheric oxygen in the presence of nitrogen oxides (which act as a catalyst). In the contact process, the oxidation of the gas occurs in the presence of a special catalyst (platinum, vanadium oxide, or iron) at a temperature of 430-450° up to 560°. Weak (chamber) sulfuric acid (65-68% sulfuric acid) can be converted into concentrated acid, or oil of vitriol (94-97%), by evaporation in special apparatuses. In contact production, sulfur trioxide is absorbed by sulfuric acid to obtain fuming sulfuric acid (so-called oleum), which is a solution of sulfur trioxide in sulfuric acid. The main processes of sulfuric acid production are: crushing of pyrites, transporting it to the furnaces, burning, purification of sulfurous gas, oxidation of it (in chambers, towers, or contact apparatuses) with subsequent absorption of sulfur trioxide by water or sulfuric acid. The operation of crushing iron pyrites (FeS₂), containing 30-52% S, 35-44% Fe, and impurities of As, Mg, Ca, Pb, Se, is associated with significant dusting in the case of the absence or insufficiency of dust-removal devices. Loading pyrites into the furnace is also associated with the release of dust during work, especially if the latter is insufficiently mechanized. The burning of pyrites currently takes place in the USSR only in special mechanized pyrite furnaces of Herreshoff, Humboldt, Lurgi, and others. In pre-revolutionary Russia and in the USSR during the pre-reconstruction period, manual Maletra furnaces and others were used. The burning of pyrites occurs at temperatures up to 655°. Hence, there is strong heating of the furnace wall (up to 120° in the upper parts of the furnace) and unfavorable meteorological conditions in the workshop: the air temperature in summer is in the range of 31.5-37.5° at the second arch and up to 40.5-44.0° at the first arch. The air temperature on different platforms is uneven. Heat radiation from the furnace surface is in the range of up to 2.3-3.9 g/cal. Irradiation is significant during work at open furnace windows (e.g., when changing rakes)—up to 6.6-8.0 g/cal. The entry of gas into the air of the workroom is especially strong when servicing manual furnaces. In the furnace department of the Deguninsky plant, Grodzovsky found (during the operation of manual furnaces): 0.71 mg per 1 l (during the loading of pyrites) and 0.134-0.279 mg above the furnaces. During the normal operation of mechanical furnaces, the escape of gas into the room is insignificant. The main reasons for gas leakage are the violation of the furnace vacuum (malfunction of gas fans, etc.), work on changing rakes, etc. At different times, from 0.006 to 0.019 mg per 1 l, 0.014 to 0.104 mg, etc., were found in the furnace departments of sulfuric acid plants. When gas fans were stopped, the gas concentration increased to 0.134-0.138 and 0.105-0.144 mg per 1 l (Lyakhov and Mirsky). During the unloading of cinders (Fe₂O₃), noticeable dusting and insignificant gas release are noted. In production using the chamber and tower methods, the entry of nitrogen oxides into the air of workrooms is observed: near chambers (in case of their lack of airtightness), near Glover towers (their lack of airtightness), when supplying nitric acid to the tower in pump departments, etc. The production of sulfuric acid by the contact method is more perfect from the point of view of occupational hygiene: the absence of a source of nitrogen oxide release, the airtightness of the process. The release of SO₂ and SO₃ can be observed during the adsorption of SO₂ by sulfuric acid and during the dilution of the latter. The presence of arsenic in pyrites causes the possibility of the formation of arsine, in particular during the cleaning of cisterns that held sulfuric acid (during preliminary washing, weak sulfuric acid reacts with the iron wall of the cistern to form hydrogen, and the latter, in turn, enters into a compound with arsenic). In the sulfuric acid concentration department, sulfurous anhydride (found in the range of 0.012-0.06 mg per 1 l) and sulfur trioxide can enter the air. Since a significant part of acid pipelines and other parts of the equipment is made of lead (acid resistance), there is a possibility of lead poisoning (lead soldering, etc.). The danger of burns from sulfuric and nitric acids is also significant (spilling of acid, its transport, repair of acid pipelines, supply of nitric acid to the tower, etc.). Acute occupational poisonings are observed rarely. According to materials from the Obukh Institute at the Deguninsky plant in Moscow (equipped at the time of the survey with manual furnaces), a higher incidence of upper respiratory tract diseases was noted compared to other groups of workers (20.5% of patients with chronic bronchitis against 16% for non-production workers of the same plant). The same place noted an increased frequency of chronic gastritis (12.5% against 9%). Leymann notes the same ratio: 15.1% of upper respiratory tract lesions against 8.8% for non-production workers and 14.4% of gastrointestinal diseases against 12.3%. In recent years, in connection with significant technical reconstruction of enterprises, the morbidity of workers in sulfuric acid plants has lost these specific features. Bruckner found that among the 313 workers of sulfuric acid plants he examined, there were 7.9% of patients with bronchitis and other catarrhs of the upper respiratory tract against 15.7% for workers in other workshops of the plant; 8.9% of patients with gastritis against 9.3% in other plants, etc. The average number of days of illness per 1 worker per year was 15.5 at sulfuric acid plants against 21.7 for non-production workers of chemical plants. Health measures should follow the path of rationalizing equipment (mechanical furnaces, mechanical loading of pyrites, pneumatic or other mechanized removal of cinders, automatic supply of nitric acid, etc.), ensuring the airtightness of apparatuses, maintaining a normal production regime, and a sensible ventilation system (dust removal in the crushing department, combating unfavorable meteorological conditions and gases in furnace departments, etc.). Lyakhov (All-Union Institute for the Organization of Labor Health in Moscow) developed a rational scheme for the ventilation of furnace departments, based on isolating the furnaces with an air jacket. Necessary special clothing for workers: woolen suits, rubber footwear, rubber gloves, and goggles. Devices for the pouring and transport of acids must be rationally designed.

3. Ivraelson.