Gases

GASES, substances in a state characterized by the fact that the molecules of the substance are separated by large distances from each other and the forces of interaction between the molecules are very small. Experimental studies of matter in the gaseous state lead to the following laws: under the influence of pressure at a constant temperature, gases undergo compression, and the product of the gas volume and the pressure referred to a unit of surface is equal to a constant value. This Boyle-Mariotte law can be expressed mathematically as follows: vp = v₀p₀ (1). Here v and v₀ represent the initial and final volumes of the gas obtained at pressures p and p₀. If a gas is enclosed in a certain envelope, the volume of which is varied, then upon heating a greater pressure will result from the side of the gas on the wall, and, consequently, if it is desired to keep the gas in a space of constant volume, a higher pressure must be applied the higher the temperature is. The relationship between pressure p and temperature t is expressed by the following mathematical formula: p = p₀(1 + αt) (2); α is a constant, and p₀ is the pressure at 0°. The expansion of gas was first studied by Lomonosov, and later more precise studies were carried out by Gay-Lussac. The coefficient α is called the coefficient of expansion of the gas; it turned out that the coefficient of all gases is identical in magnitude and equal to ¹/₂₇₃. Equation (2) can be represented in a slightly different form: p = p₀(1 + t/273) = (p₀/273)(273 + t) (3).

Here 273 + t represents that temperature which is measured from a point lying 273 degrees below the zero point. Such a temperature is called absolute temperature and is usually denoted by the capital letter T. Thus, we can write that the pressure exerted by a gas on the wall: p = (p₀/273)T (4). Using these two laws of Boyle-Mariotte and Lomonosov-Gay-Lussac, one can obtain a general law that expresses the relationship of pressure, volume, and temperature of a gas. In order to obtain a general formula connecting the two laws, one can proceed as follows. Let a gas at temperature T be compressed to a volume v₀, when it will have a pressure p₁; then vp = v₀p₁ (5). Let, further, the gas go from temperature T to temperature 0 and its pressure go from p₁ to p₀, then p₁ = p₀(T/273). Substituting this value of p₁ into expression (5), we have vp = v₀p₀(T/273), or (vp)/T = (v₀p₀)/273 = R (6), where R is a constant. The law of Boyle-Mariotte and Lomonosov-Gay-Lussac, expressed in the general form (5), which includes the pressure, volume, and absolute temperature of gases, is of the utmost importance for medical applications. The study of metabolism processes, in which gas analysis must be used, is based to a large extent on the formula indicated above. A whole series of quantitative determinations of substances in physiological analysis reduces to determining the volume of a gas, using the formula indicated above. Hygienic studies whose task is the determination of carbon dioxide in the air are connected with the same formula. In the doctrine of respiration, one has to apply the formula derived above in those cases where it is necessary to calculate the volumes and pressures exerted by gases that may be present in the lungs. Finally, in the study of blood gases, the same relationship plays a huge role.

Gases dissolve upon contact with liquids in amounts greater the higher the gas pressure is (Henry-Dalton law). If 1 cubic centimeter of water absorbed, for example, m grams of gas at a pressure of h cm, then at a pressure of 1 cm, 1 cubic centimeter of water will absorb m/h, and at a pressure of 760 mm it will absorb K = m/(h · 760). The quantity K shows the amount (in grams) of gas absorbed by 1 cubic centimeter of water at a pressure of 760 mm. This amount of gas must be referred to 0°. When gases dissolve in indifferent liquids, as Sechenov's studies showed, the surface tension of the liquid in which the gas dissolves plays a huge role. Surface tension depends on the attraction of molecules to each other. For gas molecules to pass into solution, they must pass through the capillary layer. The stronger the bond between the liquid molecules and, consequently, the greater its capillary constant and surface tension, the more difficult it will be for gas molecules to penetrate inside the liquid, and in this way the phenomena found by Sechenov can be explained. In addition to ordinary dissolution, in which gas molecules are mechanically distributed among the liquid molecules and no chemical interaction is observed, one can imagine cases where gases are bound by a number of salts present in the dissolving liquid, and in this case the law of dissolution is more complex. Finally, a gas may come into contact with substances with which it forms unstable chemical compounds. In this case, the laws of gas dissolution are completely different from what takes place in the simple dissolution of indifferent gases in liquids in which there are no substances reacting with these gases. The case of the formation of gas compounds with liquids is of great importance in the absorption of carbon dioxide by blood plasma.

From the point of view of the kinetic theory of gases, developed for the first time by Lomonosov in the form of general concepts, a gaseous substance is viewed as a state in which the molecules of the substance are not bound to each other; these molecules fly in different directions and by their impacts exert pressure on the walls of the vessels. One can derive a theoretical formula connecting the pressure p, volume v, and the average live force of motion of gas molecules (μv²)/2. The formula has the following form: pv = ¹/₃Nμv²; v is the velocity of the particles and N is the number of particles in the studied volume. From this simple formula it is clear that the absolute temperature T must be recognized as proportional to the average live force of gas molecules and that, knowing the volume, pressure, and mass of the studied gas, the average velocity of motion of its molecules can be found. This average velocity turns out to be very large and reaches thousands of meters for hydrogen, about 340 m for oxygen and nitrogen molecules. The penetration of gases through narrow openings upon efflux into a vacuum (Bunsen) depends on the translational velocity of its particles. Using the previous formula, it is easy to show that the efflux velocity is inversely proportional to the square root of the gas density. In this way, molecular weights of gases are often measured. Finally, if from the comparison of Gay-Lussac's law and the kinetic theory of gases one accepts the absolute temperature as proportional to the average live force of the gas, one comes to the conclusion that the number of gas particles per unit volume at the same pressure is identical. This circumstance was pointed out by Avogadro even before the development of the kinetic theory of gases.

Of great importance is the study of gas mixtures. In this case, in a gas mixture, each gas introduces its own special partial pressure, equal to the pressure that would result if the gas occupied the entire volume. Let us mix a number of gases at pressure p₀ and let the volumes of the gases measured at p₀ be equal to v₁, v₂, v₃ ... v_n and the entire volume be equal to the sum of the volumes v₁ + v₂ + v₃ + ... + v_n = V₀, then we can write: p₀(v₁ + v₂ + v₃ + ... + v_n) = p₀V₀ or p₀(v₁/V₀) + p₀(v₂/V₀) + p₀(v₃/V₀) + ... + p₀(v_n/V₀) = p₀, but p₀(v₁/V₀) equals the pressure p₁ that would result if gas 1 occupied the entire volume V₀ occupied by the mixture; p₁ is thus the partial pressure of the 1st gas. Calling through p₂, p₃ ... p_n the partial values of the remaining gases and taking into account that p₂ = p₀(v₂/V₀), p₃ = p₀(v₃/V₀), we have: p₁ + p₂ + p₃ + ... + p_n = p₀. The pressure of a gas mixture is equal to the sum of the partial pressures of the mixed gases.

P. Lazarev.

Compressed and liquefied gases. The liquefaction and condensation of gases has the purpose of 1) making it possible to use them in those branches of production where gases under high pressure are necessary, and 2) simplifying and reducing the cost of their storage and transportation. Liquefied and condensed gases are stored and transported in steel cylinders or flasks (see). The most widespread applications are: O, H, and N, which are contained in flasks in a condensed state under a pressure of 150-200 atmospheres; CO₂, NH₃, SO₂, and Cl, which are kept in flasks in a liquid state, and acetylene. Sulfur dioxide (SO₂) changes into the liquid state more easily than other gases. It is obtained by burning S in air and as a by-product in the roasting of sulfide ores. In the industrial production of liquid SO₂, furnace gases containing SO₂ are used. SO₂ is used for bleaching fabrics, for producing H₂SO₄ by the contact process, and for the preparation of hydrosulfurous acid salts. The preparation of liquid ammonia (NH₃) is an important branch of industry, because anhydrous NH₃ serves as the working fluid in refrigerating machines. An aqueous solution of NH₃—ammonia water, obtained as a by-product in the production of illuminating gas—is used as the starting material for obtaining liquid NH₃. When ammonia water is heated, NH₃ volatilizes and is collected under the bell of a gas holder, from which it is drawn into a double-walled compressor, where it is compressed to 3 atmospheres in the low-pressure cylinder, and then to 9.5 atmospheres in the high-pressure cylinder. The gas compressed to 9.5 atmospheres and heated during compression enters a coil located in a reservoir with cold water, where it is cooled and turns into a liquid, which is sent directly to the flasks. Carbon dioxide (CO₂) is compressed approximately in the same way as NH₃, with the only difference that heavy compressors are used for its liquefaction, because to liquefy it at room temperature it is necessary to bring the pressure to 50 atmospheres. The starting material for the preparation of liquid CO₂ is a concentrated gas obtained by absorbing CO₂ from furnace gases with a solution of potassium carbonate. Liquid CO₂ is used for carbonating water and beverages, for squeezing metal castings as they cool, and also for obtaining low temperatures, since liquid CO₂, upon expanding, strongly cools down and turns into a solid state. The liquefaction of chlorine (Cl) presents significant difficulties because Cl destroys the metal parts of the apparatus, especially in those places where lubrication is necessary: lubricants under the action of Cl form HCl, which has a destructive effect on the piston, valves, and other parts of the compressor. Therefore, to liquefy Cl, a compressor is used that has no rubbing parts and, consequently, does not require lubrication. Such a compressor has a liquid piston. Strong H₂SO₄, which does not react with Cl and does not dissolve it, is used as the piston liquid. Chlorine, compressed between the level of H₂SO₄ and the compressor cover, enters a cooler, the temperature of which is significantly below 0°. In the cooler, Cl turns into a liquid state. Liquid Cl is used for bleaching fabrics, for obtaining bleaching powder, for chlorinating water, for military purposes as a suffocating gas, and as a means of combating agricultural pests. Gaseous acetylene is obtained by the action of water on calcium carbide. Acetylene easily liquefies, but storing it in a liquid state is dangerous because it easily decomposes with the release of a huge amount of heat. Therefore, its ability to dissolve in acetone is used. The solubility of acetylene increases sharply with increasing pressure; thus, at 12 atmospheres, up to 300 volumes of acetylene dissolve in one volume of acetone. The flask is filled with some porous material, which is impregnated with acetone, and then acetylene is pumped into the flask. Upon a drop in pressure, acetylene flows continuously from the flask and is used predominantly to obtain an oxy-acetylene flame in metal welding. Oxygen is obtained by the evaporation of liquid air. Condensed oxygen is used for various medical purposes, for obtaining a hydrogen-oxygen flame, and for some technical oxidation processes. Condensed nitrogen is used for the manufacture of calcium cyanamide and for obtaining synthetic NH₃. Hydrogen can be obtained in small quantities by the action of acids on iron. For technical purposes, it is obtained by separation from illuminating water gas by the gradual condensation of CO and other impurities. Purified and condensed hydrogen is used for the hydrogenation of fats, for filling aerostats, and for obtaining a hydrogen-oxygen flame.

P. Titov.

Combustible gases. Combustible gaseous substances (illuminating gas, mine gas, etc.), liquids that easily pass into a vapor-gas state (gasoline, ether, etc.), and solid substances suspended in air in the form of the finest particles (sulfuric coal dust, etc.) can ignite under certain conditions and, possessing an explosive effect, cause various injuries to a person (along with other explosives: gunpowder, dynamite, etc.; see Explosions), including burns of varying degrees. If burning volatile substances (ether, alcohol, etc.) act on the human body, the burns are superficial and the skin looks as if shriveled (Ignatovsky). The action of burning gases and incandescent vapors in general, when a person is surrounded by them, can also spread to the respiratory tract (burns of the larynx, vocal cords, trachea). Autopsy reveals severe congestion of the lungs and in some cases the presence in the lungs of fine bloody foam, the appearance of which Reuter explains by the mixing of mucus and air with blood that has emerged from ruptured alveoli (V. Smolyannikov). Cloacal gases represent the product of the decomposition of fecal and other sewage under the influence of biological processes of an anaerobic and aerobic character. Putrefactive anaerobic processes are accompanied by the release of stinking gases: hydrogen sulfide, ammonia, mercaptan, volatile fatty acids, etc.; during aerobic processes proceeding in the presence of a sufficient amount of oxygen in strongly diluted sewage, no significant formation of foul-smelling gases occurs, since the final gaseous product of oxidation is carbonic acid. During the cleaning out and draining of sewage, hydrogen sulfide is released mainly, having previously been dissolved, adsorbed, and chemically bound. In addition, sulfur dioxide appears from the oxidation of colloidal sulfur (H₂S->-S->SO ₂-^-H_sSOi) by air and bacteria. Ammonia is formed predominantly from urine, being chemically bound in the depths of pits and only partially carried upward by other gases. Old fecal masses do not smell of ammonia. F. Erisman gives data in cubic meters on the amount of gases released per day by a cesspool—volume of sewage 18.0 cubic meters; gases released: CO₂-5.67 cubic meters; NH₃-2.67 cubic meters; H₂S-0.02 cubic meters; CH₄ and volatile fatty acids-10.43 cubic meters; oxygen absorbed-13.85 cubic meters (F. Erismann, Zeitschr. für Biologie, 1875, cited according to König). Disinfectants stop the release of gases and the absorption of oxygen due to the cessation of biological processes. According to König, corrosive sublimate acts most strongly, then sulfuric acid, iron vitriol, carbolic acid. Caustic lime, although it kills bacteria, initially intensifies the stench, causing the release of almost all ammonia. The cheapest deodorizing agents are garden soil, coal, peat (see Deodorization). The air of sewage disposal points in Moscow was investigated in 1923 by A. Khrustalyov and in 1925/26 by the Moscow Sanitary Institute. Inside the disposal buildings near the gratings, hydrogen sulfide was found in 1 liter of air from 0.148 to 0.64 mg (danger doses, according to Lehmann). Sulfur dioxide was found from 0.011 to 0.079 mg in 1 liter of air; ammonia, traces. In the drains of various foreign cities, hydrogen sulfide was found from traces to 2.99%, oxygen from 13.99 to 20.7%, ammonia from traces to 0.168%. Khlopin in 1894 found hydrogen sulfide in the street drains of Moscow from traces to 0.237 mg in 1 liter of air. Acute poisoning by cloacal gases, mainly due to the inhalation of hydrogen sulfide and lack of oxygen, is expressed in dizziness, vomiting, nausea, fainting, and death can even occur. A less sharp effect of cloacal gases is expressed in inflammation of the mucous membrane of the eyelids (irritation by hydrogen sulfide, ammonia). Workers may be exposed to the action of cloacal gases during the cleaning of cesspools, sewer wells and channels, at disposal stations, during the cleaning of sedimentation basins, and during the excavation of filled-in cesspools and garbage pits. Cloacal gases are capable of igniting (methane), which can also cause accidents with workers. Chronic poisoning by cloacal gases often occurs in the same workers, as well as in those living in houses with poorly constructed cesspools, where the possibility of gas penetration from the pit into living quarters (basements) is not excluded, especially in the cold season, due to the suction of gas from the pit by the ascending current of warm air of the residential building. Poisoning is expressed in loss of appetite, anemia, headaches. To avoid accidents with workers when descending into a pit for its cleaning, workers (so-called "pedestrians") must make sure there are no cloacal gases by lowering a candle into the pit, which should not go out. In the case of the presence of gases, the pit is freed from them by burning straw or paper at its bottom (creation of draft), lowering and raising a bedsheet, an opened umbrella, pumping in pure air with a pump; sometimes workers "scoop out" heavy gases with scoops; the same measures are applied when descending into sewer wells and channels. When descending on a rope, workers wear belts with bells, upon the cessation of the ringing of which the worker standing above learns of the onset of danger. In particularly dangerous cases, it is necessary to use gas masks and respirators with the pumping of fresh air. To protect their eyes, workers must wear special goggles. Against the penetration of cloacal gases from cesspools into premises, the only remedy is the arrangement of impermeable walls in cesspools and their location outside the foundations of buildings. The penetration of cloacal gases from sewer pipes into living quarters is prevented by the arrangement of water seals (traps) at toilet bowls, urinals, kitchen sinks and proper ventilation of the sewer network by bringing the vent pipe above the roof of the building and ensuring the inflow of air into the channels through street ventilation pipes.

V.

Gorbov, N. N. Nakladov. Powder gases. During the combustion (explosion) of ordinary, sulfur-coal-saltpeter gunpowder (black, smoke powder), a smaller part of it turns into gases (about 40%), consisting mainly of carbonic acid, nitrogen, and a small amount of carbon monoxide. Replacing some components with others in ordinary gunpowder entails a change in the volume of gases. The decomposition products of smokeless (white) gunpowder are almost all gaseous, consisting of CO₂ (less than in ordinary gunpowder), carbon monoxide (more than in ordinary gunpowder), hydrogen, water vapors, and traces of marsh gas (CH₄). When firing with ordinary gunpowder at point-blank range or almost at point-blank range, the dynamic effect of the powder gases affects the type of entrance hole of the gunshot wound. The gases, bursting with all their mass into the entrance hole, tear the skin from the underlying parts, due to which pocket-shaped cavities are formed around the wound. If the pressure of the gases overcomes the limit of skin extensibility, it tears, and the entrance hole has the appearance of a jagged wound of irregular shape, with slit-like tears of the skin radiating from the place of bullet entry. The explosive effect of smokeless gunpowder is stronger than that of ordinary gunpowder, therefore gas tears of the skin are more significant and are observed at a relatively greater distance of the muzzle of the firearm from the body. The development of the above-described phenomena is influenced by: the nature of the underlying parts—bones and thick layers of musculature favor the formation of large injuries; the size and system of the weapon (with its larger caliber—larger destruction); the amount and quality of the gunpowder; the properties of the wad and projectile. The direction of the shot to the surface of the body (perpendicularly or at an angle) affects the localization of destruction at the entrance hole. According to Paltauf, the carbon monoxide of powder gases forms CO-Hb in the hemorrhages at the edges of the entrance hole, causing their bright scarlet color. Combat gases, see Chemical warfare agents.