To the Air

Sulfur dioxide A toxic and corrosive gas emitted continuously in dilute form, principally from the burning of fossil fuels. 

Toxic gas emissions. Usually concentrated chlorine-containing gases or other harmful vapors released by accident. 

Foul-smelling gases Sulfur-containing gases such as hydrogen sulfide that have an odor even at low concentrations. 

Dust Can be anywhere that minerals or finely-divided solids are handled. 

Smoke Man-made smoke is now mainly controlled in developed countries. 

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CH2=CHC = CCH = CH2. a colourless liquid which turns yellow on exposure to the air it has a distinct garlic-like odour b.p. 83-5°C. Manufactured by the controlled, low-temperature polymerization of acetylene in the presence of an aqueous solution of copper(I) and ammonium chlorides. It is very dangerous to handle, as it absorbs oxygen from the air to give an explosive peroxide. When heated in an inert atmosphere, it polymerizes to form first a drying oil and finally a hard, brittle insoluble resin. Reacts with chlorine to give a mixture of chlorinated products used as drying oils and plastics. 

The oxime is freely soluble in water and in most organic liquids. Recrystallise the crude dry product from a minimum of 60-80 petrol or (less suitably) cyclohexane for this purpose first determine approximately, by means of a small-scale test-tube experiment, the minimum proportion of the hot solvent required to dissolve the oxime from about 0-5 g. of the crude material. Then place the bulk of the crude product in a small (100 ml.) round-bottomed or conical flask fitted with a reflux water-condenser, add the required amount of the solvent and boil the mixture on a water-bath. Then turn out the gas, and quickly filter the hot mixture through a fluted filter-paper into a conical flask the sodium chloride remains on the filter, whilst the filtrate on cooling in ice-water deposits the acetoxime as colourless crystals. These, when filtered anddried (either by pressing between drying-paper or by placing in an atmospheric desiccator) have m.p. 60 . Acetoxime sublimes rather readily when exposed to the air, and rapidly when warmed or when placed in a vacuum. Hence the necessity for an atmospheric desiccator for drying purposes. 

If difficulty is experienced in inducing the first crude crop of the a-glucoside to ciystallise, place a few drops of the solution on a watch glass and expose freely to the air, with occasional scratching meanwhile keep the main volume of the solution securely corked in the conical flask. After an interval of varying length (possibly several days), partial crystallisation occurs in the material on the watch-glass. Then seed the solution with this material crystallisation of the first main crop will rapidly follow. 

Both forms sublime very readily, even at room temperature a small sample on exposure to the air will completely volatilise in a short time, particularly on a warm day or if the sample is exposed to a gentle current of air. Hence the above method for rapid drying. A sample confined in an atmospheric desiccator over calcium chloride rapidly disappears as the vapour is adsorbed by the calcium chloride. A sample of the hexahydrate similarly confined over sodium hydroxide undergoes steady dehydration with initial liquefaction, for the m.p. of the hydrated-anhydrous mixture is below room temperature as the dehydration proceeds to completion, complete resolidification occurs. 

A fresh sample of dimethyl sulphate should be employed an old sample, or one that has been frequently exposed to the air, should be shaken with water, separated, dried over sodium sulphate, and distilled (b.p. 188"). 

Both the primary amine (D) and the tertiary amine (E) are reasonably strong bases, and will absorb carbon dioxide if exposed to the air. They should therefore be stored in ground-glass stoppered bottles or in sealed tubes. 

Benzene. Pure benzene (free in particular from toluene) must be used, otherwise the freezing-point is too low, and crystallisation may not occur with ice-water cooling alone. On the other hand, this benzene should not be specially dried immediately before use, as it then becomes slightly hygroscopic and does not give a steady freezing-point until it has been exposed to the air for 2-3 hours. Many compounds (particularly the carboxylic acids) associate in benzene, and molecular weights determined in this solvent should therefore be otherwise confirmed. 

Use approximately 0 5 ml. of glycerol, and cork the flask A securely when weighing the glycerol by difference, owing to the very hygroscopic nature of the latter. Heat on the water-bath for 60 minutes instead of 30 minutes. Excellent results are obtained by this method if a freshly opened sample of anhydrous glycerol is available a sample which has been exposed to the air for even a short period will absorb sufficient water to give inaccurate results. 

This should be free from sulphur, and obtained in small containers so that a specimen is rapidly used it should be in dark bottles and stored in the dark. When withdrawing a specimen, the acid should be exposed to the air for as short a time as possible, as both air and light promote its decomposition to iodine. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

By way of caution it should be noted that free alkali or the alkali salts of weak acids will redden the reagent like an aldehyde. It is also, of course, reddened by heat or when exposed in small quantities to the air for some time. Mineral acit greatly reduce the sensitivity of the test. 

Dissolve 5 g. of hydroxylamine hydrochloride in 10 ml. of water in a small conical flask and add a solution of 3 g. of sodium hydroxide in 10 ml. of water. Cool the solution in cold or ice water, and add 6 g. (7-6 ml.) of acetone slowly. Cool the flask, shake well, and leave overnight, during which time the oxime may crystallise out. If no crystals appear, cork the flask and shake vigorously when the acetoxime usually separates as colourless crystals. Filter the crystals at the pump, dry rapidly between filter paper (yield 2- 6 g.) and determine the m.p. (59°). Extract the filtrate with two 20 ml. portions of ether, and remove the solvent a further 0 - 5 g. of acetoxime (m.p. 60°) is obtained. Recrystallise from light petroleum, b.p. 40-60° CAUTION inflammable) to obtain the pure acetoxime, m.p. 60°. Acetoxime sublimes when left exposed to the air. 

The addition of the alcohol to the sodium, although attended by a very vigorous reaction which must be carefully controlled, is preferable to the reverse procedure of adding the sodium in small pieces to the alcohol. The latter method is longer and has the fiuther disadvantage that it necessitates frequent handling and exposure to the air of small pieces of sodium. 

The deliquescent solid must be stored in a dry, tightly-stoppered container. If exposed to the air it deteriorates rapidly, developing an unpleasant odour. Samples that have been kept for some time are best recrystallised from absolute ethanol before use. 

Chemical Conversion. In both on-site and merchant air separation plants, special provisions must be made to remove certain impurities. The main impurity of this type is carbon monoxide, CO, which is difficult to separate from nitrogen using distiHation alone. The most common approach for CO removal is chemical conversion to CO2 using an oxidation catalyst in the feed air to the air separation unit. The additional CO2 which results, along with the CO2 from the atmosphere, is then removed by a prepuritication unit in the air separation unit. 

High purity acetaldehyde is desirable for oxidation. The aldehyde is diluted with solvent to moderate oxidation and to permit safer operation. In the hquid take-off process, acetaldehyde is maintained at 30—40 wt % and when a vapor product is taken, no more than 6 wt % aldehyde is in the reactor solvent. A considerable recycle stream is returned to the oxidation reactor to increase selectivity. Recycle air, chiefly nitrogen, is added to the air introducted to the reactor at 4000—4500 times the reactor volume per hour. The customary catalyst is a mixture of three parts copper acetate to one part cobalt acetate by weight. Either salt alone is less effective than the mixture. Copper acetate may be as high as 2 wt % in the reaction solvent, but cobalt acetate ought not rise above 0.5 wt %. The reaction is carried out at 45—60°C under 100—300 kPa (15—44 psi). The reaction solvent is far above the boiling point of acetaldehyde, but the reaction is so fast that Httle escapes unoxidized. This temperature helps oxygen absorption, reduces acetaldehyde losses, and inhibits anhydride hydrolysis. 

Humidification. For wiater operation, or for special process requirements, humidification maybe required (see Simultaneous HEAT and mass transfer). Humidification can be effected by an air washer which employs direct water sprays (see Evaporation). Regulation is maintained by cycling the water sprays or by temperature control of the air or water. Where a large humidification capacity is required, an ejector which direcdy mixes air and water in a no22le may be employed. Steam may be used to power the no22le. Live low pressure steam can also be released directly into the air stream. Capillary-type humidifiers employ wetted porous media to provide extended air and water contact. Pan-type humidifiers are employed where the required capacity is small. A water filled pan is located on one side of the air duct. The water is heated electrically or by steam. The use of steam, however, necessitates additional boiler feed water treatment and may add odors to the air stream. Direct use of steam for humidification also requires careful attention to indoor air quahty. 

A filter cake from the wringer is washed to remove absorbed acid, transferred to a slurry tank of water, and quickly submerged, after which the nitrocellulose is pumped to the stabilization operation as a diluted water slurry. Exhaust systems are installed to protect personnel and equipment from acid fumes, and water sprays and cyclone separators are used for acid fume recovery before venting to the air. 

Rubber. A thin coating of mica acts as a mold-release compound in the priming of mbber goods such as tires. It prevents the migration of sulfur from the tire to the air bag when the tire is being vulcani2ed (see Tire cords). Mica is also dusted on mbber inner tubes to prevent sticking. 

As fibers in the feed mat pass between the feed toU and feed plate, they ate separated by metallic wine teeth on the lickerin toU and carried to an air venturi where they ate stripped and tumbled until they strike a moving, perforated collection surface. At the collection surface, the airborne fibers foUow paths of least resistance and accumulate in a self-leveling manner while the air passes through perforations. Fiber orientation in the web is isotropic in layers corresponding to the number of fibers transferred from the wine teeth to the air-transportation 2one, the intensity of the air, and the speed of the collection surface. 

Atmospheric photodegradation of DEHP and DBP has been shown to be rapid (51,53) with half-life times of less than 2 days, hence a large proportion of phthalate emissions to the air are broken down by photodegradation. 

AH the bis- and tri-unsaturated prostanoids display sensitivity to atmospheric oxygen similar to that of polyunsaturated fatty acids and Hpids. As a result, exposure to the air causes gradual decomposition although the crystalline prostanoids ate less prone to oxygenation reactions than PG oils or solutions. 

Release Reporting. Both the Comprehensive Environmental Response, Compensation, and Liabihty Act (CERCLA) and EPCRA have requirements for reporting releases to the air, ground, or water. Lists of reportable chemicals or family of chemicals and their reportable quantity (RQ) have been issued (9). A reportable quantity is the amount, in pounds or kilograms, below which a release does not have to be reported. CERCLA requires only the reporting of releases from the CERCLA Hst however, EPCRA requires reporting releases of both EPCRA- and CERCLA-Hsted substances. 

Soda. Ash Roasting. Some of the first processes to recover selenium on a commercial basis were based on roasting of copper slimes with soda ash to convert both selenium and tellurium to the +6 oxidation state. Eigure 1 shows flow sheets for two such processes. Slimes are intensively mixed with sodium carbonate, a binder such as bentonite, and water to form a stiff paste. The paste is extmded or peUetized and allowed to dry. Care in the preparation of the extmdates or pellets is required to ensure that they have sufficient porosity to allow adequate access to the air required for oxidation. 

A positive value iadicates vertical movement. Thea, moving from the outer wall to the air core, the axial velocity iacreases to positive values. Thus, the fluid motioa is dowa the wall of the cycloae to the apex and up the air core through the vortex finder. In the cylindrical section, the axial velocity goes negative again, approaching the vortex-finder wall. The fluid flow is then down the inner cyclone wall and the outer vortex-finder wall. There is a locus of zero axial velocity. 

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