VOLATILISATION

The precautions stated are to avoid uptake of oxygen, nitrogen and other impurities which render the metal brittle the excess magnesium and magnesium chloride can be removed by volatilisation above 1300 K. 

To prepare acetic acid, aqueous ethanol is added gradually to a hot mixture of aqueous sodium dichromate and sulphuric acid. The oxidising mixture is now always in excess, and therefore the oxidation proceeds as far as possible moreover, the reaction is carried out under reflux, so that any acetaldehyde which volatilises is returned to the oxidising mixture. Hence the final product contains only a small amount of acetaldehyde. 

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. 

Hydrolysis of />-Tolunitrile. As in the case of benzonitrile, alkaline h> drolysis is preferable to hydrolysis by 70% sulphuric acid. Boil a mixture of 5 g. of p-tolunitrile, 75 ml. of 10% aqueous sodium hydroxide solution and 15 ml. of ethanol under a reflux water-condenser. The ethanol is added partly to increase the speed of the hydrolysis, but in particular to prevent the nitrile (which volatilises in the steam) from actually crystallising in the condenser. The solution becomes clear after about i hour s heating, but the boiling should be continued for a total period of 1-5 hours to ensure complete hydrolysis. Then precipitate and isolate the p-toluic acid, CH3CgH4COOH, in precisely the same way as the benzoic acid in the above hydrolysis of benzonitrile. Yield 5 5 g. (almost theoretical). The p-toluic acid has m.p. 178°, and may be recrystallised from a mixture of equal volumes of water and rectified spirit. 

If about 10 ml. of ethanol are added to the mixture, the time required for complete hydrolysis is reduced to about 20 minutes, and any volatilised ester which tends to collect in the condenser is redissolved and returned to the flask. When hydrolysing an unknow n ester (p. 353) for identification purposes, however, it is often best to omit the ethanol to avoid confusion. 

Volatility in steam. Add about 0 1 g. of benzoquinone to 3 ml. of water in a test tube and boil gently. The benzoquinone dissolves to give a yellow solution, which rapidly darkens in colour. Note the irritating and characteristic odour of benzoquinone which has volatilised in the steam. Also given by />-toluquinone and 1,4 naphthoquinone but not by the other quinones mentioned above. 

For an actual determination, first place in J some stable liquid the boiling-point of which is at least 50 above that of the organic liquid the pour density of which is to be measured. This difference in boiling-point is important, because it is essential that the organic liquid, when nbsequently dropped into the bottom of T, should volatilise rapidly nd so push out an equivalent volume of air before the organic vapour can diffuse up the tube T and possibly condense in the cooler ttppcr portion of the tube. Suitable liquids for use in the jacket are ter, chlorobenzene (132°), rym-tetrachloro-ethane (147 ), P ... 

The liquid in B rapidly volatilises at the bottom of the tube T, the stopper being thrown off, and bubbles of air escape from D into the tube C. Continue boiling the liquid in J steadily until no more bubbles escape into C. Then carefully slip the end of D from under the tube C, close the end of C securely with the finger, and then transfer the tube to a gas-jar of water, so that the level of the water inside and outside C can be equalised. Measure the volume of air in C, and note the room temperature and the barometric pressure. The vapour density can now be calculated (see p. 428). 

Place 92 5 g. (114 5 ml.) of n-butyl alcohol and 8 55 g. of purified red phosphorus (Section 11,50,5) in a 500 ml. round-bottomed flask (attached at C) and 100 g. (32 ml.) of bromine in A. Pass a stream of cold water through the condenser F and through the double surface condenser fitted at D the condenser F prevents the volatilisation of the alcohol from the... 

Place 50 g. of anhydrous calcium chloride and 260 g. (323 ml.) of rectified spirit (95 per cent, ethyl alcohol) in a 1-litre narrow neck bottle, and cool the mixture to 8° or below by immersion in ice water. Introduce slowly 125 g. (155 ml.) of freshly distilled acetaldehyde, b.p. 20-22° (Section 111,65) down the sides of the bottle so that it forms a layer on the alcoholic solution. Close the bottle with a tightly fitting cork and shake vigorously for 3-4 minutes a considerable rise in temperature occurs so that the stopper must be held well down to prevent the volatilisation of the acetaldehyde. Allow the stoppered bottle to stand for 24-30 hours with intermittent shaking. (After 1-2 hours the mixture separates into two layers.) Separate the upper layer ca. 320 g.) and wash it three times with 80 ml. portions of water. Dry for several hours over 6 g. of anhydrous potassium carbonate and fractionate with an efficient column (compare Section 11,17). Collect the fraction, b.p. 101-104°, as pure acetal. The yield is 200 g. 

Salts of amines are generally soluble in water. Upon treatment with 10 per cent, sodium hydroxide solution, the amine will separate if it is insoluble or sparingly soluble in water if the amine is water-soluble, it can be partially volatilised by gentle warming and its presence will be suggested by a characteristic odour. 

The mixture should be colourless, otherwise difficulty will be experienced in the subsequent purification of the product. If the reaction mixture is coloured by iodine (due to volatilisation of some of the mercaptan), add just sufficient ethyl mercaptan to decolourise it. 

It will be noted that the by-products are both gaseous. In practice, a slight excess over the theoretical quantity (20-75 per cent.) of thionyl chloride is used some of this is volatilised with the gaseous by-products and the remainder is easily removed by fractional distillation (thionyl chloride has b.p. 77°). 

Pulp-like olefin fibers are produced by a high pressure spurting process developed by Hercules Inc. and Solvay, Inc. Polypropylene or polyethylene is dissolved in volatile solvents at high temperature and pressure. After the solution is released, the solvent is volatilised, and the polymer expands into a highly fluffed, pulp-like product. Additives are included to modify the surface characteristics of the pulp. Uses include felted fabrics, substitution in whole or in part for wood pulp in papermaking, and replacement of asbestos in reinforcing appHcations (56). 

Development of molybdenum electrodes in the 1950s permitted the use of electrically assisted melting in regenerative furnaces (81). In the 1990s, approximately one-half of all regenerative tanks ate electrically boosted. Operating practice has shown that effective use of electricity near the back end of the furnace, where the batch is added, can reduce fossil fuel needs. This lowers surface temperature and reduces batch volatilisation. 

A proposed method which avoids cyanide consists of treating gold ore with gaseous chlorine at elevated (<250° C) temperatures to volatilise gold as chloride Au2Clg [12446-79-6] or AuMCl, (M = Fe [12523-43-2] A1 [73334-09-5], or Ga [73334-08-4]) and recovering it by condensation (23). 

Treatment of impure gold is largely via the Miller process (30) in which chlorine is bubbled through the molten metal and converts the base metals to chlorides, which volatilise. Silver is converted to the chloride, which is molten and can be poured. The remaining gold is less pure (99.6%) than that produced by the WohlwiU process and may require additional treatment such as electrolysis. If platinum-group metals (qv) are present, the chlorine process is unsuitable. 

Ben2onitrile herbicides tend to possess a high leaching potential dichlohenil is an exception, due to its stronger sorption. The hen onitrile herbicides are also prone to volatilisation losses (340) and off-site deposition (341). 

Health and Safety Factors, Toxicology. Phosphoms oxychloride volatilises readily its vapors are extremely irritating to the eyes, skin, and mucous membranes (49). Direct contact with the Hquid can produce severe bums. Contaminated clothing must be removed immediately. Inhalation of POCl vapors can cause pulmonary edema and temporary eyesight problems. 

Roasting occurs between temperatures of 530—650°C. Virtually no volatilisation of selenium or tellurium takes place during roasting. Conversion of both elements to the hexavalent form is complete. 

Sulfation Roasting. Acid roasting technology (Fig. 2) rehes on differences in the volatiUty of the tetravalent oxides of selenium and tellurium at roasting temperatures of 500—600°C to selectively volatilise selenium from slimes. Acid roasting uses sulfuric acid as the oxidant for the conversion of selenium/selenides and tellurium/teUurides to their respective tetravalent oxides. Typical oxidation reactions are as foUow ... 

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