Halogenated vapours

When a violent reaction stops, heat the metal again. After evaporation of all the halogen from test tube 2, seal ofi constriction 3 very carefully. Repeatedly pass the halogen over the heated metal. When the halogen vapour disappears in the apparatus, distil the product into section 4 or 7 and seal it ofi. 

The application of chemiluminescence by Polanyi and his collaborators to the determination of the dissociation energies of sodium and potassium is an elegant but rather specialized study in the field. It was found that when sodium and halogen vapours react in a very dilute flame , intense chemiluminescence is produced, which can only be attributed to the reaction of halogen atoms with Na2 molecules ... 

Experiments designed to clarify photochemical processes in alkali metal and silver halides have led to some interesting studies on the diffusion of metal vapours (9, lO), halogen vapours (11) and hydrogen(12) in alkali halides. It is possible to prepare transparent single crystals of the halides of the greatest chemical purity. It was found that the halides can act as solid solvents for a number of substances, and that the properties of these mixtures or solutions permit one to study photochemical processes and diffusion. Thus, potassium... 

Radiative stabilization of a most simple kind was first observed [235] on heating of chlorine, bromine and iodine vapour to a temperature above lOOO C. The luminescence spectra of all halogen vapours were found to represent an inversion of their absorption spectra being consistent with process X + X -> Xg hv which is an inversion of photodissociation Xg -f- hv X + X. 

Liver Liver dysfxmction secondary to halogenated vapour anaesthesia has again been reported. 

Germanium forms divalent compounds with all the halogens. Germaniunil 1) chloride can be prepared by passing the vapour of germanium(IV) chloride (see below) over heated germanium. The reaction is reversible and disproportionation of germanium(II) chloride is complete at about 720 K at atmospheric pressure ... 

Aniline.—Burns with a very smoky flame, clouds of soot being produced. Typical of many aromatic substances. i,2 Dibromoethane.—Does not burn until vapour becomes hot and then burns with a slightly smoky flame. Typical of substances rich in halogens such as cldoroform, chloral hydrate, and carbon, tetrachloride. (Note, however, that iodoform evolves copious fumes of iodine when heated in this way.)... 

Other halogen carriers may be used, e.g., 1-2 g. of iron filings, or 1 g. of aluminium amalgam. The bromine must then be added slowly from a dropping funnel to the benzene warmed on a water bath the apparatu.s shown in Fig. II, 13, 9 is suitable and a trap for the hydrogen bromide must, however, be inserted into the top of the condenser. After all the bromine has been introduced, the mixture is heated on a water bath until no red vapours are visible above the liquid. The Subsequent procedure is as above. 

Halogen Melting point (°C) Boiling point (°C) Vapour density (air = 1.0) Threshold limit value (ppm) Reactivity and oxidizing strength Appearance and state at 21 " C Colour of gas/vapour... 

Combustible gases or vapours that are not water soluble but are slowly reactive with absorbing agents Combustion and absorption Quartz or ceramic furnace with absorbers Water, acid, or alkali 1-5 90-100 Can also be used for organic halogenated fumes... 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

The atmospheric pollution prevailing in special industrial or laboratory locations may induce more severe corrosion, e.g. the vapours from concentrated hydrochloric or acetic acid will etch tin, and moist sulphur dioxide will produce a sulphide tarnish, as will hydrogen sulphide at temperatures above about 100°C. The halogens attack tin readily. The commonly used volatile corrosion inhibitors are without adverse action although the benefit derived from their use is doubtful. 

Alloys containing more than 40% rhodium, while very difficult to fabricate, are almost immune from attack by aqua regia. The Pt— lORh alloy is particularly resistant to attack by free wet chlorine such as that produced by the combustion of halogenated organic vapours. 

Semi-gaseous method The articles, surrounded by a solid compound containing chromium metal, are packed in a retort chamber, and vapours of chromium halide or halogen compound are circulated in the chamber, which is maintained at 950-1 200 C. 

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