Extinguishants

A colourless gas, b.p. — 59-C/740 mm. Used as a relatively non-toxic propellant gas in fire fighting apparatus, e.g. dry-powder extinguishers. Made by the bromination of fluoro-form, CHF3. 

Most of the trichloroethylene produced is used for metal degreasing. Other important uses are in the scouring of wool and as an extractive solvent, e.g. for olive and soya bean oils. Minor uses are as a heat transfer medium, anaesthetic, insecticide and fumigant, paint remover and fire extinguisher. 

Polymeric vinylidene chloride generally produced by free radical polymerization of CH2 = CCl2. Homopolymers and copolymers are used. A thermoplastic used in moulding, coatings and fibres. The polymers have high thermal stability and low permeability to gases, and are self extinguishing. 

Figure 7 New photothermal camera versus penetrant testing on a crack (width 5 pm) at the surface of Fig 4. part The large arrow shows that the PT indication almost extinguishes at thinner width (approx. I pm) locations along the crack the photothermal signal does not. The bottom little arrow indicates a place where the crack splits in two, which is not revealed on the PT image because of the spreading of the penetrant liquuid.

Carbon dioxide is used in the manufacture of sodium carbonate by the ammonia-soda process, urea, salicyclic acid (for aspirin), fire extinguishers and aerated water. Lesser amounts are used to transfer heat generated by an atomic reactor to water and so produce steam and electric power, whilst solid carbon dioxide is used as a refrigerant, a mixture of solid carbon dioxide and alcohol providing a good low-temperature bath (195 K) in which reactions can be carried out in the laboratory. 

The blanket when required should be at once wrapped firmly around the person whose clothes are on fire, the person then placed m a prone position on the floor with the ignited portion upwards, and water poured freely both over the blanket and in between the blanket and the person s clothes until the fire is extinguished. 

Sand. Buckets of dry sand for fire-extinguishing should be available in the laboratory and should be strictly reserved for this purpose, and not encumbered with sand-baths, waste-paper, etc. Most fires on the bench may be quickly smothered by the ample use of sand. Sand once used for this purpose should always be thrown away afterwards, and not returned to the buckets, as it may contain appreciable quantities of inflammable, non-volatile materials e.g., nitrobenzene), and be dangerous if used a second time. 

Carbon tetrachloride. Although sand is of great value for extinguishing fires, it has the disadvantage that any glass apparatus around which the fire centres is usually smashed under the weight of the sand. Alternatively, therefore, for small fires carbon tetrachloride may be poured in a copious stream from a Winchester Bottle on to the... 

Carbon tetrachloride must not be dried with sodium as an explosion may result. Fire extinguishers containing this solvent (e.g., Pyrene ) cannot therefore be applied to a fire originating from sodium. 

Finally, the student should familiarise himself with the contents of the Section in the Appendix upon Laboratory Accidents, with the position of the fire extinguisher, buckets of sand, first aid cabinet, and the fireproof blanket. 

Certain mixtures of acetylene and air are explosive. All free flames in the vicinity must therefore be extinguished. 

Mix 50 ml. of formalin, containing about 37 per cent, of formaldehyde, with 40 ml. of concentrated ammonia solution (sp. gr. 0- 88) in a 200 ml. round-bottomed flask. Insert a two-holed cork or rubber stopper carrying a capillary tube drawn out at the lower end (as for vacuum distillation) and reaching almost to the bottom of the flask, and also a short outlet tube connected through a filter flask to a water pump. Evaporate the contents of the flask as far as possible on a water bath under reduced pressure. Add a further 40 ml. of concentrated ammonia solution and repeat the evaporation. Attach a reflux condenser to the flask, add sufficient absolute ethyl alcohol (about 100 ml.) in small portions to dissolve most of the residue, heat under reflux for a few minutes and filter the hot alcoholic extract, preferably through a hot water fuimel (all flames in the vicinity must be extinguished). When cold, filter the hexamine, wash it with a little absolute alcohol, and dry in the air. The yield is 10 g. Treat the filtrate with an equal volume of dry ether and cool in ice. A fiulher 2 g. of hexamine is obtained. 

Burning clothing. Prevent the person from running and fanning the flames. Make the victim he down on the floor, or throw him (her) down if necessary, and wrap the fireproof blanket firmly around the ignited clothes until the fire is extinguished. 

A small fire (for example, hquid in a beaker or flask, or an oil bath) may usually be extinguished by covering the opening of the vessel with a clean damp cloth or duster the fire usually dies out from lack of air. For larger fires, dry sand may be employed. Buckets of dry sand should be distributed round the laboratory and should be strictly reserved for this purpose. Most fires on the laboratory bench can be smothered by... 

It is usually better to use a fire extinguisher charged with carbon dioxide under pressure this produces a spray of solid carbon dioxide upon releasing the pressure intermittently and is effective for extinguishing most fires in the laboratory. 

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