Bunsen

Bunsen. Discussion on Molecular spectroscopy and molecular dynamics. Theory and experiment Ber. Bunsengesellschaft Phys. Chem. 99 231-582... 

Bunsen. Discussion on Intramolecular processes Ber. Bunsenges. Phys. Chem. 92 209 50 Bunsen. Discussion on Unimolecular reactions Ber. Bunsenges. Phys. Chem. 101 304-635 Faraday Discuss. Chem. Soc. 1983 Intramolecular kinetics. No 75... 

The basin A is then gently heated by a small Bunsen flame, which should be carefully protected from side draughts by screens, so that the material in A receives a steady uniform supply of heat. The material vaporises, and the vapour passes up through the holes into the cold funnel C. Here it cools and condenses as fine crystals on the upper surface of the paper B and on the walls of C. When almost the whole of the material in A has vaporised, the heating is stopped and the pure sublimed material collected. In using such an apparatus, it is clearly necessary to adjust the supply of heat so that the crude material in A is being steadily vaporised, while the funnel C does not become more than luke warm. 

The material to be steam-distilled (mixed with some water if a solid compound, but not otherwise) is placed in C, and a vigorous current of steam blown in from D. The mixture in C is thus rapidly heated, and the vapour of the organic compound mixed with steam passes over and is condensed in E. For distillations on a small scale it is not necessary to heat C if, however, the flask C contains a large volume of material or material which requires prolonged distillation, it should be heated by a Bunsen burner, otherwise the steady condensation of steam in C will produce too great a volume of liquid. 

A skilled worker can use a micro-Bunsen burner for most types of heating. Nevertheless, as there is a tendency for a liquid to shoot out of a small test tube when heated, it is preferable to place the tube in a hot water-bath or in a metal heating block. A small glycerol bath is suitable for distillations and heating under reflux, the glycerol being subsequently easily removed from flasks, etc., by washing with water. 

The heating of the vessels is accomplished by means of a small bath or a micro-Bunsen burner. The vessel can be clamped at such a distance from the burner that the contained liquid boils gently under reflux. Smooth boiling is ensured by the addition of 1-2 minute pieces of unglazed porcelain, or of a short piece of melting-point tubing open at both ends. 

If the solid does not dissolve in the cold solvent gently heat the mixture over a micro-Bunsen burner or in a small water-ba until the liquid boils. Continue to add o-i ml. portions of solvent until the solid dissolves. [If more than about i ml. of solvent is required, the solvent is considered unsatisfactory.] If a clear solution is obtained, cool the tube and scratch it below the surface of the solution with a very fine glass rod and proceed as suggested on p. 16. In general, the products from the choice of solvent investigation are not discarded but added to the main bulk of the crude product for recrystallisation. 

The liquid becomes progressively darker in colour, and then effervesces gently as ethylene is evolved. Allow the gas to escape from the delivery-tube in T for several minutes in order to sweep out the air in F and B. Now fill a test-tube with water, close it with the finger, and invert the tube in the water in T over the delivery-tube so that a sample of the gas collects in the tube. Close the tube again with the finger, and then light the gas at a Bunsen burner at a safe distance from the apparatus. If the tube contains pure ethylene, the latter burns with a clear pale blue (almost invisible) flame if the ethylene still contains air, the mixture in the test-tube ignites with a sharp report. Allow the... 

Hydrolysis of Ethyl Bromide. Add -a few drops of pure freshly distilled ethyl bromide to 2-3 ml. of aqueous silver nitrate solution in a test-tube and shake. Only a faint opalescence of silver bromide should be formed. -Now carefully warm the mixture in a small Bunsen flame, with gentle shaking silver bromide soon appears as a white suspension which rapidly increases in quantity and becomes a heavy precipitate. The ethyl bromide is thus moderately stable in cold water, but rapidly hydrolysed by hot water. 

For this preparation, it is particularly necessary that the sodium acetate should be free from traces of water. The anhydrous material can be prepared by gently heating the hydrated salt (CHsCOONa,3HjO) in an esaporating-basin over a small Bunsen flame. The salt dissolves in its water of ciystallisation and resolidifies as this water is driven off further heating then causes the anhydrous material to melt. Stir the molten anhydrous material to avoid charring, and then allow it to cool in a desiccator. Powder the cold material rapidly in a mortar, and bottle without delay. 

Transfer the solution into the flask, add some unglazed porcelain, and support the flask over an asbestos-covered gauze. Heat the solution cautiouslv with a Bunsen flame so that the temperature... 

Required Sulphuric acid, 27-5 ml. aniline, 24 ml. sodium nitrite, 20 g. dry potassium carbonate, 3-4 g. (To ensure that the potassium carbonate is dry, it should be gently heated in an evaporating-basin over a small Bunsen flame for 4-5 minutes with stirring, and then allowed to cool in a desiccator.)... 

Add 4 g. of malonic acid to 4 ml. of pyridine, and then add 3 1 ml. of crotonaldehyde. Boil the mixture gently under reflux over an asbestos-covered gauze, using a small Bunsen flame, for 40 minutes and then cool it in ice-water. Meanwhile add 2 ml. of concentrated sulphuric acid carefully with shaking to 4 ml. of water, cool the diluted acid, and add it with shaking to the chilled reaction-mixture. Sorbic acid readily crystallises from the solution. Filter the sorbic acid at the pump, wash it with a small quantity of cold water and then recrystallise it from water (ca, 25 ml.). The colourless crystals, m.p. 132-133°, weigh ro-i-2 g. 

When the reaction is complete, heat the stirred mixture carefully under reflux over a Bunsen burner and asbestos gauze for I hour if the mixture becomes too thick for efficient stirring, add up to 15 mL of acetic acid. Now decant the hot mixture into 500 ml. of vigorously-stirred ice-cold water wash the residual zinc thoroughly with glacial acetic acid (2 portions each of I -2 ml.), decanting the acid also into the stirred water. 

It is best now to proceed as in the Skraup Synthesis (p. 297) and warm the mixture over an asbestos-covered gauze with a Bunsen flame until the reaction starts, and have at hand a duster soaked in cold water so that when the reaction starts, the heating can be at once removed and the duster wrapped round the shoulders of the flask to aid condensation. 

There is no satisfactory chemical way of distinguishing betn een ethane and methane, both of which burn with an almost non-luminous flame this fact however is quite unimportant at this stage of the investigation. Hydrogen also burns with a non-luminous flame and w hen the open end of a test-tube full of the gas is placed in a Bunsen flame, a mild explosion with a very characteristic report takes place. 

A beaker is placed under Y and the combustion may now be started. The Bunsen burner, with the air-hole wide open, and the... 

The chief danger and main source of error in a combustion is that of moving the Bunsen forward a little too rapidly and so causing much of the substance to burn very rapidly, so that a flash-back occurs. This usually causes an explosion wave to travel back along the tube towards the purification train, some carbon dioxide and water vapour being carried with it. If these reach the packing of the purification train they will, of course, be absorbed there and the results of the estimation will necessarily be low. 

The second indication is a faint smoke-like cloudiness in the zone of the tube which is being heated by the Bunsen this is readily visible as the interior of the tube is normally quite clear and bright. This is a later stage of development of the flash-back than the rise of pressure, already mentioned, and should be counteracted by moving the Bunsen immediately to the point of the combustion tube where heating was commenced. In either case the Bunsen should then be moved slowly forwards as before. A flash-back is attended by the deposition of carbon particles, carried back by the explosion wave, on the cold walls of the tube. Care should be taken that these are completely burnt off as the Bunsen is slowly moved forward again. 

As the substance is heated in the boat—it usually melts before the Bunsen quite reaches the boat itself and runs forward to the front end—... 

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