Swan-necked flasks

Fig. 1.3 Pasteur s swan-necked flasks in the first flask, the unbroken neck hinders contamination if the neck is broken off as in the second flask, the sterile culture medium is invaded by microorganisms. After Pasteur (1862)...

In order to disprove this theory, Pasteur used swan-necked flasks unheated air could now enter the sterile culture solution. But in this case, the microorganisms in the air were deposited in the long S-shaped neck and did not enter the culture medium. If, however, the neck of a flask was broken off, they could enter the solution and multiply. 

Grys [654] studied this method in more detail and applied it to the determination of iodine, present as a free element, iodide and firmly bound iodine in milk. A 0.4-ml volume of fresh milk was placed in a 35-ml Kjehldahl swan-necked flask, mixed with 1.0 ml of 2 M potassium carbonate solution, dried at 105°C overnight and then ashed at 600—... 

The swan neck adapter of Fig. II, 56, 12 is useful for distillations as it permits the use of a capillary tube (held in position by a short length of heavy-walled rubber tubing) not sealed to a ground joint. It may also be used for inser tion of a thermometer or a gas-inlet tube in the narrow neck and a reflux condenser into the ground joint this device virtually converts a three-necked into a four-necked flask. Common sizes are cone fil9, 24, 29, or 34 socket 19, 24 or 29. 

For evaporation at the boiling point either a conical flask with a short Pyrex funnel in the mouth or a round-bottomed flask inclined at an angle of about 45° may be employed in the latter the drops of liquid, etc., thrown up by the ebullition or by effervescence will be retained by striking the inside of the flask, while gas and vapour will escape freely. When organic solvents are employed the flask should be fitted with a swan-neck tube and a condenser so that the solvent is recovered. 

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