Rubber Bung

The type of apparatus shown in Fig. 40 can be obtained with ground-in glass joints thus obviating the use of rubber bungs. 

In most of these prcpiirations. the corks or rubber-bungs can be replaced by ground-glass joints (pp. 42-47). 

The Mariotte bottle. l he perchlorate guard tube is attached by a length of ordinary rubber condenser tubing to the Mariotte bottle W. This is, in effect, a siphon bottle, and the lead-in tube X is a capillary provided with a tap T,. The bent capillaiy (drawn off slightly at the end) serves as exit tube it is fitted into W by a rubber bung and its level may be adjusted. 

The ascension tube D ca. i cm. in diameter ) rises for about 8 cm. above A, then narrows (5 mm. in diameter) to form a small condenser E (8 cm. long). The ascension tube then bends over in a flattened U-shape and descends into the gas-washer F (ca. 8 cm. long). The tube continues to the bottom of the washer, leaving a gap of only 1-2 mm. when F is closed by the insertion of the rubber bung M. The tube in this section is 2-3 mm. in diameter. The outlet tube... 

For either type pump, the bubble should stop between the 95 cc and 105 cc marks. Allow 4 minutes for the pump to draw the full amount of air. Also check the volume for 50 cc (1/2 pump stroke) and 25 cc (1/4 pump stroke) if pertinent. A +5 percent error is permissible. If error is greater than +8 percent, send the pump for repair and recalibration. Record the calibration information required on a calibration log. It may be necessary to clean or replace the rubber bung or tube holder if a large number of tubes have been taken with the pump. 

When the experiment has been completed, clean the capillary as described above and then store it by inserting through a bored cork (or silicone rubber bung — normal rubber bungs which contain sulphur must be avoided) which is then placed in a test-tube containing a little pure mercury. Lower the mercury reservoir until drops no longer issue from the capillary, then push the end of the capillary into the mercury pool. 

In use, the tube to be worked is wound with asbestos paper and htted into the large tube of the holder a rubber bung can often be used instead of the paper. 

The type of double surface condenser most often found in laboratories is the Davies improved double surface condenser which appeared in 1905, and was designed by J. Davies of A. Gallenkamp Co. as a direct development from Thresh s modification of the Bidet condenser. All rubber bungs and tubing were eliminated in the Davies condenser, which has retained its popularity for 50 years. To make a condenser of this kind the inner water jacket is connected to the outer one by two internal seals wWch are made by a sli t modification of Method 2 described on p. 75. The rest of the assembly is similar to that for an ordinary Liebig condenser. 

An unopened bottle of anhydrous aluminium chloride erupted when the rubber bung with which it was sealed was removed. The accumulation of pressure was attributed to absorption of moisture by the anhydrous chloride before packing (but see comment following text of masthead reference 2). The presence of an adsorbed layer of moisture in the bottle used for packing may have contributed. Reaction with water is violently exothermic [1], The unsuspected presence of 100 kg of the chloride in a vessel led to bursting of a glass vent when the vessel was being flushed with water [2],... 

The rubber bungs (about 25 mm x 25 mm), each with a hole bored centrally and through exactly 6.5 mm in diameter, are fitted with a rubber band or spring clip for holding them tightly in place. 

Contamination is a major problem in lipid analysis and the use of plastic containers and stoppers, rubber bungs or tubing, and any grease on stopcocks, etc., must be avoided. All solvents used should be of the purest grade and be peroxide-free and all glassware should be scrupulously clean. 

In a s-1. flask (Note 1) provided with a mechanical stirrer, a reflux condenser, and a hopper which can be opened or closed at the bottom by means of a rubber bung attached to a glass rod... 

It is routinely desirable to interpose a large pressure bottle A (Fig. 2.121) fitted with a rubber bung between the pump and the apparatus to act as a trap in the event of failure of the non-return valve and to serve as a pressure equalising reservoir. Connection to the apparatus and to a manometer (see also Fig. 2.124) is via a three-way tap B which allows for the release of the vacuum as required the two-way tap C permits the manometer to be isolated from the system when necessary. 

---