When to Use a rubber stopper？

A rubber stopper is a small, tapered plug used to seal the openings of test tubes, flasks and other laboratory glassware. Stoppers made of cork are also available for this purpose. However, rubber stoppers are preferable for applications that require a tighter seal or a greater degree of chemical resistance.

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Purpose

The primary purpose of a rubber stopper is to prevent a gas or liquid from escaping its container during a scientific experiment. Rubber stoppers can also prevent the contamination of samples by protecting the contents of laboratory glassware from air. Last, the use of rubber stoppers allows experimenters to shake or mix solutions without spilling them.

Shape

The standard stopper is cylindrical in shape, with a tapered bottom end. Some rubber stoppers contain one or two holes to allow the insertion of pipettes, tubing or test equipment (e.g., a thermometer).

Size

Rubber stoppers typically range in diameter from size 000 (0.5 inches) to size 16 (5 inches) at the top. The tapered bottom end ranges from five-sixteenths to 3.5 inches. Smaller stoppers are appropriate for test tubes and similar glassware; larger stoppers are appropriate for flasks and beakers.

Properties

The main properties that make rubber suitable for use as a laboratory stopper are its elasticity, chemical resistance and impermeability. Its elasticity allows it to form a tight seal against the inside of the glassware. Its chemical resistance makes it safe for use with many corrosive and otherwise reactive compounds. Its impermeability helps to prevent the escape of liquids and gases from the container.

Rubber stopper for flasks and test tubes

(From left to right) One-hole Rubber bung size 10, Two-hole Rubber bung size 14, and Solid Rubber bung size 16

A laboratory rubber stopper or a rubber bung or a rubber cork is mainly used in chemical laboratories in combination with flasks and test tube and also for fermentation in winery.[1][2][3] Generally, in a laboratory, the sizes of rubber stoppers can be varied up to approximately 16 sizes and each of it is specific to certain type of container. As the rubber stopper is used in many experiments, some specific experiment requires a specific material. For example, the M35 Green neoprene stopper is for chemical resistance. For food fermentation, M18 white natural gum is preferred. For high temperature application, red or white silicone rubber stoppers should be used.

Sizes

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Rubber bungs can have one or more hole(s) for plugging in tubes depending on the specification of the procedures. To prevent the liquid chemical leaks or escape the container, the rubber bung should fit tightly to the container's opening; the dimension of the rubber bung is of concern. These are some of the sizes that are commonly seen in chemical laboratory.

(From left to right) Rubber bungs are aligned from size no. 1, 2, 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, to 16, respectively. (Comparing to the ruler) Size No. Top
mm Bottom 000 12.7 8.2 12x75 test tubes 00 15 10 0 17 13 1 19 14 2 20 16 20x150 or 10ml test tubes 3 24 18 4 26 20 25x200(150) or 20ml test tubes 5 27 23 50 ml Flasks 6 32 26 250ml Erlenmeyer Flasks 7 37 30 500ml Erlenmeyer Flasks 8 41 33 ml Erlenmeyer Flasks/ Florence Flask/ Filter Flask 9 45 37 ml Erlenmeyer Flasks/ Florence Flask 10 50 42 ml Filter Flasks

ml Erlenmeyer Flasks/ Florence Flask

For more information, please visit pharmacy glass bottles.

11 56 48 12 64 54 ml Filter Flasks 13 68 58 14 90 75 15 103 83 16 127 90

Additional images

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• Rubber bung size no.5 fits tightly on 50ml Pyrex® Flask

• Other equipments such as glass tubes can be plugged into the holes of the rubber stopper

See also

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References

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