Closure of test tubes and flasks

Abstract

Test tubes and flasks need, on the one hand to be closed to prevent drying out and infection, while on the other hand a change of gases with the ‘outside air ‘must be possible to avoid a shortage of O₂ and to prevent an accumulation of gases produced, such as CO₂ and ethylene. Each closure is a compromise between these two requirements. Closure can be obtained in the following ways:

• 1. Cotton wool plugs (Fig. 7.1). These plugs, previously used a great deal, are made by hand, which is very labour intensive. There are machines now available which make these to fit particular flasks and tubes. Previously, the cotton wool plugs were burned after inoculation, but this is no longer possible since the synthetic ‘wool’ gives off gases when burned which can be very harmful (Fig. 7.2).

• 2. Steristops (Fig. 7.1). These are porous cellulose stoppers, which can be pushed into a tube, like a cork.

• 3. Aluminium caps (Fig. 7.1), which are fixed on glass with a clip.

• 4. Transparent glass or synthetic tops, which can be autoclaved.

• 5. Tubes or flasks with screwtops. Care should be taken that they are not too tightly screwed, because then no exchange of gases can take place between the tube or flask, and the outside air.

• 6. Aluminium foil. This is used especially on large Erlenmeyer flasks.

• 7. Plastic (foam) plugs.