Stoppers

STOPPERS. Cork (suber) is a protective tissue formed from dead cells separated outwardly by one of the layers of tree bark, the cork cambium. The composition of cork is poorly studied. Cork is widely used as an insulating material, for the production of linoleum, and as a sealing material. Cork has no direct medical application, but it is extremely important as a material for plugging jars, vials, and the like. For this purpose, cork is obtained from the cork oak (Quercus suber L.), a tree growing on the coast of the Mediterranean Sea; recently, experiments have been underway to cultivate the cork oak in Crimea and Transcaucasia. In this oak, the cork layer grows extremely thickly (up to 15 cm in thickness). Cork is distinguished by its elasticity and relative chemical indifference. Strong acids, alkalis, oxidizing agents (hydrogen peroxide, etc.), ammonia vapors, and halogens (bromine, iodine) destroy cork; cork does not dissolve in water and ordinary organic solvents. However, the coniferyl alcohol and vanillin contained in cork, as well as glycerides, are extracted from it by alcohol, ether, and chloroform; therefore, for example, for ether or chloroform during anesthesia, only stoppers boiled in alcohol can be used. All imports of cork and supply are concentrated in the USSR in Tsentroprobizol. According to its classification, velvet, semi-velvet, and plain corks are distinguished. Velvet corks are distinguished by elasticity, purity, and the absence of "lenticels," which are found in lower grades. Lenticels consist of a loose, crumbling mass; if present, medicines are easily contaminated with cork dust, and the seal becomes loose. Among artificial stoppers, those closest in properties to genuine ones are made from sawdust and waste of genuine cork, glued together with a water-insoluble adhesive. Stoppers glued with rubber cement cannot be used to plug containers with gasoline, benzene, carbon disulfide, chloroform, and many other organic solvents. Artificial stoppers glued with boiled linseed oil are unsuitable for plugging vessels with medicines, because they partially dissolve even in very weak alkalis (soda) and alcoholic liquids.

To replace corks in cases where wooden corks cannot be used, rubber or glass stoppers are available. For short-term sealing of liquids that corrode corks (hydrogen peroxide, tincture of iodine, etc.), corks are protected by wrapping them in tinfoil or heating them in molten paraffin. Before sealing glassware, corks are usually compressed using a press (vise) to increase their elasticity. Compression should be performed by uniform squeezing of the cork along its entire length, otherwise the cork often breaks at the edges of compression or, becoming deformed, seals the vial loosely. Preliminary steaming or boiling of corks with water also increases their elasticity.

I. Oberhard.