Bottle closures (illustrated above) are associated with specific characteristics of, and reflect the physical properties and intended use of, the product contained.  By knowing (or looking up) the correct physical properties of the contents indicated on the label, one can identify labels which do not "belong" on the bottle type in question or recognize when contents do not match the label or bottle type.  

 

Salt mouth jars are for solid contents (a true salt like sodium chloride or other plant, mineral, or chemical) and are intended to allow contents to be poured if desired or, more often, to allow entry of a spoon or spatula to remove material. The closure is generally ground glass and is moderately air-tight, given that the contents are non-volatile. 

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A Tincture is a water or water/alcohol-based solution which has low volatility and low viscosity and hence is readily poured from a narrow mouth container with minimal dripping if the lip is properly configured as in this example. As with salt-mouth jars, the closure is moderately air tight.

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A Syrup is a sugar and water, honey, or other viscous mixture of low volatility. Because a syrup will readily crystallize in the mouth of the bottle, syrup closures are not made of closely-fitted ground glass. Rather, the bottle top simply sits against the top of the bottle, with the stem serving to keep the closure in place with routine handling. 

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A Spirit is a highly volatile material like ether or chloroform, or a substance dissolved in a volatile solvent. The contents will not usually drip when poured, but it will escape to the atmosphere if not tightly sealed. Such containers have a double-ground-glass seal consisting of an inner stopper and an outer cover.  Grease or wax may be used to provide a highly airtight seal, usually only on the outer closure to prevent contamination of the contents.

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An Oil is precisely that- whether it is oil of wintergreen or just olive oil, it has a fairly high viscosity and a tendency to drip, but unlike a syrup will not crystallize in the closure. These bottles typically have a ground-glass inner pouring spout which can be removed for filling the container or for pouring large amounts of material, but which facilitates dispensing of small quantities when in place.  As the contents are not volatile, the outer closure is usually just a dust-cover, lacking the ground-glass seal seen in the spirit bottle. 

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