Glycerin is a thick liquid that is colorless and sweet tasting. It has a high boiling point and freezes to a paste. Glycerin's most common use is in soap and other beauty products like lotions, though it is also used, in the form of nitroglycerin, to create dynamite.
This liquid is popular in beauty products because it is a humectant — it absorbs ambient water. This means that it can help seal in moisture. Not only is it used in the soap making process, it's a byproduct too. Many soap manufacturers actually extract glycerin during the soap making process and reserve it for use in more expensive products. Some amount remains in every bar of soap, however, and additional may be added in order to produce a clear finish and extra moisturizing qualities. The extra also enhances the cleaning aspect of soap.
Glycerin can be dissolved easily into alcohol and water but not into oils. The pure chemical compound is called Glycerol, which indicates that it is an alcohol.
The fact that is also easily absorbs water from the surrounding air means that glycerin is hygroscopic. If some was to be left in the open, it would absorb water from the surrounding air until the liquid was eventually 20% water. A small amount placed on the tongue would cause blistering, because it is dehydrating. When beauty products containing this compound are used on skin that is well moisturized, it can help keep that moisture in.
Where glycerin comes from has changed over time. In 1889, for example, commercial candlemaking was the only way to obtain it. At that time, candles made from animal fat which served as the source. Extraction is a complicated process and there are various ways of going about it. The simplest way is to mix fat with lye. When the two are mixed, soap is formed and glycerin is then removed.
Glycerin has a variety of uses. It can be used to make dynamite, although it is not explosive alone, and it has to be processed before it can be used as an explosive. The compound is also used in prints and inks, preserved fruits, lotions and as a lubricant. It can also be used to prevent hydraulic jacks from freezing. Its antiseptic qualities permit its use in the preservation of scientific specimens.