there are two main types of stills: pot stills and reflux stills. in a pot still, the pot (like a large kettle) holding the liquid is heated. the hot gas is cooled in a simple neck, or tube, and collected. pot stills are used for making alcohol like whisky. a reflux still is much more complex. it works with a continual flow of liquid going into the boiler, and a continual flow of distilled liquid coming out. the distilled liquid can also be put through the process several times, which is why it is called a reflux still. this allows for a more pure product, and the person working the still can control the level of purity. reflux stills are used in the chemical and petroleum industries.