Everyone has a favourite reaction, reagent, molecule, or famous chemist.  I’m no exception, and I think it’s time I took some time to share with you my favourite piece of glassware: the Soxhlet Extractor.

Soxhlet_mechanism - Tomasz Dolinowski

I’m not sure how I could improve on this gif. By Tomasz Dolinowski.

The Soxhlet is a master of the slow liquid-solid extraction [1], a procedure used to separate the poorly soluble from the insoluble.  During use, the inner core of the soxlet is stuffed with an impure solid that has been wrapped in filter paper.  The extracting solvent is heated to reflux in an RBF below, and the condensate drips down into the filter.  As the hot solvent fills the extractor the compound of interest slowly dissolves, forming a low molarity solution.  When the reactor is full a siphon is triggered, and the solvent flows down to the RBF.  This cycle repeats for up to several days, removing all trace of the soluble compound from the upper chamber [2].

Somewhat strangely, I’ve never needed to use a Soxhlet in the course of my research.  There are four in the lab, grabbed when a nearby group was eliminating surplus equipment, but my solid-liquid extractions generally fall under small scale manual triturations.  The soxlets may sit unused on a high shelf, but they are loved.


[1]  For those interested in the history, there’s a nice writeup in J. Chem. Ed.

[2]  Yes, I’m sure this could make a KILLER cup of coffee.