I am sure that you all know a little about distillation by heating a liquid in a vessel with a condenser attached.  It is after all how you make whisky and other spirits.  The method was spread across Europe by alchemists and physicians who adopted spirit of wine as a medicine. 
What you are unlikely to have heard of is distillation by filter, yet it is a very common method of purification in the medieval and Tudor period.  It is of course something I do as part of my alchemy demo.  Here it is:


Simple – the capillary action of the cloth pulls the liquid up, over and down into the receiving vessel.  A bit like siphoning.  All the dirty ash and muck that is not in solution gets left behind.  Of course you have to make sure to use cloth that doesn’t have a dye that will run, as I did once and ended up with a red solution which wasn’t what I needed.  I had to start again. 

What my photograph shows is distillation by filter of a caustic solution, with ashes and lime being boiled in water to produce potassium hydroxide.  Of course there are plenty of insoluble substances in the ash so it is best to leave it all behind to get a purer liquid.  So, when has this been used in alchemy as opposed to the familiar distillation with heat? 

The 17th century English translation of The Summa Perfectionis by pseudo-Geber (late 13th century Spain) mentions distillation by filter, as shown in the above photo.  Its purpose is, like any other distillation, is “… the Purification of Liquid Matter from its turbulent faeces, and Conservation of it from Putrefaction.  For We see a Thing Distilled (by what kind soever of Distillation) to be rendered more Pure, and to be better preserved from Putrefaction.”                                                         Hence why distillation by filter is called distillation in the first place. 

Going back earlier, the tenth century Arabic text by Ar-Razi called the Kitab al-Asrar has instructions to “Purify it by filtration”, although it is not clear whether they mean through a cloth held flat and the liquid poured onto it, or by the capillary action of the filtration cloth hanging down.  It is sometimes classed with distillation, and I really can’t tell if they mean what is distillation by filter or not.  I hypothesise that distillation by filter is important to western alchemists, especially since I can find no mention of it in later Arabic works such as the “Book on Alums and Salts”, or works by pseudo-Avicenna. 

Of more relevance to later medieval re-enactors, the Book of Distillation by Heironymous Braunschweig, (first published in 1500) is important because it is one of the first popular books on distillation written for the general public.  Certainly they had been distilling long before, as the mention of an alembic in the Goodman of Paris shows, but by this time there was a literate audience wanting to learn the tricks of the trade.  Heironymous was German master surgeon who was literate and studied works on medicine and there are many woodcuts from later medieval Germany showing non-alchemists distilling. 

He defines distillation as “Wherefore it is to be understood that distilling is none other thing but only a purifying of the gross from the subtle, and the subtle from the gross, each separately from the other, to the intent that the corruptible shall be made incorruptible, …”                  (Modern transcription of the 1527 English translation by Adam Maclean)

Frankly, this reads almost exactly like it would if written by an alchemist, yet Heironymous is not an alchemist at all.  In this time the 4 element theory was dominant, and the related ideas about the four humours inside the body.  There was a well established set of names, phrases and suchlike to describe physical material, born from the work of natural philosophers.  Thus alchemists and philosophers had a common language to describe the reality they observed. 

Elsewhere the process is described as “The first without cost is done through a three-cornered filter (named distillatio per filtri).”

Admittedly he says you must have filters pure and white, 3 square, a foot in length and eight inches broad.  The illustration in his book is very similar to my photo above.  He even suggests putting multiple distillations on a stair, with the liquid flowing from vessel to vessel downstairs.  The more eagle eyed of you might have noticed the Italian term distillatio, meaning distillation.  WordPress said that Distillation was already taken as a blog name.

The problem with all the above methods is that they aren’t clear on what sort of cloth.  Linen?  Wool?  Cotton?  I’ve used woollen offcuts but perhaps a decent thick linen would do as well but I really don’t think it matters much at all. 

But the name had definitely changed by 17th century England.  In John French’s 1651 book on “The Art of Distillation”, we find the following definitions:

DISTILLATI ON is the extracting of the humid part of things by virtue of heat, being first resolved into a vapor, and then condensed again by cold.

FILTRATION is the separation of any liquid matter from its feces by making it run through a brown paper made like a tunnel, or a little bag of woollen cloth, or through shreds.

So what I have been doing is by his scheme just filtration, by shreds.  There is a recognition of them as separate methods with different capabilities.  This is also the time that the language used by natural philosophers and alchemists to describe their work was changing.  One example being the term “Chymistry” coming more into use.

So there you have it, a simple technique to use should you want to make soap from first principles or make some medicinal liquids.