In discussing early 19th Century contributions that still provide valuable lessons for chemistry, we have concentrated mostly on elemental analysis (for example, Combustion and Liebig's "Kaliapparat") and the theories that sprang from it. Techniques for separation and purification have always been equally important. Perhaps a brief discussion of early tools for distillation will help make you think about what we are doing, particular in the laboratory.

In the experimental techniques section of his "Traité Élémentaire de Chimie" (1789) Lavoisier provided a discussion of purification by distillation illustrated with etchings by Mme. Lavoisier.

Here is some of what Lavoisier says about "Simple Distillation": The simplest of all apparatus for distillation is a bottle A, plate III, fig.8 [right], of which one bends the neck of the glass itself from BC to BD. This bottle or phial is called a "cornue";* one places it either in a furnace as shown in plate XIII, fig 2, or in a sand bath under a pottery lid, as shown in plate III, fig. 1 [below right]. To collect and condense the product, one fits the cornue with a receiver E, plate III, fig. 9 [below], which one cements to it: sometimes, especially in pharmaceutical operations one uses...a glass alembic,** of which the top is a single piece, figure 13 [below]. But, since almost all distillations involve expansion of vapors that could shatter the vessel, one must equip the flask or the receiver E, fig. 9, with a little hole T, to allow the escape of vapors. Thus one sees that in this mode of distilling one loses any product that is permanently gaseous, and even those that, since they do not easily leave this state, do not have time to be condensed inside the flask. *) From French for "horn", cf. cornucopia. More commonly the vessel is called a "retort" from the Latin word meaning "twisted". **) "Alembic" is from the Arabic "al anbiq, the still" from the Greek ambix, ambix, head of a still. This is really ancient technology. Note the warning to beginning organic students down through the centuries, who have often overlooked the necessity of leaving the little hole that keeps the still from "shattering", or at least flying apart.

In the passage above, Lavoisier emphasizes the problem of losing liquids that are difficult to condense during distillation with a cornue/retort/alembic. He described some more elaborate equipment, but there is a better solution.

The solution to this problem is to use a water-cooled condenser, since water has a much greater capacity for removing heat than the air that was used to cool the ancient vessels. The familiar water-cooled condenser is traditionally referred to as a "Liebig condenser".

In lab you use a glass-jacketed Liebig condenser with rubber tubing to supply and drain water.

Liebig's own tin-jacketed condenser in his Giessen laboratory [below] used an elevated bucket with a tap to supply water to a funnel, which led it to the bottom of the jacket. The water rose in the jacket to leave at the top and drip into a second bucket, which could then be emptied into the top bucket again for recycling.

You should wonder in looking at Liebig's setup, or while connecting the tubing to your own condenser in lab, "Why should the cooling water enter at the bottom and leave at the top?" After all, this was inconvenient and required Liebig to use an extraordinarily long funnel. Of course the lab manual tells you to do it this way, but why? (click here for answer) In 1896 it was pointed out that Christian E. Weigel's 1770 M.D. thesis in Göttingen included a detailed drawing (below right) of his tin-jacketed "Liebig" condenser, which he used for "Destillatio spiritus vini." This was 32 years before Liebig's birth! Weigel also made a water-cooled condenser from glass rather than tin. Here is another example of how being in an influential position, as Liebig was in his Giessen teaching laboratory, or Kekulé in Ghent and Bonn, can make someone "famous for being famous." People are no more likely to refer to a Weigel condenser than they are to refer to Couper (rather than Kekulé) structures of organic molecules. There had been one fairly minor improvement in the 60 years between Weigel's condenser, where water pours out of the jacket (and perhaps down its bottom side), and Liebig's, where it emerges at the top through a cork into a curved tube that dumps it into the bucket. Think about how much of the inner tube is covered in water, and about how you should turn the condenser in your own distillations. Granted it doesn't make much difference, but in principle should you rotate your condenser so that the rubber tubing leaves from the top or the bottom side of the top end of the condenser? [Think about where air is in the jacket.]

Weigel's Condenser. Fig 4 is a cross section of the condenser showing the interior tube, the space for water, and three struts supporting the outer jacket.