The chemical laboratories of the first half of the 19th century
Of the complex of Justus von Liebig’s chemical laboratories in Giessen, transformed since 1920 into one of the most interesting science museums in the world, one is struck by the size, the wealth of instruments and equipment. The museum preserves the Institute of Chemistry almost intact, where Liebig worked as a teacher and scientist from 1825 to 1852. It is a unique structure, which has survived to the present day. In those rooms and laboratories, generations of chemists from all over Europe and even the United States were trained under the guidance of a great teacher. Liebig later also taught in Munich. An important space has been dedicated to him at the Deutsches Museum in this city. His laboratory is reconstructed in real size. But among the many “objects” that fill the space of his workshops, in both museums there are two that the visitor perceives as the most important. One is the apparatus for the analysis of organic substances, the other is the apparatus for distillation. In both there is a detail that makes them original. In the first it is the Kalium-apparat for the absorption of carbon dioxide, in the other it is the counter-current condenser in distillation.
But if the authorship of the Kali-apparat is Liebig, the condenser, which bears his name, is not his invention. His merit is to have made it a routine tool, precious in laboratory analysis.
But who is responsible for the invention of the counter-current condenser?
It was in 1771 that a dissertation by a young doctor Christian Ehrenfried Weigel, in his early twenties, was published for his medical degree. It is written in Latin:
Within a few pages is presented an apparatus for distillation with the cooling of vapors obtained by means of a condenser that operates in counter-current. An explanatory drawing is attached. Before going into the chapter in detail, let’s see a brief biography of the author.
The biography of Christian Ehrenfried Weigel
Christian Ehrenfried Weigel was born in 1748 in Swedish Pomerania; although of German language and culture, he was therefore a Swedish subject. His father was a doctor with interests in pharmaceutical chemistry, inventor of a preparation known as “Weigel’s drops” (a remedy against intestinal parasites); his maternal uncle was also a doctor.
He completed his studies, first at the University of Greifswald, where he attended courses in botany, chemistry and anatomy, then in Gottingen where he obtained his doctorate in medicine. All his life he held the chair of chemistry and pharmacy at the faculty of medicine at the University of Greifswald, where he was also a lecturer of the botanical garden for many years. He wrote one of the first chemistry textbooks “Outline of pure and applied chemistry” which was addressed to readers of all classes. Weigel also did a lot for German chemists by promoting their update on the developments of chemistry through his translations of works by Wallerius, Guyton de Morveau, Lavoisier and others. In 1806 he was ennobled by Emperor Francis II and two years later he became the personal physician of the Swedish royal house. He was a member of the scientific academies of Erfurt and Berlin, as well as of the Leopoldine Academy and the Academy of Sweden. He has also left important contributions in the field of botany. He was an avid naturalist, and has an entire genus named after him: Weigela, a type of East Asian “shrubby” plant from the honeysuckle family.
Christian von Weigel wrote over 76 scientific books in German, the only one written in Latin is his thesis. It is probable that the tradition of university study, this being the dissertation he gave for his degree, required the Latin language. Undoubtedly the language in which Weigel’s work was written did not favor its diffusion. Furthermore, the translation of the text from Latin presents some difficulties, because this language was used to express technical contents that did not belong to the lexicon of an ancient language.
It is possible that this is also the reason that led to a misleading interpretation, as we shall see below, of the Weigel apparatus by Prof. William B. Jensen of the University of Cincinnati. In an article that appeared in the prestigious Journal of Chemical Education, vol. 83, 2006 of the American Chemical Society entitled “The Origin of the Liebig Condenser” he describes the Weigel condenser as follows:
«In Weigel’s original design, the cooling water was confined between an inner and outer tin or zinc tube and the glass distillation tube did not come into direct contact with the cooling water but was rather suspended inside the inner metal tube… [in bold by the translator]. In Liebig’s case, these apparently consisted of eliminating the inner metal tube and narrowing the cooling jacket at each end so that the glass distillation tube could be sealed directly to the outer metal jacket by means of plugs. or sections of rubber tube, thus allowing the distillation tube to come into direct contact with the cooling water … ”
Unfortunately, Prof. Jensen’s inaccuracy has spread. Wikipedia, the on-line encyclopedia, under the entry “Liebig condenser”, reports the following passage:
«The first water-cooled laboratory condenser was invented in 1771 by the Swedish-German chemist Christian Weigel (1748–1831). The Weigel condenser consisted of two coaxial tin tubes, which were joined at their lower ends, forming a water jacket, and open at their upper ends. Cold water entered the jacket through an inlet at the bottom and escaped from the open top of the jacket. A glass tube carrying the vapors from a distillation flask is passed through the inner tin tube. ”
An English-language site promoting Rum reports Weigel’s biography aligning with previous interpretations:
«The Weigel condenser consisted of two coaxial tin tubes, which were joined at their lower ends and open at their upper ends. Cold water entered the lower end of this jacket through an inlet and escaped from the open upper end of the jacket. A glass tube carrying the vapors from a distillation flask is passed through the inner tin tube, not in contact with the cooling water.»
Doubts about the interpretation
I must say that the interpretation given by Jensen left me with some doubts, so I searched the net for Weigel’s dissertation, finding the book available. The big obstacle of the language was overcome by two distinguished Latinists from Arezzo, who together perfected the translation:
Prof. Claudio Santori, Vice President and Secretary of the Class of Letters of the Petrarca Academy and Don Natale Gabrielli, Prior of the Pieve di San Polo and head of the Ancient Library and Archives of the Bishop’s Seminary of Arezzo.
Their translations, of which I quote the most significant passages, leave no doubts of interpretation.
The content of Wiegel’s dissertation is a lucid and punctual analysis of the distillation technique used up to then which is followed by a revolutionary proposal, due to its modern aspect, to overcome the drawbacks. The mastery he shows in discussing this technique, despite his young age and student status, leads us to think that it is the result of attending the pharmaceutical chemistry laboratory of his father and uncle, from whom he received pre-university education. It was necessary to rehabilitate this talented scientist and put his thinking back into the correct perspective, because Jensen’s interpretation of Weigel’s apparatus downgrades the latter to a bizarre representation.
The degree thesis
In the first part of his dissertation Weigel examines the distillation technique then used, in particular the aspect concerning the cooling of the vapors. As can be seen from his title, the aim is to obtain alcohol with a high degree of purity, alcohol fortissimum, after repeated distillations, repetita rectificatione, starting from liquids with a low alcohol content, such as wine.
Identify the problems that arise from the use of linear or serpentine-shaped steam ducts:
(“I could have chosen a shorter tube, and passed it through a cooling barrel, according to the common method; I could thus have distilled in less time. But first the tubes passed, according to the common method, obliquely, however in straight way, cool slowly; those that pass the coils through a cooling barrel, can only be made of copper and cannot be cleaned properly due to their structure; whereby the spirit of wine is damaged or easily takes a bad smell due to impurities from previous distillations.)
Distillation appliances produce vapor losses:
“2do Nec in usu esse solet recipiens vas vitreum tubo applicare et ope vesicae adglutinare, sed solent supponere excipulum, eique imponere infundibulum, quod intrat spiritus ex tubulo profluens, quando ad instar calami straminei profluit. Coguntur ad id faciendum, quia praeuident periculum displofionis vasorum a spiritu non sufficienter refrigerato, alioquin oriundum. Qua vero methodo copiam vaporum spirituosorum in auras auolare vix mentione eget.”
(“Secondly, it is not customary to apply a glass jar to the tube (to collect the condensate) and fix it, but it is customary to place a container equipped with a funnel under the tube, into which the spirit coming out of the tube enters. To do so since the danger of breaking the collection vessels due to the insufficiently cooled spirit is prevented. It is evident that with this method many spirit vapors are dispersed in the air. “)
The problem of refrigeration, the space used, the amount of water and manpower:
“3tio Vulgare vas refrigeratorium, scilicet sufficientis capacitatis, magnum occupat spatium, quare in boratoriis minoribus maxime incommodum est instruzmentum. Requiritur insuper saepissime ministri praesentia in laboratorio, cum ad aquam vase refrigeratorio contentam agitandam, eum scilicet in finem, ut superior frigidior cum inferiore calefacta misceatur, tum ad refrigeratorium euacuandum et denuo aqua frigida replendum; unde etiam istud emergit incommodum, quod laboratorium claudere nunquam liceat. Demum notetur, non semper aequalem effectum per vulgare vas refrigeratorium obtineri posse; breui nimirum ante repetitam repletionem aqua refrigeratorii tepida euafit, hinc impotens, quae sufficienti gradu refrigeretur.”
(“Thirdly, the common refrigerant barrel, that is, of sufficient capacity, occupies a large space for small laboratories, it is an instrument of great inconvenience. It is also very often required the presence of an operator in the laboratory, both to move contained in the refrigerating barrel so that the colder one above is mixed with the warmer one below, and to empty the refrigerator and then fill it with new water: hence the other inconvenience of never being able to close the laboratory. finally noticed that with the normal refrigerant barrel it is not possible to obtain the effect that is always the same; certainly soon, before the renewed filling, the water in the refrigerator is lukewarm and therefore cannot refrigerate properly.)
After this analysis he offers a solution.
“Bona igitur, rectaque via excogitata ad incommoda adducta remouenda, quam experientia comprobatam exponemus.”
(“A better and correct way was therefore devised, to eliminate the inconveniences just mentioned, which we are going to expose, validated by experience“.)
The sentence validated by experience suggests that the best way had already been used in the family workshop, conducted by the father and uncle. In fact, in another passage of the dissertation it is expressed:
“Saepius in Parentis, maxima pietate colendi, laboratorio institui, hanc circa rem, experimenta, instrumentorumque ad hanc rem idoneorum imagines in charta delineaui, …”
(“Often times I have conducted experiments on this matter in the Father’s laboratory, always venerating, and I have traced on paper figures of instruments suitable for this technique …”)
The key part of his proposal is enriched by an image of the device, with its description.
“…Cadit aqua in infundibulum c. Infundibulum hoc intrat canalem d. (Fig. 2), cuius subftantia est bractea ferrea stanno obducta, figurae cylindricae, diametri foraminis circiter tres quartas partes digiti transuersi aequantis, longitudinis tantae, ut eius superius orificium, quod intrat infundibulum c. circiter 2, 3, 4 digitos altius sit punctis inter h. et g. possibilibus. Nunc concipias tibi tubum e. f. g. h. eiusdem Figurae tubum a. b. ambientem (Fig. 2). Tubus hic paratus ebractea ferri stanno obducta figurae cylindraceae tantae diametri, ut ubique inter binos memoratos tubos maneat spatium tertiae partis vel dimidii digiti transuersi; longitudinis duorum pedum. Inferne ab e. ad f. clauditur hic capacior tubus per bracteam transuerse afferruminatur, medio duntaxat perforatam, pro transmittendo tubulo a. b. cui quoque firmiter afferruminatur, nulla relicta apertura. Tubuli d. inferius foramen, tubo dicto e. f. g. h. afferruminatum est antea facto foramin hoc maiori. Ergo aqua fluens e tubo d. defluet in tubum e. f. g. h., illumque replebit, et tubum a. b. in medio fitum ambiet, quem tamen nunquam intrare valet, sed duntaxat refrigerabit, si fuerit calidus. E tubulo e. f. g.h. aqua perpetuo affluens perpetuo effluit per superius foramen apertum, quia locus inter g. et h. inferius situs quam suprema pars tubi d. …”
(… The water falls into the funnel c. This funnel enters the channel d. (Fig. 2), whose composition is iron sheet covered with tin, cylindrical in shape, with the diameter of the hole about three quarters of the index, of such length that its upper orifice, where the funnel c. enters, is 2.3, 4 fingers higher than the level of points h. and g. Now take the tube e.f.g.h. which in the same figure surrounds the tube a.b. This tube, made of iron sheet, covered with tin, cylindrical in shape, is of such a diameter that between the two aforesaid tubes there remains the space of a third or half index; two feet long.
At the end from e. to f. this larger tube is closed by means of a sheet welded crosswise, perforated in the middle, to insert the smaller tube a.b. to which it is firmly welded with no opening left. The lower hole of the tube d. is welded to said tube e.f.g.h. after first drilling a hole in this larger tube.)
Weigel’s description is clear. They are two concentric tubes. The end of the device is closed by a foil, with a hole that allows the smaller tube to pass. In this end, in the upper part of the largest tube, a hole is made where the stem of the funnel is inserted, from where the cooling water arrives.
“Ergo aqua fluens e tubo d. defluet in tubum e.f.g.h., illumque replebit, et tubum a.b. in medio fitum ambiet, quem tamen nunquam intrare valet, sed duntaxat refrigerabit, si fuerit calidus. E tubulo e.f.g.h. aqua perpetuo affluens perpetuo effluit per superius foramen apertum, quia locus inter g. et h. inferius situs quam suprema pars tubi d.”
(So the water flowing from tube d. Will flow into tube e.f.g.h. and fill it, and surround the tube a.b. in the middle, which it cannot enter, however, but will naturally cool it if it is hot. In the tube e.f.g.h. the water flows continuously, fed continuously through the hole opened above, because the share of g. and h. is placed below the highest part of the tube d.)
The description of the device in section
“Ut eo melius mentem meam capiat confideret Figuram 4, quae sere vera magnitudine exit faciem extremitatis superioris, tubi capacioris e.f.g.h., ho scilicet quae inter h. et g. continetur, et adspicitur si oculus in b. sit conftitutus. In hac Figura 4, minimus circulus est tubus a.b. (Fig. 2) quasi sectus confideratus; medius circulus quasi sectum repraesentat tubum e.f.g.h. (Fig. 2). Inter hos binos circulos conspiciuntur tria spatia minora z.z.z. umbra notata, quae significant binos tubulos ibi connecti per intermedias tres bracteclas adferruminatas; sed duntaxat in hac extremitate, non vero per totam longitudinem tubi e.f.g.h. Spatia y.y.y. significant spatium inter binos tubulos (a.b. et e.f.g.h. Fig. 2) intermedium. Repletur hoc spatium aqua refrigerante perpetuo affluente, et per has aperturas perpetuo frigide effluente in canalem infundibulo instructum l.m., e quo defluit (Fig.5) per pavimentum laboratorii (cuius superficiem determinat linea horizontalis n.o. in canalem ligneum p.q. (Fig.6) per quem continuatum laboratorium ab omni aqua refrigeratoria affluente liberatur…”
(In order to better understand my thought, consider Figure 4 which shows in its real proportion the face of the upper end of the larger tube e.f.g.h., that is, the face of the upper end of the larger tube between h. e g. and it can be seen clearly if the eye in b. is fixed (Fig. 2) considered as sectioned;
the middle tube represents the e.f.g.h. tube as sectioned. Between these two tubes we observe three minor areas z.z.z. indicated in dark, which represent three laminae of iron connecting the two pipes; but only at this end, but not along the entire length of the pipe e.f.g.h. The spaces y.y.y. mean the intermediate space between the two pipes (a.b.; e.f.g.h. Fig. 2). This space is filled with cooling water flowing continuously, and through this opening it flows out flowing into the channel equipped with the l.m. funnel, from which it flows through the laboratory floor into the wooden channel p.q….)
At the end, the author concludes by listing the advantages of the equipment, including:
- The space of the laboratory is not restricted due to the refrigeration vessel
- The highest degree of refrigeration is achieved
- There is no loss of alcohol vapors
- The work is carried out without having to fear any danger of fire
- It saves energy and time
The chapter shows a second more realistic drawing of the device. Note the great resemblance to the apparatus from Liebig’s laboratory.
Weigel’s discovery is relatively recent by chemical historiography. Weigel’s apparatus is mentioned in Hermann Schelenz’s book “Zur Geschichte der pharmazeutischchemischen Destilliergeräte” (On the history of chemical-pharmaceutical stills) of 1911, almost one hundred and fifty years after its invention. Schelenz dedicates a few lines to Weigel’s device, of which he reports the image. However, the structure of the condenser is not clear from his brief description .
One exception was Prof. J. Michael McBride, R. M. Colgate Professor Emeritus of Chemistry, Department of Chemistry, Yale University, who in his chemistry course in 2001 mentions Weigel’s invention and reports the design of the device interpreting it correctly.
Weigel’s ingenious intuition of the counter-current condenser was conceived half a century before the “Liebig condenser”. It is not known whether Christian Ehrenfried Weigel’s work inspired others or went unnoticed. It is certain that his name was not linked to his invention for a long time. Liebig, as well as other chemists of his level in the first half of the nineteenth century, who daily used counter-current distillation in their laboratories, never mention the name of its inventor. Today we must return Weigel’s work to its place in history and give it a correct interpretation.
Christian Ehrenfried Weigel, Observationes Chemicae Et Mineralogicae , Gottinga 1771
Chemical Educ., 2006, 83, 23.
Hermann Schelenz, Zur Geschichte der pharmazeutischchemischen Destilliergeräte, Berlin 1911
Lesson – Prof. J. Michael McBride : – http://chem125.webspace.yale.edu/125/history99/4RadicalsTypes/condensers/liebigcondenser.htm