Boerhaave’s furnace: the search for peat

Last week, I heard on the news that global oil demand is expected to fall to a record low in 2020 due to the corona crisis. Given the significant role of fossil fuel combustion in climate change, this may not be such a bad thing. It also reminded me of a fossil fuel that has all but disappeared: peat. Although peat is not strictly a fossil fuel – it is renewable, but extremely slowly -, its greenhouse gas emissions are comparable to that of fossil fuels. When Ruben Verwaal and I were working on our project on Boerhaave’s chemical oven, about which we wrote before, one of the issues we struggled with was that of peat.

Our Boerhaave furnace with some glowing peat inside
Our Boerhaave furnace with some glowing peat inside

In his Elementa Chemiae, Boerhaave states that the furnace should be fuelled by ‘a glowing Dutch coal’ (Batavi prunam candefactam), first burnt until it yields no more smoke’, which is put on a thin layer of ash on the bottom of an earthenware vessel, and covered with a layer of ash as well. This, he claims, will produce ‘an equable, moderate heat’, which ‘may be kept up for near twenty-four hours.[1] This posed a number of problems. Primarily, this instruction raised the question what Boerhaave meant by ‘Dutch coal’, as no coal was mined in the Dutch Republic at the time. The only ‘Dutch’ coal mines at the time were in the south, in the area under Austrian Habsburg rule, which makes Dutch stone coal an unlikely option. Indeed, the 1741 English translation hints at a different kind of fuel: here, the translator speaks of ‘Dutch turf’ (Italics original).[2]

‘Turf’ is the Dutch term for peat. This was in fact produced in considerable amounts in the Dutch Republic and the most widely used fuel there in the eighteenth century.[3] It has been signalled before that availability of particular kinds of fuel influenced the design and use of furnaces. The increasing deforestation of Europe saw wood replaced by peat and coal, developments which shaped pyrotechnical innovations from the sixteenth century onwards.[4] Peat generally has a much lower heating value than wood and coal – it produces less energy than those fuels when burned.[5] Yet peat burns slowly and evenly; characteristics that indeed seem desirable for a small wooden furnace that can also supposedly be used to hatch eggs, a process that requires a constant temperature of 37.5°C in case of a chicken egg.

That did not solve the problem of what to fuel our furnace with: there are different varieties of peat, so which one did Boerhaave mean? The most distinctive types of peat produced in the Dutch Republic were those from high moors and low moors (hoogveen and laagveen). These peatlands were too wet to just dig the peat up and use it. High moors, mostly situated in the east of the country, could be drained by digging canals, but low moors, which were found predominantly in the west, could only be extracted by dredging the peat from water, and spreading this ‘mud’ on fields to dry, where it would be compacted by stamping it with wooden slats, after which it could be cut into chunks.[6]

Abraham Rademaker (1676/77-1735), Production of low moor sapric peat (‘slagturf’) near Amstelveen, about 30 kilometers from Leiden. Washed ink drawing. Reproduction courtesy of Noord-Hollands Archief, Provinciale Atlas – Prenten en Tekeningen, Inventarisnummer NL-HlmNHA_359_000279_K

Hence, peat from high moors tended to have a different structure than that from low ones. Moreover, there are various classification systems in use. The most commonly used one distinguishes fibric, hemic, and sapric peat. Fibric peats are the least decomposed and consist of intact plant fibers, and tend to be won from the top layers of soil. Hemic peats contain partially decomposed plants, and sapric peat is the most decomposed variety, dug from the deepest layers.[7] Hard sapric peat, especially from the low moors, was generally considered to be most suitable for heating houses, while the more loosely structured hemic peat from the high moors was predominantly used in businesses that required intensive heating such as those of dyers, brewers, and potters. Fibric peat was mainly used to fertilize soil. As peat had great economic value, trade was well-regulated. Local markets were protected, but specific varieties of peat were transported by special boats to other provinces and even countries where that specific variety was not available.[8]

Differently produced varieties of peat, Veenpark, October 2019. Left to right: automatically dug sapric peat, manually dug sapric peat, and manually dug hemic peat, all from a high moor. Photo: author.

These insights, gained from secondary literature and interviews with volunteers at the peat museum (Veenpark) in Barger-Compascuum in the east of the Netherlands, led us to believe that the Dutch peat Boerhaave was referring to was most likely hard sapric peat from low moors near Leiden, such as the area of Zoeterwoude, which had a long history of peat extraction.[9] This however created a new problem: fuel peat is no longer won commercially in the Netherlands, as its peat lands have long been depleted. And although the country imported 2,252 million kg of peat in 2018, this was almost exclusively fibric peat for gardening and greenhouse agriculture.[10] The only fuel peat we could find for sale was automatically dug, strongly pressed Irish peat, which for some obscure reason could only be purchased through a US web shop and took weeks to ship. Although this is indeed sapric peat, it is more likely to be from a high moor, and produced through automated digging, rather than won by hand. This makes for a much denser, dryer structure then when the peat is dug manually. However, it was the best we could find, and it forced us to keep in mind that the peat Boerhaave used may have burned differently than ours.

Looking back from the situation we are in now, these concerns may seem pedestrian. Maybe we can use them as a small reminder that people in the past too struggled with energy transitions and public health issues, and that for all the stupidity and misery in the world, there is also a lot of flexibility, creativity and inventiveness.

[1] Herman Boerhaave, Elementa Chemiae : Quae Anniversario Labore Docuit, in Publicis, Privatisque, Scholis, 3 vols.,vol. 1 (Lugduni Batavorum: Isaac Severinus, 1732), p. 888.

[2] Herman Boerhaave, A New Method of Chemistry : Including the History, Theory and Practice of the Art / Translated from the Original Latin of Dr. Boerhaave’s Elementa Chemiae, as Published by Himself. To Which Are Added, Notes and an Appendix, Shewing the Necessity and Utility of Enlarging the Bounds of Chemistry. By Peter Shaw., trans. Peter Shaw (London: T. Longman, 1741), p. 590.

[3] Jan Willem de Zeeuw, Peat and the Dutch Golden Age : the historical meaning of energy-attainability (Wageningen : Afdeling Agrarische Geschiedenis Landbouwhogeschool, 1978), p. 3-31.

[4] Archibald Clow, Nan L. Clow, The Chemical Revolution. A Contribution to Social Technology (London: Batchworth Press, 1952), pp. 27-29, 271. Peat too, has been used for glassmaking, albeit to a significantly lesser extent. Mogens Schlüter, “The Use of Peat in Danish Glassworks, 1825–1945.” Journal of Glass Studies 30 (1988), 94-101.

[5] For an overview of heating values, see.g.

[6] M.A.W. Gerding, Vier Eeuwen Turfwinning in Groningen, Friesland, Drenthe en Overijssel tussen 1550 en 1950 (‘t Goy-Houten: HES Uitgevers B.V., 1995), p. 34.

[7] Take Stol, De Veenkolonie Veenendaal. Turfwinning en waterstaat in het zuiden van de Gelderse vallei (Walburg Pers / Stichtse Historische Pers, 1992), pp. 148-150. For an overview of peat classification in English, see (last consulted 22 January 2020).

[8] Stol 1992, p. 150. A.J.J. van ‘t Riet, Meeten, boren, en besien. Turfwinning in de buitenrijnse ambachten van het Hoogheemraadschap van Rijnland 1680-1800 (PhD thesis, Leiden University, 2005), pp. 214-5.

[9] Boerhaave famously only left Leiden once in his life, in 1693, when he travelled to Harderwijk to obtain his degree in medicine. On peat production near Leiden, see Milja van Tielhof, “Turfwinning en Proletarisering in Rijnland 1530-1670,” Tijdschrift voor Economische en Sociale Geschiedenis, 2005, vol. 2:4, pp. 95-121.

[10] See (last consulted 22 February 2020).

A short history of respiratory illness epidemics (2)

*This blog post first appeared in Dutch on *

Last week, I discussed that from antiquity until well into the nineteenth century, the idea that contagious diseases were caused by the influence of celestial bodies, the weather, and climate, was common. We still see these ideas in our language: think of catching a cold. This explains why until the twentieth century, quarantines and isolations were not used to battle epidemic respiratory illnesses. After all, if an illness is caused by the weather, isolating patients has little use. The best option, usually only available to the wealthy, was to stay inside, warmly wrapped up.

Quarantining was an existing practice, but it was mostly used in other diseases. During a plague epidemic in Italy in the fourteenth century for example, the crew of mooring vessels was kept on the boat for forty days (quarantaine) to prevent infections.[1] So even though the contagious nature of some diseases and the fact that their spread can be stopped by isolating (suspected) patients have been understood for centuries, isolating patients with respiratory illnesses is a much more recent phenomenon. Only in 1898 did Dutch microbiologist Martinus Beijerinck coin the term ‘virus’ to describe what, up till that point, had been considered extremely small bacteria. And only in 1901 an influenza virus was first isolated, in poultry. The Spanish flu epidemic of 1918 was, in all likelihood, the first flu epidemic in which quarantine was used widely to manage the disease.

Detail of Jan Luyken, The Apothecary (1694), ets. Rijksmuseum RP-P-OB-44.502

Of course, people did try to manage and cure respiratory illness before the late nineteenth century too. Until the 1850s, most people depended on selfcare: ‘cures’ bought at the pharmacist, from herbal healers, or made from supplies from their own garden or pantry. Those who could afford it asked a doctor for advice, who would visit the patient at home and might give them a recipe for the apothecary. Hospitals were places where poor people would go if they were at the end of their tether, and no one could take care of them at home. Most people who went into a hospital had little hopes of coming out alive.[2]

Physicians like the Amsterdam medical doctor Steven Blankaart (1650-1704) advised rest and warm coverings in case of coughing and colds, very much in line with Hippocratic understandings of colds as caused by the weather. He also prescribed cures prepared by pharmacists, which could contain ingredients that we still use in cough medicine today, such as ginger and aniseed, but also plants and substances that have been nearly forgotten now. Blankaart warned that using sugary syrups and pastilles was useless, and that so-called plasters, swaths of fabric drenched in extracts, were no good either. The only possible exception were plasters containing substances like camphor, because the smell – much like Vicks VapoRub today – could ease the patient: “Some place plasters on the chest, but I cannot see what use they have, because this means should penetrate the lungs through the breastbone, which would be absurd, therefore these means are of no importance, unless they reek of Musk, Saffron, or Camphor, &C. And that smell by breathing it in could do something useful in our blood.”[3]

Sweets and substances that are quite similar to modern liquorice were popular though, something we see reflected in books like ‘The Perfect Dutch Kitchen Maid’ (De Volmaakte Hollandsche Keuken-Meid, 1752). Here ‘chest sugar’, sugar pastilles with expensive exotic spices like saffron or cloves, and ‘tablets of liquorice’, made from liquorice extract, aniseed, Arabic gum, and rosewater were recommended for colds and coughs respectively.[4]  Less prosperous citizens had to make do with drinks made of cucumber juice or marjoram, or brews with aniseed, fennel seed, liquorice, honey, or hyssop.[5]

Cures for colds and coughs, Steven Blankaart, Verhandelinge van de Opvoedinge En Ziekten Der Kinderen (Amsterdam: Hieronymus Swierts, 1684), p. 176.

Although such preparations, either made by the apothecary or at home from the pantry, were probably easing colds, they of course did not cure respiratory illnesses – although that is not that different today. In premodern descriptions of epidemics of respiratory illness, it is often noted in a rather off-hand way that it were mostly the elderly who died from them. ‘Elderly’ is relative of course, and in the past people grieved the loss of their loved ones too. But such remarks do suggest that death was much more present in everyday life than it is today; and that would not change until the second half of the nineteenth century.

Finally, we have seen over the past few weeks that scientists are trying to find a vaccine against covid-19. The first rudimentary vaccines in Europe, against smallpox, date back to the eighteenth century. In China and Asia, such immunisation practices had existed much longer.[6] Bacterial pneumonia could increasingly be treated successfully from the start of twentieth century, especially when penicillin became commercially available.  The Spanish flu epidemic of 1918 led to a search for new treatments for flu. This would eventually result in the first flu shots during World War II, developed by the American army.

The history of our understanding of and ways of dealing with epidemic respiratory illnesses thus shows that we have come to understand the causes, spreading, and effects of respiratory infections in completely new ways over the past 150 years. However, there is still a lot of confusion among the general public about the differences between flu, colds, and infections like covid-19. We have become much more successful in treating severe cases of lower respiratory tract infections, but the treatment of upper respiratory tract infections has not changed significantly since the seventeenth century. We have relatively little experience in the prevention, curtailing, and ‘flattening’ of epidemics of respiratory infections, which partly explains the wide variety of current measures.

[1] See e.g. Monica Green (ed.) “Pandemic Disease in the Medieval World”, special issue of The Medieval Globe, vol. 1, 2014.

[2] See e.g. Ruth Richardson, Death, Dissection, and the Destitute (Chicago: University of Chicago Press, 2001).

[3] Steven Blankaart, Verhandelinge van de Opvoedinge En Ziekten Der Kinderen (Amsterdam: Hieronymus Swierts, 1684), p. 173-180: “Op de borst leggen sommige Pleisters, maar ik kan niet sien wat groote nut zy konnen uitrichten, want dit Middel zoude moeten door het Borst-been tot in de Longe doordringen, het welke absurd soude zijn, derhalven zijn die Middelen mede al van geen belang, ten zy ze riekende zijn van Moschus, Saffraan, Campher, &c. En die reuk door het inademen onse sappen en bloed eenig nut aanbracht.”

[4] De Volmaakte Hollandsche Keuken-Meid… Als Meede Eenige Huismiddelen. Voor de Verkoudheid (Amsterdam: Steven van Esveldt, 1752)

[5] Evert Jan Thomassen a Thuessink, Prysverhandeling over de Vraag, Voorgesteld Door Het Geneeskundig Genootschap […] Servandis Civibus, in Hoe Verre Zou Men, by Gebrek van de Apotheek, Uit Kelder En Keuken de Vereischte Geneesmiddelen […] Kunnen Bekomen. (Amsterdam: Petrus Conradi, 1789), p. 11, 192. Heyman Jacobaus, Schat Der Armen, of Huismedicyn Boekje, 1606, p. 49, 197.

[6] See e.g. Anne Eriksen, “Cure or Protection? the Meaning of Smallpox Inoculation, ca. 1750—1775”, Medical History 57(4):516-36 (2013).

A short history of respiratory illness epidemics (1)

*This blog post first appeared in Dutch on the NL-Lab website on 31 March 2020*

The Netherlands are in lockdown to curb the covid-19 epidemic since prime minister Mark Rutte announced social distancing rules on 13 and 15 March. Since that time, various people have asked me, as a medical historian, ‘how we handled this kind of thing in the past’. By this they mean: how did people, both in the Netherlands and abroad, deal with epidemic respiratory infections in the past? The short answer would be: very different. The long answer could fill a book, but a blog post (or two) is written and read faster. This week part 1, on the history of our understanding of respiratory illnesses. Next week part 2, on treatments and management of respiratory illnesses.

Gabriël Metsu, The Sick Child, ca. 1664 – ca. 1666. Oil on canvas, h 32,2cm × b 27,2cm. Rijksmuseum.

We now understand respiratory infections as an infection of the mucous membranes of the airways, caused by pathogens such as bacteria and viruses. On the website of the Dutch National Institute of Public Health (RIVM), we read: “Infections of the upper respiratory tract, such as colds and sore throats, are usually caused by a virus and normally pass without treatment. Infections of the lower respiratory tract or for example pneumonia and bronchitis. These can be caused by both viruses and bacteria and can lead to severe illness. Pneumonia is an important cause of death in the Netherlands.”[1]

Confusingly, respiratory infections which can present with very similar symptoms, such as the common cold, flu, and covid-19, are caused by completely different viruses, which do not belong to the same taxonomic and morphological families. Cold virus (Rhinovirus) is part if the  Picornaviridae family; the four influenza viruses (A,B,C,D) are part of the Orthomyxoviridae family, and corona viruses such as are part of the Orthocoronavirinae family. Comparing covid-19 to ‘a flu’ hence is incorrect, not only clinically, but also taxonomically speaking.

Yet this is all very recent knowledge from a historical perspective. Although it has been known since antiquity that certain diseases are very contagious, and that their transmission can be stopped by isolating the ill from healthy people, that line of thought in general was not applied to respiratory infections or illnesses. The reason for that is that only in the late nineteenth century the role of viruses and bacteria in respiratory infections became clear, and that respiratory infections therefore can be contagious. Epidemic respiratory infections with flu-like symptoms have been described with some regularity since antiquity though. In Hypocrates’ Book of Epidemics, written around 410 BCE for example, we already find a description of a very contagious disease in the north of Greece, which sounds a lot like flu. Until the Middle Ages, throughout Europe a wide variety of epidemics is described. Nearly all of these epidemics, including those that appear to have been respiratory infections, were described as ‘plague’ or ‘pest’.

In Florence in 1357 an epidemic of ‘influenza’ was first documented.[2] The word influenza literally means ‘inlfuence’ in Italian. From antiquity until late in the nineteenth century people thought that many contagious diseases were actually caused by the influence of celestial bodies, weather, or climates – a believe still reflected in contemporary language, think of ‘flu’, the ‘common cold’, or catching ‘a cold’.[3] The influenza epidemic in Florence of 1375 was indeed most likely an ‘influenza di freddo’, a ‘cold influence’ or influenza epidemic. But until the eighteenth century, the word influenza, like plague, meant a (contagious) disease more generally. It appears that the term also did not spread throughout Europe until the eighteenth century. For example, Lord Chesterfield wrote in a letter to this son in 1767: ““a little fever that kills nobody but elderly people that is now called by a beautiful name: influenza”. [4]

Titel page of Hennert’s treatise, 1785

In the Netherlands, the word influenza first appeared by the end of the eighteenth century, as a synonym for the common cold, but used metaphorically rather than medically. The Utrecht professor of philosophy and mathematics J.F. Hennert for example in 1785 published a pamphlet with the title Special Effects of the Influenza, and the Cures Against that Contagious Disease.[5] It’s actually not a text on the symptoms and treatment of colds or flu, but a squib aimed a critic who tried to slander his work. Something similar is going on in The Lighter: Being an Elaborated Treatise on the Influenza, that is Public Cold, published in 1800 by army physician Pieter van Woensel.[6] On closer inspection, it’s not about physical colds at all, but about the spreading of dangerous political ideology.

The word ‘griep’ did not appear in Dutch until around 1800, when the French armies brought their grippe, which is most likely etymologically related to the German grippen (‘to catch’). Before that time, respiratory afflictions in Dutch were described using a wide variety of terms, such as verkoudheid, longontsteking, pneumonia, peripneumonia, consumptie, zydewee, pleuris, tering or Phthisis. Lacking a microbiolological understanding of respiratory illnesses, the categories in which they were divided were also much more fluid.[7] We should also be aware of the fact that such terms, even if they seem identical to modern words, had a different meaning for the people who used them in the eighteenth century. Understandings of illness are always simultaneously clinical and social, and separating those two dimensions is nearly impossible. Therefore, we cannot simply say that eighteenth-century consumption sufferers ‘actually’ had tuberculosis – after all, TBC did not exist in social, biological, and medical reality before 1882, the year in which the tuberculosis bacteria was first identified. Hence it is not useful either to assume that the ‘zydewee’ (‘side ache’) described by a seventeenth-century doctor was the same disease as modern pleurisy.

This of course does not mean that medical people did not think critically about the causes of various respiratory illnesses. According to the Amsterdam physician Steven Blankaart (1650-1704) for example, coughing in colds was caused either by ‘a salty and sharp substance excreted by the glands that cover the inside of the lungs’ or because of the fact that ‘the air sometimes contains more sour particles than other times, which are breathed in, sharpening the blood, and dismay the lung to coughing’.[8] But how were respiratory illnesses treated before the late nineteenth century? More next week!

[1], last consulted on 27-3-2020

[2] Bruno Lina, “History of Influenza Pandemics,” in Paleomicrobiology, by D. Raoult and M. Drancourt (Berlin: Springer, 2008), 199–211,

[3] A similar etymology is found in malaria: mal’aria literally means ‘bad air’ in Italian

[4] Lina 2008, p. 202.

[5] Johann Friedrich Hennert, Bijzondere Uitwerkzelen van de Influenza, En de Geneesmiddelen Tegen Die Besmettelijke Ziekte(Utrecht: A. van Paddenburg, Akademie drukker, 1785).

[6] Pieter Van Woensel, De Bij-Lichter, Zijnde Eene Uitgewerkte Verhandeling over de Influenza, Dat Is Publieke Verkoudheid(Amsterdam: In ’t Nieuwe Licht, 1800).

[7] E.g. Vanessa Harding, “Housing and Health in Early Modern London,” in Environment, Health and History, by Virginia Berridge and Martin Gorsky (Basingstoke: Palgrave Macmillan, 2012), 23–44, pp. 38.

[8] Steven Blankaart, De Kartesiaanse Academie Ofte, Institutie Der Medicyne (Amsterdam: Johannes ten Hoorn, 1683), p. 285. “een siltige en scherpe [stof] door de kliertjes die de longe-pijps rok van binnen bekleeden, uitsypert” (…) “de locht d’eene tijd meerder suure deeltjens by sich heeft als d’andere tijd, welk dan ingeademt wordende, het bloed scherper maakt, en de long tot hoesten ontstelt”.

A cool oven: Boerhaave’s little furnace, part II

*This post was first published on the Recipes Project on 13 December 2018*

By Ruben Verwaal and Marieke Hendriksen

Ruben Verwaal is curator of the historical collections at Erasmus Medical Centre, Rotterdam, and at the Museum for Communication in The Hague. He obtained his PhD in June 2018 with a thesis on the role of bodily fluids in eighteenth-century chemistry. Marieke Hendriksen is a researcher on the Artechne Project and PI at the Art DATIS Project at Utrecht University and a long-time contributor to The Recipes Project. She specializes in the material culture of science and art in the long eighteenth century. Ruben and Marieke share an obsession with an eighteenth-century object that has since disappeared: a small chemical furnace. In a previous post, they wrote about reconstructing Boerhaave’s little furnace. Now they have two…

The newly build oven, August 2018

In August of this year, we wrote about our first attemptto recreate Boerhaave’s little furnace from old coal stoves. Meanwhile, Marieke’s dad, André, who is a skilled carpenter, was building a furnace from scratch, using Boerhaave’s description and a nineteenth-century example of a Boerhaave furnace in the collection of Museum Gouda as his guidelines. This resulted in a sturdy furnace of solid dried oak, much larger than the furnace we created from coal stoves.

The interesting thing about Boerhaave’s furnace is that many of the experiments that he described in his chemistry book, the Elementa Chemiae, for which the furnace can be used, required a very moderate degree of heat – one could say a cool rather than a hot oven. Two examples we mentioned previously were the distillation of rosemary, and the hatching of eggs, which Boerhaave said he believed his furnace could be used for too. The kind of egg is not specified, but for chicken eggs, the ideal temperature for hatching is 37,6 Celsius. Could we attain that temperature with our furnaces?

Boerhaave advised to use glowing coals or Dutch turf as fuel, with which a constant and moderate heat should be achieved that could be kept up to 24 hours. As turf is no longer won in the Netherlands, we started with some ordinary barbeque coals – and indeed managed to establish a fairly constant heat of around 30 Celsius in the large oven for an hour or so. But coals did not hatch any chicks.

Coals: a stable 30 Celsius

Suspecting that turf may give better results, we set out to buy turf, which is still won in regions in Germany and Ireland. It turned out to be surprisingly difficult to buy in the Netherlands though. Eventually we managed to purchase a box of Irish turf through the American website of the online retailer we love to hate – but it took eight weeks (!) to arrive.  Though our cool oven still hasn’t incubated a chicken, the first results look promising.

Irish peat via the US
Irish peat via the US

Meanwhile, we started thinking about the experiments we’d like to recreate once we had all necessary materials. Since Ruben wrote his PhD thesis about bodily fluids, he is keen on reconstructing an experiment with milk from different mammals. Preferably, we’d compare the effects of prolonged mild heat on cow’s milk and human breast milk. Raw cow’s milk can be purchased at some farms, so Ruben cycled out to get some, while Marieke hesitantly contacted a friend who was pumping to feed her infant daughter to ask if she was willing to donate some of her leftovers to science. Note for future generations: Marieke has the coolest friends – she instantly said yes! For weeks, she gathered the left overs that her daughter did not drink in freezer bags.

Suddenly, it is December, and we have two furnaces, a box of Irish peat, and milk in two freezers. Now we ‘only’ have to make time for this reconstruction experiment… We live an hour apart and this is our pet project, so we’re desperately searching for a couple of days when we can take time of work. It turns out that the most difficult aspect of this reconstruction project is not the building of the furnaces or the sourcing of the necessary materials, but the absence of what Boerhaave obviously did have: cheap labour in the form of young assistants, who could take turns keeping the furnaces going day and night. We can only hope that once we do manage to take those days off, the Dutch winter is still as mild as it has been up till now!

The “Gentle Heat” of Boerhaave’s Little Furnace

This post first appeared on The Recipes Project on 23 August 2018.

By Ruben Verwaal and Marieke Hendriksen

Ruben Verwaal is curator of the historical collections at Erasmus Medical Centre, Rotterdam, and at the Museum for Communication in The Hague. He obtained his PhD in June 2018 with a thesis on the role of bodily fluids in eighteenth-century chemistry. Marieke Hendriksen is a postdoctoral researcher on the Artechne Project at Utrecht University and a long-time contributor to The Recipes Project. She specializes in the material culture of science and art in the long eighteenth century. Ruben and Marieke share an obsession with an eighteenth-century object that has since disappeared: a small chemical furnace.

With the introduction of chemistry into the university curriculum in the late seventeenth century, new practical needs arose for students  such as being able to perform experiments. Would it be possible to build a chemical furnace that provides a gentle heat, yields no smoke, and is safe for students to use? Herman Boerhaave (1668–1738) believed he found the perfect solution in, what came to be called, Boerhaave’s little furnace.

Portrait of Herman Boerhaave by Cornelis Troost, c. 1730.

Boerhaave was professor of medicine, botany and chemistry at Leiden University in the early 18th century.[1] Instead of starting with the most difficult experiments with metals and minerals, he was convinced that students were better off when they learned the techniques of through simpler processes, such as distilling leaves and flowers, and fermenting bodily fluids. But most chemical laboratories were equipped with elaborate devices too complicated for freshmen students, who in the eighteenth century could be as young as fourteen. Moreover, the brick-build furnaces were designed to create high temperatures, in which small and delicate materials like rosemary leaves would burn instantly.[2] Boerhaave hence needed a device that was low-cost, user-friendly, and would provide a gentle heat.

The plan for the oven, • H. Boerhaave, Elementa Chemiae, Quae Anniversario Labore Docuit in Publicis, Privatisque Scholis, (Leiden 1732).

A small wooden oven was the answer. Boerhaave claimed he had designed this type of furnace when he himself was studying chemistry in the 1690s. He opened the chapter on instruments in his chemistry textbook with the words: “I shall begin with my simplest furnace; which I invented forty years ago, when I practiced chemistry in no large study, where there was only one little chimney, and where I required several furnaces at once.”[3]

Woman at the Virginal and stove under her feet, by Jan Miense Molenaer, 1630-1640. Rijksmuseum, Amsterdam.

This kind of device was probably inspired by ordinary foot stoves. These little stoves, also known as foot warmers, were very popular in the Dutch Republic. Coming in a wide variety of shapes (square, octagonal, cylinder), these stoves often feature in books and paintings. Filled with glowing coals or peat, women placed the little stoves under their robes or blankets to keep warm.[4] Many foot stoves were equipped with a wire bail handle for lifting and easy transportation. Such stoves were used in carriages, sleighs, at home and in church to keep one’s feet warm. This ordinary foot warmer got new applications too, namely as tea and coffee stove,   and we suspect it was the model for the ‘simplest furnace’ in the Leiden chemical laboratory.

Woman carrying a little stove, Harmen ter Borch, 1648–1677. Rijksmuseum, Amsterdam.

The gentle heat produced by Boerhaave’s small oven proved very useful in performing all kinds of chemical experiments. Take rosemary, for example, the evergreen aromatic shrub. Distilled atop a “violent fire”, it would have been turned to flame, smoke, and ashes. But when rosemary instead was distilled at “summer-heat” (approx. 85º F), the mild operation would instead reveal the most volatile, fragrant and aromatic part of the plant ordinarily exhaled in summer. The same process could be applied to Angelica, basil, and all other aromatic plants.

Students in the Leiden laboratory, in Herman Boerhaave, Institutiones et experimenta chemiae (‘Paris’, 1724). Ghent University Library.

Boerhaave, in other words, attributed the success of his device to one’s control over gentle heat. Whenever the wooden oven was filled with hot pieces of coal or Dutch turf that was no longer smoking, it established a constant and moderate heat that could be kept up to 24 hours. As such, the instrument was perfect for students to perform all kinds of heating processes and distillations. In fact, he was so excited about this apparatus, that he claimed that “I believe eggs may be hatched by it”.[5]

Was Boerhaave’s little furnace really that user-friendly and effective as he claimed it was? We checked it out by recreating Boerhaave’s stove and performing experiments with it. Check out our next blog to entry to find out whether we succeeded!

Creating an oven from two old stoves… to be continued!


[1] More on Boerhaave, see Marieke Hendriksen, “Boerhaave’s Mineral Chemistry and Its Influence on Eighteenth-Century Pharmacy in the Netherlands and England”, Ambix(2018) and Ruben Verwaal, “The Nature of Blood: Debating Haematology and Blood Chemistry in the Eighteenth-Century Dutch Republic”, Early Science and Medicine(2017).

[2] Boerhaave, Elementa Chemiae (Leiden:  Isaac Severinus, 1732), vol 2, experiment 1.

[3] Ibid., vol 1.

[4] Le Francq van Berkhey,Natuurlyke historie van Holland (Amsterdam: Yntema and Tieboel, 1769–1778), vol. 3, 706-707, 1200.

[5] Boerhaave, Elementa Chemiae, vol 1.

The devil is in the details: turpentine varnish

Corrosion cast of bronchi and trachea, possibly from a rabbit, sheep, or dog, 1880-1890
Likely prepared by Harvard anatomist Samuel J. Mixter.
The Warren Anatomical Museum in the Francis A. Countway Library of Medicine

This post first appeared on The Recipes Project on 5 June 2018.

By Marieke Hendriksen

One of the first things you learn when you do reconstruction research is that the tiniest detail can make a difference.

Recently, I wanted to prepare an injection wax for corrosion preparations according to a 1790 recipe. Corrosion preparations are anatomical preparations created by injecting an organ with a fluid coloured wax that hardens. The organ is then lowered into a container with a corrosive substance, such as a hydrochloric acid solution, which corrodes the tissue, leaving a negative image of the veins and arteries of the organ. These preparations were made from at least the mid-eighteenth century, but because of their fragility, very few remain. As they were supposedly difficult to make, corrosion preparations were not only a way of studying anatomy, but also a tool for self-fashioning and establishing one’s status as an anatomist.

I have tried to create an injected preparation in the past.[1]It was my first attempt at reconstruction research ever, and although it served me well at the time, now I do things differently.

Most importantly, I want to stay much closer to the original recipe if possible. When we made the injected preparations in 2012, we used modern substitutes for some historical ingredients for economic reasons, and we did not have the time to study every ingredient in detail, substituting those we could not find directly with something we thought would have pretty much the same effect.

The recipe I want to use, Thomas Pole’s 1790 instruction for making a corrosion preparation, calls for a coarse red wax, made from fifteen ounces of yellow bees wax, eight ounces of white resin, six ounces of turpentine varnish, and three ounces of vermillion or carmine red.[2]The wax, resin, and pigment are fairly straightforward.

What is turpentine varnish though? Back in 2012, we ended up using just turpentine rather than turpentine varnish, and although those injections were not meant to be corroded, we ran into numerous problems. For example, it turned out to be almost impossible to keep the wax and the organs at a temperature at which we could both handle it and have it fluid enough to inject. It made me wonder whether sticking with the original recipe could solve that problem, so I set out to recreate it.

This turned out to be more complicated than expected, as there is not one standard recipe for turpentine varnish. Eventually I found a Dutch recipe from 1832 listing a turpentine varnish to finish display cabinets for natural history collections.[3]The ingredients are a pound of oil of turpentine, 8 ‘loot’ (a loot being 1/32 Dutch pound) of white resin, four loot of Venice turpentine, and ½ loot of aloe or kolokwint. Raw larch turpentine has a high concentration of volatile oils that can be distilled. The fluid part is known as oil of turpentine, whereas the residue left in the retort is usually called resin, rosin, or colophony. Oil of turpentine is the essential oil that remains after distilling raw larch turpentine. Venice turpentineis a thick, viscous exudation from the Austrian larch tree, which is not used as a varnish on its own as it becomes dark and brittle when exposed to oxygen and light. Aloe vera is widely known; kolokwint (the Dutch name for Citrullus colocynthisor bitter apple) less so. It is a plant with yellow fruits that resemble small pumpkins, which are very bitter and poisonous. That quality might explain its presence in a recipe for a varnish that is meant to ward off insects. Powdered aloe is readily available from artist’s material suppliers, so I went with that.

The varnish after 10 hours in the sun. The Aloe is the clearly visible murkiness on the bottom. Photograph: author.

The preparation of the varnish was pretty straightforward: put all ingredients in a bottle, cover, and leave in the sun for a day. The only problem was that I had to wait a week for a sunny day. When it came, I put in the ingredients and just left the bottle out in the sun for a couple of hours, which allowed me to stir the ingredients together. The aloe however did not resolve properly, and just sits at the bottom of the jar. While this might not be much of a problem when the varnish is applied to a cabinet, it makes this particular turpentine varnish unsuitable for use in my injection wax. Next time, I will make another batch without aloe and use that instead.

Why do I recount this–admittedly not very exciting–story? It shows how difficult it can be to follow a historical recipe to the letter. It also shows how much you learn from reconstruction research, even if it does not always yield the results you’d like, or as fast as you’d like.

[1]Marieke Hendriksen, Elegant Anatomy, (Leiden: Brill 2015), pp. 1-9.

[2]Thomas Pole, The Anatomical Instructor ; or an Illustration of the Modern and Most Approved Methods of Preparing and Preserving the Different Parts of the Human Body and of Quadrupeds by Injection, Corrosion, Maceration, Distention, Articulation, Modelling, &C(London: Couchman & Fry, 1790), pp. 21-5, 122-42.

[3] S. de Grebber, Over de schadelijke huisinsekten, als de huisvliegen, wespen, muggen, weegluizen, vlooijen, luizen, motten, pels-, boek- en kruidkevers en wormen, hout-, blad- en schildluizen, plantmijten enz., met aanwijzing van voldoende en proefhoudende middelen, om dezelve geheel uit te roeijen, Volume 1,(Amsterdam, 1832), pp. 52-3.


This blog first appeared on The Recipes Project on 15 March 2018

Fermenting indigo at Ock Pop Tock, Laos. January 2018.

When you say indigo, the first thing many people will think of is blue – jeans blue. (Or if you’re me, you’ll think first of a seventeenth-century recipe to make decorative blue prunes from wax with indigo. Occupational deformation.) But historically, indigo has been used in many more ways, and to make more dye colours than just blue, as I recently discovered. Today, most jeans are died using a synthetic blue dye, but indigo dyes, made from some of the over 750 species of the genus Indigofera as well as from some other plants, have been used to dye textiles for at least 6,000 years, while other subspecies of Indigofera were traditionally used as analgesics with anti-inflammatory properties.

The term ‘indigo’ according to the OED started to occur from the sixteenth century onwards in various European languages to denote blue dyes from India (or east Asia more generally), but can now also refer more generally to dyes, violet-blue light, or blue hues. It might be argued that the term only really applies to dyes created from Indigofera subspecies, while it could also be said that indigo is any dye created from plants through the decomposition of the glucoside indican, which exists not merely in the indigo-plant, but in woad and various other plants too.

While on holiday in Luang Prabang, Laos, I took a weaving and dying workshop with Ock Pop Tock, an organization that was established to preserve the traditional Laotian craft of making hand-loomed textiles. There, I discovered that there is more indigo besides Indigofera, and that one indigo plant can give many more dyes than just blue. They also have a wonderful informative website on natural dyes. At Ock Pop Tock, the plant species used to create indigo dyes is Persicaria tinctoria, or long leaf Japanese indigo, a plant indigenous not to Japan but to China, Vietnam, and Laos. Depending on how the leaves are treated, it can be used to create blue, green, black, and mauve.

…give them a good pounding to create a dye.

Using the fresh leaves creates a green dye, fermenting them for at least five days and adding limestone as a mordant gives a blue dye. Traditionally, the Lao believed that the dye was female, and that it fermented because it attracted a male spirit. To coax the spirit, the pots containing the dye would be dressed in a skirt, and a knife placed on top of the lid to ward off evil spirits that could ruin the dye. The fermentation is actually a naturally occurring oxidation process, with atmospheric oxygen as the oxidant. Regular stirring ensures the process continues. The longer the indigo mixture is left to ferment, the darker it turns. If this mixture is boiled, it turns black. Alternatively, a rare indigenous plant, mak bow or bow vine, can be added to the blue dye to create mauve.

The end result: a beautiful scarf

As part of the half-day workshop, I got to dye a silk scarf with a dye of my choice. I love green hues and wanted to make a dye from start to finish, so I chose to dye my scarf ‘indigo’ green. This was, apart from some pretty intense pounding of leaves, surprisingly easy. I got to pick freshPersicaria tinctoria leaves in the beautiful garden, washed them, and mashed them vigorously in a mortar for about five minutes. Then I transferred the mashed leaves into a tub, added some cold water and then the raw silk scarf. After kneading the dye into the fabric for a couple of minutes, I could rinse my scarf and hang it to dry. The end result is a beautiful soft green scarf, that is not just a souvenir, but a tangible reminder of the traditional Laotian knowledge about natural dyes preserved and shared at Ock Pop Tock.

Teaching a Perfect Knowledge in the Arts and Sciences: Robert Dossie’s chemical, pharmaceutical, and artistic handbooks

Front page to a 1796 reprint of Dossie’s Handmaid

*This post first appeared on The Recipes Project Blog on 7 December 2017*

By Marieke Hendriksen

Robert Dossie (1717-1777) was and English apothecary, experimental chemist, and writer. Within just three years, he published three very successful handbooks: The elaboratory laid open (1758) on chemistry and pharmacy for ‘all practitioners of medicine’, Theory and practice of chirurgical pharmacy (1761) for surgeons, and The handmaid to the arts (1758), which taught ‘a perfect knowledge of the Materia Pictoriae’ such as painting, gilding, and japanning. Gibbs (1951, 1953) has written a short overview of Dossie’s life and work, with a focus on his role in the Society of the Arts, but paid no attention to the cohesion of his seemingly divergent work.

Lowengard (2006) has briefly noted that Dossie used a form typical for books about materia medica for his book on the arts, grouping the contents according to techniques employed as well as by the media to which they might be applied, yet his work has never been thoroughly analyzed. Did Dossie indeed transmit a way of structuring and presenting practical knowledge in text from one realm to another? Recipe collections and how-to books before the eighteenth century were often a mixture of medicinal and artisanal recipes and instructions, and the boundaries between medicine, chemistry, and the preparation and application of artist’s materials often so fluid as to be almost non-existent.

Moreover, some earlier printed books on painting and dying techniques did employ the format of a systematic discussion of materials and their preparations, followed by their application, for example Willem Goeree’s 1760 Verlichterie-kunde  What was novel about Dossie’s Handmaid of the Arts though was the combination of this way of presenting practical artisanal knowledge, his attempt to be encyclopaedic in his collection – listing the uses of the same base materials in the production of various artistic and decorative objects, and his very intentional use of the term ‘Materia Pictoriae’.

Rubia tinctorium (madder), one of the many plants that was both materia medica and materia pictoria

The latter appears to have been an attempt to subtly elevate the status of the visual and decorative arts by paralleling the materia pictoriae to the materia medica. Finally, the intended audience gives us more insight in how Dossie understood his own work. From the preface of the book, it appears that Dossie did not so much aim at the people creating visual and decorative objects, but at the professional preparers of artist’s materials, of whom he wrote: “a much greater share of knowledge in natural history, experimental philosophy, and chymistry, is required to the understanding the nature of the simples [sic], and principles of the composition, in a speculative light, than is consistent with the study of other subjects more immediately necessary to an artist.” (p. vii-viii)

In eighteenth-century England, high street chemists and druggists were evolving from preparers and sellers of chemical substances to compounders, stockists, and sellers of drugs and dispensers of medical advice, and it is in this light that Dossie’ work and his division between materia medica and materia pictorial must be seen. Did Dossie intentionally and successfully adapt and implement formats and language traditionally used in one field (medicine) for the organization and transmission of practical knowledge in text to others (chemistry and the arts)? To me it appears that in his mind, materia medica and materia pictoriae were both branches on the tree of chemistry, and that his corpus, which we now tend to see as divergent, was actually a cohesive body of work to him and his contemporaries.


Dupré, Sven, ed. Laboratories of Art : Alchemy and Art Technology from Antiquity to the 18th Century. Archimedes 37. Cham [u.a.]: Springer, 2014.

Gibbs, F.W. “Robert Dossie (1717–77) A Further Bibliographical Note.” Annals of Science 9, no. 2 (1953): 191–93.

Gibbs, F.W.  “Robert Dossie (1717–1777) and the Society of Arts.” Annals of Science 7, no. 2 (1951): 149–72.

Lowengard, Sarah. The Creation of Color in Eighteenth-Century Europe. Columbia University Press, 2006.

Worling, Peter M. ‘Pharmacy in the Early Modern World, 1617 to 1841 AD’, in Making Medicines: A Brief History of Pharmacy and Pharmaceuticals, ed. by Stuart Anderson (London: Pharmaceutical Press, 2005), pp. 57–76.



The Making of Technique in the Arts: Concepts and Practice from the Sixteenth to the Twentieth Century

*This blog was originally published on The ARTECHNE Project Blog on 26 September 2017*

By Marieke Hendriksen

“Peintures en huile, en miniature et encaustique,” Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 8 (plates) (Paris, 1771). Plate I: Painting, Atelier, Paint Pallet and Brushes.

The terms ‘technique’ and ‘technical’ are used widely in relation to art, art history and science today, both to refer to the technical analysis of artworks and to a more holistic analysis of creative processes. Yet we do not have a history of the shifting meanings of the term ‘technique’ in the arts and sciences. The word ‘technique’ was a neologism in the vernacular, and started to appear in treatises on arts and sciences from the middle of the eighteenth century. Rooted in the Greek techne, which was translated routinely as ‘art’ until the mid-eighteenth century, technique referred to processes of making or doing and their products. Such processes had been described to previously as ‘art’, ‘methods’, ‘manners’ or ‘mechanics’ in the vernacular, and they were recorded in text with the intention of documenting and/or transmitting practical skills and knowledge.

On 26 and 27 October, Sven Dupré and I are hosting an international workshop at Utrecht University with the aim of bridging the gap between the changing concept of technique and the practices currently described by it. Questions we seek to answer are for example: how was what we now call ‘technique’ in the arts and sciences described and understood before the term took hold? More specifically, how were techniques in the arts described between 1500 and 1900? What kind of written sources can we distinguish, which terms were used to describe and instruct technique in various languages, and who were the intended audiences of these works?

Hans-Jörg Rheinberger will give a public keynote lecture, entitled “The Hands of the Engraver – Albert Flocon meets Gaston Bachelard”

Moreover, we will look at the linguistic history of technique in the arts, with questions such as why the term ‘technique’ first emerged around 1750, and what did it mean initially to artists, art theorists, and natural philosophers? Is there a connection with the emergence of categories such as aesthetics, fine art, craft, mechanics, and technology? Did the meaning of ‘technique’ and related concepts vary between periods, practices, and European languages, and how can we use data and concept mining to understand this? What do we mean by ‘technique’ in relation to art now, and can we use the same word to describe historical knowledge and practices?

Another issue closely related to the understanding of the concept of ‘technique’ in the arts is the development of so-called somatic language. Somatic language to describe measurements and sensory characteristics of materials traditionally played an important role in technical art texts, but seems to become rarer or more standardized over time. This kind of language guides the reader’s posture, as well as the use of their own body, and tools and materials, yet it is often unspecific and metaphorical (‘shift your weight’, ‘a handful’, ‘like yoghurt’), and meanings and interpretation can vary wildly in different languages, times, and cultures. How did the use of this kind of somatic language change in Europe between 1500 and 1950? What was the influence of standardization on conservation practices?

During the workshop, we will discuss these and related questions in panels of specialists from a variety of fields, such as history, art history, intellectual history, philosophy, and linguistics. Each interdisciplinary panel will focus on a particular concept, but there will also be ample time for exchange between the various panels.

Limited seating is available, please contact if you are interested in attending.  

Transmitting technique between disciplines: the anatomical models of William Rush (1756-1833)

*This blog was originally published on The ARTECHNE Project Blog on 9 March 2017*

A travel grant from the Wood Institute at the College of Physicians of Philadelphia recently allowed me to do research in their library and archives. Established in 1786, the College holds a wonderful collection of manuscripts and printed works. As I am particularly interested in the transmission of art technical knowledge in the long eighteenth century between medical men and people we would now describe as artists or craftsmen, I started looking for connections between such people in Philadelphia. I did not have to search long, for Philadelphia in 1800 had a population of only 41,220, but it was a fast-growing trading hub with two medical colleges, and an art academy was about to be established. This meant that many Philadelphians in the middle and upper classes knew each other personally – some were even related.

William Rush, Tragedy, 1808. Pine (originally painted). Copyright: Philadelphia Museum of Art.

Philadelphia-born William Rush had started his career as a carver of ship figureheads, learning the trade from his father and the famous Edward Cutbush. He was one of the founders of the Pennsylvania Academy of the Fine Arts (est. 1805), and from the early nineteenth century onwards, he created a number of sculptures for public places in Philadelphia. Caspar Wistar (1761-1818), professor of chemistry and the institutes of medicine at the College of Philadelphia, was a skilled maker of anatomical preparations and models, which he created by injecting organs with wax. However, when the number of students attending his classes greatly increased in the early decades of the nineteenth century, he decided he needed something more dramatic as a teaching aid: enlarged models of human anatomy, which would be visible even at the back rows. Realizing that this surpassed his own modelling skills, he turned to Rush, who made at least twenty models for him.

Model of the Right Maxilla by William Rush, c. 1808

As is so often the case when people are physically close, no primary written records –such as letters- remain of this collaboration between Wistar and Rush. However, their collaboration shows that there were strong connections between medical men and visual artists and craftsmen in Philadelphia around 1800. It is likely that Wistar and Rush already knew each other before they started working together. Not only was Philadelphia’s population fairly small, William Rush was a full cousin of a colleague of Wistar’s, the famous Philadelphian physician and professor of chemistry Benjamin Rush (1746-1813). Moreover, Wistar came from a family of craftspeople himself: his grandfather and namesake (1696 –1752) was a German-born
William Rush, Portrait bust of Caspar Wistar, ca. 1812-13. Terracotta. Copyright: Pennsylvania Academy of the Fine Arts

glassmaker. Both Benjamin Rush and Caspar Wistar studied in Edinburgh, and the latter corresponded with Thomas Pole, a fellow Quaker and the Philadelphia-born author of the 1790 The Anatomical Instructor, a handbook that describes, amongst others, how to make anatomical preparations and models from a variety of materials – although wood was not one of them.

So although in this case there is no evidence that Wistar taught Rush anatomy or that Rush taught Wistar practical skills for model making, it is clear that they must have been very aware of each other’s knowledge and skills, and it is rather unlikely that they never learned anything from each other. In any case, Rush successfully transmitted his technique from one discipline to another: from artistic sculpting to anatomical model making.