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]

Picture1
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]

Picture2
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. https://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html

[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 http://www.fao.org/3/x5872e/x5872e07.htm (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 https://opendata.cbs.nl/statline/#/CBS/nl/dataset/81268ned/table?dl=2378F (last consulted 22 February 2020).

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