We tend to associate the 18th century with the use of coal and iron, and to look back on the 16th and 17th centuries as, in John U. Nef's phrase, "an age of timber." But the growing importance of coal technology, especially in England, should not obscure the dependence on forests of virtually all aspects of material culture during the 18th century. Not only did mining consume large amounts of wood; so, too, did potash plants, tanneries, glassworks, saltpeter works, train-oil works, lime production, and other industries rely on the forests for fuel and raw materials. Domestic demands included fuel for heating houses and drying grain and malt, and timber for houses, fences, ships, carts, barrels, and agricultural implements. This vital natural resource, however, was perceived to be running out in 18th-century Europe. The fear of imminent shortages spurred both legislative actions and interest in technical improvements aimed at reducing the number of trees felled.
In the 18th century, Sweden—a country devoid of fossil fuel resources for all practical purposes—was gripped by general anxiety about a dearth of timber. It was believed that the forests were laid
waste by excessive felling: "many large areas of the realm are in danger of soon becoming desolate because of the shortage of timber and. . . the mines and towns in many parts of the country are likewise threatened with ruin that cannot long be postponed if an early remedy is not found." In the worst-case scenario, "the fatherland will in the course of time be reduced to a miserable condition." Whether or not the fear of timber shortage was well founded does not concern us here. What matters is that the belief in imminent shortage was widespread and influential.
The production of bar iron accounted for about 70 percent of Sweden's exports in the 18th century. About 50,000 tons of bar iron were produced every year, and every stage of production required much timber. Blast furnaces and forges consumed charcoal equivalent to three million cubic meters of timber a year. Charcoal-burning amounted to half of the total industrial consumption of timber. There were two alternative methods of charcoal-burning: stacking the wood either horizontally in piles called liggmilor or vertically in resmilor . Despite the fear of a forest shortage and the great consumption of wood for charcoal-burning, evaluations of the two methods of extracting charcoal from wood were not easily undertaken; the question was not resolved until the early 19th century.
In 1811 the Swedish Ironmasters' Association financed a series of experiments to assess the relative merits of resmilor and liggmilor and to determine the pile design yielding the maximum amount of charcoal. The report was published as a monograph three years later by the mining official Carl David af Uhr. It was an impressive volume, comparable in scope and depth to the report on the hydrodynamic experiments undertaken at the same time, also with the support of
the Swedish Ironmasters' Association. Uhr's report described the series of experiments in charcoal burning carried out at Furudahls Ironworks in the province of Dalecarlia during the years 1811–3. No less than forty full-scale piles of different types were tested, with twenty parameters recorded for each pile (fig. 10.1). The systematic study was meticulously planned: for example, a specially designed tool was used to measure the diameter of the billets at both ends, in order to compensate for their taper ("frustra of a cone, as they truly are") when calculating the volume of a pile. The volume of the piles was measured in cubic ells to one or two decimal places. The author discusses the effect of various errors in measurement and ways to compensate for these errors. Output, measured in cubic ells of charcoal, was correlated to the total labor, measured in man-days and horse-days, needed from the day the trees were felled to the day the charcoal arrived at the ironworks. Calorimetric experiments helped determine the quality of the charcoal, prompting Uhr to discuss Lavoisier's opinion of the role of oxygen in combustion. He handled this question with the same facility he showed in computing the number of horse-days needed to build a charcoal pile. Results of this study were summarized in a handbook for charcoal-burners that appeared in three editions—a measure of its success.
One looks in vain for quantitative methods in the literature on charcoal-burning at midcentury. In assessing the relative merits of resmilor and liggmilor the quantity of wood was not specified; nor was it clear which units were used in measuring the charcoal. Consider Magnus Wallner, who published at his own expense A brief account of charcoal-burning in Sweden , a Swedish translation of his dissertation under Celsius at the University of Uppsala. The work
contained a brief description of methods and tools, statements by charcoal-burners, a few quotations from foreign literature on the subject, and some of Wallner's own ideas. Entirely lacking was any attempt to give quantities in defined units and to carry out systematic experiments under controlled conditions.
The failure in applying quantitative methods to charcoal-burning may be attributed to the lack of institutions able to recreate a laboratory environment in the forest. No retort on a laboratory bench could reveal the best type of pile for charcoal-burning. "Systematic experimentation" required building many piles of different types and supervising them day and night for several weeks. It was necessary to take into account the species, age, and moisture of the wood; the length and thickness of the billets; the stacking pattern; the total amount of wood; the outer dimensions of the pile; and the ignition method. After the piles were pulled down, the charcoal had to be shoveled into barrels of known size—"quantification in fixed units." All this was far different from laboratory work. It differed first in spatial terms—not only the size of the piles but also the area of the forest required for the tests was large. The temporal requirements were also of a different order. Because building, watching, and pulling down a pile took more than a month, a series of systematic experiments might stretch over several years. Such was the case with the investigations carried out by the Swedish Ironmasters' Association in 1811–3.
The social organization of the work process also argued against a comprehensive study undertaken by an individual and resulting in useful data. Charcoal-burning was a huge, decentralized system of production: peasants and crofters labored under the tenant's obligation to deliver charcoal to the ironworks. Production was the responsibility of individuals, tens of thousands of peasants and crofters, each working independently, deep in the forests. Work in the forest was linked with the changing of the seasons and the tilling of the soil. In autumn, after the harvest, wood was burned to charcoal in the forest
where it had been felled; in winter, when the snow made the pathless forest passable, sledges carried charcoal to the ironworks. The methods of charcoal burning were the product of local conditions and tradition; the variety of circumstances was reflected in the names of different sorts of charcoal piles. To hammer this decentralized variety of methods and measures into a standard form amenable to quantitative comparisons seemed impossible. Hence Wallner contented himself in 1746 with publishing the views he had elicited from charcoal-burners he had met and a few quotations from foreign literature, together with his own individual, casual observations.
That charcoal-burning—like most technologies at the time—was a nonverbal technology complicated the problem of quantification. Witness the failure of the encyclopedists in their attempt to gather and record technical know-how of existing practices like charcoal-burning. John R. Harris has argued that "the difficulties of imparting craft skills by literary and graphic means" limited the "technological gain" possible from the 18th-century encyclopedias. The difficulties of improving a nonverbal technology were akin to the problems of describing it. A process could not easily be formulated as an intellectual problem and reduced to quantitative terms outside the realm of practical experience.
Science first met technology at the edge of the woods, when the sledges loaded with charcoal approached the ironworks to deliver their products. Only here could the individual ironmaster exercise some control over production by making sure that the peasants and crofters delivered the agreed amount of charcoal. Here the ironmaster might enlist the aid of geometry. Two articles in the Proceedings of the Royal Swedish Academy of Sciences addressed his concerns.
They were devoted to the mathematical problem of calculating the volume of the rhombically shaped sledges that carried the charcoal (fig. 10.2). Together, however, the ironmasters could marshal resources enough to launch a concerted, large-scale attack on the technical problem of charcoal production.