Much has been written on where and when gunpowder was first introduced. This paper offers a credible hypothesis to explain why and how the unique mixture may have come about.

Saltpetre is often referred to as the heart or soul of gunpowder and indeed the nitrate ion is the sole source of the gasses that give gunpowder its explosive properties. It can be substituted, albeit with varying success, by other oxidisers but the unique burning properties of gunpowder derive almost entirely from the ability of charcoal to release those gasses. Naïve equations for the gunpowder reaction commonly depict charcoal as C, the chemical element carbon. The errors that this introduces into subsequent arguments are examined. The development of the charring process from ‘domestic’ to a well controlled industrial process is examined with evidence of the early use of ‘cylinder charcoal’.

Arguably the most important Western source on the early history of gunpowder technology is the late thirteenth century manuscript, Das Fuerwerkbuch. When it was translated into English in 2000, it contained a commentary on the chemistry of many of the formulations given. These were largely dismissed as useless alchemical nonsense which could not work. Although some mysteries remain, much of the formulation can be understood either as contemporary 'best practice' or by comparison with modern pyrotechnic and explosive knowledge. This paper re-examines the underlying chemistry and demonstrates some surprising innovations anticipating much later claims. Note An extended and peer reviewed copy of this paper was published in ICON Vol 21, 2015 available at https://www.jstor.org/stable/24721698?seq=1#page_scan_tab_contents

Medieval gunpowder recipes of potassium nitrate (KNO 3), charcoal (C), and sulfur (S 8) were investigated by bomb calorimetry to determine their enthalpies of combustion and by differential scanning calorimetry (DSC) to determine their preignition and propagative ignition enthalpies. Various sample preparation methods and several additional ingredients were also tested to determine any effects on the thermodynamic values. Gunpowder recipes were prepared and used in a replica cannon that was manufactured and operated according to medieval records. Post-firing residues were collected from the bomb calorimeter and the cannon in efforts to further characterize recipe energetics using DSC. In general, during the period of 1338−1400, the %KNO 3 increased, and heats of combustion decreased, while between 1400 and 1460, the %KNO 3 decreased, and heats of combustion increased. However, since KNO 3 was usually found in the post-bomb calorimetry and post-cannon firing residues, it was not the limiting reactant. The highest pre-ignition and propagative ignition energies occurred when the KNO 3 :S 8 ratio was 3:1 as determined by DSC, and the highest enthalpies of combustion were measured for recipes where the KNO 3 :C ratio was 1:1 as determined by bomb calorimetry.

In 2001 The Arms and Armour Society sponsored a translation of Das Feuerwerkbuch. (FWB) This manuscript contains the earliest (Western) references to gunpowder. The editorial comment of the translation contained the unsubstantiated assertion that, since certain processes were not specifically mentioned in the text, they were not carried out and that consequently the nitrate of medieval gunpowder was calcium based. This has been shown to be incorrect but the concept seems to have taken root among some historians unable to understand the clear technical evidence in the manuscript.ii Although the processes described in the FWB were evidently capable of delivering substantially pure potassium nitrate, there remains a possibility that some calcium (or magnesium) nitrate could remain as a minor impurity sufficient to affect the quality of the gunpowder. This present paper gives evidence that such contamination was sometimes (but not always) present but was neutralised during the manufacturing process.

The paper takes up again, with additions and updatings, a work already presented in Italian at the XXXXIV Settimana di studi dell'Istituto internazionale di Storia economica "F. Datini" (Prato, Italy), April 15-19 2002).

Saltpetre in medieval gunpowder; Calcium or Potassium Nitrate? Until recently, it has been accepted that the formulation of gunpowder has always been based on variable mixtures of charcoal, sulphur and potassium nitrate. This has recently been challenged. It has been asserted that early gunpowder was based on lime saltpetre that is calcium nitrate. This paper examines that claim.