In working through the Mymer manuscripts, I have been struck on more than one occasion by their repeated references to dung. While calculating his expenses, for instance, Georg Mymer lists horse manure and coal alongside the various flasks he needs for his tinctures. 
Like coal, dried horse manure was used for heating. Maintaining constant heat at fixed temperature was exceedingly difficult in Georg’s day as people lacked the help of modern furnaces. With practice, alchemists like Georg became adept at controlling temperature by manipulating the flow of air into their fires and furnaces and by changing the material being burned. As Georg notes in his inventory, dung had the added benefit of being cheaper than coal.
Fresh manure was also a useful, if fragrant, heat source. The alchemist would bury his flask in manure. As the manure decomposed, it gave off a mild, but steady heat, which triggered a reaction with the flask, known as digestion. When the manure began to cool, the alchemist could simply replace it with a fresh supply. This setup came to be known as a venter equinus (the horse’s bowels).
While Georg’s interests in manure – at least as far as I have so far found – were limited to its use as a heat source, alchemy and dung had much a richer relationship. In closing this post, let me point out two additional uses of manure: (1) as an ingredient and (2) as criticism.
Dung was mixed with crushed clay to make lute (lutum sapientiae), the putty used to seal alchemical vessels. It was also used as an ingredient in medicines. In an earlier post on this blog, Jonathan Cey discussed how Paracelsus developed fecal medicines in the early modern period. Although he had a new take on the medicinal uses of poo, Paracelsus was preceded by a medieval tradition of fecal alchemy. Centuries earlier, the philosopher Morienus described the starting material of the Philosophers’ Stone as “of cheap price and found everywhere” and “trodden underfoot.” Medieval alchemists took that description literally and used the manure found all over their streets. As early as the fourteenth century, John of Rupescissa criticized this interpretation, but the practice persisted all the same.
At the same time, alchemists were warned about searching for gold in poo. Pseudo-Arnald of Villanova quipped in a rhyming couplet:
Qui quaerit in merdis secreta philosophorum
expensis perdit proprias, tempusque laborum
He who seeks the philosophers’ secret in shit
will waste his money, time, and labor on it.
Another couplet gets right to the point:
Qui merdam seminat, merdam et metet
He who sows shit, also reaps shit.
In order to reinforce this message, in the manuscript original, this line is written across the backside of an alchemist sitting on a toilet (garderobe). Some alchemists, as we have seen, really did use dung in their recipes, but for others these poems served as a vivid warning not to use subpar ingredients.
Perhaps the best application of manure to the alchemists’ art was suggested by one of its 16th-century German critics. In 1586, Johannes Clajus published Altkumistica; or The art of making gold out of dung: Against the fraudulent alchemists and unskilled Theophrastians (Altkumistica, das ist: Die Kunst aus Mist durch seine Wirckung Gold zu machen: Wider die betrieglichen Alchimisten, und ungeschickte vermeinte Theophrasisten). The title is a pun on alchemistica: “alt” meaning “old” and “kumist” meaning “cow manure”. In that work, Clajus argues that an alchemist would be best off if he used cow manure to fertilize a field, grow wheat, feed the cows that produced the manure in the first place, and sell both for a healthy profit in gold coins.
Sadly for Georg, who finished writing his notebook in 1571, the Altkumistica appeared too late for him to benefit from Clajus’ advice.
 Leiden University Library, Vossiani Chymici F19, fols. 80r-81v.
 Morienus, De compositione alchemiae. Cited in Lawrence M. Principe, The Secrets of Alchemy. (Chicago: The University of Chicago Press, 2013), 119.
 Lazarus Zetzner, ed., Theatrum Chemicum, vol. 3. (Strasbourg, 1659), 137; Munich, Bayerische Staatsbibliothek, Clm 25110, f.21v. The image is reproduced in Lawrence M. Principe, “Laboratorium,” in Alchemie: Lexikon einer hermetischen Wissenschaft, eds. Claus Priesner and Karen Figala (Munich: C.H. Beck, 1998), 210.
Both couplets were cited in Joachim Telle, Alchemie und Poesie: Deutsche Alchemikerdichtungen des 15. bis 17. Jahrhunderts. Untersuchungen und Texte (Berlin: De Gruyter, 2013), 323. English translations mine.
Additional Works Consulted
Nummedal, Tara. Alchemy and Authority in the Holy Roman Empire. Chicago: University of Chicago Press, 2007.
Priesner, Claus, and Karen Figala, eds. Alchemie: Lexikon einer hermetischen Wissenschaft. Munich: C.H. Beck, 1998. See especially the articles on “Arbeitsmethoden,” pp. 51-57 and “Laborgeräte,” pp. 211-15, by Lawrence M. Principe.