Abstract
Objective: Given that natural saltpeter deposits are absent in Japan, the artificial production of saltpeter was necessary from the Azuchi-Momoyama period to the end of the Edo period for the manufacture of gunpowder. The methods of saltpeter production in Japan are generally known as the Kodo-hou, Baiyohou and Shousekikyu-hou methods.
Methods: In this study, the origin of these production methods was examined through a review of historical literature, on-site investigations, and analysis of subfloor soil. To clarify the origin of saltpeter production in Japan, the subfloor soil of houses built several decades ago and soil generated using the Baiyo-hou method were analyzed, historical literature on saltpeter production was reviewed, and interviews in Tanegashima were conducted.
Results and Discussion: Analysis of subfloor soil and interviews with homeowners revealed that the concentration of nitrate was higher in the subfloor soil of houses that had formerly been used for silkworm farming and livestock sheds than in the subfloor soil of ordinary households. The concentration of nitrate was higher in soil supplemented with silkworm feces than in ordinary subfloor soil. Tanegashima, which is historically known for being a site where firearms were introduced to Japan, provided an appropriate environment for saltpeter production because of its significance in the Nanban trade. Tanegashima was covered with various pastures known as Maki, indicating that soils were often enriched in nitrate around the island. During the Sengoku period, information on saltpeter production, including the Kodo-hou method, reached the Daimyos region in western and southern Japan. Saltpeter manufacturing via the Kodo-hou method was derived from Western countries given that wood ash was not used to produce saltpeter in China.
Conclusion: The Kodo-hou method of saltpeter production was possibly first used in Tanegashima, which was strategically located in a key area for maritime transport, and it facilitated the compounding of gunpowder under appropriate conditions. The Baiyo-hou method was developed from the Kodo-hou method, but both Japanese architectural structures and sericulture practices are thought to have contributed to the development of this method. The development of the niter-bed method observed in the late Edo period in Satsuma and Kaga might have been associated with the introduction of Western military tactics and herbal medicine through Dutch studies.
