Abstract
Objective: Potassium nitrate (KNO3), commonly referred to as saltpeter, was an important ingredient of
gunpowder from 16th to the 18th centuries in Japan. There were three different methods for producing
saltpeter, including Baiyo-hou, Shosekikyu-hou, and Kodo-hou.
Methods: We investigated the differences between the three methods of saltpeter production by comparing
the crystallization of KNO3, conducting ion analyses, and reviewing historical records.
Results: Baiyo-hou was the original method for making saltpeter and was conducted at locations that were
restricted : Gokayama in Kaga and Shirakawa-go in Hida. Shosekikyu-hou was equivalent to western niterbeds, whereas the main source for ammonium-nitrogen for the Baiyo-hou method was silkworm feces. Using wood ashes to boil the soils from both Baiyo-hou and cow manure (i.e., substituted for Shosekikyuhou) afforded KNO3 crystals (i.e., amorphous powders) ; however, recrystallization and purification were required, especially for the cow manure. The yielding of KNO3 crystals from Baiyo-hou was three times higher than that from Kodo-hou. Ion chromatographic analyses of the three different soils revealed that much higher levels of NO3- could be detected in soil using Baiyo-hou. Moreover, the NO3- level in cow manure made within one year was same as the level in soil conserved in an underfloor for 20 years. No detection of K+ was observed in soil using Kodo-hou, while a high level of K+ was detected when using both Baiyo-hou and cow manure. Baiyo-hou and Shosekikyu-hou were biological techniques to hasten NO3- formation due to the abundant availability of ammonium-nitrogen.
Conclusion: Based upon experimental evidence, we conclude that Baiyo-hou had a technological advantage to produce large quantities of high-quality saltpeter among the three different methods in Japan.
