French method
Niter-beds are prepared by mixing
manure with either
mortar or wood ashes, common earth and organic materials such as
straw to give porosity to a compost pile typically 4 feet (1.2 m) high, 6 feet (1.8 m) wide, and 15 feet (4.6 m) long.
[17] The heap was usually under a cover from the rain, kept moist with
urine, turned often to accelerate the decomposition, then finally
leached with water after approximately one year, to remove the soluble calcium nitrate which was then converted to potassium nitrate by filtering through the
potash.