In the earliest form of the hiragama ("flat-kettle")
system, the hot steam rising from the open pans
was simply allowed to escape into the outer air.
Soon, however, further improvements made it possible
to capture this steam and utilise it as a convenient
source of supplementary heat for raising the temperature
of the salt- concentrate solution awaiting crystallization.
This preliminary steam-heating technique proved
far more efficient and economical than the original
flat-kettle system, for, with only half the fuel
required by the older method, it could produce a
much greater volume of finished salt, with a considerable
saving in time, as well.
This system was widely used in Japan until the early
1950's.
Closed-kettle cross-section.
Closed-kettle steam-heating system in operation
(ca.1946)
|
