Graduation Works of Bad Kösen, Saxony-Anhalt
The river Saale drives a mill wheel, which produces about 40 horse powers. This power is transferred by a system of wooden transmission rods to a pump further up the hill, which pumps natural brine with about 5 % salt through a vertical shaft from a depth of 175 m (575 ft). From there, another pump transports the brine to the top of the actual graduation tower, a huge wooden framework, 375 m (7230 ft) long, stuffed with blackthorn twigs. The brine trickles down through the twigs, thereby evaporating water, and arrives as a concentrated brine. Part of the brine is pumped back to the top to concentrate it even more. The concentrate now containing about 25 % sodium chloride was then boiled down to produce salt.
Graduation of a brine has several advantages: Firstly, the evaporation of water by sun and wind reduces the consumption of wood or coal when boiling the brine down to salt. Secondly, it improves the quality of the salt because carbonates, sulfates, iron, and manganese are separated as “thorn stone” on the blackthorn twigs.
Salt production was stopped in 1859. The graduation tower remained in use for its production of salty air, which is thought to have beneficial health effects for people with respiratory conditions.
The system was installed in the 1730s and is one of the few still fully functional wooden rod transmission systems in Europe.
