History of Graduation Tower
Salt, also referred to as “white gold”, was already a coveted substance in early times. All living beings, humans included, need salt (NaCl) for their survival. People, then, set out to explore for salt deposits as far back as early times. In Germany, the extraction of salt from mines is only feasible in some places, and it involves great effort and expense. But there is yet another means of extracting salt, and that is from the salt water of the seas or from salt wells. The saline water found in wells or springs is called brine.
Brine manifests itself as a spring in many places in Germany. In those early days, it was often animals, which liked drinking salty water, that drew people’s attention to the springs. People then reflected on how to isolate salt from the saline water. It had been observed that salt was left behind when brine evaporated.
Since the evaporation process takes much longer here in our latitudes than it does in areas with much sunshine, people thought of ways of speeding it up. To this end, small ceramic crucibles were used as early as the Stone Age; the crucibles were filled with brine and then heated up. This method of extracting salt is termed briquetage.
Unfortunately, however, the brine obtained from most springs has a very low salt content. It was therefore necessary to find a means of enhancing its salt content so as to save fuel during the brine cooking process. The maximum salt content of water or brine is approximately 28 per cent. This brine concentration can most easily be achieved through natural evaporation. So-called “leakage works” were developed to meet this need. These were slightly tilted supporting frameworks clothed in straw and having a collecting channel at the bottom. Large shovels were now used to feed brine onto these walls. The brine spread over the straw bales, wind and sun caused the water to evaporate and thus enriched the salt content of the collected brine to a saturation level of roughly 24 per cent.
The operation of the ‘leakage works’, as one might guess, involved much time, costs and effort. The process therefore had to be “automated”, and this led to the invention of graduation works or graduation buildings. In the past, salt content used to be stated in terms of “grades” and not in percentage as is the case nowadays. The name graduation works is, thus, derived from “grading”, the raising of the “grade” of brine.
The working of a graduation tower is brilliantly simple: brine is made to run down an optimally rough wall, with the water drops splitting up on the rough surface. The water evaporates and the salt content of the water drops rises. The process functions much better when there is a gently blowing breeze. The brine is collected below in a container and is directed to the salt works, where it is heated up in large pans and where the salt is skimmed.