... as salt used to be termed, was one of the key factors behind Hall's prosperity (formerly Solbad Hall or "Brinebath Hall"). Salt was mined from 1244 to 1967, in what is known as the Halltal (or Hall valley), some 9 km north of the town.
Situation and formation of the salt deposits
The salt deposits mined in eight "horizons" are to be found at an altitude of between 1,334 and 1,635m. The still open, although no longer fully accessible, network of galleries is thought to be about 20,000 m in length, but when combined with the old workings is probably about 40,000 m in total. Alpine salt deposits were formed in the Permian and Triassic era, approx. 200 to 300m years ago. The huge pressure of the mountain rock crushed the soft salt and clay in the primary salt deposits lying at a great depth up through crevices and fissures into the mountain strata. This salt − a chemical compound of a metal (sodium) and a gas (chlorine) − is inseparably linked with the economic and social development of Hall (formerly known as Solbad Hall or "Brinebath Hall").
Discovery of the salt deposits
A rich vein of myths and speculation surrounds the discovery of the salt deposits. One story tells of a shepherd, who put out his fire with springwater and discovered salt encrustation on the charred embers. Also typical is the tale of game or grazing cattle, who liked the salty springwater and this attracted the attention of hunters and shepherds.
Graf von Brandis wrote: "In Anno Domini 1275 God's great gift to Hall was discovered by Niclausen von Rohrbach, when as an eager hunter he stayed on the same mountain a number of times and observed that deer and the chamois, and also the local cattle, gathered in a certain spot to lick the salty stone, whereupon men started digging and finally brought the mine to its current magnificent state." That Graf von Brandis dates the discovery of the salt-mountain at 1275 is because the oldest records pertaining to Hall's salt-mine date from around this time. However, some evidence suggests salt was mined around 1244. At that time some workers did not stop working on Sundays and on feast days, whereupon Bishop Egno of Brixen granted the Provost at Wilten Abbey the authority to stop the salt-miners from working by imposing a religious censure to ensure rest days were observed.
Exemption (Jurisdiction over the salt-mine) As well as a number of other rights and privileges, King Heinrich also granted to the saltworks rights of exemption, whereby an area free from Hall's legal jurisdiction was created. The original document: Insofar as there is any bawdiness or sacrilege in our saltworks within its confines, then justice shall be administered within and not elsewhere.
The salt-mine's exemption zone from the town's jurisdiction started at the mountain chapel in the Hall valley, extended up the valley and went as far as the salt-mine. Within this legal exclusion zone, nobody who worked at the salt-mine, could be arrested by the agents of Thaur courts of justice. Not even if he was guilty of a serious offence. Outside this area, every miner enjoyed personal exemption (but here limited to slight misdemeanours), "when he put on his rucksack and went to work at the salt-mine or was on his way home from there". Brine extraction at the salt-mine Brine is created as part of the mining process. Approx. 32 kg of sodium chloride and other salts are dissolved in a hectolitre of brine. One method of extracting the brine, known as the leaching process, has been in use for centuries: First a chamber, with a diameter of between 30 to 40m and a height of 2m, is blasted out. This chamber is connected to (and accessible from) the gallery above via a diagonal shaft known as an "Ankehrschurf" (Engl. = winze). It is also connected to the lower gallery with a blocked discharge outlet.
Water is added to the chamber via the Ankehrschurf until it reaches the chamber's ceiling. This water dissolves the salt from the adjacent Alpine rock salt (known as Haselgebirge) until full saturation at 32kg per hl is achieved. The insoluble elements in the Haselgebirge (clay, gypsum, anhydrite) sink to the bottom and form a saliferous clay. The brine thus created then flows off through a filter box and discharge pipe. This process can be repeated, until the rock above the chamber has leached away as far as the upper gallery. The leaching process takes place at the side walls and predominantly at the ceiling, while the clay residues build up on the bed of the chamber. The working cavern therefore gets constantly larger as it moves upwards. When the Haselgebirge rock is low in salt, the cavern fills with the saliferous clay residues and must be cleaned out, if it is to be used again. There were always several workings in operation each with a capacity of up to 10,000 cubic metres. The brine is fed away via a trough with partly wooden, partly cast-iron pipes down to saltworks boiler in Hall.
Salt extraction in Hall saltworks Salt extraction took place in Hall until 1951 in two fire-heated boilers with a heating surface of about 140 sq.m per boiler. Using this method, large quantities of water vapour escaped into the air and that meant a huge heat loss. So in 1951 a thermo-compression system, a much more efficient approach, was introduced. The vapours created by the evaporation of the brine were compacted by means of an electrically-driven compressor, simultaneously heated and then fed back into the vaporiser's heating system. The raw brine fed directly from the salt-mine into the boiler-room had to be cleaned before evaporation to avoid a build up of scale in the vaporiser.
During the brine cleansing stage, other salts, e.g. magnesium compounds (from the addition of lime water) or calcium compounds (by adding soda) were precipitated.
After cleansing, the brine was pre-warmed and then fed into the vaporiser. The precipitated salt crystals collected in the lower part of the vaporiser, from where they were pumped in a pulpy condition to the centrifuge via a mixer. The centrifuge reduced the moisture content in the salt down to about 2.5%. Conveyor belts then took the salt to the store, where it was packaged automatically for despatch.
Hall saltworks closed in 1967. But the Mining Museum in the heart of Hall Old Town effectively conveys to visitors the impression of life underground.