Double-draught smoke extraction duct (mining hiking trail 14)

As already explained at the information desk at the chimney, from 1854 onwards, the polluting waste gases produced during the smelting of the ores were routed through a brick-built channel to the chimney on the Bastenberg. The canal is mainly single-pass, with only one section of around 20 meters being double-pass. But why?

During the smelting process, the crushed ores were roasted in coal-fired furnaces to such an extent that the metal separated from the bound sulphur. The resulting exhaust gases consisted mainly of carbon dioxide (CO₂), sulphur dioxide (SO₂), metal oxides and water vapor. The sulphur dioxide reacted with the moisture in the air to form sulphuric acid, which settled on the ground and caused severe damage to the vegetation around the smelter.

The two-passage section of the canal, not far from the lead smelter, probably had two functions: Firstly, the stability of the canal was to be ensured, as a heavily used path ran over it. Secondly, the humidity in the air was to condense together with the sulphuric acid on the four high, cold walls. This meant that environmental damage along the further course of the canal and in the air - for example due to "acid rain" - could be largely avoided. The condensation water was collected in a channel at the bottom of the canal.

It is not known whether the "acidic" water could always be sufficiently neutralized after returning to the lead smelter. The remaining exhaust gas components - soot and metal particles - settled shortly before the chimney when the draught of the channel decreased.