Double-Chambered Smoke Exhaust Duct (Mining Trail 14)

As already explained at the information desk by the chimney, starting in 1854, the environmentally harmful exhaust gases produced during ore smelting were channeled through a brick-lined flue to the chimney on the Bastenberg. The flue is mostly single-channel; only a section of about 20 meters is double-channel. But why?

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

The two-channel section of the canal, not far from the lead smelter, presumably served two purposes: First, it was intended to ensure the stability of the canal, as a heavily trafficked road ran over it. Second, it was designed to allow the moisture in the air, together with the sulfuric acid, to condense on the four tall, cold masonry walls. This made it possible to largely prevent environmental damage along the rest of the canal’s course and in the air—such as through “acid rain.” The condensate was collected in a gutter at the bottom of the canal.

It is not known whether the “acidic” water could always be sufficiently neutralized after it flowed back to the lead smelter. The remaining exhaust components—soot and metal particles—settled just before the chimney when the draft in the flue subsided.