Royal Saltworks graduation tower, Industrial graduation tower in Arc-et-Senans, France.

The Royal Saltworks graduation tower in Arc-et-Senans was a covered timber structure 496 metres long and 7 metres high, with a diversion canal turning a water wheel that drove a pump. A horizontal pipe at 5 metres height pierced with holes dripped brine onto bundles of thorn branches, and the concentrated brine was collected in a grooved, slightly inclined fir beam. Only the hydraulic devices and the carpenter's house remain, the rest destroyed in 1920.

The graduation building was created together with the royal saltworks of Arc-et-Senans between 1775 and 1779, at the end of the 21 km brine pipeline from Salins-les-Bains. It was not designed by Claude Nicolas Ledoux. After salt production stopped in 1895, the building was demolished in 1920; only the hydraulic works and the carpenter's house survived, and the canal and the house's facades and roofs were listed as monuments historiques on 8 October 1991.

The name survives in rue des Graduations, the straight road from the Loue to the royal saltworks where the building and its annexes stood. The carpenter's house, kept because he maintained the timber frame, and the canal with its two right angles remain; the water wheel that drove the lifting pump stood at that bend.

The remains stand along the straight rue des Graduations, the old road from the Loue to the royal saltworks. The water wheel once sat where the canal makes two right angles, so follow the canal bends to locate it. Only the hydraulic works and the carpenter's house survive; the 496-metre timber gallery is gone.

The brine arrived from Salins-les-Bains through a 21-kilometre saumoduc, a wooden pipeline ending at the graduation. Inside, a horizontal pipe nearly 500 metres long, set at a height of 5 metres, dripped the brine onto bundles of thorn branches so it could evaporate. The concentrated brine was then collected in a grooved, slightly sloping fir beam and run off into a 900 m³ basin.