Stephenson's Horseshoe and Swage

1876 Scientific American  
The accompanying engravings, which we extract from The Engineer, represent a new and simple apparatus for testing the efficiency of any tanning solution or material. The prin ciple involved consists in forcing a solution containing tan nin through a piece of hide. The density of the solution is taken before and after the operation, and a comparison of the densities enables the value of the solution to be readily de termined.
doi:10.1038/scientificamerican06031876-355a fatcat:uulqvlimejfzfmn52xqtvlp6uq