Wollaston's chemical slide rule, c 1820.
© Science Museum / Science & Society Picture Library
Made in boxwood by Dring and Fage of Tooley Street, London. William Hyde Wollaston (1766-1828), the English chemist, was a pioneer of powder metallurgy and discovered rhodium and palladium. He developed the slide rule to enable calculations of chemical proportions (relative weight of reactants), using a logarithmic scale of chemical equivalents. Like most early 19th century chemists, Wollaston used equivalents rather than atomic weights in an attempt to avoid the various problems asociated with the latter. Compounds and elements are marked on the outer scale.