The William Pitt Mason Papers (MC 1) span the years 1877 to 1924, with the bulk of the material falling into the period 1885 to 1915. The papers consist primarily of letterpress books of scientific and business correspondence; investigation results and records of water analysis; bibliographical notations; notes by RPI students on experiments and water investigation; and published articles written by Mason. The majority of the manuscripts deal with Mason’s professional research interest in water analysis. Mason’s correspondence dealing with the analysis of city, town, state and private water supplies reflects not only his concern for pure drinking water, but more generally, his tendency to apply his scientific knowledge in the resolution of local concerns. Although Mason traveled throughout the United States to analyze water, many of his investigations were conducted on the Poestenkill River in Rensselaer County. The manuscripts also include handwritten pencil notes on astronomy, religion, and the history of Chemistry.