In 1985, the library of the Department of Drug Science and Technology of the University of Turin was dedicated to Icilio Guareschi, a distinguished chemist from the early Twentieth century who was a Professor of Pharmacy in Turin from 1879 to 1918. One of Guareschi's greatest interests was the method based on scientific literature. He also wrote sixty-six papers on the history of chemistry. During his studies he collected primary and secondary sources which are the basis of our current precious historical library collections. Their development over time is the focus of the present work, especially the documentation held by the last direct descendants of the Guareschi family, donated by the engineer Marco Ginatta between 2008 and 2013.