Fonds consists of general professional correspondence, 1913-1961, including Maass’ outgoing letters for 1946-1954. Topics covered include defence research, the Pulp and Paper Institute, N.R.C. appointments, visits of scientists, and political questions (e.g. letters to and from Lester Pearson on NATO and the nuclear deterrant). There are also letters of recommendation by Maass, and personal communications from colleagues. A special binder of congratulatory letters marks his election to the Royal Society (1940), and there are similar files on his retirement (1955), and of condolences to his widow at his death (1961). Maass also assembled photostat copies of letters by eminent 19th century British scientists addressed to his great uncle, Prof. Plucker of Bonn.

Studies and research are documented by a physics laboratory notebook (1908-1909), and a "summary of data on hydrogen peroxide" collected in collaboration with W. Hatcher (1918-1919). A few addresses on the Canadian Institute of Chemistry (1939), the Pulp and Paper Research Institute (1945), and the relation between the Defence Research Board and the universities are included.