APA (7th ed.) Citation

United States. Patent Office. (1931). Classification bulletin of U.S. Patent Office from Jan. 1, 1931 to Dec. 31, 1931, containing classification of subjects of invention revised by Classification Division of U.S. Patent Office. GPO.

Chicago Style (17th ed.) Citation

United States. Patent Office. Classification Bulletin of U.S. Patent Office from Jan. 1, 1931 to Dec. 31, 1931, Containing Classification of Subjects of Invention Revised by Classification Division of U.S. Patent Office. [Washington]: GPO, 1931.

MLA (9th ed.) Citation

United States. Patent Office. Classification Bulletin of U.S. Patent Office from Jan. 1, 1931 to Dec. 31, 1931, Containing Classification of Subjects of Invention Revised by Classification Division of U.S. Patent Office. GPO, 1931.