MLA

Gissing, George, 1857-1903. Gissing, Ellen S. 2 ALS to Eduard Bertz, Wakefield, [England]. Box 5, folder 87. 1890. https://collections.library.yale.edu/catalog/16495584.

APA, 6th edition

Gissing, George, 1857-1903. (["Box 5, folder 87"])(1890)[Gissing, Ellen S. 2 ALS to Eduard Bertz, Wakefield, [England]]. https://collections.library.yale.edu/catalog/16495584.