MLA

Speck, William A. (William Alfred), 1864-1928. LS : Jena, to Johann Christian Gädicke?. Box 9, folder 277. 1799 Dec 6. https://collections.library.yale.edu/catalog/2005307.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 9, folder 277"])(1799 Dec 6)[LS : Jena, to Johann Christian Gädicke?]. https://collections.library.yale.edu/catalog/2005307.