MLA

Speck, William A. (William Alfred), 1864-1928. ALS : Weimar, to Auguste von Stolberg. Box 9, folder 299. 1777 Jul 17. https://collections.library.yale.edu/catalog/2005335.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 9, folder 299"])(1777 Jul 17)[ALS : Weimar, to Auguste von Stolberg]. https://collections.library.yale.edu/catalog/2005335.