MLA

Speck, William A. (William Alfred), 1864-1928. LS : Schloss Dornburg, to Henriette Ottilie Ulrike Freifrau von Pogwisch, geborene Gräfin Henckel von Donnersmarck. Box 9, folder 293. 1828 Jul 18. https://collections.library.yale.edu/catalog/2005323.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 9, folder 293"])(1828 Jul 18)[LS : Schloss Dornburg, to Henriette Ottilie Ulrike Freifrau von Pogwisch, geborene Gräfin Henckel von Donnersmarck]. https://collections.library.yale.edu/catalog/2005323.