MLA

Speck, William A. (William Alfred), 1864-1928. ALS : Weimar, to Frau Henriette Caroline Friederike (Jagemann) von Heygendorf. Box 9, folder 279. 1825 Oct 19. https://collections.library.yale.edu/catalog/2005309.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 9, folder 279"])(1825 Oct 19)[ALS : Weimar, to Frau Henriette Caroline Friederike (Jagemann) von Heygendorf]. https://collections.library.yale.edu/catalog/2005309.