MLA

Speck, William A. (William Alfred), 1864-1928. ALS : Weimar, to "theuerster Herr und Freund". Box 9, folder 268. 1830 Nov 30. https://collections.library.yale.edu/catalog/2005298.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 9, folder 268"])(1830 Nov 30)[ALS : Weimar, to "theuerster Herr und Freund"]. https://collections.library.yale.edu/catalog/2005298.