MLA

Speck, William A. (William Alfred), 1864-1928. ALS : Berlin, to Johann Christian Gaedicke. Box 13, folder 528. 1801 Jan 26. https://collections.library.yale.edu/catalog/16724409.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 13, folder 528"])(1801 Jan 26)[ALS : Berlin, to Johann Christian Gaedicke]. https://collections.library.yale.edu/catalog/16724409.