MLA

Clésinger-Sand, Solange, 1828-1899. Edmond, Charles. Box 1, folder 26. 1895, undated. https://collections.library.yale.edu/catalog/16620194.

APA, 6th edition

Clésinger-Sand, Solange, 1828-1899. (["Box 1, folder 26"])(1895, undated)[Edmond, Charles]. https://collections.library.yale.edu/catalog/16620194.