MLA

Clésinger-Sand, Solange, 1828-1899. Langlois, ----. Box 1, folder 42. undated. https://collections.library.yale.edu/catalog/17444475.

APA, 6th edition

Clésinger-Sand, Solange, 1828-1899. (["Box 1, folder 42"])(undated)[Langlois, ----]. https://collections.library.yale.edu/catalog/17444475.