MLA

Clésinger-Sand, Solange, 1828-1899. Escamps, Henri. Box 1, folder 27. 1883, undated. https://collections.library.yale.edu/catalog/17444461.

APA, 6th edition

Clésinger-Sand, Solange, 1828-1899. (["Box 1, folder 27"])(1883, undated)[Escamps, Henri]. https://collections.library.yale.edu/catalog/17444461.