MLA

Clésinger-Sand, Solange, 1828-1899. Kaempfen, Albert. Box 1, folder 38. 1883, undated. https://collections.library.yale.edu/catalog/17444471.

APA, 6th edition

Clésinger-Sand, Solange, 1828-1899. (["Box 1, folder 38"])(1883, undated)[Kaempfen, Albert]. https://collections.library.yale.edu/catalog/17444471.