MLA

Clésinger-Sand, Solange, 1828-1899. Lambert, Madame. Box 1, folder 40. 1897 December 20. https://collections.library.yale.edu/catalog/17444473.

APA, 6th edition

Clésinger-Sand, Solange, 1828-1899. (["Box 1, folder 40"])(1897 December 20)[Lambert, Madame]. https://collections.library.yale.edu/catalog/17444473.