MLA

Drinkwater, John, 1882-1937. Bryce, Elizabeth Marion Ashton, viscountess. ALS, London. Box 2, folder 57. 1921 Jul 8. https://collections.library.yale.edu/catalog/17280583.

APA, 6th edition

Drinkwater, John, 1882-1937. (["Box 2, folder 57"])(1921 Jul 8)[Bryce, Elizabeth Marion Ashton, viscountess. ALS, London]. https://collections.library.yale.edu/catalog/17280583.