Q. How do I cite the original protocols of geneva of 1925 in chicago style?

I would treat this as a website:  

https://www.lib.washington.edu/help/guides/45chicago.pdf

I would look at example #10 and add United Nations as the author.

Or you could put it into a general format,

    Author (and/or owner, sponsor). Document Title. URL or DOI.

                           Author is  United Nations

                           Document title -  Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases, and of                               Bacteriological Methods of Warfare

                          Then the url or doi

 

I hope this helps.

Michele 

Michele Mrazik Grasso

Public Services Librarian

610-282-1100 ext. 1612