What were the duties of these specific ministries of foreign affairs?

Although this had varied from case to case, within the political context of early 20th century, the tasks of foreign ministries started to become alike in many examples of the world.

Firstly, policy making mission was given to this ministry. 

Secondly, these ministries were also given the task of staffing and supporting the missions abroad.

Thirdly, they started to coordinated foreign relations especially after the Great War (WWI). 

Fourthly, dealing with foreign diplomats hosted in the home country was also assigned to these ministries.