Question:
Which employer did Max Volmer work for in Dec, 1921?

Context:
 Max Volmer works for Humboldt University of Berlin from May, 1955 to May, 1955. 
 Max Volmer works for University of Hamburg from Jan, 1920 to Jan, 1922. 
 Max Volmer works for Frederick William University from Jan, 1916 to Jan, 1918. 
 Max Volmer works for Auergesellschaft from Jan, 1918 to Jan, 1920. 
 Max Volmer works for Technische Hochschule Berlin from Oct, 1922 to Jan, 1945. 
 Max Volmer works for Leipzig University from Jan, 1912 to Jan, 1914.

Answer:
University of Hamburg