Beer testing, Old Stock, Philadelphia Brewing Co.
The man in this picture is testing a sample of beer using a hydrometer. Hydrometers measure the density of a liquid and can be used to estimate how much alcohol and sugar are in a beer. Based on the posters in the room, we believe he is sampling Old Stock, which was a brand made by Philadelphia Brewing Company in the 1930s and 1940s.
Image source: Philadelphiana Collection -- Breweries -- Philadelphia Brewing Co., the Print and Picture Collection, Free Library of Philadelphia