Replacing one hydrogen atom of acetic acid with a chlorine one yields Chloroacetic acid. Chloroacetic acid is used in industrial chemical processes, for example in the production of dyes. It was used as poison gas in the First World War, as a so-called Yellow Cross agent. It is still used to treat warts today. Chloroacetic acid is a very strong acid that causes immediate damage to the skin. Exposing between 5% and 10% of the skin to a solution of 80% chloroacetic acid will lead to death.