Forensic chemistry is a branch of chemistry that, rather than looking at what will happen, seeks to answer what already happened. Forensic chemists might, for example, go to a neighborhood where people are getting sick and take air, water, and soil samples. They test these samples for chemicals. Once they have detected harmful chemicals, they trace where the chemicals came from and how they spread. Forensic chemistry played a role in the infamous Love Canal incident in the 1970s.