The one that gets the most publicity is the use of luminol, which is used to detect the presence of blood stains that are normally invisible to the naked eye. The luminol reacts with the iron in the blood residue, causing an eerie blue glow for about thirty seconds in a darkened room. The luminol is sprayed evenly about the room, the room is darkened, and a long-elapse time frame photography is used to capture the evidence. The use of luminol has long been popularized on television shows such as "CSI: New York" and "CSI: Miami". Other chemicals are used as well, primarily in the form of solvents to break down evidence for DNA fingerprinting. The use of chemicals in the forensics department of most crime fighting organizations has increased significantly, but it should be pointed out that what you see on television and what is actually in practice are still two different things.