Poison gases are used in industry as chemical reagents. The chemical reactions they can be used for are more important than their toxicity. Today, chemists try to avoid the use of poisonous gases, but it is often not possible. Examples of large-volume industrial poisonous gases are hydrogen sulfide, cracked from oil, chlorine, in diverse chemical uses and to disinfect drinking water, and ammonia, which is a valuable fertilizer into itself and can be converted into a range of other fertilizers, in addition to chemical uses.