List of discredited substances

This page forms a list of substances or materials which are generally considered to be discredited. A substance may be discredited in one of three ways:

1. It was widely believed to exist at one time but is not anymore. Such substances are often part of an obsolete scientific theory.
2. It was once believed to have drastically different properties from those accepted now. Significant properties it was widely claimed and believed to possess are no longer accepted.
3. It is currently believed to exist as part of a theory which has not been generally accepted by mainstream science.