Never pour a chemical back into its original bottle after measuring out too much. This can contaminate the original contants. Never combine the contents of two or more bottles of the same reagent. If one of the bottles is contaminated, the resulting combination is now contaminated. Be aware of chemical incompatibilities before mixing to avoid explosive or uncontrollable reactions, generation of toxic gases, etc.
Peroxides are a group of compounds that contain an oxygen-oxygen bond.
As a class, organic peroxides are the most explosive substances that are normally found in the laboratory. Peroxides are sensitive to light, heat, and friction, as well as to strong oxidizing and reducing agents. Explosions involving peroxides are unpredictable and violent. Store peroxides away from sources of light, heat, friction, and mechanical disturbance. A solid peroxide can often be stored more safely if it is dissolved in a nonperoxidizable inert solvent such as an aliphatic hydrocarbon.