silver nitrate (nī´trāt), chemical compound, AgNO3, a colorless crystalline material that is very soluble in water. The most important compound of silver, it is used in the preparation of silver salts for photography, in chemical analysis, in silver plating, in inks and hair dyes, and to silver mirrors. It is used in medicine in the treatment of eye infections and gonorrhea. Fused silver nitrate is also called lunar caustic. Taken internally silver nitrate is a poison. It is prepared by reaction of nitric acid with silver, and purified by recrystallization. It is darkened by sunlight or contact with organic matter such as the skin.