Greenish or yellow-brown crystals or granules. Odorless or soluble in Water. Extracted from Pickel Steel, or waste sulfuric acid  of oxide titanium. Mainly used for corrosion control of the seawater side of a condenser or for water and sewage treatment.

Technical Bulletin

http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682778.html

Product Label

IMPORTANT WARNING:
Accidental overdose of products containing iron is a leading cause of fatal poisoning in children under the age of 6. Keep this product out of the reach of children. In case of an accidental overdose, call your doctor or a poison control center immediately.

Why is this medication prescribed?.
Ferrous sulfate provides the iron needed by the body to produce red blood cells. It is used to treat or prevent iron-deficiency anemia, a condition that occurs when the body has too few red blood cells because of pregnancy, poor diet, excess bleeding, or other medical problems.