|MadSci Network: Biochemistry|
The salts of silver such as silver nitrate are caustic. Placing them on a site of bleeding does not have any clotting properties that I know of, but, what it does is burn the tissue to seal it. At the same time it acts as an astringent to dry the area and an antiseptic to prevent infection. reference: Taber's Cyclopedic Medical Dictionary 18th ed.
Try the links in the MadSci Library for more information on Biochemistry.