Blue mass

Blue mass (also known as blue pill or pilula hydrargyri) was the name of a mercury-based medicine common from the 17th to the 19th centuries. The oldest formula is ascribed to one Barbarossa, in a letter to Francis I of France.
Description.
Blue mass was used as a specific treatment for syphilis from at least the late 17th century to the early 18th. Blue mass was recommended as a remedy for such widely varied complaints as tuberculosis, constipation, toothache, parasitic infestations, and the pains of childbirth. 
A combination of blue mass and a mixture called the common black draught was a standard cure for constipation in early 19th century England and elsewhere. It was particularly valued on ships of the Royal Navy, where sailors and officers were constrained to eat rock-hard salted beef and pork, old stale biscuits (hardtack), and very little fruit, fiber, or other fresh food once they were at sea for an extended period.
It was a magistral preparation, compounded by pharmacists themselves based on their own recipes or on one of several widespread recipes. It was sold in the form of blue or gray pills, or syrup. Its name probably derives from the use of blue dye or blue chalk (used as a buffer) in some formulations. 
The ingredients of blue mass varied, as each pharmacist prepared it himself, but they all included mercury in elemental or compound form (often as mercury chloride, also known as calomel). One recipe of the period included (for blue mass syrup):
Blue pills were produced by substituting milk sugar and rose oil for the glycerol and rose honey. Pills contained one grain (64.8 milligrams) of mercury.
Toxicity.
Mercury is now known to be toxic, and ingestion of mercury leads to mercury poisoning, a form of heavy-metal poisoning. While mercury is still used in compound form in some types of medicines and for other purposes, blue mass contained excessive amounts of the metal: a typical daily dose of two or three blue mass pills represented ingestion of more than one hundred times the daily limits set by the Environmental Protection Agency in the United States today.