This section is from the "A Handbook of Useful Drugs" book, by State Medical Examining and Licensing Boards.
Blue ointment is made by mixing approximately 2 parts of mercurial ointment with 1 part of petrolatum. It represents approximately 33 per cent, of metallic mercury and conforms to the strength, though not to the composition of the international standard for mercurial ointment.
Action and Uses: Mercurial ointment is a parasiticide; it is employed for the destruction of lice, but other measures are more cleanly and less calculated to cause irritation. The rubbing of mercurial ointment into the skin allows the absorption of a part of the mercury, thus securing its constitutional effects. This is regarded by some authorities as the most efficacious method of treating syphilis except the intravenous or hypodermic method. Inunction has the great advantage of leaving the digestive tract undisturbed.
Dosage: 2 gm. or 30 grains of the ointment should be rubbed into a chosen area of the skin at night, and the part anointed should be cleansed by washing in the morning. A new area of the skin should be chosen for inunction the next evening. The ointment may be spread on cloths and bound on a part of the skin liable to some friction. If dermatitis is excited by this method of application it will subside rapidly as a rule on washing with a warm alkaline lotion and dusting with some bland powder. If irritation seems likely to arise the ointment may be diluted with an equal part of hydrous wool fat.