This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is prepared by first melting olive oil and resin together, then rubbing them, after cooling, with mercury until the globules disappear, and, lastly, incorporating the mixture with melted lead plaster, gradually added.
As in the preceding preparations, the mercury exists in this mainly in the state of minute division; and, as with them, it is probable that, so far as the mercury is concerned, it proves effective through the gradual formation, in contact with the skin, of a soluble compound of the metal.
Spread upon leather, and applied to the skin, it has produced salivation in persons peculiarly susceptible to the mercurial influence, and is sometimes used, in reference to the general effects of the medicine, in chronic inflammation of the viscera, especially of the liver and spleen; being applied immediately over the organ affected. More frequently, however, it is used for the discussion of external swellings, such as buboes, nodes, and other chronic tumefactions of the bones, or soft parts, especially when supposed to be of syphilitic origin.
Plaster of Ammoniac with Mercury (Emplastrum Ammoniaci cum Hydrargyro, U. S., Br.). This is made by first rubbing mercury with a little olive oil and sulphur previously heated together, until globules cease to appear, and then incorporating the mixture with ammoniac, prepared for the purpose by boiling it with water, straining, and evaporating to the proper consistence. The sulphur answers no other useful purpose than to aid in the extinguishment of the mercury. This plaster is used for the same purposes as the preceding, being somewhat more discutient, and sometimes beneficial in chronic swellings of the joints.