This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
In the acute inflammatory stages of eczema mercurials are usually unsuitable as being irritant, but Dr. Spender speaks highly of the use of lotio hydrarg. nigra in eczema rubrum: he adds glycerin, and applies it fresh three times in twenty-four hours, without oiled silk (British Medical Journal, i., 1878, p. 286). In subacute and chronic stages, with thickening from infiltration of the cellular tissue, moderate crusting, scaling, and dryness of skin, mercurial ointments are very serviceable; that of the red oxide often irritates, even at this stage, and that of the ammonio-chloride, diluted 1 in 4 or 8, is more generally suitable: Niemeyer specially commends it for chronic eczematous patches on the face. When there is more than average secretion or irritation, better results are obtained by a combination with equal parts of lead, or of zinc ointment, and a formula much used for eczema capitis at the Skin Hospital is the following: R. Plumbi acet. gr. x.; zinci oxidi, hydrarg. sub-chlor., ung. hydrarg. nitrat., aa gr. xx.; olei palmae purif. fl. 3 ss.; adipis recentis 3 ss., misce: such ointments are useful in the chronic general eczema of childhood especially.
For eczema mammae, which is often very obstinate, Hebra uses sublimate-lotions (1 in 120), but they require great care if any lactation is continued. For eczema of the genitals, Devergie recommended a very much weaker solution of the same; Gueneau de Mussy prefers calomel (15 gr. to 1/2 oz. of lard). For eczema about the hands, and especially for "cracks" about the fingers and nails, an oleate of 5 per cent. strength is said to be very efficacious (Practitioner, vol. x.). I have found an ointment of hydrarg. am. chlor. gr. v. to 3 j. very useful for eczema capitis et aurium after thorough removal of the crusts, also for all cases of chronic eczema. In (non-parasitic) sycosis, mercurial ointments combined with sulphur give the best results. In herpes preputialis, calomel is a useful dusting powder.