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 patches of obstinate chronic psoriasis the ointment of green iodide of mercury, or of iodide of sulphur, is very useful. I can speak well especially of the former, made in the proportion of 1 part to 8 of simple ointment. The effects are often more rapid and decided than those of tar ointment. Occasional alkaline or vapor baths should be used during the treatment.