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 early stages of acute pneumonia, formerly treated by calomel and antimony, I cannot recommend mercurials, but the time for using them with advantage is when secondary fever arises, and there is reason to fear purulent degeneration. So far as I can judge, they have seemed to exert some power in preventing this, for certain cases of the kind have improved on commencing the use of sublimate, and others have relapsed on its omission. In pleuro-pneumonia, with copious effusion, the same remedy is still more clearly indicated, and in chronic interstitial pneumonia it sometimes has excellent effect. Sometimes a syphilitic or strumous deposit occurs in the lung, rendering it partially solid, and giving the physical signs of a pneumonia, and these deposits, especially when of the former nature, seem to "melt away" under the moderate action of mercury: but careful diagnosis of such cases is required, for in true tubercular deposit the drug is injurious. Graves speaks highly of mercury "in scrofulous inflammation of the lung."