The concentrated acid acts with vast energy as an escharotic. in its first operation, it whitens the parts by forming a compound with the albumen, but in the progress of its action blackens them, probably by taking the elements of water from the tissues, and liberating the carbon. it is very rarely used in this state. For the denudation of the skin above referred to, nitric or muriatic acid is preferable in consequence of their less energetic action. in cases, however, of entropium and ectropium, or inversion and eversion of the eyelid, the acid has been employed by some eminent British surgeons; being applied, in the former case, upon the skin on the outside of the lid, and in the latter, to the exposed mucous surface. Of course, in each case, great care is taken not to allow its action to extend too far. it operates advantageously in the affection, through the contraction which attends the healing of the ulcer, left after the separation of the eschar.

Much diluted, the acid has been used as a gargle in sore-throat, as a mouth-wash in ptyalism, and as a tonic and astringent application to indolent ulcers and cutaneous eruptions. From half a fluidrachm to two fluidrachms may be added to a pint of water. An ointment prepared by mixing a drachm of it with an ounce of lard has been used in cutaneous eruptions. it occasions inflammation and sometimes ulceration, and should be weakened, when used for eruptions, by an equal weight of lard. in this feebler form, it has been employed as a rubefacient liniment in rheumatism of the joints, etc. Mixed with saffron to the consistence of a paste, it has been used by Velpeau as an escharotic, and found to answer well. Mr. Henry Thompson, of London, has found it to act efficiently in the destruction of epithelial cancer, when made into paste with dried and powdered sulphate of zinc. {Lancet, Am. ed , Jan. 1858, p. 51.)