Another form in which mercury was very antiently used, and still continues to be applied with an intention of acting immediately upon affected parts, is, its being reduced into a state of vapour, by which means it acquires a very high degree of activity. This mode of applying mercury is attended with many inconveniencies, and, in this form, its application, while it is very sudden, can at best be but temporary. It must, however, be allowed, that the active form which the mercury here assumes is a very subtile one. By this means, it becomes capable of penetrating and resolving hard and indurated tumors, which cannot be pervaded by mercury in other forms. On this account, in such tumors, especially if they have been of long standing, and in obstinate ulcers which have resisted other mercurial preparations, the form of vapour may often be tried with peculiar advantage. For this purpose, cinnabar has commonly been employed. From its being resolved into fume, the mercury and sulphur are disunited, and the activity of the medicine totally depends upon the former arising in a state of vapour.
Mercury, in whatever way it is used, is most active in these forms in which, from the addition of acids, it is reduced to a saline state. Some of these are in their nature so extremely corrosive, that they can scarcely, with safety, be used even as external applications. This peculiarly holds of those preparations which are formed by a combination of mercury with the nitrous acid. That they may be fitted for use, therefore, various means are employed to render them milder. Among other methods, one frequently practised, is, the abstraction of acids by calcination. In this manner are prepared the mercurius corrosivus ruber of the London college, and the praecipitatus ruber or calcinatus of the Edinburgh. These are forms of employing mercury which are every day in use, for application to the part immediately affected.
These preparations, even after having their action in this manner diminished, still possess a very considerable degree of corrosive power. On this account, they become particularly useful in many cases of venereal complaints, where corrosives are required. And hence it is easy to learn the foundation for the frequent and advantageous employment of these preparations in cases of fungous edged ulcers, of warts, and other such tumors.
That these preparations may be applied more commodiously, they are frequently mixed with different ointments, particularly with basilicon; but, by this means, their power of action is greatly diminished. Where it is intended they should act as escharotics, it is perhaps in every case most proper to employ them in the form of dry powders. Such dressings may then be applied above them as are best fitted to the nature of the complaint.
It may naturally be imagined, that, from mercury in this form, not only an escharotic power can be obtained, but that likewise, from its action as an antidote against the venereal virus, parts kept ulcerated, from the activity of this poison, may be healed. That, in some degree, it is fitted for this purpose likewise, is not to be doubted. But, to its employment in this way, its corrosive power is often an objection. In many cases, where it is required that an ulcer should be healed, a destruction of solid parts would be highly prejudicial. And when, in order to avoid this, the corrosive power of the mercury is diminished, from its being united with an ointment, the precipitate becomes liable to the same objection which was formerly urged against the efficacy of mercurial ointment. It is then in a state which does not admit of a ready union with the venereal virus. It may therefore, upon the whole, be concluded, that mercury in this form is principally useful in those cases, where, with the effect of an antidote against the venereal virus, it is necessary to conjoin an escharotic power.
Mercury may be rendered saline by being united with other acids as well as the nitrous. These likewise are, in general, active preparations; but they do not possess a caustic power, at least in so high a degree as the nitrous preparations. Among the most active of the other saline preparations, are those prepared with the muriatic acid, and especially the corrosive sublimate. This is a mercurial preparation which, in many cases, may be employed to act immediately on parts affected by the venereal virus; it falls, therefore, to be considered also under this head.
The stimulant power of corrosive sublimate is so great that it is never, even for external purposes, used in a solid form. But the aqua phagedænica of the Edinburgh College, which is a solution of it in lime-water, is a mercurial preparation which has often been used externally, both in venereal and other foul ulcers. This form, however, contains so large a proportion of the mercury, that it is by much too stimulant for the greatest part of sores. A more dilute solution, in common spring-water, is free from this inconvenience, while, at the same time, it serves every purpose which can be expected from the other.
The mercury in this solution is in a state sufficiently active to destroy the venereal virus, and is, at the same time, in a condition which will admit of a ready union with it. Good effects, therefore, might naturally be expected from it, especially as the form is such that it can with ease be applied.
The efficacy of this preparation has not indeed, as far as I know, been confirmed by long or extensive practice. But, where it is proper to heal superficial ulcers, no application is of greater service than dressings of lint dipt in a solution of the corrosive sublimate in the proportion of half a grain to an ounce of water. The addition of a small quantity of compound spirit of lavender to this solution will give it a colour and smell different from those of common water, which, with some patients, are necessary conditions to an effectual application. In some circumstances already mentioned, the other modes of applying mercury to act immediately upon the diseased part may be preferable to this. But, where the only requisite to the healing of an ulcer is the destruction of that venereal virus at the part which supports a diseased state there, no application will answer the purpose with greater facility, safety, and expedition, than this solution.