(a) Cartheirfer, rudimenia m. m.p. 481. Malouin, chim. mecticinale, part. iv. ch. 34.

Quicksilver, included in a flat-bottomed glass having a small hole open to the air, and kept for several months in a constant heat just not strong enough to make it evaporate, calcines by degrees into a red powder. A greater heat, sufficient to make the mercury freely distil, not only does not promote the calcination, but revives such part, as has been already calcined, into running mercury again. A weaker heat, as that of the human body, or even of boiling water, though continued for years, changes only a small part of the mercury into a blackish powder: constant triture or agitation produces similar effects to this low degree of heat, and in a much shorter time (a). If the free access of air should be found to influence the calcination of this, as it does that of the metallic bodies called imperfect, the tedious process might be expedited, by using, for the vessel, a glass tube, with both its ends bent upwards, and one of them considerably higher than the other; through which, a constant stream of fresh air would pass over the surface of the small thread of mercury at the bottom.

The red powder has been by some greatly esteemed in venereal cases, and supposed to be the most effectual and certain of the mercurials. It is accompanied with one considerable inconvenience, being greatly disposed to irritate the first passges, and occasion gripes; to prevent which, a small quantity of opium, and some warm aromatic material, are commonly joined to it: the antivenereal pills of a late celebrated empyric are supposed to have been a compo-sition of this kind. Even when thus corrected, however, it does not appear, from what I have been able to learn of its effects, to have any advantage above the mercurials in common use and of easier preparation. The dose is from half a grain to two grains: five or six grains are said to vomit and purge violently.

(a) Boerhaave, Philosopb. Transact. No. 430, 4.43, 444, & Mem. de l'acad. des scienc. de Paris, pour l'ann. 1734.

Hydrargyria calcinatus -Ph. Lond.

Pure aqua fortis, assisted by a moderate heat, dissolves equal its weight or more of quicksilver into a limpid corrosive liquor; which, largely diluted with pure water, the common spring waters turning it milky and precipitating a part of the mercury, has been employed in lotions against some kinds of cutaneous defedations, and where mercurial lotions are advisable, is perhaps one of the best of them. An ointment is likewise prepared, for venereal ulcers, etc. by mixing the corrosive solution with fats: an ounce of quicksilver is dissolved in two ounces of spirit of nitre, the solution poured hot into a pound of lard melted and just beginning to grow stiff, and the whole briskly stirred up till an uniform yellow mixture is procured.

On infpiffating the mercurial solution over a gentle fire, there remains a white mass highly caustic; which, calcined with a gradual heat, becomes first brown, then yellow, and at length, on increasing the heat, of a deep red colour. If the aqua fortis, used for the disso-lution, has been previously drawn over from a small proportion, the hundred and twenty-eighth part of its own weight, of sea salt, the red mass is supposed to assume more readily the spark-ling appearance which is looked upon as the characteristic of its goodness. This preparation is employed as an escharotic; and mixed with ointments and cerates, as a digestive; in which intention, Mr. Sharp observes, that it is very effectual.

Mifaubin's pills.

Ung. Hy-drargyri ni-trati Ph. Lond.

Ung. citri-num, Ph. Ed.

Merc. cor-rosiv. ruber, vuIgo prae-cipit. ruber Ph. Ed.

Hydrarg. nitratus ruber Ph. Lond.

Sundry methods have been tried for abating the corrosiveness of this preparation, so far as to render it safe for internal use. One of the most certain seems to be, digesting it two or three days, with a gentle heat, in about thrice its quantity of rectified spirit of wine, then setting fire to the spirit, and keeping the powder con-stantly stirring till all the spirit is burnt off. In this process, the corrosive is deprived of a little of its acid, which is partly perhaps absorbed and dulcified by the spirit during the digestion, and partly dissipated by the heat during the burning. The medicine, nevertheless, is still a very rough one, operating, generally, in doses of a few grains, both upwards and downwards. Different preparations of this kind have been kept as secrets in particular hands, but it does not appear that any of them are superiour in virtue to some other mercurials of greater safety and more equal power. The Edinburgh college has a washed precipitate of mercury from its solution in the nitrous acid, made by the addition of the volatile alkali.

If oil of vitriol be poured on half, or equal its weight of quicksilver, and gradually heated till the liquor boils and distils; the more phlegmatic parts arise, while the stronger acid corrodes the mercury into a white caustic mass. On the affusion of warm water, the mass falls into powder, and becomes immediately yellow; a part of it, satiated with acid, dissolving in the water: the larger the quantity of acid made use of, and the less thoroughly the matter has been exsiccated or calcined, the more of it will dis-solve. The yellow powder, ground with fresh quantities of water till all the soluble part is extracted, becomes insipid, and in this state, commonly called turpeth or turbith mineral, it proves, though not corrosive, strongly emetic; operating, in this intention, the most effectually of all the mercurials that can be given with safety. It is used chiefly in virulent gonorrhoeas, and other venereal cases accompanied with a great flux of humours to the parts: it is said likewise to have been employed with success, in robust constitutions, against leprous disorders, and obstinate glandular obstructions. The dose, as an emetic, is from two grains to six or eight; though some constitutions, habituated to mercurials, can bear larger quantities: 1 knew an instance of twenty grains producing no sensible evacuation or disturbance. It may be given in smaller doses, as half a grain or a grain, as an alterative, after the same manner as the red calx of mercury already mentioned: and even when intended as an evacuant, it may perhaps, as Malouin observes, be most advisable, to give only a small quantity at a time, as one grain, and repeat this dose every hour till the vomiting succeeds.