"It might be supposed, that when the nitrous acid ceases to effervesce with the mercury, it is saturated with it; but this is far from being the case: the acid, when the heat is increased, being still able to dissolve a quantity of it; with this difference, however, that the quicksilver at the beginning of the process is calcined by the acid, but afterwards is dissolved by it in a metallic form. In proof of this we may observe, that not only more elastic vapour arises, but also, that by adding either fixed or volatile caustic alkali we obtain a black precipitate; whereas, when the solution contains only calcined quicksilver, the precipitate becomes yellow by such an addition. If this black precipitate is gently distilled, it rises in the form of quicksilver, leaving a yellow powder, which is in fact that part of the mercury which, in the beginning of the operation, was calcined by the nitrous acid.

"The boiling of the solution for about a quarter of an hour is necessary, in order to keep the hydrargyrus nitratus in a dissolved state, it being much disposed to crystallize. In general, some of the mercury remains undissolved; but it is always better to take too much than too little of it, because the more metallic substance the solution contains, the more hydrargyrus muriatus mitis will be obtained.

"It is necessary to pour the mercurial solution into the solution of salt by little at a time, and cautiously, so that no part of the undissolved quicksilver may pass along with it. Two ounces of common salt are sufficient to precipitate all the mercury; but then it may easily happen that some superfluous mercurius corro-sivus attaches itself to this precipitate, which the water alone is incapable of separating completely. This is undoubtedly the reason why mercurius precipitatus albus is always corrosive. I have found that common salt possesses the same quantity as sal ammoniac, viz. that of dissolving a greater quantity of mercurius corrosivus. I therefore employ four ounces and a half of common salt, in order to get the mercurius corrosivus entirely separated."

Of all the preparations of mercury, calomel is the most frequently used; and all the virtues attributed to mercury this preparation apparently possesses. The dose is from gr. i. to Э i. according to the intention; but five or eight grains are rarely exceeded.

We have said, that probably calomel might supply every other preparation; but that accident, or the routine of practice, easily becoming a habit, sometimes fixed a preference for other forms, without their possessing any real superiority. In glandular complaints calomel seems to be preferred; but small doses of the muriated mercury are often equally efficacious."in cutaneous complaints, it is often used in combination with the antimony, though from the preparation employed, the sulphur auratum, its virtues, as a mercurial, are greatly diminished. In the early preparation of Dr. James's powder (see James), calomel formed a portion; and it has been lately fashionable to add it to the antimonial, in the early periods of fevers, to secure a discharge from the bowels as soon as possible. The exhibition of calomel with camphor and opium, in the early stages of pleurisy, as recommended by Dr. Lysons, we think a more doubtful practice; and on this account we are unable to speak of its effects from experience. If, however, it is found to supersede the necessity of frequent bleeding, as has been asserted, it will undoubtedly be useful; but we do not find that the plan has been sufficiently followed to enable us to decide on its efficacy or eligibility. In the confluent small pox calomel has been given to assist or bring on the salutary salivation; but in this disease it has been dangerous from its inflammatory stimulus, nor is there sufficient time to produce the necessary evacuation. Rubbed upon the inside of the lips, it has produced similar effects to those which are occasioned by taking it internally, particularly in the lues venerea: in cases of chancres also, used by itself, or in the following form, it is highly advantageous.

Ceratilapid. calamin. ss. calomelanospp. 3 i. m. Mercurius duplicatus philosophicus. See Rebis.

Mercurius emeticus flavus. Hydrargyrus vi-triolatus, turpethum minerale; vitriolated mercury. and turbeth mineral.

Take of purified quicksilver, vitriolic acid, of each a pound; mix in a glass vessel, and heat them by degrees, until they unite into a white mass, which is to be perfectly dried with a strong fire. This matter, on the affusion of a large quantity of hot distilled water, immediately becomes a yellow powder. Rub the powder carefully with this water in a glass mortar; after it has subsided, pour off the water; and, adding more distilled water several times, wash the matter till it becomes insipid. Pharm. Lond. 1788.

To edulcorate it more quickly and effectually, the water intended to be used in its ablution is impregnated with a determined proportion of fixed alkaline salt; and by this means the quantity of the preparation will be increased, and its strength more equal.

The yellow emetic mercury is a powerful vomit; and, like other mercurials, will excite salivation: in robust habits it hath been used in cutaneous disorders and glandular obstructions. As an emetic, if hath been given to eight or ten grains; but in this dose it operates violently, and is only employed when the shock of vomiting is required to be considerable. It is thus sometimes useful in palsies, and more certainly in amaurosis. Half a grain or a grain, given every night, is said to have produced the best effects in the most inveterate cases of the venereal disease, in obstinate rheumatisms, and ulcers that were difficult of cure. It is a powerful medicine, but yet does not appear to excel the other less violent mercurials, except in particular instances, where considerable and rapid effects are necessary, and where the constitution is robust. It is a favourable medicine with some active practitioners, particularly Dr. Maryatt, in dropsies. See Maryatt's Art of Healing.

Mercurius praecipitatus ruber. Hydrargyrus nitratus ruber. Pharm. Lond. 1788. Red precipitate. The London college directs us to take of purified quicksilver and nitrous acid each a pound; muriatic acid, one drachm by weight; to mix in a glass vessel, and 'lissolve the quicksilver in a sand bath; then to raise the fire till the matter is formed into red crystals. Pharm. Lond. 1788. As soon as it hath acquired the sparkling red colour it should be immediately removed from the fire, or it will soon lose it again.

This preparation is sometimes mixed with minium and vermilion, but then the peculiar brilliancy is destroyed. If only minium is added, it may be detected by giving a sweetish taste to vinegar. If laid also on a very hot iron, the mercury will evaporate, leaving the lead behind.

The red nitrated quicksilver is only used externally as an escharotic; and if finely powdered and mixed with the unguentum resinse flavse, in the proportion of one or two scruples to an ounce, it is an excellent digestive for foul ill conditioned ulcers, bringing on a proper purulent discharge, instead of a thin sanies.

Unguentum hydrargyri nitrati. See Trachoma.

Ceratum hydrargyri nitrati. Cerate of nitrated quicksilver. _ Unguenti hydrarg. nitrati; cerati spermatis ceti aa. ij. m. It is sometimes applied to scrofulous and phagedenic ulcers.

Mercurius praecipitatus albus. Calx hydrargyri alba. White calx of quicksilver. The London college directs the following process: take of mu-riated quicksilver, sal ammoniac, water of kali, each half a pound; dissolve first the sal ammoniac, afterwards the muriated quicksilver in distilled water, and add, the water of kali; wash the precipitated powder until it becomes insipid. Ph. Lond. 1788.

Great care is required lest more of the fixed alkali be added than is necessary, for the precipitate will then be yellow. This preparation is almost constantly confined to external uses. Half a drachm or two scruples of it, added to an ounce of pomatum, is used as an elegant cure for the itch; the same quantity may be dissolved in two ounces of a thick decoction of lintseed, as a liniment for curing chancres when situated on the glans penis, or on the inside of the prepuce; a rag being dipped in it is applied to the glans, and the prepuce may be drawn over it.

This precipitate is adulterated with starch, and with white lead. The first is discovered by its becoming glutinous on being dissolved in a small quantity of water; the second by adding one third of its weight of alkaline salt; heating the mixture in a crucible till no fumes arise. If the residuum does not melt in water, it is adulterated.

Mercurius praecipitatus dulcis. Ph. Lond. 1721. See Hydrargyrus muriatus mitis.

Mercurius praecipitatus per se. Mercurius calcinatus.

Mercurius saccharatus. Sugared mercury. A preparation designed to give the mercury in a liquid form. Equal quantities of brown sugar candy and mercury are triturated till the globules disappear, adding a few drops of the oil of juniper.

Mercurius vitae, angelicus, Algarothi pulvis. The mercury of life; the precipitate formed by diluting butter of antimony with water.

This powder when edulcorated is a calx of antimony, always nearly of the same strength, and therefore sometimes preferred to the glass in preparing tartarised antimony.