Page:EB1911 - Volume 18.djvu/177

Rh mercury compounds; it is the principal ore, occurring in nature as the mineral (q.v.), and is extensively used as a pigment, (q.v.). It is obtained as a black powder by triturating mercury with sulphur, the compound thus formed being known in pharmacy as Aethiops mineralis, and also by precipitating a mercuric salt with sulphuretted hydrogen. It is only slightly acted upon by nitric acid; it dissolves in aqua regia; chlorine gives a yellow compound, 2HgS. HgCl2; and it dissolves in potassium sulphide solutions to form double salts of variable composition.

Mercurous Sulphate, Hg2SO4, is a white, sparingly soluble, crystalline substance obtained by adding sodium sulphate to a solution of mercurous nitrate. Mercuric sulphate, HgSO4, is a white, soluble salt obtained by dissolving mercury in hot strong sulphuric acid; on digestion with water, it decomposes into a basic salt HgSO4. 2HgO known as turbith or turpeth mineral, and into an acid salt, HgSO4. 2SO3.

Mercury Phosphide, Hg3P2, is obtained as brilliant red, hexagonal crystals by heating mercury with phosphorus iodide to 300 and removing the mercuric iodide simultaneously formed by means of potassium iodide solution. Mercurous phosphate, Hg3PO4, and mercuric phosphate, Hg3(PO4)2, are obtained as white precipitates by adding sodium phosphate to solutions of mercurous and mercuric nitrates respectively.

Mercurammonium Compounds.—By the action of ammonia and ammonium salts mercury compounds yield a number of substances, many of which have long been used in medicine. By the action of dry ammonia on calomel mercuroso-ammonium chloride, NH3HgCl, is obtained; aqueous ammonia on calomel gives dimercuroso-ammonium chloride, NH2Hg2Cl. By adding ammonia to a solution of mercuric chloride, mercurammonium chloride, known in pharmacy as “in fusible white precipitate,” NH2HgCl, is obtained; “fusible white precipitate” is mercuro-diammonium chloride, Hg(NH3Cl)2, and is obtained by adding a solution of mercuric chloride to hot solutions of ammonium chloride and ammonia so long as the precipitate first formed redissolves; the substance separates out on cooling. By precipitating a strongly alkaline solution of mercuric iodide in potassium iodide (Nessler’s solution) there is obtained a yellow precipitate of NH2Hg2OI; this reaction is the most delicate test for ammonia, a yellow coloration being given by minute traces. By passing dry ammonia over precipitated mercuric oxide at 130°, a nitride N2Hg3 is obtained. The oxide and ammonia solution gives the stable and basic mercurhydroxylamine, NHg2OH. The constitution of these compounds has been especially studied by K. A. Hofmann and E. C. Marburg (Zeit. Anorg. Chem. 23, 126); these chemists formulate “in fusible precipitate” as Hg(NH2)Cl, “fusible precipitate” as Hg(NH3Cl)2 “Millon’s base” as (HO . H)2:NH2OH, thus postulating three distinct types of compounds, (1) amidochlorides; (2) amines; (3) substituted ammonium derivatives.

Analysis.—Mercury compounds, when heated in a closed tube with sodium carbonate, yield a grey to black sublimate of metallic mercury, which readily unites to form visible globules. The metal is precipitated from solutions by digestion with bright copper-foil, a coating being formed on the copper, which becomes silvery on rubbing, and disappears when the quicksilvered copper is heated in a sublimation tube.

Solutions of mercurous salts with hydrochloric acid give a white precipitate of calomel, which becomes jet-black on treatment with ammonia. Stannous chloride, in its twofold capacity as a chloride and a reducing agent, precipitates both mercurous and mercuric solutions, at first as calomel, and on addition of an excess of reagent the precipitate becomes grey through conversion into finely-divided quicksilver. Sulphuretted hydrogen, when added very gradually to an acid mercuric solution, gives at first an almost white precipitate, which, on addition of more and more reagent, assumes successively a yellow, orange and at last jet-black colour. The black precipitate is HgS, which is identified by its great heaviness, and by being insoluble in boiling nitric and in boiling hydrochloric acid. A mixture of the two (aqua regia) dissolves it as chloride.

“Mercurous” mercury is quantitatively estimated by precipitating as calomel and weighing the precipitate on a tared filter at 100°. The metal may also be estimated by distillation in a closed tube with lime, the metal being collected and weighed, or by precipitating the solution with an excess of stannous chloride. More convenient is the method of precipitating as sulphide by an excess of sulphuretted hydrogen, and weighing the precipitate on a tared filter; or by means of a Gooch crucible.

Pharmacology and Therapeutics

The use of mercury as a therapeutic agent is of comparatively recent date. To the Greeks and Romans its value was unknown, and the Arabian physicians only used it for skin affections. It was not till the middle of the 16th century that the special properties of mercury were fully appreciated, but since that time the metal has continued to hold a high though fluctuating value as a medicine. At first the metal in a finely divided state or in vapour was used; but very soon its various compounds were found to be endowed with powers even greater than those of the metal itself, and with the discovery of new compounds the number of mercurial medicines has largely increased.

The British Pharmacopeia contains some twenty-five mercurial preparations, including those of (q.v.). Only the useful preparations will be mentioned here. Free mercury is contained in Hydrargyrum cum Creta, or “grey powder,” which consists of one part of mercury to two of prepared chalk. The power of this valuable and widely used preparation varies somewhat with its age, as old specimens contain some mercuric oxide, which makes them more active. The dose is 1–5 gr., and the preparation is usually employed for children. The Pilula Hydrargyri, or “blue pill, contains one part of mercury in three, and the dose is 4–8 gr. It is usually employed for adults. There are also five preparations of free mercury for external use. Of these the most useful is the Unguentum Hydrargyri, “or blue ointment,” which contains one part of mercury in two. Weaker ointments are also prepared from the red and the yellow forms of mercuric oxide. The perchloride of mercury or corrosive sublimate is therapeutically the most important salt of mercury. The dose is – gr. It is incompatible with alkalies, alkaline carbonates, potassium iodide, albumen and many other substances, and should therefore be prescribed alone. It is decomposed by impure water, and distilled water is therefore used in making the Liquor Hydrargyri Perchloridi, in which form it is usually prescribed. This contains half a grain of the perchloride to the fluid ounce and its dose is 30–60 minims. The perchloride is also compounded with lime-water to form the Lotio Hydrargyri Flava, or “yellow wash,” which contains two grains of the salt to the fluid ounce. Mercuric iodide is an equally potent salt and has come into wide use of late years. It has the same dose as the perchloride and is largely prescribed in the Liquor Arsenii et Hydrargyri Iodidi, or Donovan’s solution, which contains 1% of arsenious iodide and 1% of mercuric iodide, the dose being 5–20 minims. An ointment widely used is prepared from the mercurammonium chloride (Unguentum Hydrargyri ammoniatum) of which it contains one part in ten. It is known as “white precipitate ointment.”

In discussing the pharmacology of mercury and its compounds, it is of the first importance to observe that metallic mercury is inert as such, and that the same may practically be said of mercurous salts generally. Both mercury itself and mercurous salts tend to be converted in the body into mercuric salts, to which the action is due. When metallic mercury is triturated or exposed to air it is partly oxidized, the first stage of its transformation to an active condition being thus reached.

Metallic mercury can be absorbed by the skin, passing in minute globules through the ducts of the sweat-glands. The mercury contained in “blue ointment” is certainly thus absorbed, actually circulating in the blood in a very different form, as described below. There is no local action on the skin. The mercuric salts, and especially the chloride and iodide, are probably the most powerful of all known antiseptics. One part of the perchloride in 500,000 will prevent the growth of anthrax bacilli, and one part in 2000—the strength commonly employed in surgery—kills all known bacteria. The action is apparently specific and not due to the fact that perchloride of mercury precipitates albumen, including the albuminous bodies of bacteria, for the iodide is still more powerful as a germicide, though it does not coagulate albumen. These salts cannot be employed for sterilizing metallic instruments, which they tarnish. As these drugs are essentially poisons they must be used with the greatest care in surgical practice, and as they are particularly deleterious to the secreting structure of the kidney they must not be employed as antiseptics in diseases where renal inflammation is already present or probable. They are therefore contra-indicated for application to the throat in scarlet-fever or to the uterus in eclampsia. The stronger mercurial ointments kill cutaneous parasites and also possess some degree of antipruritic action, especially when the cause of the itching is somewhat obscure. Mercuric salts, when in strong solution, are caustic. It is important to observe that the volatility of metallic mercury and many of its compounds causes their absorption by the lungs even when no such effect is intended to follow their external application. This fact explains the occurrence of chronic mercurial poisoning in certain trades.

Single doses of mercury or its compounds have no action upon the mouth, the characteristic salivation being produced only after many doses. Their typical action on the bowel is purgative, the effect varying with the state of the mercury. So relatively inert is metallic mercury that a pound of it has been given without ill effects in cases of intestinal obstruction, which it was hoped to relieve by the mere weight of the metal. Half a grain of the perchloride, on the other hand, is a highly toxic dose. The action of mercurials on the bowel is mostly exerted on the duodenum and jejunum, though the lower part of the bowel is slightly affected. Hence a dose of mercury usually needs a saline aperient to complete its action, as in the “blue pill and black draught” of former days. Mercurials do not cause, in therapeutic doses, much increase in the intestinal secretion, the action being mainly exerted on the muscular wall of the bowel. The bile is rapidly removed from the duodenum before any re-absorption can occur, and the bacterial action which