The pure metals exert no action on the animal system; for, although iron be administered in its metallic state, yet it must be changed by acid in the stomach to the state of an oxide before it can prove active as a remedy. Tin operates only by mechanical attrition; and mercury, which has also been given internally in the metallic form, on mistaken principles, cannot act otherwise than as a mechanical substance: but when metals suffer oxidizement, or are changed by acids to the state of salts, they constitute a class of remedies of great activity and importance. The following are employed as remedies: a. in a metallic state.

Iron. Mercury

TIN : b, variously combined with oxygen, chlorine, iodine, bromine, cyanogen, sulphur, and acids.

Aluminium. Antimony. Arsenic. Bismuth. Barium. Calcium. Copper. Iron. Lead. Magnesium. Mercury. Potassium. Sodium. Silver. Zinc. 1 Essays on Burns, etc. by Edward Kentish, 1797 and 1800

The union of oxygen with a metallic base is denominated oxidizement, and the resulting compound an oxide. This combination, for medicinal purposes, is effected in four ways: 1. By the action of atmospheric air, aided by an increased temperature; 2. by deflagration with nitrate of potassa; 3. by the action of water; and, 4. by solution in an acid, the acid being afterwards abstracted by an alkali, or some substance for which it has a greater affinity than it has for the oxide of the metal. In whatever manner the oxidizement is effected, metals in changing to oxides lose their lustre, tenacity, inflammability, and other metallic properties; and are gradually converted into earthy-like substances, the weight of which is greater than that of the portion of metal employed. Different metals combine with different quantities of oxygen, which is even the case with the same metal: the maximum and minimum of oxidizement is expressed by the terms protoxide to signify the lowest degree of oxidizement; peroxide the highest; and deutoxide, tritoxide, etc. the intermediate degrees. Some metals are capable of so high a degree of oxidizement as to acquire acid properties.

The activity of the oxides of metals on the animal system appears to be regulated, with a few exceptions, by the quantity of oxygen with which they are combined; and therefore, as Dr. Murray has justly observed, "when a process for the preparation of any metallic oxide has once been established, and practitioners have become accustomed to its powers and strength, the process ought not to be varied or changed, from the idea of some trivial improvement; as an alteration of circumstances, apparently of little consequence, may give rise to a very important change in the result. And it is nearly demonstrable, that the oxides of a metal formed by different processes, - as, for example, by a process conducted in the humid way, or by one with the application of heat, - cannot be precisely the same."1

The oxidizement of metals generally renders them capable of uniting with acids, and forming soluble salts. The metallic salts, therefore, are oxides combined with acids; and this is the case, whether an oxide previously prepared be dissolved in an acid, or whether the salt be the product of the direct solution of a metal in an acid. In the latter case, the metal first gains oxygen either from the acid itself, or from the water, which is decomposed; and the oxide thus formed is then dissolved by the remainder of the acid. The properties of the metallic salts are much varied by the previous degree of oxidizement of the metals; and in the preparation of the metallic salts, therefore, strict attention is requisite in following one established and approved process.

1 System of Mat. Med. ii. 253.

No part of chymical and pharmaceutical language is so faulty as the nomenclature of the metallic salts. Thus, although there is no instance of a direct combination of a metal with an acid, yet we have sulphate of iron, nitrate of silver, trisnitras bismuthi, acetas plumbi, etc.

Many of the metallic salts are altered by exposure to the atmosphere; some effloresce, some attract moisture, and others are reduced by the action of light: thence all of them ought to be kept in well-stopped glass bottles; and perhaps these should always be either made of dark green glass, or rendered otherwise opaque. In compositions which require these salts to be dissolved in water, distilled or filtered rain water should always be employed, and much attention is requisite to avoid combining them with incompatible substances, which may either chymically decompose them, or alter their medicinal properties.

Chlorine combines readily with metals at a common temperature, occasionally with violent action and the evolution of light and caloric. The attraction for the base of the metal is often so great that it decomposes oxides: thus when chlorine and lime, or soda, or potassa, or baryta, are brought together at a red heat, oxygen is evolved, and a chloride of the metallic base is formed.

The metallic chlorides are solid bodies; they are fusible by heat and crystallize in cooling, and some of them may be sublimed without change. All of those used in medicine are soluble in water, with the exception of the chloride of mercury; and those which are soluble may be recognized by yielding a white curdy precipitate with nitrate of silver.

Chlorine exerts little affinity for oxides; and Berzelius has attempted to prove that the bleaching solutions are mixtures of a metallic chloride on the chlorate of an oxide; but this opinion must be regarded as still sub judice.

The chlorides are very active medicines.

Iodine has a powerful affinity for metals, and forms with them compounds capable of sustaining a red heat without decomposition; they are termed iodides. When they contain 1 equivalent of iodine, they are termed protiodides; when 2 equivalents, biniodides. They are all decomposed by chlorine, bromine, and sulphuric and nitric acids. All the iodides are powerful remedies.

Bromine has less affinity for metals than chlorine, but more than iodine. In combining with metals to form bromides, caloric and light are evolved. Only one bromide, namely, that of potassium is contained in the Pharmacopoeia; but the bromide of iron is, also, a very active medicine.

Sulphur also combines with the metals, and forms sulphurets. They are also formed, when sulphuretted hydrogen gas is thrown into the acid solutions of those metals which have a weak affinity for oxygen; and, as the metallic solutions differ greatly in the degree of facility with which they are thus decomposed, sulphuretted hydrogen gas may be employed, as Proust has shown, for separating different metals held together in the same solutions. The metallic sulphurets are more used for pharmceutical purposes than as remedies, their dose not being easily appreciated, and their effects uncertain. Many of them are natural productions.

Cyanogen, which is a compound of 1 eq. of nitrogen + 2 of carbon, unites with metals, forming cyanides and bicyanides, according to the quantity of cyanogen, combined with the base.