This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Refined Silver. Br. Appendix.
Metallic silver is quite inert, and may lie for a long time in the alimentary canal without sensible effect. It is only in chemical combination that it becomes efficient. As all the constitutional effects of its preparations can be obtained by the exhibition of the nitrate, and as this is generally preferred in practice, it may conveniently represent the metal in its relations to the system at large; and all that it is necessary to say, in reference to the operation and uses of silver as a medicine, may be included in our consideration of that salt. Afterwards, nothing need be noticed, in relation to the other preparations, except what may be peculiar to them severally.
Argenti Nitras. U. S., Br. - Lunar Caustic.
This salt has been known since the times of Geber, who described the mode of preparing it. I propose to treat of it, in this place, solely in reference to its internal use. As an external remedy, it is among the most valuable; but the consideration of it, in this capacity, belongs to another part of the work. (See Escharotics and Proteclives.) It is kept in two forms; one, that of cylindrical sticks, adapted for topical use, and frequently called lunar caustic; the second, that of crystals, which are preferred when the medicine is to be given internally. It is to the latter that the following remarks apply.
The crystals of nitrate of silver are prepared by dissolving silver in nitric acid with a little water, and then evaporating, so that crystallization may take place upon the cooling of the liquid. They should be kept in well-stopped bottles, from the interior of which every thing organic should be excluded.
Crystallized nitrate of silver consists of one equivalent of nitric acid and one of protoxide of silver, without water of crystallization.
The crystals are colourless, transparent, and in the form of rhomboidal plates. They are inodorous, but of a strong, bitter, metallic, peculiar, extremely disagreeable, and adhesive taste. Water and alcohol dissolve them freely, especially the former, which takes up its own weight of the salt. At a moderate heat they melt, and at a strong heat are decomposed. In contact with the smallest portion of organic matter, they blacken on exposure to light; but they remain unchanged, even by the sun's rays, in the entire absence of such matter. Their solution in pure distilled water is similarly unaffected by sunlight, unless organic matter is present, in which case it is darkened. The change of colour is owing to a partial reduction of the silver.
Nitrate of silver is decomposed, with the formation of insoluble products, or such as are but slightly soluble, by the alkalies, alkaline earths, their carbonates, and soap; by sulphuric, muriatic, hy-driodic, phosphoric, hydrosulphuric, and tartaric acids, and all the soluble salts formed by the reaction of these acids with salifiable bases, consequently by the soluble sulphates, muriates, phosphates, tartrates, chlorides, iodides, and sulphurets; and by astringent vegetable infusions, in consequence of their tannic acid. With albumen and fibrin it unites, forming compounds insoluble in water; but it is a fact of some importance, in explanation of the operation of the salt on the system, that the albuminate of the nitrate of silver thus formed is soluble in an excess of albumen. Of like significance is also the fact, that the insoluble chloride of silver, which is formed whenever the nitrate comes into contact with muriatic acid or a soluble chloride, is rendered soluble by an excess of chloride of sodium or potassium.*
In consequence of the great number of substances which decompose the nitrate, or combine with it, and the constant presence in the stomach of one or more of these substances, especially albumen, muriatic acid, or a chloride, it is scarcely possible that it can long retain its integrity after having been swallowed; though it may do so sufficiently long to exert a direct influence on the mucous coat. That it should enter the small intestines as nitrate of silver, appears to me to be clearly impossible, unless swallowed in quantities so large as to be poisonous, or unless so incorporated with other substances in the form of pill, that, in this shape, it may pass through the stomach before the pill is broken up, and its interior exposed to the reagents there existing.
Locally, nitrate of silver is powerfully irritant, and, in a concentrated state, acts as an escharotic by combining with the albuminous matter of the tissues, and thus disorganizing them. When in contact with the mucous membranes, with ulcers, or with the skin deprived of the cuticle, it combines with the albumen of the secreted matters, and often with that of the tissue itself, forming a white and insoluble compound, which covers the surface; and this happens as well in the gastric and intestinal mucous membranes, as in those visible from without. Applied to the skin, it soon produces a black stain, in consequence of the partial reduction of the silver by reaction with the cuticle. This black stain usually remains until the cuticle separates, either gradually, or at once completely, as in vesication. It may be removed, however, by applying to the spot the tincture of iodine, and following this with a solution of hyposulphite of soda; or by the similar application of a solution of cyanide or of iodo-cyanide of potassium. (Journ. de Pharm., Nov. 1865, p. 414.) These remarks, in reference to the local effects of nitrate of silver, will be extended in a subsequent account of the escharotic and protective operation of the salt. At present, they seemed necessary to explain the effects of the medicine upon the stomach.
In very small doses, repeated two or three times a day, nitrate of silver produces no other observable effects than those of a gentle tonic and astringent; as improved appetite, invigorated digestion, and perhaps a tendency to costiveness. Taken more largely, it causes warmth of stomach, and some gastric uneasiness, indicating an irritant action, which, upon a still further increase of the quantity, is evinced by gastric pains, sometimes nausea and vomiting, and occasionally also by griping pains in the bowels, with either diarrhoea or constipation. As to the degree of irritant effect, much depends on the mode of administration, and the condition of the stomach at the time. It has been repeatedly observed that, in the form of pill, large doses produce little irritation; while a smaller quantity will violently irritate, if given in solution. Dr. Powell found that he could sometimes give fifteen grains in pill, while five grains in solution could rarely be borne by the stomach. (Med.-ehir. Trans., ix. 238.) The result is obviously owing, in the instance of the solution, to the whole quantity being brought at once into contact with the surface of the stomach, before time has been allowed for decomposition; while, in the pilular form, dissolving gradually, it acts also gradually, and is more liable to decomposition before it can act at all. When the stomach is full of food, the medicine would be much more exposed to decomposing reagencies than when it is empty, and would consequently be less likely to irritate; for all the insoluble substances resulting from the chemical changes of the nitrate in the stomach are much less irritant than the salt itself. Thus, the chloride of silver, which must be among the most common products, may be given in large doses, without observable effect.