Names for Silver Nitrate
The various names of Silver Nitrate include... Argenti Nitras; Argenti Nitras Fusum; Nitrate Of Silver; Lunar Caustic; Lapis Infernalis;
History of Silver Nitrate
NITRATE OF SILVER (Lunar caustic; Lapis infernalis) seems to have been known to Geber in the eighth century.
Chemical History.—In preparing it, according to the process of the Pharmacopoeias, by dissolving silver in diluted nitric acid, the solution is accelerated if the silver be in thin plates, or granulated by dropping the melted metal from a moderate height into water. Crystals may be obtained by evaporating and cooling the solution. The Dublin College recognizes the salt in this form ; but unnecessarily, since the crystallized salt is well ascertained to differ in no essential respect from that which is fused. All the Pharmacopeias have a process for preparing the fused nitrate of silver, which is run into moulds to form it into rods or pencils for convenience in surgical practice. In making this preparation from the solution care must be taken to drive off the whole water by a moderate heat gradually raised, till a clear liquid be obtained from which bubbles cease to be disengaged,—but not to raise the heat much higher, otherwise the salt will decompose and blacken. It is difficult, however, to prevent slight decomposition from taking place.
Uses of Silver Nitrate
Nitrate of silver possesses corrosive, irritant, and tonic properties. The nature of its corrosive action has not been carefully studied, but the corrosion is accompanied with blackness of the part on exposure to light. As a corrosive it is a poison, but by no means an active one, because it is promptly decomposed by the chloride of sodium, mucus, and other ani-mal matters, in the contents of the stomach. On account of its corrosive properties it is much employed as an escharotic for removing warts and other excrescences, and for repressing exuberant granulations upon sores ; but its efficacy in these circumstances depends not so much on its corroding down the morbid structure, as upon its causing increased absorption and altered action. To its operation in this way, and not to its corrosive properties, must also be ascribed the remarkable power now universally recognized in it by surgeons of altering the action of constitutional and other ulcers. By Mr. Higginbottom and others the applications of this salt as a local stimulant in indolent and constitutional ulcers have been made very extensive and diversified. Perhaps it has been too warmly praised and too indiscriminately used; but it is well ascertained to be one of the best, if not the very best, of all local applications in the early stage of chancre, in mercurio-syphilitic as well as true venereal ulceration of the throat, and in ulcers of the cornea. No method of treatment more frequently or more quickly disposes these forms of olceration to heal and cicatrize, than touching their surface with a solution of nitrate of silver or with a pointed rod of the salt. The author last mentioned has also strongly recommended the employment of it for the purpose of arresting external inflammation, more especially those forms of it which manifest a tendency to spread, such as erysipelas, erythema, and spreading cellular inflammation. The progress of the disease is said to be frequently arrested by rubbing a moistened rod, or painting a strong solution of nitrate of silver, over the inflamed part and some portion of the adjacent sound skin, so as to encircle the inflammation. Nitrate of silver has also been found a useful local application in some chronic cutaneous diseases, and particularly in ringworn. In this class of affections it might probably be used with advantage to a greater extent. It is one of the topical remedies which have been supposed to pos-sess the property of preventing the exolcerations and consequent scars produced by the pustular eruptions of small-pox; for which purpose it is applied to the tops of the pustules before they are fully developed. A lotion consisting of two, four, six grains or upwards to the ounce is a favourite remedy with ophthalmic surgeons for removing specks from the cornea.
Internally, nitrate of silver has been often used as a tonic. In epilepsy, it has been considered to be a powerful remedy of this kind ; but it has gone rather out of fashion, since the attention of practitioners was called to an occasional and extraordinary consequence,—the communication of an indelible bluish-gray tint to the skin. Although cures seem to have been accomplished by its long-continued use, its success has not been such as to render it a favourite remedy in face of the risk of so annoying a result. It has also been tried as a tonic or antispasmodic in hysteria, in asthma and gastrodynia, though with doubtful advantage. Various authors of last century have recommended it strongly as a hydragogue cathartic in dropsy and in worms ; there are not wanting modern writers who have repeated these recommendations; and it is said to be the basis of some nostrums for the treatment of the diseases in question.—The oxide has also been used internally as a tonic and anti-spasmodic. Very lately it has come into fashion, having been thought not liable to cause discoloration of the skin. This nolion is at variance with the best established doctrines in general therapeutics; and accordingly I know-one instance, and have been informed of others, where discoloration took place.
Nitrate of silver is given in doses varying from a quarter of a grain to two grains and upwards. Very discrepant accounts are given of its activity ; which may probably arise from too little attention having been paid to the extreme facility with which this salt may be decomposed and rendered inert, by the secretions and contents of the stomach. On account of its very disagreeable taste it ought always to be given internally in the form of pill; which may be made with sugar, mucilage, bread-crumb, or extract of dandelion. Lotions of nitrate of silver are made of every possible variety of strength.
Adulterations of Silver Nitrate
Nitrate of silver is subject to various adulterations, the chief of which are the nitrates of lead, zinc, copper, and potash; and in consequence of careless preparation, it may likewise contain some free silver. The system of tests laid down by the London College will detect all these imparities except the most frequent of them. When the dissolved salt is precipitated by an excess of chloride of sodium, the precipitate is not entirely soluble in ammonia, if lead be present; and the liquid part gives with sulphuretted-hydrogen a white precipitate if there was any zinc, but a black one if there was any copper. As this method of examination will not detect the most frequent adulteration, namely nitrate of potash, the Edinburgh College has adopted an entirely different plan, which provides against all sorts of adulterations collectively, without indicating what in any particular case the nature of the impurity may be. This method consists in precipitating a given weight of nitrate of silver by such a quantity of a pure muriate as will throw down very nearly, but not quite, the whole silver in the form of chloride— leaving, if the salt were pure, a small quantity, which, after filtration, will precipitate with more of the test. The muriate of ammonia is preferred, because it is almost always a very pure salt. Of this salt 9.12 grains will exactly precipitate 29 grains of nitrate of silver. Hence if 9 grains of muriate of ammonia be added to that quantity of pure nitrate of silver, a farther addi-tion of the test will cause farther precipitation. The data put down in the formula would allow about one per cent, of impurity; which is above the average amount in good specimens. The only other common impurity,— namely free silver,—is almost constantly present on account of the difficulty effusing the salt without a little of it being decomposed by too strong a heat; but the proportion ought to be very small. It is indicated by a black powder being left when the nitrate is dissolved in distilled water, and when abundant, by the rods presenting an unusually dark-gray colour on the surface of a fresh fracture. From what I have seen of the fused nitrate of silver of the shops, it may be suspected to contain nitre if it has a colourless fracture, and is entirely soluble without any black powder separating.
This information was taken from....
Christison and Griffith's Dispensatory 1848
(A Dispensatory or Commentary on the Pharmacopeias of Great Britan and the United States)
Lea and Blanchard publishers of Philadelphia