Characters. - White or greyish-white cylindrical rods or cones.

Preparation. - Prepared by fusing together nitrate of silver 1 part, with nitrate of potassium 2 parts, B.P.; 1 part, U.S.P.

Solubility. - It is freely soluble in distilled water, but only sparingly in rectified spirit.

Reactions. - The aqueous solution gives with hydrochloric acid a curdy white precipitate which darkens by exposure to light (silver); the filtrate from this mixture giving a yellow precipitate with perchloride of platinum (potassium), and evolving ruddy fumes when warmed with sulphuric acid and copper (nitrate).

General Action of Silver Salts. - Soluble silver salts, such as the nitrate of silver, have a strong affinity for the cement by which epithelial or endothelial cells are united, and are, therefore, much used in staining microscopic preparations. They also unite with albumen, forming albuminates of silver. When applied to the skin, nitrate of silver produces a white mark which rapidly becomes blackened by exposure to light, and the epidermis, either alone or with a slough varying in depth according to the strength of the application, is thrown off. Locally, it causes greater contraction of the vessels than other metals. In the mouth it has an unpleasant astringent taste, corrugates the mucous membrane, and acts as an irritant or caustic. In the stomach, in small doses, it acts as an astringent, and occasionally lessens vomiting, but in larger doses it acts as an irritant, and causes vomiting and symptoms of irritant poisoning (p. 396). In the intestine small doses are astringent, and, when absorbed from the blood, appear, like zinc or copper, to have a tonic action on some parts of the nervous system. When taken for a length of time it is apt to cause a livid discoloration of the skin. This discoloration appears to depend upon the amount of silver taken independently of the time during which its administration has been continued, so that it is advisable, when administering nitrate of silver to a patient, to inquire whether he has previously taken it or not, as the silver remaining in the system, together with that administered in the second instance, might cause a darkening of the skin which the quantity employed in the second course alone would not have produced. When taken for a long time, silver salts appear to produce fatty degeneration of the tissues. They are probably very slowly eliminated by means of albuminous secretions such as bile.

Uses. - Nitrate of silver may be applied to destroy parasitic fungi and remove tinea; to destroy the epidermis itself or epidermic structures such as warts, and to check the bleeding from leech-bites. In solution it relieves the itching of pruritus and of lichen. When sponged over the skin it hardens the epidermis and may prevent the formation of bed-sores. It is said to arrest vesication in herpes if painted over the surface as soon as the vesicles begin to form. It is also said that the pitting of smallpox is prevented by opening the vesicle and touching the surface beneath with a solution of the salt, or even by painting the solution over the skin. It has been recommended as a remedy in erysipelas, and is applied either by painting the strong solution over and beyond the inflamed surface, or by drawing a line with solid nitrate of silver upon the skin a little way beyond the margin of the inflammation. The alteration produced in the tissues underneath this line is said to prevent the extension of the inflammation beyond the limit thus formed. It is of little use in poisoned wounds, such as the bite of a mad dog (p. 347). Dilute solutions may be applied to the eye in tinea tarsi and conjunctivitis. In the mouth it may be used as an application to ulceration of the tongue, soft palate, or tonsils, and is often employed for this purpose on account of the readiness with which it can be applied; it is especially useful in follicular tonsillitisand pharyngitis. In thus applying it care should be taken that it is well fixed in the holder, as otherwise a quick motion of the patient may break off the portable stick of nitrate of silver, which will probably fall into the pharynx, be swallowed, and may produce symptoms of irritant poisoning. The treatment of poisoning is to give common salt in order to form insoluble, and therefore inert, chloride of silver. Where the stick of nitrate of silver has been swallowed in substance this treatment has not always proved efficacious, and salt should therefore then be administered in combination with mucilaginous substances such as porridge and gruel, along with an emetic, so that the stick of silver may be at once evacuated from the stomach, while the mucilaginous envelope prevents it from doing any harm to the oesophagus on its way. It has been used to destroy the false membrane in croup, and as a useful application to the larynx in laryngeal phthisis. It may be applied either in solution of the strength of 30 grains to the ounce in laryngeal phthisis, by means of a brush, or in the form of lycopodium, which, after being dipped in the solution and then dried, may be blown by a curved tube into the larynx (cf. p. 480). It is sometimes used as an injection in gonorrhoea. Internally, it may be employed in irritable stomach, and also as an astringent in chronic diarrhoea and dysentery, and as a nervine tonic in chorea and epilepsy.