Silver

Silver sulphide, Ag2S, found native in the minerals silver glance or argentite, is formed by direct union of its elements or by precipitating a silver solution with sulphuretted hydrogen. Silver sulphate, is produced by dissolving the metal in hot concentrated sulphuric acid, sulphur dioxide being given off ; it can also be produced by adding strong sulphuric acid to a silver solution. It is a white crystalline substance sparingly soluble in water, but dissolving in ammonia to give 2NH3,Ag2SO4.

Silver selenide, Ag2Se, occurs in nature in the double selenides naumannite, and eukairite, Cu2SeAg2Se. Silver tel luride, Ag2Te, occurs in the mineral hessite. Fulminating silver, which must not be confused with silver fulminate, is a black, ex ceedingly explosive powder, first obtained by Berthollet in 1788 by the action of strong ammonia upon silver oxide. When dry it is exceedingly unstable, as merely touching it with a feather is sufficient to cause violent detonation. It is probably variable in composition as the formulae and AgNH2 have been assigned to it by different observers. Silver fulminate, Ag2C2N202, pro duced by the action of alcohol on a solution of silver nitrate con taining free nitric acid, forms a grey crystalline powder. Silver azide, AgN3, the silver salt of hydrazoic acid, is formed by precipitating a silver solution with a soluble azide or by the inter action of silver nitrate and hydrazine sulphate. It is a white curdy precipitate physically resembling silver chloride. The two last compounds are used as detonators for high explosives.

Silver cyanide, AgCN, formed by the addition of a soluble cyanide to a silver solution, is a white curdy precipitate, soluble in excess of alkali cyanide or in ammonia. On ignition it is de composed into silver, cyanogen and paracyanogen, and can be thus distinguished from the chloride which it resembles in many respects. It is, however, not decomposed on exposure to light.

Certain silver gaits yield stable co-ordinative compounds with ethylenethiocarbamide (etu), the complex chloride [Ag,3etu] Cl is readily soluble in water, and not affected by light ; two complex nitrates are known, one sparingly soluble (NO3)2, and the other readily soluble [Ag,4etu]NO3 (Morgan and Burstall, 1928).

Bivalent Silver.

In the foregoing silver salts the metal is in variably present in the univalent condition. A co-ordinative com pound of bivalent silver has, however, been described by Barbieri, 1912; which has the constitution [Ag, that is argentic persulphate with four molecules of pyridine of crystallization; it is a sparingly soluble, yellow, crystalline substance.

Further evidence of the existence of complex derivatives of bivalent silver is furnished by W. Hieber and F. Miihlbauer (1928), who employ the organic diamine, o-phenanthroline (pha), in preparing the brown persulphate, [Ag, 2pha] S208, and also the perchlorate, chlorate, nitrate and acid sulphate, [Ag, 2pha] X2, where X = CL04, CL03, or HSO4.

Medicinal Use.

Two compounds of silver are in the British Pharmacopoeia: (I) Argenti nitras (U.S.A. and British Pharma copoeia), lunar caustic, incompatible with alkalis, chlorides, acids (except nitric and acetic), potassium iodide and arsenical solu tions. From the nitrate are made (a) argenti nitras indurata, toughened caustic, containing 19 parts of silver nitrate and one of potassium nitrate fused together into cylindrical rods; (b) argenti nitras mitigatus, mitigated caustic, in which one part of silver nitrate and two parts of potassium nitrate are fused together into rods or cones.

(2) Argenti oxidum, incompatible with chlorides, organic sub stances, phenol, creosote, etc., with which it forms explosive com pounds.

Therapeutics.—Externally the nitrate has a limited caustic action, destroying the superficial tissues and separating the part acted on as a slough. It may be employed to destroy warts or small growths and to reduce exuberant granulations, or it may be applied to bites. In granular lids and various forms of ophthalmia, solutions of silver nitrate (2 gr. to 1 fl.oz.) are employed. A I% solution is also used as a prophylactic for ophthalmia neonatorum.

The effect of the nitrate being both astringent and stimulating as well as bactericidal, solutions of it are used to paint indolent ulcers, and in chronic pharyngitis or laryngitis. Silver salts are most useful as an injection in sub-acute and chronic gonorrhoea; one uses either the nitrate (I--5% solution) or protargol (I% solution), which is a proteid compound containing 8% of silver; they also benefit in leucorrhoea. In pruritus of the vulva and anus, a weak solution of silver nitrate will relieve the itching, and strong solutions painted round the base of an incipient boil will abort its formation.

Internally the nitrate has been used in the treatment of gastric ulcer, in ulcerated condition of the intestine, and in chronic dysentery. For intestinal conditions it must be either given in a keratin-coated pill or injected high up into the rectum. The oxide has been given in epilepsy and chorea. Nitrate of silver is eliminated from the system very slowly and the objection to its continuous use as a drug is that silver is deposited in the tissues causing argyria or chronic silver poisoning, of which the most prominent symptom is the dark slate-blue colour of the lips, cheeks, gums and later of the skin. Taken in large doses, nitrate of silver is a powerful poison, causing violent abdominal pain, vomiting and diarrhoea, with the development of gastro enteritis. In some cases nervous symptoms and delirium super vene. The treatment consists in the use of solutions of common salt, followed by copious draughts of milk or white of egg and water, or soap in water, in order to dilute the poison and thus to protect the mucous membranes of the oesophagus and stomach.

(F. E. M.)