=Silver, Ni'trate of.= AgNO_{3}. _Syn._ ARGENTI NITRAS, L. This article is found in commerce under two forms:--
1. CRYSTALLISED. _Prep._ By dissolving grain silver in nitric acid diluted with about twice its weight of water, evaporating the solution until it is strong enough to crystallise on cooling, and then allowing it to cool very slowly. Colourless; transparent, anhydrous rhombic prisms or tables; soluble in an equal weight of cold and in half their weight of boiling water; soluble in alcohol; fuse when heated, and at a higher temperature suffer decomposition; blackened by light, and by contact with organic substances. Its solution in distilled water is not sensibly darkened by light, in the absence of organic matter. Used for solutions, and in photography.
2. FUSED (LUNAR CAUSTIC; ARGENTI NITRAS--B. P., Ph. L. & E., A. N.
FUSUM--Ph. D.). _Prep._ (Ph. D.) Refined silver, 3 oz.; pure nitric acid, 4 fl. oz.; distilled water, 5 fl. oz.; mix in a glass flask, and apply in a gentle heat until the metal is dissolved; transfer the solution to a porcelain capsule (or a large porcelain crucible), decanting it off a heavy black powder which appears at the bottom of the flask, and, having evaporated it to dryness, raise the heat (in a dark room) until the mass liquefies; then pour it into a brass mould (iron moulds--Ph. E. & Ph. L.
1836), furnished with cylindrical cavities of the size of a goose-quill, and which then admits of being opened by a hinge; preserve the concreted salt in well-stopped bottles, impervious to the light. The formulae of the Ph. E. & Ph. L. 1836 are similar.
_Obs._ In preparing this salt care should be had that the silver is free from copper. Pure nitrate of silver may, however, be prepared from silver containing copper, by evaporating the nitric solution to dryness, and cautiously heating the mixed nitrates to fusion. A small portion of the melted mass is examined from time to time, until a little dissolved in water, and treated with ammonia in excess, ceases to strike a blue colour.
When this point is arrived at, the fused nitrate is allowed to cool, when it is redissolved in water, filtered or decanted from the insoluble black oxide of copper, and evaporated in the usual way.
The heat employed in preparing the fused nitrate should not exceed 420 Fahr., and the fusion should be effected completely, but with moderate expedition, to prevent loss of nitric acid. Formerly, a mass of well-tempered white clay, perforated by means of a well-greased goose-quill, was used instead of metal moulds. In the Ph. E. & Ph. L. 1836 the moulds are ordered to be greased; when this is done, the sticks of caustic should be wiped clean before rolling them in paper. The moulds should be gently heated before pouring the fused nitrate into them. Mr Benzoin, the celebrated Danish pharmaceutist, recommends mould formed of the massive white Bohemian talc or of English slate.
_Pur., &c._ Pure nitrate of silver, whether crystallised or fused, is entirely soluble in water, yielding a colourless solution, from which metallic silver is precipitated by a piece of bright copper; both are originally white, but are darkened by exposure to light and contact with organic matter.
_Uses, &c._ Nitrate of silver is a powerful tonic, antispasmodic, astringent and escharotic.--_Dose_, 1/8 to 1 gr., gradually increased, twice or thrice a day, made into a pill with crum of bread; in cholera, epilepsy, &c., preceded by purgatives. It has been highly extolled by Mr Ross as a remedy in cholera. Its continued use permanently colours the skin. It is also extensively employed externally as a caustic. It is powerfully poisonous. A solution of common salt, emetics, and demulcents, constitute the treatment in such cases. Nitrate of silver is much employed in the manufacture of 'indelible ink' for linen, and hair dyes.
=Silver, Di'oxide of.= Ag_{2}O_{2}. _Syn._ ARGENTI SUBOXYDUM, L. _Prep._ From dry citrate of silver heated to 212 Fahr., in a stream of hydrogen gas, until it turns dark brown, when it is dissolved in water; the solution is next treated with potassa, and the precipitate is carefully washed and dried. A black powder, easily decomposed, and soluble in ammonia.
=Silver, Oxide of.= Ag_{2}O. _Syn._ PROTOXIDE OF SILVER; ARGENTI OXYDUM, A. PROTOXYDUM, L. _Prep._ 1. (Lane.) Nitrate of silver, 2 parts; hydrate of potassa, 1 part; dissolve each separately in distilled water, mix the solutions, and, after frequent agitation during an hour, collect and wash the precipitate, and dry it by a gentle heat in the shade. A pale brown powder.
2. Recently precipitated chloride of silver is boiled in a solution of hydrate of potassium of the sp. gr. 125, with frequent stirring and trituration, until, on testing a little of it, it is found to be entirely soluble in dilute nitric acid, when it is washed and dried, as before. A black and very dense powder. Chemically pure.
3. Nitrate of silver, 1/2 oz.; water, 4 fl. oz., dissolve, and pour the solution into a bottle containing lime water, 2 quarts, or q. s.; agitate the mixture well, collect and wash the sediment, and dry it at a heat not exceeding 212 Fahr. A dark olive-brown powder. Pure.
_Prop., &c._ Very soluble in solutions of ammonia and of the alkaline hyposulphites; slightly soluble in water; reaction alkaline; decomposed by light.--_Dose_, 1/2 to 2 gr.; in epilepsy, gastralgic irritations, &c. It is much used in France, and has been highly extolled in menorrhagia. By some, however, it is not considered superior to the nitrate.
=Silver Pencils, Nitrate of.= According to A. Huber, very thin pencils of nitrate of silver, such as are sometimes required for intra-uterine applications may be prepared in the following manner:--Silver nitrate is fused in a capsule, and the liquid drawn up by slow and cautious suction into a glass tube, the calibre of which is a trifle larger than the required diameter of the pencil. Especial care is to be taken that no cavities filled with air-bubbles are produced in the contents of the tube.
When entirely cold the tube is warmed by turning over a spirit-lamp until the outer surface of the stick has become soft, when it may be easily pushed out by means of a knitting needle. With a little practice very handsome pencils of considerable length may be obtained in this manner.
=Silver, Perox'ide of.= _Syn._ ARGENTI PEROXYDUM, L. A black crystalline substance which forms on the positive electrode of a voltaic arrangement employed to decompose solution of nitrate of silver.
=Silver, Sul'phate of.= Ag_{2}SO_{4}. _Syn._ ARGENTI-SULPHAS, L. _Prep._ By boiling silver in sulphuric acid; or, by precipitating a solution of the nitrate by another of sulphate of sodium. It dissolves in 80 parts of hot water, and falls in small colourless needles as the solution cools.
=Silver, Sul'phide of.= Ag_{2}S. _Syn._ SULPHURET OF SILVER; ARGENTI SULPHURETUM, L. Prepared by passing sulphuretted hydrogen through a solution of nitrate of silver; or, by melting its constituents together.
It possesses a greyish-black colour, and is a strong sulphur-base.
=Silver, Ox'idised.= The high appreciation in which ornamental articles in oxidised silver are now held, renders a notice of the process followed interesting. There are two distinct shades in use, one produced by chlorine, which has a brownish tint, and the other by sulphur, which has a bluish-black tint. To produce the former, it is only necessary to wash the article with a solution of sal ammoniac. A much more beautiful tint may, however, be obtained by employing a solution composed of equal parts of sulphate of copper and sal ammoniac dissolved in vinegar. A fine black tint may be produced by a slightly warm solution of sulphide of potassium or of sodium. ('Chem. Techn.')
=SILVER DUST.= _Syn._ SILVER POWDER; ARGENTI CROCUS, A. PULVIS, L. _Prep._ 1. Pure pulverulent silver, obtained by any of the methods explained on the previous page. Used to coat pills, by japanners, &c.
2. Heat oxide of silver to dull redness in a porcelain crucible, cool, triturate the powder in an agate mortar, and pass it through a fine sieve.
Used at the hospital of Montpellier.
=SILVER SHELLS.= These are prepared and used like gold shells.
=SIL'VERING.= The art of covering the surfaces of bodies with a thin coating of silver. Leather, paper, wood, &c., are silvered by covering them with silver leaf, by a similar process to that employed for gilding them.
=Silvering of Glass.= Two distinct methods are adopted for this purpose--one of which consists in employing a layer of tin-foil and mercury, falsely called 'silvering,' the other in using a coating of real silver precipitated from a solution of that metal.
1. Plane surfaces, as those of mirrors, &c., are commonly silvered as follows:--A sheet of tin-foil corresponding to the size of the plate of glass is evenly spread on a perfectly smooth and solid marble table, and every wrinkle on its surface is carefully rubbed down with a brush; a portion of mercury is then poured on, and rubbed over the foil with a clean piece of very soft woollen stuff, or a hare's foot, after which two rules are applied to the edges, and mercury poured on to the depth of a crown-piece, when any oxide on the surface is carefully removed, and the sheet of glass, made perfectly clean and dry, is slid along over the surface of the liquid metal, so that no air, dirt, or oxide can possibly either remain or get between them. When the glass has arrived at its proper position, gentle pressure is applied, and the table sloped a little to carry off the waste mercury, after which it is covered with flannel and loaded with heavy weights; in 24 hours it is removed to a wooden table and further slanted, and this position is progressively increased during a month, until it becomes perpendicular.
For silvering convex or concave surfaces a mould of plaster of Paris is employed, so that the amalgamated foil may be accurately fitted to the surface.
Globes and other hollow vessels are commonly silvered by the application of one of the silvering amalgams noticed at page 117.
2. In the HUMID WAY.--_a._ (Drayton.) A mixture is first made of nitrate of silver (in coarse powder), 1 oz., ammonia, 1/2 oz., and water, 2 oz., which, after standing for 24 hours, is filtered (the deposit upon the filter, which is silver, being preserved), and an addition is made thereto of spirit (by preference, rectified spirit at 60% o. p.), or naphtha, 3 oz.; from 20 to 30 drops of oil of cassia are then added; and, after remaining for about 6 hours longer, the solution is ready for use. The glass to be silvered (first well cleaned and polished) is placed in a horizontal position, and a wall of putty, or other suitable material, formed around it; the above solution is then poured over it to the depth of from 1/8 to 1/4 inch; from 6 to 12 drops of a mixture of oil of cloves and spirit of wine (in the proportion of 1 part, by measure, of oil of cloves, to 3 of spirit of wine) are next dropped into it, at different places; or the diluted oil of cloves may be mixed with the solution before it is poured upon the glass, a larger quantity, in both cases, increasing the rate of the deposit. When the glass is sufficiently silvered, the solution is poured off; and as soon as the silver on the glass is perfectly dry, it is varnished with a composition formed by melting together equal quantities of beeswax and tallow. The solution, after being poured off, is allowed to stand for 3 or 4 days, in a close vessel; as it still contains silver, and may be again employed after filtration, and the addition of a sufficient quantity of fresh ingredients to supply the place of those which have been used. 18 gr. of nitrate of silver are sufficient for one square foot of glass. Hollow vessels may he silvered by pouring the solution into them. By the addition of a small quantity of oil of caraway, oil of cloves, or oil of thyme, the colour of the silver may be varied. ('Patent Journ.')
_b._ (Thomson & Mellish.) Nitrate of silver, 2 oz.; water and rectified spirit, of each 3 fl. oz.; dissolve, add of spirit of hartshorn or liquor of ammonia, 1 fl. oz., mix, and after a short time filter the solution; to each ounce of this add of grape sugar, 1/4 oz., previously dissolved in a mixture of rectified spirit and water, of each 1/2 pint; after 3 or 4 hours' repose it is fit for use. This solution is applied to the glass, heated to about 160 Fahr., in a similar manner to the last. Patented.
_c._ The best plan of silvering plain or slightly curved surfaces is, however, the method employed for coating the specula of the silvered-glass Newtonian telescopes. This method is very easy, and has the advantages of giving a brilliant and durable surface on both sides, and the film is sufficiently firm to admit of being polished with rouge and fine wash-leather.
One half ounce of pure nitrate of silver is dissolved in 4 oz. of distilled water, and divided into two equal portions. One is treated with dilute ammonia until the brownish precipitate is entirely redissolved; and to this clear solution, 1/2 oz. of pure hydrate of potassium dissolved in 8 oz. of water added; and the brown precipitate, and grey sediment that remains after the brown precipitate disappears, dissolved by the cautious addition of ammonia, stirring well all the time. The remaining nitrate of silver solution is now added, stirring well until it gives a greyish precipitate that does not disappear after well stirring. The bulk of the solution is next made up to 100 oz., and allowed to settle, when the clear solution is poured off for use.
The reducing solution is prepared by dissolving 1/2 oz. of pure milk sugar in 10 oz. of hot water, and adding 10 minims of pure alcohol.
This quantity of silvering solution will coat over two square feet of glass surface with a brilliant film of pure silver. The glass must be perfectly clean, and is to be suspended face downwards on the surface of the solution and allowed to stand one hour; the temperature of the solution being best about 80 Fahr.
_d._ (R. Siemens.) As a reducing agent, acetic aldehyde is used in the form of aldehyde ammonia, prepared by passing dry ammoniacal gas into aldehyde. Four grams of silver nitrate and 2-1/2 grams of aldehyde ammonia are separately dissolved in a litre of distilled water, and the solutions mixed and filtered. The article to be silvered, after washing out with potassium carbonate, and then with spirits of wine and distilled water, to remove every trace of grease, is filled with this solution (as far as it is desired to silver), and then hung up in the water bath.
It is now gradually heated, and as soon as the temperature reaches 50 C.
the separation of the silver mirror begins, and soon spreads over the whole inner glass surface. Its formation is soon finished, usually between 55 or 60. When the beauty of the silver surface reaches a maximum it is time to withdraw the article from the water bath, and pour off the contents, or the brilliancy of the mirror will be impaired. The article is finally rinsed in distilled water.
_e._ (Martin.) M. Martin makes use of four liquids, viz., first, a 10 per cent. solution of nitrate of silver; second, liquor ammoniae, sp. gr. 970; third, a 4 per cent. solution of caustic soda; and fourth, a 12-1/2 per cent, solution of white sugar, to which he adds 2-1/2 per cent. of nitric acid, and after twenty minutes' boiling he adds to it 25 parts of alcohol and water, to make up the bulk to 250. The silvering solution is made by mixing together 12 parts of solution No. 1, 8 parts of No. 2, 20 parts of No. 3, and 60 parts of distilled water, and finally, in twenty-four hours, 10 parts of No. 4. The object to be silvered is then immersed, when it will be covered with a film of reduced silver, which in ten minutes' time will be sufficiently thick for use. After having been washed with distilled water and dried the surface may be polished with chamois leather and rouge.
=Silvering of Metals.= 1. (LEAF SILVERING.) This is performed with leaf silvering in the way described under GILDING for the gilding of polished metals.
3. (COLD SILVERING.) Mix chloride of silver, 1 part, with pearlash, 3 parts, common salt, 1-1/2 part, and whiting, 1 part; and well rub the mixture on the surface of the brass or copper (previously well cleaned), by means of a piece of soft leather, or a cork moistened with water and dipped into the powder. When properly silvered the metal should be well washed in hot water slightly alkalised, and then wiped dry.
3. (ELECTEO-SILVERING.) This is described under ELECTROTYPE.
=Silver, A New Imitation of.= A patent for an alloy has been taken out by M. Lemarquand, which is said to bear a close resemblance to silver in appearance, and to be unaffected by atmospheric influences. It has the following composition:--
Pure copper 750 parts.
Nickel 140 "
Black oxide of cobalt 20 "
Tin, in sticks 18 "
Zinc 72 "
=SIMAROU'BA.= _Syn._ SIMARUBA (Ph. E. & D.), L. The root-bark of _Simaruba amara_ or _officinalis_, the mountain damson. Tonic, bitter, and astringent.--_Dose_, 20 to 30 gr.; in intermittents, obstinate diarrha, dysentery, and dyspepsia.
=SIN'AMINE.= C_{4}H_{6}N_{2}. A basic substance formed, along with sulphide of lead, when thiosinamine is treated with oxide of lead. It is very bitter tasted, has a powerful alkaline reaction, and, when slowly obtained from its concentrated aqueous solution, forms brilliant colourless crystals.
=SIN'APISM.= _Syn._ SINAPISMUS, L. A mustard poultice.
=SIN'APOLINE.= C_{7}H_{12}N_{2}O. A basic substance, formed, along with carbonic acid, when the volatile oil of mustard, or sulphocyanide of allyl, is treated with oxide of lead. It is soluble in water and alcohol, has an alkaline reaction, and crystallises in colourless plates.
=SINKS.= "In no case," says Mr Eassie,[165] "should the waste pipe of sink, laboratory, or bath lead direct into the drains; yet how frequently is this the case, and a special card sent out to disease and death.
[Footnote 165: 'Healthy Houses,' by Wm. Eassie, C.E. Simpkin, Marshall & Co.]