Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 210

Average production prior to disease, 81,600.

1863 Bales, 50,600 Deficit, 38 per cent.

1864 " 38,000 " 53 "

1865 " 38,700 " 52 "

1866 " 39,600 " 51 "

1867 " 44,000 " 46 "

1868 " 41,000 " 49 "

1869 " 47,300 " 42 "

1870 " 69,900 " 14 "

1871 " 76,300 " 6 "

1872 " 68,000 " 16 "

The value of the coc.o.o.ns grown in the whole world in 1870 was said to be as follows:--France, 4,334,000; Italy, 11,260,000; Spain and other European countries, 984,000; giving a total for Europe of 16,588,000.

China, 17,000,000; India, 4,800,000; j.a.pan, 3,200,000; Persia, 920,000; other Asiatic states, 2,192,000; giving a total for Asia of 28,112,000. Africa, 68,000. America, 20,000. Making a general total of 44,788,000.

=Silkworm Gut.= See GUT.

=SIL'LABUB.= _Prep._ Grate off the yellow peel of a lemon with lump sugar, and dissolve the sugar in 3/4 pint of wine; add the juice of 1/3 a lemon, and a 1/4 pint of cream; beat the whole together until of a proper thickness, and then put it into gla.s.ses.

_Obs._ 3/4 to 1 pint of new milk is often subst.i.tuted for the cream, and strong cider or perry for the wine. Grated nutmeg is often added. When 'whipped' to a froth it is called 'WHIPPED SILLABUB,' See CREAM (Whipped).

=SILVER.= Ag. _Syn._ ARGENTUM, L. This metal, like gold, appears to have been as much valued in the remotest ages of antiquity of which we have any record, as at the present time. It is found in nature, both in the metallic state and mineralised, in the state of alloy, and combined with sulphur, chlorine, and other metallic sulphurets. In Great Britain it is found in combination chiefly with lead. It is extracted from its ores princ.i.p.ally by the process of amalgamation, founded on its easy solubility in mercury, and by subsequent cupellation. It is only prepared on the large scale.

Chemically pure silver may be obtained by the methods noticed subsequently.

_Prop._ Pure silver has a very white colour, a high degree of l.u.s.tre, is exceedingly malleable and ductile, and is the best conductor of heat and electricity known. Its hardness is between that of copper and gold; its sp. gr. is 10475 to 10500; it melts at about 1873 Fahr.; or bright redness (Daniell); is freely soluble in nitric acid, and dissolves in sulphuric acid by the aid of heat; it refuses to oxidise alone at any temperature, but, when strongly heated in open vessels, it absorbs many times its bulk of oxygen, which is again disengaged at the moment of solidification; its surface is rapidly tarnished by sulphuretted hydrogen and by the fumes of sulphur.

_Pur._ "Entirely soluble in diluted nitric acid. This solution, treated with an excess of muriate of soda, gives a white precipitate entirely soluble in ammonia water, and a fluid which is not affected by sulphuretted hydrogen." (Ph. E.)

_Tests._ 1. The compounds of silver, mixed with carbonate of soda, and exposed on a charcoal support to the inner flame of the blowpipe, afford white, brilliant, and ductile metallic globules, without any incrustation of the charcoal.--2. The salts of silver are non-volatile and colourless, but most of them acquire more or less a black tint by exposure to full daylight.

The soluble salts of silver give--1. A white curdy precipitate (chloride of silver) with hydrochloric acid and the soluble metallic chlorides, which is soluble in ammonia and insoluble in nitric acid, and blackened by exposure to light;--2. White precipitates with solutions of the alkaline carbonates, oxalates, and ferrocyanides;--3. Yellow precipitates with the alkaline a.r.s.enites and phosphates;--4. With the a.r.s.eniates, red precipitates;--5. With the fixed alkalies, brown precipitates;--6. With sulphuretted hydrogen and hydrosulphuret of ammonia, a black powder, which is insoluble in dilute acids, alkalies, alkaline sulphurets, and cyanide of pota.s.sium, but readily soluble, with separation of sulphur, in boiling nitric acid; and--7. With phosphorus, and with metallic copper or zinc, pure silver.

_a.s.say._ 1. The method of a.s.saying silver by cupellation has been explained under a.s.sAY and CUPELLATION; and that method is alone applicable when the alloy contains a very small quant.i.ty of silver, as a few ounces only per ton. When the reverse is the case, as with the silver of commerce, the following is a much more accurate method:--

2. _Humid a.s.say of silver._--_a._ Dissolve 10 gr. of the silver for a.s.say in 100 gr. of nitric acid, sp. gr. 128, by the aid of heat, the solution being made in a tall stoppered gla.s.s tube, furnished with a foot; then place it in a very delicate balance, bring it into an exact state of equilibrium, and add the test solution (see _below_), gradually and cautiously, until the whole of the silver be thrown down, the number of grains now required to restore the equilibrium of the balance or scales gives the exact quant.i.ty of pure silver in 1000 parts of the sample.--_Obs._ To ensure accuracy, after each addition the stopper should be placed in the tube, and the latter violently agitated for a short time, when the liquor will rapidly clear and enable us to see when the operation is concluded. We must then, as a check, add a small quant.i.ty of a solution of nitrate of silver to the liquor in the tube, after having first carefully taken the weight. If too much of the test liquor has been added, this will produce a fresh precipitate, and the a.s.say cannot then be depended on.--Instead of weighing the quant.i.ty of test liquor used, a tube graduated into 100 parts, and holding 1000 gr., may be employed, every division of which, required to throw down the silver, will represent the 1/10th of a grain. See ALKALIMETRY and ACIDIMETRY.

_b._ The precipitate of chloride of silver may be collected in a paper filter, and be dried, washed, fused, and weighed. The previous weight of the paper, deducted from the gross weight of the filter and its contents, gives the quant.i.ty of chloride of silver present, which multiplied by 075278, gives the weight of the pure silver in the sample.

_Test liquor._ Dissolve 5427 (54-1/4) gr. of pure sea salt in 994573 gr.

(or 22 oz. and 320-3/4 gr. avoirdupois) of distilled water; filter, and keep the liquor in a stoppered bottle for use. Pure sea salt is obtained by boiling together, for a few minutes, in a gla.s.s vessel, a solution of common salt with a little pure bicarbonate of soda; then adding to the filtered liquor sufficient hydrochloric acid to render it neutral to litmus and turmeric paper, and, lastly, evaporating and crystallising.

_Obs._ The presence of mercury, lead, or sulphuret of silver, interferes with the accuracy of the above a.s.say. When mercury is present, the precipitate blackens less readily by exposure to light; and when it contains 4/1000 or 5/1000 of chloride of mercury, it remains of a dead white; with 3/1000 it is not sensibly discoloured by the diffused light of a room, with 2/1000 only slightly darkened, with 1/1000 more so, but with pure chloride of silver, the effect is very rapid and intense. When this metal is present, which is, however, seldom the case, the a.s.say sample must be placed in a small crucible, and exposed to a full red heat, before solution in the acid. Another method, proposed by M. Levol, and modified by M. Gay-Lussac, is to add to the nitric solution of the silver sufficient acetate of ammonia or crystallised acetate of soda to saturate all the nitric acid existing in the liquor, either in the free state or combined with the silver. When the alloy contains lead, shown by the precipitated chloride being partly soluble in water, it may either be laminated and subjected to the action of acetic acid before solution in the nitric acid; or, the test solution of chloride of soda should be replaced by one of chloride of lead; (139355 gr. of the latter are equiv.

to 58732 gr. of the former). The presence of sulphuret of silver is detected whilst dissolving the sample in nitric acid, by the black flakes which may be observed floating about in the liquor in an insoluble state.

These flakes may be dissolved by fuming nitric acid, or by adding pure concentrated sulphuric acid to the solution, which should be then heated for about a 1/4 hour in a steam-bath. When thus treated, the precipitate produced by the test liquor represents the whole of the silver contained in the alloy.

Dr Grager[164] gives the following process of the preparation of pure metallic silver:--He dissolved the alloy of silver in nitric acid, taking care to use as small a quant.i.ty of the acid as possible. The solution is then transferred to a large-sized porcelain basin, and gradually neutralised with previously lixiviated chalk free from chlorine. The neutralised liquid is next boiled, and chalk again added to it, while boiling, until the fluid has become colourless. (In order to test more accurately, a drop of the liquid is poured on a piece of white filtering-paper, and next to that drop is placed one of a solution of ferrocyanide of pota.s.sium; as long as the well-known red colouration, copper reaction, hereby ensues, chalk is added.) The fluid is next filtered to separate the carbonate of copper, and the filtrate (a solution of nitrate of silver, and nitrate of lime) is again boiled, and either further treated with carbonate of lime, or better still, with carbonate of soda. The bright yellow-coloured precipitate thereby ensuing, a mixture of carbonate of silver, and carbonate of lime, is washed, dried, and ignited, leaving a greyish-white ma.s.s of metallic silver, mixed with carbonate of lime. This mixture is treated with dilute hydrochloric acid, washed with distilled water, and then fused along with borax, yielding pure silver.

The bright green coloured carbonate of copper can be used as a pigment for painting purposes.

[Footnote 164: 'Chemical News,' xxv, No. 641, 119.]

Kruger says:--In frequently experimenting with silver salts, a mixture of solution of precipitates is obtained, in which silver exists in all kinds of combination. When such mixtures are shaken up with an ethereal solution of phosphorus, the solution and the precipitate soon separate, the former being more or less yellow, the latter intensely black. If light-coloured particles are perceived in the precipitate, the quant.i.ty of phosphorus solution employed is not sufficient, and more must be added till the precipitate is uniformly black. The precipitate is next filtered, washed, and dried, or placed while still damp, in a porcelain dish and boiled with potash solution. Pure metallic silver is thus obtained. If a solid fused ma.s.s is required, pure pota.s.sium hydrate is fused in a crucible, and to this the dried precipitate is added in small portions.

_Uses, &c._ Metallic silver, unless in a state of very minute division, has no action on the human body. A plate of silver is ordered, in the Ph.

L., as a test of the presence of nitric acid in the acetic and phosphoric acids; and metallic silver (preferably granulated) is employed by the other colleges in the preparation of the nitrate. Its numerous applications in the arts are well known. The standard silver of England contains 111 parts of silver and 9 parts of copper.

_Concluding Remarks._ The researches of Tillet, D'Arcet, and Gay-Lussac have clearly shown that the percentage of silver in an alloy, as indicated by cupellation, is always below its real richness in that metal, owing to loss in the process; and, that the cupelled b.u.t.ton always retains a trace of lead and copper, the precise quant.i.ty of which is variable. The following table exhibits the additions to be made on this score, when the quant.i.ty a.s.sayed (a.s.say pound) is 20 gr.:--

+-------------------------+---------------+--------------+ Actual richness Percentage Weight after cupellation. in _pure_ of richness in _silver_. _pure silver_. +-------------------------+---------------+--------------+ 19979 20 100 1895 19 95 1792 18 90 16917 17 85 15914 16 80 1491 15 75 13905 14 70 12905 13 65 11906 12 60 10906 11 55 9906 10 50 7921 8 40 5948 6 30 3949 4 20 1982 2 10 +-------------------------+---------------+--------------+

In a.s.saying lead ores very poor in silver the best quant.i.ty to be taken for cupellation is 500 gr.; and from that quant.i.ty 00148 of silver, including compensation for loss, represents one ounce of silver to the ton. A cupel may absorb its own weight of lead. If the quant.i.ty of lead to be absorbed is more considerable, another cupel may be turned topsy-turvy, and the cupel in which the a.s.say is to be made may be placed upon it. See a.s.say, and M. Gay-Lussac's elaborate memoir on the '_Humid a.s.say of Silver_,'

For the recovery or reduction of silver from the chloride and its other compounds, several methods are employed:--

_a._ The washed chloride is placed in a zinc or iron cup, along with a little water strongly acidulated with sulphuric acid; or in a gla.s.s or porcelain cup along with a zinc plate; the whole may then be left to itself for some hours; or, to hasten the reduction, gently heated, or even boiled; the precipitated silver is washed with pure water, and dried.

_b._ (Hornung.) Digest the chloride with some ammonia and pure copper filings, for 24 hours, then wash and dry the powder.

_c._ (M. Levol.) The washed chloride is mixed with an equal weight of sugar, and the mixture is digested in an excess of a moderately strong solution of caustic pota.s.sa, with occasional agitation for 24 hours; or the whole is boiled for some time; the reduced silver is washed with distilled water.

_d._ (Mohr.) The dry chloride is mixed with 1-3rd of its weight of powdered black resin, and moderately heated in a crucible until the flame ceases to have a greenish-blue colour; the heat is then suddenly increased so as to melt the metal into a b.u.t.ton or ingot.

_e._ (M. Gay-Lussac.) If the chloride, dry it, and throw it, in successive portions, into twice its weight of carbonate of pota.s.sa fused in a red-hot Hessian crucible; effervescence ensues, and the pure silver subsides to the bottom.--If a "soluble salt," as the nitrate, acidulate the solution, and precipitate it by means of a polished plate of copper; the silver is then obtained in the form of powder. The products of the above processes, when the latter are carefully conducted, are chemically pure silver.

=Silver, Acetate of.= _Syn._ ARGENTI ACETAS, L. _Prep._ By adding a solution of acetate of pota.s.sa to a like solution of nitrate of silver, washing the precipitate with cold water, redissolving it in a little hot water, and setting the solution aside to crystallise. Small colourless needles.

=Silver, Ammoniuret of.= See FULMINATING SILVER (Berthollet's, Nos. 1 and 2, _page_ 768).

=Silver, Ammonio-chloride of.= _Syn._ ARGENTOCHLORIDE OF AMMONIA; ARGENTI AMMONIO-CHLORIDUM, L. _Prep._ Add, gradually, chloride of silver (recently precipitated and well washed) to concentrated liquor of ammonia, as long as it is dissolved on agitation, applying a gentle heat towards the end; then heat the solution to the boiling-point, concentrate a little, and allow it to cool very slowly; collect the crystals which form, dry them by pressure (with care) between folds of bibulous paper, and at once preserve them from the light and air.--_Dose_, 1/16 to 1/8 gr.

=Silver, Ben'zoate of.= AgC_{7}H_{5}O_{2}. Thin transparent plates, which are blackened by exposure to the light. See BENZOATE.

=Silver, Bro'mide of.= AgBr. Resembles the chloride.

=Silver, Car'bonate of.= Ag_{2}CO_{3}. _Syn._ ARGENTI CARBONAS, L. A white insoluble powder, obtained by precipitating a cold solution of nitrate of silver with another of carbonate of sodium. It is decomposed by heat.

=Silver, Chlo"ride of.= AgCl. _Syn._ ARGENTIC CHLORIDE. _Prep._ Precipitate a solution of nitrate of silver by dilute hydrochloric acid or a solution of common salt; wash the precipitate, and dry it in the shade.--_Dose_, 1/4 to 3 gr., thrice daily; in epilepsy, chronic dysentery, cholera, diarrha, &c. Dr Perry regards it as preferable to the nitrate. When fused, chloride of silver forms horn silver, the 'luna cornea' of the older writers.

=Silver, Cy'anide of.= AgCN. _Syn._ ARGENTIC CYANIDE, HYDROCYANATE OF SILVER. _Prep._ Add dilute hydrocyanic acid to a solution of nitrate of silver, as long as a precipitate falls; wash this with distilled water, and dry it.

_Prop., &c._ Cyanide of silver is a white powder, soluble in ammonia, and decomposed by contact with vegetable substances; light turns it violet-coloured.--_Dose_, 1/16 to 1/8 gr.; in syphilis, &c. It has been proposed as a source of hydrocyanic acid. (Everitt.)

=Silver Hyposul'phite of.= Ag_{2}S_{2}O_{3}. _Syn._ ARGENTI HYPOSULPHIS, L. A white substance, insoluble in water, and very p.r.o.ne to decomposition.

It is very soluble in the alkaline hyposulphites, forming compounds possessing an intensely sweet taste. See HYPOSULPHUROUS ACID.

=Silver, I'odide of.= AgI. _Syn._ ARGENTIC IODIDE; ARGENTI IODIDUM, L.

_Prep._ Precipitate a solution of nitrate of silver with another of iodide of pota.s.sium; wash the precipitate with distilled water, and dry it in the shade. Pale greenish-yellow; insoluble in water and in liquor of ammonia; soluble in a solution of hyposulphite of soda. Used in some of the French hospitals in the stomach affections of scrofulous subjects: also in epilepsy.--_Dose_, 1/12 to 1 gr.