silver metal copper chloride lead sulphate solution process method acid
SILVANUS, an ancient Italian god of the woods (silica), closely allied to Faunus. Virgil speaks of him as a god of fields and cattle, and says that the Pelasgians dedicated a grove to him near Caere. Horace calls him the god of boundaries. Pigs were sacrificed to him, and at harvest festivals he received offerings of milk. He appears sometimes, especially in inscriptions, as a domestic god, :7Y and is occasionally associated with the Lares and Penates. Virgil describes him as crowned with fennel and lilies or carrying an uprooted Flu. 4. - Loricaria lanceolata, from the upper Amazons. Natural size.
cypress in his hand. On a relief he appears tion is but sparsely represented, chiefly in mountain- with a crown of pine branches in his hair, a pine branch streams, by small loath-like Siluroids, in which various in his left hand, a skin filled with fruits hanging about kinds of peculiar apparatus are developed to enable them to his neck, a pruning-knife in his right hand, and a dog by hold on to stones, this preventing his side. On votive tablets he is oftener represented as their being swept away by the the god of planting and gardening than as the rough current ; in Pseudecleeneis the woodland deity.
adhesive apparatus consists of SILVER' is widely diffused throughout the earth's transverse plaits of the skin on crust, including the ocean, which contains a trace of the thorax between the pectoral the noble metal - minute, it is true, in a relative sense, fins; in Ex- but in absolute amount approaching 10,000 million tons.
ostoma the -..)011 7, Of the varieties of silver ores, the following chiefly are mouth is metallurgically important : - (1) Jleguline Silver, generally modified in-.40 - op-----;-, ,_ s,,f, alloyed with mercury or gold, and if with the latter – _44 to a sucto- - -;:-•--"Y.- - -... k i including sometimes a trace of platinum; (2) hone Silver, rial organ, native chloride, Aga •; (3) Silver Glance, native sulphide, IrL. ' . --' ' probably 1 Ag2S ; (4) Silver-Copper Glance, (Ag,Cu)„S; (5) Pyrargyrwith the ite (" Rothgtiltigerz "), Ag,SbS, ; (6) Stephanite, Ag,SbS,; Fm. S. - Callichthys armatrs, from the upper Amazons.
, (e) Polybasite, 9(Ag„,Cu,2)S+(S132,As2)S3. Silver is also same font- Natural size.
VII. The small section of Siluridx Opisthopterx com- What we call " silver ores " are all more or less complex prises South-American forms, the majority of which mixtures in which the non-argentiferous components are inhabit waters at high altitudes up to 14,000 feet above usually decidedly in the majority. Their metallurgic treat-the level of the sea. All have a short-rayed dorsal fin, went depends chiefly on the nature of these admixtures, placed above or behind the middle of the length of the the state of combination of the silver being as a rule irrobody, above or behind the ventrals, which may be absent. levant in the choice of a process, because some at least of Also the anal is short. The nostrils are remote from the noble metal is always present as sulphide, and our each other, and the gill-membranes are not confluent with modes of treatment for it include all other native forms.
similar external physical conditions.
(vol. xiv. p. 376-7), while for the treatment of sulphureous their axes so that the several ingredients are forced into constantly varying contact with ore another. The salt solution copper ores one method is so to smelt the ore (with, if feces-takes up a small proportion of chloride, which in this (dissolved) sary, an addition of galena or some form of oxide of lead) form is quickly reduced by the iron to the metallic state as to produce a regulus of lead and a " mat" of sulphide (2AgC1+ Fe- FeC12+ 2Ag), so that there is, so to say, room made in the brine for another instalment of chloride of silver, which is of copper, (Cu2S), which latter should contain as little reduced in its turn, and so on to the end, - the metal formed lead as possible. The silver follows chiefly the lead, and uniting with the mercury into a semi-fluid amalgam. Of this the is extracted from it by cupellation ; but some silver bulk at least readily unites into larger continuous masses, which, remains in general even with a lead-free mat. Compare on account of their high specific gravity, are easily separated account of the Lautenbach process under LEAD.
from the dross mechanically. The amalgam is pressed in linen bags to eliminate a quantity of relatively silver-free liquid mercury A modern mode of extracting the silver from a copper mat is to (this of course is utilized as such in subsequent operations), and the roast it at a very low temperature, so as to produce a relatively remaining solid amalgam is subjected to distillation from iron re- large proportion of metallic sulphate, and then to destroy the bulk torts, whereby its mercury is recovered as a distillate while a more or of the sulphate of copper by a judiciously-regulated higher temless impure silver remains in the retort. This process, after having perature. The silver all remains as sulphate, which is extracted been long wrought in Freiberg with great success, is now super- by hot dilute sulphuric acid and wrought by the Augustin method. sedld there by the Augustin method (see below), but it survives Very interesting is the process which was patented by Claudet in 'some other places, as, for example, the Washoe or Comstock for the remunerative extraction of the few hundredths of a per cent. district in the Sierra Nevada (United States). It is not used in of silver contained in that kind of cupriferous iron pyrites which Chili, Peru, and Mexico because of the scarcity of fuel. is now used, almost exclusively, for the making of vitriol. The The Mexican, process, though far less perfect than that of Freiberg, "cinders," as returned by the vitriol maker, arc habitually worked evades this difficulty. It was tried for the first time, if not up for copper by roasting them with salt and lixiviating the actually invented, by Bartolomeo de Medina in 1557. It was roasted mass with water, when the copper dissolves as chloride, adopted in Mexico in 1566 and in Peru in 1574, and is in use in Cu2C12 and CuC12. The silver goes with it, but for its precipitaboth countries and in Chili to this day. The stamped ore is tion no method was known until Field found that silver dissolved ground into a fine paste with water ; this paste, after having been as AgCl in a chloride solution can be precipitated exhaustively by allowed to dry up a little in air, is placed. on a stone floor along addition of the calculated proportion of a soluble iodide, as Agl. with a quantity of salt, and the two are trodden together by Claudet's process is only an adaptation of Field's discovery. After mules. On the following day there are added certain proportions having diluted the copper liquor with a certain proportion of water of "magistral" (a kind of crude sulphate of copper made by lie adds the weight of iodine, calculated from the assay, as solution roasting copper pyrites) and of mercury, and the mules are kept of iodide of zinc, which produces a very impure precipitate of iodide going until the silver is as far as possible converted into amalgam, of silver. From it he re-extracts the iodine, by treatment with which takes from fifteen to forty-five days. The rationale of the zinc and dilute sulphuric acid, as iodide of zinc, which is used over process is not quite understood. According to Bonssingault, the again. The "silver precipitate," which now contains its silver as cupric chloride (formed by the salt from the sulphate) chlorinates metal mixed with a large quantity of (chiefly) sulphate of lead, part of the sulphide of silver, thus - goes to the metal-refiner, who treats it as a lead ore.
sulphide of silver, thus - base metal. To produce perfectly pure metal the most Cu,C12+Ag2S-2Agel+Cu2S, popular method is to first prepare pure chloride (by applyand in this way all the sulphide of silver is gradually converted ing the method given below under " Chloride " to a nitric into chloride. The chloride is reduced to the metallic state by the solution of any kind of ordinary "silver "), and then to mercury (AgC1+ Hga-HgCl+ Ag) with formation of calomel, the reduce the chloride to metal, which can be done in a great metallic silver uniting with the surplus mercury into amalgam.
The calomel is allowed to go to waste. variety of ways. One way is to mix the dry chloride The Augustin process of silver extraction is only a peculiar mode intimately with one-fifth of its weight of pure quicklime of metallifying and collecting the silver of an ore after it has or one-third of its weight of dry carbonate of soda, and to been by some preliminary operation converted into chloride or fuse down the mixture in a fire-clay crucible at a bright sulphate. Either salt is brought into solution - the chloride by means of hot brine, the sulphate by means of hot water, acidified red heat. In either case we obtain a regulus of silver with oil of vitriol ; the solution is separated from the insolubles, lying under a fused slag of chloride-2AgC1 + (Ca0 or and made to filter through a bed of precipitated copper. The Na2CO3) = 2Ag + (CaC12 + 0 or 2NaC1 + CO2 + 0). The copper reduces the silver to metal, which remains on the bed as a fused metal is best granulated by pouring it from a suffispongy mass, while an equivalent quantity of copper chloride (or sulphate) passes through as a solution. The silver sponge is col- cient height, and as a thin stream, into a mass of cold lected, freed from adhering copper by inuriatic acid in contact water. A convenient wet-way method for small quantities with air, and then sent to the furnace. From the copper liquor is to boil the recently precipitated chloride (which must that metal isprecipitated in its original form by means of iron. have been produced and washed in the cold) with caustic The silver furnished by any of these methods is never pure, even in the commercial sense. A general method for its purification is soda-ley and just enough of sugar to take away the. to fuse it up with lead and subject the alloy to cupellation (see oxygen of the Ag20 transitorily produced. The silver in LEAD, Vol. xiv. p. 376). Cupel-silver is apt to contain small this case is obtained as a yellowish-grey heavy powder, quantities of lead (chiefly), bismuth, antimony, copper, and more which is easily washed by decantation ; but it tends to or less of gold, of which metals, however, only the first three are reckoned "contaminations" by the metallurgist. They can be retain unreduced chloride, which can be removed only by removed by a supplementary cupellation, without added lead, at a fusion with carbonate of soda.
high temperature. Addition of lead would remove the copper Stas recommends the following process as yielding a metal which likewise, but it is usually allowed to remain and the alloy sent out comes nearer ideal purity. Slightly cupriferous silver is made into as cupriferous silver, to be alloyed with more copper and thus con- dry nitrate and the latter fused to reduce any platinum nitrate that verted into some kind of commercial " silver " (see below). If gold may be present to metal. The fused mass is taken up in dilute is present to the extent of 0'1 per cent. or more, it is recovered by ammonia and diluted to about fifty times the weight of the silver treatment of the metal with nitric acid or boiling vitriol. The it contains. The filtered (blue) solution is now mixed with an ex-gold in either case remains as such ; the silver becomes nitrate or cess of solution of sulphite of ammonia, S03(NII4)2, and allowed to sulphate, and from the solution of either salt is recovered by stand. After twenty-four hours about one-half of the silver has precipitation with metallic copper. Although nitric acid is the separated out in crystals ; from the mother-liquor the rest comes more expensive of the two parting agents, it is often now preferred down promptly on application of a water-bath heat. The rationale because photography has created a large demand for nitrate of of the process is that the sulphite hardly acts upon the dissolved silver. Compare Goma, vol. x. p. 749. oxide of silver, but it reduces some of the oxide of copper, 2CuO, For the "incidental "extraction of silver from essentially to Cu with formation of sulphate SO./(NH4)2. This Cu20 deoxidues its equivalent of Ag.,0, forming Ag+Cu,0„ which latter is base-metallic ores the method in the case of all lead reduced by the stock of sulphite and reconverted. into Cu20 which ores' is simply to proceed as if only lead were present, now acts upon a fresh equivalent of Ag20 ; and so on to the end.
Pure silver (ingot) has a beautiful white colour and lustre ; it is almost as plastic as pure gold, and, like it, very soft. It does not tarnish in natural air ; but in air contaminated with ever so little sulphuretted hydrogen it gradually draws a black film of sulphide. The specific gravity of the frozen metal is 10.42 to 10.51, rising to 10.57 after compression under a die. It is the best conductor of heat and electricity. The expansion of unit length from 0° to 100° C. is 0.001936 (Fizeau). The specific heat is 0.0570 (llegnault), 0-0559 (Bunsen). It fuses at 954° C. (Violle) - i.e., far below the fusing point of copper or gold - without oxidation, unless it be in contact with a surface of silicate (porcelain glaze, &c.), when a trace of silicate of AO is produced. It volatilizes appreciably at a full red heat; in the oxyhydrogen flame it boils, with formation of a blue vapour. The fused metal readily absorbs oxygen gas (under fused nitre as much as twenty times its volume - Gay-Lussac). When the oxygenated metal freezes the absorbed gas goes off suddenly at the temperature of solidification, and, by forcing its way through the solid crust produces volcanic eruptions of metal which are sometimes very beautiful. The presence of even very little base metal in the silver prevents this "spitting," the base metal combining with the oxygen faster than it can be reabsorbed. Pure silver retains a trace of the absorbed oxygen permanently, and Dumas in an experiment on one kilogramme of metal extracted from it 82 milligrammes of oxygen in an absolute vacuum at 400°-500° C. Water, and ordinary non-oxidizing aqueous acids generally, do not attack silver in the least, hydrochloric acid excepted, - which, in the presence of air, dissolves the metal very slowly as chloride. A. solution of common salt acts similarly, the liberated sodium becoming NaOH. Aqueous hydriodic acid, even in the absence of air, dissolves silver perceptibly, with evolution of hydrogen (Deville). Aqueous nitric acid dissolves the metal readily as nitrate; hot vitriol converts it into a magma of crystalline sulphate, with evolution of sulphurous acid. Silver is absolutely proof against the action of caustic alkali leys, and almost so against that of fused caustic alkalies even in the presence of air. It ranks in this respect next to gold, and is much used to make vessels for chemical operations involving the use of fused caustic potash or soda. The ordinary "fine" metal is good enough for this purpose.