Cooley's Cyclopaedia of Practical Receipts Volume I Part 268

116 (20 Baume). The remainder of the process is similar to that above described. Two a.s.says are made in the same manner, with a third on pure gold or gold of a known fineness; and no conclusion is drawn, unless the a.s.say of the latter comes out accurately, and that of the first two correspond to each other.

For alloys containing platinum, which usually consist of copper, silver, platinum, and gold, the method of a.s.saying is as follows:--The alloy is 'cupelled' in the usual way, the loss of weight expresses the amount of copper; and the b.u.t.ton, made into a riband and treated with sulphuric acid, indicates, by the portion dissolved, that also of the silver present. By submitting the residuum to quartation, the platinum becomes soluble in nitric acid. The loss after digestion in this menstruum expresses the weight of that metal, and the weight of the portion now remaining is that of the pure gold. Gold containing palladium may be a.s.sayed in the same manner.

2. In the wet way:

The richness in gold of any substance, whether liquid or solid, when the quant.i.ty is small (and indeed in all other cases), is most simply and economically performed by the common method of chemical a.n.a.lysis. The gold may be thrown down from its solution by adding a solution of protosulphate of iron; the precipitate, after being washed, dried, and gently heated, may be weighed as pure gold.

_Pois., &c._ The soluble preparations of gold (chlorides) are violent poisons. The symptoms resemble those occasioned by corrosive sublimate, but are somewhat less violent. Metallic gold in a minute state of division is also capable of producing very unpleasant consequences, and even endangering life. The antidote is iron filings or a solution of sulphate of iron, given conjointly with an emetic.

_Uses._ The numerous applications of gold in the arts and the daily transactions of life need only be alluded to here. In _medicine_, gold has been given in the form of powder, in scrofula and syphilis, by Chrestein, Niel, and others, with apparent advantage.--_Dose_, 1/4 gr. to 1 gr., 3 or 4 times a day, in pills, or as a friction on the tongue and gums. An ointment made of 1 gr. of powdered gold and 30 gr. of lard has been applied by Niel to the skin deprived of the epidermis (endermically) in the above diseases.

The more important chemical compounds containing gold, the alloys and commercial forms of the metal, together with certain fact.i.tious substances popularly called 'gold', are noticed in alphabetical order _below_:--

=Gold, Alloys and Preparations of:--=

=Gold, Dutch.= MANNHEIM GOLD, MOSAIC G., OR-MOLU, PINCHBECK, PRINCE'S METAL, RED BRa.s.s, SIMILOR, TOMBAC. These names are applied to several varieties of fine gold-coloured bra.s.s, differing slightly in tint and in the proportions of copper and zinc. The terms tombac, prince's metal, similor, and Mannheim gold, are used by some authors to designate alloys consisting of about 85% of copper and 15% of zinc; whereas, according to other authors, prince's metal and Mannheim gold are synonymous, and are composed of 75% copper and 25% zinc; according to another author, similor consists of about 71-1/2% copper and 28-1/2% zinc, and Mannheim gold of 80% copper and 20% zinc; and, again, according to another author, similor and Mannheim gold are synonymous, and are applied to alloys of copper containing from 10 to 12% zinc and from 6 to 8% tin. Seeing that such inextricable confusion exists in the employment of the terms above mentioned, it is desirable to discard them altogether. At the celebrated works of Hegermuhl, near Potsdam, the proportions copper, 11 parts, to zinc, 2 parts, are employed to produce a metal which is afterwards rolled into sheets for the purpose of making Dutch leaf-gold. This alloy has a very rich, deep gold colour. Its malleability is so remarkable that it may be beaten out into leaves not exceeding 1/52900 inch in thickness.

=Gold, Facti"tious.= _Prep._ From copper, 16 parts; platinum, 7 parts; zinc, 1 part; fused together. This alloy resembles in colour gold of 16 carats fine, or 2/3, and will resist the action of nitric acid, unless very concentrated and boiling.

=Gold, Grain.= _Syn._ AURUM GRANULATUM, L. _Prep._ From cupelled gold, 1 part; silver, 3 parts; melted together, and poured in a small stream into water; the silver being afterwards dissolved out by digestion in boiling nitric acid, and the grains, after being well washed in water, heated to redness in a crucible or cupel. Used to make preparations of gold.

=Gold, Jew'eller's.= This term is applied to alloys of gold used for trinkets and inferior articles of jewelry, ranging from 3 or 4 carats fine upwards; or which are too inferior to receive the 'Hall mark'. The lowest alloy of this cla.s.s is formed of copper, 16 parts; silver, 1 to 1-1/2 part; gold, 2 to 3 parts; melted together. This is worth only from 8_s._ 6_d._ to 9_s._ 6_d._ the oz.

It has recently been found that gold of the quality of 12 carats, or less, if alloyed with zinc instead of the proper quant.i.ty of silver, presents a colour very nearly equal to that of a metal at least 2-1/2 to 3 carats higher, or of 8_s._ or 10_s._ an ounce more value; and the consequence has been that a large quant.i.ty of jewellery has been made of gold alloyed in this manner; and the same has been purchased by some shopkeepers, very much to their own loss as well as that of the public; inasmuch as a galvanic action is produced, after a time, upon gold so alloyed, by means of which the metal is split into several pieces, and the articles rendered perfectly useless.

=Gold, Leaf.= _Syn._ GOLD-LEAF. Gold reduced to leaves by hammering it between thin animal membrane. Its preparation const.i.tutes the trade of the goldbeater. These leaves are only 1/28200 of an inch in thickness. Gilt silver is hammered in the same way, but the leaves are thicker. The latter is called party gold. Both are used by artists and gilders, and by druggists to gild pills, &c.

=Gold, Powdered.= _Syn._ DIVIDED GOLD, GILDING POWDER, GOLD BRONZE, GOLD COLOUR; AURI PULVIS. _Prep._ Gold, 1 part; mercury, 7 parts; form an amalgam, and expose it to heat until all the mercury is volatilised; or the mercury may be dissolved out with hot nitric acid. In either case the residuum is to be powdered, washed, and dried. If the quant.i.ty operated on is considerable, the process should be so conducted as to save the mercury.

From gold leaf and honey ground together, as the last, by means of a stone and muller. This is the plan commonly adopted in the small way by artists.

From a solution of gold in aqua regia precipitated by protosulphate of iron, the resulting powder being washed, dried, and gently heated, This gives pure gold.

_Uses, &c._ Powdered gold is employed in gilding by j.a.panners and by artists. It is either sold in powder (gold in powder), or made up into sh.e.l.ls (gold in sh.e.l.ls). Its use in medicine has been already noticed.

=Gold, Standard.= The standard gold of this country is an alloy of pure gold, 11 parts, with pure copper, 1 part. Formerly the alloy consisted partly of silver, as found in some of the older coins now in circulation.

It is often spoken of as 22 carats fine.

=Gold, Chlorides of:=

1. =Monochloride.= AuCl. _Syn._ AUROUS CHLORIDE, PROTOCHLORIDE OF GOLD. A yellowish-white ma.s.s, formed when a solution of trichloride of gold is evaporated to dryness, and the residuum is exposed to a heat of about 440 Fahr., until fumes of chlorine cease to be evolved. It is insoluble in water, which decomposes it, slowly when cold, but rapidly by the aid of heat, into metallic gold and the trichloride.

2. =Trichloride.= AuCl_{3}. _Syn._ AURIC CHLORIDE, TERCHLORIDE OF GOLD, TRICHLORIDE OF GOLD, AURI CHLORIDUM. _Prep._ Gold, 1 part, dissolved by aid of heat in nitro-hydrochloric acid, 8 parts, and evaporated down to near dryness, and allowed to crystallise.

_Prop._ Orange-red crystalline needles, or ruby-red prismatic crystals; deliquescent; soluble in water, ether, and alcohol, forming a deep-yellow solution; at the heat of 500 Fahr. it suffers decomposition, chlorine being given off and pure gold left behind. It is reduced by ferrous sulphate, oxalic, sulphurous, formic and phosphorous acids, as well as by most of the metals, to metallic gold. It combines with several of the metallic chlorides, forming a series of double salts, which are mostly yellow when in crystals, and red when deprived of water.

_Uses, &c._ It has been employed by Duportal, Chrestien, Niel, Cullerier, Legrand, and others, as a subst.i.tute for mercury, in scrofula, bronchocele, chronic skin diseases, &c.; also as a caustic.--_Dose_, 1/20 gr., dissolved in distilled water, or made into a pill with starch; or, in frictions on the gums, in quant.i.ties of 1/16 to 1/10 gr. Its most important use, however, is as a reagent in photography, large quant.i.ties being manufactured for use as a chief agent in toning photographic prints.

To some extent it is also used for electro-gilding, and mixed with excess of bicarbonate of pota.s.sium, it forms a good yielding solution for small articles of copper. These are to be first cleaned with dilute nitric acid, and then boiled for some time in the mixture.

The above is the salt generally referred to under the name of the 'chloride of gold,' or in commerce occasionally as the 'muriate of gold.'

=Gold, Chloride of, and Sodium.= AuCl_{3}. NaCl. 2Aq. _Syn._ AUROCHLORIDE OF SODIUM; SODII AUROCHLORIDUM. _Prep._ Auric chloride, 85 parts; chloride of sodium, 16 parts; dissolve in a little distilled water, evaporate until a pellicle forms, then put it aside to crystallise. It forms beautiful orange-coloured rhombic prisms.

_Dose, &c._ 1/20 to 1/12 gr., made into a pill with starch or lycopodium, in the same cases in which the terchloride is ordered. Mixed with 2 or 3 times its weight of orris powder, it has been used in frictions on the tongue and gums, and an ointment made with 1 gr. of the salt, mixed with 36 gr. of lard, has been applied to the skin deprived of the epidermis by a blister.

=Gold, Cyanide of.= AuCy_{3}. _Syn._ AURIC CYANIDE. _Prep._ Add a solution of pure cyanide of pota.s.sium to a solution of pure auric chloride as long as a precipitate forms, carefully avoiding any excess; wash, and dry the precipitate.

_Prop., Uses, &c._ The salt is a pale-yellow powder, insoluble in water, but very soluble in a solution of cyanide of pota.s.sium, forming the double cyanide of gold and pota.s.sium so largely used in the electrotype process.

Cyanide of gold is employed to a certain extent in medicine.--_Dose_, 1/12 to 1/10 gr., made into a pill, in the usual cases in which gold is administered. The first formula is essentially similar to that of the French Codex.

=Gold, Extraction of, by Sodium Amalgam.= (Crookes' Method, Patented.) In the extraction of gold by amalgamation serious difficulties are often occurring through the 'flouring' or 'sickening' of the mercury employed, and the prevention of the amalgamation by a coating of tarnish on the gold. So much is this the case that losses of from 30 to 60 per cent. of the gold are usually incurred, and, in many cases a still more serious loss of mercury.

When certain minerals, as tellurium compounds, pyrites, &c., occur in the gold ore, the mercury is apt, on trituration, to become subdivided into excessively minute globules, which, owing to their tarnished condition, refuse to unite, and are consequently washed away, it being almost impossible to separate them from the heavier portions of the ore. This is technically called 'flouring,' 'granulating,' &c. Besides this, certain of these minerals affect the mercury in another way, that is, by 'sickening'

it, or causing it to lose its bright surface and fluidity, and prevents its amalgamating with the gold. Besides the inconvenience and loss thus caused, a further loss of gold takes place from the inability of the ordinary mercury to touch or amalgamate tarnished gold, unless it is ground with it, for a more lengthy period than is found practicable in most cases.

Mr Crookes, F.R.S., has, by means of the addition of a certain proportion of sodium, in the form of an amalgam, to the mercury, effectually prevented this serious loss of gold and mercury. By adding certain quant.i.ties of amalgams B and C, an amount which, differing from each ore, is ascertained by experiment, the 'flouring' and 'sickening' of the mercury is effectually prevented, the mercury remaining throughout in the best condition. The addition of about one tenth per-centage of amalgam A, at intervals of some hours, increases most powerfully the affinity of the mercury for the precious metals, and secures a more thorough amalgamation.

This invention has met with general approval, and experiments conducted at many mines show its great practical value, giving an increase of from 5 to 30 per cent. in the yield of gold, and, in fact, with many pyrites that yielded no gold to the ordinary amalgamation process, gave a considerable yield of gold to the sodium amalgamation process. This has led to its use in most mines, both silver and gold, in America.

=Gold, Iodide of.= AuL_{3}. _Syn._ AURIC IODIDE, TRI-IODIDE OF GOLD, GOLD TERIODIDE, AURI IODUM. _Prep._ Add a solution of trichloride of gold to one of iodide of pota.s.sium. The resulting precipitate is at first redissolved on agitation, a soluble double iodide being formed; subsequently the iodide of gold is precipitated, leaving the supernatant liquor free of colour.

_Prop., Uses, &c._ A dark-green powder, easily soluble in hydriodic acid.

It is occasionally employed as a medicine, and, like other preparations of gold, is of an alterative character.--_Dose._ About 1/16th of a grain.

=Gold, Oxides of=:--

1. =Monoxide.= Au_{2}O. _Syn._ AUROUS OXIDE, PROTOXIDE OF GOLD. _Prep._ Formed by treating the aurous chloride with strong pota.s.sium hydrate.

Green powder, somewhat soluble in pota.s.sium hydrate solution, and readily decomposing into metallic gold and auric oxide.

2. =Trioxide.= Au_{2}O_{3}. _Syn._ AURIC OXIDE, OXIDE OF GOLD, PEROXIDE OF GOLD, AURIC ACID, AURI OXIDUM. _Prep._ Magnesic oxide, 4 parts; auric chloride, 1 part; water, 40 parts; mix, boil, and wash the precipitate with water, dilute nitric acid, and again with water. It must be dried in the shade.

Reddish-yellow powder, easily decomposed by heat; readily soluble in hydrochloric and hydrobromic acids and strong nitric acid, but insoluble in water and the other acids. Forms unstable salts with the alkalies.

_Uses, &c._ Trioxide of gold has been given in scrofula, &c., in doses of 1/12 to 1/2 gr., or 1 gr., in scrofula, syphilis, &c., made into a pill with extract of mezereon.

=Gold, Ammoni'uret of*.= _Syn._ AURATE OF AMMONIA, BERTHOLLET'S FULMINATING GOLD; AURUM AMMONIATUM, AMMONIae AURAS, L. _Prep._ By adding ammonia to a solution of gold in aqua regia (trichloride), as long as a reddish-yellow precipitate (fulminating gold) forms; the latter must be collected, washed, and dried with the greatest possible caution.

_Obs._ Ammonia fails to precipitate trioxide of gold from solutions which are not tolerably concentrated, and in those containing free acid or ammoniacal salts the precipitate only forms upon boiling the solution.

Before adding the ammonia, it is, therefore, proper to drive off the excess of acid, if any, by the application of heat. See FULMINATING COMPOUNDS.

=Gold, Sul'phide of.= Au_{2}S_{3}. _Syn._ SULPHURET OF GOLD, TERSULPHURET OF G.; AURI SULPHURETUM, L. _Prep._ Transmit a current of sulphuretted hydrogen gas through a solution of terchloride of gold in water; or add hydrosulphuret of ammonia to the same solution; collect the precipitate, wash it with cold distilled water, and dry it in the shade.

=GOLD DETER'GENT.= _Prep._ (Upton.) Take quicklime, 1 oz.; sprinkle it with a little hot water to slake it, then gradually add boiling water, 1 pint, so as to form a milk. Next dissolve pearlash, 2 oz., in boiling water, 1-1/2 pint; mix the two solutions, cover up the vessel, agitate occasionally for an hour, allow it to settle, decant the clear, put it into flat half-pint bottles, and well cork them down.

_Use._ To clean gilding, &c., either alone or diluted with water. It is applied with a soft sponge, and then washed off with clean water. It is essentially a weak solution of pota.s.sa, and may be extemporaneously prepared by diluting solution of pota.s.sa (Ph. L.) with about 5 times its volume.

=GOLD Sh.e.l.lS.= Gold leaf or powdered gold ground up with gum-water, and spread upon the insides of sh.e.l.ls. Used by artists.