Lastly, neutralize the liquid by adding Carbonate of Soda until all effervescence ceases, and a green precipitate forms; this is _Carbonate of Copper_, which must be allowed several hours to separate thoroughly. The Chloride of Gold is thus freed from Copper and Silver, with which the metallic Gold is alloyed in the standard coin of the realm. The solution so prepared will be _alkaline_, and consequently prone to a reduction of metallic Gold: a slight extra quantity of Hydrochloric acid should therefore be added, sufficient to redden a piece of immersed litmus-paper. The weight of a half-sovereign is about 61 grains, of which 56 grains are pure Gold. This is equivalent to 86 grains of Chloride of Gold, which will be the quantity contained in the solution. The following process for preparing Chloride of Gold is more perfect than the last:--Dissolve the Gold coin in Aqua-Regia as before; then boil with excess of Hydrochloric Acid, to destroy the Nitric Acid,--dilute largely with distilled water, and add a filtered aqueous solution of common Sulphate of Iron (6 parts to 1 of Gold); collect the precipitated Gold, which is now free from copper; redissolve in Aqua-Regia, and evaporate to dryness on a water bath. Avoid using _Ammonia_ to neutralize Chloride of Gold, as it would occasion a deposit of "Fulminating Gold," the properties of which are described in the next page. _Properties of Chloride of Gold._--As sold in commerce it usually contains excess of Hydrochloric Acid, and is then of a bright yellow colour; but when neutral and somewhat concentrated, it is dark red (_Leo ruber_ of the alchemists). It gives no precipitate with Carbonate of Soda unless heat be applied; the free Hydrochloric Acid present forms, with the alkali. Chloride of Sodium, which unites with the Chloride of Gold, and produces a double salt, Chloride of Gold and Sodium, soluble in water. Chloride of Gold is decomposed with precipitation of metallic Gold by Charcoal, Sulphurous Acid, and many of the vegetable acids; also by Protosulphate and Protonitrate of Iron. It tinges the cuticle of an indelible purple tint. It is soluble in Alcohol and in Ether. GOLD, FULMINATING. This is a yellowish-brown substance, precipitated on adding Ammonia to a strong solution of Chloride of Gold. It may be dried carefully at 212°, but explodes violently on being heated suddenly to about 290°. Friction also causes it to explode when dry; but the moist powder may be rubbed or handled without danger. It is decomposed by Sulphuretted Hydrogen. Fulminating Gold is probably an Aurate of Ammonia, containing 2 atoms of Ammonia to 1 atom of Peroxide of Gold. GOLD, HYPOSULPHITE OF. Symbol, AuO S{2}O{2}. Atomic weight, 253. Hyposulphite of Gold is produced by the reaction of Chloride of Gold upon Hyposulphite of Soda (see page 133).