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 in 1 part of gold); collect the precipitated gold, which is now free from copper; re-dissolve in aqua-regia, and evaporate to dryness on a water bath. Avoid using ammonia to neutralize chloride of gold, as it would be liable to occasion a deposit of "fulminating gold," the properties of which are described immediately following. _Properties of Chloride of Gold._--As sold in commerce it usually contains excess of hydrochloric acid, and is then of a bright yellow color; 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 about to 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. The salt sold in commerce as sel d'or is a double hyposulphite of gold and soda, containing one atom of the former salt to three of the latter, with four atoms of water of crystallization. It is formed by adding one part of chloride of gold, in solution, to three parts of hyposulphite of soda, and precipitating the resulting salt by alcohol; the chloride of gold must be added to the hyposulphite of soda, and not the soda salt to the gold. _Properties._--Hyposulphite of gold is unstable and cannot exist in an isolated state, quickly passing into sulphur, sulphuric acid, and metallic gold. When combined with excess of hyposulphite of soda in the form of sel d'or, it is more permanent.