Miscellaneous Chemicals. It is proposed, in this place, to give a concise description of the chemical compounds referred to in the various departments of this book. A complete list of chemicals would not be necessary for the scope of the work, which is a purely practical one; such information only is therefore given as is deemed necessary to render the whole thoroughly intelligible, and as complete as possible. A considerable number of them are inserted, for the sake of clearness, in connection with the process or special purpose for which their use is directed. These will be found in their proper place by reference to the Index.

4075. Chloride of Gold

4075. Chloride of Gold. Gold unites with chlorine under two different proportions, and are distinguished as the protochloride and the terchloridc of gold.

The terchloride of gold, or auric chloride, consists of 3 equivalents of chlorine and 1 of gold, and is obtained by dissolving 1 part gold in 3 parts nitro-muriatie acid (aqua-regia); evaporate until vapors of chlorine begin to be disengaged, and then set the solution aside to crystallize. It forms orange-red crystalline needles, or ruby-red prismatic crystals ; is deliquescent, and soluble in water, ether, and alcohol, forming a deep yellow solution. ( Cooley.)

The protochloride of gold, or aurous chloride, consists of 1 equivalent each of chlorine and gold, and is obtained by evaporating the terchloride to dryness and exposing it to a heat of 4C0° (440° Fownes) Fahr., until chlorine ceases to be evolved. It forms a yellowish- white mass, insoluble in water; but it is decomposed by water, slowly when cold, and rapidly by the aid of heat, into metallic gold and terchloride of gold. (Cooley.)

4076. Tests for the Presence of Gold in Solutions

4076.    Tests for the Presence of Gold in Solutions. Protosulphate of iron gives a brown precipitate, which acquires a metallic lustre when rubbed.

Protochloride of tin (preferably containing a little perchloride) gives a violet, purple, or blackish precipitate, insoluble in muriatic acid.

Sulphuretted hydrogen and hydrosulphuret of ammonia give a black precipitate, insoluble in simple acids.

Ammonia gives a reddish-yellow precipitate (fulminating gold) with tolerably concentrated solutions, either at once, or on boiling the liquid.

Liquor of potassa gives, with neutral solutions of gold, a similar precipitate to that formed by ammonia, insoluble in excess.

4077. Fused Nitrate of Silver

4077.    Fused Nitrate of Silver. Take 3 ounces refined silver, 2 fluid ounces nitric acid, and 5 fluid ounces distilled water; mix in a glass flask and apply a gentle heat until the metal is dissolved. Transfer the solution to a porcelain capsule or crucible, decanting it off a heavy black powder which appears at the bottom of the flask; evaporate the solution to dryness; raise the heat, in a dark room, until the mass liquefies, then pour it into hinged brass or iron moulds furnished with cylindrical cavities of the size of a goose-quill. Keep tho product, which is Lunar Caustic, or fused nitrate of silver, in well stopped bottles, impervious to the light.

Crystallized (or crystals of) Nitrate of Silver is obtained by dissolving grain silver (see No. 3217 (Silver Dust)) in nitric acid diluted with twice its weight of water; evaporating tho solution until it will crystallize on cooling very slowly. (See No. 3213 (Solvent for Silver).)