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. Au2S3. 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, 11⁄2 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 potassa, and may be extemporaneously prepared by diluting solution of potassa (Ph. L.) with about 5 times its volume.
GOLD SHELLS. Gold leaf or powdered gold ground up with gum-water, and spread upon the insides of shells. Used by artists.
GOLD SIZE. Syn. Gilding size, Gilder’s s., Gold colour. Prep. 1. (Oil size.) Drying or boiled oil thickened with yellow ochre or calcined red ochre, and carefully reduced to the utmost smoothness by grinding. It is thinned with oil of turpentine. Improves by age. Used for oil gilding.
2. (Water size.) Parchment or isinglass size, mixed with finely ground yellow ochre. Used in burnished or distemper gilding.
GOLD-BEAT′ER’S SKIN is prepared from
the peritoneal membrane of the cæcum of the ox. It is used to separate the leaves of gold whilst under the hammer, as a nearly invisible defensive dressing for cuts, as a fabric for court plaster, &c.
GOLDEN SEAL. See Hydrastis canadensis.