Home >> Encyclopedic Dictionary Of Photography >> Formula to Or Film Negative Process >> Glycin


gold, chloride, acid, solution, soluble and weight

GLYCIN (Formula C,H,(OH), NH. CH„ CO. OH. Synonym, hydroxyphenol Obtained by the action of chloracetic acid on amidophenol. It takes the form of a light lustrous powder soluble in water in presence of a caustic alkali or alkaline carbonate, forming a colorless solution which can be rendered stable by the addition of a sulphite. It acts as a powerful but slow acting developer, giving clear images of a grayish bladk color. Potassium bromide acts as a restrainer.

GOLD (Symbol, Au.; atomic weight, I96.85.)—The most widely and universally sought metal in the earth's crust, and too well known to require any description. It is only used in pho tographic chemistry in combination with other substances. A $io gold piece weighs 268i grains, and contains 246 grains of pure gold.

GOLD CHLORIDE.—There are two gold chlorides known to be in existence —aurous chloride (AuCl) and auric chloride The existence of another gold chloride called auro auric chloride has been asserted by some chemists and denied by others. The gold chloride used in photographic operations is the auric chloride, molecular weight, 302.5; synonyms, terchloride or perchloride of gold, etc. It is formed by dissolving gold in aqua regia (a mixture of nitric and hydrochloric acids) and drying on a porous tile over concentrated sulphuric acid for several days.

A simple method of making gold chloride for photographic purposes is the following : Mix in a suitable vessel four fluid drachms of nitric acid and two ounces of hydrochloric acid. Into this place a gold coin—the newer the better—and apply a gentle heat. For this purpose a sand or water bath is preferable. A considerable quantity of gas will be evolved, and the gold will disappear. If the acids are weak, and complete solution of the metal cannot be effected, a little more of the acids mixed in the same proportion should be added. The solution of perchloride

of gold in excess of acid thus obtained is next evaporated in a sand or water bath, and the crystals formed are preserved in hermetically-sealed bottles, as they are very deliquescent.

Commercial chloride of gold takes the form of reddish orange needle-like crystals, extremely deliquescent and soluble in alcohol and ether. It is sold in small hermetically-sealed tubes, containing x5 grammes of gold chloride. This weight, however, is no criterion of its value, but the weight of the actual gold contained in it.

Many inferior makes of gold chloride are sold, most of which are, correctly speaking, gold sodio-chloride, with formula NaCl, Nearly every substance which is capable of combining with oxygen or with chlorine tends to reduce the metal from a solution of gold chloride, and it is for this reason that gold chloride is used for the purpose of toning silver prints. For this it is mixed with the soluble salts of free acids, such as the phosphates, acetates, carbonates, etc. The action of the different toning solu tions is given by C. J. Leaper in the following equations, assuming in each case that the darkened silver reduction product consists of silver oxychloride Gold chloride is very freely soluble in water, giving a yellow solution. It is, however, only feebly soluble in alcohol. To test for salts of gold, note that solutions containing them give the following reactions : A blackish-brown precipitate with sulphuretted hydrogen, and a brownish precipitate with ferrous sulphate or oxalaic acid. A solution of ferrous sulphate is usually employed to precipitate the gold from old or spoilt toning baths.