The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Gold, Sodio-Chloride
from acid, which does not deliquesce or effloresce, and gives toning baths of constant and reliable action. One hundred parts of gold are dissolved in aqua regia, and hydrochloric acid added to the solution. To the solution of pure chloride of gold thus prepared are added 38 parts of chloride of potassium. The mixture thus obtained is carefully evaporated till crystallisation, when the dish or vessel is placed under a bell jar containing concentrated sulphuric acid or quicklime. The mother liquid is poured off, and this again evaporated and treated as above. The crystals thus obtained are dried under a bell jar, and heated to 100 - 110oC. to drive off the remaining traces of free hydro-chloric acid. The salt thus procured forms yellow hexagonal needles, easily soluble in water.
Gold, Sodio-Chloride (Ger., Chlorgoldnatrium; Fr., Chlorure double a"or et de sodium ; Ital., Chlortiro doppio d'oro e di sodio. AuCl3NaCl + 2HaO. This is usually the commercial salt, and yellowish-brown needles, which are very deliquescent, soluble in alcohol and water. It may be prepared by dissolving 5 parts by weight of gold chloride, and 1 part by weight of sodium chloride in as little water as possible, and allowing the solution to crystallise. Another method is to dissolve 1 part of gold in 10 parts of aqua regia by the aid of heat, dilute with 100 parts of water, filter through glass wool, precipitate the gold with saturated solution of sulphate of iron, and collect and wash the precipitate, which is pure gold; add 3 parts of sodium chloride to every 1 of gold ; dissolve the mixture in aqua regia and evaporate. The following table shows the equivalent quantities of the various salts used in photography: -
The following calculation will show that home-made chloride may be cheaper than commercial if nothing is allowed for the work, and probability of loss. An Australian sovereign contains H3grs. of pure gold, which will makegrs. of pure chloride,
237-9 grs. of potassio-chloride, and 228-6 grs. of sodio-chloride,