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Silver Bromide

soluble and presence

SILVER BROMIDE (Fr., Bromure d'argent ; Ger., Bromsilber) Synonym, bromide of silver. AgBr. Mole cular weight, x88. Solubilities, practically in soluble in water, alcohol and ether, soluble in ammonia, potassium cyanide and sodium hypo sulphite. It is a yellow amorphous powder, ob tained by adding any soluble bromide to silver nitrate solution. For photographic purposes it is always prepared in the presence of some vehicle which holds it in suspension in the form of an emulsion and prevents it from forming coarse granules. If, as is usually the case, the bromide is precipitated in the presence of ammonia, a much more sensitive salt is obtained, and the sensitiveness can be increased by digestion in the warmth for some time or merely by allowing the emulsion to stand. Under these conditions the grain of the silver bromide probably increases in size, and also the light which it absorbs alters in character. Freshly prepared gelatino-bromide

emulsion is transparent and a deep ruby colour ; by the action of ammonia or heat it becomes more opaque, and the light transmitted changes to orange, and by further ripening to yellow, green, greenish blue, and blue, these changes being accompanied by increases in sensitiveness.

Silver bromide is the most light-sensitive silver salt, but, unlike silver chloride, does not give rise to dark-coloured products on prolonged exposure, except in the presence of some halogen absorber such as silver nitrate, potassium nitrite, or metabisulphite. Its spectrum sensitiveness varies with its method of preparation and degree of ripening, but practically it may be considered to extend from the ultra-violet to about F in the bright blue, with the maximum about Pi G.