The Dictionary Of Photography

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

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Table of Specific Gravities of Some Acetates.
Hydroquinone (Ger., Hydrochinon; Fr., Hydroquinone; Ital., Idrochinone). C6H4(OH)2 = 110. Synonyms: Hydrokinone, Hydrochinone, Quinol. It is prepared commercially by oxidising aniline sulphate with bichromate of potassium. Solubility: 58 per cent, in water ooC, 10 per cent, in water at 300 ; soluble also in alcohol, ether, and glycerine. It is allied to pyrogallol in che-mical composition, pyro being a trihydroxylbenzine, C6H4(OH)3; and quinol, or hydroquinone, being a dihydroxylbenzine. It was first suggested as a developer by Captain Abney, and attracted but little attention in consequence of the unsuitable character of the accelerator, - ammonium hydrate, or liq. ammoniae, - which was recommended, and also from the prohibitive price of hydro-quinone ; but, as more experiments were made with it, and better formulae were given for its use, it crept gradually into general favour, and an enormous reduction in price has led to its widespread adoption. When used with the carbonates of potassium and sodium its action is somewhat slow, and only since the general use of the hydrates of these alkalies has it given satisfaction. The question as to whether it is better than pyro is one that cannot be decided, so much depending upon the personal bias of the user. Many old operators who have used alkaline pyro since its first introduction still cling to it,