The Dictionary Of Photography

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

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hydrobromates, see Hydr iodic Acid) are largely used in photography.
Hydrocarbons. Compounds of carbon and hydrogen - which are very numerous - are so called. Hydrocarbons of special interest to photographers are benzine or benzole and Acetylene {q.v.).
Hydrochinon. See Hydroquinone.
Hydrochloric Acid (Ger., Chlorwasserstoffsaure; Fr., Acide chlorhydrique; Ital., Acido chloridricd). HC1=36*5. Synonyms: Muriatic acid, Spirits of salts. Made by decomposing common salt with sulphuric acid. Specific gravities of the aqueous acid of various strengths are given under the heading Hydrometers and Hydrometry. It reacts with alkalies and hydrates of basy-lous radicles to form chlorides or hydrochlorates.
Hydrofluoric Acid. See Fluorhydric Acid.
Hydrogen. H = i. The
prefix hydro- or hydr- of technical words is often a secondary derivative from hydrogen.) A gaseous element of very frequent occurrence in nature in a combined state, especially in the form of water. It is taken as the unit of atomic weights. It is used for the production of the lime-light.
Hydrogen Peroxide (Ger., Wasserstoffstiperoxyd; Fr., Eau oxygenee ; Ital., Aequo, ossigenatd). H203 = 34. Synonyms: Hydroxyl, Hydrogen dioxide. A powerful oxidiser and bleach-ing agent, sometimes used to free prints and negatives from the last traces of hypo, which it does by oxidising it into sulphate; but it must be used very weak (about 2 drms. to 5 ozs.), or the density of the negatives and the tones of the prints may be reduced and sulphur deposited. Also acts on silver oxide as a reducing agent, and with an alkali will develop the latent image - a matter of some theoretical interest.
Hydrometer and Hydrometry. The hydrometer is a spindle-like float, generally made of glass, and with a graduated stem which indicates the specific gravity of a liquid by the depth to