Magnesium Chloride Manganese
or mountain limestone - an impure carbonate. The metal is silvery white in colour, and is met with commercially in the form of wire, ribbon, and powder. It is now of common use for pro-ducing negatives by night, as the metal ignites at a comparatively low temperature, giving an extremely actinic and brilliant light. A list of books dealing with the production of artificial light for photographic purposes will be found under the heading Arti-ficial Light, and these deal largely with magnesium. See also instructions for using magnesium under the headings Flash Light and Portraiture. Magnesium has been suggested as a means of precipitating silver from old fixing baths. (See Residues.)
Magnesium Chloride (Ger., Chlormagnesium; Fr., Chlorure de magnesium ; Ital., Cloruro di magnesio). MgCL>,6HaO = 203. White crystals or needles, very deliquescent. It has been employed in gelatino-chloride emulsions, and was proposed by Liesegang as a Fixing Agent. Solubility : 160 per cent, in cold, 370 per cent, in boiling water; 50 per cent, in absolute alcohol; 500 per cent, in boiling alcohol.
Magnesium Sulphate (Ger., Magnesiumsuiphat, Schwefel-saures Magnesium ; Fr., Sulfate de magnesie ; Ital., Solfato di magnesia). Synonyms: Sulphate of Magnesia, Epsom Salts. MgS047H20. Occurs naturally in certain springs, but is usually made by dissolving dolomite in dilute sulphuric acid, and subse-quent purification and crystallisation. It has been recommended as a preventive of frilling. Solubility : 104 per cent, in cold, and 700 per cent, in hot, water; insoluble in alcohol.
Magnets, Photographic Action of. Reichenbach, about 1850, asserted that a magnetic pole was not only visible in the dark to some persons, but would also affect the sensitive (Daguerreotype) plate. More recently, Braham, Brooks, and others have obtained magnetographs on emulsion plates.
Magnifier. (See Amplifier.) The ordinary uses of the term, as in " Focussing Magnifier," requires no explanation.
Manganese, Bin-oxide Of (Ger., Mangandioxyd, Braunstein; Fr., Peroxyde de manganese; Ital., Perossido di manganese). MnO;j=86. Synonyms: Manganese Dioxide, Black Oxide of Manganese. Occurs native as the ore of manganese as a black