The Dictionary Of Photography

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

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Equivalent Focus                                                       Ether
Equivalent Focus. See Focus.
Equivalent Terms. See Synonymes.
Erythrosine. C20H6I4O5K2. Synonym : Potassium Salt of Tetraiodofluorescine. This is a derivation of fluorescine, and closely allied to Eosine (q.v.). It is used in orthochromatic photography.
Etching, Photographic. See Photogravure, Fish Glue Process, Daguerreotype (etching of), Zincography, Asphalt Process, and Chemigraphy.
Ether. C4HI0O = 74. Sometimes called Sulphuric Ether, as a survival of an old and mistaken view of its nature. A volatile, inflammable, colourless liquid, prepared from alcohol by distilla-tion with sulphuric acid, and subsequent purification. It has a peculiar, strong, sweet odour, and a hot, burning taste, evaporates quickly on exposure to the air, and when applied to the skin leaving a feeling of considerable coldness. It boils at 950 F., and gives off at ordinary temperatures a heavy, inflammable vapour. Water takes up about one-tenth of its volume of ether, and vice versa; a much greater miscibility with water proves the presence of alcohol, often present in commercial samples, as ether mixes in all proportions with alcohol. Specific ^gravity of good commercial ether should be about 735, It is a solvent of all fixed and essential oils, iodine, bromine, and sparingly of sulphur and phosphorus. It dissolves most resins and balsams, also india-rubber and caoutchouc. Good commercial ether contains about 8 per cent, of alcohol.
Pure or A bsolute Ether is prepared from commercial by shaking it with half its weight of distilled water, which dissolves any alcohol, and decanting the supernatant ether and distilling it with chloride of calcium, which extracts the small amount of water absorbed by the ether.
Methylated Ether is prepared precisely as above, but from methylated spirit. It is, if carefully purified, almost as satis-factory for the preparation of collodion as that from rectified spirit. One test as to whether a sample be suitable for preparing collodion is to put one drop of tincture of iodine into an ounce of methylated ether, and expose to daylight. If the colour is discharged after a few hours, the sample should be rejected.
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