The Dictionary Of Photography

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

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Eosin                                               Equivalence, Chemical
positive may be made on any lantern plate and developed with any developer. Care should be taken to make it as perfect as possible, and all small imperfections, etc., should be retouched or spotted out on the positive. By making a cloud positive on a separate slide, and using it as a cover glass like a lantern slide, clouds may be obtained in the enlarged negative. The enlarged negative may, of course, be developed with any developing agents ; but in this, as when developing the small positive, care should be taken to keep the whole rather thin, a delicate, full-of-detail negative and positive, giving the best results. The large negative may also obviously be made by using a negative in the first instance, and obtaining a positive by enlargement, and then obtaining a negative from this by contact printing. Celluloid coated with gelatino-bromide emulsion may also be obtained commercially ; and this may be utilised either for positives, trans-parencies, or negatives, the necessary treatment being precisely the same as indicated above, for paper, opals, or plates, according to the method of viewing for which the enlargement is required.
Eosin. A generic name given to various colouring matters obtained from fluorescine, which have been used in ortho-chromatic work.
Equivalence, Chemical; Calculations and Data. No short
instruction or elaborate tabulation of formulae or equivalent numbers can make one who has not a fundamental chemical training quite safe in determining equivalent quantities, but we shall endeavour to give such general instructions as may assist the novice; also tabular matter. Each chemical element is represented in the symbolic language of the chemist by an abbreviated form of the name; this abbreviated form being some-times the initial letter, or the initial letter together with another characteristic letter ; but in some cases Latinised, Latin, or other names are thus abbreviated. Thus Ag stands for silver (argen-tum), K for potassium (kalium), and Na for sodium (natrium). In the following table, which gives the elements as tabulated by chemists of the present time, a symbol is given against the name of each element, also a number (commonly called the Atomic Weight); these numbers indicating the proportions by weight in which the elements interact on each other. As regards these numbers, which are the basis of calculations as to chemical
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