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MODERN DEVELOPERS The light sensitive film with which our plates, films, and printing papers Reduction ltte coated consists of gelatine emulsion in which silver haloids, e. g. silver bromide or chloride, in an extremely fine state of division, are very evenly distributed. We do not know the precise nature of the change or alteration effected by the action of light in this sensitive film during exposure. But we do know that certain chemical compounds, which are easily oxidized, have a preferential action on the silver haloids, reducing to metallic silver those on which light has acted and having little or no action on those not so acted upon by light. This we call developing power since it makes the form and details of the picture image visible to the eye. Thus, by development, which is here seen to be a process of chemical reduction, we get, in the case of a dry plate or film exposed in the camera, a negative picture image on glass or transparent film; and, in the case of printing papers exposed behind a negative, a positive picture image on paper. In this process the developer is the active reducing agent, the other ingredients of the developing solution doing other and different work. Most of the compounds which have ~~e the been found to possess this preferential action as to silver haloids, or power to reduce silver bromide or chloride to metallic silver, are derivatives or substitution products of benzene or naphthalene. As these are known as "organic compounds," so the developers obtained from them are called organic developers, and the chemistry of development is an interesting branch of organic chemistry. Without venturing too far into this world of wonders, we can get a fairly clear notion of the origin and source of our modern developers by a little study of benzene and some of its derivatives, which we will now proceed to do. Benzene, the venerable parent of Beu.zene almost all the developers used in photoggraphy during the last fifty years, and of great importance in the making of dye stuffs and pharmaceutical preparations, was discovered by Faraday in 1825, and is commercially manufactured De;~:=~

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Modern Photographic Developers  

A Practical Handbook to the New Developers Telling What They Are and How to Use Them with Reliable Formulae by The Photo Miniature, January...

Modern Photographic Developers  

A Practical Handbook to the New Developers Telling What They Are and How to Use Them with Reliable Formulae by The Photo Miniature, January...

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