A manual of photographic chemistry : including the practice of the collodion process . orine or Iodine, by whieh elements the Oxygen isreplaced in these Hydraeid Salts. The explanation of this apparent difficulty is as follows:When a Chloride or Iodide of a noble metal is reduced by adeveloper, an atom of water may be supposed to take a partin the reaction. This atom of water consists of Oxygen andHydrogen ; the former of which elements passes to the deve- 32 ON THE DEVELOPMENT OF loper, tlie latter to the Chlorine or Iodine, as the case maybe. By a reference to Part III. it will be seen that
A manual of photographic chemistry : including the practice of the collodion process . orine or Iodine, by whieh elements the Oxygen isreplaced in these Hydraeid Salts. The explanation of this apparent difficulty is as follows:When a Chloride or Iodide of a noble metal is reduced by adeveloper, an atom of water may be supposed to take a partin the reaction. This atom of water consists of Oxygen andHydrogen ; the former of which elements passes to the deve- 32 ON THE DEVELOPMENT OF loper, tlie latter to the Chlorine or Iodine, as the case maybe. By a reference to Part III. it will be seen that the classof elementary substances to which Chlorine belongs are cha-racterized by having a strong affinity for Hydrogen as wellas for tbe metals; therefore the decomposition of a Chlorideor Iodide of Silver in the reaction we have now explained isfacilitated by the fact of this atom of Hydrogen being athand, ready to combine with the Chlorine or Iodine immedi-ately on their separation from the Silver. Perhaps the following simple diagram may assist the com-prehension of the Q0 OO Compound Atom ofIodide of Silver. Compound Atomof Water. Atom ofGallic Acid. The letter S stands for Silver, I for Iodine, H for Hydro-gen, and 0 for Oxygen. Observe that the molecules H and 0 separate from eachother and pass in opposite directions ; 0 unites with the GallicAcid; II meets I, and forms with it an atom of HydriodicAcid; whilst S, the atom of Silver, is left alone. On the Presence ofxi soluble Salt of Silver as favouring theReduction of Chloride and Iodide of Silver.—There is noreason whatever, upon theoretical grounds, why the Iodide ofSilver plus an atom of water should not suffer reduction uponthe application of a developer. The Chloride of Gold, whichis a corresponding salt of a noble metal allied to Silver, veryquickly deposits metallic Gold when mixed with Gallic Acid,and the supernatant liquid is found to contain free Hydro-chloric Acid (HC1). Nevertheless a sensitive la
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