A manual of photographic chemistry : including the practice of the collodion process . the film. A transparent film receivesthe impression of a feeble ray as speedily, and perhaps moreso, than a creamy film, and it gives under those circumstancesan equal amount of intensity on the application of the deve-loper. But if the light is unusually strong—such, for instance,as the diffused light of the sky—then in that case the intensityis greatest with the more dense film. All this seems to show that a molecular change of some kindis set up which proceeds to a greater or less extent in propor-tion to
A manual of photographic chemistry : including the practice of the collodion process . the film. A transparent film receivesthe impression of a feeble ray as speedily, and perhaps moreso, than a creamy film, and it gives under those circumstancesan equal amount of intensity on the application of the deve-loper. But if the light is unusually strong—such, for instance,as the diffused light of the sky—then in that case the intensityis greatest with the more dense film. All this seems to show that a molecular change of some kindis set up which proceeds to a greater or less extent in propor-tion to the number of the particles. What then, it may be asked, is this molecular change ?Clearly it is not of such a nature as to alter to any materialdegree, either the composition or the properties of the Iodine leaves the surface !—if so, there would be a differ-ence in the appearance of the film, or in its solubility in Hypo-sulphite of Soda. The following diagrams may perhaps be useful in assistingto form a notion of what is meant by#a molecular change. Fi l. Fifr. Fig. 1 represents a compound molecule of Iodide of Silver,the component atoms of which are associated closely together. Fig. 2. The same after the action of a disturbing force. Thesimple molecules have not altogether separated from each other,but they are prepared to do so, touching only at a single point. Now the effect produced on such a combination by a deve-loper is understood, if Ave suppose that in the first case theaffinity of the Iodine for Silver is too great to allow of itsseparation ; but in the second, this affinity having been loosen-ed, the structure gives way, and metallic silver is the result. This hypothesis has at all events the merit of simplicity,but we have no security whatever that it is really the correctexplanation. The fact of no development being attainablewithout the presence of free Nitrate of Silver, renders it ??• 92 ON THE PHOTOGRAPHIC ACTION OF THE exceedingly diffi
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