Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: PART I. THE INFLUENCE OF THE SOLAR RAYS ON COMPOUND BODIES, WITH ESPECIAL REFERENCE TO THEIR PHOTOGRAPHIC APPLICATION. SECTION I. ON METALLIC COMPOUNDS. CHAPTER I. PREPARATIONS OF SILVER. (50.) Oxide Of Silver exposed for a few hours to good sunshine, passes into a more decided olive colour, than characterises it when first prepared by precipitation from the nitrate of silver, and consequently the covered portions are lighter than those exposed. Prolonged exposure to the sun’s rays, for a week or more, renders this olive colour very much lighter, and the covered parts are found to be many times darker, than those on which the Light has acted directly. In some instances, where the oxide of silver has been spread on paper, I have noticed a very decided whitening process in some parts, after a few days’ exposure; the cause of which, although diligently sought for, has not been detected. The oxide of silver dissolved in ammonia is a valuable photographic fluid. One application of a strong solution forms an exceedingly sensitive surface. The pictures on this paper are easily fixed by salt or weak ammonia. (51.) Nitrate Of Silver. ? This salt in a state of purity, whether solid, or in solution in distilled water, does not appear to be sensibly affected by Light, but the presence of the smallest portion of organic matter renders it exceedingly liable to change under luminous influence. This property, induced Sir John Herschel, in his early photographic experiments, to combine organic matter with the solution of the nitrate of silver, previously to its being applied to paper, and afterwards to introduce into the pores of the paper organised salts of silver, but without any remarkable results. The organic combinations have, however, since that time, been found of exceedi…
