The Silver Sunbeam: A Practical And Theo

Excerpt from The Silver Sunbeam: A Practical and Theoretical Text-Book on Sun Drawing and Photographic Printing; Comprehending All the Wet and Dry Processes at Present Known, With Collodion, Albumen, Gelatin, Wax, Resin and SilverThe first remark in reference to the cause of the change of color in Silver salts is due to the distinguished Swedish chemist, Scheele.* He regarded the blackening effect of chloride of silver, when exposed to the rays of the sun, as caused by a species of reduction of the salt to the metallic state and the accompanying formation of hydrochloric acid. He undertook a course of experiments, to ascertain whether all the colors of the spectrum had an equal inuence in col oring or blackening this salt, and arrived at the conclusion that the maximum chemical or decomposing action of the spectrum was in the neighborhood of the violet part, and that it gradually diminished toward the red, where it was scarcely perceptible. The researches of Scheele in this track terminated here; and no application of the property of black ening of the chloride of silver to photogenic purposes wfs made until after the lapse of several years.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.