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 Silver
1st Edition
Published on 27. November 2019
978-0-259-72717-0 (ISBN)
Description
Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. The 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 influence 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.
