Curious Facts in Molecular Physics

Abstract

SOME of the phenomena of photography present features of a very curious nature, yet seem to be very little known to philosophers who devote their time to researches in molecular physics. For instance, when a glass plate coated with collodion containing an iodide—say iodide of cadmium—is dipped into a “bath” solution of nitrate of silver, strength twenty-five grains to the ounce, in from three to four minutes a good dense precipitate of yellow iodide of silver is formed in the spongy collodion film, and the plate is ready for photographic use. But, let a plate be covered with collodion containing bromide of cadmium, (ten grains to the ounce) instead of iodide of cadmium, an immersion of ten or fifteen minutes is necessary to obtain a good film of bromide of silver, though the collodion skin upon the glass surface is only of the same thickness as in the former instance, and not only is this much longer immersion necessary, but the nitrate of silver solution must be increased in strength to about sixty grains to the ounce to get the best results. When the strength of the nitrate of silver is only twenty-five grains to the ounce, the bromide of silver forms more on the surface of the collodion than within it, and sometimes breaks away in scales from the collodion, and falls to the bottom of the bath.