I CONTENTS. PART I. THEORETICAL. Page Introductory 9 1 .—The Chemical Composition of Collodion Emulsion 13 2 .—Increasing General Sensitiveness by means of Chemical and Organic Sensitizers 16 3 .—Sensitizing of Collodion Emulsion for Different Parts of the Spectrum - 17 4 .—The Chemical Composition of Colour Sensitizers ; their suitability and selection - - ' - - - - 22 5 .—Elementary Principles of Trichromatic Work 28 6 .—Chemical Changes which take place during Development, Fixing, Inten sifying and Reducing ... 3! 7 .—Dark-Room Illumination and Selection of Dyes Suitable for Light Filters 33