PART I. THE SCIENCE OF PHOTOGRAPHY.
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Introduction	1
CHAPTER I.
Historical Sketch of Photography	6
CHAPTER II. THE SALTS OF SILVER EMPLOYED IN PHOTOGRAPHY.
Section I.—The Chemistry of the Salts of Silver.—The preparation and properties of the Nitrate of Silver—of the Chloride, Bromide, and Iodide of Silver.—The Chemistry of the Oxides of Silver	12
Section II.—The Photographic Properties of the Salts of Silver.—The action of Light upon Nitrate of Silver—upon Chloride, Bromide, and Iodide of Silver.—The blackening of Chloride of Silver explained.—Simple experiments with sensitive Photographic Paper	18

CHAPTER III. ON THE DEVELOPMENT OF AN INVISIBLE IMAGE.
Simple experiments illustrating the process	25
Section I.—Chemistry of the Substances, employed as Developers.—Development shown to be a process of reduction.—The chemistry of the principal reducing agents, Gallic Acid, Pyrogallic Acid, and the Protosalts of Iron	26
Section II.—The Reduction of Salts of Silver by Developing Agents.—Reduction of Oxide of Silver—of Nitrate and Acetate of Silver.—Varied appearance of Metallic Silver when finely divided.—The reduction of the Iodide and other Salts of Silver containing no Oxygen	30
Section III.—Hypothesis on the Formation and Development of the Latent Image.—Explanation of the terms under- and over-exposure.—Diagram of Molecular change.—Moser's experiments on development.—Curious perversions of development	34
CHAPTER IV. ON "FIXING" the PHOTOGRAPHIC IMAGE.
Chemistry of the various substances which may be employed as Fixing Agents.—Ammonia, Alkaline Chlorides, Bromides, and Iodides.—Hyposulphite of Soda.—Cyanide of Potassium	41
CHAPTER V. ON THE NATURE AND PROPERTIES OF LIGHT.
Section I.—The compound Nature of Light.—Its decomposition into elementary coloured rays.—Division of these rays into Luminous, Heat-producing, and Chemical Rays	46
Section II.—The Refraction of Light.—Phenomena of simple refraction by parallel and inclined surfaces.—Refraction from curved surfaces.—The various forms of Lenses.—The Foci of Lenses.—Formation of a Luminous Image by a Lens	49

Section III.—The Photographic Camera.—Its simplest form.—The field of the Camera.—Chromatic aberration.—Spherical aberration.—The use of Stops.—The double, or Portrait combination of Lenses.—Variation between the Visual and Chemical Foci in Lenses	54
Section IV.—The Photographic Action of Coloured Light.—Diagram of Chemical Spectrum.—Illustrative experiments.—Superior sensibility of Bromide of Silver to coloured light.—Mode in which dark-coloured objects are Photographed	60
Section V.—On Binocular Vision and the Stereoscope.—Phenomena of Binocular Vision.—Theory of the Stereoscope.—Wheatstone's reflecting Stereoscope.—Brewster's Stereoscope.—Rules for taking Stereoscopic pictures	66

CHAPTER VI.

THE PHOTOGRAPHIC PROPERTIES OF IODIDE OF SILVER UPON COLLODION.

Section I.—Collodion.—Pyroxyline—its varieties—its chemical composition.—Means of obtaining Nitro-Sulphuric Acid of the proper strength.—Solvents for Pyroxyline.—Variation of physical properties in different samples of Collodion.—The changes which Iodized Collodion undergoes by keeping	75
Section II.—The Chemistry of the Nitrate Bath.—Its solvent action on Iodide of Silver.—Acidity and Alkalinity of the Nitrate Bath.—Formation of Acetate of Silver in the Bath.—The substances which decompose the Bath.—Changes in the Nitrate Bath by use	86
Section III.—The Conditions which influence the Formation and Development of the Latent Image.—Causes which increase or diminish the sensitiveness of the film to Light.—Conditions which hasten or retard development	91

Section IV.—On certain irregularities in the Developing Process.—Effect of particular states of the Bath, and of the Collodion, in producing clouding of the Image, and of acids in obviating it

103

CHAPTER VII.

ON POSITIVE AND NEGATIVE COLLODION PHOTOGRAPHS.

Definition of the terms Positive and Negative.—The same Photograph often capable of representing both varieties	106
Section I.—On Collodion Positives.—The Collodion and Nitrate Bath best suited for Positives.—Peculiarities of Pyrogallic Acid, and the Protosalts of Iron employed to develope Collodion Positives.—The colour of Positives affected by the length of exposure to light.—A Process for whitening Glass Positives by means of Bichloride of Mercury	108
Section II.—On Collodion Negatives.—The Collodion and Nitrate Bath best adapted for Negatives.—Use of Glycyrrhizine to increase the intensity.—Developing solutions for Negatives.—Conversion of finished Positives into Negatives	113

CHAPTER VIII.

ON THE THEORY OF POSITIVE PRINTING.

Section I.—The Preparation of the Sensitive Paper.—Its darkening by light.—The conditions which affect its sensitiveness and the vigour of the Image.—The colour of the print influenced by the preparation of the paper	121
Section II.—The Processes for Fixing and Toning the Proof.—Conditions of a proper fixing.—The Salts of Gold used as toning agents.—The properties of the single fixing and toning Bath, with the conditions which affect its action	128
Section III.—The Author's Photographic Researches.—The chemical composition of the Photographic Image.—The various agencies destructive to Photographs.—The action of damp air upon Positive Prints.—The change in properties of the fixing Bath by constant use	140

Section IV.—The Fading of Photographic Prints.—The causes which produce it.—The comparative permanency of Prints.—The mode of testing permanency

160

CHAPTER IX.

ON THE DAGUERREOTYPE AND TALBOTYPE PROCESSES.

Section I.—The Daguerreotype.—The nature of the sensitive film.—Development of the Latent Image.—The strengthening of the Image by means of Hyposulphite of Gold	171
Section II.—The Processes of Talbot, etc.—The Calotype.—The Waxed Paper Process of Le Grey.—The Albumen Negative Process.—Taupenot's Collodio-Albumen Process	176

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