Chapter II: Preface: To the Fourth Edition

The Author has endeavoured to keep pace with the improvements which are daily being introduced in the science and art of Photography. In the present Edition alterations have been made in the style and general arrangement of the work, and additional matter has been inserted.

Since the publication of the Third Edition, a series of experiments have been made on the manufacture of Collodion, the results of which have thrown further light upon the conditions affecting the sensitiveness of the excited film, and have enabled the writer to introduce an organic substance, "Glycyrrhizine," which will be found of service in making Photographic copies of Engravings and similar works of Art.

Dr. Norris, of Birmingham, has within the last few months communicated a paper on _dry Collodion_, which places the theory of that subject upon a better footing than before. The Oxymel preservative process is now also thoroughly understood, and may be considered certain.

In addition to the above, the "Albuminized Collodion" of M. Taupenot, which experience proves to be one of the best dry processes at present known, is included in this Edition.

_King's College, London, April 6th, 1857._

ERRATA.

Page 24, line 5, _for_ conditions _read_ condition.
Page 115, line 32, _for_ Iodide _read_ Iodine.
Page 194, line 15, _for_ p. 88 _read_ p. 188.

[_Transcriber Note--Corrections have been applied_]

CONTENTS.

PART I.

THE SCIENCE OF PHOTOGRAPHY.

Page

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

PART II.

PRACTICAL DETAILS OF THE COLLODION PROCESS.

CHAPTER I.

PREPARATION OF COLLODION.

Mode of preparing soluble Pyroxyline by the mixed Acids--by the Nitre
process.--Purification of the Ether and Alcohol.--Preparation of
the iodizing compounds in a state of purity 185

CHAPTER II.

FORMULÆ FOR SOLUTIONS REQUIRED FOR COLLODION PHOTOGRAPHS.

Section I.--_Formulæ for direct Positive Solutions._--The
Collodion.--The Nitrate Bath.--Developing fluids.--Fixing
liquids.--Whitening solution 201

Section II.--_Formula for Negative Solutions._--The Collodion.--The
Nitrate Bath.--Developing fluid.--Fixing liquid 208

CHAPTER III.

MANIPULATIONS OF THE COLLODION PROCESS.

Section I.--_Manipulations with moist
Collodion._--Cleaning the Plates.--Coating with
Collodion.--Exciting.--Exposing.--Developing. --Fixing 213

Section II.--_Simple directions for the use of Photographic
Lenses._--Portrait Lenses.--View Lenses.--Mode of finding the
chemical Focus 227

Section III.--_On copying Engravings, Etchings, Diagrams, etc._--Mode
of intensifying the Collodion 231

Section IV.--_Rules for taking Stereoscopic Photographs._--Mr.
Latimer Clark's arrangement for working with a single Camera 232

Section V.--_The Photographic delineation of Microscopic
Objects.-_-Arrangement of the apparatus.--Mode of finding the
chemical Focus.--Use of artificial light 235

CHAPTER IV.

THE DETAILS OF PHOTOGRAPHIC PRINTING.

Section I.--_Positive Printing by the ordinary process._--Selection
of the paper.--Preparation of Albuminized paper--of plain
paper--of Ammonio-Nitrate Paper.--Preparation of the fixing and
toning Bath.--Manipulatory details of Photographic Printing.--Mode
of washing and mounting the Proofs 240

Section II.--_Positive Printing by Development._--A process on
Chloride and Citrate of Silver.--On Iodide of Silver.--On Bromide
of Silver 259

Section III.--_The Sel d'Or Process for toning
Positives._--Preparation of the toning Bath.--Manipulatory details
267

Section IV.--_On Printing enlarged Positives, Transparencies, etc.,
upon Collodion_ 272

CHAPTER V.

CLASSIFICATION OF CAUSES OF FAILURE IN THE COLLODION PROCESS.

Section I.--_Imperfections in Negative and Positive Collodion
Photographs._--Fogging.--Transparent and opaque spots.--Markings
of all kinds--under- and over-exposure, etc. 276

Section II.--_Imperfections in Paper Positives_ 285

CHAPTER VI.

LANDSCAPE PHOTOGRAPHY BY THE COLLODION PRESERVATIVE AND COLLODIO-ALBUMEN PROCESSES.

The Honey Keeping Process.--The Oxymel Process.--Photography on dry
Collodion.--Taupenot's Collodio-Albumen Process 288

PART III.

OUTLINES OF GENERAL CHEMISTRY.

CHAPTER I.

THE CHEMICAL ELEMENTS AND THEIR COMBINATIONS.

The more important Elementary Bodies, with their Symbols and
Atomic Weights.--The Compounds formed by their union.--The
class of Salts.--Illustrations of the nature of Chemical
Affinity.--Chemical Nomenclature.--Symbolic Notation.--The Laws of
Combination.--The Atomic Theory.--The Chemistry of Organic Bodies
305

CHAPTER II.

Vocabulary of Photographic Chemicals 327

APPENDIX.

Quantitative testing of Nitrate Baths.--Recovery of Silver from
waste solutions.--Reduction of Chloride of Silver.--Mode of
taking the Specific Gravity of liquids.--On Filtration.--The use
of Test-papers.--The removal of Silver stains from the hands,
etc.--Dr. Ure's tables of the strength of Sulphuric and Nitric
Acid of different densities.--Table of Weights and Measures 371

A MANUAL

OF

PHOTOGRAPHIC CHEMISTRY.