Chapter LV: Appendix

QUANTITATIVE TESTING OF SOLUTIONS OF NITRATE OF SILVER.

The amount of Nitrate of Silver contained in solutions of that salt may be estimated with sufficient delicacy for ordinary Photographic operations by the following simple process.

Take the _pure_ crystallized Chloride of Sodium, and either dry it strongly or fuse it at a moderate heat, in order to drive off any water which may be retained between the interstices of the crystals; then dissolve in distilled water, in the proportion of 8-1/2 grains to 6 fluid ounces.

In this way, a standard solution of salt is formed, each drachm of which (containing slightly more than one-sixth of a grain of salt) will precipitate exactly half a grain of Nitrate of Silver.

In order to use it, measure out accurately one drachm of the Bath in a minim measure and place it in a two-ounce stoppered phial, taking care to rinse out the measure with a drachm of distilled water, which is to be added to the former; then pour in the salt solution, in the proportion of a drachm for every 4 grains of Nitrate _known to be present_ in an ounce of the Bath which is to be tested; shake the contents of the bottle briskly, until the white curds have perfectly separated, and the supernatant liquid is clear and colourless; then add fresh portions of the standard solution, by 30 minims at a time, with constant shaking. When the last addition causes no _milkiness_, read off the total number of drachms employed (the last half-drachm being subtracted), and multiply that number by 4 for the weight in grains of the Nitrate of Silver present in an ounce of the Bath.

In this manner the strength of the Bath is indicated within two grains to the ounce, or even to a single grain if the last additions of standard salt-solution be made in portions of 15, instead of 30 minims.

Supposing the Bath to be tested is thought to contain about 35 grains of Nitrate to the ounce, it will be convenient to begin by adding to the measured drachm, 7 _drachms_ of the standard solution; afterwards, as the milkiness and precipitation become less marked, the process must be carried on more cautiously, and the bottle shaken violently for several minutes, in order to obtain a clear solution. A few drops of Nitric Acid added to the Nitrate of Silver facilitate the deposition of the Chloride; but care must be taken that the sample of Nitric Acid employed is pure and free from Chlorine, the presence of which would cause an error.

RECOVERY OF SILVER FROM WASTE SOLUTIONS,--FROM THE BLACK DEPOSIT OF HYPO-BATHS, ETC.

The manner of separating metallic Silver from waste solutions varies according to the presence or absence of alkaline Hyposulphites and Cyanides.

a. _Separation of metallic Silver from old Nitrate Baths._--The Silver contained in solutions of the Nitrate, Acetate, etc. may easily be precipitated by suspending a strip of sheet Copper in the liquid; the action is completed in two or three days, the whole of the Nitric Acid and Oxygen passing to the Copper, and forming a blue solution of the Nitrate of Copper. The metallic Silver however, separated in this manner, always contains a portion of Copper, and gives a blue solution when dissolved in Nitric Acid.

A better process is to commence by precipitating the Silver entirely in the form of _Chloride of Silver_, by adding common Salt until no further milkiness can be produced. If the liquid is well stirred, the Chloride of Silver sinks to the bottom, and may be washed by repeatedly filling the vessel with common water, and pouring off the upper clear portion when the clots have again settled down. The Chloride of Silver thus formed may afterwards be reduced to metallic Silver by a process which will presently be described (p. 374).

b. _Separation of Silver from solutions containing alkaline Hyposulphites, Cyanides, or Iodides._--In this case the Silver cannot be precipitated by adding Chloride of Sodium, since the Chloride of Silver is soluble in such liquids. It is necessary therefore to use the Sulphuretted Hydrogen, or the Hydrosulphate of Ammonia, and to separate the Silver in the form of Sulphuret.

Sulphuretted Hydrogen gas is readily prepared, by fitting a cork and flexible tubing to the neck of a pint bottle, and having introduced Sulphuret of Iron (sold by operative chemists for the purpose), about as much as will stand in the palm of the hand, pouring upon it 1-1/2 fluid ounce of Oil of Vitriol diluted with 10 ounces of water. The gas is generated gradually without the application of heat, and must be allowed to bubble up through the liquid from which the Silver is to be separated. The smell of Sulphuretted Hydrogen being offensive, and highly poisonous if inhaled in a concentrated form, the operation must be carried on in the open air, or in a place where the fumes may escape without doing injury.

When the liquid begins to acquire a strong and persistent odour of Sulphuretted Hydrogen, the precipitation of Sulphuret is completed. The black mass must then be collected upon a filter, and washed by pouring water over it, until the liquid which runs through gives little or no precipitate with a drop of Nitrate of Silver.

The Silver may also be separated in the form of Sulphuret from old Hypo-Baths, by adding Oil of Vitriol in quantity sufficient to decompose the Hyposulphite of Soda; and burning off the free Sulphur from the brown deposit.

Conversion of Sulphuret of Silver into metallic Silver.--The black Sulphuret of Silver may be reduced to the state of metal by roasting and subsequent fusion with Carbonate of Soda; but it is more convenient, in operating on a small scale, to proceed in the following manner:--first convert the Sulphuret into Nitrate of Silver, by boiling with Nitric Acid diluted with two parts of water; when all evolution of red fumes has ceased, the liquid may be diluted, allowed to cool, and filtered from the insoluble portion, which consists principally of Sulphur, but also contains a mixture of Chloride and Sulphuret of Silver, unless the Nitric Acid employed was free from Chlorine; this precipitate may be heated, in order to volatilize the Sulphur, and then digested with Hyposulphite of Soda, or added to the Hypo-Bath.

The solution of Nitrate of Silver obtained by dissolving Sulphuret of Silver, is always strongly acid with Nitric Acid, and also contains _Sulphate_ of Silver. It may be crystallized by evaporation; but unless the quantity of material operated on is large, it will be better to precipitate the Silver in the form of Chloride, by adding common Salt, as already recommended.

REDUCTION OF CHLORIDE OF SILVER TO THE METALLIC STATE.

The Chloride of Silver is first to be carefully washed, by filling up the vessel which contains it, many times with water, and pouring off the liquid, or drawing it off close with a siphon. It may then be dried at a gentle heat, and fused with twice its weight of dry Carbonate of Potash, or better still, with a mixture of the Carbonates of Potash and Soda.

The process for reducing Chloride of Silver in the moist way, by metallic Zinc and Sulphuric Acid, is more economical and less troublesome than that just given; it is conducted as follows:--The Chloride, after having been well washed as before, is placed in a large flat dish, and a bar of metallic Zinc laid in contact with it. A small quantity of Oil of Vitriol, diluted with four parts of water, is then added, until a slight effervescence of Hydrogen gas is seen to take place. The vessel is set aside for two or three days, and is not to be disturbed, either by stirring or by moving the bar. The reduction begins with the Chloride immediately in contact with the Zinc, and radiates in all directions. When the whole mass has become of a grey colour, the bar is to be carefully removed and the adhering Silver washed off with a stream of water; the Zinc usually presents a honeycombed appearance, with irregularities upon the surface, which however are not metallic Silver;--they consist only of Zinc or of Oxide of Zinc.

In order to ensure the purity of the Silver, a fresh addition of Sulphuric Acid must be made, after the Zinc bar has been removed, and the digestion continued for several hours, in order to dissolve any fragments of metallic Zinc which may have been inadvertently detached. The grey powder must be repeatedly washed, first with Sulphuric Acid and water (this is necessary to dissolve a portion of an insoluble Salt of Zinc, probably an oxychloride) and then with water alone, until the liquid runs away _neutral_, and gives no precipitate with Carbonate of Soda; it may then be fused into a button, to burn off organic matter if present, and subsequently converted into Nitrate of Silver by boiling with Nitric Acid diluted with two parts of water.

In reducing Chloride of Silver precipitated from old Nitrate Baths _containing Iodide of Silver_, the grey metallic powder is sometimes contaminated with unreduced Iodide of Silver, which dissolves in the solution of Nitrate of Silver formed on treating the mass with Nitric Acid. To avoid this, wash the purified Silver with solution of Hyposulphite of Soda, and then again with water.

MODE OF TAKING THE SPECIFIC GRAVITY OF LIQUIDS.

Instruments are sold, termed "Hydrometers," which indicate specific gravity by the extent to which a glass bulb containing air, and properly balanced, rises or sinks, in the liquid; but a more exact process, and one equally simple, is by the use of the specific gravity bottle.

These bottles are made to contain exactly 1000 grains of distilled water, and with each is sold _a brass weight_, which counterbalances it when filled with pure water.

In taking the specific gravity of a liquid, fill the bottle quite full and insert the stopper, which being pierced through by a fine capillary tube allows the excess to escape. Then, having wiped the bottle quite dry, place it in the scale-pan, and ascertain the number of grains required to produce equilibrium; this number added to, or subtracted from, _unity_ (the assumed specific gravity of water), will give the density of the liquid.

Thus, to take examples, supposing the bottle filled with _rectified Ether_ to require 250 grains to enable it to counterbalance the brass weight,--then 1· _minus_ ·250, or ·750, is the specific gravity; but in the case of _Oil of Vitriol_ the bottle, when full, will be heavier than the counterpoise by perhaps 836 grains; therefore 1· _plus_ ·836, _id est_ 1·836, is the density of the sample examined.

Sometimes the bottle is made to hold only 500 grains of distilled water, in place of 1000; in this case the number of grains to be added or subtracted must be multiplied by 2.

In taking specific gravities, observe that the temperature be within a few degrees of 60° Fahrenheit (if higher or lower, immerse the bottle in warm or cold water); and wash out the bottle thoroughly with water each time after use.

ON FILTRATION AND WASHING PRECIPITATES.

In preparing filters, cut the paper into squares of a sufficient size, and fold each square neatly upon itself, first into a half-square, and then again, at right angles, into a quarter-square;--round off the corners with a pair of scissors, and open out the filter into a conical form, when it will be found to drop exactly into the funnel, and to be uniformly supported throughout.

Before pouring in the liquid, always moisten the filter with distilled water, in order to expand the fibres; if this precaution be neglected, the pores are apt to become choked in filtering liquids which contain finely divided matter in suspension. The solution to be filtered may be poured gently down a glass rod, held in the left hand (_a silver spoon_ may be used, in case of necessity, for Nitrate Baths, and all liquids not containing Nitric or Hydrochloric Acid), and directed against the side of the funnel, near to the upper part. If it does not immediately run clear, it will usually do so on returning it into the filter and allowing it to pass through a second time.

_Mode of Washing Precipitates._--Collect the precipitate upon a filter and drain off as much of the mother-liquor as possible; then pour in distilled water by small portions at a time, allowing each to percolate through the deposit before adding a fresh quantity. When the water passes through perfectly pure, the washing is complete; in testing it, a single drop may be laid upon a strip of glass and allowed to evaporate spontaneously in a warm place, or the proper chemical reagents may be applied, and the washing continued until no impurity can be detected. Thus, for example, in washing the Sulphuret of Silver precipitated from a Hypo-Bath by means of Hydrosulphate of Ammonia, the process will be completed when the water which runs through causes no deposit with a drop of Nitrate of Silver solution.

ON THE USE OF TEST-PAPERS.

The nature of the colouring matter which is employed in the preparation of litmus-paper has already been described at page 353.

In testing for the alkalies and basic oxides generally, the blue litmus-paper which has been reddened by an acid may be used, or, in place of it, the _turmeric_-paper. Turmeric is a yellow vegetable substance which possesses the property of becoming brown when treated with an alkali; it is however less sensitive than the reddened litmus, and is scarcely affected by the weaker bases, such as Oxide of Silver.

In using test-papers, observe the following precautions:--they should be kept in a dark place, and protected from the action of the air, or they soon become purple from Carbonic Acid, always present in the atmosphere in small quantity. By immersion in water containing about one drop of Liquor Potassæ or Ammoniæ, or a grain of Carbonate of Soda to four ounces, the blue colour is restored. As the quantities which are tested for in Photography are often infinitesimally small, it is essential that the litmus-paper should be in good condition; and test-papers prepared with porous paper will be found to show the colour better than those upon glazed or strongly-sized paper. The mode of employing the paper is as follows:--Place a small strip in the liquid to be examined: if it becomes at once _bright red_, a strong acid is present; but if it changes _slowly to a wine-red_ tint, a weak acid, such as Acetic or Carbonic, is indicated. In the case of the Photographic Nitrate Bath faintly acidified with Acetic Acid, a purple colour only may be expected, and a decided red colour would suggest the presence of Nitric Acid. In the Hypo fixing and toning Bath which has acquired acidity, the litmus-paper will perhaps redden in about three or four minutes.

Blue litmus-papers may be changed to the red papers used for alkalies by soaking in water acidified with Sulphuric Acid, one drop to half a pint; or by holding for an instant near the mouth of a bottle containing Glacial Acetic Acid. In examining a Nitrate Bath for alkalinity by means of the reddened litmus-paper, at least five or ten minutes should be allowed for the action, since the change of colour from red to blue takes place very slowly.

REMOVAL OF SILVER STAINS FROM THE HANDS, LINEN, ETC.

The black stains upon the hands caused by Nitrate of Silver, may readily be removed by moistening them and rubbing with a lump of Cyanide of Potassium. As this salt however is highly poisonous, many may prefer the following plan:--Wet the spot with a saturated solution of Iodide of Potassium, and afterwards with Nitric Acid (the strong Nitric Acid acts upon the skin and turns it yellow, it must therefore be diluted with two parts of water before use); then wash with solution of Hyposulphite of Soda.

Stains upon white linen may be easily removed by brushing them with a solution of Iodine in Iodide of Potassium, and afterwards washing with water and soaking in Hyposulphite of Soda, or Cyanide of Potassium, until the yellow Iodide of Silver is dissolved out; the Bichloride of Mercury (neutral solution) also answers well in many cases, changing the dark spot to white (p. 151).

A TABLE SHOWING THE QUANTITY OF ANHYDROUS ACID IN DILUTE SULPHURIC ACID OF DIFFERENT SPECIFIC GRAVITIES. (URE.)

+---------+------------++---------+------------++---------+------------+
| |Real Acid || |Real Acid || |Real Acid |
|Specific | in 100 ||Specific | in 100 ||Specific | in 100 |
|Gravity. |parts of the||Gravity. |parts of the||Gravity. |parts of the|
| | Liquid. || | Liquid. || | Liquid. |
+---------+------------++---------+------------++---------+------------+
| 1·8485 | 81·54 || 1·8115 | 73·39 || 1·7120 | 65·23 |
| 1·8475 | 80·72 || 1·8043 | 72·57 || 1·6993 | 64·42 |
| 1·8460 | 79·90 || 1·7962 | 71·75 || 1·6870 | 63·60 |
| 1·8439 | 79·09 || 1·7870 | 70·94 || 1·6750 | 62·78 |
| 1·8410 | 78·28 || 1·7774 | 70·12 || 1·6630 | 61·97 |
| 1·8376 | 77·46 || 1·7673 | 69·31 || 1·6520 | 61·15 |
| 1·8336 | 76·65 || 1·7570 | 68·49 || 1·6415 | 60·34 |
| 1·8290 | 75·83 || 1·7465 | 67·68 || 1·6321 | 59·52 |
| 1·8233 | 75·02 || 1·7360 | 66·86 || 1·6204 | 58·71 |
| 1·8179 | 74·20 || 1·7245 | 66·05 || 1·6090 | 57·89 |
+---------+------------++---------+------------++---------+------------+

A TABLE SHOWING THE QUANTITY OF ANHYDROUS ACID IN THE LIQUID NITRIC ACID OF DIFFERENT SPECIFIC GRAVITIES. (URE.)

+---------+------------++---------+------------++---------+------------+
| |Real Acid || |Real Acid || |Real Acid |
|Specific | in 100 ||Specific | in 100 ||Specific | in 100 |
|Gravity. |parts of the||Gravity. |parts of the||Gravity. |parts of the|
| | Liquid. || | Liquid. || | Liquid. |
+---------+------------++---------+------------++---------+------------+
| 1·5000 | 79·700 || 1·4640 | 69·339 || 1·4147 | 58·978 |
| 1·4980 | 78·903 || 1·4600 | 68·542 || 1·4107 | 58·181 |
| 1·4960 | 78·106 || 1·4570 | 67·745 || 1·4065 | 57·384 |
| 1·4940 | 77·309 || 1·4530 | 66·948 || 1·4023 | 56·587 |
| 1·4910 | 76·512 || 1·4500 | 66·155 || 1·3978 | 55·790 |
| 1·4880 | 75·715 || 1·4460 | 65·354 || 1·3945 | 54·993 |
| 1·4850 | 74·918 || 1·4424 | 64·557 || 1·3882 | 54·196 |
| 1·4820 | 74·121 || 1·4385 | 63·760 || 1·3833 | 53·399 |
| 1·4790 | 73·324 || 1·4346 | 62·963 || 1·3783 | 52·602 |
| 1·4760 | 72·527 || 1·4306 | 62·166 || 1·3732 | 51·805 |
| 1·4730 | 71·730 || 1·4269 | 61·369 || 1·3681 | 51·068 |
| 1·4700 | 70·933 || 1·4228 | 60·572 || 1·3630 | 50·211 |
| 1·4670 | 70·136 || 1·4189 | 59·775 || 1·3579 | 49·414 |
+---------+------------++---------+------------++---------+------------+

WEIGHTS AND MEASURES.

_Troy, or Apothecaries' Weight._

1 Pound = 12 Ounces. 1 Ounce = 8 Drachms. 1 Drachm
= 3 Scruples. 1 Scruple = 20 Grains. (1 Ounce Troy = 480
Grains, or 1 Ounce Avoirdupois _plus_ 42·5 grains.)

_Avoirdupois Weight._

1 Pound = 16 Ounces. 1 Ounce = 16 Drachms. 1 Drachm
= 27·343 grains. (1 Ounce Avoirdupois = 437·5 grains.) (1 Pound
Avoirdupois = 7000 Grains, or 1 Pound Troy _plus_ 2-1/2 Troy Ounces
_plus_ 40 grains.)

_Imperial Measure._

1 Gallon = 8 Pints. 1 Pint = 20 Ounces. 1 Ounce = 8
Drachms. 1 Drachm = 60 Minims. (A Wine Pint of water
measures 16 Ounces, and _weighs_ a Pound.)

An Imperial Gallon of water _weighs_ 10 Pounds Avoirdupois, or
70,000 Grains. An Imperial Pint of water _weighs_ 1-1/4 Pound Avoirdupois.
A fluid Ounce of water _weighs_ 1 Ounce Avoirdupois, or
437·5 Grains. A Drachm of water _weighs_ 54·7 Grains.

_French Measures of Weight._

1 Kilogramme = 1000 Grammes = something less than 2-1/4 Pounds
Avoirdupois.

1 Gramme = 10 Decigrammes--100 Centigrammes = 1000
Milligrammes = 15·433 English Grains.

A Gramme of water _measures_ 17 English Minims, nearly.
1000 Grammes of water _measure_ 35-1/4 English fluid Ounces.

_French Measures of Volume._

1 Litre = 13 Decilitres = 100 Centilitres = 1000 Millilitres =
35-1/4 English fluid Ounces.

1 Litre = 1 Cubic Decimetre = 1000 Cubic Centimetres.

1 Cubic Centimetre = 17 English Minims.

A Litre of water _weighs_ a Kilogramme, or something less than
2-1/4 Pounds Avoirdupois. A Cubic Centimetre of water _weighs_ a
Gramme.

INDEX.[56]

[56] The preparation and properties of the Chemicals used in Photography will be found in the Alphabetical List commencing at page 327.

Aberration, chromatic, 54;
spherical, 56.
Accelerating agents, their mode of action in Collodion explained, 95.
Acetate of Silver, its preparation and formula, 365;
its formation in Nitrate Bath explained, 89;
ensures absence of free Nitric Acid, 116;
tends slightly to favour fogging and spots, 104;
contra-indicated for glass Positives, 111.
Acetic Acid, properties and mode of testing purity of, 327;
useful in preventing fogging, 104;
in rendering the development slow and even, 99;
does not coagulate Albumen, 329;
a good commercial form of acid, 212;
Acetic Acid essential in Calotype, waxed paper, and Albumen
processes, 177;
also in printing paper Positives by development, 260.
Aceto-Nitrate of Silver, term explained, 177.
Achromatic Lenses, their construction explained, 55;
the visual and chemical foci often coincident in, 60.
Acids, nature of, 308.
Actinism, explained, 61;
importance of distinguishing Actinic from visual rays, 62;
mode of finding Actinic focus, 229.
Affinity, chemical, 312.
Albumen, its chemistry, 328;
forms a compound with oxide of Silver, 20;
used in Positive printing to produce a fine surface layer, 122;
to increase sensitiveness, 125;
affects the colour of the prints, 127;
protects the image from oxidation, 150;
putrifies when exposed to moisture, 155;
discolours the Nitrate Bath, 245.
Albumen negative process, its invention, 10;
theory of, 180;
Collodio-Albumen process of M. Taupenot, 294.
Albuminized paper, formula for, 241;
slow in fixing, 131;
not well adapted for toning by Sel d'or, 269;
good for stereoscopic subjects and small portraits, 249;
cannot be sensitized with Ammonio-Nitrate of Silver, 246.
Alcohol, its chemistry, 330;
sometimes too dilute for making Collodion, 84;
mode of rectifying, 196;
must not contain impurities, 96;
effects of adding to Collodion, 84, 96;
to developer, 205.
Alkalies, nature of, 308.
Alkalinity of Nitrate Bath, explained, 88;
the evils it produces, 104;
how to test for it, 377;
how to remove it, 277.
Amber varnish, 226.
Ammonia, preparation and properties, 331;
its use in fixing, 42;
Mr. Shadbolt's formula for, 271;
its action upon Chloride of Gold, 343;
effect of concentrated Ammonia upon Oxide of Silver, 362.
Ammonio-Nitrate of Silver, its chemistry, 262;
used in Positive printing to increase sensitiveness, 125;
to give black tones, 127;
cannot be used with Albumen, 246;
increases permanency of print, 169;
old Nitrate Baths not easily convertible into Ammonio-Nitrate, 248;
mode of preparing, 247;
best applied to the paper by brush or rod, 248;
Oxide of Silver in Nitrate of Ammonia, a useful substitute for it, 249.
Ammonio-Nitrate paper, formula for, 246;
a more simple formula, but less sensitive than the last, 258.
Atomic theory explained, 322.

Bath for fixing and toning Positives. _See_ Fixing and toning Bath.
Bichloride of Mercury, whitening action on glass Positives
explained, 113;
solution for, 207;
used to intensify Negatives, 118;
bleaches paper prints, 151;
should not be added to paste used in mounting prints, 164;
removes Silver stains, 377.
Binocular vision, phenomena of, explained, 66.
Blackening Negatives, 37, 117.
Black tones, mode of obtaining, in paper Positives, 168, 246.
Bromide of Silver, its preparation and properties, 17;
its superior sensibility to coloured light, 63;
less acted on by white light than Chloride, 19;
less sensitive to invisible image than Iodide, 25;
employment in Collodion, 101;
found useful in Photographing by artificial light, 66;
diagram of chemical spectrum on, 64.
Bromo-Iodide of Silver, 173.
Brushes, mode of applying Silver solutions by, 248.

Calotype process, theory of, 176.
Camera, its first invention, 7;
theory of its construction, 54;
mode of testing accuracy of, 229;
cause of the image being inverted, 53;
the term "flatness of field" explained, 54;
best position of the Camera for portraits, 220;
for architectural subjects, 231;
a funnel-shaped tube placed in front of the lens, 229;
stereoscopic Camera, 234;
microscope Camera, 236.
Causes of failure in Collodion process, 276.
Chemical affinity, illustrations of, 312.
Chemical elements, 306.
Chemical focus, directions for finding, 229;
shorter than visual in non achromatic lenses, 60;
longer than visual in microscopic objectives, 237;
varies slightly with the nature of the light, 238.
Chemical spectrum, 61.
Chemicals, Photographic, Vocabulary of, 327.
Chloride of Silver, its preparation and properties, 14;
more sensitive to white light than Bromide or Iodide, 19;
less sensitive to invisible image, 24;
its blackening by light explained, 20, 141;
accelerated by excess of Nitrate, 19;
by organic matter, 20, 142;
experiments illustrating darkening of papers prepared with, 21;
simple explanation of the mode of preparing sensitive papers with, 22;
agents which dissolve it, 42;
mode of reducing it to metallic state. 374.
Chloride of Gold, its preparation and properties, 342;
action of Ammonia upon it, 343;
use of an alkaline solution of, for toning, 132, 271;
compounds formed on adding it to Hyposulphite of Soda, 133;
mode of preparing the fixing and toning Bath with, 250;
the Sel d'or Bath with, 267.
Chromatic aberration, 54.
Citric Acid, forms a red compound with Suboxide of Silver, 21, 338;
used in printing to give purple tones, 128;
formula for preparing paper with, 246.
Cleaning glass plates, theory of, 39;
details of, 213.
Collodion, its discovery, 10;
chemistry of Pyroxyline, 75;
physical effect of Ether and Alcohol in, 83;
of water in, 85;
glutinosity of, 83;
coloration of iodized, explained, 85;
sensitiveness and intensity affected by the change, 97, 99;
details of manufacture of Collodion, 185;
Positive Collodion, theory of, 108;
formula for, 201;
Negative Collodion, theory of, 113;
formula for, 208;
Collodion for copying engravings, 231;
for keeping processes, 298;
for hot climates, 210;
for working by artificial light, 238;
to remove the brown colour from Collodion, 86.
Collodion film, the proper time for immersing it in the Bath, 219;
a thin film often good for direct Positives, 109;
a thicker film for Negatives, 113;
cause of the film falling away from the glass, 83, 293;
spots and markings on, 281;
conditions which affect its sensitiveness to light, 92;
causes influencing its behaviour with the developer, 98;
mode of preserving sensitiveness of film, 289.
Collodio-Albumen process, theory of, 181;
practical details of, 294.
Colours, their nature explained, 47;
their chemical action on sensitive film, 64;
their photographic action assisted by reflection of white light, 66.
Combination, laws of, 307.
Conjugate foci, explained, 52, 272.
Crookes, Mr., remarks upon chemical spectrum, 63;
upon waxed paper process, 180;
preservative process for Collodion films, 289.
Curvature of luminous image formed by lens, explained, 53.
Cyanide of Potassium, its fixing action explained, 44;
preparation of solution of, 207;
used to remove stains, 377.
Daguerreotype, its invention, 8;
theory of the process, 171.
Development of invisible image, explanation of, 34-40;
second, or intensifying stage explained, 37;
details of developing glass Positives and Negatives, 221-223;
development of paper Positives, 259;
conditions which increase or diminish rapidity of development, 98;
irregularities of development, 103.
Developers, their preparation and properties, 26;
comparative strength of, 98;
theory of, for Positives, 111;
for Negatives, 117;
formulæ for Positive developers, 205;
for Negative, 211.
Diagrams, mode of copying, 232.
Diaphragms for lenses. _See_ Stops.
Double decomposition, illustrated, 14;
explained, 314.
Dry Collodion process, 298.

Elementary bodies, table of, 306;
combination of, 307.
Engravings, mode of copying, 231;
often yield dark-coloured prints, 255.
Equivalent proportions, 320.
Ether, properties of, 339;
purification of, for Photography, 195;
must be kept in a dark place, 196;
should not be distilled from residues of old Collodion, 96.
Experiments, illustrating action of Light upon Chloride of Silver, 21;
illustrating formation and development of invisible images, 25;
illustrating photographic action of coloured light, 62.
Exposure in the Camera, rules for Positives, 221;
for Negatives, 225;
for preserved Collodion plates, 292;
for microscopic photographs, 238;
effects of under and over-exposing, 35;
exposure required in Calotype process, 177;
in waxed paper, 180;
in Albumen negative process, 181;
in dry Collodion process, 301;
in Taupenot's process, 297.

Fading of Positives, explained at length, 160;
Author's researches on, 153.
Film, sensitive. _See_ Collodion film.
Filters, mode of cutting, 376.
Fixing, theory of, 41;
of paper prints explained, 128;
solution for fixing glass Positives and Negatives, 212;
manipulatory details of fixing, 225;
fixing paper Positives with Ammonia, 271.
Fixing and toning Bath, its preparation, 250;
conditions which favour or retard its action, 135;
certain states of the Bath injurious to the proofs, 136;
importance of keeping it in an active condition, 168;
must not be employed immediately after mixing, 251;
must not be allowed to become acid by constant use, 168;
theory of the gradual change of properties it undergoes, 156.
Foci, actinic and luminous, 60;
actinic, mode of finding, 229;
variation between them in microscopic objectives, 237.
Focussing the object, 220.
Fogging, theory of, 103;
mode of detecting causes of, 276.
Formulæ for solutions required in Collodion process, 201;
for papers used in Positive printing, 241;
want of correspondence between, 257.

Gallic Acid, its preparation and properties, 27;
used in paper processes, 178;
becomes mouldy by keeping, 261.
formula for developing paper Positives with, 261.
Gallo-Nitrate of Silver, 177;
discolours rapidly when developing dishes are not clean, 179.
Gelatine, its properties, 341;
forms a compound with an Oxide of Silver, 21;
employed in dry Collodion process, 299;
modified form of, 302;
affects the colour in printing processes, 128;
used in Positive printing to form an even surface layer, 126;
as a cement to mount Photographs, 257.
Glass plates, rules for cleaning, 39;
details of cleaning, 213;
mode of coating with Collodion, 215;
with Albumen, 180.
Glutinous Collodion, explained, 83.
Glycyrrhizine, its nature, 342;
its action in Collodion, 114;
formula for solution of, 209.
Gold, Chloride of. _See_ Chloride of Gold.
Gold salts, their use in Photographic printing explained, 131;
in the Daguerreotype process, 175.
Gradation of tone, in Collodion Photographs, affected by the density of
the film, 109, 113;
by use of Glycyrrhizine, 115.
Gradation of tone, in paper Positives, conditions affecting it in prints
obtained by direct exposure, 123;
in Positives printed by development, 266.

Hadow, Mr., researches on Collodion, 77;
formula for making Pyroxyline, 187.
Heliography, invented by M. Niépce, 7.
Historical sketch of Photography, 6.
Honey keeping process, 289.
Hunt, Mr., introduces Protosalts of Iron in developing, 111.
Hypo Bath. _See_ Fixing and Toning Bath.
Hyposulphite of Silver, its peculiar changes in colour, 129;
the sweet compound which it forms with Hyposulphite of Soda, 44.
Hyposulphite of Soda, preparation and properties, 43;
theory of its fixing action, 43;
blackens Nitrate of Silver, 129;
causes a milkiness with acids, 137;
its decomposition by constant use in fixing, 138;
the salts it forms with Chloride of Gold, 133;
its conversion into sulphuretting Tetrathionate by Iodine and
Perchloride of Iron, 139;
test for presence of, 169.

Iceland moss, its use in Positive printing, 128;
formula for preparing paper with, 245.
Imperfections in Collodion Negatives, 282;
in Positives, 284;
in paper Positives, 285.
Intensity, explanation of term, 92;
mode of increasing in Negatives, 99, 114;
effect of Acetate of Silver upon, 116;
of Nitrite of Silver upon, 102;
mode of diminishing, in glass Positives, 109, 110;
conditions affecting intensity in paper Positives, 123;
in developed paper Positives, 266.
Invisible images, theory of formation of, 34;
development of, 36;
experiments illustrating, 25.
Iodate, how formed in Collodion film, 94;
produces insensitiveness, 198.
Iodide of Ammonium, preparation of, 198;
not fitted for iodizing Collodion required to be kept long, 210.
Iodide of Iron, an accelerator to Collodion, 116.
Iodide of Potassium and Silver, properties of, 42;
mode of iodizing Calotype papers by, 177.
Iodide of Potassium, tests of purity of, 197;
extent of solubility in Alcohol, 351;
dissolves Iodide of Silver, 42.
Iodide of Silver, its preparation and properties, 16;
unaffected by direct action of light, 19;
highly sensitive to invisible image, 24;
hypothesis of formation of latent image on, 34;
possibility of its reduction by Pyrogallic Acid shown, 33;
excess of Nitrate of Silver essential to its blackening by
developer, 36;
diagrams of chemical spectrum on, 61, 64;
fixing agents for, 42;
its solubility in the Nitrate Bath, 86;
retards the action of Hypo fixing and toning Bath, 136;
superior permanency of developed prints on, 167;
details of Negative printing process on, 263.
Iodine, in Collodion, diminishes sensitiveness, 94;
forms Nitric Acid and Iodate in the Bath, 94;
often useful in Positive Collodion, 110;
in Negative Collodion, if fogging occurs, 105;
mode of removing from Collodion, 86.
Iodized Collodion. See Collodion.

Kaolin, properties of, 335;
used to decolorize Nitrate Baths, 91;
importance of purifying it before use, 245.

Landscape Photography, with preserved Collodion plates, 288.
Latent image. See Invisible image.
Laws of substitution explained, 78.
Le Grey, M,, his toning process with Chloride of Gold, 132;
his waxed paper Negative process, 178.
Lenses, various forms of, 51;
foci of, 52;
formation of images by, 53;
use of stops, 58;
portrait, 59;
chemical foci of, 60;
chromatic aberration of, 54;
spherical aberration of, 56;
simple directions for using lenses, 227;
for finding chemical focus, 229.
Light; its action upon Silver Salts, 19;
experiments illustrating, 21;
formation of invisible images by, 24;
its alternating action upon Daguerreotype plate, 39;
its compound nature, 46;
photographic action of coloured light, 60;
refraction of light, 49.
Llewellyn, Mr., his Oxymel process, 291.

Manipulations of Collodion process, 213;
of Photographic printing, 251;
of toning by Sel d'or, 267.
Manuscripts, mode of copying, 231.
Markings on Collodion Pictures, 281.
Measures and Weights, 379.
Microscopic Photography, 235.
Moser, M. Ludwig, his researches on the development of invisible
images, 37.
Mounting Positive Prints, substances which should be avoided in,
155, 164;
details of, 257.

Negative processes for printing Positives, 259, 263.
Negatives, definition of, 106;
Collodion Negatives, theory of production of, 113;
Calotype, 176;
waxed paper, 178;
Albumen, 180;
Collodio-Albumen (Taupenot), 181;
mode of developing Collodion Negatives, 37, 117, 223;
of converting Positives into, 117;
formula for solutions for Negatives, 208;
the Collodion best adapted for Negatives, 114;
spots and markings upon Negatives, 282;
decomposition of Pyroxyline a cause of fading of, 166.
Nitrate of Silver, preparation and properties of, 12;
preparation of from standard coin of realm, 362;
often contains free Nitric Acid, 13;
when very strongly fused, contains Nitrite
(_see_ Nitrite of Silver), 14;
not acted on by light, 18;
its reduction by Pyrogallic Acid explained, 31;
the melted Nitrate more certain in its action, 13, 101;
its presence essential in developing the image, 36, 98;
increases sensitiveness of Collodion plate, 92;
dissolves Iodide of Silver, 86;
discoloured by Albumen, 245, 329;
forms a compound with Honey, 289;
with various other organic bodies, 21;
very little acted on by Glycerine, 342;
mode of recovering the Silver from, 372.
Nitrate Bath, mode of preparing for glass Positives, 110, 203;
for Collodion Negatives, 116, 211;
its power of dissolving Iodide of Silver, its occasional acidity and
alkalinity explained, 86;
the mode in which Acetate of Silver may be formed in it, 89;
a list of the substances by which it is decomposed, 90;
changes by use, 91;
effect of these changes on sensitiveness, 97;
on intensity, 102;
care required to prevent it from yielding foggy pictures, 104;
a caution against the too frequent addition of alkali, 204;
quantitative testing of the Bath, 371.
Nitrite of Silver, adds to rapidity of development, 102;
tends slightly to produce fogging, 104;
solarizes the high lights, 111.
Nitric Acid, its preparation and properties, 355;
its oxidizing powers, 12;
impairs sensitiveness of Collodion film, 93;
lessens rapidity of development, 98;
tends to prevent fogging, 104;
sometimes usefully employed for glass Positives, 110;
contra-indicated for Negatives, 116;
its accumulation in the Nitrate Bath explained, 94;
mode of removing it, 90;
cannot exist in contact with Acetate of Silver, 116;
produces stains on cloth, 215;
mode of determining the strength of Commercial Nitric Acid, 186;
table of strength of Nitric Acid of different densities, 378.
Nitro-Sulphuric Acid, explained, 77;
process for making by mixed acids, 186;
by Oil of Vitriol and Nitre, 190;
should not be used cold, 83.
Nomenclature, chemical, 315.
Norris, Dr., his dry Collodion process, 298.
Notation, chemical, 318.

Organic bodies, chemistry of, 324.
Oxide of Silver, preparation and properties, 17;
dissolves in the Nitrate Bath, rendering it alkaline, 88;
properties of its solution in Ammonia, 362;
preparation of ditto, 247;
its solution in Nitrate of Ammonia used in Photography, 249.
Oxymel, keeping process, 291;
preparation of Oxymel, 360.
Paper, Photographic, selection of, 240;
peculiarity of English papers, 241.
Paper, sensitive, for printing. _See_ Sensitive Paper.
Perchloride of Iron, preparation of toning Bath with, 160.
Permanence of Positives, mode of testing, 169.
Photographic image, chemical composition of, 140;
action of destructive tests on, 145.
Photographic properties of Salts of Silver, 18;
of Iodide of Silver upon Collodion, 74.
Photographic researches by the Author, 140.
Photography, historical sketch of, 6;
the term explained, 61.
Portrait lenses, theory of their construction, 59;
rules for their use, 227;
mode of finding chemical focus, 229.
Portraits, drapery for, 66;
directions for taking, 220;
the position of the Camera, and other points of importance, 228;
the time of exposure, 221.
Positive printing, on Albuminized paper, formulæ for, 241;
on plain paper, formulæ for, 245;
on Ammonio-Nitrate paper, formula for, 246, 258;
by development, formulæ for, 259;
manipulatory details of printing, fixing, toning, washing, and
mounting, 251;
process of toning by Sel d'or, theory of, 134;
practice of, 267;
reasons for the want of correspondence between different formulæ, 257;
use of Chloride of Gold in toning, 132, 271;
theory of the preparation of the sensitive paper for Positives, 122;
theory of the process of fixing, 129;
of toning by Gold, 132;
the Author's researches, 140;
rationale of the printing process, 120;
composition of the image, 140;
fading of Positive prints, 160;
destructive action of Sulphur on, 145;
of oxidizing agents on, 148;
of Chlorine, acids, boiling water, etc., on, 151;
of combustion of coal-gas on, 153;
effect of damp air on, 153;
theory of mode of washing Positives, 162;
comparative permanency of prints, 166;
mode of testing permanency, 169.
Positives, definition of, 106;
Collodion Positives, theory of production of, 108;
formulæ for solutions for, 201;
development of, 111, 221;
Collodion and Nitrate Bath best adapted for, 109;
mode of whitening by Bichloride of Mercury, 112;
solution for whitening, 207;
mode of backing up, 226;
spots and markings on, 284;
mode of printing Positives on Collodion, 272.
Positives, enlarged, mode of printing, 272.
Practice of Collodion process, 183.
Preservative processes for Collodion plates, 289.
Printing, Photographic, theory of, 120;
practical details of, 240.
Prism, refraction of light by, 51;
diagram of formation of spectrum by, 47;
explained, 54.
Prismatic spectrum, 47, 61.
Protonitrate of Iron, preparation of, 206;
a feeble developer when free from excess of Sulphate of Iron, 98;
theory of its mode of action, and rules for its use, 112;
cannot be prepared in quantity by adding Nitrate of Potash to Sulphate
of Iron, 314;
sometimes requires the addition of Nitrate of Silver, 206.
Protosulphate of Iron, its preparation and properties, 29;
its characteristics as a developer for Collodion Positives, 111;
not well adapted for developing Collodion Negatives, 117;
preparation of the solution for Positives, 205;
mode of applying it to the plate, 221;
to remove iron stains on glass, 215.
Pyrogallic Acid, its preparation and properties, 28;
solution for developing glass Positives, 205;
for Negatives, 211;
cannot be used without Acetic Acid, 105;
less adapted for developing paper pictures, 178;
requires addition of Nitric Acid when used for Positives, 111;
superior to Sulphate of Iron for developing Negatives, 117, 144;
mode of obviating the brown discoloration of developing solutions, 212.
Pyroxyline, its nature and properties, 75;
preparation of, by Mr. Hadow's formula, 186;
by a rule-of-thumb mixture of the acids, 188;
by the Oil of Vitriol and Nitre process, 190;
details of immersing, washing, and drying, 191;
the glutinous variety produced by cold acids, 83;
recapitulation of the effects of varying the strength of the acid
mixture, 193;
spontaneous decomposition of Pyroxyline, 166.

Reduction of metallic oxides by developers, theory of, 26;
of Silver salts by developers, theory of, 30;
practical details of reducing Silver compounds to metallic state, 372.

Salts nature of, 310.
Salts of Silver, their preparation and properties, 12;
their Photographic action, 18;
theory of their reduction by developer, 30;
directions for obtaining metal from, 372.
Sel d'or, toning process by, its theory, 134;
its practical details, 267;
its advantages, 271;
gives permanent prints, 167.
Sensitiveness, term explained, 92;
conditions favourable to, 97.
Sensitiveness of Collodion film, causes influencing, 92;
superior sensitiveness partially explained, 74;
preservation of sensitive film, 288.
Sensitive paper, theory of preparation of, 22, 122;
its darkening by light described, 123;
preparation of Albuminized paper, 241;
of plain paper, 245;
of Ammonio-Nitrate paper, 246, 258;
of paper for Negative processes, 259;
causes which affect the sensitiveness of Positive paper, 123;
which alter the colour of the image, 126;
spots and markings on, 285;
a large excess of Nitrate of Silver essential, 124;
the paper should not be kept too long, 130, 286.
Serum of Milk, preparation of, 262, 355;
used in Negative printing process, 262.
Shadbolt, Mr., his Honey keeping process, 289;
employs artificial light in Micro-Photography, 237.
Silver, properties of, 362;
estimation of, in Nitrate Baths, 371;
recovery from waste solutions, 372;
reduction from Chloride, 374;
stains, removal of, 377.
Size, mode of removing, from paper Positives, 255.
Solar spectrum, 47, 61.
Soluble paper. _See_ Pyroxyline.
Specific gravity of liquids, mode of finding, 375.
Spherical aberration, 56.
Spirits of Wine, preparation and properties, 330;
not always sufficiently strong for Collodion, 84;
mode of rectifying, 196;
sometimes contaminated with, fusel oil, 96.
Spots on Collodion plates, 279;
on paper Positives, 285;
on prints obtained by development, 266;
on preserved Collodion plates, 293.
Stains, Silver, removal of, 377.
Stereoscope, invention of, 67;
theory of, 68;
Wheatstone's, 69;
Brewster's, 70.
Stereoscopic Photographs, rules for taking, 71;
practical details of, 232.
Stops, theory of use of, 57;
simple mode of making, 228;
position of the stop often important, 230.
Strength of acids, tables of, 378.
Subchloride of Silver, its preparation and properties, 15;
decomposed by fixing agents, 141.
Suboxide of Silver, its properties, 18;
forms compounds with organic matters. Citric Acid, Albumen, etc., 21.
Substitution, laws of, explained, 78.
Sulphate of Iron. _See_ Protosulphate of Iron.
Sulphate of Quinine, absorption of chemical rays by, 65.
Sulphuric Acid, table of strength of, 378.
Sutton, Mr., theory of Sel d'or toning process, 134;
practical details of, 267;
Negative printing process, 262;
preparation of Serum of Milk for, 355.
Symbols, use of, 318.
Syruped Collodion film, 289.

Talbot, Mr., his discoveries, 9;
theory of Calotype process, 176.
Taupenot, M., his Collodio-Albumen process, 181;
practical details of, 294.
Temperature, its effect upon development of Collodion film, 102;
upon fogging, 105;
upon keeping Collodion, 210;
upon action of fixing Bath for paper Positives, 130;
upon Hypo toning Bath, 136.
Test-papers, use of, 376.
Toning Bath for Positives, with Sel d'or, 134, 267;
with Hyposulphite and Gold, _see_ Fixing and Toning Bath;
with Chloride of Iron and Hyposulphite, 160.
Toning of Positives, term defined, 121;
may injure the stability of the proof, 154;
points to be kept in view to avoid fading, 167;
manipulatory details of, 253;
by Sel d'or, 267.
Transparencies, mode of printing, 273.

Varnishes for Collodion Photographs, 226.
View Lenses, directions for using, 230.
Vocabulary of Photographic chemicals, 327.

Washing Positive prints, rules for, 162;
details of, 255.
Waxed paper process, theory of, 178.
Weights and Measures, table of, 379.

PRINTED BY JOHN EDWARD TAYLOR, LITTLE QUEEN STREET, LINCOLN'S INN FIELDS.

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Transcriber Note

Minor typos have been corrected. Images moved to prevent splitting paragraphs.