Chapter XLI: Part 2 (2)

_Nitrate of Silver Bath_ (_for Positives_). Recrystallised nitrate of silver, 5 dr., dissolved in 10 oz. of distilled water. Filter the solution until it is quite clear, then add 3 drops of nitric acid and 10 drops of collodion. Shake well together and filter. Blue litmus paper should slightly redden in this bath; should it turn very red, add a little ammonia, or oxide of silver; should it not redden at all, add a little acid carefully drop by drop. It is preferable to have a slight excess of acid.

_Developing Solution_ (_for Positives_). Protosulphate of iron, 2 dr., dissolved in 8 oz. of distilled water; add 2-1/2 dr. of glacial acetic acid, 2-1/2 dr. of alcohol, and 5 minims of nitric acid, filter, and pour into a well-stoppered bottle; do not expose to the air.

_Fixing Solution_ (_for Positives_). 50 gr. of cyanide of potassium dissolved in 5 oz. of distilled water; that is to say, for every fluid ounce of solution required, mix 10 gr. of cyanide of potassium in 1 oz. of distilled water. Filter and keep in a well-stoppered bottle, and label “Poison.”

_Positive Paper._ Plain paper requires preparing or salting before it is ready for use, or it may be purchased already salted.

Procure some sheets of plain Saxe paper, and immerse them for five minutes (removing air-bubbles) in the following solution:——

Chloride of ammonium 100 gr.
Chloride of barium 100 gr.
Citrate of soda 20 gr.
Water 20 oz.

Hang the sheets up to dry. For portraits and most other uses the paper is albuminised on one side. When photographs are printed to be afterwards coloured, unalbuminised paper is used.

_Albuminised Paper._ There are several well-known papers sold; _Rive’s_, which is a French paper, has a high glaze and fine surface; the _Saxe_, which is more uniform in its texture, is made in Germany. Another maker is _Towgood_. Positive paper is albuminised by placing it in a mixture composed of white of eggs and salt. To the white of each moderate-sized egg use 15 gr. of common salt reduced to a fine powder; whisk until the albumen is all white froth. Leave this froth in a glazed earthen pan for about 12 hours, by which time most of it has settled into clear albumen; pour the clear portion into a flat porcelain tray. This tray should be somewhat larger than the sheets of paper to be albuminised. Lift the paper up by the ends and lay it carefully on the albumen, keeping the side marked as “inferior” uppermost and dry.

The paper should be slightly damp before it is thus treated, as it then takes the albumen more regularly, and is not so liable to air-bubbles. The paper must be lifted at each end, and should any air-bubbles appear, brush them off with a card or small brush, replacing the paper in the bath. Wherever the albumen does not come into actual contact with the paper, a white mark will appear in the print. Remove the paper from the bath and place it to dry on a cardboard frame, or suspend it at the corners by clips. Paper glazed with pure albumen acquires too brilliant a glaze for portraits; the albumen may be diluted with from a 1/4 to 1/3 its bulk of water. It should be kept in tin or zinc cases.

_Plain Paper._ Albuminised paper may be used as plain paper if, instead of sensitising the glazed side, the plain side is placed in the sensitising solution.

_Nitrate of Silver Bath_ (_for Negatives_). Recrystallised nitrate of silver, 1/2 oz.; distilled water, 7 oz.; collodion, 7 drops. Shake well together until the crystals have dissolved, then filter.

The purity of the negative bath is a matter of great importance, hence the necessity of employing the very best nitrate of silver, and also of excluding all foreign matters of every kind. When the bath gets out of order, it should be diluted with an equal bulk of distilled water, and exposed to the sun for a few days, in a white glass bottle, then filtered, and sufficient nitrate of silver added to restore the strength to 35 grains an ounce, as indicated by the argentometer.

_The Argentometer._ This instrument is for ascertaining the strength of the nitrate of silver solution, which becomes weakened to a certain extent, after the immersion of every plate.

_Developing Solution_ (_for Negatives_). Protosulphate of iron, 75 gr.; glacial acetic acid, 2 dr.; alcohol, 2 dr.; distilled water, 5 oz. Dissolve the crystals in the water, then add the acid and alcohol, and filter. In hot weather a little more acetic acid may be added, and if it does not flow readily, the alcohol may be increased.

_Intensifying Solution_, No. 1 (_Negatives_). Pyrogallic acid, 10 gr.; citric acid, 10 gr.; distilled water, 5 oz. When it becomes brown it is useless. No. 2. Recrystallised nitrate of silver, 40 gr.; distilled water, 1 oz.; dissolve and filter. This latter will keep for any length of time in the dark.

_Another Intensifying Bath_ (_Negatives_). A saturated solution of bichloride of mercury in water. Place the negative plate in a bath of the solution, remove when the film assumes a milky-white appearance, wash, and then plunge into a solution of 1 oz. of liquid ammonia to 10 oz. of water. Remove the plate, wash, and place to dry. This mode of intensifying may be regulated by leaving the plate in the bichloride of mercury a shorter time, when it will require a weaker ammonia bath than that above given.

_Fixing Solution_ (_for Negatives_). Hyposulphite of soda, 5 oz.; distilled water, 5 oz.; dissolve and filter.

_Sensitising Solution_ (_for Paper_). Nitrate of silver, 5 dr.; distilled water, 5 oz.; nitric acid, 2 drops; kaolin, 1 oz. Dissolve the nitrate of silver in the water, and then add the acid and kaolin; the kaolin will not dissolve, its use being to prevent the solution becoming discoloured after using. This solution will not require filtering; it must be allowed to become quite clear, and when required for use must be carefully decanted. This solution should be occasionally tested with the argentometer, and sufficient nitrate of silver added to restore it to its original strength.

_Another Negative Collodion._ Ether, 1/2 oz.; gun-cotton, 7 gr.; bromide of cadmium, 1/2 gr.; bromide of ammonium, 1-1/2 gr.; iodide of calcium, 1 gr.; iodide of potassium, 1 gr.; iodide of ammonium, 1 gr. For intensifying, flood with chloride of gold, 1 gr.; water, 15 oz.; then wash, and flood with pyrogallic acid, 2 gr.; water, 3 oz.

_Toning Baths._ 1. Chloride of gold, 4 gr.; acetate of soda, 1/4 oz.; distilled water, 10 oz.; dissolve and filter. 2. _To produce black to bright sepia tones, according to length of immersion._ Take carbonate of soda sufficient to cover a threepenny piece, dissolve it in a teaspoonful of cold water in a cup, add 2 gr. of chloride of gold, then add 3 oz. of boiling water; use in 15 minutes. This will suit Hart’s albuminised paper.

_Fixing Solution_ (_for Paper Prints_). Hyposulphite of soda, 8 oz.; distilled water, 1 pint. This solution must only be used once.

_Stopping-out Negatives._ Small, round, transparent spots are frequently found on glass negatives, which, if not stopped, occasion corresponding black spots on the print. Lay the plate on a slab of glass, having either direct or reflected light shining up through it. Then cover the spots with a mixture composed of 10 parts of ivory black, 2 parts of saturated solution of gum Arabic, 2 parts of white honey, 1 part of sugar-candy; well mix and apply with a fine camel-hair brush. Should the spots on the negative be black or opaque, white spots will be formed on the print; these are easily tinted with a little water colour, to match the other portions of the print; it is seldom necessary, therefore, to alter the negative on this account.

_Ferrotypes._ In these, instead of a glass plate being used to receive the picture, as in a positive glass photograph, a thin plate of black varnished iron is employed. Of course no black backing is required; with this exception the photograph is produced in every particular by the same means and in the same manner as the glass positive is.

_To Clean Glass Plates._ (Mr Hughes.) The description of glass known as “flatted crown” is well suited for positives, but before using it requires careful cleaning. The sharp edges should be first removed with a “corundum” file, or by drawing the sharp edge of one piece over the sharp edge of another; then place the glass on a clean flat surface, or put it in “a plate-cleaning holder,” and pour a few drops of the plate-cleaning solution in the middle. Rub it carefully over every part with a bit of clean soft rag; turn the glass over, and do the other side the same. Then polish each side with a clean cloth, and finish with a soft chamois leather kept expressly for this purpose. Now breathe on the glass, and if the breath deposits evenly the plate is clean. If the plate, however, shows patches and marks, it must be recleaned. Let the edges be carefully wiped, and the plate is ready for use.

The following preparation makes a good plate-cleaning solution for glasses that require mechanical friction to make them clean:——Ordinary water, 5 oz.; alcohol, 5 oz.; iodide of potassium, 15 gr.; iodine, 3 gr. When dissolved, add tripoli, prepared chalk, whiting, or rotten-stone, in sufficient quantity to make a creamy paste.

This thin pasty solution is to be rubbed on the plates on both surfaces and polished off as already described. This amount of cleaning will generally be sufficient for new glasses, but when they have been used they require more labour.

They must then be well washed under the tap, to get rid of all collodion and chemicals, and be wiped on cloths kept expressly for the purpose. Should the plates have been varnished they must be soaked for some hours in a saturated solution of washing soda till the varnish and film come freely off. The glasses must then be immersed for a few minutes in a solution composed of common nitric acid, 2 oz., water, 10 oz., and be well washed and treated as already described. It is a good plan when working to have a dish of water at hand, and to place the spoilt pictures in it at once while they are wet, and at the end of the day to wash the glasses and put them away clean. By thus not allowing the films to dry on the glasses they are much easier cleaned, and fewer failures will arise from dirty glasses.

Collodion is a good material for cleaning glasses when they are not very dirty. Pour a few drops on the glass and well rub it with a clean cloth, and you will entirely remove all grease; a hint may thus be taken how to use up waste collodion.

_Various Solutions used in the Dry Process._ These are employed in cases where bromo-iodised collodion and the nitrate bath are used.

In all processes in which the bromo-iodised collodion is employed 2 grains of bromide of cadmium should be added to each ounce of the collodion.

Mr Bartholomew advises diluted alcohol to be poured over the plate previous to developing.

_Acid Pyro Developer._ This developer is formed as follows:

Pyrogallic acid 1 gr.
Glacial acetic acid 30 minims.
Water 1 oz.

The plate, after being wetted with dilute alcohol and washed, has this solution flowed over it, to which has been added 2 or 3 drops of a 10-grain nitrate of silver solution.

_Plain Pyro Developer._ The strength of this may vary from 1 to 5 gr. in an ounce of water. Two grains may be taken as a medium. The dry plate being flooded with alcohol and water, and washed so as to well wet the film, this solution is floated over it.

_Alkaline Pyro Developer._

No. 1.——Pyrogallic acid 96 gr.
Absolute alcohol 1 oz.

No. 2.——Carbonate of ammonia 96 gr.
Water 1 oz.

No. 3.——Bromide of potassium 10 gr.
Water 1 oz.

At the time of using, make up the following solution:

Water 1 oz.
Solution No. 1 10 minims.
Solution No. 3 5 ”

Pour this over the wetted plate, allow it to remain on a few seconds only, and then pour back into the developing cup, and add to it 5 minims of solution No. 2, and apply again.

_The Collodio-Albumen Dry Process._ (Mr Mudd.) In this process the ordinary bromo-iodised collodion is employed. The plate being sensitised is washed well first with distilled, then with common water, and placed in a dish half filled with solution of iodide of potassium (3 gr. to the oz.), and allowed to remain while the next plate is being prepared. It is then removed from the solution and well washed with clean water, after which the following solution is poured over its surface:

Distilled water 2-1/2 oz.
White of eggs 10 oz.
Iodide of potassium 50 gr.
Bromide of ammonium 10 gr.
Strongest solution of ammonia 120 minims.

Introduce these materials with some pieces of broken glass into a bottle capable of holding twice the quantity, and agitate till the whole forms a froth, and then, when settled, it is ready. A piece of camphor placed in the solution will help to preserve it. It must be filtered before using. After the plate has been coated with the above it is finished by drying before the fire.

In this process all the above operations may be performed in ordinary white light. To render the plate sensitive, heat it as hot as the hand will bear, and when cool immerse it again in the following aceto-nitrate of silver bath for one minute, using only a yellow light, then wash thoroughly in clean water, and dry in the dark.

Nitrate of silver 30 gr.
Distilled water 1 oz.
Glacial acetic acid 1/2 dram.

The development may be commenced by either plain or alkaline pyro; Mr Mudd gives the preference to the plain, and intensifying after with acid silver.

Dr RYLEY’S _Modified Collodio-albumen Dry Process_. In this method the plate has to be sensitised as usual, and washed thoroughly. When the plate has been well drained, and while still wet, it is coated with the following solution:

Albumen 1 oz.
Water 2 oz.
Ammonia 30 minims.

The solution is beaten to a froth, allowed to settle, and filtered before using. Pour sufficient over the plate to cover it, letting it flow backwards and forwards so as to soak into the film. Pour the albuminous solution away and thoroughly wash the plate, the last rinsing being with distilled water. Let the plate dry; when perfectly dry, moisten the plate with distilled water, and pour over the following solution:

Gallic acid 2 gr.
Water 1 oz.

Filter the solution before using. Pour it on and off the plate to well permeate the film, then set the plate up to drain, and dry without washing off the gallic acid solution. When the surface is dry finish by the heat of a dull fire.

_Bromide of Silver, Wet Process._ To every ounce of good collodion add 8 gr. of bromide of cadmium. The nitrate bath must be made 80 gr. to the oz., and slightly acidulated with nitric acid. The plate must remain in the bath the full time it requires to form a dense opaque film. When the plate is ready (it must not be removed from the bath until the film is much denser than in the ordinary wet process) it must be washed thoroughly to remove all silver. It must then have poured over it a 3-grain solution of gelatin made slightly alkaline with carbonate of soda, or diluted albumen (albumen, 1 oz.; water, 4 oz., well beaten together). When the plate is in this condition it may be exposed wet, or it may be allowed to dry. Prior to development it must be well washed, and the alkaline method must always be adopted. If the plates are used dry, a preliminary coating of dilute albumen is necessary, but if used wet, this is not necessary.

_Bromide of Silver, Emulsion Process._ By this method the nitrate bath is not necessary, as the sensitive material is contained in the collodion. The purchase of the material ready-made for working this process is recommended in preference to its direct manufacture, as its preparation demands the use of considerable technical skill, together with the employment of a gun cotton not usually attainable. Mr Hughes says the ‘Liverpool Dry Plate Company’ supply an excellent emulsion. It is only necessary to pour the emulsion on to a plate and to allow it to dry, when the plate is ready for use. The development is by the alkaline process.

_Gelatino-bromide of Silver, Emulsion Process._ In this process the use both of the nitrate bath and of collodion are abolished.

The material employed is very troublesome to prepare, and on this account, as well as because of the risk of failure attending the use of home-made articles, it is far preferable it should be purchased. It may be obtained under the name of ‘Kennett’s Sensitised Pellicle.’

This pellicle consists of shreds of dry gelatin containing the sensitive salts.

Fresh directions accompany each packet of the “Sensitised Pellicle.”

_The Honey Process._ Let the plate be cleaned, coated, and sensitised in the usual manner; then place it in a bath of distilled water, washing it more or less, as it may be required to be kept for a longer or shorter time. Pour on the plate a solution made of equal parts of honey and distilled water in the same manner as when using collodion; throw away the first portion, and repeat the operation, letting the solution soak in for one or two minutes; pour back the honey solution into its bottle; drain the plate on blotting paper, and keep it in the dark free from dust. The time required for exposure of the plate is about double as long as in the ordinary wet process.

The plate should be soaked in distilled water previous to being developed, in order to soften or remove the film of honey; the older the plate the longer it will require to be soaked, afterwards dip the plate in the silver bath, and develop in the usual manner.

_The Carbon Process._ In this process, the adoption of which is daily increasing, the material employed consists of a layer of gelatin containing carbon, or some other permanent pigment, spread on paper.

In this condition the paper is not sensitive to light, but if it be treated with a solution of bichromate of potash, dried in the dark, and afterwards exposed to sunlight under a negative, those portions of the paper which have been acted upon by the light will become insoluble, whilst those parts that have been protected from it will be soluble. When, therefore, after sufficient exposure, the prepared paper is removed from the negative, a picture the reverse of the negative will have been formed, in which the pigmented gelatin alone remains, and performs the part of the reduced silver in the ordinary photograph.

If the film, after exposure to light under a negative, is soaked in warm water, all the parts which have been protected from the action of the light can be dissolved, and a relief is formed which, when dry, is sufficiently hard to transmit its shape to lead. From the mould or plate thus obtained a comparatively large number of impressions can be taken, either with coloured gelatin or with fatty colours, the well-known Woodbury-type being the most successful of the several processes based on the fact.

=Photographic Varnish.= See VARNISHES.

MISCELLANEOUS RECIPES:

_To Clean Glass Plates._ (Mr Mayall.) Shake up together alcohol, 30 parts; strong liquid ammonia, 10; water, 40; and fine tripoli, 30 parts. The plates are to be rubbed hard and evenly with balls of cotton wool dipped in this mixture. Rub again, when dry, with a clean ball of cotton; lastly, dust the back and edges with a clean hog-hair brush.

_To Clean off Collodion Pictures._ This may be done whether they have been varnished or not, by means of a tuft of cotton wool dipped in wood spirit.

_To Colour Photographic Prints._ This may be done variously in water and oils. A simple way is to rub in slowly with a small camel-hair brush a minute piece of dry colour laid upon the part, as of flesh tint for the face, &c. When properly distributed, the paper may be breathed upon, and the tint will not easily be rubbed off. Or it may be carefully coated with gelatin.

M. Minotto has described a plan of colouring on the back of the paper. The picture, being held up to the light, is first faintly outlined, on the reverse side; colours are then laid on, of water or oil, as preferred, on this side. When dry the paper is rendered transparent by a varnish, and the colours will then appear through it with all the delicacy and effect of a miniature on ivory. Good strong writing paper is best for this purpose; the colours must be vivid; and the varnish may consist of Canada balsam dissolved in turpentine, or a mastic varnish may be used, or turpentine and wax, or oil.

_To Remove Stains from the Hands._ The powerfully poisonous character of cyanide of potassium renders its employment for the above purpose an operation attended with considerable danger. Iodide of potassium and iodine may both be substituted, but the first is expensive, and the second requires considerable nicety in its application, lest a coloured stain be left on the skin. Instead of the above substances, M. Fortin recommends to wash the hands with a concentrated solution of either sulphate or chloride of zinc, to which some acid is added at the same time. He advises the deepest and blackest stains being touched with metallic zinc, whereby the reduction of the oxide of silver or that of the gallate of iron is promoted, and all metallic stains adhering to or penetrating into the skin removed. Since most of the salts of zinc are colourless, and soluble in water, the hands soon become quite clean. They should then be washed, first with pure water, and next with soap and water.

The reader desirous of further information on the subject of photography cannot do better than consult Mr Ernest Spon’s valuable manual, entitled ‘Workshop Receipts,’ and Mr Hughes’ ‘Principles and Practice of Photography,’ to both of which we are largely indebted. Captain Abney’s work on ‘Photography,’ cannot be too highly commended. See COLLODION, PHOTOGRAPHIC.

=Photographic Waste Products, Recovery of.= We extract the following from the ‘American Chemist’ for February, 1876. The contributor, Mr. C. A. Pitkin, A. B., states that the methods given have been collected from the ‘Philadelphia Photographer,’ the ‘British Photographic Journal,’ Hardwick’s ‘Photograph Chemistry,’ &c., &c.; also that they include suggestions by Professor Hill.

1. Nitrate bath, α, recovered; β, renovated.

2. Hyposulphite bath.

3. Reduction of silver chloride, oxide, or sulphide.

4. Gold waste, α, recovered; β, separated from silver,

5. Paper waste and washings from positive prints.

6. Cyanide solution.

7. Developer.

I. _Nitrate Bath_,

α, _Recovered_.

1. Add solution of caustic potash or lime, as long as there is a brown precipitate. Allow to settle, pour off liquid, and collect silver oxide for reduction; _vide_ III, below.

2. For 1 lb. of silver, add 1 oz. sulphuric acid and 1/2 lb. zinc, and allow to stand two days. Precipitate as chloride, wash eight or ten times by decantation, and dissolve gradually in nitric acid.

NOTES.——Test complete washing by hydrochloric acid. Wash with water till zinc nitrate is removed. If zinc clings to silver wash with hydrochloric acid.

3. Suspend sheet of copper in bath for two or three days.

4. Acidify as nitric acid, precipitate as silver chloride by sodium chloride or hydrochloric acid, and reduce as _vide_ III, below.

5. Immerse in bath two strips of copper attached to the poles of a Daniell’s or Smee’s cell. Silver deposited on the copper as in 3, above.

6. Add sodium bicarbonate or sodium hydrate. Reduce as 3 below, or if pure enough, dissolve precipitate at once in nitric acid.

7. Concentrate bath, make alkaline by sodium carbonate, and add aqueous solution of oxalic acid neutralised with sodium carbonate. Filter, dry, and fuse with equal weight of sodium bicarbonate.

8. Deposit, either with or without battery, on iron. (Iron can be obtained purer than zinc or copper, and possesses the additional advantage that the iron salts, as iodides, &c., are all quite soluble). Fuse with potassium nitrate and sodium carbonate.

β. _Renovated._

1. Dilute with three volumes of distilled water, expose to sunlight, filter, add sodium carbonate till slightly turbid. Expose to sunlight six hours more, filter, add sodium carbonate till silver all thrown down. Wash, precipitate by decantation, and dissolve in nitric acid. Filter again, make up to 35 grammes; neutralise, expose to sun a week, and bath is ready for use.

2. Neutralise with ammonia till just alkaline; boil till black; let cool, filter, acidify with pure nitric acid, and evaporate to crystallisation, then fuse. When cool, add distilled water, shake and let stand exposed to light. Filter and add drained crystals. Dissolve and make solution acid with pure nitric acid. Expose again to sunlight, filter, and bath is ready for use.

3. Add potassium permanganate, expose to sunlight, filter, acidify, put in clean bottles four-fifths full, cork, and freeze in a tray; thaw gradually till ball of ice one-eighth size of bottle remains. This contains impurities to be reduced as III, below. Use rest for new bath at once.

II. _Hyposulphite Bath._

1. Precipitate as silver sulphide by potassium sulphide. Reduce as III, below, or dissolve in nitric acid.

2. Precipitate by hydrosulphuric acid, and reduce as III.

3. Decompose hyposulphite by waste nitro-sulphuric acid from manufacture of gun-cotton for collodion. Have silver sulphide and sulphur, with sodium nitrate and sulphate in solution. Suspend zinc in solution, then boil two or three hours; wash on filter, dry, fuse with borax and sodium carbonate.

4. Suspend sheet copper in bath.

5. Add hydrochloric acid, which sets free sulphur and precipitates silver chloride. Oxidise sulphur by aqua regia, and reduce silver chloride as in III.

6. Add sodium hypochlorite to the alkaline solution. Wash, precipitate, and fuse with mixed carbonates. This gives sodium bisulphate and chloride as by-products, no sulphur, no fumes.

III. _Reduction of Silver Chloride, Oxide, or
Sulphide._

1. Mix with one third weight of colophony. Heat moderately in crucible till greenish-blue flame ceases, then suddenly increase heat, and obtain a button of metal.

2. Melt with alkaline carbonates enough to cover surface from air; then mix with 75 per cent. of chalk and 4 per cent. of charcoal, and heat.

3. Ignite with nitre on red-hot plate carefully, and in small quantities to avoid explosion, run down to button with borax and sodic carbonate.

4. If chloride, reduce to oxide by boiling with strong potash, then reduce by glucose; or boil the chloride with glucose and sodium carbonate.

5. Add silver chloride dissolved in ammonia to a boiling solution of one part glucose and three parts sodium carbonate in 40 per cent. of water, keeping up the boiling all the time.

6. Add to silver chloride sodium hydrate in solution and grape sugar, and expose to sunlight in open dish with occasional stirring. Reduce to dark brown oxide of silver, soluble in nitric acid.

7. Mix with five times weight of sodium carbonate. Fill hessian crucible half full, and sprinkle sodium chloride over the top. Heat slowly in anthracite fire. After half an hour increase heat till crucible is white-hot. When complete fusion has taken place, allow to cool, and break out button of silver.

8. Fuse with two parts mixed carbonates (sodium and potassium).

9. Add pure zinc and dilute sulphuric acid, and let stand two days. Wash silver off with water acidulated with sulphuric acid, to remove all zinc; finally fuse to a button.

10. Mix with half weight dry sodium carbonate and one-fourth weight of clean dry sand, and ignite.

IV. _Gold Waste_, α, _Recovered_.

1. Make just acid with hydrochloric acid, add solution containing 2 oz. pyrogallic acid, shake, let stand 24 hours; filter. Dissolve in aqua regia, and product after evaporation will be found better for toning than that precipitated by iron.

2. Acidify toning bath, and add sulphate of iron (2 grammes to 1 gramme chloride of gold.)

β. _Separated from Silver._

1. Treat button obtained by fusing waste from hypo-toning and fixing baths with dilute nitric acid. Wash insoluble part with ammonia to remove silver chloride, if present, and dissolve in aqua regia.

2. Digest 20 grammes in flask with 1 fl. dr. hydrochloric acid, 15 m.m. of nitric acid, and 2 dr. of water. After quarter of an hour boil, add 2 oz. water; filter. Silver chloride with organic matter, &c. left undissolved. Reduced as III, above.

3. Add excess of pure potassium hydrate, and then boil in flask with excess of solid oxalic acid.

V. _Paper Waste._

1. Soak paper in strong solution of saltpetre, and burn.

2. Treat with nitric acid, precipitate with sodium chloride or potassium hydrate, then put with III, above, for reduction.

_Washings from Positive Prints._

Precipitate by sodium chloride, potassium hydrate, or on copper plates, &c., as above, and reduce, as in III.

VI. _Cyanide Solution._

1. Dilute with water, precipitate by (1) potassium sulphide, (2) sodium chloride, and reduce as 3.

2. Decant bath into iron kettle, warm, add ferrous sulphate slowly till slight precipitate of oxide. Make alkaline, and add solution of grape sugar till brownish-yellow colour. Allow to settle, syphon off liquid. Wash sediment on filter, and ignite to recover silver.

NOTE.——Ferrous sulphate forms ferrocyanide, therefore no free alkaline cyanide should be present.

VII. _Developer._

1. _Vide_ II. (3, 4, 5, 6), with hypo bath; (1) and (2) not applicable, for sulphide of iron would be formed.

2. Reduced by its own iron (if ferrous sulphate).

=PHOTOM′ETRY.= The art of determining the relative intensities of different lights. Various methods have been adopted, at different times, for this purpose, among which, however, a few only are sufficiently simple for general application. The principle adopted by Bouguer and Lambert depends on the fact that, though the eye cannot judge correctly of the proportional force of different lights, it can generally distinguish with great precision when two similar surfaces or objects presented together are equally illuminated, or when the shadows of an opaque object produced by different lights are equally dark. Now, as light travels in straight lines, and is equally diffused, it is evident that its intensity will progressively lessen as the distance of its source increases. This diminution is found to be in the duplicate ratio of the distance. To apply this principle to candles, lamps, gaslights, &c., we have only to arrange two of them so that the light or shadow resulting from both shall be of equal intensity, after which we must carefully measure the distance of each of them from the surface on which the light or shadow falls. The squares of these distances give their relative intensity. In general, some known light, as that from a wax candle (4 to the lb.), is taken as the standard of comparison.

Dr Ritchie’s ‘photometer’ consists of a rectangular box, about 2 inches square, open at both ends, and blackened inside to absorb extraneous light. In this, inclined at angles of 45° to its axis, are placed two precisely similar rectangular plates of plain silvered glass, and fastened so as to meet at the top, in the middle of a narrow slit about an inch long and the eighth of an inch broad, and which is covered with a strip of tissue or oiled paper. In employing this instrument, the “lights must be placed at such a distance from each other, and from the instrument between them, that the light from each shall fall on the reflector next it, and be reflected to the corresponding portion of the oiled paper. The photometer is then to be moved nearer to the one or the other, until the two portions of the oiled paper corresponding to the two mirrors are equally illuminated, of which the eye can judge with considerable accuracy.”

In Prof Wheatstone’s ‘PHOTOMETER’ the relative intensity of the two lights is determined by the relative brightness of the opposite sides of a revolving silvered ball illuminated by them.

In the method of photometry usually, but erroneously, ascribed to Count Rumford, the shadows of an opaque object formed by different lights, and allowed to fall on a white wall or paper screen, are contrasted. A wire about 3/16ths of an inch thick, and about a foot in length, with the one end bent so as to form a handle, is commonly used to form the shadows. The method of proceeding is similar to that first above noticed.

It is generally supposed that the equality of two shadows can be appreciated with greater certainty than that of two lights.

=PHTHIS′IC.= A popular name for difficulty of breathing, from its supposed resemblance to phthisis. See BRONCHITIS, and _below_.

=PHTHISIS.= (A wasting away.) This is the formidable disease ordinarily or popularly known as “consumption,” although, strictly speaking, there are points of difference between consumption and phthisis, as well as between these and another variety of the malady known as tuberculosis. The statistics which follow, however, apply to all those diseases of the lungs accompanied by wasting, and as such include the mortality from phthisis, tuberculosis, and consumption.

In the Registrar-General’s returns for many years past, under the heads ‘phthisis,’ or ‘tubercular disease,’ have been included chronic bronchitis, emphysema, fibroid changes of the lungs and kindred affections. ‘It is, however, probable that the figures representing the mortality are fairly accurate, as the errors are to a certain extent compensating; and, indeed, tubercles are often found even in the diseases above mentioned.’[99]

[Footnote 99: Dr Wynter Blyth.]

The following table, taken from the Registrar-General’s returns for 1848-75, shows the annual number of deaths in England from phthisis, during a period of 28 years:——

1848 51,663
1849 50,299
1850 46,618
1851 49,166
1852 50,594
1853 54,918
1854 51,284
1855 52,290
1856 48,950
1857 50,106
1858 50,442
1859 50,149
1860 51,024
1861 51,930
1862 50,962
1863 51,072
1864 53,046
1865 53,734
1866 55,714
1867 55,042
1868 51,423
1869 52,270
1870 54,231
1871 53,376
1872 52,589
1873 51,355
1874 49,379
1875 52,943

Dr Farr in his letter to the Registrar-General on the causes of death in England in 1875, writes, “Phthisis is a most fatal disease, although it has declined within the last twenty-five years.”

According to the same authority, the mean rate of mortality from this disease was 2·811 per 1000 in the five years from 1850 to 1854, and 2·283 in the five years from 1870 to 1874.

One of the most prominent facts revealed even by a cursory study of the statistics of phthisis, is the large share which the breathing of impure or tainted air has in the origin and dissemination of the disease.

Hence it follows that thickly populated and overcrowded localities suffer much more from its ravages than those which are less densely inhabited. This is exemplified in the following table:——

-----------+-------+---------+-------------------------------------------
| | |Proximity| Average Annual Mortality |
| | | or | to 100,000 living. |
| |Density|nearness +--------------------+---------------------+
| | of |of Person| | Other diseases |
| |Persons| to | Phthisis. | of the |
| | to a | Person. | | Respiratory Organs.|
| | Sq. +---------+------+------+------+------+------+-------+
| | Mile. | |15 |25 |35 |15 |25 |35 |
| | | Yards. | to | to | to | to | to | to |
| | | | 25| 35| 45| 25| 35| 45 |
+----------+-------+---------+------+------+------+------+------+-------|
|Healthy | | | | | | | | |
| districts| 135 | 163 | 336 | 398 | 330 | 34 | 45 | 67 |
|London |19,470 | 14 | 264 | 395 | 493 | 45 | 69 | 148 |
|Lancashire| 1,008 | 60 | 419 | 475 | 484 | 46 | 86 | 195 |
|England | | | | | | | | |
| and Wales| 308 | 108 | 362 | 438 | 407 | 38 | 61 | 113 |
-----------+-------+---------+------+------+------+------+------+--------

In the very badly ventilated Leopoldstadt, in Vienna, 378 prisoners out of 4280 died between the years 1834 to 1847, or at the rate of 86 per 1000; and out of these as many as 220, or 51·4 per 1000, died from phthisis. Contrasting with this the rate of mortality from the same disease in the well-ventilated House of Correction in the same city, we learn that out of 3037 there died in five years (from 1850-1854) 43, or 14 per 1000, and of these 24, or only 7·9 per 1000, died from the same disease.

The great prevalence of phthisis that used to prevail, not only in our army, but in the principal European ones, has been clearly shown to have been referable to the overcrowding and defective ventilation of the barracks. And this applied equally to the barracks of military stations possessing such mild and genial climates as Gibraltar, Malta, Ionia, Jamaica, Trinidad, Bermuda, &c.[100]

[Footnote 100: Dr Parkes.]

The sanitary Commissioners appointed some years back to inquire into the prevalence of consumption amongst our soldiers, came to the conclusion that the foul atmosphere of the barracks was the cause of it. The correctness of our decision has been corroborated by the greatly diminished number of deaths which have followed the improved ventilation in our barracks, recommended by the Commissioners. At the present time, owing to those hygienic improvements, the mortality from phthisis is not more than half what it was in our army prior to 1867. The same satisfactory results have been obtained by the introduction into the French barracks of similar sanitary improvements.

Animals are affected in precisely the same manner as human beings. Thus, it is that phthisis attacks monkeys when shut up in badly ventilated buildings, and cows confined in close sheds.

After these statements we shall be prepared to find that indoor trades and occupations swell the bills of mortality from phthisis much more than those carried on in the open air. That this is the case is shown by the following table:——

_Deaths from Phthisis at Victoria Park Hospital,
showing the influence of Occupation._

+------------------------+-----------------------------------------------+-------+
| | AGES UNDER | |
| Cause of Death. +---+---+---+---+---+---+---+---+---+---+-------+Totals.|
| | | | | | | | | | | | Not | |
| |20.|25.|30.|35.|40.|45.|50.|55.|60.|65.|stated.| |
+------------------------+---+---+---+---+---+---+---+---+---+---+-------+-------+
| | | | | | | | | | | | | |
|Female lives | 45| 41| 25| 15| 12| 3| 1| 1|...|...| ... | 143 |
|Indoor occupation | 32| 31| 30| 24| 15| 9| 5|...|...|...| 4 | 150 |
| { Mixed occupation| 10| 7| 7| 5| 4| 3| 4|...|...|...| 1 | 41 |
|Males { Outdoor occup. | 9| 21| 21| 13| 12| 11| 8| 2| 1|...| 2 | 100 |
| +---+---+---+---+---+---+---+---+---+---+-------+-------+
| | 96|100| 83| 57| 43| 26| 18| 3| 1|...| 7 | 434 |
| +---+---+---+---+---+---+---+---+---+---+-------+-------+
| _The same reduced to | | | | | | | | | | | | |
| a per centage._ | | | | | | | | | | | | |
|Female lives | 32| 28| 18| 10| 8| 2| 1| 1|...|...| ... | 100 |
|Indoor occupation | 21| 21| 20| 16| 10| 7| 3|...|...|...| 2 | 100 |
| { Mixed occupation| 24| 17| 17| 12| 10| 7| 10|...|...|...| 3 | 100 |
|Males { Outdoor occup. | 9| 21| 21| 13| 12| 11| 8| 2| 1|...| 2 | 100 |
| +---+---+---+---+---+---+---+---+---+---+-------+-------+
| | 86| 87| 76| 51| 40| 27| 22| 3| 1|...| 7 | 400 |
+------------------------+---+---+---+---+---+---+---+---+---+---+-------+-------+

The influence of occupation in developing phthisis is forcibly illustrated in the following table:——

+-----------------+--------------------------+--------------------------+
| | |Death-rate by Phthisis and|
| | | other Lung Diseases at |
| District. | Nature of principal | between 15 and 25 years |
| | Industry in the District.| of age, per 100,000 of |
| | | each class referred to. |
+-----------------+--------------------------+-------------+------------+
| | | Male. | Female. |
| | | | |
|Berkhampstead |}Extensive female {| 219 | 578 |
|Leighton Buzzard |} employment in {| 319 | 554 |
| |} straw-plaiting {| | |
| | | | |
|Newport Pagnell |}Extensive female {| 301 | 615 |
|Towcester |} employment in {| 239 | 577 |
| |} lace-making {| | |
| | | | |
| |{Extensive female (with }| | |
|Yeovil |{ some males) employment}| 280 | 409 |
| |{ in glove-making }| | |
| | | | |
|Leek |}Extensive employment {| 437 | 856 |
|Congleton |} (more female than {| 566 | 790 |
|Macclesfield |} male) in silk work {| 593 | 890 |
| | | | |
|Standard Northern| | | |
| District | Agriculture | 531 | 333 |
+-----------------+--------------------------+-------------+------------+

The above figures may be supplemented by the others, which show the difference between the deaths from phthisis and other lung diseases occurring amongst the agricultural and the manufacturing populations, and are another illustration of the nature of the toiler’s occupation upon his liability to consumption. Thus, for every 100 deaths by phthisis and other lung diseases that take place amongst the men in various agricultural districts of England between the ages of fifteen to fifty-five, there are in Coventry 163 deaths; in Blackburn and Skipton, 167; in Congleton and Bradford, 168; in Leek, 182; in Macclesfield, 184; in Bolton, 190; in Nottingham, 192; in Rochdale, 193; in Derby, 198; in Salford and Ashton-under-Lyne, 203; in Leeds, 218; in Preston, 220; and in Manchester, 263.[101]

[Footnote 101: Quoted by Dr Wynter Blyth.]

As bearing directly upon the above portion of our subject, we may quote the sixth report of the medical officer of the Privy Council, who therein states——“In proportion as the people of a district are attracted to any collective indoor occupation, in such proportion, other things being equal, the district death-rate by lung diseases will be increased.”

The much larger number of cases of lung disease amongst those who pursue indoor callings than amongst others whose occupations are carried on out of doors, arises principally from the defective ventilation of the workshops or rooms in which the labour is carried on.

When indoor occupations are practised in large and efficiently ventilated apartments, or existence is passed in healthy houses, as in the dwellings of the rich and upper classes, who have also the additional advantages of good food and warm clothing, the liability to phthisis becomes immensely diminished.

The much greater immunity from the disease which the richer enjoy over the poorer classes has been carefully pointed out by Dr Guy, who, writing on this subject in the ‘Journal of the Statistical Society,’ says——“The ratio of deaths from consumption follows the same order as the average age at death, being lowest where the average age is highest, and the reverse. Thus the average age at death of the class of gentlemen is 58·61, and the ratio of deaths from consumption 1 to 2·60; while in the class of artisans the average age is 48·06, and the proportion from consumption is 1 to 2·29.

+----------+-----+-----+-----+-----+-----+----+----+-----+-----+------+---------+---------+
| | | | | | | | | | | | |Number of|
| | | | | | | | | | | | | Deaths |
| | | | | | | | | | | | +----+----+
| | | | | | | | | | | | | | O |
| | | | | | | | | | | | | | t |
| | | | | | | | | | | | | | h |
| | | | | | | | | | | | | C | e |
| | | | | | | | | | | A | | o | r |
| | | | | | | | | | | v | | n | |
| | | | | | | | | | | e a | | s | D |
| | | | | | | | | | | r t | | u | i |
| | | | | | | | | | | a | | m | s |
| | | | | | | | | | | g D | | p | e |
| | 15 | 20 | 30 | 40 | 50 | 60 | 70 | | | e e | | t | a |
| | | | | | | | |Under|Under| a | Ratio. | i | s |
|Condition.| to | to | to | to | to | to | to | 30. | 40. | a t | | o | e |
| | | | | | | | | | | g h | | n | s |
| | 20. | 30. | 40. | 50. | 60. | 70.| 80.| | | e . | | . | . |
+----------+-----+-----+-----+-----+-----+----+----+-----+-----+------+---------+----+----+
|Gentlemen,| | | | | | | | | | | | | |
| &c. |10·84|18·67|27·11|19·27|15·06|6·03|3·01|29·51|56·62|39 |1 to 5·00| 166| 835|
|Tradesmen | 8·46|24·34|26·98|20·11|12·70|6·35|1·06|32·80|59·78|38 |1 to 2·60| 189| 491|
|Artisans | 7·25|23·69|26·24|22·79|13·34|6·26|0·43|30·94|57·18|38-1/2|1 to 2·29|2318|5308|
+----------+-----+-----+-----+-----+-----+----+----+-----+-----+------+---------+----+----+

“Again, the class of gentry presents a smaller proportional number of deaths under thirty and forty than either of the other classes. It is also worthy of observation that the per-centage proportion of deaths from consumption under thirty and forty is higher in the class of tradesmen than in that of the artisan and labourer, although the ratio of cases of consumption is greater in the latter class. This is doubtless accounted for by the fact already established, that the strong exertion which a considerable portion of the labouring class employed within doors use in their occupations, and the large number employed out of doors, has the effect of retarding the effect of pulmonary consumption. The tradesman, it will be seen, occupies the intermediate place between the indoor and outdoor labourer——between the artisan using little exertion and the artisan using much exertion.

... Another point attracts attention, viz. the great proportion of deaths from consumption occurring in the class of gentry from fifteen to twenty years of age. Does not this show that the liability to the disease is greater in this class than in the two others, and does it not tend to strengthen the position that the excess of the deaths from consumption in the other classes is due to the unfavorable circumstances in which they are placed?

“The ratio of deaths from consumption in the class of gentry, low as it is, would have been still lower if the medical men, who are included in it, were omitted. The number of cases of pulmonary consumption occurring in members of that profession is very remarkable, and it is a subject of regret with the author that they were not made a separate class.”

Much less clearly and satisfactorily established is the question as to whether consumption is or is not contagious. The instances which have occurred of its extensive and rapid spread in overcrowded barracks, prisons, men-of-war, merchant vessels, large workshops, &c., not unreasonably seem to lend weight to the opinion that the germs of the disease might have been conveyed by the atmosphere charged with them from an unhealthy to a healthy subject, on whom they might develop the malady.

“But,” as Dr Blyth writes, “it must be remembered that, in all crowded localities, there is direct vitiation of air, and it is difficult to say whether the foul air or actual contagion have most to do with the propagation of the malady.” He adds “that consumption, under ordinary conditions, is certainly not contagious; but, under special insanitary influences, certain forms of consumption may be contagious, although it is still a matter not proven.” Dr Guy bases his objection to the doctrine of the generally contagious nature of consumption upon the fact of the small fluctuations in the annual number of deaths caused by it.

The lowest rate of mortality for phthisis for a million of inhabitants in London was, he states, for any one of the fifteen years from 1840 to 1854 inclusive, 2645, and the fluctuation was very slight. The figures in three consecutive years were——1849, 2777; 1850, 2645; 1851, 2970. “If, then,” Dr Guy says, “any one were to assert that this disease is contagious, which is tantamount to saying that it may be epidemic, the figures I have quoted would in themselves furnish an answer in the negative. They are suggestive of a domestic disease, influenced, as is bronchitis, by the seasons and the weather.”

The statistics before quoted as to the correlation between the prevalence of consumption and unhealthy surroundings, lead to the belief, that before this connection between the two was so well defined, cases of phthisis were often erroneously referred to hereditary taint, when they may simply have arisen from the patient having been environed with the same unfavorable hygienic conditions as his parents; these unfavorable conditions, including not only polluted air, but bad food, deficient apparel, and want of exercise. Hence it is that most of the later pathologists, without denying the existence of the transmitted form of the disease, believe the hereditary influence has been greatly over estimated.

“As regards the origin of tubercle,” writes Dr Douglas Powell, “opinions are extremely various, and indeed irreconcileable; but the tendency of modern research——the experiments of inoculation in animals, and the very powerful advocacy of Prof. Niemeyer, is certainly to show that tubercles is much more commonly a secondary disease than has until lately been suspected——that people are, in fact, only exceptionally, if ever, born to die of tuberculosis.

“A due appreciation of this doctrine, so different from that even now accepted by many, is of almost national importance in giving encouragement to those hygienic and other measures of prevention, the neglect of which has too often been sanctioned by a foregone conclusion.

“It would I think be extremely injudicious to deny hereditary predisposition to tubercles altogether. Moreover, when we come to the question of hereditary predisposition to the forms of consumption which originate in catarrhal pneumonia, it is freely admitted that the offspring of consumptive parents have a tendency to this form of pulmonary phthisis, that the scrofulous have a like tendency (Niemeyer), and that scrofulosis is sometimes hereditary.”

As allied to this portion of the question may be mentioned the opinion of some pathologist, that phthisis may be either caused or promoted by habitual drunkenness; and that a drunkard may transmit it to his offspring.

The proneness to consumption is greatly modified by sex and age, the influences of which upon the disease are very defined and unmistakable. Thus, women are more liable to its attacks than men, and young and middle aged persons of both sexes than old ones.

“In Edinburgh the ratio of deaths from phthisis was found to decline from ·285 at twenty years to ·052 above sixty years; at Nottingham, from ·416 to ·017 in the same period of time; at Chester, from ·245 to ·054; at Carlisle, from ·290 to ·097; and in Paris, according to Louis, from ·325 to ·042; while the general average decline was from ·285, or 28·5 per cent., at twenty to thirty, to ·078, or 7·80 per cent., above 60.”[102]

[Footnote 102: Blyth.]

Amongst other conditions unfavorable to the consumptive patient, in addition to the breathing of a polluted atmosphere, may be named insufficiency of nourishing food and apparel, variable weather, and a damp soil. This latter is particularly inimical to phthisical sufferers. Indeed so closely is dampness of soil associated with the spread of phthisis, that the disease has been conclusively shown to have diminished in localities in proportion as these have been properly drained. Dr Andrews, of Chicago, says that consumption is most prevalent near the sea, and that it diminishes in proportion to the distance of the inland locality from the ocean. A damp atmosphere also provokes the disease.

Phthisis seems to be a malady peculiar to temperate climates. As to the influence of the season upon the disease, Dr Haviland says, “In England we learn from the statistical returns that the spring is the most fatal to consumptive patients, whether male or female, but with regard to the other seasons there is considerable variability. For instance, suppose we take the seasons of 1838 in the order of their fatality to males, they would stand thus——spring, 1137; winter, 1048; summer, 968; autumn, 904. To females——spring, 972; summer, 937; winter, 896; autumn, 825. Then again, although the spring invariably takes the lead, the other seasons change places with each other from year to year; and what is remarkable, this inconsistency does not seem to be dependent upon the temperature, as we shall presently see. In the returns for 1853, the following statistics in deaths from consumption appear:——Winter, 1872; spring, 1971; summer, 1745; autumn, 1914. The order of fatality in the years above quoted would therefore be:——

1838.——_Males._
1. Spring. 2. Winter. 3. Summer. 4. Autumn.

1838.——_Females._
1. Spring. 2. Summer. 3. Winter. 4. Autumn.

1840.——_Total._
1. Spring. 2. Winter. 3. Summer. 4. Autumn.