Photography, from φως, light, and γραφειν, I delineate or paint, is the name given to the art of delineating or painting by light, whether solar, sidereal, or artificial, or by invisible rays which accompany those different varieties of light.

This art is one of modern invention, which, though some steps to it were taken by preceding writers, we owe to M. Nicephorus Niepce, Mr Fox Talbot, and M. Daguerre. So early as June 1802, Mr Thomas Wedgwood published in the Journal of the Royal Institution An Account of a Method of Copying Paintings upon Glass, and of making Profiles by the agency of Light upon Nitrate of Silver, with observations by Sir Humphry Davy. "When white paper or white leather," says Mr Wedgwood, "covered with a solution of nitrate of silver (one part of nitrate to ten of water) is placed behind a painting on glass exposed to the solar light, the rays transmitted through the differently-painted surface produce distinct tints of brown and black, sensibly differing in intensity according to the shades of the picture, and where the light is unaltered, the colour of the light becomes deepest." Mr Wedgwood applied this method to take profiles or shadows of figures, by throwing the shadows on the prepared paper, the part concealed by the shadow remaining white. He employed it also in delineating the woody fibres of leaves, the wings of insects, and also to the copying of prints; but though he obtained pretty accurate representations of all objects that were partly opaque and partly transparent, yet he failed in the copying of prints. To copy the images of the camera obscura was the first object of Mr Wedgwood, but "the images were found to be too faint to produce in any moderate rate an effect upon the nitrate of silver. He succeeded, however, in copying, without difficulty, the images of small objects produced by the solar microscope. Mr Wedgwood found that the muriate of silver was more sensible to light than the nitrate, and that both were more readily acted upon when moist than when dry.

Mr Wedgwood tried in vain to fix the copies which he obtained; that is, to prevent the uncoloured portion of the picture from being darkened by light. He was therefore obliged to keep his photographs "in an obscure place," and to examine them only in the shade for a few minutes, or by the candle or lamp light. The process of Mr Wedgwood seems to have excited very little notice. So long ago as 1803 Sir David Brewster called the attention of the public

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1 See Photography, art. iii. 2 See Photographic Journal, vol. v., p. 58, Nov. 6, 1858. 3 Vol. i., p. 70. This paper was republished in Nov. 1892 in Nicholson's Journal of Natural Philosophy, &c., 8vo series, vol. iii., p. 167. 4 Manual of Photography, 5th edit., pp. 269, 270. 5 Ibid., vol. v., p. 97, Dec. 11, 1858. Photography.

to it in a Scotch journal, but no person seems to have improved or even repeated the process during the next thirty years. Some time previous to 1834, Mr Henry Fox Talbot, without any knowledge of what had been done by Mr Wedgwood, had been led to the same process; and in the spring of that year he had actually taken pictures in the camera by the agency of light upon paper washed with nitrate of silver, and had succeeded in fixing them. To this new art he gave the name of Calotype, from καλός, beautiful, and νεῦρον, an impression.

At an earlier period another branch of photography had taken its rise in France. So early as 1814, M. Nicephorus Niepce had attempted to fix the pictures produced in the camera obscura, and to copy engravings by means of light transmitted through them upon substances made sensible to its action. The substance used by M. Niepce was a tablet of copper coated with highly-polished plate silver; and he gave to his process the name of heliography, from ἥλιος, the sun, and ἐγράφω, I delineate. In the year 1824, M. Daguerre had made experiments with the view of fixing the pictures in the camera, but he seems at that time to have obtained no definite results. M. Niepce, however, foreseeing the value of his art, went to London in December 1827, and submitted to the Royal Society an account of his heliographic experiments, and several plates, which proved that he possessed a method of taking pictures on metal (covered with a film of asphaltum or Jew's pitch) by the solar rays, and preventing them from being subsequently obliterated by the action of light. The society seems to have taken no notice of this interesting communication; and, thus discouraged, M. Niepce seems to have abandoned his researches, and to have given his heliographs to some of the members of the society who had seen their value.

Having heard of each other's labours, MM. Niepce and Daguerre entered into a copartnery in December 1829, in order to pursue for their mutual benefit the study of heliography. The processes of the two artists were essentially different. M. Niepce used as the groundwork of his picture a thin film of a solution of asphaltum, dissolved in essential oil of lavender, and spread over the clean surface of a plate of silvered copper. After the plate was exposed in the camera for about five hours, the picture was developed by covering it with a mixture of one part of essential oil of lavender with ten parts of oil of white petroleum. The parts of the picture upon which the light fell being more soluble in proportion to its intensity, a positive heliograph was obtained. In order to produce a better effect, M. Niepce darkened the silver surface with a film of iodine, which no doubt suggested to Daguerre the use of that material.

Into this process M. Daguerre introduced considerable improvements; and in the course of his investigations he discovered an entirely new photographic process, in the success of which M. Niepce did not live to share. He died in July 1833; and soon afterwards a copartnery was formed between his son, M. Isidore Niepce, and M. Daguerre, in which it was admitted that the process discovered by the latter was essentially a new one, and should be called the daguerreotype, after its inventor.

In order to reward the eminent inventors of heliography, M. Arago, who had been previously entrusted with the secret of the daguerreotype process, induced the French government to give Daguerre an annual pension of 6000 francs (£1250), and to Niepce a pension of 4000 francs (£160); and a bill for this purpose was unanimously passed by both chambers, and signed by the king on the 16th June 1839. In proposing this measure to the Chamber of Deputies, M. Arago stated that "France had adopted the discovery, and that from the first moment she had cherished a pride in liberally bestowing it a gift to the whole world." Notwithstanding this declaration, M. Daguerre risked his public character in selling his invention to Mr Miles Berry, to whom the officers of the crown in England granted a patent in the face of a remonstrance by a few individuals who had the manliness to oppose it. England was thus restrained for eight years from the use of this important process; but the specification was afterwards found defective, and the patent invalidated. It is a curious fact, that Mr Talbot's patent for the sister art of talbotype was also invalidated by an English jury; and it will never be forgotten in the history of art, that the rights of property over the two noblest inventions of the age, which the patent laws were enacted to secure, were wrested from their owners by the unjust decisions of an English jury, prompted by the selfish interests of individuals who had been fattening on the genius of the inventors.

While these two ingenious Frenchmen were occupied with heliography, Mr Henry Fox Talbot was, as we have already stated, occupied with the same subject. On the 30th January 1839, six months before M. Daguerre gave his process to the world, Mr Talbot communicated his discovery to the Royal Society; and in the following February published his process of photogenic drawing, to which he afterwards gave the name of calotype, which his friends changed to talbotype, in imitation of the example set by those of Daguerre. In this process he made paper sensible to light by nitrate of silver, and fixed the image by common salt.

About the same time (in April 1839) the Rev. J. B. Reade was led by Mr Talbot's paper to delineate objects of natural history by the agency of light, from their images taken by the solar microscope. He washed writing-paper with a strong solution of nitrate of silver, and immediately before using it he washed it with an infusion of nut-galls, and while it was wet he received upon it the microscopic images. These pictures were fixed by hypomelhite of soda.

On the 29th May 1839, our countryman Mr Mungo Ponton announced to the Royal Scottish Society of Arts, that paper soaked in a saturated solution of bichromate of potash became of a deep orange tint when exposed to the sun; so that in copying upon it dried plants or engravings a negative picture of them was produced. These negatives are dark orange on a yellow ground, and may be fixed by immersion in water, which readily dissolves the portion of the salt not acted upon by the light. This important discovery led M. E. Becquerel to his photographic paper with iodide of starch, Mr Hunt to his chromatype, Mr Sella of Piedmont and Mr Pouncy to their processes, and Mr Macraw of Edinburgh to one of great value. The photographic property of this salt is also the foundation of Mr Paul Pretsch's photo-galvanography, of Mr Talbot's photoglyptic process, and of some attempts at photo-lithography.

Notwithstanding the beauty of some of the pictures obtained by Mr Talbot with the process which he had polished, the art was but in its infancy. The discovery of a more sensitive process was necessary; and after much experimental research, he was led to the valuable photographic method which he secured by a patent, sealed on the 8th February 1841. Mr Talbot subsequently took out a patent for an instantaneous process, a patent for photographic engraving, and, more recently, another for what he calls the polyglotyptic process, which promises to be of great value.

The talbotype process, after it became accessible to the public, underwent numerous improvements by Herschel,

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1 We of course suppose that Daguerre's invention had been justly secured by patent in England before he had been rewarded by the French government. Photography.

Cundell, Bingham, Channing, Le Gray, Martin, Müller, Stewart, Hunt, Fyfe, Furlong, Blanquart, Everard, Collen, Ryan, Woods, Horne, Saguenay, Flacheron, and others; but the most important improvements were made by M. Victor Niepce and Mr Scott Archer, who introduced into photography, the one the use of albumen, and the other that of collodion, as substitutes for paper. A brief account of the most important of the photographic processes will exhaust the space allotted to us for this article.

Art. I.—Account of the Daguerreotype Process.

A plate of copper is coated with silver, and polished in the highest degree by means of animal charcoal and spirits of wine, or tripoli and essential oil of lavender. It is then rendered sensitive to light by the vapours of iodine or bromine, either separately or combined in various proportions, after it has been covered with the vapour of iodine. This is done in a box, the bottom of which is strewed with iodine, covered with a glass plate or a card; and the plate is held above it till it has a fine straw-yellow colour. In order to accelerate the action of light upon this film, the plate is exposed to the vapour of bromine until it attains a rose colour.

When the plate, thus prepared, has been placed in the camera, and received an impression from the figure or landscape to be photographed, it is put into a dark box containing mercury, having in it a little pane of yellow glass, through which the surface of the plate can be seen. By the application of heat, the mercury rises in vapour, adhering to the lights of the picture in proportion to their intensity, so that the shadows are represented by the polished surface of the silver. When the picture, as seen through the yellow pane, is completely developed, it is fixed by immersing it in a solution of hypoalbite of soda; and when this salt has been completely removed by water, a solution of a salt of gold (the double hypoalbite of sodium) introduced by Fizeau) is poured upon the picture, so as to cover it, and the gold is then burnt in by the heat of a lamp spirit lamp. The picture is then brought out with singular brilliancy. The plate is then washed and dried, and is ready to be put into its case or frame. When the surface of the silvered plate reflects white light, the shadows become white, and the lights dark, thus forming a negative picture; so that, in order to see a daguerreotype picture in perfection, the polished surface should reflect to the eye of the observer the darkest objects.

Great improvements in the practice of the daguerreotype have been made by Daguerre himself, Mr Claudet, Mr Hunt, Mr Foxton, Goddard, Bingham, Guerin, Seguin, and others.

The theory of the daguerreotype is still in its infancy. Much light has been thrown upon it by Mr Claudet, Edmund Becquerel, Hunt, and Shaw.*

Art. II.—Account of the Talbotype Process.

In Mr Talbot's first process of 1839, a sheet of smooth and good writing-paper was dipped in a weak solution of common salt, and after being wiped dry, one of its surfaces was brushed over with a solution of nitrate of silver; namely, a saturated solution diluted with six or eight times its volume of water. When the leaves of flowers or engravings are laid upon the nitrated surface of this paper after it is dried, covered with a glass plate, and exposed to the sun, very perfect images of these objects will be obtained in a short time. As the light blackens the parts of the paper exposed to it, the pictures are delineated in white in place of black lines, or are negative pictures. For the same reason, the images of persons or of landscapes formed by the camera obscura upon mirrors will be negatively delineated. In order to fix the pictures, Mr Talbot at first washed them in a highly-diluted aqueous solution of ledite of potassium, but he afterwards used in preference a strong solution of common salt. When the negatives thus obtained were placed upon another sheet of paper prepared as before, a positive copy was produced, in which "the lights and shadows were brought back to their original disposition."

Mr Talbot's second and more perfect process, to which we have already referred as the one patented in 1841, is as follows:—Wash one side of the paper with a solution composed of 100 gr. of nitrate of silver in 6 oz. of distilled water, by means of a soft camel-hair brush. When dry, immerse it in a solution of ledite of potassium, consisting of 50 gr. in a pint of distilled water. The paper is then to be dipped in water, and dried, either by heat, blotting-paper, or spontaneously.

When a sheet of this paper is to be made sensitive for use, wash it with the following solution, which may be called No. 1.—Dissolve 100 gr. of nitrate of silver in 2 oz. of distilled water, and add one-third of its volume of strong acetic acid. Make another solution (No. 2), by dissolving crystallized gallic acid in cold distilled water, and mix the two solutions together in equal proportions when they are required for use. This mixture, called nitrate of silver—is then spread by a brush on the untreated side of the iodized paper, which, when it has absorbed the solution, should be dipped in distilled water, and then dried, first with blotting-paper, and afterwards by heat. In this state it is ready for use, and should be used within a few hours.

After the paper has received the impression of a figure or landscape in the camera, it is taken to a dark room, and may appear either with or without the trace of a picture. In either case the picture, which is a negative, is developed by brushing it over with the gallic-nitrate of silver. When it is sufficiently distinct, it must be dipped in water, then partly dried by blotting-paper and afterwards fixed by washing it with a solution of bromide of potassium (or a strong solution of common salt), consisting of 100 gr. of the salt dissolved in 8 or 10 oz. of water.

From this negative, positive pictures are obtained by the processes described in art. xvi.

Art. III.—Account of the Albumen Process.

The great defect of the talbotype was in the use of paper as the material. M. Niepce de St Victor, in 1848, substituted for it a film of albumen spread upon glass. The following is the process by which Messrs Ross and Thomson have produced their splendid photographs (16 inches by 15), which have excited so much interest. The whites of several eggs, having 18 drops of a saturated solution of iodine added, and mixed for each egg, are beaten up into a heavy mass of froth, and allowed to stand for ten or twelve hours till the whole falls into a liquid. It is then poured plentifully over a plate of glass (which, by means of a bent wire and a piece of worsted thread, is made to revolve at a moderate rate before a clear fire), till, by the influence of the centrifugal force, a very perfect film of albumen is spread over the glass. When the albumen begins to crack at the edges, the plate is withdrawn from the fire, and appears covered with minute cracks over the whole of its surface. It is now dipped in a solution of nitrate of silver (70 grams to an ounce of water), having in it a twentieth part in quantity of strong acetic acid. When taken out, it is washed once or twice with water, and before it is dry, the picture is taken on it. If the object is a light one, four minutes will be sufficient to impress the image; but any dark red or green will take longer time. The picture is developed by pouring on the albumen a saturated solution of gallic acid, and spreading it with a piece of cotton wool. The negative will then appear slowly and gradually of a reddish colour, and when brought out as far as it will come, a little of the nitrate of silver solution, mixed with gallic acid, is spread over it with a piece of clean cotton wool. It now becomes darker and more distinct, and when fixed with hypoalbite of soda, and washed with clean water, positive pictures may be taken from it in the usual manner.

The albumen process is not suited for portraits, on account of the time required to take the picture, but its sensibility may be increased by the addition of grape-sugar or gum arabic. M. Niepce, in place of albumen, has proposed to employ 70 grams of starch rubbed down in 70 grams of water, and then mixed with 3 or 4 oz. of common salt. After allowing 34 hours of iodide of potassium, the whole is boiled till the starch is dissolved. When laid upon glass, it is said to give films of great sensibility.

For architectural subjects, and for still life, the albumen process comes nearest to the daguerreotype in delicacy.

We are not aware that this art has been to any extent practised Albumen either in this country or abroad. The following new process has positives been just published by R. M. Grier:—"A plate coated with asphalt upon glass varnish, known in Prussia by the name of cicalack, diluted with rectified benzole or benzine (first product obtained by distillation of coal tar at a low heat), and when barely dry, and still slightly sticky, was placed in contact in the pressure-frame with a plate of albumen, and exposed to the direct rays of the sun for half an hour. On removal from the pressure-frame, the plate was washed on over its whole surface, until the image became distinctly visible, the parts charged by the rays of light absorbing moisture, and those covered by the blacks of the negative remaining unchanged, and repelling it. In this state, the image being distinctly visible

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1 See Comptes Rendus, &c., April 1844. 2 Manual of Photography, 5th edit., 1837, p. 184. 3 Phil. Trans., 1847. 4 Hunt's Manual, p. 189. 5 These photographs represent Edinburgh as seen from the Calton Hill, the interior of Holyrood Chapel, two views of Melrose Abbey, the Golden Gate of St Andrews cathedral, the north door of Dunfermline cathedral, Bonaw, and Benvenue. It was quickly covered by the bronze powder known as aurum nitricum, which at once changed the almost invisible image to a direct positive on black and gold, the gold adhering to the parts that had been protected from the light, and not adhering to those where the actinic rays had effected such a change in the molecular structure of the film as rendered them capable of absorbing moisture, thus producing a complete picture detailed in all its parts," which the editor of the Photographic Journal pronounces to be "a great novelty, and well worthy of attentive inspection."

The cineclack used by Mr Grier is made as follows:—To 176 lb. of asphalt, melted over a charcoal fire in a pear-shaped iron vessel, is added 279 lb. of oil of turpentine, 15 lb. of well-boiled linseed oil well heated, and so hot that boiling water allowed to cool down as far as possible without becoming solid. The whole is then incorporated and heated until perfectly liquid." It resembles treacle when cold, and when diluted with benzine, and made to flow over the plate, it gives a film of a dark amber colour as really transmitted.

ART. IV.—Account of the Wet Collodion Process.

The use of collodion, first suggested by M. Le Grey, was introduced by Mr Archer in 1850. It is the most valuable, the easiest, and the most sensitive of all the photographic processes, the daguerreotype and the albumen process being the most difficult. The number of first-class daguerreotypists has been very small, and we believe the albumen process has been practised professionally by no British photographers but Messrs Ross and Thomson; while the collodion process is universally employed.

Collodion is a fluid like sherry, and is made by dissolving 15 grs. of gun-cotton in a mixture of nine fluid ounces of rectified sulphuric ether, and one ounce of alcohol, 60° proof. The gun-cotton may be mixed with 70 grs. of fine saltpetre, 3 drs. of nitric acid, and sulphuric acid in the proportions of 3, 4, and 5 oz. When the cotton has been stirred and washed in this bath with two glass rods, it is taken out, and when freed from every trace of acid by copious washing in boiling water, it is hung up to dry. After the cotton, thus prepared, is put into the mixture of ether and alcohol above mentioned, it will be almost wholly dissolved, with the exception of some fibres which fall to the bottom. To the collodion thus made add 5 gr. of iodide of potassium, or iodide of ammonia, dissolved in the smallest quantity of alcohol, and also about 3 oz. of sulphuric ether, to make it run freely over the plate of glass. The sensibility of the collodion may be increased by dissolving a few grains of iodide of mercury instead of potassium, the supersaturated iodide being allowed to settle before using it.

Six operations are necessary for obtaining a negative picture:—

1. The plate of glass (patent plate is the best) must be freed from stains, grease, &c., by a mixture of 2 drs. of cyanide of potassium, 2 drs. of tripoli, and 2 oz. of water, the tripoli being added to the solution of the other two. Cloths free from soap or grease must be used with the mixture, and when the plate is perfectly clean, particles of dust must be removed by a piece of chamois leather.

2. In order to coat the plate, it is held horizontally in the left hand by a corner, while the right hand pours upon its centre a pool of collodion sufficient to cover the whole surface. The plate is then inclined, to make the fluid run to one of the nearest corners, and into the mouth of the bottle the superuous collodion being drained off into a bottle by the last corner to which it reached. When a solid film has been left on the plate by the evaporation of the ether, it is ready to be excited, or made sensitive.

3. The exciting fluid recommended by Mr Thornthwaite is composed of:

- Nitrate of silver, fused......6 dr. - Alcohol.........................12 oz. - Iodide of potassium...........3 gr. - Distilled water................2 drs.

Dissolve the six drams of the nitrate in 13 oz. of the distilled water, and the 3 grams of the iodide in 1 dram of distilled water; mix the two solutions, and shake them well together until the precipitate which is first thrown down is re-dissolved. When this takes place, add the remaining 10 ounces of the distilled water, and the 2 drams of alcohol. This solution is poured into a dyeing-bath, and the coated plate is immersed "steadily and unhesitatingly" into the fluid, and kept there from two to four minutes—for two minutes when the temperature is 60° and longer at lower temperatures, but always rather longer than shorter. After the bath has been immersed half a minute, the plate should be lifted out of the liquid two or three times, and as often replaced, to get rid of the ether on its surface. These operations are performed in a room lighted only through an orange or red pane of glass.

4. When the plate has been lifted out of the solution, and the liquid drained off into the bath, it must be placed wet in the Photography camera, and kept there for a sufficient number of seconds, which experience only can determine, depending on the intensity and character of the light, and on the sensitiveness of the film, which is so great that in fine weather, and in a well-lighted studio, the picture can be taken instantaneously.

5. The best developing solution, according to Mr Thornthwaite, is obtained by mixing and filtering the following materials:—

- Pyrogallic acid..................5 gr. - Glacial acetic acid.............1 dr. - Distilled water..................6 oz. - Alcohol..........................½ dr.

Having added to a sufficient portion of the above mixture (¼ oz. for a plate 5 inches by 4) 12 drops of a solution of nitrate of silver, consisting of 50 gr. in an oz. of water, pour it quickly over the surface of the plate till the picture is completely developed. When this is done the solution must be poured off, and the surface, when held horizontally, washed by pouring water over it.

6. In order to fix the image, which is done by removing the yellow iodide of silver, pour over the surface a solution of hypo-sulphite of soda of the strength of 4 oz. in a pint of water. Every trace of the hypo-sulphite must then be washed away by pouring water slowly over the picture. The plate must now be varnished, either by spirit varnish or by Dr Dyson's varnish, consisting of amber dissolved in chloroform.

With the negative picture thus prepared positives may be obtained, as shown in art. xvi.

This process is, we think, the most important in photography. Collodion When collodion was first introduced, it was shown by Mr Horns that process for the negative pictures could be converted into positives ones by mixing positives a small quantity of nitric acid with the pyrogallic; and Mr Fry on glass, subsequently proved that a better effect would be obtained with the protosulphate or protonitrate of iron. When

- Protosulphate of iron...........10 gr. - Distilled water..................1 oz. - Nitric acid.......................2 drs.

are mixed, pour it over the plate to develop the picture. When one part of the protonitrate, with three of water, is used instead of the protosulphate, a fine clear picture is produced.

When the negative picture has been developed by either of the above solutions, a mixture of pyrogallic acid and hypo-sulphite of soda is immediately immersed over, and when it has been slightly warmed, the darkened parts will become of a bright white by the formation of metallic silver. The picture must then be placed upon black velvet.

Mr Hennah, in producing positives, uses a thinner collodion than usual, excites with the ordinary bath, and exposes the plate not more than half the time necessary for a negative. The picture is brought out by immersing it in a bath containing

- Protosulphate of iron...........40 gr. - Acetic acid......................30 gr. - Nitric acid.......................2 drs. - Alcohol..........................1 oz. - Distilled water..................1 oz.

The pictures are then fixed, as is usual, with hypo-sulphite of soda.

Mr Archer has obtained delicate white pictures by treating the negative picture, when fixed and thoroughly washed, in the following manner:—Take a saturated solution of the bichloride of mercury, and after diluting one part of it with six of water, pour a small quantity over the picture at one corner, so as to allow it to flow uniformly over the surface. The tone of the picture will be immediately deepened, and though the negative image has nearly disappeared, a brilliant white will immediately supervene, and a fine, delicate, white, positive picture will emerge, its negative character being wholly destroyed. It is singular, however, that this picture can be changed to a deep-toned black negative, very much darker than the original one, by immersing it after a thorough washing in a weak solution of hypo-sulphite of soda, or of ammonia.

"It is very singular," as Mr Hunt remarks, "that the picture can be alternately changed from a white positive to a black negative many times in succession, and very often with improvement."

A new method of taking collodion pictures on glass, by Mr William Ackland, is well worthy of the attention of photographers. He lodges his collodion with the following mixture:—

- Iodide of potassium.............12 gr. - Solution of iodine, (4 gr. in 1 oz. of alcohol),..............4 drops. - Alcohol..........................1 oz.

and it must be mixed with the collodion at least 12 hours before it is used, in order to allow any sediment to subside. He develops the latent picture with

- Protosulphate of iron...........2 dr. - Glacial acetic acid.............2 dr. - Nitrate of barium...............14 dr. - Alcohol..........................3 dr. - Rain or distilled water...........10 oz.

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1 See Journal of the Photographic Society, Nov. 22, 1858, p. 87. 2 This method is elaborately explained, and occupies fourteen closely-printed pages in Mr Thornthwaite's Guide to Photography, 14th edit., 1857. And he fixes with one scruple of cyanide of potassium (a poison), dissolved in 8 oz. of rain or filtered water.

When the plate has been fixed and dried it is varnished on the collodion side, and when this is dried it may be placed in a frame with a black velvet or cloth ground to form the proper shades. In place of using the black velvet back of the frame or case, it is usual to cover the glass side, not the collodion side, of the picture with a black varnish. In this case the sides of the portrait are reversed, anything on the right side appearing as it were on the left; so that the picture is not an accurate representation of the sitter. A soldier, for example, without his right arm, would appear to have lost his left arm; and a sitter blind on the left eye would appear blind on the right one. To avoid this, the black varnish may be applied on the collodion side after the application of the transparent varnish.

The art of transferring collodion pictures from the glass plate to glazed cloth or leather has been practised in Paris for a long time, and is now becoming more common in this country. As the pictures thus transferred may be sent by post, and resist various kinds of injury, this art has become a very important one.

Mr. W. Newton was the first who transferred collodion positives to paper. He passed over the collodion picture a varnish composed of 1 oz. of pure gum mastic dissolved in 5 fluid oz. of alcohol, and 2 drams of oil of poppies. A piece of thin paper, a little smaller than the glass, and saturated by a camel-hair pencil in the same varnish, is then placed in contact with the collodion film, so as to exclude air, and the whole is allowed to become dry by evaporation.

The following is the simplest method of transferring the picture to leather or cloth. Dry the glass plate, and having heated spirits of wine upon it, allow it to drop; then take the black leather or cloth (which may be glazed or not), and dip it uniformly with spirits of wine. Lay this on the prepared plate, pass the hand over it so as to expel air-bubbles, if there are any. Then turn over the plate, and observe if there are any air-bubbles beneath the collodion. Lay the plate on a flat surface with the glass side uppermost, and apply pressure with suitable weights for half an hour. After this operation the collodion picture will be easily detached from the glass plate.

Mr. Ostall of Carlisle adds 4 or 5 drops of nitric acid to half an ounce of spirit of wine, and he pours this over the positive collodion picture after it has been dried at the fire or otherwise. It is then laid on the leather or cloth, the air-bubbles expelled, and pressure applied for about half an hour, by placing the combined plate and leather in the printing-frame. By holding the glass side towards the light it will be seen when the glass is leaving the collodion film. Mr. Ostall recommends a stronger mix of collodion, having either more gun-cotton in it, or made stronger with a few drops of the nitrate bath. The picture may be transferred to paper by means of a varnish.

Mr. Ross of New York pours upon the collodion, when it is still wet from the fixing, a solution of sulphuric acid diluted to three degrees, and leaves it for one or two minutes. The cloth is then heated till it is soft and pliable, and while there is still a thin stratum of humidity upon the collodion, the film is applied to the cloth, and any bubbles of air driven off by passing the finger lightly over it. It is useful to wet the cloth with a little alcohol before it is applied. One of the corners of the film is then raised to see if it adheres, and if it does not, a stream of water is passed between the glass and the film thus raised to produce their separation.

Mr. Howell of Ashburnham, Ohio, prepares the glass plate by coating it with a thin film of wax. The picture is then taken in the ordinary way, until it is fixed, washed, and dried; it is "covered by brown silk-like black varnish, made more adhesive by a little Canada balsam." When the varnish is nearly dry, the paper (previously cut to shape, and soaked in water) is laid on and pressed into close contact with the varnish by means of a small roller covered with a cushion of cloth.

ART. V.—An Account of the Dry Collodion Process.

Although the wet collodion process possesses a high degree of sensibility, yet it loses it upon the drying or consolidating of the film. This is a great disadvantage to the travelling photographer, or to any person who takes a picture at a distance from his studio; and in order to remedy the evil, he must either take a portable tent with him, or use a "cold" yellow light, or one of those ingenious cameras which will enable him to excite the plate, and develop the picture in the interior of the instrument.

One of the earliest methods of preserving sensitive collodion plates was employed by Messrs Spiller and Crooks, who used nitrate of magnesia and nitrate of zinc, which, by their deliquescent proper-

ties, keep the plate of collodion slightly moist. When the plate of Photography has been excited in the nitrate bath for five minutes, it is then drained, and immersed in a bath consisting of—

Nitrate of magnesia .......... 4 oz. Glacial acetic acid .......... 1 dr. Nitrate of silver .......... 12 gr. Water .......... 12 oz.

where it is left five minutes, and then drained for about half an hour, by placing it upright upon blotting-paper. Plates thus prepared have been kept three weeks without deterioration. The picture is developed as in the wet process.

Mr. Sanderson's formula consists of 2 volumes of pure honey and 5 volumes of distilled water, stirred with a glass rod till the honey is dissolved. One volume of alcohol is added to it when it has been filtered (a work of some hours) through blotting-paper. A portion of this syrup is poured two or three times over the collodion when it has been excited in the usual way. Glycerine has been used in place of honey by Mr. Llewellyn, Mr. Pollock, and other photographers. Mr. N. Makolynsky seems to have first discovered it.

Barnes' dry collodion is thus composed:—

Plain collodion .......... 4 oz. Camphor .......... 4 gr. Solution of iodide of potassium .......... 5 dr. Epsom tincture of chloride of gold .......... 10 drops. Pyro-acetic spirit, purified .......... 4 dr. Tincture of iodine .......... 2 dr.

To this mixture 1 oz. of old collodion and 4 oz. of new should be added, to give it firmness. Plates thus prepared have acted well at the end of six weeks.

The following process for dry collodion has been successfully used by M. Dupuis, officer of health to the French army of occupation at Rome—The collodion is formed of

Ether, sp. gr. 0.60-0.80 cubic centimeters. Gum-cotton .......... 1 gramme. Alcohol, do. 36-40 do. do. Iodide of zinc .......... 1 gramme.

The exciting bath consists of

Fused nitrate of silver .......... 10 grams. Distilled water .......... 150 grams. Acetic acid of commerce .......... 15 grams.

The developing solution consists of

Pyrogallic acid .......... 1 gram. Distilled water .......... 300 grams. Citric acid, crystallized .......... 1 gram.

Plates thus prepared by M. Dupuis at Rome on the 6th of May 1857 were brought to London by Sir David Brewster, and developed there on the 27th of June. Some had received the picture at Rome, and others were only prepared. After being kept fifty-one days, the plates gave very fine pictures.

The following dry collodion process, given by the Rev. J. Lawson Sisson, has been regarded by competent judges as both simple and certain—Having placed four dishes in a row, pour distilled water into Nos. 1, 2, 3, sufficient to cover a plate. Into No. 4 pour a mixture of half an oz. of raspberry syrup and 3 oz. of distilled water. A plate of collodion, made sensitive in the ordinary way, is put, with the collodion side upwards, into No. 1. A second sensitive plate is prepared, and, while wet, the plate is removed from No. 1 and placed in No. 2, and the second plate is placed in No. 1. A third sensitive plate being ready, plates 1 and 2 are moved on to the next dish, and plate 3 placed in dish No. 1. In like manner, when a fourth plate is prepared, plate 1 is placed in the syrup dish No. 4; the others are moved onward, and plate 4 placed in dish No. 1. After preparing a fifth plate, plate 1 is lifted from the syrup dish, and is then placed upright upon blotting-paper to drain and dry. In this order the process is continued, the time required for coating and making sensitive a plate being exactly the time during which any plate should continue in one of the four dishes. Plates thus prepared are as sensitive and will keep as long as any of those prepared by the existing keeping processes.

One of the best dry processes is that of Dr. Hill Norris, who roughens the edges of the glass to the extent of 1/12th of an inch and pours upon it collodion rather old, made with

Rectified ether .......... 5 dr. Soluble cotton .......... 5 gr. Absolute alcohol .......... 5 dr. Iodide of potassium .......... 5 gr.

the iodide being dissolved in 5 drops of water, and added to the collodion. Immerse the plate in a 30-grain solution of nitrate of silver, perfectly saturated with nitrate of silver; and, when well wound and dried vertically, dip its surface with a solution of 9 grams of pure gelatine (Nikon's patent) in 1 oz. of water and 4 th oz. absolute alcohol. When dried quickly, the plate will keep sensitive for six weeks. Before developing, cover the plate for a minute or two with distilled water, and then develop it well with a saturated solution of gallic acid in water, to every ounce of which 10 minims of a 40-grain neutral solution of nitrate of silver has been added. The development usually occupies from two to four hours.

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1 See Phot. Jour., vol. v., p. 10, Aug. 21, 1858. 2 See Phil. Mag., May 1857; and Phot. Jour., i., p. 223, and ii., p. 6. 3 See Phot. Jour., vol. ii., p. 273. Mr. Pollock adds 6 drops of glycerine to 1 oz. of collodion (ibid., p. 309). 4 See Phot. Jour., ii. 151, and iii. 84, 179. M. Muller of Bolbec has given a dry collodion process in which he forms two solutions—the first of albumen in distilled water, with 10 to 12 drops of creosote; the second, of honey, 250 grammes, animal charcoal, 5, and water, 100. These two solutions are mixed, every 20 of the first with ten of the second, and applied to the collodion film when excited. Plates thus prepared retain their sensibility more than a month.

**ART. VI.—Account of the Oxymel Process.**

The oxymel process, as first proposed by Mr Llewellyn, has been published in many of our treatises on photography, and has undergone various modifications by himself and others. After much experience of the process, Mr Llewellyn has, so recently as August 1858, published the following as his process:—An excited collodion plate, washed in two or three waters, is plunged for a few seconds into a bath containing

- Bromide of potassium ..... 5 gr. - Alcohol ..... ½ dr. - Water ..... 1 oz.

When all traces of the free bromide have been washed away for about five minutes in several waters, the plate is excited, and the film preserved by the following solution:

- Ordinary oxymel ..... 4 dr. - Citric acid ..... ½ gr. - Water ..... 1 oz. - Nitrate of silver ..... ½ gr.

which is poured on and off the film two or three times, after which the plate is placed vertically to drain and dry. One ounce will be sufficient for small plates, 10 x 12. It must be kept from white light. It will keep for a day or more. Before developing, the film should be wetted with water, and the ordinary pyrogallic solution with a few drops of an 8-grain solution of nitrate of silver, used to develop the picture.

**ART. VII.—Account of the Collodio-Albumen Process.**

This process, invented by M. Taupenot, consists in first collodionizing the plate, dipping it in the silver bath, washing it with distilled water, and pouring over it albumen iodized in the proportion of 1½ per cent. The collodion plate placed upright to drain and dry. The plate is excited during ten or twenty seconds in the aceto-nitrate bath containing 10 parts of nitrate of silver, 10 of acetic acid, and 100 of distilled water. The albumen used by Taupenot consists of

- Honey ..... 10 parts. - Iodide of potassium ..... 1½ part. - Albumen ..... 100 parts. - Yeast ..... a little.

After fermentation, the liquid is filtered, and stored in bottles containing from three to six fluid ounces.

The defect of this process is the production of blisters in the film at the time of exciting. M. Julien Blot prevents the blistering by the use of dextrine, which permits the baking of the albumen without altering at all its iconographic properties, and gives the possibility of restoring the albumen film, if cracked by the heat, to its normal condition, by cooling, or by breathing over it. The plate will remain sensitive for eight days in winter.

For an elaborate account of Taupenot's process, we must refer the reader to the Photographic Journal, vol. iii., p. 102, which contains an able article by a French photographer. This article is followed by a long and valuable paper on the same process by Mr William Ackland. A variation of this process by Mr Pothier, in which no honey is used, will be found in the Photographic Journal for September 1858.

**ART. VIII.—Account of the Wax-Paper Process.**

This process, which has been used with great success by M. Le Gray and Mr Roger Fenton, is one of considerable interest. The best paper is that made by M. Lacroix of Angouleme, or the Messrs Casson Brothers of Amnonay. It is laid on a metallic plate, which is rubbed over while hot with a cake of pure white wax, and when it has cooled, the paper is removed. It may be backed with some sheets of smooth bibulous paper, and smoothed with a moderately hot iron till it becomes equally transparent throughout. It is then iodized by immersing it for ten minutes in a bath thus composed:

- Iodide of potassium ..... 4 dr. - Honey ..... 1 oz. - Bromide of potassium ..... ½ dr. - Distilled water ..... 1 pint. - Iodine ..... 4 gr.

After being drained and dried, it is excited by the following aceto-nitrate:

- Nitrate of silver ..... 3 dr. - Animal charcoal ..... 2 scr. - Glacial acetic acid ..... 3 dr. - Distilled water ..... 8 oz.

After exposure in the camera for eight minutes, when the lens is 14 inches in focal length, and the stop half an inch, the picture is developed by immersion in a saturated solution of gallic acid in 20 oz. of distilled water and when well fixed, it is fixed by the usual hypo-salts. The transparency, if diminished, may be restored by building it before a moderate fire.

Mr Hunt gives the following formula from Le Grey for iodizing the paper:—Into 54 parts of distilled water put 4000 grains of rice; steep them till the grains are slightly broken, so that the water may contain only the glutinous portion. In a little less than a quart of the rice solution dissolve

- Sugar of milk ..... 600 gr. - Cyanide of potassium ..... 12 gr. - Iodide of potassium ..... 225 gr. - Fluoride of potassium ..... 7 gr.

The wax paper is dipped in this solution, and drained and dried. It is excited by 774 (and for portraits by 150) grains of nitrate of silver dissolved in 2325 grains of distilled water, to which is added 186 grams of acetic acid. The picture is developed in a bath of 60 grams of gallic and 40 fluid oz. of distilled water, to which 15 or 20 drops of aceto-nitrate of silver is added. It may remain in it from ten minutes to two hours.

Dr Keith of Edinburgh iodizes with the following solution:

- Pure water ..... 4 oz. - Sugar of milk ..... 3 oz. - Iodide of potassium ..... 750 gr. - Common salt ..... 30 gr. - Bromide of ditto ..... 250 gr. - Iodine ..... 8 gr.

in which the thin paper (Casson Brothers' or Turner's for negatives) must be soaked for ten hours, and then hung up to dry. The paper is rendered sensitive by immersion for ten or twelve minutes in a bath containing the following solution:

- Nitrate of silver ..... 200 gr. - Glacial acetic acid ..... 13 dr. - Water ..... 12 oz. - or citric acid ..... 20 to 30 gr.

The strength of this bath must be kept up by adding two or three grains of the nitrate for every sheet rendered sensitive. When the sheet is well washed in a large basin of water, and the superfluous moisture blotted off, it is ready for use when required.

To develop the picture, place the sheet in a saturated solution of gallic acid, having one grain of pyrogallic acid added to 4 oz. of the solution. After it has remained four or five minutes, add 12 drops of the aceto-nitrate, agitating the bath to mix it. The development will require from twenty minutes to several hours. When well washed in several waters, the picture is then fixed by the hypo-salts of soda.

**ART. IX.—Account of the Metagelatine Process.**

M. Le Gray and other French photographers employed gelatin or lainglass in the calotype process on paper; but it is to Mr Maxwell Lyte that we are indebted for the application to collodion for a preservative process. It is a well-known property of gelatin that, after it has been dissolved in hot water, allowed to gelatinize, and again boiled, and this process repeated many times in succession, the jelly gradually loses its tenacity and continues liquid even while cool. In this altered condition Mr Maxwell Lyte gave it the name of Metagelatine, and has found it superior to all other substances as a varnish for preserving the collodion film in a dry state. In order to prepare it, "take 1½ oz. of fine white gelatine, and dissolve it in 10 fluid oz. of boiling distilled water; then add 2 fluid drs. of strong sulphuric acid which has been previously diluted with 2½ fluid oz. of distilled water, and boil these together gently for a quarter of an hour; then turn the vessel off the fire, and let it stand for two or four hours; then boil gently again for fifteen minutes, and again remove it from the fire, and let it cool for an hour or two. Heat up the liquid once more to a boiling heat, and saturate the acid by adding powdered whiting till effervescence ceases. Separate the sulphate of lime which is thus formed by pressure in a linen cloth, and then stir into the liquid about a tea-spoonful of animal black, and filter once more through paper till perfectly clear. Add water to bring up the liquid to the bulk of 18 fluid oz., and then add two drops of creosote to prevent the liquid from becoming mouldy."

In order to prepare the preservative syrup, Mr Lyte takes

- Solution of gelatine ..... 5 scr. - Fine honey ..... ½ oz. - Distilled water ..... 5 oz.

When the collodion plate is withdrawn from the nitrate bath, it must be held for an instant with its corner resting on blotting-paper. The syrup is then to be poured upon it like the collodion, Photography.

and run off at a corner. Fresh portions of syrup must then be poured on and off several times, till it takes evenly over the whole surface. When it is to be used in the camera it should be dipped in cold distilled water, and then excited, developed, and fixed in the usual manner.

Art. X.—Account of the Bichromate Process—Chromotype, &c.

We have already referred to the valuable photographic properties of bichromate of potash, discovered by Mr Mungo Ponton, and to the experiments of Bequerel and Mr Hunt to which it led.

The chimie type of Mr Hunt is founded on Mr Ponton's process, which we have already described. A solution of 1 oz. of sulphate of copper in 1 oz. of distilled water, with ½ oz. of a saturated solution of bichromate of potash, is applied to the surface of good paper, which, when dried, is fit for use. It is changed to a dull brown by the action of light, and gives a negative picture if checked at this stage; but if the action of light is prolonged, the dull brown disappears, and we have a positive yellow picture on a white ground. "In either case," says Mr Hunt, "if the paper is removed from the sunshine, and washed over with a solution of nitrate of silver, a very beautiful positive picture results." In order to fix these pictures, the nitrate of silver must be removed by washing in pure water.

According to Mr Bingham, the paper is more sensitive by using sulphate of nickel in place of sulphate of copper. Another bichromate process, and a very valuable one, has been proposed by M. Joseph Sella of Biella in Piedmont, following, as he himself observes, "the suggestions of Mr Ponton."

1. The paper, when immersed in a saturated aqueous solution of bichromate of potash, is dried in the dark between sheets of bibulous paper.

2. It is exposed in the camera about two-thirds of the usual time, and then immersed for half an hour in water, which must be changed three or four times.

3. It is then immersed for three or four minutes in a filtered solution of proto-sulphate of iron containing 5 gr. of the salt to 100 gr. of water. It is then washed in several waters, and soaked for half an hour.

4. The picture is then immersed in a solution of gallic or pyrogallic acid more or less concentrated, and in a few minutes the image will be developed, having a beautiful black tint bordering on violet, and one highly appreciated by artists.

If, instead of pyrogallic acid, we use the yellow prussiate of potash, the picture will be in Prussian blue; with acetic, it will become green; and with alkaline solution it will become deeper, and border on violet. The process may be applied to albumen, gelatine, &c. Its advantages are, "economy of time and silver, ease of execution, certainty of result, and permanence of the picture."

The following bichromate process, by Mr William Macrae of Edinburgh, being an improvement on the above, was communicated by Sir David Brewster to the British Association at Leeds in September 1858, and proved to be of great value, both from the extraordinary cheapness of the materials, and the permanence of the pictures which it gives. In proof of its excellence, we have now before us two beautiful photographs, one of a female figure, and the other of Sir Walter Scott's monument, which were shown to the meeting.

First. To 25 per cent. of a saturated solution of common salt add the white of eggs, to be well beaten up and allowed to subside; float the paper on the albumen for thirty seconds, and hang up to dry.

Secondly. Make a saturated solution of bichromate of potash, to which add 25 per cent. of Beaufoy's acetic acid. Float the ordinary albumenised paper on this solution for an instant, and while dry it is fit for use. This must be done in the dark room.

Thirdly. Expose under a negative, in a protected frame, in the ordinary manner, until the picture is sufficiently printed in all its details, but not over-printed, as is usual with the old process. This requires not more than half the ordinary time.

Fourthly. Immerses the pictures in a vessel of water in the darkened room; the un-decomposed bichromate and albumen then readily leaves the lights and half-tints of the picture. Change the water frequently, until it comes from the prints pure and clear.

Fifthly. Immerses the pictures now in a saturated solution of proto-sulphate of iron in cold water for five minutes, and again rinse well in water.

Sixthly. Immerses the pictures again in a saturated solution of gallic acid in cold water, and the colour will immediately begin to change to a fine purple black. Allow the pictures to remain in this until the deep shadows show no appearance of the yellow bichromate; repeat the rinsing.

Seventhly. Immerses, finally, in the following mixture:

Pyrogallic acid, 2 gr.; water, 1 oz.; Beaufoy's acetic acid, 1 oz.; saturated solution of acetate of lead, 2 dr.

This mixture brightens up the pictures marvellously, restoring the lights that may have been partially lost in the previous parts of the process, deepening the shadows, and bringing out the detail; rinse finally in water, and the pictures are complete when dried and mounted.

The advantages of this process may be briefly stated as follows:—First. As to its economy: bichromate of potash, at 2½ per oz., is substituted for albumen, at 15 per oz. Secondly. Photographs in this way can be produced with greater rapidity than by any old mode. Thirdly. The pictures being composed of the same materials which form the constituent parts of writing-ink, it may be fairly inferred that they will last as long as the paper upon which they are printed.

The bichromate of potash is an essential element in the process of printing on carbon, invented by Mr Pouncy. Pictures thus printed have been submitted to the Paris committee, appointed by the Duke de Laynes to adjudge the prize which he has offered for the best process of producing permanent photographs; and M. Gerard has found that the black material in them is truly carbon, and that they resist the prolonged action of concentrated nitric and hydrochloric acids, aqua regia, cyanide of potassium, cyanide of potassium with iodine, and alkaline sulphites, none of which, though energetic agents, affected it in the least.

The following is Mr Pouncy's process, in so far as he has published it in his provisional specification of the 10th April 1858. He prepares the paper or other material which is to receive the picture by applying over its whole surface a composition of vegetable carbon, gum-arabic, and bichromate of potash. Upon this surface the negative is placed, and exposed to the light in the usual way. The positive thus produced is washed with water, which dissolves the composition at the parts on which the light has not acted, but does not affect the part on which the light has acted. Mr Pouncy sometimes substitutes for the vegetable carbon, bitumen or other colouring matter.

Art. XI.—Account of Fothergill's Dry Collodion Process.

This process has been much praised by practical photographers as simple in its application and perfect in its results. The object of the process is to protect the sensitive film from the action of the atmosphere by a varnish of albumen, which is done thus:—

Having coated the plate with collodion, place it in a bath of 35 gr. of nitrate of silver in an ox. of water, "saturated with iodide in the usual way;" and after it has been in half a minute, move it up and down, and when taken out pour lightly on it at one corner four drops only for a stereoscopic size plate, or sixteen drops for a proportional quantity being used for larger plates, causing the water to flow freely all over the plate for 15 to 20 seconds, till all appearance of greenishness is removed. Having made a solution of albumen, consisting of 10 oz. of white of eggs, distilled water 6 oz., and pyrogallic liquor of ammonia 50 minims, agitated into a froth and strained for use, coat the collodion surface with this, letting it run several times from corner to corner, and having poured it off, place the plate in a dish of water, so as to cover it to the depth of 3-5ths of an inch. Wash it well with two waters, moving the dish backward and forward, so that the water may flow over the plate. When taken out, place it on end upon several thicknesses of blotting-paper, and put it in a dark place to dry. After exposure in the camera, moisten the picture with distilled water, and develop with:

Pyrogallic acid .......... 1 gr. Alcohol .............. 10 min. Glacial acetic acid ...... 20 min. Distilled water .......... 1 oz.

adding to each dram one or two drops of the silver bath.

Art. XII.—Account of the Salts of Iron Process—the Ferrotype and the Catalotype.

Under the name of the catalotype, Mr Hunt published an account of a process in which the salts of iron were used; but he afterwards adopted the more appropriate name of ferrotype, as applicable to all processes in which these salts were employed. Good Paper is washed over with the following solution:—

Sodium acid pure .... 5 gr. Common salt ............. 5 gr. Water .............. 1 fluid oz. Mucilage of gum-arabic ... ½ dr.

The paper when dry is drawn over the surface of a solution of 60 gr. of nitrate of silver in one oz. of water. When dried in the dark the paper is of a pure white, and may be kept for a consider- able time in a portfolio, for use, carefully preserved from the least light. After exposure in the camera, the picture is developed by drawing the prepared side of the paper over a saturated solution of potassium iodide of iron and 2 or 3 drs. of mucilage of gum-arabic. The picture will appear almost immediately. The paper, when well washed, is fixed as usual.

Under the name of the cyanotype process, Dr Woods of Parisontown has given the following iron process:—A sheet of white paper is steeped for a few minutes in a mixture of two drs. of hydrochloric acid in 100 drs. of water; then washed, and immersed for a mixture of half a dr. of the syrup of iodide of iron, water 24 drs., and tincture of iodine 1 drop. When dried with bibulous paper, it is washed over evenly, in the dark, with a 10 gr. solution of nitrate of silver in an oz. of water. The paper is now ready for the camera, and the sooner it is used the better. The exposure should be from two to thirty seconds, and in clear weather without sunshine, fifteen seconds on an average. The picture, invisible at first, develops itself gradually till it arrives at a state of perfection, which is not attained by photography produced by any other process. The picture is then fixed with a solution of bromide of potassium, 15 or 20 gr. to the oz., and iodide of potassium, 5 gr. to the oz.

Dr Woods has more recently recommended the following formula, which gives a darker negative, and in which soaking in the hydrochloric solution is not necessary.

Syrup of iodine........... 2 drs. | Tincture of iodine..... 10 to 12 drops. Distilled water.................. 2 drs.

With this solution brush over the paper, dry it after a few minutes, and after exposure in the camera, wash it with 1 dr. of nitrate of silver in 1 oz. of pure water. Fix it after washing in a solution of iodide of potassium, 5 gr. to the oz. of water, and then wash it again.

ART. XIII.—On the Nitrate of Uranium Process for obtaining Positives on Paper.

This valuable process consists in substituting nitrate of uranium in place of nitrate of silver. M. Niepce de St Victor has described three methods of obtaining positive pictures with this salt,—viz., with nitrate of silver, and with the chloride and chloridate of mercury.

1. Dissolve 20 parts of the nitrate of uranium in 100 of distilled water, and on the surface of this solution, kept from light, float the paper (thin paper is preferable) for five minutes, and suspend it in the air free from light. When exposed under a negative from one to ten minutes in the sun, and from fifteen to sixty in the shade, the picture will be slightly brownish, and will remain dark one or two days before it is developed. In a bath of 6 parts of nitrate of silver in 100 of distilled water, immerse the picture rapidly, and it will be developed in thirty or forty seconds, having a grey sepia tint, which becomes brown when kept ten minutes in the bath. The proof is now to be washed in two or three waters, and will be permanent, because unassailable by boiling cyanide of potassium.

2. In using chloride of gold, immerse the picture in a bath of 2 grammes of chloride of gold in 1000 grammes of water, adding some drops of hydrochloric acid. The picture will appear instantly, its blue tone deepening into black when the exposure to the sun has been double that which is required with the nitrate of silver. When developed, withdraw it rapidly, wash it, and fix it.

3. The chloride of mercury is given to the picture grey-black tones, and the black of mercury. The paper prepared by the nitrate of uranium must be exposed three times as long as in the two preceding processes. It is then immersed in a bath of 100 grammes of ordinary water and of chloride of mercury to saturation, at a temperature of 50° Fahr. After two or three minutes the proof loses its colour, and when it becomes white it is carefully washed, put into the silver bath, where it develops itself slowly, and in from ten to fifteen minutes arrives at a black. It is then washed in several waters.

M. Crepon of Nimes, Mr Brebisson, and other photographers, have obtained very fine positives by this process; but M. Humbert de Molard has found its excellence and permanency of the pictures produced by it; while M. Bayard asserts that he has produced as good and permanent pictures with the ammonium-tin of iron and the nitrate of silver, or the chloride of gold.

In the year 1855, at the meeting of the British Association in Glasgow, Mr C. J. Burnett described a new process for obtaining positives on paper by means of the nitrate or other salts of uranium.

He exhibited specimens developed in four different ways: 1. By photographic salts of silver, fixed by the hypophosphite of soda, and toned by an acid, neutral or alkaline, gold chloride bath, or by platinum palladates or aurates. Paper thus prepared will keep very long in hot climates, especially if the picture is developed with salts of iron. One of Mr Burnett's specimens showed a radiation of actinium absorbed by a newspaper. 2. By solutions of gold, acid, alkaline, and neutral; 3. By hypo-salts of potassium, prepared by a very weak iron bath; and 4. By the ferric-aurate of potassium.

The uranium printing process, based on the fact that all bodies absorb light more or less, has been recently patented by Mr Wm. Clark. It is called "Photography by Absorption of Light," and is thus performed:—A sheet of paper that has been a number of days in the dark is impregnated by immersion in a solution of salt of uranium, which the patentee says "has the property of absorbing a very large quantity of light." He prefers a solution of the nitrate of the oxide of uranium. When of a nice straw-yellow colour it is dried, and kept in the dark. After exposure to the sun, under a negative, it is exposed for a quarter of an hour. The negative is removed, and the picture is brought out with a solution of 3 parts of nitrate of silver and 100 of water. It is then fixed with ether. The chemicals picture thus produced may be made black by a solution of chloride of gold, and red or blue by combinations of the salts of gold and silver.

In using the uranium process, M. Hagen obtains great sensitiveness by removing the size from the paper with boiling water. When pressed between sheets of blotting-paper, and still damp, it is floated on the uranium solution. Pictures of greater intensity are obtained by adding a little alcohol or ether to the silver salt.

ART. XIV.—Photography on Porcelain, Parian, Alabaster, Enamelled Glass, Ivory, and Enamelled Metals.

So early as 1851 Mr Fox Talbot and Mr Malone took out a patent for taking negative photographs on semi-transparent unglazed porcelain, the results of which we have not seen. On the 14th July 1857 Mr Tanny and Mr Macraw exhibited to the Photographic Society of Scotland the results of processes, to which the one gave the name of vitro-heliography, and the other that of citrotype. On the 5th November Mr Tanny communicated to the Photographic Society in Edinburgh the process by which he obtained portraits upon porcelain, parian, enamelled glass, and enamelled metal. A plate of any of these substances is coated with collodion and alum, separately or combined, and then collodion is excited in the nitrate of silver bath, and exposed in the camera. When taken into a dark room, the film is saturated with weak protosulphate of iron or pyrogallic acid, which is immediately washed off. It is then momentarily exposed to subdued daylight or artificial light, and immediately treated with a developing fluid, when the latent image will appear as a positive, with the lights and shadows correct. The picture is then developed as usual. The picture thus obtained is left-hand negative; and in order to remedy this Mr Macraw places a negative photograph of the object to be depicted on the porcelain at such a distance in front of the camera, with a mirror placed behind the image at an angle of 45°, so that a well-defined image is obtained on the porcelain.

We have now before us two very fine female portraits, of great softness and delicacy, executed on porcelain by Mr Macraw.

In July 1857 Mr C. J. Burnett pointed out the importance of burning in photographic portraits in porcelain, and he described processes for this purpose, and exhibited specimens which he had produced by them.

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1 Phot. Jour., iv, 189, 200; Comptes Rendus, &c., xlv, 811; xlvii, 448, 452. 2 See Comptes Rendus, Sept. 3, 1858, p. 277, and Oct. 1, 1858, p. 395. 3 See Photographic Notes, March and April 1857; and Liverpool and Manchester Phot. Jour., Aug. 1 and Dec. 1, 1858. 4 Phot. Notes, vol. iii., p. 278, Dec. 18, 1858. 5 Phot. Jour., vol. iv., p. 88, Nov. 21, 1857. 6 Phot. Jour., vol. iv., p. 15, Aug. 1857. 7 See Report of the British Association for 1858. Photographs under the name of alabasterines have been advertised as a new discovery by Messrs Squire & Co. They are, however, only glass positives with another name, and are produced by what is called the alabasterine solution, the composition of which is a secret.

**Art. XV.—On the Recent Discoveries in Photography of M. Niepce de St Victor.**

Having exposed to the sun for a quarter of an hour an engraving which had been kept several days in the dark, he applied it to a sheet of sensitive paper, and after four hours' contact in the dark, he obtained a negative picture of the engraving. If the distance between the engraving and the paper is one-eighth of an inch, or if a film of collodion or gelatine is interposed, the picture will still be obtained, but not if the film consists of mica, glass, or rock-crystal. If we take an opaque tube, closed at one end, and lined with white paper, and expose the open end to the sun for an hour, and if at the end of twenty-four hours we place a sensitive paper on the open end of the tube, we shall obtain a negative image of the opening. If we place a sheet of white paper that had been in the dark in the camera, to receive for three hours a picture brilliantly illuminated by the sun, and having taken care to apply it to a piece of sensitive paper, it will in twenty-four hours reproduce in the dark a very visible copy of the picture in the camera.

This is the activity, or "storing up of light," as M. Niepce calls it; he exhibits in the following experiment:—A glass or paper negative having been placed on a sheet of paper that has been several days in the dark, he exposes it for a sufficient time to the sun's rays, and after taking out the paper in the dark, he develops the picture with a solution of nitrate of silver, and fixes it by merely washing it in pure water.

In another Memoir, just published, M. Niepce has described another action of light, which opens up a new and immense field to photography, in so far as it proves that almost all chemical actions are fit to give photographic pictures. Take a solution of any soluble substance whatever, and impress it on a sheet of paper. Allow the impregnated sheet to dry in the dark; expose it under a negative to the sun, and having taken it out in the dark, treat it with any re-agent capable of transforming the soluble substance, or causing it into combination with it, and we shall have a visible image, the chemical becoming a photographic action. The process may be reversed with the same result, by impregnating the paper with the re-agent and developing with the soluble substance. The principal re-agents to be employed are the salts of gold and silver, the dyes of turmeric and curcuma, and iodide of potassium for common paper sized with soap. If nitrate of uranium is the soluble substance, and red prussiate of potash the re-agent, the picture will be of a fine blood-red colour, and will be fixed by washing in pure water. If the picture is put into a solution of a salt of copper without washing, it will take different shades according as the heat is more or less intense. If the picture is treated with the prussiate of iron instead of the prussiate of potash, its colour will be a beautiful blue.

**Art. XVI.—On the Processes for Printing Positives.**

When a good negative picture—that is, one in which the lights are black and the shades white—has been produced, positive pictures may be obtained by placing the negative above paper or any other substance sensitive to light; cover it with a thick plate of colourless glass, pressed against it in what is called a copying-frame, and exposing it to the sun, or to daylight, or to artificial light. The best copying-frames are those which have a jointed back to allow the artist to observe the progress of the picture without displacing the negative.

The best paper for positives are Turner's positive, and the new German positive, or papier Sozé. When the paper is cut of the proper size, it is soaked for five or ten minutes in a solution of 110 grs. of nitrate of soda (common salt) in 24 oz. of water, or 30 grs. of soda upon 1 scr. of nitrate of ammonia in 10 oz. of water. They are then hung up in a place where it is impossible to press them to dry. The sensitive solution (which was first suggested by Mr Alfred Smees) is obtained by dissolving 108 grs. of nitrate of silver in 3 oz. of water, and adding liquor ammonia, drop by drop, until the dark precipitate which is formed by the first drops is nearly dissolved, a slight turbidity remaining. A sheet of the salted paper, when dry, is laid on a flat board in ordinary light, with its smooth side uppermost, and marked with a pencil. It is then brushed over with a camel-hair pencil or a pellet of cotton, and when dry may be placed in the copying-frame beneath the negative, and exposed to the sun. When it is printed it is soaked for an hour or two in water, and then fixed and toned in a bath thus composed:—To a solution of 4 oz. of hypophosphite of soda in 6 oz. of water add 2 dr. of a solution of chloride of gold in 4 oz. of water; and afterwards add a solution of 30 grs. of nitrate of silver in 1 oz. of water. The picture is kept in this bath from 10 minutes to an hour, till it has acquired an agreeable tint, and is sufficiently fixed.

The sensitive solution most commonly used is a solution of 1 dr. of nitrate of silver in 1 oz. of distilled water. It is applied to the paper in the same manner as the ammonio-nitrate, and the picture is toned and fixed in the same manner as before.

The paper may be better fixed by the following process.—Take the whole of an egg 1 scr., and water 1 scr., beat them into a froth, adding 10 grs. of nitrate of ammonia or soda to each ounce of the mixture. Float the paper upon this solution for a few minutes, pressing out any air-bubbles, and then hang it up to dry. A hot iron is then passed over its surface to set the albumen, and render it insoluble. When wanted for use it is excited by a solution of 60 grs. of nitrate of silver in 1 oz. of water; and it is toned and fixed by the process already described. All positives, however produced, must be long soaked in hot and cold water repeatedly changed.

**Art. XVII.—On Microscopic Photographs.**

In our article on the Microscope we have devoted a separate chapter to the "Application of Photography to the Microscope," and we have briefly referred to microscopic photographs, or those which are so exceedingly minute that the objects are invisible to the unassisted eye. Mr Dancer of Manchester seems to have been the first photographer who executed these remarkable productions. It was obvious that no new principle was involved in the execution of these portraits; but one could not but admire the dexterity and deftness of manipulation in taking photographs between the 30th and 40th of an inch square, in developing and fixing them, and in placing them between two plates of glass, with Canada balsam in between.

Mr Dancer did not describe the optical process which he employed; but Mr Shadbolt, who executed and exhibited photographs from the 20th to the 40th of an inch in diameter so early as March 1854, has given a drawing and description of the method which he employed. In this delicate art a structureless collodion is necessary, which is obtained by the formula—

Pure ether,......................... 5 dr. Chloroform.......................... 20 min. Alcohol (90 overproof)........... 3 dr. Iodide of potassium.............. 5 gr. Soluble cotton till the solution is slimy.

After adding the chloroform to the ether and cotton, and one dram of alcohol, add the other 2 dr. of alcohol containing the iodide.

An achromatic object-glass, 1 or 1½ inches in focal length, is made the lens of a small camera, and the negative picture to be reduced is placed in front of it at such a distance that the image in its focus is sufficiently minute; or it may be stuck into the stage of the microscope, as done by Mr Shadbolt, and the focusing and union of the actinic and luminous rays affected by another object-glass in its place in the microscope. Mr Jackson and Mr Hardwick had small cameras, the one made by Ross, and the other by Horne and Thorntonwhite. Either daylight or artificial light may be employed in illuminating the negatives, which may be taken directly from living figures.

**Art. XVIII.—On the Production of Photographs from Coloured Objects.**

Although M. Biot in 1840 regarded it as an illusion to attempt to obtain the colours of nature photographically, yet in the same year Sir John Herschel actually procured upon photographic paper a coloured image of the solar spectrum; and by subsequently using paper more kept, he obtained a better representation of it, kept in a dark room. Mr Hunt frequently obtained coloured pictures of the spectrum, dark spots, light ground; but the most beautiful were upon "the daguerreotype haloidated tablets." By preparing metallic plates with chlorine, M. E. Becquerel obtained, and exhibited to the Academy of Sciences, "a photographic image of the solar spectrum, and coloured photographs from the camera obscura." These colours, though durable for a long time in the dark, resisted every attempt to fix them. M. Niepce de St Victor has been more successful, by using the purest silver; and he is said to have obtained "all the colours of a picture by preparing a bath composed of the denso-chloride of copper." Some of these discoveries in the possession of Mr Malone were, as seen by Mr Hunt, perfectly coloured in correspondence with the drawings of which

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1 See Comptes Rendus, &c., tom. xlv., p. 811, Nov. 1857, and tom. xlv., pp. 448 and 489, May 1858. 2 Ibid., tom. xlvii., p. 866, Nov. 29, 1858. 3 Vol. xlv., p. 801. 4 Phot. Jour., i., p. 194. 5 Ibid., iv., p. 79. 6 The linen of old cambric is recommended by Mr Hardwick (Phot. Jour., iv., p. 82). 7 Phot. Jour., iv., p. 81. 8 Ibid., iv., p. 93. Photography—they were copies;" but no successful mode of fixing them has yet been discovered, though M. Niepce de St Victor has made a hundred attempts to do this.

The colours of nature have been produced accidentally by several photographers. In taking a stereoscopic picture on collision of rains covered with ivy, a gentleman in Durham, who signs himself "Magnet," was surprised to find the ivy green, the trunks of old trees brown, the stones gray, and "the whole with its colours varied in a high degree." The colours were not altered in fixing the picture, but in developing it, so that the effect, with the exception of the green, which remained perfectly distinct. The same effect was produced in a second picture, taken in a bright sun in twenty seconds. The collision employed was perfectly colourless, and was two months old. It gave a thin film. It was prepared with iodide of potassium and a little bromine.

M. Raymond, a French photographer, has observed similar colorific effects. When a picture upon collodion began to be developed under the combined action of the pyrogallic and acetic acids, he exposed it to light without previously washing it; and he observed it transform itself quickly into a direct positive, and came out with more or less perfection the colours of the subject. The perfect picture he obtained required a quarter of an hour for its development. It lost none of its brightness; by an exposure of some months to the air, and even after two years it was not completely effaced.

Some of the colorific effects observed by photographers are the colours of thin plates, and have no connection whatever with the colours of nature. The action of light upon the collodion film changes either its thickness directly, or indirectly by changing its solubility; so that the light and dark parts of the picture exhibit different tints in Newton's scale of colours. We have observed this effect in very thin films of collodion on glass, and also in the same films after having been transferred to paper.

ART. XIX.—On the Applications of Photography.

Our limits will not permit us to dwell at any length on the numerous and important applications of this beautiful art. The employment of photography in the arts of painting and sculpture has been recommended by artists of the highest name. Instead of superseding the arts of design, photography will supply them with new materials—with collections of costume, with studies of drapery and of form, and with scenes in life and facts in nature which, if they possess at all, they possess imperfectly, and without which the Art must be stationary. We do not believe that photography can be used in the instance of the artist, as it is called, of taking pictures on collodion in half a second, has enabled the artist to delineate "a thoroughfare in London with its noonday crowd," to seize the momentary attitudes and expressions of passion, and to fix on his tablet the gestures of the orator and the furious movements of the lunatic. Such pictures have been erroneously represented as the results of mere mechanical dexterity, to which the mind of the artist had not imparted "the impress of thought;" but if the portrait is taken with optical truth, which has yet to be done, and if, in the twinkling of an eye—if in half a second, a portion of time less than the duration of the expression of thought or sentiment—a portrait is taken, the portrait must be perfect and superior to any that the artist can produce. It is almost a truth that which art cannot arrive. It is as true as that portraits of the sitter seen by reflection in the most perfect mirror; and though the artist might improve the material picture by a deviation from truth, he cannot add a single iota to its expressions of thought or of feeling.

To the sculptor, photography, whether simple or binocular, is of inestimable value. He can fill his portfolio with copies of all the treasures of the Vatican, the British Museum, and the repositories of art in Berlin, Munich, and other European cities. They all exhibit to him forms more than human, though human still, embodying all that is true and beautiful in what might be seen, and when taken separately, would not be seen by the stereoscope into true size and solidity, as if the originals were placed before him. The living, the dying, and the dead may thus be modelled without the rude contact of a mask, and those noble forms perpetuated which affection or gratitude has endeared.

To the pursuits of the architect, the engineer, and the mechanist, photography is equally applicable; and in the diffusion of knowledge, and for the purposes of education, its power will be speedily recognised. Nor will it be less influential in humanising the humbler classes of society. Portraits of their families in beautiful frames and morocco cases can be purchased for a shilling, and even for sixpence each. The emigrant may carry to his distant home the portraits of those from whom he has been obliged to part, and the humblest peasant may adorn his cottage not only with likenesses of his family and friends, but with accurate photographs of various objects in art and in nature which he may desire to contemplate.

The calico-printer may multiply his patterns photographically; and the carpet manufacturer and general decorator may fix in paper all the beautiful patterns which are given by the kaleidoscope.

In the sciences of astronomy, zoology, geology, meteorology, ethnology, electricity, and magnetism, photography has been advantageously employed. The spots of the sun, the surface of the moon, the forms of the planets, and even groups of stars, have been delineated by their own light; and it has been stated that the photographic moon indicates the atmospheric stratum of considerable density. Mr. De la Rue has obtained pictures of this lunar anomaly analogous to binocular ones, which, when aided by the stereoscope, exhibit her as a solid globe. The meteorologist registers photographically in his absence the indications of the barometer, thermometer, and hygrometer; the variations of the earth's magnetism are recorded for every minute on chemically-prepared paper, and the electricity of the atmosphere, brought down into the observatory, is made to exhibit on paper the number of its variations and the intensity of its action. The ethnologist has begun to collect accurate pictures of the different races of man. The zoologist has obtained forms of animal life which the painter had attempted in vain to procure. The geologist has obtained delineations of phenomena which defied the highest efforts of his pencil; and the botanist has transferred to imperishable tablets those beautiful and complex forms of vegetable life which we seek in vain in the richest botanical collections.

The last, and certainly the least application of photography, is one which was introduced last year at Nice. The Duke of Parma had his portrait at full length placed upon his visiting-cards. Some English gentlemen imitated his example; and it has been partially followed in London and in Paris. In order to diminish the expense, M. Besson of Paris takes 24 negatives at once on the same sheet of paper with a 24-lens camera; and he is thus able to print 24 cards at the same time, and greatly reduce the expense of their production.

ART. XX.—On the method of taking correct Photographic Portraits.

In our article OPTICS, we have devoted a separate section to prove that all portraits taken by large lenses are monstrous representations of the human form, and that all pictures of solid bodies so taken are incorrect. The defects of such lenses may be shortly enumerated.

1. They introduce into the picture parts of the solid figure which cannot be seen from any one point of sight.

2. Every picture taken by a large lens is a combination of an infinite number of insensible pictures, as seen from every point of the lens.

3. A large lens introduces into a picture objects eclipsed by or placed behind other objects.

4. In portrait lenses consisting of two separate lenses there are eight surfaces, each of which reflects back upon the sensitive surface a portion of light more or less intense.

5. In such lenses their combined thicknesses is such as to injure the distinctness of the picture, if there is any defect (as there must be, however small) in the homogeneity of the glass.

6. In the images formed by such lenses, lines which should be straight are curved, and curved lines are not their proper curvature.

With the more perfect lens, the parts of objects at different distances have different degrees of distinctness on the gray glass. The degree of indistinctness increases with the diameter of the lens, because it is measured by the section of a cone of rays whose base is the lens itself.

8. In passing through such a thickness of glass, many of the actinic rays are lost by absorption.

From all these objections small lenses are free; and as very sensitive photographic processes have been discovered, we would press