THEOEY AND PEACTICE 
 
 OF 
 
 THE PHOTOGEAPHIC ART, 
 
! 
 
THEORY AND PRACTICE 
 
 THE PHOTOGKAPHIC ART 
 
 INCLUDING 
 
 ITS CHEMISTRY AND OPTICS, 
 
 MINUTE INSTRUCTIONS IN THE PRACTICAL MANIPULATION OF THE VARIOUS 
 PROCESSES, DRAWN FROM THE AUTHOR'S DAILY PRACTICE. 
 
 BY W. SPARLING, 
 
 ASSISTANT TO MR. FENTON, HONORARY SKCRETARY TO THE PHOTOGRAPHIC SOCIETY. 
 
 LONDON : 
 
 HOTJLSTON Am STONEMAN, 65, PATERNOSTEE EOW; 
 W^. S. ORE AND CO., AMEN CORNEE. 
 
 MDCCCLVI. 
 
PHOTOGRAPHED UPON THE WOOD WITHOUT PENCILLING. 
 
 PHOTOGEAPHIC ART. 
 - — 4 — 
 
 Introduction. — "Witliin the last quarter of a century there has not been a dis- 
 covery more useful, interesting — I may say, more fascinating — than photography. 
 "Whether employed as an assistant to the artist, or a means of sending home from far- 
 off scenes of war and death the portrait of a friend, or the spot whereon, perhaps, he 
 died or conquered, what can equal its truthfulness ? what can surpass its beauty ? 
 By the aid of the sunbeam the physician may now delineate the gradual changes 
 produced by disease, with a faithfulness hitherto unknown ; the architect can obtain 
 the most elaborate details of a building in a few seconds. The art has been made sub- 
 servient to the purposes of the artist, the naturalist, and the mechanic, and even to the 
 antiquary, who, 
 
 " Bending o'er some mossy tomb 
 "Where valour sleeps," 
 
 may be enabled to preserve a lasting memorial by this art. Viewed in these lights, 
 Photography may justly be considered the most important application of chemical 
 philosophy to develop the powers of nature which modern science has discovered. 
 Premising that the science is at present in its infancy, I shall endeavour to make the 
 present manual as plain, as practical, and as comprehensive as possible, saying nothing, 
 which might require to be afterwards unsaid, nor leaving anything unsaid which may 
 be necessary to elucidate the subject, so far as our present knowledge extends. 
 
 Wedgwood's Discovery, — The property possessed by the salts of silver, when 
 decomposed by the action of light, was well known to the earlier chemists ; and 
 M. Charles, a well-known French physician, exhibited in his lectures at the Louvre a 
 paper capable of taking silhouette figures by the action of solar light, but he has left 
 no account of his process. Mr. Wedgwood, therefore, was undoubtedly the first person 
 
10 
 
 WEDGWOOD S DISCOVERY. 
 
 wh.0 recorded Ms attempts to use the sunbeams for photographic printing. In the year 
 1802 he published a paper in the Journal of the Eoyal Institution, which he describes 
 as " aa account of a method of copying paintings upon glass, and of making profiles 
 by the agency of light upon nitr^ite of silver, with obseryations by H. Davy," — a gen- 
 tleman afterwards better known as Sir Humphry Davy. From this paper, the earliest 
 we are aoq[u:aiiited with in wMch the discovery of these processes present themselves, 
 the following extracts ar-e tak«n : — 
 
 " White paper, or white leather, moistened with a solution of nitrate of silver, 
 undergoes no change when kept iu the dark ; but on being exposed to the day-light it 
 I speedily changes colour, and after passing through different shades of gray and brown, 
 i becomes at length nearljr black. The alterations of colour take place more speedily in 
 I proportion as the light is more intense. In the direct beam of the sun, two or three 
 mifflutes are sufficicait to produce the full cffi ct ; in the shade, several hours are re- 
 j quired ; and light transmitted through different coloured glasses act Avith different 
 degrees of intensity. Thus it is found that red rays, or the common sunbeams i^assed 
 through red glass, have Yery little effect upon it. Yellow and green are more effective, 
 but violet or blue produce the most powerful and decided effect." j 
 " "When the shadow of any figure is thrown upon the prepared surface, the part i 
 concealed by it remains white, and the other parts speedily become dark. For copying | 
 paintings on glass, the solution should be applied on leather ; and in this case it is | 
 more readily acted on than when paper is used. After the colour has been once fixed 
 on the leather or paper, it cannot be removed by the application of water, or water and | 
 soap, and it is in a high degree permanent. Tbe copy of a painting or the profile, ! 
 immediately after being taken, must be kept in an obscure place ; it may, indeed, be • 
 examined in the shade, but in this case the exposure should be only for a few minutes ; j 
 by the light of candles or lamps, as commonly en ployed, it is not sensibly affected, i 
 No attempts that have been made to prevent the uncoloured parts of the copy or profile 
 from being acted upon by light, have as yet been successful. They have been covered 
 by a thin coating of fine varnish, but this has not destroyed their susceptibility of 
 becoming coloured ; and even after repeated washings, sufficient of the active part of ; 
 the saline matter will adhere to the white parts of the leather or paper to cause 
 them to become dark when exposed to the rays of the sun. Besides the applications of j 
 this method of cop5-ing that have just been mentioned, there are many others ; and it ] 
 will be useful for making delineations of all such objects as are possessed of a texture 
 partly opaque and partly transparent. The woody fibres of leaves, and the wings of \ 
 insects, may be pretty accurately represented by means of it ; and in this case it is I 
 only necessary to cause the direct solar light to pass through them, and to receive the I 
 shadows upon leather. 
 
 " The images formed by means of a camera obscura have been found to be too i 
 faint to prodiice, in any moderate time, an effect upon the nitrate of silver. To j 
 copy these images was the first object of Mr. Wedgwood in his researches on the 
 subject; and for this purpose he first used nitrate of silver, which was mentioned . 
 to him by a friend as a substance very sensible to the infiuence of light ; but all his 
 numerous experiments as to their primary end proved unsuccessful. In following ■ 
 these processes, I have found that the images of small objects, produced by means of \ 
 the solar microscope, may be copied without difficulty on prepared paper. This will i 
 probably be a useful application of the method ; that it may be employed successfully, j 
 however, it is necessary that the paper be placed at but a small distance from the lens." i 
 
BERARD AND DAGUERRE's DISCOVERY. 
 
 11 
 
 Here we have the first indication of this great discovery. Suhsequently, about the 
 years 1810-11, Seebeck made some interesting discoveries as to the production of 
 colour on chloride of silver by solar radiations, the violet rays rendering it brown, 
 the blue producing a shade of blue, the yellow preserving it white, and the red con- 
 stantly giving a red shads to that salt. 
 
 Bexard's Discovery, — In the year 1812, M. Berard brought the result of some 
 i valuable researches before a commission composed of MM. BerthoUet, Chaptal, and 
 i Biot, who state in their report that M. Berard had discovered that the chemical inten- 
 ! sity was greatest at the violet end of the spectrum, and that it extended, as Bitter and 
 "Wollaston had previously observed, a little beyond that extremity. When he left 
 substances exposed for a certain time to the action of each ray, he observed sensible 
 effects, though with an intensity continually decreasing in the indigo and blue rays. 
 Hence they considered it as extremely probable, that if he had been able to employ 
 agents still more sensible, he would have observed analogous effects. To show clearly 
 the great disproportion which exists in this respect between the energies of different 
 : coloured rays, M. Berard concentrated, by means of a lens, all that part of a spectrum 
 i which extends from the green to the extreme violet ; he also concentrated, by means of 
 I another lens, all that portion which extends from the green to the extremity of the red. 
 This last pencil formed a white so brilliant that the eyes were scarcely able to endure 
 it ; yet the muriate of silver remained exposed more than two hours to this brilliant 
 point of light without undergoing any sensible alteration. On the other hand, when 
 exposed to the other rays, which were much less bright and less hot, it was blackened 
 i in less than six minutes. 
 
 ! After some further remarks on the importance of M. Berard' s experiments, they 
 proceed as follows :— " If we consider solar light as composed of three distinct substances, 
 one of which occasions lir/ht, another heat, and the third chemical combinations, it will 
 follow that each of these substances is separable by the prism into an infinity of different 
 modifications like light itself ; since we find by experiment, that each of these proper- 
 ties is spread, though unequally, over a certain extent of the spectrum ; and we must 
 suppose, on that hypothesis, that there exist three spectrums one above the other ; 
 namely, a calorific, a colorific, and a chemical spectrum. We must likewise admit that 
 each of the substances which compose the three spectrums, and even each molecule of 
 unequal refrangibility which constitutes these substances, is endowed, like the mole- 
 cules of visible light, with the property of being polarized by reflection, and of escaping 
 from reflection in the same positions as the luminous molecules." 
 
 From that time numerous experiments were conducted by several eminent re- 
 searchers, including the discovery of the more celebrated MM. Niepce and Daguerre. 
 
 Daguexze and Niepce's Discovery. — To the inventive genius of these gentle- 
 men we are indebted for the first practical application of this great discovery ; but, like 
 most great conceptions of the human mind, this art, as we have seen, advanced by slow 
 steps, and was indicated from time to time by the isolated facts [we have briefly 
 alluded to. 
 
 The researches of M. Niepce were commenced in 1814, but it was not till 1826 that 
 he was made aware, by the indiscretion of an optician employed by both, that M. Daguerre 
 was pursuing the same course of experiments. A correspondence between the two 
 philosophers was the result, and henceforth their researches were pursued in common ; 
 and some years later resulted in the discovery of this branch of the art since known 
 as the Daguerreotype. In 1833, M. Niepce died, having communicated all his dis- 
 
12 
 
 TALBOTYPE DISCOVERY. 
 
 coveries to M. Daguerre, and, in 1839, that gentleman, with a most laudable abnega- 
 tion of self, communicated his discoveries to the public. 
 
 Fox Talbot's Discovery.— About the same time Mr. Fox Talbot, stimulated, 
 no doubt, by the patriotic example of M. Daguerre, published the calotype process, thus 
 giving birth to a new branch of the art. 
 
 That gentleman, it appears, had been carrying on his experiments for five years 
 previously, in perfect ignorance of what Daguerre and others were doing, and had 
 aimed at a method by which the sensitiveness of the salts of silver was increased to a 
 marvellous degree. I cannot do better than give an extract from his own communica- 
 tion. 
 
 After saying how marvellous it seems that, in a few minutes, a picture is produced, 
 displaying the thousand florets of an Agrostis, with all its capillary branchlets, and so 
 accurately delineated, that not one is without its little bivalve calyx, requiring to be 
 examined through a lens, he proceeds : — 
 
 " And, again, to give some more definite idea of the rapidity of the process, I will 
 state that, after various trials, the nearest valuation which I could make of the time 
 necessary for obtaining the picture of an object, so as to have pretty distinct outlines 
 when I employed the full sunshine, was half a second." He was then speaking of the 
 paper used in the solar microscope. 
 
 Mr. Fox Talbot also published an account of his first pJiotogenic experiments (for 
 this term was first introduced by that gentleman), and I shall again make use of extracts 
 from it, as they will better convey an idea of his discoveries and their importance than 
 any words of mine : — 
 
 "In order to make what may be called ordinary photogenic paper," he says, "I 
 select paper of a good firm quality and smooth surface. I do not know that anything 
 answers better than superfine writing-paper. I dip it into a weak solution of common 
 salt, and wipe it dry, by which the salt is uniformly distributed throughout its sub- 
 stance. I then spread a solution of nitrate of silver on one surface only, and dry it at 
 the fire. The solution should not be saturated, but six or eight times diluted with 
 water. When dry, the paper is fit for use. 
 
 " I have found, by experiment, that there is a certain proportion between the 
 quantity of salt and that of the solution of silver which answers best, and gives the 
 maximum efiect. If the strength of the salt is augmented beyond this point, the eifect 
 diminishes, and, in certain cases, becomes exceedingly small. 
 
 " This paper, if properly made, is useful for all photogenic purposes. For example, 
 nothing can be more perfect than the images it gives of leaves and flowers, especially 
 with a summer sun,— the light, passing through the leaves, delineates every ramifica- 
 tion of their nerves. 
 
 " Now, suppose we take a sheet of paper thus prepared, and wash it with a 
 saturated solution of salt, and then dry it. We shall find (especially if the paper 
 is kept some weeks before the trial is made) that its sensibility is greatly diminished, 
 and, in some cases, seems quite extinct. But if it is again washed with a liberal quan- 
 tity of the solution of silver, it becomes again sensible to the light, and even more so 
 than it was at first. In this way, by alternately washing the paper with salt and silver, 
 and drying it between times, I have succeeded in increasing its sensibility to the degree 
 that is requisite for receiving the images of the camera obscura. 
 
 " In conducting this operation, it will be found that the results are sometimes more 
 and sometimes less satisfactory, in consequence of small and accidental variations in the 
 
PHOTOGRAPHIC CHEMICALS. 
 
 13 
 
 proportions employed. It happens sometimes that the chloride of silver is disposed to 
 darken of itself without any exposure to light ; this shows that the attempt to give it 
 sensibility has been carried too far. The object is to approach, as near as possible, to 
 this condition, without reaching it, so that the substance may be in a state ready to 
 yield to the slightest extraneous force, such as the feeble impact of the violet rays 
 when much attenuated. Having, therefore, prepared a number of sheets of paper 
 with chemical proportions slightly different from one another, let a piece be cut from 
 each, and, having been duly marked or numbered, let them be placed, side by side, in a 
 very weak diffused light for a quarter of an hour. Then, if any one of them, as 
 frequently happens, exhibits a marked advantage over its competitors, I select the 
 paper which bears the corresponding number to be placed in the camera obscura." 
 
 CHEMISTRY OF PHOTOGEAPHY. 
 
 General Remarks.— The wonderful discoveries announced by M. Daguerre 
 and Niepce, and Mr. Fox Talbot, produced a host of followers, who have brought them 
 to the highest perfection. M. Claudet, one of the earliest, discovered a mode of taking 
 objects by subjecting the plate to vapour of chloride of iodine. Messrs. Fizeau, 
 Caudin, and Leon Foucault, by the aid of divers preparations of bromine, obtained 
 impressions with great rapidity ; and, in 1840, M. Fizeau succeeded in fixing the 
 image by means of chloride of gold. 
 
 Having thus introduced the subject in the words of the respective authors, and 
 given a brief history of subsequent discoveries, I shall now, previous to going into the 
 manipulating branches of the science, devote some little space to the chemical agents 
 which we shall use, and recommend the reader to make himself as much acquainted 
 with their nature and photographic properties as possible ; for I can assure him that if 
 he does not do so, the time spent on the study of the science wiU be almost thrown 
 away. 
 
 The first of the photographic chemicals which will come under our notice, taking 
 them alphabetically, wiU be — 
 
 Acetic Acid.— The strongest acetic acid, named "Glacial," and sometimes "con- 
 centrated acetic acid," from its property of becoming solid at low temperatures, contains 
 only about one-sixtieth of its bulk of water. The crystals melt, at about 50", into a 
 pungent limpid liquid, with a smell resembling strong vinegar, of which, in fact, it is 
 the base ; the distilled vinegar of the shops being acetic acid diluted with from 5 to 7 
 parts of water. It is often contaminated with a trace of sulphuric acid, which may be 
 detected by the addition of a little chloride of barium, when, if any sulphuric acid be 
 present, we obtain a white precipitate. 
 
 Acetic acid is of the greatest use in all the photographic processes which require 
 development, as it governs or checks the action of pyrogallic and gallic acids, and the 
 sulphate of iron on the salts of silver undergoing decomposition ; it preserves the whites 
 or parts of the picture not acted on by light ; it also keeps the picture clean by prevent- 
 ing any decomposition, except that caused by the light. I may add, that tartaric and 
 formic acids are sometimes used for the same purpose, but I am inclined to give the 
 preference to the acetic acid. 
 
 Acetic acid is also the best acid for correcting the alkalinity of the nitrate of silver 
 bath, which will be explained at length as we proceed. 
 
14 
 
 PHOTOGRAPHIC CHEMICALS. 
 
 Albumen, or white of egg, is Tory much used ia preparing the surface of paper 
 for positive printing. It is thoroughly beaten up with water and salt, the action of 
 the nitrate of silver partly coagulates the albumen, and in turn is converted into 
 chloride of sodium by an excess of nitrate of silver— a combination extremely favour- 
 able to the production of a picture by the action of light. Albumen, containing small 
 quantities of sulphur and phosphorus, gradually discolours the solution of nitrate of 
 silver used for exciting or making sensitive. This discolouration may be easily re- 
 moved by scraping some pipe-clay into the solution, stirring it up, and'allowing it to 
 remain for a day or two, and then filtering carefully. Albumen cannot be used with 
 ammonia nitrate of silver, as the alkaline action of the ammonia would prevent 
 coagulation in the albumen, and cause its separation from the paper. 
 
 ^foo^o^.— Alcohol must not be confounded with " spirits of wine," as the latter 
 contains a considerable quanti:y of water, which would prove almost fatal to the col- ■ 
 lodion process, causing a precipitate of the cotton and a separation from the ether : a 
 proof of this may be seen at once n a collodion picture that has been taken with a 
 collodion containing much water in the alcohol. Upon drying it, and viewing it by 
 transmitted light, you will at once perceive that it has a c/rain something similar to 
 fine muslifi, so that it is of the greatest consequence to obtain the alcohol as free from 
 water as possible. To do so it will be best to mix quick lime, powdered, and alcohol 
 together in equal weights, by distilling both together ; the alcohol will come over 
 pure, leaving the water with the lime, for which it has a great affinity. 
 
 Ammonia is, or ought to be, only used photographically for the purpose of making 
 ammonia nitrate of silver; for which process see Sike>\ It should be kept in a stop- 
 pered bottle, as it rapidly absorbs carbonic acid from the air, which converts it into 
 carbonate of ammonia. 
 
 Bichloride of ALerciiry, or corrosive sublimate, is a highly poisonous salt, very 
 sparingly soluble in water, unless free hydrochloric acid be present. It is used for the 
 purpose of improving glass pictures— of which more anon— and for removing the yellow- 
 ness sometimes caused in the lights of a print, when the gold colouring bath is used. 
 
 Bromine.— This is a deep reddish-brown liquid, fuming strongly at common 
 temperatures, and highly suffocating. It exists in sea-water combined with magnesium, 
 and is closely analogous to chlorine and iodine, having stronger affinities than the 
 latter and weaker than the former ; that is to say, bromine would displace iodine, and 
 chlorine would displace bromine. It is sparingly soluble in water, soluble in alcohol, 
 more so in ether. 
 
 Bromide of Potassium is a mixture of bromine and caustic potash, heated to red- 
 ness to drive off the oxygen from the hromate of potash, the latter becoming bromide 
 of potassium on the loss of its oxygen. It is used for the formation of bromide of 
 silver (see Silver). 
 
 Chlorine is a greenish-yellow gas, of a pungent and suffocating odour. As has 
 been remarked, closely analogous to the other two of the group, bromine and iodine, 
 the gas has a density of two and a half times heavier than air. It is found abun- 
 dantly in nature in combination with sodium, in solution in sea-water and rock- salt ; 
 and is very useful in the arts for its bleaching properties. It has such a strong 
 affinity for hydrogen that it absorbs it greedily, thus breaking up the structure of the 
 organic substance, the latter being bleached by destroying its colour. It can be always 
 discovered, either free or in combination, by a solution of nitrate of silver, with which 
 it forms a white precipitate (chloride of silver). 
 
PHOTOGRAPHIC CHEMICALS. 
 
 15 
 
 Chloride of Sodium, or common table salt, is very useful to the photograplier, 
 as it bears the same relation to the positive printing that iodides and bromides do to 
 the negative. Its sources are inexhaustible, being found in large quantities m the 
 ocean as a solution, in the earth as a solid. It is a combination of chlorine and 
 sodium. It fuses without decomposition at a dull red heat ; but if the heat be pushed 
 too far it sublimes, and the melted salt on cooling becomes a hard white concrete mass. 
 It is sparingly soluble in weak alcohol, but nearly insoluble in absolute alcohol ; it is 
 soluble in three times its weight of water, and crystallizes in cubes which are anhy- 
 drous (without water). As chloride of sodium is often contaminated with chlorides of 
 magnesium and calcium, also sulphate of soda, it is best if you can obtain it pure. 
 You must do so by neutralizing hydrochloric acid (spirits of salt) by carbonate of 
 soda. As has been already noticed, it is a very important salt in photography, being 
 used most extensively in the preparation of positive-paper. 
 
 Chloride of Ammonia, or muriate of ammonia, is a soluble salt formed by the com- 
 bination of chlorine and ammonia. It contains more chlorine than an equal weight of 
 chloride of sodium, and may be used instead of that salt in the preparation of positive 
 printing paper. 
 
 Chloride of Silver, formed by a combination of chlorine with a solution of nitrate of 
 silver (see Silver). 
 
 Chloride of Gold.— Take three parts nitro- muriatic acid, put it into a cup, and drop 
 a piece of pure gold into it one-third its weight ; let it evaporate until chlorine 
 vapour is disengaged, then let it crystallize. An impurity sometimes found in the 
 iodide of potassium (which see). 
 
 Chloride of Fotassium.-When there is much carbonate of potash in the iodide, it 
 may bs recognised by the crystals being very small and deliquescent (becoming moist 
 when exposed to the air). The carbonate of potash is strongly alkaline to test-paper, 
 and not very soluble in alcohol ; indeed it is a question if it is' at all soluble in absolute 
 alcohol, but it is soluble in some degree in the weaker alcohols, to which it communi- 
 cates an alkaline reaction. 
 
 The next impurity which comes under our notice is the sulphate of potash. This salt 
 is decidedly not soluble in absolute alcohol, and the iodide of potassium may be freed 
 from it by being dissolved in very strong alcohol. The presence of the sulphate of potash 
 may be detected thus : —Make a solution of chloride of barium, and add a little to a solu- 
 tion of iodide of potassium ; a slight milkiness need not be noticed, but if a decided 
 white precipitate fall down, then you must either reject the iodide of potassium, or 
 dissolve it in the strongest alcohol, when the sulphate being insoluble will remain 
 undissolved. 
 
 We have now to consider the chloride of potassium. The presence of this salt is not 
 so easily ascertained as either of the others ; indeed it is rather difficult, and to discover 
 an alkaline chloride in the iodide of potassium you must proceed thus :— Make a solution 
 of the iodide suspected, and make a solution of nitrate of silver of the same strength, 
 say twenty grains of each to one ounce of distilled water, mix and add to the iodide of 
 silver a little liquor ammonia ; if any chloride of silver (or chloride of potassium, 
 which would form a chloride of silver) be present, it will dissolve in the ammonia, and 
 after filtration may be precipitated by the addition of pure nitric acid ; the iodide of 
 silver must be well washed previous to the addition of the nitric acid, for as the latter 
 often contains traces of chlorine, the presence of any free nitrate of silver, by combining 
 with the chlorine on neutralizing, would very likely cause an error ; it is of great im- 
 
PHOTOGRAPHIC CHEMICALS. 
 
 portance that the iodide of potassium should be pure, as otherwise it may cause a 
 great deal of trouble ; it would not matter so much if the nature of the impurity were 
 known, as in that case we could take steps to counteract its influence. 
 
 Cyanide of Potassium is a highlij poisonous salt, formed by the combination of 
 cyanogen gas and potassium. It generally contains a large per centage of potash, from 
 which it may be freed by boiling in alcohol, which on cooling deposits it in crystals. 
 It has a strong smell of prussic acid, and is freely soluble in water. It dissolves iodide 
 of silver, and is used for that purpose in clearing away all the unaltered iodide of 
 silver from the negative (a positive if on glass). It also removes the stains of nitrate 
 of silver from the skin or linen. When using it on the fingers, be careful that it does 
 not get into any cuts or sores, as it is almost as poisonous as prussic acid itself. 
 
 Ether is a highly volatile, inflammable spirit, obtained by distilling alcohol with 
 sulphuric acid ; the latter in its re-action removes one atom of water, and by so doing 
 converts one atom of alcohol into one of ether. There are three kinds of ether sold in 
 the shops— ordinary rectified ether, washed ether, and washed and re-rectified ether. 
 Ether is a most important photographic chemical, being the sohentof "gun cotton," 
 with which it forms collodion ; and it is very necessary that it should be pure. It 
 should not have an acid re-action with test-paper ; it should not turn an alcoholic 
 sohition of iodide of potassium rapidly brown ; it should not have a high specific { 
 gravity from' too much alcohol or water ; and it should be free from any smell of ' 
 essential oils or of acetic ether. Provided ether be free from these defects, it matters I 
 very little which ether be used ; if the ordinary rectified ether be pure, it will be the 
 most economical. I shall treat this subject more fully when speaking of collodion. 
 
 Formic Acid is a fuming liquid with a pungent odour ; it reduces the oxides of ■ 
 gold, silver, and mercury to the metallic state, and is itself oxidized into carbonic acid, j 
 The alkaline formiates possess the same properties. It is rather difficult to determine I 
 the strength of the commercial formic acid, it being always more or less dilute. It 
 may be obtained in its full strength by distilling formiate of soda with sulphuric acid, ' 
 It inflames the skin in the same manner as the sting of an ant, from which it gets ■ 
 its name, being originally discovered in the red ant {formica rufa), but is now pre- 
 pared on a large scale by distilling starch with binoxide of manganese and sulphuric 
 acid. I 
 
 Gallic Acid.—This. is obtained from gall-nuts, of which the best kind come from i 
 Turkey, being called " Aleppo galls." The galls are exposed, after being powdered, 
 to the action of the air for a long time— five or six weeks. The mass must be kept 
 moist during the operation by the addition of a little water from time to time. Thus 
 the gallic acid is gradually formed from the tannic acid first produced, the gallic acid 
 crystallizes in long, needle-like, silky crystals, having an astringent taste, taking about 
 100 times their weight of cold water to dissolve them ; though, when boiling, three 
 times will be enough. They can be easily purified and separated from the mass by 
 boiling up in water, filtering the mixture while hot, and setting aside to cool ; the 
 gallic acid will crystallize on cooling. Gallic acid is but feebly acid, and is a very 
 important agent inreducing the silver in the Talbotype process. 
 
 Although not strictly in its alphabetical order, I shall now introduce a substance of 
 great importance, produced by the action of heat on the gallic acid. 
 
 Fyrogallic Acid.— At a. tem^^xnXurc of about 410" Fah., gallic acid is decomposed, I 
 and a white sublimate forms, which condenses in lamellar-crystals. Unlike gallic acid, j 
 the new substance is exceedingly soluble in water, and is of the greatest importance in 
 
PHOTOGRAPHIC CHEMICALS. 17 
 
 the development of collodiou negatives, from the avidity with which it absorbs oxygen. 
 Although termed an acid, it is perfectly neutral. 
 
 Gelatine. — This is an organic substance, obtained by boiling bones, horns, hoofs, 
 calves' feet, or similar animal refuse, into a jelly, which, in the mass, is termed " ske ;" 
 or, when dried and cut into slices, " glue." Isinglass is a similar substance, obtained 
 from the air-bladders of a species of sturgeon, and heretofore has been prepared chiefly 
 in Russia, 
 
 Gelatine softens and swells in cold water, but scarcely dissolves until the water be 
 heated ; on cooling, it forms a tremulous jelly. An ounce of water will dissolve, when 
 hot, about three grains without gelatinizing on cooling. It is somewhat analogous to 
 albumen, but does not form any compound with the oxide of silver, as the latter does ; 
 hence its different action. 
 
 Gold. — Chloride of Gold when in solution is a bright yellow colour when diluted, but 
 a deep red when concentrated. In the solid state it is a red deliquescent mass, without 
 any apparent regular formation ; and, although chemically neutral, it is acid to test- 
 paper. Its chief use in photography is the property it possesses of blackening the 
 shadows of a positive print, which it does to a wonderful extent. It is easily 
 decomposed by sulphurous acid, charcoal, and many of the vegetable acids ; also by 
 protosulphate and protonitrate of iron. The addition of ammonia to perchloi'ide of gold 
 forms the dangerous compound ^^fulminating gold." Hyposulphite of gold, or Sel d'Or, 
 is a double hyposulphite of gold and soda, and is formed by the reaction of hyposxJpbite 
 of soda on chloride of gold. It is very valuable in colouring positives on paper, and is 
 very easily decomposed. It will be more fully noticed under the head of " The Colour- 
 ing Bath." 
 
 Z Hydrochloric Acid is a volatile gas, exceedingly soluble in water, forming the hydro- 
 chloric or muriatic acid of commerce, which contains from thirty to forty per cent, of 
 gas. It is used in the formation of chloride of gold, in combination with nitric acid, 
 and /or producing the yeUow perchloride of iron. 
 
 Hydrosulphate of Ammonia is formed by passing sulphuretted hydrogen gas through 
 ammonia. It is used for the purpose of separating silver from hyposulphite of soda, 
 to darken negatives, and for testing solutions for silver, &c. 
 
 Hyposulphite of Soda, and the hyposulphates of gold and silver, wiUbe fully described 
 under the head, " The Colouring Bath." 
 
 Iodide of Fotassium. — This salt, as the reader already knows, and I think there can 
 be no objection to these facts being often repeated, is one of the salts chiefly used for 
 the production of iodide of silver. Iodide of potassium is generally mado by dissolving 
 iodine in solution of potash until it acquires a slightly brown colour. This solution 
 contains not only iodide of potassium, but iodate of potash, which may be got rid of by 
 evaporation and heating the residue to redness, when the iodate parts with its oxygen 
 and is converted into iodide of potassium. 
 
 Iodide of potassium has the following properties : — It forms white cubic and pris- 
 matic crystals, which should be hard, and scarcely, if at all, deliquescent ; it is soluble 
 in less than its own weight of water ; alcohol will dissolve from two to eight grains to 
 the drachm, according to its strength— the stronger the alcohol the less it will dissolve ; 
 ether will not dissolve it at all. Iodide of potassium as sold in the shops is nearly 
 always slightly impure from the presence of carbonate and sulphate of potash. 
 
 Litmus Paper. — This is of the greatest use to the photographer, as it enables him to 
 teU almost at once whether his solutions are acid or alkaline. It is made by soaking 
 
18 
 
 PHOTOGRAPHIC CHEMICALS. 
 
 porous paper in a solution of litmus, digested in hot water ; the paper when dry ia 
 quite blue, but in the presence of any acid becomes red, which changes back again to 
 blue when brought in contact with an alkali ; the red litmus paper is made by dipping 
 the blue paper in water containing one or two drops of sulphuric acid to the pint. 
 Litmus is a vegetable substance procured from various lichens which grow on rocks 
 near the sea. 
 
 Protosiilphate of Iron is the green copperas of commerce. It dissolves in about its 
 own weight of water, and when in solution it is used as a developer for positives on 
 glass ; it improves by use and exposure to the air, and is extensively used by photo- 
 graphers. 
 
 Protonitrate of Jrow.— This is another salt of iron, used for the development of 
 positives on glass; but has nothing to recommend it for use in preference to the 
 protosulphate. 
 
 Nitric Acid is much used in the preparation of pyroxylin e, for which purpose it 
 ought to be of the strongest possible description. It is often contaminated with 
 chlorine or sulphuric acid ; the presence of chlorine may be detected by diluting the 
 acid with an equal bulk of distilled tvater, and then adding a few drops of nitrate of 
 silver solution — a milkiness (chloride of silver in suspension) denotes the presence of 
 chlorine. Sulphm-ic acid may be detected by the addition of a little chloride of barium, 
 which, with the sulphuric acid, will form an insoluble precipitate of sulphate of baryta. 
 
 Nitrate of Potash, or saltpetre, is a very abundant natural product. It often con- 
 tains a large proportion of chloride of potassium, which may be detected by dissolving 
 a ^rnall portion, and adding a few drops of nitrate of silver ; when, if the chloride of 
 potassium be present, the never-failing chloride of silver will be formed. 
 
 Nitrate of Lead is made by dissolving the metal, or its oxide, in excess of niti-ic 
 acid diluted with two parts of water. It forms, with sulphuric acid or soluble sul- 
 phates, an insoluble sulphate of lead. 
 
 Silver Solutions. — Silver and its different solutions are all-important to the 
 photographist. 
 
 Nitrate of Silver. — Nitrate of silver, or, more correctly speaking, nitrate of the 
 oxide of silver, is made by dissolving pure silver in nitric acid (aqua fortis), which 
 parts with oxygen to the silver, forming an oxide of silver, and that in turn becomes 
 dissolved by another portion of the nitric acid. Nitrate of silver crystallizes in white 
 scales. When the solution has been boiled down nearly to dryness, the crystals have 
 a bitter metallic taste, and are very soluble in water, which will dissolve about its own 
 weight. The nitrate used for photographic purposes should be dissolved in distilled 
 water and re-ciystallized, so as to be deprived of all traces of the nitric acid. A 
 solution of nitrate of silver in distilled water is scarcely, if at all, affected by light, 
 unless it be brought in contact with organic matter, when it becomes speedily decom- 
 posed, and thus it becomes so useful in photography ; for if we wash a sheet of paper 
 over with a solution of the nitrate of silver, and place on its surface any opaque figure, 
 such as a coin, a leaf of a tree, or, what is better, a piece of black network, pressed to 
 the surface by a sheet of glass, we shall, by exposure to the rays of the sun for a 
 few minutes, obtain a correct copy of the figure ; but with reversed effects, the parts 
 uncovered being black, the parts covered remaining white. We thus form what we 
 call a negative picture ; for example— If we take three letters cut out of cardboard 
 (Fig. 1), and place them on a piece of paper washed with a solution of nitrate of 
 silver, press them close by means of a sheet of glass, and expose it to the sun's rays for 
 
SILVER SOLUTIONS. 
 
 19 
 
 five or six minutes, we shall obtain a picture similar to Fig. 2, and this also is the 
 process by which the portrait at the head of this Treatise was obtained by a very able 
 
 HXY 
 
 Fig. 1. Fig. 2. 
 
 experimentalist. The negative was obtained by the usual Talbotype process, and the 
 positive by placing the negative upon the prepared wood. 
 
 Now it is very obvious that, by removing the nitrate of silver from the white parts 
 of the paper, and thus protecting them from any further action of light, we can, by 
 repeating the experiment and using the negative just obtained, instead of the card- 
 board letters, obtain a perfect copy of the latter. This is the principle of photographic 
 Beproduction — Having once produced a negative, whether in the camera or by contact, 
 the number of copies that may be obtained from it are almost without limit. 
 
 Nitrate of silver, when melted in a crucible, and cast into moulds giving it a shape 
 resembling pieces of pipe stems, becomes the lunar caustic used in surgery ; but this is 
 scarcely pure enough for photographic purposes. It will be always better for the 
 amateur to procure the white re-crystallized nitrate. If the nitrate obtained from the 
 chemist or otherwise exhibit traces of nitric acid, the latter may be got rid of by heating 
 the crystals carefully to some few degrees above boiling water for a short time. This 
 must be done in a glass or porcelain vessel, as almost every metal has the property of 
 decomposing the nitrate. So loosely is it combined with the oxygen that even light, 
 as I have already shown, reduces it. If you take a solution of nitrate of silver, no 
 matter what is the strength, and immerse in it a clean strip of copper, brass, iron, 
 zinc, tin, or any other of the base metals, you will at once see that an action com- 
 mences, the silver being thrown down as a metallic powder, and the other metal 
 becomes dissolved ; in. other words, the silver has so slight an affinity (or liking) for 
 oxygen, that the slightest force is able to separate them. This gives us another reason 
 why silver is so very useful in photography. 
 
 tialts of Silver. — We can very easily obtain a great many salts of silver by double 
 decomposition. I shall explain the meaning of double decomposition by a simple ex- 
 periment, and one also that is essentially photographic : — Take nitrate of silver, 30 
 grains ; distilled, or boiled rain water, 1 ounce (when the nitrate is dissolved take in 
 another measure) ; common salt (chloride of sodium), 10 grains ; water, not necessary 
 to be distilled, 1 ounce. Now, if we pour the common salt solution into the silver 
 one, we obtain dnectly a white curdy precipitate, perfectly insoluble even in boiling 
 water or nitric acid. This is chloride of silver, or a mixture of metallic silver and 
 chlorine. The double decomposition takes place thus : — 
 
 Nitrate of silver 
 
 Common salt. 
 
 C Nitric acid 
 \ Silver — 
 
 5 Chlorine — 
 Sodium — 
 
 • Chloride of silver 
 
 Nitrate 
 of 
 
 Soda. 
 
 The chlorine, having a strong affinity for the silver, joins it; and t'le nitric acid being 
 
20 
 
 SILVER SOLUTIONS. 
 
 set free, very good-humouredly goes over to the sodium. "We thus obtain one of the 
 most important salts used in photographic printing. Expose the white powder to the 
 light after washing it several times in fresh water, an operation easily performed 
 because of its insolubility ; and you will observe that it darkens all over, and presently 
 becomes black. But do not for a moment suppose that it has blackened all through. 
 No ; the smallest possible quantity of the surface only has been acted on, the thinnest 
 possible layer only blackened ; remove the upper surface in the slightest degree, and 
 you will find the part underneath perfectly white. Bear this fact in mind, as I shall 
 have to refer to it more fully on another occasion. 
 
 Iodide of Silver. — This is produced in a similar way to the cbloride, with the ex- 
 ception that we here use iodide of potassium, which by double decomposition, as before, 
 produces — 
 
 Nitrate of silver . . | ™^ ZZI" ^--^ Mtrate 
 
 Iodide of silver. J> of 
 
 Iodide of potassium |p°tassWlI— -^^^ potassium. 
 
 When the two solutions are mixed in the following proportions: — Nitrate of silver, 
 20 grains ; distilled water, 1 ounce ;— iodide of potassium, 20 grains ; water, 1 ounce — 
 a copious yellow precipitate is produced, which, like the chloride, is insoluble in water 
 and nitric acid. 
 
 This salt, when perfectly pure, is not changed by the action of light ; but if any 
 excess of nitrate of silver be present, it becomes decomposed. The decomposition, in 
 this ease, has the property of proceeding onwards to blackness by the agency of the 
 numerous developing solutions that we use, and that after the decomposition has once 
 commenced. In this salt and the bromide of silver, being nearly alike in their nature, 
 we observe the base of all the solutions for papers used in the camera. * 
 
 Bromide of Silver. — This salt is produced in the same manner as the iodide, using 
 bromide of potassium instead of the iodide. If you use any bromide or iodide, such as 
 the iodide of tin, iron, zinc, mercury, cadmium, sodium, &c., you will obtain the same 
 result, the oxygen going to the metal, the iodide or bromine going to the silver. In 
 photographic experiments, however produced, the iodide of silver and the bromide of 
 silver are always the same when in the solid or crystalline state. 
 
 The iodide of potassium, and the bromide also, have the power of dissolving the 
 iodide or bromide of silver when added in sufiicient quantities, a property of which 
 we avail ourselves for the formation of iodized and brominized papers, to be explained 
 more fully hereafter. 
 
 Acetate of Silver. — The acetate of silver will be found very useful in correcting a 
 new nitrate of sUver bath for collodion negatives, and may be made thus : — Neutralize 
 one ounce of acetic acid by adding sufficient carbonate of soda, and add it to one ounce 
 of distilled water, containing about 100 grains of nitrate of silver in solution. The 
 action is thus represented : — 
 
 Nitrate of ( Nitric acid - 
 
 silver solution. I Silver \- ^^■"-^...^^^ Nitrate 
 
 "^Acetate of silver of 
 
 Neutralized /Acetic acid ^ ^-"'^ soda. 
 
 acetic acid. \ Soda ■ 
 
 Hyposulphite of Silver. — This salt is formed by the action of hyposulphite of soda 
 
RECOVERING SILVER IN SOLUTIONS. 
 
 21 
 
 on nitrate of chloride of sUver, and will be more fully treated under tlie head of 
 Colouring Baths. It is very soluble in an excess of hyposulphite of soda, and its chief 
 photographic use is in connection with that salt, to impart those rich brown or purple 
 tints so much admired in finished photographs. 
 
 Ammonia Nitrate of Silver. — This is one of the most useful and important compound 
 salts of silver ; it is extensively used in printing, and may be made thus :— Dissolve in 
 one ounce" of distilled water fifty grains of nitrate of silver, and then add, drop by drop, 
 liquor ammonia until the brown precipitate first formed is gradually redissolved ; 
 when filtered it should be put away in a dark bottle and kept from the light. 
 
 On the Means of Recovering Silver from Old Solutions. — This may be done in various 
 ways. One of the most simple of the many is to insert a strip of clean zinc or copper 
 in the solution of silver, and let it remain until the silver is all thrown down ; but 
 old hyposulphite of soda solution, containing silver, must be treated in a diiferent 
 manner. 
 
 To recover silver from the latter, it will be necessary to pass a stream of sul- 
 phuretted hydrogen through the solution, or to add a sufiicient quantity of hydrosul- 
 phuret of ammonia to precipitate the silver, which will be thrown down as a 
 sulphuret in either case. The first is the most troublesome, but by far the cheapest 
 method. 
 
 To make and pass the sulphuretted hydrogen gas you will proceed thus :— Get a 
 large bottle, to which fit a piece of gutta pcrcha tube bent thus (Fig. 3), which 
 
 miist fit in the neck or mouth of the 
 bottle air tight, then put into the bottle 
 about a quarter of a pound of sulphuret 
 of iron, and about three-quarters of the 
 contents of the bottle of water, to which 
 has been added an eighth part of sul- 
 phuric acid (oil of vitriol), place the 
 gutta-percha tube in its place, and the 
 other end must go in the solution of 
 hyposulphite of soda and silver, touch- 
 ing the bottom of the vessel ; the sul- 
 Fig. 3. phuretted hydrogen escaping up through 
 
 the liquid decomposes its parts, and throws down the silver, the latter, as I have said, 
 becoming a sulphuret of silver. A represents the bottle, B the vessel containing the 
 hyposulphite-solution, C C the gutta-percha tube, D the solution of water and sul- 
 phuric acid, E the solution of hyposulphite of soda and silver, F the bubbles of sulphu- 
 retted hydrogen, and G the sulphuret of iron. The action must be continued until all the 
 silver is thrown down, which may be ascertained by adding a little hydrosulphuret of 
 ammonia, or by agitating the solution and smelling it ; in the former case, if any silver 
 remain there will be a black precipitate, and, in the latter, if the smell of the sulphu- 
 retted hydrogen be very strong from the liquid, it is a proof that all the silver has been 
 thrown down. It may be as well to state hero that the fumes, or gas, of the sulphu- 
 retted hydrogen is very poisonous when in a concentrated state, and, therefore, the 
 operation should be carried on out of doors. The hyposulphite solution should be 
 frequently stirred. 
 
 "When all the silver is thrown down, it must he collected and washed on a filter by 
 pouring water through it until the latter passes through quite clear, and will not give 
 
22 
 
 UECOVERING SILVER IN SOLUTIONS. 
 
 a precipitate with a few drops of nitrate of silver solution ; the black mass remaining 
 may now be boiled up with nitric acid one part, water two ; when all the red fumes 
 cease to be evolved, the solution is to be dilated with water and filtered to get rid of 
 any insoluble matter, which principally consists of sulphur with perhaps a small 
 portion of chloride of silver and sulphuret ; if the nitric acid contains any trace of 
 chlorine, or if the insoluble portion be large in quantity, you may heat it pretty strongly ^ 
 on a piece of iron plate to get rid of the sulphur, and dissolve the remaining "portion in : 
 a strong solution of hyposulphite of soda, and add it to the colouring hypo-bath. The 
 solution that has been passed through the fiHer will be a solution of silver in nitric 
 acid, or nitrate of silver, but will not be pure enough for photographic use ; it will be 
 better to convert it into chloride of silver by adding a solution of common salt, and : 
 washing the precipitate two or three times. The chloride, or sulphuret of silver may ; 
 be converted to metallic silver by fusing it in a crucible with twice its weight of car-- ' 
 bonate of potash, or a mixture of carbonate of potash and soda. When the heat has i 
 been carried on sufficiently, the whole flux may be poured out of the crucible, or | 
 the crucible and its contents may be allowed to cool, when the silver, a beautifully 
 bright button, will be found at the bottom. 
 
 On the Means of Converting Chloride into Nitrate of Silver. — As we already know 
 that nitric acid, even when boiling, will not act on the chloride of silver, we must go a 
 little round to bring the two together, and the best method of obtaining that important 
 result will be as follows :— After well washing the chloride, pour it out into a flat dish, 
 in which place a bar of metallic zinc in contact with the chloride, a small quantity of 
 oil of vitriol diluted with four parts of water is then added, until a slight effervescence 
 is seen to take place. The dish must then be set aside for two or three days, and must 
 not be disturbed in any manner. The reduction commences with the chloride imme- 
 diately in contact with the zinc, and afterwards radiates in all directions. When the ; 
 whole mass has become of a gray colour, the bar of zinc is to be carefully removed and 
 the adhering silver washed off with a small stream of water. In order to insure the i 
 purity of the silver, a fresh addition of oil of vitriol must be made after the zinc has 
 been removed, in order to dissolve any fragments of metallic zinc which may have 
 become detached by accident, and after the digestion has been continued for a few hours, 
 the gray powder is to be washed several times with water, until the water which runs 
 off will not give a precipitate with carbonate of soda ; it may then be converted into 
 nitrate of silver by boiling with nitric acid one part, water two, and evaporated to 
 crystals. The above formula is not so expensive or troublesome as the fusing with i 
 carbonate of potash. Bear in mind, that you must pour the oil of vitriol into the ' 
 water, and the vessel in which they are mixed must be such as will stand heat. . ; 
 
 Oxide of Silver is an olive brown powder obtained by adding potash to nitrate of 
 silver. It is soluble in hyposulphite of soda, cyanide of potassium, ammonia, and 
 nitrate of ammonia. 
 
 Sulphuric Acid, or oil of vitriol, is an acid possessing intense chemical powers, and 
 readily displaces the greater number of acids from their salts ; it clears organic sub- 
 stances by depriving them of water, and converts alcohol into ether by the same 
 means, and is one of the elements used for the production of gun-cotton. Its action in 
 the latter case will be more fully explained further on. 
 
 Tetrathionic Acid.— {See " Colouring Bath.") 
 
OPTICS OF PHOTOGRAPHY. 
 
 23 
 
 ON THE OPTICS OF PHOTOGRAPHY. 
 
 Action of Light.— Having, for the present, finished the necessary remarks on 
 Photographic Chemiatry, I shall proceed to explain the optical and actinical (or 
 chemical decomposing ray power) action of light on surfaces prepared photogra- 
 phically ; and I may remark, en passant, that, but for our knowledge of the chemical 
 action of light through glass, all our chemical knowledge of the theory of photo- 
 graphy would be perfectly useless ; we could no more obtain a perfect copy of a 
 tree, a house, or a hay-stack, than we could fly — this being another proof, if such be 
 necessary, of how dependent one branch of science is on another. 
 
 Light, the agent by which we are enabled to depict nature or art with an accuracy 
 that bafiles the most experienced artist, is derived from the sun. True it is that there 
 are other sources of light ; but at present we have nothing to do with them — we 
 must confine our attention to solar light, and the chemical change it produces. 
 This glorious light, which 
 
 " "Was given to quicken slumbering nature, 
 And lead the seasons' slow vicissitudes 
 Over the fertile breast of mother earth," 
 
 now pours forth its beams, and in a sense not dreamed of by the poet, dispenses 
 
 " Life and light on every side ; 
 Brightening the mountain cataract, dimly spied." 
 
 And yet how little do we know of the nature of a sunbeam. A solar beam of light 
 is a bundle of rays, a ray being the smallest portion of light which can emanate 
 from a luminous body. Each of these rays possesses 
 distinctive characters, both as regards their chemical 
 functions and colours. Sir Isaac Newton proved that 
 the white light emitted from the sun is not so simple 
 as it appears, but is composed of vivid coloiirs and 
 tints which we may prove to our own satisfaction, 
 by performing the beautiful experiment called " New- 
 ton's Analysis of Light," being a prism (Fig. 4), 
 or triangular mass of glass, which is so contrived 
 that it may be adjusted to any angle, or placed in 
 any required position. The shutters of the room 
 being closed, we may admit a ray of light either by 
 boring a hole in the shutters or separating them a 
 little. 
 
 The ray of light A E (Fig. 4), being admitted into 
 the darkened room by means of a hole A in the shutter. It will be seen that the space 
 between the shutter and the spectator is traversed by the sunbeam or ray of light, which 
 appears to cause little particles of dust to dance in the atmosphere of the room. This 
 appearance, however is owing to the illuminating power of the sunbeam contrasting with 
 the other darkened or non-illuminated space in the room, which renders the small 
 particles of dust floating in the air visible. As soon as the prism B C (Fig. 4) is placed 
 in the path of the sunbeam, so as to allow it to fall on one of its angles B, the ray 
 will be refracted, or bent out of its course, so as to pass towards the back of the 
 prism (as in the line D), and not in the same line A E that it would otherwise have 
 
 D 
 
 Fig. 4. 
 
24 
 
 NATURE OF LIGHT. 
 
 done, had not tlie prism been interposed. Another eifect also takes place : an. elon- 
 gated delicately-coloured image is formed upon the wall D E ; and if you stand at 
 a short distance from the prism you wiU see that these colours are spread out in a 
 triangular form, the base of which is on the wall, and the apex, or point of origin, at 
 the back C of the prism, Eemove the prism, and it is seen that the splendid dis- 
 play of colours upon the wall has disappeared, and a round spot of white ligbt E is 
 seen below the place occupied by the solar spectrum. 
 
 Th e coloured image upon the wall is called the prismatic or 
 solar spectrum, which, according to Sir Isaac Newton, is composed 
 of seven different colours (Fig. 5). The colour at the lower portion 
 of the image, or that nearest to the round white spot E on the 
 wall when the prism was removed is of a red colour, and the one 
 at the other end is of a violet colour ; the whole intermediate parts 
 being occupied by five other colours, and the whole arranged accord- 
 ing to the table exhibited below, the proportion of tfach colour 
 having been measured by Fraunhofer with the greatest care, with 
 the results placed opposite to each corresponding with the 360 
 degrees of a circle, the red ray being the least, and the violet the 
 most refracted of this chromatic image :— 
 Top. 
 
 Violet 
 
 Indigo 
 
 Blue 
 
 Green 
 
 Yellow 
 
 Red 
 Bottom. 
 
 109 
 47 
 48 
 46 
 27 
 27 
 56 
 
 360 
 
 Since Newton's time, various experiments have been instituted and other rays 
 detected ; for instance, a crimson or extreme red ray has been discovered below the red 
 ray, by examining the solar spectrum through a deep blue glass ; and Sir John Herschel 
 observed a lavender beyond the violet ray, by throwing the spectrum upon a piece of 
 yellow paper. Mr. Stokes has also proved the existence of an extra spectral ray far 
 beyond the violet ; but, as we have remarked before, our 
 consideration of light does not extend beyond its practical 
 use to photographers. 
 
 Sir Isaac Newton was of opinion that white light was 
 composed of seven primary rays, each possessed of a 
 certain degree of refrangibility, or capability of being 
 turned out of its natural course ; and he also considered 
 that the colour of a ray indicated its angle of refraction. 
 Sir David Brewster has demonstrated that the seven 
 primary colours, as Sir Isaac Newton called the rays of 
 the solar spectrum, are not primary, but that only three ^• 
 of them are so— viz., blue, yellow, and red ; the rest are compounds of the three 
 primary colours, which form the spectrum by overlapping each other ; and these are 
 explained in the annexed diagram (Fig. 6). 
 
THE SOLAR SPECTRUM. £5 
 
 Such are a few of the phenomena relating to light regarded hy the philosphers : its 
 application to photography are as follows :— 
 
 Of the real nature cf the rays, which form the sunbeam, little is known. The 
 theory of Newton consisted in supposing the ray of light was produced by the emission 
 of minute particles of matter travelling at an enormous velocity from a luminous body, 
 and, when these minute particles impinged on any body, they were either thrown back, 
 reflected, or absorbed, according to the surface on which they fell. 
 
 These particles entering the human eye, produce the sensation of light on the retina 
 which sensation is conveyed through the optic nerve to the brain. ' 
 
 The theory of the celebrated Huygens pre-supposes that the space beyond our 
 atmosphere, and the interstices between the molecules, or ultimate atoms of all bodies 
 are filled with an imponderable ether, and that Ught is produced by the oscillation or 
 vibration of this ether, which undulation is set up by some self-luminous body-of 
 course, the sun. 
 
 Another theory may here be mentioned, although but very slenderly supported— 
 namely, that set forth by Oersted, who considered that light was the effect of a rapid 
 succession of minute electrical discharges taking place between a luminous body and 
 the eye. Leaving these theories, however, to the philosopher, let us see how they 
 afltect the photographer. 
 
 The sunbeam-the ray of white light-contains powers within it of which the 
 earlier phUosophers had but a faint idea; besides its accompanying heat, there is a 
 principle associated intimately with it, which has the power of decomposing and of 
 determining the recomposition of chemical compounds. This principle has been already 
 alluded to-it IS " Actinism," and is as perfectly distinct in the nature of its properties, 
 from light, as light is from the principle of heat, with which it is also closely connected 
 
 Actinism may then be considered [as the fundamental principle on which photo- 
 graphy is based ; and we would wish, before entering on a description of the various 
 methods of obtainmg sun pictures, to draw a broad distinction between light and 
 actinism, more especially as many apparent difficulties present themselves, and seem 
 almost insurmountable until tried by the principle we are about to lay down. 
 
 From what has been said, it will be supposed that what we consider light exerts a 
 decided influence over certain chemical salts having a metallic base ; but it now 
 becomes necessary to show that light does no such thing-it is not light, but a compo- 
 nant part of light which exerts this influence. In order to explain this seeming 
 anomaly, let us consider the subject a little more carefully. A ray of white light 
 consists of the three primitive colours-blue, yellow, and red ; and their combinations 
 forming the following :-Violet, indigo, blae, green, yellow, orange, red; 
 
 these colours and shades being produced by the decomposition of white light by means 
 of a prism. Of these shades, the violet has the greatest reducing or decomposing 
 power. . By this, I mean that the violet part of the decomposed portion of light exerts 
 the most powerful influences on the unstable metaDic salts, reducing them to their 
 bases. ^ This action is the actinic of the photographers ; and the study of the 
 action Itself may be properly designated as actinic-chemistry. Every beam of lio-ht 
 which we receive from the sun is composed of the three primary colours ; these blencHng 
 one with the other, form shades or tnixtures of the three ; thus we get four shades 
 independent of the primitive colours, viz., indigo from blue and violet, green from 
 blue and yellow, orange from yellow and red. 
 
 It may be asked, where does the violet come from It is easily accounted for 
 
26 
 
 ACTINIC CHEMISTRY. 
 
 l^s-if we decompose a Single ray of white ligM, get the following component 
 parts by means of the prism : — 
 
 Violet. 
 
 Fig. 7, 
 
 Now, if we decompose another ray, just below the above, we get the same parts 
 reproduced, thus-violet comes first, or next the red, and is evidently produced by the 
 mixture of red and blue (the next primary colour), or, more properly speaking, by the 
 mixture of a deep red, which slightly extends lower than the red of the visual spec- 
 trum, with the indigo of the ray immediately above the under one ; now this ray, or 
 portion of a ray, has the power of more perfectly decomposing the unstable salts of 
 silver than any other of the series ; and, therefore, has acquired the term actinic ray. 
 
 The actinic power, and the light-giving power, may be more fully explained m the 
 following diagram : — 
 
 ce of extra spectral blue, ob- 
 tained by a solution of quinine, 
 and some of the mineral oils. 
 
 5 Lavender. 
 
 Actinism, or chemical 
 radiant power. 
 
 Light. C 
 
 Fig. 8. 
 
 In the above diagram, the greatest actinic, or chemical action, is shown opposite 
 
REFRACTIVE POWER OF DIFFERENT SUBSTANCES. 
 
 27 
 
 the violet ray E, and the least opposite the mixture of the yellow and orange C ; 
 below the red at A the actinic power becomes active again, because the extreme 
 or deep red is about to pass into the violet with the indigo of the blue in the ray next 
 below ; at the same time, the part of the ray giving the brightest light is opposite the 
 yellow and orange light C. We observe, also, that the point giving the greatest heat 
 is just below the red D ; but with that we have nothing to do. "We thus ascertain that 
 the chemical, or photographic action is confined, as already stated, to only a portion of 
 the visu.il ray of light. 
 
 To speak more plainly, certain colours or shades act more powerfully than others, 
 which can be proved by the following simple experiment : — Prepare a sheet of paper 
 thus — float it on a weak solution of common salt, say ten grains to the ounce, and 
 when dry, float it again on a solution of nitrate of silver, say thirty grains to the ounce- 
 This must be done and the sheet dried while it is protected from white light. When 
 dry, place on it three pieces of coloured glass, viz., red, yellow, and blue ; expose the 
 whole to the sun's rays for a short lime, when it will be found that the paper has 
 become rapidly discoloured under the blue glass, but remains unchanged under the red 
 and yellow, although the last is by far the most transparent. This property of red or 
 yellow colours of intercepting the actinic rays of light, we make the greatest use of in 
 photography ; but this subject will be treated of more fully under the head of "The 
 Dark Chamber." 
 
 A ray of light is always more or less refracted or bent, depending on the density of 
 the medium or substance through which it passes. The refractive power of some 
 substances is immense, while that of others is very trifling, as the following table of 
 some of the most important will show : — 
 
 Air . . 
 Water. 
 Alcohol 
 Oil of cloves 
 Crown fflass 
 
 1-000294 
 
 1-336 
 
 1-372 
 
 1-535 
 
 1-534 
 
 Plate glass .... 1-542 
 
 Flint glass .... 1-830 
 
 Do. containing much lead . . 2-028 
 
 Diamond 2-439 
 
 A ray of light, passing through a vacuum, progresses in a perfectly straight line, 
 and were it possible, under such conditions, to look at a brilliantly illuminated point, we 
 should see it in its true position, viz., the numerous rays coming undisturbed directly 
 to the eye. But all matter, however 
 attenuated it may be, has the pro- 
 perty of refracting or bending the 
 ray of light ; consequently we do not 
 see the stars in their true position, 
 owing to the refractive power of the 
 xtmosphere. 
 
 The law of refraction can be 
 sasily and decidedly demonstrated 
 thus — take a basin, in the bottom of 
 which place half-a-crown, or any other small bright substance, and removing a sufficient 
 distance from it to lose sight of the coin, it will appear as in Fig. 9 ; A representing 
 aalf-a-crown, and B the eye of the observer. The balf-a-crown, of course, is invisible. 
 Then.. request some person to pour water into the basin, taking care to keep your eye 
 
28 
 
 REFRACTIVE POWER OF DIFFERENT LIQUIDS. 
 
 fixed on the same spot during the operation. The half-a-crown begins to appear, and 
 gradually becomes more visible until it comes entirely into view. This fact is owing 
 to the ray of sight (or light) being refracted, or beaten back, as in Fig. 10 ; C 
 
 representing the water, and B A the 
 ray of light refracted. 
 
 The explanation of this pheno- 
 menon is, that the ray of light pro. 
 ducing vision in the eye is bent, on 
 emerging from the water, and has 
 all the effect of conveying our sight 
 round a corner. 
 
 jjjp. The refractive power of water is also 
 
 observable when we thrust a straight 
 stick or instrument into it, on aiming at any object. We see that the stick seems to be bent, 
 and fails in reaching the point which 
 we desired it should reach. On this 
 account, the aim by a person not directly 
 over a fish, must be made at a point 
 apparently below it, otherwise the 
 weapon will miss by flying too high. 
 Persons who spear salmon in rivers 
 require to calculate upon this refractive 
 power in taking their aim. 
 
 Another illustration of refraction is 
 to allow a sunbeam S (Fig. 11), passing 
 through a hole in the window- shutter 
 of a dark room, to fall upon the surface 
 of a fluid contained in a glass vessel, 
 C C ; instead of proceeding onward to 
 D, it will be found to alter its course 
 at the surface of the fluid, and pass along the line to D. Every substance has different 
 refractive powers in virtue of its t 
 physical constitution ; but a ray 
 of light incident perpendicularly \^ 
 onarefracting meditim, as the ray 
 E (Fig. 11), suffers no refraction. 
 
 Again, if we float, one upon 
 the other, fluids, B, C, D, having 
 different powers of refraction, 
 we shall then see the relative 
 phenomena exhibited by the 
 bending of the ray B B, as it 
 passes through these difi'erent 
 media, as represented in Fig. 12. 
 
 The mode of the refraction 
 depends on the comparative 
 density or rarity of the respec- Fig. 12. 
 
 tive media. If the medium which the rays enter be denser, they move through 
 
 Fitr. 11. 
 
VARIOUS-SHAPED LENSES. 
 
 29 
 
 it in a direction nearer to tlie perpendicular drawn to its surface. On the contrary, 
 when light passes out of a denser into a rarer mediuro, it moves in a direction farthei 
 from the perpendicular. This refraction is greater or less— that is, the rays are more 
 or less bent, or turned aside from their course— as the second medium through which 
 ttey pass is more or less dense than the first. To prove this in a satisfactory manner, 
 and at the risk of repetition, we make the following experiment .-—Take an upright 
 empty vessel into a darkened room, which admits but a single beam of light obliquely 
 through a hole in a window shutter. Let the empty vessel stand on the floor, a few 
 feet in advance of the window which admits the light, and let it be so arranged that, 
 as the beam of light descends towards the floor, it just passes over the top of the side of 
 the vessel next the window, and strikes the bottom on the side farthest from the window. 
 Let the spot where it falls be marked. Now, on filling the vessel with water, the 
 ray, instead of striking the original spot, will fall considerably nearer the side towards 
 the window. And if we add a quantity of salt to the vessel of water, so as to form 
 a dense solution, the point where the ray strikes the bottom will move still nearer to 
 the window. In hke manner, if we draw oS the salt water, and supply its place with 
 alcohol, the beam of light will be still more highly refracted ; and oil will refract yet 
 more than alcohol. 
 
 Our next care is to study the practical appUcation of these laws of refraction to the 
 manufacture of "lenses." By lens is meant what is commonly called a magnifying 
 glass, which may be composed of any transparent substance ; but in its application to 
 photography it is generally made of glass as pure and colourless as can be procured, 
 therefore we shall consider that a lens is a glass ground into such a form as to collect 
 or disperse the rays of light which pass through it. These are of different shapes, 
 and thence receive different names. The following figures individually represent 
 sections of the variously-shaped lenses and other glasses used in optics. A is a trian- 
 
 A B C D E F C H ! 
 
 Fig-. 13. 
 
 gular stalk of pure glass, of which we have here a cross sectional or end view, and 
 which is called a prism. Each side of the prism is smooth. B is a section of a pic-cc 
 of plane glass, with sides parallel to each other. C is a sphere or ball of glass, and 
 consequently is convex on all parts of its surface. D is a piece of glass convex or 
 bulging on its two sides, and is called a double convex lens. It is this kind of lens 
 which is used for magnifying objects, in spectacles, telescopes, and other instruments. 
 E is a plano-convex lens, flat on one side and convex on the other. F is a double 
 concave lens, or glass hollowed on each side. G is a plano-concave lens, or planed on 
 one side and concave on the other. H is a meniscus, or lens convex on one side and 
 concave on the other, both surfaces meeting, and of which we have an example in 
 watch-glasses. I is an example of the concavo-convex lens, in which the surfaces 
 disagree, or do not meet when continued. In all these lenses an imaginary line, re- 
 
30 
 
 CONSTRUCTION OF LENSES. 
 
 Fig. 14. 
 
 presented by M G N, and passing througk the centres of the surfaces, is called the 
 axis. Thus, the line said to pass through the centre of any lens, in a direction perpen- 
 dicular to its surface, is called its axis. 
 
 The design in forming lenses is to procure a medium through which the rays of 
 light from any object may pass, and converge to a corresponding po^nt beyond. The 
 manner in which the rays proceed through the glass, and then centre in a focal point, 
 will depend on the form of the lens, its capacity for refraction, and the distance of 
 the object. 
 
 If we take a piece of glass, flat on one side and cut into different faces on the other, 
 
 and then look through it from the 
 flat side at any object — for instance, 
 a pea — we shall see as many peas as 
 there are faces receiving rays from 
 the single pea. We may exemplify 
 this principle of multiplication by 
 the annexed figure (Fig. 14), in 
 which A B is a lens flat on one side, 
 and cut into three faces on the other, 
 G H. Y is the eye of the spectator, 
 and P the pea to be looked at. The 
 eye receives a pencil of rays direct 
 through the lens at I, and sees the 
 object without refraction. A pencil 
 also proceeds from P to face G A, and another pencil proceeds from C to the face H B, 
 and in both oases the rays are bent and refracted to the eye. This eye, however, does 
 noc recognise the path of either of these oblique rays, but perceives the image of a pea 
 at D and at E ; and thus three peas seem to be seen in place of only one. 
 
 In smoothly ground lenses, in M'hich there are no distinct faces to multiply the 
 images of an object, the rays bend, as we have said, so as to meet in a corresponding 
 point beyond them. A lens may consist of a perfect globe of glass, or globe filled with 
 pure water, in which case the refractive power will be considerable. A double convex 
 lens, which is the more common kind, may be viewed as a portion cut out of the side 
 of a sphere, as seen in Fig. 15. Here, as in all cases of convexity, the focus of the 
 parallel rays passing through the 
 lens is at F, which is the centre of 
 the sphere, of which the farther, or 
 anterior side, is a portion, or a point 
 at half the diameter of the sphere 
 from it. (H)df the diameter is tech- 
 nically called the radius.) Should 
 we take a plano-convex] lens, the 
 focal point would be considerably different 
 kind of lens, which evidently possesses only half the refractive power of the double 
 convex glass. Here the parallel rays, falling on the convex side of the lens, are seen to 
 converge at the distance of the whole diameter of the sphere. Thus, the focal point 
 at which the rays of light fall is always regulated by the degree of cui-vature of the 
 lens. I shall illustrate this by various diagrams, and ask the reader's careful attention, 
 for the subject is difficult, and cannot be comprehended by a superficial glance. 
 
 Fig. 15. 
 
 Fig. 16. 
 
 In Fig. 16 we have an example of this 
 
POWER OF LENSES. 
 
 31 
 
 We take a double convex lens, represented by A B C (Fig. 17), the axis of whicli is 
 
 the line G' C D'. The ray D' G', being 
 straight through the centre, suffers no re- 
 fraction ; but the rays i) A and D" B are 
 refracted, so as to meet at the focal point 
 G'. We now observe that the parallel rays 
 E A, E' C, and E" B, and also F A, F' C, 
 and F" B, falling obliquely on the lens, 
 will, in a similar manner, be refracted, and 
 have their foci at G and G'', at the same 
 distance from the lens. Those lines which 
 pass through the centre, as £' C G" and 
 F' C G, do not alter their direction, not 
 being refracted. Thus, in whatever way parallel rays pass through a lens, we have a 
 focal point beyond it, be it straight forward or in an oblique direction. 
 
 The distance at which the rays meet beyond the lens is exemplified in the next 
 diagram (Fig. 18). Dr. Arnott, in his Treatise on Physics, says—" Eays faUing from A 
 
 on a comparatively flat or weak lens at L, might meet only at D, or even farther oif, 
 while, with a stronger or more convex lens, they might meet at G or at B. A lens 
 weaker still might only destroy the divergence of the rays, without being able to give 
 them any convergence, or to bend them eaough to bring them to a point at all, and 
 then they would proceed all parallel to each other, as seen at E and F ; and if the lens 
 were yet weaker, it might only destroy a part of the divergence, causing the rays from 
 A to go to G and H, after passing through, instead of to, I and H, in their original 
 direction. 
 
 " In an analogous manner, light coming to the lens in the contrary direction from 
 BCD, (fee, might, according to the strength of the lens, be all made to come to a focus 
 at A or at L, or in some more distant point ; or the rays might become parallel, as M and 
 N, and therefore never come to a focus, or they might remain divergent. 
 
 " It may be observed in the annexed figure, that the farther an object is from the 
 lens, the less divergent are the rays darting from it towards the lens, or the more 
 nearly do they approach to being parallel. If the distance of the radiant point be very 
 great, they really are so nearly parallel that a very nice test is required to detect the 
 non-accordance. Rays, for instance, coming to the earth from the sun, do not diverge the 
 millionth of an inch in a thousand miles. Hence, when we wish to make experiments 
 with parallel rays, we take those of the sun. 
 
32 
 
 QUALITIES OF A CONVEX LENS. 
 
 " Any two points so situated on the opposite sides of a lens, as that when eithei- 
 becomes the radiant point of light, the other is the focus of such light, are called con- 
 jugate foci. An object and its image formed by a lens, must always be in conjugate 
 foci ; and when the one is nearer the lens, the other will be in a certain proportion 
 more distant. 
 
 " What is called the principal focus of a lens, and by the distance of which from the 
 glass we compare or classify lenses among themselves, is the point at which the sun's 
 rays — that is, parallel rays — are made to meet ; and thus, by holding the glass in the 
 sun, and noting at what distance behind it the little luminous spot or image of the sun 
 is formed, we can ascertain the solar focus of a glass, as at A for the rays E and F." 
 
 From the preceding explanations it will be understood, that when an object is 
 placed at any distance from a lens, an image of it will be formed in the corresponding- 
 conjugate focus ; but to see this image distinctly, the eye must generally be placed at 
 least six inches behind it, that is, farther from the lens. When, however, the object 
 is placed in the principal focus, the rays are refracted parallel, and the image in this 
 case is distinct when seen at any distance. But the most remarkable quality of a 
 double convex lens remains to be noticed ; we allude to its magnifying power. This 
 quality is entirely a result of the refractive power of ^the glass ; embraced within the 
 
 sphere of the rays from the 
 
 A 
 
 lens, the object is apparently 
 expanded in size, and seems 
 brought nearer to the eye. This 
 may be elucidated, for small 
 objects seen near, by a refer- 
 ence to the diagram (Fig. 19.) 
 
 Let E be the eye, and M N 
 the diameter of its pupil, E W 
 a small object placed at the 
 least distance of distinct vision 
 (about six inches from the eye 
 for small objects), and let R W 
 be its apparent size when seen by the unaided eye. If a convex lens A B is 
 now interposed between the eye and the object, so that the object E W shall be in 
 the principal focus of the lens, an enlarged image R' W of the arrow will then be 
 seen, its extremities R' W' lying in the directions E A, E B. The directions of these 
 rays are determined thus :— From R and W draw the central rays R C P, W C Q, 
 through the centre C of the lens ; then the rays of the conical pencil, proceeding from 
 the point R to every point of the nearer surface of the lens, are refracted in such a 
 manner by the lens, that they all emerge in directions parallel to the central ray 
 R C P ; but of the whole refracted pencil only a small portion enters the eye, namely, 
 the pencil A M N A, limited by the size of the pupil M N ; and the head A of the arrow, 
 whence this pencil proceeds, appears to lie in the direction of the pencil E A R' at R'. 
 It is shown exactly in the same manner, that the point W will appear in the direction 
 E B W at W. The enlarged image of the small arrow R W is therefore R' W'. The 
 proportion in which the image is enlarged will be easily ascertained thus : — The 
 triangles E R' W', C R W, are similar, aud therefore the ratio of R' W' to R W, is that 
 of E R' to C R, or of E M to C M ; that is, as the least distance E M of distinct vision, 
 to the focal length C M of the lens. If, therefore, the least distance of distinct vision 
 
MAGNIFYING POWER EXPLAINED. 33 
 
 be divided by the focal length of the lens, the quotient will be its magnifying power. 
 If E M be reckoned 6 inches for small objects, and if the focal length C M be 2 inches • 
 then, since 6, divided by 2, gives 3 for a quotient, the magnifying power is 3 times! 
 If C M were one quarter of an inch, then 6, divided by J, gives 24 for a quotient, and 
 the magnifying power would in this case be 24 times. 
 
 A more simple explanation may be attempted as follows .—Turn to Fig 14, repre- 
 senting the lens with three faces on one side and flat on the other. There it is observed 
 that the vision travels in the direction of the ray from the object, as it passes through 
 the glass, and therefore sees an appearance of three objects. JSTow, in the ^bove case of 
 a magnifying lens, the vision in the same manner travels from the eye at E in the 
 direction of the angle of refraction ; it goes on to R' and W, and thus the actual object 
 being drawn out, as it were, to meet these points of vision, or seemingly expanded* by 
 the bent rays, we of necessity see an apparently larger object. If the glass were cut 
 in faces, instead of being smooth, the object would not appear drawn out, but would be 
 multiplied in as many points as there are faces. 
 
 The inversion of the image by a lens may be illustrated by the diagram, (Fig. 20.) 
 A B C is an arrow, with the point uppermost, placed beyond the focus at F, of a 
 
 double convex glass d e f. In virtue of 
 the refractive power of the lens, the rays 
 which proceed at A meet at Z, and form an 
 image of the arrow-point inverted; while 
 the rays from C meet at X, and form a 
 similarly inverted image of the feather part 
 of the arrow. The rays proceeding from B 
 unite at 5. Here, only rays from A, B, and 
 C are represented, for the sake of clearness ; 
 but, in point of fact, rays from all parts 
 Fig. 20. of tlie object proceed through the lens, and 
 
 hence an entire image is formed in an 
 inverted position. Should the object A B C be brought nearer the lens, the image 
 wiU be removed to a greater distance, because then the rays are rendered more 
 divergent, and cannot so soon be collected into corresponding points beyond. To 
 procure a distinct image, the object must be removed farther than the focal point F from 
 the glass. In this exemplification, the object seems to be diminished ; but if we 
 make the small arrow the object, the larger one will be the image of it magnified. 
 
 In order to explain the power of lenses in magnifying distant objects, and bringing 
 them near us, let us suppose an object placed at one hundred feet distance from the 
 eye of a spectator. Let us place a convex glass of twenty-five feet focal distance half 
 way between the object and the eye ; then, as has been previously observed, an in- 
 verted image of the object, and of the same size, will be formed fifty feet behind the 
 lens. If this picture is looked at six or eight inches behind it, it will be very distinctly 
 seen, afld nearly as well as if the object itself had been brought to within six or eight 
 inches of the eye of the spectator. If, however, instead of a lens of twenty-five feet 
 focal length, a lens of a shorter focus is made use of, and so situated with respect to 
 the eye and the object that its conjugate foci are at the distance of twenty and eighty 
 feet from the lens— -that is, the object is twenty feet before the lens, and its image 
 eighty feet behind it— then the size of the imago will be four times that of the object. 
 \l the eye, therefore, looks at this magnified image six inches behind it, it will be seen 
 
34 
 
 CHROMATIC ABERRATION. 
 
 with great distinctness. In this case the image is magnified four times directly by the 
 lens, and 200 times by being brought 200 times nearer the eye ; so that its apparent 
 magnitude is 800 times larger than before. At distances less than the preceding, the 
 rule for finding the magnifying power of a lens, when the eye views the image which 
 it forms at six inches distance, is, according to Sir David Brewster, as foUows :— " From 
 the distance between the image and object in feet, subtract the focal distance of the 
 lens in feet, and divide the remainder by the same focal distance. By this quotient 
 divide twice the distance of the object in feet, and the new quotient will be the magni- 
 fying power, or the number of times that the apparent magnitude of the object is 
 increased. "When the focal length of the lens is quite inconsiderable, compared with 
 the distance of the object, as it is in most cases, the rule becomes this : — Divide the 
 fooal length of the lens by the distance at which the eye looks at the image; or, as the 
 eye will generally look at it at the distance of six inches, in order to see it most dis- 
 tinctly, divide the focal length by six inches, or, what is the same thing, double the 
 focal length in feet, and the result will be the magnifying power." 
 
 Having given the laws of optics sufficient notice, we shall next consider that portion 
 which is more intimately connected with photography. One of the first objects to be 
 
 considered in tbe manu- 
 
 facture of a lens for pho- 
 tographic purposes, is to 
 produce one with the least 
 spherical aberration. Now, 
 if we take a double convex 
 lens and produce the im- 
 age of a figure (Fig. 21), 
 we observe that the pro- 
 duced image is curved; 
 and a little consideration 
 will show that it is not 
 possible that such a curv- 
 ed surface as that represented coiild produce an image of equal distinctness over every 
 part of a plane surface : the rays cannot meet, as they are refracted from curved surfaces 
 along any straight line ; and supposing we receive on the surface of a lens a bright cir- 
 cular image, it will be brilliant and well defined around the centre, the light becoming 
 fainter towards the edge, and at 
 length passing into a cloudy halo, 
 exhibiting the prismatic colours. 
 
 This is called spherical alerration, ^ . 
 
 and to it is due that want of dis- 
 tinctness which commonly is found _____ 
 around the edges of pictures taken ' ' 
 in the camera obscui-a. 
 
 It is, therefore, important, in the — ~ 
 selection of lenses, that we look for 
 sharpness of definition over the whole 
 of a perfectly flat field. But by 
 attention to the two facts, that a 
 
 lens, one surface of which is a section of an ellipse, and the other of a circle struck 
 
 Fig. 21. 
 
SPHERICAL ABERRATION. 
 
 35 
 
 from the farthest of the two foci of that ellipse, as in Fig. 22, produces no aberration, 
 i much may be effected. A lens of this form, therefore, with a convex surface, part 
 of an ellipsoid, the focal distance of which coincides with its farther focus, and a 
 concave surface, part of a sphere, whose centre is that focus, will meet all our require- 
 ments. The mechanical difficulties of producing such lenses are great, but they may, 
 by cautious manipulation, be to a great extent overcome. 
 ' If Ave take such a lens as we have been describing, and stop its centre with a 
 i blackened disc, leaving only a small portion of the edge for the light to pass through, 
 i and thi-ow its image on a screen, we shall find it bordered with fringes of colour. At 
 I one distance red will prevail, at another violet. This is the result of chromatic aber- 
 j ration, and arises from the unequal refrangibility of the dissimilar rays. The red ray 
 
 Fig. 23. 
 
 is less bent than the violet ; consequently, supposing the rays R R (Fig. 23) to fall on the 
 \ edge of a lens, they will converge to a point at F, whereas if the rays V V fall along 
 I the same circular line, they will, being more refi'acted, meet at F. Now if we place a 
 I disc at E, just the size of the cone of light, it will be edged with violet; but if we 
 i move it to A, the coloured border will be red. 
 
 ^ By the table of the refractive powers of transparent bodies (page 119), it will be 
 ' seen that, for a beam of white light, the difference between the most refractory flint 
 I glass and crown glass, in their refracting powers, is as 2-028 is to 1534; and this 
 i proportion is maintained nearly, but not exactly, for all the coloured rays. If, there- 
 : fore, we have a crown glass lens, the refractive power of which will place the focus 
 ' at a for the violet rays, and at b for the red rays, and we grind to fit it a flint-glass 
 lens, the refracting power of which would place the fpci of the rays at c, d (Fig. 24), 
 
 i 
 
 i it will be seen that the result of such a combination would be the formation of a 
 i colourless image at a mean point between them, by re-comhining the rays into white 
 i light ; and such becomes the achromatic lens of the camera. In fact, to combine the 
 violet and blue rays with the less refrangible red is all that is required ; for this 
 reason :— Suppose there be two prisms B F C and C D F, placed in juxtaposition and 
 
36 
 
 DISPERSIVE POWERS OF PRISMS. 
 
 Fig. 25. 
 
 turned in contrary directions, as in Fig. 25. If we first assume these prisms to be of 
 
 the same substance, the refracting angle C F D 
 of the second being smaller than the refracting 
 angle B C F of the first, the two prisms will pro- 
 duce the same effect as one prism B A F ; that 
 is, the white light which passes through them 
 will not only be bent, but decomposed. But 
 if the first prism B C F be made of crown glass, 
 and the second of flint, we can destroy the dis- 
 persion, while preserving the refraction. The 
 flint being more dispersive than the crown, 
 and the dispersion produced by a prism dimin- 
 ishing with the p-ngle of refraction in the' prism, it follows that in suitably 
 diminishing the angle of refraction C F D in the flint prism, with relation to the 
 angle of refraction B C F in the crown prism, we can render the dispersive power of 
 these two prisms equal ; and as from their position the dispersion occurs in opposite 
 directions, it is compensated ; that is, the emergent rays E 0 are obviously reduced to 
 a parallelism, and consequently give white light. 
 
 The relation of the angles B C F and C F D, however, which bring to a paral- 
 lelism red and violet rays, not having the same effect on the intermediate colours, it 
 follows that with two prisms we can in reality achromatize only two rays of the 
 spectrum ; so that, in order to obtain perfect achromatism, it would be necessary to 
 have seven prisms, of substances unequally dispersive, and -whose angles of refraction 
 should be suitably determined. 
 
 So that one cause of rapidity in a lens is the perfection of the coincidence of 
 the chemical and visual foci. Another cause, is the shortness of the focus. The 
 greater length of focus possessed by a lens, the larger the picture produced, as a 
 lens is generally calculated to cover, that is, have an uniform action over two- 
 thirds its length of focus ; or, to explain more fully, a lens of twelve inches focus will 
 cover eight inches square, or nine by seven. It may seem strange that a lens that will 
 cover nine by seven, could not cover nine by nine, but a little reflection will prove the 
 contrary. Thus, if wo draw a circle of the size 
 properly covered by a twelve inch focused lens, and 
 make a square, as represented by the solid lines (Fig. 
 26), we can observe that by taking an inch off" one 
 side we may add it to the other, or nearly so— the 
 change being represented by the dotted lines— and 
 that without going out of the circle; so that a lens 
 of twelve inches focus covering eight square 
 inches, would not be half as rapid as a lens of six 
 inches focus, covering four square inches. The 
 amount of light reflected from the same object being 
 four times as much in one case as in the other. To 
 copy an object requiring to be done quickly, we 
 must therefore use tivo large lenses, placed some distance asunder, by which the length 
 of focus is diminished and the rapidity is increased ; the back lens catching the 
 refracted rays of the front one, and refracting them still more. We thus obtain what is 
 called a double lens, or more properly a double combination of lenses,'as shown iuFig. 27. 
 
COMBINATIONS OF LENSES, 
 
 37 
 
 Combinations of tenses,— These combinations can be obtained so as to take 
 both portraits and -views. The lenses for portraiture are arranged as represented in 
 Fig. 27. If the lenses are removed from the cells, especial care must be taken to 
 replace them in their former position, thus : — The flat- 
 test side of the lens B, the concave side of the inner 
 lens A, and the least convex side of the outer lens 
 ^ A, must be turned towards the interior, of the camera, 
 and the ring of brass must be placed between the two 
 lenses A so as to separate them. If views, pictures 
 statuary, &c., are to be taken, the cell containing the 
 lens A must be unscrewed and removed ; the hood E 
 ^^^S- -7. and the cell containing the lens B must be unscrewed ; 
 
 the sliding tube holding the lens is now to be pulled out of the cell, and one of the 
 circular plates of metal with a central aperture (called a stop) dropped into its place ; 
 the tube holding the lens is now reversed aad pushed 
 in so that the convex side of the lens is towards the 
 interior of the camera, and the whole arrangement as 
 represented by Fig. 28, where C is the sliding tube, B the E 
 lens, and D the stop. Three stops with different sized 
 apertures belong to each set of lenses ; but which is to 
 be selected for use in any particular case, must depend on 
 the judgment of the operator. In dull weather, and in Fig. 28. 
 
 copying objects indifferently illuminated, the largest size aperture stop is used ; the 
 middle size stop is for general use in moderate light, and the smallest size where the 
 object to be copied is exposed to full sunshine or where gi-eat sharpness is required ; 
 it may be taken as a general rule, within certain limits, that the smaller the aperture 
 which admits the light, the greater is the sharpness of the picture produced, but the 
 time of exposure must be increased where such small apertures are employed. 
 
 Claudet on Lenses. — The following observations on lenses by M. Claudet may not be 
 out of place here :— " The question of the actinic focus is involved in another kind of 
 mystery, which requires some attention. I have found that, with the same lenses, there 
 exists a constant variation in the distance between the two foci. They are never in the 
 same relation to each other ; they are sometimes more or less separate ; in some lights 
 they are very distant, and in some others they are very near, and even coincide. For 
 this reason I constantly try their position before I operate. 1 have not been able to dis- 
 I cover the cause of that singular phenomenon, but I can state positively that it exists, 
 j An optician, according to M. Lerebours' calculation, can at will, in the com- 
 bination of the two glasses composing an achromatic lens, adapt such curvatures 
 or angles in both that the visual focus shall coincide with the actinic focus ; but he 
 can obtain this result only for one length of focus. The moment the distance is 
 altered the two foci separate, because the visual and actinic rays must be refracted at 
 I different angles in coming out of the lens, in order to meet at the focus given tor one 
 distance of the object. If the distance is altered, the focus becomes longer or shorter ; 
 and as the angle at which different rays are refracted remains nearly the same, thev 
 cannot meet at the new focus, and they form two images. If the visual and actinic 
 rays were refracted parallel to each other, in coming out of the lens they would always 
 coincide for every focus ; but this is not the case. It seems, therefore, impossible that 
 lenses can be constructed in which the two foci will agree for all the various distances, 
 
38 
 
 ON FOCIMETEES. 
 
 Fipr. 29 
 
 until we have discovered two kinds of glasses in -whicli the densities or the refractiye 
 
 pov er will be in the same ratio as the dispersive 
 power." 
 
 Before concluding my present remarks on 
 lenses, let me tell the reader that without a 
 good lens he need not expect good pictirres ; and 
 that 'economy in a lens produces twice the outlay 
 in other ways. Let him not imagine, as many 
 have—" Oh, I only want something to try with.'' 
 He cannot come to a more false conclusion, as bad 
 materials— bad lens especially— have been the cause 
 of many a beginner never being anything else. I 
 shall have to say something more about lenses 
 hereafter, which will be more fully understood by 
 the reader then than now. 
 
 Focimeteis.— There is a neat little instru- 
 ment made use of by most photographers for testing 
 the lens they are about to use, and determining whether it works to focus or not ; 
 it is called the focimeter, and is the invention of 
 M. Claudet. It is composed of fans placed at 
 some little distance from each other, and numbered 
 from 1 to 8. Supposing it is wished to try a 
 lens, let the focus be tried upon say No. 4, and 
 if that number prove to be the sharpest on the 
 prepared plate or paper, the lens works to focus. 
 If 2 or 3 should be sharper, then the lens must be 
 pushed nearer to the ground glass, and the lens is 
 not enortgh cori-ected. If, on the other hand, 5 or 
 6 should be sharpest, then the lens is over corrected, 
 and must be drawn out a little more from the 
 ground glass. There is one other quality to be 
 looked for in a lens, and that is flatness of field. 
 This can be easily ascertained at once by focusing 
 on a window, when if you are using a 12-inch lens, pig, 30. 
 
 and it gives an image 'of a window sash about 8 
 
 inches on the ground glass, you may be certain, if it show the bars perfectly straight, 
 that it has a flat field, a property of the greatest importance in a good lens. Some 
 amateurs reject a really good lens on ac- 
 count of air bubbles, but these are not in 
 the slightest degree hurtful ; one of the best 
 lenses I ever saw had a dnzcn of them. 
 
 The visumeter was invented by the 
 author for ascertaining the best position 
 for the camera, withoutthe trouble of putting 
 it up. It folds up so small as to go in the waistcoat pocket The square A (Fig. 31) 
 is cut out, and bears a proportion to the ground glass of the camera ; by looking 
 through the small hole B we see the view, as if it were framed ; Fig. 32 the same 
 in the act of being folded. 
 
 Fig. m. 
 
THE CAMERA DESCRIBED. 
 
 39 
 
 THE PHOTOGEAPHIC APPAEATUS. 
 
 The first subject coming under our consideration, agreeable with the method I 
 intend pursuing, that of making the reader acquainted with all the details and acces- 
 sories before attempting to combine them, will be 
 
 The Camera Obscura, or Darkened Chamber.— This instrument was the 
 invention of Baptista Porta, of Padua. Its principle will be best understood by the 
 very simple experiment of darkening a room by closing the window-shutters, and 
 admitting a pencil of light through a small hole in them. If a piece of paper is held 
 at a little distance from this hole, the figures of external objects will be seen delineated 
 upon it ; and, by putting a small lens over the hole, they are rendered much more 
 evident from the condensation of the rays by the spherical glass. This will be best 
 understood by the following diagram (Fig. 33), Let C D be a window-shutter^having 
 
 Fig. 33. 
 
 a small aperture A, and E F a piece of paper placed in a dark chamber. Then, if an 
 illuminated object, E G B, is placed on the outside of the shutter, we shall observe an 
 inverted image of this object painted on the paper aAr g b. In order to understand 
 
 how this takes place, let us suppose the object E G B to have three distinct colours 
 
 red at E, green at G, and blue at B ; then it is plain that the red light from E will 
 pass in straight lines through the aperture A, and fall upon the paper E F at In 
 like manner, the green from G, and the blue light from B, will severally fall upon the 
 paper at g and 6, and an inverted image r g b oi the object E G B will be painted upon 
 
 it, every coloured point in 
 the object E G B having 
 a coloured point corres- 
 ponding with it on the 
 piece of paper E F, 
 
 If, instead of a dark- 
 ened rooro, we substitute 
 a darkened box (Fig. 34), 
 the same effect will be 
 seen. Suppose, in the 
 first place, the box to be 
 witliout the lens, the rays 
 would pass from the external arrow in nearly right lines through the opening. 
 
40 
 
 CONSTRUCTION FOR DIFFERENT PURPOSES. 
 
 refracted only in passing the solid edges of the hole, and form an image on the back of 
 the dark box. The lens refracts the>-ays, and a smaller but a more perfectly-defined 
 picture is the result. This is the camera obscura. 
 
 Although highly appreciated for the magical pictures it produced, this instrument 
 
 Fig. 35. Fig. 3G. 
 
 remained little more than a scientific toy until the discovery of MM. Daguerre and 
 Niepce developed its powers. It is now so well known as scarcely to require 
 
 description. The camera is a dark box with 
 doors attached, having a tube for containing 
 the lenses in one of its ends, through which 
 the radiations from external objects pass, and 
 form a diminished and reversed image upon the 
 ground glass at the other extremity. The dis- 
 position of the varioTia parts of this apparatus 
 will be understood by reference to Figs. 35 and 
 36, where A represents the body of the camera ; 
 B, the lens ; C, the ground glass focusing 
 plate ; and D, the dark slide, or back, for 
 holding the prepared plate. 
 There are four grand distinctions in cameras, as to their structure, each being 
 adapted to some peculiar branch of the photographic art ; they 
 have been named, from the nature of their configuration, Eigid, 
 Sliding-body, Folding, and Semi-folding. The sliding-body 
 camera will be found of most service in the glass operating 
 room, from the capability it has of admitting a vast range of 
 adjustment, which enables it to be used for almost every 
 purpose. The peculiarities of this form of camera will at once 
 become apparent by referring to Fig. 37, in which A represents 
 the fixed body of the instrument, to which, at the front part, 
 is fixed the lens ; B is the second, or inner body, which slides 
 along the board C, fastened to the fixed body ; the groove for 
 holding the focusing glass and the dark slide (Fig. 38) is in 
 the hinder part of the sliding box, and is represented by the letter D. There is a slit 
 in the bottom board, in which works the screw and button fastened to the moveable 
 body, which allows of the latter being fixed after its proper position has been deter- 
 mined. From this description, it will be quite evident that a very long range of 
 
THE FOLDING CAMERA. 
 
 41 
 
 focus is obtained by this arrangement ; and this will be found of the utmost convenience 
 where we wish to obtain large portraits, or pictures 
 small enough to mount as miniatures in a brooch. 
 
 The great desideratum in a camera is perfect 
 lenses. They should be achromatic, and the utmost 
 transparency should be obtained ; and, under the 
 closest inspection of the glass, not the slightest 
 wavy appearance should present itself, or dark 
 spot be detected ; at the same time, a curvature 
 should be secured which prevents, as much as pos- 
 sible, all spherical aberration. The effect pro- 
 duced by this last defect is a convergence of per- 
 pendicularity : as, for instance, two towers of any 
 building would be represented as leaning towards 
 each other, or in a portrait the features would 
 seem contracted, distorted, and mingled together, thus throwing the features out of 
 drawing. A variety of moveable diaphragms or caps to cover the front aperture 
 are useful, as the intensity of the light requires to be modified by them, and they 
 should always accompany an instrument. A handy operator can always supply himself 
 with these diaphragms. The engraving (Fig. 39) represents a section of a single lens ; 
 A, the lens ; B, rack and pinion ; C, the stop or diaphragm ; D, sections of the camera. 
 As in the phenomena of vision, so in the camera obscura, the image is produced by 
 
 S' the radiations pi-oceeding from 
 
 the external object ; and as these 
 radiations progress from various 
 parts, more or less illuminated, 
 so arc the high lights, the middle 
 tints and shadows, most beauti- 
 fully preserved in the spectral 
 Fig. 40. appearance. The colours also, 
 
 being in the first instance the effect of some physical modification of the primary 
 cause, are repeated under the same influence ; and the definition, the colour, and soft 
 gradation of light and shadow, are so perfect, that few more beautiful optical effects 
 can be produced than those presented by the 
 camera obscura. 
 
 By a slight modification of the above simple 
 box, we can form a camera in which we may 
 expose a prepared sensitive plate or sheet of 
 paper to the action of the rays which pass 
 through the lens, the plate or paper being at the 
 same time perfectly protected from the action 
 of any other ray. Some cameras are very simple 
 in construction, merely consisting of a single 
 box, with the lens so mounted or fixed that it 
 can be moved in or out to get the focus, which 
 may be done by means of one tube sliding into 
 another, or of one box having another sliding 
 into it, the lens being fixed as in Fig. 40. The next form is the folding camera, invented 
 
 Fig. 41. 
 
42 
 
 MAJOR HALKETT'S PORTABLE CAMERA. 
 
 by Mr. Ottewill, represented in Figs. 41, 42, and 43. In 41 it is represented packed as 
 a knapsack, in 42 it is fully^fixed, and in 43 half open. This is a very portable camera 
 for travelling, and is kept steady and firm by the front board, which holds the lens, 
 sliding into a groove made to 
 hold it. 
 
 I shall next, with the 
 reader's permission, introduce 
 a camera which I invented 
 and made for the late Major 
 Halkett, of the 4th Light Dra- 
 goons, who was subsequently 
 killed in the glorious charge 
 at Balaklava. I shaU only re- 
 mark, that to the amateur who 
 practices the paper processes 
 it will prove very portable 
 
 indeed. The form of this camera is that of a box when closed, in size about 
 
 13 inches long, 11 inches deep, and 
 6 inches wide, with a brass handle 
 on the top by which to carry it (Fig. 
 44). A camera of the above dimen- 
 sions will take pictures 11 X 8| 
 inches. 
 
 To shut up the camera, from 
 Fig. 45, you first undo the supports 
 E, which will let down the dia- 
 phragm, take out the screws G, G, G, 
 
 Fig. 43. 
 
 rig. 44. 
 
 open the air-hole Z, and shut H back into A ; put the screws G, G, G in also, and 
 
 I 
 
 Fig. 45. 
 
 place the two lids, L' and L", side by 
 side on the front, and fasten them there 
 by the two hooks V, V ; then turn F up 
 against D, and fasten it there by its 
 % own hook V. When you get home 
 you take out the pre&sure-board, and 
 inverting the paper frame, the paper 
 holders will aU fall back again out of 
 the box F. 
 
 When the camera is opened for use, 
 as in Fig. 45, take out the pressure- 
 board and put in eight or ten slides with prepared paper, securing each 
 paper-slide with a screw-pin K, through its eye T ; you then replace the 
 pressure-board, and the frame is charged with prepared paper. To place the 
 focusing glass in its position, you lift the frame D about half an inch, and 
 draw it back, when it will separate from A, as shown at Fig. 46, and make room for 
 the focusing glass ; having obtained a proper focus, you replace the frame D, pull up 
 the sSding-shutter M, and the first sheet of paper is exposed ; you shut dovra the 
 shutter M, pull back the pressure-board a little, turn the first screw-pin back until 
 you hear the paper-holder drop into the box F ; you push in the pressure-board again, 
 
DETACHED PARTS OF THE CAMERA. 
 
 43 
 
 and paper No. 2 is ready to undergo the same process. The first paper-holder may be 
 without an eye, as the pressure-board will keep it in its place until after exposure, and 
 the pressure-board itself can hold another paper on its inside surface, thus increasing 
 the number of pictures which may be taken during one excursion. I 
 
 Explanation of Figures. — The light tint indicates brass, the middle tint wood, and 
 the dark shading india-rubber material. 
 Fig. 44. Side view, camera when closed. 
 Fig. 45. Side view, camera when open. A, frame of 
 camera ; B, body of ditto ; C, cone also of india-rubber 
 material, extended in front of the lens by three sup- 
 ports E, ; D, frame for prepared paper, each paper held 
 in a separate holder (S, Fig. 49) ; E, communication' between D and F, 
 made of india-rubber material, through which the prenared paper in 
 
 Brass. j|j 
 
 Wood. Ilj 
 
 India- I i 
 rubber. 
 
 Ml 
 
 Back Lateral 
 view. view. 
 Fig. 46. 
 
 its holder passes into F, a box made to receive it after being exposed in the camera ; 
 
 Fig. 47.— Major Halkett's Camera. 
 
 G, G, G, nuts and screws used when the camera is open ; H, upright frame for front 
 of camera ; I, diaphragm in front of lens ; K, screw-pins to retain paper in frame until 
 after exposure ; L' and L", lids of camera; M, shutter in front of prepared paper; 
 
BETACHED PAKTS OF THE CAMERA. 
 
 Fig. 48. 
 
 rig. 49. 
 
 N, lens screwed into W from inside ; P, rack and pinion adjustment for focusing ; 
 V, V, V, V, hooks and eyes. 
 
 Fig. 46. Diagram showing the way in which D is fastened to A. 
 Fig. 48. Front of camera. I, diaphragm ; C, cone ; H, frame ; "W, 'W, front plate 
 of camera holding the lens ; E, E, E, rests 
 to support the diaphragm ; Y, Y, plates 
 to retain the front in its frame ; X, 
 graduated support to alter the horizontal 
 line ; Z, opening to allow passage to the 
 air in opening and shutting the camera. 
 
 Fig. 49. Holder in which the paper is 
 retained, made of mill-board ; frame S, 
 S, S, made of veneer, joins S at W, and 
 doubles down on the dotted lines when the paper is in its place ; T, an eye through 
 which the screw-pin K passes. 
 
 Fig. 50. Lid No. 1. A, A, the lid ; B, plate by which it is screwed on the stand ; 
 C, guiding slit in plate ; D*, hole by which that end is 
 screwed to A (Fig. 45) ; F, F, guiding pins ; X, X, 
 focusing rack. 
 
 Fig. 51. Lid No. 2. A, A, the lid; B, slit for H 
 CFig. 45) ; C, C, guiding slits in plates ; D, pinion ; P, 
 handle to ditto ; E, groove for X, _X, to work in ; F, 
 guiding pin ; G, nut for screw in screwing the lids 
 together. 
 
 Fig. 52. Section of prepared paper frame. D, D, 
 space occupied by paper slides; 0, pressure-board to 
 keep the paper against the sliding shutter. 
 
 Fig. 53. End view of camera. 0, pressure-board ; K, K, K, screw-pins to retain 
 the paper until after exposure. 
 
 In fact, the forms of the camera are 
 innumerable, and it matters little how 
 they are made, provided that they are 
 solid when working, and have a means 
 of substituting the prepared plate or 
 paper for the ground (or focusing) glass, 
 and impervious to all light, except that 
 which passes through the lens. When 
 speaking of the collodion process, I intend 
 to mention one or two other cameras, i.'ig. 53. 
 
 more particularly adapted to that pro- 
 cess. A very portable camera is constructed by Vogtlander, the German optician, 
 described as entirely made of brass, so that variations of climate do not affect it, and 
 it occupies a very small space, when packed, even with all the materials for operating. 
 The instrument known as the copying camera-box has an extra slide in the back end, 
 by which it may be considerably lengthened at pleasure. We must not omit to men- 
 tion that of M. Marten, which is known as the Panoramic Camera. The object of 
 this invention is to reproduce, with an objective of medium dimensions, landscapes of 
 great length, analogous to the panoramic feature. 
 
 Fig. 51. 
 
PHOTOGKAPHIC APPARATUS. 
 
 45 
 
 Camexa Stands.— The best constructed stands are made of maple or walnut 
 wood, having a cast-iron or hrass socket for receiving 
 the camera, and having screws for elevating or depress- 
 ing the instrument (Fig. -54). 
 
 I shall next present my readers with a drawing 
 of a dark frame for two pieces of paper and a glass, 
 against which paper is pressed with a sheet of blotting- 
 paper between. B B 
 (Fig. 55), clips to 
 fasten the frame when 
 shut ; a a, the slides 
 or shutters. 
 
 Figs. 56 and 57 
 represent two useful 
 articles, viz., the ni- 
 trate bath and dipper, 
 and the board and 
 rod for spreading solu- 
 tions on paper. This 
 consists of a piece of wood covered with soft flannel or blotting paper, on which the 
 paper is laid, and B a 
 glass rod, by means of 
 which the solution is 
 spread evenly over the 
 surface of the paper. 
 
 Our next figures re- 
 present as follows : — 
 Fig. 58, a precipitating 
 glass used for the purpose 
 iig. .50. Qf making double iodide 
 
 of silver. Fig. 59, glass rods for spreading solutions on the paper ; and Fig. 60, nip- 
 
 Fig. 55. 
 
 Fig. 57. 
 
 Fjg. 58. 
 
 Fig. 61. 
 
 Fig. 62. 
 
 pers for lifting paper out of the various solutions ; while Figs. 61 and 62 represent a 
 graduated measure glass and a cup for pouring out the several liquids into their 
 respective bottles. 
 
46 
 
 MR. FOX Talbot's discoveries. 
 
 THE CALOTYPE PEOCESS. 
 
 "We have seen that the first person who discovered the preparation of a photo- 
 graphic paper, possessing such exquisite sensitiveness that it might be impressed with 
 the image of a natural object in a minute or less in the camera, was Mr. Fox Talbot. He 
 called this the calotype process ; but some photographers, out of compliment to the dis- 
 coverer, have since called it Talbotype, as the Daguerreotype is so called after Daguerre, 
 who was the first to discover the properties of the process so named. M. Biot, a 
 French chemist of great authority, who seems to have paid considerable attention to 
 the subject, was called upon to report to the Academic des Sciences on the results of 
 the new process. In his report he proceeds to say, after paying some attention to the j 
 Daguerreotype process : — j 
 
 "It is scarcely expected that photogenic drawings, produced on paper, can at ' 
 first equal the clearness and fineness of those obtained on level and polished metaUic 1 
 plates, because the texture of the paper, the roughness of its surface, the irregularity I 
 of its imbibitions, and the capillary communication established between the various i 
 unequally-marked parts of its surface, are so many obstacles to absolute strictness of | 
 delineation, as well as to the regular gradation of tints in the camera obscura ; and ■ 
 the influence of these obstacles is greater when the chemical operation is slowly ! 
 carried on. But where there is no pretence or necessity for submitting to the ^ 
 delicacies of art— when it is merely required, for example, to copy rare manuscripts ; 
 faithfully — if we have papers which are very susceptible of receiving impressions in 
 the camera obscura, they wiU suffice perfectly ; particularly when they present, like 
 those of Mr. Talbot, the facility of immediately procuring copies of the primitive 
 drawing. It wiU, indeed, be found more commodious, and much more prac- 
 ticable, to put four- or five hundred drawings in a portfolio, than to carry about i 
 a smaller provision of metallic plates with those indispensable squares of glass to 
 protect them. Attempts are being made, at this time, to fix the images produced by 
 the Daguerreotype— perfect prints, it is true, but which are as light as the vapour 
 from which they are produced ; and, indeed, to bring a voluminous collection of these 
 fragile products through the accidents incident to long, and sometimes perilous voyages, 
 is a task requiring no ordinary care. But whoever has attentively studied the com- 
 bination of physical conditions whence these beautiful images result, will find it very 
 difficult— I should not like to say impossible —to fix them without destroying, or at 
 least without essentially altering, the causes which produce their charm ; for the pur- 
 poses, then, Avhich I have mentioned, papers very susceptible of impression would 
 still have the advantage of being less troublesome in removal from place to place, and 
 much more easily preserved. 
 
 " Early in 1830, drawings on paper were handed about 'in the scientific circles of 
 London and Paris, which were a great advance upon anything that had been pre- 
 viously done. These were the results of a new process discovered by Mr. Fox Talbot ; 
 but for several years after his process was made public, little or no progress was made 
 in the art ; and it is no injustice to Mr. Talbot to ascribe this interruption to the 
 circumstance of that gentleman having protected his discovery by a patent. It is 
 gratifying to be able to announce that Mr. Talbot has since made the country a free 
 gift of his patents. 
 
 " The utility of sensitive papers for copying inscriptions was a natural consequence 
 of the clearness of the copies of engravings which Mr. Talbot had already presented to ' 
 
I M. biot's report on calotype. 47 
 
 I the Academy. He has included, amongst others just sent, specimens of this special 
 i application of the art, which are copies of a Hebrew psalm, of a Persian gazette, and 
 of an old Latin chart of the year 1279. Our brethren of the Academic des Belles 
 Lettres, to whom I exhibited these impressions, were pleased to remark the fidelity 
 of the characters, and their clearness, for they are rendered as legible as the original 
 text. By this process, an old manuscript may be copied more quickly, and much 
 more accurately, than by hand, even when the language in which it is written is 
 understood. 
 
 " But this important extension will require much physical perfecting, towards 
 which experimenters should direct their efforts. The first thing will be to increase the 
 sensibility of the paper as much as possible, in order that the capillary communication 
 of its various parts may not have sufiicient time to deteriorate the effects of the local 
 and immediate action of the light. I should be led to believe that to this kind of 
 communication is principally to be attributed the fact remarked by Mr. Talbot, that, 
 in experiments by application, it is more difficult to copy clearly a tissue of black lace 
 spread on a white ground, than white lace on a black ground. But another more 
 general and more hidden difficulty seems to me to proceed from the unequal faculty of 
 various substances for reflecting the radiations which strike them, and perhaps from 
 their aptitude for making them undergo physical modifications. For example, you 
 wish to copy by radiation in the camera obscura a picture painted on canvas, wood, or 
 porcelain : the different colouring substances employed by the painter are placed and 
 distributed in such a manner that each of them absorbs certain portions of the total 
 incidental light, and reflects especially towards your eye the complementary portions, 
 wherein predominate the rays proper to form the tint of which it would give you the 
 sensation. But the chemically active re-agent which the same parts of the picture 
 receive and reflect is distinct from the light which affects your retina. In order that 
 the chemical effect which it produces on the sensible paper, or on M. Daguerre's layer 
 of iodine, may present, in light or in shade, the equivalent of the coloured parts, it is 
 requisite— 1st, that this reflected radiation be chemically active ; 2nd, that the energy 
 of its action be proportional to the intensity of illumination operated in the eye by 
 the portion of luminous radiation reflected from the same point of the picture. Now 
 this latter concordance certainly should not be fulfilled in an equal degree by the 
 various colouring matters, which affect the eye in the same manner, and which the 
 painter may substitute for one another in his work. Substances of the same tint may 
 present, in the quantity or the nature of the invisible radiations which they reflect, 
 as many diversities or diversities of the same order as substances of a different tint 
 present relative to light ; inversely they may be similar in their property of reflecting 
 chemical radiations when they are dissimilar to the eye ; so that the differences of tint 
 which they presented in the picture made for the eye will disappear in the chemical 
 picture, and will be confused in it in a shade, or of an uniform whiteness. These are 
 the difficulties generally inherent in the formation of chemical pictures ; and they 
 show, I think, the illusion of the experimenters who hope to reconcile, not only the 
 intensity, but the tints of the chemical impressions produced by radiations, with the 
 colours of the objects from which these radiations emanate. However, the distant or 
 near relations of these two species of phenomena are very curious to study, not only 
 i as regards the photogenic art, but likewise as regards experimental physics. I doubt 
 I not that examples of these peculiarities may be remarked in the images of natural 
 objects and coloured pictures executed by the Daguerreotype ; but vciy apparent ones 
 
48 
 
 M. BIOT S REPOKT ON CALOTTPE. 
 
 may be seen among Mr. Talbot's present impressions. Thus, some of them represent 
 white porcelain vases, coloured shells, a candlestick (of metal) with its taper, a stand 
 of white hyacinths. The whole of these objects are felt and perceived very well in 
 their chemical image ; but the parts which reflect the purely white light, probably 
 also the radiations of every kind, are, relatively to the others, in an exaggerated pro- 
 portion of illumination, which, it seems to me, must result partially from the capillary 
 communication during the continuance of the action ; so that the inequality would be 
 less if the paper were more sensitive or more rapidly acted on. In the hyacinth, the 
 stalk and the green leaves have produced scarcely a faint trace of their configuration ; 
 but they are strongly defined, especially in the parts of the outline, where more or less 
 perfect specular reflection takes place. The points of the candlestick (metallic) where 
 this reflection occurred are copied by white stains locally applied, and which deterio- 
 rate the eff'ect of the whole by their disproportion. But this is seen especially in a 
 picture by Correggio, the frame of which was very vividly copied, whilst the figure on 
 the canvas was hardly perceptible. This disproportion of lustre in the reproduction of 
 some white parts, especially when they are dull and consequently very radiating, is 
 sensible in certain parts of views taken by Mr. Talbot, to the point of rendering 
 difficult the interpretation of the object to which they belong. However, these views 
 are very satisfactory, as being obtained on paper, in the present season. Moreover, by 
 an advantage peculiar to the chemical preparation which Mr. Talbot uses, it appears 
 that the operations once completed, the drawings are no longer alterable by radiation, 
 even acting with much energy. 
 
 " Indeed, we have here, as an example, four proofs of the same view of Mr. Talbot's 
 house, with an identical disposition of lights and shades ; so that some, at least, if not 
 three out of four,'must have been procured by superposition. Mr. Talbot is right in 
 representing this property of reproduction as an especial advantage of his process, and 
 it would indeed be very useful in voyages. I have exposed one of these drawings to 
 the action of the sun — not very powerful, it is true— for several hours, and I have not 
 perceived the slightest alteration in the lights. I think I understand that, in Mr. 
 Talbot's opinion, the shades alone are strengthened under this influence. According 
 to what I have just said, it should be expected that the triumph of this process, as of 
 every other photogenic reproduction, would take place with objects of white and dull 
 plaster. Indeed, Mr. Talbot's parcel contains eight copies of busts and statues ; six of 
 which chiefly, of various forms and sizes, present very remarkable results, especially 
 taking into consideration the unfavourable season at which they were produced. There 
 is not found in them the strict perfection of trace, nor the admirable gradations of 
 lights and shades, which constitute the charm of M. Daguerre's impressions. But 
 representations on sensitive papers must be considered as principally applicable to a 
 difierent object, which does not impose such strict conditions of art, requiring only 
 faithful images,'sufiiciently clear in their details to be readily recognised, and which, 
 moreover, being obtained with rapidity, by an easy manipulation, may be kept with 
 very little care, comprised in great number in a small compass, and moved from place 
 to place with facility. Mr. Talbot's papers already present many of these essential 
 qualities, with the advantage of being able to furnish numerous copies immediately. 
 His efforts, and those of others occupied with the same subject, will conclude by adding 
 to them everything which may be desirable, provided that expectation, or the preten- 
 sion of a perfection of art physically incompatible with operations on paper, do not 
 give a false direction to their endeavours. However, I may here add, that tlie height 
 
THE TALBOTYPE PROCESS. 
 
 49 
 
 of success would consist in discovering a substance very susceptible of receiving im- 
 pressions, which might be applied on a papyraceous leaf without penetrating deep into 
 it, and which might, however, be fixed in it after the operation, as in Mr. Talbot's 
 impressions. It does not seem necessary even that the first impression thus rapidly 
 obtained should copy the lights and shades in their proper places, provided that its 
 transparency and fixedness were such, that we might deduce them from the application 
 of copies wherein the inversion would be corrected. And perhaps, by this decom- 
 position of the problem into two successive operations, one of the best ways is opened 
 by which it may be resolved." 
 
 " But so much improvement has taken place in the manufacture of paper for the 
 purpose, as well as in the manipulation, that many of the early obstacles have been 
 overcome ; and photographs on paper, as may be seen at the present year's exhibition 
 of the Photographic Society, have attained a degree of excellence not anticipated by 
 the French savant. Paper has, moreover, qualities of its own for the purpose ; it 
 wants the glitter arising from the polished surface of the metal plate, so that its 
 beauties can always be seen." 
 
 The Talbotype Process has been largely improved upon by Mr. Cundall and 
 others ; but it may be interesting to my readers to have the process described as 
 practised by the inventor ; adding, however, as I proceed, some of the more important 
 improvements upon his formulae. 
 
 The apparatus required are, two or three square shallow porcelain dishes, an ample 
 supply of distilled water, a glass graduated measure and funnel (Fig. 63), a supply of 
 blotting-paper, large flat and soft hair pencils, and a supply of the best cTn""^ 
 writing paper of medium thickness, perfectly smooth surface, transparent, ATIT/L- 
 compact, and uniform in texture, and without speck, water mark, or e^^^^^^ 
 maker's name. Also a supply of the following solutions, viz. : — \S3~7^ 
 
 No. 1. A solution of 100 grains of nitrate of silver, dissolved in li-r-s 
 six ounces of distilled water. 
 
 No 2. A solution of 500 grains of the iodide of potassium in one /\^f\ 
 pint of distilled water. (Mr. Cundall uses 400 grains iodide of potas- \sa=-=*<»^ 
 slum, and 100 grains of common salt, as an improvement analogous vig. 63. 
 to that of M. Claudet in the Daguerreotype process.) 
 
 No. 3. A solution of 100 grains of nitrate of silver in two ounces of cold distilled 
 water, adding to it a sixth part of its quantity of concentrated acetic acid. 
 
 No. 4. A solution of crystallized gallic acid, saturated in distilled water. (This 
 should be prepared in small quantities, as it will only keep for a few days.) 
 
 N<). 5. A solution of 100 grains bromide of potassium in eight or ten ounces of 
 distilled water. 
 
 Having selected suitable paper, and cut it to the proper size, which snould be at 
 least an inch each way larger than the object to be represented, mark one of the 
 corners with a pencil, so that the side on which the preparation is laid may be known, 
 pin the paper by two of its corners to a board, and by means of a soft brush apply the 
 preparation No. 1 carefully and smoothly to the surface of the paper, taking care to 
 wash it thoroughly over without any mark of the brush, and that the solution is 
 thoroughly absorbed. The paper may be suffered to dry by hanging from the board in 
 the air, but without exposure to light. 
 
 When thoroughly dry it is ready for the next operation, which consists in pouring 
 a portion of the second solution, just sufficient to cover the surface, into a shallow 
 
50 
 
 THE TALBOTYPE PROCESS, 
 
 porcelain dish, which should be large enough to receive the paper. As only the pre- 
 pared side of the paper should receive this solution, fold a narrow upright margin all 
 round the paper, turning in the corners, holding it by two comers ; let the side to 
 which the previous solution has been applied, be drawn gently and smoothly over 
 the surface of the solution, resting on it till it is thoroughly saturated. In this state 
 it may remain for a few seconds, but not more than a minute, otherwise the nitrate 
 I solution may be decomposed by the iodine liquid. 
 
 The paper, now thoroughly saturated with the iodized liquid, is hung up in a proper 
 place imtil about half dry. The paper is now thoroughly imbued with the preparation, 
 and the nitrate of silver thoroughly decomposed ; but it is now necessary to remove 
 every trace of the salts with which the paper has been saturated. This Mr. Cundall 
 accomplishes by floating the paper with its upturned margin on a basin of pure water 
 for eight or ten minutes, drawing it occasionally gently along the surface to remove 
 the soluble salts, which will separate from their own gravity ; while the iodide of 
 silver, being insoluble in water, remains upon the paper, presenting the surface required 
 for a successful operation. 
 
 The paper should now be left to dry spontaneously, without being touched or the 
 surface disturbed. When dry, it may be subjected to sufficient 'pressure to smooth it. 
 In order to preserve its sensibility, it should be carefully sechided from the light, and ! 
 placed in a portfolio. The paper thus prepared is called iodized paper ready for use. j 
 
 For the third operation Mr. Talbot made use of the solutions 3 and 4 in the 
 following manner : — Mix equal parts of the two solutions by means of the graduated 
 drachm tube, but only in quantities required for immediate use, as it quickly loses its 
 quality ; Gallo-nitrate of silver is obtained by this means. With this iiizture the 
 iodized paper is washed over by means of another soft brush, using increased care in | 
 laying it on, so as to secure a smooth and even surface and equal distribution. Leave i 
 the solution to settle for eight or ten seconds, then dip the surface in pure water, still 
 holding it by its upraised corners, and drawing the paper gently over the water several 
 times ; it is again drawn through a second course of fresh water two or three times. After 
 being dried in the dark and at a distance from the fire, it is fit for use, and may be placed | 
 in the camera while the surface is dry, but still moist, or it may be placed in a portfolio ' 
 with blotting-paper for future use. Mr. CundaU, and other recent operators, find it i 
 necessary to apply the gallo-nitrate as follows : — Pour out the solution upon a clean ! 
 slab of glass, diffusing it over the surface to a size corresponding with that of the { 
 paper. Holding the paper by the narrow upturned margin, the sensitive side is j 
 applied to the liquid upon the slab, and brought in contact ; so that by passing the f 
 fingers gently over the back of the paper, the surface is thoroughly wetted with the 
 gallo-nitrate. Mr. Cundall further recommends, that in all cases when extreme sensi- \ 
 tiveness is not required, the liquid should be diluted to one-half the strength ; 
 indicated above, otherwise the paper is apt to be stained or embronzed, unless the j 
 manipulation be extremely well-managed. Eain, river, or spring water answers per- | 
 fectly to tvash the papers, distilled water being required for the silver solutions only. j 
 
 These operations Mr. Talbot recommends should be performed with as little light I 
 as possible, and that should be candle light. | 
 
 And now the paper is ready to place in the camera, where the operator is to use his \ 
 own judgment in forming his pictures, and his experience in getting proper eflect. j 
 According to the intensity of light and colour of the object, is the length of exposure, I 
 j which may vary from five seconds to two minutes. j 
 
PHOTOGENIC PAPKB. 
 
 "When the operation is terminated, it is necessary to develop the image by washing the 
 surface over with a brush charged with the gallo-nitrate of silver, exposing it at the same 
 time to a gentle heat from a hot iron or other similar body, held at the distance of an inch 
 I or two, the iron being held vertically, and the paper moved backwards and forwards 
 i so that it may all dry simultaneously. In the course of a few seconds the picture will 
 j become visible, usually of a fine blackish-brown colour. 
 
 I When sufficiently developed, it is necessary to wash it immediately in pure water 
 } to remove the gallo-nitrate of silver. This last process of washing should be done 
 before the paper has become quite dry, and, if necessary, the drying should be retarded 
 by the application of hot vapour or a jet of steam. The final process is fixing the 
 image. 
 
 This was accomplished by Mr. Talbot by dipping it first in water, and, after drying, 
 washing it over with a' solution of bromide of potassium. (Solution No. 5.) And, 
 after a last washing in water, it is finally dried. A strong solution of common salt 
 was substituted for the bromide of potassium, but was not so successful. 
 
 The present practice, as described by Mr. Cundall, is as follows : — In order to remove 
 the sensitive matter from the picture, it is to be soaked, he says, " in warm water, but 
 not warmer than may be borne by the finger. This water is to be changed twice, and 
 the pictures are then to be well drained or dried in clean and dry blotting-paper, to 
 prepare them to imbibe a solution of the hyposulphate of soda, which is prepared by 
 dissolving an ounce of that salt in a quart (forty ounces) of water. Having poured a 
 little of the solution into a flat dish, the picture is to be introduced into it ; daylight will 
 not now injure them. Let them soak for two or three minutes, or even longer, if they 
 are strongly printed, turning them occasionally. The remaining unreduced salts of 
 silver are thus thoroughly dissolved, and may now, with the hyposulphate, be entirely 
 removed by soaking in water and pressing alternately in clean blotting-paper ; but if 
 time can be allowed, soaking in water alone will have the desired efiect. 
 
 The impression now obtained is a negative, that is, the parts of the object which is 
 white in nature are here represented black, and vice versa. From this impression, 
 however, any number may be taken, having the lights and shadows as in nature. 
 I This is performed by placing upon the negative a piece of properly-prepared photo- 
 I graphic paper, and in immediate contact with it, having previously rendered it as 
 transparent as possible. By exposure to the light, the second impression is formed. 
 The progress of the impression may be watched by raising one of the corners of the 
 negative from time to time. The mode of rendering the negative transparent, as 
 I adopted by Mr. Fox Talbot, was as follows : — Grate some virgin wax on the back of 
 I the paper, and, having placed it between two pieces of white paper, draw a hot iron 
 j gently over it until the dissolved wax has throughly penetrated the paper of the nega- 
 I tive, and rendered it somewhat transparent. 
 
 j When many impressions are taken, the original loses a portion of its vigour, which 
 I may, however, be restored by dipping it again in the gallo-nitrate of silver, washing it 
 in hot water, and fixing it as before directed. These impressions may be obtained by 
 using calotype paper, but Mr. Talbot recommends photogenic paper prepared as 
 follows : — 
 
 Having dissolved 25 grains of common salt in one ounce of distilled water, dip 
 the paper selected and cut to a proper size in this liquid, leaf by leaf, leaving it there 
 to soak for a short time, and place it between leaves of clean blotting-paper to dry ; 
 dissolve afterwards 90 grains of crystallized nitrate of silver in an ounce of distilled 
 
52 
 
 IMPROVED PROCESSES OF CALOTYPE. 
 
 water, wash the paper on the seen silver side, with a soft pencil charged with this 
 liquid, dry it a little, and pass another coating of the liquid over it, dry it thoroughly, 
 suspending it for that purpose by one of the corners. 
 
 A more simple preparation of photographic paper is produced by dissolving 100 
 grains of bromide of potassium in an ounce of distilled water ; dip the paper in this 
 solution, place it as before between the leaves of blotting-paper, and when nearly dry 
 wash the sensitive side with a solution of 100 grains nitrate of silver, dissolved in an 
 ounce of distilled water ; diy the paper in a darkened place, and, if required to be very 
 sensitive, apply a second wash of the solution. This paper has presented the best 
 results. 
 
 The impression obtained upon these papers in the manner described, form the calo- 
 type process. Their sensibility is such, that images of feathers, leaves, and other 
 similar objects, are said to be obtained by the light of a jet of gas while still moist; 
 holding the paper four or five inches from the flame, the impression will appear in 
 three or four minutes. 
 
 The precautions to be taken during the preceding operations are as follow : — 
 
 1. It is necessary to have a clean brush for every solution, and to wash them care- 
 fully every time they are used. The brush used for the gallo-nitrate of silver is 
 quickly destroyed. 
 
 2. The same blotting-paper should never be used but for the same solution, and it 
 is better to have separate Wotting-books prepared, with the names of the solution 
 written on each. 
 
 3. The distilled and other waters should be changed with every operation. 
 
 4. Dr. Eyan observed that if the paper remained too long in the solution No. 2 
 (iodide of potassium), the iodide of silver was formed. He recommends, therefore, 
 that the leaf should be dipped and removed promptly to prevent this formation. 
 
 5. Mr. Mitchell modifies the process in the following particulars : — He first applies 
 the solution No. 2 (iodide of potassium), drys it; then the solution No. 1 (nitrate of 
 silver), drys that also ; and having dipped the paper for one moment in a solution of 125 
 grains of iodine, in an ounce of water, washes it in distilled water, and finally drys it. 
 By this means Mr. Mitchell obtains a paper more sensitive, and, as is said, vrith the 
 substances more equally distributed than by Mr. Talbot's process. 
 
 Improved Talbotype Process. — Many improvements have taken place in the Talbo- 
 typc process. Mr. Talbot has himself introduced the following: — In order to get rid 
 of the vellow tint in images taken on paper prepared with a solution of nitrate of 
 silver, he proposes to plunge the paper after it is impressed into a hot bath, composed 
 of hypo-sulphate of soda or other hypo-sulphate dissolved in ten times its weight of 
 water, heated to ebullition. The paper should remain about ten minutes in this bath, 
 then be washed in cold water, and dried. By this means it is rendered both more per- 
 manent and more transparent ; the lights are brought out better. The transparency 
 of the paper can still be increased after this operation by the application of wax as 
 already directed. 
 
 Another improvement consists in placing a hot iron plate behind the darkened 
 frame, which covers the paper while it takes the image in the camera, thus communi- 
 cating heat to the paper, and rendering it more sensitive. 
 
 I have been induced to give the formulaj of these different photographic authors, 
 so that if the reader cannot arrive at a satisfactory result by one process, he may try 
 another. And here I may as well remark, that the amateur should not be led too 
 
 « 
 
SIR w. J. Newton's process. 
 
 53 
 
 easily to try all the different processes he may hear or read of, for acquirement of a i 
 perfect knowledge of one of them is quite enough for a lifetime. j 
 I am now about to introduce the reader to two photographers who have dis- j 
 tinguished themselves by their successful practice in this process. I need scarcely 
 say that the two gentlemen I speak of are Sir William J, Newton, and J . D- 
 Llewellyn, Esq. 
 
 Sir W. 3. Newton's Process. — This gentleman has taken great interest in the 
 art, and has materially contributed to its advancement by his own manipulation. 
 I cannot, therefore, do better than give his formula in his own words, copied from the 
 Journal of the London Photographic Society, to the writers of which I feel exceedingly 
 indebted for much valuable information. 
 
 " To Iodize the Paper. — 1st, Brush your paper over with muriate of barytes (half an 
 ounce, dissolved in nearly a wine-bottle of distilled water) ; lay it flat to dry. 2nd, 
 Dissolve sixty grains of nitrate of silver, in about an ounce of distilled water. Ditto 
 sixty grains of iodide of potassium in another bottle with the like quantity of water. 
 Mix them together and shake Avell; let it subside ; pour off the Avater, and then add 
 hot water ; shake it well ; let it subside ; pour off the water again, and add three ounces 
 of distilled water, and afterwards as much iodide of potassium as will redissolve the 
 iodide of silver. 
 
 " Brush your previously-prepared paper well with this, and let dry ; then place them 
 in water, one by one, for about one hour and a-half or two hours, constantly agitating 
 the water. As many as a dozen pieces may be put into the same water, one after the 
 other, taking care that there are no air-bubbles ; take them out, and pin to the 
 edge of a board at one comer. "When dry they will be ready for exciting for the 
 camera by the following process : — 
 
 (These are supposed to be in six 1-ounce bottles with glass stoppers.) 
 
 1. 
 
 1 drachm of No. 4, 6 drachms 
 of distilled water. 
 
 2. 
 
 20 min. of No. 3, 6 drachms 
 of distilled water. 
 
 3. 
 
 A saturated so- 
 lution of gallic 
 acid. 
 
 4. 
 
 25 grains of nitrate of silver 
 to half an ounce of water. 
 Add 45 minims of glacial 
 acetic acid. 
 
 5. 
 
 2 drachms of 
 No. 4, 6 drs. of 
 water. 
 
 6. 
 
 Equal parts of Nos. 1 and 2. 
 
 N.B. — This must be mixed 
 just before using, and the 
 bottle cleaned afterwards. 
 
 " To Excite for the Ca7nera.— Mix equal parts of Nos. 1 and 2, and with a glass rod 
 excite the iodized paper and blot off ; and it may be put in the slide at once, or the 
 number you require may be excitei^, and put into a blotting-paper book, one between 
 each leaf, and allowed to remain until required to be placed in the slide. 
 
 " Time of Exposure. — The time varies from three minutes to a quarter of an hour. 
 
64 
 
 SIR w. J. Newton's peocess. 
 
 according to the nature of the subject and the power of the sun ; but five minutes is 
 generally the proper time. 
 
 " To Bring Out. — Bring out with No. 3, and when the subject begins to appear, add 
 No. 5 ; and when sufficiently developed, hold it up, and pour water upon it ; then put 
 it into hyposulphite of soda to fix it, for about an hour or more, and then into 
 water ; this is merely to fix it for the after process, at your leisure. 
 
 " To Clean the Negative.— Get a zinc tray about three or four inches deep, with another 
 tray to fit in at the top, about one inch deep ; fill the lower tray with boiling water, so 
 that the upper tray may touch the water ; put your solution of hyposulphite of soda, 
 not strong, in the upper tray, and then your negatives one by one, watching them with 
 care until the iodine is removed ; then put them in hot water, containing a small piece 
 of common soda (the size of a nutmeg to about two quarts of water), for about ten 
 minutes ; pour off' the dirty water, and then add more hot water, shaking them gently 
 for a short time ; pour off the water again, and then add fresh hot water, and let it 
 remain until it is cold, after which take them out carefully one by one, and put them 
 in clean cold water for an hour or two ; then take them all out together, and hold up 
 to drain for a short time, and then put them between three or four thicknesses of linen, 
 and press as much of the water out as you can ; then carefully (for now aU. the size is 
 removed) lay them out flat separately upon linen to dry. 
 
 " Mode of Waxing the Negatives. — Melt the pure white wax over a lamp of moderate 
 heat, just merely to keep it in a liquid state ; then fill the same deep tray as above 
 described with boiling water, and with another similar to the upper one before described 
 (which must be kept for this purpose only) ; put a clean piece of blotting-paper in this 
 tray, and lay your negative face downwards, and with a soft flat hog's-hair brush, 
 about an inch wide, dip it into the liquid wax, and brush the negative over, when it 
 will be immediately transparent, and it can be done so that there is very little redun- 
 dant wax ; after which it may be put between two or three thicknesses of blotting- 
 paper and ironed if necessary, which, however, should not be very hot, when it is ready 
 to take positives from. 
 
 " Positives on Negative' Paper. — Take one part of the iodide of silver before described, 
 and add two parts of water ; then add as much iodide of potassium as will redissolve it. 
 Brush your paper with the foregoing, let dry, put into water, and proceed, in all respects, 
 as above described for the negatives. 
 
 Excite for Positives. — Excite with No. 1 ; blot off ; lay it in your press, place the 
 negative face downwards ; expose to the light from ten seconds to half a minute, or 
 more, according to the light (not in the sun), and bring out with No. 3 ; and when it 
 is nearly developed add No. 1 ; then take it up and pour water upon it, and then place 
 it in hyposulphite of soda (cold) until the iodine is removed ; after which put it into 
 alum water, about half a teaspoonful of powdered alum in two quarts of water ; this 
 will readily remove the hyposulphite, and also fix the positive more particularly ; it 
 will also take away any impurities which there may be in the paper ; after which put 
 it into clean cold water, and change two or three times. 
 
 " I have been thus particular in describing the process which I have adopted, more 
 especially for beginners ; and with great cleanliness and care in each process, and 
 especially in keeping all the bottles with the chemicals free from dirt of every kind, the 
 foregoing will lead to favourable results." 
 
 Mr. Iilewellen's Piocess. — This gentleman, after stating that his method of 
 manipulating is almost similar to Mr. Fox Talbot's process, says : — 
 
MR. Llewellyn's process. 
 
 55 
 
 " I have carefully followed the steps of its progress, and have, I believe, tried 
 nearly all the modifications which have been at various times suggested, and it is 
 remarkable that, in the long period which has now elapsed, no important improvements 
 in paper photography should have been introduced. 
 
 " The paper which I use is manufactured by Turner, of Chaiford Mills, and bears 
 the vrater-mark of ' Turner's Patent Talbotype.' It is not free from faults ; black 
 specks, arising from brass and iron used in its manufacture, will often appear, but it is 
 a firm compact texture, and makes good negatives, free from the woolliness which is 
 fatal to other samples of paper which in other respects are superior. 
 
 " A sheet of this paper should be fastened with silver pins to a piece of flannel 
 stretched over a board, and liberally brushed on one side with a solution of nitrate of 
 silver, of the strength of thirty-three grains to the ounce of distilled water. 
 
 " In doing this, and in the subsequent manipulations, I use a brush formed 
 of a flock of cotton wool, partly drawn through a glass tube, which thus makes 
 a convenient handle; this arrangement was suggested by Mr. Buckle, and I 
 believe, bears his name ; it is known as a Buckle brush, and in my experience pos- 
 sesses advantages over a glass rod or triangle, or any of the other many contrivances 
 which have been suggested, for the convenience of spreading solutions. 
 
 " As soon as the sheet of paper is partially, but before it is quite dry, say in about 
 two minutes, it is^to be immersed in a bath of iodide of potassium, of the strength of 
 twenty grains to the ounce of water ; all air-bubbles must be carefully got rid of ; 
 and the sheet will speedily assume a primrose-yellow colour, the back appearing 
 nearly as bright as the face. 
 
 " It may now be shifted at once to a bath of water, which should be changed four 
 or five times, and the paper allowed to soak in it for two or three hours, so as to 
 insure the removal of all soluble salts, and leave a pure iodide of silver distributed 
 throughout the substance of the paper. 
 
 " The whole of the process may be performed in full daylight. 
 
 "When thoroughly washed, each sheet is to be hung upj separately, and when 
 dry is improved by exposure for an hour or two to the full rays of the sun. 
 
 " It may then be subjected to strong' pressure in a screw frame and kept for use ; 
 it will keep good for any length of time. 
 
 " To excite it for camera use, take three' drops of aceto-nitrate of silver {the aceto- 
 nitrate consisting of fifty grains nitrate of silver with one ounce of water and one and a 
 half drachm of acetic acid), and three drops of a saturated solution of gallic acid; add 
 these to one drachm of distilled water, which quantity will be about sufficient for a 
 sheet of the ordinary size of 9 X 7 inches. 
 
 " In summer weather the above proportions are sufficient, but in winter, when the 
 air is cold, four or five drops of aceto-nitrate, and four or five of gallic acid may be 
 safely used to the drachm of water. 
 
 " This exciting solution should be liberally applied, in the same manner as that 
 described for iodizing ; the paper should be evenly and thoroughly wotted, and when 
 well soaked, blotted off with a sheet of clean white blotting-paper. A round ruler 
 rolled over it with a firm pressure, answers very well, and insures a uniform application. 
 
 " The paper is now ready for the camera, and should be screwed firmly into the 
 holder, so as to exclude all air as much as possible. Under these circumstances it will 
 keep damp for many hours, and may be depended upon to retain its whiteness, even 
 in summer weather, for twelve hours. 
 
56 
 
 MR. LLEWELLYN'S PROCESS. 
 
 " "With a three-inch Eoss lens, and a quarter-inch diaphragm, the time of expo- 
 sure will vary from eight to fifteen minutes, according to the character of the light 
 and the colour of the object to he copied. The exact time can only be taught by 
 experience. 
 
 " In developing I make use of aceto-nitrate of silver, and solution of gallic acid 
 in equal proportions, the same as directed for the exciting compound, but Mathout the 
 addition of any water. This must be mixed only immediately before it is wanted, as 
 it decomposes with great rapidity ; having prepared a sufficient quantity for a single 
 sheet, say about one and a-half drachm, brush it over the excited side of the paper 
 with a clean new brush. 
 
 " The picture ought now gradually and evenly to appear, beginning with the sky, and 
 then faintly exhibiting traces of the darker parts and the shadows. At this point of 
 the development I abandon the use of the compound mixture, and continue the action with 
 the gallic acid alone. A Buckle brush (Fig. 63) is here of great service, as it enables 
 the operator to add more of nitrate of silver, or more 
 of gallic acid, as the case may require, to the different 
 portions of the picture ; and this is a very proper place 
 to describe that article. A Buckle brush, then, is made 
 as follows : — Procure a piece of glass tube, B, about 
 half an inch in diameter and six inches long ; have 
 either a piece of silver wire, A, a little longer than the 
 tube, and with a loop at one end, or a piece of silk 
 thread, pass the wire or thread through the tube, and fasten to the end which comes 
 through a tuft of clean cotton wool, C ; by pulling the other end of the wire, it forms a 
 very nice sort of brush for spreading solutions ; the wool can be thrown away when 
 dirty, and a fresh piece substituted ; the loose end of the wire may be held in its 
 place by bending it over^the edge of the tube. 
 
 " In those parts where it develops too slowly, nitrate of silver may be chiefly used, 
 while, on the other hand, the parts which are inclined to darken too quickly, may be 
 brushed with the solution of gallic acid alone ; and thus a more complete control over 
 the development of the picture is obtained than can be effected by the use of the glass 
 rod, or any other method that I am acquainted with, 
 
 " By this practice I have saved many pictures that must otherwise have been lost, 
 and in many others again, have obtained a higher degree of excellence than would 
 have been practicable under other treatment. 
 
 *' In order to obtain a negative that will print well, it is better to carry the deve- 
 lopment further than may at first sight appear desirable, and it should be carefully 
 examined by transmitted light before the operator is satisfied. When a full definition, 
 even in the parts where the shadows of the landscape were the darkest, has been 
 obtained, the photograph should, without delay, be well washed in cold water, and 
 then immersed in a saturated solution of hyposulphite of soda, and left in this until all 
 trace of the yellow iodide of silver has been removed. 
 
 *' If this should prove tedious and difficult, as will sometimes be the case, it is well 
 to pour away the solution into a stock bottle, and make a little fresh (just enough to 
 cover the sheet), which will always, on application to the half-cleared picture, complete 
 the removal of the y.allow colour ; and the new solution may be added to the stock 
 bottle, and thus aid in keeping up its strength. 
 
 " The proof must now be thoroughly Avashed for an hour or more, in several 
 
j M. GUSTAVE LE GRAY'S PROCESS. 57 
 
 j waters, to get rid of all trace of hyposulphite of soda, which, if suffered to remain, 
 I Avould gradually destroy the picture. 
 
 " "When thoroughly dried, it should be waxed, which may be done without risk, 
 by laying the sheet between two pieces] of blotting-paper saturated with ordinary 
 white wax, and passing a moderately hot box-iron over the whole. A sufficient 
 quantity of wax will be absorbed by the photographic negative, which will thus 
 become transparent when viewed by transmitted light. ?, ,.. 
 
 " It will print much quicker, and is less liable to injury from any chance contact 
 with liquid, or from the humidity of the air, than if left unwaxed. 
 
 " The photograph is now finished. 
 " In the foregoing description I have descended into particulars which will, I fear, 
 seem tediously minute, to those who are not aware how much, in photography, depends 
 upon trifles. But I am convinced that the difference between the works of different 
 operators mainly consists in the observance or the neglect of trifles seemingly alto- 
 gether unimportant. Other formulae besides those which I describe will, I well 
 know, produce excellent results in the hands of skilful manipulators. I only speak of 
 those methods which for some time past I have myself exclusively used, and by aid of 
 which I have succeeded in making my best negatives. 
 
 " The practice is simple and certain, and I recommend it with confidence." 
 
 M. lie Gray's Process.— Among the many modifications of the calotype, we 
 have that of M. Gustavo Lc Gray, who gives us the following directions : — 
 
 " First Operation. — Dissolve three hundred grains of isinglass in one pint and three 
 quarters of distilled water (for this purpose use a water bath). 
 
 " Take one-half of this preparation while warm, and add to it as under .— 
 
 Iodide of Potassium .... 200 grains 
 
 Bromide of ditto 60 „ 
 
 Chloride of Sodium .... 34 „ 
 
 Let these salts be well dissolved, then filter the solution through a piece of linen, put 
 it, still warm, in a large dish, and plunge in your paper completely, leaf by leaf, one 
 on the other, taking care to prevent the air-bubbles from adhering to the paper. 
 
 " Put about twenty leaves at a time into the dish, then turn the whole, those at the 
 top to the bottom, then take them out one by one, and hang them by one corner with 
 a pin bent like the letter S, to dry spontaneously. 
 
 " When hung up, attach to the opposite corner a piece of bibulous paper, which 
 will facilitate the drying. 
 
 " When the paper is dry cut it the size required, and preserve it in a folio for 
 use ; this paper may be made in the daytime, as it is not sensitive to light in this state. 
 
 " The bromide does not, in this case, act as an accelerator, as it does on the silver 
 plates of the Daguerreotype, because, instead of quickening, it retards the operation a 
 little ; its action is to preserve from the gallic acid the white of the paper, which 
 would blacken more rapidly if you employed the iodide of potassium alone. 
 
 " Second Operation. — Prepare, by the light of a taper, the following solution in 
 a stoppered bottle — distilled water, six fluid ounces; crystallized nitrate of silver, 
 250 grains. 
 
 " When the nitrate is dissolved, add one ounce of crystallizahle acetic acid ; be 
 careful to exclude this bottle from the light, by covering it with black paper. This 
 solution will keep good until the whole is used. 
 
58 
 
 M. GUST AVE LE GRAY's PROCESS. 
 
 " "When you wish to operate, pour the solution upon a porcelain or glass slab, sur- 
 rounded with a glass or paper border to keep the liquid from running oflf. I usually take 
 the solution out of the bottle by means of a pipette, so as to prevent the distribution of 
 any pellicle of dust or other impurity over the glass slab. 
 
 " Take a sheet of the iodized paper by two of the corners, holding them perpendicu- 
 larly, and gently lower the middle of the paper upon the centre of the slab ; gradually 
 depress until the sheet is equally spread ; repeat this operation several times until the 
 air-bubbles disappear ; take also the precaution to keep the upper side of the paper 
 dry. 
 
 " In order to prevent the fingers from spotting the paper, pass a bone paper-knife 
 under the corner of the sheet, to lift it from the slab between that and the thumb. 
 
 " Let the sheet remain upon the slab until the formation of the chloro-bromo-iodide 
 of silver is perfect. 
 
 " This may be known by the disappearance of the violet colour which the back of 
 the paper at first presented ; it must not be left longer, otherwise it would lose its sensi- 
 tiveness. 
 
 "The time required to effect this chemical change is from one to five minutes, 
 depending upon the quality of the paper. 
 
 " Spread upon a glass, fitted to the frame of the camera, a piece of white paper well 
 soaked in water ; upon this place the prepared sheet, the sensitive side upwards. 
 
 " The paper which you place underneath must bo free from spots of iron and other 
 impurities. 
 
 " It is also necessary to mark the side of the glass which ought to be at the bottom 
 of the camera, and to keep it always inclined in that direction when the papers are 
 applied ; if this precaution is neglected, the liquid collected at the bottom, in falling 
 over the prepared paper, would not fail to produce spots. The paper thus applied to 
 the glass will remain there for an hour without falling off, and can be placed within 
 that time in the camera. 
 
 "When I am going to take a proof at a distance, I moisten the sheet of lining paper 
 with a thick solution of gum arabic, and can thus preserve for a longer time its 
 humidity and adhesion. I can also in this case make use of two glasses, between which 
 the paper is placed, according to the dii'ection of M. Blanqiiart Everard; but it is 
 necessary to take great cave that the plates of glass are perfectly clean, and to have 
 them re-polished if scratched. j 
 " I employ for this purpose, blotting-paper to clean them, as well as my plates ; it | 
 is much superior to linen, and absorbs liquids and impurities that adhere to it. I never ' 
 spare the blotting-paper, for I would rather use a leaf too much than be uncertain j 
 about the cleanness of my glass. i 
 "When the sheet of lining pnper adheres well to the glass, it should not be removed, i 
 but only moistened afresh with water, after which you may apply another sheet of the j 
 sensitive paper. i 
 " In preparing several sheets of the sensitive paper at a time, it is not necessary to ; 
 wash the slab for each sheet ; you need only draw over it a piece of white paper to . 
 remove any dust or pellicle formed. 
 
 "AVhen your operations are finished, you may pour back the aceto-nitrate of silver 
 into a bottle, and reserve it for another time. 
 
 " The necessity of employing M. Gray's papers in a wet state is their most objection- 
 I able qitality, but certaialy the results obtained by strict attention to his directions are j 
 
DR. diamond's process. 09 
 
 often exceedingly beautiful. For developing the image the following is recommended, 
 which does not, however, diifer essentially from the developing processes already 
 described : — 
 
 " Make about a pint bottle of saturated solution of gallic acid, having acid in excess, 
 and using distilled water ; decant a portion into a smaller bottle for general use, and 
 fill up the other bottle ; you will thus always have a clear saturated solution. 
 
 " Pour upon a^lab of glass, kept horizontal, a little of this liquid, spreading it 
 equally with a slip of paper, then apply the paper which has been exposed in the same 
 manner as described for the negative paper, being careful to keep the back dry. Watch 
 its development, which is easily observed through the back of the paper ; you may 
 leave it thus as long as the back of the image does not begin to spot. 
 
 " "When it is rendered very vigorous, remove it quickly to another clean" slab, and 
 well wash it in several waters, occasionally turning it, and gently passing the finger 
 over the back ; by this means you remove any crystals of gallic acid which might spot 
 the picture. 
 
 " The appearance of thei mage at the end of this process will enable you to judge if 
 it was exposed in the camera the proper time. 
 
 " If it becomes a bluish grey all over, the paper has been exposed to long ; if the 
 strongest lights in the object, which should be very black in the negative, are not 
 deeper than the half tints, it has still been too long exposed ; if, on the contrary, it has 
 been exposed too short a time, the lights are but slightly marked in black. 
 
 " If the time has been just right, you will obtain a proof which wilFexhibit well- 
 defined contrasts of black and white, and the light parts very transparent. The opera- 
 tion is sometimes accelerated by heating the gallic acid, and by this process the dark 
 parts of the pictiire are rendered very black. 
 
 " To fix these negative proofs, a very strong solution of hyposulphite of soda, about 
 one ounce of the hyposulphite of soda to four fluid ounces of water, is employed, and 
 the picture is allowed to remain in it until every trace of yellowness is removed from 
 the paper." 
 
 Hx. Diamond's Process. — There is one more formula which deserves notice — I 
 mean that of Dr. Diamond, who has been a very successful follower of this process ; 
 and I think the reader will be much benefited by a careful perusal of his remarks 
 in his own words : — 
 
 "More failures," he says, " than any others depend upon not having good iodized 
 paper, which may result — 
 
 " 1. From the quality of the paper ; 
 
 " 2. The mode of preparing it ; 
 
 " 3. The want of proper definite proportions for a particular make of paper ; because 
 I find very different results ensue unless these things are relatively considered. I have 
 not met with satisfactory results in iodizing the French and German papers, and the 
 thick papers of some of our English makers are quite useless. 
 
 "Turner's paper of the ' Chafford Mills' make is greatly to be preferred, and 
 therefore I will presume that to be used, and of a medium thickness. The great fault 
 of Turner's papers consists in the frequent occurrence of spots, depending upon minute 
 portions of brass coming from the machinery, or from the rims of buttons left in the 
 rags when being reduced to pulp ; and thus a single button chopped up will contami- 
 nate a large portion of paper. Occasionally these particles are so large that they 
 reduce the silver solutions to the metallic state, which is formed on the paper ; at 
 
60 
 
 DR. diamond's process. 
 
 other times they are so minute as to simply decompose the solutioD, and white spots 
 are left, much injuring the effect of the picture. 
 
 " Whatman's paper is much more free from hlemishes, hut it is not so fine and i 
 compact in its texture, the skies in particular exhibiting a minutely-speckled appear- \ 
 ance, and the whole picture admitting of much less definition. j 
 " It may not be inappropriate to mention here, in reference to the minuteness : 
 attainable by paper negatives, that a railway notice of six lines is perfectly legible, and j 
 oven the erasure for a new secretary's name is discernible in a specimen, which was j 
 obtained with one of Ross's landscape lenses, without any stop whatever being used, 
 and after an exposure of five minutes (hiring a heavy rain. The sky was scarcely so | 
 dense as could be desired, which will be accounted for by the dull state of the atmos- | 
 phere during the exposure in the camera. ; 
 
 " Having selected your paper as free from blemishes as possible, which is most ! 
 readily ascertained by holding it up to the light (the rejected sheets doing perfectly 
 well for positives, it is well to reject all those upon which any doubt exists), mark the 
 smoothest surface ; the touch will always indicate this, but it is well at all times not 
 to handle the surfaces of papers more than can be avoided. There is much difference 
 in this respect ; some individuals will leave a mark upon the slightest touch, whereas 
 others may rub the paper about with perfect impunity. 
 
 " I prefer the paper to be iodized by the single process, because, independently of 
 the ease and'economy of time, I think more rapidity of action is attained by paper so 
 treated, as well as a greater intensity of the blacks, so requisite for producing a clear 
 
 I picture in after-printing. 
 
 " Take sixty grains of nitrate of silver and sixty grains of iodide of potassium, 
 dissolve each separately in an ounce of distilled water, mix and stir briskly with a 
 glass rod so as to insure their perfect mixture ; the precipitated iodide of silver will 
 fall to the bottom of the vessel ; pour off the fluid, wash once with a little distilled 
 water, then pour upon it four ounces of distilled water, and add 650 grains of iodide of 
 potassium, which should perfectly re-dissolve the silver and form a clear fluid ; should ] 
 it not (for chemicals differ occasionally in their purity), then a little more should be { 
 very cautiously added until the effect is produced. 
 
 " The marked side of the paper being laid upon the surface of this fluid in a proper 
 porcelain or glass dish, immediately remove it, lay it upon its dry side upon a piece of 
 blotting-paper, and stroke it over once or twice with a glass rod ; this as effectually 
 expels all the particles of air as complete immersion, it is also more economical, and 
 has the advantage of requiring much less time in the after-immersion in the 'hypo' 
 when it is required to remove the iodide. Either pin the paper up, or lay it down 
 upon its dry side, and when it becomes tolerably dry (perfect dryness is not requisite) 
 
 ; immerse it in common cold water for the space of four hours, changing the water 
 
 I during that time three or four times, so that all the soluble salts may be removed ; 
 
 i often move the papers, so that when several sheets are together, the surface of each 
 may be equally subjected to the water. j 
 
 " If this paper is well made it is of a pale straw colour, or rather primrose, and 
 perfectly free from unevenness of tint. It will keep good for several years ; if, how- 
 ever, the soluble salts have not been entirely removed, it attracts damp, and becomes 
 bro\vn and uncertain in its application. 
 
 " Upon the goodness of your iodized paper, of course, depend the future results. 
 
 j Although it is not requisite to prepare it by candle-light, which in fact is objectionable 
 
I DR. diamond's process. 61 
 
 from your inability to see if the yellow tint is equally produced, I think it should not 
 be exposed to too strong a light ; and as the fly-fisher in the dull winter months pre- 
 pares his flies ready for the approaching spring, so may the photographer, in the dull 
 1 weather which now prevails, with much advantage prepare his stock of iodized paper 
 I ready for the approach of fine weather. Many other ways have been recommended 
 
 ■ which have proved successful in different hands. Dr. Mansell, of Guernsey, pours the 
 ; iodide solution upon his paper, which previously has had all its edges turned up so as 
 I to resemble a dish; he rapidly pours it off again after it has completely covered the 
 ! paper, and then washes it in three waters for only ten minutes in all ; he considers 
 j that thereby none of the size of the paper is removed and a more favourable action is 
 i obtained. In the experiments I have tried with the air-pump, as recommended by 
 ! Mr. Stewart, I have met with much trouble and little success ; and I am inclined to 
 I attribute the very beautiful specimens which he has produced to his own good manipu- 
 I lation, under favourable circumstances. 
 
 I " To excite the paper take 10 drops (minims) of solution of aceto-nitrate of silver, 
 i and 10 drops of saturated solution of gallic acid, mixed with 3 drachms of distilled 
 I water. 
 
 I " The aceto-nitrate solution consists of— 
 
 I • Nitrate of silver 30 grains. 
 
 ! Glacial acetic acid 1 drachm. 
 
 j Distilled water 1 ounce. 
 
 I "If the weather is warm, 6 drops of gallic acid will suffice ; and the excited paper 
 
 ■ thus prepared may be kept longer. 
 
 " This may be applied either directly by means of the glass rod, or by floating, as 
 before, and then with the glass rod. If floating is resorted to, then a larger quantity 
 must be prepared. The paper should be blotted oflf by means of blotting-paper (which 
 should never be used more than once, although preserved for other purposes), and put 
 into the dark frames for use. It is not requisite that the paper should be perfectly 
 dry. This exciting should be conducted by a very feeble light ; the paper is much 
 more sensitive than is generally supposed ; in fact, it is then in a state to print from, 
 by the aid of gas or the light of a common lamp, and very agreeable positives are so 
 produced by this negative mode of printing. 
 
 " I would advise the aceto-nitrate of silver and the solution of gallic acid to be 
 kept in two bottles with wooden cases differing in their shape, so as not to mistake 
 when operating in comparative darkness. A quarter of an ounce of gallic acid put 
 into a tbree-ounce bottle, and quite filled up with distilled water as often as any is 
 used, will serve a very long time. 
 
 " I would advise that the paper should be excited upon the morning of the day 
 when it is intended to be used ; for there is no doubt the longer it is kept, the less active 
 and certain it becomes. I have, however, used it successfully eight days after excite- 
 ment, and have a good negative produced at that length of time. The general medium 
 time of exposure required is five minutes. In the negatives exhibited, the time has 
 varied from three minutes to eight, the longer time being when the day was very dull. 
 
 " The pictures should be developed by equal quantities of the aceto-nitrate of silver 
 and the saturated solution of gallic acid, which are mixed and immediately applied to 
 the exposed surface. This may be done several hours after the pictures have been 
 removed from the camera. Care should be taken that the back of the picture does not 
 become wetted, as this is apt to produce a stain which will print off upon the positive. 
 
C2 
 
 DR. DIAMOND'S PROCESS. 
 
 " If, upon the removal of the paper from the slide, the picture is very apparent, by- 
 first applying a little gallic acid and immediately afterwards the mixed solutions, less 
 likelihood is incurred of staining the negative, from its being more evenly and intensely 
 developed. 
 
 " If browning takes place, a few drops of strong acetic acid wiU generally check it. 
 Should the picture be very tardy, either from an insufficient exposure, want of light, 
 or other cause, a few drops of a solution of pyrogallic acid, of three grains to the ounce 
 of water, and a drachm of acetic acid, will act very beneficially. It sometimes gives 
 an unpleasant redness upon the surface, but produces great intensity upon looking 
 through it. Until the pyrogallic solution was added, there was scarcely anything 
 visible upon this paper, the failure having in the first instance happened from the 
 badness of the iodized paper. 
 
 " As soon as the picture is sufficiently developed it should be placed in water, which 
 should be changed once or twice ; after soaking for a short time, say half an hour, it 
 may be pinned up and dried, or it may at once be placed in a solution almost saturated, 
 or quite so, of hypo-sulphite of soda, remaining there no longer than is needful for the 
 entire removal of the iodide, known by the disappearance of the yellow colour. 
 
 "When travelling, it is often desirable to avoid using the hyposulphite, for many 
 reasons— among others, getting rid of extra chemicals ; and it may be relied on that 
 negatives will keep even under exposure to light for a very long time. I have kept 
 some myself for several weeks. 
 
 " The hyposulphite, lastly, should be effectually removed from the negative by 
 soaking in changed waters. 
 
 " Some prefer to use the ' hypo ' quite hot, or even boiling, as thereby the size of 
 the paper is removed, allowing of its being readily afterwards waxed. I have always 
 found that pouring a little boiling water upon the paper effectually accomplishes the j 
 object ; some negatives will readily wax even when the size is not removed. A very ^ 
 hot box-iron is best for the purpose ; but the most important thing to attend to is, that j 
 the paper should be perfectly dry ; and it should therefore be passed between blotting- j 
 paper and well ironed before the wax is applied. Negatives will attract moisture from j 
 the atmosphere, and therefore the ironing should be resorted to immediately before i 
 the application of the wax. | 
 
 " Before concluding these remarks, I would draw the attention of the reader to the I 
 great convenience afforded by a yellow bag, made so large as to cover entirely the head | 
 and shoulders, and confined round the waist by means of a stout elastic band. In a 1 
 recent excursion, I have with the greatest ease been enabled to change all my papers | 
 without any detriment whatever, and thereby dispensed with the weight of more than 
 a single paper-holder. The bag is no inconvenience, and answers perfectly well, at 
 any residence you may chance upon, to obstruct the light of the window, if not pro- 
 tected with shutters. 
 
 " I would also beg to mention that a certain portion of the bromide of silver intro- 
 duced into the iodized paper seems much to accelerate its power of receiving the green 
 colour, as it undoubtedly does in the collodion. Although it does not accelerate its 
 general action, it is decidedly a great advantage for foliage. Its best proportions I 
 have not yet been able to determine. 
 
 " I would also offer a caution upon too great reliance being placed upon the use of 
 gutta-percha vessels when travelling, as during the past summer I had a bottle con- 
 taining distilled water which came into pieces, anS I have now a new gutta-percha 
 
MR. STEWART'S PROCESS. 
 
 63 
 
 tray which has separated from its sides. This may appear trivial, bi;t when away 
 from home the greatest inconvenience results from such accidents, which may he 
 easily avoided." 
 
 Mr. Stewart's Process has been alluded to by Dr. Diamond, and having some 
 claim to the merit of originality, I shall introduce it here, as it may prove useful to some 
 of our amateur photographers, premising that the use of the air-pump, as directed by 
 Mi-. Stewart, is highly useful in iodizing the paper in the wax paper process. In the 
 description of his process, Mr. Stewart says : — 
 
 " I shall confine myself, for the sake of brevity, to the manipulatory details neces- 
 sary for the production of negatives. 
 
 Paper. — I prefer to all others Whatman's make, as supplied to me by Mr. Sand- 
 ford ; it is rather thick, and does not readily absorb the wax necessary to render it 
 sutficiently transparent ; but these objections can be overcome, as will be hereafter 
 explained, while it gives a minuteness as well as mellowness of detail which I have not 
 found in any other. Canson's French paper, and the paper known as ' Papier Saxe,' 
 are good papers, and the most easily handled, being strong and tenacious in their 
 texture. Both stand the action of the air-pump perfectly ; the former requires to be 
 carefully selected, it is so irregular and full of defects, but gives very intense blacks ; 
 the latter is regular and good, as far as ray experience of it goes ; it requires longer 
 exposure than the others, being less sensitive when prepared. 
 
 " To Iodize the Faper, prepare a solution in the following proportions : — Dissolve 
 one ounce (480 grains) of iodide of potassium, and 30 grains of bromide of potassium 
 (I often omit the bromide) in twenty ounces of distilled water, and filter. 
 
 " For "Whatman's paper it is advisable to reduce the iodide of potassium one-fifth 
 — to about 380 or 400 grains. Poiir this solution into a tray, and having cut sheets 
 of paper a little larger than the size finally required for the camera (this is desirable, 
 as the borders are always more or less defective in iodizing, and the paper may, after 
 that operation, be cut to the exact size required), place one sheet floating on the solu- 
 tion, then slip the next sheet edgeways underneath the first, as it floats — doing 
 this smartly, so that the sheet may not lose its rigidity before it has been slid fairly 
 imder the first sheet; repeat this with every successive sheet — as many, if necessary, 
 as the depth of the solution in the tray will permit. Any other mode of placing the 
 sheets in the tray will answer, but the above is a rapid, simple, and effectual way of 
 immersing the sheets in the bath, so as to avoid the presence of air-bubbles, and may be 
 employed on all similar occasions. "When all the sheets are immersed, cover the upper 
 one with the liquid by raising the whole bundle of the sheets together, and reversing 
 them in the bath, the upper sheet being thus undermost. In four or five minutes, 
 while still in the bath, roll this bundle of sheets up loosely, small enough to be 
 dropped into the glass cylinder, in connection with an air-pump. 
 
 " The pump I use is a simple direct-action one ; the flexible tube attached to it, 
 and through which the air is exhausted, finishes in a flat lid lined with Indian-rubber 
 (having a valve in the middle), which is placed on the top of, and hermetically closes, 
 an upright glass cylindrical vessel. When the roll of paper is dropped into the glass 
 cylinder, pour over it the solution in the tray in sufiicient quantity to cover the paper, 
 and force a piece of gutta-percha or glass down to the top of the roll, in order to 
 prevent its rising in the cylinder, while the air is being exhausted. Then placing the 
 lid on the ground top of the cylinder, a few strokes of the pump sufiice to exhaust 
 the air, and the action may be continued as long as the air-bubbles are observed to 
 
64 
 
 MR. Stewart's process. 
 
 escape from the paper to the surface. Generally speaking, four or five minutes suffice 
 for this operation, and the paper may be left a few minutes more in vacuo before being 
 removed from the pump. The roll is then picked out, or upset into the tray, and the 
 liquid again poured over it, so that the floating sheets may be easily separated as 
 they are taken out and hung up one by one on an extended cord to dry without 
 previous washing in water. They are now ready for use as required. The operation 
 may be conducted in ordinary daylight. 
 
 " "With Canson's paper and the ' Papier Saxe,' their sizing is so tenacious there 
 is no fear of continuing the action of the pump too long ; but care must be taken 
 with Whatman's paper in submitting it to the action of the pump, as it loses its sizing 
 with great facility. I believe this has been obviated in the more recent manufacture, 
 but it has been an obstacle to the use of that paper. The unsizing is indicated while 
 under the pump, by the presence of a glutinous froth on the surface of the liquid, 
 which does not disappear as bubbles do in water. When the quantity of size set free 
 is very small, the paper may still be used with safety ; but the defect is generally 
 discovered in the first sheet used, while developing in the bath of gallic acid. The 
 destruction of the body of the paper, hitherto imperceptible, is now seen, if it exist, 
 while examining the sheet by transparence ; and in that case the whole batch iodized 
 had better be set aside, as it is probable most of the sheets are injured. This paper, 
 when perfect, will keep many months, or a year; and as paper thus prepared is 
 employed in all the following processes, a quantity sufficient for a month's con- 
 sumption can be iodized at once, and put to the necessary test. Should Whatman's 
 paper be now manufactured of sufficient tenacity to resist the action of the pump, 
 there Avill remain no uncertainty as to its being perfectly iodized and uninjured, and 
 the only cause of failure with that paper removed. 
 
 " The solution of iodide of potassium can be preserved indefinitely (replenished 
 only with fresh to replace the quantity absorbed), if it is regularly filtered after use. 
 Should it become very yellow, putting into the bottle a small quantity of starch, and 
 allowing it to digest for some hours, then filtering it, will restore to it its primitive 
 purity. 
 
 " To Render the Paper Sensitive. — This operation must be performed by the light 
 of a candle or a yellow curtain. In five ounces of distilled water dissolve half an ounce 
 (or 240 grains) of nitrate of silver, and thereto add five drachms of glacial acetic acid, 
 and filter the solution. 
 
 " Method. — Pour the above solution into a perfectly clean 'tray (which should 
 never be employed for any but silver solutions), and float a sheet of iodized paper on 
 its surface, extending the sheet rapidly, beginning at one end, and lifting it once or 
 twice by the corners, to see that there are no air- bubbles ; then cover it up, and leave 
 it thus floating on the silver solution for ten to twelve minutes, or even a quarter of an 
 hour, as it is essential that the solution should thoroughly penetrate the thickness of 
 the paper. 
 
 " Should the quantity of the silver bath at hand be small, in lieu of pouring it into 
 a tray (which is rarely quite flat), sufficient may be poured on a plate of glass (the glass, 
 if need be, of a slider), levelled so that none should flow over the sides, and the sheet 
 of paper floated thereon for the same length of time. During this interval, prepare 
 the glass or slate of the camera slides by placing it beside you carefully levelled. If 
 a glass, it had better be finally cleaned with a few drops of acetic acid, to remove any 
 grease, so that water may flow readily over it. Upon this glass or slate pour a layer 
 
MR. Stewart's process. 
 
 65 
 
 of rain or distilled water, just sufficient to cover it. Then taking a sheet of thick 
 bibulous paper (printing) cut to the size of the glass, lay it thereon, so that it at once 
 imbibes the water on the glass, to which it adheres without air-bubbles, and becomes 
 a wet lining to receive presently the sensitive sheet of paper ; the excess of water 
 must be removed by lifting up the glass by the corner. Pour over this lining another 
 layer of pure water, and then, on the expiration of the ten or twelve minutes, lift the 
 sheet of sensitive paper carefully up from its bath by the corners, allowing it to drain 
 for a moment ; deposit it, floating on the paper lining, the sensitive side (that which was 
 in contact with the silver bath) uppermost towards the operator. The intervening 
 layer of water permits of the sheet being easily adjusted in its proper position ; then 
 seizing the glass, and corners of the sheets to prevent them slipping between the 
 fingers and thumb, tilt up the glass slowly and gently so as to allow the intervening 
 water to escape by one corner, when the two sheets will adhere firmly to each other 
 and to the glass, without the presence of air-bubbles. Leaving the glass for a minute 
 or two upright, with the same corner downwards, to allow all the excess of moisture 
 to disappear, it may now be placed in the slider, ready for exposure, taking care not 
 to reverse its position for some few minutes more, lest any drop should re-traverse the 
 sheet and leave a stain. The chief use of the layer of water in this operation, is to 
 prevent the presence of air-bubbles ; it also secures the proper position of the sheet 
 without handling it, which, with Whatman's paper, as at present made, is to be avoided 
 as much as possible, it tears so easily. An experienced manipulator can, however, 
 dispense altogether with the layer of water. 
 
 " The paper thus prepared for exposure preserves its extreme sensitiveness with its 
 moisture, which, according to weather and climate, may endure an hour or two, within 
 which limit, therefore, the sheet ought both to be exposed and developed. In winter, 
 and cold damp weather; it may remain moist eight or ten hours. When the view to 
 be taken can be reached within that interval of time, this mode of preparing the paper, 
 on which the image is intended to fall directly on the sheet of paper without interven- 
 tion, the most rich and delicately beautiful results are obtained. 
 
 " The time of exposure depends as usual upon the intensity of the light, and upon 
 the nature of the view, whether abounding or not in deep shadows, ajid also upon the 
 length of the focus and diameter of the diaphragm. With a 3-inch lens, focus of 14 to 
 15 inches, and diaphragm of 6-lOths of an inch diameter, the exposure for ordinary 
 landscape may vary from a quarter of an hour to half an hour. Paper thus prepared j 
 bears very prolonged exposure without injury ; I am therefore guided in my opera- 
 tions by the nature and composition of the view ; by its darker portions, without much 
 reference to the brighter lights. I also find it safer to expose it a few minutes longer 
 than may be sufficient, no injury resulting from so doing. 
 
 "2«<f Method, — In order to preserve the paper moist in aU weathers for one or two 
 days, so as to permit of distant excursions, the following modification of the preceding 
 plan should be adopted. In this operation it is necessary to employ double glasses to 
 the sliders, the paper being placed between the glasses : — 
 
 " Plunging the iodized sheet into the silver bath, instead of merely floating it on the 
 surface, cover it entirely with the liquid, avoiding air-bubbles. After remaining 10 
 minutes in the bath, lift up the sheet, allowing it to drain for a moment, and convey i 
 it into another bath of distilled or clean rain-water, to wash ofl:" some of the excess of I 
 the nitrate of silver. If the paper is to be used within ten or twelve hours, five i 
 minutes' washing will quite suffice ; if not till the next day, the washing should be j 
 
66 
 
 MK. STEWART'S PROCESS. 
 
 prolonged to ten or fifteen minutes. Sliould the distilled water, after washing several 
 sheets, become milky, it had better be renewed. 
 
 Placing the smaller glass (that which is nearest the lens during the exposure), 
 carefully cleaned with a few drops of acetic acid, on a level, * pour on it a layer of 
 distilled or rain-water. Upon this, float as before the sheet of sensitive paper removed 
 from its water-bath. In this instance it is of no consequence which side of the sheet 
 is downwards, as it is sensitive throughout and on both sides. Inclining the glass, the 
 paper will adhere to it by the escape of the water. Then replacing the glass, with its 
 adhering sheet, on the level, let it be immediately covered with a sheet of wet bibulous 
 paper (or a layer of water can first be extended, and the lining sheet be at once soaked 
 by being floated thereon and adjusted to cover the sensitive sheet, and the intervening 
 water drained off as before), and retaining the glass in the left hand, with the edge of 
 the second glass of the slider grasped in the right hand, inclined at an angle of forty-five 
 degrees, rub twice down the surface of the bibulous paper from one end of the glass to 
 the other, sufficiently hard to force out all the moistture possible, without tearing the 
 paper itself. The second glass is then immediately applied to the paper, to which it 
 clings firmly, is evenly adjusted to the other, and wiped dry ; the two adhering glasses, 
 with their imprisoned sheets, are then placed in the slider ready for exposure. Sheets 
 thus prepared remain moist a day or two, and are but little less sensitive than those 
 XDrepared as first described. 
 
 " A Third Method, which in certain circumstances may be convenient, is to prepare 
 an iodized sheet, by leaving it immersed as above in the silver bath for ten or twelve | 
 minutes, washing it in distilled or rain-water for twenty minutes thereafter, and again 
 in a second bath of distilled M'^ater, if desired to remain sensitive for more than one or 
 two days. On removal from the water, hang it up to dry, or, if hurried, dry it between 
 several successive sheets of clean and new blotting-paper. 
 
 " To those in the habit of using Mr. Lc Gray's waxed-paper process, or any of its 
 modifications, I would recommend, in preference to this last method, to iodize their 
 wax-paper with the air-pump, and use a silver solution of the strength here noted. I 
 have found a decided superiority in the waxed-paper prepared in vacuo ; it possesses 
 greater vigour, and is capable of much longer exposm-e without injury. 
 
 " In aU these processes, the iodide of silver not being confined to the surface of 
 the paper, as in other paper processes, but penetrating the body of the paper, a some- 
 what greater quantity of silver is expended :' and I would recommend all beginners, 
 until they have had some' expeiience, to use in every instance fresh solutions if 
 possible. 
 
 "The aceto-nitrate of silver solution should always be colourless ; it does not, how- 
 ever, long remain so — discolouring in a day or two. The most efiectual way of purifying- 
 it, preferable to the use of charcoal d noir animal, is, I find, to treat it as follows : — Put 
 a small quantity — say a teaspoonful or less — of kaolin (decomposed felsjjar employed 
 by the porcelain mauufactui-ers) into about eight or ten ounces of the solution, in a 
 transparent bottle, where it acts as a filter ; shake up the solution and expose it to the 
 ordinary daylight for a few minutes, in order to complete the decomposition already \ 
 commenced, by which time the felspai- has subsided, and then the liquid filtered will | 
 
 * I employ, as a very light portable level, a triangle of brass, formed of three pieces, attached 
 together at the corners by screws, which at the same time cun be raised or depressed to produce a 
 level. The withdrawal of oue of the screws permits of the pieces being shut up into the size of a 
 small ruler. 
 
ME. STEVVAllT'S PKOCESS. 
 
 67 
 
 pass clear ; a few crystals of the nitrate of silver can be added, to restore the strength 
 of the solution. 
 
 *' To Develop the Picture. — An operation also to be conducted by yello-w light. The 
 sheet, picked off the slate or removed from between the glasses, is extended as rapidly 
 and uniformly as possible on the surface of, and then immediately covered with, a 
 saturated solution of gallic acid ; say a drachm of gallic acid dissolved in a pint and a 
 half of water. This solution should only be prepared when required, and heated a little 
 to hasten its dissolution if necessary. 
 
 " A sheet prepared by the first method should be placed in the gallic acid for develop- 
 ment, before it has become quite dry, lest it should detach itself from the slate and 
 become stained by touching the slider. For the sheets between glasses, several hours 
 may intervene between the exposure and development. 
 
 " If the paper has been sufficiently acted upon by the light, as is almost invariably 
 the case, the development will take place effectually in the simple gallic acid bath. 
 The length of time required varies with the circumstances and, the paper employed. 
 Canson's paper develops rapidly, in one or two hours on the average. The paper 
 Saxe is longer in beginning to appear, and then proceeds rapidly. Whatman's paper, 
 though the most sensitive, is the slowest to develop, but supports best the action of 
 the gallic acid. Sometimes two or three hours will suffice for it, but very often ten or 
 twelve hours are not too much, and, if convenient, by removal into a fresh bath of 
 gallic acid, after the first has become dissolved and turbid, it may be left with safety, 
 and often with advantage, double that time in the gallic acid bath. The completion of 
 the development is best ascertained by examining the sheet by transparence. "When 
 the whites begin to lose their brilliancy, when the blacks become opaque and well 
 penetrated, it should then be transferred to a tray of clean water. A little experience 
 will serve to indicate when the development is complete, without the necessity of 
 lifting or handling the sheet frequently ; the view then appears to be almost lost under 
 a misty veil. The development should even be pushed beyond this point, as the details 
 in the whites (which represent the shadows of the picture) only appear at the very 
 last. 
 
 " The stains similar to marbling that are complained of as frequently occurring at 
 this stage of the operations, proceed sometimes from insufficient saturation in the silver 
 bath, but often also from want of cleanliness. To assist in guarding against this last 
 cause, it is well to adopt the practice] of never separating the sensitized sheet from its 
 paper lining ; but removing the two sheets together from the slider, immerse them so 
 in the gallic acid bath, and leave them thus, the lining undermost, until the develop- 
 ment is complete. The sheet is thus preserved by the bibulous paper from the stains 
 occasioned by the deposit on the bottom of the tray. This practice has farther the 
 advantage of enabling the manipulator to handle a large sheet of paper without fear of 
 its tearing, as it otherwise so frequently does by its own weight when lifted. 
 
 " In the case of papers sensitized by the second or third methods described above, 
 some eight or ten drops of the silver solution may be added to the gallic acid bath, 
 after the sheet has lain in the bath some ten or fifteen minutes ; but this is not always 
 necessary. 
 
 " After an hour's immersion in the gallic acid bath, should any of these sheets, 
 when examined by transparence, show blacks still very feeble, owing to insufficient 
 exposure, they can be placed in a fresh gallic acid bath to which ten or twenty drops 
 of the silver solution have been previously added ; the opacity of the black is thus 
 
68 
 
 MR. STEWART'S PROCESS. 
 
 considerably increased ty the deposit of silver on them which is thus determined. 
 But this resource should be employed with much circumspection, because it tends to 
 diminish, the harmony of the view, by rendering the contrast bet-ween the lights and 
 the shadows harsher than they are in nature, depriving the shadows of their due trans- i 
 parency, and producing the unnatural effects seen in some photographic landscapes, j 
 The various accelerating processes so frequently recommended, appear to be but this : j 
 the exposure in the camera being too rapid to permit of the image appearing under the ! 
 influence of feeble re-agents, recourse is had to those more powerful, which will always j 
 produce an image, provided the paper itself can, without staining, support their action. 
 Hence these processes only succeed well on glass, which can resist their action 
 uninjured. But these chemical re-agents destroy the natural harmony of the image, 
 substituting an artificial efi'ect ; because their action, bearing in preference on the 
 blacks, proceeds faster than in the proportion of the action of the light upon each point 
 in the camera. Thus very rapid, but less perfect, proofs are obtained. 
 
 " To Fix the Negative. — On the removal from the gallic acid bath, the sheets (still 
 by candle-light) should be washed in two or three waters for a quarter of an hour, or i 
 they may be left in the water indefinitely till it is convenient to proceed with them ; 
 then plunged in a bath of either hyposulphite of soda, or bromide of potassium of 
 the strength of one ounce of either to six or eight ounces of water, or stronger. This 
 process is preferable when abroad, as it does not expose the operator to the risk of stain- 
 ing his work, which the former is so apt to do. When the negative has lain in the hypo- 
 sulphite bath for about fifteen minutes, it may be examined by daylight to see whether 
 the yellow colour, visible on the back of the negative, or more easily by transparence, 
 has disappeared. If so, the dissolution of the yellow iodide of silver is effected and 
 the operation is terminated. The sheet is then thoroughly washed in water, frequently 
 changed, for several hours. A quarter of an hour or half an hour in the bromide bath 
 suffices to fix the negative temporarily ; but it must be fixed as above by hyposulphite 
 of soda on return home. 
 
 " The final process, which is generally necessary (though with some of these papers 
 it may be dispensed with), is to wax the negative, when perfectly dry, in order to 
 render it more transparent when required for printing. The most simple mode of 
 accomplishing this is to place the negative face downwards on a sheet of clean paper, 
 rubbing a piece of white wax on a clean heated German iron till the wax melts ; spread 
 it all over the proof, as much as it will imbibe. When the sheet is saturated, place it 
 successively on two or three sheets of thick blotting-paper, ironing it all the time till 
 it has parted with its excess of wax. Care must be taken that the iron employed is 
 not too hot ; the wax should melt freely when it touches, but without ebullition. 
 
 " Whatman's make of paper is sometimes inconveniently thick for printing from, 
 and also r eceives the wax with diflicultJ^ In that case, after fixing, but before av axing, 
 the negative should be submitted for about half an hour to a bath of concentrated 
 sulphuric acid in the proportion of one ounce to six ounces of water, and then 
 thoroughly washed in several waters. This destroys the sizing, and renders the nega- 
 tive very transparent without injury. 
 
 " These directions appear much more tedious in description than they will be 
 found in practice ; by following them, paying special attention to cleanliness, the 
 results are so regular and constant, accompanied with so little variation in their repe- 
 tition under any circumstances, that I think very little experience will suffice to render 
 any beginner expert and certain in his operations. Unless some accident, independent 
 
NEW PROCESSES. 
 
 69 
 
 of the process, intervenes, it rarely indeed happens that on going out for the day with 
 three or four sheets, I do not return with as many different and passable views, no 
 matter almost what the weather may be. 
 
 "The second of the preceding methods I find the most convenient for use when 
 absent from home ; and where one can carry a small hood, or any means of changing 
 the papers in the sliders protected from daylight, it is necessary to have but one 
 slider, as a thin box will carry six, eight, or ten double glasses with their prepared 
 sheets, to be successively exposed in the same slider as required. I have little doubt, 
 with the aid of the nitrate of zinc, these may, without any material diminution of sen- 
 sibility, be preserved moist for many days, since at present, with a little precaution 
 they retain their moisture two or three days, particularly if thick English paper has 
 been used." 
 
 New Processes. — Many new applications of the calotype processes have been 
 proposed and practised with some success, showing how universal the principle involved 
 prevails in nature. A brief summary of some of these may not be uninteresting to the 
 reader : — 
 
 Cyanotype was so called by Sir John Herschel, cyanogen in combination with 
 iron forming a leading part in the process. A piece of paper is washed over with a 
 solution of ammonio-citrate of iron, sufficiently strong to be of a sherry colour. Ex- 
 pose the paper in the camera, and develop the picture by washing it sparingly with 
 common yellow ferro-cyanate of potass, when the negative disappears, and is replaced 
 by a positive of a violet colour, on a greenish-yellow ground. 
 
 The Energetype consists in the application of a solution of succinic acid two drachms, 
 common salt five grains, mucilage gum arabic half a fluid drachm, distiUed water one 
 fluid drachm and a-half, to paper which is afterwards, when nearly dry, washed with 
 solution nitrate of silver, containing one drachm of the salt, to an ounce of distilled 
 water ; the paper is exposed in the camera. The image is brought out by the appli- 
 cation of a solution containing a drachm of concentrated solution of green sulphate 
 of iron, in two drachms and a-half of mucilage gum arabic. 
 
 Amphytype is also a discovery of Sir John Herschel, and receives its name from 
 the fact, that negative and positive pictures can be produced by one process. Paper 
 may be prepared either with the ferro-tartrate or the ferro-citrate of the protoxide of 
 mercury or of lead, by using the cream of the salts, or by successive applications of the 
 nitrates of their oxides, alternating with solutions of the ammonia-tartrate of iron. The 
 proportions of the process are not yet fixed. 
 
 THE WAX PAPER PROCESS. 
 
 Dr. Percy's Process. — We shall now consider a twin branch of the art. I 
 allude to the wax paper process, first practised by M. Le Gray, and since very success- 
 fully by several eminent photographers, amongst the most successful of whom stands 
 Mr. Fenton, whose beautiful views of several cities and places in Russia were all 
 taken by this process ; in fact, it is the most useful of any to the traveller who does 
 not wish to be troubled with the incumbrances necessary to the successful practice of 
 collodion ; and the remarks of Dr. Percy, which I subjoin, bear me out in this assertion. 
 
 Dr. Percy, after remarking that " there is no field in science which promises, at 
 the present time, a richer harvest to those who possess the scientific acquirements 
 which qualify them for its cultivation than photography," continues : — 
 
70 
 
 DR. Percy's process. 
 
 " Last summer, 1852, it will be remembered, tlie temperature was unusually high, 
 particularly in the early part of July, the thermometer frequently indicating 90" Fah. 
 in the shade. We shall all long remember the tropical character of that sultry season, j 
 — the sun shining -without a cloud for days in succession. I heard numerous complaints ; 
 from photographers, to the effect that they had great difficulty in obtaining pictures, ! 
 whether on collodionized plates, or on paper; and I met with numerous failures 
 myself with the paper process. There can be no doubt, I think, that these failures 
 were entirely occasioned by the high temperature of the season. I had, before, been 
 constantly accustomed to work successfully with the ordinary paper process in taking 
 landscape views ; the iodized paper being excited on the morning of a calo type- excur- 
 sion, and the image developed in the evening on returning home, after wandering over 
 hill and dale many a mile. 
 
 " In cold weather, I have taken tolerably good pictures some days after the ex- I 
 citement of the paper ; but, in the season mentioned, I was unable to produce pictures 
 at all satisfactory, unless the process of development took place immediately, or 
 very shortly, after the slide was withdrawn from the camera. The image, if deve- i 
 loped at a later period, was most unsatisfactory — the defect being especially conspicuous ! 
 on viewing the negative by transmitted light. It was porous, and particularly so on 
 the darker parts. The process which I employ is as follows : — 
 
 " 1. Solution for the Single Wash.~1o 100 grains of nitrate of silver, dissolved in 
 five fluid ounces of water, add 980 grains of iodide of potassium, which is rather more i 
 than sufficient to form a clear solution with that quantity of nitrate. j 
 
 " 2 Exciting Liquid. — Seventy-five grains of nitrate of silver, dissolved in one and i 
 a-half fluid ounce of water, to which are added two drachms of glacial acetic acid. | 
 One or two drops of this solution (known as aceto-nitrate of silver) to one drachm of ; 
 distilled water, to which are added one or two drops of aqueous solution of gallic acid, i 
 
 " 3. Developed by aceto-nitrate and gallic acid diluted with once or twice the ; 
 volume of water. ' 
 
 " "With the waxed paper, on the contrary, I met with excellent results during the 
 hottest part of that sultry season, having obtained a good picture after subjecting it to i 
 the following severe test : — I excited the pdper in the morning about ten o'clock, and 
 immediately afterwards exposed it in the camera. I withdrew the slide containing 
 the paper, covered it with a black velvet bag, and left it during many hours of the day 
 freely exposed to the brightest sunshine. I developed the image at ten in the evening, 
 and with perfect success. The experiment was made on one of the hottest days in the 
 early part of July. I have made several experiments on this subject, and with the 
 same result. 
 
 " Hence it would seem, that one special advantage in the use of the waxed paper 
 is, that it will keep well in hot weather. It may, therefore, be confidently recom- ; 
 mended to travellers in hot climates. For travellers, there is no photographic process, , 
 which, in respect to convenience, can be compared to the paper process ; but unless 
 the paper will keep a reasonable time when excited, the application of this process for 
 landscapes is necessarily very limited. The traveller should be able to excite the , 
 paper over night, and walk from place to place with his camera,— take any views '■ 
 which he may desire, and return home in the evening to develop them. Unless he i 
 can do this, he must have his portable tent, and carry about with him all the necessary : 
 apparatus for manipulation. In certain cases, as in rambles in the East, it may be [ 
 desirable, from other considerations, to have such a tent, in which calotype manipula- | 
 
ADVANTAGES OF THE WAXED PAPER PROCESS. 
 
 71 
 
 tions may be also practised ; and, in such cases, the objection to the processes, in 
 which the excited surfaces vill not keep, does, not so strongly apply. But, even then | 
 it is far better,, when practicable, that instead of returning from time to time to his 
 tent for the purpose of developing, he should be enabled to take his views at once, and I 
 conduct all the developments together. A process, then, is required for travellers, 
 especially in hot climates, in which the greatest portability of apparatus may be 
 obtained; and where the material upon which the image is to be received will keep 
 for a sufficient time after excitemeat and exposure in the camera, and without the 
 liability to be injured or broken like glass. Now the paper process is exactly adapted i 
 to meet these conditions ; and, with respect to landscapes, our efforts towards improve- 
 ment should be specially directed to that process. I 
 
 " As the waxed paper will keep so well after excitement and exposure in the i 
 hottest weather, it might be anticipated that, ceteris paribus, it would keep propor- ! 
 tionately longer than ordinary paper under ordinary circumstances of temperature in j 
 this climate. And the anticipation generally accords, I think, Avith the experience of | 
 photographers. One of the best negatives I ever saw was on waxed paper ; it was • 
 taken by Vicomte de Vigier a month after excitement. The scene was part of the ! 
 Forest of Fontainebleau. I have also myself obtained pretty good results with the use 
 of waxed, paper excited several days previously. 
 
 " In the ordinary paper process, however, I have not succeeded in obtaining an ! * 
 image, worthy of being called a picture, longer than five days after exciting ; though j 
 some photographers have informed me that they have obtained good pictures a con- | 
 siderably longer period after the exciting process. 
 
 It is not my intention to enter upon an exact comparison of the relative merits of \ 
 the waxed and the ordinary paper process. As the waxed paper process is at present 
 effected, I have no hesitation in expressing my strong predilection in favour of the old 
 paper process for landscapes in this country, under ordinary circumstances of tempera- 
 ture.^ The long time required in bringing out the image in the waxed paper process is 
 a serious objection— several pictures requiring many hours' attention in their develop- ' 
 
 "■In the waxed paper process, the sky is generally obtained of a beautiful and ' 
 intense black, and the limit between it and veiy distant objects is, generally, well- 
 preserved. In negatives obtained by the ordinary paper process, the sky may also be ^ 
 occasionally obtained very black ; but, in my experience, this blackness of the sky in 
 the latter process is not nearly so uniformly attained as in the waxed paper process. 
 Much might be said on the special conditions of weather which appear to be most 
 favowable to the obtaining of well-defined distances in calotypes of landscape? 
 trees, &c. ' 
 
 " On the other hand, I am not quite satisfied, that in an exact comparison between 
 a good negative on paper, such as Turner's, and a waxed paper negative, the superiority 
 must not be ascribed to the former. From what I have seen, I should, especially in 
 respect to beautiful gradation of tint, be inclined to say that the oM paper process has 
 the advantage. W^ben we reflect that in the ordinary process the image is compara- 
 ratively superficial, whilst, in the waxed-paper process it penetrates and exists in the 
 very substance of the paper itself, we might expect that, in regard to the quality 
 mentioned, the former would excel the latter. In the one case, there is only the irre- 
 gularity of the surface to deal with ; whereas, in the other, there is the irregularity of 
 the entire thickness of the paper itself." 
 
72 
 
 M. LE gray's wax PAPER PROCESS. 
 
 IVC. lie Gray's Fzocess. — Next for consideration will be the original method, as 
 practised by Le Gray himself, with modifications by others of his successful followers. 
 To M. Le Gray we are indebted for this and several other improvements in the calotype, 
 and for the following modification of the wax paper process. He dissolves, in a bain- 
 marie or flat iron pan, 300 grains of good isinglass, in a litre of distilled water ; of the 
 gelatine thus formed he takes about eleven ounces, to which he adds half an ounce of 
 iodide of potassium, 120 grains of bromide of potassium, and 60 grains of chloride of 
 sodium. When this mixture is thoroughly incorporated and filtered through fine linen, 
 and before it is cool, he dips his previously selected paper, piece by piece nto it, with- I 
 drawing it at the end of some few minutes, when it is suspended by a corner to dry. 
 This operation can be performed in a fuU light, and the paper thus prepared is said to 
 preserve its sensibility for months. 
 
 More recent French photographers suppress the bromide of potassium and the 
 chloride of sodium altogether, augmenting the iodide of potassium to 300 grains. At a 
 subsequent period M. Le Graj- claimed the discovery of the wax process, although it 
 seems doubtful if he was the first who practised it ; at least the following statement 
 gives a different version of the discovery. 
 
 M. Fabre's Process. — AVe find in the journal La Leimiere a highly interesting 
 communication from this gentleman from Eome, which seems to be the first public notice 
 ♦ of the waxed paper process. "I have long discontinued the glass in favour of a modifi- 
 cation of the wax paper and albumen process," he says, " and with most satisfactory 
 resiilts. The blacks and whites are excellent, and the half tints much softer than in the 
 other process." The writer proceeds to describe his process, which is as follows : — 
 
 Selecting the most suitable paper within his reach, a leaf, dipped in pure melted 
 wax, is placed between two other leaves free from wax. An iron, such as is in use 
 in the laundry, made moderately hot, is drawn over the paper, and suffices to wax the 
 two other leaves with the superfluous wax, In this manner thirty or forty pieces may 
 be waxed at once. To the waxed paper thus prepared albumen is applied as directed 
 for the glass process. The coating of albumen being dry, a bath of acetic acid is ! 
 applied to the albuminized side. The aceto-nitrate bath is now made use of, as in the i 
 ordinary paper process, to excite the albuminized side of the paper. The result was, as \ 
 we have stated, highly satisfactory to the author of the paper. 
 
 On the publication of M. Fabre's note, M. Le Gray claimed the credit of having 
 previously communicated the process in a paper addressed to the Academic des Sciences ; 
 however that may be, M. Fabre appears to have made the first public announcement 
 of an application of wax-paper to photography. M. Le Gray's process is as follows : — . 
 
 " First Process : To Wax ihe Paper, — This process divides itself into several parts, 
 waxing the paper being the first. For this purpose he takes the paper prepared by 
 Lacroix d'Angouleme, or that of Canson brothers of Annonay. A large plate of 
 silvered copper, such as is employed for the Daguerreotype, is obtained and placed upon 
 a tripod, with a lamp underneath it, or upon a bain-marie. The sheet of paper is 
 spread upon the silver plate, and a piece of pure white wax is passed to and fro upon 
 it until, being melted by the heat, it is seen that the paper has uniformly absorbed the 
 melted wax. "When this has thoroughly taken place, the paper is to be placed between 
 some folds of blotting-paper, and^then an iron, moderately hot, being passed over it, 
 the bibulous paper removes any excess of wax, and a paper of perfect transparency 
 is cbtuiiioil. 
 
 " Second Process : To Prepare the Negative Paper. — In a vessel of porcelain or earthen- 
 
LE GRAY'S WAX PAPER PROCESS. 
 
 73 
 
 ware capable of holding five pints and a quarter of distilled water, put about four 
 thousand grains of rice, and allow them to steep until the grains are but slightly 
 broken, so that the water contains only the glutinons portion. In a little less than a 
 quart of the rice solution thus obtained, dissolve — 
 
 Sugar of milk 620 grains. 
 
 Iodide of potassium 225 „ 
 
 Cyanide of potassium 12 „ 
 
 Fluoride of potassium 7 „ 
 
 The liquid, when filtered, will keep for a long time without alteration. 
 
 "When you would prepare the paper, some of this solution is put into a large dish, 
 and the waxed paper, sheet by sheet, is plunged into it, one over the other, removing 
 any air-bubbles which may form. Fifteen or twenty sheets being placed in the bath, 
 they are allowed to soak for half an hour, or an hour, according to the thickness of the 
 paper. Turning over the whole mass, commence by removing the first sheet immersed, 
 and hooking it up by one corner with a pin bent in the shape of the letter S, fix it on 
 a line to dry, and remove the drop from the lower angle by a little bundle of blotting- 
 paper. M. Le Gray remarks that French and English paper should never be mixed 
 in the same bath, but prepared separately, as the ' English paper contains a free acid 
 which immediately precipitates an iodide of starch in the French papers, and gives 
 to them a violet tint.' The paper, being dry, is to be preserved for use in a port- 
 folio ; even in this state it is not absolutely insensible. 
 
 " Third Process : To render the Waxed Paper Sensitive.— Make a solution of 
 
 Distilled water 2325 grains. 
 
 Crystallized nitrate of silver , , . 77 „ 
 and when this is dissolved add of 
 
 Crystallized acetic acid . . . .186 ,, 
 
 " Papers prepared with this solution will keep well for a few days. M. Le Gray, 
 however, recommends for his waxed paper, and for portraits, that the quantity of 
 nitrate of silver be increased to 155 grains ; the paper must be used moist. 
 
 "The method of preparing these papers is to float upon an horizontal plate of glass 
 either of the above solutions, and taking a piece of the iodized paper, to carefully place 
 it upon the fluid, taking great care that no air-bubbles interpose. The paper must 
 remain a short time in contact with this sensitive fluid until chemical combination is 
 eifected. Four or five minutes are required for some papers, and eight or ten seconds 
 are sufficient for other kinds. When a violet tint appears the paper should be removed. 
 
 " For those papers which it is desirable to keep for some time, as during a journey, 
 it is recommended that into one vessel of porcelain you put about five or six millilitres 
 of the strong aceto-nitrate above described, and into another somel distilled water ; 
 plunge completely both sides of the waxed and iodized paper in the first fluid, and 
 allow it to remain about four or five minutes ; withdraw it, and plunge it immediately 
 into the bath of distilled water, in which let it soak for not less than four minutes. 
 '^V^len these papers are carefully dried they may be preserved for some time for use, 
 and by lessening the dose of nitrate of silver this period may be considerably pro- 
 longed. It will, of course, be understood by all who have followed the processes 
 described up to this point, that the papers which are prepared for keeping are not 
 those which are the most sensitive ; hence it is necessary to expose them a much longer 
 time in the camera than those prepared by the stronger solution of silver. The more 
 
74 MK. teasdale's process. 
 
 sensitive paper, under ordinary circumstances of light, will require an exposure in 
 tlxe camera of about twenty seconds, the less sensitive demanding about ten or filteen 
 minutes, according to the circumstances of light. 
 
 " Fourth Process : The Development of the Image. — The picture is developed by the 
 aid of gallic-acid dissolved in distilled water. Le Gray finds the following to be the 
 best proportions : — 
 
 Distilled water .... 40 iiuid ounces. 
 Gallic acid . : . . . GO graijis. 
 
 " The paper is to be plunged into this solution, and allowed to remain until it is 
 fully developed. The time will vary from ten minutes to two hours, or more, according 
 to the intensity of the raj's incident en the paper when in the camera. The develop- 
 ment of the image is much accelerated by the addition of fifteen or twenty drops of 
 the aceto-nitrate of silver. 
 
 " Fifth Process: Fixing. — It is often found convenient, when on a journey, to give 
 a temporary fixedness to the pictures obtained, and to complete the process with the 
 hyposulphite at any time on your return home. A wash "of 360 grains of bromide of 
 potassium to two quarts of water is the strength which should be employed. The 
 process of fixing with hyposulphite consists, as in other preparations, simply in soaking 
 the paper until the yellow tint of the iodide has disappeared." 
 
 The reader cannot do better than study the conclusions arrived at by Mr. "W- 
 Teasdale, as the results of a number of carefully -performed experiments on the wax- 
 paper process, and which he has put in a tabular form, for the more easily comparing 
 one process with another. After enumerating the peculiarities which give the practice 
 of the paper processes advantages in many respects over the Daguerreotype, the col- 
 lodion, and the albumen processes, he proceeds to the consideration of the employment 
 of waxed paper as a prominent modification. The value of the wax depends not merely 
 on its filling up the pores and producing a uniform surface, but on its giving greater 
 transparency, strength, and a tenacity, which is very advantageously experienced in 
 the washings. He considers, also, that the pictures are more free from spots or 
 stains. 
 
 " Paper. — The choice of paper (Mr. Teasdale says) is of less importance than in the 
 ordinary calotype process. The texture shouldbe uniform, and the sizing wholly organic. 
 >yhatman's. Turner's, and other papers made in England, though smooth, firm, and of 
 even texture, are all sized with gelatine (glue), which not only has a tendency to retard 
 photographic action, but renders the paper so dense, that the author has found it neces- 
 sary to soak it in warm water and dry it before waxing. They also curl up strongly 
 when floated on one side ; are less transparenf , so that air-bubbles are more readily over- 
 looked in the exciting and other operations; they do not assume the desirable violet 
 tint after iodizing, and the finished negative prints very slowly. Some of these 
 papers, however, seem to bear prolonged development better than the French. The 
 papers of Canson, Laeroix, and other French makers, are almost wholly sized with 
 starch ; this increases their sensibility, and is readily permeable by the wax. Though j 
 very thin, these papers are remarkably tenacious ; but the texture, especially of the i 
 ^Laeroix' and ' New French,' is not exactly all that could be desired. The principal 
 defect in Canson's is the presence of minute particles of metallic substance, which, 
 unless removed by the process hereafter described, or some other, produce spots and 
 spoil the beauty of the negative. The paper preferred is what is known here as ' New 
 French,' the only defect of which is the texture, which does not allow of the sharpness 
 
 I 
 
JMK, TEASDALE'S process. 
 
 75 
 
 of outline required by the architect or engineer ; but this would doubtless lead the 
 artist to pi-efer it. 
 
 " IFaxing. — A cheap and easy method is to employ a thick oven-shelf, which, when 
 once heated, will be arailable for a considerable number of sheets. On this is placed 
 a clean sheet of common tin plate, which must be used for this purpose alone, and 
 kept carefully wrapped in paper when not in use. Each sheet of paper is to be laid on 
 the tin plate, and rubbed over with a piece of wax ; the perfect penetration of the 
 paper may then be assisted by rubbing with an ivory paper-knife or the handle of a 
 tooth-brush. The author employs the economical and easilj'-regulated heat of a 
 number of gas-jets, over which the plate stands on a common kitchen trivet. When 
 the requisite number of sheets have been waxed, they are ironed separately in blotting- 
 paper ; not, as is usually directed, to extract as much as possible of the wax, but to 
 remove only as much as is necessary to produce a smooth surface. 
 
 " Iodizing. — This operation is of the first importance. It is therefore desirable to 
 consider the photographic oiFeet the various substances are calculated to produce. 
 
 " Bice-water is commonly recommended as the vehicle, on account of the starch it 
 contains ; it is useful for unsized or previously washed papers, but for French papers, 
 which usually contain an excess of starch, the author prefers pure water, especially if 
 the solution contains organic substances, such as sugar of milk, albumen, &c., in 
 addition to the alkaline salts. 
 
 " Iodide of Potassium. — The quantity recommended by Le Gray and others is far too 
 small, unless thick paper is used and the light is strong. To obtain intense blacks and 
 graduated shades on French papers, the author at least doubles the quantity, unless 
 operating under a bright sunny sky. 
 
 " Bromide of Potassium. — Using achromatic lenses, the author employs a small 
 quantity of this salt, which accelerates the effect by its peculiar sensitiveness to certain 
 rays, but if much bromide is added the paper is rendered slow ; however, if insuf- 
 ficiently exposed, it bears prolonged development without injury to the whites of the 
 negative. It is probably the large proportion of this salt in the Vicomte Vigier's 
 solution, that renders papers prepared with it capable of retaining their sensibility 
 so long. 
 
 " Cyanide of Potas&ium the author was long opposed to, on account of its retarding 
 eifect and the reductioti of intensity ; but these disadvantages are more than compen- 
 sated by its penetrating the wax so readih^, taking from it the greasy appearance, 
 facilitating the saturation with the other salts, preserving the whites, and rendering 
 the negative cleaner and more transparent. 
 
 " Fluoride of Potassium the author uses in small quantity, like many other persons, 
 solely on the authority of the French operators, who attribute to it a power of in- 
 creasing the sensibility greatly, which no one seems to deny. 
 
 " CldoriiU of Sodium, used sparingly, is a valuable agent in giving intensity to the 
 blacks, and slightly increasing the sensibility ; if in excess, great care is requisite to 
 prevent solarization. 
 
 " Organic Substances. — With the exception of the starch sizing, sugar of milk is the 
 principal; like other matters of the same class, it facilitates the reduction of the metallic 
 salts, gives dense black skies, and modulates the tones of the pictures. The author 
 uses a small quantity of honey, because continental photographers state that it in- 
 creases the sensibility ; probably the use of gum arable, as recommended by Mr. 
 Ramsden, answers the same purpose. White of egg (albumen) is commonly used. 
 
76 
 
 MR. TEASDALE's process. 
 
 witliout any particular reason being given. The author employs it simply for the 
 sake of improving the appearance of the finished negative, to which it gives a slight 
 gloss. Mr. Fenton thinks it renders the paper slower. Isinglass is used only by 
 Le Gray. The author does not attribute any advantages to it, and finds it renders the 
 solution so thick and glutinous that air-bubbles can scarcely be avoided. 
 
 " Iodine. — By far the greatest improvement in all the iodizing solutions is the addition 
 of free iodine in considerable quantity, as suggested by Mr. Crookes. This certainly 
 has the power of removing metallic specks from the paper ; and as the iodized papers 
 have, before being excited, a dark purple colour, the presence of an air-bubble cannot 
 escape detection, and the process of exciting is rendered easy and certain. If the 
 solution contains any cyanide of potassium, a much greater quantity of free iodine 
 will be required than when none of this salt is present. 
 
 " Exciting. — It is stated by Mr. Hunt, that when iodide of silver is made by mixing 
 solutions of nitrate of silver and iodide of potassium, the more dilute the original 
 solutions are, the more sensitive will the precipitated iodide be. The author's experi- 
 ments confirm the doubt this raises as to the truth of the common opinion, that the 
 sensibility of the paper is in direct proportion to the strength of the silver solution ; and 
 he employs a weak solution of nitrate of silver, using a proportionately larger quantity 
 of this solution, whereby (he thinks) the manipulation is rendered easier, and the sensi- 
 bility greater and more equal over the whole sheet. 
 
 " "With the view of increasing the sensibility of papers not required to be kept long, 
 the author has tried the effect of exciting solutions containing less acetic acid (gene- 
 rally fifteen grains of glacial acetic acid to every ten grains of nitrate of silver in 
 the solution) than is recommended by Le Gray and others ; but has had more failures 
 from this cause than from any other, the pictures becoming brown in the development, 
 especially if long continued. 
 
 " The method employed to prepare, say six or eight sheets, is as follows :— Upon a 
 large piece of plate glass levelled by screws, are poured four drachms of a fifteen-grain 
 solution of aceto-nitrate of silver ; the marked side of a sheet of iodized paper is floated 
 upon this, prevented from curling up by breathing gently on it, and carefully raised at 
 each corner to see that every part of the under surface is wetted. It is allowed to remain 
 untouched for four or five minutes after the last traces of colour have disappeared from 
 the upper surface, which must be preserved from contact with the solution, to avoid 
 the probable production of black spots on the back. Eemoved from the silver solution, 
 the paper must be floated for a few minutes upon a pint or so of water (which will 
 serve for the whole six or eight sheets), holding the sheet by the corner and slightly 
 agitating it. Then it is pinned up to dry, without blotting off", merely attaching a 
 morsel of blotting-paper to the lower corner to assist the rapid draining away of the 
 liquid. If the upper corner is dried by pinching it between the thumb and finger, 
 silver pins need not bo used, as then no liquid will run down. For every fresh sheet, 
 add about two drachms of fresh aceto-nitrate solution to that on the glass plate, and 
 proceed as before. "When the sheets are all excited, pour the aceto-nitrate remaining 
 on the plate into a separate bottle for use in the development ; the quantity barely 
 sufficing, none is wasted except what is lost in the washings, and this may be recovered 
 if thought worth while. It may be better, but is by no means necessary, to use dis- 
 tilled water or filtered rain-water for washing. The water used by the author is well- 
 water, containing salts which precipitate silver, hut he finds no difference in the result, 
 whether he uses this or perfectly pure water. 
 
MR. teasdale's remarks. 77 
 
 " It is conYenient, for many reasons, to use one standard size of paper, such as a 
 quarter-sheet, 11X9 inches, for a 31 lens, or a sixth, 9 X 7u inches, for one of 2| 
 inches diameter. The latter is always used by the author. 
 
 " It is a generally received opinion that in iodizing the sheet, the maximum of sensi- 
 bility is attained at the moment when the last trace of violet or purple colour vanishes, 
 and that it then begins to diminish, unless the paper is removed. The author considers 
 this to be erroneous ; he believes the paper only attains its maximum of sensibility 
 several minutes after the colour disappears, and that the sensibility is not diminished if 
 the paper is left five, ten, or fifteen minutes longer on the exciting solution. 
 
 " Exposure— The requisite time of exposure depends on so many circumstances — the 
 lens, the diaphragm, the season, weather, hour of the day, character of view, &c. — that 
 no safe general rule can be given. Perhaps for a landscape in difi^used light, in fine clear 
 weather, an average of twenty minutes with a Ross lens two and three-quarters inches, 
 and a half-inch diaphragm, will be about the best. "With paper used wet, as in Flache- 
 ron's process, probably three or four minutes would suffice ; but the whole manipulation 
 would then bo different, and the view must be taken and developed soon after exciting. 
 The author cannot state how long his paper might be kept after exciting. Sheets kept 
 eight or ten days in autumn had not lost much ; requiring perhaps five minutes longer 
 exposure. 
 
 Developing. — It is best to prepare gallic acid in a quite saturated solution, four 
 ounces of which should be poured into the dish and cne ounce of pure water added. 
 When thoroughly mixed, the marked side of the negative is to be floated on it, breathing 
 on the back slightly as in exciting, for the same reason ; it should be left five or 
 ten minutes at least before adding any aceto-nitrate, and if the operator has not time 
 to watch the development and arrest it at the right moment, the picture may be safely 
 left for many hours floating on the gallic acid solution ; this, if the picture has been 
 over-exposed, will be the best method to prevent its being spoiled by solarization. In 
 either case, when the operator has time, the negative should be taken from the dish 
 with one hand, while with the other the two or three drachms of the refuse aceto- 
 nitrate solution above mentioned should be added and well mixed, and the negative 
 then replaced upon it. The time required to develop the image will enable the 
 operator to judge whether an additional quantity of aceto-nitrate should be added. 
 When the image is fully brought out, drain off the developing liquor, pour clean water 
 into the dish, changing it once or twice, then turn the negative face upward and brush 
 it with a camel's-hair pencil kept expressly for this purpose. If not convenient to fix it 
 at once with the hyposulphite of soda, it may be kept for a length of time, along with 
 others, in a portfolio. 
 
 " Considerable latitude is allowable as to time of exposure, as error in this respect 
 may be counteracted subsequently. If too short, so that in the longer development 
 required the picture turns brown and will scarcely print, the transparency may be 
 restored ^vitllout injury to any of the blacks, by immersion in a dilute solution of 
 cyanide of potassium, about sixty grains to one pint. This will sometimes remedy solari- 
 zation also. If the development has been arrested too soon, the fixed and finished 
 negative may be improved by floating it on a solution of chloride of gold, such as is 
 used for giving a deep violet tint to positives. 
 
 " The reason for floating the negative and developing on one side only, is to 
 preserve the cleanliness of the picture, and to prevent the stains and marbling often 
 arising from dirty dishes; the black deposit formed during the long development sinks 
 
78 
 
 TABULAR VIEW OF WAX PAPER PROCESSES. 
 
 to the bottom of the dish, and is never touched by the floating negative. Le Gray re- 
 commends acetic acid for removing stains and spots, but the author does not find this 
 agent available, while the partial use of cyanide of potassium, which alone produces 
 the effect, spoils the beauty of the negative." 
 
 I may here remark that, to amateurs generally, one of the most annoying causes of 
 failure in the wax-paper process is the marbling appearance which occurs with some 
 of the most beautiful negatives, and spoils them as perfectly as if they were soaked in 
 ink. This arises from the use of dirty dishes for the various solutions, particularly 
 those for the nitrate and gallic acid baths, but more especially the latter. Even though 
 they may seem clean, and though the picture is not even allowed to touch the bottom of 
 the dishes, the marbling may show itself in the picture during development. To insure 
 perfect cleanliness, then, which is more necessary in the waxed paper than in any 
 other photographic process, the dishes should always be thoroughly washed and rubbed 
 dry with a clean cloth, both before and after use, and a separate dish should be used 
 for each solution. In this, and in all the other photographic process, it is almost an 
 impossibility to be clean enough, therefore never spare clean cloths and plenty of water, 
 and having once put the sheet of waxed paper into either the exciting or developing 
 dish, never take it out again, or lift it without previously skimming the surface of the 
 liquid ; this is done by means of a strip of blotting-paper held by each hand, and drawn 
 along the surface, edge down. 
 
 The following, being Mr. Teasdale's Table of Comparison, may be useful to the 
 photographer. 
 
 TABLE OP THE WAXED PAPER PKOCESS. 
 
 Iodizing Solutions. 
 
 Vehicle, 
 
 Iodide of potassium 
 
 Bromide 
 
 Cyanide 
 
 Fluoride 
 
 Chloride of sodium 
 
 Sugar of milk 
 
 Honey 
 
 Albumen 
 
 Isinglass 
 
 Gum-Arabic 
 
 Free Iodine .. 
 
 I. 
 
 Le Gray. 
 
 Riee 
 water. 
 
 120 
 
 360 
 
 480 
 120 ? 
 
 1 or 2 
 
 11. 
 
 Pulcli. 
 
 Distilled 
 water. 
 
 140 
 
 81 
 8^ 
 4i 
 
 132 
 88 
 480 
 
 III. 
 
 Vigier. 
 
 Boiled 
 whey. 
 
 220 
 35 
 17 
 13 
 
 480 
 
 IV. 
 
 Feiiton. 
 
 Either 
 distilled 
 or rice 
 water. 
 
 350 
 10 
 17 
 
 26 
 350 
 
 44 
 
 slierry 
 colour. 
 
 V. 
 
 Ramsden 
 
 Rice 
 water. 
 
 90 
 
 240 
 
 50 
 nenrly a 
 port wine 
 tint. 
 
 VI. 
 
 Crookes. 
 
 Distilled 
 water. 
 
 480 
 
 sherry 
 coli'Xir. 
 
 VII. 
 W. Hunt 
 
 nice 
 water. 
 
 120 
 70 
 
 48 
 70 
 160 
 
 ad libi- 
 tum. 
 
 VIII. 
 
 Teasdale 
 
 Distilled 
 water. 
 
 240 
 
 20 
 8 
 
 10 
 
 10 
 240 
 
 50 
 480 
 
 deep port 
 tint. 
 
 Exciting Solutions. 
 
 Nitrate of silver... 32 
 
 Gl. Acet. Acid 
 
 36 
 
 36 
 (less if to 
 be kept 
 longer.) 
 
 35 
 35 
 
 15 
 15 
 
 10 or 12 
 used wet 
 
 15 
 20 to 25 
 
M- geoffboy's process. 
 
 79 
 
 " Remarks on ilis Table. — I. The large proportion of organic matter in M. Le Gray's 
 solution, renders it too thick and glutinous. The albumen represents one ounce, or 
 the white of a single egg, expressed in grains to preserve uniformity, and to facilitate 
 eomparison of the proportion of organic substances in each solution. The small pro- 
 portion of iodide is not suited for thin paper ; it howerer 'possesses the advantage of 
 sustaining uninjured the prolonged action of the developing agent better than many 
 others. 
 
 " II. Mr. Pulch's solution is very sensitive, but does not keep well ; and turns 
 brown if the development be continued too long. 
 
 "III. Viscount Vigier's solution will keep uninjured, after exciting, longer than 
 any other (say in winter six or eight weeks), but is very slow in its action. 
 
 " IV. Mr. Fenton's solution is very good, especially for the thin old Canson's paper 
 made some years ago. 
 
 " V. Although I have not been very successful in using Mr. Ramsden's solution, it 
 has produced, in other hands, the best negatives I have ever seen. It would be better, 
 I think, to double the quantity of iodide. 
 
 " VI, Mr, Crookes' solution has given me one or two good pictures, but requires at 
 least the addition of some organic matter, such as sugar of milk or rice water. 
 
 " VII. Mr, Hunt has given this solution as the result of a connected scries of 
 carefully made experiments on the use of the bromides ; but it is to be regretted that 
 he used common meniscus lenses, in operating with which I think the peculiar value 
 of the bromides is not apparent. 
 
 " VIII. I have been led to adopt my own iodizing solution for general use from 
 experiments with, and consideration of most of the preceding." 
 
 M. Geoffrey's Process. — Before leaving the wax paper for the present we 
 shall devote a few minutes to the consideration of a new method of preparing waxed 
 paper, by M. Stephane Geoffroy, of Eoanne : — 
 
 " L. M. Geoffroy places 500 grammes (about eighteen ounces avoirdupois) of 
 yellow or white wax, and one litre (about a quart) of alcohol of commercial strength 
 in a glass retort, and boils the alcohol until the wax is completely dissolved, having pre- 
 viously attached a receiver to the retort to collect all the products of distillation, he 
 then pours the still fluid mixture into a glass vessel, and as it cools the myricine and 
 cerine solidify, while the ceroleine remains in solution ; this liquid is separated by pass- 
 ing it through fine linen, and, as a final operation, mixing it with the alcohol which 
 passed over in the distillation, and filtering it through paper in a glass funnel. A store 
 of this liquid is kept in a carefully stoppered bottle, to be used as required in mixtiu-e 
 with the following. 
 
 "2. He then dissolves in loO grammes (about five ounces) of alcohol of Se^" 
 twenty grammes (five drachms Apoth. W.) of iodide of ammonium (or potassium), 
 one gramme (aboiit fifteen grains) of bromide of ammonium or potassium, and one 
 gramme (about fifteen grains) of fluoride of potassium or ammonium. 
 
 " Taking a capsule he pours drop by drop upon about one gramme (about fifteen 
 grains) of iodide of silver freshly prepared, as much of a concentrated solution of 
 cyanide of potassium as is required to dissolve it. 
 
 " This dissolved iodide of silver he adds to the preceding mixture, and agitates it 5 
 there remains at the bottom of the bottle a rather thick deposit of all the above salts, 
 which serves to saturate the alcohol, with which that already saturated is successively 
 I replaced, and removed in the manner and proportions to be described. 
 
80 lespiault's process. 
 
 "3. These two bottles being ready, -when about to prepare negatives, he takes about 
 200 grammes (six and-a-quarter ounces Apoth. "W".) of the solution No. 1, of ceroleine 
 and alcohol, with -which he mixes twenty grammes (five drachms Ap. W.) of the solution 
 No. 2. Filtering the mixture with care, to avoid undissolved crystals, which spot the 
 paper, he makes a bath in a porcelain dish, wherein he soaks for about a quarter of an 
 hour, five or six at a time, papers previously selected and cut to size ; continuing to do 
 so until the solution is exhausted. Taken out, hung up by a hook in one corner and 
 dried, these papers, which have acquired a very uniform rose tint, are covered up from 
 dust and kept dry. In rendering them sensitive with nitrate of silver, developing with 
 gallic acid, and fixing the proofs with hyposulphite of soda, the ordinary method is 
 followed — generally that of M. Le Gray — adding one or two grammes (fifteen to thirty 
 grains) of camphorated spirit of wine to one litre (about one quart) of the solution of 
 gallic acid." 
 
 The great advantages M. Geoiiroy found in preparing his negatives by this method 
 are as follows : — 
 
 " All who use paper Avaxed by M. Le Gray's process, are aware of the slow and difii- 
 cult preliminary operations required previous to rendering it sensitive with nitrate of 
 silver. They know how much precaution is required to obtain paper uniformly coated 
 and unspotted, in the midst of such long operations, where the chances of accident are 
 so numerous, the constant attention required to guard against the impurities of the wax 
 of commerce, against dust during the impregnation of the paper and the ironing, 
 against too great heat in the latter, and against bad quality of the paper used for ab- 
 sorbing. Photographers also know how much wax is lost in this process, and what the 
 quantities of paper necessarily cost in absorbing properly. The difiiculty and tedious- 
 ness of the imbibition of an aqueous solution by paper previously waxed is equally 
 known. On the other hand, by the method here described, the iodizing and waxing 
 are effected ia one simple and rapid operation ; the imbibition is, as may be imagined, 
 very uniform and complete, from the facility with M'hich alcohol penetrates ; and that 
 granular appearance which is so troublesome in ordinary waxed proofs, is avoided by 
 this method, owing to the character of the ceroleine — this substance possessing elas- 
 ticity in a remarkable degree. 
 
 "The solution of ceroleine in alcohol is moreover very easily prepared, and com- 
 paratively cheap, for the residues of stearine and myricine may be either sold or used 
 with excellent effect for waxing fixed proofs. 
 
 " The solution made by the above formula is photogenic in a very high degree ; 
 indeed, when used with either thin or thick papers, it gives, from the first bath of gallic 
 acid, blacks of an intensity which it is impossible to obtain with Le Gray's paper, and, 
 which other papers scarcely acquire after having been treated a second time with acetic 
 acid or bichloride of mercury. At the same time, they preserve the whites and half- 
 tints in a manner which surprised me. The transparency of the proofs is also admirable, 
 and the clearness of the image yields in nothing to that of proofs obtained upon 
 albumen." 
 
 Lespiault's Pxocess. — The following process by Lespiault is considered useful 
 in some cases, and is very easily prepared ; but I cannot personally speak as to its 
 merits, not having tested it : — 
 
 " The prepared papers do not," says M. Lespiault, " keep very long in the hot 
 season ; but if they are sensitized in the morning, or even overnight, they wiU keep 
 the whole day if care is taken to wash them in three fresh waters. I am speaking of 
 
lespiault's process. 
 
 81 
 
 the papiers Saxe, the only sort that I habitually use. Turner's keeps much better, but 
 
 it is only half so rapidly sensitized. This is the formula for the preparation of the 
 iodide : — 
 
 Eau de vie, from 18° to 20" . 500 grammes (16 ounces). 
 
 Sugar of milk . . to saturation. 
 
 Iodide of zinc . . 10 grammes (150 grains). 
 
 Bromide of zinc . • 2 grammes (30 grains). 
 
 " The quantities of iodide and bromide indicated above may also be dissolved in 250 
 grammes (8 ounces) of distilled water ; saturated with sugar of milk ; and 250 grammes 
 (8 ounces) of alcohol added to this solution. 
 
 " The papiers Saxe immersed in this liquid for four or five minutes take a very 
 even rose tint in drying. The paper can be kept in this longer without any bad effect. 
 
 " These papers, once dry, will keep indefinitely ; when it is wished to sensitize 
 them, float them on a bath of aceto-nitrate of silver of five per cent, with the addition 
 of from seven to eight per cent, of glacial acetic acid. 
 
 " The paper becomes little by little very white ; at the end of four or five minutes, 
 when the tint is very equal, it is taken out, and immersed in a bath of distilled water : 
 this should be renewed three times, allowing a quarter of an hour between each time, 
 and dried afterwards with blotting-paper, and the operations continued the same as with 
 the wax-paper. 
 
 " If the bath of aceto-nitrate were more concentrated, by ten per cent, for example, 
 the paper would not keep, and the print would want delicacy ; if it were weaker it 
 would be liable to unsensitized patches, or it would be necessary to keep the paper 
 much longer in the liquid. This observation applies, I believe, to all negative papers, 
 and, above all, to those which are not waxed. 
 
 " Using a lens of three inches in diameter, fifty centimetres (about thirty inches) 
 of focal length, with a diaphragm of fifteen millimetres, a quarter of an hour's ex- 
 posure, instead of thirty-five minutes, is sufacient for photographing an old building 
 or a street. Trees can be taken in the same space of time, if a diaphragm with an 
 opening large enough is employed, but, with the same diaphragm, it takes forty 
 minutes. It takes an hour and a-half with waxed or albuminized paper. I attribute 
 this enormous difference in rapidity to two causes : first, to the different bases of the 
 iodides ; and, secondly, to the absence of any fatty substance, such as wax, which 
 retards more or less the formation of the image. If the paper has not been altered 
 by the heat and the remains of the nitrate which has not been removed by the 
 washing, the whites can be preserved two hours in the bath of gallic acid. The 
 prints so obtained are delicate, and without roughness ; and the blacks are always 
 sufficient when the time of exposure has been suitable." 
 
 In conclusion, I must say that half the failures result from impure wax. The fact is 
 well known that the white wax generally sold as purified wax is more than half adulterated 
 viiih. foreign substances ; here we have a cause of failure to be only got rid of by going 
 to a respectable wax-bleacher, and telling him for what purpose the wax is required. 
 Another cause of failure or graining in the negative, although that just mentioned is the 
 greatest, is using the iron too hot when waxing. More than half the success of the wax 
 paper process depends on the perfect manner in which the paper is waxed and the 
 purity of the wax employed. 
 
 Summary Having given, in the preceding pages, the different formulae of some 
 
82 
 
 MANIPULATOKT SUMMARY. 
 
 of the most eminent and successful operators, it now remains to give the reader some 
 practical observations on the manipulatory portion of the information already con- i 
 veyed. To begin, then, with the beginning, the first subject for examination will be ■ 
 the causes of failure in " The Calotype Process." ( 
 The causes of failure in the calotype, as in all the other branches of photography, | 
 are numerous ; and, I am sorry to say, in reference to the science in general, that the j 
 causes of these failures are nearly alwaj'S to be .traced to the inattention, carelessness, [ 
 or dirty habUs of manipulation, in the operators. I saj dirti/ habits, for there is nothing j 
 so easily acquired, or so difficidt to rjet rid of, as a slovenly, dirty, method of manipu- | 
 lation. As an instance, I had a friend — in fact, a pupil — some short time back, who was ; 
 constantly writing to know the cause of this failure and of that. Now, he was remark- ; 
 ably clean and neat in his habits and person, so much so that I never for a moment j 
 thought, after I first mentioned the subject, that his failures could arise from any want ' 
 of care in that direction, and I was fairly puzzled to account for some of them, knowing ! 
 ttat his chemicals and apparatus were of the first quality. At last I determined to pay { 
 him a visit. I found that he had gone to some degree of expense as an amateur in fitting j 
 up a glass-house, dark-room, &c. ; and could plainly see that it was not from want of 
 expensive materials, or persevering trials, that he failed ; so I said to him, " "Well, I have 
 come to see you work ; so commence as soon as you like — I shall be your sitter." He 
 commenced in a first-rate style of activity, took up a glass plate (he was working the 
 collodion), picked up a piece of old linen that w^as lying on the developing bench in 
 his dark room, with which he polished his glass, coated it,, and plunged it in the bath. 
 He then proceeded to arrange and focus me ; he had a curtain over a beam, for the 
 purpose of shading one side of the face, and in his usual energetic manner he gave this ! 
 curtain a pull, in order that he might place it where he wished, and drew it suddenly 
 along the beam (which I am sure had a month's dust on it), and set a cloud floating 
 about the room that would take at least three hours to clear away. He then put the 
 plate in the camera, and, after exposing, he took up the glass holding the developing 
 I solution from out of a mess of wet, &c. ; and, in pouring the developing solution on to i 
 the plate, he let a couple of drops fall on the latter from the bottom of the developing ' 
 glass, furnished by some of the indescribable mess in which it had been previously 
 standing. Considering this, and also that the atmosphere in which the plate was 
 taken out of the bath was saturated with dust, and the state of the interior of the 
 camera in which it was exposed, recollecting, at the same time,, that the cloth with 
 which he wiped the glass was taken ofi" the sloppy bench, it is not to be wondered at | 
 that the resulting negative was somewhat similar to the first cfi'ort of a schoolboy in | 
 drawing a portrait over which he subsequently upset his ink. " There, sir," says he, | 
 " how do you account for that " I said at the time, wishing to see if he would go on ' 
 in the same way, " Well, I scarcely know ; try again." Everything was repeated exactly 
 as in the first instance, with this addition — he actually washed his gla'ss in the water 
 which had just washed the hyposulphite of soda off his last picture ! 
 
 I then told him to get his curtains taken down and dnsted, his beams and floor 
 washed out, his dark-room well scrubbed, and a small shelf put up for his developing 
 glass, covered with half-a-dozen thicknesses of blotting-paper, his cloths well washed 
 without soap, a few nails put up on which to hang them, one to be kept for cleaning out 
 the slide (or, M'hat is better, some papier Joseph), another for wiping the glasses after 
 washing, and a third for polishing them, strict care being taken that there should be 
 no dust or slop of any kind ; and the result was, that he has never had occasion to 
 
CAUSES OF FAILURE, AND REMEDIES. 
 
 83 
 
 write to me since. Now, what holds good with collodion holds good with every other 
 branch; it must be always borne in mind that the greatest care, the strictest cleanli- 
 ness, and the most undeviating perseverance, are necessary to the successful practice of 
 photography. 
 
 And now, then, to return to what I commenced with — the causes of failure in the 
 calotype process. 
 
 Causes of Failure. — If the negative in developing assume a disagi-ecable reddish 
 or foxy brown, the cause, probably, is a deficiency of acetic acid in proportion to the 
 strength of the silver used, or from the presence of nitrate of potash left in the paper ; 
 by not washing the iodized papers sufficiently, or from not using a sufiicient quantity 
 of water for the removal of the salt named. It may also arise from not using the 
 iodized paper for a considerable period after it has been prepared. It must be noted, 
 that the sooner the iodized paper is used after preparation, the more brilliant and 
 satisfactory the picture will be. 
 
 Remedy. — After well washing the negative, when fully developed, and before sub- 
 mitting it to the fixing bath, immerse it in the following solution until the required 
 black tone is acquired. Take 
 
 Chloride of gold, 1 drachm. I Hyposulphite of soda, 3 drachms. 
 
 Distilled water, f pint. | "Water, | pint. 
 
 "When dissolved, stir the water, and, stirring all the' time, add the chloride of gold 
 solution in small portions at a time. This bath will convert the foxy red colour of the 
 negative into pure black, and it must be afterwards fixed in a solution of four parts 
 water and one part hyposulphite of soda ; after which it must be well washed in 
 plenty of water. Perhaps it may be necessary to explain ■\\'hat I mean by well 
 washed. Place your photograph in a shallow dish under a water tap, and turning the 
 tap so that you may have a stream about the diameter of a good-sized quill, allow it to 
 run over your photograph for three or four hours ; after which hang up to dry. I 
 should then consider the photograph sufficiently well washed. 
 
 Spots and Stains, showing the grain of the flesh in the points of the fingers. These 
 are invariably caused by carelessly allowing the fingers to come in contact with the 
 paper when preparing it, more especiallj^ when making it sensitive in the nitrate of 
 silver bath, or in any part of the process when the fingers have been dabbling in hypo- 
 sulphite of soda previoTisly. 
 
 Remedy. — Keep the fingers particularly clean, and never touch the surface of the 
 paper at all ; handle it by the corners in every operation. 
 
 A Black Uneven Line, running from one corner in the direction of the opposite one. 
 This is caused by the use of a brass pin, for the purpose of pinning up the sheet by one 
 corner ; it partly reduces the silver, and the combined solutions running down in the 
 direction of the lowest corner causes the stain. 
 
 Remedy. — Carefully wipe your pins, and before you pass them through the papers 
 blot off' the comer to be pinned, and double a piece of blotting-paper over the corner 
 before you insert the pin. This is more necessary when using the silver solution 
 than at any other time. 
 
 Blacheniny in the Bath. — The negative will blacken all over in the developing bath. 
 This may be caused by over exposure, but in that case there will be a feeble image of 
 the object on the negative ; or it may be caused by light getting entrance to the camera 
 
84 
 
 CAUSES OF FAILURE, AND HEMEDIES. 
 
 1 
 
 independent of the lens ; or the prepared sheet may have been accidentally exposed to the 
 light previous to development. 
 
 Remedy. — Should the universal blackening be caused by accidental light, remedy 
 the defect ; if caused by oyer exposure, expose for a shorter time. 
 
 The Negative will become red, or foxy all over. This arises from the want of suf- 
 ficient acetic acid to regulate the decomposition of the silver salt, and keep it in such a 
 state that it can only be decomposed by light. 
 
 Remedy. — Increase the quantity of acetic acid. Acetic acid differs very much in its 
 strength, therefore any quantity mentioned in this treatise means that quantity of glacial 
 acetic acid. 
 
 Woolly Appearance.— A. woolly rough appearance in the negative, which of course \ 
 would be worse in the positive ; this may arise from too much washing when the paper | 
 was iodized — a paper too rough in its texture — using a rough grained blotting-paper after | 
 exciting — or using paper that has been iodized for a very longtime. It may also occur ! 
 from want of proper focusing, or the agitation of the camera during exposure from wind, ! 
 or other causes. As it would be impossible for me to say which of the above would cause 
 this appearance in any particular negative without seeing it, I can only point out the 
 cause of the effect to the reader, leaving it to him to ascertain what the particular 
 cause may be, and then he can easUy remedy it himself if he has carefully considered 
 the principles involved. 
 
 White or Black Spots, with streaks from them. These are nearly always caused by 
 the most minute particles of iron, copper, or brass, getting into the paper either acci- 
 dently or from the wear and tear of the machinery used in making it, of course there 
 is no remedy for these but to choose paper quite free from them. 
 
 Marhlings do not appear until after the first or second preparation of the paper, 
 when spots of irregular form, markings of a dozen shapes, all arise from want 
 of care, either in not skimming the surface of the developing or exciting solution, 
 when immersing or lifting negatives into or out of it, or not thoroughly washing and 
 cleaning the dishes or measures used, especially when one dish or measure has to 
 receive two or three solutions, or from not properly cleaning the glass against which 
 the paper is pressed in the paper slide, or from other similar causes. 
 
 Remedy. — More care and attention to cleanliness. Let me again impress on the 
 operator the necessity, if possible, of keeping separate dishes and measures for each 
 solution ; and even then wash and clean them, as if they had contained solutions of a 
 different nature. 
 
 Causes of Failure in the Wax Process. — Almost all the observations made with regard 
 to the calotype relate also to the wax paper process ; but the use of wax as a preliminary 
 preparationtnecessitates a few additional observations. In the calotype many of the 
 causes of failure — I mean more particularly the wooUiness of the negative — cannot be 
 traced to the same causes in the wax paper process ; for instance, the washing or 
 blotting off with rough paper, because the first operation in the latter process is to fill 
 the pores or body of the paper with wax ; this paper, of coui'se, will stand aU the 
 washing and blotting you may wish to give it, as the presence of the wax renders it 
 hard and smooth on its surface. But similar effects may be caused by the adulteration 
 of the wax,— a thing so common that, unless you go to a first-rate establishment (and 
 that must he a wax bleacher's), you cannot obtain a pure specimen ; even in the last 
 case, you must tell the principal for what purpose you want it ; but the wax you 
 will then obtain will not be white. The principal substance of adulteration is sperma- 
 
PHOTOGRAPHY ON GLASS. 
 
 85 
 
 ceti, and the woolliness or roughness is owing to the unequal action of the chemicals 
 on the atoms of wax and spermaceti. Another great cause of unequal action arises from 
 using an iron too hot, as in that case it removes the wax, and that unequally. These few 
 observations, added to the foregoing, will he quite sufficient. I would have the reader 
 bear in mind that, although the surface of waxed paper is not so easily damaged by 
 washing as the prepared paper, still it will be well to prevent any friction ; it is, 
 therefore, better to float or immerse the papers in the diff'erent solutions than 'to use 
 the glass rod ; the finest-grained blotting-paper should also be used. 
 
 ; PHOTOGEAPHY ON GLASS. 
 
 The Albumen Process — The art is indebted to Sir John Herschel for the 
 adaptation of glass plates to receive sensitized organic substances. In order to deter- 
 mine how far organic matter was indispensable to the discoloration of silver solutions 
 he prepared a solution of salt, extremely dUuted, which he mixed with nitrate of silver,' 
 so dilute as to form together a liquid only slightly milky. This was poured on a plate 
 of glass laid horizontaUy at the bottom of a flat vessel, from which, after several days, 
 the liquid was drawn off by a syphon tube, and the last portion, drop by drop, by a 
 syphon composed of a few fibres of hemp laid parallel, and moistened without twisting. 
 The glass was not touched till quite dry, when it was found coated with a uniform film 
 of chloride of silver, which adhered with considerable tenacity to the glass, but was not 
 sensitive to light. On dropping on it a solution of nitrate of silver, and spreading it 
 over by inclining the plate to and fro, it became highly sensitive. Exposed in this state 
 to the focus of a camera, it became impressed with a remarkably well-defined negative 
 picture. These experiments, communicated through the Journal of the Eoyal Society, 
 had no doubt their influence on the ardent minds who were then pursuing this wonder- 
 ful and fascinating art. 
 
 Among others who had devoted themselves to the investigation was M. Niepce de 
 St. Victor, the nephew of the discoverer of the Daguen-eotype process. This gentleman, 
 as early as 1847, had made considerable progress in developing the albumen process, 
 and seems fairly entitled to'^the merit of perfecting the idea thrown out by Sir John 
 Herschel. However that may be, from that date the use of glass was rapidly brought 
 to perfection. This process derives its name, our readers need scarcely be told, from 
 the organic substance chiefly used, namely, the white of eggs. Albumen forms one of 
 the constituents of many animal substances ; amongst others, and in combination with 
 different fatty matters, it is found in its purest state in the white of an egg. 
 
 Mr. J. E. Mayall has entered so very fully into this process in his address to the 
 Photographic Society, that we cannot do better than quote his paper. " Albumen," 
 Mr. Mayall proceeds to say, " is the true starting-point from which all animal tissues 
 are formed, as the egg contains no other nitrogenous compound except albumen ; the 
 yolk containing, besides albumen, a yellow fat only. Its chief characteristic is its 
 coagulability by heat. "We shall speak of its two conditions,— soluble, or uncoagulated 
 albumen, and insoluble, or coagulated albumen. 
 
 '■^Soluble Animal albumen of the soluble kind may be obtained in a solid 
 
 form by evaporating at a temperature below 120° ; it is then a dry, yellowish, homy, 
 and brittle mass. 
 
86 
 
 MR. mayall's albumen pkocess. 
 
 " This can be powdered, and treated succcsBively with ether and alcohol, which 
 free it from fat, salts, and other foreign matter, until we obtain it pure. 
 
 " "When thus completely dry it is without taste or odour, and has neither acid nor 
 alkaline reaction. | 
 
 " In the dry state it may be heated even to the temperature of boiling water, with- ! 
 out passing into the insoluble coagulated form. Moistened Tvith water, it swells up, j 
 becomes transparent, and by the addition of more water it dissolves into a colourless, j 
 tasteless fluid. j 
 
 " If this solution be heated to a temperature of 140", it passes into the coagulated j 
 form. Less concentrated solutions require a heat of 160°, and very dilute solutions . 
 require even boiling before the albumen will coagulate. j 
 
 " Albumen is insoluble in alcohol and ether. It is soluble to a certain extent in 
 distilled water, but much more easily in water that contains an alkaline salt or chloride 
 of sodium. 
 
 " Mulder has given great attention to its analysis. His most recent investigation 
 gives : — 
 
 Carbon 53 5 
 
 Hydrogen 7'0 
 
 Nitrogen 15 5 
 
 Oxygen 22'0 
 
 Sulphur 1'6 
 
 Phosphorus 0'4 
 
 100-0 parts. 
 
 " Albumen easily putrefies in the moist state, by the action of the atmospheric 
 agents, for which reason it requires to be used immediately after it is mixed with the 
 chemicals ; in winter the time may be prolonged to forty-eight hours, but in summer 
 not longer than six hours. 
 
 " The greater number of the metallic salts, according to Lehmann, precipitate 
 albumen, the precipitate containing either a combination of basic salt with albumen, or 
 a mixture of two compounds, one of which consists of the acid of the salt and albumen, 
 and the other of the base of the salt and albumen. The albumen generally passes into 
 the insoluble form. 
 
 The precipitated and washed albumen, when dissolved in of caustic potash, and 
 digested for one hour at a temperature of 160°, converts the sulphur and phosphorus into 
 a phosphate and sulphide. The filtered solution, if now treated with acetic acid in 
 slight excess, yields a gelatinous precipitate of protein ; which Mulder, its discoverer, 
 designates as the basis of albumen, fibrin, and casein. 
 
 " For the object of this inquiry it is sufficient to know, that albumen cannot exist 
 in the soluble state ' in the absence of mineral constituents ; that a slight alkaline 
 reaction is the best condition for photographic operations. The phosphorus which it 
 contains is a most important element of success, while the sulphur does not appear to 
 have any prejudicial eff'ect on the subsequent process with the aceto-nitrate of silver, 
 
 " The earnest inquirer is referred to Lehmann's ' Physiological Chemistry,' pub- 
 lished by the Cavendish Society ; article Albumen, vol. i. p. 330 ; and Fluids of Eggs, 
 vol. ii. p. 353; a work that ought to be carefully studied by every chemist who desires 
 to obtain accurate and recent information on this important subject. 
 
 " For the photographer's purpose the albumen of the hen's egg is the easiest of 
 
* 
 
 PREPARING THE GLASS PLATE. 
 
 87 
 
 ; access. The eggs must be fresh, not more than five days old. They ought to be kept 
 in a cool place. Those from the country are better than town-laid eggs, and I advise, 
 where practicable, that tlie hens should hayo carbonate and phosphate of lime strewn 
 about for them to peck at. This enriches the albumen and renders it more limpid. 
 Each egg must be broken separately into a shallow cup, and the yolk retained in the 
 shell as well as the germ ; then poured into a measure until the required quantity 
 of limpid albumen is obtained. 
 
 " To M. Niepce de St. Victor we are indebted for the first application of albumen 
 to photography. In the latter part of 1848 I first saw an imperfect impression of 
 some chimney-pots, at Cha. Chevallier's, optician, Paris ; he could not, or would not, 
 tell me how it was done. It was sufficient to know that the thing was possible, to 
 make me attempt it again. 
 
 " I shall in this paper confine myself to the negative process, merely remarking, 
 that the only difference between the negative and the positive process consists in sub- 
 stituting the chloride of sodium for the bromide of potassium. 
 
 " Cleaning the New patent plate-glass is the best. Get into the habit of 
 
 placing the face-side towards the wall, and into the boxes with the face towards the 
 left hand. Solution :— Alcohol, 30 grammes (450 grains) ; strong liquid ammonia 
 10 grammes (150 grains) ; water, 40 grammes (600 grains) ; tripoli, 30 grammes (450 
 grains). Shake up to mix. 
 
 " Tie up three pieces of clean cotton wool in round balls, each about the size of a 
 small hen's-egg ; then fix the glass firmly in a wooden screw-vice perfectly flat ; with 
 a piece of cotton and the above solution rub hard and evenly the surface of the glass, 
 in a similar manner as for Daguerreotype plates ; then more gently ; rear it up to dry. 
 Take another glass, which rub in the same manner, and so on for twelve dozen. 
 Change the ends to dry the upper edge of the glass. Wlicn dry, wipe the edges, 
 as also the back, slightly with another ball of cotton, without touching the surface to 
 I free it from dust. Rub off the surface with a clean ball of cotton, firmly at first, then 
 softly and evenly ; then, with a clean hog's-hair brush, dust the back and edges, and, 
 put the glass into a dry clean box, face towards the left hand. My boxes hold fifty 
 plates each. The plate must be albuminized the same day ; if left, it will be neces- 
 sary to clean them again. This plan of cleaning is both for negative and positive glass. 
 
 " Spreading on the Plate. — For twelve dozen plates the albumen should be prepared 
 as follows :— Take 450 fluid grammes (about 12 ounces) of albumen; 7J fluid ditto (112 
 j grains) saturated solution iodide of potassium; U ditto (23 grains) bromide of potas- 
 sium ; 1 drop of solution of caustic potash ; 1 gramme (15 grains) of water. 
 
 " The iodide and bromide of potassium ought to be each a saturated solution in 
 distilled water-, at a temperature of 60", and weighed in a cup carefully balanced. The 
 utmost care is necessary to observe these proportions ; if too much of the salts be used, 
 they crystallize in the albumen and make spots ; the drop of caustic potash renders 
 the albumen more limpid ; pour the above ingredients into a -wide-mouthed and rather 
 large bottle (say half-gallon), shake up until the bottle is completely filled with white 
 foam. This wiU take ten minutes. Let it stand six hours in a cool place ; then pour 
 off the clear albumen into a tall glass measure that does not taper towards the bottom, 
 but rather, like a decanting vessel, broader at the bottom, to allow any particles of 
 germ to full down and not stick to the sides. The solution should be poured into this 
 j vessel one hour before it is required. 
 
 I " It is now necessary to avoid most carefully the formation of air-bubbles, which, 
 
88 
 
 PKEPARING THE GLASS PLATE. 
 
 in the act of spreading, deteriorate the impression by making streaks; these are 
 caused by the partial drying and decomposition of the chemicals in the albumen. 
 
 " I have found the following the most effectual way to avoid these faults. I 
 have a glass fimnel with a long beak that just reaches to the bottom of my glass pint- 
 measure, upon which funnel I place a flat plate of glass turned up at the edges, -with a 
 hole in the centre ; the whole is lined with moistened muslin, so that when the 
 albumen falls on to the glass dish, in the act of pouring, it glides gently down into the 
 measure placed under. The funnel is supported by a convenient wooden stand, 
 termed in the laboratory a filter support. 
 
 " I place a wet sponge — also covered with clean muslin — on a table near at hand, 
 between the above arrangement and the drying-box. 
 
 " Let us suppose then that the dish is ready, the drying-box placed perfectly level, 
 the plates of glass all clean, a soft flat camel's-hair brush well dried and at hand. I 
 take a glass, balanced on the tips of the fingers of the left hand, brush off the dust, 
 and from the measure of albumen pour on to the surface sufficient to well cover the 
 plate ; keeping it as level as possible, then suddenly turn it down on its edge, to allow the 
 excess of albumen to run into the glass dish ; wiping it carefully for eight seconds on 
 the edge of the muslin, then again eight seconds on the sponge cushion, and placing it 
 in the drying-box. A few trials will give the exact moment necessary to deposit 
 sufficient albumen on the surface ; if too much remains, the plate will be streaked 
 and uneven ; if too little, the proof will be thin and weak. Continue spreading 
 till the drying-box is full. The French albumen drying-boxes are the only ones I can 
 use, and I therefore recommend them. Each board should be tried with a spirit- 
 level. The plates will be perfectly dry in three days ; put them into boxes in a dry 
 place, where they will keep for any length of time, though it is best not to prepare 
 more than one month's supply beforehand ; four dozen plates can be coated in an 
 hour. 
 
 " To Iodize the Plates.— As before stated, an alkaline reaction is the best condition 
 for spreading the albumen, as it renders it more limpid ; but this alkalinity is detri- 
 mental to the silvering process (an acid reaction now being of equal importance). The 
 plates have, therefore, to be passed over the vapour of iodine, just like a Daguerreotype 
 plate, to completely saturate the alkaline reaction ; this will take from two to four 
 minutes, according to the temperature ; the albumen surface ought to have a yellow 
 tinge, by the vapour of iodine ; this operation ought to be done a few hours before 
 silvering. 
 
 '■'■Silvering the Plates. — The process of silvering is performed as follows: — Take 
 1,500 grammes (50 ounces) of water, 150 grammes (about 4 ounces) of nitrate of silver, 
 and 150 grammes (about 4 ounces) of glacial acetic acid. Filter; use gutta-percha 
 baths as for collodion. I use two baths and a bath of distilled water, and so arrange 
 the dipping that each plate remains in the bath one minute and a-half. I then put 
 each plate in succession into the bath of distilled water, washing the back with 
 common, and the face with distilled, water ; rearing up to dry in a place free from dust. 
 
 " This operation is quite mechanical, and much easier to do than to describe. At 
 first the operator is afraid to run sufficient water on the plate to'wash it ; but he need 
 have no fear, as the iodo-bromide of silver is precipitated into the substance of the 
 albumen and cannot be washed out. The washing serves to make the operation more 
 certain. 
 
 " Renew' the silver bath as follows : — For every 100 plates add thirty grammes (450 | 
 
DEVELOPING THE IMAGE. 
 
 89 
 
 grains) of nitrate of silver, twenty grammes (300 grains) of glacial acetic acid, and water 
 to make up the original quantity, 
 
 " To Prepare the Flutes.— In preparing the plates for the camera, pass them over the 
 vapour of iodine half a minute previous to placing them in the camera slide ; expose in 
 the camera from thirty seconds to ten minutes, according to the intensity of the light, 
 the colour of the ohject, and the aperture of the camera; if required to be verv quick, 
 the plate should he plunged into a dilute bath of gallic acid— one of acid to" ten of 
 water. This last suggestion is made for plates to be used immediately. 
 
 " To Develop the Image.— In order to develop the latent image, use (B) a saturated 
 solution of gallic acid. (C) 400 grammes (13 ounces) of water, thirty grammes (450 
 grains) of nitrate of silver, and eighty grammes (3 ounces) of acetic acid. (D), a pint 
 bottle filled with three parts of gallic acid solution and one part water. Pour into a 
 dish, kept expressly for this purpose, about half an inch of liquid in depth, drop into 
 it eight drops of solution (C), shake it up ; then run distilled water on to the plate 
 just taken from the camera, and plunge it into the gallic acid (D) as above prepared ; 
 shake it about, fill the dish with plates, and continue to shake up, adding every hour 
 eight to twenty drops of solution (C), until the image is fully developed. The opera- 
 tion may be continued with safety for three days if necessary, though it is best to 
 complete the developing in twelve to sixteen hours. Wash well with water, rear it up 
 to dry. 
 
 "Another and quicker method of developing is with the pyrogallic acid:— 300 
 grammes (9 ounces) of water, one gramme (15 grains) of pyrogallic acid, five grammes 
 (75 grains) of glacial acetic acid, and one gramme (15 grains) of formic acid. The 
 plates will develop in half an hour in this solution, and in warm weather in less time ; 
 but I find the half-tones are not so well preserved as in the slow process. 
 
 Fixing.— Tl\x& fixing is performed as follows:— 100 water, ten hyposulphite of 
 soda. Continue the fixing till all the yeUow iodide disappears ; wash well— dry— and 
 the plate is finished. 
 
 "The hyposulphite solution should be kept entirely apart from the albuminizing ; 
 in fact, it should not be in the same room, 
 
 " The positive plates are prepared in the same way, only substituting chloride of 
 sodium for the bromide of potassium. The exposure by superposition ought to be in 
 north light ten seconds to one minute and a-half, according to the intensity of the 
 negative proof. 
 
 " I find collodion negatives print much quicker than albumen negatives ; collodion 
 is more transparent. 
 
 " I recommend the'glass to be an inch larger each way than the desired view, to 
 allow for marginal error. 
 
 " Also always, if possible, to use new glass, as I find that which has been already 
 used is uncertain, 
 
 " I have taken one hundred plates, prepared as above directed, without having a 
 single failure. In fact, each plate receives precisely the same treatment, and if the 
 directions are strictly followed, failure is almost impossible. 
 
 " Should the operator be compelled to use his glasses over again, I recommend that | 
 the albumen surface be washed off with caustic potash, and a scratch made with a ! 
 diamond on the albumen side, so as to use the other ; then wash the glass plates with I 
 common water, then with nitric acid and cotton, then much water again, then warm 1 
 water, and rear up to dry, after which, clean as for new glass. 
 
90 
 
 MR. NEGEETTl'S ALBUMEN' PROCESS. 
 
 " The solutions must be carefully corked up to avoid evaporation, tlie gallic acid 
 bottles kept full, the room free from dust, and dark thick yellow curtains to exclude the 
 actinic rays. The plates will keep excited for fourteen days, and may be developed 
 six days after the view is taken, which, to many photographers, may be an advantage. 
 
 " Never allow a sulphur match to be lighted in the albumen room ; avoi'd 
 vulcanized india-rubber rings, the sulphur from which produces spots ; wash the 
 developing dishes every time they arc used with nitric acid, and much water after- 
 wards ; wash the silver baths with distilled water, and then turn them iipside down 
 to avoid dust. 
 
 " I recommend French weights and measures : the gramme weight is 15-43 grains 
 (nearly 15^), the fluid oimce is equal to 31 grammes." 
 
 Mr. Negretti's Albumen Process.— After some directions for selecting and 
 cleaning the plate of glass, the w^riter proceeds as follows : — 
 
 " The Albumen— The manner of making albumen is very simple. You provide a 
 rather large basin — I would recommend a Berlin evaporating basin with a small Hp ; 
 you then procure a wooden fork, which is to be bought at most fancy bazaars ; but a 
 silver one is as good. Now get some good large eggs, all of a size, if possible. We 
 reckon a large egg to contain thirty grammes (very nearly an ounce) of albumen, and 
 we very seldom make more than 300 grammes (or 10 ounces) of albumen at a time, for 
 which purpose we employ ten eggs. AYe always prefer having, or making, it fresh. 
 Break the eggs one by one on the edge of a cup, and separate the yolk from the albumen, 
 using the shells themselves for the purpose. Care must be taken not to leave any of the 
 germ in the albumen. Throw the produce of one egg into the basin, and then break all 
 the others one by one on the edge of the cup, after each operation emptying it into the 
 basin. Into the albumen put one per cent, of iodide of ammonium or potassium, and 
 twenty per cent, of distilled water. I mostly mix the iodide and distilled water in a 
 glass vessel graduated into grammes, previous to putting it into the albumen; but 
 either plan will answer. Now with the fork you heat the albumen into a thick froth. 
 This wiU take about a quarter of an hour. The froth must be so thick and hard, that 
 a piece may be pulled up bodily with a fork stuck into it. "VVe prefer using 
 iodide of ammonium, for we have found that iodide of potassium has sometimes caused 
 the blacks in our negatives to become full of minute holes. The albumen having been 
 beaten a sufficient time, cover the basin with a clean sheet of paper and put it away 
 somewhere out of the dust. Many persons decant the albumen off from the basin, but 
 I prefer using it out of the basin itself, because the albumen, after it has subsided, 
 leaves a thick crust on the top, and in order to pour it on the plate it has to force itself 
 through this crust, consequently it filters itself at the sam.e time. 
 
 " The Drying j5oa;.— The box for drying the plates must be well made, with a number 
 of grooves running parallel to each otber, and the exact width of your glasses. In 
 each alternate groove there is a board, made so as not to twist easily by being heated, 
 and sliding freely in the grooves ; the box must also have an arrangement for rendering 
 it perfectly level. This box, previous to its being used, must be well dusted inside ; 
 the boards also must be well cleaned, and each well dried and heated— if in summer, in 
 the sun, or in winter before a fire. If your box and boards are not thoroughly desic- 
 cated and rendered absorbent, your plates will not dry easily. Having now- your box, 
 glasses, and albumen ready, carry all these things at oi2ce into your albuminizing roorn. 
 I say, at once, for if you go in and out of the room you will create such a dust that it 
 will not be possible for you to cover the plates nicely and cleanly. 
 
APPLICATION OF THE ALBUMEN. 
 
 91 
 
 " The room should he prepared some t^o or three hours before you want to use it ; 
 and it should be well watered and swept, and if there are any shelves, or other places 
 likely to harbour dust, they should be well wiped with a wet sponge ; for it must be 
 borne in mind that dust is your great enemy in the albumen process. 
 § . ''Tlate-holder.—'^Q albuminize the glasses you must provide a plate-holder. The 
 one I recommend is a round stick, about half an inch in diameter, and eight or nine 
 inches long, tapering at one end ; it has at the other end a small cup, about one inch 
 or more in diameter. Bound the edge of the cup, which is about a quarter of an inch 
 thick, is melted some gutta-percha. This makes the best holder I have yet tried. 
 
 " Spreading the Albumen.— ^ovr get a sheet of clean paper, and spread it on a 
 table before you ; also light a spirit-lamp, and have a small glass rod and a fine camel's- 
 hair pencil on the same table, taking one of the glasses, which should be marked with 
 a small adhesive label to indicate the side you do not intend to albuminize. Place 
 this glass with its best side flat on the sheet of paper ; then take the plate-holder and 
 warm the gutta-percha gently over the spirit-lamp. Upon placing the warm part on 
 the back of the glass, you will find that in a few seconds you will be enabled to lift the 
 glass, and handle it, or turn it as you wish. The albumen is now poured upon the 
 glass ; should it not spread evenly, the little glass rod will enable you to guide the albu- 
 men wherever you like. The albumen is allowed to drain off first at one corner and 
 then at the other. Turning it over, allow it to descend to the bottom, and that will 
 be the second time the albumen has gone over the glass. It is then turned back again, 
 and allowed to go half way. At this stage a rotatory motion is imparted to the glass 
 by means of the holder, which is continued for about seven or eight seconds ; then the 
 holder is taken hold of close under the glass and the plate forced ofiF the gutta-percha. 
 The glass is now placed in one of the grooves of the drying-box, which is shut close until 
 you are ready with the next plate. Of course, the operation must not take so long a 
 time to perform as I have taken to describe it. The smaU camel's-hair pencil serves to 
 pick off any dust that might accidentally fall on the plate during the time you are 
 spreading the albumen ; draw the pencil between your lips and use the point thus made 
 for that purpose. After remaining in the drying-box a few hours, your plates will be 
 hard enough for the next operation, which is — 
 
 " Making the Flates Sensitive— Th.^ bath we use for this purpose is a horizontal 
 one ; it is a flat dish made with a piece of plate-glass, having tight wooden sides like a 
 shallow box, the plate-giass forming a nice flat bottom. The dish should be about one- 
 third longer than your plates. The solution is composed of distilled water, nitrate of 
 silver, and glacial acetic acid, in the proportion of ten of nitrate of silver and ten of 
 acetic acid to every hundred of water. The quantity required is, of course, according 
 to the size of your plate. This solution is to be poured, say a quarter of an inch deep, 
 into the dish, one end of -w hich is raised as much as you can without spilling the 
 solution ; the albuminized plate is then placed face upwards in the upper or empty 
 part of the dish ; then, by a little dexterous movement, you suddenly, by bringing the 
 dish level, cause the solution to flow quickly and evenly over the plate, which is left in 
 the bath about forty seconds. It is as well to raise the plate up several times, and 
 otherwise agitate the bath ; for this purpose you use a small piece of silver wire 
 flattened and bent at right angles at one end. The flat part is inserted between the 
 glass and the dish, and the plate lifted by it. You must be very particular in rendering 
 your plate sensiti\e, for if you do not get your solution quicldy and evenly over the 
 plate, you will have a sharp and clear outline wherever you have stopped, precisely as 
 
92 
 
 DEVELOPING BY MR. NEGRETTl'S PROCESS, 
 
 if the negative had been cracked. The plate is now taken out of the bath, and -will 
 present a nice light-blue tint. It is immediately well washed with distilled or rain 
 water, and must be washed back and front, especial care being taken that not any of 
 the aeeto-nitrate is left on the plate, or your picture will at that spot turn black. The 
 water must flow evenly over the plate, and no greasy streaks be perceptible ; until that 
 takes place, your plate is not washed enough. The plate is now placed in a large box 
 having some blotting-paper at the bottom to facilitate draining, and is then ready for 
 use. 
 
 " Exposure in the Camera. — If your object is near, your plate will be more sensitive 
 if used wet at once ; but for keeping, it is best to let the water dry oW previously to the 
 plate being placed in the slide. 
 
 " The time of exposure depends of course on the light, the object you have to take, 
 and on the focal length of your lens ; but in summer we have taken a good negative 
 with ten minutes' exposure. In France or in Italy good albumen negatives are taken 
 in three or four minutes. A little practice, however, will soon determine the proper 
 time of exposure required. 
 
 ^'■Developing the Image. — I take a saturated'solution of gallic acid, and a solution of 
 nitrate of silver of two per cent., viz., two grammes (31 grains) of nitrate to one hundred 
 of distilled water. I get a nice soft brush or pencil, with hair about three-quarters or one 
 inch long. After placing the plate on a level developing stand, I warm my gallic acid 
 to a temperature of about 80^ Fah., and pour on the plate enough to cover it, using the 
 brush to spread it over the plate rapidly (you need not have the least fear in using the 
 brush, for it will almost require a knife to injure the albumen). After allowing the 
 gallic acid to remain about one or two minutes, I pour part of it off, and add to it some 
 of the nitrate solution, the brush being instantly at work in mixing the two solutions 
 together, forming a gallo-nitrate. The mixing on the plate must be instantaneous ; in 
 fact, I usually pour the nitrate |on the brush, which I rest on the plate. My picture 
 begins now to appear. Should I find, after a little time, that the image does not 
 show itself, which would be the case if the plate were under-exposed, I throw off this 
 solution, and begin again with the warm gallic acid, adding nitrate solution, repeat- 
 ing the operation again and again, until my picture is fully developed. By these means, 
 and by repeatedly re-changing the bath, you are enabled to coax into a very good 
 picture a jilate that you have not been enabled to expose sufficiently, either by reason 
 of some one having accidentally moved your camera, or by your being obliged to leave 
 the spot, and which would thus, in any other process, have been a failure. 
 
 " The same rule holds good, if, whilst developing, you find you have not sufficient 
 time to finish your picture. You have merely to well wash ofl? the solutions, put the 
 plate away in the dark, and you can resume the development at your leisure, a week 
 after if you wish. 
 
 " "We do not always succeed in developing our pictures sp quickly, but by attention 
 and care negatives should never take more than from half-an-hour to three-quarters ; it 
 is not imperative to warm the gallic acid, but by so doing you greatly accelerate the 
 development. The picture is now washed and ready for 
 
 ^'Fixing. — This is done with hyposulphite of soda, just in the same way as in fixing 
 a collodion negative ; but no cyanide must be used, for that will take off your albumen. 
 
 " Positive pictures on glass are generally printed on plates extra thinly albuminized 
 for the purpose, which is effected simply by rotating the plate more rapidly and for a 
 longer time. These also must be developed as quickly as possible ; but do not be 
 
THE COLLODION PROCESS. 93 
 
 tempted to use stronger nitrate solution for that purpose, or you will spoil your pictures. 
 The great fault of the albumen positives I have seen produced in England is, that it 
 has evidently taken such a long time to develop them that they have looked opaque, 
 like bad Daguerreotypes, having a metallic deposit on them which is disgreeable to the 
 eye, and which renders them anything but transparent." 
 
 ^ There is a modification of the albumen process much used in America, and I believe 
 with good results— it is called " Whipple's Albumen Process," having been introduced 
 by Mr. Whipple of Boston, a gentleman well known in the photographic world. 
 
 Mix in the usual manner : —Albumen, eight ounces ; honey, seven ounces ; iodide 
 of potassium, three drachms ; bromide of ditto, twenty grains ; chloride of soda, nine 
 grains. 
 
 For foliage, increase the bromide of potassium up to fifty grains. 
 ^ This mixture is poured on the glass plate in the same manner as collodion, and then 
 dried over a spirit-lamp. The plate is then immersed for ten to twenty seconds only 
 in the following bath : — 
 
 Nitrate of silver, one and a-half ounces; water, sixteen ounces; acetic acid, 
 four ounces. 
 
 After the dipping, the plate must be well washed, and if all the free silver is washed 
 off, the plates wiU keep for four weeks. Develop with a saturated solution of gallic 
 acid and nitrate of silver, and fix in the usual manner with hyposulphite of soda. 
 
 Collodion Process — Collodion as a photographic medium is, without doubt, far 
 before any other. The beauty of the details obtained in good pictures taken by this 
 process, the exceeding sensibility of the medium itself, and the comparative ease of its 
 manipulation, place it at the head of all photographic agents. I shall, therefore, go 
 mto this branch of the art as fuUy as possible, preferring rather to say too much than 
 too Uttle. 
 
 Mr. Archer, who was the first, in conjunction with Mr. Fry, to introduce this impor- 
 tant addition to the art, deserves our utmost thanks for enabling us to obtain eflTects so 
 utterly impossible to be obtained by any other means. Some idea of the value of the 
 discovery may be formed from the fact, that instantaneous pictures have been taking by 
 Mr. Fenton, of clouds, waves, shipping, animals, figures, &c., by a single lens. On one 
 occasion, where a man was running, the leg that was on the ground when the lens was 
 uncovered was perfectly defined, while the other left three or four impressions in its 
 transit during the moment of exposure. 
 
 Choice of Glass.— This may be classed under five heads Cleaning the plates, 
 coating with collodio-iodide of silver, exposure in the camera, developing the image, 
 fixing the image ; but first a few words on the choice of the glass. Here we can 
 follow no more faithful guide than Mr. Hardwich :— 
 
 " Much care should be taken in the selection of glass intended to be used for pho- 
 tographic purposes. The ordinary window-glass is often inferior, having scratches 
 upon the surface, each of which causes an irregular action of the developing fluid. 
 Also the squares are seldom perfectly flat, so that they do not touch the slide at every 
 point, and hence a part of the image is out of focus. A more serious inconvenience, 
 arising from want of flatness, is, that the plates are apt to be broken in compression 
 during the printing process. 
 
 " The patent plate answers perhaps better than any other description of glass, but 
 if that cannot be procured the ' flatted crown' may be substituted. 
 
 '^Cieminff the Plates.— Beforo proceeding to wash the glasses, each square should be 
 
94 
 
 PREPARING THE PLATE. 
 
 roughened on the edges by means of a file or a sheet of emery-paper. If this precau- 
 tion be omitted, not only are the fingers liable to injury, but the collodion film is apt 
 to contract and separate from the sides, 
 
 " In the process of cleaning the glasses, it is not sufiicient— as a general rule— to 
 wash them simply with water ; other liquids are required to remove grease, if any is 
 present. For this purpose, perhaps, caustic potash, sold in druggists' shops under the 
 name of ' liquor potassaj,' is as good as any ; or, if that is not at hand, a warm solution 
 of common ' washing soda,' which is carbonate of soda. 
 
 "Liquor potassas, being a very caustic and alkaline liquid, requires care in the 
 handling ; it softens the skin, and dissolves it away even more so than acids. A safe 
 plan of proceeding is to dilute the potash with about four parts of water, and to apply 
 it to the glass by means of a cylindrical roll of flannel ; after wetting both sides of tho 
 glass thoroughly, allow it to stand for a time until several have been treated in the 
 same way ; afterwards wash well with water and rub dry in a cloth. 
 
 " The cloths used for cleaning glasses should be kept expressly for that purpose ; 
 they are best made of a material sold as ' fine diaper,' and very free from flocculi and 
 loosely adhering fibres. They are not to be washed in soap and water, but always in 
 pure water or in water containing a little carbonate of soda. 
 
 " After wiping the glass carefully, complete the process by polishing with an old silk 
 handkerchief, avoiding contact v.dth the skin of the hand. Some object to silk, as tend- 
 ing to render the glass electrical, and so to attract particles of dust, but in practice no 
 inconvenience will be experienced from this source. Before deciding that the glass is 
 perfectly clean, never omit to hold it in an angular position and to breathe upon it. 
 
 " The use of an alkaline solution is usually sufiicient to clean the glass, but occa- 
 sionally we meet with plates dotted on the surface with small white specks, which are 
 not removed by the potash. These specks consist frequently of hard particles of car- 
 bonate of lime ; and when that is the case they dissolve very readily in dilute sulphuric 
 acid, in about four parts of water, applied by means of a roll of flannel. Nitric acid, 
 also diluted in four parts water, also answers the same purpose ; but it destroys any 
 dress it comes in contact with, unless it is at once treated with liquor ammonia or some 
 other alkali." 
 
 Some operators employ cyanide of potassium, and others ammonia, in cleaning the 
 plates. A mixture of Tripoli powder and spirits of wine is preferred by those who fear 
 injuring the skin by the use of alkalies and acids. 
 
 "When positives are to be taken, it is advisable to use additional care in preparing 
 the glass, and especially so with the pale, transparent fllm and neutral nitrate bath. 
 
 After a glass has once been coated with collodion, it is not necessary in cleaning a 
 second time to use anything but pure water; but if the film has been allowed to 
 harden and dry upon the glass, possibly the dilute oil of vitriol, or cyanide of potas- 
 sium, may be required to remove stains. 
 
 If, under similar circumstances, a greasincss is perceived, which prevents the plate 
 from being wetted evenly by a stream of water poured upon it, it may be removed by 
 a second application of alkaline liquid. 
 
 The Collodion.— Of the collodion itself, no better instructor can be followed 
 than Mr. Edward Ash Hadow, whose address to the Photographic Society we cannot 
 do better than quote : — 
 
 " Having," says that gentleman, "experienced some difficulty in producing at all 
 times a collodion of uniform sensitiveness, tenacity, and fluidity, although making use 
 
PREPARING COLLODION. 
 
 95 
 
 of the same materials for its preparation, and this as I find being the complaint of many 
 others, it has been my study lately to determine the variations in quality to which the 
 ingredients are liable, and the effects of those variations on the sensitive fiJm ; and like- 
 wise to ascertain whether the qualities depend on the materials in ordinary use, or on 
 some substances accidentally or intentionally added. Eesearches on the preparation of 
 collodion may appear superfluous, now that it is supplied of the best quality by so 
 many makers ; but as some persons of an independent turn of mind still prefer manu- 
 facturing their own, I venture to bring forward the subject with the hope of assisting 
 them. In this beautiful process success depends so much on the quality of the collo- 
 dion, that, when in possession of a good specimen, it becomes one of the easiest and 
 most simple, and ought to be the most certain of all the processes ; for no material, 
 such as paper, of uncertain composition is introduced, we have nothing to fear from 
 plaster of Paris, alumina, or specks of iron or copper, which continually endanger or 
 modify the calotype process ; each ingredient can and ought to be obtained in a state 
 of perfect purity, and with this knowledge the degree of success depends upon the skill 
 of the operator himself. 
 
 " Of all the substances used in this process, the gun-cotton is usually the only one 
 actually prepared by the operator himself; in this case he cannot fail to have observed 
 the great variations in solubility, and, when dissolved, in the transparency and tenacity 
 of the films, to which it is liable ; the various processes also tbat are given appear at 
 first sight unaccountably different, some directing ten minutes', others a few seconds' 
 immersion. I have examined into the cause of these variations, with a view to obtain 
 certainty, and have also endeavoured to discover how far they aifect the sensitiveness 
 of the prepared surface. If we take a mixture of the strongest nitric and sulphuric 
 acids, and immerse as much cotton as can be wetted, after some minutes squeeze out 
 the acid as far as possible, then immerse a second portion of cotton, and again express 
 the acids for a third portion of cotton, and so on until the liquid is exhausted, we shall 
 find, on comparing the cottons thus treated, after washing and drying them, that there 
 is a gradual alteration in their properties, the first being highly and perfectly explosive, 
 and each succeeding portion less so, until the portion last immersed wiU be found 
 hardly explosive at all, leaving distinct traces of charcoal or soot when burned. 
 
 " This may not appear surprising at first sight, as it may be imagined tbat the 
 latter portions are only a mixture of gun-cotton and common cotton ; this, however, is 
 not the case, for if each quantity be immersed sufiiciently long, it will not contain a 
 fibre of common cotton, and may yet become charred on burning like unaltered cotton. 
 The most remarkable difi'erenee, however, is discovered on treating them with ether 
 containing a little alcohol, when, contrary to what might have been anticipated, the first 
 or strongest gun-cotton remains quite untouched, while the latter portions dissolve 
 with the utmost ease, without leaving a trace behind ; this alone is a sufiicient proof 
 that no unaltered cotton remains. This difi'erenee in properties is owing to the gradual 
 weakening of the acid mixture, in consequence of the nitric acid being removed by the 
 cotton, with which it becomes intimately combined, at the same time that the latter 
 gives out a proportionate qirantity of water. 
 
 " In consequence of these experiments, a great many mixtures of these acids were 
 prepared of various strengths, each being accurately known, both to determine whether 
 there were more than one kind of soluble gun-cotton ; and, if there were, to ascertain 
 exactly the mixture required to produce that most suitable to photographic purposes. 
 By this means, and by, what I believe has not been pointed out, varying the tempera- 
 
96 
 
 PHOTOGRAPHIC PROPERTIES OF COLLODION. 
 
 ture, at least five Tarieties were obtained :— First, gun-cotton properly so called, as 
 before stated, quite insoluble in any mixture of alcohol and sulphuric ether. Secondly, 
 an explosive cotton, likewise insoluble, but differing chemically from the first, obtained 
 by a mixture of certain strength when used cold. If warm, however, either from the 
 heat produced spontaneously on mixing the two acids, or by raising the temperature 
 artificially to about 130'', the cotton then immersed becomes perfectly soluble, pro- 
 ducing a third variety ; if, however, it be thoroughly dried it becomes in a great 
 measure insoluble. The fourth is obtained by the use of weaker acids used cold, and 
 the fifth when the mixture has been warmed to 130° previous to the immersion of the 
 cotton ; in either of the last two cases the product is perfectly soluble, but there is a 
 remarkable difference between their properties, for on dissolving six grains of each in 
 one ounce of ether, the cotton treated with warm acids gives a perfectly fluid solu- 
 tion (which is likewise the case with the third variety produced by acids somewhat 
 stronger), while that obtained by the use of cold acids makes a mixture as thick as 
 castor-oil. 
 
 " Having obtained these more strongly-marked varieties, as well as intermediate 
 kinds with all gradations of solubility, it was necessary, before I could select any par- 
 ticular formula for prepari ng the cotton, to compare their photographic properties, with 
 especial reference to sensitiveness, opacity of the reduced silver in negatives, and its 
 colour in positives. A certain weight of each being dissolved in a portion of the same i 
 mixture of alcohol and ether previously iodized, the comparison was made, by taking j 
 the same objects with each collodion in succession, and likewise by pouring two samples | 
 on the same plate of glass, and thus exposing them in the camera together side by side. 
 This last proved to be much the most satisfactory plan, and was repeated many times 
 for each sample, taking care to reverse the order in which they Avere poured on, that 
 there might be no mistake arising from the ditference of time elapsing between the 
 pouring on of the collodion and its immersion in the sensitive bath. By these experi- 
 ments I had confidently hoped to have solved the question as to the cause of difference 
 in sensitiveness and other photographic properties of collodion ; but in this I was dis- 
 appointed, for, after repeated experiments, I believe I may safely af&rm that they arc 
 precisely similar as regards their photographic properties. The same, I believe, may ! 
 be said of Swedish paper collodion, judging from a few comparative experiments I j 
 have made, and indeed it is difficult to discover what is the superiority of this material 
 over clean cotton-wool. The ease of manipulation, which some allege, is a matter of 
 taste ; but I should decidedly prefer the open texture of cotton to that of a substance ' 
 like filtering paper, composed of a mass of compacted fibres, the innermost of which arc ; 
 only reached when the acids have undergone a certain degree of weakening by the i 
 water abstracted from the outer fibres ; and when we consider that from cotton alone | 
 we have the means of preparing all varieties of collodion, from the most powerfully I 
 contracting and transparent to the weakest and most opaque, and each if required with : 
 equal and perfect certainty, there appears to be choice enough without resorting to j 
 another material, differing only in being more rare and more difficult to procure. But j 
 although the photographic properties of these varieties of collodion-wool are so similar, ; 
 other circumstances, such as fluidity, tenacity, and transparency, render its preparation i 
 of some importance, and indicate that the acid mixture should always be used warm ; ■ 
 and it is chiefly in consequence of this very circumstance, that greater success attends | 
 the use of nitrate of potash and sulphuric acid than that of mixed acids ; for the former j 
 when mixed produce the required temperature, and must be used while warm, since on | 
 
EXPERIMENTS ON COLLODION. 
 
 97 
 
 cooling the mixture becomes solid, whereas acids when mixed do not usually produce 
 so liigh a temperature, and being fluid can be used at any subsequent period. Another 
 obstacle to their use is the great uncertainty of the strength of the nitric acid found in 
 the shops, requiring a variation in the amount of sulphuric acid to be added, which 
 wo-uld have to be determined by calculation or many troublesome trials. When a 
 proper mixture is obtained, the time of immersion is of no importance, provided it be 
 not too short, and the temperature be maintained at about 120° or 130°; ten minutes 
 is generally sufficient (though ten hours would not render the cotton less soluble, as is 
 sometimes asserted). 
 
 " In using the mixed acids, the limits are the nitric acid being too strong, in which 
 case the product is insoluble, or too weak, when the cotton becomes immediately 
 matted, or even dissolved if the mixture is warm. I have availed myself of these facts 
 in order to produce collodion wool by the use of acids, without the trouble of calcu- 
 lating the proper mixture according to their strength. Five parts by measure of sul- 
 phuric acid, and four of nitric acid of specific gravity not lower than 1-4, are mixed in 
 an earthenware or thin glass vessel capable of standing heat ; small portions of water 
 are added gradually (by half drachms at a time, supposing two ounces to have been 
 mixed), testing after each addition by the immersion of a small portion of cotton ; the 
 addition of water is continued until a fresh piece of cotton is found to contract and 
 dissolve on immersing ; when this takes place, add half the quantity of sulphuric acid 
 previously used, and (if the temperature does not exceed 130°, in which case it must be 
 allowed to cool to that point) immerse as much cotton, well pulled out, as can be 
 easily and perfectly soaked ; it is to be left in for ten minutes, taking care the mixture 
 does not become cold ; it is then transferred to'cold water and thoroughly washed. This 
 is a matter of much importance, and should be performed at first by changing the 
 water many times, until it ceases" to taste acid, treating it then with boiling rain- 
 water until the colour of blue litmus remains unchanged ; the freedom from all trace 
 of acid is insured by adding a little ammonia before the last washing. Cotton thus 
 prepared should dissolve perfectly and instantaneously in ether containing a little 
 alcohol, without leaving a fibre behind, and the film it produces be of the greatest 
 strength and transparency, being what M. Gaudin terms ' rich in gun-cotton.' The 
 mixture of nitrate of potash and sulphuric acid is defective chiefly from the want of 
 fluidity, in consequence of which the cotton is less perfectly acted on ; this may be 
 remedied by increasing the amount of sulphuric acid, at the same time adding a little 
 water. A mixture of five parts of dried nitre, with ten of sulphuric acid, by weight, 
 together with one of water, produces a much better collodion wool than the ordinary 
 mixture of one of nitre with one and a-half of sulphuric acid. The nitre is dried 
 before weighing, in order that its amount, as well as that of the water contained in 
 the mixture, may be definite in quantity ; it is then finely powdered, mixed with the 
 water, and the sulphuric acid added ; the cotton is immersed while the mixture is hot, 
 and afterwards washed with greater care even than is required when pure acids are 
 used, on account of the difficulty of getting rid of all the bisulphate of potash that 
 adheres to the fibres, which both acts as an acid and likewise causes the collodion to 
 appear opalescent when held up to the light— whereas the solution should be perfectly 
 transparent. 
 
 " Having obtained good collodion wool, the next point of inquiry was with regard 
 to the solvent : to ascertain whether the addition of alcohol beyond what is absolutely 
 necessary to cause the solution of the gun-cotton in ether,' was beneficial or otherwise. 
 
S8 
 
 CHEMICAL QUALITIES OF COLLODION. 
 
 Tot this purpose ether and alcohol wore prepared perfectly pure, and mixtures were 
 made of one of alcohol to seven of ether, two to six, three to five, four to four, and five 
 to three. In one ounce of each were dissolved six grains of gun-cotton and four grains 
 of iodide of ammonium (iodide of potassium could not he employed, since it requires a 
 certain amount, both of water and alcohol, to keep it in solution) ; they were then 
 compared, using a thirty-five grain solution of nitrate of silver, both by pouring on 
 separate glasses, and likewise by covering two halves of a plate with two samples, as 
 in examining the gun-cottons, thus placing them under the same circumstances during 
 the same time ; in this way the effect of adding alcohol was very clearly perceived, 
 since the differences between the collodions was much greater than could have been 
 anticipated. The first mixture containing only one-eighth of alcohol was quite unfit 
 for photographic purposes, it being almost impossible, even with the most rapid 
 immersion, to obtain a film of uniform sensitiveness and opacity throughout, the surface 
 generally exhibiting nearly transpai-ent bands, having an iridescent appearance by 
 reflected light. The second mixture, with one-fourth of alcohol, is liable to great uncer- 
 tainty, for if there be any delay in poming off the collodion, the same appearances are 
 seen as in the first, and, like it, the surface is very insensitive to light, while, if the 
 plate be rapidly plunged in the bath, the collodion film becomes much more opaque 
 than before, and is then very sensitive. The third proportion of three of alcohol to 
 five of ether, is decidedly the best, giving without the least difficulty a film beauti- 
 fully uniform and highly sensitive, at the same time perfectly tough and easily 
 removable from the glass if required. A farther addition of alcohol, as in the last two 
 collodions, was not attended with any corresponding advantage or increase of sensitive- 
 ness ; on the contrary, the large proportion of alcohol rendered them less fluid, though 
 with a smaller quantity of gun-cotton they would produce very good collodions, capable 
 of o-iving firm films. The cause of the weakness of the film observed on adding much of 
 the ordinary alcohol is the large amount of water it usually contains. 
 
 " This surprising improvement, caused by the addition of a certain quantity of 
 alcohol, is referable to causes partly chemical, partly mechanical, for on examining the 
 films it will be found in the first, and occasionally in the second collodion, that the 
 iodide of silver is formed on the surface, and can be removed entirely by friction with- 
 out destroying the transparent collodion film below, while in those collodions that con- 
 tain more than one-fourth of alcohol, the iodide of silver is wholly in the substance, and 
 in this state possesses the utmost sensitiveness. This difference of condition is owing 
 to the very sparing solubility of ether in water, which in the first case prevents the 
 entrance of the nitrate of silver into the film, consequently the iodide and silver solu- 
 tions meet on the surface ; but on the addition of alcohol, its solubility enables the two 
 to interchange places, and thus the iodide of silver is precipitated throughout the sub- 
 stance in a state of the utmost division. 
 
 " This difference is clearly seen under the microscope, the precipitate being clotted 
 in the one case, while in the other the particles are hardly discoverable from their fine- 
 ness. The presence of a little water considerably modifies these results, since it in 
 some degree supplies the place of alcohol, and is so far useful ; but in other respects it 
 is injurious, for accumulating in quantity, if the collodion is often used, it makes the 
 film weak and gelatinous, and what is worse, full of minute cracks on drying, M'hich is 
 never the case when pure ether and alcohol are used. Since the ether of the shops 
 almost always contains alcohol, and frequently water, it is important to ascertain their 
 amount before employing it for the preparation of collodion. The quantity of alcohol 
 
99 
 
 may be easily ascertained by agitating the ether in a graduated measure glass (a minim 
 glass does very well) with half its bulk of a saturated solution of chloride of calcium. 
 This should be poured in first, its height noticed, and the ether poured on its surface, 
 the thumb then placed on the top, and the two agitated together ; when separated, the 
 increase of bulk acquired by the chloride of calcium indicates the quantity of alcohol 
 present, and for this, allowance should be made in the addition of alcohol to the collo. 
 dion afterwards. Water is readily detected, either in ether or alcohol, by allowing a drop 
 to fall into spirit of turpentine, with which they ought to mix without turbidity ; this 
 ia immediately produced if they contain water. For detecting water in alcohol, benzole 
 is a more delicate reagent than spirit of turpentine (Chemist, xxix. 203). Ii is also 
 necessary that ether should be free from a remarkable property it acquires by long 
 keeping, of decomposing iodides and setting free iodine, which thus gives the collodion 
 a brown colour. The same property may be developed in any ether, as Schonbein dis- 
 covered, by introducing a red-hot wire into the vapour in the upper portion of a bottle 
 containing a'little ether and water ; if it be then shaken up and a solution of an iodide 
 poured in, the whole rapidly becomes brown. This reaction is veiy remarkable and 
 difficult to explain, for even a mixture of ether and nitric acid fails to produce a colour 
 immediately. Ether thus affected can only be deprived of this property by rectification 
 ^vith caustic potash. 
 
 " Iodized Collodion. — I have now a few remarks to ofi'er on the modes of iodizing or 
 rendering the film capable of becoming sensitive, by the addition of some soluble 
 iodide. Those that have been recommended are chiefly the iodides of potassium, am- 
 monium, cadmium, and zinc : of these the last three have the great advantage of being 
 readily soluble in any collodion, and may therefore be added at once to the solution of 
 gun-cotton ; but iodide of potassium requires a little water, and even then, if added to 
 collodion without having been previously dissolved in some of the alcohol, will be 
 found to dissolve but very slowly. 
 
 " In preparing collodion with this salt, four grains were dissolved in three drachms 
 of strong alcohol, and ether was added to make up the ounce. I found that the first 
 two and a-half drachms of ether began to precipitate the iodide, and after addition of 
 the five drachms required, a dense deposit had formed, which was not re-dissolved 
 until twelve drops of water had been added. This I merely mention to show that there 
 must be a little water in the mixture, although in using ordinary ether and alcohol 
 this might not be perceived. Before comparing collodion prepared with different 
 iodides, it appeared probable that those of potassium and ammonium would produce 
 greater sensitiveness than those of zinc and cadmium ; for this reason, that the nitrates 
 of ammonia and potash, which are produced together with iodide of silver, on im- 
 mersing films prepared with the first two iodides in the nitrate bath, are perfectly 
 neutral, while the nitrates of zinc and cadmium, which result when collodions con- 
 taining those metals are used, have a feebly acid reaction on litmus paper, and thus 
 by their presence in the film might, like weak acids, retard the action of light. In 
 actual GXporiment, however, I did not find this to be the case, for when carefully and 
 similarly prepared with equivalent quantities of each iodide, and used while colourless, 
 the collodions appear similar in sensitiveness, gradation of tints, and all other respects. 
 In a few days, however-, they begin to differ in consequence of partial decomposition 
 and liberation of free iodine, which occurs more readily with the iodides of ammonium 
 and zinc than with potassium, while the iodide of cadmium, if I may conclude from 
 one sample I have by me, remains perfectly colourless for any period of time, retaining 
 
100 
 
 FOGGING, AND ITS REMEDIES. 
 
 its original sensitiveness, the other varieties having lost theirs in proportion to the 
 colour they have acquired. The iodide of cadmium, in addition to this valuable 
 property of giving a stable collodion, is likewise extremely soluble, without being 
 deliquescent, , and being beautifully crystalline, is not liable to adulterations or im- 
 purities, and therefore well deserves to be generally tried. 
 
 " In order to preserve or, as it is stated, to improve the sensitiveness of collodion, 
 some persons recommend the addition of a little ammonia. This, however, appears 
 very unadvisable, since it necessitates the use of an acid bath; and although it may 
 render the collodion less liable to change, it produces a contrary effect on the bath, 
 since every plate immersed tends to neutralize a portion of acid, and at length rendering 
 it neutral or even alkaline, brings about exactly the phenomena (fogging) described by 
 Mr, Fcnton. 
 
 " The cause of fogging (which is blackening of the whole negative on the addition 
 of the developing solution) is owing to the bath becoming alkaline. This alkaline 
 reaction is caused by oxide of silver in a state of solution in the bath. 
 
 " Oxide of silver is not soluble in water, nor in water containing nitrate of silver ; 
 but it ia, in either case, abundantly dissolved if nitrate of ammonia be present, and the 
 solution will be found to restore rapidly the colour of reddened litmus paper. 
 
 " The ' alkaline nitrate of silver bath,' therefore so called, is a solution containing, 
 besides nitrate of silver, oxide of silver, dissolved in nitrate of ammonia. 
 
 " The nitrate of ammonia is produced by double decomposition when compounds of 
 ammonium are used for * iodizing' instead of those of potassium. Iodide of ammonium 
 plus nitrate of silver equals iodide of silver plus nitrate of ammonia. 
 
 " The oxide of silver, which by its solution causes the alkalinity, is formed either 
 by using collodion containing a little free ammonia in addition to the other ingredients, 
 as sometimes recommended, or by attempting to neutralize an acid bath with potash or 
 ammonia, and inadvertently adding an excess. 
 
 " So that if ammonia or salts of ammonia in any shape have been added to the 
 collodion, or to the bath, it will be necessary from that time forward to examine more 
 carefully than we otherwise should have done, that the faintly acid condition of the 
 bath, so essential to the production of a good picture, is not destroyed. 
 
 " With ordinary collodion, however, even when quite colourless, the bath may 
 always be used perfectly neutral, permitting the developing solution to be left on twice 
 or three times as long as is necessary, without the slightest fogging, provided that the 
 nitrate of silver is pure and the bath has not acquired fogging propensities by prolonged 
 use. No pure alkaline iodide can ever render the bath alkaline ; the only effect on 
 immersing a plate covered with collodion is to remove a portion of silver and substi- 
 tute an equivalent quantity of potassium, ammonium, &c., so that a portion of nitrate 
 of silver is merely replaced by a portion of nitrate of potash or ammonia, which, being 
 neutral, cannot in this respect affect the state of the bath. "With the iodides of the 
 metals, such as iron, zinc, cadmium, or arsenic, the bath, on the contrary, will soon 
 become apparently acid from the presence of the nitrates of those metals which, as 
 before stated, redden litmus. 
 
 " In all cases, excepting when free ammonia has been added to the collodion, the 
 silver solution has a tendency to become acid rather than alkaline, both from the 
 frequent presence of free iodine in the collodion, which sets free nitric acid in the 
 bath, and also from the slow formation of acetic acid from the alcohol and ether 
 washed out from the plates that have been immersed. The effect of free iodine in the 
 
MR. ASH HADOW'S EXPERIMENTS. 
 
 101 
 
 : collodion, is not, however, chemically the same as that of nitric acid in the bath ; for 
 I nitrate of silver is, like all other nitrates, a nitrate of the oxide of silver. When, 
 • therefore, free iodine acts on the silver solution, it liberates oxygen as -well as nitric 
 i acid, the result being that an iodate as well as an iodide of silver is formed ; the eflfect 
 ' of the former should therefore be ascertained, in order to clearly understand the action 
 i of brown collodion. "When a great deal of iodine has been set free by long keeping, 
 j making the collodion very dark-coloured and insensitive, I found that the addition of a 
 little oil of cloves, in the proportion of four drops to each ounce, causes a surprising 
 ! increase of sensitiveness ; and some time ago I always used such a mixture for the 
 , production of positives on glass, from a belief that a better colour and more perfect 
 gradation of tints were obtained in this way than by any other method. 
 
 " At this time my pictures were constantly liable to solarization (or darkening of 
 those parts that ought to be whitish), when using the ordinary collodion and developing 
 by pyrogallic and nitric acids ; but lately, while seeking for difficulties in order to 
 discover their causes, this tendency to solarization quite disappeared, although using 
 I the simplest materials ; neither was I able to produce it by taking objects in the most 
 unfavourable conditions of light and shade, nor by any addition to the collodion. 
 Accidentally trj'ing the effect of a minute quantity of nitrite of silver in the nitrate 
 bath, I obtained it again in perfection, and was able at once to understand how it 
 occurred formerly, for at that time I always made use of nitrate of silver that had 
 been strongly fused, and in which a portion of nitrite had thus been formed, while 
 latterly only the crystallized salt had been employed. The effect of oil of cloves and 
 iodine in the collodion was to counteract that of the nitrite ; but when pure crystallized 
 nitrate is used, no such additions are required. 
 
 " It is remarkable, that although oil of cloves greatly increases the sensitiveness 
 when brown collodion is used, no such effect is produced by its addition to colourless 
 collodion with an acid bath, proving that free iodine in the former is not exactly 
 similar to nitric acid in the latter. To compensate for the bad effects of the nitrite on 
 the colour of positives, it has the important property of much increasing the sensitive- 
 ness and rapidity of the surface, allowing pictures to be taken instantaneously with far 
 less light than is usually required ; and it is thus particularly suited to negatives, in 
 which the colour by reflected light is of no importance, while it adds to the opacity of 
 the dark parts of the picture. Its effect on the colour of positives is chiefly seen when 
 pyrogallic acid is xised for developing, and becomes more marked as the picture dries, 
 when the tint of the reduced silver becomes darker, and of a greenish colour in the 
 most exposed parts, while with pure nitrate, as the moisture evaporates, it becomes 
 lighter, and the details appear more distinctly represented in various shades of one 
 colour. As this nitrite is formed when the nitrate is overheated, it generally exists in 
 i ' lunar caustic' to a greater or less extent ; but as this substance, from a want of 
 ! crystalline form, is easily and frequently adulterated, it is much better to add the 
 ! nitrite to a solution of the crystallized nitrate in quantities less than half a grain to an 
 ! ounce of a thirty-five grain solution, for too large an amount causes a fogging of the 
 1 clear parts of the picture. It is easily obtained by fusing pretty strongly a mixture of 
 I equal parts of nitre and nitrate of silver ; the fused mass being dissolved in a small 
 quantity of boiling water, and left to cool ; the nitrite of silver then crystallizes in 
 the shape of long, slender needles, which may be removed, and pressed in blotting- 
 paper to dry them ; by re-crystallizing they are obtained quite pure. 
 
 " The strength of the solution of nitrate of silver ought to be proportional to the 
 
 B 
 
102 
 
 MK. ASH HADOW'S EXPERIMENTS. 
 
 quantity of iodide in tlie collodion, at least so far that it cannot be diminished beyond 
 a certain point (depending on the collodion used) without a great loss of sensitiveness, 
 or, what is exactly similar, if we uSe a bath of a certain strength, the quantity of 
 iodide cannot be increased to any amount, but must be limited by the propoi-tion of 
 nitrate of silyer: with a thirty -five grain solution of the latter, four grains of iodide 
 to the ounce of collodion answers very well ; but if the quantity be increased to six 
 grains, there is a great loss of sensitiveness and intensity, the effect being similar to 
 that arising from an insufficient amount of alcohol in the collodion, in consequence of 
 the iodide of silver being deposited superficially, or even falling off the surface into the 
 silver bath. The mistake of over-iodizing the collodion is generally committed with 
 the view to obtain greater opacity of the reduced silver, apparently from an idea that 
 the iodide only is reduced, while in fact a large portion of the reduced silver is derived 
 from the nitrate, so that a very little iodide in the film is sufficient to give intense 
 negatives. For this purpose the collodion should be colourless, or nearly so, or at 
 least, if coloured, it must not be owing to free iodine (which is ascertained by allowing 
 a drop to evaporate on a piece of starch or a crumb of bread, and then moistening with 
 water ; a trace of iodine is detected by the black colour resulting) ; the bath should 
 likewise be neutral, or nearly so, and the developing fluid should contain no more 
 acetic or tartaric acid than is sufficient to prevent blackening- of clear parts ; after the 
 pyrogallic solution has apparently done its utmost, the intensity may be further in- 
 creased by pouring on a fresh portion, mixed with some of the silver solution, which 
 immediately adds to the opacity of the negative, a fresh deposit taking place on the parts 
 already reduced. By the use of the nitrate as before mentioned, still greater opacity 
 may be obtained, together with the utmost rapidity ; at the same time there is none of 
 that violent contrast of light and shade which appears to result from the addition of 
 iodide of iron, as an accelerating agent, to the collodion. I believe that salts of iron 
 have not as yet been used for developing negatives, in consequence of the want of 
 opacity in the reduced parts. I find, however, that the proto-acetatc of iron obtained 
 by mixture of solution of acetate of lead and sulphate of iron, is capable of producing 
 intense negatives, resembling in all respects those obtained by pyrogallic acid, while 
 it has the advantage in point of economy ; but I have not as yet made a sufficient 
 number of experiments to enable me to determine the strength of the solution best 
 suited to the purpose ; it need not be very great, somewhat less than eighteen grains 
 to the ounce, for if it contain so much as this, it is liable to produoe universal 
 blackening when first prepared ; but in a few days, when a portion of peracctate has 
 formed, it answers very well. My object in endeavouring to find a substitute for 
 pyrogallic among the iron compounds, is not to add to the number of developing fluids 
 and the perplexity of a beginner. Where pyrogallic acid can be obtained pure, and 
 is found to answer perfectly, in that case it is preferable to anything else ; but as this 
 may not always be, it is useful sometimes to know of a substitute that can be prepared 
 wherever gi-een vitriol and sugar of lead can be found, for these substances, even when 
 impure, are very easily purified by re-crystallizing from a solution in boiling water; 
 which is not the case with pyrogallic acid, to which noxious ingredients might easily 
 be added, accidentally or intentionally, from which it would puzzle a chemist to 
 free it. 
 
 " By knowing the qiiantity of iodide contained in a collodion, it is easy to ascertain 
 the amount of silver that the bath loses for each ounce, and thus to know exactly how 
 much nitrate should be added to maintain the same strength ; thus, with a collodion 
 
MR', hahdwich's experiments. 
 
 103 
 
 containing four grains of iodide of ammonium to the ounce, each ounce expended 
 removes four seven-tenths grains of nitrate of silver, but with four grains of iodide of 
 potassium the quantity of nitrate consumed is only four one-tenth grains. In the first 
 case nitrate of ammonia, in the second nitrate of potash, accumulates in similar pro- 
 portions, but the ammonia salt has the advantage of being easily dissipated on evapo- 
 rating the bath and gently fusing, leaving only salts of silver behind, while the nitrate 
 of potash is quite fixed." 
 
 mx. Hardwich's Researches.— Having thus quoted' Mr. Ash Hadow's paper, 
 I shall proceed to make the reader acquainted with the results of some most valuable 
 researches as to the nature, properties, and capabilities of this most useful photo- 
 graphic medium, conducted by Mr. F. Hardwich, of King's College, London. I 
 may add, that both these gentlemen well deserve the thanks of every photographer, 
 for the care with which they have studied this important branch of the art, and the 
 generous manner in which they have given the results of their researches to the public. 
 Mr. Hardwich's remarks I quote from the Photographic Journal. This gentleman 
 was led to consider the condition of the film most favourable for the production of 
 pictures to be viewed by reflected light, by a paper translated from the French of M. 
 Gaudin, and published in the Journal of the Photographic Society. 
 
 " My attention," he says, " was first directed to the positive process, quite, as I 
 may say, accidentally ; and when I was comparatively ignorant of the effects which 
 would be produced by varying the proportions of the ingredients in the sensitive collo- 
 dion ; having adopted Archer's method of iodizing, viz., by adding a certain quantity 
 of a saturated alcoholic solution of double iodides of potassium and silver, I failed, 
 from the alcohol I employed being in too concentrated a state. I had previously 
 rectified it from carbonate of potash, and its solvent power being thus diminished, the 
 amount of iodides taken up was not sufficient for the purpose. When I say ' I failed,' 
 I mean it in the sense that I was not able to obtain good negative pictures, which was 
 the object I had then in view. They were all sadly wanting in ' intensity,' and I 
 found it impossible to ' print' from them with anything like success. However, I soon 
 observed that these unsatisfactory negative pictures looked exceedingly well when 
 viewed as positives by reflected light ; there was a nice gradation of tone about them 
 ■which pleased me, and I adopted the plan of backing them up with black varnish, 
 and preserving them in that form. 
 
 Now at this time, as I said before, I was not aware that I was employing a collo- 
 dion with an unusually small proportion of iodide ; but if I had been, I should not 
 have referred my success in producing positives to that cause. I had never seen it 
 stated in any work with which I was acquainted, that a difference ought to be made 
 in the two cases. The directions I had received were these :— ' If you wish to obtain 
 a positive, expose in the camera for half the usual time, and develop with sulphate of 
 iron, to get a bright deposit of metallic silver.' Now the object I have in view is to 
 pi-Gve that, if we wish to obtain the best results, we must use not only a different 
 developing fluid, but also a different collodion and a different nitrate bath, in the case 
 of negative and positive pictures respectively. It may be asked, ' What is the infe- 
 riority of which you complain in the positives produced by collodion, as it is ordinarily 
 sold?' I answer, it is this : ' That the whole of the picture is not to be seen at once 
 upon the surface of the glass.' Suppose you are taking a portrait, which I think will 
 readily be allowed to be one of the most severe tests of a collodion that can easily be 
 applied, it will be found that the high lights, such as the forehead, the hands, and 
 
104 
 
 MR. habdwich's experiments. 
 
 especially the shirt of the sitter, come out with exceeding rapidity, and in a degree out 
 of all proportion to the time taken hy the shadows and half-tints to impress them- 
 selves ; the consequence of this is, that, stop the action of the light when you will, you 
 do not obtain a perfect picture. After backing up with the black varnish, it will be 
 seen either that the high lights are good, and the rest of the figure almost invisible, or, 
 on the other hand, that the coat, dress, &c., are very clear, whilst the face and hands 
 present an unvaried white and flat surface, without any detail or distinction of parts. 
 These peculiarities do not depend upon the time of exposure, nor in any way on the 
 developing fluid, but simply on the fact that the collodion employed is not capable of 
 giving such a film of iodide of silver as is adapted to produce impressions visible by 
 reflected light. 
 
 " Having thus stated the principal difficulties which we have, ordinarily speaking, 
 to encounter, I proceed to show how they may be overcome, and what is the best 
 sensitive mixture for that purpose. In making my experiments, I first prepared simple 
 collodion by dissolving soluble cotton, four grains, in five drachms of ether and three 
 of highly-rectified alcohol. These are the proportions recommended by Mr. Hadow, 
 and I believe them to be the best that can be used. They do not, of course, apply to 
 commercial ether, which already contains a considerable quantity of alcohol. In order 
 to iodize my collodion, I employed iodide of ammonium (purified with care) in four 
 different proportions, viz., four grains to the ounce, two grains, one and a-half grain, 
 and one grain. 
 
 " The films produced by these four mixtures, after dipping the plate in the nitrate 
 bath, were very difierent in appearance ; the lowest of all was pale, of a bluish 
 opalescent tint, so transparent that the letters of a newspaper could be read through it 
 with facility ; the second somewhat similar ; the third of a grayish hue, but stiU com- 
 paratively transparent ; the highest of all, viz., the four-grain, creamy and opaque. 
 
 " The photographic properties of the films differed considerably ; after comparing 
 numerous results, I was satisfied that the two-grain solution was superior to the four- 
 grain for the purpose I intended it ; more of the details of the picture were visible at 
 once on the surface of the glass, and there was less tendency to the over-done, flat 
 appearance before complained of. Between the ' two-grain' collodion, the ' grain and 
 a-half,' and ' the grain,' there was likewise a difference, but not to the same extent ; 
 on the whole I was disposed to give the preference to the ' grain and a-half,' the last 
 of all requiring too long an immersion in the bath to be used with advantage. 
 
 " It was not my intention, at the time I began these experiments, to make any 
 variation in the amount of soluble cotton generally used ; I found that four grains to 
 the ounce gave a strong and even film upon the glass, and such being the case, there 
 appeared nothing more to be desired ; however, a fact that came under my notice soon 
 afterwards, altered my determination ; I began to suspect that the weak solutions of 
 nitrate of silver I was employing did not penetrate the film properly, and consequently 
 I I wished, if possible, to remove this objection by diminishing its thickness. The 
 I result of the change proved even better than I had anticipated, although the solutions 
 j were rather more troublesome to manipulate with ; I obtained invariably more perfect 
 : pictures ; the gradation of tints was now decidedly superior to anything that I had 
 met with before, and although I could not immediately explain the reason, I was 
 satisfied that I had gained an advantage. 
 
 " The composition of the collodion which I found after many trials to work the 
 best, is as follows : — Ether, five drachms ; alcohol, three drachms ; soluble cotton, one 
 
MK. hardwich's experiments. 
 
 105 
 
 and a-half grain ; iodide of ammonium, one and a-half grain — instead of this, two 
 grains of each may be used, or even as little as one grain, without very materially 
 affecting the result ; but in the latter case the mixture is so fluid, that it is apt to run 
 down the neck of the bottle while attempting to pour it on to the plate. These pro- 
 portions become very simple when it is considered that they are at once produced by 
 diluting down an ordinary negative collodion rather more than one half, with the 
 proper mixture of alcohol and ether. 
 
 "There is one point which I ought to mention : by diminishing the proportion of 
 iodide in the film, and by diminishing the soluble cotton, the sensitiveness is increased. 
 "Why is it that these weak films give better half-tones than the opaque ones ? Because 
 they are more sensitive to feeble rays of light ! I made many experiments to deter- 
 mine this, and I have no hesitation in stating that such is the fact. Neither is it 
 difiicult to conceive why it should be so, because, as it has been remarked, the more 
 dilute the solutions from which iodide or chloride of silver is precipitated the more 
 gradual the precipitation, and the more finely divided will the particles of the precipi- 
 tate be ; we can well understand that, such being the case, they ought to be more 
 sensitive to light ; we must not, however, confound ' sensitiveness ' with * intensity.' 
 I would use this latter term to signify that the deposit of metallic silver producing the 
 image is thick, and obstructs the luminous rays of light strongly, so as to show well as 
 a negative ; ' intensity,' I imagine, relates in some degree to the number of the 
 particles of iodide of silver — in other words, to the thickness of the film ; but ' sensi- V 
 tiveness' is independent of this. Now, ' intensity' is required for negative pictures, but 
 it is not required for positives, and therefore, in such a case, I would have as little 
 iodide as possible. 
 
 " At the risk of repetition, I will give a short recapitulation of the conclusions 
 which I wish to establish. They are these : — That no proportion of alkaline iodide in 
 collodion beyond that which gives the transparent opalescent film, is adapted to pro- 
 duce a perfect image, visible in every part by reflected light. Allowing that a photo- 
 graphic picture is produced by chemical rays of light acting in various degrees on the 
 several parts of a sensitive surface, it becomes necessary that the particles of iodide 
 composing that surface should be in a peculiar state both as to number and as to 
 fineness of division, in order that the more intense and the feebler rays should work 
 uniformly together, the tendency being in the former, so to speak, to get a-head and 
 outrun the latter ; while a diminution in the proportion of iodide assists the action of 
 the feeble rays by producing a more finely-divided deposit, and curbs the violence of 
 the more energetic rays by lessening the number of the particles. 
 
 " I shall now proceed," Mr. Hardwich continues, in a subsequent paper, " to 
 consider the proper strength of the nitrate bath and of the developing fluid. 
 
 " "With regard to the nitrate bath, there were two points of interest to be ascer- 
 tained, — 1st, whether the salt of silver could be used in an accurately neutral condi- 
 tion, and, if so, what are the best proportions ; 2nd, the effects of adding nitric acid 
 in graduated quantities. 
 
 " Three solutions of nitrate of silver were prepared, of different strengths ; A, forty 
 grains to one ounce of distilled water ; B, thirty grains ; C, twenty grains : all were 
 carefully neutralized, and saturated with iodide of silver. 
 
 " On immersing a plate coated with a four-grain iodide collodion in each of these, 
 it was found that with bath C the decomposition of the alkaline salt was imperfect. 
 However, with the proportion of iodide reduced from four grains to two grains, or 
 
106 
 
 MR. HAKDWICH's nitrate BATH EXPERIMENTS. 
 
 one and a-half grain, the appearance of tlie film was the same in each bath, showing 
 that even the lowest proportion of nitrate of silyer was sufficient for the conversion of 
 the whole of the iodide of ammonium into iodide of silver. 
 
 " A comparison was next made of its photographic properties., the one and a-ialf 
 grain collodion being used in every case. 
 
 " 1st. Sensiiiveness. — Here the difference was not very marked, perhaps the twenty- 
 grain solution had a little the advantage ; at all events it was plain that nothing had 
 been lost in this respect bj^ diminishing the proportion of nitrate. 
 
 " 2nd. Clearness of Image. — In every case the image was perfectly clear, in the 
 sense that there was no ' fogging ' or reduction of metallic silver on the transparent 
 parts, but there was a difference in the appearance of the ' lights when baths A and 
 B were employed, they were always slightly obscured, especially the shirt and fore- 
 head of the sitter, by a yellowish deposit of silver, which seemed as if it had been pre- 
 cipitated after the proper development was complete. I conclude that this deposit was 
 derived from the free nitrate of silver on the surface of the film, which being in a 
 more concentrated state in the two former cases, was the more readily acted upon by 
 the developing fluid ; however, it may not be that the efiect here alluded to will 
 invariably follow when a neutral bath so strong as forty grains to the ounce is used ; 
 much depends, no doubt, upon the nature of the developing agent ; indeed the two 
 must be associated together, the strength of one varying inversely with that of the 
 other. 
 
 " The conclusions arrived at are these, that with the dilute iodized collodion, 
 nitrate of silver in the proportion of twenty grains to the ounce, gives equal sensi- 
 bility and in every respect the same perfection of image as when used of greater 
 strength ; besides this, it has the merit of economy and superior cleanliness of manipu- 
 lation ; if the proper precautions are observed, such a bath will remain constant in its 
 action for a length of time. 
 
 " Before proceeding to the developing fluid, there yet remains to be considered, as 
 originally proposed, the efi'ect of adding nitric acid in graduated quantities to the 
 neutral nitrate bath ; my experiments in this direction are, I am sorry to say, as yet 
 incomplete ; however, two or three facts of importance are manifest, viz., that it is 
 impossible to lay down any general rule as to what the effect of adding the acid will 
 be, unless we take into account all the other cii cum stances of the case ; no doubt there 
 will invariably be a loss of sensitiveness, but whether or not advantages will be gained 
 in other respects, seems to depend upon further considerations. When collodion posi- 
 tives are taken by solutions modified as I have proposed, it will be found that the 
 Bmallest amount of free acid, even such as cannot at once be detected by test-paper, 
 will sadly injure the ' half-tones ' of the picture. 
 
 " On the other hand, many photographers advocate the use of nitric acid, and state 
 that they obtain a better result by means of it. 
 
 " In explanation of this seeming discrepancy I would suggest (and the views I 
 entertain are borne out by my experiments as far as they have gone), that the amount 
 of free nitric acid which may be added to the bath with impunity depends mainly 
 upon the strength of the solution of nitrate of silver ; strength of bath is favourable to 
 reduction, nitric acid is opposed to it, consequently the two, to a certain extent, 
 balance each other. But besides this, I am inclined to think that something 
 depends upon the thickness of the film of iodide of silver ; perhaps it may be that 
 the particles of iodide being less in number are more easily attacked ; but, at all j 
 
MR. HARDWICH'S DEVELOriNG EXPERIMENTS. 
 
 107 
 
 events, it seems necessary to regulate the acid, both iu the bath and the developing 
 fluid, with greater care when weak films are employed than under contrary ; 
 conditions. 
 
 " It is important then, and indeed essential, that the dilute nitrate bath should be 
 preserved accurately neutral ; this may easily be effected by adding a little carbonate 
 of soda and so setting free carbonate of silver, which can be allowed to remain con- 
 tinually at the bottom of the bottle in which the bath is kept ; if, however, iodide of 
 ammonium is used in the collodion, this plan does not succeed, because nitrate of 
 ammonia, which will then be formed in the bath, has the property of dissolving car- 
 bonate of silver and forming with it an alkaline solution ; in that case it is better to 
 keep a piece of blue litmus-paper always in the solution of nitrate, and when the 
 colour is perceived to be changed by the small amount of acid liberated by the free 
 iodine in the collodion, to add ammonia graduated to fortieths of a minim until the 
 evil is removed. 
 
 " Having now finished what I have to say on the subject of the nitrate bath, it 
 only remains that I should speak of the development of collodion positives, in order to 
 complete my paper. The deposits which constitute the light portion of these pictures 
 consist, in all cases, excepting where the bichloride of mercury is used, of metalKc 
 silver ; but it may be useful to class them under two heads, according as they do or do 
 not possess metallic lustre. 
 
 " The first is a surface bright and sparkling like frosted silver, very white when 
 produced in perfection, but with occasionally a greyish or tinfoil hue. 
 ^ " The second is dull and without lustre, of a whitish tint slightly inclining to 
 yellow or grey ; there is no appearance of a metal about it, the colour being more like 
 that of a piece of chalk. 
 
 "These two varieties require exactly opposite conditions of developing fluid to 
 produce them. From what I can gather from my own experiments, and from the 
 observation-of others, it would seem that the first is obtained by means of a reducing 
 agent, checked, as it were, in its action by the presence of a strong acid, consequently 
 th« development proceeds slowly and gradually, and the particles of silver are large 
 and crystalline ; on the other hand, the second variety results when the action of the 
 developer is sudden and violent, no impediment being offered by the presence of acid 
 except in minute quantity. The particles of metallic silver are here smaller than 
 before, and being comparatively amorphous, they reflect light in a different manner. 
 The distinction in the two cases, if these views are correct, lies in the amount 
 and strength of the acid used; in the one it is simply sufficient to whiten the 
 picture slightly by preventing the precipitation of oxide ; in the other, being 
 increased in quantity, it tends to retard the development as well. In conducting 
 these experiments the action of several different developing agents was compared, viz., 
 pyrogallic acid, the same with subsequent whitening by bichloride of mercury, proto- 
 nitrate of iron, and protosulphate of iron. 
 
 " 1st. Fyrogallic Acid. — This gives, under certain circumstances, a beautifully white 
 deposit of silver, free from lustre ; it should be used in the proportion of three 
 grains to the ounce, with a small quantity of nitric acid ; if too much of this sub- 
 stance be added, the deposit is more metallic, but the half-tones are not properly 
 brought out, so that pyrogallic acid is not adapted to produce what I have termed the 
 first variety ; so also it does not succeed when the proportion of nitrate of silver in 
 the bath is reduced to twenty grains to the ounce ; in that case the development 
 
108 
 
 MR. HARDWICH'S DEVELOPING EXPERIMENTS. 
 
 becomes imperfect in parts of the plate, and large patches of a blue or greenish colour 
 are seen. 
 
 "2nd. Pyrogallic and Acetio Acid, with subsequent Whitening by Bichlonde of Mercury. 
 —I was unsuccessful in my attempts to produce good pictures by this plan ; the colour 
 of the image was not sufficiently white, but had invariably a bluish tint, which was 
 particularly unpleasant ; other photographers, I am aware, have produced excellent 
 results with bichloride of mercury, and it may be that the extreme tenuity of the film 
 I employed was one cause of the blueness and transparency. Another objection ap- 
 peared to be that the details of the picture were slightly injured by the action of the 
 bichloride, and the whole image reduced to a certain extent in intensity ; this was 
 more apparent after blackening by means of ammonia, and then again whitening a 
 second time. 
 
 " 3rd. Frotonitrate of Iron. — This substance is peculiar in producing an image of 
 brilliant metallic lustre, without the addition of any free acid, hence it may at first 
 sight seem to be an exception to the observations that have just been made on this 
 subject ; it is remarkable, however, that protonitrate of iron should be so feeble a 
 reducing agent when compared with the corresponding sulphate ; probably the reason 
 may be, that in passing into the state of persalt, a portion of the oxygen required is 
 furnished by the decomposition of the nitric acid itself, and hence less would be 
 abstracted from other sources. In experimenting with proto-nitrate of iron, I found a 
 difficulty sometimes in bringing out the half-tones of the picture properly. To obviate 
 this, it is advisable to use the solution of the salt in as concentrated a state as it can 
 be procured, and to increase the proportion of nitrate of silver in the bath, if required, 
 from thirty-five grains to forty grains to the ounce. 
 
 " With the dilute nitrate bath of twenty grains to the ounce, protonitrate of iron 
 failed entirely to develop the image, thus affording most conclusive proof of the close 
 relation which the strength of the bath bears to the energy of the development. 
 
 " 4th. Protosulpkate of Iron. — This salt appears better adapted for the purpose 
 than either of the others when the twenty-grain bath is employed. In order to obtain 
 the tint which has been characterized as a dead white with absence of metallic lustre, 
 it must be used of such a strength that the picture comes out almost instantaneously 
 in all its details ; it occurred to me at first that the gradation of tone would be injured 
 somewhat by this violent method of proceeding, but I did not find on trial that such 
 was the case ; neither is there any indication of fogging or over-development if the 
 solution be poured off from the plate tolerably quickly. 
 
 " The proportions I have been in the habit of using are these :— Protosulphate of 
 iron pure, fifteen to eighteen or twenty grains; acetic acid (glacial) minims viij. ; dis- 
 tilled water one ounce. 
 
 " In the place of the acetic acid, strong sulphuric acid minim half, or nitric acid I 
 minim a quarter, with fifteen drops of alcohol may be used ; the alcohol certainly has 
 the effect, as has been stated, of causing the solution to fiow more evenly ; but it 
 appeared to me, that if present in too large quantity, the liability to ' specks ' and 
 ' dirty marks ' was increased. 
 
 " If the solution of protosulphate is in too concentrated a state, it will be difficult 
 to pour it on the plate sufficiently quickly to cover the whole surface before the action 
 begins ; in such a case, after fixing with the cyanide, curved Lines will be seen, such 
 as would be produced by a wave of fluid flowing forwards and resting for an instant at 
 a particular spot. 
 
MR. HORNE's process. 
 
 109 
 
 " On the other hand, if the solution is too dilute, the image becomes slightly grey 
 and metallic on drying. 
 
 " For fixing the picture hy removal of the unaltered iodide of silver, cyanide of 
 potassium appears preferable to the hyposulphite of soda ; it may be used of such a 
 strength as will clear the plate gradually in about half a minute or so, and is easily 
 washed away by pouring a stream over the plate for a short time. 
 
 " For ' backing up * I employ two varnishes, both of which dry speedily ; the 
 solvent is difierent in the two cases, and that of the black japan does not appear to act 
 upon the transparent layer beneath. A complaint is sometimes made that collodion 
 positives do not show to advantage through the glass, but I have not myself been able 
 to distinguish at all between the two sides, excepting in cases where the picture was | 
 slightly over-exposed. j 
 
 " With regard to the time required for taking a portrait on a tolerably bright day, i 
 as giving some indication of what the degree of sensitiveness of the plates might be, I 
 would say that with a Eoss's portrait lens of two and a quarter inches, having a 
 diaphragm of an inch and three quarters aperture, an exposure in the camera of two to 
 three seconds is the average ; when distant objects are taken with the full aperture of 
 the lens, it is hardly possible to remove and replace the cap with sufficient quickness." 
 
 Mr, Hoxne's Pzocess. — Mr. Home has been one of the earliest and most suc- 
 cessful operators, and has published an account of the particular manipulations required 
 in the collodion process. By his permission, I am enabled to give the process he adopts 
 in his own words. As regards the choice and preparation of the plate itself, the 
 operator cannot do better than follow the directions of Mr. Hardwich, which I have 
 already recorded. The plate selected, having a clean and 
 perfectly dry surface, and taking care to handle it as 
 little as possible, the next operation is that of 
 
 " Coating the Plate. — Taking it from the clean dry 
 leather in which it has been wrapped, there are 
 several ways by which the iodized collodion may be 
 applied, some preferring a piece of India-rabber 
 fastened to the back as a handle, others supporting it 
 on the ends of the fingers of the left hand (Fig. 64) ; 
 while others, again, content themselves by sacrificing a 
 small portion of one corner, or by the use of an instru- 
 ment called the pneumatic plate-holder, which appears 
 to answer well. But whichever plan is adopted, the 
 plate must be held by the left hand perfectly hori- 
 zontal, and then with the right a sufficient quantity of 
 coUodio-iodide should be poured into the centre, so as to diffuse itself equally over the 
 surface. This should be done coolly and steadily, allowing it to flow to each corner in 
 succession, taking care that the edges are all well covered. Then gently tilt the plate, 
 that the superfluous fluid may return to the bottle from the opposite corner from which 
 the plate is held. At this moment the plate should be again brought into a vertical posi- 
 tion, when the diagonal lines caused by the fluid running to the corner will fall one into 
 the other, and give a clear flat surface. To do this neatly and efiectually, some little 
 practice is necessary, as in most things ; but the operator should by no means hurry the 
 j operation, but do it systematically and quietly, at the same time not being longer 
 j over the operation than is actually necessary, for collodion, being an ethereal com- 
 
110 ME. HORNE's exciting PROCESS. 
 
 pound, evaporates very rapidly. Many operators waste tlieir collodion by performing 
 tliis operation in great haste ; but haste is not necessary, for an even coating can 
 seldom be obtained if the fluid is poured on and off too rapidly ; it is better to do it 
 steadily, and submit to a small loss from evaporation, and at any future time, if the 
 collodion becomes too thick, to thin it with the addition of a little fresh and good 
 ether. 
 
 " Exciting the Plate. — Previous to this it is necessary to have the bath ready, which 
 is made as follows : — 
 
 Nitrate of silver . . . .10 drachms. 
 Distilled water .. . . .20 ounces. 
 Iodide of silver .... 5 grains. 
 Dissolve and filter. 
 
 " The object of putting the iodide of silver is that the nitrate may be saturated with 
 it, or the plates would otherwise be robbed of a certain portion. Now to saturate the 
 nitrate properly, it is necessary the iodide should be freshly precipitated, therefore the 
 best plan is to proceed as follows : — ■ 
 
 " Dissolve the ten drachms of nitrate of silver in two ounces of distilled water, and 
 add to this five grains of iodide of potassium previously dissolved in about two drachms 
 of distilled water. Upon mixing these, the iodide is thrown down, and redissolved by 
 the concentrated solution of silver, when the remainder of the water, namely, eighteen 
 ounces, may be added, and the solution very carefully filtered. 
 
 " The quantity of this fluid necessary to be made must depend upon the form of 
 trough to be used, whether horizontal or vertical, and also upon the size of plate. 
 The trough used by the writer is the vertical, though many still prefer the former, 
 and attach, as before described, a piece of India-rubber to the back of the plate as a 
 handle whUst applying the collodion, and to keep the fingers from the solution whilst 
 dipping in the bath. With the vertical troughs a glass dipper is provided upon which 
 the plate rests, preventing the necessity of any handle or the fingers going into the liquid. 
 Having then obtained one or other of these two, and filtered the liquid, previously free 
 from any particles of dust, &c., th.e plate is to he immersed in it steadily and without 
 hesitation, for if a pause should be made at any part, a line is sure to be formed, which 
 will print in a subsequent part of the process. 
 
 " The plate, being immersed, must be kept there a sufficient time for the liquid to 
 act freely upon the surface, particularly if a negative picture is to he obtained. As a 
 general rule it will take from two to four minutes, varying with temperature and make 
 of the collodion. In very cold weather, or indeed anything below 50° Fah., the bath 
 should be placed in a warm situation, or a proper decomposition is not obtained under 
 a very long time. Above 60° the plate will be almost certain to have obtaraed its 
 maximum of sensibility by two minutes' immersion, but as the plate cannot injure by 
 remaining a longer time in the bath, it is better in all cases, when a negative picture is 
 required, to give time for the whole of the iodide in the collodion to be thoroughly 
 acted on by the nitrate of the bath. 
 
 " To facilitate the action, let the temperature he what it may, the plate must be 
 lifted out of the liquid two or three times, which also assists in getting rid of the ether 
 from its sui-face. If this is not thoroughly done, a uniform coating cannot be obtained ; 
 but on no account should it be removed until the plate has been immersed about half a 
 minute, or marks are ax^t to be produced. 
 
MR. HOKNE's NITEATE BATH PROCESS. 
 
 Ill 
 
 " Having obtained the desired coating, the plate is then extremely sensitive to 
 . wMte light, and every precaution ^should he taken to exclude ordinary daylight. The 
 best way to do this is to hang over the window two or three thicknesses of yellow 
 calico, by which means the light which passes through will be amply sufficient for 
 manipulation, and at the same time produce no injury to the sensitive plate. If this 
 cannot be done, the room must be closed against any portion of daylight, and a candle 
 alone employed, placed however, at a distance from the operator, to give the requisite 
 light. 
 
 " The plate thus rendered sensitive must then be lifted from the solution and held 
 over the trough, that as much liquid as possible may drain oif previous to being placed 
 in the frame of the camera, otherwise the action will not be equal over the whole 
 surface. It must not be allowed to dry, however ; but, in order to obtain its full 
 maximum of sensibility, it should be damp without superfluous moisture. It is thus 
 imperative that the exposure takes place within a few minutes after removing the plate 
 from the bath. This renders collodion of very little value for taking views, as in such 
 situations we cannot command the use of a dark-room. 
 
 " The question is often asked — How soon after the coating the plate with coUodio- 
 iodide, should it be immersed in the nitrate bath "We have said the time of immer- 
 sion is dependent upon temperature and make of collodion, so likewise must we be 
 governed as to time before immersion. To make coUcdio-iodide or xylo-iodide — for, 
 chemically speaking, there is no difference in the two — it is necessary that the ether 
 should contain a certain quantity of alcohol, or the different articles are not soluble ; 
 therefore, if we take a fresh bottle and coat the plate from this while it contains its full 
 dose of etber, and with the thermometer ranging between 60° and 70°, the evaporation 
 of this article will be very rapid, and consequently a tough film soon formed ; but if, 
 on the other hand, we are using an article which has been in use some time, and many 
 plates, perhaps, coated, the proportion of alcohol wUl be much greater, and not being 
 of so volatile a nature, will necessarily take a longer time to acquire the necessary 
 firmness for immersion. Hence it is evident we must be guided by circumstances. If, 
 for instance, after coating a plate, we find on immersion it does not colour freely, we 
 have then reason to suppose the plate has not been immersed sufficiently quick ; but 
 if, on the other hand, we find the film very tender, and it cracks upon drying, then we 
 have reason to know that plates prepared from that bottle must not be immersed quite 
 so soon. The larger the proportion of alcohol the more tender the film, but the more 
 sensitive will be the plate, and the quicker and more even will be the action of the 
 bath. 
 
 " The next question also often asked is — How long must be the exposure in the 
 camera ? a question more difficult to anrwer than the last, and which practice alone can 
 determine, combined with close observation of those parts which should be the shadows 
 of a picture. If, for instance, in developing, we find those parts less exposed to the light 
 than othei's develop immediately the solution is applied, then we have every reason to 
 suppose the exposure has been too long ; but if, on the contrary, they develop very 
 slowly, we have proof that the time allowed has not been sufficient to produce the 
 necessary amount of action. In a good picture we should see first the whites of the 
 dress appear, then the forehead, after which we shall find, if the light has been pretty 
 equally difi'used, the whole of the face and then the dress. 
 
 " Much will, of coiu'se, depend upon the arrangement of light, for if the sitter is 
 not placed in a good aspect, by which is meant a good diffused light, the prominent 
 
112 
 
 MR. HORNE's developing PROCESS. 
 
 parts only will come out ; in other words, to produce the necessary amount of action to 
 obtain the others, the high lights are so overdone that the picture prints raw and cold. 
 
 " Can I produce portraits at my drawing-room window ? This is another common 
 question, and the reply must necessarily be, Yes, if you have sufficient light, and can so 
 place your camera that the sitter may be pretty equally illuminated, and not one half 
 receiving nearly all the light ; if it does, one side may be amply developed and the 
 other scarcely visible. 
 
 " In cases of this description the necessary effect may often be produced by placing 
 a white screen so as to reflect a portion of light upon the darkened side ; but, upon the 
 whole, a light of this character is better adapted for producing positive than negative 
 pictures upon glass. 
 
 " The Development of the Image. — To effect this it must be taken again into the room 
 where prepared, and with care removed from the slide to the levelling stand. It will 
 bo well also to caution the operator respecting the removal of plate. Glass, as before 
 observed, is a bad conductor of heat ; therefore if, in taking it out, we aUow it to rest 
 too long on the fingers at any one spot, that portion will be warmed through to the face, 
 and as this is not done until the developing solution is ready to go over, the action will 
 be more energetic at those parts than at others, and consequently destroy the even- 
 ness of the picture. We should, therefore, handle the plate with care, more as if it 
 already possessed too much heat to be comfortable to the fingers, and we must therefore 
 get it on the levelling stand as soon as possible. 
 
 " Having then got it there, we must next cover the face with the developing solu- 
 tion. This should be made as follows : — 
 
 Pyrogallic acid . . . .10 grains. 
 Distilled water . ' . . . 5 ounces. 
 Glacial acetic acid . . . 1 drachm. 
 Spirits of wine . . . . | a drachm. 
 Mix and thoroughly filter. 
 
 " Now, in developing a plate, the quantity of liquid taken must be in proportion to 
 its size. A plate measuring five inches by four wiU require half an ounce, less may be 
 used, but it is at the risk of stains ; therefore we would recommend, that half an 
 ounce of the above be measured out into a perfectly clean measure, and to this from 
 eight to twelve drops of a fifty-grain solution of nitrate of silver added. 
 
 " Pour this over the surface, taking care not to hold the measure too high, and not 
 to pour all at one spot, but having taken the measure properly in the fingers, begin at one 
 end, and carry the hand forward ; immediately blowing gently upon the face of the plate, 
 which has the effect, not only of diffusing it over the surface, but causing the solution 
 to combine more equally with the damp surface of the plate ; it also has the effect of 
 keeping any deposit that may form in motion, which if allowed to settle, causes the 
 picture to come out mottled. A piece of white paper may now be held under the plate, 
 to observe the development of the picture ; if the light of the room is adapted for view- 
 ing it in this manner, well ; if not, a light must be held below ; but, in either case, 
 arrangements should be made to view the plate easily whilst under this operation, a 
 successful result depending so much upon obtaining sufficient development without 
 carrying it too far. 
 
 " In some instances it is better not to mix the nitrate of silver solution with the 
 pyrogallic until after the latter has been poured over the plate, but in no case must it 
 be mixed on the plate, the solution must be poured off into the measure and the nitrate 
 
MR. HORNE'S fixing PROCESS. 
 
 113 i 
 
 added. In this way we can judge better of the intensity of the picture, for when the 
 solution is off, the plate can be held up to the light and the image viewed through. 
 Care should be taken that the nitrate of silver solution is free from deposit. 
 
 " The author has also found a weak developing solution, as given above, far more 
 successful in obtaining gradation of tone than when stronger, for, in the latter ease, the 
 action will be very energetic on those parts reflecting the most light, and, consequently, 
 become overdone before other portions, such as dress, &c., have become sufficiently 
 visible. The addition of an extra portion of nitrate of silver will be found to improve 
 the tone, but this may be eff'ected also without adding it to the pyrogallic solution ; 
 and, in many instances, it will be found a better plan to re-dip the plate in the bath, 
 after exposure in the camera, particularly if any considerable time has elapsed between 
 the excitement of the plate and development of the picture, for the plate having dried 
 unequally does not allow the same uniform development as when well moistened over 
 the surface. 
 
 " As soon as the necessary development has been obtained, the liquid must be 
 poured off, and the surface washed with a little water, which is easily done by holding 
 the plate over a dish and pouring water upon it, taking care, both in this and a sub- 
 sequent part of the process, to hold the plate horizontally, and not vertically, so as to 
 prevent the coating being torn by the force and weight of the water. 
 
 " Fixing the Image. — "Which is simply the removal of iodide from the surface of 
 a plate, is effected by pouring over it, after the water, a solution of hyposulphite 
 of soda, made of the strength of eight ounces to a pint of water. At this point day- 
 light may be admitted into the room ; and, indeed, we cannot judge well of its removal 
 without it. We then S3e the iodide gradually dissolve away, and the different parts 
 left more or less transparent, according to the action of light upon them. 
 
 " It then only remains to thoroughly wash away every trace of hyposulphite, for, 
 should any of this salt be left, it gradually destroys the picture. The plate should, 
 therefore, either be immersed with great care in a vessel of clean water, or, what is 
 better, water poured gently and carefully over the surface. After this it must be put 
 in a proper place to dry, or held before a fire. 
 
 " It may be as well to state, any clean filtered water will answer for washing, dis- 
 tilled being only required for the solutions of nitrate of silver, &c. 
 
 " Having, by the foregoing means, obtained and fixed a negative photographic 
 image on glass, and which is capable of producing positives upon paper by the ordinary 
 photogenic printing ; it is as well, previous to obtaining these, to render the tender film 
 of collodion less liable to injury. This is best accomplished by — 
 
 " Varnishing the Plate. — There are two kinds of varnishes which may be used for 
 this purpose — the spirit and turpentine ; of the latter kind the gum-dammer answers 
 best, and indeed the only objection to its use is, that it requires forty-eight hours to 
 diy — whereas with the former, which consists of spirit and a great variety of gums, 
 the plate may be printed from within a few minutes. Some amount of care is necessary 
 in the use of the latter, for if it is poured on the plate cold, the gums chill, and the 
 picture is rendered opaque ; therefore the best plan of proceeding is as follows : — j 
 
 " Hold the back of the plate to a fire until warm through, care being taken not to ■ 
 make it too hot, or the varnish will not run properlj' ; then pour the varnish on in the |; 
 same manner as the collodion, returning the superfluous liquid to the bottle. Hold the j 
 plate again to the fire to drain off the spirit, when a beautiful surface will be obtained, 
 making it difficult, at first sight, to judge which side has been varnished. 
 
114 
 
 POSITIVE PICTURES BY MR. HORNE'S PROCESS. 
 
 " The damraer varnish may be applied cold, care being taken to make it very thin, 
 either with turpentine or camphine, otherwise it -will be days before it ia sufficiently 
 dry to print from. 
 
 " There is also another kind of varnish which has been recommended by Dr. 
 Diamond, viz., gum-amber dissolved in chloroform. This is used by many photo- 
 graphers, as it can be put on odd, and yet it dries directly upon evaporation of the 
 chloroform, otherwise it possesses no advantage over the spirit, and is necessarily much 
 more expensive. 
 
 Positive Pictures u2}on Glass. — Hitherto we have described the method of producing 
 negative pictures only, but by sliglitly varying the process in developing tbe collodion 
 pictures, most beautiful positives, equal to Daguerreotypes, may be obtained, and 
 without their metallic reflection. These pictures are strictly, positive, for, when held 
 to the light, they scarcely show as a negative. To produce them, a much shorter time 
 is necessary for a sitting than for the production of a printing negative. They also 
 require a modification in the development, that as bright a surface may be obtained as 
 possible. 
 
 *' It was shown by the author, in the early days of collodion, that this result might 
 be obtained, to a certain extent, by mixing with the pyrogallic solution a very small 
 quantity of nitric acid ; but it has since been proved by Mr. Fry and others, that a 
 better result may be obtained by the use of proto-sulphate and proto-nitrate of iron. 
 
 " The former salt is readily obtained, and in a very pure form. It should be used 
 as follows : — Proto-sulphate of iron, ten grains ; distilled water, one ounce ; nitric 
 acid, two drops. To develop the image, pour the above over the plate, taking care not 
 to cany the development too far. 
 
 " Tbe proto-nitrate may be obtained either by double decomposition, as recom- 
 mended by Dr. Diamond, or by dissolving sulphuret of iron in dilute nitric acid, as 
 recommended Mr. Ellis. The latter, being the most economical, we will describe first. 
 
 " To one ounce of nitric acid, and seven of water, add a small quantity of sulpburet 
 of iron broken into fragments. Stand the vessel aside, that the sulphuretted hydrogen I 
 may escape, and the acid become saturated with iron. Pour off the liquid, and filter, i 
 Boil it again in a Florence flask to get rid of the sulphur, and again filter, when a dark { 
 green liquid will be obtained, which is the proto-nitrate of iron. This should be kept j 
 in well-stoppered bottles, and from air as much as possible, to prevent its changing ' 
 into a per-nitrate, in which stage it is quite useless as a photographic agent. ; 
 
 " To develop the picture, mix one part of the above proto-nitrate with three of ' 
 water, and apply it to the plate in the ordinary way, when a most beautiful clear image ! 
 will be obtained. 
 
 " Dr. Diamond's method we take from the Art Journal. 600 grains of proto- 
 sulphate of iron are dissolved in one ounce of water, and the same quantity of nitrate ! 
 of baryta in six ounces of water ; these being mixed together, proto-nitrate of iron and | 
 sulphate of baryta are formed by double decomposition ; the proto-nitrate of iron being 
 in solution, and the sulphate of baryta precipitated, the latter being easily removed by ' 
 filtering the solution. 
 
 " The negative image being developed, a mixture of pyrogallic and hyposulphate of \ 
 soda, which has undergone partial decomposition, is poured over the plate, M'hich is gently 
 w-armed. Upon this the darkened parts are rendered brilliantly white by the forma- 
 tion of metallic silver. This picture being backed up with black velvet, assumes the 
 air of a fine Daguerreotype, without any of the disadvantages arising from the reflection 
 
THE AWTHOR'S process. 
 
 115 
 
 of ligkt from tlie polished silver siri'face. We have also seen a similar effect produced 
 by Mr. Fry and Mr. Berger, by the use of the proto-sulphate of iron solution and 
 pyrogallic acid. The image is first developed by the iron solution, which is then 
 poured off, and another solution of pyrogallic is poured on, until the effect ia produced. 
 The pictures aie fixed with the hyposulphite in the usual method." 
 
 The Anthax's Process. — I have now to offer some remarks on the collo- 
 dion process as practised by myself, and I commence by reiterating my caution in 
 favour of care and cleanliness, which is the motto it is impossible to impress too 
 strongly on the mind of the reader. Before commencing operations, have everything 
 as nearly as possible, in the following state : — The glass house must be scrupulously 
 clean, and free from slops and dust ; care must be taken that no ray of white light 
 gains admittance through any chink or hole— the door will be the part most subject to 
 this ; the light used should be obtained through a piece of orange or red glass — a foot 
 square will be quite large enough — and it should not face the sun. It may be neces- 
 sary in very bright weather to have a curtain of yeUow calico on a roller, so that it 
 may be used or not, as may be required. There should be a deep tray to receive the 
 washings, and this should have a waste-pipe, if possible, to prevent the accumulation 
 of slops ; the tray and water-tap should be as nearly as possible under the light, and 
 if the water has to fall from any height, so as to fall with force, it will be necessary to 
 tie a piece of old linen on the opening of the tap— by this means you will obtain a 
 plentiful supply of water, which will fall so gently as scarcely to be felt by the finger; 
 by this precaution you will not run any danger of washing off the collodion film. It 
 will also be a great advantage to have the tap fastened to the supply-pipe by a couple 
 of feet of vulcanized India-rubber, or flexible gutta-percha tubing, so that the plate 
 especially a krge one) may be supported on the tops of the thumb and fingers of one 
 hand, while the other can swill the water over the surface with ease in every direc- 
 tion. 
 
 Have your exciting bath so placed that the yellow light may ra/ce the surface of 
 the plate when you lift it out to examine the state of the iodized and excited collodion 
 film, but this should never be done until the plate has been at least a minute in the 
 bath. You must also take care that the bath is sufficiently far away from the washing 
 tap to prevent the risk of splashings from the latter when washing the plate. The 
 developing glass should have a small stand for itself, covered with a sheet of blotting- 
 paper folded half a dozen times, to be renewed when it becomes wet through. The 
 collodion bottle should stand on another shelf, and the vessel holding the solution of 
 hyposulphite of soda or cyanide of potassium should occupy another shelf— this must 
 never be used for any other purpose, neither should the hypo-vessel ever be placed any 
 where else— this latter shelf should be much lower than the others. You should have 
 a towel for the hands, another for wiping out the slide after each plate — but "papier 
 Joseph" is better— and a cloth for wiping up all slops. The developing-room I consider 
 most convenient would resemble the following sketch (Fig. 65), sxipposed to be made 
 when looking down from the roof — the shelving being about the height of a common 
 table or a little higher : — 
 
 A, the window of orange glass ; B, the shelf for the developing-bottle and vessel ; 
 C, the water-tap ; D, the waste-pipe ; E, the washing-tray ; F, the main shelf or 
 bench; G, the exciting bath ; H, the shelf for collodion bottles; I, shelf on which 
 may stand the dark slide when not in use ; J, the shelf for the hyposulphite vessel ; K, 
 the body of the room ; L, a curtain running on a rod with rings, to be drawna across 
 
116 
 
 THE DARK CHAMBER. 
 
 after the door is shut ; M, the door ; N and 0, hooks for towels. The above will be 
 found to be a most convenient dark-room ; and it may be as well to say here, in refer- 
 ence to such places in general, never allow bottles, or any other articles not in use, 
 
 somewhat from that recommended by Mr. Hardwich: — I mix up some Tripoli 
 powder or whiting, with one part liquor ammonia, two parts alcohol, and three parts 
 I water ; dip a piece of clean cotton wool into this mixture, and proceed to cover the 
 surface of a glass plate already washed and dried. Do this in circles, and with some degree 
 of force at first, leaning less weight as you are about to finish ; treat half-a-dozen 
 or more glasses in the same way. Put them to dry with their faces (the surface covered 
 with the Tripoli, &c.) next the wall, and when dry take a second piece of cotton-wool, 
 and by briskly drawing it over the surface remove the dry dust left on the latter by 
 the evaporation of the Tripoli mixture, and from off the edges also ; then take another 
 clean and dri/ piece, and finish off with the greatest care. As each is finished, place 
 it in a box with grooves, and take care that the faces are all in the same direction. I 
 should recommend the clean side towards the back of the box or from you, because, if 
 you should not have an empty box, you would place them resting on the collodion 
 shelf with the clean side next the wall ; then filter your bath of nitrate of silver, the 
 developing solution, and the collodion (the latter must be filtered through a papier 
 Joseph). It will answer as well, in most cases, if the collodion is gently decanted from 
 the bottle, holding it into another, (previously washed out with a small quantity of 
 ether), keeping back the bottom portion, which will contain any portions of undis- 
 solved cotton, &c., that may be present. The collodion should have been mixed some 
 hours before use ; if even a day it would be all the better. 
 
 Coating t/ie Glass. — Supposing now that you are about to operate, you will proceed 
 as follows : — Go into the dark-room, and wash out the glass you intend to use for 
 
 -A 
 
 to remain on the 
 shelves or in the 
 dark-room; have 
 everything in its 
 proper place, and 
 have everything 
 put away, and 
 the dark-room 
 cleared and swept 
 out after the 
 work is done for 
 the day, so that 
 it may be clean 
 and free from dust 
 for the next day's 
 operations. 
 
 rig. 65. 
 
 Preparing the 
 Glass. — As every- 
 thing depends on 
 a clean glass, I 
 adopt this mode 
 of preparation, 
 which differs 
 
THE author's manipulation. 
 
 117 
 
 Fig:. 66. 
 
 developing. A glass called a precipitating glass, such as is here figured (Fig. 65), is 
 the best for this purpose. Put the requisite amount of developing solusion in it; 
 then take the bottle holding the collodion that you intend to use, and, taking out the 
 stopper, insert very carefully the point of one of your fingers so 
 as to remove any portion of dry collodion that may remain there. 
 Take care th at there is not any more remaining about the neck 
 or body of the bottle, or anything else that might fall on the glass 
 plate. Taking a glass plate on a holder, or, what is far better, the 
 tips of the fingers of the left hand, pour gently, and without any 
 haste or flurry, a suflicient quantity of collodion on its clean sur- 
 face. There are many methods of doing this, but the most success- 
 ful that I know of is to pour the collodion on the plate thus (pre- 
 mising that you are holding the glass on the fingers of the right-hand 
 as in Fig. 64) : — Commence at A (Fig. 67), and as you pour on the 
 collodion, allow it, by inclining the glass, to take the course pointed 
 out by the line proceeding from A to E. In doing this, do it slowly and evenly, and 
 recollect that it is not necessary to allow, or, more properly speaking, to wait, for the 
 
 collodion to run right up to the corner, for when it 
 arrives near B, that comer of course will be the 
 lowest; but in altering the inclination so as to 
 cause it to flow towards C, we do not raise B but 
 depress C until B and C are about equal ; that being 
 the case, the side of the plate between B and C 
 becomes the lowest, and by the time the collodion 
 arrives near the corner C, it will have flowed fully 
 Fig. 67. up to B ; the same action takes place between C 
 
 and D, and so on. The advantage gained is, that the collodion never flows back again 
 over a part already coated. 
 
 The Nitrate Bath. — By a little practice the reader will be able to coat any 
 sized plate. Eeturn the surplus collodion into the bottle from E, rapidly sliding 
 the fingers up to C, E resting on the mouth of the bottle, and thus preventing 
 any unequal evaporation from the parts which would be otherwise over the points 
 of the fingers ; and when the collodion has nearly all run off, move the plate 
 backwards and forwards a few times, so as to prevent the formation of any lines in 
 the film of collodion ; in other words, 
 change the position of the plate from 
 Fig. 68 to Fig. 69. When the collodion 
 ceases to drop, and the fiGlm becomes 
 pretty well set, place the plate on the 
 dipper, and (having previously skim- 
 med the surface of the nitrate of silver 
 solution in the bath with a small strip 
 of blotting-paper) proceed to immerse 
 the dipper and plate slowly and evenly, 
 recollecting that if you make a stop 
 or hesitate for a moment, you surely 
 spoil the plate. The latter once in the 
 exciting bath, leave it there and carefully wipe out the slide, then covering the bath 
 
 Fig. 68. 
 
 Fig. 69. 
 
118 
 
 THE AUTHORS MANIPULATION. 
 
 ■witli a light-proof cover, open the door of the dark-room, and proceed to focus and 
 arrange the sitter or object to be copied. 
 
 The plate may be coated with collodion and immersed in the bath without the 
 necessity of having the door of the dark-room closed, as the sensitive iodide of silver 
 is not formed on the instant of immersion ; but in this case it will be necessary to 
 cover the bath ^vith a light-proof cover, or to shut the door immediately. 
 
 Flacing in the Camera. — Having obtained tbe proper focus and adjustment of the 
 object to be copied, put the cap on the lens, and remove tlw ground glass, then, going 
 into the dark room close the door, and draw the curtain. If a minute at least has elapsed 
 since the immersion of the plate, draw it out of the bath, and examine the surface to see 
 if all greasiness has disappeared, otherwise the plate will be all mottled and streaky. When 
 the surface of the plate appears smooth and even, dip it and withdraw it two or three 
 times afterwards. Then allow it to drain for nearly a minute, allowing it to become 
 nearly dry, and never attempting to take a collodion picture while the plate is dripping ; 
 — this is an essential point, and should be strictly attended to if a good picture be 
 desired. "When the plate has been sufficiently drained, place it carefully in the dark 
 slide ; placing the slide gently in the camera, pull the shutter up quietly, and uncover the 
 lens for the proper time. Take especial care not to push the shutter down with a bang, 
 or with force, that being sure to cover the plate with spots and stains. I have seen an 
 amateur hitting and thumping the shutter of his dark slide when it stuck from being 
 swollen by wet, or some other cause, and I need scarcely add, that the resulting pic- 
 ture was a brilliant specimen of spots and messes. In fact, every operation in the collo- 
 dion process should be performed as if you were working in the den of a sleeping tiger ! 
 
 Developing. — Upon entering tbe dark-room with the exposed plate, previous to deve- 
 lopment, gently shut the door and draw the curtain (it is better to have the curtain tacked 
 permanently across the inside of the door, and without plaits — in this case it must be 
 pushed on one side when entering or leaving the dark-room), then place tbe slide, 
 leaning against the wall, on the left hand, taking care not to knock it, and looking 
 round to see if your developing glass contains the required solution, and that every- 
 thing else is ready ; take out the back of the slide, and holding the upper part of the 
 latter in the left hand, lean it gently over until the excited plate falls out against the 
 thumb and spread fingers of the right, placed in a proper position to receive it. By 
 lowering the hand, the plate becomes level, and may be lifted away from the dark 
 slide at once on the tops of the fingers. You next 
 proceed to transfer it to the left hand, and take up 
 the developing-glass in the right ; then slowly, and 
 without hurry, but at the same time evenly and with- 
 out hesitation, commence to pour the solution on the 
 surface of the plate ; this will require no little prac- 
 tice, and should be done in such a manner that the 
 plate will be just covered by the time all the solu- 
 tion has left the glass— the former should flow evenly 
 over from end to end. To cover a large plate well, 
 proceed thus :— Let the corners A B be lower than C D, 
 Fig. 71. but in the same horizontal line in the direction from 
 
 A to B, or looking at the side of the plate (Fig. 
 70), then commence to pour on to the plate at C, and draw the glass backwards 
 and forwards as you go down the plate (Fig. 71). It will not be necessary to go over 
 
ME. HARDWICH'S FOEMUL^. 
 
 119 
 
 more than half the plate with the developing glass, as the amount of liquid will by 
 that time have flooded the whole. Then, by moving the hand and fingers, cause the liquid 
 to flow from end to end, and from side to side, pouring it back into the glass and on 
 to the plate again, until the desired amount of intensity and development are obtained; 
 this may be ascertained by looking through the plate when the developing solution 
 has been poured back into the glass. 
 
 When fully developed, wash it well before using the fixing agent. This is the 
 more necessary when hyposulphite of soda is employed, as that salt would be decom- 
 posed by the presence of the acetic or other acid used, and by throwing down sulphur 
 injure the brilliancy of the negative. After all traces of the iodide of silver have dis- 
 appeared, the plate must then be well washed with plenty of water, covering it fully 
 each time, swilling it about on the surface for a few moments, and pouring it ofl' 
 again ; then set it up to dry. The lower edge should rest on a strip of blotting-paper. 
 When dry, examine it for a sort of whitish powder, something like fi'ost ; should this 
 appear on the surface, it is owing to the presence of hyposulphate of soda, and shows 
 that the plate was not sufficiently washed. Should the plate be perfectly free from 
 any such appearance, it may then be varnished. This is done by slightly warming 
 the plate, covering the surface with varnish as you did with collodion, and, returning 
 the excess to the bottle, holding the plate to the fire until it dries without chilling. The 
 negative, or positive, is now finished, and by carefully following the preceding 
 directions, a good picture should be the residt ; but if not, we must endeavour to find 
 out the cause. 
 
 Mr. Haxdwich's Foxmulse. — ^These remarks on the manipulation which has 
 been adopted in Mr. Fenton's establishment I would have followed by my own 
 formulse for preparing each of the solutions required, but Mr. Hardwich has treated 
 this branch of the subject so fully and so ably in his " Chemistry of Photography" 
 that I willingly avail myself of his permission to quote this and other portions of his 
 book ; and I do so the more readily as it would be nearly a matter of impossibility for 
 me to do the subject justice otherwise than in his own woi'ds. That the reader may 
 understand my meaning more fully, I may quote the passage from the preface to 
 Mr. Hardwich's work, in which he mentions my connection with his experiments. 
 '■'■lam also indebted," he says, " <o Mr. Sparling for repeating many of my experiments 
 upon a larger scale, and carefully chronicling the results." Such being the case, I can 
 scarcely do otherwise than give the formulae, the result of these experiments, in Mr. 
 Hardwich's words, while I acknowledge his courtesy in granting me permission to do so. 
 
 As there is much difficulty in ascertaining the proper strength of the materials em- 
 ployed, Mr. Hardwich goes at considerable length into the question, and in a future 
 page I may give the substance of his researches. His formulse we shall quote in the 
 order in which he gives them : — 
 
 " Formula for Soltttions for Direct Positives.— The solutions are taken in the 
 following order : — The collodion ; the nitrate bath ; developing fluids ; fixing liquids ; 
 whitening solution. 
 
 " The Collodion. 
 
 Purified ether, sp. gr. '720 ..... 5 drachms. 
 
 Purified alcohol, sp. gr. •S25 3 „ 
 
 Pyroxyline 2 to 3 grain?. 
 
 Pure iodide of ammonium 2 grains. 
 
120 ME. HABDWICH'S formula. 
 
 Or, Eectified ether, sp. gr. -750 6 drachms. 
 
 Spirits of wine, sp. gr. -836 2 „ 
 
 Pyroxyliue 2 to 3 grains. 
 
 Iodide of potassium 2 to 3 „ 
 
 " The exact quantity of pyroxyline required cannot be stated, since some samples 
 produce a more glutinous solution than others. The rule is to keep the texture of the 
 film slight. If the quantity specified yields a solution fluid like water, and running 
 down the neck of the bottle in the attempt to pour it on the plate, it may be increased. 
 
 " The appearance of the film, after dipping in the bath, is a guide to the proper 
 quantity of ingredients ; it should be blue and transparent. If it is pale, increase the 
 quantity of pyroxyline, at the same time with that of the iodide. 
 
 " The iodides of potassium, ammonium, or cadmium may be used. Collodion 
 iodized with the cadmium salt possesses great keeping qualities ; but the writer prefers 
 the alkaline iodides, and especially the iodide of ammonium, if it be pure. Iodide of 
 potassium does not dissolve in quantity greater than two grains to the ounce if the 
 ether and alcohol are highly rectified. 
 
 " With regard to the length of time this collodion can be kept in working order, 
 everything will depend on the condition of the ether. If recently distilled, probably 
 the colour will scarcely have passed the orange-yellow stage at the expiration of a 
 fortnight, or even with iodide of potassium three weeks or a month. A lemon-yellow 
 tint does no injury to the most delicate film, but when the colour reaches to a decided 
 brown, the iodine may be removed. 
 
 " The writer does not, from experience, advise keeping a stock of the dilute collodion 
 uniodized for more than a month or six weeks ; the tendency to decomposition in the 
 other seems to be increased by the solution of the pyroxyline. 
 
 " Many operators take positives with a more highly iodized collodion intended for 
 negatives, adding nitric acid to the bath, if the intensity is too great. This process is 
 likely to yield pictures very clear and free from fogging, but is less sensitive than that 
 just described, and often gives the shadows dark and sombre. 
 
 " The Nitrate Bath.~lt is necessary to saturate this solution with iodide of silver, 
 and to remove any free nitric acid which may be present. Therefore, having weighed 
 out the following quantity of crystals of nitrate, &c., for the bath, viz. :— Nitrate of 
 silver, crystallized and dried, but not fused, 25 grains ; acetic acid (glacial), i minim ; 
 distilled water, 1 ounce ; dissolve in about two parts of water. Then take iodide of 
 potassium or ammonium, half a grain to each 100 grains of nitrate, dissolve in half a 
 drachm of water, and add to the strong solution ; a yellow deposit of iodide of silver 
 first forms, but on stirring is completely redissolved. IVhen the liquid is clear, drop 
 in a solution of potash or carbonate of soda until a distinct turbidity, not removed by 
 agitation, is produced (an excess does no harm) ; then dilute down the concentrated 
 solution with the remaining portion of the water, stirring all the time, and filter out 
 the milky deposit. If the liquid does not at first run clear, it will probably do so on 
 passing it again through the same filter. 
 
 "Ammonia may also be used to neutralize free nitric acid, but it must be added 
 very cautiously, or a quantity of oxide of silver will be dissolved, forming with the 
 acetic acid, advised in the formula, acetate of silver in excess, which is injurious in 
 a positive nitrate bath. 
 
 "After using any alkali or carbonate, the bath is left in a faintly alkaline con- 
 
MR. HARDWICH'S formulae. 
 
 dition, and unfit for use until the acetic acid has been added. If the glacial acetic 
 acid be employed, it should be tested for impurities. 
 
 " Many, unaccustomed to chemical manipulations, may desire to avoid the trouble 
 of saturating the bath with iodide of silver, and of removing the free nitric acid ; in 
 that case make it a little stronger than the formula, thirty grains to the ounce, omit 
 the acetic acid, and remove the sensitive plate as soon as the layer of iodide of 
 silver is formed. 
 
 " If the operator uses a collodion somewhat thicker than that recommended ; or if 
 large bluish patches of non-development occur in bringing out the image, the strength 
 of the bath may be increased to thirty or thirty-five grains to the ounce. 
 
 " "With regard to the length of time the bath will remain in working order no positive 
 opinion can be given. If it begins to yield foggy pictures, try the efltect of nitric acid, 
 one minim to the half-pint of solution. 
 
 " The addition of alcohol to a positive nitrate bath is not recommended. 
 
 « The Developing Fluids.— Eii^ei of the three following formulae may be used, accord- 
 
 ing to the taste of the operator. 
 
 Formula No, 1. 
 
 Sulphate of Iron, recrystallized . . . . 12 to 20 grains. 
 
 Acetic Acid (glacial) 20 minims. 
 
 Alcohol 10 minims. 
 
 Water 1 o™ce. 
 
 Formula No. 2. 
 
 Pyrogallic Acid 2 grains. 
 
 Nitric Acid 1 <irop. 
 
 Water 1 o^^ice. 
 
 Formula No. 3. 
 
 Solution of Protonitrate of Iron .... 1 ounce. 
 
 Alcohol 20 minims. 
 
 Remarks upon these Formulte.— Formula No. 1 is the most simple, since the solution 
 can he used as a bath, the same portion being employed many times succesively. If it 
 acts too rapidly, lessen the proportion of sulphate of iron. An addition of nitric acid, 
 half a minim to the ounce, makes the image whiter and more metallic ; but if too much 
 is used, the development proceeds irregularly, and spangles of silver are formed. 
 
 " The Alcohol and acetic acid render the development uniform by causing the solution 
 of protosulphate to combine more readily with the film. The latter also has an effect 
 in whitening the image and increasing its brightness. 
 
 " Solution of sulphate of iron becomes red on keeping, from a gradual formation of 
 persaU. When it is too weak, add more of the protosulphate. The muddy deposit 
 which settles to the bottom of the bath is metallic silver, reduced from the soluble 
 nitrate upon the plates. 
 
 " Some operators add nitrate of potash to this developing solution (it must be pure 
 nitre and free from chloride), so as to form a small portion of protonitrate of iron. It 
 is said to improve the colour slightly. The proportions are ten grains of nitrate of 
 potash to about fourteen or fifteen grains of protosulphate of iron. 
 
 " Formula No. 2.— In this formula, if the colour of the image is not sufficiently 
 white, try the effects of increasing the amount of nitric acid slightly. On the other 
 
122 
 
 MB. HAEDWICH'S formulae. 
 
 hand, if the development is imperfect in parts, and patches of a green colour are seen, 
 use three grains of pyrogallic acid in place of two, with less nitric acid. Supposing 
 this not to succeed, a few drops of nitrate of silver solution added to the pyrogallic, 
 immediately before use, will augment the energy of development. 
 
 " Fm-mula No. 3, or protonitrate of iron, does not require any addition of acid; but 
 it will be advisable, in some cases, to add to it a few drops of nitrate of silver imme- 
 diately before developing. This gives a bright metallic image, resembling that obtained 
 by adding nitric acid to protosulphate of iron. 
 
 " The following are the processes commonly followed for preparing protonitrate 
 of iron : — 
 
 " 1st, By the Action of Dilute Nitric Acid upon Sulphuret of Iron. — Dilute an 
 ounce of nitric acid with six ounces of water, and add to it about half an ounce of 
 sulphuret of iron, previously broken into very small fragments. Set the vessel aside 
 for several hours, in a place where the offensive and poisonous sulphuretted hydrogen 
 gas may escape without doing injury. When all effervescence has ceased, pour off the 
 green solution, add to it twenty grains of powdered chalk or whiting, and boil it in a 
 flask for five minutes. Allow it to cool, and filter from it the black deposit, if any has 
 formed. In this process the nitric acid, being in a diluted state and employed cold, does 
 not act as an oxidizing agent, but simply displaces sulphuretted hydrogen and forms 
 protonitrate of iron. The chalk is added in order to neutralize a small portion of free 
 nitric acid, which commonly remains after the action is complete. If a black deposit 
 is noticed on boiling, it is sulphuret of iron produced by the excess of sulphuretted 
 hydrogen, dissolved in the liquid, again reacting upon the protosalt of iron as the 
 solution becomes neutral. 
 
 "2nd, Jiy Double Decomposition. — This plan is somewhat less economical than the 
 last, but probably superior to it in most other respects. Take of nitrate of baryta three 
 hundred grains ; powder and dissolve by the aid of heat in three ounces of water. 
 Then throw in by degrees, with constant stirring, crystallized sulphate of iron powdered, 
 320 grains. Continue to stir for about five or ten minutes. Allow it to cool, and filter 
 it from the white deposit, which is the insoluble sulphate of baryta. 
 
 " In place of nitrate of baryta, the nitrate of lead may be used (sulphate of lead 
 being an insoluble salt), but the quantity required will be different. The atomic 
 weights of nitrate of baryta and nitrate of lead are as 131 to 166 ; consequently 300 
 grains of the former is equivalent to 380 grains of the latter. 
 
 The Fixing Solution.— Cyamde of potassium, two to twelve grains; common 
 water, one ounce. 
 
 " Cyanide of potassium is usually preferred to hyposulphite of soda for fixing direct 
 positives ; it is less liable to injure the purity of the white colour. The per centage of 
 carbonate of potash in commercial cyanide of potassium is so variable, that no exact 
 directions can be given for the formula. It is best, however, to use it rather dilute— of 
 such a strength that the plate is cleared gradually in from half a minute to a minute. 
 
 " The solution of cyanide of potassium decomposes slowly on keeping, but it will 
 usually retain its solvent power for several weeks. In order to escape inconvenience 
 from the pungent odour evolved by this salt, many employ a vertical bath to hold the 
 solution ; but in that case the plates must be carefully washed before fixing, as the iron 
 salts hasten the decomposition of the cyanide. 
 
 " The Whitening Solution.— Bichloride of mercury, thirty grains ; distilled water, 
 one ounce. 
 
MR. HARDWICH'S formula. 
 
 123 
 
 "By a gentle application of heat, the corrosive sublimate dissolves and forms a 
 solution as nearly as possible saturated at common temperatures. The addition of a 
 portion of muriatic acid enables the water to take up a larger quantity of bichloride ; 
 but this concentrated solution, at the same time that it whitens more quickly than the 
 other, is apt to act unequally upon different parts of the image. 
 
 " Before applying the bichloride, the image is to be fixed and the plate well washed. 
 Either the protosulphate of iron or the pyrogallic acid with acetic may be used for the 
 development; but the whitening process is more rapid and uniform in the latter case, 
 the metallic particles being more finely divided. 
 
 " FoHMUL^ FOR Negative Solutions.— T/w Co;/o«^w«.— In making negative col- 
 lodion the writer has succeeded best with pyroxyline prepared from paper (strips or 
 squares of paper cut into smaU pieces, and dissolved in sulphuric acid and nitre, and 
 washed in pyroxyline), which seem, from some unknown cause, to give more inten- 
 sity than cotton. If the following solution is very fluid with three or four grains of 
 pyroxyline to the ounce, as is often the case when the temperature of the nitro- 
 sulphuric acid was high, it is useful to add a grain or so of a glutinous sample made 
 from cotton, by which the requisite degree of viscidity is obtained. In this way, by 
 combining the two, a collodion may be made which will yield excellent half-tones 
 with any amount of intensity. 
 
 Purified ether, sp. gr. "720 5 drachms. 
 
 3 drachms. 
 3 to 6 grains. 
 3 to 4 grains. 
 6 drachms. 
 
 2 drachms. 
 
 3 to 5 grains. 
 
 4 to 5 grains. 
 
 alcohol, sp. gr. -825 . 
 Soluble pyroxyline . 
 
 „ iodide of ammonium . 
 Or, Kectified ether, sp. gr. -750 
 Alcohol, sp. gr. -836 
 Soluble pyroxyline . 
 Iodide of potassium . 
 
 " The film of iodide when formed in the bath should be tolerably dense, and more 
 pyroxyline must be added to the collodion if it is blue and transparent; this increases 
 the opacity better than an addition of alkaline iodide, the quantity of which should 
 never exceed four, or at most five grains to the ounce. 
 
 "If the collodion is glutinous, and produces a wavy surface, with less than four 
 grains of pyroxyline to the ounce, it is probable (unless the alcohol employed is 
 inferior) that the soluble cotton was badly made. In that case, try Mr. Shadbolt's 
 formula of adding of chloroform ten drops to each ounce of the fluid, and set it aside 
 for twenty-four hours. 
 
 " In place of iodide of ammonium, in the first formula, a mixture of iodide of 
 potassium and ammonium, or of potassium and cadmium, may be used ; the former is 
 especially recommended. 
 
 " If flakes of iodide of silver are seen loose upon the surface of the film, and 
 falling away into the bath, the collodion is over-iodized, and it will be impossible to 
 obtain a good picture. 
 
 " After the collodion has been employed to coat a number of plates, the relative 
 proportions of alcohol and ether contained in it become changed, from the superior 
 volatility of the latter fluid. Therefore, when it ceases to flow readily, and gives a 
 more dense film than usual, thin it down by addition of a little rectified ether. 
 
 " Most operators adopt the plan of keeping on hand a stock of the plain collodion, 
 
124 
 
 MR. HARDWICH's formulae. 
 
 and iodizing as required by the addition of alcoholic solution of iodide of potassium. 
 Ihe plain collodion, however, does not keep well beyond a certain length of time 
 without a considerable development of the acid principle. 
 
 In dissolving the pyroxyline, any fibrous or flocculent matter which resists the 
 action of the ether must be allowed to subside, the clear portion being decanted for 
 use. ihe iodide of potassium is to be finely powdered, and digested with the spirit 
 for several days ; if a saturated solution is required, it is better not to apply any heat. 
 Both iodide of ammonium and iodide of cadmium should dissolve almost immediately, 
 II the salts are pure. 
 
 When this collodion becomes very highly coloured and insensitive, a part of the 
 . Iree lodme may be removed by a strip of pure zinc or silver foil; also the metallic 
 Vosvdev obtained by reducing nitrate of silver with sulphate of iron acidified with 
 nitric acid, answers well for the same purpose. 
 
 "Many operators, where sensitiveness is not an object, prefer working with an 
 old collodion, thinking that it gives more intensity combined with half-tone. The 
 latter part of this rule, however, is not universal, for if the quantity of iodide of silver 
 m the film is small, the half-tones are best at the lemon-yellow stage of colouration. 
 It IS certain that some peculiar change takes place in collodion after iodizing, bv 
 which the intensity of the image is increased; and it is probable that this maybe 
 independent of colouration, for the author has observed that a grain or two of fresh 
 iodide, added to a sample in excellent working order, immediately diminishes the 
 intensity although the excess of free iodine remains the same. 
 
 " The Nitrate Bath. 
 
 Nitrate of silver, crystallized and dried . . .30 grains. 
 
 Acetic acid (glacial) i ^^^^^ 
 
 Distilled water 1 ^^^^^^ 
 
 This bath is first to be saturated with iodide and carbonate of silver, and the 
 acetic acid is to be added subsequently. 
 
 "A negative nitrate bath, carefully shielded from the light, will remain in working 
 order for many months. The proportion of nitrate of silver present becomes less aifter 
 a time, but not to the extent that might d priori be imagined. About five grains of 
 fresh nitrate per ounce will restore it to the original strength, even after a la.rge 
 number of plates have been coated. 
 
 If a very brown sample of coUodion is constantly employed, and the appearamce 
 of the negatives (misty and pale, greenish by transmitted light) leads at last to a s.us- 
 picion of free nitric acid beginning to accumulate, add a single drop of ammonia to the 
 half-pint of solution. The operator, however, should bear in mind that if the biath 
 was neutralized when first prepared, it will take many ounces of brown collodioni to 
 liberate a perceptible quantity of free nitric acid in a twelve-ounce solution, and it; is 
 always better not to add an alkali, unless really required. 
 
 " The Developing Solution.— The quantity of acetic acid required in the followiing 
 solution will vary with the strength of the acid and the temperature of the atmosphe}re. 
 An excess enables the manipulator to cover the plate more easily before the action begims " 
 but gives a bluish, inky hue to the image. In cold weather, use less acid and miore 
 free nitrate of silver in the developer : — 
 
DEFECTS AND REMEDIES. 
 
 125 
 
 Pyrogallic acid 1 grain- 
 Acetic acid (glacial) 10 to 20 minims. 
 
 Alcohol 10 minims. 
 
 Distilled water 1 ounce. 
 
 "•If the image cannot be rendered sufficiently black, two drops of the nitrate 
 batHi solution may be added to each drachm towards the end of the development. 
 
 '"Also, the proportion of pyrogallic acid may, if required, be increased to two or 
 evern three grains to the ounce. 
 
 "'If the solution be kept for some time after its first preparation, it is apt to 
 beccome brown and discoloured. In oi:der to avoid this, it has been recommended to 
 makke it about four times more concentrated than is necessary, and to dilute down with 
 distillled water when required for use. 
 
 '"2%e Fixing liquid.— For remarks on the cyanide of potassium fixing bath see 
 pag(;e 214. 
 
 Cyanide of potassium 2 to 12 grams. 
 
 Water 1 ounce. 
 
 O^r, Hyposulphite of soda i ounce. 
 
 Water 1 ounce." 
 
 : Defects and Remedies.— I have now to call the reader's attention to the failures 
 he : is pretty certain to meet with in his first attempts at photography, pointing out 
 at tithe same time the usual causes, as far as they can be traced, and their remedies. In 
 thiss study, however, as in all others, the operator must think for himself, and try to 
 disccover the causes of failure, as well as the required remedies, for it is not to be expected 
 thatt they can all be foreseen in a treatise like the present. Among other annoyances, 
 a m-umber of small white or transparent spots in the negative will present themselves, 
 cauased by plunging the plate too rapidly in the nitrate bath, or dashing the developing 
 soluution too rapidly over the surface of the plate ; in either case a number of minute 
 air 1 bubbles have been formed, which no after manipulation can remove or bring up 
 to tithe same degree of intensity as the surrounding portions of the plate. 
 
 The plate blackens all over when the developing solution is used. This arises 
 fronm many causes, viz., the plate may have been exposed accidentally to white light 
 durring some part of the process, or the camera or dark slide may admit light ; this 
 muast be ascertained. Or it may be owing to over exposure ; in this case the picture 
 wiim be clean, but very feeble, and all the details may be made out. This may be very 
 easiiily detected from another cause of blackening, owing to the bath or collodion being 
 alkaaline in a slight degree, and well known by the term " fogging." In this case we 
 obtaain an even black all over without the slightest trace of a picture. Should the 
 blaackening be owing to any of the causes named except the last, the cause at once 
 sugggests the remedy. If by the last named, it may be remedied by adding a drop or 
 twoo of acetic acid to the nitrate of silver bath, or five or ten drops of tincture of iodine 
 to tthe collodion. The latter must be done if the bath does not change slightly red- 
 denaed litmus-paper into blue. Instead of adding the acetic acid to the bath, if you 
 havve time to expose it to the sun for some hours in a white glass bottle, it will be the 
 safe'er way of bringing it back again. Should the blackening be of an irregular descrip- 
 tionn, more on one part of the plate than another, it will probably arise from the rays 
 of tthe sun shining nearly into the lens, or from some light reflected from the edge or 
 
126 
 
 DEFECTS AND THEIR REMEDIES. 
 
 inside tube of the lens, all which it will be necessary to look for in order to remedy 
 the defect. 
 
 There are other means used to neutralize the acid bath. Mr. Hardwich recom- 
 mends that the ammonia should be used in a very dilute state ; but I think the use of 
 ammonia in any shape very injurious. A writer in the Photographic Journa'. 
 recommends a piece of rough white marble to be suspended in the bath by means of a 
 piece of thread for a few days. Another recommends the addition of a few drops o: 
 dilute solution of caustic potash. That I also think objectionable. By far the best, 
 simplest, and most successful plan, and one which I have used for some time, and 
 which will succeed best in the hands of the amateur, as he cannot very well overdo 
 it, is to scrape a small piece of pipe-clay or whiting into the bath, as much as will go 
 on a sixpence to the pint ; this effectually neutralizes the nitrate bath, which may 
 be used immediately after being filtered. 
 
 Mr. Home recommends a veiy good plan for restoring the bath when it becomes 
 out of order through excess of iodide of silver in solution. He directs that a portion 
 of pure distilled water should be added, say four ounces to a bath containing twenty or 
 thirty ounces ; this will precipitate the iodide, or a great part of it. The bath must 
 then be filtered, and to it be added two drachms of nitrate of silver in crystals. The 
 bath will then be in first-rate working order. 
 
 I shall again impress upon the amateur that nothing will neutralize an acid bath 
 so wen as a small piece of pipe-clay or whiting. In testing with litmus-paper after 
 the addition of the whiting, &c., the test-paper will appear purple ; but this will be 
 owing to the carbonic acid, and will disappear if the paper be pressed between blotting- 
 paper and dried at the fire. Chalk, being of the same nature as whiting (carbonate of 
 lime), will answer quite as well. 
 
 Spots ofhlach, printing white on the positive, more especially at the bottom of the 
 latter. These are caused by dust, want of care in closing the shutter — viz., shutting 
 it down with a bang — dirty developing glass, allowing drops of decomposed solution 
 to fall on the plate from the bottom of the developing glass, or other piece of careless- 
 ness. The causes must be sought for by the amateur, and as they are always caused by 
 careless manipulation, he must find out the remedy himself. There is an appearance 
 often noticed in positives and negatives — in the one black, in the other white — similar 
 to snow melting and freezing again into icicles, at the bottom of the picture ; this is 
 always caused by the top part of the plate-holder not being well wiped dry before tlie 
 introduction of the plate ; but, in some cases, the same appearance almost, but at the 
 top part of the positive, takes place . This is generally caused by the plate being allowed 
 to stand so long that the surplus solution of nitrate of silver drains off the surface of tie 
 plate, and accumulating at the end of the plate, which would be downwards at the time 
 (the top in the positive), after being decomposed by contact with the surface of the 
 plate-holder, reascends by capillary attraction. This is easily known by wave-liie 
 markings appearing at the top of the positives. These markings may be prevented by- 
 placing a slip of blotting-paper at the bottom part of the plate, on the back and lowest 
 edge, when placing it in the dark slide ; or merely placing a narrow strip in tlie 
 bottom of the latter will do as well. 
 
 A Mack spot in one comer of the negative, about the size of a shilling, with several 
 short lines from it, printing white in the positive. This is always produced by tlie 
 contact of the finger with the excited plate, more especially if the finger has had on ilt 
 the least trace of hyposulphite of soda. 
 
DEFECTS AND THEIR REMEDIES. 
 
 127 
 
 Avoid the cause, and bear in mind that the fingers will always cause stains wherever 
 they touch the surface of any photographically prepared plate or paper ; and the fingers 
 of some persons more than others, owing to the degree of moisture, holding chlorides, 
 &c., in solution, they may possess. 
 
 Halo Light. — The positive has a sort of halo of light about the centre of the picture. 
 The same appears in the negative, but reversed, ».e., black ; at the same time, there is 
 a want of distinctness. 
 
 This is caused by reflected light in or from the Ions. To ascertain the cause it will 
 only be necessary to remove the ground glass, leaving the lens uncovered, place the 
 focusing-cloth over the camera and look at the lens, when you will see an immense 
 quantity of light reflected from its edges. This may be remedied by a very narrow 
 diaphragm, or, what will do as well, a narrow streak of black varnish painted round 
 the outside rim of the lens. It is a most curious fact, that some of our best lens 
 makers, will not take any pains to remedy this defect, although it has been often 
 pointed out to them ; and, I may add, that I have never seen a lens without this defect 
 more or less. The streak of black varnish, or the diaphragm, need not be wider than 
 an eighth of an inch, just sufiicient to cut off the light reflected from the edge of the 
 lens. In double lenses used for portraiture there should always be a diaphragm between 
 the front and back lens. 
 
 Irregular oily looking lines and spots resembling marble paper, or the appearance 
 caused by attempting to cover a greasy surface with water. These are always to be 
 traced to one of the following causes : — 
 
 Eaising the plate out of the bath before it has been sufficiently long immersed 
 (a minute at least) ; removing the plate too soon from the bath or before the ether has 
 been washed away ; re-dipping the plate after exposure (which should never be done), 
 and proceeding to develop before the nitrate has been well drained off the surface ; or 
 reversing the plate from the position in which it was taken out of the bath, causing 
 the silver solution to flow back again in lines, thus producing irregular action in the 
 development. 
 
 Transparent spots and streaks are caused by impure ether, pouring the developing 
 solution on the one spot, dirty glasses, more especially when the collodion is thin 
 and the bath neutral. These more frequently occur when the glass is colder than 
 the air in the room, the latter becomes condensed on the surface of the glass, 
 which should not be covered until the moisture has evaporated again. When those 
 spots are owing to some fault in the collodion, they may always be seen on the 
 plate before exposure ; and should any occur in an important part of the plate, it would 
 be better not to use it. A reticulated appearance of the film is owing to impure 
 alcohol or ether used in making the collodion, or to immersing the plate in the 
 bath too quickly after being coated with collodion. One or two sti-aight lines across 
 the plate, transparent or nearly so, are caused by checking the plate in immersing it in 
 the nitrate bath. 
 
 Irregularly-curved or circular black lines, separating a dark portion of the plate 
 from another not so intense, are caused by not pouring on the developing solution 
 evenly ; for if you allow it to stop for a single instant on any one part of the plate, 
 it will surely cause a line. There is a very nice arrangement for applying the deve- 
 loping solution, especially the protosulphate of iron. It is as follows : — A gutta- 
 percha bath is made, part of which retui-ns at right angles, or nearly so (Fig. 71), in 
 which the plate A is shown resting against the back of the upper part C, C, C, on two 
 
128 
 
 NITRATE BATHS AND APPARATUS. 
 
 small pieces or blocks of gutta-percha ; the bottom part, B, B, holds the developing 
 
 solution, and by turning it down (Fig. 72) the 
 solution flows evenly over the surface. The 
 same sort of bath will answer very well for the 
 nitrate of silver bath. It should not be made at 
 right angles, as the plate will rest more safely to 
 drain, &c., when the bath is turned up again if it be 
 made thus (Fig. 73). As the collodion dries round 
 the neck of the bottle, it will be necessary to 
 remove it carefully with the finger, previously 
 to coating each plate, otherwise it will fall and 
 spoil the film. When the collodion is too thick 
 it will not flow evenly ofif the plate, and cause 
 a cloudy irregular surface ; it must then be thinned 
 by adding ether alone, as the latter has evaporated in greater quantity than the alcohol. 
 
 If, after a reasonable exposure in a good 
 light, the negative is intensely black and 
 white, with absence of half-tone, the bath is 
 too acid, and must be neutralized by carefully 
 adding a small quantity of ammonia-nitrate 
 of silver solution, made by adding liquor 
 ammonia to a solution of nitrate of silver, 
 drop by drop, until the brown precipitate 
 first formed be redissolved. The portions 
 added to the nitrate bath should be very 
 small indeed, and the bath tried after each 
 addition. If so much be added as will cause fogging, then you must add a drop 
 or two of acetic acid. AU this must be done very carefully, 
 or you will surely spoil the bath. The more acid the bath, 
 the longer will be the exposure required ; but amateurs will 
 succeed better with a slightly acid bath than with a perfectly 
 neutral one, the latter requiring much more care and delicate 
 manipulation than the former ; but the neutral bath will 
 always produce the firmest photographs. Under-exposure and 
 over-development will produce efiects almost similar to an acid 
 bath. 
 
 As collodion loses its sensitiveness when dry, there have 
 been several methods thought of for preserving it moist for a 
 considerable length of time ; but I am inclined to give the preference to the plan 
 proposed by Messrs. Spiller and Crookes, as I have taken a picture in that manner 
 three days after the plate was made sensitive. They take advantage of the property 
 possessed by certain "deliquescent" salts, which remain moist for any length of 
 time when once melted ; and many of them absorb moisture so eagerly from the air, 
 that it cannot be easily driven off except by considerable heat. Nitrate of zinc and 
 acetate of potash were the salts originally selected, but nitrate of magnesia has been 
 substituted. Messrs. Spiller and Crookes' process is as follows : — 
 
 " The plate, coated with collodion in the usual manner, is to be rendered sensitive 
 in a thirty-grain nitrate of silver bath, in which it should remain rather longer than 
 
 Fig. 73, 
 
SPILLER AND CROOKES' PROCESS. 
 
 129 
 
 is generally considered necessary (about five minutes) ; it must then be slightly drained 
 and immersed in a second bath, consisting of 
 
 Nitrate of magnesia . . . .4 ounces. 
 Nitrate of silver . . . .12 grains. 
 Glacial acetic acid .... 1 drachm. 
 Water 12 ounces. 
 
 And there left for about five minutes, then removed and placed in a vertical position 
 on blotting-paper, until all the surface-moisture has drained off and been absorbed. 
 This generally takes about half an hour, and they may then be packed away in any 
 convenient box until required for use. 
 
 " Not only is the sensitiveness unimpaired by this treatment, but we think, on the 
 contrary, that it is slightly increased ; instantaneous negatives have been taken on 
 plates which had been prepared some days previously. We are not yet in a position 
 to give the length of time that may elapse between the preparation of the plate and 
 development of the picture ; such experiments necessarily require a more lengthened 
 period than we have at present been able to give, but as long as they have yet been 
 kept (upwards of three weeks) there has been no appearance of deterioration. 
 
 " Before the development, we find it advisable to moisten the collodion film by 
 immersion in the silver bath for about half a minute, as otherwise the pyrogallic acid 
 or iron solution would not flow evenly over the plate. The fixing, &c., is of course 
 conducted as usual. 
 
 " It will be as well to draw attention to a few points which, although not absolutely 
 essential, may possibly be found useful in practice. The glass plates should be 
 cleaned with more care than is necessary when they are to be used immediately ; we 
 have found strong nitric acid applied with a tooth-brush most convenient. With 
 regard to the collodion, we have tried many different samples, and with tolerably 
 uniform success. The greater number of our experiments have been made with a 
 tolerably thick collodion, the alcohol and ether of which were in the proportion of 
 1 : 2, made sensitive with four grains of iodide, and half a grain of bromide of ammo- 
 nium to the fluid ounce. We have also employed a collodion containing iodide and 
 bromide of cadmium with good success. 
 
 " Of the thirty-grain silver solution for exciting the plate, we have only to recom- 
 mend the use of acetic instead of nitric acid, to give the bath that faintly acid reaction 
 which is by some operators considered desirable. 
 
 " There are one or two circumstances to be attended to in the preparation of the 
 magnesia bath. Commercial fused nitrate of magnesia is very liable to contain chlo- 
 rine, and also to have an alkaline reaction on account of the fusion being carried too 
 far. Of course the quantities of acetic acid and nitrate of silver given in the formula 
 for the bath, are on the supposition that the nitrate of magnesia is pure ; if this be not 
 the cage, it should be rendered perfectly neutral with acetic acid, the chlorine exactly 
 precipitated with nitrate of silver, and then the proper amounts of acid and silver added. 
 However, if the impurities are very considerable, it will be safer to reject the salt at 
 once. This bath will keep in good order for a long time ; the only point to be 
 attended to is to drain the plates slightly after coming from the silver bath, and, if 
 necessary, to remove the liquid from the back with blotting-paper, so as to introduce 
 as little silver as possible into the nitrate of magnesia. A solution of one grain of 
 silver to the ounce is quite sufficient to keep the plates sensitive ; and when the 
 
130 
 
 KITRATE OF MAGNESIA. 
 
 strength rises, as it will in time, to above a certain limit, the slight evaporation that 
 alwaj s takes place wUl render the silver solution sufficiently strong to dissolve oif the 
 iodide in small holes. If this occur, the bath can be restored by nearly, but not quite, 
 precipitating the silver with a solution of chloride of magnesium, and then filtering. 
 
 " One of the most important things to be attended to is, the necessity of preserving 
 the plates where they are perfectly free from any light. It will be evident to all, 
 that anything short of absolute darkness, when the sensitive surface is exposed to its 
 action day after day, and perhaps week after week, must be fatal to its subsequent 
 cleanliness. The necessity for protecting the plates from any deleterious gases — 
 ammonia, for instance — is too obvious to require comment." 
 
 As it is not very easy to obtain the nitrate of magnesia pure enough for photo- 
 graphic purposes, the following observations by Mr, Hardwich may be interesting 
 here : — 
 
 " Kitrate of Magnesia. — Nitrate of magnesia may be prepared by dissolving 
 magnesia or its carbonate in dilute nitric acid. It crystallizes with difficulty in 
 rhomboidal prisms, which are deliquescent and soluble in an equal weight of water. 
 "When intensely heated, it loses both water and acid, and magnesia remains. 
 
 " Commercial nitrate of magnesia usually contains chloride of magnesium, and if 
 it has been strongly fused, nitrite of magnesia and oxide of magnesium ; it will be 
 better, therefore, to prepare it purposely for photography. 
 
 " A solution of nitrate of magnesia, of about the strength recommended by Mr, 
 Spiller for preserving the sensitiveness of collodion plates, may easily be obtained as 
 follows : — Take five fluid ounces of a colourless sample of nitric acid of the common 
 strength, sold at about tenpence per pound (specific gravity, 1"36 to 1'4), and dilute it 
 with seven ounces of water ; then weigh out carbonate of magnesia four ounces, and 
 add it by degrees until all effervescence has ceased, and an excess of magnesia 
 remains, rendering the liquid milky. Next add the nitrate of silver recommended in the 
 formulae, viz., twelve grains, which, however, may conveniently be increased to half 
 a drachm ; agitate well until a piece of reddened litmus-paper changes to blue on 
 immersion it in, showing that the bath is alkaline, and then filter from the white 
 deposit and add of glacial acetic acid one drachm, as recommended, 
 
 " In this process, the carbonate of magnesia first neutralizes the nitric acid, con- 
 verting it into nitrate of magnesia ; the nitrate of silver decomposes any soluble 
 chloride which may be present, precipitating it in the form of chloride of silver, and 
 also reacts upon the excess of carbonate of magnesia, producing carbonate of silver, 
 which renders the bath alkaline ; lastly, the acetic acid removes the alkalinity, leaving 
 in the liquid a trace of acetate of silver, thus giving absolute security against the 
 existence of any free nitric acid, which would destroy the sensitiveness of the pre- 
 served plates. 
 
 " The solution when completed will usually contain a small quantity of soluble 
 sulphate (evidenced by chloride of barium) ; the precipitated carbonate of magnesia 
 being rarely washed sufficiently to free it from all traces of sulphate of soda and 
 chloride of magnesium or sodium." 
 
 More recently Mr. Shadbolt has proposed to improve the process of Messrs. Spiller 
 and Crookes by using honey instead of the nitrate of magnesia. Although honey cannot 
 be classed with the deliquescent salts, in common with other uncrystaUizable sugars, it 
 has the property of remaining moist for a considerable time. 
 
 Mr. Shadbolt's process is'as follows : — " Having prepared and excited the collodion 
 
MR, SHADBOLT'S honey PROCESS. 131 
 
 in the usual manner, on its removal from the bath of nitrate of silver it is to be drained 
 pretty closely for about half a minute, and then immersed in a second bath, eonsistin"- 
 of distilled water twenty to thirty ounces to one ounce of the exciting bath (the exact 
 quantity is not of great moment), and allowed to remain in the latter mixture until the 
 liquid flows evenly on lifting the plate up, which will happen in about from two to 
 three minutes after immersion. The object of this proceeding is to wash away all but 
 a slight trace of free nitrate of silver, as one of the causes of deterioration of the plate 
 is the crystallization of this salt on the surface of the coUodion, This distilled water 
 bath should be in a vertical vessel, similar to that used for exciting, and the same bath 
 if freed from impurities as they accumulate, will do for an indefinite time. To dis- 
 tinguish it, I shall term it the washing bath. 
 
 " The plate may be removed from this bath as soon as the liquid flows freely, and 
 again drained closely, when a portion of the preservative syrup is to be poured on and 
 and oflP once or twice, being careful to avoid bubbles, or any minute particles of matter 
 being left on the plate ; which is then to be placed upright upon clean blotting-paper 
 with the collodion-side towards the wall to drain. In about ten minutes' time the 
 lower edge of the plate where the syrup has been collected, may be touched lightly 
 with fresh blotting-paper to remove the superfluity, and then placed in the dark frame 
 or stored away in a box for future use. It is not necessary to perform this operation 
 until convenient. 
 
 " The preservative syrup is thus made :— Take of pure honey and distiUed water 
 equal parts by measure, mix thoroughly and filter. In my former directions a sixth 
 part of the volume of alcohol was included ; but further experience leads me to con- 
 eider this unnecessary, if not detrimental. 
 
 "If thoroughly excluded from the action of light, plates thus prepared will keep 
 good for a very long time. The sensibility is certainly less than when fresh plates are 
 used, and I judge that the exposure required is about double the time, for the same 
 collodion, if used immediately after its removal from the nitrate bath ; but I cannot 
 detect any further diminution for the first twenty-four hours, and I have taken a 
 picture no less than three weeks after excitation, but with at least four times the 
 exposure required for a fresh plate. I do not, however, recommend the plates to be 
 kept longer than is really necessary, as the chances of change from very little actinic 
 force are certainly great. 
 
 " The plates may be developed even as long as twelve hours after exposure. This 
 part of the process is conducted as follows : — 
 
 _ " The plate is to be again immersed in the washing bath and left from one to ten 
 minutes to soak, occasionally lifting it up and down to facilitate the removal of the 
 superfluous syrup, and thoroughly to soften what remains upon the plate. The longer 
 the latter has been kept, the longer it should be allowed to soak. 
 
 " When taken out, a sufficient quantity of the developing solution is to be poured 
 over the pkte in the ordinary way, and, provided the paper has been properly soaked 
 in tne washing bath, there is no greater difficulty experienced in getting it to flow over 
 than when a fresh plate is used. The image should appear very slowly, and when all 
 the details are out but very faintly ; the developing solution is to be returned into rhe 
 measure (taking especial care not to allow the small portion remaining on the plate to 
 run m lines), a feat readily performed if done quickly, and the plate instantly restored 
 to a horizontal position. A small quantity of the exciting bath (a thirty-grain solution 
 of nitrate of silver), from an eighth to a sixth of the volume of the solution that was 
 
132 
 
 CAPTAIN CAKON'S DRY COLLODION PROCESS. 
 
 poured from the plate into the measure, together with a like proportion of the pre- 
 servative syrup, should now be added to the liquid in the measure and well mixed up ; 
 this is to be poured on the plate and kept moving until the picture is sufficiently 
 intense, which can be carried to any degree if the exposure has been proportionately 
 prolonged. So intense can the high lights be made, that a whole day's exposure to 
 direct sunshine will not print through them. Of course I only mention this to show 
 what can be efifected— not what is desirable. 
 
 " The developing solution I adopt consists of one grain to the ounce of water solu- 
 tion of pyrogallic acid, one-fourth of the menstruum being the ordinary acetic acid 
 of the druggists, or, if glacial acetic acid is used, one-twelfth part is sufficient." 
 
 There have been other suggestions for keeping the collodion plate moist, and 
 therefore sensitive ; such as keeping the excited film between two glasses, &c. I fear 
 that they are all of no use ; amongst the number, the following promises to be the 
 most successful, but I must add that I have never tried it :— 
 
 Captain Oaron, of the French artillery, has addressed to the Societe d' Encourage- 
 ment the description of the following process of photography upon dry collodion :— 
 
 " The manipulations in the employment of dry collodion are the same as for the 
 moist; the difference lies in the substitution of chlorides for the iodides, which, 
 without exception, lose their sensibility by drying. The chloride of silver is as sen- 
 sitive in the dry state as when moist ; and although its sensibility is not equal to that 
 of moist iodized collodion, it nevertheless remains superior to that of collodion preserved 
 by sugar, honey, mucilage, or salts, which besides have the inconvenience of becoming 
 soiled by dust. The following are M. Caron's preparations :— 
 
 '< Take of pure collodion three and a-half fluid ounces, add ten, twelve, or fifteen 
 drops of chloride of iodine— as an average, twelve ; spread on the glass ; plunge in a 
 bath of fused nitrate of silver (forty grains to the ounce), wash with common water; 
 let the glass drain, and dry it. From the dampness of the weather, M. Caron has 
 always dried rapidly at the fire ; he is not sure whether this is indispensable. 
 
 " Take the impression in the camera or behind a negative. Ee-dip the plate in 
 the bath of nitrate of silver for several seconds ; develop the image with pyrogallic 
 acid, as for moist coUodion ; pyrogallic acid fifteen and a-half grains, water ten ounces, 
 acetic acid two and a-half drachms ; with the following bath, pyrogallic acid fifteen 
 and a-half grains, water one and a-half pint (imperial), acetic acid two and a-half 
 drachms, the image comes out more slowly, but better. Fix with cyanide of potassium 
 of one five-thousandth (' au cinq millieme ') ; wash, dry. 
 
 " The following fact will give an idea of the duration of the exposure :— On a dull 
 day, to print through a negative on collodion, required an exposure of two to three 
 seconds. So long as the image does not acquire a red colour with pyrogallic acid, the 
 exposure has not been sufficient. 
 
 " This process is evidently exceedingly simple ; and if it gives good impressions, 
 it will be generally adopted. M. Caron says nothing respecting the quality of those 
 that he has obtained ; it^is true, however, that we are in the midst of winter. 
 
 " MM. Duboscq and Tavernier have tried this process, and their results promise 
 much. The collodion applied in this way has all the advantages of albumen, and the 
 drying by the fire appears of great utility." 
 
 The process published by Mr. Shadbolt, which certainly possesses great advan- 
 tages, is very ably followed up by Mr. ManseU, of Guernsey, who published a modifi- 
 cation or improvement on Mr. Shadbolt' s process. It is nearly as follows :— 
 
MR. MANSELL's improved PROCESS. 133 
 
 After paying some merited compliments to Mr. Shadbolt for his valuable invention, 
 Mr. Mansell adds—" The plate having been carefully cleaned and iodized as usual', 
 the subsequent manipulation resolves itself into three heads. ' 
 
 " FiKST. To reduce the amount of free nitrate of silver on the plate to nearly the 
 minimum necessary for its sensitiveness in the camera. 
 
 " Having drained the plate, immerse it in a vertical bath of distilled water for one 
 or two minutes; take it out, and drain it by resting one edge on blotting-paper. 
 Another method is to pour on the plate, very gently, and not on one spot, a°s much 
 distilled water as it will carry, leaving it on for two minutes. I prefer the washing- 
 bath ; but the second method may be useful on occasion. 
 
 "iJmaT-yts.— The addition of nitrate of silver to the washing-bath is superfluous ; 
 the capillarity of the villous surface of the iodized film retains as much as is necessary! 
 The bath of course soon acquires nitrate of silver from the plates ; but this is no injury 
 till it becomes excessive. When the amount exceeds one grain per ounce, the bath 
 must be diluted. 
 
 " Skcond. To preserve the surface of the plate moist, and the free nitrate of silver 
 on it from crystallizing, by means of a hygrometric coating of syrup. 
 
 " Give the washed plate two doses of syrup, leaving each on for about two minutes, 
 with waving. I use syrup which has done duty as the second dose of one plate, for 
 the first dose of the next plate, always finishing with fresh syrup. Oscilate the plate 
 from angle to angle, resting on blotting-paper, to obtain a perfectly mirrored surface, 
 and store away for use. The plates will keep for a month or six weeks. ' 
 
 " Hemarks.—The syrup is made by taking, half and half, pure honey and distilled 
 water, and filtering ; in fact, it ought to be as dense as can pass through ordinary 
 white filtering-paper. The greatest care should he taken to avoid the reduction of any 
 portion of the free nitrate of silver in long-kept plates, by having the hygrometric film 
 as free from it as possible. 
 
 "Third. To remove the syrup perfectly from the plate before developing. 
 " On this the perfection of the result mainly depends. The syrup, after it has been 
 on the plate a short time, consists of two layers; an outer one, which remains soft and 
 hygrometric for a long time, and is soluble in cold water, and an inner film, a com- 
 pound of syrup and nitrate of silver, which is insoluble in cold water. This is easily 
 proved by washing the plate in a vertical glass bath, where this layer is seen separating 
 in bran-like scales, the water mechanically removing it. These scales mav also be 
 collected on a filter and examined. This inner layer (with a mean temperature of 
 46° Fah., and a mean degree of humidity of -836), after about 150 hours, becomes 
 adherent to the collodion— at first round the margins of the plate, and then to the 
 whole surface, covering it as with a varnish, which no amount of washing in cold 
 water will remove. This indurated syrup is soluble in hot water; but it is far more 
 effectually and safely got rid of by steaming. On removing the plate from the dark 
 shde, immerse it in the washing-bath for five minutes, to remove the outer syrup ; 
 drain it, then hold it, collodion downwards, over the steam of boil'ng water, poured in 
 a pan, for about ten minutes (the water is to be renewed if the steam does not rise 
 freely), taking care to keep the plate four or five inches from the surface of the water ; 
 the indurated syrup wiU be seen gradually to dissolve, and, by inclining the plate^ 
 may be run off at any angle you choose. In the process of steaming, if any part of the 
 surface is disposed to dry, as will sometimes be the case, where the coating of syrup 
 happens to be thinner than elsewhere, it must be kept wet by causing the fluid on the 
 
134 
 
 MR. MATALL's dry COLLODION PROCESS. 
 
 plate to run over it. Allow the plate to drain, tlicn remove the remaining syrup hy 
 gently pouring distilled water over it once or twice. Drain the plate, and pour on 
 pyrogallic acid (no image whatever appears under this) ; after a minute or two, when 
 the iodized film has been well impregnated, pour off the pyro into a glass containing 
 about an eighth of its volume of a thirty-grain nitrate of silver solution, and imme- 
 diately pour it over the plate. The image rapidly comes out, and may be developed 
 as usual to any extent. 
 
 Remarks. — The first washing-off of the outer layer of syrup may be effected by 
 pouring one or two waters on the plate, leaving them on for a few minutes. I prefer 
 the washing-bath, and only mention this as a makeshift for travellers, who may thus 
 avoid the necessity of carrying one. The development is so even, that on a 9 X 7 
 plate it is almost impossible to say where it commences ; the uniform anastasis of the 
 picture is one of the most beautiful experiments that can be witnessed — it rises up like 
 an exhalation, and its perfection is exquisite. The negative high lights are as trans- 
 parent as glass, and the half-tones and blacks all that can be desired. The steamed 
 and washed plate, before development, consists of a film of iodide of silver, nearly 
 pure, in a state of actinic tension, the free nitrate of silver having been almost entirely 
 removed ; indeed, by repeating the steaming and washing, this can be done so perfectly 
 that the plate may be exposed to diffused daylight without injury. This is a remark- 
 able experiment, which throws so much light on the theory of this truly wonderful art, 
 that it will amply repay any one who has leisure and talent to follow it up. The 
 negatives obtained from plates that have thus been deprived of their original free 
 nitrate of silver, are equal in every respect to others that have not been so treated. 
 Among other advantages, steaming the plates cleanses them so perfectly, and gives us 
 such complete mastery over this method, that I now always use it, whether kept a 
 long or a short time ; the trouble is nothing, the result certain." 
 
 Mr. nXayall's Dry Collodion Process. — As the subject of preserving collo- 
 dion plates for a long time without destroying their sensitiveness is one of vital 
 importance, I cannot refrain from giving Mr. Mayall's process for using a dry collodion ; 
 and I may add that the same gentleman, at a considerable sacrifice of time and money, 
 gave one of the most instructive lectures on the albuminized process on glass ever 
 brought before the Ijondon Photographic Society. I have already given the sub- 
 stance of this lecture, and shall now give his method for using dry collodion, as copied 
 from the pages of the London Photographic Journal : — 
 
 " The object of this paper," he says, " is to explain a process by which collodion 
 can be used dry. It may be well, before describing the mere process, if we endeavour 
 to comprehend somewhat of the chemical action which is necessary to the production 
 of a good collodion, and to explain the law of substitution, upon which the reactions of 
 this highly complex organic compound may be said to depend. 
 
 " It is well known to chemists that there are a number of organic substances, 
 which, when treated with chlorine gas, take up a number of measures of that gas, 
 equal to the number of measures of hydrogen that are taken from it by another portion 
 of the chlorine. Gay Lussac was the first to observe this phenomenon, and Dumas 
 afterwards remarked the same change in oil of turpentine, and founded upon it his 
 ' theory of substitution.' 
 
 " Example :— Acetic acid, C4H4O4, is converted by the action of chlorine" into 
 chloracetic acid, Q HCI3 O4, without altering the forni or appearance of the 
 original acid. 
 
MR. MAYALL's dry COLLODION PROCESS. 
 
 135 
 
 " This latter product forms with oxide of silver a soluble salt, without any preci- 
 pitation of chloride of silver ; whereas chlorine, in all the inorganic compounds of 
 which it forms the electro -negative element, yields with silver solutions a precipitate 
 of chloride of silver. 
 
 " Again, ether may be taken as oxide of ethyl, C4H5O, ethylene being the primary 
 nucleus, C4H4 + H 0 ; by the successive action of chlorine it may be converted as 
 follows : — ■ 
 
 Oxide of ethyl . . . . C4 H.- 0 
 
 By action of chlorine becomes . . C4 H4 CI 0 
 
 H, CI., 0 
 C4CI5O' 
 
 "It will be observed that the chlorine displaces an atom of hydrogen, and this 
 action continues until hydrogen vanishes from the series. 
 
 "Now, although chlorine was the first electro-negative" element that was observed 
 to have this property of substitution, more recent investigation has shown that iodine, 
 bromine, and even fluorine and some of the metals, have the property also, and form 
 with ether : — 
 
 Oxide of ethyl • • . . C4 H- 0 
 
 Iodide of ethyl 
 Bromide of ethyl 
 Chloride of ethyl 
 Zincethyl 
 
 C4 H,I 
 C4 R, Br. 
 
 C, Hg CI. 
 
 C. H. Zn. 
 
 And the metal ethyls again form iodides, bromides, &c. 
 
 " Now these ethyls on a first glance should be analogous to the true iodides, 
 chlorides, bromides, and should immediately yield precipitates with the usual tests 
 employed for their detection ; but they do no such thing ; they are completely masked, 
 and do not exhibit any of their usual characteristics. If, with Berzelius, in his' 
 Binary Theory, we regard them as compounds of chlorine, iodine, and the radical ethyl 
 C* H5, they do not precipitate silver solutions. The- chlorine, iodine, bromine, exist 
 in their constitution in a totally difierent manner. 
 
 Similarly, marsh gas . . . . C, 
 
 produces Chloroform . . . , , C", H CI 
 
 Bromoform C^' H Br3 
 
 Iodoform . . . . . C, H I3 
 
 *' Laurent and Gerhardt, in the French school, have greatly expanded this subject, 
 and, in the opinion of chemists, have even gone too far to accord with well-established 
 views in chemistry. Much remains for the experimentalist before the true limits of 
 substitution can be properly defined. 
 
 "One thing, however, is established without fear of controversy; that is, that 
 oxide of ethyl when brought into contact with chlorine, first loses its hydrogen, and is 
 transformed into a chlorethy], and eventually every atom of its hydrogen is abstracted. 
 
 " Iodine produces a similar effect, until at last the iodide of ethyl has completely 
 replaced the original ether, arid has produced that decomposition which it is the 
 province of the light to effect. Hence a collodion that has undergone this change is no 
 longer, or only feebly, sensitive to the electro-negative ray of light, and this will 
 account for the deterioration of excited collodion. 
 
 " Now, as every excited collodion becomes deteriorated by keeping, the question 
 
I 136 MR. mayall's dry collodion process. 
 
 has strongly impressed me — Is it possible to impregnate the ether with any substance 
 rich in hydrogen that would repair the waste going on in the excited collodion ? And, 
 after trying various substances, I have found four that do actually repair, or rather 
 ■ that give off their hydrogen first, and so keep the ether intact. These ace — 
 
 I Benzine . . . C14 H5 O2 
 
 Naphthaline . . Cjo Hg 
 
 Hellenin . . . Cjs Kg 
 
 Terpenole . . C^s Hj, 0 
 
 I " Very small quantities of these substances added to the ether pi'cvent it running 
 i into iodides, bromides, and chlorides of the ethyls, still leaving in the coUo- 
 : dion sufficient of electro-positive elements to enable the light to push the iodide of 
 silver out of its feeble combination. 
 
 " What Liebig calls the eremecausis of organic bodies — that is, the slow decomposi- 
 tion by the absorption of oxygen — is one of the leading characteristics of highly 
 complex organic forms rich in hydrogen, analogous to putrefaction of nitrogenized 
 substances. In the instances above quoted there are two affinities in action : — first, 
 the affinity of nitrogen for hydrogen, and of carbon for oxygen, and both facilitate 
 1 the disruption of the elements of the complex organic form ; decay and utter annihila- 
 tion of organism takes place ; the elements are again restored to the inorganic world. 
 Those who wish to pursue the inquiry as a purely chemical investigation, I refer to 
 Liebig' 8 ' Vegetable Physiology.' 
 
 " The chemistry of this process is somewhat obscure. However, some of our 
 ablest photographic chemists are now investigating it, and no doubt from their labours 
 much may be expected. 
 I " The usual plain collodion is excited with — > 
 
 "No. 1.— .3 grains of iodide of cadmium. 
 1 grain of chloride of zinc. 
 1 ounce of collodion, 
 i ounce of alcohol. 
 
 " Dissolve the chemicals in the alcohol, and then mix with the collodion. 
 
 j Or, No. 2. — 3 grains of iodide of zinc. 
 
 1 grain bromide of cadmium, 
 j Or, No. 3. — 2 grains iodide of cadmium, 
 
 i 1 grain bromide of cadmium. 
 
 I Jjf grain bromide of iron. 
 
 ! grain bromide of calcium. 
 
 ! " In the last it will be necessary to dissolve one grain of bromide of iron in 
 
 j one drachm of alcohol, and use one fluid grain of the solution. Similarly three grains 
 
 I of bromide of calcium must be dissolved in one drachm of alcohol, and one fluid 
 
 I grain used. 
 
 ' " The excited collodion will require to stand a few days to settle completely. 
 
 I Decant into a dry bottle, to avoid sediment. Spread as usual. 
 
TlvSTS OF THE STRENGTH OF ACIDS. 
 
 " Bath — which for distinction sake we will call albuminate of silver : — 
 16 ounces distilled water. 
 
 1 ounce albumen. 
 
 1^ ounce nitrate of silver (neutral), 
 li ounce glacial acetic acid. 
 
 2 grains iodide of potasssium. 
 
 " The albumen and water must be well mixed first, then the glacial acetic acid 
 added ; shake up, and let stand three hours ; then the nitrate of silver in crystals, 
 shake and filter, stand twenty-four hours ; then add the iodide of potassium, filter 
 again, ready for use. Coat the plate, as usual, with collodion, and use the albuminate 
 of silver bath as an ordinary silver bath ; wash in another bath of distilled water five 
 minutes, then wash the back of the plate with common water, the front with distilled ; 
 set the plate aside to dry in a vertical position, in a place free from dust. It will 
 keep three weeks. Expose in the camera as usual, from two minutes to ten, according 
 to the light, diaphragm, &c. Pass into the silvering bath again three minutes. 
 Develop with — 
 
 6 to 8 grains prntosulphate of iron. 
 
 1 ounce distilled water. 
 
 1 drachm glacial acetic acid, 
 
 "Wash, and fix with — 
 
 1 cyanide of potassium. 
 20 water. 
 
 " It is about as quick as albumen in the camera. The albuminate of silver bath 
 must on no account be exposed to daylight, nor the developing solution. Potassium 
 and ammonium salts will do to excite the collodion ; but it will not keep so long as 
 with the metallic iodides. 
 
 Tests of the Strength of Acids.— One of the great causes of failure, to which 
 the best photographers are liable, is to be found in the adulteration and impurity of the 
 chemicals used. To this question Mr. Hardwich directed much of his attention, and 
 the following are some of the tests and remedies his experiments suggested to him : — 
 
 " Nitro-Sulphuric Add. — Plan for making nitro-sulphuric acid, the specific gravity 
 of the two acids not having been previously determined : — Take a strong sample of 
 nitric acid (the yellow nitrous acid, so called, succeeds very well), and mix it with oil 
 of vitriol as follows : — 
 
 Sulphuric acid . , . 10 fluid drachms. 
 Nitric acid .... 10 ,, 
 
 " Now immerse a thermometer, an indispensable article, and note the temperature. 
 If the oil of vitriol is good, it should be about 130'. If it sinks below 120°, place the 
 mixture in a capsule (a teacup will answer the purpose), and float upon boiling water 
 for a few minutes. 
 
 " Having done this, a preliminary experiment with a small tuft of cotton wool will 
 speedily indicate the actual strength of the nitro-sulphuric acid. Stir the tuft in the 
 mixture for five minutes. Remove it with a glass rod, and wash with water for ten 
 minutes until no acid taste can be perceived. If the wool becomes matted, and gela- 
 tinizes slightly on its first immersion in the acid ; or if, in the subsequent washing, the 
 fibres appear to adhere and to be disintegrated by the action of the water, the nitro- 
 sulphuric acid is too weak. In that case, add to the acid mixture oil of vitriol three 
 
138 DISSOLVIXG THE COLLODION. 
 
 drachms. If the cotton was actually dissolved in the first trial, an addition of half a 
 fluid ounce of oil of vitriol may be required. 
 
 " Supposing the cotton not to be gelatinized and to wash well, then wring it out 
 very dry, pull out the fibres, and treat it in a test-tube with rectified ether, to which a 
 few drops of alcohol have been added, If it is insoluble, dry it by a gentle heat and 
 apply a flame. A brisk explosion indicates that the nitro-sulphuric acid employed is too 
 strong. In that case, add to the twenty drachms of mixed acids, water one drachm, 
 or even one drachm and a half, if the compound was very highly explosive. 
 
 " There is a third condition, somewhat difi'erent from either of the above, which is 
 puzzling to a beginner. It is this : — The fibres of the cotton mat together very 
 slightly or not at all on immersion, and the washing proceeds tolerably well ; the cpm- 
 pound formed is scarcely explosive, and dissolves imperfectly in ether, leaving little 
 nodules or hard lumps of unaltered cotton. The ethereal solution yields, on evapora- 
 tion, a film which is opaque instead of transparent. In this case, the acid mixture, is 
 slightly too weak, or the temperature is too low, being probably about 90° instead of 
 120° to 130°. When the acid mixture has been brought to the proper strength by a 
 few preliminary trials, proceed according to the directions given a few pages in 
 advance. 
 
 Preparation of Nilro-sulphurie Acid. — The process by oil of vitriol and nitre is \ 
 recommended, in preference to the other, to the amateur who is unable to obtain nitric ! 
 acid of convenient strength. The common oil of vitriol sold in the shops is often very \ 
 good for photographic purposes ; nevertheless it is best, if possible, to take the specific | 
 gravity. At a temperature of 58° to 60°, specific gravity 1-833 is about the usunl i 
 strength, and if it falls below this, it will be better to reject it. | 
 
 " The nitre should be the purest sample which can be obtained. Commercial -piti c 
 often contains a large quantity of chloride of potassium, detected on dissolving the j 
 nitre in distilled water, and adding a drop or two of solution of nitrate of silver. If a I 
 milkiness and subsequent curdy deposit is formed, chlorides are present. ; 
 
 "These chlorides ai'e injurious ; after the oil of vitriol is added, they destroy a poi- 
 tion of nitric acid by converting it into brown fumes of peroxide of nitrogen, which ; 
 alters the strength, of the solution. j 
 
 " Therefore, if pure nitrate of potash, free from chlorides, can be obtained, the slight ! 
 additional expense is not worth being taken into account ; but if not, the finest crystals [ 
 of commercial nitrate may be picked out, and will probably answer the purpose. | 
 
 " Nitrate of potash is an anhydrous salt — it contains simply nitric acid and potash, 
 without any water of crystallization ; still, in many cases, a little water is retained 
 mechanically between the interstices of the crystals, and therefore it is always better to | 
 dry it before use. This may be done by laying it in a state of fine powder upon blot- ' 
 ting-paper, close to a fire, or upon a heated metallic plate. 
 
 " Whether previously dried or not, the sample .must be reduced to a fine powder 
 before adding the oil of vitriol ; otherwise portions of the salt escape decomposition. 
 
 ''Supposing these preliminaries to have been properly observed, weigh out pure 
 nitre, powdered and dried, 600 grains. This quantity is equivalent to one and a quarter 
 ounce troy or apothecai'ic.s' weight, and to one and a quarter ounce avoirdupois weight 
 -f- 54 grains. Place this in a ica-cup or any other convenient vessel, and pour upon it 
 water one fluid drachm and a half mixed, v.'.ilh oil of vitriol twelve fluid drachms. Stir 
 well with a glass rod for two or three minutes, uiitil all efl'ervescence has ceased, and an 
 even pasty mixture, free from lumps, is obtained. 
 
WASHING AND DRYING THE PYROXYLINE. 
 
 139 
 
 " During the whole process, abundance of dense fumes of nitric acid will be given | 
 off, which must be allowed to escape up the flue or into the open air. 
 
 " The above formula will invariably succeed with a good sample of oil of vitriol and 
 pure nitre. When tried, however, with commercial nitre, it failed in the writer's hands, 
 the cotton being gelatinized and dissolved. Therefore, iu a second experiment, the 
 addition of water was omitted, and the result proved satisfactory." 
 
 Mr. Hadow recommends the following for employment with commercial nitre : — 
 
 Nitre, powdered and dried . . 510 grains. 
 Oil of vitriol .... 165 drachms. 
 Water ...... Ih drachm. 
 
 " Observe that the quantity of oil of vitriol in this formula is increased, to allow of 
 the water being retained. The resulting mixture is very iluid and transparent, and the 
 manipulation easy. The writer has seen this formula tried twice, with samples of 
 common nitre purchased at an oil-shop. In the first the product was highly satisfac- 
 tory, but in the second not quite so good, being only partially soluble and giving an 
 opalescent film. In this case, probably, a better result would have been obtained by 
 halving the quantity of water directed. 
 
 " Washing and Drying the Pyroxyline.—T'iiQ mixture of sulphuric acid and nitre 
 requires to be used immediately after its preparation, as it solidifies into a stiif mass 
 on cooling ; but the mixed acids may be kept for any length of time in a stoppered 
 bottle. 
 
 " The fibres of the cotton should be well pulled out, and small tufts introduced 
 singly, stirring with a glass rod in order to keep up a constant interchange of particles 
 of acid. The paper is cut into small squares or strips, and treated in the same way. 
 
 "The quantity of either must not be too great, or some portions will be imperfectly 
 acted upon ; about twenty grains to each fluid ounce of the mixture will be sufiicient. 
 
 " Time of immersion vai-ies from ten minutes with cotton to twenty minutes, or 
 even haK an hour, with the paper. When an unusually large proportion of sulphuric 
 acid is used, as in the formula given for the commercial nitre, the cotton should be 
 removed at the expiration of six or seven minutes, as there is a tendency to partial 
 solution of the pyroxyline in the acid mixture under those circumstances. 
 
 " After the action is complete, the nitro-sulphuric acid is left weaker than before, 
 from addition of various atoms of water necessarily formed during the change. Hence, 
 if the same portion be used more than once, an addition of sulphuric acid will be 
 required. 
 
 " In removing the pyroxyline from the nitro-sulphuric acid, press out as much of 
 the liquid as possible, and wash it rapidly in a large quantity of cold water, using a 
 glass rod in order to preserve the fingers from injury. If it were simply thrown into 
 a small quantity of water and allowed to remain, the rise in temperature and M-eakening 
 of the acid mixture might do mischief. 
 
 " The washing should be continued for at least a quarter of an hour, or longer in 
 the case of paper, as it is most essential to get rid of every trace of the acid. When 
 the nitre plan has been adopted, a portion of the bisulphate of potash formed adheres 
 very tightly to the fibres, and if not carefully washed out, an opalescent appearance is 
 seen in the collodion, resuliing from the insolubility of this salt in the ethereal 
 mixture. 
 
 " If no ncld ta.^tc can be percaivcf", and a piece of blue litmus-paper remains in 
 
140 
 
 RECAPITULATION. 
 
 contact with tbo fibres for five rainules without changing in colour, the product is 
 thoroughly washed. Nevertheless, if time can he spared, it is a safe plan to place the 
 pyroxyline in warm water, and allow it to soak for several hours. 
 
 " Lastly, wring it out in a cloth, pull out the fibres, and dry by a gentle heat, 
 always bearing in mind that the compound is more or less explosive, and therefore 
 must not be brought too near to the fire. After drying, it may be kept for any length 
 of time in a stoppered bottle. It has been stated, on good authority, that pyroxyline is 
 in some cases liable to a spontaneous decomposition, attended with evolution of red 
 fumes of peroxide of nitrogen. This, however, must be rare, as the writer has not 
 often met with it in the course of his experience. 
 
 " Recapitulatiok.— Z^e Acid Mixture too strong.— The appearance of the cotton is 
 not much altered on its first immersion in the mixture. It washes well, without any 
 disintegration. On drying, it is found to be strong in texture, and produces a peculiar 
 crackling sensation between the fingers, like starch. It explodes on the application of 
 flame, without leaving any ash ; it is insoluble in the mixture of ether and alcohol, 
 hut dissolves if treated with acetic ether. 
 
 " The Acid Mixture of the proper strength— '^io agglutination of the fibres of the ' 
 cotton on immersion, and the product washes well ; soluble in the ethereal mixture, j 
 and yields a transparent film on evaporation. I 
 
 " The Acid Mixture too weak. — The fibres of the cotton agglutinate, and the pyroxy- | 
 line is washed with difficulty. On drying, the texture is found to be short and rotten. 
 It does not explode on being heated, but either burns quietly with a flame, leaving 
 behind a black ash (in which case, probably, it consists simply of unaltered cotton), or 
 is only slightly combustible, and certainly not explosive. Treated with the ethereal 
 mixture, it dissolves only partially, leaving behind lumps of unchanged cotton. The 
 solution does not form an even transparent layer on evaporation, but becomes opaque 
 and cloudy as it dries. This opacity, however, may be seen to a small extent with 
 any sample of pyroxyline, if the solvents contain too much water. 
 
 " By studying these characters, and at the same time bearing in mind that a 
 drachm and a half of water in the quantities of acid given for the formulae will suffice 
 to cause the difi'erence, it is hoped that the operator will overcome all difficulties. j 
 
 ^'■Purification of Collodion Solvents. — The purity of the ether employed is a matter | 
 of more importance in the manufacture of a good collodion than that of any other ! 
 ingredient. This point must be attended to in order to secure a good result. 
 
 " There are three kinds of ether sold by manufacturing chemists : — First, ordinary ! 
 rectified sulphuric ether, as it comes from the distilleries, containing a certain per 
 centage of alcohol, and also of water ; if it is good, the specific gravity is about -750. 
 Second, the washed ether, which is the same agitated with an equal bulk of water, in 
 order to remove alcohol. By this proceeding the specific gravity of the fluid is reduced 
 considerably. Third, ether both washed and re-rectified, so as to contain neither 
 alcohol nor water; in this case the specific gravity should not be higher than •720. 
 
 " The first of these commercial varieties is the one usually employed by photo- ; 
 graphers, since it is sold at a lower price than the others ; sometimes it is exceedingly i 
 pure and good, and is then to be preferred to the washed ether ; but often this is not 
 the case. 
 
 " Some of the qualities which render ether unfit for photographic purposes, are as | 
 follows :— A peculiar and disagreeable smell, either of some essential oil or of acetic ■ 
 ether; an acid reaction to test-paper; a property of turning alcoholic solution of I 
 
ON PURIFYING ETHER. 
 
 141 
 
 iodide of potassium brown with unusual rapidity ; a high specific gravity, from super- 
 abundance of alcohol and water. 
 
 " The ether which has been both washed and redistilled is always the most uniform 
 in composition, and especially so if the second distillation was conducted from quick- 
 lime, carbonate of potash, or caustic potash. These alkaline substances certainly retain 
 the impurities, which appear to be of an acid nature, and leave the ether in the best 
 possible state for use. 
 
 " The redistillation of ether is a simple process, and therefore it will be decribed. 
 In dealing with ether, however, in any form, the greatest caution must be exercised, 
 on account of its inflammable nature. Even in pouring ether from one bottle into 
 another, if a light of any kind be near, the vapour is apt to take fire ; and severe 
 injuries have been occasioned from this cause. 
 
 " Furification of Ether. — Take ordinary rectified sulphuric ether, and agitate it well 
 with an equal bulk of water, in order to wash out the alcohol ; stand it for a few 
 minutes until the contents of the bottle separate into two distinct strata, the lower 
 of which — i.e., the watery stratum — is to be drawn off and rejected. Then introduce 
 caustic potash finely powdered, in the proportion of about one ounce to a pint of the 
 washed ether ; shake the bottle again many times, in order that the water — a small 
 portion of which is still present in solution in the ether — may be thoroughly absorbed. 
 Afterwards set aside for twenty-four hours (not longer), at the end of which time it 
 will probably be observed that the liquid has changed to a straw-yellow colour, and 
 that a flocculent deposit has formed in small quantity. Lastly, transfer to a retort 
 of moderate capacity, supported in a saucepan of warm water, and properly connected 
 with a condenser. On applying a gentle heat, the ether distils over quietly, and 
 condenses with very little loss ; care must of course be taken that none of the alkaline 
 liquid contained in the body of the retort finds its way, by projection or otherwise, 
 into the neck, so as to run down and contaminate the distilled fluid. 
 
 " A more economical plan of purifying ether is, without previous washing with 
 water, to agitate with carbonate of potash or with quicklime, and redistill at a low 
 temperature. 
 
 " In order to preserve ether from decomposition, it must be kept in stoppered 
 bottles, quite full, and put away in a dark place ; also the stoppers should be tied over 
 with a bladder, or a considerable amount of evaporation will take place, unless the neck 
 of the bottle has been ground with unusual care. After the lapse of some months, 
 probably a certain amount of decomposition— evidenced by the liberation of iodine 
 from iodine of potassium — will be found to have taken place, in spite of all pre- 
 cautions. This, however, is small in amount and not of a character to injure the fluid, 
 except when very transparent films are employed, in which the amount of iodide of 
 silver is reduced to a minimum. 
 
 " Furification of Spirits of Wine. — The object of this operation is to remove a 
 portion of water from the spirit, and so to increase its strength. Alcohol thus purified 
 may be added to collodion almost^ to any extent, without producing glutinosity and 
 rottenness of film. 
 
 " The salt termed carbonate of potash is a 'deliquescent' salt — that is, it has a 
 great attraction for water ; consequently, when spirits of wine are agitated with 
 carbonate of potash, a portion of water is removed, the salt dissolving in it and forming 
 a dense liquid which refuses to mix with the alcohol, and sinks to the bottom. At the 
 expiration of two or three days, if the bottle has been shaken frequently, the action 
 
142 
 
 IODIZING COMPOUNDS. 
 
 is complete, and the lower stratum of fluid may be drawn off and rejected. Pure I 
 carbonate of potash is an expensive salt, and therefore a commoner variety may be 
 taken. Even pearlash — a highly impure form of carbonate — will succeed, if no better j 
 is at hand. | 
 " The quantity of carbonate of potash used may be about an ounce and a half to ; 
 half a pint of spirit ; an excess, however, does no harm. I 
 " After the distillation is complete, a fluid is obtained containing about 90 per j 
 cent, of absolute alcohol, the remaining 10 per cent, being water. The specific j 
 gravity at 00° Fahrenheit should be about ■823 ; commercial spirit of wine being 
 •836 to -840. 
 
 ^^ Preparation of the Iodizing Compounds. — These are the iodides of potassium, 
 ammonium, and iron, also the double iodide of potassium and silver. | 
 " The Iodide of Potassium. — Iodide of potassium, as sold in the shops, is often con- \ 
 taminated with various impurities. The first and most remarkable is carbonate of ■ 
 potash. When a sample of iodide of potassium contains much carbonate of potash, it < 
 forms small and imperfect crystals, which are strongly alkaline to test-paper, and ■ 
 become moist on exposure to the air, from the deliquescent nature of the alkaline ' 
 carbonate. Sulphate of potash is also a common impurity ; it n ay be detected by 1 
 chloride of barium. Commercial iodide of potassium, however, is rarely so pure that \ 
 no change whatever is produced by chloride of barium ; therefore a mere opalescence j 
 or slight milkiness on adding the test solution may be disregarded , but if a decided \ 
 white precipitate is formed, it will be better to reject the sample, or to purify it by 
 solution in strong alcohol. 
 
 " A third impurity of iodide of potassium is chloride of potassium; it is detected 
 as follows : — Precipitate the salt by an equal weight of nitrate of silver, and treat the 
 yellow mass with solution of ammonia ; if any chloride of silver is present, it dissolves 
 in the ammonia, and after filtration is re-precipitated in white curds by the addition of 
 an excess of pure nitric acid. If the nitric acid employed is not pure, but contains 
 traces of free chlorine, the iodide of silver must be well washed with distilled water 
 before treating it with ammonia, or the excess of free nitrate of silver dissolving in the 
 ammonia would, on neutralizing, produce chloride of silver, and so cause an error. 
 
 " Iodide of potassium may be rendered very pure by re-crystallizing from spirit, 
 or by dissolving in strong alcohol of specific gravity -823, in which both sulphate and 
 carbonate of potash are insoluble. The proportion of iodide of potassium contained in 
 saturated alcoholic solutions varies with the strength of the spirit. 
 
 " The Iodide af Aii.moniimi. — This salt may be prepared by adding carbonate of 
 ammonia to iodide of iron, but more easily by the following process : — A strong solu- 
 tion of liydrosulphate of ammonia is first made, by passing sulphuretted hydrogen gns 
 into liqiior ammonia. To this liquid iodine is added until the whole of the sulphui t ; 
 of ammonium has been converted into iodide. When this point is reached, the solution 
 at once colours brown from solution of free iodine. On the first addition of the iodine, 
 an escape of sulphuretted hydrogen gas and a dense deposit of sulphur take place. 
 After the decomposition of the hydrosulphate of ammonia is complete, a portion of I 
 hydriodie acid — formed by the mutual reaction of sulphuretted hydrogen and iodine — 
 attacks any carbonate of ammonia which may be present, and causes an effervescence. 
 The effervescence being over, the liquid is still acid to test-paper, from excess of 
 hydriodie acid ; it is to be cautiously neutralized with ammonia, and evaporated by the 
 heat of a water-bath to the crystallizing point. 
 
COLLODIO-ALBUMEN PROCESS. 
 
 143 
 
 " The crystals should be thoroughly dried over a dish of sulphuric acid, and then 
 sealed in small tubes containing each about half a drathm of the salt. 
 
 " The writer invariably employs the iodide of ammonium for the purpose of iodizing 
 collodion, and finds that at the expiration of two years from the time of preparation 
 the salt is still perfectly colourless. 
 
 " Iodide of ammonium is very soluble in alcohol ; but it is not advisable to keep it 
 in solution, from the rapidity with which it decomposes and becomes brown. 
 
 " The most common impurity of commercial iodide of ammonium is sulphate of 
 ammonia ; it is detected by its sparing solubility in alcohol. 
 
 " The Iodide o/Jrow.— Iodide of iron, in a state fit for photographic use, is very 
 easily obtained by dissolving about a drachm of iodine in an ounce of ' proof spirit' — 
 that is, a mixture of equal bulks of spirits of wine and water, and adding an excess 
 of iron filings. After a few hours, a green solution is obtained without tlie aid of 
 heat. The presence of metallic iron in excess prevents the liberation of iodine and 
 deposit of peroxide of iron, which would otherwise speedily occur. 
 
 '■^ Double Iodide of Potassium and Silver— In preparing this compound, first form 
 iodide of silver by dissolving equal weights of iodide of potassium and of nitrate of 
 silver in separate portions of rain or distilled water, and washing the resulting yellow 
 I precipitate upon a filter. The w^ashing is to be conducted, first, with water to wash away 
 i the nitrate of soda, and afterwards wiih a small portion of alcohol to displace the water. 
 I " Then digest the yellow mass with excess of iodide of potassium in spirits of 
 j wine, until a saturated solution of the double salt is obtained. 
 
 I " An analysis of a saturated solution of double iodide of potassium and silver in 
 alcohol of specific gravity -836, gave, as the quantity of both salts present in one fluid 
 ounce, iodide of potassium, sixty-four grains ; iodide of silver, twenty-four grains. 
 Therefore in the preparation one and a-half drachm of powdered iodide of potassium, 
 and about twenty grains of iodide of silver, obtained by precipitating fifteen grains of 
 nitrate of silver by an equal weight of iodide of potassium, may be digested for some 
 hours in an ounce of the spirits of wine. 
 
 " Iodide of Cadmium.— This salt is formed by heating filings of metallic cadmium 
 with iodine, or by mixing the two together with addition of water. 
 
 " Iodide of cadmium is very soluble both in alcohol and water ; the solution 
 yielding on evaporation large six-sided tables of a pearly lustre, which are permanent 
 in the air. The crystalline form of this salt is a sufficient criterion of its purity." 
 
 The CoUodio-Albumen. Process. — Another process for facilitating the use 
 of the collodion, has been brought forward by Mr. Ackland, a gentleman connected with 
 Messrs. Horne and Thornthwaite's establishment, which, with their permission, we are 
 enabled to give : — 
 
 " This is a process, invented by Dr. Taupenot, for obtaining negatives on glass, 
 which bids fair to outrival all others, being easy of manipulation, and giving results 
 of the most exquisite minutice and beauty. Glass plates, when prepared and excited 
 by this process, may be kept at least a fortnight before being developed, and these 
 plates when exposed in the frame may be developed immediately, or kept for days 
 before commencing this operation. Indeed it is quite possible to prepare and excite a 
 number of plates before leaving home to go on a tour of twelve or fourteen days ; to 
 expose the plates at any time or place during the journey, and bring them home to be 
 developed. 
 
 " The manipulation may be said to consist of nine distinct operations : — 
 
COATING THE COLLODION WITH ALBUMEN. 
 
 " 1. Gleaning the Flate. — For which the directions already given will suffice. 
 
 " 2. Coating with Iodized Collodion. — The collodion necessary to be used in this 
 process must be one yielding good negative pictures— that supplied by Home and 
 Thoi-nthwaite, under the name of negative collodion, answers admirably. This is 
 supplied either ready iodized, or the collodion and iodizing in separate bottles. As 
 this collodion becomes less sensitive, after being iodized a fortnight, it is advisable to 
 iodize no more than will be used in that time — therefore, obtain the collodion and the 
 iodizing solution separate, as the mode of iodizing this collodion is very simple. Half 
 an ounce of the iodizing solution is mixed with one ounce and a half of collodinn, and 
 the mixture allowed to settle twelve hours before being used ; and it is even advisable 
 to pour off the cler.r solution into a perfectlj' clean bottle, in order to get rid of any 
 insoluble matter which may fall to the bottom. The plate having been thoroughly 
 cleaned, and received its final polish by the use of a prepared chamois leather, is coated 
 with the negative collodion, which has been iodized at least twelve hours, and allowed 
 to settle. 
 
 " 3. Exciting tht Collodion Film. — After the ether has evaporated, and the surface of 
 the collodion appears set, the plate must be laid, collodion side upwards, on a glass 
 dipper, and plunged, with one downward movement, into a bath filled to within an inch 
 of the top with collodion bath solution, prepared by dissolving one ounce of nitrate 
 of silver in two ounces of distilled water, and two grains of iodide of potassium in 
 one drachm of distilled water ; mix the two solutions and shake well together, until 
 the precipitate which is first thrown down is redissolved ; when this takes place, add 
 fourteen ounces of distilled water, and two drachms of alcohol. On the addition of 
 the water, a turbidness ensues, which must be removed by the solution being very 
 carefully filtered through filtering-paper ; and the filtered liquid should be clear and 
 transparent, free from any deposit or floating particles, and must possess a slightly 
 acid reaction of test-paper. 
 
 " In order to ascertain if the solution thus prepared possesses the necessary amount 
 of free acid without superabundance, proceed to test and to correct it, if necessary. 
 The solution must be carefully filtered through filtering- paper before being used. 
 After the plate has been allowed to remain in the bath one minute, it is lifted 
 out three or four times, in order to facilitate the removal of the oily appearance 
 which the plate now presents. When the surface appears wetted uniformly, on being 
 drawn out of the solution the plate is removed from the dipper, and the excess of 
 solution drained off, and is then placed, collodion side iipwards, on a fixing stand, and 
 distilled or filtered rain water poured over the surface, so as to remove as much as 
 possible of the bath solution from the surface. The plate is now removed from the 
 fixing stand, the back M-ell washed with water, and then placed nearly upright on 
 blotting-paper, with the face against a wall for one minute, to drain. This and subse- 
 quent operations (except exposure in the camera) must be performed in a dark room. 
 " 4. Coating with Albumen. — Having allowed the plate to drain one minute, place it 
 • again on a levelling stand, with the film upwards, and pour over it as much of the 
 I iodized albumen as the plate will hold, from a glass measure containing not more than 
 enough of the albumen to coat two plates, pour off the excess into the measure and 
 again cover the plate with albumen three separate times ; ultimately, drain off as 
 much as possible of the excess of albumen, and place the plate nearly upright against 
 tlie wall, with the coated side inwards, to dry, which takes place in an ordinary 
 temperature in about one hour. 
 
EXCITING THE ALBUMEN'. 
 
 145 
 
 " In coating with albumen, the presence of air-bubbles or dust muat be guarded 
 against. The former can easily be done by taking care, in pouring the albumen into 
 the measure and on the plate, not to pour so as to generate air-bubbles in the liquid. 
 But should any be detected, hold the plate horizonl.ally and give it another coating of 
 albumen ; then incline the plate so that the bulk of the liquid shall pass over and 
 carry off the bubbles with the running stream. Dust on the plate must be pre- 
 vented by operating in a room as free from this photographic enemy as possible. 
 
 " In order to render the coating of albumen as uniform as possible, the plate must 
 stand to dry on two or three layers of filtering-paper, and the upper surface must 
 touch the wall at one point only, and not be allowed to rest against it along its entire 
 upper edge. 
 
 " When the albumen coating is thoroughly dry (and not till then), the plate is ready 
 to be excited; but if more have been prepared than are likely to be used for taking 
 pictures on during the next ten days or fortnight, they may be stowed away in a plate 
 box, ready to receive the sensitive coating at any time. The author's experience has 
 led him to believe that these albuminized plates will keep good any length of time, 
 as plates which had been coated a month, when excited, exposed, and developed, 
 appeared to possess all the properties of recently prepared plates. 
 
 " 5. Exciting the Albumen Coating.— 'Prior to the plates being excited they must be 
 thoroughly dry and free from any particles of loose dust on the surface, back, or edge. 
 Sufficient of the albumen bath solution must be filtered through filtering paper to fill 
 a dipping bath of the required size, so that the plate can be immersed in it. 
 
 " The careful filtering of the fluid is very necessary in order to free it from any 
 floating particles, and to separate the animal charcoal. 
 
 " A bath having been prepared by dissolving an ounce and a half of nitrate of silver 
 in sixteen ounces of distilled water ; adding one ounce of glacial acetic acid, with 
 two drachms animal charcoal, which has been kept for use in a closely stoppered 
 bottle — the plate is now taken and laid, albumen side upwards, on the dipper, and then 
 lowered into a bath with one steady downward movement, where it is allowed to remain 
 one minute ; it is then taken out, the excess of liquid drained off, and placed on the 
 fixing stand, with the albumen surface uppermost, and a stream of water poured over 
 it for at least one minute, so as to remove every particle of the hath solution. This 
 complete washing is very necessary, in order to prevent stains in the after develop- 
 ment, which invariably takes place around the edges, if not thoroughly washed. The 
 plate, having been thoroughly washed, is leaned against a wall to dry, or, if required 
 for immediate exposure, may be dried on a plate of heated metal or foot-warmer ; 
 but in no case must the exposure in the camera take place until the surface is 
 thoroughly dry. 
 
 "6. Exposure in the Camera.*^ — As before stated, this operation may take place 
 immediately the plate is thoroughly dry after being excited, or a fortnight may inter- 
 vene between the exciting and exposure, provided the plate is kept very carefully 
 excluded from light and any chemical or sulphurous vapours, in a plate box adapted 
 for that purpose, with the sensitive surface towards the back of the box. "When the 
 exposure is about to take place, or at any time previously, the camera backs may 
 each have a plate placed in them ready for exposure ; to do this, the camera back 
 must be taken into the operating room and the door closed, so as to exclude aU white 
 • &ire muBt be taken that the direct rays from the; sun shall not fall on the lens or enter the 
 camrru civ.ring the exposure of a plate. 
 
• , 
 
 ; 146 FOCUSSING IN THE ALBUMEN PROCESS. 
 
 I light. The hinged flap of the camera back is opened, and the prepared plate laid, 
 1 with its sensitive surface dowmmrds, or next the sliding flap, so that its corners may 
 i rest on the silver wire corners of the plate frame previously placed within the camera 
 I back ready to receive it. The hinged flap is now closed and kept from opening by 
 i turning the flap button over it ; the sliding flap is examined to see that it is pushed 
 ' closely down so as to guard any access of light, and it is then ready to be placed in 
 
 the camera, and may be taken into the open air with impunity. Should the exposure 
 ! not take place immediately, or should the camera back have to be carried any 
 
 distance, it is advisable either to wrap it up in a black cloth, or secure the flaps 
 
 from the chance of coming open, during transit, by stout string being tied around 
 
 the back. 
 
 j " The focusing is conducted in the samie' way as usual, and the cap replaced on 
 the lens ; the focusing glass is now removed, and the camera back fitted into the j 
 same aperture, with the sliding flap next the lens. The sliding flap is pulled up to its 
 fullest extent, placing; the hand on the camera back, to prevent it rising out of the i 
 camera -CT^th this acti<jn. The cap of the lens is then removed, so that the light may 
 be admitted into the camera, and to fall on the sensitive surface of the plate. After j 
 the necessary time of exposure has taken place, the cap is replaced on the lens, the j 
 sliding flap is pnshed down, and the camera back withdrawn from the camera ; the , 
 plate can then be taken into the operating room to be developed, or this operation may 
 be deferred for days, ■ or even a week or more if convenient. The time of exposure 
 in the camera varies according to the intensity of the light and the aperture afid focal { 
 length of the lens ; therefore, to give the exact time of exposure would be impossible, ' 
 still it may assist the amateur if I give the time required in summer with full sun- i 
 shine, and merely state that this time may be increased to double in winter or dull ; 
 weather. 
 
 " In the ordinary sunshine of a summer's day the time of exposure will be— 
 
 " 30 seconds with a lens of 4-ineh focus and ^-inch stop. 
 
 " 21 seconds with a lens of 4-inch focus and f-inch stop. 
 
 " 5 seconds with a lens or 4-inch focus and IJ-ineh aperture, with no stop. 
 
 " Ig minute with' a lens of 6-inch focus and ^-inch stop. 
 
 " 4^ seconds with a lens of 6-inch focus and 2^-inch aperture, with no stop. 
 
 " 2 minutes with a lens of 8-inch focus and ^-inch stop. 
 
 " 1^ minute with a lens of 8-inch focus and f-inch stop. 
 
 " 3^ minutes with a lens of 10-inch focus and |-inch stop. 
 
 " 2 minutes with a lens of 10-inch focus and |-inch stop. 
 
 " 5 seconds with a lens of 10-inch focus, 3^-inch aperture, with no stop. 
 
 " 6^ minutes with a lens of 14-inch focus and J-inch stop. 
 
 " 4 minutes with a lens of 14-inch focus and f-inch stop. 
 
 " 2\ minutes with a lens of 14-inch focus and |-inch stop. 
 
 " 8J minutes with a lens of 16-inch focus and g-inch stop. 
 
 " 5\ minutes with a lens of 16-inch focus and |-inch stop. 
 
 " 2f minutes with a lens of 16-inch focus and f-inch stop. 
 
 " 7. Developing the Image. — The camera back is taken into the operating room, 
 from which all white light is carefully excluded, the plate removed from the camera 
 back, and laid, albumen side upwards, on the fixing stand ; as much distilled water is 
 now poured on it as the surface will hold, taking care that every part of the sensitive 
 surface is covered with the liquid ; allow the water to remain on the surface for one 
 
FIXING AND VARNISHING. 
 
 147 
 
 ! minute, then pour oS and drain slightly ; replace the plate on the stand, and pour 
 I over the surface, so as thoroughly to cover every part, the pyrogallic solution, which must 
 ! be carefully filtered just before being used ; allow this to remain on the plate for one 
 I minute, then drain off into a perfectly clean measure, and add to it an equal bulk of 
 ' silver developing solution ; mix these thoroughly together with a glass rod, and then 
 pour the mixed liquids over the plate ; allow them to rest until the picture begins to 
 appear, which generally takes about from three to five minutes ; then pour off and on 
 repeatedly^ until the developing fluid becomes opaque, which then contains floating 
 particles, and these, if allowed to do so, would settle on the plate, to the injury of the 
 picture ; but this may be prevented by brushing the surface with a camel's-hair brush 
 frequently during the development. "When this opacity of the developing fluid takes 
 place, drain all the fluid off the plate, and thoroughly wash with water ; then mix 
 another quantity of pyrogallic and silver developing solution in the same proportions 
 as before, and pour this on and off the plate as before, until the picture appears suffi- 
 ciently intense, and the middle shades well brought out ; when this takes place, drain 
 off, and wash with water, so as to clean the surface thoroughly, and the plate is then 
 ready for the next step, ' fixing the image.' 
 
 " Should the picture begin to develop in less than three minutes after the applica- 
 tion of the mixed developing fluids, thoroughly drain the plate, and wash well with 
 water ; then continue the development with a solution of three parts pyrogallic solu- 
 tion, prepared by dissolving fifteen grains pyrogallic acid in seven ounces of distilled 
 water, then adding two drachms glacial acetic acid mixed with two drachms of alcohol 
 and one part silver developing solution, consisting of one drachm nitrate of silver, 
 dissolved in seven ounces distilled water, adding two drachms acetic acid. Should the 
 picture, however, not begin to appear in five minutes, the addition of half a drachm of 
 the albumen bath solution to each ounce of mixed developing solution will be neces- 
 sary, in order to obtain the middle shades and the required intensity. 
 
 " It may be stated, as a guide, that the best negatives which the author has pro- 
 duced occupied from ten to twelve minutes in developing. 
 
 " 8. Fixing the Lmge.— The plate, having been thoroughly freed from the deve- 
 loping fluid by careful washing, is now placed on the fixing stand, and the surface 
 covered by the fixing solution, prepared by dissolving two ounces hydrosulphate of 
 soda in one pint water. This solution being poured over it, in a few seconds the 
 yellow opalescent colour of the film will begin to disappear, and its complete removal 
 may be hastened by blowing gently on the plate, so as to disturb the fluid. 
 
 " When every particle of yellowness has disappeared, the fixing solution is 
 I drained off, and the surface thoroughly washed; and it is then leaned against the wall to 
 drain and dry. 
 
 ** 9. Varnishing the Plate.— The plate, being thoroughly dry, is ready to receive a 
 coating, of transparent varnish, in order to protect the albumen surface from injury 
 during the printing process. To do this effectually, the plate must be held before 
 a fire or over a lamp, until it is slightly warm all over ; then pour over its surface 
 'Horne and Thornthwaite's negative varnish,' in' the same manner as collodion ia 
 applied ; allow the superfluous varnish to drain back into the bottle ; hold the plate 
 again before the fire until the whole of the spirit is evaporated ; and, when cold, the 
 plate is ready to be printed from, so as to produce any number of positive pictures on 
 paper. 
 
 " It will be obsei'ved that, in describing this process, the operator has been sup- 
 
148 
 
 MK. ACKLAND's camera. 
 
 I posed to be so situated, that, in case a second view of the same spot were required, he 
 j could return to his operating room, remove the plate which had been exposed from 
 the camera back to the plate box, and place another in the camera back, ready for 
 taking another view. But, unfortunately, this is not at all times practicable. "We 
 therefore require some means of removing the plates, after being exposed, from the 
 camera back into the plate box, and substituting others in their stead, whilst we are in 
 ; the open air. 
 
 ! " In order to eflfect this, the ' Field Plate Box ' has been devised by Mr. Ackland, 
 I by the aid of which the plates may be removed from the box, exposed in the camera, 
 j and again returned into the box, without any possibility of access of light falling 
 on it. 
 
 " This box is but a trifle larger than the ordinary one, and is furnished with two 
 j sliding bottoms, working in grooves, one over the other ; the lower bottom has a 
 grooved channel, into which the side of the camera back slides ; the camera back has 
 an aperture through the side, closed by a narrow slide, and the lower bottom of the 
 field-box has a corresponding one. We now suppose the field-box to have been 
 previously filled with excited glass plates, having their sensitive sides toivards the back 
 of the box, and the box lid closed. The bottom slide is now pushed on until the 
 aperture is in a line -with any particular groove of the field-box (which position is 
 indicated by a numbered scale and index point). The camera back is then slid on 
 to its place on the field-box, so that the hinged flap is towards the front of the box, 
 and its narrow slide drawn out. The upper slide is then withdrawn, and the box 
 inclined, so that the plate in that groove opposite the aperture in the lower slide ma^' 
 pass through into the camera back. When this has taken place, push in the narrow 
 slide of the camera back, invert the box, and push in the inner slide ; then withdraw 
 the camera back from its channel, and expose the plate in the camera. When this is 
 done, slide the back again into its channel, draw out the inner box slide, then the 
 narrow camera back slide, invert the box, and the plate will then leave the camera 
 back and pass into the field-box, occupying the same groove as before. 
 
 " In order to get out another plate, slide the lower bottom, so that the index points 
 to the number on the scale, as that of the groove in which the required plate is situate. 
 Then proceed as before directed." 
 
 Dr. Mansell, of Guernsey, recommends, for changing plates in the open air, a 
 bag made of three thicknesses of yellow glazed calico, one yard wide and one and a half 
 yard long. Into this bag, the plate box containing the sensitive plates, the camera 
 back, and the head, shoulders, and arms of the operator are placed. The bag is then 
 tightly tied around the waist by tapes inserted into its neck. In this the operator 
 can change his plates from the box to the back, or vice versd, with impunity, as the 
 yellow material prevents the admission of any rays that would damage the plates. 
 
 The foregoing process will be found very useful to travelling photographers, espe- 
 cially to those who do not use large glasses, as the weight of the latter would be 
 rather an incumbrance ; but by means of a light spring hand-cart, that difficulty could 
 be got over. I must say that Mr. Ackland's plan for changing the glass plates, is one 
 of the most ingenious I have ever seen. 
 
 Gutta-pexcha as a Sensitized IMEedium. — I shall now beg leave to introduce 
 to the reader a new substance in photography, but as I have not had an opportunity 
 of testing its capabilities I must make use of the inventor's words ; even this will 
 I not be so easy, as it is diflScult to say who is the inventor, because, although Mr. 
 
GUTTA-PERCHA AS A SENSITIZED MEDIUM. 
 
 149 
 
 Archer has taken out a patent for the use of the substance, the Rev. Mr. J. B. Eeade 
 has communicated the self-same process to the Photographic Journal ; and it is rather 
 singular, in reference to patents, that the same gentleman made almost the same dis- 
 coveries in the calotype that Mr. Fox Talbot made, and actually made them known 
 before Mr. Talbot patented his discoveries. 
 
 The substance above alluded to is gutta-percha, and the following is the substance 
 of a paper read to the Photograpic Society in November 1855, by Mr. Eeade . — 
 
 "It is known to many," he says, " that a substitute fur glass is a great desideratum 
 to the practical photographer. The cost of glass is a serious diminution to the profits 
 \ of the professional artist, and loss from breakage, especially when many valuable nega- 
 ; tives are destroyed, compels a man to ask whether he cannot be supplied with an article 
 as clear as glass and as tough as leather. I venture to offer gutta-percha as a substi- 
 tute. It possesses the good qualities of glass in its perfect transparency and evenness 
 of surface, while its cost is trifling, and its cohesion perfect. 
 
 " My experiments have recently been carried on in conjunction with my friend Mr. 
 Millar, the resident medical superintendent of the Bucks Lunatic Asylum at Stone, and 
 we can now present gutta-percha in such a form as warrants us to ask for the opinion 
 of photographers upon it. 
 
 "In the first place we dissolve gutta-percha in benzole, one of the peculiar hydro- 
 carbons of coal-tar naphtha, or in chloroform. Thirty grains of gutta-percha added 
 to an ounce of either solvent, is poured upon a plate of glass, and the excess drained off 
 into the bottle, as in the^ use of collodion, produces the film upon which we have 
 i worked. 
 
 '* The benzole dissolved the common sheet gutta-percha of the shops (not a per- 
 fectly pure article) with great readiness, upon the application of heat ; immersing the 
 bottle in hot water being sufiicient. The colouring matter, producing the well-known 
 pinkish tint, fell to the bottom of the bottle, and above it was a solution as clear and 
 colourless as water. 
 
 " This was poured upon a glass plate as I have described, and immediately dried, or 
 nearly so, by holding it over a spirit-lamp. This precaution for securing an evenness 
 of surface is more necessary with the benzole then with the chloroform solvent, though 
 its advantage even in the latter case is apparent. The film adheres perfectly to the 
 glass, and has no tendency to separate from it on subsequent immersion in the nitrate 
 bath if the edges of the glass are roughened ; but if, as in some cases, they are smooth 
 and polished, it is advisable, when the film is dry, to secure it firmly and certainly by 
 passing the four edges of the coated glass through the flame of a spirit-lamp. By this 
 i method about one-eighth of an inch of the film is dissolved, or nearly so, all round the 
 surface of the glass, and no separation can be produced by any amount of immersion 
 in water. This film, now firmly fixed upon the glass, is treated in the subsequent 
 process as if it were glass. 
 
 "The iodized collodion is poured upon it and sensitized in the usual way, and the 
 picture is taken, developed, fixed, and varnished. The point of a knife is now carried round 
 the edge of the glass for the purpose of scraping off the small portion of the film which 
 had been semi- dissolved by heat to secure its perfect adherence. It is then placed in water 
 for a minute or two, one edge of the film is slightly raised so that the fingers can take hold 
 of it, and the whole separates with great facility and floats. By raising the glass up to 
 it, it can be taken out on its surface, placed with the film downwards on blotting-paper, 
 and the glass drawn from it. When dry, place the film between two pieces of paper. 
 
150 MR. archer's patented PROCESS. i 
 
 hold It up to the light and cut the paper— at the same time the film, which is perfectly I 
 visible through the paper — to any required size. I 
 
 " We have now a negative ready for the printing frame, taken on a material as 
 durable and manageable as glass, but occupying only a small portion of its space, and j 
 perfectly free from the peculiar risks which so often put valuable negatives altogether j 
 Tiors de combat. \ 
 " Benzole having the property of becoming solid at a temperature of 32^, the gutta- i 
 percha dissolved in it, unless it be a very thin film, has a tendency to become opaque, which | 
 might possibly interfere with the subsequent printing from the negative. This defect i 
 is wholly avoided by dissolving the benzole film, when dry, in chloroform, and then j 
 using the chloroform -film, which never becomes opaque, for the purpose proposed. I i 
 understand from Mr. De la Rue, that one of the products of Birmese naphtha, which he j 
 is about to introduce. Mall form the best solvent, and produce a thick transparent film 
 at all temperatures. The pure chloroform solution obtained, as above described, may be | 
 used, according to the happy suggestion of Mr. Pollock, as a protecting varnish for ; 
 positives, and if applied to both sides of the picture, injury from atmospheric influence | 
 seems scarcely possible. ; 
 
 " I may add that it is not difficult to iodize the solution of gutta-percha itself, | 
 taking pictures upon it quite independently of the use of collodion, and also that a | 
 mixture of collodion and gutta-percha is not bad ; but I think, upon the whole, the | 
 proper place for the gutta-percha to occupy is this which I propose, as a substitute for | 
 the glass. We then deal with collodion, which is by far the best preparation put into j 
 our hands for sensitizing, and upon which we take pictures. We deal with it in the \ 
 usual way, and put upon the film as if we were putting upon glass. You are then j 
 quite independent of glass, and may keep a stock in a small portfolio. | 
 
 " Perhaps I may be allowed, in addition, to state, that when the film is of a certain i 
 degree of thinness it has a tendency, when perfectly drj^, to curl ; but if you breathe j 
 upon it that tendency ceases, and it remains perfectly flat, and can be put into the i 
 printing frame with the greatest facility. In taking pictures you would adopt practi- j 
 cally a useful thickness." j 
 
 Mr. Archer says in allusion to his patented process : — " Ever since my introduction , 
 of the collodion process, it has been my desire to do away with the inconvenience of j 
 glass for negatives. ! 
 
 " According to my early publications, when on a journey, I used to remove the ; 
 collodion film from the glass, roll the pictures up between blotting-paper, and expand 
 them again on glass when at home ; but this occupied much time, and required very | 
 delicate manipulation. 
 
 " These difiiculties induced me to try experiments with a variety of substances 
 likely to preserve the delicacy of the picture on the collodion film, and to be sufiiciently 
 strong to bear handling when in use. 
 
 " After much labour I have succeeded in my object, and in August last I patented 
 my process, which I hope will be found to remove the only great impediment to the 
 universal use of collodion in photography. The material used is a solution of gutta- 
 percha in benzole. Other solvents can be used, but this is preferable to any. 
 
 " There are two methods of ajjplying this solution of gutta-percha (both included 
 in the patent) to accomplish the object in view, viz., the removal of the collodion film 
 from the glaps. I will describe them in detail. 
 
 " The first method is this :— Pour on the clean glass plate a quantity of the solution 
 
MR. archer's field CAMERA. 
 
 161 
 
 of gutta-percha, in a similar manner as for coating the glass with a film of collodion. 
 When this film is dried, the iodized collodion is poured on and immersed in the silver 
 bath. The plate is exposed, developed, and fixed. The glass plate, with gutta-percha 
 and collodion film attached to it, is immersed in a vessel of cold water, which presently 
 causes the two combined films to separate readily from the glass. 
 
 " The second method ;— Prepare the glass with iodized collodion, and proceed with 
 the process in the ordinary manner. 
 
 " "When the collodion picture is dried, pour on to it the solution of gutta-percha ; 
 when the plate is covered, hold it in a horizontal position for about a minute to 
 thicken. Draw off very gently through a funnel into the bottle the excess of solution, 
 and gradually raise the plate vertically over the funnel. 
 
 " The benzole will evaporate rapidly, leaving on the coUodion picture, and in 
 intimate contact with it, a coating of gutta-percha. 
 
 " The plate must now be gently held with its back towards a clear fire, to accelerate 
 I the hardening of the gutta-percha and to prevent its chilling on the surface. 
 
 " When cold, the plate is immersed in a vessel of cold water, which causes the 
 combined films to separate, in one sheet, from the glass." 
 
 " In this operation the benzole solution does not come in contact with the glass, 
 nor is the surface of the glass in any way injured by its application to the collodion. 
 
 " Thus the glass can be used again after the ordinary cleaning. One great objection 
 to the first method is, if the collodion picture be not successful, the gutta-percha 
 coating is lost; whereas, in the second, the solution is only applied to a perfect 
 picture, or such as the operator wishes to preserve. 
 
 " Another objection to the first method is, the great difficulty in getting the gutta- 
 percha film sufficiently even when used thick enough to support the film." 
 
 The only objection I see to the process just noticed is, that the gutta-percha film 
 will not stand the heat of a summer's sun, as I have seen solid gutta-percha, and 
 pretty thick too, melt in the heat of summer ; and I must say that I should not like to 
 see a negative that I set some value on melt, and perhaps draw out to about twice 
 its length. 
 
 It may not be out of place to describe here the camera constructed by Mr. Archer, for 
 out-of-door practice with coUodion. It is a wooden box eighteen inches long and twelve 
 inches wide and deep. In front is a sliding door with a circular opening to admit the 
 lens ; this sliding door enables the operator to raise or depress the point of view. The 
 camera has in the sides a hole into which sleeves of India-rubber cloth are fixed, furnished 
 with India-rubber bands, into which the hands of the operator are admitted, the bands 
 closing at the wrists and excluding the light while he arranges the collodion frame. 
 
 The back of the camera has a hinged door, fitted at its upper part with an opening 
 of just sufficient size for the eyes, and shaped so as to fit close to the face. A black 
 cloth is tied round this end of the camera, to prevent any ray of light penetrating the 
 opening in the top of the instrument. Near the front is inserted a frame of yellow 
 glass hinged like a door to admit a regulated yellow light. The interior of the box 
 is furnished with a sliding frame to support the ground glass, the bath and the pre- 
 pared plate, with a focusing slide, by which images of from three to fifteen inches 
 can be obtained, the bottom being furnished with a gutta-percha tray, one inch deep, 
 to hold the washings when in operation. 
 
 This instrument allows of the preparation of the most sensitive surfaces on the 
 spot, of their immediate use, ready development, and fixing of the image at once. 
 
152 
 
 MR. Clarke's siphon. 
 
 Mr. Clazke's Siphon. — The following ingenious contrivance of Mr. E. T. Clarke 
 may not he out of place here, he calls it "J bottle siphon for the silver bath," and 
 he uses it for the purpose of emptying his nitrate bath when he has finished 
 working : — 
 
 "The upright baths are very awkward things, as made at present, to pour 
 from. I employ a siphon bottle such as is here 
 represented (Fig. 74). 
 
 ■ " Place the short leg of the siphon A in the 
 bath, which must be raised on a block or other- 
 wise. Exhaust the air from the bottle by the 
 mouth-tube B, and you will draw ofi" your bath 
 into its bottle at once, without danger to your- 
 self or loss of liquid. The lips must be with- 
 drawn of course as soon as the siphon begins to 
 act. You have only now to take out the appa- 
 ratus, which is merely a cork with two pieces 
 of quill tubing, and replace the glass stopper." 
 
 Before dismissing the subject of collodion, I 
 may add, that, with careful manipulation, a total 
 absence of all flurry, performing each part gently, 
 extreme cleanliness, care that there is no floating 
 dust in the camera or dark-room, great care in 
 focusing, proper attention to light and shade, 
 bath, collodion, and developing solution well 
 filtered, measures and vessels well cleaned, absence 
 of any fluid left in the frame by a former plate, 
 gently raising up and shutting down the slide, a 
 proper length of exposure, and, above all, observation, success is certain. Before con- 
 cluding, I shall describe a very useful piece of apparatus nearly identical with Mr. 
 Clarke's siphon, which is used by Mr. Hardwich for clearing collodion. The collodion 
 being iodized some hours previously, and allowed to settle down and become clear in a 
 bottle with a large mouth, in which a cork with perforated holes for two glass tubes is 
 placed, as represented in Mr. Clarkd's drawing. By gently blowing at the point of the 
 shorter tube, the other glass tube is filled, and the fluid drawn off more closely and 
 cleanly than could be done by simply pouring from one bottle to another. I shall con- 
 clude my remarks on this part of the science. The next will be — 
 
 On the Fixing and Colouring of Positives. — As this is a subject of vital 
 importance to photography (their being'but little use in producing first-rate negatives 
 if you cannot from them obtain beautiful and lasting copies), it has met with an 
 unusual amount of study and experiments at the hands of some of the most eminent 
 photographers. Among these no man has given the subject more consideration than 
 Mr. Hardwich. I again make use of his pages, giving, in some instances, his own 
 words, in others their substance. 
 
 This subject Mr. Hardwich divides into five sections :— 1st, Positive printing by the 
 ordinary direct process; 2nd, Mr. Sutton's mode of toning positives ; 3rd, Positive print- 
 ing by the negative process ; 4th, Remarks on the fading of positives ; 5th, On printing 
 enlaro-ed or reduced positives, transparencies, &c., which I shall briedy notice in their 
 turn. 
 
 Fig. 74. 
 
POSITIVE PRINTING. 
 
 153 
 
 Positive Printing upon Chloride of Silver. — This includes preparation of 
 sensitive paper — of fixing and toning baths— manipulatory details of the process. 
 
 In the preparation of sensitive paper there are three kinds of surfaces, viz., albumi- 
 nized paper, plain salted paper, and paper prepared with serum of milk, which may be 
 used. A photographic paper should be very smooth and uniform in texture ; of 
 equal thickness in each part, and free from spots. These spots consist usually of small 
 metallic particles, which, when the paper is rendered sensitive, act as centres of 
 chemical action and spoil the effect. 
 
 The foreign papers, French and German, are porous and sized with starch, the 
 English being dense and sized with gelatinous animal matter, which gives a brown 
 tint to the reduced chloride of silver in the same manner as albumen. The density of 
 English papers makes the fixing and toning of the positives a slower process than when 
 foreign papers are used. There is also a tendency to curl up when laid upon the liquid 
 for albuminizing, and Mr. Hardwich recommends the thin negative papers of Canson and 
 de la Rive, or the papier Saxe, where they can be obtained. A difference in smooth- 
 ness between the two sides of the paper is perceptible, which may be detected by holding 
 the sheet in such a manner that the light strikes it at an angle ; the wrong side is that 
 on which broad wavy bands are seen, caused by the strips of felt on which the paper 
 was dried. 
 
 Preparation of Allnminized Paper. — This includes the salting, albuminizing, and 
 sensitizing with nitrate of silver. 
 
 Take chloride of ammonium, or pure chloride of sodium fifteen grains, water 
 (distilled if at hand, if not rain water) one ounce. 
 
 Mix any number of ounces according to this formula, and add a third part by 
 measure of the whites of new-laid eggs. Then with a bundle of quills tied together 
 beat the whole into a perfect froth. As the froth forms, it is to be skimmed off and placed 
 in a flat dish to subside, when it should form a perfectly homogeneous mass. The suc- 
 cess of the operation depends entirely upon the manner in which this part of the pro- 
 cess is conducted. If the albumen is not thoroughly beaten, flakes of animal membrane 
 will be left in the liquid, and will cause streaks upon the paper. When the froth has 
 partially subsided, transfer it to a tall and narrow jar, and allow it to stand for several 
 hours, that the membranous shreds may settle to the bottom. Then pour off the upper 
 portion, which should now be clear and fit for use. Albuminous liquids are too glutinous 
 to run well through a paper filter, and therefore it is better to clear them by subsidence. 
 
 To apply the albumen, pour a portion of the solution into a flat dish to the depth 
 of half an inch. Then, having previously cut the paper to the proper size, take a sheet 
 by the two corners, bend it into a curved form, convexity downwards, and lay it upon 
 the albumen, the centre part first touching the liquid and the corners being lowered 
 gradually. In this way all bubbles of air will be pushed forward and excluded. One 
 side only of the paper is wetted ; the other remains dry. Allow the sheet to rest upon 
 the solution for one minute, and then raise it off, and pin up by two corners. If any 
 circular spots, free from albumen, are seen, caused by bubbles of air, replace the sheet 
 for the same length of time as at first. 
 
 Most practical operators lay stress upon removing the sheet from the albumen 
 speedily ; and it certainly is the case that if you take a thick porous paper, like 
 Canson's positive, and leave it upon an albumen bath for a long time the surface is 
 roughened and irregular from imperfect absorption of the last layer of liquid. 
 
 Albuminized paper will keep any length of time in a dry place. Some have 
 
154 
 
 PREPARATION OF PLAIN SALTED PAPERS. 
 
 recommended to press it with a heated iron, in order to coagulate the layer of alhumen 
 upon the surface ; but this precaution is imnecessary, since' the coagulation is perfectly 
 effected by the nitrate of silver used in the sensitizing. Also, it is doubtful whether a 
 layer of dry albumen would admit of coagulation by the simple application of a 
 heated iron. 
 
 To Render the Paper Sensitive. — This operation must be conducted by candle or yellow | 
 light, and with a solution of nitrate of silver, sixty grains ; distilled water, one ounce. 1 
 If the sample of nitrate of silver contains much free nitric acid it may be of service 
 to neutralize it with carbonate of soda, filtering out the excess of white carbonate 
 of silver, and then adding one or two drops of glacial acetic acid. 
 
 Prepare a sufficient quantity of this solution, and lay the sheet upon it in the 
 same manner as before. Three minutes contact will be sufficient with the thin 
 negative paper, but if the Canson positive paper is used, four or five minutes must be 
 allawed for the decomposition. The papers are raised from the solution by a pair of 
 bone forceps or common tweezers tipped with sealing-wax, and hung up to dry. A 
 small strip of blotting-paper suspended from the lower edge of the paper will serve to 
 drain off the last drop of liquid. 
 
 After the solution of nitrate of silver has been in use some time, it becomes dis- 
 coloured from a partial formation of sidphuret of silver. The brown colour may be 
 removed by the employment of animal charcoal, or the white china clay, or " pipe- i 
 clay." I 
 
 After a large quantity of paper has been sensitized, add fresh nitrate of silver in 
 the pif)pnrtion of about ten grains to the ounce, in order to keep the bath at its 
 original strength. 
 
 Sensitive albuminized paper, prepared as above, will usually keep one or two 
 days, if protected from the light ; but afterwards it turns yellow from partial decom- 
 position. 
 
 Freparation of Plain Salted Paper. — Take of purified gelatine one grain; chloride 
 of sodium or ammonium, ten grains ; water, one ounce. Either of the foreign papers 
 may be used for this formula — Canson's positive and papier Saxe being especially re- 
 commended. Towgood's positive gives a fine brown nearly approaching to black ; it 
 must be salted in the same manner as the others. 
 
 Weigh out the proper quantity of gelatine for the required number of ounces, and 
 dissolve it in a small bulk of warm water. Then add the remainder of the water and 
 the salt. The mode of salting the paper is the same as for albumen, but if the weather 
 is cold, it will be well to hang the sheets near to the firo, to prevent any gelatinizing, 
 which might otherwise occur. 
 
 Mode af Sensitizing the Salted Paper. — Gelatine paper may be sensitized by floating 
 upon the ordinarj- sixty -grain solution of nitrate of silver ; or with the ammonio- 
 nitrate of silver prepared as follows : — Take of nitrate of silver, eighty grains ; dis- 
 tilled water, one ounce. Dissolve the nitrate of silver in one-half of the total quantity 
 of water. Then take a pure solution of ammonia and drop it in carefully, stirring 
 meanwhile with a glass rod. A brown precipitate of oxide of silver first forms, but on 
 the addition of more ammonia it is redissolved. When the liquid appears to be clearing 
 up, add the ammonia very cautiously, so as not to incur an excess. In order stUl 
 further to secure ^the absence of free ammonia, it is usual to direct, that when the 
 liquid becomes perfectly clear, a drop or two of solution of nitrate of silver should be 
 added, until a slight turbidity is again produced. Lastly, dilute with water to the 
 
SERUM OF MILK SOLUTION. 
 
 155 
 
 proper bulk. If the crystals of nitrate of silver employed contain a large excess of 
 free .nitric acid, no precipitate will be formed on the first addition of ammonia. The 
 free nitric acid, producing nitrate of ammonia with the alkali, keeps the oxide of silver 
 in solution. This cause of error, however, is not likely to happen frequently, since the 
 amount of nitrate of ammonia required to prevent all precipitation would be con- 
 siderable. From the same reason, viz., the presence of nitrate of ammonia, it is useless 
 1 to attempt to convert a nitrate bath, already used for sensitizing, into ammonio-nitrate. 
 
 Aramonio-nitrate of silver should be kept in a dark place, being more prone to 
 reduction than the nitrate of silver. 
 
 Sensitizing Salted Paper ivith Ammonio-Nitrate.—Mo&i operators prefer brushing on 
 the solution of ammonio-nitrate, the properties of the solution being altered by the 
 reaction with the salt, free ammonia being thus formed in the ammonio-nitrate bath, 
 which has the effect of changing the half-shadows of the print to a reddish-pink 
 tone. Even in brushing the same ammonia is not to be used too often. Brushes are 
 sold manufactured purposely for applying silver solutions ; but the hair is soon de- 
 stroyed, unless care is taken to keep the brush clean. In sensitizing paper by brushing, 
 lay the salted sheet upon blotting-paper, and wet it thoroughly by drawing the brush 
 first lengthways and then across. Allow it to remain flat for a few minutes, in order 
 that a sufiicient quantity of the silver solution may be absorbed, and then pin up by 
 the corner in the usual w^ay. 
 
 Ammonio-nitrate papers cannot be kept long ; they become discoloured after the 
 lapse of a few hours. 
 
 Gelatine paper sensitized with plain nitrate of silver will remain good for several 
 days ; it turns a little yellow, but this is removed by the toning bath. 
 
 Preparation with Serum pf Milk. — The serum of milk is prepared as follows : — 
 Take pure milk from the cow, and curdle it by a piece of rennet, or if that cannot be 
 obtained, by dropping into it a little acetic acid or common vinegar. The quantity of 
 vinegar required will, perhaps, be about two or three drachms to the quart of milk, 
 which must be boiling hot at the time the acid is added. The caseine coagulates im- 
 mediately, and is to be strained out through a cloth and rejected. "When the serum 
 has become nearly cold the white of an egg is added, previously beaten up in a cup to 
 insure thorough mixture ; then place the serum in a pipkin over a slow fire, and heat 
 it to ebullition. The albumen coagulates, forming a fine network, and carrying up 
 with it globules of oil, thus clearing the liquid. When it is cold, strain again through 
 muslin or calico, and afterwards through blotting-paper. The latter filtration is often 
 ! tedious, and occupies several hours ; if started over night in a large filter, it will 
 probably be completed by the morning. The serum, when properly prepared, should 
 have a straw-yellow tint, and be perfectly clear and transparent. 
 
 The serum being thus prepared, take of chloride of ammonium ten grains, of the 
 serum of milk one ounce ; to this add one grain of gelatine thoroughly dissolved in a 
 drachm and a half of boiling water ; pour the hot solution into the serum, and stir 
 with a glass rod or silver spoon ; then add one ounce of alcohol to each ten ounces 
 of the solution. 
 
 Sensitizing the Serttm Surface. — Lastly, measure the bulk of the liquid, and dissolve 
 the salt in the proportion of ten grains to each ounce. 
 
 The papers which appear to give the finest tints with serum of milk are Le Eive's 
 negative, papier Saxe, and Canson's positive paper. Towgood's positive paper gives a 
 shade of brown, very warm and pleasing. 
 
156 REMARKS ON THE VARIOUS FOUMVLM. 
 
 The sheets are laid upon the salting bath in the usual way, and allowed to remain 
 from one to two minutes, according to the thickness and degree of porosity of the 
 paper, the thin papers requiring less time. 
 
 They are sensitized on the nitrate bath of sixty grains to the ounce of water. 
 From two to three minutes' contact will be sufficient. The serum discolours the 
 nitrate of silver to a certain extent, but not in so marked a manner as albumen. 
 
 Papers prepared by this method turn yellow more qiiickly than usual ; they 
 should therefore be sensitized, if possible, only a few hours before use. Mr. Shadbolt 
 recommends the addition of acetic acid to the nitrate of silver bath, to obviate the 
 tendency of albuminized and other papers to discolour by keeping. 
 
 Hints in selecting from the above Formulce. — Albuminized paper is, perhaps, the 
 most generally useful ; it gives a warm, bright appearance to the shadows, and the 
 tint is of a pleasing brown. 
 
 Serum of Milk Paper gives fine purple tones, and is free from the glossiness of 
 surface which many object to in albumen. Plain salted paper is recommended for 
 obtaining pure black tones suitable for portraits and engravings. The negatives, 
 however, should be intense, or the result will be inferior ; good brown tones may be 
 obtained with a comparatively pale negative, but not the finest blacks. Canson's 
 positive paper and papier Saxe are, perhaps, the best for black tints. 
 
 Ammonia-Nitrate Paper gives blacks possessing great depth and brilliancy, but it 
 is troublesome to manipulate with, and requires more care than the others. 
 
 Preparation of ihe Fixing and Toning iSo^m^mw^.— Bath for fixing and toning posi- 
 tive proofs may be prepared in either of the following ways : — By perchloride of iron, 
 ■with iodine, and with chloride of gold. 
 
 1. With Perchloride of Iron. — Dissolve four ounces of Jiyposulphite of soda in seven 
 ounces of water, and thirty grains of nitrate of silver in one ounce of water. Pour 
 into the solution of hyposulphite by degrees, stirring all the time, six drachms of 
 perchloride of iron. The addition of this salt produces a fine purple colour, which 
 soon disappears. When the liquid has become again colourless, which it does in a few 
 minutes, add the dissolved nitrate of silver, stirring bn'skly. Perfect solution will take 
 place without any formation of black sulphuret. 
 
 A toning bath prepared with chloride of iron will be ready for use twelve hours 
 after mixing, but it will be still more active at the expiration of a week. The solution 
 soon becomes acid to test-paper, and milky from a deposit of sulphur ; this may be 
 removed by filtration, but it is scarcely necessary to filter out any solid deposit, as the 
 close texture of paper upon which positives are printed prevents it from doing injury. 
 
 The bath may be employed either in an acid or neutral state. If the weather is 
 cold, probably the colouring action will be slow, and in that case it is best to allow the 
 acid to remain. But if the thermometer indicates 60° or higher, the colouration of the 
 print is etfected with more rapidity, and there is danger of the half-tones being eaten 
 away by the acid bath ; and, therefore, it will be advisable to neutralize it by shaking 
 up the solution for five minutes with as much powdered chalk or whiting as will stand 
 upon a shilling, and afterwards allowing it to settle down, or filter it through blotting- 
 paper. Chalk is the only practicable remedy, because the solution contains proto- 
 chloride of iron, which on the addition of an alkali forms first oxide, and then, by 
 reacting on the sulphuretted principles present, sulphuret of iron. 
 
 For this reason ammonio-nitrate prints cannot be toned in a solution prepared 
 with chloride of iron. 
 
PHOTOGRAPHIC PRINTING. 
 
 157 
 
 After the bath has been neutralized, there is a constant tendency to a return of 
 the acidity, 
 
 2. Fixing and Toning Bath with JoaVMe.— Dissolve the thirty grains nitrate of 
 silver in an ounce of the water, as before. Then, from four ounces of hyposulphite of 
 soda, weigh out carefully hyposulphite of soda sixty grains. Dissolve in an ounce of 
 the -water, and throw into it thirty grains commercial iodine. Agitate the vessel until 
 the whole has disappeared, which will happen in the course of a few minutes. If after 
 the solution of the iodine a brown tint is acquired, there is an excess of iodine ; in that 
 case, cautiously add hyposulphite of soda, a single grain at a time, until the liquid 
 becomes colourless ; then pour in nitrate of lead forty grains, previously dissolved in an 
 ounce of the water. The addition of nitrate of lead causes the separation of the greater 
 portion of the iodine in the form of yellow iodide of lead, which is useless, and may be 
 rejected. Throw the whole upon a paper filter, and allow it to drain for a short time ; 
 then pour upon it by degrees two ounces of water, in order to wash out as much of the 
 soluble tetrathionate of soda as possible. When all has run through, add three ounces 
 of water ; dissolve the hyposulphite of soda, and mix in the nitrate of silver solution 
 with continual stirring as before. 
 
 This bath is not very active when first prepared, probably on account of a little 
 iodide of lead remaining dissolved ; but at the expiration of a few days or a week it will 
 yield very fine tones, and is then superior to Formula No. 1, 
 
 It will continue in good working order for about a month or six weeks, but after 
 that time loses its activity to some extent, even if it be not used. The immersion of 
 prints by removing sulphur has the same effect, the tones being produced more slowly; 
 and a fresh addition of iodine being required, 
 
 3, Fixing and Toning Bath with Chloride of (?oZ<f.— Dissolve four ounces hyposul- 
 phite of soda in four ounces of water, solution of chloride of gold, a quantity equivalent 
 to four grains, in three oimces of water; thirty grains nitrate of silver in one ounce. 
 Pour the diluted chloride by degrees into the hyposulphite, stirring with a glass rod ; 
 and afterwards the nitrate of silver in the same way. This order of mixing the solu- 
 tions is to be strictly observed ; if it were reversed, the hyposulphite of soda being 
 added to the chloride of gold, the result would be the reduction of metallic gold. The 
 dificrence depends upon the fact, that the hyposulphite of gold M-hich is formed is an 
 unstable substance, and cannot exist in contact with unaltered chloride of gold. It is 
 necessary that it should be dissolved by hyposulphite of soda immediately on its forma- 
 tion, and so rendered more permanent by conversion into a double salt of soda and gold, 
 
 A toning bath prepared with chloride of gold is most active at the expiration of a 
 few days after mixing. On keeping for some weeks it loses much of its efiicacy by a 
 process of spontaneous decomposition, and requires the addition of fresh chloride of gold. 
 
 Photographic Printing. — These include the exposure to light, or printing, 
 properly so called ; the fixing and toning ; and the washing, drying, and mounting of 
 the proof. 
 
 The Exposure to Light.— Fox this purpose frames are sold, so constructed that they 
 admit of being opened at the back, in order to examine the progress of the darkening 
 by light, without producing any disturbance of position. 
 
 Simple squares of glass, however, succeed equally well, when a little experience 
 has been acquired. They may be held together by the wooden clips sold at the 
 American warehouses at one shilling per dozen. The lower plate should be covered 
 with black cloth or velvet. 
 
158 
 
 TIME OF EXPOSURE TO THE LIGHT. 
 
 Supposing the frame to be employed, the shutter at the back is removed, and the 
 negative laid fiat upon the glass, collodion side uppermost. A sheet of sensitive paper 
 is then placed upon the negative, sensitive side downwards, and the whole tightly com- 
 pressed b); replacing and bolting down the shutter. 
 
 This operation may be conducted in the dark room ; but unless the light is very 
 strong, such a precaution will scarcely be required. The time of exposure to light 
 varies much with the density of the negative and the power of the actinic rays, as 
 influenced by the season of the year and other obvious considerations. As a general j 
 rule, the best negatives print slowly ; whereas negatives which have been under-exposed ! 
 and under-developed are more rapid. ' 
 
 In the early spring or summer, when the light is powerful, probably about ten to 
 fifteen minutes will be required ; but as much as three-quarters of an hour may be 
 allowed in the winter months, even in the direct rays of the sun. 
 
 It is always easy to judge of the length of time' which will be sufficient, by 
 exposing a small slip of the sensitive paper, unshielded, to the sun's rays, and observing 
 how long it takes to reach the coppery stage of reduction. Whatever the time may 
 be, about the same will be occupied in the printing, if the negative is a good one. ' 
 
 When the darkenhrg of the paper appears to have proceeded to a considerable ^ 
 I extent, the frame is to be taken in and the picture examined.* If squares of plate glass 
 are used, in place of a printing-frame, to keep the negative and sensitive paper in ; 
 contact, some difficulty will be experienced at first in returning it precisely to its ' 
 former position after the examination is complete ; but this will easily be overcome by . 
 practice. The finger and thumb should be fixed on the lower corners or edge, and the ; 
 plate raised gently. ! 
 
 If the exposure to light has been sufficiently long, the general aspect of the print j 
 appears slightly darker than it is intended to remain. The toning bath dissolves away 
 the lighter shades and reduces the intensity, for which allowance is made in the 
 exposure to light. A little experience soon teaches what is the proper depth to print ; ! 
 but the following general rules may be useful as a guide. The acid toning bath, pre- 
 pared with iodine or perchloride of iron, dissolves away the lighter shades more than 
 the neutral bath, with chloride of gold. When the proofs are to be immersed for a : 
 long time in order to secure black tones, it is necessary to over-print more strongly ' 
 than when the purple tints are desired. 
 
 If, on removal from the printing-frame, a peculiar spotted appearance is seen, i 
 produced by imequal darkening of the chloride of silver, either the nitrate bath is too j 
 weak, the sheet removed from its surface too speedily, or the paper is of inferior j 
 quality. 
 
 I On the other hand, if the general aspect of the print is a rich chocolate-brown., in 
 the case of albumen, a dark slate-blue with gelatine or ammonio-nitrate paper, or a 
 reddish-purple with paper prepared on serum of milk, probably the subsequent 
 colouration will proceed well. I 
 
 If, in the exposure to light, the shadows of the proof become very decidedly 
 coppery before the lights ai-e sufficiently printed, the negative is in fault. Ammonio- 
 i nitrate paper is particularly liable to this fault of excess of reduction, and especially 
 I so if the light is powerful ; hence it is best, as a rule, not to print by the direct rays | 
 I of the sun. This point is important also, because the excessive heat of the sun's rays i 
 ! often cracks the glasses by unequal expansion, and glues the negative firmly down to | 
 the sensitive paper. I 
 
FIXING AND TONING. 
 
 159 
 
 The Fixing and Toning of the Froof. — Tlie print may be immersed in tlie toning 
 bath immediately on its removal from the frame; but noninjury results from putting 
 it aside for a time, if it be kept in a dark place. 
 
 After its immersion, move it about for a short time to displace air-bubbles, which, 
 if allowed to remain, produce spots. In a few minutes the rich chocolate-brown or 
 violet-blue tints disappear, and the red tones take their place. 
 
 Albumen proofs become brick-red ; gelatine and ammonio-nitrate a brownish- 
 black. If the colours are unusually pale and red, very probably the silver bath is too 
 weak, or the quantity of chloride of ammoniiun used was insufficient ; a pink tint in 
 the ease of ammonio-nitrate pictures, if very nmikcd, generally gives a bad result. 
 The action of the bath must be continued until the desired elfect is obtained. This 
 may happen in from twenty minutes to half an hour, if the solution is in good working 
 order and the thermometer at 60° ; but much depends upon the temperature. 
 
 The purple tones are an earlier stage of colom ation than the black tones, and 
 therefore the latter require more time. It must be borne in mind, however, that pro- 
 longed immersion in a tetrathionate bath, prepared with iodine or perchloride of iron, 
 is decidedly favourable to yellowness of the whites ; and with an albumen print it will 
 be diflS.cult to obtain pure whites if the colouring is carried beyond the purple stage. 
 "With the gold bath the action may be pushed further with impunity. 
 
 Ammonia-nitrate and gelatine papers are less prone to turn yellow than paper 
 prepared with albumen. The yellow colour is not often seen decidedly whilst the 
 print is in the bath, but it comes out in the after-processes of washing and drying. 
 
 The error most frequently committed in colouring positive proofs is, continuing 
 the action of the hypo bath for too long a time with the idea of obtaining darker tones. 
 The injurious effects so caused are most evident when the print has been washed and 
 dried ; it is then seen that much of the brilliancy and richness of the tint is lost, 
 whereas if the proof had been removed at an earlier period it would have been im- 
 proved. These remarks apply in all cases, but especially so to the tetrathionate bath 
 without gold. 
 
 Some advise that on removal from the bath the print should be soaked in new 
 hypo for ten minutes, in order to complete the fixation ; but this precaution is not 
 required with solutions of such a strength as those given in the formulas. An analysis 
 of an old hypo bath, which had been very extensively used, indicated only ten grains 
 of hyposulphite of silver to the ounce, so that it was at that time far from being 
 saturated. 
 
 With a bath prepared by the perchloride of iron process, if any red deposit upon 
 the surface of the print (peroxide of iron) occurs during the washing, a portion of the 
 protochloride of iron may be removed from the fibres of the paper by soaking in 
 new hypo. 
 
 The addition of fresh ci-ystals of hyposulphite of soda occasionally, in order to 
 keep up the strength of the bath, is a safe plan to adopt, the exact quantity added not 
 being material. 
 
 On the Washing Positive Proofs. — It is essential to wash out every trace of hj'po- 
 sulphite of soda from the print if it is to be preserved from fading, and to do this 
 properly requires considerable care. 
 
 Always wash with running water when it can be obtained, and choose a large 
 shallow vessel, exposing a considerable surface in preference to one of lesser diameter. 
 Nothing is better than the ordinary leaden sink carefully washed out, and a tube 
 
160 
 
 WASHING AND DRYING. 
 
 inserted into the exit pipe, that the "water may not flow away until it reaches to 
 the depth of a few inches. A constant dribbling of water must be maintained for 
 about five or six hours, at the end of which time the tap may he stopped, and the 
 print left in the water until the following morning. This is the plan pursued by 
 the author, and found by him to be sufficient for prints toned either with or without 
 gold. 
 
 Even in washing by running water, however, some precautions must be observed; 
 the prints should not lie together too closely, or the water does not find its way 
 between them. You may easily prove this by wetting five or six prints fresh from the 
 frame, and, having placed them in a shallow pan of water, tm-ning on the tap until 
 the water runs off quite clear ; then separate the papers from each other, when a 
 milky liquid will pass out from between them, thus showing that a stationary layer of 
 fluid existed at that point. Therefore, in washing, the prints should be kept as much 
 as possible separate from each other, and should be constantly moved and turned over 
 to expose every part of the surface to the action of the running water. 
 
 When running water cannot be obtained, proceed as follows : — First wash the 
 print gently, to remove the greater part of the hyposulphite solution. Then transfer 
 to a large shallow pan, in which may be placed as many prints as it will hold without 
 laying thickly on each other. Leave them in for about a quarter of an hour, with occa- 
 sional movement, and then pour off quite dry. This point is important, as the chemist 
 well knows — viz., when washing a deposit to drain off the last portion of liquid 
 completely before adding fresh water. Eepeat this process of changing at least five or 
 six times, or even more, according to the bulk of water, number of prints, and degree 
 of attention paid to them. Lastly, place them together in a larger vessel of water, and 
 allow to soak for several hours, stirring occasionally. Then blot off with filtering 
 paper, and hang up to dry. 
 
 Drying. — The fluid which drains from the edge of a washed print may be tested 
 for hyposulphite of soda, by touching with a rod dipped in solution of protonitrate of 
 mercury ; a black colour, which is sulphuret of mercury, indicates the presence of 
 hyposulphite. The common plan of tasting the lower corner for the sweet hyposul- 
 phite of soda and silver is now thought by the writer to be insufficient. 
 
 When the print is nearly dry, it is recommended ^by some to place it between two 
 layers of blotting-paper, and press with a moderately hot iron. This appears to darken 
 the tint slightly if produced in a feeble colouring bath, but when the bath is active it 
 causes but little appreciable change. 
 
 Albumen proofs when dry are sufficiently bright without further treatment ; but 
 in the case of plain paper, salted simply, or with serum of milk, the effect is improved 
 by laying the print face downwards upon a square of plate glass and rubbing the back 
 with an agate burnisher, sold at the artist-colourman's. This hardens the grain of 
 the paper and brings out the details of the picture. 
 
 Mounting. — In mounting the proofs, be careful not to employ sour paste, which 
 may possibly injure the tint, and keep them in a place free from damp and mould. 
 Thick gimi- water answers very well as a cement, or gelatine dissolved in hot water. 
 Some use caoutchouc dissolved in mineral naphtha, which has the advantage of drying 
 speedily, and does not make the card board cockle up. 
 
 Mr. Sutton's Process for Toning Positives. — This process was communi- 
 cated to the Photographic Journal in the month of March, 1855. It is somewhat more 
 troublesome than the plans ordinarily followed, but possesses advantages which will 
 
MR. Sutton's toning bath. 
 
 presently be enumerated. The description may be divided into preparation of the toning 
 bath and manipulatory details : — 
 
 Preparation of the Toning Bath. — Dissolve chloride of gold one grain, and hypo- 
 sulphite of soda three grains, each in two ounces of distilled water ; then mix quickly 
 by pouring the former solution into the latter, and add five minims hydrochloric acid. 
 If the chloride of gold is neutral the liquid will have a red tinge, but if acid, then the 
 solution is colourless. 
 
 " In place of making an extemporaneous hyposulphite of gold by mixing the 
 chloride with hyposulphite of soda, Mr. Sutton employs the crystallized sel d'or, half a 
 grain to the ounce of water, acidified as before, but the objection to the use of this salt 
 is its expense, and also the difficulty of obtaining it in a pure form ; some samples con- 
 taining no more than five per cent, of gold. 
 
 " The quantity of solution given in the formula is sufficient to tone more than a 
 dozen prints of five inches by four ; and, therefore, as chloride of gold is sold at two- 
 pence per grain, this process cannot be objected to on the score of economy. 
 
 " The bath is most active when first prepared, but it will keep for some time, pro- 
 vided the prints be properly freed from soluble nitrate of silver. 
 
 " The paper may be prepared by either of the three foi-mulaj given by Mr. Hard- 
 wich, according to the tint desired. The printing is not carried quite to the usual 
 intensity, as the gold bath dissolves the half-tones scarcely or not at all. 
 
 " On coming from the frame the prints are washed thoroughly in common water 
 until it ceases to become milky ; which will not happen until the greater part^'of the 
 nitrate of silver is removed. The washing must be conducted in a dark place, but it 
 is not necessary to hurry it ; the proofs may be thrown into a pan of water covered 
 with a cloth, and allowed to remain until required for tinting. 
 
 " A trace of free nitrate of silver usually escapes the washing unless it has been 
 done very carefully and with hot water. This would cause a yellow deposit (probably 
 hyposulphite of silver or a salt of a similar kind, mixed with metallic gold) on the 
 print, and also in the toning bath. It must, therefore, be removed either by adding a 
 little salt to the water during the last washings, or better still by means of a dilute 
 solution of ammonia. 
 
 " To prepare this alkaline bath, take liquor ainmoniEe one drachm, common v/ater 
 one pint. The exact quantity is not material ; if the liquid smells of ammonia it will 
 be sufficient. 
 
 " Place the washed prints in this bath, two or three at a time and allow to remain 
 until the evanescent purple tint begins to give place to a red tone. The action must bfe 
 watched, because if the ammonia bath is strong the proof soon becomes pale and red, 
 and when that is the case you lose a little brilliancy in the after tinting. Albuminized 
 and English papers, from their dense structure, require a longer time in the ammonia 
 than porous papers simply sorted. 
 
 " With ammonio-nitrate prints this bath may be omitted ; the proofs being trans- 
 ferred to the toning solution immediately after washing. 
 
 " As 'chloride of silver is comparatively insensitive to light, when the excess of 
 nitrate is washed away, it is not necessary to darken the room ; but a bright light 
 proceeding from an open door or window should be avoided. 
 
 " The ammonia having done its work, soak the prints again for a few minutes 
 or longer in common water to wash out the alkali. Then place them in the toning 
 bath of gold and acid ; do not put in too many at once, and move them about occasion- 
 
162 
 
 POSITIVE PRINTING BY THE NEGATIVE PROCESS. 
 
 ally to prevent spots of an imperfect action at the point where the sheets touch each 
 other. j 
 " The foreign papers, plain salted, colour rapidly in two or three minutes. English ! 
 papers require from five to ten minutes ; albuminized, ton minutes to a quarter of an | 
 hour. I 
 "By removing the print before the deposit of gold has fully taken place, you obtain j 
 a dark red-purple tint, and by a longer action a violet purple approaching to black, i 
 When this tone is reached a continuance of the action produces but little change ; there ! 
 
 j is a slight diminution of brightness, but not that yellow tint so commonly seen with old j 
 
 j and acid hypo baths. 
 
 j " The toning being completed, the prints are again placed in water (the same used 
 ] for washing out the ammonia does very well) to remove the greater part of the acid. 
 I This washing must not be continued longer than five or ten minutes, or there will be a 
 
 danger of decomposition of a salt of silver, producing a yellowness of the whites ; this, 
 j however, ought never to happen with proper precautions. 
 
 "Lastly, the proofs are fixed in anew solution of hyposulphite of soda, one part to 
 
 four of water. This bath alters the tone slightly. In the case of ammonio-nitrate 
 1 prints the purple black passes by degrees to a black almost pure. 
 
 ; " In order that the fixing may be properly performed, the time of immersion should 
 ! not be less than ten minutes with a porous paper, plain salted, or fifteen to twenty 
 minutes in the case of an English or albuminized paper. 
 
 " It will sometimes happen in this process, from the toning bath having but little 
 solvent action on the light shades, that the prints, after being washed and dried, appear 
 too dark ; this may be remedied by laying them for a few minutes in a very dilute 
 solution of chloride of gold, and washing for an additional quarter of an hour. Five or ] 
 six drops of solution of chloride to a few ounces of water, not enough to change the | 
 colour of the liquid, will suffice. [ 
 
 " Advantages of Toning hy this Process. — 1. The toning solution can be prepared in i 
 a few minutes with its full amount of efficacy, and will yield a similar tint any i 
 number of times successively. On the other hand, fixing and toning baths of hypo I 
 and gold, by the continued immersion of prints, alter in composition, and in their i 
 action upon the print, almost daily. 
 
 " 2. The free nitrate of silver is removed from the print before it enters the fixing 
 bath ; hence the purity of the whites is very perfectly preserved. 
 
 " 3. Bronzing of the deep shadows of the print is removed very perfectly. 
 
 " 4. Overprinting is scarcely or not at all required. 
 
 " 5. A pure black and white tint can be obtained with certainty, if the negative is 
 sufficiently intense, by printing upon plain salted paper or ammonio-nitrate paper." 
 
 Positive Printing by the Negative Process. —The negative process for 
 printing positivess will be found useful in the dull winter months, and at other times 
 when the light is too weak to act directly upon chloride of silver : — 
 
 " A very good iodized paper for illustrating the development of a latent image may 
 be made as follows : — Take of 
 
 Iodide of potassium . . . .10 grains. 
 "Water 1 ounce. 
 
 Float the paper on this solution in the ordinary manner, and hang up to drv ; then by 
 yellow light render it sensitive upon a bath of the following strength : — 
 
SIR W. NEWTON 8 NEGATIYE PKOCESS. 
 
 163 
 
 Nitrate of silver . , . ,30 grains. j 
 Acetic acid (glacial) . . . .30 minims. i 
 Distilled water .... 1 ounce. ' 
 
 Three minutes' contact will be sufficient; after which dry thoroughly, carefully 
 excluding all rays of white light. 
 
 " Develop with a saturated solution of gallic acid, which may conveniently be 
 applied by the ingenious contrivance of Mr. Buckle, already described. Ordinary 
 camel' s-hair brushes are quickly destroyed by the mixture of gallic acid and nitrate of 
 silver, unless kept scrupulously clean. 
 
 "Gallic acid is soluble in about one hundred parts of cold water ; therefore, to 
 prepare a saturated solution, add five grains to each ounce, and apply a gentle heat. 
 The aqueous solution decomposes, and becomes mouldy by keeping ; this may be partly 
 obviated by adding acetic acid (a drachm of the glacial acid to twelve ounces of the 
 solution), or by a drop or two of oil of cloves. 
 
 " Sir W. Newton's Process for Frinting Fosilives. — Bromide of potassium or calcium 
 is used in place of iodide of potassium, as yielding a better tint and more purity of the 
 white parts of the picture. Take of 
 
 • Bromide of calcium . . . .10 grains. j 
 Gallic acid ..... 5 grains. I 
 AVater 10 ounces. ' 
 
 " Cut up a bit of camphor of the size of a nut into small pieces, and digest it with 
 the water for twelve hours, to obtain a saturated solution. Then add two or three 
 lumps of white sugar, the gallic acid, and the bromide, as advised in the formula. 
 
 "Apply the solution to the paper by brushing, and when dry, excite with the 
 following bath : — 
 
 Nitrate of silver .... 12 grains. ' 
 Acetic acid (glacial) . . : .20 minims. ' 
 Distilled water .... 1 ounce. 
 
 This solution must be applied by brushing, since, in adopting the ordinary plan of 
 floating, the bath would be discoloured by the gallic acid in the paper. 
 
 "The following directions are given for the exposure and development of the 
 picture : — Expose to the light (not sun) in the printing frame until a slight change 
 takes place in the colour of the margin— from half a minute upwards, according to the 
 light. A very little experience will, however, regulate this point. After which 
 develop by immersion in gallic acid (of course in a yellow light) ten grains to ten i 
 ounces of distilled water, in a flat dish, as many as ten or a dozen at a time. During | 
 the process of developing, a small quantity of aceto-nitrate of silver may be added, ; 
 occasionallj"^ gently agitating at the same time. 
 
 " Unless Canson's paper be albuminized, it will not answer the object ; if, however, 
 it be albuminized, it should be floated over the diff'erent solutions. I do not like the 
 French paper, but much prefer Whatman's." 
 
 Mr. Sutton's Negative Process. — The paper is prepared with serum of milk, with or 
 without bromide of potassium. The serum is used to impart a warmer tone to the 
 reduced silver than that obtained on plain paper. 
 
 " In the preparation of serum of milk, Mr. Sutton advises to separate the caseine 
 by rennet (previously washed to remove salt), in preference to using acetic acid. The j 
 
164 
 
 ON THE FADING OF POSITIVE PROOFS. 
 
 serum must be filtered very carefully. The papers are immersed several at a time, 
 and subsequently hung up to dry. The addition of bromide of potassium, five grains, 
 to each ounce of serum, greatly increases the sensitiveness of the paper. 
 
 " Aceto-nitrate of silver is used in sensitizing, prepared by the following 
 formula : — 
 
 Nitrate of silver . . . 20 to 30 grains. 
 Acetic acid (glacial) . . . .30 minims. 
 Distilled water .... 1 ounce. 
 
 Immerse the papers, taking care tliat both sides are evenly wetted, and allow to remain 
 three minutes ; then hang up to dry in a perfectly dark place. 
 
 " The development is conducted by immersion in solution of gallic acid, either 
 saturated, or if that should act too quickly, as it will sometimes do in hot weather, the 
 same diluted with an equal bulk of water. This part of the process occupies about 
 five minutes. 
 
 " Remar'k$ on Printing by the Negative Process. — Mr. Ilardwich advises the amateur 
 to master the manipulation of the ordinary positive process before trying that by 
 development. Perfect cleanliness is most essential, and the solutions should all be 
 filtered with care to free them from fine particles in suspension, which would 
 cause spots. 
 
 " "\Yhite light must be excluded with all the precautions exercised in the case of 
 collodion negatives. 
 
 "The exposure to light is conducted in the ordinary printing-frame ; it extends 
 from a few seconds upwards. On removing the negative a very faint image is seen, 
 which develops rapidly when the gallic acid is applied. 
 
 " The development being completed, the prints are well washed and fixed in hypo- 
 sulphite of soda, one part to four of water. The tint is improved by adding a little 
 nitrate of silver (a few drops of the exciting bath) to the gallic acid towards the end 
 of the process ; but a better plan is to tone the prints in the gold bath, described at 
 page 245, before fixing. 
 
 " In that case, after developing, they must be well washed, then placed in salt and 
 water, or in dilute ammonia, and after-wards toned and fixed in the manner already 
 fully described. 
 
 " The appearance of prints taken by the negative process is artistic and good ; but 
 it is difficult to get the same elaborate definition and clearness of shadow, as by the 
 ordinary positive process upon chloride of silver." 
 
 On' the Fading of Positive Proofs. — The fading of paper positives has 
 long been a source of annoyance to photographers ; a gradual loss of brilliancy and a 
 yellow tint is seen to commence at the margins and half-shadows of the print, and to 
 extend by degrees over the whole surface. 
 
 " This matter has of late become of such importance that the council of the Photo- 
 graphic Society decided a few months since upon appointing a committee, of which 
 the writer has the honour of being a member, to examine and report upon it. 
 
 " The experiments required, in order to be decisive, must necessarily extend over a 
 long period of time, and it will be many months before the results can be fully knoAvn. 
 The proofs which fade most frequently are those which have been fixed and also 
 toned. It is this part of the process, so necessary to the artistic effect, which 
 increases the danger. 
 
RESULTS OF IMPERFECT WASHING. 
 
 165 
 
 " If a positivo picture, as taken from the frame, be immersed in a solution of old 
 hyposulphite, that is, hyposulphite associated with a compound containing loosely com- 
 bined sulphur— and when properly tinted, be removed and hung up to dry without any 
 previous washing, it soon turns yellow and becomes altogether pale and faint. Some 
 have thought that the change is caused by the black sulphuret of silver absorbing 
 oxygen and being converted into sulphate of silver ; but this cannot bo, because a solu- 
 tion of an alkaline sulphuret, which blackens sulphate of silver, has no eflfect in restor- 
 ing the original colour of this yellow substance. 
 
 " It appears more probable that the yellow fading is due to an excess of sulphura- 
 tion, or of sulphuratioa and oxidation combined. 
 
 " The action of sulphuretted hydrogen gas or an alkaline sulphuret upon darkened 
 chloride of silver has been studied by more than one observer. It first blackens the 
 brown tone and then changes it to a greenish-yellow. This indeed is the same effect as 
 that produced by the ordinary sulphuretted hypo toning bath, which always causes 
 yellowness when too long continued." 
 
 If we then bear the fact in mind that an excess of sulphur destroys the print, it wiU 
 be easy to understand some of the more obvious causes of fading. Some of these causes, 
 in an abbreviated form, I give from Mr. Hardwich's " Chemistry of Photography." 
 
 Imperfect JFashing —ThiB, he says, is the most important of all, and the most 
 frequent. If hyposulphite of soda, even in minute quantity, be allowed to remain in 
 the print it will certainly cause fading. In that case you have sulphur liberated by a 
 slow process of spontaneous decomposition ; and the sulphur acting, alone or in con- 
 junction with oxygen, on the already sulphuretted print, turns it yellow. 
 
 Dilute fixing and toning baths are often preferred from their yielding very bril- 
 liant tints ; but it cannot be shown that their employment is unscientific and wrong- 
 TJpon the surface of the print, as it comes from the frame, there is much free nitrate of 
 silver, which, when immersed in the fixing bath, forms hyposulphite of silver, a spon- 
 taneously decomposing salt. This should be dissolved immediately by an excess of 
 hyposulphite of soda, if it is to be rendered permanent. Therefore if a bath is pre- 
 pared so dilute as to contain only one part of hypo to about six or eight parts of 
 water, the strength of the solution being insufiicient, a shade of brown may be observed 
 passing over the surface of the print on its first immersion, and a large deposit of sul- 
 phuret of silver soon forms as the result of this decomposition. On the other hand, 
 with a strong hyposulphite bath there is little or no discolouration and the black deposit 
 is absent. 
 
 The most scientific mode of printing is, no doubt, that in which the nitrate of 
 silver is washed out of the proof immediately on its removal from the frame. This 
 point being attended to, a picture is obtained with the lights pure and free from any 
 salt of silver, which may be proved by subsequent immersion in hydrosulphate of am- 
 monia, whereas in the ordinary process there must be decomposition more or less at 
 
 j every part of the surface, as shown by the rapid change of properties which the bath of 
 new hyposulphite experiences. 
 
 I On Mounting Proofs.— AW. cements that are of an acid nature or liable to spon- 
 taneous decomposition should be avoided. Sour and mouldy paste is very objectionable, 
 
 I but even this is better than paste containing corrosive sublimate, and sold as " ever- 
 lasting." 
 
 Light and, Moisture as Causes of Fading — The print should certainly be kept in a 
 dry place, free from damp and mouldiness ; on this all are agreed. The exact action 
 
 M 
 
166 ENLARGING AND REDUCING POSITIVE PICTURES. 
 
 of light, however, upon paper positives is not so well known, although it is generally 
 considered that they retain their brilliancy more perfectly when exposure to bright 
 light is avoided. This point is one to which the attention of photographers is espe- 
 eiallv directed. 
 
 Toning ivithout Gold.— li has been said that the prints toned in hyposulphite of 
 soda containing no gold invariably fade ; but such a statement cannot be substan- 
 tiated, since many are in the possession of photographers of that kind which have stood 
 for years. The coloured surface of a merely sulphuretted print is easily susceptible of 
 injury, since the simple pressure of the warm hand (leaving behind probably a little 
 acid) will often produce a yellow mark. The employment of gold salts in photographic 
 printing, however, by causing a deposit of metallic gold, increases the chance of per- 
 manency under unfavourable conditions. 
 
 The process of II. Le Grey with chloride of gold used alone, and that of Mr. Sutton 
 with the hyposulphite of gold and hydrochloric acid, are both likely, on theoretical 
 grounds, to' give great permanency. The toning bath in both cases is acid to litmus- 
 paper, but the acidity is different to that generated by old hyposulphite of soda, and 
 does not tend to produce yellowness of the proof. 
 
 ■ Negative Printing as Obviating Fading.— li the print be simply developed by gallic 
 acid, and afterwards fixed in solution of hyposulphite of soda newly made, it would 
 then be in the condition of an ordinary calotype negative, which the experience of 
 many years has shown to be permanent. But it is difficult to obtain brilliancy of tone 
 by this mode, and if a gold bath be used to darken the shadows, the case is altered. 
 A developed print, toned and fixed, may be more indestructible than one obtained by 
 the ordinary process. 
 
 " The following is a simple plan by which the permanency of a positive proof 
 may often be tested. Lay the washed print, whilst still damp, upon a clean sheet of 
 glass, and allow water to drip slowly upon it for twenty-four hours ; if it retains its 
 brilliancy unimpaired at the end of that time, it may be considered permanent. A 
 convenient plan is to fill a small basin with spring water, and to hang a piece of stout 
 cotton over the side ; this acts as a syphon, and keeps up a constant dropping. The 
 action of the air and water together will produce fading and yellowness, if the picture 
 is not properly washed. 
 
 On Printing Enlarged and Reduced Positives.— li a collodion negative be placed at 
 a certain distance in front of a camera, and, by a tube of black cloth or some similar 
 contrivance, the light be admitted into the dark chamber only through the negative, 
 an image will be formed upon the ground glass which is reduced in its dimensions ; 
 but if the negative be advanced nearer, the image will increase in size until it becomes 
 first equal to, and then larger than, the original negative. At the same time, it is 
 formed at a point more and more distant from the lens ; that is, it recedes as the 
 negative is brought nearer. 
 
 Again, if a negative portrait of a sitter be placed in the camera slide, and the 
 instrument being carried into a dark room, a hole be cut in the window-shutter so as 
 to admit light through the negative, the luminous rays, after refraction by the lens, 
 will form an image of the exact size of life upon a white screen placed in the position 
 originally occupied by the sitter. These two planes in fact, that of the object and of 
 the image, are strictly conjugate foci, and, as regards the result, it is immaterial from 
 which of the two, anterior or posterior, the rays of light proceed. 
 
 Therefore, in order to obtain a reduced or enlarged copy of a negative, it is 
 
ENLARGING AND REDUCING PHOTOGRAPHS. 
 
 167 
 
 necessary only to form an image of the size required, and to project the image upon a 
 sensitive surface either of collodion or paper. 
 
 A good arrangement for this purpose may be made by taking an ordinary portrait 
 camera, and prolonging it in front, by a deal box blackened inside and with a double 
 body to admit of being lengthened out as required, or, more simply, by a framework of 
 wood covered in with black cloth ; a groove in front carries the negative, or receives 
 the slide containing the sensitive layer, as the case may be. 
 
 In reducing pliotographs, the negative is placed in front of the lens, in the position 
 ordinarily occupied by the object, but in making an enlarged copy it must be fixed 
 behind the lens, or, which is equivalent, the lens must be turned round so that the 
 rays of light, transmitted by the negative, enter the back glass of the combination 
 and pass out at the front. Mr. Shadbolt, who has given attention to the subject, shows 
 the necessity of attending to this point, in order to avoid indistinctness of image from 
 spherical aberration. 
 
 A portrait combination of lenses of two and a half or three and a quarter inches 
 is the best form to use, and the actinic and luminous foci should accurately correspond, 
 as any diflFerence between them would be increased by enlarging. A stop of an inch 
 or an inch and a half aperture placed between the lenses obviates to some extent the 
 loss of sharp outline usually following enlargement of the image. 
 
 The light may be admitted through the negative by pointing the camera towards 
 the sky; or direct sunlight may.be used, thrown upon the negative by a plane 
 reflector. A common swing looking-glass, if clear and free from specks, does very 
 well ; it should be so placed that the centre on which it turns, is on a level with the 
 axis of the lens. 
 
 The best negatives for printing enlarged positives are those which are distinct 
 and clear ; and it is important to use a small negative, taken at a considerable distance, 
 which strains the lens less, and gives a better result in every way than one of larger 
 size. In printing by a two and a quarter lens, for instance, prepare the negative upon 
 a plate about two inches square and afterwards enlarge it four diameters. 
 
 Paper containing chloride of silver is not sufficiently sensitive to receive the 
 image, and therefore the print must be formed upon collodion, or on iodized paper 
 developed by gallic acid. 
 
 The exposure required will vary greatly, not only with the intensity of the light 
 and the sensibility of the surface used, but also with the degree of reduction or enlarge- 
 ment of the image. 
 
 In printing upon collodion, the resulting picture is positive by transmitted light ; 
 it should be backed up with white varnish, and then becomes positive by reflected 
 light. The tone of the blacks is improved by treating the plate first with bichloride 
 of mercury, and then with ammonia. 
 
 ON THE DAGUERREOTYPE. 
 
 I have already stated, in the brief history of this discovery, the circumstances 
 under which it originated and acquired its name from one of the original discoverers. 
 The Daguerreotype picture is taken on a copper plate, with a silvered surface. "We 
 have seen that the paper process, and afterwards the glass plate coated with various 
 
168 
 
 PREPARING THE PLATES. 
 
 organic substances, have gradually superseded the silvered plate, especially in this 
 country ; but as a branch of Photographic Art it forms an important chapter. 
 
 The beautiful process by which the Daguerreotype picture is obtained, was published 
 to the world in July, 1839, after] the French government of the day had rewarded 
 M. Daguerre with a pension of 6000 francs, and M. Isidore Niepce, the son of his 
 colleague in the discovery, with another of 4000, with a half in reversion to their 
 widows— a liberal endowment, worthy of imitation on the part of the British govern- 
 ment on similar occasions. The process divides itself naturally into six operations, 
 which we shall describe in the following order :— 
 
 Pxepaxing the Plates.— The object in this operation is to obtain a perfectly 
 pure and polished surface of silver ; it is therefore of the greatest importance that the 
 articles used, in the latter part of the process, should be perfectly free from grease, or 
 any other article of a fixed oily nature. Many ways and substances have been pro- 
 posed for these purposes ; but the following methods I have generally found produce 
 the best results, they are most simple in their details. The materials required are 
 calcined tripoli, prepared lampblack, rouge, and olive oil. 
 
 There are several varieties of these plates, under the names of English and French, 
 manufactured, as the names import, in those countries. The plates manufactured in 
 England are generally thicker and have more silver on them than the foreign, from 
 which circumstance they receive a finer surface, and are more useful for beginners, 
 as they will bear cleaning for a great number of times. The French plates, being 
 cheaper than the English, can be employed when practice has enabled the operator to 
 be nearly certain of his results. They are usually marked 1-40 and 1-30, indicating 
 the thickness of silver on them, and consequently their quality ; those marked 1-40 
 will scarcely admit of being used a second time, but the other may, perhaps, with 
 care, be polished three or four times without removing the silver altogether. 
 
 In the preparation of plates, hammering seems to be absolutely necessary, binding 
 together, as it were, the materials of the metal ; but to be effective it requires to be 
 done with skill, intelligence, and much care. The anvil, as well as the hammer, 
 requires to be very slightly rounded, so that each stroke produces a smooth and even 
 surface, wtthout cavities. It is also necessary to have near the anvil a pair of 
 bellows, which the operator can move with his foot, and from which a blast of wind 
 is thrown upon the surface of the plate, which has the effect of removing any 
 grains of the metal, or other corpuscles raised either by action of the hammer or 
 of the atmosphere. The hammering, when accomplished in this manner^ with 
 a deposit of silver sufficiently thick, renders the plate capable of the highest 
 polish. 
 
 Coating the. Plates.— In reference to the Daguerreotype plates of commerce, and the 
 necessity of the silver of the plate being chemically pure, the following experiment 
 of M. le Baron Gros, is conclusive. Having procured a new plate, double silvered in 
 the ordinary manner, he plunged one half of the plate into a galvanic trough, and 
 gave it a fresh coating of pure silver, submitting it afterwards to the usual preparations. 
 The image obtained on the plate presented the following characteristics :— In the 
 part of the plate which was left in its original state, the image was scarcely visible, 
 while that portion which had received the galvanic deposit, presented a fully deve- 
 loped picture. 
 
 This experiment of the Baron Gros was highly satisfactory to the Daguerreotypist, 
 inasmuch as it not only teaches him how to render an imperfect plate useful, but how 
 
COATING THE PLATES BY ELECTRO-DEPOSITION. 
 
 169 
 
 he may use any old plates. It is not necessary to give the reader all the details of 
 the process here, seeing he can refer to Mr. Gore's treatise on Electro-deposition ; but 
 I shall briefly detail the process adopted by the Baron, referring to Mr. Gore's 
 treatise for the principles. 
 
 If the plate is a new one, which it is wished to renew or increase the silvering, 
 the process commences by drilling small holes in two of the corners of the plate, for 
 the purpose of suspending it in the solution; the back of the plate is now to be 
 varnished all over with a non-conducting varnish, either copal or sealing-wax dissolved 
 in naphtha will serve the purpose. 
 
 The form of battery now most universally employed for electrotype and other 
 galvanic purposes is Smee's (Fig. 75). It consists of a piece of platinized silver. A, 
 on the top of which is fixed a beam of wood, B, to prevent contact with the silver. 
 The binding screw, C, is soldered on to the silver plate, to connect it with any de- 
 sired object by means of the copper wire, C. A 
 plate of amalgamated zinc, D, varying with the 
 fancy of the operator from one half to the entire 
 width of the silver, is placed on each side of the 
 wood. ;This is set into a glass vessel, P, the 
 extreme ends of the wood resting upon its edge, 
 on which the acid with which it is charged has no 
 eifect. The jar is charged with sulphuric acid 
 (common oil of vitriol), diluted in eight parts its 
 bulk of water. The zinc plates of the battery 
 have been amalgamated with quicksilver, and when 
 the battery is set into the jar of acid, there should 
 be no action perceived upon them when the poles, 
 F, G, are not in contact. Should any action be 
 perceived, it indicates imperfect amalgamation ; this ^^S- 75. 
 
 can be easily remedied by pouring a little mercuiy upon them immediately after 
 removing them from the acid, taking care to get none upon the centre plate A. 
 
 Directions for Use. — A sheet of silver must be attached to the wire connected with 
 the centre plate. A, of the battery, and placed in the silver solution— prepared as 
 directed below. The plate to be silvered is first cleaned with diluted sulphuric acid, 
 and then attached to the wire, G, proceeding from the zinc plates, D, D, and placed 
 in the silver solution, opposite the silver plate attached to the pole, F, and about half 
 an inch from it. A slight effervescence will now be perceived from the battery, and 
 the silver will be deposited upon the Daguerreotype plate, while at the same time a 
 portion of the silver plate is dissolved. 
 
 To Prepare the Solution of Silver. — Dissolve one ounce of chloride of silver in a 
 solution of two ounces of cyanide of potassium, previously dissolved in one "quart of 
 water. The oxide of silver may be used instead of the chloride. This solution is put 
 into a tumbler or other vessel. 
 
 Polishing the Plates. — To polish Daguerreotype plates so as to make them per- 
 fect, requires two distinct conditions — one mechanical, the other chemical : the per- 
 fecting of the metallic surface, and the exquisite cleanliness requisite to insure the 
 purity of the sUver surface which is to receive the photographic image. The 
 importance of chemical purity has already been shown. 
 
 Many fanciful theories were formed on the subject of preparing the surface of the 
 
170 
 
 THE POLISHING TABLE. 
 
 plate for receiving the Daguerreotype. MM. Belfield and Foucault attributed their own 
 success to a coating of organic matter, which diffused itself over the plate ; and M. 
 Daguerre himself fancied he had discovered a galvanic action in a combination of three 
 or four metals, which favourably disposed the plate to receive the coating of iodide of 
 silver and bromine, but experience soon demonstrated the inefBcacy of his fancied dis- 
 covery. Let us then throw aside all these theories. Every mode of polishing, what- 
 ever it may be, that insures to the plate a perfectly smooth surface, and great chemical 
 purity, may in practice be adopted without inconvenience. Among the methods of 
 polishing which have received the sanction of experience, we shall describe those only 
 which are simple and efficacious. 
 
 The Polishing Ja*?e.— Formerly, when about to polish, following the instructions 
 of M. Daguerre, it was thought sufficient to place the plate on several sheets of paper, 
 which were renewed as soon as soiled, and kept in its place with the fingers of the 
 left hand, while the right directed the pledget of cotton. These means were soon 
 found insufficient, and a small polishing board, fixed on a table by means of a 
 small press, was devised. The plate was fixed on this board by means of two small 
 copper catches, whose raised extremities were pierced by a small groove, to which 
 the corners of the sheet of the plate were fixed. M. Levret was the first who 
 conceived the happy thought of substituting for the raised edges of the copper 
 catch a small flat metallic button at each corner of the plate. By this contrivance, 
 now generally adopted, no obstacle opposes the action of the pledget of cotton or 
 other polisher used. 
 
 Figure 77 represents the polished board under this last form; its surface is of 
 rather smaller dimensions than that of the plate, and it is covered with a piece of 
 
 thick cloth or flannel fixed to 
 it with strong glue. This 
 precaution is indispensable to 
 insure the perfect contact of 
 the plate with the board. At 
 the corners of the small board 
 four little copper grooves will 
 be observed, B, B, B, B, each 
 surrounded with a small flat 
 button of the same metal. 
 Under each, of these is fas- 
 tened a corner of the plate. 
 Four Uttle bolts, provided 
 with screws and handles, are 
 placed underneath the board, 
 which permit it to be moved 
 backward and forwards, and 
 adjusted according to the will 
 of the operator. 
 
 The cotton-velvet polishers employed by M. Claudet, and even those of deer-skin 
 since adopted, would quickly be spoiled by the sharp edges of the plate, if care were 
 not taken to turn down the edges in such a manner that the polisher cannot be caught 
 by them. This simple operation is performed with the assistance of a steel burnishing 
 stick. A small board of wood is taken, furnished with a steel ruler, while the out- 
 
 ris. 77. 
 
POLISHING PROCESS. 
 
 171 
 
 ward edge is covered with leather. The plate is disposed upon this board, the silvered 
 face up, so that its edge is in 
 contact with the sharp cut- 
 ting of the steel ruler. Pass- 
 ing the hurnishing stick over 
 it once or twice round the 
 edge of the plate sufficiently 
 for the purpose. This ope- 
 ration is of course repeated Fig. 79. 
 all round the plate. The four corners of the plates are now placed, by means of 
 flat pincers, under the four buttons of the polishing board. 
 
 Figures 78 and 79 represent a very useful machine for the operation just 
 described ; it consists of a wooden frame furnished with a steel ruler. The outside 
 edge of this shelf has a second ruler of iron, or of hard wood, perpendicular to the 
 first, which serves to guide the plane A (Fig. 79). In Fig. 79, the letter B indicates a 
 moveable cheek of wood, which serves to adjust the plate, and prevents it from moving 
 backward while the plane is in action. The use of this plane is easily understood ; a 
 small pair of steel nippers in Fig. 78, which cuts at an angle, and which acts concurrently 
 with the steel rule, is fixed on the board, and serves to depress the edge of the plate. 
 
 And now let us give our attention to the polishers. Fig. 76 represents one of 
 these ; it consists of a small board of soft wood, from twenty to twenty-four inches in 
 length and about six broad, and in thickness about one and a half, furnished with a 
 handle a little resembling that of a joiner's ijlane. Over this board is stretched, by 
 means of some carpet nails, some thickish material like flannel. Over this again is 
 placed a very fine sheet of pasteboard, and over the whole a piece of white cotton 
 velvet or doeskin, firmly nailed to the edges of the board. Four polishing brushes, 
 two of velvet and two of deer's-skin, stretched tightly over them, are required; and, 
 we need not add, these polishing instruments require extreme cleanliness, and should 
 be carefuUy'put away, each in their separate box, every time after being used. 
 
 M. le Baron Gros recommends for the first operations of polishing, small pledgets 
 of his own contrivance, the use of them are both simple and economical. In Fig. 80, 
 is seen the model of one of these pledgets, or dabbers, which may 
 be made in wood. The square part is finished with a thick surface 
 of India-rubber, over which a small square of cotton velvet is 
 arranged, which is renewed whenever it is required. This square of 
 velvet, whose oppositel^corners press against the contracted parts of 
 the pledget, is kept in its fplace^ by the fingers] of the operator, the 
 round stuffed part of the pledget being placed in the palm of the 
 hand. 
 
 After numerous experiments in which nearly all the substances 
 that can be reduced to fine powder, have been successively tried, the greater part 
 of them have been abandoned, and tripoli powder, blacklead, and English rouge are 
 almost exclusively used. It is known that a perfect polish is not easily obtained with 
 pumice-stone and tripoli, for, besides the difficulty of a trick of using the hand that is 
 not easily acquired, these substances, such as we can procure them in commerce, even 
 when washed, are far from being in a state of sufficient purity to produce the required 
 surface on the silvered plate. It is thus necessary to subject these substances to a 
 new washing and decantation. This is performed as follows :— 
 
172 POLISHING POWDEUS. 
 
 Into a large decanter or glass jar filled with water, pour a handful of pumice- 
 stone or of tripoli powder; shake the glass well, then let it remain for four or five 
 ; minutes to settle the pumice stone, and two or three for the tripoli ; then hy intro- 
 i ducing a syphon into the glass, the lower end of which should not be dipped more 
 i than half the depth of the liquid, the water containing in suspension the thinnest 
 I particles of the pumice-stone, as tripoli is drawn oS ; when this powder is half 
 dry, it is placed in a porcelain crucible, or if there is no crucible at hand, in the 
 top of an earthen pipkin, and a strong heat applied by means of a spirit lamp. It is not 
 necessary, however, to carry this calcination to a red heat ; it is sufficient that the powder 
 is quite free from moisture. With pumice stone or tripoli powder thus prepared, a perfect 
 polish may be obtained ; but to give the last touch to the plate, and so burnish it to an 
 ~ intense black, it is necessary that English rouge should be used, and it is well to be 
 very particular as to its quality. 
 
 Polishing powders should be shut up in small glass bottles, with a large 
 opening, and the orifice closed with a metallic gauze ; thus the inconvenience of soiling 
 the fingers will be avoided. These bottles should be carefully shielded from moisture ; 
 and it is best in damp weather to place them near the fire, that the enclosed powders 
 may be well dried. 
 
 The plate being fixed to the polishing board, two or three drops of essence of 
 turpentine are poured over it, and a little prepared pumice and tripoli added, with a 
 cotton pledget that need not be new, rub round and round, forming a number of small 
 circles very near but not touching each other, carefully going equally over every part 
 of the surface. After about a minute a black greasy substance will be formed on the 
 silver, of which the largest part must be removed, continuing to rub round with the 
 same cotton. After a time add a small quantity of dry pumice or tripoli to the plate, 
 and with a new pledget rub on, still in a circle, till the surface of the plate takes a 
 vivid brightness. This is the first stage of the work. 
 
 Arrived at this point, pour over the plate three or four drops of a mixture of 
 essence of turpentine, and of alcohol in the proportion of one part of alcohol to half 
 of turpentine ; to this add a little pumice or tripoli, spreading it lightly over the 
 whole surface of the plate, with the same pledget used in the preceding operation. 
 "When this coating of tripoli is spread regularly over the surface let it dry. There 
 will then form upon the plate a thick crust of a dead white colour; in less than a 
 minute the drying is completed; and to finish polishing there is only the coating of 
 tripoli to be removed. 
 
 For this purpose a new pledget is taken, and this time the plate is rubbed in a con- 
 trary direction ; in a very short time the burnishing will be perfect, and the plate 
 ready for iodizing. 
 
 The process just described saves much time, and can be applied to all plates, whe- 
 ther they are new or have been previously used. The essence of turpentine having 
 been once employed, it would appear that no trace of old impressions ever reappears on 
 the plate. This remarkable consequence is attributable to a chemical influence, of a 
 particular nature, which the essence exercises upon the coating of silver ; and the 
 superiority of the method of Messrs. Belfield and Foucault is attributed to a mechanical 
 action exercised on the metal by the essence of turpentine and other essential oils, which, 
 it seems, have the effect of destroying and completely removing the coating of silver 
 combined with iodine, and producing an entirely new surface. 
 
 Another remarkable effect of essence of turpentine is, that plates thus polished 
 
M. claudet's process. 
 
 173 
 
 can absorb a much larger quantity of accelerating substance without inconvenience. 
 That upon a plate polished in the old manner, for instance, the least excess of bromine 
 betrays itself by a mist more or less thick, which obscures all or part of the image ; 
 with the essence, on the contrary, it would require the excess of bromine to be very 
 considerable to cause a cloud on the impression. 
 
 M. Claudet's Process. — The Daguerreotype has had no more zealous fol- 
 lower in this country than M. Claudet, and his system comprehends all that has since 
 been introduced as new improvements under the title of American inventions. The 
 principal aim of M. Claudet has been, in preparing his plates, to dispense with the use 
 of cotton, which leaves a slimy coating on the surface. In order to attain this end he 
 submitted them to three successive operations, namely, the softening or polishing pre- 
 paration, the separating, and the burnishing processes. 
 
 In the first operation, the irregularities the hammering has left on the surface, is to 
 be removed ; or, in the case of old plates, fresh silvered with chloride of gold. Every 
 trace of former impressions from the surface, whether fixed or not, is to be removed. 
 
 The first polishing requires a tm-ning lathe, on the mandrels of which is mounted a 
 disk of wood, varying in size and thickness according to the size of the plate. This disk 
 is to be first covered with a thick woollen or cotton material, and over this fresh 
 covering a piece of white cotton velvet is tightly stretched ; this covering must be 
 without roughness or colour, and it should be boiled for an hour in pure water and then 
 dried. A few drops of olive oil are now poured over the plate, which is then sprinkled j 
 over with a little powdered pumice-stone or tripoli powder, carefully prepared, washed, 
 calcined, and dried. The silvered surface of the plate is now applied to the velvet 
 disk, and kept in this position by means of a wooden block supplied with a coat- 
 ing of India-rubber to soften the pressure of the disk. The turning-lathe is 
 now put in motion, and the velvet-covered disk is made gradually to run over the 
 whole surface of the plate. By a series of eccentric strokes the plate is crossed on ' 
 every side, and in a very short time the surface of the plate will be brought up per- 
 fectly even and softened. 
 
 The Separation The plates have now to be cleared of the coating of oil adhering to \ 
 
 its surface, tarnishing its brightness and rendering it incapable of photogenic action, j 
 This point is attained by boiling the plate for about half an hour in a saturated solution | 
 of carbonate of soda plunging it afterwards in boiling water, and gradually drying it 
 on a piece of clean calico conveniently stretched for the purpose. The plates are 
 now ready to undergo the last polish. 
 
 For the third polishing, another disk is prepared and covered with perfectly clean 
 cotton velvet, and mounted on the lathe ; over the face of the disk is sprinkled a small 
 quantity of English rouge, applying it to the silvered surface of the plate also, and in a 
 few turns it will acquire a perfectly burnished surface, presenting an intensely black 
 appearance when exposed to the light at a proper angle. All that now remains to be 
 done is to restore the transverse direction of the polish, which should be perpendicular 
 to the intended image. This is done by means of a polishing brush formed of wood, 
 with a handle capable of being held in the hand, and supplied with two or three 
 thick coverings of cloth, and finally with cotton velvet. A few grains of rouge should be 
 sprinkled over, taking this brush in one hand and holding the plate with the ends of the 
 fingers of the other ; rub it quickly, hut very lightly, till the polish has taken the required 
 direction. Quick and repeated nibbing of the plate immediately before iodizing has 
 the advantage of rendering it quicker, more sensitive and more equal in its distribution. 
 
174 
 
 THE POLISHING LATHE. 
 
 The operations just described can only be conveniently executed on a large scale, 
 and the process adopted by M. Claudet is modified by each practitioner, according to 
 his own requirements and means, combining it as much as possible with that of 
 Messrs. Belfield and Foucault. 
 
 By using essence of lavender for oil, some Daguerreotj'pists dispense entirely with 
 the second operation of Claudet, having no occasion in this case to clean the plates ; the 
 annoyance caused by the grease mixed with oil being avoided. 
 
 AVith their usual mechanical ingenuity, the Americans have added some excellent 
 
 improvements to the appliances previously 
 in use for polishing plates. We cannot 
 finish this subject more appropriately than 
 by describing some of the best of these; and 
 first let us describe Davie's improved latho, 
 a recent and decided improvement for 
 polishing plates (Fig. 81). 
 
 There is no part of the Daguerreotype 
 process requiring more thorough manipula- 
 tion than that of cleaning and polishing the 
 plate, and none wherein the operator has 
 met with less satisfaction. The hand buff, 
 though good, does not give that finely 
 finished surface so desirable in a good pic - 
 ture ; and the lathes commonly used are 
 apt, in some instances, to go to the other 
 extreme, and wear the plate bare of silver. 
 Of the many efforts made to improve the 
 buffing-wheel, none have come so near per- 
 fection as the above alluded to. 
 
 It occupies but little space, and requires 
 slight exertion. The bufiPer is a cone of cast iron, twenty-three inches in diameter, 
 neatly covered with wood, and forming a free surface six and a half inches wide. 
 This cone runs in a well-adapted case, which stands firmly on four handsomely turned 
 legs, attached to the box by screws. The cone is turned by a treadle with the left foot. 
 Connected with the machine, are four holders for the difierent sizes of plates. It is 
 certainly a very neat aifair, and Avill undoubtedly do its work quicker and better than 
 anything of the kind now in use. 
 
 Flate Blocks and Vices. — There are several kinds of this article in use ; I shall de- 
 scribe the two best only : — 
 
 Fig. 82 gives an idea of the improvement on the English hand 
 block. The top A is perfectly flat and smooth— a little smaller 
 than the plate, so as to permit the latter to project a very 
 little all round — having at opposite angles C C two clasps, one 
 fixed, the other moveable, but capable of being fastened by the 
 thumb screw D, so as to secure the plate tightly upon the block. E 
 This block turns upon a swivel B, which is attached to the table Fig. 82. 
 
 by the screw C. This block is only used for holding the plate while undergoing the first 
 operation in cleaning. 
 
 Fig. 83 shows the form of Lewis's newly patented plate vice, which, for durability, 
 
POLISHING VICE. 
 
 175 
 
 rig. 83. 
 
 simplicity, and utility, is preferable to all others. It consists of a simple platform and 
 arm of cast iron, the former A having a groove D in. the centre for fixing the dif- 
 ferent sizes of plate beds, E, and the latter 
 supporting the levers E F. On this vice, 
 ■which is secured to a table or bench, the 
 plate receives its finishing polish with rouge, 
 or prepared lampblack. Mr. Lewis gives 
 the following directions for its use: — "As 
 the cam wears, tighten it with the adjusting 
 screw, G, so as to allow the levei', F, to fall 
 back into a horizontal position ; tlie plate 
 being in its place at the time. Oil the wear- 
 ing parts occasionally." For all ordinary 
 purposes, this vice is sufficient ; but in larger 
 establishments, where the lathe is necessary, 
 that above described will be found eminently useful. 
 
 Coating Boxes. — The American coating box is also ingenious. The usual form for 
 
 iodine and bromine boxes is seen at 
 Fig. 84, and consists of a wooden 
 box A, having firmly embedded 
 within it a stout glass jar, the edges 
 of which have been ground. Over 
 this jar is placed the sliding cover 
 B, double the length of the box, one 
 half occupied by a piece of ground- 
 glass, E, tightly pressed upon the 
 glass jar by a spring beneath the 
 cross bar G, and which fits the jar 
 so accurately that it effectually prevents the escape of the vapour of the iodine, bromine, 
 or other accelerating liquid contained therein. The other half of the lid is cut through, 
 shoulders being left at the four angles for the different sizes of frames, designed to receive 
 the plate while undergoing the coating process. "When the plate is put into the frame, 
 the cover B is shoved under the second lid H, and exposed to the vapour ; when coated 
 to the proper degree, it resumes its former position, and the plate is placed in the holder 
 of the camera box. To test the tightness of the box, light a piece of paper, put it into 
 the jar and cover it with the sliding lid. The burning paper expels the air from the 
 jar, and if it be perfectly tight you may raise the whole box by the lid. 
 
 jSie?/.— Daguerreotypists should always use distilled water for solutions and wash- 
 ing the plates. For the purpose of distilling water, the apparatus represented at Fig. 85 
 is both convenient and economical. 
 
 It may be either wholly of good stout tin or of sheet iron tinned on the inside, and 
 may be used over a common fire or on a stove. A is the body, which may be made to 
 hold from one to four gallons of water, which is introduced at the opening B, which is. 
 then stopped by a cork. The tube D connects the neck F of the still with the worm 
 tub or refrigerator, C, which is kept filled with cold water by means of the funnel, and 
 drawn ofi', as fast as it becomes warm, by the cock P. The distilled water is condensed 
 in the worm, and passes off at the cock G, under which a bottle or other vessel 
 should be placed to receive it. The different joints are rendered tight by luting, 
 
176 
 
 HAND POLISHING. 
 
 or in its absence some stiff paste, spread upon a piece of linen and wrapped around them, 
 ■will answer very well ; an addition of sealing-wax over all will make them doubly 
 secure. 
 
 Fig 85. 
 
 Preparing Materials — In whatever manner the materials are to be used, whether 
 by the hand or the lathe, it is essential that they be properly prepared for the purpose, 
 j The tripoli requires to be reduced to a perfectly impalpable powder by calcination, 
 i and perfectly free from large particles capable of scratching the surface of the plate, 
 I and kept for use in a metal or wooden box or bottle contrived for [the purpose, 
 j Prepared lampblack is made by burning it to a red heat in a crucible till vapour 
 I ceases to arise from it, when the crucible is removed from the fire closely covered up, 
 . and suffered to cool. It is then reduced to a fine powder in a mortar, and kept apart 
 in another similar box or bottle. 
 
 The rouge requires to be the finest washed that] can be procured, and should also 
 be kept in a separate box or bottle. The following mode of using these, as practised 
 in an establishment where a great number of plates are required, is probably as 
 effective as the more elaborate processes described : — " In this establishment there 
 is a lathe, to the head of which can be adapted, by means of the proper screws, 
 a series of circular buffs, the usual number being three. These buffs consist of 
 circular disks of wood, one side of which is covered with a fold or two of unbleached 
 cotton velvet. The buff No. 1 is prepared with olive oil and tripoli ; No. 2 with 
 tripoli alone ; and No. 3 with lampblack and a small quantity of rouge, or lampblack 
 alone. The plate to be polished is placed in a shallow cavity on the surface of a flat 
 piece of metal, having a projecting tube at its back, and into which is placed a circular 
 iron rod, mounted with a wooden handle, for the purpose of pressing this metal-holder 
 and its contained plate against the circular buff. 
 
 The method of proceeding is as follows : — Screw on the buff No. 1, adding, if 
 necessary, some fresh tripoli and oil, and place the lathe-rest about three inches from 
 its surface ; the plate is now pressed lightly against the buff, a short distance from its 
 centre, supporting the iron pivot against the rest. The lathe being put in motion by 
 
APPLYING THE BROMINE AND IODINE. 
 
 177 
 
 Fig. 87. 
 
 the foot, causes the plate to revolve very rapidly over the buff, and very quickly 
 removes from it any former picture, scratch, or tarnish. The plate 
 and its holder should now be lightly wiped with a portion of cotton 
 wool, to remove as much as possible of the superfluous oil, &c. The 
 buff No. 2 is now to be substituted for the oil buff, and the plate 
 again applied in the way just described, till all appearance of oil is 
 removed, and the plate appears equally polished. The plate is now 
 laid, silver side upwards, on a stand, similar to the one here repre- 
 sented (Fig. 86), and the flame of a spirit lamp applied underneath till 
 a slight smoke appears to rise from it, and its surface assumes a slight 
 Fig. 86. white tint ; by this process the remaining traces of oil are burnt 
 away, and the plate is ready to receive its final polish by means of the buff No. 3. 
 
 When the plate is properly polished, its surface should look quite black and free 
 from scratches when viewed in a particular light. If this is not the case, it must be 
 applied some time longer to the buff No. 3 till that result is produced. 
 
 The other method of polishing where a lathe cannot be obtained, or would not ; 
 be admissible on account of its cumbrous nature, consists in employing a series of | 
 cotton-velvet buffs, varying in size from three inches by twelve inches to nine inches 
 by eighteen, according to the size of the plates. The least number required is four ; 
 the first buff is prepared with tripoli and oil, the second and third with tripoli alone, 
 and the fourth with prepared lampblack and a very small quantity of rouge ; they 
 must be kept separate from each other, and each carefully reserved for its own par- 
 ticular use. The method of proceeding is to lay the plate face downwards, upon the 
 oil buff No. 1, and then, by means of a similar plateholder to that employed for the 
 lathe, or else one made of wood of the form represented in Fig. 87, the plane surface 
 of which is rendered adhesive by some prepared India-rubber, the plate is briskly 
 moved over its surface with a very slight pressure for the space of a minute or so ; it 
 is then cleared from adhering oil, &c., with some cotton wool, and rubbed lightly first 
 on No. 2 buff, and afterwards on No. 3, adding some fresh dry 
 tripoli as required. The plate is now heated with a spirit-lamp, 
 as before described, and finished on the buff No. 4. 
 
 If the plate to be polished be very free from scratches, and 
 has not been subjected to the setting process with salt of gold, 
 the use of the oil buff may be 
 dispensed with, and those pre- 
 pared with tripoli and lampblack 
 alone used. 
 
 The following are the most important precautions 
 to be observed to insure the proper result in the fore- 
 going'processes. The buffs and polishing materials should 
 be carefully preserved from dust, dirt, and damp ; the 
 former of these is easily accomplished by keeping each 
 separate buff in its own case, which may be made either 
 of wood or parchment, and the latter by keeping them 
 Fig. 88. in some dry place. If there should be any doubt relative 
 
 to the buffs being perfectly dry, it will be advisable to place them, well protected 
 from dust, before a fire, a short time previous to using. 
 
 "When the plate is polished by either of the processes described it may be protected 
 
178 
 
 ACCELERATING MATERIALS. 
 
 Fig. 89. 
 
 from injury in a wooden or metal box, similar to the one represented in Fig. 86. 
 AVhen the plate is about to be used, it should receive a final polish, and have its 
 grain laid in a particular direction, by means of a buff, either covered with cotton 
 velvet, or a piece of smooth, sofi doeskin, of the shape here represented (Fig. 89) . 
 
 The plate, if a small one, can be supported on the ends of the fingers of the left 
 hand, using the buff with the right ; if the plate be too large or 
 thin to be supported on the fingers, any convenient form of 
 plateholder can be employed, taking care that it is perfectly free 
 fiom dust or grease. The buff should be briskly rubbed over 
 the plate witli a slight degree of pressure for a few seconds, or 
 till all the fine lines on the surface of the plate appear in one uniform direction, 
 bearing in mind that for portraits the lines should not be in the direction of the face, 
 but across it ; and for views, in the direction of the view. The plate is now ready, and 
 should immediately be subjected to the next operation, which is — 
 
 Applying the Sensitive Coating. — The simplest form of apparatus necessary for 
 this purpose consists of two porcelain or glass pans, ground on the edges and furnished 
 with plate-glass covers, ani a series of wooden or metal frames of the size of the plate 
 to be prepared ; one of these pans is for holding the iodine, and the other the accele- 
 rating material. The plate to be prepared is placed in its proper frame, and substituted 
 I'or the plate-glass cover of either pan, as may be required ; the progress of the pre- 
 paration being observed from time to time by the tint of colour produced on the plate 
 v/hen removed for an instant, and viewed at such an angle that the light transmitted 
 through a sheet of white paper held before the plate may be reflected to the eye. 
 When the proper colour is obtained, the plate is exposed for an instant or two longer, 
 to remove any effect of the light, and then rapidly placed in the camera frame ; the 
 glass cover is now replaced. 
 
 In consequence of being obliged to remove the cover of these pans to observe the 
 
 colour of the plate, the vapour of iodine, 
 &c., within the pan becomes disturbed, 
 and rarely produces an even coating; 
 this is avoided by using the glass pans 
 of greater depth, and mounted as shown 
 in Fig. 90. 
 
 The plate to be prepared is placed 
 in the proper opening at the top of the 
 box, and on removing the glass sliding- 
 cover and replacing it again before the plate is removed, a much better result is obtained. 
 
 The only form of apparatus that can be relied upon for producing a uniform good 
 result is that shown in Fig. 91, or one 
 constructed on similar principles. It is 
 technically termed a bromine apparatus, 
 and consists of two deep glass pans 
 with polished sides, and mounted in a 
 wooden box, at the back of which are 
 two openings, corresponding to the two 
 pans, over which is fastened a piece 
 of white paper. In the front of the 
 box, and immediately opposite the back openings, are two small doors opening 
 
 Fig. 90. 
 
 Fig. 91. 
 
EXPOSURE IN THE CAMERA. 
 
 179 
 
 outwards, and each, lined with a piece of looking-glass. Two glass covers, and a 
 series of wooden frames sliding over tliem on tlie top of the box, complete the appa- 
 ratus. From half to one ounce of pure crystallized iodine is placed at the bottom 
 of one of the pans and the accelerating material in the other, and they are then closed 
 with their respective covers, and the whole apparatus placed before a window with a 
 moderate light. The accelerating material which I have uniformly found produce the 
 best and most certain results is a chloride of bromine, made by mixing one ounce of a j 
 satutrated solution of bromine with one drachm of strong hydrochloric acid. This 
 preparation must be kept in a stopped phial. Water is poured into the glass pan of 
 the bromine apparatus to the depth of about half an inch, and sufficient of the chloride 
 of bromine added to bring the whole to the colour of very pale sherry. 
 
 The plate to be rendered sensitive to light is placed in its required frame at the 
 top of the bromine apparatus, and immediately over the pan containing the iodine ; 
 the plate-glass cover is then removed so as to expose the plate to the vapour of the 
 iodine below; the small mirror is now so adjusted that, by looking into it, the white 
 paper at the back can be seen reflected from the surface of the silver plate, and any 
 change of colour immediately perceived. When the plate has assumed a light straw i 
 colour, the cover is to be returned over the iodine, and the slide holding the plate i 
 shifted over the pan containing the chloride of bromine ; the cover is now to be ; 
 withdrawn, the mirror adjusted as for the iodine ; and the glass cover being removed, j 
 the plate is exposed to the vapour till it becomes of a deep yellow colour, when it is j 
 returned over the iodine till of a rose tint, and immediately placed in the camera | 
 frame. The dilute solution of chloride of bromine will serve to prepare a considerable | 
 number of plates ; and when it fails to produce its effect, it will always be found the j 
 better plan to mix a fresh quantity rather than increasing its strength by the addition | 
 of more of the strong solution. ! 
 
 There are a great many preparations of bromine known by the names of eau I 
 bromee, bromide of iodine, Hungarian solution, Woolcott's American accelerator, j 
 bromide of lime, &c., which are employed by some operators with much success. j 
 
 When the bromide of iodine, or Hungarian solution, is employed, it should be ' 
 diluted with four or five times its bulk of water, and the plate, previously iodized to a j 
 deep yellow, exposed to it till a deep rose or violet colour. Woolcott's accelerator ; 
 and bromide of lime both require the same tints as the chloride of bromine before 
 described. The bromide of lime, chloro-bromide of lime, and other dry accelerators j 
 of that character, are used in the bromine apparatus, spread evenly over the bottom of | 
 one of the pans to the depth of about a quarter of an inch. 1 
 
 Should the plate by accident be left too long over the iodine in the first prepa- 
 ration, and show some indications of a rose tint, it must be brought to a full rose over 
 the accelerator, and then to a blue over the iodine ; this will often produce a good 
 result, and save the trouble of re-polishing the plate. 
 
 The plate, after being prepared by one or other of the foregoing processes, must 
 be returned to the dark box or camera back till required for the next process, viz. : — 
 
 Exposure in the Camera. — The mode in which this is effected must, of course, 
 depend upon the construction of the camera, whether it have a lens, as originally 
 proposed by Daguerre, or a concave mirror or speculum, which is the apparatus 
 patented in this country by Mr. Beard. Both kinds have their advantages. The 
 refracting camera, as recently improved, appears to possess all the capabilities 
 without many of those inconveniences which attend on the manipulation with the 
 
180 
 
 MERCURIALIZING THE PLATE. 
 
 reflecting camera, and being withal less expensive, is now the form generally 
 used. 
 
 The first thing to be attended to, before introducing the plate, is to place the 
 camera on some firm support, and opposite to the object wished to be copied ; after 
 which the focus should be adjusted with the greatest care till a perfectly clear and 
 distinct image of the object is seen on the piece of ground-glass, which should be 
 placed in exactly the same position as the plate is to occupy, taking especial care that 
 the ground side of the glass should correspond to the prepared surface of the plate. 
 When the focus is obtained, the light should be shut off by a brass cap, or other con- 
 trivance for that purpose, till the plate is introduced, or the camera may be taken into 
 a dark room, and have the plate put into its place, when it can be brought into the light, 
 having, of course, made those obvious arrangements, that the object and the camera be 
 placed in precisely the same relative positions they occupied when the focus was adjusted. 
 
 The camera may then be opened to allow the light to fall on the plate through the 
 lens. The time requisite for it to remain open wiU depend, in a great measure, upon 
 the season of the year, time of the day, and the brightness or clearness of the atmos- 
 phere. The time usually required with a good achromatic and a well-constructed 
 camera varies from one to sixty seconds. 
 
 When the camera has been opened a suf&cient time, which can only be determined 
 by observation and experiment, close the front aperture, and take it into a dark room, 
 when the picture, which is impressed on the sensitive surface of the plate, is to be made 
 visible by being exposed to the fumes of mercury. 
 
 Mercurializing the Plate. — The apparatus required for this operation is called a mer- 
 cury box, and is shown in the accompanying cut : — 
 
 The body. A, is made of wood, and has an iron cup, fixed in 
 the bottom, for holding the mercury, which is heated by a spirit 
 lamp, F ; the upper part of the box, A, is grooved, so as to re- 
 ceive the same sliding frame, B, that fits the back of the camera 
 and holds the prepared plate, or else the prepared plate alone ; 
 at the front of the box is a small yellow glass window, C, over 
 which slides a shutter, D. When about to be used, pour a small 
 quantity of pure mercury (four to six ounces) into the metal cup 
 at the bottom of the box ; the mercury should then be heated 
 by means of a spirit lamp, till the outside of the metal cup can 
 be touched with the finger without much inconvenience. The 
 plate may then be taken from the camera and placed in the mer- 
 cury a short time, by cautiously applying a lighted taper to the 
 side, and looking through the glass in front, the development of the picture can easily 
 be perceived. 
 
 If the mercury be made very hot, the picture soon makes its appearance ; but, gene- 
 rally speaking, when done too rapidly, the minor details are lost and the plate is apt to 
 become spotty ; it is always advisable, where time is not a great object, to do the opera- 
 tion rather slowly than otherwise, as a much clearer and sharper outline of the picture 
 will be obtained by this means than if done rapidly. The usual time required is from 
 five to twenty minutes. 
 
 If the mercury box be furnished with a thermometer, which is sometimes the case, 
 the temperature may be kept about 90 degrees. 
 
 The mercury should be perfectly dry and free from any particle of oxide, and should 
 
 fig. 92. 
 
THE COLOURING PROCESS. 
 
 181 
 
 be poured into a bottle after each series of experiments. When it loses its brilliancy, 
 it may be purified by filtering through a paper cone, having a very fine opening at the 
 bottom. The mercury box ought also to be carefully dusted out before using. 
 
 "When the picture has become su£S.ciently distinct, it should be removed from the 
 mercury box and subjected to the next operation, viz. :— 
 
 Removing the Sensitive Coating. —The solution required for this is made by dissolving 
 two ounces of hyposulphate of soda in one pint of water ; this solution will serve many 
 times, if it be filtered before using. The solution is placed in some convenient shallow 
 vessel, and the plate quickly immersed in it ; the colour will be observed to gradually 
 disappear, and when that is the case it should be placed in a vessel of filtered water, to 
 remove the excess of hyposulphite, and subsequently a small quantity of distilled water 
 poured over its surface. 
 
 Fixing/ the Picture.— The solution of gold which is required for this process is pre- 
 pared by dissolving 15 gr. of chloride of gold in one pint of water, and adding it little 
 by little, to a mixture of 60 gr. of hyposulphite of soda and eight ounces of water, the 
 whole being well agitated between each addition. The solution, at first slightly yellow, 
 becomes afterwards perfectly limpid. Before the surface of the plate becomes dry, it is 
 to be placed, face upwards, upon the fixing stand, which is so constructed as to preserve 
 j it in a perfectly horizontal position by means of levelling screws, and the solution of 
 j gold being poured over its surface, until it is perfectly covered, and the flame of a large 
 spirit lamp applied to the under surface, moving it gently beckwards and forwards, 
 that every part may be equally heated, the picture will be seen to brighten, and become 
 in a minute or two of great force. When this effect is produced, the liquid should be 
 thrown off, and the plate instantly dipped into water, washed, and dried. If the plate 
 be a large one, it is most conveniently dried by placing it on a smooth and clean piece 
 of copper or tin plate, and some boiling distilled water poured over its surface, at the 
 same time inclining the plate so that the water may run off from one of its lower cor- 
 ners, and it will in a very short time become perfectly dry. 
 
 If the plate be of a small size, it can be conveniently dried over a spirit lamp. It 
 should be held by means of a small pair of pliers, by one of its corners, and some 
 filtered distilled water poured over its surface ; by inclining the corner held by the 
 pliers, the greater portion of the liquid will flow to that part, and can be removed by 
 touching it with a piece of rag or blotting-paper ; the spirit lamp may then be applied 
 to the upper corner^f the plate till it begins to dry, and the flame gradually brought 
 lower down, tiU the Avhole surface is finished. Gently blowing downwards on the plate 
 will expedite the process, as well as prevent, in a great measure, the formation of spots. 
 
 It sometimes happens that, while the plate is being heated with the solution of gold, 
 a film of silver detaches itself and swims in the liquid, of course destroying part of the 
 picture. This accident is probably owing to the oxidation of the silver while under the 
 influence of too much heat. 
 
 The lamp should be removed as soon as the small bubbles of air appear to form on 
 the surface of the metal. When the picture is not perfectly fixed, it is better to make 
 a second trial, rather than run the risk of spoiling a good picture by trying to fix it 
 perfectly the first time. 
 
 Colouring Daguerreotypes. — As theobjects copied by the Daguerreotype process are only 
 represented in light and shade, not in the colours as they appear in nature, it has been 
 suggested, after the picture has been set, to colour them by hand, similar to a painting ; 
 and certainly, when done in an artistic skilful manner, it produces a very pleasing 
 
182 
 
 M, daguerre's improved process. 
 
 effect. The simplest method is to use dry colours, ground extremely fine, with some 
 dry gum or starch. The picture must be well set with gold, and the colour applied or 
 dusted on with a fine camel's-hair pencil, taking up a very small quantity of colour at 
 a time, removing the superfluous colour by blowing it oS with a caoutchouc bottle ; 
 when the desired tint is produced, breathing on the plate will cause the colour to adhere. 
 M. Claudet's method is to mix a small quantity of the colour with spirit of wine, apply- 
 ing it to the plate with a camel's-hair pencil, and if not sufficiently dark, some of the dry 
 colour is applied over it, to which it will adhere. As a general rule, the colours should 
 be applied very cautiously, as it is very difficult to remove them when once on the 
 plate. The best colours to be used are carmine, chrome yellow, and ultra-marine, by 
 combining which any desired tint may be obtained. 
 
 Daguerre's Improvements. — The Daguerreotype process is, as we have seen, much 
 more complicated in its manipulation, and less satisfactory in its results than either the 
 collodion, wax-paper, or calotype. The preparation of the plates is a mechanical opera- 
 tion, requiring great delicacy in handling, and the application of the sensitizing 
 vapours are processes requiring great care and considerable knowledge of chemical j 
 manipulation. The uncertainty of the results, even of the best operators, led M. j 
 Daguerre, to return to the subject for the purpose of reviewing his process, ' 
 which he does in the " Comptes Eendue," of March, 1842. The uncertainty he . 
 attributes to two principal causes ; first the defective operation of polishing, in conse- : 
 quence of the impossibility of entirely divesting the surface of traces of the liquid, 
 cotton, and other substances, used in the operation, which prevents the iodine from 
 coming into direct contact with the silver, and consequently retards the photogenic 
 action. And, second, in the alterations in the temperature of the air with which the j 
 plate is in contact, from the earliest operations to the mercurial bath, in consequence 
 of the colder body of the metal condensing moisture from the surrounding air. 
 
 The following process recommended is very simple, and obviates both the incon- 
 veniences above mentioned ; it frees the silver as much as possible from all dirt or 
 dust, and neutralizes the humidity produced by the elevation of temperature in the 
 mercurial box. 
 
 The process consists in covering the plate, after having polished it, with a layer 
 of very pure water, and heating it very strongly over a spirit lamp, pouring off the 
 first layer of water in such a manner that the dust which has been raised, floats away 
 without touching the plate. 
 
 It is necessary, in order to accomplish this, to have a frame of iron wire, of the 
 size of the plate, at one of its angles having a handle, and in the middle, on the two 
 opposite sides, two small cramp-irons, to retain the plate when it is inclined. After 
 having placed this frame on a horizontal plane, the plate is placed on it, and is 
 again covered with a laj^er of very pure water, putting as much as the siirface can 
 retain. The bottom of the plate is afterwards very strongly heated, and very small 
 bubbles are formed at the surface. By degrees these bubbles become larger, and 
 finally disappear ; the heat must be continued to ebullition, and then the water must 
 be poured ofi^. The operator should commence by placing the lamp under the angle of 
 the frame where the handle is ; but before removing the frame, this angle must be very 
 powerfully heated, and then, by gradually moving it by its handle, the water imme- 
 diately begins to run ofi". It must be done in such a way that the lamp shall follow, 
 under the plate, the sheet of water in its progress, and it must be only gradually 
 inclined, and just sufficient for the layer of water, in retiring, not to lose in thick- 
 
ACCELEUATING PROCESSES. 
 
 183 
 
 ness ; for if the water were dried up, there would remain small isolated drops, which, 
 not being able to flow off, would leave on the silver the dust which they contain. After 
 that, the plate must not be rubbed ; very pure water does not destroy its polish. 
 
 This operation should be perforn^ed just before iodizing the plate. Whilst it is 
 yet warm, it is placed in the iodizing box, and, without allowing it to cool, it is sub- 
 mitted to the vapour of the accelerating substances. Plates thus prepared may be 
 kept one or two days (although the sensibility diminishes a little), provided that 
 several plates be placed opposite to one another, at a very short distance apart, and 
 carefully enveloped to prevent change of air between the plates. 
 
 It is one of the most important points to obtain a fine polish on the plate, but the 
 brilliancy often disappears when substances which adhere to the surfece of the silver arc ! 
 used, such as the peroxide of iron, which has been very generally made use of for \ 
 giving the last polish. This substance, indeed, seems to burnish tlie silver, and to give j 
 it a more perfect polish ; but this polish is factitious, since it is not really in contact on | 
 the silver, but is, in fact, on a very fine layer of oxide of iron. It is for this reason : 
 that there is required for polishing them a substance which docs not adhere to the i 
 silver ; pumice leaves less residue than any other substance. j 
 As regards the liquid to be employed : in the first operations nitric acid of five i 
 degrees must be employed, but for the last operations it must be reduced to one j 
 degree. The polishing with oil and the heating may be suppressed. 1 
 The layer produced by the descending vapours of the iodine and of the j 
 accelerating substance forms with silver a more sensible compound than is obtained : 
 with the ascending vapours. I make this observation only to lay down a fact, for it j 
 would be difficult to employ descending vapours, on account of the dust which might j 
 fall during the opei-ation, and from stains. I 
 The resistance which light experiences in passing through a white glass is well i 
 known. This resistance is even greater than it appears, and may be attributed not \ 
 only to the dust which is left on the glazing in cleaning it, but also to that which is ' 
 naturally deposited on it. The object-glass of the camera obscura is certainly in the 
 same case. To ascertain this, I put the object-glass in cold water, which I boiled; I 
 knew that it was impossible to remove it without the sides. This operation had, 
 therefore, no other object than to raise the temperature of the glass to 212° F. C, and 
 I then immediately poured on the two sides of the object-glass very pure boiling water 
 to remove the dust. By operating directly with the object-glass, thus cleansed, I still 
 further increased the promptitude. This means presents too many difficulties to bo 
 put in practice ; only care should be taken to clean the object-glass every day. 
 
 The atmospheric dust, which is the scourge of photogenic images, is, on the 
 contrary, favourable to images which are obtained by contact or at a very short dis- 
 tance. To be convinced of this, we have only to clean the two bodies which we wish 
 to put in contact with the boiling water, as I have just indicated, and to keep them 
 both at the same temperature as the air ; there will then be no impression, which 
 evidently proves that these images have no relation with the radiation which gives 
 photographic images. 
 
 if. FizeaiC s Preparation. — The preparation of bromine water is thus described by M. 
 Fizeau :— " To prepare a solution of bromine, of a fixed proportion and convenient 
 strength to operate with, I, in the first place, make a saturated solution of bromine in ^ater 
 this is prepared by putting into a bottle of pure water a great excess of bromine, agitating 
 strongly for some minutes, and before using allowing the bromine to separate. Now, a I 
 
]84 
 
 MR. BINGHAM'S PROCESS. 
 
 definite quantity of this saturated water is to be mixed with a definite quantity of plain 
 water, which will give a solution of bromine always in the same strength : this mixture 
 is conveniently made iu the following manner : — The apparatus necessary is a dropping 
 tube, which is also required for another part of the process, capable of holding a small 
 definite quantity, and a bottle having a mark to indicate a capacity equal to thirty 
 times that of the dropping tube : fill the bottle with pure water to the mark, then add, 
 by means of the dropping tube, the proper quantity of the saturated solution of bromine. 
 
 " The purity of the water is of some importance : the foregoing proportions refer to 
 the pure distilled water, and it is well known that the waters of rivers and springs is 
 not pure ; but these different varieties can be used as absolutely pure water by adding 
 a few drops of nitric acid till they taste slightly acid ; two or three drops to the pint 
 is generally sufiicient. 
 
 "The liquid produced, which is of a bright yellow colour, ought to bo kept in a 
 well-stoppered bottle ; it is the normal solution, and I shall call it simply bromine 
 water, to distinguish it from the saturated solution. 
 
 " The box I employ for subjecting the plate to the vapour of the bromine water is 
 constructed in the following manner : — It consists of a box lined with a varnish, which 
 is not acted on by bromine ; its height is about four inches ; the other dimensions are 
 regulated by the size of the plate, which ought to be at least half an inch all round, 
 short of the sides of the box ; it is composed of three separate portions — the cover, 
 which is the frame holding the plate, the body of the box, and the bottom, upon which 
 is placed the vessel for the bromine ; this moveable bottom is slightly hollowed, so that 
 the bromine vessel may always be placed in exactly the same position." 
 
 Bromide of iodine is prepared by M. Valicour's method thus : — Into a bottle of 
 the capacity of two ounces, pour thirty or forty drops of bromine, the precise quantity 
 not being of importance. Then add, grain by grain, as much iodine as the bromine 
 will dissolve till quite saturated. This point may be ascertained by some of the iodine 
 remaining undissolved. In this state it is too concentrated for use ; but by dropping 
 fifteen or twenty drops into half an ounce of distilled or filtered rain-water, the requi- 
 site strength may be obtained. 
 
 Mr. E. J. Bingham, in an article published in the " Philosophical Magazine," 
 October, 1846, gives an improvement in the Daguerreotype process by the application of 
 some new compounds of bromine, chlorine, and^^iodine. " In warm weather," he re- 
 marks, " a considerable deposition of moisture takes place upon the glass or slate cover 
 used to confine the vapour in the bromine or accelerating pan. This moisture must 
 also necessarily condense upon the cold metallic surface of the plate during the time it 
 is exposed to the bromine vapour. In fact, it is difficult to obtain perfect pictures 
 during the excessive heat of the late season. This appears to be owing to the deposi- 
 tion of moisture upon the plate, arising from the water in which the bromine is 
 dissolved. To obviate this, some have recommended the pan to be kept at a low tem- 
 perature in a freezing mixture ; and M. Daguerre, in a communication to the French 
 Academy of Sciences, recommends the plate to be heated : but in practice both these 
 are found to be unsuccessful. 
 
 " It appeared to me, that if we could avoid the use of water altogether in the 
 accelerating mixture, not only would the difficulty I have mentioned be avoided, but a 
 much more sensitive surface would be obtained on the plate. With this view, I 
 \ endeavoured to combine bromine with lime, so as to form a compound analogous to 
 j bleaching powder. In this I was successful, and find that bromine, chloride of iodine. 
 
USE OF CHLORINE IN COMBINATION WITH BROMINE. 
 
 185 
 
 and iodine, may be united with lime, forming compounds having properties similar to 
 the so-called chloride of lime. 
 
 " The bromide of lime may be produced by allowing bromine vapour to act upon 
 hydrate of lime for some hours. The most convenient method of doing this is to place 
 some of the hydrate at the bottom of a flask, and then put some bromine into a glass 
 capsule supported a little above the lime. As heat is developed during the combina- 
 tion, it is better to place the lower part of the flask in water at the temperature of 
 about 50° Fah. : the lime gradually assumes a beautiful scarlet colour, and acquires an 
 appearance very similar to that of the red iodide of mercury. The chloro-iodide of lime 
 may be'formed in the same manner — it has a deep brown colour. Both these compounds, 
 when the vapour arising from them is not too intense, have an odour analogous to that 
 of bleaching powder, and quite distinguishable from chlorine, bromine, or iodine alone. 
 
 " Those Daguerreotypists who use chlorine in combination with bromine, as in 
 "VVoolcott's American mixture, or M. Guerin's Hungarian solution, which is a com- 
 pound of bromine, chlorine, and iodine, may obtain similar substances in the solid 
 state, which may be used with great advantage. By passing chlorine over bromine, 
 and condensing the vapours into a liquid, and then allowing the vapour of this to act 
 upon lime, a solid may be obtained, having all the properties of the American accele- 
 rator ; or by combining the chloro-iodide of lime with a little of the bromide, a 
 mixture similar to that of M. Guerin's may be produced : but I greatly prefer, and 
 would recommend, the pure bromide of lime, it being, as I believe, the quickest 
 accelerating substance at present known. By slightly colouring the plate with the 
 chloro-iodide, and then exposing it for a proper time over the bromide, proofs may be 
 obtained in a fraction of a second, even late in the afternoon. A yellow colour should 
 be given by the use of the first substance ; and the proper time over the bromide is 
 readily obtained by one or two trials. With about a drachm of the substance in a 
 shallow pan, I give the plate ten seconds the whole of the first day of using the prepara- 
 tion, and add about three seconds for every succeeding one. The compound should be 
 evenly strewed over the bottom of the pan, and will last, with care, about a fortnight. 
 
 "The great advantage of this compound is, that it may be used continuously 
 for a fortnight without renewal ; and, unlike bromine water, its action is unafiected 
 by the ordinary changes of temperature." 
 
 M. Fizeau, who has carefully studied this branch of the science, gives the fol- 
 lowing directions for giving greater permanence to the Daguerreotype picture : — 
 
 " Dissolve eight grains of chloride of gold in sixteen ounces of water, and thirty- 
 two grains of hyposulphite of soda in four ounces of water : pour the solution of gold 
 into that of the soda, a little by little, agitating between each addition. The mixture, at 
 first slightly yellow, becomes perfectly limpid. This liquid now contains a double 
 hyposulphite of soda and gold. 
 
 " To use this salt of gold, the surface of the plate should be perfectly free from any 
 foreign substance, especially dust ; consequently it ought to be washed with some precau- 
 tion, which might be neglected if it was to be finished by the ordinary mode of washing, 
 " The following manner generally succeeds the best : — The plate being yet iodized, 
 and perfectly free from grease on its two surfaces and sides, should have some drops of 
 alcohol poured on the iodized surface ; when the alcohol has wetted all the surface, 
 plunge the plate into a basin of water, and after that into a solution of hyposulphite 
 of soda. 
 
 " This solution ought to be changed for each experiment, and to consist of about 
 
I 
 
 186' 
 
 STEREOSCOPIC PHOTOGRArHY. 
 
 one part of the salt to fifteen of the water ; the rest of the washing is done in the 
 ordinary way, only taking care that the water should be as free as possible from dust. 
 
 "The use of the alcohol is simply to make the water adhere perfectly all over the 
 surface of the plate, and prevent it from quitting the sides at each separate immer- 
 sion, which would infallibly produce stains. 
 
 " When a picture has been washed, with these precautions, the treatment with the 
 salt of gold is very simple. It is sufficient to place the plate on a support, and pour 
 upon its siu-face a sufficient quantity of the salt of gold, that it may be entirely 
 coyered, and heat it with a strong spirit-lamp ; the picture will be seen to brighten, and 
 become, in a minute or two, of great force. When this etfcct is produced, the liquid 
 should be poured off, and the plate washed and dried. 
 
 " In this operation the silver is dissolved, and the gold precipitated upon the silver 
 and mercury, but with very different results ; in effect, the silver, which, by its reflec- 
 tion, forms the shades of the picture, is in some way darkened by the thin film of gold 
 which covers it, from which results a strengthening of all the dark parts. The mer- 
 cury, on the contrary, which, in the state of an infinite number of small globules, 
 forms the lights, is augmented in its solidity and brightness by its union with the 
 gold, from which results a great degree of permanency, and a remarkable increase in 
 the lights of the picture." 
 
 STEREOSCOPIC PHOTOGRAPHY. 
 
 Binoculax Vision. — There is scarcely anything more interesting in the study of 
 optics than the theory of binocular vision. Few persons are aware of the fact, that 
 without two eyes it is impossible to form a correct judgment of distances ; this may, at 
 first sight, appear strange, but the fact may be proved beyond a doubt. Previously to 
 my proceeding to do so, I shall mention a few cases to the point. A gentleman, a friend 
 of mine, lost the sight of one of iiis eyes some couple of years ago, and to this day he 
 cannot measure distances — for instance, it sorely puzzles him to snuff a candle, to dip 
 his pen in an ink-bottle, to take hold of anything a little distance from him, &c., &3 . ; 
 and it is a curious fact that he, and others like him, are nearly always short of the 
 object. 1 kncAV a lad3r, who had met with the same misfortune, and have often been 
 amused at seeing her try to pour wine out of a bottle into a decanter, or threading a 
 needle. To descend a little lower in the scale of creation, I had a young cat at one 
 time who lost the sight of one eye, and the mistakes she used to make in playing with 
 a ball were truly laughable. For instance, when the ball would roll away for a fe w 
 feet, she would make a bound, but could never get within three or four inches of it, amd 
 if she made a jump to get on a wall, &c., she invariably fell short. These are but a 
 few of the numerous instances that I could mention, but they arc 
 
 cnou-h to introduce the subject. And now for some of the proofs. 
 
 Expiriment 1st. — Insert the prongs of a fork into a door or wall, 
 about three feet six inches, or four feet from the floor, and on the bardie 
 or haft of the fork place a cork upright (Fig. 92). Now provide your- 
 self with a cane, or thin walking-stick, go to the other end of the 
 
 room, and, shutting one eye, walk briskly up towards the cork, and ^.^ 
 raising the cane at the moment strike at the cork without any stop or 
 hesitation, keeping one eye shut all the time, the chances are that you will not liiit 
 the cork once out of six times. 
 
PROOFS OF BINOCULAR VISION. 18'i 
 
 Experiment 2nd. — Procure a small piece of pipe-stem, and insert it in the cork of 
 a bottle (Fig. 93). [Then stand away from the bottle, about 
 eighteen inches or two feet, and, taking a pointed pencil in 
 your fingers shut one eye, and try to place the point of the pencil 
 on the top of the piece of pipe-stem. You may take what time 
 you please to calculate the distance, providing you keep the 
 one eye shut all the tiine, and that you do not repeat the experiment 
 without ivithdraidng the hand each time, the chances are that you 
 will not do it once in twelve times. The pipe and pencil appear 
 as in Fig. 94 to the single eye, being a front view ; but to any 
 person looking at them from the side they would appear as in Fig. 95 or Fig. 96, but 
 more generally the former. ' 
 
 Experiment 3rd. — This is by far the most conclusive experiment of the three. 
 
 stead of a pipo-stem, procure the end of a 
 quill, or the round end of a magnum bonum 
 steel pen, which insert in the cork as in Fig. 
 97, and, shiMing one eye, endeavour to drop 
 into the open end of the pen or quill a grain of 
 shot : you may hold the shot within an inch 
 of the pen before you drop it. The chances 
 are you will not drop it in once in twenty times. These 
 few simple experiments go far to prove the almost impos- 
 sibility of calculating distances correctly with one eye. 
 
 The next subject for consideration is, in what manner are we able to calculate dis- 
 tances by using two eyes. 
 
 This subject will be more fully explained by the following experiments : — 
 Experiment 4)!^.— Stand a book ou its edge as in Fig. 98, and so place it that, 
 having the right eye only open, you can see nothing but 
 the back. Shut the right eye and open the left, when the 
 book will appear as in Fig. 99. Of course the same effect 
 would be produced on the other side by using the left eye 
 in the first instance ; but if the book be placed exactly 
 between the eyes, then it will appear as in Fig. 100 ; but not 
 immediately ; for as the rays from the eyes can only meet 
 at one point from the latter at the same time, or, as it may 
 be considered, the eyes can only focics at one point at once, the back of the book 
 appears correctly defined, and the right or left eye sees its own side, which ever predo- 
 minates. It may not be generally known that most persons only use one eye to take in 
 an object or figure, the other being only used to check or determine the distance or 
 relative size of that object, as in the case of focussing in the camera, when you obtain 
 the object perfectly sharp and distinct ; then, without altering the eyes or their point 
 of sight, open and shut one alternately, and you will at once perceive that only one eije 
 sees the image properly. This arises from the fact, that the ray or pencil of light com- 
 ing through the lens cannot be by any possibility refiected on different points at once. 
 AVe therefore can see only one object at any distance at any one time, although we may 
 be perfectly conscious of other objects nearer or further away. To bear out both 
 these assertions, it will perhaps be necessary to try the following simple experi- 
 ment : — 
 
 Fig. 99 
 
188 
 
 BINOCULAR PHENOMENA. 
 
 Pig. 10]. 
 
 Experiment 5th. — Place a small mirror at about two feet six inches from you, and 
 so arranged that it may take in a picture which will ahout half fill it, and be about 
 eight or nine feet in your rear. This will appear to be exactly in the centre of the mir- 
 ror, as in Fig. 101. Now, although we are looking at the picture, 
 we are also conscious that the looking-glass is there, and that 
 wo can see the frame. Having satisfied ourselves of this, we 
 next proceed to prove that one eye sees more than the other. For 
 instance, shut the right eye— still looking at the picture — and if 
 we see more with the left than the right, the picture will re- 
 main in its original position ; hut if wo habitually see more 
 ■with the right than with the lofL, then the picture will immediately change over 
 so to speak, and appear as in Fig. 101. This fact proves, in the first instance, that we 
 cannot see more than one object at once ; for although we 
 were conscious of the existence of the frame of the mirror, 
 we could not see it distinctly. And it proves, secondly, that 
 we see more with one eye than the other, or the picture 
 would not change its position in the mirror by shutting or 
 opening the eyes ; and thus we have A (Fig. 103), the left 
 eye, and what it sees ; B, the right eye, and what it sees ; C being the picture. 
 
 It must be recollected, that the picture being apparently so far behind the mirror, 
 
 the latter only intersects the rays pro- 
 ceeding to the eyes, as if it were a 
 plain piece of glass through which we 
 were looking at the picture (Fig. 104). 
 
 The fact of the rays from the eyes 
 meeting, or hein^ focussed on an object 
 at a certian distance, and only on that 
 object at the time, may be further 
 proved by the following experi- 
 ments : — 
 
 Experiment Qth. — Place a lighted 
 candle about two feet from you, and 
 hold a pencil half the distance he- 
 tween, and in the centre of the eyes 
 (Fig. 105). Now keep all steady and 
 look at C (the pencil) and you will 
 see two candles, one on each side ; then 
 look at the candle and you will see two pencils, one on each side. In the former case 
 the pencil will be lighted on each 
 side ; and in the latter case the ^ 
 two pencils will be lighted on a 
 the inside of each. 
 
 The following diagrams will 
 explain this more fuUy. When | 
 looking at the pencil we see, by 
 opening and shutting each eye 
 alternately, the object looked at 
 distinctly, and the other indistinctly, but still we see it ; therefore, when looking at Ithe 
 
 Fig. 104. 
 
BINOCULAR PHENOMENA. 
 
 189 
 
 pencil with the left eye, or A, we see it and the candle as in Fig. 106, and with the 
 right eye as in Fig. 107. 
 
 At first, from looking at these diagrams, one would think that we saw the pencil at 
 C when looking with both eyes ; and . 
 were also conscious of one candle at -^^ 
 D, as Fig. 107 would lead us to sup- ^-^ 
 pose. Here we see Figs. 106 and 107 
 united (Fig. 108), and would naturally ^ ^ 
 
 imagine that we would only see one ^^^^ 
 candle and one pencil ; but the re- 
 verse is the fact, for as one eye is not able to judge of distance, and both are 
 
 focussed on the pencil at C, they 
 ? are each conscious of a candle 
 
 P D Itfi F behind C, and naturally bring- 
 
 \ / \ ing the second object into the 
 
 • \ / \ plane of focus, or nearly so (Figs. 
 
 / \ / \ 109, 110). 
 
 The same result occurs in a 
 reverse way when we look at 
 the candle instead of the pencil ; 
 but, in this case, the rays cross 
 each other, throwing the pen- 
 cil back apparently with the 
 candle. But, in the latter case, 
 ■pig^ 106. Fig. 107. I' ig- the left eye, or A, sees the candle 
 
 and pencil as in Fig, 111 ; and the right eye, or B, as in Fig. 112. 
 
 In all the nreceding diagrams, the solid lines represent the line of sight, and the 
 dotted ones the line of light of the figure of the presence of which we are conscious. 
 
 c9 
 
 Fig. 112. 
 
 The foregoing facts will prove, satisfactorily I hope, that without two eyes we 
 
190 
 
 THE STEREOSCOPE. 
 
 cannot form a correct judgment of distance, and in the same manner of size, form, &c. 
 The next subject will therefore be, how do we take advantage of this fact in photo- 
 graphy ? We do it simply thus : We consider that a picture or portrait taken by owe 
 lens and one camera is exactly in the position of a similar one looked at by one eye ; 
 and, to obtain the manifest advantages derived from the use of two eyes, we either 
 employ two cameras and two lenses at certain angles apart, or we take the same view 
 or portrait twice, each taken from a different angle. The former method, for many 
 reasons, is decidedly to be preferred. 
 
 The pau' of stereoscopic pictures will convey to the mind of the observer [by means of 
 a properly constructed instrumint) all the effects obtained by the use of two eyes ; that is to 
 say, the picture which nature would present to the left eye is seen by the left eye, and 
 that to the right by the right. We therefore observe, when viewing a stereoscopic 
 picture in a stereoscope, that the figures, houses, trees, &c., are perfectly correct as to 
 size, natural position, and relative distance from each other. This fact is so well 
 known, and truly wonderful, that it need not be repeated. 
 
 The next subject for consideration will be — 
 
 The Stesreoscope.— The almost magical effect of two plain flat pictures viewed in 
 the stereoscope is so vivid, when seen for the first time, that the result seems to be a de- 
 ception of the imagination; in fact, we are incUncd to remove the stereoscope and see for 
 ourselves, somewhat like the Indian who went to look behind the looking-glass for the 
 image he saw reflected on its surface. And even when we become accustomed to the 
 use of the instrument we always take a pleasure in looking at the views we may have 
 often seen before; in fact, every object seems to stand out with all the solidity of 
 nature ; and in some cases, where the ealotype has been properly coloured, the effect, 
 especially in portraiture, is perfectly marvellous. 
 
 In the stereoscope, then, we have the most interesting optical instrument ever dis- 
 covered, reproducing, as it were, in all the reality of nature, the favourite scenes of 
 youth or the semblance of some beloved friend who is gone, perhaps, alas ! for ever. 
 
 The most simple, most portable, and, I may say, the most correct in principle, is 
 that invented bj^ Sir David Brewster. 
 
 This instrument consists of two semi-lenses, placed at such a distance that each eye 
 views the picture or drawing opposite to it, through the margin of the semi-lens, or through 
 parts of it equi-distant from the margin (Fig. 113). A lens, A A', being cut in two halves, 
 
 these are fixed into a frame, Land 
 L, and adjusted to such distances 
 that the centres of the semi- 
 lenses correspond with the pupil 
 of the eyes. The distance of the 
 centre of one pupil from the other 
 is at an average of two inches 
 and a half, and to this the serai- 
 lenses may be adjusted; but if 
 the instrument is provided with the means of effecting a little change in this respect, it 
 will often bo found to be of considerable advantage. 
 
 Sir David Brewster says, " AVhen wc thus view two dissimilar drawings of a solid 
 object, as it is seen by each eye separately, we are actuolly looking through two prisms, 
 which produce a second image of each draM'ing ; and when these second images unite, 
 or coalesce, we see the solid image which they represent. But in order that the tmo 
 
 riff. 113. 
 
THE STEREOSCOPE, 
 
 191 
 
 Fis-. 114. 
 
 images may coalesce, without any effort'or strain on the part of the eye, it is necessary 
 that the distance of the similar parts of the two drawings be equal to twice the separa- 
 tion produced by the prism. 
 For this purpose measure the 
 distance at which th.e semi-lenses 
 give the most distinct view of 
 the drawings; and having as- 
 certained, by using one eye, the 
 amount of the refraction pro- 
 duced' at that distance, or the 
 
 quantity by whicb the image 
 
 of one of the drawings is displaced, place the drawings at a 
 distance equal to twice that quantity ; that is, place the 
 drawings so that the average distance of similar parts in 
 each is equal to twice that quantity. If this is not correctly 
 done, the eye of the observer will correct the error by 
 making the images coalesce without being sensible that it 
 is making any such, effort. When the dissimilar draw- 
 ings are thus united, the solid will appear standing, as 
 it were, in relief, between the two plane representations." 
 The annexed are front and sectional views of the ordi- 
 nary stereoscope constructed on Sir David's 
 plan (Figs. 114, 115, 116). 
 
 Mr. Wheatstone has invented an arrange- 
 ment which enables us to view larger pic- 
 tures than we could possibly do in the above. 
 It is called the "reflecting stereoscope," to 
 distinguish it from the lenticular stereoscope, 
 just described. 
 
 Two plain mirrors are fixed on a centre 
 support capable of adjustment (Fig. 116.), which 
 is fixed on a mahogany frame into which slide 
 the two arms for holding the pictures. These 
 arms have each adjustments in all directions, 
 so as to bring the two pictures exactly coin- 
 cident when viewed through the lenses placed 
 in front of the mirrors. These lenses are not 
 essential to the action of the instrument, but 
 In very perfect instruments, 
 
 the mirrors are replaced by two polished prisms of glass. 
 
 In these stereoscopes the prints must be reversed as they are placed in the drawing, 
 the left-hand one should be the view seen by the right eye in nature, as they are 
 reversed again by being reflected in the mirrors. 
 
 There are many rules given for the distance the two cameras should be apart for 
 taking views, &c. ; but the reader need not take any trouble about them. The best 
 stereoscopic views ever taken were taken with the two cameras close together. The 
 chief things to be attended to are, that the cameras should be perfectly level, the same 
 heig ht, and that some object in the vieiv sho^lld come exactly in the centre of each ground- 
 
 Fig. 115. 
 
 add much to the facility of use and beauty of effect. 
 
•192 
 
 THE STEREOSCOPIC CAMERA. 
 
 glass. The latter should be lined (Fig. 118), in order that the amateur may at once 
 be able to do so : — 
 
 I need scarcely add that 
 the focus should be perfect 
 in both, and the focal length 
 of the lenses the same. 
 When only one camera is 
 used, it will be necessary 
 to remove it about twelve or 
 fourteen inches, and take 
 care that the same object 
 comes in the centre of the 
 focussmg-glass in each case, 
 and that the camera is placed 
 
 (Fig. 117.) 
 
 perfectly horizontal and at the same height when moved. 
 
 Mr. Latimer Clark has published, 
 in the " London Photographic Jour 
 nal," a very ingenious arrangement 
 for taking stereoscopic pictures with 
 a single camera. 
 
 The principle and method of 
 working cannot be better explained 
 than by a reference to his own 
 words . — 
 
 Fig. 118. 
 
 " The camera frame, or plate-holder, contains a narrow dark chamber, of the 
 usual construction, capable of receiving a glass plate about 6| inches by 3i inches. We 
 will call this portion the slide ; it slides to and fro freely within the frame through a 
 space of 2~ inches, or 2f , which is about the distance between the eyes. To admit of 
 this, the frame must necessarily be 10 or 11 inches long, and it therefore requires some 
 simple adaptation to fit it to the end of an ordinary-sized camera. In the front of the 
 frame is an aperture about 2a inches square, closed by a sliding door, and capable of 
 being contracted by an oval or other shaped diaphragm, which determines the size and 
 form of the two pictures impressed on the plate, and which may be varied at pleasure. 
 The distance between the two pictures is determined by the lateral motion of the slide, 
 viz., 2f inches, as stated before. After one of the two images has been impressed, 
 the slide has to be shifted laterally at the same instant, and in the same direction as 
 tlie camera itself, by means which I will presently describe. The second image is then 
 taken, and the frame removed. 
 
 " In the foregoing contrivance it is necessary to obtain the focus by a separate 
 glass ; but in the Daguen-eotype arrangement the focussing-glass forms part of the 
 apparatus ; the slide is here in three pieces : the centre piece is the focussing-glass, 
 which, being hinged at the bottom, does not slide, but falls back out of the way. The 
 two side pieces (each of which is a perfect dark chamber, containing a sensitive 
 plate) are now in a position to be drawn successively into the field of vievr opposite the 
 front aperture, and the images impressed. This makes a very compact arrangement, 
 and requires no door in front of the frame, the plates being exposed to light only when 
 brought opposite to the central opening (Fig. 11 9). 
 
 " We now come to the means employed to guide the camera in its lateral movement, 
 
THE STEREOSCOPIC CAMERA. 
 
 the object being all the while retained in focus. A strongly-framed camera-stand 
 carries a flat table about twenty inches wide by sixteen, furnished with the usual 
 adjustments. 
 
 Upon this are laid two flat bars of wood, in the direction of the object and parallel, 
 and about the width of the camera asunder ; they are eighteen inches in length ; their 
 
 Fig. 119. 
 
 front ends carry stout pins, which descend into the table, and form centres upon which 
 they turn ; their opposite ends also carry similar pins, but these are directed upwards, 
 and fit into two corresponding holes in the tail-board of the camera. Now when the 
 camera is placed upon these pins, and moved to and fro laterally, the whole system 
 exactly resembles the common parallel 
 ruler ; the two bars form the guides, and 
 the camera, although capable of free lateral 
 motion, always maintains a parallel position. 
 In this condition of things, it is only suited 
 to take stereoscopic pictures of an object at 
 an infinite distance ; but to make it move 
 in an arc, converging on any object at 
 any nearer distance, it is only necessary to 
 make the two guide-bars approximate at 
 their nearer end so as to converge slightly 
 towards the object ; and by a few trials some 
 degree of convergence will be readily found 
 at which the image will remain, as it were, 
 fixed on the focussing-glass, while the 
 camera is moved to and fro ; to admit of this 
 adjustment, one of the pins descends through a slot in the table," and carries a clamp- 
 ing-screw, by means of which it is readily fixed in any required position.fi In ordei', 
 however, to render the motion of the camera smoother, it is advisable not to place it 
 directly upon the two guides, but to interpose two thin strips of wood lying across 
 them at right angles beneath the front and back of the camera respectively (and which 
 
 Fig. 120. 
 
19i 
 
 THE STEllEOSCOPIC CAMERA. 
 
 may be fixed to the camera, if preferred), aud to dust the surfaces with powdered soap- 
 stone or French chalk, 
 i " Lastly, it is necessary that the slide should be shifted laterally at the same 
 instant as the camera. The means used for this are simple, and consist only of a pulley 
 fixed to the right-hand side of the camera, round which passes a string which is tem- 
 porarily attached to the slide, the other end being fixed to the left-hand side of the 
 table. When the camera is drawn to the left hand, this string is long enough to allow 
 the slide to be drawn to the left hand also ; but when the camera is moved to the 
 right, the re-actijn of the string draws the slide also over in the same direction, the 
 variations in adjustment being compensated by the intervention of an elastic band. 
 " The operation of taking a portrait is therefore thus performed. The focus having 
 
 been adjusted for both 
 positions, and the camera 
 and the slide both drawn l 
 to the left hand, the door 
 is raised and the plate 
 exposed — say, for five se- 
 conds — by one motion of 
 the hand ; the camera is 
 then shifted to the right 
 hand, the slide moving at 
 the same time spontane- 
 ously ; this occupies less 
 than a second of time ; 
 
 rig. 121. and the plate in its new 
 
 position having been exposed five seconds longer, the door is closed, and the operation 
 completed — the whole sitting having been supposed to occupy eleven seconds." 
 
 The following practical observations by Mr. G. S. Wood will conclude this portion 
 of the present treatise : — 
 
 " In the first place, let us ask what it is we have to effect in stereoscopic views It is 
 simply this — -to form upon paper, or glass, or silver (according to the process we may be 
 pursuing), two pictures of the object or objects precisely analagous to those which would 
 be produced on the retinas of the eyes, were we viewing that object or those objects 
 by direct unassisted vision ; and the characteristics of those pictures severally should 
 be, that the parts or objects composing such pictures should occupy different relative 
 positions, because, when viewing them in nature, we do so under different angles, or, j 
 in other words, that lines drawn from the object or objects under consideration to | 
 either eye severally, would form different angles. And it is from the impression which 
 is produced by what may be called the unity of these two pictures (doubtless) in the 
 brain, that we at once have the sensation of rotundity or depth and thickness. And I 
 here I would remind those who may not bo very conversant with the laws of vision, 
 that the above remark may be easily proved by viewing an object or landscape with 
 one eye only ; for then all sensation of depth, space, and thickness vanishes ; but upon 
 opening the secondeye everything stands out in its proper proportions. And I would also 
 observe that the stereoscope has not, strictly speaking, anything to do with producing 
 those impressions of which we have been speaking, but, as we have before stated, the 
 relative positions of the objects viewed by the two eyes severally. The only use of 
 the optical part of the instrument in question is, that by the aid of half lenses placed 
 
KULES FOR PRODUCING STEREOSCOPIC PICTURES. 195 ■ 
 
 in a certain position, we may cause an extraordinary and oblique refraction of the 
 images of the two pictures viewed, in order that they may be produced on those 
 several parts of the retinas, which it should be borne in mind is indispensable in order 
 to give distinct single vision. 
 
 " What has to be done, then, in taking these pictures is this : — After having decided 
 upon the position whence our first view is to be taken, to notice, by a contrivance 
 hereafter to be mentioned, the amount of displacement, so to speak, which the objects 
 composing the view undergo when viewed by either eye singly : of course, keeping the 
 head stationary during the observation, and moving the camera either to right or left 
 (as the case may be), to such an amount that the objects composing the picture, pro- 
 duced on the focussing-glass, shall occupy exactly the same relative positions as the 
 objects themselves did when viewed with each eye singly, as before mentioned. 
 
 " And thus, after having stated the broad principles to be observed, I now come to 
 what may more immediately be called tlie modus operandi of the whole aifair. 
 
 " After having placed my camera — I say camera, for I prefer only one— in a chosen 
 position to take the first view, I place a piece of small wire, or a nail will answer all 
 the purpose, in an orifice made to receive it at the top of the frame of the focusing- 
 glass, so that it may project an inch or two above the frame ; and having furnished 
 myself with a staif or stick about five feet long, I force this into the ground about six 
 inches or more from the front of the camera, and as near the centre as possible, without 
 the light entering the lens being interfered with. "We will suppose the principal 
 portion of the view to be made up of a dwelling-house, I place, say the right eye ; ' 
 about an inch or so from the wire on the top of the frame before mentioned, and 
 closing the left, I now move the head to such a position that the wire and stafi" may 
 cut each other, or, in other words, that these two and the eye may be in a line, and 
 notice carefully the part of the landscape whereon these conjointly fall ; and we mav | 
 for illustration sake say, that they are produced on the central bar of the left-hand ! 
 window of the house. I then, without moving the head, open the left eye and close ! 
 the right, and I now find that the staff has apparently altered its relative position ■ 
 it now is produced, say on the extreme right-hand corner of the house itself Having ' 
 made these observations, I next note the particular part of the landscape falling upon ' 
 the centre of the ground-glass, and we will suppose this to be the right-hand side of j 
 the doorway of the house. I now proceed to take my first picture. Having done ! 
 this, I move the camera so much to the left that the wire on the top of the camera j 
 and the staff, and the right-hand corner of the house, may cut each other (as the two j 
 first-mentioned and the bar of the window did in the first observation), at the same i 
 time observing that the right-hand corner of the doorway occupies the same psition 1 
 on the ground-glass as it did previous to taking the first picture. I need hardly add, ' 
 that in either position the camera should be, as near as can be seen by the eye, at the 
 same level. 
 
 " It will at once be seen that it takes infinitely longer to describe the course of pro- ' 
 ccdure than the actually working it out ; for the apparatus might be placed in its two 
 positions, and the views taken, all within the space of a few minutes. 
 
 I may add, in conclusion, that where these rules are observed in taking stereoscopic 
 pictures, of whatever character the view itself may partake, or however distant some I 
 of the objects composing such view may bo, they wil], when viewed through a stereo- j 
 scope, convey to the mind impressions precisely corresponding to nature. | 
 
 Mr. Hardwich gives the following useful hints to the amateur wishing to study I 
 
196 
 
 STEREOSCOPIC PICTURES OF MICROSCOPIC OBJECTS. 
 
 the photographic delineation of microscopic objects, for -which he acknowledges him- 
 self indebted to the personal kindness of Mr. Joseph Delves, of Tunbridge ; as he does also 
 j to Mr. Shadbolt, for obligingly demonstrating his mode of -working -with artificial light. 
 
 Some of the specimens of micro-photography -which have been exhibited are exceed- 
 1 ingly elaborate and beautiful ; and their production is not difficult to one thoroughly 
 j acquainted -with the use of the microscope, and with the manipulations of the collodion 
 I process. It is important, however, to possess a good apparatus, and to have it properly 
 I arranged. 
 
 The object-glass of the ordinary compound microscope is the only part actually 
 i required in photography, but it is useful to retain the body for the sake of the adjust- 
 j ments, and the mirrors used in the illumination. The eye-piece, however, which simply 
 I magnifies the image formed by the object-glass, is not necessary, since the same effect 
 of enlargement may be obtained by lengthening out the dark chamber, and th^iowing 
 the image further off. 
 
 Arrangement of the Apparatus. — The microscope is placed with its body in a hori- 
 zontal position, and the eye-piece being removed, a tube of paper, properly blackened 
 in the interior, or lined with black velvet, is inserted into the instrument, to prevent 
 irregular reflection of light from the sides. 
 
 A dark chamber of about two feet in length, having at one end an aperture for the 
 insertion of the eye-piece end of the body, and at the other a groove for carrying the 
 slide containing the sensitive plate, is then attached ; care being .taken to stop all 
 crevices likely to admit diffused light. An ordinary camera may be employed as the 
 dark chamber, the lens being removed, and the body lengthened out, if required, by a 
 conical tube of gutta-percha, made to fasten into the flange of the lens in front. The 
 whole apparatus should be placed exactly in a straight line, that the ground-glass used 
 in focussing may fall at right angles to the axis of the microscope. 
 
 The length of the chamber, measuring from the object-glass, may be from two to 
 three feet, according to the size of image required ; but if extended beyond this, the 
 \ pencil of light transmitted by the object-glass is diffused over too large a surface, and 
 a faint and unsatisfactory picture is the result. The object should be illuminated by 
 sunlight, if it can be obtained, but a bright diffused daylight will succeed with low- 
 power glasses, and especially when only positives are taken. Employ the concave 
 mirror for reflecting the light on the object in the latter case, but in the former the 
 plane mirror is the best, except with powers exceeding a quarter of an inch, and of 
 large angular aperture. 
 
 The image upon the gi-ound-glass should appear bright and distinct, and the field of 
 a circular form evenly illuminated ; when this is the case, all is ready for inserting the 
 sensitive plate. 
 
 The time of exposure must be varied according to the intensity of the light, the 
 sensibility of the collodion, and the degree of magnifying power ; a few seconds to a 
 minute will be about the extremes ; but minute directions are not required, as the 
 
 I operator, if a good photographer, will easily ascertain the proper time for exposing. 
 
 j At this point a difficulty will probably occur from the plane of the chemical focus 
 not corresponding, as a rule, with that of the visual focus. This arises from the fact 
 that the object-glasses of microscopes are "over corrected" for colour, in order to com- 
 pensate for a little chromatic aberration in the eye-piece. The violet rays, in consequence 
 of the over-correction, are projected beyond the yellow, and hence the focus of cliemical 
 action is further from the glass than the visible image. 
 
IMPERFECTLY DEVELOPED PROCESSES. 
 
 197 
 
 The allowance may be made by shifting the sensitive plate, or, -what amounts to 
 the same thing, by removing the object-glass a little away from the object with a fine 
 adjustment screw, the latter is the most convenient. The exact distance must be 
 determined by careful experiment for each glass ; but it is greatest with the low powers, 
 and decreases as they ascend. 
 
 Mr. Shadbolt gives the following as a guide: — "An inch and a half objective of 
 Smith and Beck's make, required to be shifted -Jg of an inch, or two turns of their fine 
 adjustment ; a | of an inch, of an inch or half a turn ; and a of an inch, -j-^^j^ 
 of an inch or about two divisions of the adjustment. With the \ and higher powers, 
 the difference between the foci was so small as to be practically unimportant." 
 
 There is also reason to think that the kind of light employed has an influence upon 
 the separation of the foci. Mr. Delves finds that with sunlight the difference between 
 them is very small even with the low powers, and inappreciable with the higher ; where- 
 as in using diffused day -light, which has undergone a previous reflection from white 
 clouds, it is considerable. 
 
 The object glasses of tlie same maker, and particularly those of different makers, 
 also vary much ; so that it vrill be necessary to test each glass separately, and to register 
 the allowance which is required. 
 
 Having found the chemical focus, the principal difliculty has been overcome, and 
 the remaining steps are the same in every respect as for ordinary collodion photographs. 
 
 IMPEEFECTLY DEVELOPED PKOCESSES. 
 
 In the preceding pages we have traced the history, step by step, of this wonderful 
 art, through its various stages of Daguerreotype, Calotype, AVaxed and Albuminized 
 Paper, and, finally, to the simple and almost perfect Collodion Process. Nevertheless, 
 it must be admitted that numerous indications present themselves, proving that it is yet 
 in its infancy. In this section, therefore, it is proposed to treat of those branches of 
 j the subject which are only imperfectly developed, but which are too important to be 
 altogether overlooked. Among these the most remarkable are the results of certain 
 experiments for producing images, with their natural colours, by jAotogenic action. 
 "While numerous experiments have been conducted having this object in view, the 
 American photographers seem to have come closest upon the great desideratum ; and 
 the name Hillotype has been given to the process, in honour of the discoverer, Mr. 
 Hill, of West Hill, in the state of New York. 
 
 Mr. Hill states that he had undertaken a series of experiments with the object of 
 procuring coloured photographs, but for a long time with little prospect of success ; 
 but in one of his experiments certain phenomena presented themselves which greatly 
 surprised him, and persuaded him that the object was attainable. One colour — red — 
 in the figure of a vestment, developed itself in the most brilliant ruby colour ; he 
 repeated his experiment many times, but without meeting again the same result, 
 from which he concluded that all the circumstances were not present. Believing, how- 
 ever, that in certain circumstances the latent colour of the image was present, he 
 proceeded with his experiments, and found that the vapour arising from many metals, 
 such as arsenic, cadmium, zinc, selenium, bismuth, potassium, and sodium, possessed 
 the power of developing latent images with their lights and shades. The same result 
 
198 PHOTOGRAFHS IN NATURAL COLOUR. i 
 
 was obtained with different gases, but the images differed little from the usual results ; 
 and he was on the point of abandoning the pursuit, despairing of success. 
 
 His joy was, therefore, great when ho observed one day that his plate presented a 
 perfect impression in colours. He has followed the same experiment with varying 
 results ; but in January, 1851, he obtained forty-five designs, which presented all the 
 different colours and with perfect gradations, the objects represented surpassing the 
 richest Daguerreotypes. These pictures are durable, and soft in their aspect; no doubts 
 are expressed of their permanency, and it is stated that the light does not act upon 
 them. Mr. Hill has not described his process further than that it neither resembles 
 that of M. Daguerre, nor M. Eecqr.erel. Another process, which is quicker in its ope- , 
 ration, is mentioned, but without details, except that the yellow coloui- is that he has i 
 the greatest difhculty with. 
 
 Sir John Herschel had his attention drawn to this subject so early as 1840. " I 
 got," he says, " some specimens of paper long heiit, which gave a representation of the 
 spectrum in its natural colours, and that light on a dark ground ; but at present I am 
 not prepared to say that they will prove an available process for coloured photographs, 
 though it brings the hope nearer." 
 
 M. Biot thinks there are difficulties inherent in photographic pictures, which 
 shoAV that the hopes of the experimenters, who expect to discover the tints of chemical 
 impressions produced by radiation in their natural colours, are illusory. 
 
 Mr. Eobert Hunt's experiments have, in many instances, given him coloured pictures 
 of the prismatic spectrum dark upon a light ground ; but the most beautiful has been 
 obtained upon the Daguerreotype iodized tablets, on Avhich the colours have at the 
 same time had a peculiar softness and brilliancy. Again, during January, 1854, ho 
 prepared some paper with the bichromate of potash and a very Aveak solution of 
 nitrate of silver, which he exposed behind four coloured glasses, which admitted the 
 passing— 1st, of violet, indigo, and blue rays ; 2nd, of blue, green, and a portion of 
 yellow rays; 3rd, of green, yellow, and orange rays; and 4th, of orange and red 
 rays. Being allowed to lie for two days— extremely foggy days — opposite a window 
 baving a southern aspect, it was found on examination that the paper had become 
 tinted of a blue, green, and red ; beneath the yellow glass the change was uncertain, 
 from the peculiar colour of the paper. All this took place without a single gleam of 
 sunshine. This and some other experiments proved to his satisfaction, that the possi- 
 bility admitted by Sir John Herschel amounted to a probability. 
 
 M. Becquerel has succeeded in obtaining bright impressions of the spectrum in 
 colours, and in copying highly-coloured drawings on metallic plates prepared with 
 chlorine ; and M. Niepce de St. Victor observed that chloride of sodium was employed 
 upon a silver plate plunged into a solution of sulphate of copper, and the plate became 
 more susceptible of receiving a yellow colour tban any other. 
 
 Looking at these results, and assuming that Mr. Hill's statements are trustworthy^ 
 it seems probable that means will be found for producing coloured images both on 
 silvered i^lates and on paper. 
 
 Photogiaphy Applied to lithography. — Some very important applications 
 of the art to engraving on steel and lithographic stone are also named. Among these 
 we may quote the process of Mr. Macpherson, of Rome, as communicated by Mr. 
 Ramsay to the British Association. Mr. Macpherson had succeeded in obtaining beau- 
 tiful photo-lithographs, specimens of which had been hung up in the Photographic 
 Institution in Buchanan Street, Glasgow. The steps of tbe process are as follows : — 
 
PHOTOGRAPHY APPLIED TO LITHOGRAPHY. 
 
 199 
 
 1. Bitumen is dissolved in sulphuric ether, and the solution is poured on an 
 ordinary lithographic stone. The ether quickly evaporates, and leaves a thin coating 
 of bitumen spread uniformly over the stone. This coating is sensitive to light — a 
 discovery made originally by M. Niepce, of Chalons. 
 
 2. A negative on glass or waxed-paper is applied to tKe sensitive coating of 
 bitumen, and exposed to the full rays of the sun for a period longer or shorter, 
 according to the intensity of the light, and a faint impression on the bitumen is thus 
 obtained. 
 
 3. The stone is now placed in a bath of sulphuric ether, which almost instanta- 
 neously dissolves the bitumen, which has not been acted on by the light, leaving a 
 delicate picture on the stone, composed of bitumen on which the light has fallen. 
 
 4. The stone, after being carefully washed, may be at once placed in the hands of 
 the lithographer, who is to treat it in the ordinary manner with gum and acid ; after 
 which proofs may be thrown off by the usual process. 
 
 Professor Eamsay then proceeded to state that the above process, modified, had 
 been employed with success to etch plates of steel or copper, without the use of the 
 burin: — 1. The metal plate is prepared with a coating of bitumen, precisely in the 
 manner noticed above. 2. A positive picture on glass or paper is then applied to the 
 bitumen, and an impression is obtained by exposure to light. 3. The plate is placed 
 ill a bath of ether, and the bitumen not acted upon by the light is dissolved out ; a 
 beautiful negative remains on the plate. 4. The plate is now to be plunged into a 
 galvano-plastic bath, and gilded ; the gold adheres to the bare metal, but refuses to 
 attach itself to the bitumen. 5. The bitumen is now removed entirely by the action 
 of spirits and gentle heat ; the lines of the negative picture are now represented in 
 bare steel or copper, the rest of the plate being covered by a coating of gold. 6. Nitric 
 acid is now applied as in the common etching process ; the acid attacks the lines of 
 the picture formed by the bare metal, but wiU not bite into the gilded surface, A 
 perfect etching is thus said to be obtained. 
 
 Application of Photogiraphy to Astronomy. — The Eoman astronomers state 
 that they have procured photographic impressions of the nebula of the sword of Orion ; 
 and Mr. Brooke has invented an apparatus intended for the self-registration of the 
 vertical and horizontal oscillations of the magnet, and the various readings of the 
 barometer and thermometer throughout the day and night, by means of artificial light 
 and photographic paper. This is a very useful and important application of photography 
 to self-registering purposes, and has been found to give perfectly accurate results, and, 
 of course, much more complete than the former system of hourly observations, to make 
 which an assistant had to sit up throughout the night. This invention is altogether 
 due to Mr. Brookes. 
 
 The only other application which has hitherto been made of photography to astrono- 
 mical purposes, so far as we are aware, has been in taking Daguerreotype images of the 
 moon and the solar spots. In the former case, the ordinary preparation of the silvered 
 plate and glass, as used in the Daguerreotype and Collodion processes for taking portraits, 
 is quite delicate enough. A very beautiful image of the moon, when about half-full 
 1ms been taken in this manner with the great telescope of twenty-three feet focal length 
 and fifteen inches aperture, at Cambridge in the United States. It was taken by Mr. 
 Bond and was four or five inches in diameter. It has likewise been attempted with the 
 great equatorial at the Cambridge Observatory, but the clock motion, for keeping the 
 telescope pointed to the same part of the heavens, has not yet been found steady enough 
 
200 
 
 PHOTOGKAPHS FROM ARTIFICIAL LIGHT. 
 
 for that purpose, and the photographs obtained have heen imperfect. In taking them, 
 the image given by the object-glass alone (without any intermediate lenses) has been 
 received on the plate. 
 
 In the case of the solar spots, any ordinary photographic paper is, of course, quite 
 delicate enough. In many observatories an image of the sun's disc has been taken from 
 time to time in this manner. 
 
 An image of a douUe star has likewise been taken, but the other remarkable sidereal 
 objects, as nebulee, clusters, &c., shine with too faint a light to be registered by the 
 most delicate preparation of the plate yet known. It has hitherto failed altogether 
 with Lord Rosse's gigantic reflector, though an image of the moon taken by this 
 instrument would be of great value. 
 
 Photographs from Electric Light— It was at one time assumed that artificial 
 light possessed no chemical rays ; but Mr. Brande set aside this notion, having dis- 
 covered that although the concentrated light of the moon, or even the light of olefiant 
 gas, composed of equal parts of carbon and hydrogen in its most intense form, had no 
 eff'ect on chloride of silver or on chloride and hydrogen. Yet the light emitted hy 
 electrized charcoal blackens the salt, while pictures have been taken upon sensitized 
 paper by means of the electric light. For portraits this process is rendered difficult hy 
 the intensity of the light affecting the sitter's sight ; hut for microscopic objects, and 
 especially with the oxyhydrogen microscope, it has been more successful. A corres- 
 pondent, who pursued these investigations with great success, thus explains him- 
 self:—" The object of my experiments was to obtain good photographs of microscopic 
 objects, and having the opportunity of employing Mr. Haite's electric light, I did so 
 with very satisfactory results. I also succeeded in obtaining one or two portraits by it, 
 but the latter were marked by great severity of shadow, even when the light was pain- 
 fully intense and unpleasantly hot. I concluded therefore that the amount of actinic 
 ray was but small in comparison with the luminous character of the light; the calorific 
 rays were, however, abundant. The same disproportion I have observed with respect 
 to the Drummond light and with gas. While the direct rays are actinic, artificial light 
 does not appear to have the same radiating power on the atmosphere which we observe 
 in solar light, and which produces the fine illumination of objects in partial or com- 
 plete shadow. This deficiency, I believe, I have observed in some states of the atmos- 
 phere in daytime, when, with a comparatively strong light, actinic effects have been 
 feeble, and particularly deficient in the radiant quality." 
 
 To those who cannot devote their time to photography during the day, Mr. Shad- 
 bolt's observation on the use of artificial light may be of service. He employs campliine, 
 which appears to give a whiter flame than either gas or the moderator lamp ; placing 
 the source of light in the focus of a plano-convex lens of two and a half to three inches 
 diameter (the flat side towards the lamp), and condensing the parallel rays, so obtained, 
 on the object, by a second lens of about an inch and a half diameter and three inch focus. 
 
 This mode of illumination, being feeble as regards chemical rays, is best adapted for 
 object-glasses of low power. The exposure required to produce a negative impression 
 with the one-inch glass may be from three to five minutes. The development is con- 
 ducted in the ordinary manner. 
 
 Particular stress is laid upon the object-glass of the microscope being a good one 
 for the purpose ; and indeed all who have given attention to the subject are agreed 
 upon this point— that there is a considerable difference in the photographic value of 
 objectives, and this, too, independent of the angular aperture of the glass. 
 
PHOTOGRAPHS FROM THE OXYHYDROGliN MICROSCOPE. 20] 
 
 The Rev. W. Towler Kin gsley has communicated a process by which very beauti- 
 ful microscopic photographs have been obtained. He illuminates (in the absence of 
 sunlight) with the brilliant light produced by throwing a jet of mixed oxygen and 
 hydrogen gases upon a small cone of lime or magnesia. His process is as follows :— 
 
 It is not necessary to describe the method of making collodion. "With it a very 
 small quantity of iodide of silver, dissolved in iodide of potassium or in cyanide of 
 potassium, is mixed. This is now to be poured on a plate of glass, and the excess 
 poured off again, so as to leave a film of the preparation on the glass surface. The 
 plate is now to be plunged into a bath of nitrate of silver, 30 grains to the ounce of 
 water ; and as soon as the whole of the plate will retain the water without running 
 into streaks, the plate is to be exposed to the action of the light ; it is then to be 
 plunged into a bath of pyrogallic acid, 3 grains; water, 1 ounce; glacial acetic acid, 
 1 drachm. This deiodizing and deoxidizing bath develops the image ; the unreduced 
 iodide is then to be removed by hyposulphite of soda. This is the ordinary process, 
 and the method is simple and good. If we add to the collodion mixture a small quan- 
 tity of iodide or bromide of iron, and develop with protonitrate of iron, the process is 
 rendered much more energetic ; for we obtain on the plate, as soon as it goes into the 
 silver bath, nitrate of iron, which deiodizes the plate as soon as the light strikes it. I 
 do not find these preparations of iron to keep well, and therefore the preparation should 
 be made only a short time before it is to be used. Iodide and bromide of arsenic are 
 also admirable accelerators, and appear to keep for months without change ; with them 
 either the pyrogallic solution or protonitrate of iron may be used. I may here mention 
 that albumen, treated exactly the same as the collodion, only dried and heated after 
 being poured on the glass, acts just as well and as quickly. 
 
 I shall now describe the method of preparing the paper used. I prefer Canson's 
 paper. I have no doubt that many others are just as good. 
 
 It is used either waxed or not, with nearly the same results ; but the waxed paper 
 is the more easily managed, on account of its not becoming so tender from soaking. 
 The paper is first to be soaked for some hours in a bath composed as follows : — 
 
 Distilled water 1 pint. 
 
 Iodide of potassium ...... half an ounce. 
 
 Bromide of potassium ...... half a drachm. 
 
 Fluoride of potassium 1 drachm. 
 
 The whites of two eggs. 
 
 If this is done under the air-pump so much the bettor. The paper is now to be 
 hung up to dry, sheet by sheet; and so prepared it keeps well, certainly for months. 
 If arsenic be added, as in the collodion, the paper is more sensitive. "When it is 
 to be used, it is to be plunged into a bath composed as follows : — 
 
 Nitrate of silver 30 grains. 
 
 Acetic acid ....... ^ drachm. 
 
 Distilled water 1 ounce. 
 
 After the paper has become saturated in this bath, it is to be placed on a sheet of 
 pure blotting-paper, and that on a sheet of glass, to which it will adhere from the 
 superabundant fluid ; it is now to be exposed to the action of the light for the required 
 time, which of course depends upon the intensity of the light; with my microscope, 
 from two to five minutes is quite enough. It is then to be developed in a bath of 
 saturated gallic acid ; if the image does not seem dark enough in an hour, a few drops 
 
202 
 
 PHOTOGRAPHY APPLIED TO MICROSCOPIC OBJECTS. 
 
 of the silver bath should be added. Hyposulphite of soda, as usual, is the fixing 
 agent. The silver may be used over and over again, if it be filtered -with animal 
 charcoal after each time it is used, or as soon as it shows the least sign of becoming 
 discoloured. 
 
 In these processes we have the affinity for the iodine disturbed by the action of 
 the light; the developing agent carries this further, and the oxygen of the air or 
 vrater or acid, which has always a slightly greater affinity than iodine for silver, 
 combines with the liberated silver and produces the dark parts of the impression ; if the 
 action is carried still further we get the silver revived ; and in the collodion process 
 this produces a positive. To obtain these collodion positives, the quantity of silver in 
 the collodion should be small, and the exposure only for an instant; after the plate 
 is developed and fixed it should be put into a bath containing either aldehyde or 
 grape-sugar, which will revive the silver with great brilliancy. The paper pictures 
 may be developed by placing them in the mercury box ; but it is not to be recom- 
 mended. There is one use of the collodion which is of service. In the use of very 
 high powers with very delicate objects, it is not easy to see the image formed on the 
 vesculine screen, as described hereafter. When, therefore, an approximate focal dis- 
 tance has been obtained, a collodion positive on a small scale of a portion of the image 
 
 Fig. 122. 
 
 can be taken in a few moments, and so the correctness of the arrangements tried before 
 placing the paper in its place. 
 
 I shall now proceed to describe the instrument used. Sunlight is of course far 
 superior to any artificial light, when we can obtain it ; but as the sun will not shine 
 whenever we choose, it is of the greatest importance to construct the instrument for 
 artificial light, and then modify it so as to be applicable to sun light. The light I 
 use is the common oxyhydrogen light; magnesia or quartz may be substituted for 
 lime-ball with advantage. 
 
 The optical parts of the instrument divide themselves into four groups— the light- 
 collecting, the condensing, the objective and magnifying lenses. The first group (1), 
 for collecting the light, consists of three lenses; the first a meniscus of about three 
 inches focal length and two and a half diameter, the second plano-convex with the 
 radii of the surfaces one and six; the focal lengths of these two lenses being 
 respectively six and eight inches. 
 
 The second group, or condensing lenses (2), is a similar one turned the other wa)', 
 and on a reduced scale, to suit the different object-glasses ; between these two systems 
 there is a plano-convex placed at its focal length from the focus of the collectors, so 
 as to allow the rays to pass parallel to the condenser. This lens and the condensers 
 must be changed with tlio object-glasses; for it must be borne in mind that we have 
 
FORM OF OXY-HYDROGEN MICROSCOPE. 
 
 203 
 
 to arrange the instrumout so as to make the image of the lime-ball just cover the 
 paper to be acted upon; and if we diminish the focal lengths of the condensers at 
 the same time that we increase the magnifying power of the instrument, we shall 
 have just as great an amount of light with the highest as with the lowest powers. 
 
 The next group of lenses are those of the object-glass (3), which requires to be very 
 much -under corrected for visible colour, leaving strong red fringes. A very simple 
 ■way of making the object-glasses of an ordinary good microscope do for photographic 
 purposes is to have a new front lens made for them, so that they can be used for either 
 tlie ordinary or the photographic microscope. At this point of the arrangement we 
 have a very good form of the oxy-hydrogen microscope ; but it is a bad one for photo- 
 graphy, as we cannot have the screen on which the image is to be formed so near as to 
 enable us to use the slow motions of the various arrangements at the time we are look- 
 ing at the image, except for very low powers. 
 
 We now come to the last group , which occupies the place of the eye-piece of the 
 ordinary compound microscope. This group is a form of the Ramsden or positive eye- 
 piece, which ordinarily consists of two plano-convex lenses, placed at two-thirds their 
 focal length, which is the same in both, and with their plane sides out (4). This eye- 
 piece is not achromatic, being under corrected. The addition of a plano-concave Hint 
 lens to a double convex crown is used in the place of the lens next the object. This 
 enables me, by a slight change of distance, to make the correction perfect. 
 
 Fig. 123. 
 
 I have now only to describe the best way of using this instrument ; and here, it 
 must be remembered, that all depends upon the object-glass being good. It is very easy 
 to get one of small angle that will give very sharp outlines of objects, but we must not 
 be content with such images as these ; we must get object-glasses of large angular 
 aperture, made perfect for this purpose, so as to show the structure of objects, as well 
 as their outlines. This is quite feasible. Suppose, then, that we have got a perfect 
 instrument. 
 
 At the place of the focus of the object-glass place a screen of assculine, and a dark 
 blue glass between the collectors and condensers ; we shall now, " thanks to Professor 
 Stokes," see the chemical image ; and the correction for spherical aberration must now 
 be made in the ordinary manner. Now put in the eye-glass or magnifier, and the 
 gesculine at the screen, and adjust the focus. This focus will be found, even in the 
 case of chemically corrected lenses, beyond the visible ; but in the case of the ordi- 
 nary best object-glasses, the difference is enormous; for instance, in the case of a 
 very fine one-fifth in my possession, if I form an image of one foot from the eye- 
 glass, I find the chemical image ten feet further back; of course such a lens is of no 
 use for photography. 
 
 The aesculine also enables one to see at once when the light on the screen is the most 
 intense for chemical action. 
 
201 
 
 PHOTOGRAPHS OX WOOD. 
 
 In conclusion, I have to state that some of my specimens sent were taken upon a 
 disc of five feet diameter, which was illuminated equally; and therefore anything may 
 be taken on that scale on paper with artificial light, and I dare say on a very much larger 
 scale still. I look upon it, therefore, that we must give our chief attention to the cor- 
 rections of the lenses, as all the other parts of the process seem to require little further 
 than mere care in the use of common formulas. I have also to add, that the focal length 
 of the condenser being selected, in order to give the image of the incandescent spot of 
 lime on the right scale, its angular aperture should be a shade less than that of the 
 object-glass. 
 
 By this process, if a spot of tinfoil be placed on the condenser, we can get the object 
 bright on a dark ground ; and if an opaque object be placed in the focus of the col- 
 lecting lenses, and the object-glass and eye-piece be turned round to the front of the 
 object, a very good image may be got with low power. 
 
 Photographs on Wood — Among other applications of this art, we must not 
 omit to name it as an aid to the wood-engraver, to the extent of giving a perfectly 
 faithful tracing of the landscape or portrait which he proposes to engrave. At the 
 first page of our treatise we have given the negative and positive of a very charac- 
 teristic portrait traced on the wood by this process, and engraved without penciling 
 after it had been laid aside for nearly two years. It was supposed for a long time that \ 
 the chemical means required to make the wood sensitive to the actinic action would 
 destroy its fibre, and render engraving impossible ; but this is not the case. The cor- 
 respondent who kindly made these experiments for us thus explains himself. After 
 explaining the difiiculties experienced from imperfect apparatus, he says : 
 
 " I must tell you what I conceive I have achieved by this block, and point out the 
 probabilities of ultimate success. I have produced a positive picture without staining 
 the wood, and which is removable when the engraving is done, should that be 
 necessary. All, then, that remains to be done is to get a perfect negative, that will I 
 
 give a reverse image on the wood ; and this may be accomplished in this manner : 
 
 The cameras constructed for Daguerreotypes have a reversing prism, which gives a 
 correct image, and consequently would produce a correct negative; when this is 
 transferred to the wood, it would produce a reverse positive picture (the thing 
 wanted). I should wish to have this block engraved and printed, to make sure that 
 there is nothing on the wood itself to prevent or interfere with the printing process. 
 I am sure there is nothing to interfere with the engraver's art, as the scratch of a 
 pin reveals the white wood. I consider, that if the engraving and printing are suc- 
 cessful, the success of the other part is certain. There are a great many chances yet of 
 something else turning up ; but it would require a camera constructed on purpose, so as 
 to allow blocks of wood to be adjusted in it — no very diflficult problem. I can produce a 
 white picture on a black ground directly from the object; but I much fear that the 
 blackening of the wood would spoil the block for the engraver ; and also, I think thia 
 promises to answer every purpose." 
 
 Colouring Photographic Pictures.— Artificial colouring, whether applied to 
 Daguerreotype or photography, is by no means a happy idea. To colour them in a 
 satisfactory manner requires the talent of a first-class miniature painter ; and it need 
 not be stated that this can rarely be obtained. Nevertheless, some of our readers 
 may desire to try the experiment ; we transcribe here various colouring processes for 
 those so disposed. 
 
 Nearly, if not quite all the various colours used in painting mav be made from the j 
 
COLOURING PHOTOGRAPHS. 
 
 205 
 
 five primitive colours, black, white, blue, red, and yellow ; but for the Daguerrean 
 artist it would be the best policy to obtain such as are required by their art already 
 prepared. In a majority of cases, the following will be found sufficient, viz., carmine, 
 Prussian blue, white, chrome yellow, gamboge, for drapery; yellow ochre for the face, 
 or all three; light red; indigo; burnt sienna; bistre, or burnt umber. 
 
 If, in colouring any part of a lady's or gentleman's apparel, it is found necessary 
 to produce other tints and shades, the following combinations may be used:— 
 
 Orange— Mix yellow with red, making it darker or lighter by using more or less 
 
 red. 
 
 Purple — This is made with Prussian blue, or indigo and red. Carmine and Prussian 
 blue producing the richest coloiir, which may be deepened in the shadows by a slight 
 addition of indigo orbrown. 
 
 Oreens — Prussian blue and gamboge makes a very fine green, which may be varied 
 to suit the taste of the sitter or operator, by larger portions of either, or by adding 
 white, burnt sienna, indigo, and red, as the case may require. These combinations, 
 under diiferent modifications, give almost endless varieties of green. 
 
 Brown — May be made of different shades of umber, carmine and lamp-black. 
 
 Neutral tint — Is composed of indigo and lamp-black. 
 
 Crimson — Mix carmine and white, deepening the shaded parts of the picture with 
 addititional carmine. 
 
 Flesh colour— The: best representative of flesh colour is light red, brightened in the 
 more glowing or warmer parts with carmine, softened off in the lighter portions with 
 white, and shaded with purple and burnt sienna. 
 
 Lead colour — Mix indigo and white in proportions to suit. 
 
 Scarlet — Carmine and light red. 
 
 For jewelry — Cups of gold and silver preparations accompany each box for Da- 
 guerreotypists, or may be procured separately. 
 
 The method of laying colours on Daguerreotypes is one of considerable difficulty, 
 inasmuch as they are used in the form of perfectly dry impalpable powder. The rules 
 we shall give for colouring Daguerreotypes depend, and are founded, upon those 
 observed in miniature painting, and are intended more as hints to Daguerreotype artists 
 in hopes of leading them to attempt improvements, than as instructions wholly to be 
 observed. 
 
 The writer is confident that some compound or ingredient may yet be discovered 
 which, when mixed with the colours, will give a more delicate, pleasing, and natural 
 appearance to the picture than is derived from the present mode of laying them on, 
 which in his estimation is more like plastering than colouring. 
 
 In colouring Daguerreotypes, the principal shades of the head are to be made with 
 bistre mixed with burnt sienna, touching some places with a mixture of carmine and 
 indigo. The flesh tints are produced by the use of light red, deepened towards the 
 shaded parts with yellow ochre, blue, and carmine mixed with indigo, while the warmer 
 or more highly-coloured parts have a slight excess of carmine or lake. Colour the 
 shades about the mouth and neck with yellow ochre, blue, and a very little carmine, 
 heightening the colour of the lips with carmine and light red, letting the light red pre- 
 dominate on the upper and the carmine on the loAver lip ; the shades in the corner of 
 the mouth being touched slightly with burnt sienna mixed with carmine. 
 
 In colouring the eyes, the artist will of course be guided by nature, observing a 
 very delicate touch in laying on the colours, so as to preserve as much transparency as 
 
206 
 
 COLOUUING PHOTOGEAPHS. 
 
 possible. A slight touch, of blue— iiltramarine would be best if it would adhere to the 
 Daguerreotype plate — in the whites of the eyes near the iris, will produce a good effect. 
 
 In colouring the hands of men it will be necessary to use the darker tints with 
 more freedom, according to the complexion of the sitter. For women the warmer tints 
 should predominate, and in order to give that transparency so universal with the softer 
 sex — and which gives so much loveliness and beauty to the face — a little white may be 
 judiciously intermingled with the red tints about the lighter portions of the face. 
 
 In taking the likeness of a lady with light or auburn hair, by the Daguerreotype 
 process, much of the beauty of the face is destroyed, on account of the imperfect man- 
 ner in which light conveys the image of light objects to the spectrum of the camera ; 
 and this, I conceive, is an instance where defects may be obviated in some measure by 
 proper colouring. To do this touch the shaded parts with burnt sienna and bistre, 
 filling up the lighter portions with yellow ochre, delicate touches of burnt sienna, and 
 in those parts which naturally have a bluish tint, add very delicate touches of purple — so 
 delicate, in fact, as hardly to be perceived. The roots of the hair at the forehead should 
 also be touched with blue, and the eyebrows near the temples made of a pinkish tint. 
 The chin of a woman is nearly of the same colour as the cheeks in the most glowing parts. 
 In men it is stronger and of a bluish tint, in order to produce the effect given by the beard. 
 
 In portraits of woman — the middle tints on the side of the light, which are per- 
 ceived on the bosom and arms, are made of a slight mixture of ochre, blue and lake, 
 (or carmine), to which add, on the shaded sides, ochre, bistre, and purple ; the latter in 
 the darker parts. The tints of the hands should be the same as the other parts of the 
 flesh, the ends of the fingers being a little pinkish and the nails of a violet hue. If any 
 portion of the fleshy parts is shaded by portions of the dress, or by the position of the 
 hand, this shade should be coloured with umber mixed with purple. 
 
 To CoLOTJE, THE DuAPEKY. — VMet vclvet. — Use the purple made of Prussian blue 
 and carmine, touching up the shaded parts with indigo blue. 
 
 Green velvet. — Mix Prussian blue and red orpiment, shade with purple, and touch up 
 the lights with a little white. 
 
 Bed velvet. — Mix a little brown with carmine, shading with purple, marking the lights 
 in the strongest parts with pure carmine, and touch the most brilliant slightly with white. 
 
 White feathers— May be improved by delicately touching the shaded parts with a 
 little blue mixed with white. IFhiie muslin, linen, lace, satin, silk, &c., may also be 
 coloured in the same way, being careful not to lay the colour on too heavily. 
 
 Furs. — Eed furs— may be imitated by using light red and a little masticot, shaded 
 with umber. 
 
 Graxj furs — black and white mixed and shaded with bistre. 
 Bahle — white shaded lightly with yellow ochre. 
 
 These few directions are quite sufiicient for the art, and it is quite unnecessary for 
 me to pursue the subject further. I would, however, remark that the Daguerreotypists 
 would find it greatly to their advantage to visit the studies of our best artists, our'public 
 galleries of paintings and statuary, and wherever else they can obtain a sight of line 
 paintings, and study the various styles of colouring, attitudes, folds of drapery, and 
 other points of the art. In colouring Daguerreotypes, artists will find the magnifying 
 glass of much advantage in detecting imperfections in the plate or in the image, 
 which may be remedied by the brush. In selecting brushes choose those most sus- 
 ceptible of a fine point, which may be ascertained by wetting them between the lips or 
 in a glass of water. 
 
GLYCERINED COLLODION. 
 
 207 
 
 Glycerined Collodion, — I need scarcely tell the reader that there are, discoveries 
 in Photography being made daily. Even while this treatise is going through the 
 press, several of importance have been published, both in the chemical and mechanical 
 part of the science ; for instance, in close alliance with the moist collodion, the honey 
 collodion, and the coUodio-albumen processes, comes the employment of glycerine for 
 the purpose of preserving the sensitiveness of collodion for a lengthened period. Mr. 
 H. Pollock writes as follows : — 
 
 " I have lately adopted a mode of applying glycerine to collodion plates in order to 
 make them keep, which is, I believe, new, and which, from its simplicity and (as far 
 as I have tried it) certainty, will, I trust, prove of general utility. 
 
 "1. To ordinary collodion add glycerine in the proportion of six drops to the oiince. 
 
 " 2. Make a nitrate of silver bath in the usual manner, ezccpt that, instead of dis- 
 tilled water, a mixture of glycerine and distilled water, in the proportion of one of 
 the former to five of the latter, is to be used. 
 
 " 3. Make a second bath, containing only six grains of nitrate to the ounce. 
 
 '" 4. Coat the plate with 1, and immerse it in 2, in the usual manner, after which 
 immerse it in 3, for a minute ; drain it as usual, and you have a keeping plate, which 
 I find to be as good at the end of a week as when fresh from the hath. 
 
 " 5. Before developing, moisten the plate with distilled water, then proceed as 
 usual, taking care to add two drops of a 50-grain solution of nitrate of silver to the 
 developing solution before pouring it on to the plate. 
 
 "Note 1. For a short time I imagined (contrary to my expectation) that glycerine 
 did not decompose a solution of nitrate of silver ; I was, however, misled by the slow- 
 ness of the action, for it does produce decomposition, although very slowly, even in the 
 dark. This does not appear to damage the bath (it certainly does not for a month), but 
 makes it necessary to filter it about once a week. In time the hath would probably 
 become alkaline and require the addition of fresh nitrate and acetic acid. 
 
 " Note 2. Six drops of glycerine to the ounce of collodion is perhaps a maximum 
 dose. If too much is added, the film will have a honey-combed structure ; the quantity 
 which can be added without producing this, will vary with the quantity of water pre- 
 sent in the collodion ; hence the collodion best fitted for this process is that made with 
 anhydrous ether and alcohol, and it must be borne in mind that in actual use the pro- 
 portion of glycerine will gradually increase, because the ether and alcohol evaporate, 
 but the glycerine remains. 
 
 " Note 3. If Note 1 is supposed to contain an objection to this method, a horizontal 
 bath can be used holding but little, and a new bath be mixed once a fortnight. 
 
 "Note 4. The glycerine used is prepared, by decomposing fats by high-pressure 
 steam, by Price's Patent Candle Company, and which can be easily procured. 
 
 " Note 5. My experience of this process is very short. I therefore have given 
 proportions, not as being the best, but such as I have found succeed. ' More extended 
 experience must show what is the minimum of glycerine which will pi-oduce the maxi- 
 mum keeping efl:ect." 
 
 And Mr. Maxwell Lyte has brought before the world a new system of printing 
 which "depends on the power which aqua regia possesses of destroying sulphide of 
 silver, or any similar compound of sulphur, converting the metal into a chloride, 
 while at the same time the combined sulphur becomes sulphuric acid. The sulphur 
 thus becomes soluble, while the silver takes the form of a chloride ; and having thus 
 got rid of the sulphur, we again darken the chloride of silver by acting upon it 
 
208 
 
 ^EW PRINTING PROCESS. 
 
 with a combination of gallic acid and potash, which reconverts it to the black metallic 
 state. Take ordinary positive paper. The papier Saxe is, perhaps, most suited to the 
 purpose, as giving the greatest fineness and most perfect definition. Having chosen 
 the right side, lay that side downwards on a solution of chloride of ammonium of five 
 per cent. "When it has thoroughly imbibed, lift it ofi", and hang it up to dry ; then lay 
 the same face down on a bath of nitrate of twenty per cent., and after it has been for 
 at least five minutes in contact with this bath, again suspend it to dry. 
 
 " Print the picture in the usual way, only let it be printed somewhat darker than 
 will be ultimately required, as the after process tends rather to tone it down. 
 
 " The print withdrawn from the pressure-frame must now be placed in a bath of 
 plain water, in order to extract as much as possible of the free nitrate ; then in a bath 
 of water in which is dissolved a little salt. This converts all the free nitrate remaining 
 in the proof into chloride of silver, and from thence it is to be carried to a bath of new 
 hyposulphite of soda of 25 per cent., to which has been added 0*5 per cent, of carbonate 
 of soda. Here it is to remain till fixed, which process may be deemed accomplished 
 after it has lain for from a quarter of an hour to half an hour in the bath. It is now 
 to be thoroughly washed in several waters till all the hypo be removed. 
 
 " The picture will now be most probably of an ugly red colour, the more strongly 
 so in proportion as the hypo is more freshly made ; and if by age of the hypo the 
 picture may happen to be of a better tone, then the presence of sulphide of silver in the 
 proof always seems to threaten its destruction if left there, but the existence of which 
 the following treatment obviates. The well-washed and still wet proof is now placed 
 in a bath composed of aqua rcgia, eight or ten parts ; water, one hundred parts. Here 
 it is seen rapidly to fade, and after a short time will have almost completely disap- 
 peared, the dark silver forming the picture having all become converted into chloride ; 
 while the sulphur, if any there is, is at the same time converted into sulphuric acid, 
 and dissolved out into the liquid. It is now transferred into a bath of water, to which 
 has been added a morsel of carbonate of soda, or a few drops of ammonia, so as to get 
 rid of the acid, and may then be placed in the following bath : — "Water, one pint ; 
 gallic acid (saturated solution in alcohol), two or three drops; liquor potassse, one drop; 
 to be mixed at the moment of using. In this mixture the proof rapidly darkens, 
 re-appearing in all its minutest details, and requiring no further treatment than a slight 
 washing in clean water, when it has arrived at its maximum of intensity. 
 
 " I may here add a few remarks. The paper employed for this process should not 
 be sized with gelatine, albumen, or any other animal preparation, but Avith the vege- 
 table preparation used for the machine-made papers which are made on the continent. 
 
 " The bath of gallic acid absorbs oxygen very rapidly from'the atmosphere, becoming 
 red, so it soon spoils ; therefore the ingredients should not be put together until the 
 moment when they are required for use. The small quantity of these substances used 
 at each time prevents all question as to expense, and the time employed in producing a 
 picture scarcely, if at all, exceeds that demanded by any other process, long as this 
 description may appear. This method is, of course, equally applicable for the treatment 
 of positives made by the negative process, i.e., by development ; but to my idea this 
 last-named process possesses one great disadvantage, viz., our being unable to watch 
 the progress of the printing, and thereby to stop it at just the right point — a condi- 
 tion absolutely necessary to the production with certainty of perfect positives. 
 
 " As the above mode of printing abstracts all the size from the paper, it is necessary 
 either to resize it, or to rub it over with an encaustic prepared thus : take some white 
 
PREPARATIONS FOR SENSITIZING PAPER. 
 
 209 
 
 wax and dissolve it in turpentine to form a mixture of about the consistence of pomatum, 
 and add to this a quantity of alcohol equal in bulk to half the turpentine employed. 
 Having then fixed the proof either into a frame for stretching drawing-paper in, or 
 having pasted it on a 'piece of paper and fixed it down, rub into the face of it the 
 paste of wax, &c., and as quickly rub it off with a piece of clean flannel. Enough of 
 the wax remains on the face of the picture to render it beautifully bright and clear, and 
 at the same time to render it impervious to air and moisture, and it may be now cut 
 down and mounted. 
 
 " Lastly, as each paper sensitized extracts from the bath a certain amount of nitrate, 
 it becomes necessary to add, for each whole sheet or number of small sheets equalling a 
 whole sheet, which have been sensitized, one drachm of nitrate of silver in crystals, 
 adding at the same time water to make up the quantity of the liquid to its original 
 volume ; and also, to avoid loss by the drip from the paper when hung up, it is well to 
 draw its lower surface, i.e., the side which has lain on the bath, over a glass rod held in 
 an oblique position in such a manner as that the liquid which it scrapes ofi" from the 
 face of the paper may fall back again into the bath." 
 
 SUMMARY OF PEOCESSES FOE, PEEPARING PAPEE. 
 
 1. Bayard's Process. — Take some drawing-paper, spread over it a solution of bromine 
 of potassium, afterwards a solution of nitrate of silver ; expose this paper for some 
 minutes to the action of light in a dark room ; make the image visible by means of mer- 
 curial vapour, as in Daguerre's process. 
 
 2. Becquerel's Process. — A modification of the method of Panton, which see. 
 
 3. Chenning's Process. — 1st. Dissolve sixty grains of nitrate of silver in one ounce 
 of water. 2nd. Dissolve ten grains of iodine of potassium, or a mixture of one part of 
 bromine of potassium and two parts of iodine of patassium, in one ounce of water. 3rd. 
 "Wash the paper with the first, and afterwards with the second solution, and dry it. 
 
 4. Cundell's Process. — 1st. Spread over the paper a solution of thirty grains of 
 nitrate of silver. 2nd, Plunge it into a solution of iodine of potassium, two hundred 
 grains of this salt in seven thousand parts of water, to which add thirty grains of sea 
 salt. Place the prepared side of the paper in contact with the surface of this liquid. 
 3rd. Leave the paper for five or six minutes floating on the distilled water, dry it in 
 the air, and press it and make it smooth. 4th. Make the impression appear by a solu- 
 tion of concentrated gallic acid, mixed with the same quantity of solution of nitrate of 
 silver, fifty grains of salt, dissolved in one ounce of distilled water, and with a sixth 
 part of acetic acid. 
 
 6. Daguerre's Process. — Chloride of silver paper. Take some paper slightly covered 
 ■with isinglass, plunge it in hydrochloride water dried in the open air. "When dried put 
 it on the prepared side in contact with a solution of nitrate of silver ; dry it and preserve 
 it without exposing it to the light. 
 
 6. Fyfe's Process. — 1st. Dip the paper in a solution of phosphate of potash (one part 
 of this salt in eightparts of water), then dry it. 2nd. Cover it, with the help of a paint 
 brush, with a solution of nitrate of silver (one part of this salt in six parts of water), then 
 dry it again. 3rd. Dip it a second time in the solution of phosphate of potash. 4th. 
 Fix the impression by means of a spreaded solution of one part of ammonia in six parts 
 of water, which will only dissolve the salt of silver, not impressed by the light, whilst it 
 does not aff"ect the blackened salt. 
 
 7. Gaudin's Process. — 1st. Expose the paper during one minute to the vapour of 
 
210 PREPARATIONS FOR SENSITIZING PAPER. 
 
 of hydrochloric acid. 2nd. Cover it over with a solution nearly saturated with nitrate of 
 silver. 3rd. Develop the image, after the action of light in the dark room, covering 
 the paper with a concentrated solution of sulphate of iron slightly acidulated with sul- 
 phuric acid. 4th. Fix the image by washing with water containing a tenth part of 
 caustic ammonia. 
 
 8. Process of Heeron. — 1st. Plunge some thin white paper, for a quarter of an hour, 
 in a solution of nitrate of silver, prepared by mixing one part of salt in five parts of 
 water ; then plunge it for the same space of time in a solution saturated with sea salt ; 
 wash it with distilled water, press it out and dry it between sheets of blotting-paper. — 
 Note. This photographic paper is used to judge of the intensity of light in the prepara- 
 tion of Daguerreotype plates. 
 
 9. EerscheVs Process. — 1st. Mix, with the help of a gentle heat, a solution of nitrate 
 of silver, of 1'200 density, with two parts of tartaric acid of 1'023 specific gravity, by 
 treating the ferro-tartaric of ammonia with acetate of lead, and decomposing the preci- 
 pitate with diif used sulphuric acid. 2nd. "Wash the paper again with this solution and 
 dry it in the dark. 
 
 10. Eerschel's Chrysotype Process. — 1st. Dip the paper in a solution of one hundred 
 grains of crystallized ammoniacal citrate of iron in one hundred grains of water. 2nd. 
 Let it be half-dried. 3rd. Develop the image by a solution of chloride of gold dissolved 
 in water, completely neutralized by potash. 4th. Dip it at first into the water, then 
 for two minutes in a solution of iodine of potassium ; then wash it again in the water. 
 
 11. EerscheVs Cyanotype Process. — 1st. Dry in equal portions a concentrated 
 solution of corrosive sublimate with a solution of ammoniacal citrate of iron, mixed with 
 eleven parts of water. 2ad. Cover the paper with it, and dry it. 3rd. Wash the 
 image with a concentrated solution of cyano-ferrate of potash, mixed with three times 
 its volume of gum- water. 
 
 12. Eorsletj's Process. — 1st. Dip the paper in a Avatery dilution of sea salt, or one 
 hundred and twenty grains of sal-ammonia in one ounce of water, and dry it. 
 2nd. Impregnate the paper with a liquor made of a mixture of one hundred and eighty 
 grains of ammonia, sixty grains of nitrate of silver, and five grains of suberic acid, 
 and dry it by the fire. 3rd. Leave it from five to ten minutes in the camera. 4th. Fix 
 the image with hyposulphate of potash, wash the paper, and dry it by the fire. 
 
 13. Eunfs Process.— 1st. Dissolve one part of nitrate of silver in four parts of 
 distilled water, and cover one side of the paper with this solution. 2nd. Dip the 
 paper, after drying it, in a solution of iodine of potassium (one part of the salt in 
 eight parts of water), leave it there during one minute, and wash it afterwards with 
 distilled water. This paper will keep a long time, and can be rendered sensitive 
 immediately by washing it with a solution of cyano-ferrate of potassium (one part of 
 salt in four parts of water). 
 
 14. Eunt's lEnergetype Process. — Wash the paper with a saturated solution of 
 succinic acid one hundred and twenty grains, ninety grains of water, and thirty grains 
 of gummy mucilage. 2nd. Dry the paper, and spread over it a solution of nitrate of 
 silver (sixty grains of salt in thirty-seven grains of distilled water). This paper, 
 which may be preserved white, should remain from two to eight minutes in the dark 
 chamber. The impression is developed by a mixture of sixty grains of sulphate of iron 
 and one hundred and twenty to one hundred and eighty grains of gummy mucilage, 
 and is fixed by washing with the ammonia on a solution of hyposulphate of potash. 
 
 15. Kobell's Process. — 1st. Dip the paper into a solution of sea salt (one part of salt 
 
PREPARATIONS FOR SENSITIZING PAPER. 
 
 211 
 
 in fifteen of water). 2nd. Dry it, and place it in a flat vessel containing a solution of 
 nitrate of silver. 3rd. Fix the image by means of caustic ammonia, or hypo-sulphate 
 of potasli. After fixing the impression, the salt is removed by washing with water. 
 
 16. Martiii's Process.— Negative Impression — 1st. Spread over the paper a solu- 
 tion of thirty-six grains of iodine of potassium in one drachm of water. 2d. Dry it in 
 blotting-paper. 3rd. Lay over it a solution of fifty-six grains of azotate of silver in 
 one drachm of water. 4th. Dry it with another clean sheet of blotting-paper. 5th. 
 Eepeat all these operations. 6th. Wash it with distilled water with a paint-brush, and 
 dry it in blotting-paper. 7th. Expose it in the dark chamber. 8th. Wash it over 
 with dissolved gallo-nitrate of silver, twenty- seven grains of gallic acid azotate of 
 silver, in one drachm of water. 9 th. AVash it with distilled water. 10th. Spread it 
 over twice with a solution of iodine and bromine of potassium, wash it two or three 
 times with distilled water, and dry it thoroughly. Positive Imaf/e—lst Cover the paper 
 two or three different times with a solution of nitrate of silver, moisten it with a 
 dabber of cotton wetted through with gallic acid, dry it with care ; when the image 
 appears, bring it out with a solution of gallic acid, then dry it. 2nd. Let the paper 
 float on the surface of distilled water for three or four minutes ; wash it with a solution 
 of one part of hyposulphate of soda in eight or ten parts of water, then wash it two 
 or three times in distilled water. 
 
 17. G'Shaughneseijs's Pro(Te5s.— Substitute a solution of gold for one of nitrate of 
 silver. The images thus obtained have, it is said, more brilliant tints, with shades of ; 
 red, purple, and green. i 
 
 18. Osann's Process.— This process consists in the employment of a solution of formate . 
 of silver in water. The author prepares this production by means of double decompo- | 
 sition, using sulphate of silver in a concentrated solution of formate of bary tes. Fix the 
 image by plunging it several different times in warm water. 
 
 19. Panton's Process. — Dip the paper in a concentrated solution of bichromate of pot^ 
 ash and dry it rapidly by the fire. The image is yellow on an orange ground. If to the 
 bichromate of potash is added sulphate of indigo, various different shades of green will 
 be obtained, and a deepened tone. 
 
 20. SchaffhocuW s Process— Ut. Dissolve two parts and a half of nitrate of silver in six 
 parts of distilled water. 2nd. Pour this solution into a large flat dish, and in it dip one 
 side of the paper. 3rd. Expose this paper, while damp, to the action of the boiling 
 vapours of hydrochloric acid. 4th. Dry it, and in order to render it yet more sensitive, 
 pass it once more upon the. solution of nitrate of silver. 5th. Fix the image by plunging 
 the paper for five or ten minutes in alcohol ; dry it, and pass it through some diffused 
 hydrochloric acid, in which some drops of pernitrate of mercury have been poured . 
 wash the image with distilled water, and dry it at about 60°. 
 
 21. SchaffhceuWs new Process— Positive Images— 1st. Use paper impregnated with 
 chloride of silver, after the method which has just been shown, 2nd. Lot it blacken in 
 the light, and during half an hour keep it plunged in a liquor composed of nine to ten 
 parts of alcohol, and one part of a solution of pernitrate of mercury. 3rd. Pass it (quickly 
 over the diffused hydrochloric acid (one part acid and seven to eight parts of water). 
 AVash it rapidly in water, and dry it by a mild heat. This paper is whitened by the 
 rays of the sun, and the images fixed by plunging it in the alcohol, which dissolves the 
 excess of the corrosive sublimate. 
 
 22. Stnith's Process (Tritypic).— 1st. Dissolve two grains of carbonate of soda in 
 four grains of water. Filter the solution, and add to it twelve drops of sulphuric or 
 
212 
 
 PREPARATIONS FOR SENSITIZING PAPER. 
 
 hydrochloric acid. 3rd. Cover the paper agaia with this liquor, and dry it in the dark. 
 With this paper is obtained, after twenty minutes to an hour and a half, positive copies 
 of prints. The lights are yellow, the shades violet ; by using a double quantity of acid 
 red shades are obtained. 
 
 23. Talbot's Process (Chloride of Silver Paper). — 1st. Choose some thin letter paper, 
 dip it into a weak solution of sea salt, and dry it with a linen rag. 2nd. Spread over 
 one side only, a solution of nitrate of silver (a solution saturated and diffused with six 
 or eight times its weight of water), and dry it slightly, 
 
 24. Talbot's Process (Bromine of Silver Paper).— Cover some good common paper 
 with a solution of nitrate of silver, then with dissolved bromine of potassium, then 
 again with dissolved nitrate of silver. Mte. After each operation, care must be taken 
 to dry the paper by the fire. 
 
 25. Talbot's Process (Calotype).— 1st. Prepare the four following liquids : — First 
 liquid, one hundred grains of nitrate of silver dissolved in two hundred and fifty grains 
 of distilled water. Second liquid, five hundred grains of iodine of potassium dissolved 
 in seven thousand grains of distilled water. Third liquid, one hundred grains of 
 nitrate of silver dissolved in two ounces of distilled water; to this solution add a 
 sixth part of its quantity of acetic acid. Fourth liquid, a saturated solution of crys- 
 tallized gallic acid. 1st. Spread the paper over, one side only, with liquid No. 1, and 
 dry it with care by the fire. 2nd. Dip it in liquid No. 2, and let it remain from two 
 to three minutes ; afterwards place it in a glass vessel, and dry it, first between sheets of 
 blotting-paper, afterwards by the fire; keep it in darkness ; before making use of it, 
 spread over again a mixture of equal parts of Nos. 3 and 4. Dip it for half an hour 
 in water, dry it, at first, between blotting-paper, then by the fire. 
 
 This paper is left only a few minutes in the dark-room, and the image is made 
 visible by spreading over the mixture of liquids indicated (gallo-nitrate of silver). To 
 fix it, the paper is plentifully washed ; it is dried between sheets of paper ; it is 
 passed with rapidity over one hundred grains of dissolved bromine of potassium in one 
 hundred and forty-eight to three hundred and ten grains (eight to ten ounces) of 
 water; it is once again washed and dried. 
 
 26. Taylor's Process (a modification of Talbot's method).— 1st. Impregnate the 
 paper with a solution of nitrate of silver in ammonia. 2. Fix the images by plunging 
 the paper in boiling water, and leaving it there for two or three days. 
 
 27. Verignon's Process. — 1st. "Wash the white paper with water containing a small 
 quantity of hydrochloric acid, and dry it. 2nd. Let it imbibe a solution formed of two 
 parts of sal-ammonia, one part of chloride of strontium, and twenty parts of water ; 
 and dry it. 3rd. Dip it into a solution of silver much difi"used. 4th. Blacken it by 
 exposing it for half an hour to the action of light. 5th. Let it be impregnated with a 
 very suffused solution of iodine of sodium in the dark, and place it yet wet in the 
 dark-room. The action is finished at the end of twelve minutes. The image is fixed 
 by employing a very diluted solution of hypo-sulphite of silver and iron ; after which 
 it is washed in distilled water. 
 
 28. WoocPs Process. — 1st. Dip the paper in water, of which three ounces contain 
 two drops of hydrochloric acid. 2nd. 'Vi'^ash it with a mixture of iodine of iron, half a 
 drachm, and one drop of the tincture of iodine in a drachm and a half of water. 
 3rd. Dry it with blotting-paper, and wash it evenly over with a solution of nitrate of 
 silver (thirty grains of salt in three ounces of water).