" The greatest and most important Literary Enterprise of the day." — Critic. CABINET EDITION OF THE ENCYCLOPEDIA METROPOLITANA, Sr^oraugblg llcMstir aitir atruniraittln lllustrattb, Pablisliing ia Volumes, each coataining a Complete Treatise, Crown Octavo, Clotli. Tolumcs now Ready. Vol. I., price 2s., cloth lettered, INTRODUCTORY DISSERTATION ON THE SCIENCE OF METHOD. By Samuel Taylor Coleridge. With a Synopsis. Si.xth Edition. Vol. II., price 5s., cloth lettered, UNIVERSAL GRAMMAR, or the Pure Science of Language. By Sir John Stoddart, Knt., LL.D. Third Edition, Revised. "The soundest and most philosophical treatise of the kind in the English language." — North British Revitva. Vol. III., price 3s., cloth lettered, LOGIC. By the Most Rev. Richard Whately, D.D., Archbishop of Dublin. The Original Edition, with Synopsis and Index by the Editor. Vol. IV., price 3s. 6d., cloth lettered, RHETORIC. By the Most Rev. Richard Whately, D.D., Archbishop of Dublin. The Original Edition, with Synopsis and Index by the Editor. Vol. v., price 63., cloth lettered, HISTORY OF THE CHRISTIAN CHURCH in the First Century. By the Right Rev. SAJitJEL Hinds, D.D., Bishop of Norwich, and the Rev. J. H. Newman, D.D. Third Edition, Revised. " Erudite research is here combined with independent thought." — Scottish Guardian. Vol. VI., price 4s., cloth lettered, POLITICAL ECONOMY. By Nassau Willum Senior, Esq., late Professor of Political Economy in the University of Oxford. Third Edition. Vol. VII., price 2s. 6d., cloth lettered, HISTORY OF THE JEWS, from the time of Alexander the Great to the De- struction of Jenisalein by Titus, A.5L 3595, B.C. 409 to a.d. 70. By the Venerable Archdeacon Hale, A.II., Master of the Charter-house. Fourth Edition. VoL VIIL, price 6s., cloth lettered, SACRED HISTORY AND BIOGRAPHY, from the Antediluvian Period to the Time of the Prophet Malachi, a.m. 1 to a.m. 3607, b.c. 397. Edited by the Rev. F. A. Cox, D.D., LUD. ' ' Pleasing and good, and worthy of general attention. ' '— United Presbyterian Magazine. Vol. IX, price 7s. 6d., cloth lettered, HISTORY OF GREEK LITERATURE. By the Hon. Sir T. N. Talfourd, D.C.L., the Right Rev. C. J. Blomfield, D.D., Bishop of London ; R Whitcombe, Esq., M.A., Trinity College, Cambridge ; E. Pocockk, Esq. ; the Rev. J. B. OTTLEr, M.A. ; and the Rev. II. TnoMi'soN, JI.A., St. John's College, Cambridge. " Full of Information, expressed in the choicest language."— ./4(A^ <^eei- 'v:^l-l'~f t^iirfi- ENCTCLOPiiDIA METROPOLITANA SSBtem of Sanibctsal iSnotoleligc ; ON A METHODICAL PLA.V PEOJECTED BY SAMUEL TAYLOE COLEEIDGE. SECOND EDITION, REVISED. PHOTOGRAPHY. yOURTH EDlTlOJi, REVISKD. Price 3s. 6d., uniform -with this Volume, A MANUAL ov ELECTRO-METALLURGY. BY JAMES NAPIER, F.C.S. SECOND EDITION, REVISED. Digitized by tine Internet Arcinive in 2011 witii funding from Researcii Library, The Getty Researcii Institute http://www.archive.org/details/manualofphotograOOhunt Ti-ij- lfcc3oMH StUicferii T lai. li iim t CSajAtw MANUAL PHOTOGRAPHY. ROBERT HUNT, PHOFKSSOR OF PHYSICAL SCIENCK IN THE METEOPOLITAN SCHOOL OF SCIENCE — KEEPER OF MINING HECGEDS IN THE MUSEUM OP PRACTICiL GEOLOGY — AUTHOR OP "RESEARCHES ON LIGHT," "THE POETRY OF SCIENCE," &C. FOURTH EDITION, REVISED Illitsitvateti bg 'Nuntaroua iEngvafaings. LONDON AND GLASGOW: RICHARD GRIFFIN AND COMPANY, PUBLISHERS TO THE UNIVEBSITT OP GLASGOW. 1854 GLASGOW : W. a. BI.ACKIK ANU CO., PRlNrKK?, VlI.I.Al'lKI.n. PREFACE, The opportunity offered in preparing a fourth edition of the Manual of Photography for the press, has been embraced for the purpose of making some alterations in the arrangements of the several divisions of the subject, and of placing thereby each particular phenomena in a clearer view. By this the amateur will advance more readily in his Photographic studies, and the experienced artist will find the references more easy to any particular mode of manipulation which he may desire to consult. All the most recent improvements have been compre- hended ; the processes of Photographic etching have been embraced ; and, it is believed, nothing omitted which can serve to maintain the flattering position which the " Manual" has secured for itself as a standard work on Photography. ROBERT HUNT. London, March, 1854. PEEFACE TO THE THIRD EDITION. The rapidity with which the second edition of this work has been exhausted, is a most satisfactory proof that a collection within convenient compass of all the facts con- nected with the progress and practice of Photography, was required by the increasing niunber of amateurs and artists who are interested in its very beautiful phenomena. In the present edition a new system of arrangement has been adopted, which will, it is thought, prove generally convenient. The first division contains the history of the progress of Photographic discovery, in which the gi'eatest care has been taken to insure exactness, and to give to each discoverer the full merit of his labours : the date of publication being taken in all cases where it could possibly be obtained. The second division embraces the science of the art ; and it is a section to which the attention of the intelligent student in Photography is particularly directed, as he may, by the knowledge he will thus acquire, relieve him- self from many of the annoyances attendant upon frequent failui-es, and probably advance himself in the path of new discovery. The manipulatory details, given with all necessary minuteness, are included in the third division. A very large portion of the present volume consists of new matter — the Waxed Paper and the Collodion Pro- cesses, amongst other sections, may be referred to ; and VUl PREFACE. the appended chapter, On the Production of Pictm*es for the Stereoscope, "\vill be found to afford much useful in- formation. The additional wood-cut illustrations which have been introduced will be found to render important aid to the amateur. I must acknowledge the ready as- sistance, in the way of correction and information, which has been afforded me by several of the most practised photographic artists of the metropolis. To Mr. Claudet and Mr. Home, in pai-ticular, I am indebted for many novel and most useful details in the practice of the Daguerreotype and the Collodion processes ; and to Mr. Sandford, who has furnished me with many valuable facts relating to the preparation of paper for Photography, I am under many obligations. Those gentlemen who have kindly hastened to supph^ me with the results of their practice, which is duly acknowledged in the text, will accept my thanks. In conclusion, let me hope that the arrangement of the present volmue will be found an improvement upon the former editions, and that this Manual may deserve to maintain its place as as a Text- Book on Photography. ROBERT HUNT. London. December, 1852. CONTENTS, PAET I. HISTORY OF DISCOYEEIES IN PHOTOGRAPHY. CHAPTER I. Early Researches on the Chemical Action or the Solar Rays ........ 3 CHAPTER II. Heliography— The Process of M. Niepce , . .12 CHAPTER III. Mr. H. Fox Talbot's Photogenic Drawings, Calotype, &c. 18 Section I. Photogenic Di'awing . . .18 „ II. Calotype . „ III. Improvements in Calotype „ IV. Pictures on Porcelain „ V. Instantaneous Process CHAPTER IV. Daguerreotype — The Discovery of M. Daguerre . . 34 Section I. The Original Process of M. Daguerre . 34 „ II. Improvements in Daguerreotype . 43 CHAPTER V. The Photographic Processes on Paper of Sir John Herschel 48 Section I. Cyanotype . . . .48 „ II. Chiysotype . . . .54 „ III. Photographic Properties of Mercury . 57 „ IV. Ferro-Tartrate of Silver . . .58 „ V. The AmphityjDe . . . .59 „ VI. The Colouring Matter of Flowers . 61 X CONTENTS. CHAPTER VI. MiSCELLANEOtrS PROCESSES . . . . .69 Section I. Mr. Ponton's process. (Bickromate of Potash) . . . . .69 „ II. The Chromatype . . . .71 „ III. The Ferrotype . . . .73 „ IV. The Catalysotype . . .75 „ V. Ferrocyanide of Potassium . . 79 „ VI. The Fluorotyjie . . . .80 „ VI.*Bromide of Silver and Mercurial Vapour 81 „ VI r. Positive Photographs by One Process . 82 „ VIII. On the Application of the Daguerreotype to Paper . . . .85 „ IX. Salts of Gold as Photographic Agents . 89 „ X. The Influence of Chlorine and Iodine in rendering Wood sensitive to Light . 90 CHAPTER VII. Photographs on Glass Plates and Recent Improvements 92 Section I. Precipitates of Silver Salts . . 92 „ II. Albumen . . . .95 „ III. Collodion . . . .95 CHAPTER VIII. Portraiture by the Daguerreotype . . . .96 CHAPTER IX. General Summary of the History of Photography . 101 PART II. SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. CHAPTER I. General Remarks on the Solar Agency producing Chemi- cal Change ....... 107 CHAPTER II. Chemical Changes on Sensitive Preparations Section I. Nitrate of Silver „ II. Chloride of SUver „ III. Iodide of Silver . „ IV. Bromide of Silver „ V. Miscellaneous Salts of Silver 114 114 115 118 118 120 CHAPTER III. The Theory of the Daguerreotype . • . .124 CONTENTS. xi CHAPTER IV. On THE Photographic Registration of Philosophical Instru- ments, AND THE MEANS OF DETERMINING THE VARIATIONS OF Ac- TiNic Power, and for Experiments on the Chemical Focus 139 Section I. PhotogTaphic Registration . . 139 „ II. Instruments for Measuring Actinic Varia- tions, &c. .... 143 The Photographometer . .143 The Focimeter . . . 145 The Dynactinometer . . 146 CHAPTER V. Thermography . . . . . . .151 CHAPTER VI. On the Possibility of Producing Photographs in their Na- tural Colours ...... 158 CHAPTER VII. On Lenses for the Photographic Camera . . .163 PAET III. PEACTICE OF PHOTOGRAPHY. CHAPTER I. Selection of Paper for Photographic Purposes . .176 CHAPTER II. On the Apparatus necessary for the first Practice of Pho- tography on Paper . . . . , .183 CHAPTER III. On the modes of Manipulation adopted in the Preparation OF Sensitive Papers . . . . . .193 Section I. Nitrate of Silver . . .193 „ II. Chloride of Silver . . . 194 „ III. Iodide of Silver . . . .197 CHAPTER IV. On Fixing the Photographic Pictures . . . 199 CHAPTER V. The Calotype as now practised, and its Modifications . 206 Section I. Calotype on Paper . . . 206 „ II. Calotype on Gelatine or Albumen . 222 „ III. Calotype Process on "Waxed Paper . 227 XU CONTENTS. CHAPTER VI. The Dagtterreottpk ...... 2.31 Section I. Daguerre's improved Manipulation . 231 „ II. Polishing the Plate . . . 235 „ III. To give the Sensitive Surface to the Plate 236 „ IV. To Develope the Image formed on the Plate . . . . .243 „ V. Fixing the Daguerreotyiie Image . 245 „ VI. Simplification of the Daguerreotype . 248 CHAPTER Vri. The Collodion Process ..... 252 CHAPTER VIII. The use op Albumen on Glass Plates, &c. . . . 276 Section I. Albumen on Glass . . . 276 „ II. ]Mr. Malone's Process . . . 278 „ III. M. Martin's Process . . .280 „ IV. Miscellaneous Processes . . . 282 ;, V. Positive Photographs from Etchings on Glass Plates . . . .283 CHAPTER IX. On the Production of Positive Photographs by the use of the Salts of Iodine ...... 285 CHAPTER X. General Remarks on the Use of the Camera Obscura — The Photographic Pentagraph .... 298 Section I. Buildings, Statues, Landscapes, and Fo- liage . . . . .298 „ II. Portraits from the Life . . .300 „ III. Photographic Pentagi'ajDh . . 302 CHAPTER XI. The Stereoscope ...... 304 CHAPTER XII. Photographic Engraving ..... 314 Appendix ....... 321 Photogi^aphic Patent Right . . . .321 Correspondence of English and French Weights and Measures . ... 324 Index ....... 325 PAET I. HISTORY DISCOVEEIES IN PHOTOGEAPHY. CHAPTER I. EARLY RESEARCHES ON THE CHEMICAL ACTION OF THE SOLAR RAYS. It is instructive to trace the progress of a discovery, from the first indication of a truth, to the period of its full development, and its application to purposes of ornament or utility. The progress of discovery is ordinarily slow, and it often happens that a great fact is allowed to lie dormant for years, or for ages, which, when eventually revived, is found to render a fine interpretation of some of Nature's harmonious phenomena, and to miuister to the wants or the pleasures of existence. Of this position, Photo- gi-aphy is peculiarly illustrative. The philosophers of antiquity appear to have had theh" atten- tion excited by many of the more striking characters of light : yet we have no account of their having observed any of its che- mical influences, although its action on coloured bodies — deepen- ing their colour in some cases, and discharging it in others — must have been of every-day occui-rence. The only facts which they have recorded are, that some precious stones, particularly the amethyst and the opal, lost their sparkle by prolonged exposure to the rays of the sun. It has been stated — but on doubtful authority — that the jug- 4 HISTORY OF PHOTOGRAPHY. glers of India were for many ages in possession of a secret process, by which they were enabled in a Tjrief space to copy the profile of any individual by the agency of light. However this may have been, it does not appear that they know anything of such a process in the present day. The alchemists, amidst the multiplicity of their processes — in their vain seai'ch for the philosopher'' s stone and the elixir vitce — stumbled upon a pecvdiar combination of silver with chlorine, which they called horn-silver — as, by fusion, the white powder they obtained by precipitation was converted into a horn-like substance. They observed that this horn-silver was blackened by light, and as they taught that " silver only differed from gold in being mercmy interpenetrated by the sulphiu-eous pi-inciple of the sun's rays," they concluded that this change was the commencement of the process by which their ch-eams were to be realized. Failing, however, to produce gold 6-om horn-silver, the fact of its blackening was simply recorded, and no fiu'ther investigations were made into this remarkable jihenomenon. Petit, in 1722, noticed that solutions of nitrate of potash and mimate of ammonia crystallized more readily in the light than they did in darkness. The illustrioxis Scheele (1777), in his excellent TraiiS de VAir et du Feu, gave the world the fii-st philosophical examina- tion of this pecidiar change in a salt of silver, and proved the dissimilar powers of the different rays of light in effecting this change. He -wi-ites, " It is well known that the solution of silver in acid of nitre poured on a piece of chalk, and exposed to the beams of the sun, grows black. The light of the sun reflected from a white wall has the same effect, but more slowly. Heat without light has no effect on this mixture." Again, " Fix a glass prism at the window, and let the refracted sun-beams fall on the floor; in this coloured light put a paper strewed with luna cornua, and you will observe that tliis horn-silver grows sooner black in the violet ray than in any of the other rays." Senebier repeated these experiments, and he states that he found chloride of silver darkened in the violet ray in fifteen seconds to a shade which requii-ed the action of the red i-ay for twenty minutes. He also experimented on the influence of light in bleaching Avax. In the Fhiloso2:>hiccd Transactions for 1798 Avill be found a memoir by Count Rumford, entitled, " An Inquiry concerning the Chemical Properties that have been attiibuted to Light." In tliis i)aper a number of experiments are broiight forward to prove that all the effects produced upon metallic solutions by bright sunshine, can be obtauied by a prolonged exposui-e to a tempo- EARLY RESEARCHES ON THE SOLAR RAYS. rature of 210*^ Fahrenheit. We are now, however, in a position to show that the chemical effects produced by rays of dark heat, are of a very different character from those usually attributed to light. Mr. Robert Harrup, in a communication to Nicholson's Journal in 1802, refuted the experiment of Count E-umford, sho^ving that several salts of mercuiy were reduced by light alone, and not heat. In 1801, Ritter proved the existence of rays a considerable distance beyond the visible spectrum, which had the property of speedily blackening chloride of silver. These researches excited the attention of the scientific world : M. Berard, Seebeck, Ber- thoUet, and others, dii'ected their attention to the peculiar con- dition of the different rays in relation to their luminous and chemical influences ; while Su- William Herschel and Sir Henry Englefield investigated the calorific powers of the colom-ed rays, and were followed in these investigations by Seebeck and Wimsch. Dr. Wollaston pursued and published an interesting series of experiments on the decomposition effected by light on gum- guaiacum. He found that paper washed with a solution of this gum in spiiits of ^vine, had its yellow colour rapidly changed to green by the violet rays, while the red rays had the proj^erty of restoring the yellow hue. Sii- Humphry Davy observed that the puce-colovu-ed oxide of lead became, when moistened, red by exposure to the red ray, and black when exposed to the violet ray ; and that the green oxide of mercury, although not changed by the most refrangible rays, speedily became red in the least refrangible. Morichini and ConfigHachi, M. Berard, and more recently, Mrs. Somerville made some curious experiments on the power of the violet rays to induce magnetism in steel needles. Seebeck and Berzelius investigated this involved subject: it has again and again engaged the attention of experimentalists ; biit to the present time it must be regarded as an u.nsettled point, whether magnetism can be induced in steel by the solar rays. A statement has been made by the French, to the effect that M. Charles was in possession of a process by which porti-aits could be obtained by the agency of sunlight, producing a dark impression upon a prepared surface. This is, however, exceed- ingly doubtful, and even the Abbe Moigno, in his Repertoire, states, that M. Charles never disclosed any fact connected with this discovery, and that he left no evidence behind him of being in possession of such a process. In addition to the interesting facts already mentioned, it will be instructive to add a few particulars of other inquiries pur- sued about the same time on various phenomena connecting b HISTORY OF PHOTOGRAPHY. themselves with, the solar radiations. Although these do not bear directly on Photography, they stand in very close relation with, it, and will serve possibly to indicate lines of research which have not been fully followed out. Desmoi-tiers in 1801 published a paper in Gilbert's Annals, entitled, " Recherches stir la Decoloration spontanee du Bleu de Pi-usse," subsequently translated into Nicholson's Journal, in which he has mentioned the influences of the solar rays in producing the change. Boekman about the same time observed that the two ends of the spectrum acted differently on phos- phorus; and Dr. Wollaston, examining the chemical action of the rays of the specti-um, arrived at nearly the same results as Bitter. He states, " This and other effects usually attributed to light are not in fact owing to any of the rays usually per- ceived." Wedg-wood was certainly the first person who made any attempts to use the sunbeam for delineatiug the objects it illu- minated: it is therefore necessaiy that some more particular account should be given of his processes. In 1802, he published a paper in the Joiu-nal of the Boyal Institution, imder the fol- lowing title : "An Account of a Method of Copying Paintings upon Glass, and of making Profiles by the Agency of Light ujjon Nitrate of Silver ; with Observations by H. Da\"y." From this communication, the following extracts, containing the more important indications, are made. " White paper, or white leather, moistened with solution of nitrate of silver, undergoes no change when kept in a dark place, but, on being exposed to the daylight, it speedily changes coloiu-, and after passing through different shades of gray and bro^^^l, becomes at length nearly black. The alterations of colour take place more speedily in proportion as the light is more intense. In the dii'ect beam of the sun, two or three minutes ai-e sufficient to produce the fidl effect ; in the shade several hours are required ; and light transmitted through different coloured glasses acts upon it ^-ith diffei'ent degrees of intensity. Thus, it is foimd that red rays, or the common simbeams, passed through red glass, have very little action upon it ; yellow and gi'een are more efficacious ; but blue and violet light produce the most decided and powerful effects. " When the shadow of any figure is thrown upon the prepared sui-face, the part concealed by it remains white, and the other jjarts 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 EARLY RESEAKCHES OX THE SOLAR RAYS. 7 removed by the application of water, or water and soap, and it is in a liigh degree permanent. The copy of a painting, or the profile, immediately after being taken, must be kept in an obseiu-e place; it may, indeed, be examined ia the shade, b\it in this case the exposm-e should be only for a few minutes : by the light of candles or lamps, as commonly employed, it is not sensibly affected. No attempts that have been made to prevent the uncoloured parts of the copy or profile fi-om being acted upon by light, have as yet been successful. They have been covered by a thin coating of fine vamish, but this has not destroyed then- susceptibility of becoming coloiu'ed ; and even after repeated washings, sufiicient of the active part of the saline matter will adhere to the white parts of the leather or paper to cause them to become dai-k when exposed to the rays of tlie sun. Besides the applications of this method of copying that have just been mentioned, there are many others ; and it will be useful for making delineations of aU such objects as are possessed of a textm-e pai'tly opaque and partly transparent. The woody fibres of leaves, and the wings of insects, may be pretty accm-ately represented by means of it ; and in this case it is only necessary to cause the direct solar light to pass through them, and to receive the shadows upon leather. " The images formed by means of a camera obscura have been found to be too faint to produce, in auy moderate time, an efiect upon the nitrate of silver. To copy these images was the first object of jMi-. Wedgwood La his researches on the subject ; and for this pxirpose he first used nitrate of silver, which was mentioned to him by a friend as a substance very sensible to the influence of hght ; but all his munerous experiments as to then- primary end proved unsuccessful. In following these processes, I have found that the images of smaU objects, pro- duced by means of the solai' microscope, may be copied without difliculty on prepared paper. This will probably be a useful application of the method ; that it may be employed successfully, however, it is necessaiy that the paper be placed at but a small distance from the lens. (Davy.) " In comparing the effects produced by light upon mui'iate of silver with those produced upon the nitrate, it seemed evident that the miu'iate was the most susceptible, and both were more readily acted upon when moist than when dry — a fact long ago known. Even in the twilight, the colour of the moist muriate of silver, spread ujDon paper, slowly changed from white to faint violet ; though, vmder similar circiunstances, no immediate alteration was produced upon the nitrate. " Nothing but a method of preventing the imshaded parts of 8 HISTORY OF PHOTOGRAPHY. the delineations from beiag coloured by exposure to the day, is wanting to render this process as useful as it is elegant." An experiment on the dark rays of Ritter, by Dr. Young, included in his Bakerian Lecture,* is a very important one. Dr. Young, after refening to the experiments of Ritter and Wol- laston, goes on to say : " In order to complete the comparison of their properties (the chemical rays) with those of visible light, I was desirous of examining the effect of their reflection from a thia plate of air capable of producing the well-known rings of colom-s. For this purpose I formed an image of the rings, by means of the solar microscope, with the apparatus which I have described in the Journals of the Royal Institution ; and I threw this image on paper dipped in a solution of nitrate of sUver, placed at the distance of about nine inches from the microscope. In the course of an hour, portions of three dark rings were very distinctly visible, much smaller than the brightest rings of the coloured image, and coinciding very nearly, in their dimensions, with the rings of violet light that appeared upon the interpo- sition of violet glass. I thought the dark rings were a little smaller than the violet rings, but the difference was not suffi- ciently great to be acciu-ately ascertained : it might be as much as 3^Q or ^-Q of the diameters, bvit not greater. It is the less surj^rising that the difference should be so small, as the dimen- sions of the coloured rings do not by any means vary at the violet end of the spectrum so rapidly as at the red end. The experiment in its present state is sufficient to complete the analogy of the invisible with the visible rays, and to show that they are equally liable to the general law, which is the principal subject of this paper :" that is the interference of light. M. B. G. Sage, in the Journal de Physique, 18U2, mentions a fact observed by him, that " the realgar which is sublimated at the Solfaterra under the form of octahedi-al crystals, knowoi under the name of ruby of arsenic, effloresces by the light ; " and that ordinary native realgar from Japan changes to orpi- ment by exposure to sunshine. In 1806, Vogel exposed fat, carefully protected from the influence of the air, to light, and found that it became in a short time of a yellow colour, and acquired a high degree of i-ancidity. Vogel subsequently discovered that phosphorus and ammonia exposed to the sun's rays were rapidly converted into phosj)hu- retted hydrogen, and a black powder, phosphuret of ammonia. He also noticed that the red rays produced no change on a solution of corrosive subUmate (bichloride of mercury) in ether, * PldlosopMcal Transactions, 1804. CHEMICAL ACTION OF THE SOLAR RAYS. 9 but that the blue rays rapidly decomposed it. Dr. Davy, much more recently, repeated a similar set of experiments to those of Vogel. He found that corrosive sublimate was not changed by exposure ; but that the Liquor Hydrary. Oxymur. of the old London Pharmacojjoeia quickly xmderwent decomposition in the sunshine, depositing calomel (chloride of merctuy). Seebeck, in and subsequently to 1810, made some important additions to our knowledge of the influences of the solar radiations, the most striking of his statements being the pro- duction of colour on chloride of silver ; the violet rays rendering it brown, the blue producing a shade of blue, the yellow pre- serving it white, and the red constantly giving a red colour to that salt. Sir Henry Englefield, about the same time, was enabled to show that the phosphorescence of Canton's phos- phoi-us was greatly exalted by the blue rays. Gay-Lussac and Th^nard, being engaged in some investigations on chlorine, on which elementary body Davy was at the same time experimenting, observed that hydrogen and chlorine did not combine in the dark, but that they combined with great rapidity, and often with explosion, in the sunshine, and slowly in diifused light. Seebeck collected chlorine over hot water, and, combining it with hydi-ogen, placed different portions of it in a yellowish-red bell glass and in a blue one. In the blue glass combination took place immediately the mixture was exposed to daylight ; but \vithou.t explosion. The mixture in the red glass was exposed for twenty minutes without any change ; but it was found that the chlorine had undergone some alteration, probably a similar one to that subsequently noticed by Dr. Draper, who found that chlorine having been exposed to simshine woidd unite with hydi'ogen in the dark. If the gases were placed in a white glass and exposed to sunshine, they exploded ; but if the gas had been previously exposed to the action of the solar radiations in the yellow-red glass, it combined with hydi'ogen in the white glass in the brightest sunshine without any explosion. Berzelius noticed some peculiar conditions in the action of the solar rays upon the salts of gold ; and Fischer pursued some researches on the influence of the prismatic rays on horn-silver. The most important series of researches, however, were those of Berard in 1812, which were examined and rej)orted on by BerthoUet, Chaptal, and Biot. These jihilosophers write : " He (M. Berard) found that the chemical intensity was greatest at the violet end of the spectriun, and that it extended, as Bitter and Wollaston had observed, a little beyond that extremity. When he left substances exposed for a certain time to the action 10 HISTORY OF PHOTOGRAPHY. of each ray, he observed sensible effects, though "vvith an inten- sity continually decreasing in the indigo and blue rays. Hence we nl^^st consider it as extremely probable, that if he had been able to employ reactions still more sensiljle, he woidd have observed analogous effects, but still more feeble, even in the other rays. To show clearly the great disproportion which exists in this respect between the energies of different rays, M. Berard concentrated, by means of a lens, all that part of the S23ectruni which extends from the green to the extreme violet ; and he con- centrated, by means of another lens, all that portion which ex- tends from the green to the extremity of the red. This last pencil formed a tuhite point so brilliant that the eyes ivere scarcely able to endure it ; yet the muriate of silver remained exposed more than tioo hours to this brilliant point of light without undergoing any sensible alteration. On the other hand, when exposed to the other pencil, which was much less bright and less hot, it was blackened in less than six minutes." This is the earliest inti- mation we have of any hypothesis that the luminous and chemical powers may be dixe to dissimilar agencies. On this, the Com- missioners remark : — " If we wish to consider solar light as composed of three distinct substances, one of which occasions light, another heat, and the third chemical combinations, it ^vill 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 the three properties, chemical, colorize, and ccdoriAc, is spi-ead, though imequally, over a cer- tain extent of the spectrum. Hence we must suppose, on that hypothesis, that there exist three sj^ectrums, one above another ; namely, a calorific, a colorific, and a chemical spectnvm. "We must likewise admit that each of the substances which compose the three spectrums, and even each molecide of unequal refran- gibility which constitutes these substances, is endowed, like the molecules of visible light, with the property of being polai-ized by reflection, and of escaping fi'om reflection in the same positions as the Imninous molecules, &c." From the time when the difficulty of fixing the photographs which they obtained, stopped the progi-ess of Davy and Wedgwood, no discoveries were made until 1814, when M. Niepce, of Chalons, on the Soane, appears to have first dii'ected his attention to the production of pictures by light. It does not seem that his early attempts were very successful ; and, after piirsuing the subject alone for ten years, he, from an accidental disclosure, became acquainted with M. Daguerre, who had been for some time endeavouring, by various chemical pro- cesses, to fix the images obtained with the camera obscura. In CHEMICAL ACTION OF THE SOLAR RAYS. 11 December, 1829, a deed of copartnery was executed between M. Niepce and M. Daguerre, for mutually investigating the subject. M. Niepce had named his discovery Heliography.* In 1827, he presented a paper to the Royal Society of London, on the subject ; but as he kept his process a secret, it could not, agree- ably with one of theii* laws, be received by that body. This memoir was accompanied with several heliographs on metal (plated copper and pewter) and on glass plates ; which were afterwards distributed in the collections of the curious, some of them still existing in the possession of Mr. Robert Brown, of the British Museum. They jirove M. Niepce to have been then acquainted with a method of forming pictiu-es, by which the lights, semi-tints, and shadows, were rej)resented as in nature ; and he had also succeeded in rendei'ing his Heliogra2)hs, when once formed, impervious to the further effects of the solar rays. Some of these specimens appear in a state of advanced etchings ; but this was accomplished by a process similar to that pursiied in common etchings. The ease with which nitric acid could be applied to etch these Heliographic j^lates will be apparent when the process of obtaining the pictures is understood. * Sun-drawing : a more appropriate name than Photogi'aphy, since it remains a problem (1853) of difficult solution, whether Light, or some agent associated with Light, is active in pi'oducing the chemical changes we are considering. CHAPTER 11. HELIOGRAPHY. THE PROCESS OF M. NIEPCE. M. NiEPCE was the first inqiiirer wlio appears to have produced permanent pictiu'es by the influence of the sun's rays. This process — Heliography — is in many respects peculiar, which renders it necessary, although his prepai-ation was only acted on by an exjiosure of many houi-s to full sunshine, to give a parti- cular account of it ; the more so, as some points of considerable interest require further elucidation. The substance employed by M. Niepce was asphaltum, or bitumen of Judea, He thus directs its preparation : — " I about half fill a wine-glass -with this jwlverized bitumen ; I pom* upon it, .drop by drop, the essential oil of lavender,* until the bitumen is completely saturated. I afterwards add as much more of the essential oil as causes the whole to stand about three lines above the mixture, which is then covered and siibmitted to a gentle heat until the essential oil is fully impregnated with the colouring matter of the bitumen. If this varnish is not of the requii-ed consistency, it is to be allowed to evaporate slowly, without heat, in a shallow dish, care being taken to protect it from moisture, by which it is injured, and at last decomposed. In winter, or during rainy weather, the precaution is doubly neces- sary. A tablet of plated silver, or well cleaned and warm glass, is to be highly polished, on which a thin coating of the varnish is to be applied cold, with a light roll of very soft skin : tliis will impart to it a fine vennilion colour, and cover it with a veiy thin and eqiial coating. The plate is then placed u})on heated iron, which is wi'a]iped round Avith several folds of paper, fi-om which by this method all moisture had been previously exjielled. When the varnish has ceased to simmer, the plate is withdraAvni from the heat, and left to cool and dry in a gentle temperature, and protected from a damp atmosphere. In this part of the operation a light disk of metal, with a handle in the centre, * The English oil of lavender is too expensive for this pnrpose. An article sold as the French oil of lavender, redrawn, is very much cheaper, and answers in every respect as well, if not better. HELIOGRAPHY. THE PROCESS OF M. NIEPCE. 13 slioiJcl be held before the mouth, in order to condense the mois- tiu'e of the breath." The jilate thus prepared is now in a fit state for use, and may- be immediately fixed in the correct focus of the camera. After it has been exposed a siif&cient length of time for receiving the impression, a veiy fiiint outline alone is visible. The next opera- tion is to bring ou.t the hidden picture, which is accomplished by a solvent. Tliis solvent must be carefidly adapted to the pmi30ses for which it is designed : it is difiicult to fix ^dth certainty the pro- portions of its components, but in all cases it is better that it be too weak than too strong ; in the former case the imao-e does not come out strongly ; in the latter it is completely de- stroyed. The solution is prej)ared of one part — not by weight, but volume — of the essential oil of lavender, poiu-ed ujDon ten parts, by measiu-e also, of oil of white petroleum. The mixture which is first milky, becomes clear in two or three days. This compound -ndll act until it becomes satiu-ated with the asphaltum, which state is readily distinguished by an opaque appearance, and dark brown coloui'. A tin vessel somewhat larger than the pho- tographic tablet, and one inch deep, mvist be provided. This is to have as much of the solvent in it as will cover the plate. The tablet is plimged into the solution, and the operator, observing it by reflected light, begins to see the images of the objects to which it has been exposed slowly unfolding their forms, thouo-h stiU veiled by the gradually darkening supernatant fluid. The plate is then lifted out, and held in a vertical position, till as much as possible of the solvent has been allowed to drop away. When the dropping has ceased, we proceed to the last, and not the least important operation, of washing the plate. This is performed by carefully placing the tablet upon a board, B, fixed at a large angle, in the trough a a, the supports being joined to it by hinges, to admit of the necessaiy changes of inclina- tion, under different cii-cum- stances : two small blocks, not thicker than the tablet, are fixed on the board, on which the jjlate rests. "Water must now be slowly poured upon the ujiper part of the board, and allowed to flow evenly over the siu-face of the picture. The descending stream clears away all the solvent that may yet 14 HISTORY OF PHOTOGRAPHY, adhere to the varnish. The plate is now to be di-ied with great care by a gentle evaporation : to presei-ve the pictui-e, it is requisite to cover it iip from the action of light, and protect it from himiidity. The varnish may be applied indifferently to metals, stone, or glass ; but M. Niepce prefers copper plated with silver. To take copies of engravings, a small quantity of wax is dissolved in essential oil of lavender, and added to the varnish already described : the engra\Tiig, first varnished over the back, is placed on the siu^face of the prepared tablet, face towards it, and then exposed to the action of the light. In the camera obscura an exposure of from six to eight hours, varying with the intensity of light, is required ; wliile from foiu* to six hours is necessary to prodvice a copy of an engraving. The pictm-e, in the first instance, is rej^resented by the contrast between the polished silver and the varnish coating. The discoverer afterwards adopted a plan of darkening the silver by iotline, which appears to have led the way to Daguerre's beautiftil process. To darken the tablet, it was placed in a box in which some iodine was strewed, and watched until the best effect was produced. The varnish was afterwards removed by spirit of wine. Of the use of glass plates M. Niepce thus speaks : — " Two experiments in landscape upon glass, by means of the camera, gave me results which, although imperfect, aj^pear deserving of notice, becaiise this variety of application may be brought more easily to perfection, and in the end become a more interesting dei^artment of heliography. " In one of these trials the light acted in such a way that the varnish was removed in proportion to the intensity with which the light had acted, and the picture exhibited a more marked gi-adation of tone ; so that, viewed by transmitted light, the landscape produced, to a certain extent, the well-known efiects of the diorama. " In the second trial, on the contrary, the action of the luminous fluid having been more intense, the parts acted upon by the strongest lights, not lia\'ing been attacked by the solvent, remained transparent ; the difierence of tone residted from the relative thickness of the coatings of varnish. " If this landscape is viewed by reflection in a miiTor, on the varnished side, and at a certain angle, the efiect is remarkably striking ; while, seen by transmitted hglit, it is confused and shapeless : but, what is equally surprising, in tliis position the mimic tracery seems to affect the local colour of the objects." A statement that M. Niepce was enabled to cngi-ave by light, went the round of the press; but this docs not a2)pear to have HELIOGEAPHY. THE PROCESS OP M. NIEPCE. 15 been the case. All that the author of heliography effected, "was the etching of the plate, after it had undergone its various processes, and the di-a"«dng was completed by the action of nitric acid in the usual manner : the parts of the copperplate pro- tected by the varnish remained, of course, unacted on, whilst the other parts were rapidly attacked by the acid. Niepce re- marks that his process cannot be used during the winter season, as the cold and moistiu-e render the varnish brittle, and detach it from the glass or metal. M. Niepce afterwards used a more unctuous vaniish com- posed of bitumen of Judea, dissolved in animal oil of Dijypel. This composition is of much greater tenacity and higher colour than the former, and, after being applied, it can immediately be submitted to the action of light, which appears to render it solid more quickly, from the gi-eater volatility of the animal oil. JVI. Daguerre remarks, that this very property diminishes still farther the resources of the process as respects the lights of the drawings thus obtained. These processes of M. Niepce were much improved by M. Daguerre, who makes the following remarks on the subject : — " The siibstance which should be used in preference to bitu- men is the residuimi obtained by evaporating the essential oil of lavender, which is to be dissolved in alcohol, and applied in an extremely thin wash. Although aU bituminous and resinous substances are, without any exception, endowed with the same property — that of being affected by light — the preference ought to be given to those which are the most unctuous, because they give greater finxmess to the di-awings. Several essential oils lose this character when they are exposed to too strong a heat. " It is not, however, from the ease with which it is decomposed, that we are to prefer the essential oil of lavender. There are, for instance, the resins, which, being dissolved in alcohol, and spread upon glass or metal, leave, by the evaporation of the spirit, a "v eiy white and infinitely sensitive coating. But this greater sensibility to light, caused by a quicker oxidation, renders also the images obtained much more liable to injiuy from the agent by wliich they were created. They gi'ow faint, and disappeai- altogether, when exposed but for a few months to the sun. The residuum of the essential oil of lavender is more effectually fixed, but even this is not altogether unin- fluenced by the eroding effects of a direct exposure to the Sim's light. " The essence is evaporated in a shallow dish by heat, till the 16 HISTORY OF PHOTOGRAPHY. resinous residuum acquires such a consistency, that when cold, it rings on being struck with the poiut of a knife, and flies ofi" in pieces when separated from the dish. A small quantity of this material is aftei^wards to be dissolved in alcohol or etlaer ; the solution formed should be transparent, and of a lemon-yellow colour. The clearer the solution, the more delicate 'wiU be the coating on the plate : it must not, however, be too thin, because it would not thicken or spread out into a white coat ; indis^ien- sable requisites for obtaining good effects in photographic designs. The use of the alcohol or ether is to facilitate the application of the resin under a veiy attenviated form, the spmt being entirely evaporated before the light effects its delineations on the tablet. In order to obtain gi-eater vigour, the metal o\ight to have an exquisite polish. There is more charm about sketches taken on glass plates, and, above all, much greater delicacy. "Before commencing operations, the experimenter must care- fully clean his glass or metal plate. For this purpose, emery, reduced to an impalpable powder, mixed with alcohol, may be used ; applying it by means of cotton- wool : but this paii; of the process must always be concluded by diy-poUshing, that no trace of moistm'e may remain on the tablet. The plate of metal or glass being thus prepared, in order to supply the wash or coating, it is held in one hand, and with the other, the sohition is to be poured over it from a flask or bottle having a wide mouth, so that it may flow rapidly, and cover the whole sm-face. It is at first necessary to hold the plate a little inclined; but as soon as the solution is pom-ed on, and has ceased to flow freely, it is raised perpendicularly. The finger is then j)assed behind and below the plate, in order to di'aw off a portion of the liquid, which, tend- ing always to ascend, would double the thickness of the covering : the finger must be wiped each time, and be passed very rapidly along the whole length of the plate from below, and on the side opposite the coating. When the liquid has ceased to run, the plate is di'ied in the dark. The coating being well di'ied, it is to be placed in the camera obscm-a. The time requii-ed to pro- cm-e a photogi-aphic copy of a landscape is from seven to eight hom-s ; but single monuments sti'ongly illuminated by the sun, or very bright in themselves, are copied in about three hours. " When operating on glass it is necessary, in order to increase the light, to place the plate upon a piece of paper, -vWth great care that the connection is j^ei-fect over every part, as, other- wise, confusion is produced in the design by imperfect reflection. " It frequently hapj)ens that when the plate is removed from HELIOGEAPHY. THE PROCESS OF M. NIEPCE. 17 tlie camera, tliei-e is no trace of any image iijion its surface : it is therefore necessary to use another process to bring out the hidden design. " To do this, provide a tin vessel, larger than the tablet, having all round a ledge or border 50 millimeters (2 EngKsh inches) in depth. Let this be three-q\iarters full of the oil of petroleum ; fix yom- tablet by the back to a j)iece of wood which completely covers the vessel, and place it so that the tablet, face downwards, is over but not touching the oil. The vapour of the petroleum penetrates the coating of the plate in those parts on which the light has acted feebly ; that is, in the portions which correspond to the shadows, imparting to them a transparency as if nothing were there. On the contrary the points of the resinous coating, on which light has acted, having been rendered impervious to the vapour, remain unchanged. "The design miist be examined from time to time, and -s\dth- dra^vTi as soon as a vigorous efiect is obtained. By iirging the action too fax*, even the strongest lights will be attacked by the vapoiu', and disappear, to the destruction of the piece. The pic- ture, when finished, is to be protected from the dust by being kept covered with a glass, which also protects the silver plate from tarnishing." It may perhaps appear to some that I have needlessly given the particulars of a j^rocess, now superseded by others, possessing the most infinite sensibility ; producing in a few minutes a better effect than was obtained by the heliographic process in several hoiu's. There are, however, so many ciu'ious facts connected with the action of light on these resins, that no treatise on pho- tography could be considered complete without some description of them ; and tliis process is now revived with a view to the pro- duction of etchings directly from nature. M. Daguerre remarks, that numerous experiments tried by him -with these resinous preparations of M. Niepce, prove that light cannot fall upon a body without leaving traces of decompo- sition ; and they also demonstrate that these bodies possess the power of renewing in dai'kness, what has been lost by luminous action, pi'ovided total decomposition has not been effected. Tliis heliographic process must be regarded as the earliest successful attempt at fixing on solid tablets the images of the camera ob- scura, and at developing a dormant image. CHAPTER III. MR. H. FOX TALBOT's PHOTOGENIC DRAWINGS, CALOTYPE, ETC. Section I. — Photogenic Drawing, On the 31st of January, 1839, six montlis prior to the puLlica- tion of M. Dagiierre's process, Mr. Fox Talbot communicated to the Royal Society his photographic discoveries, and in February he gave to the world an account of the process he had devised for preparing a sensitive jiaper for photographic drawings. In the memoir read before the Royal Society, he states — " In the spring of 1834, 1 began to put in practice a method which I had devised some time previously, for employing to piu'poses of utility, the very curious property which has been long known to che- mists to be possessed by the nitrate of silver, namely, its dis- coloration when exposed to the violet rays of light." From this it appears that the English philosopher had pursued his researches ignorant of what had been done by others on the Continent. It is not necessary to enlarge, in this place, on the merits of the two discoveries of Talbot and Daguerre; but it may be as well to show the kind of sensitiveness to which Mr. Talbot had arrived at tliis early period, in his prepai'ations ; which will be best done by a brief extract from his o^vn com- munication. "It is so natural," says this exj)erimentalist, "to associate the idea of labour with gi'eat complexity and elaborate detail of exe- cution, that one is more struck at seeing the thousand florets of an Ayrostis depicted with all its capillary branchlets, (and so accui-ately, that none of all this multitude shall want its little bivalve calyx, requiring to be examined through a lens), than one is by the picture of the large and simple leaf of an oak or a chestnut. But in truth the difficulty is in both cases the same. The one of these takes no more time to execute than the other ; for the object wliich woidd take the most skilful artist days or weeks of labour to trace or to copy, is efiected by the boundless powers of natural chemistry in the space of a few seconds." And again, "to give some more definite idea of the rapidity of the process, I will state, that after various trials, the nearest valua- talbot's photogenic drawing. 19 tion 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.'''' This is to be understood of the paper then used by Mr. Talbot for taking ob- jects by means of the solar microscope. In the Philosophical Magazine, Mr. Fox Talbot published the first account of his Photogenic experiments. Tliis term was in- troduced by this gentleman : and his experiments cannot be better described than in his own words. " In order to make what may be called ordinary photogenic paper, I select, in the first place, paper of a good firm quality and smooth sm-face. I do not know that anything answers better than superfine wi'iting- paper. I dip it into a weak solution of common salt and wipe it dry, by which the salt is uniformly distributed throughout its substance. I then spread a solution of nitrate of silver on one surface only, and diy it at the fii'e. The solution shoidd 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 propor- tion 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 efiect diminishes, and, in certain cases, becomes exceedingly small. " This paper, if properly made, is very useful for all photoge- nic purposes. For example, nothing can be more perfect than the images it gives of leaves and flowers, especially with a sum- mer Sim, — the light passing thi-ough the leaves, delineates every ramification of their nerves. " Now, suppose we take a sheet thus prepared, and wash it with a saturated solution of salt, and then diy it. We shall find (es- pecially 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 quantity of the solution of silver, it becomes again sensible to Kght, 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 ca- mera obscui'a. "In conducting this operation, it will be found that the re- sxdts are sometimes more and sometimes less satisfactoiy in con- sequence of small and accidental variations in the proportions employed. It happens sometimes that the chloride of silver is disposed to darken of itself without any exposm-e to light : this 20 HISTORY OF PHOTOGRAPHY. shows that the attempt to give it sensibUity has been earned too far. The object is to approach to this condition as near as pos- sible withont reaching it, so that the snbstance may be in a state ready to yield to the slightest extraneous force, such as the feeble imj^act of the violet rays when much attenuated. Having, therefore, prepared a number of sheets of paj)er A^th chemical proportions slightly diitferent 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 hovu". Then, if any one of them, as frequently hap- l^ens, exhibits a marked advantage over its competitoi-s, I select the papier which l)ears the corresponding niimber to be placed in the camera obscuj^a." The increased sensitiveness given to paper by alternate ablu- tions of saliue and argentine washes, the striking difierences of eifect produced by accidental variations of the proportions in which the chemical ingredients are applied, and the spontaneous change which takes place, even in the dark, on the more sensitive varieties of the paper, are all subjects of great interest, which demand fiu'ther investigation than they have ever yet received, and which, if followed out, promise some most important expla- nations of chemical phenomena at present involved in imcer- taiuty, particularly those which appear to show the influence of time, an element not sufficiently taken into account, in over- coming the weaker affinities. Few fields of research promise a greater measure of reward than these ; already the ai-t of making suu-pictiu"es has led to many very important physical discoveries, but most of the phenomena ai-e yet involved in obscurity. Section II. — The Calotype. Although, in order of date, the investigations of Sii' John Herschel and others have a priority over those particular expe- riments of ]Mr. Talbot's which resulted in the discoveiy of his very beautiful process, the calotype, yet to avoid confusion, it is thought ad^-isable to group together the discoveries of each in- vestigator, whei'e this is piucticable, in our historical division. The earliest productions of Mr. Talbot were simply such pre- pai-ations as those already described, in which a chloride of silver was formed on the siu'face of the jiaper, ^vitll some niti-ate of silver in excess. These need not be any fiu'ther described than they have ah-eady been. Early in 1840, ch-awings on paper were handed about in the scientific circles of London and of Paris, wliich Avere a great ad- THE CALOTYPE. 21 Tance upon anytliirg wliich had been previously clone. These ^yere the results of a new process discovered by ]Mr. Talbot, and then attracted so much attention, that M. Blot made them the subject of a commiuiication to the Academy of Sciences in Paris. His remarks are printed in extenso in the Goviptes Rendus, from, which the following passages are translated, as they bear j^articnlarly on many of the defects which still continue to prove an- noyances in the photogra2:)hic process to which they have reference. Many of the remarks have a i^eculiar vahie from the sugges- tions they contain, and they are woi-thy of record as marking the period when the French were first made acquainted with the 25rocesses on paper, as practised in England. Some disjio- sition has been sho^vn on the part of several continental photo- graphers to claim originality for processes published in England many years before their o^\ti were devised, and which singularly resemble them. After remarking that many very important physical facts were being developed by the study of photograj)hy, M. Biot continues : — " It is not to be expected that photogenic drawings, made on paper, can ever equal the clearness and fineness of those obtained on level and polished metallic plates. The texture of paper, its superficial roughnesses, the depth of the imbibitions, and the capillaiy communication established between the various un- equally marked parts of its siuface, are so many obstacles to absolute strictness of delineation, as well as to the regular gradation of tints in the camera obscm-a ; and the influence of these ol)stacles is greater when the chemical operation is slowly carried on. But when there is no pretence or necessity for submitting to the delicacies of art — when it is required, for example, to coj)y rare manuscripts faithfully — if we have papers which are very suscej^tible of receiving impressions in the camera obscura, they will suffice perfectly ; particularly when they present, like those of Mr Talbot, the facility of immediately procm-ing copies of the primitive di^awing. It will, therefoi'e, doubtless be found more commodious, and often even more pi*acticable, to put fovu' or five hundred drawings in a portfolio, than to carry about a similar provision of metallic plates with those indispensable protectors, squares of glass, to cover them. Attempts are being made, at this time, to fix the images pro- duced by the Dagiierreotyjie — perfect prints, it is true, but which are as light as the vapovu- 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 combination of physical conditions whence 22 HISTORY OF PHOTOGRAPHY. these admirable images result, will find it very difficult — T am far from saying impossible — to fix tbem, watbout destroying, or at least without essentially altering, tbe cavises wbicb produce their charm ; and then, for the piu-poses which 1 have mentioned, papers very susceptible of impression would still have the advan- tages of being less troublesome in removal from place to place, as also of more easy preservation. " The utility of sensitive papers for copying texts was a natural consequence of the clearness of the copies of engravings which Mr. Talbot had aheady obtained by application, and which were presented to the Academy. He has included others among those just sent : there are also added specimens of this especial apjili- cation, consisting of copies of a Hebrew psalm, of a Persian Gazette, and of an old Latin chai-t of the year 1279. Our brethren of the Acadcmie des Belles Lettres, to whom I exhibited these impressions, were pleased to remark the fidelity of the chai^acters, and their clearness, by which they ai'e rendered as legible as the original text. Doubtless an old manuscript may be copied more quickly and more accurately by this means than by hand, even when the language in which it is written is understood. However, we must stop here. These copies are obtained by application : we must be enabled to obtain them by ianmediate radiation in the camera obsciu-a. It is the only means of extending the process to papyrus and other opaque manuscripts, or which are not sufficiently transparent for i-adia- tion to traverse them. Moreover, the application of leaves is very difficult when they are bound vip in a volume, and cannot be detached from one another. "But this important extension will requfre much physical per- fecting, towards which experimenters should direct their efibrts. The fii-st thing will be to augment the sensibility of the paper as much as possible, in order that the capillaiy communication of its various parts may not have sufficient time to deteriorate the effects of the local and immediate action of the radiation, I should be led to believe that it is jirincipally to this kind of communication should be attributed the fact remarked by IMi-. Talbot, that, in experiments by application, it is more difficidt to copy clearly a tissue of black lace spread on a white ground, than white lace on a 1)lack gi-ouud ; two cases of which he here gives examples. But another more liidden and more general difficulty seems to me to proceed from the imequal 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 radia- tion in the camera obscm-a a pictui'e painted on canvas, wood, THE CALOTYPE. 23 or porcelain : the different colouring substances employed by the painter are placed and distributed in such a manner that each of them absoi-bs certain portions of the total incidental light, and reflects especially towards youi" eye the complementary por- tions, wherein predominate the rays proper to form the tint of which it would give you the sensation. But the chemically active reagent which the same parts of the picture receive and reflect, is distinct from tbe light which affects yoiu* 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 ; 2d, 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 tliis 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 : in- versely 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, evidently, the illu- sion of the experimenters who hope to reconcile, not only the intensity, but the tints of the chemical impressions produced by radiations, with the coloiu-s of the objects from which these I'adiations emanate. However, the distant or near relations of these two species of phenomena are very ciu-ious to study, not only as regards the photogenic art, since that name has, very improperly, been given it, but likewise as regards experimental physics. I doubt not that examples of these jDcculiarities may be remarked in the images of natural objects and coloured pictures executed by the Daguen-eotype ; but very apparent ones may be seen among Mr. Talbot's present impressions. Thus, some of them represent white procelain vases, coloured shells, a candlestick (of metal) with its tajier, 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 piu-ely white light, probably also the radiations of every kind, are, relatively to the others, in 24 HISTORY OF PHOTOGRAPHY. an exaggerated proportion of illumination, wliicli, it seems to me, must result, partially, from the capillaiy comnninication diu-ing 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 candle- stick (metallic), where this reflection occiuTed, are copied by white stains locally applied, and which detei'iorate the effect of the whole by theii- cHspropoi-tion. But this is seen especially in a pictm-e by Correggio, the frame of wliich was very vividly copied, whilst the figm-e on the canvas was hardly perceptible. This dispi'oportion of lustre in the reproduction of some white parts, especially when they are didl and consequently very radiating, is sensible in certain parts of views taken by Mr. Talbot, to the point of rendering cUflicult the interpretation of the oly'ect to which they belong. However, these views are very satisfactoiy, 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 liei'e, as an example, four proofs of the same view of Mr. Talbot's house, with an identical dispo- sition of lights and shades ; so that some, at least, if not three out of foui', must have been procured by superposition. Mr. Talbot is right in representing this property of repi'oduction as an especial advantage of his process, and it would indeed be veiy useful in voyages. I have exposed one of these di'a\vings to the action of the sun, not very powerful, it is true, for sevei'al hours, and I have not perceived the slightest altei-ation 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 siiid, it should be expected that the triimiph 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 cluefly, of various forms and sizes, pi-esent very remark- able results, especially taking into consideration the imfavounible season at which they were produced. Tndy, there is not foimd in them the strict perfection of tiace, nor the admii'able gi'ada- tions of lights and shades, which constitute the chanu of M. Dagueire s impressions ; and I again repeat it, that my expres- sions may not be exaggerated. But I also rei:)eat, that repre- sentations on sensitive papers must be consideretl as principally THE CALOTYPE. 25 applicable to a different object, which does not impose such strict conditions of art, reqnii'ing only faithful images, sufficiently clear in their details to be readily recog-nized, and which, more- over, 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 ah'eady present many of these essential qualities, with the advantage of being able to fm-nish numerous copies immediately. His efforts, and those of others occupied with the same subject, will conclude by adding to them every thing which may be desirable, provided that expectation, or the pretension of a perfection of art physically incompatible mth operations on paper, do not give a false dii-ection to their endeavours. How- ever, not to appear to despair too much of the future, I may add that the height of success would consist in discovering a sub- stance very susceptible of receiving impressions, which might be applied on a papyraceous leaf -svithout 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 necessaiy even that the fii'st impression thus rai:)idly obtained should copy the lights and shades in theu* proper places, provided that its tmns- j)arency and fixedness were such that we might deduce them from the application of copies wherein the inversion would be corrected. And perhaps, by this decomjiosition of the problem into two successive operations, one of the best ways is opened by which it may be resolved." Numerous improvements have been introduced, but still physi- cal difiiculties, such as those which he has indicated, siirround the photograjihic processes, and even where M. Biot has proved wrong in his conjectm'es, his remarks form a cmious chapter hx the history of the art. Mr. Talbot's descrijition of his process, the patent for wliich is dated 1841, is as follows : — * Take a sheet of the best Avi-iting-paper, having a smooth sur- face, and a close and even texture. The water-mark, if any, should be cut off, lest it should injure the appearance of the picture. Dissolve 100 gi'ains of crystallized nitrate of silver in six oimces of distilled water. "Wash the paper with this solution, with a soft brush on one side, and put a mark on that side, whereby to know it again. Diy the paper cautioiisly at a dis- tance from the fii'e, or else let it diy spontaneously in a dai'k * Mr. Talbot, by a letter in the Times of August 13, 1852, gives to the public the right of using any of his patents for any purpose not involving the production of portraits from the life. The letter is printed in the Appendix. .26 HISTORY OF PHOTOGRAPHY. room. When diy, or nearly so, dip it into a solution of iodide of potassium, containing 500 grains of that salt dissolved in one pint of water, and let it stay two or tlii'ee minutes in the solu- tion. Then dip the paper into a vessel of water, dry it lightly with blotting-paper, and finish drying it at a fire, which will not injure it even if held pretty near : or else it may be left to dry spontaneously. All this is best done in the evening by candle- light : the paper, so far j)repared, is called iodized paper, because it has a uniform pale-yellow coating of iodide of silver. It is scarcely sensitive to light, but nevertheless it ought to be kept in a portfolio or drawer until wanted for use. It may be kept for any length of time without spoiling or undergoing any change, if protected from sunshine. When the paper is required for use, take a sheet of it, and wash it with a liquid prepared in the following manner : — Dissolve 100 grains ot crystallized nitrate of silver in two ounces of distilled water; add to this solution one-sixth of its volume of strong acetic acid. Let this be called mixture A. Make a saturated solution of crystallized gallic acid in cold distilled water. The quantity dissolved is very small. Call tliis solution B. Mix together the liquids A and B in equal volimaes, but only a small quantity of them at a time, because the mixtui-e does not keej) long without spoiling. This mixture Mr. Talbot calls the gallo-nitrate of silver. This solution must be washed over the iodized paper on the side marked, and being allowed to remain upon it for half a minute, it must be dipped into water, and then lightly dried with blotting-paper. This operation in particular requfres the total exclusion of daylight ; and although the paper thus jirepared, has been found to keep for two or three months, it is advisable to use it within a few hours, as it is often rendered useless by sjiontaneous change in the dark. Paper thus prepared is exquisitely sensitive to light ; an ex- posure of less than a second to diffused daylight being quite suflficient to set up the process of change. If a piece of this paper is partly covered, and the other exposed to daylight for the briefest i^ossible 2)eriod of time, a veiy decided impression will be made. This imj^ression is latent and invisible. If, how- ever, the pai:»er be placed aside in the dark, it will gradually develops itself; or it may be brought out immediately by being washed over with the gallo-nitrate of silver-, and held at a short distance from the fire, by which the exposed portions become broAvn, the covered jiarts remaining of their original colour. The pictures being thus procured, are to be fixed by washing in clean water, and lightly drying between blotting-paper, after which IMPROVEMENTS m CALOTYPE. 27 tliey are to be washed ovei' with a sohition of bromide of potas- sium, containing 100 grains of that salt, dissolved in eight or ten ounces of water ; after a minute or two, it is again to be dip^Ded into water, and then finally dried. Such was, in all its main features, the description given by Mr. Talbot in his specification of his process for producing the Calotype, or beautiful pictu7-e (as the term signifies) : he, in a second patent, included the points stated in the next section. Section III. — Improvements in Calotvpe. Such is the term employed by Mr. Talbot, and these im- provements consist of the follomng particulars, constituting that gentleman's second claim. 1. Removing the yellowish tint which is occasioned by the iodide of silver, from the paper, by plunging it into a hot bath of hyposulphite of soda dissolved in ten times its weight of water, and heated nearly to the boiling point. The picture should remain in the bath about ten minutes, and be then washed in warm water and dried. Although this has been included by Mr. Talbot in his specifi- cation, he has clearly no claim to it, since, in February 1840, Sir John Herschel published, in his Memoir " On the Chemical Action of the Rays of the Solar Spectrum," a process of fixing with the hot hyposulj)hite of soda. After imdergoing the operation of fixing, the picture is placed upon a hot ii-on, and wax melted into the pores of the paper to increase its transparency. 2. The calotype })aper is rendered more sensitive by placing a warm iron behind in the camera whilst the light is acting upon it. 3. The preparation of io-gallic paper, which is simply washing a sheet of iodized paper with gallic acid. In this state it wiU keep in a portfolio, and is rendered sensitive to light by washiBg it over with a solution of nitrate of silver. 4. Iodized paper is washed with a mixture of twenty-six parts of a saturated solution of gallic acid to one part of the solution of nitrate of silver ordinarily used. It can then be dried without fear of spoiling, may be kept a little time, and used without fiu'ther preparation. 5. The improvement of photographic drawings by exposing them twice the usual time to the action of sunlight. The shadows are thus rendered too dark, and the lights are not sufiiciently white. The drawing is then washed, and plunged into a bath of 28 HISTORY OF PHOTOGRAPHY. iodide of potassium, of tlie strength of oOO gi-ains to eacli pint of water, and allowed to remain in it for one or two minutes, which makes the pictm-es brighter, and its lights assiune a pale- yeDow tint. After this, it is washed, and immei*sed in a hot bath of hyposulphite of soda imtil the pale-yellow tint is removed, and the lights remain quite wliite. The pictiu'es thus finished have a pleasing and peculiar effect. 6. The appearance of photographic pictures is improved by- waxing them, and placing white or coloui'ed paper behind them. 7. Enlarged copies of daguerreotypes and calotyjies can be obtained by thromng magnified images of them, by means of lenses, upon calotype paper. 8. Photographic printing. A few pages of letterpress are printed on one side only of a sheet of paper, which is waxed if thought necessaiy, and the letters ai-e cut out and sorted ; then, in order to compose a new page, a sheet of white paper is riUed with straight lines, and the words are formed by cementing the separate letters in their proper order along the lines. A nega- tive photographic copy is then taken, having white lettei-s on a black ground ; this is fixed, and any nimiber of positive copies can be obtained. Another method proposed by the patentee is to take a copy by the camera obscm-a fi'om large letters painted on a white board. 9. Photographic publication. This claim of the patentee con- sists in making, fu'st, good negative di-a-vvings on papers prepai-ed with salt and ammonio-nitrate of silver ; secondly, fixing them by the process above described ; thii'dly, the formation of positive drawings from the negative copy, and fixing. These claims, taken from the specification as published in the Repertory of Patent Inventions, ai-e preseiwed, in then- original form, for the pui-pose of showing how much that is now fidly accomplished was foreseen by Mr. Talbot as the resvdt of his discoveries. Sectiox it. — Pictures on Porcelain Tablets. A third patent has been obtained by ]\Ii\ Talbot, mainly in- volving the use of porcelain as a substitute for glass, and con- tains some usefid facts noticed by Mr. Malone. The fii-st pai-t of the patentee's invention consists in the use of plates of imglazed porcelain, to receive the photogi-aphic image. A plate intended for photographic jim-poses should be made of the finest materials employed by the mauufactm-ers of porcelain ; it should also be flat, very thin, and semi-transparent ; if too thin, so PICTURES ON PORCELAIX TABLETS. 29 that there woidd be a cliance of breaking, it may be attacbed bj means of cement to a piece of glass, to give it strength. The sub- stance of the plate should be slightly porous, so as to enable it to imbibe and retain a sufficient quantity of the chemical solutions employed. To prepare the plate for wse, it is fii'st requu'ed to give it a coating of albumen, or white of eggs, laid on very evenly, and then gently di-ied at a fire. According as the plate is more or less porous, it requires more or less of the albiiminous coating ; it is best to employ a veiy close-gi'ained porcelain, which requii-es but little white of egg. The prepared plate may be made sensi- tive to light in the same way in which a sheet of paper is rendered sensitive ; and we generally find the same methods ap- plicable for photographic pictiu'es on paper, applicable to those on porcelain plates, and one of the processes employed by the jjatentee is nearly the same as that patented by Mr. Talbot in 1841. The prepared plate is clipped into a solution of nitrate of silver, made by dissolving twenty -five grains of nitrate in one ounce of water : or the solution is spread over the jjlate uni- formly ^Yiih a brush; the plate is then dried, afterwards dipjied into a solution of iodide of potassium, of the strength of about twenty-five grains of iodide to one ounce of water, again di-ied, and the surface rubbed clean and smooth with cotton. The plate is now of a pale-yellow coloru', owing to the formation on its sui'face of iodide of silver. The plate, prepared as above dii'ected, may be kept in this state until requu'ed, when it is to be rendered sensitive to light by washing it over with a solution of gallo-nitrate of silver, then placed in the camera; and the image obtained is to be rendered "visible, and sufficiently strengthened, by another washing of the same liquid, aided by gentle warmth. The negative pictiu'e thus obtained is fixed by washing it with water, then with bromide of potassiiun, or, w^hat is still better, hyposidphite of soda, and again several times in water. The plate of porcelain being semi-transparent, positive pictures can be obtained from the above-mentioned negative ones by copying them in a copying-frame. The pictui-e obtained on porcelain can be altered or modified in appearance by the application of a strong heat, a process not applicable to pictm'es taken on paper. With respect to this part of theii" invention, the patentees claim : — " The obtaining by means of a camera, or copying-frame, photograpliic images or pictures upon slabs or plates of porcelain." The second part relates to the process which has been discovered and improved upon by Mr. Malone, who is associated with Mr. Fox Talbot in the patent. The patentees' improvement is a method of ob- taining more complete fixation of photographic pictures on paper. 30 HISTORY OF PHOTOGRAPHY. For tliis purpose, tlie print, after undergoing the usual fixing process, is dipped into a boiling solution of strong caustic potash, which changes the colour of the print, and usually, after a certain time, acquires something of a greenish tint, which indicates that the process is terminated. The picture is then well washed and dried, and if the tint ac- quired by it is not pleasing to the eye, a slight exposure to the vapours of sulphuretted hydrogen will restore to it an agi-eeable brown or sepia tint. Under this treatment the picture dimi- nishes in size, insomuch that if it were previously cut in two, and one part submitted to the potash process, and the other not, the two halves, when afterwards put together, would be found not to correspond. The advantages of this process for re- moving any iodine which, even after fixing with the hyposulpliite, remains in the paper, is great, and it will tend much to preserve these beautiful transcripts of natui'e. The patentee also claims as an improvement the use of var- nished, or other transparent paper, impervious to water, as a substitute for glass, in certain circumstances, to support a film of albumen for photographic purposes. A sheet of wi'iting-paper is brushed over with several coats of varnish on each side : it thus becomes extremely transparent. It is then brushed over on one side with albumen, or a mixture of albumen and gelatine, and dried. This film of albumen is capable of being rendered sensitive to light by exposing it to the vapour of iodine, and by following the rest of the process indicated in the preceding section of this specification. The advantages of using varnished or oil paper do not consist in any superiority of the images over those obtained upon glass, but in the greater convenience of using paper than glass in cases where a large number of pictui-es have to be made and earned about for considerable distances : besides this, there is a well-known kind of photographic pictures giving panoramic views of scenery, which are produced upon a ciu-ved svurfiice by a movement of the object-glass of the camera. To the production of these images glass is hardly applicable, since it cannot be readily bent to the required curve and again straightened ; but the case is met by emjiloying talc, varnished paper, oiled paper, &g., instead of glass. It will be seen that the varnished paper acts as a support to the film of albumen or gelatine, which is the siirface on which the light acts, and forms the picture. The next improvement consists in forming photo- graphic pictures or images on the siu-faccsof polished steel plates. For this jiuqDose, one part (by measure), of a saturated solution of iodide of potassium is mixed with 200 parts of albumen, and spread as evenly as possible upon the surface of a steel plate INSTANTAJfEOUS PROCESS. 31 and dried by the lieat of a gentle fire. The plate is then taken, and, whilst stiU warm, is washed over with an alcoholic solution of gallo-nitrate of silver, of moderate strength. It then becomes very sensitive, and easily receives a photographic image. If the plate be cold, the sensibility is considerably lower. The image obtained is fixed by washing with hyposulphite of soda, and finally with water. Section V. — Instantakeous Process. The next invention and patent of Mr. Fox Talbot possesses many peculiarities, and as the results are of a remarkable character, it is important that the process should be given iincui'tailed in its main particulars. The following description must be regarded as an abstract of Mr. Talbot's communication to the Athenceum, Dec. 6, 1851. An experiment was tried in June, at the Royal Institution, in which an instantaneous image was produced ; but as the process was the subject of another patent, it was not pub- lished until the above date. The experiment in question was that of obtaining a photographic copy of a printed paj^er fastened to a wheel, which was made to revolve as rapidly as jjossible, by illuminating it for a moment by the light obtained fi'om the dischai'ge of a Leyden battery : the bill was faithfully printed, not even a letter being indistinct. A glass plate is employed, and Mr. Talbot thus directs that it should be prepared. 1. Take the most liquid portion of the white of an egg, re- jecting the rest. Mix it with an equal quantity of w^ater. Spread it very evenly upon a plate of glass, and dry it at the fire. A strong heat may be used without injuring the plate. The film of dried albumen ought to be uniform and nearly iuvisible. 2. To an aqueous sokition of nitrate of silver add a conside- rable quantity of alcohol, so that an ounce of the mixtm-e may contain three grains of the nitrate. I have tried various pro- portions, from one to six grains, but perhaps three grains answer best. More expei'iments are here requii'ed, since the results are much influenced by this part of the process. 3. Dip the plate into this solution, and then let it dry spon- taneously. Faint prismatic colours will then be seen upon the plate. It is important to remark, that the nitrate of silver appears to form a true chemical combination with the albumen, rendering it much harder, and insoluble in liquids which dis- solved it previously. 4. Wash with distilled water to remove any superfluous por- tion of the nitrate of silver. Then give the plate a second 32 HISTORY OF PHOTOGRAPHY. coating of albumen similar to the fii"st, but, in drying, avoid beating it too much, which would cause a commencement of decomposition of the silver. 5. To an aqueous solution of proto-iodide of iron add, first, an equal vohmie of acetic acid, and then ten volumes of alcohol. Allow the mixture to repose two or thi'ee days. At the end of that time it wiU have changed colom-, and the odoiu* of acetic acid as well as that of alcohol will have disappeared, and the liquid will have acquii'ed a peculiar but agreeable vinous odour. It is in tliis state that I prefer to employ it. 6. Into the iodide thus jjrepared and modified, the plate is dipped for a few seconds. All these operations may be per- formed by moderate daylight, avoiding, however, the direct solar rays. 7. A solution is made of nitrate of silver, containing about 70 grains to one ounce of water. To thi-ee parts of this add two of acetic acid. Then, if the prepared plate is rapidly dipped once or twice into this solution, it acquii-es a very great degree of sensibility, and it ought then to be placed in the camera without much delay. 8. The plate is Avithdrawn from the camera, and in order to bring out the image, it is dipped into a solution of protosulphate of iron, containing one part of the saturated solution diluted with two or three parts of water. The image aj)pears very rapidly. 9. Having washed the plate with water, it is now placed in a solution of hyj^osulphite of soda, Avhich in one minute causes the image to brighten up exceedingly, by remoxdng a kind of veil which previously covered it. 10. The plate is then washed "wdth distilled water, and the process is terminated. In order, however, to guai'd against future accidents, it is well to give the picture another coating of albumen and of varnish. " These operations may appear long in the description, but they are rai^idly enough executed after a little practice. In the jjrocess which I have now described, I trust that I have effected a harmonious combination of several previously ascei'tained and valuable facts, especially of the, iiihotorjvaphic property of iodide of iron, which was discovered hy Dr. Woods, of Parsonstoion, in Ireland ; and that of sulphate of iron, for tvhich science is indebted to the researches of Mr. Robert Hunt. In the time adjustment of the proportions, and in the mode of operation, lies the difficulty of these investigations, since it is possible, by adopting other proportions and manipulations not very gi-eatly differing from the above, and which a cai'eless reader might Talbot's ufSTANTANEOus process. 33 consider to be the same, not only to fail in obtaining tlie MgMy exalted sensibility wLich. is desii'able in this process, but actually to obtain scarcely any photographic result at all." Mr. Talbot proposed the name of AmfMtype, or doubtful image, for these pictures. Tliis name had, however, been adopted previously, at Mr. Talbot's recommendation, by Sir John Her- schel, and in the Collodion processes, to be by-and-by described, we have similar phenomena, to which the name applies with equal force. It is not improbable but the high degi'ee of sensibility which is certainly obtained in this process, is rather due to the forma- tion of an iodide of ethyle in the mixture, than to the combination, as INIr. Talbot supposes, of the proto-iodide and the proto-sulj)hate of iron. My own researches convince me that we should seek for the highest degrees of sensibility amidst the numerous com- binations of the ethyle and methyle compounds with the metallic oxides. The last invention of Mr. Fox Talbot is one by which he obtains etchings of objects ; the images of which are produced by radiant action upon steel plates. This process, and analogous ones by others, will be described in Part III. CHAPTER IV. DAGUERREOTYPE — THE DISCOVERY OF M. DAGUERRE. Section I. — The Original Process of Daguerre. It has been already stated tliat Niepce and DagueiTe having by accident discovered they were prosecuting expex-iments of the same kind, entered into a partnership. On the 5th Dec, 1829, Niepce communicated to Daguerre the particulars of the process employed by him, which has been ah-eady described (Chap. II.), under the term Heliography. Niepce died in July 1833, biit he has left some letters which clearly show that he had been a most industrious investigator. One extract appeal's of particular importance : — " I repeat it, sir," he says, " I do not see that we can hope to derive any advantage from this process {the use of iodine) more than from any other method which depends upon the use of metallic oxides," &c. Again, he says, " a decoction of Thlaspi (Shepherd's purse), fumes of phosphorus, and particulai-ly of svdphur, as acting on silver in the same way as iodine, and caloric, produce the same effects by oxidizing the metal, for from this cause proceeded in all these instances then- extreme sensibility to light." After the death of M. Nicephore Niepce, a new agreement was entered into between his son M. Isidore Niepce and Daguerre, that they should pursue their investigations in common, and share the profits, whatever they might eventually prove to be. The discovery of Daguerre was reported to the world early iu January, 1839 ; but the process by wliich liis beautiful pictiu-es were produced was not made known until the July following, after a bill was passed secvu'ing to himself a pension for life of 6000 francs, and to M. Isidore Niepce, the son of M. Niepce above mentioned, a pension for life of 4000 francs, with one-half in reversion to their widows. It was regi'etted, that after the French Government had thus liberally purchased the seci-et of the process of the Daguerreotype, for '■'the glory of endoiinng the world of science and of art tvitlb one of the most surpvising THE DISCOVERY OF M. DAGUERRE. 35 discoveries that honour their native land," on the argument that " the invention did not admit of being secured by patent, for as soon as publislied all might avail themselves of its advantages," that its author should have guarded it by a patent right in England. From the primary importance of this very beautiful branch of the photographic art, I shall devote some sj^ace to a description of the original px'ocess, reserving for the division devoted to the manipulatory details the description of each improvement which has been published, having any practical advantage, either by lessening the labour required, or reducing the expense. The pictui'es of the daguerreotype are executed upon thin sheets of sUver plated on copper. Although the copper serves principally to support the silver foil, the combination of the two metals appears to tend to the perfection of the effect. It is essential that the silver should be very pure. The thickness of the copper should be sufficient to maintain perfect flatness, and a smooth surface ; so that the images may not be distorted by any warping or luievenness. Unnecessary thickness is to be avoided on account of the weight. The process is divided by Daguen-e into five operations. The first consists in cleaning and polishing the plate, to fit it for receiving the sensitive coating on which light forms the picture. The second is the formation of the sensitive ioduret of silver over the face of the tablet/ The third is the adjusting of the plate in the camera obscura, for the purpose of receiving the impression. The fourth is the bringing out of the photograpliic pictiu-e, which is invisible when the plate is taken fi-om the camera. The fifth and last operation is to remove the sensitive coating, and thus prevent that susceptibility of change under luminous influence, which would otherwise exist, and quickly destroy the picture. First Operation.— A small pliial of olive-oil — some finely carded cotton — a muslin bag of finely levigated pumice — a phial of nitric acid, diluted in the projjortion of one part of acid to sixteen parts of water, are required for this operation. The operator must also provide himself with a small spii-it-lamp, and an iron wire frame, upon which the plate is to be placed whilst being heated over the lamp. The following figures represent this frame. The first view is as seen from above. The second is a section and elevation, showing the manner in which it is fixed. The plate being first powdered over with pumice, by shaking the bag, a piece of cotton dipped into the olive-oil is then carefully i-ubbed over it with a continuous circular motion, com- mencing from the centre. When the plate is well polished 36 HISTORY OF PHOTOGRAPHY. It is then to be it must be cleaned by jwwdering it all over with pumice, and then rubbing it "with (hy cotton, always rounding and crossing the strokes, it being imi^ossible to obtain a true surface by any other motion of the hand. The sm-face of the plate is now nibbed all over with a pledget of cotton, slightly wetted with the di- luted nitric acid. Frequently change the cotton, and keep rubbing briskly, that the acid may be equally diffused over the silver, as, if it is permitted to mn into di'ops, it stains the table. It will be seen when the acid has been properly diffused, from the appearance of a thin film equally spread over the surface, cleaned off with a little iHimice and diy cotton. The plate is now placed on the wire frame — the sUver upwards, and the spirit-lamp held in the hand, and moved about below it, so that the flame plays upon the copper. This is continued for five minutes, when a white coating is formed all over the sm*face of the silver ; the lamp is then withdra'wn. A charcoal fire may be used instead of the lamp. The plate is now cooled suddenly, by placing it on a mass of metal, or a stone floor. When per- fectly cold, it is again polished Avith cby cotton and pumice. It is necessary that acid be again applied two or three times, in the manner before dii'ected, the diy pmnice being powdered over the plate each time, and polished off gently with diy cotton. Care must be taken not to breathe upon the plate, or touch it with the fingers, for the slightest stain upon the surface will be a defect in the drawing. It is indispen- sable that the last operation with the acid be performed immediately before it is in- tended for use. Let every pai'ticlc of dust be removed, by cleaning all the edges, and the back also, with cotton. After the firet polishing, the plate c is fixed on a board by means of four fillets, b B B B, of plated cop]ier. To each of these are soldered two a %> a a small projecting pieces, which hold the ^• tablet near the corners ; and the whole is i-etained in a proper position by means of screws, as represented at D D D D. r-irf>- :2s3 THE DISCOVERY OF M. DAGUERRE. 37 A- Second Operation. — It is necessary for this operation, wliicli is really tlie most important of all, that a box, similar to figs. 4 and 5, be provided. Figiu-e 4 represents a section, supposed to pass down the middle of the apparatus by the line A b in fig. 5, which represents the box as seen from above, c is a small lid which accurately fits the in- terior, and divides the boxes into two chambers. It is kept con- stantly in its place when the box is not in use ; the jjurpose of it being to concentrate the vapour of the iodine, that it may act more readily upon the plate ^ when it is exposed to it. D is the little capsule in which the iodine is placed, which is covered with the ring, J, upon which is stretched a piece of fine gauze, by which the particles of iodine are prevented fi'om rising and staining the plate, while the var- poiu', of coiu'se, passes freely thi'ough it. e is -B the board with the plate attached, which rests on the four smaller pro- jecting pieces, F, fig. 5. G is the lid of the box, 5 which is kept closed, ex- cept when the plate is removed or inserted. H represents the supports for the cover c. K, tapering sides aU romid, forming a funnel-shaped box within. To prepare the plate : — The cover c, being taken out, the cup, D, is charged with a sufficient quantity of iodine, broken into small pieces, and covered with the gauze, J. The board, E, is now, with the plate attached, placed face do^vnwards, in its pro- per position, and the box cai'efiilly closed. In this position the plate remains until the vapoui" of the iodine has jiroduced a definite golden yellow colour, nothing more nor less.* If the operation is prolonged beyond the point at which this efiect is produced, a violet coloiu" is assumed, * If a piece of iodine is placed on a silver tablet, it will speedily be sur- rounded with coloured rings: these being the colours of thin films, as described .\ 7- ktZZZZ^ 38 HISTORY OF PHOTOGRAPHY. "wliicli is mucli less sensitive to light ; and if the yellow coating is too pale, the pictm-e produced will prove very faint in all its parts. The time for this cannot be fixed, as it depends entirely on the temperature of the sun'ounding air. No artificial heat must be applied, unless in the case of elevating the temperatu.re of an apartment in which the operation may be going on. It is also important that the tempei^ature of the inside of the box should be the same as it is without, as otherwi.se a deposition of moistiu-e is liable to take place over the surface of the plate. It is well to leave a portion of iodine always in the box ; for, as it is slowly vaporized, it is absorbed by the wood, and when required it is given out over the more extended surface more equally, and with greater rapidity. As, according to the season of the year, the time for pro- ducing the required effect may vary from five minutes to half an hour, or more, it is necessaiy, from time to time, to inspect the plate. This is also necessary, to see if the iodine is acting equally on eveiy part of the silver, as it sometimes happens that the colour is sooner produced on one side than on the other, and the plate, when such is the case, must be tvuned one quarter round. The plate must be inspected in a darkened room, to which a faint light is admitted in some indirect way, as by a door a little open. The board being lifted from the box with both hands, the operator tiirning the plate towards him rapidly, observes the colour. If too pale, it must be returned to the box ; but if it has assumed the violet colour it is useless, and the whole process must be again gone thi'ough. From description, this operation may appear veiy difficult ; -tol t£3l 1 T ' B B f i J — J E (J but with a little practice the precise interval necessaiy to pro- duce the best effect is pretty easily guessed at. When the by Sir Isaac Newton. Close examination will show the formation of two yellow rinf/s, one within and the other without the series. If we cover one-half of the circle with a card, and expose the other part to light, the rings will be found to change colour, the outer and the inner yellow darkening the most readily, and to an equal shade ; thus proving the advantage of obtaining this yellow tone. THE DISCOVERY OF M. DAGUEERE, 39 proper yellow colom- is produced, the plate must be put into a frame, whicii fits the camera obscvu'a, and the doors are instantly closed upon it, to prevent the access of light. The figvu-es represent this frame, fig. 6, with the doors, B B, closed on the plate ; and fig. 7, with the doors opened by the half cii-cles, A A. D D are stops by which the doors are fastened until the mo- ment when the plate is reqviii'ed for use. The thii-d o^jeration should, if possible, immediately succeed the second : the longest interval between them shoidd not exceed an hour, as the iodine and silver lose their requisite jihotogenic properties.* It is necessary to observe, that the iodine ought never to be touched with the fingers, as we are very liable to injure the plate by touching it with the hands thus stained. Third Operation, — The thii-d operation is the fixing of the plate at the proper focal distance fi-om the lens of the camera obscura, and placing the camera itself in the right position for taking the view we desire. Fig. 8 is a perpendiciilar section, lengthwise, of Daguerre's camera. A is a ground glass by which the focus is adjusted ; it is then removed, and the photogi-apliic plate su.bstitu.ted, as in c, fig. 9. B is a miiTor for observing the efiects of objects, and selecting the best points of view. It is inclined at an angle of 45*^, by means of the support, L. To adjust the focus, the mir ror is lowered, and the piece of ground glass. A, used. The focus is easily adjusted by sliding the box, D, out or in, as repi'esented in the plate. When the focus is adjusted, it is retained in its place by means of the screw, H. The object glass, j, is achi'omatic and periscopic ; its diameter is about one inch, and its focal distance rather more than four- teen inches. M, is a stop a short distance from the lens, the * This is contrary to the experience of the author of this volume; and Dr. Draper, of New York, states that he has found the plates improve by keeping a few hours before they are used ; and M. Claudet states, that even after a day or two the sensibility of the plates is not impaired. 40 HISTORY OF PHOTOGRAPHY. object of whicli is to cut off all those rays of light which do not come dii'ectly fi-om the object to which the camera is dii-ected. This instrument reverses the objects; that which is to the right in nature being to the left in the photograph. This can be remedied by using a miri'or outside, as K J, in figiu-e 9. This arrangement, however, reduces the quantity of light, and in- creases the time of the operation one-third. It will, of course, be adopted only when there is time to spare. After having placed the camera in front of the landscape, or any object of which we desu'e the representation, our first attention must be to adjust the plate at such a distance from the lens, that a neat and sharply defijied picture is produced. This is, of coui'se, done by the obscured glass. The adjustment being satisfactorily made, the glass is removed, and its place suppHed by the frame contaim'jig the prepared plate, and the whole secui*ed by the screws. The doors are now opened by means of the half cii'cles, and the plate exposed to receive the pic- tui'e. The length of time neces- saiyfor the production of the best effect, varying with the quantity of light, is a matter which re- quires the exercise of considei-able judgment, particularly as no im- pression is visible upon the tablet when it is withdi'awn from the camera. At Paris this varies from three to thirty minutes. The most favourable time is from seven to three o'clock. A cfrawing which, in tlie months of June and July, may be taken in three or foiu' minutes, will require five or six in May or August, seven or eight in April and September, and so on, according to the season. Objects in shadow, even diu'ing the brightest weather, will require twenty minutes to be correctly delineated. From what has been stated, it will be evident that it is impossible to fix, with any precision, the exact length of time necessary to obtain photogi-aphic designs ; but by l^ractice we soon learn to calculate the required time with con- siderable correctness. The latitude is, of coiu'se, a fixed clement in this calculation. In the sunny climes of Italy and southern France, these designs may be obtained much more promptly THE DISCOVERY OF M. DAGUERRE. 41 than in tlie uncertain clime of Great Britain. It is veiy im- poi-tant that the time necessaiy is not exceeded, — prolonged solarization has the effect of blackening the plate, and this de- stroys the clearness of the design. If the operator has failed in his first exj^erunent, let him immediately commence "wdth. another plate ; coiTecting the second trial by the first, he will seldom fad to produce a good photograph. Fourth. Operation. — The apparatus reqnii-ed in this operation is represented by fig. 10. A, is the lid of the box ; B, a black board with grooves to receive the plate ; c, cup containing a little mercury, J ; d, spii-it -lamp ; F, thermometer ; G, glass through which to inspect the ojjeration ; H, tablet as removed from the camera ; i, stand for the spirit-lamiJ. All the in- terior of this apparatus should be covered with hard black varnish. The board and the affixed plate being ^vithdi-awn from the camei-a, are placed at an angle of about 45'^ within this box — the tablet with the pictiu'e do'wnwards, so that it may be seen through the glass G. The box being carefidly closed, the spii'it-lamp is to be lighted and placed under the cup containing the mercury. The heat is to be appHed until the thermometer, the bulb of which is covered with the mer- ciuy, indicates a temperatiu'e of 60° centigi-ade (140'" Fah.) The lamp is then withdrawn, and if the thermometer has risen rapidly, it will continue to rise without the aid of the lamp ; but the elevation ought not to be allowed to exceed 75° cent. (167'' Fah.) After a few minutes, the image of natui-e impressed, but tiH now invisible, on the plate, begins to appear ; the operator assiu-es himself of the progress of this develojDment by examin- j ing the pictiu-e thi'ough the glass, g, by a taper, taking care that the rays do not fall too strongly on the plate, and injiu-e the nascent images. The operation is continued tiU the ther- mometer sinks to 4:0° cent. (113*^ Fah.) When the objects 42 HISTORY OF PHOTOGRAPHY. have been strongly illuminated, or when the plate has been kei)t in the camera too long, it mil be found that this operation is completed before the thermometer has fallen to 55 ^' cent. (131'^ Fah.) Tliis is, however, always known by observing the sketch thi'ough the glass. After each operation the apparatus is care- fully cleaned in every part, and in particular the strips of metal which hold the plate are well imbbed with pumice and water, to remove the adhering mercury and iodine. The plate may now be deposited in the grooved box (fig. 11), in which it may be kept, excluded from the light, iintil it is convenient to perform the last fixing n. operation. Fifth Operation. — This process has for its object the removal of the iodine from the plate of silver, which prevents the further action of the light. A saturated solution of common salt may be used for this purpose, but it does not answer nearly so well as a weak solu- tion of the hyposulphite of soda. In the first place, the plate is to be placed in a trough of water, plimging and withdi-awing it immediately ; it is then to be plunged into one of the above saline solutions, which would act upon the di-awing if it was not previously hardened by washing in water. To assist the effect of the saline washes, the plate must be moved to and fro, which is best done by jiassing a Avire beneath the plate. When the yellow colour has quite disappeared, the plate is lifted out, great care being taken that the impression is not touched, and it is again plunged into water. A vessel of wai'm distilled water, or very piu'e rain-water boiled and cooled, being provided, the plate is fixed on an inclined plane, and the water is poured in a continuous stream over the picture. The drops of water which may remain upon the plate must be re- moved by forcibly blowing ujion it, for otherwise, in drying, they would leave stains on the ch-amngs. This finishes the drawing, and it only remains to preserve the sUver from tarnishing and from dust. The shadows in the Daguerreotype pictiires are represented by the polished surface of the silver, and the lights by the ad- hering mercury, which will not bear the slightest rubbing. To preserve these sketches, they must be placed in cases of paste- board, Avith a glass over them, and then framed in wood, They are now imalterable by the sun's light. IMPROYESrEJTTS m DAGUERREOTYPE, 43 Tlie same plate may be employed for many siiccessiye trials, proyided the silyer be not poUsbed tbrongb to the copper. It is yery important, after each trial, that the merciuy be remoyed immediately by polishing vnth pnmice-powder and oil. If this be neglected, the mercmy finally adheres to the silyer, and good di'a-s\-ing-s cannot be obtained if this amalgam is present. Section II. — Improvements in Daguerreotype. It was announced that the inyentor of the DagiieiTeotype had succeeded in impro\TJig the sensibility of his plates to such an extent, as to render an instantaneous exposure sufficient for the production of the best effects ; consequently, seciu-ing faithful imj^ressions of moying objects. In a communication with which I was fayoiu'ed from M. Daguerre, he said, — " Though the principle of my new discoyery is certain, I am deteiinined not to publish it before I haye succeeded in making the execution of it as easy to eyeiybody as it is to myself. I haye announced it immediately at the Royal Academy of Paris, merely to take date, and to ascertain my right to the priority of the inyention. By means of that new process, it shall be possible to fix the images of objects in motion, such as public ceremonies, marhet- places covered vnth people, cattle, d'c. — the effect being instan- taneous." In 1844, M. Daguerre, in. a letter to M. Arago, published this process ; but it proyed so complex in its manipulatoiy details, and so yeiy uncertain, that it has not been adopted. As it is, howeyer, cxu-ious, and inyolves the use of some agents not ordi- narily employed, it is thought advisable to make some extracts from the Comptes Eendus for April, 1844, in which it was pub- lished : — " By superposing on the plate several metals, reducing them to powder by friction, and by acidulating the empty spaces which the molecules leave, I have been enabled to develope galvanic actions which permit the employment of a much thicker layer of iodide, without having to fear, dui-ing the operation of light in the camera obscura, the influence of the liberated iodine. "The new combination which I employ, and which is com- posed of several metallic iodides, has the advantage of giving a sensible layer capable of receiving impressions simultaneously by all the degrees of tone, and I thus obtain, in a veiy short space of time, the representation of objects -v-i^-icUy enlightened with demi-tints, all of which retain, as in natiu-e, their trans- pai'ency and their relative value. 44 HISTORY OF PHOTOGRAPHY. "By adding gold to the metals wMch I first used, I am enabled to avoid the gi'eat diiEciilty which the use of bromine, as an accelerating substance, presented. It is known that only very experienced persons coiild employ bromine "vvith success, and that they were able to obtain the maximum of sensibility only by chance, since it is impossible to determine this point very pre- cisely, and since immediately beyond it the bromine attacks the silver, and is opposed to the formation of the image. " With my new means, the layer of iodine is always saturated with bromine, since the plate may, without inconvenience, be left exposed to the vapoxu- of this substance for at least half the necessaiy time ; for the application of the layer of gold is op- posed to the formation of what is called the veil of bromine. The j)rocess which I am about to give may, perhaps, be found rather complicated; but, notwithstanding my desire to simplify it as much as possible, I have been led, on the contrary, by the results of my experiment, to multiply the substances employed, all of wlrich play an important part in the whole process. I regard them all as necessary for obtaining a complete result, which must be the case, since I have only gi'advtally arrived at discovering the properties of these different metals, one of which aids in promptitude, the other in the vigour of the im- pression, &c. " The ojieration is divided into two principal parts : the first, which is the longest, may be made a long time previously, and may be regarded as the completion of the manufacture of the plate. This operation, being once made, serves indefinitely ; and, without recommencing it, a gi-eat number of impressions may be made on the same plate. The new substances employed are : — Aqueous solution of bichloride of mercuiy : solution of cyanide of merciuy : white oil of petroleum, acidvdated with nitnc acid : solution of clilorine of gold and platinum. These are prepared as follows : — "Aqueous Solution of Bichloride of Mercury. — 8 grains of bichloride of mercury in 10,000 grains of distilled water. " Solution of Cyanide of Mercury. — A flask of distilled water is saturated with cyanide of mercury, and a certain quantity is decanted, which is diluted with an equal quantity of distilled water. "Acidulated White Oil of Petroleum.*— This oil is acidulated by mixing with it one-tenth of pm"e nitric acid, lea\Tiig it for at * The most suitable oil of petroleum is of a greenish yellow tint, and takes, at different angles, azure reflections. I have given the preference to this oil over the fixed oils, because it always remains limpid, although strongly acidulated. My object iu employing an IMPROVEMEKTS IN DAGUERREOTYPE. 45 least forty-eight houi-s, occasionally agitating the flask. The oil which is acidulated, and which then powerfully reddens litmus- paper, is decanted. It is also a little coloured, but remains very limpid. " Solution of Chloride of Gold and Platinum.— In order not to miiltiply the solutions, I take the ordinary chloride of gold, used for fixing the impressions, and which is comjjosed of 15 grains of chloride of gold, and 50 grains of hyposulphite of soda, to a quart of distilled water. "With respect to chloride of platinum, 4 grains must be dissolved in 3 quai-ts of distilled water ; these two solutions are mixed in equal quantities. " First Preparation op the Plate. — For the sake of brevity in the following description, I will abridge the name of each substance. Thus, I will say, to designate the aqueous solution of bichloride of mercury, sublimate; for the solution of cyanide of mercviry, cyanide; for the acidulated oil of petroleum, oil; for the solution of chloride of gold and platinum, gold and 2}latinum; and for the oxide of iron, o^ouge only. "The plate is first polished with sublimate and tripoli, and afterwards with rouge, until a beautiful black is arrived at. Then, the plate is laid on the horizontal plate, and the solution of cyanide is poiu'ed on it and heated over a lamp, as in fixing an impression with chloride of gold. The mercury is deposited, and forms a whitish layer. The plate is allowed to cool a Httle, and, after having poured ofi" the Hqu-id, it is dried by rubbing with cotton and sprinkling with rouge. " It is now necessary to polish the whitish layer deposited by the mercuiy. "With a piece of cotton steeped in oil and rouge this layer is nibbed until it becomes of a fine black. In the last place, it may be rubbed very strongly, but with cotton alone, in order to render the acidulated layer as thin as possible. The plate is afterwards placed on the horizontal plane, and the solu- tion of gold and platinum is poiired on. It is heated in the ordinaiy manner ; it is then allowed to cool, the liquid is poiu-ed ofi, and it is dried by gentle friction with cotton and rouge. This operation must be performed with care, especially when the impression is not immediately continued ; for, otherwise, some lines of liquid would be left on the plate, which it is difiicult to get rid of. After this last friction the plates shoidd be only acidulated oil is to reduce the metals to powder, and to retain this powder on the surface of the plate, at the same time giving greater thickness to the layer by its unctuous properties ; for the naphtha which results from the distillation of this oil does not produce the same effect, because, being too fluid, it carries away the powder of the metals. It is for the same reason that I have lately recommended the employment of essence of lavender rather than that of essence of turpentine. 46 HISTORY OF PHOTOGRAPHY. dried, and not polislied. This includes the first preparation of the plate, which may be made a long time previously. "Second Preparation. — I do not think it fit to allow a longer interval than twelve hovirs to intervene between this operation and iodizing the plate. We left the plate with a deposit of gold and platinum. In order to polish this metallic layer, the plate is rubbed with a jiiece of cotton, and oil and rouge, imtil it again becomes black ; and then with alcohol and cotton only, in order to remove this layer of rouge as much as possible. The plate is again inibbed very strongly, and passing several times over the same places, with cotton impregnated "with cyanide. As this layer dries very promptly, it might leave on the plate traces of inequality; in order to avoid this, the cyanide must be again passed over it, and, while the plate is still moist, we qtiickly iiib over the whole siu"face of the plate with cotton imbibed with a little oil, thus mixing these two substances; then, with a piece of chy cotton, we rub, in order to unite, and, at the same, to dry the plate, taking care to remove from the cotton the parts which are moistened with cyanide and oil. Finally, as the cotton still leaves traces, the plate is like"svise sprinkled with a little rouge, which is removed by gently nibbing. "Aftel'^vards the plate is again rubbed with cotton impreg- nated with oil, only in such a manner as to make the burnish of the metal return ; it is then sprinkled with rouge, and then very gently rubbed round, to remove all the rouge, which carries with it the superabimdance of the acidulated layer.* Finally, it is strongly rubbed ^\ith a rather fii'm pledget of cotton, in order to give the last polish. t " It is not necessaiy often to renew the pledgets of cotton im- bibed with oil and rouge; they must only be kept free from dust. *' On Iodizing'. — The colour of the impression depends on the tint given to the metallic iodide ; it may, therefore, be varied at will. However, I have found the violet rose colour most suit- able. " For transmitting the iodine to the plate, the sheet of card- board may be replaced by an earthenwai-e plate deprived of enamel. The iodine transmitted by this means is not decom- * This must be done as gently as possible ; for otherwise the rouge would adhere to the plate, and would form a general film. f In operating on a plate a long time after it has received the first prepara- tion, it is necessary, before employing the acidulated oil and red oxide, to mani- pulate, as I indicate further on, for the plate which has received a fixed impres- sion. This precaution is necessary for destroying the stains which time may Lave developed. I IMPROVEMENTS IN DAGUERREOTYPE. 47 posed. It is useless, I may even say injimous, to heat the plate before exposing it to the vapoiu' of iodine. "WasMng with Hyposulphite of Soda.— In order to remove the sensitive layer, the solution of hyposulphite of soda must not be too strong, because it destroys the sharpness of the impres- sion. 60 grammes of the hyposulj^hite are sufficient for 1 quart of distilled water." The elaborate nature of this process is a barrier against its use, since the results are rarely equal to those obtained by the ordinary Daguerreotype, as it is now practised, and the labour to be expended on the preparation infinitely greater. The advantages which have been derived from the employ- ment of compounds of iodine and bromine, or chlorine, by which the sensibility of the Daguen-eotype has been greatly improved, are so great, that, with the incidental notice that we owe the application of bromine to Mr. Goddard, the consideration of them are postponed to the Thu'd Pai-t, as more entirely belong- ing to the manipulatory details. CHAPTER V. THE PHOTOGRAPHIC PROCESSES ON PAPER OF SIR JOHN HERSCHEL. The researches of Sir Jolin Herschel have been principally directed to the investigation of the physical laws which regidate the chemical changes we have been considering. His analyses of the prismatic spectrum have been most complete, and, as far as they have been carried out, go to prove the operation of forces other than those with which we are acquainted. At the same time, however, as this philosopher has been engaged in investigations of this high order, he has, from the multitude of his experiments, been successful in producing several processes of great beauty. There are not any which are to be regarded as peculiarly sensitive — they are indeed for the most part rather slow — but the manipidation required is of the easiest character, and the residts are most cuiious and instructive. The philosophy which is for ever united with the scientific investigations of Sir John Herschel, is too valuable to be omitted from any description of the processes which he recommends ; the following quotations are therefore taken from his communi- cation to the Royal Society, and linked together by my own remarks in such a manner as it is hoped will be most easily tmderstood by the unscientific amateur. Section I. — Cyanotype. The processes in which cyanogen is employed are so called : — Sir John Herschel makes the following i-emarks on the subject of his expeiiments with the cyanides : — " I shall conclude this paii; of my subject by remai'king on the great number and variety of substances which, now that atten- tion is di'awn to the subject, appear to be photogi'ai)hicaUy impressible. It is no longer an insulatetl and anomalous afiec- tion of cei-tain salts of silver or gold, but one which, doubtless, in a gx'eater or less degree pervades all natm'c, and connects itself intimately with the mechanism by wliich chemical combi- nation and decomposition is operated. The general instability SIR J. herschel's cyanotype. 49 of organic combinations might lead vis to expect the occurrence of numerous and remarkable cases of this affection among bodies of that class, but among metallic and other elements inorganic- ally arranged, instances enough have ah-eady appeared, and more are daily presenting themselves, to justify its extension to all eases in which chemical elements may be supposed combined with a certain degi-ee of laxity, and so to speak in a tottering equilibrium. There can be no doubt that the process, ia a great majority, if not in all, cases which have been noticed among in- organic substances, is a deoxidising one, so far as the more re- frangible rays are concerned. It is obviously so in the cases of gold and silver. In that of the bichromate of potash it is most probable that an atom of oxygen is parted with, and so of many others. A beautiful example of such deoxidising action on a non-argentine compound has lately occiuTed to me in the exami- nation of that interesting salt, the ferrosesquicyanuret of potas- sium, described by Mr. Smee in the Philosophical Magazine, No. 109, September, 1840, and which he has shown how to manu- facture in abundance and purity, by voltaic action on the com- mon, or yellow feiTocyanm'et. In this process nascent oxygen is absorbed, hych-ogen given off; and the characters of the residting compoimd in respect of the oxides of iron, forming, I as it does, Prussian blue with protosalts of that metal, but jDro- Iducing no precipitate with its persalts, indicate an excess of electro-negative energy, a disposition to part with oxygen, or, I which is the same thing, to absorb hydi'ogen (in the presence of moisture), and thereby to return to its pristine state imder cir- cumstances of moderate solicitation, such as the affinity of protoxide of iron (for instance), for an additional dose of oxygen, &c. " Paper simply washed with a solution of this salt is highly I sensitive to the action of light. Prussian bhie is deposited (the j base being necessarily supplied by the destiiiction of one I jjortion of the acid, and the acid by decomposition of another). After half an hoiu* or an hour's exposiu'e to sunshine, a very beautiful negative photograph is the result, to fix which, all that is necessary is to soak it in water in which a little sulphate of soda is dissolved, to ensure the fixity of the Prussian blue de- posited. While dry the impression is dove-colour or lavender blue, which has a curious and striking effect on the greenish- yellow groimd of the paper, produced by the saline solution. After washing, the ground colour disappears, and the photograph becomes bright blue on a white gi'oim.d. If too long exposed, it gets 'over sunned,' and the tint has a brownish or yellowish tendency, which, however, is removed in fixing ; but no increase 50 HISTORY OF PHOTOGRAPHY. of intensity beyond a certain point is obtained by continuance of exposure. " If paper be waslied with a solution of anunonio-citrate of iron, and dried, and then a wash passed over it of the yellow ferrocyaniu'et of potassium, there is no inunediate formation of true Prussian blue, but the paper rapidly acquires a violet- purple colour, which deepens after a few minutes, as it dries, to almost absolute blackness. In this state it is a positive photo- gi'aphic paper of high sensibdity, and gives pictures of great depth and sharpness ; but with this peculiarity, that they darken again spontaneously on exposiu'e to the air in dai'kness, and are soon obliterated. The paper, however, remains susceptible to light, and capable of receiving other pictures, which in theu- turn fade, without any possibility (so far as I can see) of arresting them; which is to be regretted, as they are very beautiful, and the paper of such easy preparation. If washed wdth ammonia or its carbonate, they are for a few moments entu'ely oblite- rated, hut presently reappear, loith reversed lights and shades. In this state they are fixed, and the ammonia, with all that it will dissolve, being removed by washing in water, their colour becomes a piu-e Prussian blue, which deepens much by keeping. If the solution be mixed, there resiilts a very dark \'iolet-coloui'ed ink, which may be kept uninjured in an opaque bottle, and will readily furnish, by a single wash, at a moment's notice, the positive paper in qviestion, which is most sensitive when wet. " It seems at first sight natiu-al to refer these cm-ious and complex changes to the instability of the cyanic compounds; and that this opinion is to a certain extent con-ect, is proved by the photographic impressions obtained on papers to which no iron has been added beyond what exists in the feiTOcyanic salts themselves. Nevertheless, the following experiments abun- dantly prove that in several of the changes above described, the immediate action of the solar rays is not exerted on these salts, but on the iron contained in the ferniginous solution added to them, which it deoxidizes or otherwise altei-s, thereby presenting it to the ferrocyanic salts in such a fonn as to precipitate the acids in combination with the peroxide, or protoxide of iron, as the case may be. To make this evident, all that is necessary is simply to leave out the ferrocyanate in the preparation of the paper, which thus becomes reduced to a simple washing over with the ammonio-citric solution. Paper so washed is of a bright yellow colour, and is apparently little, but in reality highly sensitive to photographic action. Exposed to strong sunsliine, for some time indeed, its bright yellow tint SIR J. herschel's CYA^'OTYPE. 51 is dulled into an oclu-ey line, or even to grey, but the change altogether amounts to a moderate per-centage of the total light reflected, and in short exposures is such as would easily escape notice. Nevertheless, if a slip of this paper be held for only foiu- or five seconds in the sun (the effect of which is quite im- percej^tible to the eye), and, when withdi'awn into the shade, be washed over with the ferrosesquicyanate of potash, a conside- rable deposit of Pi-ussian blue takes place on the part sunned, and none whatever on the rest ; so that on washing the whole with water, a pretty strong blue impression is left, demonstrat- ing the reduction of ii-on in that portion of the paper to the state of protoxide. The effect in question is not, it shoidd be observed, peculiar to the ammonio-citrate of iron. The am- monio and potassia-tartrate fidly possess, and the perchloride exactly neutralized, partakes of the same propei-ty : but the experiment is far more neatly made, and succeeds better, with the other salts." In fui-ther development of these most interesting processes Sir John Herschel says : — " The varieties of cyanotype pro- cesses seem to be innumerable, but that which I shall now describe deserves pai-ticular notice, not only for its pre-eminent beauty while in progi'ess, but as illustrating the peculiai- j30wer of the ammoniacal and other persalts of iron above-mentioned to receive a latent pictiu-e, susceptible of development by a gi'eat variety of stimvdi. This process consists in simply passing over the ammonia-citrated paper on which such a latent pictxu-e has been impressed, very sparingly and evenly, a wash of the solution of the common yellow ferrocyanate (prussiate) of potash. The latent pictiu-e, if not so faint as to be quite in- visible (and for this purpose it should not be so), is negative. As soon as the liquid is applied, which cannot be in too thin a film, the negative picture vanishes, and by very slow degi'ees is replaced by a positive one of a violet-blue colovu' on a greenish- yellow ground, which at a certain moment possesses a high degree of sharpness, and singailar beauty and delicacy of tint. If at this instant it be thrown into water, it passes immediately to Prussian blue, losing at the same time, however, much of its sharpness, and sometimes indeed becoming quite blotty and confused. But if this be delayed, the picture, after attaining a certain maximum of distinctness, gi'ows rapidly confused, es- pecially if the quantity of liquid applied be more than the paper can easily and completely absorb, or if the brush in applying it be aDowed to rest on, or to be passed twice over any part. The efi'ect then becomes that of a coarse and ill-printed woodcut, all 52 HISTORY OF PHOTOGRAPHY. the strong shades being run together, and a total absence pre- vailing of half lights. " To prevent this confusion, gum-arabic may be added to the prussiated solution, by which it is hindered from spreading un- manageably within the pores of the paper, and the precipitated Prussian blue allowed time to agglomei'ate and fix itself on the fibres. By the use of tliis ingredient also, a much thinner and more equable film may be spread over the surface ; and lohen perfectly dry, if not svifficiently developed, the application may be repeated. By operating thus I have occasionally (though rarely) succeeded in producing pictures of great beauty and richness of efiect, which they retain (if not thrown into water) between the leaves of a portfolio, and have even a cei'tain degree of fixity — fading in a strong light, and recovering their tone in the dark. The manipulations of this process are, however, delicate, and complete success is comparatively rare. " If sulphocyanate of potash be added to the ammonio-citrate or ammonio-tartrate of iron, the peculiar red coloiu' which that test induces on persalts of the metal is not produced, but it appears at once on adding a di'op or two of dilute sulphuric or nitric acid. This circumstance, joined to the perfect neutrality of these salts, and their power, in such neutral solution, of enduring, undecomj:»osed, a boding heat, contraiy to the usual habitudes of the peroxide of iron, together with their singular transformation by the action of light to proto-salts, in apparent opposition to a very strong affinity, has, I confess, incUned me to speculate on the possibility of their ferruginous base existing in them, not in the ordinary form of peroxide, biit in one isome- ric with it. The non-formation of Prussian blue, when their solutions are mixed with pi-ussiate of potash, and the formation in its place of a deep violet-colom-ed Liquid of singular instability under the action of light, seems to favom* this idea. Nor is it altogether impossible that the peculiar "prepared" state super- ficially assumed by iron under the influence of nitric acid, fii-st noticed by Kcir, and since made the subject of experiment by M. Scohnbein and myself, may depend on a change sujiei-ficially operated on the iro7i itself into a new metallic body isomeric with iron, unoxidable by nitric acid, and which may be consi- dered as the radical of tliat peroxide which exists in the salts in question, and possibly also of an isomeric protoxide. A combi- nation of the common protoxide with the isomeric peroxide, rather than with the same metal in a simply higher stage of oxidation, would afford a not unplausible notion of the chemical nature of that peculiai" intermediate oxide to which the name of SIR S. HEESCHEL's CYAIfOTYPE. 53 ' Ferroso-ferric' has been given by Berzelius. If (to render my meaning more clear) we for a moment consent to designate such, an isomeric form of iron by the name siclerium, the oxide in question might be regarded as a sideriate of iron. Both phos- phorus and arsenic (bodies remarkable for sesqui-combinations) admit isomeric forms in their oxides and acids. But to retm-n from this digression. " If to a mixture of ammonio-citrate of iron and sulphocyanate of potash, a small dose of nitric acid be added, the resulting red liquid, spread on paper, spontaneously whitens in the dark. If more acid be added till the point is attained when the discolora- tion begins to relax, and the paper when dry retains a conside- rable degree of colour, it is powerfully affected by light, and receives a positive picture with great rapidity, which appears at the back of the paper with even more distinctness than on its face. The impression, however, is pallid, fades on keeping, nor am I acquainted at present with any mode of fixing it. "If paper be washed with a mixture of the solutions of ammonio-citrate of iron and ferrosesquicyanate of potash, so as to contain the two salts in about equal proportions, and being then impressed with a jiicture, be thrown into water and dried, a negative blue image will be produced. Tliis picture I have found to be susceptible of a very curious transformation, pre- ceded by total obliteration. To effect tliis it must be washed with solution of proto-nitrate of mercury, which in a little time entirely discharges it. The nitrate being thoroughly washed out and the picture dried, a smooth iron is to be passed over it, somewhat hotter than is used for ironing linen, but not sufficiently so to scorch or injure the paper. The obliterated pictm'e immediately reapjiears, not blue, but brown. If kept for some weeks in this state between the leaves of a jDortfolio, in complete darkness, it fades, and at length almost entirely dis- appears. But what is very singular, a fresh application of the heat revives and restores it to its full intensity. " This curious transfonnation is instructive in another way. It is not operated by light, at least not by light alone. A certain temperature must be attained, and that temperature suffices in total darkness. Nevertheless, I find that on exposing to a very concentrated spectrum (collected by a lens of short focus) a slip of paper duly prepared as above (that is to say, by washing wi'th the mixed solutions, exposure to sunshine, washing, and dis- charging the uniform blue colour so induced as in the last article), its whiteness is changed to brown over the whole region of the red and orange rays, but not beyond the luminous spec- trum. Three conclusions seem unavoidable : — 1st, that it is the 54 HISTORY OF PHOTOGRAPHY. heat of these rays, not theii' light, -which operates the change ; 2ndly, that this heat possesses a peculiar chemical quality which is not possessed by the purely calorific rays outside of the visible spectrum, thotigh far more intense ; and, 3rdly, that the heat radiated fi-om obscurely hot iron abounds especially in rays analogous to those of the region of the spectrum above indicated." Sir John Herschel then proceeds to show that whatever be the state of the iron in the double salts in qxiestion, its reduction by blue light to the state of protoxide is indicated by many other reagents. Thus, for example, if a slip of paper prepared with the ammonio-citrate of iron be exposed partially to sun- shine, and then washed with the bichi-omate of potash, the bichromate is deoxidised, and precipitated upon the sunned portion, just as it would be if directly exposed to the sun's rays. I have proved this fact with a great number of preparations of cobalt, nickel, bismuth, platinum, and other salts which have been thought hitherto to be insensible to solar agency ; but if they are partially sunned, and then washed with nitrate of silver, and put aside in the dark, the metallic silver is slowly reduced upon the sunned portion. In many instances days were required to produce the visible picture ; and in one case, paper, being washed with neutral chloride ofplatiniim, was sunned, and then washed in the dark with nitrate of silver: it was some weeks before the image made its appearance, but it was eventually per- fectly developed. This specimen has been kept for several years, and continues constantly to improve in clearness and definition. Section II. — Chrysotype. A process of an analogo\is character to that which has just been described, and in which the chloride of gold is an agent, must be next described : this was discovered at the same time as the cysmotype, and has been termed the clirysotype. " In order to ascertain whether any portion of the iron in the double ammoniacal salt emjiloyed had really iindergone deoxida- tion, and become reduced to the state of j^rotoxide, as supposed, I had recourse to a solution of gold exactly neutralised by cai'bonate of soda. The proto-salts of iron, as is well kno^\Ti to chemists, precipitate gold in the metallic state. The effect proved exceedingly striking, issiiing in a jjrocess nowise in- ferior in the almost magical beauty of its effect to the calotype process of Mr. Talbot, which in some respects it nearly resembles ; SIR J. herschel's chrysotype. 55 with tliis advantage, as a mattei* of experimental exhibition, that the disclosure of the dormant image does not reqviu-e to be per- formed in the dark, being not interfered with by moderate day- light. As the experiment will probably be repeated by others, I shall hei'e describe it ab initio. Paper is to be washed with a moderately concentrated solution of ammonio-citrate of iron, and dried. The strength of the solution should be such as to diy into a good yellow colour, not at all bro"«Ti. In this state it is ready to receive a photographic image, which may be im- pressed on it either from nature in the camera obscura, or from an engraving on a frame in sunshine. The image so impressed, however, is veiy faint, and sometimes hardly perceptible. The moment it is removed from the frame or camera, it must be washed over with a neutral solution of gold of such strength as to have about the colour of sherry wine. Instantly the picture appears, not, indeed, at once of its full intensity, but darkening with great rapidity up to a certaia point, depending on the strength of the solutions used, &c. At tliis point nothing can surpass the sharpness and perfection of detail of the resulting photograph. To arrest this process and to fix the pictiu-e (so far at least as the further agency of light is concerned), it is to be thrown into water veiy slightly acididated with sulphuiic acid, and weU soaked, di-ied, washed with hydrobromate of potash, rinsed, and di-ied again. " Such is the outline of a process to which I propose applying the name of ChrysotyjJe, in order to recall, by similarity of struc- ture and termination, the Calotype process of Mr Talbot, to which, in its general effect, it affords so close a parallel. Being very recent, I have not yet (June 10, 1842) obtained a complete command over aU its details, but the termination of the session of the Society being close at hand, I have not thought it advisable to suppress its mention. In point of direct sensibility, the chiysotype paper is certainly inferior to the calotyi:)e ; but it is one of the most remarkable peculiarities of gold as a photo- gi'aphic ingredient, that extremely feehle impressions once made hy light go on afterwards dcirhening sj)ontaneously and very slowly, apparently imthout limit, so long as the least vestige of unreduced, chloride of gold remains in the paper. To illustrate this curious and (so far as applications go), highly important property, I shall mention incidentally the results of some experiments made, during the late fine weather, on the habitudes of gold in presence of oxalic acid. It is weU known to chemists that this acid, heated with solutions of gold, precipitates the metal in its metallic state ; it is upon this property that Berzelius has founded his determination of the atomic weight of gold. Light, 56 HISTORY OF PHOTOGRAPHY. as well as heat, also operates this precipitation ; but to render it effectual, several conditions ai'e necessary : — 1st, the solution of gold must be neutral, or at most veri/ slightly acid ; 2nd, the oxalic acid must be added in the fonn of a neutral oxalate ; and 3rdly, it must be present in a cei-tain considerable ouantity, which quantity must be greater the greater the amount of free acid present in the chloride. Under these conditions, the gold is precipitated by light as a black powder if the liquid be in any bulk, and if merely washed over |)aper a stain is produced, which, however feeble at first, under a certain dosage of the chloride, oxalate, and free acid, goes on increasing from day to day and from week to week, when laid by in the dark, and especially in a damp atmosphere, till it acquires almost the blackness of ink ; the unsunned portion of the paper remaining unafiected, or so slightly as to render it almost certain that what little action of the kind exists is due to the efiect of casual dispersed light incident in the preparation of the paper. I have before me a sj^ecimen of paper so treated in which the efiect of thirty seconds' exposure to sunshine was quite in\-isible at fii-st, and which is now of so intense a piu'ple as may well be called black, while the unsunned portion has acquired comparatively but a very slight brown. And (which is not a little remarkable, and indicates that in the time of exposm-e mentioned the maximum of efiect was attained) other portions of the same paper exposed in graduated progression for longer times, viz. 1 min., 2 min., jind 3 min., are not in the least perceptible degree darker than the portion on which the light had acted during thii-ty seconds only. " If paper prepared as above recommended for the crysotype, either with the ammonio-citrate or ammonio-tartrate of iron, and impressed, as in that process, with a latent pictm-e, be washed with nitrate of silver instead of a solution of gold, a veiy sharp and beautiful pictui-e is developed, of great intensity. Its dis- closure is not instantaneous ; a few moments elapse without apparent efiect ; the dark shades are then fii-st touched in, and by degrees the details appear, but much more slowly than in the case of gold. In two or three minutes, however, the maximum of distinctness will not fad to be attained. The picture may be fixed by the hyposidphite of soda, which alone, I believe, can be fully depended on for fixing argentine photographs. " The best process for fixing any of the photographs prepared ■with gold is as follows : — As soon as the picture is satisfactorily brought out by the auriferous liquid, it is to be rinsed in spring water, which must be three times renewed, letting it remain in the third water five or ten minutes. It is then to be blotted ofi* PHOTOGRAPHIC PROPERTIES OF MERCURY. 57 and dried, after wliicli it is to be washed on both sides with a somewhat weak solution of hydriodate of potash {iodide of potas- sium). If there be any free chloride of gold present in the pores of paper, it will be discoloured, the lights passing to a ruddy brown ; but they speedily whiten again spontaneously, or at all events on throwing it (after lying a minute or two,) into fresh water, in. which, being again rinsed and dried, it is now perfectly fixed." Section III. — Photographic Properties of Mercury. " As an agent in the daguerreotype process, it is not, strictly speaking, photographically affected. It operates there only in virtue of its readiness to amalgamate with silver properly pre- pared to receive it. That it possesses direct photographic sus- ceptibility, however, in a very eminent degree, is proved by the following experiment. Let a paper be washed over with a weak solution of jDeriodide of iron, and, when dry, with a solution of pi'oto-nitrate of mercury. A bright yellow paper is produced, which (if the right strength of the liquids be hit) is exceedingly sensitive while wet, darkening to a bi"own colour in a very few seconds in the sunshine. Withch-awn, the impression fades rapidly, and the pajier in a few hom's recovers its oi'iginal colour. In operating this change of colour, the whole spectrum is efiec- tive, with the exception of the thermic rays beyond the red. " Pi'oto-nitrate of mercuiy simply washed over paper, is slowly and feebly blackened by exposiu-e to sunshine. And if jiaper be impregnated with the ammonio-citrate of iron, already so often mentioned, partially sunned, and then washed with the proto-nitrate, a reduction of the latter salt, and consequently blackening of the paper, takes place very slowly in the dark over the sunned poi'tion, to nearly the same amoimt as in the direct action of the light on the simply nitrated paper. " But if the mercurial salt be subjected to the action of light in contact with the ammonio-citrate or tartrate, the eflect is far more powerfvd. Considering, at present, only the citric double salt, a paper prepared by washing first with that salt and then with the mei'curial proto-nitrate (drying between) is endowed with considerable sensibility, and darkens to a very deep brown, nay, to comjilete blackness, on a moderate exposiu-e to good sun. Very sharp and intense photographs of a negative cha- racter may be thus taken. They are, howevei", difficult to fix. The only method which I have found at all to succeed has been by washing them with bichromate of potash and soaking them for twenty-fovu- hoiu'S in water, which dissolves out the chi'omate 58 HISTORY OF PHOTOGRAPHY. of merci;ry for the most part ; leaving, however, a yellow tint on the ground, which resists obstinately. But though pretty effectually fixed in this way against light, they are not so against time, as they fade considerably on keeping. " When the proto-nitrate of mercury is mixed, in solution, with either of the animoniacal double salts, it forms a precipitate, which, worked up with a brush to the consistence of cream, and spread upon paper, produces very fine pictures, the intensity of wliicli it is almost impossible to go beyond. Most unfoi-tvmately, they cannot be preserved. Every attempt to fix them has resulted in the destruction of theii- beauty and force ; and even when kept from light, they fade with more or less rajiidity, some disappearing almost entii-ely in three or four days, while others have resisted tolerably well for a fortnight, or even a month. It is to an over-dose of tartaric acid that their more rapid deterio- ration seems to be due, and of coiu'se it is important to keep down the proportion of this ingredient as low as possible. But without it I have never succeeded in producing that peculiar velvety aspect on which the charm of these pictures chiefly depends, nor anything like the same intensity of colour without over-sunninsc." Section TV. — Ferro-Tartrate of Silver. Extending his inquiries still fiu'ther into these very remai-kable changes, the following process presented itself to Sir J. Herschel, which is in many respects remarkable. If nitrate of silver, specific gravity 1-200, be added to ferro- tartaric acid, specific gi'avity 1"023, a precipitate falls, which is in great measure redissolved by a gentle heat, leaving a black sediment, which, being cleared by subsidence, a liquid of a pale yellow coloiu- is obtained, in which a fm-ther addition of the nitrate causes no tiu'bidness. When the total quantity of the nitrated solution amounts to about half the bulk of the ferro- tartaric acid, it is enough. The liquid so prepared does not alter by keeping in the dark. Spread on paper, and exposed wet to the sunshine (partly shaded) for a few seconds, no impression seems to have been made ; but by degrees (although withcU-a-wn from the action of the light) it developes itself spontaneously, and at len,gth be- comes very intense. But if the paper be thoroughly diicd in the dark (in which state it is of a very pale greenish-yellow colour), it possesses the singular property of receiving a dormant or invisible pictui-e ; to jiroduce which (if it be, for instance, an SIR J. herschel's amphitype. 59 engraving that is to be copied), from thirty seconds' to a minute's exposui'e in the sunshine is requisite. It should not be continued too long, as not only is the ultimate effect less striking, but a picture begins to be visibly produced, which darkens spont- neously after it is Avithdi-awn. But if the exposure be discon- tinued before this effect comes on, an invisible impression is the result, to develope which' all that is necessary is to breathe upon it, when it immediately appears, and veiy speedily acquires an extraordinary intensity and sharpness, as if by magic. Instead of the breath, it may be subjected to the regulated action of aqueous vapovu' by laying it in a blotting-paper book, of which some of the outer leaves on both sides have been damp, or by holding it over warm water. Many preparations, both of silver and gold, possess a similar property, in an inferior degi-ee ; but none that I have yet met with, to anything like the extent of that above described. These pictures do not admit of being peiTaanently fixed ; they are so against the action of light, but not against the operations of time. They slowly fade out even in the dark ; and in some examples which I have prepared, the remarkable phenomenon of a restoration after fading, but with reversed lights and shades, has taken place. Section Y. — The Ajniphitype. The following very remarkable process was communicated by Sii- John Herschel, at the meeting of the British Association at York. The process cannot be regarded as perfect, but from its beauty when success is obtained, and the ciu-ious nature of all its phenomena, it is deemed important to include it, in the hope of inducing some investigator to take it up. Sir John Herschel says, alluding to the processes just de- scribed, " I had hoped to have perfected this process so far as to have reduced it to a definite statement of maniprdations which would insure success. But, capricious as photographic processes notoriously are, this has proved so, even beyond the ordinary measure of siich caprice. * '"' * Paper proper for producing an amphitype picture may be prepared either with the ferro- tartrate or the feiTO-citrate of the protoxide or the peroxide of mercmy, or of the protoxide of lead, by using creams of these salts, or by successive apjilications of the nitrates of the respec- tive oxides, singly or in mixture, to the paper, alternating with solutions of the ammonio-tartrate or ammonio-citrate of iron, the latter solution being last applied, and in more or less ex- 60 HISTORY OF PHOTOGRAPHY. cess. * * ■"' Paper so prepared and dried takes a negative picture, in time varying fi-om half an liour to five or six hours, according to the intensity of the light ; and the impression pro- duced varies in apparent force from a faint and hardly percep tible picture to one of the highest conceivable fulness and rich- ness both of tint and detail, the colour in this case being a superb velvety brown. This extreme richness of effect is not produced except lead be present either in the ingredients used, or in the paper itself. It is not, as I originally supposed, due to the presence of free tartaric acid. The pictvu-es in this state are not permanent. They fade in the dark, though with veiy difierent degrees of rapidity, some (especially if free tartaric or citric acid be present) in a few days; while others remain for weeks unimpafred, and requii'e whole years for thefr total ob- literation. But, though entirely faded out in appearance, the picture is only rendered dormant, and may be restored, chang- ing its character fr-om negative to positive, and its colour from brown to black (in the shadows) by the following process : — A bath being prepared by pouring a small quantity of solution of per-nitrate of mercury into a large quantity of water, and letting the sub-nitrated precipitate subside, the pictm'e must be immersed in it (carefidly and repeatedly cleai'ing off the air- bubbles) and allowed to remain till the picture (if anywhere visible) is entu-ely destroyed, or if faded, till it is judged suffi- cient from previous experience ; a term which is often marked by the appearance of a feeble positive picture of a bright yellow hue on the pale yellow ground of the paper. A long time (several weeks) is often requii-ed for this, but heat accelemtes the action, and it is often complete in a few houi-s. In this state the pictiu-e is to be very thoroughly rinsed and soaked in piire warm water, and then cfried. It is then to be well ii-oned with a smooth iron, heated so as barely not to injm-e the paper, placing it, for better security against scorching, between smooth clean papers. If, then, the process have been successful, a per- fectly black positive pictm-e is at once developed. At fii-st it most commonly happens that the whole picture is sooty or dingy to such a degree that it is condemned as spoiled, but on keeping it between the leaves of a book, especially m a moist atmosphere, by extremely slow degrees this dingmess disajv pears, and the picture disengages itself with continually in- creasing sharpness and clearness, and acqiui-es the exact effect of a cojiperplate engraving on a paper more or less tinted with pale yellow. " I ought to observe, that the best and most uniform speci- mens which I have procured have been on paper previously THE COLOURING MATTER OF FLOWERS. 61 washed with certain preparations of uric acid, which is a veiy remarkable and powerful photographic element. The intensity of the original negative picture is no critei'ion of what may be expected in the positive. It is from the production, by one and the same action of the light, of either a positive or a negative picture, according to the subsequent manipulations, that I have designated the process thus generally sketched out, by the term " Amphitype ;''' a name suggested by Mr. Talbot, to whom 1 communicated this singular result ; and to this process or class of processes (which I cannot doubt when pursued will lead to some very beautiful results) I propose to restrict the name in question, though it applies even more appropriately to the fol- lowing exceedingly curious and remarkable one in which sHver is concerned. At the last meeting I announced a mode of pro- ducing, by means of a solution of silver in conjunction with ferro-tartaric acid, a dormant picture brought out into a forci- ble negative impression by the breath, or moist air. The solu- tion then described, and which had at that time been prepared some weeks, I may here accidentally remark, has retained its limpidity and photographic properties quite unimpaired during the whole year since elapsed, and is now as sensitive as ever — a property of no small value. ISTow, when a picture (for example, an impression from an engraving) is taken on paper washed with this solution, it shows no sign of a picture on its back, whether that on its face be developed or not ; but if, whUe the actinic influence is still fresh upon the face {i.e. as soon as it is removed from the light), the hack be exposed for a very few seconds to sunshine, and then removed to a gloomy place, a positive picture, the exact complement of the negative one on the other side, though wanting of course in sharpness if the paper be thick, sloioly and gradually malces its app)earance there, and in half an hour requires considerable intensity. I ought to men- tion that the ferro-tartaric acid in question is prepared by pre- cipitating the feiTO-tartrate of ammonia by acetate of lead, and decomposing the precipitate by dilute sulphuric acid." Section YI. — The Colouring Matter of Flowers. The results obtained by Sir John Herschel on the colouring juices of flowers are too remarkable to be omitted in a treatise in which it is desirable that every point should be registered up to the date of publication, which connects itself with the pheno- mena of chemical change applied to photography. " In operating on the colours of flowers, I have usually pro- ceeded as follows : — The petals of the fresh flowers, or rather 62 HISTORY OF PHOTOGRAPHY. such parts of them as possessed a uniform tint, were crushed to a pulp in a marble mortar, either alone, or with addition of alcohol, and the juice exjjressed by squeezing the pulp in a clean linen or cotton cloth. It was then spread on paper with a flat brush, and dried in the au" without artificial heat, or at most with the gentle warmth which rises in the ascending current of air from an Amott stove. If alcohol be not added, the applica- tion on paper must be perfoi'med immediately, since exposure to the air of the juices of most flowers (in some cases even but for a few miniites) ii-recoverably changes or destroys their co- lour. If alcohol be present, this change does not usually take place, or is much retarded; for wliich reason, as well as on account of certain facilities afibrded by its admixture in pro- curing an even tint (to be presently stated), this addition was commonly, but not always, made. "Most flowers give out their colouring matter readily enough, either to alcohol or water. Some, however, as the Escholzias and Calceolarias, reftise to do so, and require the addition of alkalies, others of acids, &c. When alcohol is added, it should, however, be observed that the tint is often apparently much enfeebled, or even discharged altogether, and that the tincture, when spread on pajier, does not reappear of its blue intensity till after complete diying. The temjjoraiy destniction of the colour of the blue heartsease by alcohol is cui-ious, nor is it by any means a singidar instance. In some, but in "vexy few cases, it is destroyed, so as neither to reappear on drying, nor to be capable of revival by any means tried. And in all cases long keeping deterioi-ates the coloiu's and alters the qualities of the alcoholic tinctures themselves ; so that they should always be Tised as fresh as possible. " If papers tinged with vegetable colours are intended to be preserved, they must be kept perfectly diy and in dai-kness, A close tin vessel, the air of which is dried hj quickhme (care- fully enclosed in double paper bags, well pasted at the edges to prevent the dust escaping), is used for this purpose. Moisture (as already mentioned, especially assisted by heat) destroys them for the most paii/ rapidly, though some (as the colour of the Senecio splendens) resist obstinately. Their destructibility by this agency, however, seems to bear no distinct relation to their photograpliic properties. " This is also the place to observe that the colour of a flower is by no means always, or usually, that which its expressed juice imparts to white paper. In many cases the tints so imparted have no resemblance to the original hue. Thus, to give only a few instances, the red damask rose of that intense variety of THE COLOURING MATTER OF FLOWERS. 63 colour commonly called by floi-ists the black rose, gives a dark slate blue, as do also tbe clove carnation and the black holly- hock : a fine dark brown variety of sparaxis give a dull olive green ; and a beautiful rose-coloured tulip, a dirty bluish green ; but perhaps the most striking case of this kind is that of a com- mon sort of red poj)py (Papaver Rlievuni), whose exj)ressed juice imparts to paper a rich and most beautifid blue colom", whose elegant properties as a photographic material will be further alluded to hereafter. * " This change of colour is probably owing to different causes in different flowers. In some it undoubtedly arises from the escape of carbonic acid, but this, as a general cause for the change from red to blue, has, I am aware, been controverted. In some (as is the case with the yellow ranunculi) it seems to arise from a chemical alteration depending on absorption of oxygen ; and in others, especially where the expresssd juice coagulates on stand- ing, to a loss of vitality or disorganization of the molecules. The fresh petal of a single flower, merely crashed by rubbing on dry paper, and instantly dried, leaves a stain much more nearly ap- proximating to the original hue. This, for examjjle, is the only way in which the fine blue coloiu* of the common field veronica can be imparted to paper. Its expressed juice, however quickly prepared when laid on with a bnish, affords only a dirty neutral grey, and so of many others. But in this way no even tint can be had, which is a first requisite to the experiments now in ques- tion, as well as to their application to photography. " To seciu'e this desirable evenness of tint, the following mani- pulation will genei-ally be found successful ; — The paper should be moistened at the back by sjjonging and blotting off. It should then be pinned on a board, the moist side downwards, so that two of its edges (suppose the right-hand and lower ones) shall project a little beyond those of the boai-d. The board being then inclined twenty or thirty degrees to the horizon, the alco- holic tinctiu-e (mixed mth a very little water, if the petals them- selves be not very juicy) is to be applied with a brush in strokes from left to right, taking care not to go over the edges which rest on the board, but to pass clearly over those which project, and observing also to carry the tint from below iipwards by quick sweeping strokes, leaving no dry spaces between them, but keeping up a continuity of wet surface. When all is wet, cross them by another set of strokes from above downwards, so managing the brush as to leave no floating liquid on the paper. * A semi-cultivated variety was used, having dark purple spots at the bases of the petals. The common red poppy of the chalk {Pajjavier hylridum) gives a purple colour much less sensitive and beautiful. Gi HISTORY OF PHOTOGRAPHY. It must then be di-ied as quickly as possible over a stove, or in a ciuTent of warm aii' ; avoiding, however, such heat as may injm-e the tiat. The jDresence of alcohol prevents the solution of the gummy "principle, which, when present, gives a smeary surface; but the evenness of tint given by this process results chiefly fi"om that singular intestine movement which always takes place when alcohol is in the act of separation from water by evaporation ; a movement wliich disperses knots and blots in the film of liquid with great energy, and spreads them over the surrounding surface. "Corchorus Jajjonica. — The flowei's of this common and hardy but highly ornamental plant are of a fine yellow, somewhat in- clining to orange, and this is also the colour the expressed juice imparts to paj)er. As the flower begins to fade the petals whiten, — an indication of their photographic sensibility which is amply verified on exposure of the stamed paper to sunshine. I have hitherto met with no vegetable coloiu* so sensitive. If the flowers be gathered in the height of then- season, paper so coloiu-ed (which is of a very beautifid and even yellow) begins to discoloui' in ten or twelve minutes in clear sunshine, and in half an hour is completely whitened. The colom* seems to resist the fij-st impression of the light, as if by some remains of vitaKty, which being overcome, the tint gives way at once, and the discolora- tion, whem commenced, goes on rapidly. It does not even cease m the dark when once begun. Hence it happens that photographic impi'essions taken on such paper, which, when ft-esh, are very sharp and beautiful, fade by keeping, visibly from day to day, however carefully presei-ved from light. They requii'e from half an hour to an hoiu- to complete, according to the sunshine. Hydi'iodate of potash cautiously aj)plied retards considerably, but does not ultimately prevent, this spontaneous discharge. "Cofnmon Ten ^Yee^is Stocks : Mathiola annua. — Paper stained Avith the tincture of this flower is changed to a vivid scarlet by acids, and to green by alkalies ; if ammonia be used the red coloiu' is restored as the ammonia evaporates, proving the absence of any acid quality in the coloiu-ing matter sufiiciently energetic to coerce the elastic foi'ce of the alkaline gas. Sulphurous acid whitens it, as does the alkaline sulphites ; but tliis efiect is transient, and the red colour is slowly restored by free exposure to ail", especially with the aid of light, whose influence in this case is the more remarkable, being exactly the reverse of its ordinary action on this colouring principle, wliich it destroys irrecoverably, as above stated. The following experiments were made to trace and illustrate this curious change : — " Two photographic copies of engravings taken on paper tinted THE COLOLTIING MATTER OF FLOWERS. 65 "witli this colour were placed in a jar of suli^lim'oiis acid gas, by which they were completely whitened, and all traces of the pic- tiu'es obliterated. They were then exposed to free au', the one in the dark, the other in sunshine. Both recovered, but the fonner much more slowly than the latter. The restoration of the pictiu-e exposed to the sun was completed in twenty-foiu- hours, that in the dark not till after a lapse of two or three days. " A sKp of the stained paper was wetted with liquid sidphu- rous acid, and laid on blotting-paper similarly wetted. Being then crossed with a strip of black paper, it was laid between glass plates and (evaporation of the acid being thtis prevented) was exposed to frill sunshine. After some time the red colour (in spite of the jiresence of the acid) was considerably restored in the portion exposed, while the whole of the portion covered by the black paper i-emained (of coiu'se) perfectly white. " Slips of paper, stained as above, were placed under a receiver, beside a small capsule of liquid sulphiu-ous acid. When com- pletely discoloiu-ed, they were subjected (on various occasions, and after various lengths of exposure to the acid ftmies, from half an houi' to many days) to the action of the spectram ; and it was found, as indeed I had expected, that the restoration of colour icas ojjerated by rays complementary to those which destroy it in the natural state o/the jxqjer; the violet rays being chiefly active, the blue almost equally so, the gi-een Kttle, and the yel- low, orange, and most refrangible red, not at all. In one expe- riment a pretty-well defined red solar image was developed by the least refrangible red rays also, being precisely those for which, in the unprepared paper the discolouring action is abiiiptly cut off. But this spot I never succeeded in rej^roducing ; and it ought also to be mentioned, that, according to difierences in the preparation not ob\'ious, the degree of sensibiHty, generally, of the bleached paper to the restorative action of light, differed gi'eatly ; in some cases a perceptible reddening being produced in ten seconds, and a considerable streak in two minutes, while in others a veiy long time was required to produce any effect. The dormancy of this colouring principle, under the influence of sidphurous acid, is well shown by dropping a Kttle weak sulphu- ric acid on the paper bleached by that gas, which immediately restoi'es the red colour in aU its vigoiu-. In like manner alka- lies restore the colour, converting it at the same time into gi-een. "Pccpaver orientale. — The chemical habitudes of the sulphu- rous acid render it highly probable that its action in inducing a dormant state of the colorific principle, consists in a partial deoxidizement, unaccompanied, however, with disorganization of its molecules. And this view is corroborated by the similar ac- 66 HISTORY OF PHOTOGRAPHY. tion of alcohol already spoken of; similar, that is, in kind, though less complete in degree. Most commonly, vegetable colours, weakened by the action of alcohol, are speedily restored on the total evaporation of the ingredient. But one remarkable instance of absolute dormancy induced by that agent has oc- curred to me in the case of Papaver orientale, a flower of a vivid orange coloiu*, bordering on scarlet, the coloui'ing matter of which is not extractable otherwise than by alcohol, and then only in a state so completely masked as to impart no more than a faint yellowish or pinkish hue to paper, which it retains when thoroughly dry, and apparently diu'ing any length of time, with- out perceptible increase of tint. If at any time, however, a drop of weak acid be applied to paper prepared with this tincture, a vivid scarlet colour is immediately developed ; thus demon- stating the continued though latent existence of the coloui-ing principle. On observing tliis, it occurred to me to inquire whe- ther, in its dormant state, that principle still retained its sus- ceptibility of being acted on by light, since the same powerful and delicate agent which had been shown, in so many cases as to con- stitute a general law, capable of disorganizing and destroying vegetable colours actually developed, might easily be presumed competent to destroy the capacity for assuming colour, in such organic matter as might possess it, under the influence of their otherwise appropriate chemical stimuK. A strip of the paper was therefore exjiosed for an hour or two to the spectrum, but Avithout any sensible eflfect, the whole surface being ecpially red- dened by an acid. As this experiment sufliciently indicated the action of light, if any, to be veiy slow, I next placed a strip, partly covered, in a south-east window, where it remained from June 19 to August 19, receiving the few and scanty sunbeams which that interval of the deplorable summer of 1841 afibrded. When removed, the part exposed could barely be dLstinguished from the pai-t shaded, as a trifle yellower. But on applying acid, the exposed and shaded poi-tions were at once (hstiuguished by the assumption of a vivid red in the latter, and the former remaining unchanged. " A mezzotinto pictui'e was now pressed on a glazed frame over another portion of the same pajiier, and abandoned on the iijiper shelf of a gi-een-house to whatever sun might occiu* from August 19 to October 19. The interval proved one of almost uninter- rupted storm, rain, and darkness. On removal, no appearance whatever of any impressed picture coidd be discerned, nor was it even possible to tell the top of the pictiu-e from the bottom. It was then exposed in a glass jar to the fumes of muriatic acid, when, after a few minutes, the development of the dormant pic- THE COLOUING MATTER OF FLOWERS. 67 ture commenced, and slowly proceeded, disclosing the details in a soft and pleasing style. Being then laid by in a cb-awer, with free access of aii", the picture again faded, by very slow degrees, and on January 2, 1842, was found quite obliterated. Being then subjected to the acid vapour the colour was reproduced. " Viola odorata. — Chemists are familiar mth the colour of this flower as a test of acids and alkalies, for which, however, it seems by no means better adapted than many others ; less so, indeed, than that of the Violar tricolor, the common purple iris, and many others which might be named. It offers, in fact, another and rather a striking instance of the simultaneous existence of two coloui-ing ingx-edients in the same flower, compoi-ting them- selves differently, not only in regard to light but to chemical agents. Extracted with alcohol, the juice of the violet is of a rich blue colom*, which it imparts in high perfection to paper. Exposed to simshiue, a poi-tion of this coloiu' gives way pretty readily, but a residual blue, rather inclining to greenish, resists obstinately, and requires a very much longer exposure (for whole weeks, indeed) for its destruction, which is not even then com- plete. Photogi-aphic impressions, therefore, taken on tliis paper, though very pretty, are exceedingly tedious in their- preperation, if we would have the lights shai^jily made out. " Sparaxis tricolor ?, var. — Stimulating Effects of Ahalies. — Among a great many hybrid varieties of this genus, lately for- warded to me from the Cape, occiu-red one of a veiy intense pur- plish-brown colour, nearly black. The alcoholic extract of this flower in its Kquid state is rich crimson-brown. Spread on paper, it imparted a dark olive-green colour, which proved perfectly in- sensible to very prolonged action, either of sunshine or the spectrum. The addition of carbonate of soda changed the coloirr of this tincture to a good green, slightly inclining to olive, and which imparted the same tint to paper. In this state, to my surprise, it manifested rather a high degree of photographic sen- siljility, and gave very pretty pictiu'es with a day or two of ex- posure to sunshine. When prepared with the fresh jmce there is hardly any residual tint, bixt if the paj)er be kept, a great amount of indestructible yellow remains outstanding. The ac- tion is confined chiefly to the negative end of the spectrum; all but the fii-st five or six parts beyond the yellow show little more than a trace of action. A photograph impressed on this paper is reddened by miu-iatic acid fumes. If then transferred to an atmosphere of ammonia, and when super-saturated the excess of alkali allowed to exhale, it is fixed, and of a dark green colour. Both the tint and sharpness of the picture, however, suffer in this process. C8 HISTORY OF PHOTOGRAPHY. " Red Pojypy : Papaver Eheimi ? — Among tlie vegetable colovu's totally destroyed by light, or wlucb leave no residual tint, at least when fresh pi'epared, perhaps the two most rich and beautiful are those of the red poppy and the double purple gi-oundsel (Senecio sj^lendens). The former owes its red coloiu- in all j)robability to free carbonic acid, or some other (as the acetic), completely expelled by diying : for the colour its tinctm-e imparts to paper, instead of red, is a fine blue very slightly verging on slate-blue. But it has by no means the orthnary chemical characters of blue vegetable colo\u"s. Carbonate of soda, for instance, does not in the least degree tiu-n the expressed juice green ; and when washed with the mixture, a papei- results of a light slate-gi'ey, hardly at all inclining to gTeen. The blue tinctiu-e is considerably sensitive, and from the richness of its tone and the absence of residual tint, paper stained with it affords photograpliic impressions of great beauty and sharpness, some of which will be found among the collection submitted with this paper for inspection. '^Senecio &plendens. — This flower yields a rich pm-ple juice in great abundance and of siu^prising intensity. Nothing can exceed the rich and velvety tint of paper tinted while it is fresh. It is, however, not very sensible to light, and many weeks are necessary to obtain a good photograpliic impression." In the progress of my own researches on this subject, I found that the gi'een coloming matter of the leaves of herbaceous plants, when spread upon paper, changed with tolerable i-apidity when exposed to simshine. There are, however, some very cui-ious points connected with the phenomena of these changes wliich demand a far more extensive investigation than they have yet received. I find that the jmces taken from the leaves in the spring, change more rapidly than when expressed from the same plants in the autumn ; and the juices of those flowering plants which have been cidtivated under the artificial cfrcumstances of a store-house, or conservatory, are more readily affected than such as are grown in the open aii". Many of the experiments just described furnish very instructive examples of the o^iera- tions of the solar rays u])on organic bodies, from which we may deduce impoi'tant truths connected with natm'al phenomena. CHAPTER VI. MISCELLANEOUS PROCESSES. Section I. — Me. Ponton's Process. (Bichromate of Potash.) Under the general term of the ChromatyjDe, I would projwse to include all those processes which involve the xise of any of the salts of chromium. It was originally introduced to distinguish a jjarticnlar process which I discovered, and published at the meeting of the British Association at Cork, in Augiist 1843j but it appears very convenient to adopt the principle intro- duced by Sir John Herschel, of grouping the phenomena of l^hotography under special terms derived from the most prominent chemical preparation employed. There are many preparations which are affected by light in a similar manner to the salts of silver. Several have been tx'ied as photographic materials, but as yet without much success, with the exception of the bichromate of potash, which was first an- nounced as a useful photographic agent by Mr. Mimgo Ponton, in the Edinburgh New Pliilosophical Jovimal ; from which I quote Mr Ponton's own account. " AVhen paper is immersed in the bichromate of potash, it is powerfully and rapidly acted on by the sim's rays. When an object is laid in the usual way on this paper, the portion exposed to the light si^eedily becomes tawny, passing moi-e or less into a deep orange, according to the strength of the light. The por- tion covered by the object retains the original bright yellow tint which it had before exposure, and the object is thus x-epresented yellow upon an orange ground, there being several gradations of shade, or tint, according to the gi-eater or less degree of trans- parency in the different parts of the object. " In this state, of com-se, the di\awang, though very beautiful, is evanescent. To fix it, all that is requii-ed is careful immersion in water, when it will be found that those portions of the salt which have not been acted on by the light are readily dissolved out, while those which have been exposed to the light are com- pletely fixed on the paper. By the second process the object is obtained white upon an orange ground, and quite permanent. If exposed for many hoiu's together to strong sunshine, the colour of the gTound is apt to lose in depth, but not more so than most other coloming matters. This action of light on the bichromate 70 HISTORY OF PHOTOGRAPHY. of potash differs from that lapon the salts of silver. Those of the latter which are blackened by light are of themselves insoluble in water, and it is difficult to impregnate paper with them in a uniform manner. The blackening seems to be caused by the for- mation of oxide of silver. " In the case of the bichromate of potash, again, that salt is exceedingly soluble, and pajier can be easily satm-ated with it. The agency of light not only changes its colovu-, but deprives it of solubility, thus rendering it fixed in the paper. This action appears to consist in the disengagement of free chi-omic acid, which is of a deep red coloirr, and which seems to combine with the paper. Tliis is rendered more probable from the circum- stance that the neutral chi'omate exhibits no similar change. The best mode of preparing paper with bichromate of potash is to use a satm-ated solution of that salt ; soak the paper well in it, and then diy it rapidly at a brisk fu-e, excluding it from day- light. Paper thus prepai'ed acquires a deep orange tint on ex- posure to the sun. If the solution be less strong, or the diying less i-apid, the colom- will not be so deep. A pleasing variety may be made by using sulphate of indigo along with the bichi'O- mate of potash, the colom- of the object and of the paper being then different shades of green. In this way, also, the object may be represented of a darker shade than the ground." Pajjer prepared with the bichi-omate of potash, though as sensitive as some of the papers pi'epared with the salts of silver, is much inferior to most of them, and is not sufficiently sensitive for the camei-a obscui-a. This paper, however, answers quite well for taking drawings fi-om di-ied plants, or for copying prints. Its great recommendation is its cheapness, and the facility with which it can be prepared. The price of the bichromate of potash is about two shillings per poimd, whilst the nitrate of silver is five shillings the ounce. As the deep oi-ange ground of these pictures prevents the per- meation of the chemical rays of light, it is very easy to prociu-e any number of facsimiles of an engi-aAong, by ti"ansfer from the fii-st negative photogi-aph. The correct copies have a beautifid sharpness; and, if carefully managed, but little of the minute detail of the original engi-aving is lost. A photogi'apliic paper prepared with the bichi-omate of potash of another kiiid is desciibed by iVI. E. Becquerel. He states, — It is sufficient to steep a paper prepared in Mr. Ponton's manner, and upon which there exists a faint copy of a dni-ndng, in a solution of iodine in alcohol, to wash this pajjer in alcohol, and then diy it : then the parts which were white become blue, and those which were yellow remain more or less clear. MR. PO>TrON's PROCESS. 71 M. E. Becquerel has piirsued. his investigations into the action of the chromic acid on organic compounds, and has shown that the mode of siting the papei-s influences their coloi-ation by- light, and that -v\dth unsized paper coloration is effected only- after a long time. Perceiving that the principal reaction re- sulted ft'om the chromic acid contained in the bichromate of potash, on the starch in the size of the paper, it occiuTed to M. E. Becquerel, that, as starch has the property of forming with iodine a combination of a very fine blue colour, it should pro- duce deep shades of that tint, whilst the lights still remained an orange-yellow. His method of proceeding is to spread a size of starch very vmifoi-mly over the surface of the paper. It is then steeped in a weak alcoholic solution of iodine, and afterwards washed in a great quantity of water. By this immersion it shovdd take a very fine blue tint. If this is xmiform, the paper is considered fit for the experiment ; in the contraiy case it is sized again. It is then steeped in a concentrated solution of bichromate of potash, and pressed between folds of blotting-paper, and dried near the fire. To be effective, it should be very diy. It is now fit for use. When the copy is effected, which re- quires in siinshine about five minutes, the photograph is washed and dried. When dry, it is steeped in a weak alcoholic solution of iodine, and afterwards, when it has remained in it some time, it is washed in water, and carefully dried with blotting-paper, but not at the fire, for at a little below 100° Fahr. the combi- nation of iodine and starch discolours. If it be considered that the di-awing is not sufficiently dis- tinct, this immersion may be repeated several times; for by this means may be obtained the intensity of tone that is de- sired, which intensity can be changed at will by employing a more concentrated solution of iodine. When the paper is damp, the shades are of a very fine blue, but when it is dry the colour becomes deep violet. If while the di'awing is still wet it be covered with a lawyer of gum arable, the colour of the drawing is greatly preseiwed, and more beautiful when it is dry. When a paper is thus pi-epared, it loses at fii'st a little of its tone, but it afterwards preseiwes its violet tint. Section II. — The Chromatype. This process, devised by the author, is a pleasing one in its results : it is exceedingly simple in its manipulatory details, and 72 HISTOEY OF PHOTOGRAPHY. produces veiy cliarmiag positive pictiu*es by the fii'st applica- tion. The chromatype is foimded on the above process of Mr. Ponton's: — One drachm of sulphate of copper is dissolved in an ounce of distilled water, to wliich is added half an ounce of a satm-ated solution of bichromate of potash ; this solution is apjiHed to the sm-face of the paper, and, when chy, it is fit for use, and may be kept for any length of time without spoiling. When exposed to sunshine, the first change is to a dull brown, and if checked in this stage of the process we get a negative pictiu-e, but if the action of the light is continued, the browning gives way, and we have a positive yellow pictm^e on a white ground. In either case, if the paper, when removed from the simshine, is washed over with a solution of nitrate of silver, a very beautiful positive picture results. In practice, it will be found advantageous to allow the bleaching action to go on to some extent; the picture resulting from tliis will be clearer and more defined than that which is procured when the action is checked at the browTi stage. To fix these pictures it is necessary to remove the nitrate of silver, wliich is done by washing in jmre water : if the water contains any muriates the picture sufiers, and long soak- ing in such water obliterates it, or if a few gi-ains of common salt are added to the water, the apparent destruction is very rapid. The pictui'e is, however, capable of restoration ; all that is necessary being to exjDose it to sunshine for a quarter of an hour, when it revives ; but instead of being of a red coloiu-, it becomes lilac, the shades of coloiu- depending upon the quantity of salt used to decompose the chi'omate of silver which forms the shadow parts of the picture. Mr. Bingham remarks on this process, that if we substitute sulphate of nickel for the sulphate of copper, the paper is more sensitive, and the pictm-e is more clearly developed by nitrate of silver. The follo-\ving modification of this process possesses some ad- vantages. If to a solution of the sul})hate of copper we add a solution of the neutral chromate of potash, a very copious browoi precipitate falls, which is a true clu-omate of copper. If tliis jjrecipitate, after being well washed, is added to water acidulated with sulphuric acid, it is dissolved, and a dichromatic solution is formed, which, when spread upon paper, is of a piu-e yellow. A veiy short exposiu-e of the pajters washed with this solution is (juite sufiicient to dischai-ge all the yellow from the paper, and give it perfect whiteness. If an engraving is to be copied we proceed in the usual manner; and we may either bring out the picture by placing the paper in a solution of carbonate of soda THE FERROTYPE. 73 or potash, by -wliicli all the shadows are represented by the clu'omate of copper, or by washing the paper with nitrate of silver. It may sometimes happen that, owing to deficient Light, the photograph is darkened all over when the silver is applied : this colour, by keeping, is gi-adually removed, and the pictvu-e comes out clear and sharp. If the chromate of copper is dissolved in ammonia, a beautiful green solution results, and if applied to paper acts similarly to those just described. The chi'omatyjje pictures, under certain conditions, afford a beautiful example of the changes which take place, slowly, in the dark, from the combined operations of the materials em- ployed. If we take a cliromatyj^e picture after it has been developed by the agency of either nitrate of silver, or of mercury, and place it aside in the dark, it will be found, after a few weeks, to have darkened considerably both in the lights and shadows. This darkening slowly increases, until eventually the picture is obliterated beneath a film of metallic silver or mercuiy; but, while the pictiu"e has been fading out on one side, it has been developing itself on the other, and a veiy pleasing image is seen on the back. After some considerable time the metal on the front gives way again, the paper slowly whitens, and eventually the image is presented on both sides of the paper of equal in- tensity, in a good neutral tint upon a gi'ey gi'Oimd. These I'esults, it "will be remembered, are of a very similar character to those already described as pecxiliar to the amphitype process of Sir John Herschel. Section III. — The Ferrotype. This process, which is of remarkable sensibility, was discovered by the author, and published in the Athenceum, under the name of the Energiatype ; bxxt from a desire to group all those pictm^es under a general head into which iron salts enter as an element, the present name is preferred. The prej^aration of the paper is as follows: — Good letter-paper (Whatman's is the best) is washed over ^vith the following solution, viz. : Five gi-ains of succinic acid (it is important that succinic free fr'om any oil of amber, or adventitious matter, should be obtained) are to be dissolved in one fluid omice of water, to which are added about five grains of common salt, and half a drachm of mucilage of giun ai-abic. When dry, the paper is drawn over the siu'face of a solution of sixty grains of nitrate of silver in one ounce of dis- 74 HISTORY OF PHOTOGRAPHY. tilled water. Allowed to dry in the dark, the paper is now fit for use, is of a pure white, retains its colour, and may be pre- served for a considerable time in a portfolio, until wanted for tLse. The preparation of this paper is by no means difficult, but requires care and attention. The solutions must be applied very equally over the paper, which should be immediately lumg upon a frame or clothes' horse to dry. Extreme care must be taken that the paper be not exposed to light, after the niti-ate of silver solution has been applied, until required for iLse. Many of the disappointments experienced by the experimenters on the ener- giatype are occasioned by a neglect of this precaution ; as, although no apparent effect may have been produced by the ex- posure, the clearness of the siibsequent pictm-e will be seriously injured. The succinic acid miist also be very pm-e. We shall now briefly describe the method of applying this process to the different purposes for which it is best adapted, premising that the varying circiunstances of time, place, and light, vnll render necessary such modifications of the following dii-ections as the experience of the operator may suggest. As a genei-al rule, an open situation, sunshine, and, if possible, the morning sun, should be prefeiTed, as the image is sharper, and the colovu' produced more intense, and less afiected by the subsequent fixing process. In the camera, for a building or statue, an exposiu'e of half a minute in strong sunshine is \isually sufficient ; for a porti-ait, taken under ordinary conditions, two or tkree minutes are required. When the paper is taken fi-om the camera, nothing is visible upon it ; but by attending to the following directions the latent pictiu-e will quickly develope itself. Ha-s-ing mixed together about one ch-achm of a saturated sohition o{ protosnlphate of iron and two or three drachms of mucilaye of gum arabic, pour a small quantity into a flat dish. Pass the prepared side of the paper taken from the camera rapidly over this mixtm-e, taking care to insure complete contact in every part. If the paper has been sufficiently impressed, the picture will almost immediately appear, and the fui-ther action of the iron must be stopped by the appli- cation of a soft sponge and plenty of clean water. Shoiild the image not appear immediately, or be imperfect in its details, the iron solution may be allowed to remain upon it a short time ; but it must then be kept disturbed, by rapidly but lightly brush- ing it up, othei'wise n\imeroi;s black specks vnll form and destroy the photograph. Great care should be taken that the iron sohition does not touch the back of the pictm-e, which it THE CATALYSOTYPE. 7§ will inevitably stain, and, the pictiire being a negative one, be rendered useless as a copy. A slight degree of beat ^^^ll assist the development of the image where the time of exposure has been too short. The pictm-e should be carefully washed to take off any super- ficial blackness, and may then be permanently fixed by being soaked in water to which a small quantity of ammonia, or, better still, hyposulphite of soda, has been added. The paper must again be well soaked in clean water, to clear it from the soluble salts, and may then be di'ied and pressed. Exact copies of prints, feathers, leaves, &c., may be taken on the succinated paper by exposing them to the light in the copying-frame, until the margin of the prepared paper, which should be left uncovered, begins to change coloiu" veiy slightly. If the object to be copied is thick, the siu'face must be allowed to assiune a darker tint, or the light "\vill not have penetrated to the paper. Positive copies of the camera negatives are procured in the same manner as the copies of the prints, &c., just described. Instead, however, of using the iron solution, the paper must be exposed to the light, in the frame, a sufiicient time to obtain perfect copies. The progress of the pictvire may be obseiwed by turning up the corner of the paper, and, if not sujBSciently done, replacing it exactly in the same position. They should be fixed with hyposulphite, as before directed. At the meeting of the British Association at York in 1844, 1 showed, by a series of photographs, that the protosulphate of iron was most efiective in developing any photogitiphic images, on whatever argentiferous prepai-ation they may have been re- ceived. Every subsequent result has shown that with proper care it is the most energetic agent for developing with which we are acquainted. The difficulty of obtaining, and of preserving, the salt free of any peroxide, or a basic salt which falls as a brownish-yellow powder, has been the principal cause why it has not been so generally employed as the galKc acid : this can be insured by adding a few drops of sidphimc acid and some iron filings to the solution of the protosulphate of iron. Section IY. — The Cataxysotype. This process of Dr. Wood's is capable of producing pictures of superior excellence. Owing to the inconstancy of the iodine compovmds, it is a little uncertain, but, care being taken to in- siu-e the same degree of strength in the solutions, a very uniform 76 HISTORY OP PHOTOGRAPHY. good result may be obtained. The process and its modifications are thus described by the inventor. "Let well-glazed paper (I prefer that called wove post) be steeped in water to which hych-ochloric acid has been added in the proportion of two drops to thi-ee ounces. When well wet, let it be washed over with a mixture of syrup of iodide of iron half a drachm, water two drachms and a halij tinctiu-e of iodine one di'op. " When this has remained on the paper for a few minutes, so as to be imbibed, dry it lightly with bibulolus paper, and being removed to a dark room, let it be washed over evenly, by means of a camel-hair pencil, with a solution of nitrate of silver, ten grains to the oimce of distilled water. The jiaper is now ready for the camera. The sooner it is used the better ; as when the ingredients are not rightly mixed it is liable to spoil by keeping. The time I generally allow the paper to be exposed in the camera varies from two to thirty seconds ; in clear weather, without sunshine, the medium is about fifteen seconds. With a bright light, the pictm-e obtained is of a rich brown colour ; with a faint light, or a bright light for a veiy short time continued, it is black. For portraits out of dooi-s, in the shade on a clear day, the time for sitting is from ten to fifteen seconds. " If the light is strong, and the view to be taken extensive, the ojierator should be caiitious not to leave the paj^er exposed for a longer period than five or six seconds, as the picture will ap- j)ear confused from all parts being equally acted on. In all cases, the shorter the time in which the picture is taken the better. " When the paper is removed from the camera no pictm-e is visible. However, when left in the dark, without any other preparation being used, for a period wliich varies with the length of time it was exposed, and the strength of the light, a negative picture becomes gradu.ally developed, until it arrives at a state of perfection which is not attained, I think, by photography produced by any other process.* It would seem as if the salt of silver, being slightly affected by the light, though not in a degi'ee to produce any visible eftect on it if alone, sets up a catalytic action, which is extended to the salts of iron, and which * The picture, when developed, is not readily injured by exposure to mo- derate light; it ought, however, to be fixed, which may be done by washing it with a solution of bromide of potassium, fifteen or twenty grains to the ounce, iodide of potassium, five grains to the ounce. It may either be applied with a camel-hair-pencil or by immersion. The picture must then be well washed in water to remove the fixing material, which would cause it to fade by exposure to light. THE CATALYSOTYPE. 77 continues after the stimulus of the light is withchuwn. The catalysis which then takes place has induced me to name this process, for want of a better word, the Catalysotype. Sii" J. Herschel and Mr. Fox Talbot have remarked the same fact with regard to other salts of iron, but I do not know of any process being employed for photographic pmposes, which depends on this action for its development, except my own. " My reason for using the muriatic solution previous to washing with the iodide of iron is this : I was for a long time toi-mented by seeing the pictui'es spoiled by yellow patches, and covild not remedy it, luitil I observed that they presented an appear- ance as if that portion of the nitrate of silver which was not de- composed by the iodide of iron had flowed away from the part. I then recollected that Sir J. Herschel and Mr. Hunt had proved that iodide of silver is not very sensitive to light, unless some free nitrate be present. I accordingly tried to keep both together on the paper, and after many plans had failed, I suc- ceeded by steeping it in the acid solution, which makes it freely and evenly imbibe whatever fluid is presented to it. I am sure that its iitility is not confined to this efiect, but it was for that purpose that I fii'st employed it. " My reason for adding the tincture of iodine to the syrup is, that having in my first experiments made use of, with success, a syrup that had been for some time prepared, and afterwards remarking that fresh syi'up did not answer so well, I exammed both, and foxmd in the former a little free iodine ; I therefore added a little tincture of iodine with mtxch benefit, and now always use it in quantities proportioned to the age of the syi'up. " The following hints will, I think, enable any experimenter to be successful in producing good pictures by this process. In the first place, the paper used should be that called wove post, or well-glazed letter paper. When the solutions ai-e applied to it, it should not immediately imbibe them thoroughly, as would happen with the thimier sorts of paper. Tf the acid solution is too strong, it produces the veiy effect it was originally intended to overcome ; that is, it pi-oduces yellow patches, and the picture itself is a light brick colour on a yeUow grovmd. When the tincture of iodine is in excess, partly the same restdts occur ; so that if this effect is visible, it shows that the oxide of silver which is tlu-own down is partly i-e-dissolved by the excess of acid and iodine, and their quantities should be diminished. On the contrary, if the silver solution is too strong, the oxide is depo- sited in the dark, or by an exceedingly weak light, and in this case blackens the yellow parts of the picture, which destroys it. When this efiect of blackening aU over takes place, the silver so- 78 HISTORY OF PHOTOGRAPHY. lution should be weakened. If it be too weak, the paper ramains yellow after exposure to light. If the iodide of ii-on be used in too great quantity, the pictiu'e is dotted over with black spots, which afterwards change to white. If an excess of nitrate of silver be used, and a photograph immediately taken before the deposition of the oxide takes })lace, there will be often after some time a positive picture formed on the back of the negative one. The excess of the nitrate of silver makes the paper blacker where the light did not act on it, and this penetrates the paper ; whereas the darkening produced by the Hght is confined to the surface. The maximiun intensity of the spectiiim on the paj)er, when a prism of crown glass is used, lies between the indigo and blue ray. The difference of effect of a strong and weak light is beautifully sho^vn in the action of the spectrum : that part of the paper which is exposed to the indigo ray is coloured a red- dish brown, and this is gradually darkened towards either ex- tremity, vmtil it becomes a deep black. " I have not had many opportnities of experimenting with the catalysotype, but it certainly promises to repay the trouble of further investigation. The simplicity of the process, and the sensibility of the paper, should cause it to be extensively used. It has all the beauty and quickness of the calotype, without its trouble, and very little of its uncertainty ; and, if the more fre- quent use of it by me. as compared with other processes, does not make me exaggerate its facility of operation, I think it is likely to be practised successfully by the most ordinary experimenters." Dr. Woods subsequently made the following addition : — " Since the preceding paper was written, I have been ex- perimenting with the catalysotype, and one day having had many failures, which was before quite imusual with me, I am induced to mention the cause of them, for the benefit of sub- sequent exjjerimenters. The paper I used was very stiflf and highly glazed, so that the solution first applied was not easily imbibed. The blotting ])a])er was very dry and biblulous. When using the latter, I removed nearly all the solution of iron fi'om the first, and, of course, did not obtain the desired residt. "While varying the process in endeavoiu-ing to find out the cause just mentioned, I discovered that the following proportions gave very fine negative pictiu-es, from which good j)ositive ones were obtained : — Take of syrup of iodide of ii'on, distilled water, each two drachms ; tinctiu'c of iodine, ten to twelve ch'ops : mix. Fii-st brush this over the paper, and after the few minutes, having dried it with the blotting pajier, wash it over in the dark (before ex])osure in the camera) with the following solution, by means of a camel-hair pencU : — Take of niti'ate of sdver one diachm ; FERROCYA^IDE OF POTASSIUM. 79 pure water one ounce : mix. This gives a darker pictm-e than the original preparation, and consequently, one better adapted for obtaining positive ones ; it also requires no previous steeping in an acid solution. To fix the pictui-e let it be washed first in. water, then allowed to remain for a few minutes in a solution of iodide of potassium (five grains to the ounce of water) and washed in water again. The paper I use is the common imglazed copy paper, but such as has a good body. I have tried the same paper with the original preparation, and find it to answer ex- ceedingly well ; it does not require in this case, either, an acid solution. The same precautions and hints apply to the amended as to the original process ; such as, when it blackens in the dark, there is too much caustic used ; when it remains yellow, or that it is studded with yellow spots, too much iodine ; when marked with l)lack spots, too much iron. It is necessary to mention these, on account of the vaiying strength of the materials em- ployed." Section Y. — Ferrocyanide of Potassium. At the meeting of the British Association at Plymouth in 1841, I fii'st dii'ected attention to the use of the ferrocyanide of potassiiun in combination with the iodide of silver. The process resulting from this being very important in many points, the abstract of the paper then read, as given in the Transactions of the Sections, is repi-iuted. The author having been engaged in experiments on those varieties of photographic di-awings which are formed by the action of the hydriodic salts on the darkened chloride of silver, and with a view to the removal of the iodide formed by the process from the paper, was led to observe some peculiar changes produced by the combined influences of sunshine and the ferrocyanide of potassiiun. It was found that the ordinary photographic paper, if allowed to darken in sunshine, and then slightly acted on by any hydi-iodic solution, and, when dry, washed with a solution of the feiTocyauide of potassium, became extremely sensitive to light, changing from a light brown to a full black by a moment's exposure to sunshine. Following out this result, it was dis- covered that perfectly piu-e iodide of silver was acted on with even greater rapidity, and thus it became easy to form an ex- quisitely sensitive photographic paper. The method recommended is the following : — Highly glazed letter paper is washed over with a solution of one drachm of nitrate of silver to an ounce of distilled water; 80 HISTORY OF PHOTOGRAPHY. it is qiiickly cWed, and a second time washed with the same so- hition. It is then, when dry, placed for a minute in a sohitiou of two drachms of the iodide of potassium in six ounces of water, placed on a smooth board, gently washed by allowing some water to flow over it, and di-ied in the dark at common temperatiu-es. Papers thus prepared may be kept for any length of time, and are at any time rendered sensitive by simply washing them over with a solution formed of one drachm of the ferrocyanide of potassium to an ounce of water. These papers, washed with the ferrocyanide and dried in the dark, are, in this diy state, absolutely insensible, but they may at any moment be rendered sensitive by merely washing them with a little cold clean water. Papers thus pi-epared are rendered quite insensible by being washed over with the above hydriodic solution. They are, how- ever, best secured against the action of time by a solution of auimonia. Section YI. — The Fluorotype, So called from the introduction of the salts of fluoric acid, con- sists of the following process of manipulation : — J Bromide of potassium, 20 grains. ( Distilled water ... 1 fluid oimce. J Fluoride of sodimn . 5 grains. ( Distilled water ... 1 fluid oimce. Mix a small quantity of these solutions together when the papers are to be j)i'epared, and wash them once over with the mixture, and, when dry, apply a solution of nitrate of silver, sixty grains to the oimce of water. These papers keep for some weeks withovit injury, and l^ecome impi*essed with good images in half a minute in the camera. The impression is not siiffi- ciently strong when removed from the camera for producing positive pictures, but may be rendered so by a secondaiy process. The photograph should first be soaked in water for a few minutes, and then placed upon a slab of porcelain, and a weak solution of the proto-sulphate of iron brushed over it ; the picture almost immediately acquires an intense colom", which should then be stopped dii-ectly by phmging it into water slighlly acidulated mth miiriatic acid, or the blackening will extend all over the paper. It may be fixed by being soaked in water, and thou dipped into a solution of hypo-sulpliite of soda, and again soaked in water as in the other processes. BROMIDE OF SILVER AKD MERCURIAL VAPOUR. 81 Mr. Bingliain has the following remarks on tliis process, and he gives a moditied form, into wliich a new photographic element is introduced: — " We find it is better to add to the proto-sulphate of ii-on a little acetic or sidphiu'ic acid : this will be found to jirevent the darkening of the lights of the picture to a great extent, and it will be foimd better not to prepare the paper long before it is required for use, this being one reason why the picture often becomes dusky on application of the proto-sulphate. " Reasoning upon the principle that the action of light is to reduce the salts of silver in the paper to the metallic state, and that any substance which woidd reduce silver would also quicken the action of light, we were led to the following expeiiment : — The protochloride of tin possesses the projierty of reducing the salts both of silver and of gold : a paper was prepared with the bromide of silver, and previously to exposing it to light it was washed over with a very weak solution of the chloride of tin ; the action of light upon the paper was exceedingly energetic ; it was almost instantaneously blackened, and a copy of a print was obtained in a few seconds." The use of fluorides has been recently introduced as a novelty by some French photographers, but reference to the author's Researches on Light, published in 1844, will distinctly show that I was the fii-st to employ these salts, as photographic agents. Section Ylf — Bromide of Silver and Mercurial Vapour. In my fii'st publication on this subject, in Griffin's Scientific Miscellany, I introduced the following process, which, although it has never yet been properly worked out, involves many points of interest : — Some extremely cuiious results, led me to examine the effect of the mercmial vapour on the jDiu-e precipitated iodides and bromides. 1 was long perplexed with exceedingly anomalous I'esvilts, but being satisfied from particiilar experi- ments that these reseai'ches promised to lead to the discovery of a sensitive preparation, I persevered. To prepare this sensitive paper we proceed as follows : — Select the most perfect sheets of well-glazed satin post, quite free from specks of any kind. Placing the sheet carefully on some hard body, wash it over on one side by means of a very soft camel's hair pencil, with a solution of sixty grains of the bromide of potassium, in two fluid oimces of distdled water, and then diy it quickly by the fixe. Being dry, it is again to be washed over 82 HISTORY OF PHOTOGRAPHY. with tlie same solution, and dried as before. Now, a solution of nitrate of silver, one hundi'ed and twent}'^ grains to the fluid oiince of distilled water, is to be applied over the same siu'face, and the paper quickly di-ied in the dark. In this state the papers may be kept for use. When they are required, the above solution of silver is to be plentifully applied, and the paper jtlaced loet in the camera, the greatest care being taken that no day -light, not even the faintest gleam, falls upon it, imtil the moment when we are pi-epared, by removing the screen, to per- mit the light, radiated from the objects we ^\T.sh to copy, to act in producing the picture. After a few seconds, the light must be again shut off, and the camera removed into a dark room. It will be found, on taking the paper from the box, that there is but a very slight outline, if any, as yet visible. Place it aside, in perfect darkness, until quite diy, then fix it in a mercm-ial vapoiu" box, and apply a very gentle heat to the mercury. The moment the mercuiy vaporizes, the pictiu-e will begin to develope itself. The spirit lamp must now be removed for a short time, and when the action of the mei'cmy appeal's to cease, it is to be very carefidly applied again, luitil a well-defined pictiu'e is visible. The vapoi-ization must now be suddenly stopped, and the photograph removed from the box. The di'awing \\dll then be very beautiful and distinct ; but much detail is still clouded, for the development of which it is only necessary to place it cau- tiovisly in the dark, and allow it to remain undistm-bed for some hours. There is now an inexpressible charm about the pictm-e, equalling the delicate beaiity of the daguerreotypes ; but being still veiy susceptible of change, it must be viewed by the light of a taper only. The nitrate of silver must now be removed from the paper by well washing in soft water. When the picture has been di-ied, wash it quickly over with a soft Inrush, dipped in a warm solution of the hyposulphite of soda, and then well wash it for some time in the manner directed for the ordinary photographs, in order that all the hyposidphite may be removed. The drawing is now fixed, and we may use it to procure positive pictures, many of which may be taken from one original. Section VII. — Positive Photographs by One Process. About the same time Mr. Talbot, Sir John Herschel, Dr. Fife, and myself, discovered the very remarkable property of the iodides in bleaching the darkened salts of silver. Many very beautiful results may be thus obtained. The manipulatory POSITIVE PHOTOGRAPHS BY ONE PROCESS. 83 details piiblislaed by Dr. Fife were simple in tlieii- character, but arrived at by a long series of inquii-ies. It is now quite easy to prepare pliotograpliic papers, on which the iodine solutions shall act ■\\'ith perfect uniformity : — Soak the paper for a few minutes in phosphate or miu-iate of soda, removing mth a soft biiish any aii- bubbles which may form on it. The superfluous moistui-e must be ^\dped off with very clean cotton cloths, and the papers dried at common temperatures. When dry, the paper must be pinned out on a board, and the silver solution spread over it, boldly but lightly, with a very soft sponge brush. It is to be instantly exposed to simshine, and, if practicable, carried into the open air, as the more speedily evaporation proceeds the less does the silver penetrate the paper, and the more delicate it is. The fixst siu-face is very irregular, being as before described, and represented iu fig. 2. As soon as the siu-face appears chy, the silver solution must be again applied as before, and the exposure repeated. It must now be exposed imtil a fine chocolate-brown colour is produced equally on all parts of the sui-face, and then, until required for use, be carefully preserved fi*om the further influence of light. If the paper is to be kept long, the darkening must not be allowed to proceed so far as when it is to be speedily made use of. In darkening these papers, the greatest possible attention must be paid to the quantity of light to which they are sub- mitted, evei-thing depending on the rapidity of the blackening process. The morniug sun should be chosen, for the reasons before stated. A perfectly cloudless sky is of great advantage. The injurious consequence of a cloud obsciuing the sun during the last darkening process, is the formation of a siu-face which has the appearance of being washed with a dii'ty bi-ush. This is with diificidty removed by the iodides, and the resulting pictures want that clearness which constitutes theii' beauty. Papers darkened by the diffused light of a cloudy day are scarcely, if at all, acted on by these salts. Great care must be taken to prevent the silver solution from flowing over the edges of the paper, as thereby an extra quantity of darkened silver is formed on both sides, which requires a long-continued action of the iodides and sunshine to bleach. The kind of paper on which the silver is spread is an object of much importance. A paper known to stationers as satin post, double-glazed, bearing the mark of J. AYhatman, Tiu'key Mill, is decidedly superior to every other kind I have tried. The dark specks which aboimd in some sorts of paper must be avoided, and the spots made by flies very carefully guarded 84 HISTORY OF PHOTOGRAPHY. against. These are of small consequence during the darkening process, but when the bleaching ■wash is applied, they form centres of chemical action, and the "whitening process goes on around them, independently of light, deforming the di-awing ■with smaU rings, ■which ai*e continually extending their diameters. The saline ■washes may be considerably varied, and combined to an indefinite extent, ■with a continued change of efiect, "which is singularly interesting. In their appUcation ■we should be guided, as in the negative process, by their combining propor- tions. The follo^wing list of the salts ■which will give the best effects, selected fi-om upwards of seven hundi-ed combinations, ■will show the variety of coloui's produced. They are placed in the order of the sensitiveness they appear to maintain, when used as neai'ly as possible under the same circumstances : — Colour of Picture. Mi"TiiATE OF Ammonta.. Red, changing to black in the sunshine. CHLORroE OF SODITM — Ditto, ditto. Chloride of Stroxtitm A fine hroicn. Chloride of Barium ...A rich brown, inclining to purple. Sol. Chloride of Lime Very red. Sol. Chloride of Soda A bricJc red. Iodide of Potassium.... Fe/fo?m/< 6ro?r«. Chloride of Potas- J Variable, sometimes yeWyunsh, often a siUM I steel blue. Phosphate of Soda Mouse colour. Tartrate of Soda Da rk brown. Urate of Soda. Yellowish broion. Chloride of Iron Deep brown, which blackens. Bromide of Sodium. Red brown of a peculiarly rich tint. The change mentioned in the colour of the finished picture is that which ai'ises fi-om a fi-esh exposure to the solar rays ; where no change is mentioned, it is too slight to be worth notice. Allien papers prepared "with any of the above, except the phosphates, ai-e soaked for a little time in water, and dried in the sunshine, the pictm-e produced. — it matters not what iodide is used. — is rendered pecvdiai-ly red. and does not change by re-exposure. By washing some of the papere "with weak solution of ammonia, this peculiaiity is produced in a very str ikin g manner. In the other di^"isions ^"ill be found some further remarks on the veiy pecvdiar physical jihenomena presented by the action of the comjx>\mds of iodine on these dai'kened salts of silver, and details of yet more perfect foi'nis of manipulation. ON THE APPLICATIOX OF THE DAGUERREOTYPE TO PAPER. 85 Section VIII. — On the Application of the Daguerreotype TO Paper. The expense and inconvenience of metallic tablets rendered it in the highest degree desirable that paper should be emjiloyed in their place. A very extensive series of experiments at length led to the pleasing conclusion of being enabled to prepare a paper which answered in every respect as well as the silver plates, and in many much better. This discovery formed the subject of a communication to the Royal Society, which that learned body did me the honour to print in their Transactions. My memoir is entitled, — " On the Influence of Iodine in rendering several Argentine Compounds, spread on Paper, sensitive to Light ; and on a New Method of Pro- ducing, toitk greater distinctness, the Photograpihic Imaged This paper contains the substance of the following remarks ; but since the publication of the Transactions I have been successful in simplifying the process of preparation. My experiments established, in the most satisfactory manner, that even on the silver tablets a semi-oxidized surface was pre- sented to the iodine. They also proved that perfectly 2>^ire untarnished silver was by no means readily acted on by the iodine. From this I was led to prepare oxides of silver in many different ways, which enabled me to spread them over paper, and the residt was instructive. Any of the ordinary photo- graphic papers allowed to darken to a fall brown, which is a stage of induced oxidation, become, by long exposure to iodine, of a steel-blue or violet coloiu-. If exposed in this state to sunshine for a long period, theii' colour changes from gray to a clear olive. Now, exposui-e to sunshine for a minute, or to dif- fused daylight for five minutes, produces no apparent change j but merciu'ial vapour speedily attacks the portions which have been exposed to light, and a faithful pictiu-e is given of whatever may have been superposed. There is, however, a want of suffi- cient contrast between the lights and shadows. By alloM'ing the fii'st darkening to proceed until the paper acquires the olive colour, which indicates the formation of a time oxide of silver, it will be fovind, although it is not more speedily acted on by the iodine, that it is more sensitive, and that a better picture is formed. The kind of photographic preparations used appears to have but little influence on the residts, — a chloride, iodide, or bromide of silver, allowed to darken, answers equally weU. There ai-e many things, unfortunately, which prevent our 86 HISTORY OF PHOTOGRAPHY. availing ourselves of this easy method of producing a tolerably sensitive DagueiTeotype paper. These are, certain irregular formations of oxides in different states, and the revival of metallic silver in some parts of the sm-face. I next spread papers with the pure oxide formed by chemical means, and also the protoxide, and many of its salts. These papei-s were not veiy readily affected by iodine, or influenced by light dimng short exposures. Silver is revived fi'om its solutions by hydrogen gas ; conse- qently, notliing is more easy than, by washing a paper with nitrate of silver in solution, to procure a fine silver paper, by passing a cun-ent of hydrogen gas over it. A pictm-e of a peculiarly delicate character may be produced on this kind of paper ; but it has not the requii-ed sensibility, and there is a gi*eat want of conti'ast in the lights and shadows. It may be interesting to state, that the yellow-brown phosphate of silver is as readily acted on by iodiiie as the oxides, and is quite as sensitive to luminous influence. Phosphuretted hydrogen gas effects the revival of metallic silver, and the surface produced by means of this gas, used as the hydrogen was in the former case, is of a fine steel-blue, which colour arises from a portion of phosphorus having entered into combination with the silver. These kinds of paper comported themselves in every respect as the metallic tablets — were equally sensitive, and produced pictures as delicately beautiful. Unfortimately, however, owing to the sjwntaneously inflammable nature of the phosphui-etted hydrogen gas, it is not safe to operate with it. After various ineffectual contrivances to overcome this difficulty, I was obliged to abandon the use of this gas entirely — warned of the danger I iucured, — by several violent but fortunately hannless explo- sions. The vapour of phosphorus and of sulphur was also tried, and many very beautiful effects were produced. At length, however, I stopped at sulphuretted hydrogen, which ansrs'ers in every respect.* To prepare this, soak a paper of very firm texture, not too much glazed, in a weak solution of the muriate of ammonia. It miist then be wiped with clean cloths, and carefully dried. The paper is then dipped into a weak solution of the nitrate of silvei-, and the small bubbles which fonn on its surface are carefully removed with a camel's hau' pencil. When the paper is nearly, but not quite, dry, it must be exposed in a closed vessel to sul- A very interesting account of the revival of gold and silver from their folu- tions by these gases, will be found in a tract on Combustion, published by Mrs. Fulhame. Olf THE APPLICATION OF THE DAGUERREOTYPE TO PAPER. 87 phuretted hydrogen gas, slowly fonned from the siilphiiret of antimony and hydrochloric acid : in a few minutes it will become of an iron-brown coloiu', having a fine metallic lustre. It is again to be passed tlu'ongh a solution of silver, somewhat stronger than the first, and dried, taking care that no shadow falls on the paper whilst it is drying. It is then a second time sub- mitted to sidphuration, and, by careful management, the process is now generally completed. If, however, the paper is not considered to be siifficiently dark, it must be once more washed in the solution of silvei', and again subjected to the action of sidphuretted hyth'ogen. If the above paper be allowed to remain in the sulphuretted hydrogen gas after the maximum blackness is produced, it is again whitened ^vith some quickness. This may be accounted for in two ways : the gas may be mixed with a portion of mimatic acid vapour, or a quantity of chlorine sufficient to pro- duce this efiect may be liberated from the preparation on the paper to react on the sulphm-et of silver. The perfection of these papers consists in having a deep black ground to contrast with the mercurial deposit, by which means the pictures have the advantage of being seen equally well in all positions, whereas Daguerre's pictures on the metal plates can only be seen to advantage at certain angles. The sulphuretted paper may be rendered sensitive in the same manner as the plates by exposiu'e to the vapour of iodine. I, however, prefer drawing the paper over a solution thus formed : — A saturated solution of any salt of iodine is made to dissolve as much pure iodine as possible, and of this liquid two drachms are mingled with four ounces of water. Care is re- quired that one side only of the paper is wetted, which is by no means difficult to effect, the fluid is so greedily absorbed by it ; all that is necessaiy being a broad shallow vessel to allow of the paper touching the fluid to its full ^vddth, and that it be drawn over it with a slow steady movement. When thus wetted, it is to be quickly dried by a warm, but not too bright fire ; of course daylight must be carefully excluded. Papers thus iodidated do not lose their sensitiveness for many days if carefully kept from light. On examining the sheet after the Daguerreotype processes in the camera, and of mercm-ialization, have been completed, a very perfect pictiu'e is found upon it ; but it is still capable of vast improvement, which is, by the foUowdng simple plan, accom- plished in a way which is at once magical and beautiful. Action of Corrosive Sublimate.— Dip one of the Daguerreo- type pictui-es, formed on the siUphui'etted paper, into a solution 88 HISTORY OF PHOTOGRAPHY. of corrosive sublimate : the drawing instantly disappears, but, after a few minutes, it is seen im^folding itself, and gradually becoming far more distinct than it was before ; delicate lines, before invisible, or barely seen, are now distinctly marked, and a rai-e and singular perfection of detail given to the drawing. It may appear, at first sight, that the bichloride of mercury dissolves off the metal, and agaia deposits it in the form of chloride (calomel). But this does not account for the fact, that if the paper has been prepared with the nitrate of silver, the mercury disappears, and the di-awing vanishes, the deposit taking place only on those parts upon which light has acted but feebly ; as, for instance, on the venations of leaves, leaving those portions of surface which were exposed to full luminous influence without a particle of quicksilver. When the paper has been either a chloride or iodide, the efiect is as above, and the thickness of the deposit is as the intensity of the light has been ; consequently, the semi-tints are beautifidly preserved. If the di'awing remains too long in the solution, the precipitate adheres to the dark parts and destroys the effect. The suigida- rity of tliis operation will be more striking if the pictiu'e has been soaked some time in the solution of the hyposulphite of soda, and then dipped into the bichloride of mercvuy. As the drawing disappears, a series of circles, formed of a white powder, appear to arise from the paper, generally commencing at the centre, and slowly extending over the whole surface : the powder is afterwards deposited, and the sheet is buried in the precipi- tate ; but on taking the paper from the liquid, and passing a stream of water over it, the precipitate is entii^ely removed from all the parts except the lights of the picture. I have also found the invisible photographic image become evident, without the aid of merciu'ial vapoiu", by simply soaking for some time in a solution of corrosive sublimate. When these papers are prepared with due care, they are ex- tremely sensitive, and if used for copying engravings diu'ing bright sunshine, the effect is instantaneous. The great difficulty is to present the paper to the s\in, and ^vithdraw it with suffi- cient celerity. In the weak light of the camera a few minutes during sunshine is quite sufficient for the production of the best effects. One great advantage of these pictures over those pro- cured on the plated copper is, that the mercury does not lie loosely as on the tablets, but is firmly fixed, being al)sorbed by the paper ; therefore these pictures may be kept without injmy in a portfolio. If, instead of immersing the paper in a vessel fidl of sulphu- retted hydrogen gas, a stream of the gas is made to play upon it, SALTS OF GOLD AS PHOTOGRAPHIC AGENTS. 89 it assvimes a most richly ii'idescent surface ; tlie various colours ai"e of different degi'ees of sensibility, but for svu-face di'a wings they may be used ; and ia copying of leaves or flowers, beautiful pictures, which appear to glow with the nativral colours, are procured. Section IX. — Salts of Gold as Photographic Agents. It is well known that gold is revived from its ethereal solution by the action of light, and that the same effect takes place when the nitro-miu'iate of gold is spread on charcoal. "We are mainly indebted to Herschel's paper, published in. 1840, for the know- ledge we possess of gold as a photograpliic agent. Considering it probable that the required unstable equilibrium might be induced in some of the salts of gold, I was induced to piu'sue a great many experiments on this point. In some cases, where the paper was impregnated with a mordant salt, the salt of gold was darkened rapidly, without the assistance of Kght ; in others, the effect of light was very slow and uncertain. By washing paper with muriate of barj'tes, and then with a solution of the chloride of gold, a pajier, having a slight pinky tint, is prociu'ed ; by exposing this paper to sunshine it is at first whitened, and then, but very slowly, a darkening action is in- duced. If, however, we remove the paper from the light, after an exposure of a few minutes, when a veiy faint impression, and oftentimes not any, is apparent, and hold it in the steam of boil- ing water, or immerse it in cold water, all the parts which were exposed to the light are rapidly darkened to a full pui"ple brown, leaving the covered poi-tions on which the light has not acted, a pure white, producing thus a fine negative ch-a-wing. If, while such a paper, or any other paper, prepared ^viih the chloride of gold, is exposed to the sun, we wash it with a weak solution of the hych'iodate of potash, the oxidation is very rapidly brought on, and the darkness produced is much greater than that ob- tained by the other method ; but this plan is not often applicable. I have not yet been enabled to produce with the salts of gold any paper which shovdd be sufficiently sensitive for use in the camera obscura. Sir John Hei-schel devoted much attention to the examination of the salts of plantinum as well as gold. He found plantinum under nearly all circumstances very little sensitive to light, but the following were the results obtainedjwith the salts of gold: — If paper impregnated with oxalate of ammonia be washed with chloride of gold, it becomes, if certain proportions be hit, pretty 90 HISTOBT OF PHOTOGRAPHY. sensitive to light ; passing rather rapidly to a violet pnrple in the sun. It passes also to the same purple hue in the dark, though much more slowly; so that, as a photographic combina- tion, it is useless. Paper impregnated with acetate of lead, when washed with perfectly neutral chloride of gold, acquires a brownish-yellow hue, and a sensibility to light, which, though not great, is at- tended with some peculiarities highly worthy of notice. The first impression of the solar rays seems rather to whiten than to darken the paper, by discharging the original colour, and sub- stituting for it a pale grayish tint, which by slow degrees in- creases to a dark slate colour. But if arrested while yet not more than a moderate ash gray, and held in a current of steam, the colour of the part acted on by the sunshine, and that only, darkens immediately to a deep pui-ple. The same effect is pro duced by immersing it in boiling water. If plunged in cold water, the same change comes on more slowly, and is not com- plete tin the paper is di-ied by heat. A dr>/ heat, however, does not operate this singular change. If a neutral solution of the chloride of gold is mixed with an equal quantity of the solution of bichromate of potash, paper washed with this solution, and exposed to light, speedily changes, first to a deep brown, and ultimately to a bluish black. K an engi-aving is superposed, we have a negative copy, blue or brown, upon a yellow ground. If this photograph is placed in clean water, and allowed to remain in it for some hours, very singula!- changes take place. The yellow salt is all dissolved out, and those parts of the paper left beautifidly white. All the dark portions become more decided in their character, and aeeorling as the solarization has been prolonged or otherwise, or the light has been more or less intense, we have either crimson, blue, brown, or deep black negative photographs. SEcnoy X. — The I>rFLrEycE of Chlordte .ksx) Toddte ev REXDERIS'G SOME KISDS OF TVOOD SEySITIYE TO LiGHT. Having on many occasions subjected the simply nitrated pho- tographic paper to the influence of chlorine and iodine in close wooden boxes, I was often struck with the sudden change which light produced on the wood of the box, particularly when it was of deal ; changing it in a few minutes from a pale yellow to a deep green. This curious effect frequently occxuring, led me to observe the change somewhat more closely, and to pursue some INFLUENCE OF CHLORINE ON WOOD. 91 experiments on tlie subject. These produced no very satisfac- tory result. They proved the change to depend much on the formation of hych'ochloric and hydi-iodic acids, and the decom- position of water in the pores of the wood. I found well-baked M^ood quite insiisceptible of this very curious phenomenon. The woods of a soft kiud, as the deal and willow, were much sooner influenced than the harder varieties, but all the light-coloured woods appeared more or less capable of undergoing this change. All that is necessary is, to place at the bottom of an au--tight box, a vessel containing a mixtm-e of manganese and miiriatic acid, or simply some iodine, and fix the piece of wood at some distance above it. Difierent kinds of wood require to be more or less saturated with the chlorine or iodine, and consequently need a longer or shorter exposui-e. The time, therefore, neces- sary for the wood to remain in the atmosphere of chlorine can only be settled by direct experiment. Wood is impregnated very readily with iodine, by putting a small portion in a capsule a few inches below it. It does not appear to me at present that any practical result is likely to arise out of this peculiar pro- perty ; it is only introdviced as a singidar fact, which is perhaps worthy a little attention. CHAPTER YII. PHOTOGRAPHS ON GLASS PLATES, AND RECENT IMPROVEMENTS. To Sir John Herschel we are indebted for the first use of glass plates to receive sensitive photographic films. Section I. — Precipitates of Silver Salts. The interest which attaches to this is so great, and there appear to be in the process recommended by the English experi- mentalist so many suggestive points, from which future photo- graphists may start, that the j^assages are given in Sir John Herschel's own words : — " With a view to ascertain how far organic matter is indis- pensable to the raj)id discoloration of argentine compounds, a process was tried which it may not be amiss to relate, as it issued in a new and very pretty viu-iety of the photographic art. A solution of salt of extreme dilution was mixed with niti-ate of silver, so dilute as to form a liquid only slightly milky. This was poiu'ed into a somewhat deep vessel, at the bottom of which lay horizontally a very clean glass plate. After many days the greater part of the liquid was decanted off with a siphon tube, and the last portions very slowly and cautioixsly drained away, drop by droj), by a siphon composed of a few fibres of hemp, laid parallel and moistened without twisting. The glass was not moved till quite diy, and was foimd coated with a pretty tm.iform film of chloride of silver, of delicate tenvuty and che- mical purity, which adhered with considerable force, and was very little sensitive to light. On ch-opping on it a solution of nitrate of silver, however, and spreading it over by inclining the plate to and fro (which it bore without discharging the film of chloride) it became highly sensitive, although no organic matter could have been introduced with the nitrate, which was quite pure, nor coidd any indeed have been present unless it be sup- posed to have emanated from the hempen filaments, which were barely in contact with the edge of the glass, and wliich were PRECIPITATATES OF SILVER SALTS. 93 constantly abstracting matter from its surface in place of intro- ducing new. " Exposed in this state to the focus of a camera with the glass towards the incident light, it became impressed "ndth a remark- ably well-defined negative pictm-e, which was direct, or reversed, according as looked at from the front or the back. On pouring over this cautiously, by means of a pipette, a sokition of hypo- sulphite of soda, the picture disajopeared, but this was only while wet ; for on washing in pure water and diying, it was restored, and assimied much the air of a daguerreotype when laid on a black ground, and still more so when smoked at the back, the silvered portions reflecting most light, so that its characters had, in fact, changed from negative to positive. From such a pic- tiu*e (of coui'se befoi*e smoking) I have found it practicable to take photogi-aphic copies ; and although I did not, in fact, suc- ceed in attempting to thicken the film of silver, by connecting it, under a weak solution of that metal, with the reducing pole of a voltaic pile, the attempt afforded distinct indications of its practicability with patience and perseverance, as here and there, over some small portions of the surface, the lights had assumed a ftdl metallic brilliancy imder this process. I woxxld only men- tion further, to those who may think tliis experiment worth repeating, that all my attempts to secure a good resiilt by dry- iug the nitrate in the film of chlox-ide have faded, the crystalliza- tion of the salt distui-bing the imiformity of the coating. To obtain delicate pictmes the plate must be exposed wet, and when withdi-awn must immediately be plunged into water. The nitrate being thus abstracted, the plate may then be dried, in which state it is half fixed, and it is then ready for the hypo- sulphite. Such details of manipulation may appear minute, but they cannot be dispensed with in practice, and cost a gi-eat deal of time and trouble to discover. " This mode of coating glass with films of precipitated argen- tine or other compounds, afibrds, it may be obsei-ved, the only efiectual means of studying then- habitudes on exposure to light, free from the powerful and ever-vaiying influence of the size in paper, and other materials used in its manufacture, and estimat- ing theii" degree of sensibility and other particulars of their deportment under the influence of reagents. I find, for example, that glass so coated with the iodide of silver is much more sen- sitive than if similarly covered with the chloride, and that if both be washed vfith one and the same solution of niti'ate, there is no comparison in respect of this valuable quality ; the iodide being far superior, and of coui-se to be adopted in preference for the use of the camera. It is, however, more difficult to fijc, the 94 HISTORY OF PHOTOGRAPHY. action of the hyposiJpliites on this compound of silver being comparatively slow and feeble. " When the glass is coated with the bromide of silver, the action, per se, is very slow, and the discoloration ultimately produced far short of blackness ; but when moistened with nitrate of silver, sp. gr. I'l, it is still more rapid than vnih the iodide, tvu'ning quite black in the coiu-se of a very few seconds' exposure to sunshine. Plates of glass thus coated may be easily preserved for the use of the camera, and have the advantage of being ready at a moment's notice, requiring nothing but a wash over with the nitrate of silver, which may be delayed until the image is actually thrown on the plate, and adjusted to the correct focus with all deliberation. The sensitive wash being then applied with a soft flat camel-hair brush, the box may be closed and the picture impressed, after which it only requires to be thrown into water, and dried in the dark, to be rendered comparatively in- sensible, and may be finally fixed with hyposulphite of soda, which must be applied hot, its solvent power on the bi'omide being even less than on the iodide." Sir John Herschel suggested a trial of the fluoride of silver upon glass, which, he says, if proved to be decomposable by light, might possible efiect an etching on the glass, by the cor- roding property of the hydrofluoric acid. The metallic fluorides have been found to be decomposable, and a very sensitive pi'ocess on paper, called the fluorotype, Avill be described in the chapter on Miscellaneous Processes. I am not aware that any experiments have been made du-ectly upon glass, but it is certainly worthy of a careful trial. Herschel has remarked that we cannot allow the Avash of nitrate to diy upon the coating of the chloride or iodide of silver. If, however, we diji a glass which has one film of chloride upon it into a solution of common salt, and then spread upon it some nitrate of silver, we may very materially thicken the coating, and thus produce more intense efiects. Mr. Towson employed glass plates prepared in this manner Avdth much success. The mode adopted by that gentleman was to have a box the exact size of the glass plate, in the bottom of wliich was a small hole ; the glass was placed over the bottom, and the mixed solution, just strong enough to be mUky, of the salt and silver poured in. As the fluid finds its way slowly around the edges of the glass, it filters out ; the peculiar surface action of the solid glass plate, probably a modified form of cohesive force, separating the fine precipitate, which is left behind on the sxirface of the plate. By this means the opei-ation of coating the glass is much quickened. Another method by which films of any of the salts of silver Ciin ALBUMEN COLLODION. 95 be produced upon glass plates, is the foUo^ving modificatiou of the patent processes of Drayton and of Thompson for silvering glass: — Take a very clear plate of glass, and having put around it an edging of wax about half-an-inch in depth, pour into it a solu- tion of nitrate of silver made alkaline by a few drops of am- monia, taking care that no oxide of silver is precipitated ; mix with this a small quantity of spii'its of 'sviue, and then add a mix- tiu-e of the oils of lavender and cassia, or, wliich is perhaps the best process, a solution of grape sugar. In a short time the glass will be covered with a very beautiful metallic coating. The solution is now poured off, the edging of wax removed, and the silver is exposed to the action of diluted chlorine, or to the vapom- of iodine or bromine, until it is converted into a compound of one of these elements, after which we may proceed as recommended by Sir John Herschel. Section II. — Albumen. In the Teclmologiste for 1848, M. Niepce de Saint- Victor published his mode of aiDplyiug albumen to glass plates. M. Blanqviart Everard followed, and successively albumen, gelatine, and serum were employed. Messrs. Ross and Thomson, of Edinbui-gh, have been eminently successful operators with albumen on glass plates, many of their pictures leaving little to be desii'ed. The manipulatoiy details of the albumen process wiU be fbimd in the technical division of this work. Section III. — Collodion. The successful apjilication of a solution of gim-cotton in ether, to form the film for receiving the sensitive smiace on glass, has been claimed respectively by Mr. Fry and Mr. Archer. There is some difficulty in fixing precisely this point, since there was no actual pu.blication of the process until long after it was generally in use. Mr. Fry cei-tainly introduced the use of gutta percha in combination with collodion. The last novelty to which reference need be made is the wax paper process of M. Le Gray, which will be fully described. CHAPTER VIII. PORTEAITURE BY THE DAGUEREEOTPYE. Whex Daguerre publLshed his process, a period of twenty minutes was required to obtain a good copy of any external object : hence this period was far too long to admit of its being employed for portraiture. Mr. Towson, of Devonport, in a very valuable paper which appeared in the Philosophical Magazine in 1839, offered several suggestions on the use of large lenses, &c., which he supposed might lead to the use of the daguerreotype for the purposes of portraiture. Dr. Draper, of New York, acting on the suggestions of Mr. Towson relative to the adjustment of the focus, succeeded in accelerating his process so far as to obtain portraits from the life. He published his process in the London and Edinburgh Phihsophical Magazine for September 1840. From this paper I shall take the liberty of making copious extracts. It was first stated that it was neces.sary, to prociu'e any impression of human features on the daguerreotype plate, to paint the face white, or dust it over with a white powder, it being thought that the light reflected from the flesh would not have sufficient power to change the iodized sm-face. This has been shown to be an error, for, even when the sun shines but dimly, there is no difficulty in obtaining a correct delineation of the features. "When the sxm, the sitter, and the camera, are situated in the same vertical plane, if a double convex non-achromatic lens of four inches diameter and fourteen inches focus be employed, ])erfect miniatures can be procured in the open air in a periwl varying with the character of the light from 20 to 90 seconds. The di'ess also is admirably given, even if it should be black ; the slight differences of illumination are sufficient to characterize it, as well as to show each button and button-hole, and every fold. Partly o\ving to the intensity of such light, which cannot be endured without a distortion of the features, but chiefly owing to the circumstance that the rays descend at too great an angle, such pictures have the disadvantage of not exhi}>iting the eyes with distinctness, the shadow from the eyebrows and forehead encroaching on them. To procui-e fine proofs, the best position is to have the line joining the head of the sitter and PORTRAITURE BY THE DAGUERREOTYPE. 97 tlie camera so arranged as to make an angle with the incident rays of less than ten degrees, so that all the space beneath the eyebrows shall be illuminated, and a slight shadow cast from the nose. This involves, obviously, the use of reflecting mirrors to direct the ray. A single mirror would answer, and would economise time, but in practice it is often convenient to employ two ; one placed, with a suitable mechanism, to direct the rays in vertical lines, and the second above it, to direct them in an invariable coiirse towards the sitter. " On a bright day, and with a sensitive plate, portraits can be obtained in the course of five or seven minutes, in the difiused day-Kght. The advantages, however, which might be supposed to accrue fi'om the features being more composed, and of a natin-al aspect, are more than counterbalanced by the difficulty of retaining them so long in one constant mode of exj)ression. But in the reflected simshine, the eye cannot bear the efiidgence of the rays. It is therefore absolutely necessary to pass them through some blue medium, which shall abstract from them their heat and take away their ofiensive brilliancy. I have used for this purpose blue glass, and also ammoniaco-sulphate of copper, contained in a large trough of plate glass, the interstice being about an inch thick, and the fluid diluted to such a point, as to permit the eye to bear the light, and yet to intercept no more than was necessary. It is not requisite, when coloured glass is employed, to make use of a large surface ; for if the cameiu operation be canied on untU the proof almost solarizes, no traces can be seen in the portrait of its edges and bovm- daries ; but if the process is stopped at an earlier interval, there will be commonly foimd a stain corresponding to the figiu'e of the glass." "The chau' in which the sitter is placed has a staff at its back, terminating in an iron ring, that supports the head, so an'anged as to have motion in directions to suit any stature and any attitude. By simply resting the back or side of the head against this ring, it may he kept sufficiently still to allow the minu.test marks on the face to be copied. The hands should never rest upon the chest, for the motion of respiration distiu'bs them so much as to bring them out of a thick and clumsy appearance, destroying also the repi'esentation of the veins on the back, which, if they are held motionless, are copied with sui-prising beauty. " It has already been stated, that certain pictorial advantages attend an arrangement in which the light is thrown upon the face at a small angle. This also allows us to get rid entirely of the shadow from the background, or to compose it more grace- 98 HISTORY OF PHOTOGRAPHY, fully in the pictiire ; for this, it is well that the chair should be brought from the back-gi-ound, from thi-ee to six feet. "Those who -undei-take daguen-eotj^De poitraitm-es will of course arrange the back-gi'oimds of theii- pictures according to their own tastes. "When one that is quite uniform is requii-ed, a blanket, or a cloth of a drab colour, properly suspended, will be found to answer very well. Attention must be paid to the tint : white, reflecting too much light, would solarize upon the proof before the face had time to come out, and, owing to its reflecting all the rays, a blur or irradiation would appear on all edges, due to chi-omatic aberration. " It will readily be imdei-stood, that if it be desired to intro- duce a vase, an mTi, or other ornament, it must not be an-anged against the back-gi-oimd, but brought forward \mtil it appears perfectly distinct upon the obscured glass of the camera. " Different parts of the dress, for the same reason, require intervals, differing considerably, to be faii'ly copied ; the white paiiis of a costume passing on to solarization before the yellow or black tints have made any decisive representation. We have, therefore, to make use of tempoi-ary expedients. A person dressed in a black coat and open waistcoat of the same colour, must put on a temporary front of a drab or flesh colour, or, by the time that his face and the fine shadows of his woollen clothing are evolved, his shirt wtU be solai'ized, and be blue, or even black, with a white halo around it. Where, however, the white parts of the di-ess do not expose much surface, or expose it obhquely, these precautions ai-e not essential ; the whit« collar will scarcely solarize imtU the face is passing into the same condition. " Precautions of the same kind are necessary in ladies' dresses, which should not be of tints contrasting strongly. " It will now be readily imderstood, that the whole art of taking daguen-eotype miniatures consists in directing an almost horizontal beam of light, through a blue-coloured medium, upon the face of the sitter, who is retained in an unconsti-ained postm-e by an appropriate but simple mechanism, at such a distance from the back-groimd, or so aiTanged with respect to the camera, that his shadow shall not be copied as a pai-t of his body." Professor Draper used a camera having for its objective two double convex lenses, the united focus of which for jmrallel rays was only eight inches; they were four inches in diameter in the clear, and were mounted in a ban-el, in front of which the apertm-e was naiTowed down to thi-ee and a half inches, after the manner of Daguerre's. He also adopted the principle of bringing PORTRAITUEE BY THE DAGUERREOTYPE. 99 the plate forward out of the best visible focus, into the focus of the violet rays, as was first suggested by Mr. Towson, of Devouport, who also made many experiments, about the same period, with cameras having mirrors instead of lenses. A patent was taken out by Mr. Woolcott, a philosophical instrament-maker of New York, for a camera for poi-traiture, "with an elliptical mirror ; which form of apparatus was also patented by Mr. Beard, in England, who having somewhat modified Dr. Draper's arrange- ments, succeeded still better in obtaining copies of " the human face divine." A camera obscura of this description is constructed as follows. Fig. 12 is a sectional view of the apparatus. At one end of a ---- :: -iiiiv_-=^D ^rjrjrji"" -— -- . II c la 3'""'''^'^"'f??I^!^^ box shaped as in the figure, and having an opening at d, is placed an elliptical mirror, A. The prepared plate B is fixed to the sliding frame c, by which it is adjusted to the best focus. The rays of light, radiating from a figiu'e placed at F, will, it must be evident, pass through the opening at D, and Ml on the mirror, as represented by the dotted lines, and will be thence reflected to the plate B. The mirror has certainly the advantage of throwing a greater quantity of light upon the plate, but it has the great dis- atlvantage of limiting the size of the picture. With a mirror of seven inches diameter, we only procui-e pictures which will be perfect over two square inches ; whereas, with a lens of three inches diameter and four-teen inches focal length, pictures of a foot sqiiare may be worked. From this it will be seen that the miiTor is only applicable where single objects are to be copied. Eventually the sensibility of the sui-face of the plates was greatly increased. Mr. Goddard appears to have been the first to employ bromine in combination with iodine ; and it was sub- sequently foiuid by M. Claudet and others, that chlorine had an accelerating power, but not to the same extent as the bromine. These discoveries led to that amazing: desree of sensitiveness which now enables us, in good light, to take a picture in less than a second of time. CHAPTER IX. GENERAL SUMMARY OF THE HISTORY OF PHOTOGRAPHY. It is thouglit that it may prove of some interest to append tlie foUo\riug table, compiled w-itli much, care for tlie British Asso- ciation, by the author, and printed by that body in their Reports for 1850, and to which now numerous additions are made. It is believed that the dates of discovery are accm-ately given, the date of publication being, of coui'se, in aU cases, taken where there was the slightest doubt : — Silver. Nitrate of (photographically employed) ■vN'ith organic matter . with salts of lead .... Chloride of (l^hotographicaUy employed < darkened, and hydriodic salts Iodide of (photographically used) < ^^dth fen-ocyanate of potash with infusion of galls . with gallic acid (Calotype) . with protosulphate of ii'on (FeiTotyije) . -with iodide of iron (Catalyso- tyi^e) Bromide of Fluoride of FluorotyiJe Oxide of with ammonia Phosphate of Tartrate — Urate — Oxalate — Bo- i*ate, (fee Patter . . . . 1801 Wedgwood «fe Da^-y 1802 J. F. Herschel . 1839 J. F. Hei-schel . 1839 C. W. Scheele . 1777 Wedgwood . . 1802 Talbot .... 1839 Fyfe, Lassaigne . 1839 Herschel . . . 18-40 Ryan .... 1840 Himt .... 1841 J. B. Reade . . 1839 Talbot . . . 1841 Himt .... 1844 Woods . . . 1844 Bayard . . . 1840 Channing . . 1842 Himt .... 1844 Davy .... 1803 Uncertain. Yyfe .... 1839 . 1840 Herschel GENERAL SUMMARY. 101 Silver — continued, Benzoates of Hunt FoiToiates of Do. Fulminates of Do, 1844 1844 1842 Silver Plate, With vapour of iocline (Daguerreo type) ...... With, bromine and iodine . With chloriue and iodine . With vapoiu' of sulphur . . . With vapoiu" of phosphorus Daguerre , , 1839 Goddard . . 1839 Claudet . 1840 Niepce . 1820 Niepce . 1820 Glass Plate. Precipitates of silver Herschel . . . 1839 Albumen on NiepcedeSt, Victor 1848 Collodion Uncei-tain , , 1850 Gold. r^-i T ■ 1 J? f Ruinford . . . 1798 Chloride oi < tt i i i o ^ n ( Herschel . . . 1840 Etherial solution of Rumford . . . 1798 Etherial solution of, with percya- nide of potassium . . . Himt . . . . 1844 Etherial solution of, with protocya- nide of potassium . . . Do 1844 Chromate of Do 1844 Plate of gold and iodine vapour , Goddard . . , 1842 Platinxtm. Chloride of . . Herschel , . 1840 Cldoride of, in ether . . . . . Do. . . . . 1840 Chloride of, with lime , . . . Do. . . . . 1832 Iodide of . . Do. . . . . 1840 Bromide of . . Himt . . . 1844 Percyanide of . , Do, . . , 1844 Mercury, Protoxide of Uncertain, Peroxide of Guibourt, Cai-bonate of Hunt , . 1844 102 HISTORY OF PHOTOGRAPHY. Mercury — continued. Chromate of Hunt . Deutiodide of Do. Nitrate of Herschel Protonitrate of Herscliel Chloride of Boullay Bichloride of Voeel . 1843 1843 1840 1840 1803 1806 Iron. Protosulpliate of Persulphate of Ammouio-citrate of Tartrate of Attention was first called to the very peculiar changes produced in the iron salts in general, by Cyanic compounds (Prussian blue, &c.) . Ferrocyanates of Iodide of Oxalate of . Chromate of Several of the above combined "svith Himt Herschel Herschel . { Scheele \ Desmortiers Fischer Dr. Woods Hunt . . Do. . . mcrcxuy Herschel 1844 1840 1845 1786 1801 1795 1844 1844 1844 1843 Copper. Chromate of (Chromatype) Sulphate of Carbonate of ... . Iodide of Copper-plate iodized . Mangaijese. Permanganate of potash Chloride of Lead. Oxide of (the puce-coloured) . . Red lead and cyanide of potassium Hunt . . . Do. ... Do. ... Do. ... Talbot . . . . 1843 . 1844 . 1844 . 1844 . 1841 Frommherz . Hunt . . . . 1824 . 1844 Davy . . . Hunt . . . . 1802 . 1844 Nickel. Nitrate of Iodide of Hunt 1844 GENERAL SUMMARY. 103 Tin. Purple of cassius Uncertain. Cobalt Hunt .... 1844 Arsenic sulphnret of .... Sage . . . . 1803 Arsenical salts of Antimony " Bismuth Cadmium -Hunt . . . . 1844 Ehobium ......... ^ Chromium. Bichromate of potash .... with ioclide of starch . . . Mungo Ponton . E. Becquerel . 1838 1840 Chlorine and Hydrogen. Chlorine (tithonized) and ether Cahours Glass, manganese, reddened . . . Faraday J Gay-LussacandThe- ( nard . . . 1809 Draper . . . 1842 . . 1810 1823 { Pelouse & Richard- Cyanogen, solution of < 1 ayju. Phosphorus [^^f"-^ \ Kitter . in nitrogen Becknian and ammonia Vogel . Nitric Acid decomposed by light . Scheele Methyle Compounds Cahovirs f Petit Crystallisation of salts influenced j p, , i" byHght (DizF. 1838 1727 1801 1800 1806 1786 1846 1722 1788 1789 104 HISTORY OF PHOTOGRAPHY. Eesdtous Bodies {Heliography) Asphaltvun Resin of oil of lavender . . Guaiacum Bitumens all decomposed All residua of essential oils . Mowers, colours of, expressed, spread upon paper . Yellow wax bleached . . and Niepce . . . 18U Mepce . . . 1814 Niepce & Daguerre 1830 Wollaston . . 1803 Daonierre . . . 1839 Daguerre Herschel Senebier Licetas Kirclier Canton Biot . ^E. Becquerel Influence of light on electrical phenomena E. Becquerel Phosphorescent influences of solar rays 1839 1842 1791 1646 1646 1768 1840 1839 1839 In the foregoing chapters every thing has been included which appeared necessary to the complete illustration of the history of Photography. It may be thought by many that the manipulatory details included in this division should have been reserved for that which is more strictly technical. The difiiculty of doing this -udthout an annoying repetition, has led me to adopt what I consider to be the cleai'er com'se. PAET II. SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. CHAPTER I. GENERAL REMARKS ON THE SOLAR AGENCY PRODUCING CHEMICAL CHANGE. Previously to explaining the practice of photography, to which a separate division is given, it appears important that the phy- sical conditions of the elements with which we have to work should be xmderstood. The sun-beam is our pencil, and certain delicate chemical preparations form our drawing-boax'd. Every beam of light which flows fi-om its solar soiu'ce is a bimdle of rays, having each a very distinct character as to colour and its chemical functions. These rays are easily shown by allowing a pencil of sunlight to fall on one angle of a prism : it is bent out of its path, or refracted, and an elongated image is obtained, present- ing the various colours of which light appears to be constituted — red, orange, yellow, green, blue, indigo, and violet. This coloured image is called the solar or the prismatic spectrum. The red ray, being the least refracted, is foimd at the lower edge, and the violet, being the most so, at the other extremity of this chromatic series. Below the ordinaiily visible red, another ray of a deeper red, distinguished as the extreme red, or crimson ray 108 SCIE^■nFIC IS~\-ESTIGATIOyS OX PHOTOGRAPHY. may be detected, by examining the whole through a colialt blue glass ; and, bj thro-^ving the spectrum u^x)!! a piece of yeUow Violet. I Indigo. Blue. Green. YeUow. Orange. Ked. paper, another ray appears at the yiolet extremity, named by Sir John Herschel the layender ray. Yet more recently, IMr. Stokes has proyed a most remai'kable extension of the luminous rays. By throwing a prismatic spectrum into a solution of qui- nine in diluted sulphui'ic acid, or an infusion of the bark of the hoi'se-chestnut tree, a set of extra specti'al rays, extending far be- yond the yiolet, make theii' appeai'ance, proying the existence of light oyer a space which has hitherto been thought incajjable of producing any luminous phenomena. The original spectnim of seyen bands of colour was examined by Su' Isaac Newton, and that eminent philosopher determined that a giyen degi-ee of refi-ungibility indicated a giyen colour ; that the colotu- of a ray at once indicated its angle of refraction, Since the days of Newton, vmtil our own time, this iX)sition had neyer been called in question ; the seyen rays were regai'ded as the primaiy coloui-s of white Hght, and the law of Newton receiyed as tnith upon his authority. Sir Dayid Brewster has, howeyer, argued that this law Ayill not stand the test of exami- nation. He imagines that the prismatic spectrum consists of thi-ee chi'omatic spectni oyerlapping each other, and that those thi'ee colovu's — red, yellow, and blue — can be detected in eyery part of the image. Sii' John Herschel has added two I'ays to the luminous or yisible spectnmi, — thus making the number nine instead of seyen ; but these may, equally with the others, be but combinations of the three primaiies. There is, howeyer, much reason to doubt if the new extra spectral rays can be comprehended within these three. The colours of light will be rendered most familiar by calling to memory the conditions of that yery beautiful natural pheno- menon, the rainbow. The primary bow is usually accomj^anied THE AGENT PRODUCING CHEMICAL CHAA'GE. 109 by a secondary image, in wliicli tlie ordei" of the coloiu's is re- versed. From close examination of the prismatic spectnun, I am disposed to believe that whenever we obtain this chromatic division of white light, it is accompanied by a secondary spectrimi, and that the real conditions of the coloiu'S are as follows : — The yellov.^ is the most luminous ray, and the illuminating power chminishes on either side of it ; on one side it blends with the blue, to form the green, and on the other with the red, giving rise to the orange ray. The blue diminishing in intensity sinks towards blackness, and thus produces the indigo, the extreme edge of which represents the limit of the oi'dinaiy spectmm at that end ; as the outer edge of the red forms its limits, as far as the human eye is concerned, on the other. Beyond the indigo we have the violet ray : this would appear to be the blending of the red of the supplementaiy spectrum with the blue of the ordinary one, the lavender ray resulting from the intercombina- tion of the less luminous rays with the coloured surface upon which it is thrown. Then the extreme red or crimso7i ray will be seen to residt from the blending of the extreme blue of the extraordinaiy with the red of the ordinary spectral image. This passage is still retained ; but I have eveiy reason to believe that it will before long require some modification, the discoveiy of Ml". Stokes materially altering the conditions. Sir William Hei-schel, and Sir Heniy Englefield, detennined the heating powers of these rays to be very varied. A thermo- meter was placed in each, and the following results obtained : — In the blue ray, in 3' the thenuom. rose £ " green '• 3 " " '• yellow " 3 " full red " 21 ''edge of red" 21 Qmte out of visible light in 2|' " Sir John Herschel, by another form of experiment, has fully confirmed these results, and shown that the calorific, or heat- producing radiations, being less refracted by the prism than the ^i^^if-exciting rays, exist a considerable distance further from the \isible rays than has been hitherto suspected. Light and heat have not, therefore, the same degrees of refrangibility ; their influences are not coincident, their maxima in the solar sjiectrum are wide asunder. Melloni has shown that, by the use of coloured media, these agencies can be, to a considerable extent separated fi'om each other. Glass stained "with oxide of coj^per, and washed on one side ^Ath. a coloiu'less solution of alum, admits the light rays most £i*eely, but obstructs 95 per cent, of 55° to 56°, or 1° 54 " 58 ■' 4 56 " 62 ' 6 56 '•' 72 • 16 58 61 '• 731 " 79 ' 151 •■ 18 no SCIENTIFIC DTV'ESTIGATIOXS OX PHOTOGRAPHY, the lieat rays. On the contrary, a slice of obsidian or black mica obstructs neai-ly all the light radiations, but offers no im- pediment to the passage of heat. The chemical influences of the prismatic rays vaiy as their heating powei-s, but in the contrary dii-ection. If vre place a piece of photographic paper in such a position that the spectnim falls upon it, it will be fovind to be Tery imequally impressed by the vaiious rays. Some veiy extraordi- nary peculiai'ities have been obseiTed by Sir John Herschel and myself ; biit it Nvill be sufficient for our present pm-pose to state the general features of the impression under ordinaiy condi- tions. For some distance below the visible red ray, the paper will be found uncoloured ; on the part where the red ray falls, a tinting of red or pink will be evident. The orange and yellow rays leave no stain, and the green in general but a faint one. In the place occupied by the blue ray, the fii"st decided darkening is evident, which increases through the indigo and violet rays. Over this space the extra '^ spectral or fluorescent > rays become visible. ) K^ U and extends some distance beyond them. The shaded wood- engraving (Fig. 14) will serve to assist the reader in compre- THE AGENT PRODUCING CHEMICAL CHANGE. Ill hending the phenomena. The chemical radiations have a higher refi*angibility than the ordinary luminous rays, and consequently they extend in full action to a considerable space beyond the lavender rays, where no light exists which can produce excite- ment on the optic nerve of the human eye, unless aided by some pecxiliar conditions of transparent media, or of optical arrange- ments. Whenever we throw a prismatic spectrum upon any photo- graphic siu'face, it is always accompanied by a sufficient quantity of difiused light to produce some chemical change, which shows itself in darkening, over the parts beyond the coloured image. However, thei'e are two points where this change does not take place, and where the paper is preserved positively white ; these are the points of maximum light and heat — the yellow and crimson rays. Here we have the evidence of the interference of these agencies with the chemical radiations. As we can separate heat and light from each other by the use of colovired media, so can we isolate the chemical and luminous principles of the sun's rays. By a yellow glass stained with silver we may cut off the agency producing chemical change so completely, that the most sensitive photographic material may be exposed to a full flood of sunshine, without its undergoing any alteration in colour. If, howevei", we take a dark-blue glass, such as is usu- ally prepared with the oxide of cobalt, of so deep a colour that it obstnicts a considerable quantity of light, and place under it the same, or any photographic preparation, it will be found to darken as rapidly as if no glass had been interposed between it and the sun. Thus we obtain conclusive proof that it is not light, luminous power, which produces the chemical change. That it is not HEAT is shown in the same manner by the protecting influence exerted by the maximum calorific rays; and therefore we are driven to the hypothesis of the existence of a new agency — a new imponderable element — or a noble form of force which is broadly distinguished from these principles or forces in its effects. To mark this the term Actinism has been proposed, and it is now very generally adopted. The word sigiiifies nothing more than ray power, and therefore, as involving no theoiy, it is free from many of the objections which would apply to any other tenn adopted from preconceived ideas. Photography appears to be a misnomer, since the pictures so called are not drawn by light. It is, however, too firmly rooted in the public mind to admit of the hope that any other may be adopted. If I might venture a suggestion, I would advocate a retiu-n to the term introduced by Niepce, whose processes are 112 SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. described in the historical section — Heliography, Sun-drawing, which most clearly expresses the fact, leaving the question of the pai-ticidar agent effecting the chemical change stiU open for exa- mination. The annexed figiu-e (15) shows the conditions as they are at present known. r Space of extra spectral \ rays. b Lavender B Violet. Indigo. Blue. Green. Yellow. Orange. Eed. A. a Extreme Bed. Actini.sm, or chemi cal radiant power. ;;} Light, c Heat. D From A to b exhibits the Newtonian spectrum, a and h being the rays which belonged to modern discoveiy previously to the I'ecent observation that the pecidiar blue rays seen in solution of quinine and some mineral oils belong to a yet higher order of refrangibility. The cnrves c, D, and E, represent the relative maxima of heat, light, and actinism, f being a second apparent maximum — indicated in the red ray — of the chemical powere. This may, however, be proved eventually to be a function of heat, since we know that calorific power will produce chemical change even when it is exercised as a radiant force. The operation of these antagonistic forces is somewhat i-e- markably sho-vvn over different regions of the eai'th. Advancing from our 0W11 lands towards the tropics, it is found that the difficulties of obtaining pictures by the solar infliiences increase ; and, under the action of the glowing liglit of equatorial climes, a much longer period is reqiiired for impressing a photograph than is occupied in the process either in London or Paris. It THE AGENT PRODUCIXG CHEMICAL CHANGE. 113 has been stated by Dr. Draper, that in his progress from New York to the Southern States he found the sjjace jirotected from chemical change by the yellow rays regularly increasing. The same result is apparent in the cliiFei-ences between the spring and summer. Usually in March and April photographs ai-e more readily obtained than in June and July. It is worthy of notice, that the morning svm, between the hoxu's of eight and twelve, produces much better effects than can be obtained after the hoxu* of noon : this was obseiTed at a veiy early period by DagueiTe. For dra^vings by application, this is but slightly, if at all, felt, but with the camera it is of some consequence to attend to this fact. We are not yet in a position to record more than the fact, — the cause of the diffe- rence is not determined ; probably it may be found to exist in a gi'eater absorptive action of the atmosphere, caused by the eva- poration of aqueous vapoiu" from the earth. In the neighbour- hood of large towns it might be accounted for by the circumstance of the au" becoming, dimng the day, more and more impregnated with coal smoke, tire, which offers very powerful interruption to the free passage of the chemical rays. This "wtII, however, scarcely account for the same interference being found to exist in the open country, some miles from any town. Until our meteorological observers adopt a system of registering the varia- tions of light and actinic power by means of some well-devised instrument, we cannot expect to arrive at any very definite restdts. The subject involves some matters of the first import- ance in photometry and meteorology^, and it is to be desii-ed that ovr public observatories should be fiu-nished with the requii'ed instrviments for carrying out a series of observations on the diurnal and monthly changes in the relative conditions of the solar radiations. We have now evidence which proves that changes, almost inappreciable, in the condition of the atmo- spheric media, thi-ough which the solar rays traverse, are capable of producing a most remarkable influence iipon the coloiu's of the spectrvan and their chemical power. Many of the phenomena of vegetable life will be found to be dii-ectly dependent upon the operation of these piTnciples ; and it would be important to mai'k any abnormal states of gi'owth — such as not unfrequently occur — and to be enabled to refer them to peculiar solar conditions.* * See Researches on Liylit, 2nd Edition, by the Author. CHAPTER II. CHEMICAL CHANGES ON SENSITIVE PREPARATIONS. It is of some moment to the photographic artist that he is acquainted with the changes which occur in the several agents which he employs. A few of these are therefore selected. Section I. — Nitrate of Silver. 1. The ciystallised salt, in a pure state, should be procured. The commercial salt often contains nitrate of potash. The fused nitrate, which is sold in cylindi'ical sticks, is yet more liable to contamination. A preparation is sometimes sold for nitrate of silver, at fi-om sixpence to ninepence the oimce less than the ordinary price, which may induce the unwary to pvu-chase it. This reduction of price is effected by fusing with the salt of silver a proj^ortion of some other metallic salt. The fraud is readily detected by observing if the salt becomes moist on expo- sm'e to the aii-, — the adulterated nitrate of silver being delique- scent. The evils to the photographer are, want of sensibility upon exposure, and the perishability (even in the dark) of the finished drawing. As all the silver salts are prepared from the nitrate, it is of consequence that its character and changes be clearly understood. Experiment 1. — Dry nitrate of silver, free of organic matter, wiU not blacken by sunshine; and, when dissolved in peifectly pure distilled water, it may be exposed for a long time to solar influence without undergoing any visible change. Add, how- ever, to the solution the smallest appreciable quantity of any organic matter, and it will almost immediately begin to blacken. This is so certain, that nitrate of silver is the most sensitive test that we have for the presence of organic matter in water. Experiment 2. — Place a stick of charcoal in pure water con- taining nitrate of silvei-, most beautiful ciystals of silver A\ill form around the charcoal. We here see that carbonaceous matter has the power of effecting the decomposition of the silver salt. In the fii-st example, we have the metal precipitated as a black NITEATE OF SILVER. 115 powder — oxide of silver and metallic silver ; in the last, it is revived as a piu'e white metal, the crystals being of exceeding brilliancy. Thus we leam that the organic matter of the paper or of the size, is necessary to determine the change on which the photogTaphic phenomena depend. These salts have veiy remarkable colorific Section II. — Chloride of Silver. For the fonnation of the chloride of sUver, any of the follow- ing salts may be added to a solution of nitrate of silver : — 1. Chloride of Sodium (Common Salt). 2. Chloride of Potasium. 3. of Barium. 4. of Strontium. 5' ■ of Calcium. 6. Hydi'ochloride of Ammonia. properties. 7. of Peroxide of iron. J 8. Hydrochloric Acid (S])irits of Salts). 9. Solution of Clilorine in water. The above salts are only necessary for the piu'pose of giving a variety of colour to the artist's productions ; either one of them may be used. This is a point of much interest, as the result of tising these difierent materials as the base deter- mining the tone of the finished picture, enables us to produce efiects which are in accordance with the subject wliich we desire to represent. A few experiments of an easy character will be instructive, as pointing out the character of those changes which sensitive surfaces undergo. Experiment 3. — Poiir some of the solution of common salt into the solution of nitrate of silver ; immediately, a very copious white precipitate takes place. Pour off the supernatant liquor, and well wash it, by the dim light of a candle, with piu-e dis- tilled water ; then expose it to daylight : it will change colour very slowly, passing from white to gi'ey. Drop a little nitrate of silver upon the white precipitate, it "will darken much more rapidly than before ; add a little organic matter, and the change occurs still quicker ; and the degree of darkness which it eventually attains will be considerably deeper than before. In this experiment we prove that, although the white salt of silver changes colour alone, the addition of nitrate of silver and organic matter considerably quickens the operation ; therefore, 116 SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. in preparing the papers, it is always necessary for the nitrate of silver to be in excess. Scheele, in his " Experiments on Air and Fire" has some ex- periments which are remarkably to the point. " I precipitated a solution of silver by sal ammoniac ; then I edulcorated and dried the pi'ecipitate, and exposed it on a piece of paper to the beams of the sun for the space of two weeks, when the siu"face of the wliite powder grew black ; after which I stirred the powder, and repeated the same several times. Hereupon I poured some caustic spirit of sal ammoniac on this, in all ap- pearance, black powder, and set it by for digestion. This men- struum dissolved a quantity of luna cornua (horn silver), though some Islack powder remained vindissolved. The powder having been washed, was for the greater part dissolved by a pure acid of nitre, which, by the operation, acqidred volatility. This solu- tion I precipitated again, by means of sal ammoniac into horn silver. Hence it follows that the blackness which the luna cornua acquires is silver hy reduction" Experiment 4. To determine the character of the change set up hy sunshine. — A solution, No. 1, is nitric acid and oxide of silver dissolved iu water, and a solution. No. 2, is chlorine and sodiiun. When these sokitions are mixed, a white precipitate — chloride of silver — falls. The chlorine of the common salt seizes the silver, and as this is nearly insoluble, it is precipitated ; the nitric acid combines at the same time with the soda, and this remains in solution. The chloride of silver being carefidly washed, is placed in very pm-e distilled water, to which a minute portion of organic matter has been added, and then exposed to sunhine. After it has darkened, remove the water, and it will be found to contain chlorine ; by adding some nitrate of silver, we shall obtain a fresh precipitate, and we may thus determine exactly the amount of decomposition which has taken place. In the process, the strong affinity existing has been broken up. Metallic silver, in a state of veiy fine division, is produced ; and the chlorine set free dissolves in the water, from which we can precijiitate it again as chloride of sUver, and consequently readily ascertain its quantity. It is necessary now to direct attention to the effects of organic matter ui accelerating the blackening process. Sir John Herschel, whose researches in this branch of science are marked with his usual care, has given j^articular attention to this matter. As it is impossible to convey the valuable information that Sir John has published, more concisely than in his own language, I shall take the liberty of extracting rather freely from his memoir, published in the Philosophical Transactions. CHLORIDE OF SILVER, 117 " A great many experiments were made by precipitating organic liquids, both vegetable and animal, with solutions of lead ; as also, after adding alum, with alkaline solutions. Both alumina and oxide of lead are well-known to have an affinity to many of these fugitive organic compounds which cannot be con- centrated by evaporation without injury, — an affinity sufficient to cany them down in combination, when precipitated, either as hydrates or as insoluble salts. Such precipitates, when col- lected, were applied, in the state of cream, on paper, and, when diy, were washed with the nitrate. It was here that the first prominently successful result was obtained. The precipitate thrown down from a Kquid of this description by lead, was found to give a far higher degTee of sensitiveness than any I had before obtained, receiving an equal depth of impression, when exposed, in comparison with mere nitrated paper, in less than a fifth of the time ; and, moreover, acquiring a beautiful ruddy brown tint, almost amoimting to crimson, with a peculiarly rich and velvety efiect. Alumina, similarly precipitated from the same liquid, gave no such result. Struck by this difierence, which manifestly referred itself to the precipitate, it now occurred to me to omit the organic matter (whose necessity I had never before thought of questioning), and to operate with an alkaline precipitant on a mere aqueous solution of nitrate of lead, so as to produce simply a hydrate of that metal. The resu.lt was in- sti-uctive. A cream of this hydrate being applied and dried, acquired, when washed with nitrate of silver, a considerable in- crease of sensitiveness over what the nitrate alone would have given, though less than in the experiment where organized matter was present. The rich crimson hue also acquired in that case ujider the influence of light, was not now produced. Two peculiarities of action were thus brought into view ; the one, that of the oxide of lead as a mordant (if we may use a term bon-owed from the art of dyeing), the other, that of organic matter as a colorific agent. " Paper washed with acetate of lead was impregnated with various insokible salts of that metal — such as the sidphate, phos- phate, muriate, hydriodate, borate, oxalate — and others, by wash- ing with their appropriate neutral salts, and, when cUy, applying the nitrate of sUver as usual. The results, however, were in no way striking, as regards sensitiveness, in any case but in that of the muriatic applications. In all cases where svich applications were used, a paper was produced infinitely more sensitive than any I had at that time made. And I may here observe, that in this respect the muriate of strontia appeared to have decided advantage." 118 SCIEXTIFIC IXVESTIGATIONS OX PHOTOGRAPHY. It would oe tedious and useless to mention all tlie combina- tions of alkaline and earthy muriates ■wkich have been devised to vaiy the effect, or increase tbe sensitiveness of the silver pre- parations : the veiy considerable differences produced through the influence of these salts will afford peculiarly interesting results to any inquirer, and furnish him with a cvu'ious collection of photographic sjDecimens. As a general rule, all the solutions should be made in the combining proportions of the material used. With a scale of chemical equivalents at hand, the photo- graphic experunentalist need not eiT, taking care that a slight excess of pure nitrate of sUver prevails upon his paper or plate. These changes should be well undei-stood, before the photo- graphic amateirrs proceed to the preparation of the sensitive papers employed for the ordinary processes. Section III. — Iodide of Silver. If iodide of silver is precipitated by mixing together solutions of iodide of potassium and nitrate of silver in a concentrated state, a hea^y yellow powder falls, which will scai-cely change in colour by an exposure of many days to simshine. But if the solutions are infinitely diluted, so that on mixing they only become milky, and the light powder which occasions the opacity falls but slowly to the bottom of the vessel, it will be found that it is sensitive to the weakest solar i-adiations. There does not appear to be any chemical difference between the iodides thus obtained ; but there are some remarkaUe physical peculiarities, and it is believed that attention to these will be found eventually to be of the utmost importance. ' Section IY. — Bromide of Silver. In many of the works on chemistry, it is stated that the chloride is the most sensitive to light of all the salts of silver ; and, when they are exposed in a perfectly formed and pure state to solar influence, it will be found that this is nearly correct. Modem discovery ha.s, however, shown that these salts may exist in jieculiar conditions, in which the afiinities are so delicately balanced as to be disturbed by the faintest gleam ; and it is singular that, as it regards the chloride, iodide, and bromide of silver, when in this condition, the order of sensibility is reversed, and the most decided action is e-vident on the bromide before the eye can detect any change in the chloride. BROMIDE OF SILVER. 119 The slight additional expense of the bromides is not 'worthy consideration, particularly as their use may be confined to papei's for the camera obscura, the pictures on which are of course of the negative character, and the positive photographs can be formed by transfer on the chloridated papers of a highly sensitive kind. Since there has been some question as to the use of the iodide of silver without an infringement of patent, it is not a little siu'prising that the bromide has not been more generally employed. It will be found that the bromide and iodide are much alike in the singular want of sensibility which they sometimes exhibit under the cii-cumstances already alluded to, which are not easy of explanation. If a paper first washed with a solution of nitrate of sHver has bromide of potas- sium applied to it in difierent propor- tions, say 20 grains, 15 grains, and 10 grains each, in two di-achms of water, and, when diy, be again washed over with the silver solution, it will be found, unless, as is occasionally the case, some organic combination interferes, that the 16 order of sensitiveness will begin with the weakest solution, the strongest being the least influenced by light. The different degrees of darkness induced are faiiiy repre- sented in the margin. (Fig. 18.) As the different bromides give to photographic paper varieties which much resemble those enumerated under the muriates, I have thought it unnecessaiy to give an account of any of them. The paper prepared with the bromide of potassium is the kind I have adopted, after having tried upwards of two himdred combinations of silver with the other bromides. To pi-epare a highly sensitive paper of this kind, select some sheets of very superior glazed post, and wash it on one side only with bromide of potassium — forty gi'ains to one ounce of distilled water, over wliich, when dry, pass a solution of one hunch-ed grains of nitrate of silver in the same quantity of water. The paper must be ch-ied as quickly as possible without exposing it to too much heat ; then again washed with the silver solution^ and, when dry, carefully preserved for use. It will be perceived that I adopt a slightly different manipu- lation from that recommended by Mr. Talbot. Instead of wash- ing the paper with the solution of silver first, and aj^plying the bromide or the mui'iate over this, and then the silver wash again, I use the alkaline salt first, and apply the metallic washes one 120 SCIENTIFIC mVESTIGATIOXS ON PHOTOGRAPHY. on the other. I have been induced to this from observing that the photographic preparation penetrates less deeply into the paper than when laid on as originally prescribed, and, con- sequently, the sensibility of it is increased. It will be found that an addition of about one-twelfth of spirits of wine to the solution of silver will much increase the l)lackness of the paper when solarised ; and I think we may safely say that the sensi- bility is also improved by it, — at all events it is not impaired. M. Biot has expressed his opinion that it is not possible to find any substance more sensitive to light than the bromide of silver : this is trae to a ceii;ain extent, but in combination with deoxidizing agents other preparations will be named which have a decided superiority over the pui-e bromide of silver. Section Y. — Miscellaneous Salts of Silver. Fluoride of Silver. — The tise of this salt appeal's to have been first suggested by Sir John Hei-schel ; it foiins the basis of a process by the author, already described. It has lately been claimed as a new photographic agent by the French, but the date of publication determines this question in the author's favour. Phosphate of Silver.— Dr. Fyfe apjjeai-s to have been the first to suggest the use of the phosphate of silver as a photo- graphic material, but I am obliged to confess it has not, in my hands, proved anything like so successful as, from Dr Fj^e's description, it was in his own. Indeed, he himself obsei-ves, iu speaking of its i;se in the camera obscui-a : — " Though repre- sentations may be got in this way, yet, so tar as I have foimd, they have not the minute distinctness of those got by the method already mentioned (i. e. by application). Owing to the inter- ference of the lens, the light does not act nearly so powerfidly on the paper, as when it has to permeate merely a fi"ame of glass." For aU practical piu^oses, the method which Dr. Fyfe has given of prepai'ing these papers is, perhaps, the best : — " The paper is fii'st soaked in the phosphate of soda, and then dried, after which the niti-ate is spread over one side by a binish ; the paper again di'ied, and afterwards again put thi'ough the salt, by which any excess of silver is converted to phosphate. As thus prepared, it acquii-es a yellow tinge, which becomes black by exposiu-e to light." It will be e^•ident from these directions, that what Avas formerly .said about the necessity of ha\-ing the nitrate of silver in excess, is here, according to Dr. Fyfe, MISCELLANEOUS SALTS OF SILVER. 121 objectionable. It certainly does not appear to be so essential in this preparation, that anything but pure phosphate of silver should be used ; yet I cannot help fancying that a slight advan- tage is gained, even here, by allowing a little excess of nitrate. Dr. Fjie has given a process for applying the phosphate of silver, mixed as a paint, on metal, glass, or paper. It, however, requires the skill of an artist to produce an even svu-face, and unless a xmiform ground is given, the picture is deformed by waving lines of different shades. A method of precipitating argentine salts on smooth sm^faces will be given in the following pages, by which means the most uniform face is jjrocvired, and many beautiful effects produced.' Fulminate of Silver. — Notwithstanding the extraordinary degree of sensibility which has been given to paper and to the metallic plates by the industrious experiments of chemists, I am convinced that we may hope to obtain agents of far higher natural sensibility than those we now possess ; and I look with much anxiety to some of the combinations of organic radicals with metallic bases. The fulminates and the ethyle compounds present a veiy promising line of inquiry. Mr. John Towson, of Devonport, who jinu'sued, conjointly with myself, a most extensive series of researches on photogTaphic agents, was endeavouring to form a solution of silver, in which the elements should be so delicately balanced as to be overturned by the action of the faintest light. To do this, he dissolved some very pure silver in nitric acid, to which spirits of wine was added somewhat suddenly in proportions equal to the acid used, and the precipitation of the fulminate prevented by a quick effusion of cold water, sufficient to bring the specific gravity of the solution to TIT, and to this a few drops of am- monia were added. Pieces of Bank post paper dipped in this solution became, the instant they were presented to the declin- ing light of an autumnal evening, a beautiful black having a pui'ple tinge. This effect did not seem to come on gradually, but, as by a sudden impulse, at once. Both this gentleman and myself have often endeavovu-ed to repeat this, but in no one instance have either of us succeeded in producing anything nearly so sensitive. It should be stated, that the solution pre- pared in the evening had become, by the following morning, only ordinarily sensitive, and that papers prepared with it were deliquescent and bad. In repeating any modification of this experiment, the greatest care should be taken, as explosions of considerable violence are othei"wise likely to occvir. Another series of expeiiments on the fulminates of silver have produced veiy pleasing photographic results, but I am not 122 SCIENTIFIC INVESTIGATIOXS OX PHOTOGRAPHY. enabled to specify any particular method of preparing them, which may be certain of I'ejiroduciQg the results to wliich I allude. Nothing can be more capricious than they are ; the same salt darkening rapidly to-day, which -will to-morrow appear to be absokitely insensible to radiation, and wliich will again, in a few days, recover its sensitiveness, to lose it as speedily as before. The beautiful researches of Professor Frankland, of Owen's CoUege, Manchester, however, most satisfactorily jjrove that a great many of the metals will combine with organic radicals in the sunshine which will not so combiae in darkness. Organic and other Salts of Silver.— With the exception of the carbonate, tartrate, acetate, citrate, oxalate, and one or two others, the salts of silver, besides those ah-eady described, do not appear to be sensibly influenced by light. Many have been mentioned by authors as absolutely insensible to its influence ; but recent experiments have produced modifications of these salts, which are delicately sensitive to the solar ray. Amongst othei-s, the chromate has been named, and certainly it has not yet been rendered sensitive to an exposure of some hoiu's to daylight ; but one exjaeriment of mine has proved that the solar beam -will, in a few days, produce a fine revival of metallic silver from its chromate ; and another experiment with it, has the most pleasing result of bringing within the range of probabilities, the production of photographic pictiu-es in their natm-al colours. Researches having this object in view led to the discovery of the chromatype ; but this beautiful salt (chromate of sUver) has not yet been applied directly as the photographic agent. In the present state of oxxr knowledge, we cannot veutm'e to affirm that any salt of silver, or, indeed, of any of the other metals, exists, having an absolute insensibility to light, or in which the required unstable equilibrium may not be induced, so that the sun's beam might change the character of its combinations. I am, indeed, convinced that no body in natiu-e is entirely imin- fluenced by the action of the sun's rays. Papers washed with either of the alkaline carbonates, and then with a solution of nitrate of silver, resemble in theu" character those prepai'ed with the mui'iates, but are not darkened so readily. The tartrate of silver possesses some very extraordinary pecu- liarities. Papers may be prepared, either by spreading the tar- trate at once over the surface, or better, by soaking the jia^'er in a solution of Rochelle salt (the tartrate of potash and soda), and then applying two washes of the solution of nitrate of silver. The fii'st action of light is very feeble, but thei'c gi-adually comes on a stronger discoloiu-ation, which eventually proceeds with rapidity, and at length blackens to an extent beyond almost ORGAIv^IC COMPOUNDS WITH SILVER. 123 every other paper. This cliscoloiu-ation may be wonderfully accelerated by washing over the tartrated paper with a very dilute solution of the hydi-iodate of potash, dui'ing the process of darkening. It is not easy to use this when copying anything, but there are cases in which the extreme degree of darkness which this preparation acquii'es, renders it valuable. The acetate of silver compoi-ts itself in the same manner as the tartrate. The citrate, oxalate, &c., are only intei'esting as forming part of the series of argentine preparations which exliibit decisive changes when exposed to light. The methods of rendering them available will be sufficiently imderstood from the foregoing details, and it wotJd only be an unnecessaiy waste of words to give any more particular directions as it regards them. CHAPTER III. THE THEORY OF THE DAGUERREOTYPE. Numerous speculations having been ventured as to the pecu- liar chemical changes which light produces on the iodidated silver tablets, I shall make no apology for introducing a few remarks on this very interesting subject. Numerous experiments on j^lated copper, pure silver plates, and on silvered glass and papei-, have convinced me that the fii'st operations of polishing with nitric acid, &c., are essential to the production of the viost sensitive siuface. All who will take the trouble to examine the subject will soon be convinced that the acid softens the silver, bringing it to a state in which it is ex- tremely susceptible of being either oxidized or iodized, according as the circumstance may occur, of its exposui-e to the atmosphere or to iodine. The process, adopted, I believe, fii'st in America, of producing a deposit of chemically pure silver on the plated metal, by means of the voltaic batteiy, which certainly gives rise to some peculiar conditions, appears to prove that the soft sui'face of sUver is of advantage. The sensitive sm-face is a combination of iodine, or of iodine and bromine, with the silver. When exposed to i-adiant in- fluences in the camera, a molecidar change is effected, and there is much doubt if any iodine or bromine is removed from the sm-face. Some have thought that the superficial film being decomposed, the iodine and bromine attack a lower sui-face of the plate ; but experiments are still wanting. I have discovered that all the rays of the prismatic spectrum act on the Daguerreotyjie plate, except the yellow, and a circle of light of a peculiar and mysterious character, which surrounds the visible spectnim. The light acting on a prepared tablet, appears to decompose the film of iodide of silver to different depths, according to the order of reft-angibUity of the rays : the \'iolet ray and extra-si)ectral rays efiecting the deepest decom- I^osition, whilst the red acts to a depth inappreciably slight. Th\is it is that the spectrum impressed on a Daguen-eotype plate reflects natui'al tints of the same kind as Sir Isaac Newton's thin films ; the thickness of each film of reduced silver ON THE THEORY OF THE DAGUERREOTYPE. 125 on the plate being in exact proportion to the chemical agency of the colovired ray by which it was decomposed. On photographic papers, the decomposed argentine salt exists, in all probability, in a state of oxide, mixed with revived silver ; but on the silver tablet the iodide is changed over all the parts on which the light acts, and pure silver in a state of extreme division results. The depth to which the decomposition has been effected being in exact relation to the intensity and colour of the light radiated from the object which we desire to copy, the mercurial vapour unites with different proportions of silver, aids in encreasing the decomposition of the silver salt, and thus are formed the lights and middle tints of the picture. The shadows are produced by the unchanged silver from which the iodine is removed by the hyposulphite of soda. Daguerre himself laid much stress upon the necessity of ex- posing the plate to receive the vapour of mercury at an angle of 45°. This, perhaps, is the most convenient position, as it enables the operator to view the plate distinctly, and watch the develop- ment of the design : but beyond this, I am satisfied there exists no real necessity for the angular position. Both horizontally and vertically, I have often produced ecpially effective daguerreo- types. Looking at a dagaierreotype picture in such a position that the light is incident and reflected at a large angle, the drawing appears of the negative character ; the silver in such a position appearing white, and the amalgam of mercury and silver a pale grey. View the plate in any position which admits of but a small angle of reflection, and we then see the design in all its exquisite beauty, correct in the arrangement of its Kghts and shades, — the silver appearing black, while the amalgam, by contrast in part, and partly in reality, appears nearly white. The cause leading to the tmiform deposition of tlae mercurial vapour is difficult of solution. It does not appear to me that any one of the hypotheses put forth, satisfies all the conditions of this peculiar phenomenon. Few papers have been published which so completely investi- gate the phenomena of the chemical change in the daguerreotype, as that of Mr. George Shaw. As giving a large amount of valuable information, I transfer it from the Philosophical Magazine. " It is well known that the impression produced by light on a plate of silver rendered sensitive by M. Daguerre's process, is wholly destroyed by a momentary exposure of the plate to the vapour of either iodine or bromine. Although this fact has long been known, the natiu-e of the action by Avhich so extra- ordinary an effect is produced has not yet been satisfactorily 126 SCIENTIFIC mVESTIGATIONS ON PHOTOGRAPHY. explained. lu the hope of elucidating this subject, a series of experiments was instituted, the results of which are recorded hi the following remarks. " A silver plate prepared by exposure to iodine or its com- pounds with bromine, may be exposed to the vapour of mercury ^vithout being in any way affected by the exposure. If, however, the prepared plate be previously exposed to light, or made to receive the luminous image formed in the camera obscura, the mercui-ial vapovu' attacks it ; forming, in the former case, a white film, and in the latter, a pictm-e corresponding to the luminous image which had been allowed to fall on it. " If a prepared plate, after receiving a vertical impression by light, be exposed to the vapour of iodine or bromine, it is found that the vapoiu- of mercmy no longer attacks it ; or, in other words, the impi-ession produced by light is destroyed. '' The first experiments made for the piurpose of amving at the cause of tliis phenomenon had reference to the relation between the time of the exposure to light and the time of ex- posure to the vapour of iodine or bromine necessary to destroy the effect produced by light. Prepared plates were exposed in the camera obscura for a length of time, which previous experi- ment had determined to be sufficient for a full development of the pictiu-e ; some of those plates were exposed diu'ing two seconds to an atmosphere feebly charged with the vapour of bromine, while others were carefidly ]3reserved fi-om contact with the vapom-s of iodine or bromine. The atmosphere "of bromine employed, was produced by adding thu-ty di-ops of a satiu-ated solution of bromine in water to an ounce of water : the solution was poured into a glass vessel, and the plate was exposed to the vapour in the vessel during the time specified. The plates were then introduced into the mercury box, and by volatilizing the metal, pictiu'es were developed on all those which had not been exposed to the vapovir of bromine, while those which had been exposed to it exhibited no trace of a picture under the action of mercury. " The same experiments were repeated with iodine, with exactly similar results. " Prepared plates were exposed to difi'used light in the shade, and others were exposed to the direct rays of the sun ; the object being in both cases the production of a more intense impression than that produced by the feeble light of the camera obscura. Some of these plates were exposed to the vapour of bromine, and others to the vapour of iodine, while othei-s were carefidly preserved fi-om the vapours of these substances. On subsequent exposure to the vapour of mercury, those plates which had not ON THE THEORY OF THE DAGUERROTYPE. 127 been exposed to iodine or bromine, exhibited, by tbe large quan- tity of merciuy which, condensed on them, tbe effects of expo- stu'e to intense light : while those which had been subjected to the action of either bromine or iodine were in no way affected l^y the vapour of merciuy. Many repetitions of these experi- ments demonstrated that the effect of exposiu-e to the most intense Hght, was completely destroyed by the shortest exposure to the vapour of bromine or iodine. " Exj)ei'iments were now instituted for the purpose of ascer- taining in what condition the prepared plate was left, after having been fii'st exposed to light and afterwards exposed to the vapour of bromine or iodine. In these experiments a method of ti'eat- ment somewhat different from, and more convenient than that described, was resorted to, as in practising that method eflects occasionally presented themselves which interfered with the re- sults, and rendered it dilhcult to determine with certainty, how far some of the appearances produced were due to the action of light. It is well known, that a prepared plate has a maximum of sensitiveness when the iodine and bromine are in a certain re- lation to each other : if there be a deficiency of bromine, the maximum sensitiveness is not obtained, and, if there be an excess, the plate is no longer sensitive to light ; but when exposed to the vapoiu' of merciuy, without having been exposed to light, be- comes white all over, by the condensation of mercury thereon ; that is to say, it exhibits the appearance of a plate which had been properly prepared, and which had been exposed to light. From this it aviU be evident, that a plate properly prepared in the first instance, and then exposed to light, may, by subsequent exposiue to the vapoui- of bromine, have the impression produced by light wholly destroyed ; and yet, by the accumulation of bro- mine, may exhibit, on exposure to merciuy, an appearance similar to that due to light. In other words, it is impossible (in the case supposed) to distinguish between an effect produced by light and an efiect due to excess of bromiae. By using iodine in the place of bromine, there is no risk of producing the appeai'ance which accompanies excess of bromine ; but, on the other hand, by augmenting the quantity of iodine, the sensitive- ness of the plate is diminished. These difficulties were over- come by using a solution containing both iodine and bromine, in such proportions that the evaporation of each should take place in the proportion in which they produce on silver the most sensitive siu-face. The solution employed was made by adding alcoholic solution of iodine to a solution of chlorate of potash, until the latter would take up no more of the former ; and to each ounce, by measiuCj of this solution, ten di'ops of a saturated 128 SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. solution of bromine in water were added. The solution of chlorate of potash was made by diluting one part of a saturated solution of the salt with ten pai-ts of water. The use of the chlorate is simply as a solvent of iodine. In the subsequent ex- periments, the plate was exposed to the vapoiu' of this mixtiu-e of iodine and bromine with precisely the same effect as when either was used sepai-ately, and without the inconvenience, or uncertainty, which attended theii* use. " A nimiber of prelimiuaiy experiments, the detail of which would be iminteresting, appeared to indicate, that not only is the effect of light on a daguerreotype plate destroyed by iodine or bromine, but that the plate is restored to its origLaal condi- tion ; in other words, that its sensitiveness to light is restored. In order to determine this point, the following experiments were made. " A prepared plate was exposed to light, and aftenvards to the mixed vapour ;* mercurial vapour produced no effect xipon it after a long exposiu'e ; the plate on removal fi-om the mei'cury box was a second time exposed to light, and again introduced into mercm-ial vapoui'. The appearance of this plate was very little changed, and it was concluded that no effect, or, if any, very little, was produced by the second exposm-e to light. This conclusion was, however, erroneous, as the following exjjeriments proved : — " A prepared plate was exposed to light, and afterwards to the mixed vapoiu* : mercmial vapoiu' was foiind to have no effect upon it ; the plate was then partly covered with a metallic screen, fixed close to, but not in contact A\'ith it, and the whole was exposed to light. On placing the plate in the mercury box, a broad white band, neai'ly corresponding to the edge of the defended part, made its appem-ance ; the whole of the defended part (excepting the band in question) was imaffected, and the exposed part exhibited very little change. By a careful exami- nation of the plate after it was removed fi'om the mercury box, the white band in the middle aj^peared to be produced by the feeble light which had passed under the edge of the metal plate which had screened the light from part of the prepared siu'face ; and the very d;u-k, and apparently unaltered appearance of the exposed pari;, was occasioned by an excess of action, for mercury was foimd to have condensed on that part in large qiiantities, and to have produced the dark lead colour which is commonly called solarisation ; but which effect, in the case in question, * " I shall hereafter call the mixed vapours of iodine and bromine produced in the way described in the last paragraph but one, mixed vapour, in order to avoid circumlocution. — G. S." ON THE THEORY OF THE DAGUERREOTYPE. 129 "was so excessive, that the coloui' of tlie part on wliicli mercury had condensed differed but very slightly from that on which no light had fallen. It was now evident that the ap^^arent absence of effect in the last experiment was in reality occasioned by an ex- cess of action ; and by rejieating that experiment, and making the time of the second exposiu'e to light much shorter than before, the plate assumed, under the action of mercury, an in- tense and beautiful whiteness. " From these experiments, then, it was perfectly clear that the impression produced by the light on a Daguerreotype plate is wholly destroyed by the mixed vapoiu-, and that its sensitive- ness to light is restored. " It now remained to discover to what extent the sensitive- ness is restored by the treatment in question. It was not at first expected that the sensitiveness to light was as great after this treatment as after the original prejxiration of the plate ; but experiments aftei"wards proved that the surface lost none of its sensitiveness by this treatment, nor even by numerous repe- titions of it. A prepared plate was exposed to light ; the im- pression was destroyed and sensitiveness restored by the mixed vapour; the plate was a second time exposed to light and a second time to bromine ; still its sensitiveness appeared unim- paired, for a fovu-th or fifth exposiu-e gave, on treatment with mercimal vajjoiu-, a \•i^'id impression. In order to detennine with the greatest accuracy if the sensitiveness of the prepared sui-face was at all imjmii-ed by these repeated exposures to light, the caviera ohscu.ra was resorted to. A series of plates was pre- pared with the utmost attention to uniformity ; some of these were exposed in the camera obsciira, and pictures obtained by the subsequent exposui'e to vapour of merciuy : the time re- quisite for the proper development of the jiicture was noted ; others were first exposed to the direct rays of the sun, and after- wards to the mixed vapour, and these were exposed in the camera obscura for the same length of time as those which had not been exposed to light. On treatment with mercurial vapour, perfect pictiu-es were prodviced, which could not be distinguished from those taken on plates prepaied by the ordinaiy method. So completely does the mixed vapoiu- restore the sensitiveness of prejjared jDlates after exposm-e to Hght, that the most beau- tiful imj)ressions were obtained in the camera obscura in two seconds on plates which had previously been /our times exposed to the dii-ect light of the sun, and after each such exposure treated with the mixed vapour. " As the plates experimented on, to this stage of the inquiry, had been wholly exposed to t]ie sun's light previous to exposure 130 SCIENTiriC INVESTIGATIONS ON PHOTOGRAPHY. in the camera ohscura, it was thought that possibly some slight effect was produced, which, from being the same on all parts of the plates, escaped obsei-i^ation ; and in order to avoid the possi- bility of ei*ror fiwm this cause, the impressions of light which it was intended to destroy by bromine were afterwai'ds made in the camera ohscura. Prepared plates were impressed with virtual images of different kinds, the camera obscitra being pointed first at a house, afterwards to a bust, next to a tree, and finally to a living figure, the plates after each impression, excepting the last, being momentarily exposed to the mixed vapom*. In eveiy in- stance, the most perfect impressions of the objects to which the camera ohscura was last directed were obtained, and no trace of the previous impressions was left. " Experiments were next instituted for the purpose of ascer- taining if the prepared surface, after the process of mercm-iali- zation, could be made to receive another impression by treatment with mixed vapour. Impressions were taken with the camera ohscura, and after the full development of the pictiu'e by vapour of mercmy, the plates were exposed to bromine and again placed in the camera ohscura, the instiiiment being directed in different experiments to difierent objects : on exposure to mercurial vapour, other pictiu-es made theu' appeai-ance, and although con- fused from superposition on the fii\st pictiu-es, could be cleai'ly traced, and were found perfect in every part. This production of pictiu-e upon jjicture was repeated, until, by the confusion of the superposed images, the efiects of further exposiu'e could be no longer distinguished. " In all the experiments hitherto described, the destruction of the impressions by bromine was effected in the dark, the ap- paratvis being situated in a room into which only a veiy feeble day- light was admitted. It remained to be discovered if the mixed vapour liad the power of destroying the effect of light while the plate was still exposed to light, or if the vapoiu' had the jiower o^ suspending or preventing the action of light on a daguerreotype plate. In order to determine this point, the apparatus was placed near the window of a well-lighted room, and so ari-anged that, during the whole time of the preparation of the plate, by exposure first to iodine and afterwards to bromine, it was ex- posed to full daylight, and by a mechanical arrangement, of too obvious a natm-e to render description necessaiy, the plate was withdi'awn fi'om the bromine vessel into a dark box ; that is to say, it was withdi-a^vn at the same movient from the influence of both light and bromine : on being placed in the camera ohscura, plates so prepared receiA'ed impressions which by mercurialization. produced excellent pictures, and there was no trace of the action ON THE THEORY OF THE DAGUERREOTYPE. 131 of any light save tliat of the camera ohscura. It follows, then, that light is incapable of exerting any appreciable influence on daguerreotype plates during the time they are receiving their coatings of iodine and bromine. " Although these experiments afford no information on the subject in reference to which they were originally undertaken, they are yet not without interest, both in their theoretical bearing and in their practical application. They demonstrate not only that the change (whatever it may be) effected by light on silver plates prepared by Dagvierre's process, is completely suspended in the presence of the vapour of either iodine or bro- mine, but that after that change has been produced the impres- sion may be destroyed, and the plate I'estored to its original condition, by a momentary exposure to either of these vapours. In their practical application, these experiments show that all the care which has been taken to exclude light from daguerreo- type plates dm'ing their preparation is unnecessary ; that so far from a dark room being essential to the operations of the da- guerreotype artist, the light of day may be allowed to fall on the plate dvu-ing the whole time of its prej^aration ; and that it is only necessary to withdraw it at the same moment from the action of bromine and light by sliding it from the bromine vessel into the dai'k box in which it is carried to the camera ohscura ; and where, from the situation or otherwise, there is a difiicidty in observing the coloiu" of the plate during the process of iodizing, it may be removed from the iodine vessel, and its^colour examined by the direct light of the sun, without risk or injury : for when returned to the iodine or bromine vessel for a moment, the effect of light is wholly destroyed. " Pei'haps the most valuable practical application of these facts is in the use of the same plate for receiving several impressions. When, on taking the portrait or picture of any object liable to move, there is reason to suppose that the motion of the person or object has rendered the operation useless, it is not necessary to throw aside the plate on which the imperfect impression has been taken, and resort to the tedious process of cleaning and preparing another ; it is only necessary to treat the plate in the manner already pointed out, and it is agaia equal in every respect to a newly-prepared plate ; and this treatment may be repeated, until, by the slow accumulation of too thick a film of iodide of silver, the plate no longer possesses the same degree of sensitiveness to light." The researches of M. Claudet are ot considerable importance, particularly as being those of a thoroughly practical photo- graphic artist. 132 SCIENTIFIC IXVESTIGATIOXS OX PHOTOGRAPHY. The phenomena w^hich M. Claudet considers have not yet been satisfactorily explained, and of "which he treats, are those referring to the following points : — 1. Which is the action of light on the sensitive coating ? 2. How does the merciu-ial vapour produce the daguerreotype image 1 3. What are the particular rays of light that impart to the chemical surface the affinity for mercuiy ? 4. Which is the cause of the difference in achi-omatic lenses between the visual and photogenic lenses ? why do they con- stantly vary 1 5. What are the means of measui-ing the photogenic rays, and of finding the true focus at wliich they produce the image 1 At the meeting of the British Association at Swansea, M. Claiidet expressed his opinion that the decomposition of the chemical svu-face of the dagueiTeotype plate, by the action of certain rays of light, produced on that svirface a white precijii- tate, insoluble in the hyposvdphite of soda, which, when examined by the microscope, had the appearance of crystals reflecting light, and which, when seen by the naked eye, were the cause of a positive dagueiTeotype image. These were probably particles of pure white silver. The opinion of Daguerre himself, and other writers, was, that the action of light on the iodide of silver had only the effect of darkening the surface, and consequently of producing a negative image. But it escaped them, that, under the darkened iodide of silver, another action could take place after a continued ex- posure to light, and that the hyposulphite of soda washing coukl disclose a positive image. M. Claudet proved this fact in ob- taining, by the action of light only, and Avithout mercury, images having the same appearance as those developed under the action of mercurial vapour. This direct and immediate effect of light is certainly remarkable ; but the daguen-eotype process is not founded on that princiiJe, on account of the slowness of its action ; and it is fortunate that, long before light can produce the white precipitate alluded to, it operates another effect, which is the wonderful property of attracting the vapour of mer- cury. This vapour is condensed in the form of a white powder, having also, when examined by the microscope, the appearance of reflectiug crj-stals. It is probable that light exercises a two-fold action on the iodide of silver, whether it is combiued or not with chloriue or bromine. By one, the iodide is decomposed, and the silver set free is pre- cipitated on the surface in the form of a white powder or small crystals ; by the other, which begins long before the former, ON THE THEORY OF THE DAGUEKREOTYPE. 133 the parts affected by liglit have been endowed -svith an afllnity for mercurial vapom-. By means of his photographometer, this investigator has been able to ascertain that the pui-e light of the sun performs in about two or three seconds the decomposition of the bromo- iodide of silver, which is manifested by the white precijiitate ; while the same intensity of light determines the affinity for mer- cui'ial vapour in the short space of about j o\)o^^ P'^^'^ '^^ ^ second. So that the affiauty for merciuy is imparted by an iiatensity of light 3000 times less than that which produces the decomposi- tion manifested by the white precipitate. For this reason it is difficult to suppose that the two actions are the same. We must admit that they are different. Long before it can effect the decomposition of the siu-face, light im- parts to the sensitive coating the affijiity for mercimal vapour ; and this appears to be the principle of the formation of the image in the daguerreotype process. In a paper communicated to the Royal Society on the 17th of June, 1847, M. Claudet stated that the red, orange, and yellow rays were destroying the action of white light, and that the siu-face was recovering its former sensitiveness or unaffected state after having been submitted to the action of these rays. It was inferred from that ciu'ious fact that light could not have decomposed the surface ; for if it had, it Avoidd be difficult to understand how the red, orange, or yeUow rays coidd combine again, one with another, elements so volatile as bromine and iodine, after they had been once separated fi'om the silver. These experiments have much in common with those of M. Edmond Becquerel, who has been led to a division of the spec- trum into exciting rays and continuating rays. But he had not yet been able to ascertain that, when light has decomposed the bromo-iodide of silver, the red, orange, or yellow rays cannot restore the siu-face to its former state. The action of light, which can be destroyed by the red, orange, or yellow rays, does not determine the decomposition, which would requii-e an inten- sity 3000 times greater ; it is the kind of action produced by an intensity 3000 times less, giving the affinity for mercury, wliich is completely destroyed by the red, orange, or yellow rays, ^\'Tiite Hght, or the chemical rays which accompany it, communi- cate to the siu-face the affinity for merciuy ; and the red, orange, or yeUow rays withdraw it. This is in effect the same pheno- menon as Dr. Wollaston obseiwed with the tincture of gum guaiacum ; one set of rays restoring the coloiu' which another set had removed. A singidar anomaly requires notice : viz. that when the sensitive sui-face is prepared only with iodine without 134r SCIENTTFIC DmSTIGAnOXS ox PHOTOGRAPHY. bromine, the red, orange, or Tello-w rays, instead of destroying the action of -vrhite light, continue the effect of decomposition as "well as that of affinity for mercnry. Still there is a double compound of iodine which is far more sensitive than the simple compound, and on which the red, orange, or yellow rays exeixise their destructive action as in the case of the bromo-iodide. The phenomenon of the continuing action of the red, orange, or yeUow rays, on the simple compound of iodide of silver, was discovered by M. Ed. Becquerel ; and soon after M. Gaudin found, that not only those rays continue the action by which mercury is deposited, but that they develope without mercuiy an image having the same appearance as that produced by mer- curial vapour. M. Gaudin, not having observed the &ct of the white precipi- tate, which is the result of the decomposition by the action of light, could uot explain the cause of the image brought out under the influence of the yellow ray. M. Claudet states that the iodide of silver without bromine is about 100 times more sensitive than the bromo-iodide to the action of the rays which produce the decomposition of the com- pound forming the white precipitate of sUver, while it is 100 times less sensitive for the effect which gives the affinity for mercury. It may be that, in the case of the iodide of silver alone, the decomposition being more rapid, and the affinity for mercury slower than when bromine is added to the compound, the red, orange, or yellow rays having to act upon an incipient decomposition, have the power, by their own photogenic influ- ence, of continuing the decomposition when it has begun. This may explain the development of the image under red, orange, or yellow glasses, according to M. Gaudin's discovery. But in the case of the bromo-iodide of silver, the red, orange, or yellow rays have to exert their action on the affinity for mercury, begun a long time before the decomposition of the compound; and they have the property of destroying that affinity. So that it would appear that all the rays of light have the pro- perty of decomposing the iodide of silver in a longer or shorter time, as they have that of producing the affinity for mercury on the bromo-iodide of silver : with the difference, that, on the former compound, the separate actions of the several rays con- tinue each other, and that on the second compound these separate actions destroy each other. We can understand that, in the first case, all the rays are capable of operating the same decomposi- tion : and that in the second, the affinity for mercury when im- parted by one ray is destroyed by another. This would explain the various phenomena of the formation of the two different de- ox THE THEOBT OF TEE DAGUZEBEOTTPE. 135 posits, and also the anomaly of the continuation of the action by the red, orange, or yellow rays, accordiag to !M. Ed. Becquerel's discoveries on the iodide of silrer ; and of the destruction of that action by the same rays, according to !3iL Claudets observations on the bromo-iodide of sHver. The red, orange, and yellow rays, when acting on an unaffected surfeee, are considerably less capable than the most refi-angible ravs, of imparting the affinity for mercurial rapour on both the iodide and bromo-iodide of silTer : and they destroy that affinity when it has been produced on the bromo-iodide of silver by the photogenic rays. It foUows from this feet, that when the red, orange, or vellow ravs are more abundant in the lisht than the most refrangible rays, the photogenic effect is retarded in pro- portion to the excess of these antagonistic rays. This happens when there exist in the atmosjihere some vapours which absorb the most refrangible rays. In these circumstances the light ap- pears rather yellow : but it is very difficult to judge by the eye of the exact colour of the light, and of the propc«rtion of photo- genic rays existing in the atmosphere at any given moment. The vapours of the atmosphere which render the light yellow, act as any other medium intercepting the blue rays, and those which have the same degree of refrangibility. If we cover an engraving one-half -with light yellow glass, and place it before a camera obscura. in order to represent the whole on a daguerreotype plate, "we shall find that during the time which has been necessary to obtain the image of the half not covered, not the slightest effect has been prcduced on the half covered with the yeUow glass. Xow. if we cover one-half with deep blue glass, and the other with the same light yellow glass, the engraving will be seen very distinctly through the yellow glass, and not at all through the blue. In representing the whole, as before, on the daguerreotype plate, the half which was clearly seen by the eye has produced no effect ; and in the other, which could not be seen, is as fiilly represented, and in nearly as short a time, as when no blue glass had been interposed. Thus we might construct a room lighted only through an inelo- sure of pale yeUow glass, in which light would be very fiaz7lirig to the eye, and in this room no phot<^aphic operation could be performed :* or in a room inclosed by deep blue glass, which would appear very dark, and ia which the photographic opera- tion would be nearly as rapid as it would be in open air. * I have recently proved that this statement requires some mcNiification : the ravs permeating manv yellow glasses act poTerfolly on the sensitive sm&ces of collodion and iodine. 13G SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. Thus we may conceive certain states of the atmosphere under which there will be an abundance of illuminating rays, and very few actinic rays ; and some others, imder which the reverse will take place. Considering how difficult it is to judge by the eye alone of the chemical state of light, we can understand why the photographer is constantly deceived in the efiect he tries to pro- duce, having no means to ascertain beforehand, with any degree of certainty, the intensity of light. For these reasons M. Clau- det tiu-ned his attention to contrive an apparatus by which he could test at the same time the sensitiveness of the daguerreo- type plate and the intensity of light. This instrument he called a Photographometer. " By this instiixment," says the inventor, " I have been able to discover at what degree of intensity of light the eifect called solarization is produced : on well-prepared plates of bromo-iodide it does not begin under an intensity 512 times greater than that which determines the first efiect of mercury ; and also at what degree the decomposition producing the white precipitate without mercury manifests itself, both on iodide and on bromo-iodide of silver. On the fii'st, it is 100 times quicker than on the bromo- iodide : and on the last it is produced by an intensity 3000 times gi-eater than that which developes the fii'st affinity for^^^ mercury. " In the course of my experiments I noticed a curious fact, which proved veiy puzzling to me, xmtU I succeeded in assigning a cause to it. I shall mention it here, because it may lead to some fui'ther discoveries, I observed that sometimes the spaces under the round holes, wliich had not been afiected by light dming the operation of the photogi-aphometer in a sufficient degree to determine the deposit of merciuy, were, as was to be expected, quite black ; wliile the spaces sui-rounding them were in an unaccountable manner slightly afiected by merciuy. At first I could not explain the phenomenon, except by supposing that the whole plate had been previously by accident slightly afiected by light, and that the exposure thi-ough the holes to another sort of light had destroyed the former efiect. I was natuially led to that explanation, having before observed that one kind of light destroys the efiect of another ; as, for example, that the efiect of the Hght from the north is destroyed by the light fi'om the south, when certain vapoiu-s existing in the latter portion of the atmosphere impart a yellow tint to the Hght of the sun. But after repeated experiments, takiug gi-eat care to protect the plate from the least expos\u-e to light, and recol- lecting some experiments of M. INIoser (see Chapter on Tlier- mography), I found that the afiinity for mercury had been im- parted to the surface of the Daguerreotype plate by the contact ox THE THEORY OF THE DAGUEEEEOTTPE. 137 of the metallic plate having the roimd holes, while the space under the hole had received no similar action. Bnt it must be observed that this phenomenon does not take place eveiy time ; some days it is frequent, and in some others it does not manifest itself at all. Considei'ing that the plate fui-nished with round holes is of copper, and that the Dagvierreotype plate is of silver plated on copper, it is probable that the deposit of mercury is due to an electric or galvanic action determined by the contact of the two metals ; and perhaps the circiimstance that the action does not take place every time, will lead to the supposition that it is developed by some peculiar electric state of the ambient atmosphere ; and by a degree of dampness in the air which would increase the electric current. May we not hope that the conditions being known in which the action is produced, and by availing ourselves of that property, it will be possible to increase on the daguerreotype plate the action of light 1 for it is not improbable that the affinity for mercury imparted to the plate is also due to some electrical influence of light. How could we otherwise explain that affinity for mercury given by some rays and withch'awn by some others, long before light has acted as a chemical agent ? " 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 sepa- rate ; in some lights they are very distant, and in some others they are very near, and even coincide. For this reason I con- stantly try thefr position before I oj)erate. I have not been able to discover the cause of that singular phenomenon, but I can state positively that it exists. At first, I thought that some variations in the density or dispersive power of the atmosphere, might produce the alteration in the distance between the two foci ; or that when the yellow rays were more or less abundant, the visual rays were refracted on different points on the axis of the foci, according to the mean refi*angibility of the rays com- posing white light at the moment. But a new experiment has proved to me that these could not be the real causes of the variation. I generally employ two object-glasses; one of shorter focus for small pictm-es, and the other of longer focus for larger images. In both, the actinic focus is longer than the visual focus ; but when they are much separated in one they are less so in the other : sometimes, when they coincide in one, they are very far apart in the other, and sometimes they both coincide. This I have tried every day during the last twelve months, and 138 SCIENTIFIC INTESTIGATIONS ON PHOTOGRAPHY. I have always found tlie same variations. The density of the atmosphere, or the colour of light, seems to have nothing to do with the phenomenon, otherwise the same cause would produce the same effect in both lenses. I must observe, that my daily expei'iments on my two object-glasses are made at the same moment and at the same distance for each, otherwise any alteration in the focal distance would disperse, more or less, the actinic rays, which is the case, as it is easy to prove. The lengthening or shortening the focus, according to the distance of the object to be represented, has, for effect to modify the achromatism of the lenses. An optician, accorditig to M. Lere- bours' calculation, can at will, in the combination of the two glasses composing an achi'omatic lens, adapt such curvatures or angles in both that the visual focus shall coincide with the actinic focus ; but he can obtaia this result only for one length of focus. The moment the distance is altered, the two foci separate, because the visual and actioic rays must be re- fracted at different angles in coming out of the lens, in order to meet at the focus given for 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, they cannot meet at the new focus, and they foi-m two images. If the visual and actiaic rays were re- fracted 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, until we have discovered two kinds of glasses in wliich the densities or the refractive j)ower will be in the same ratio as the dispei'sive power." CHAPTER lY. ON THE PHOTOGRAPHIC REGISTRATION OF PHILOSOPHICAL INSTRU- MENTS AND THE MEANS OF DETERMINING THE VARIATIONS OF ACTINIC POWER, AND FOR EXPERIMENTS ON THE CHEMICAL FOCUS. Section I. — Photographic Registration. There are so many advantages attendant on self-registration, as to make tlie pei-fection of it a matter of much interest to every scientific enquirer. The fii'st who siiggested the use of photo- graphic paper for this piu-pose was Mr. T. B. Jordan, who brought the subject before a committee of the Royal Cornwall Polytechnic Society, on the 18th of February, 1839, and exhi- bited some photographic registers on the 21st of March of the same year. The plan this gentleman adopted was to fiu-nish each instrument with one or two cylinders containing scrolls of photogi-aphic j)aper. These cylinders are made to revolve slowly by a very simple connection with a clock, so as to give the paper a progressive movement behind the index of the instrument, the place of which is registered by the representation of its own image. The application of this principle to the barometer or thermo- meter is most simple ; the scale of either of these instruments being perforated, the paper is made to revolve as close as possible to the glass, in order to obtain a well-defined image. The cylinder being made to revolve on its axis once in forty-eight hom^s, the paper is divided into forty-eight parts by vei'tical lines, which are figui-ed in correspondence with the hour at which they respectively arrive at the tubes of the instruments. The graduations on the paper correspond to those on the dial of the barometer or scale of the thermometer, and may be printed on the paper from a copperj)late, or, what is much better, may be printed by the light at the same time from opaque lines on the tube, which would of course leave a light impression on the paper ; by this means we should have all that part of the paper above the mercury darkened, which would at the same time be gi-aduated with white lines, distinctly marking the fluctuations in its height for every minute dming daylight, and noting the time of every passing cloud. 140 SCIENTIFIC im'ESTIGATIONS ON PHOTOGRAPHY. Mr. J ordan has also piiblLshed an account of Lis very inge- nious plan of applying tlie same kind of paper to the magne- tometer or diiu-nal variation needle,* and several other philo- sophical instruments ; but as these applications were not at the time entirely successful, owing principally to the difficulty of finding a suitable situation for so delicate an instrument, it is thought unnecessary to occupy these pages with any particular description of the an-angements adopted, which, however, were in all essential points similar to those employed by Mr. Ronalds, and adopted in some of ovir magnetic and meteorological obser- vatories. Those of Mr. Brooks are of somewhat more refined a character, and require special notice. A reflector is attached to the end of a delicately suspended magnet ; this reflects a pencil of strong artificial light upon photographic paper placed between two cylinders of glass, which are kept in motion by a small clock arrangement. As the paper moves in a vertical direction whilst the magnet oscillates in a horizontal one, a zigzag line is marked on the paper ; the extent of movement on either side of a fixed line showing the deviation of the magnet for every hour of the day. By means of this arrangement many most remarkable phenomena comiected with terrestrial magnetism have been discovered, and since the methods of adjustment have been rendered more perfect, and the inven- tion applied to a great variety of instruments, we may ho^^e for yet more important results. The registration of the ever-varying intensity of the light is so impox-tant a subject, that it has occupied the attention of several eminent scientific observers. Sii' John Herschel and Dr. Daubeny have applied their talents to the inquiiy, and devised instniments of much ingenuity for the piu-jjose. The instrument constructed by Sir John Herschel, wliich he has named an actinograph, not only registers the direct efiect of solar chemical radiation, but also the amoimt of general actinic power in the visible hemisphere ; one portion of the apparatus being so aii-anged that a sheet of sensitive paper is slowly moved in such a direction, that the du-cct rays of the sun, when unobscured, may fall upon it through a small slit made in an outer cylinder or case, while the other is screened from the incident beam. The paper being fixed on a disc of brass, made to revolve by watch-work, is affected only by the light which " emanates from that definite cu'cumpolar region of the sky to which it may be considered desirable to limit the observation," and which is admitted, as in the other case, through a fine slit in the cover of the instrument. * See the Sixth Annual Report of the Eoyal Comwall Polytechnic Society. PHOTOGRAPHIC REGISTRATION. 141 Mr. Jordan tas devised an instmment for mimerically regis- tering the intensity of the incident beam, which appears to have some pecuhar advantages ; a description of which I shall take the liberty of transcribing. Figiu-e 17 is an elevation of the instrument ; it consists of two copi^er cylinders supported on a metal ft-ame : the interior one is fixed to the axis and does not revolve, being merely the support of the prepared paper ; the exterior cylinder is made to revolve about this once in twenty-foui- hours by a clock movement. It has a triangular apertiu'e cut dowTi its whole length, as sho-\vn in the figtu-e, and it carries the scale of the instrument, which is made to spring closely against the prepared paper. This scale or screen is composed of a sheet of metal foil between two sheets of var- nished paper, and is divided into one hundred parts longitudinally, every other pai-t being cut out, so as to admit the light to the prepared paper without any transparent medium intervening. The lengths of the extreme divisions, measuring round the cylinder, are proportioned to each other as one to one hundred ; consequently the lower division A\all be one hundred times longer passing over its own length than the upper one over its own length, and the lines of prepared paper upon these divisions will, of com'se, be exposed to the light for times bearing the same proportion to each other. Now, as the sensitiveness of the paper can readily be adjusted, so that the most intense Kght will only just tint it through the upper division diu-ing its passage under the opening, and the most feeble light will produce a similar tint through the lower division diu'ing its ^^assa^re, the number of lines marked on the paper at any given time will fui-nish a comparative measure of the intensity of solar light at that time, and may be registered as so many degrees of the Heliograph, the name Mr. Jordan 142 SCIENTIFIC IXVESTIGATIONS ON PHOTOGRAPHY. has given liis instrument, jnst as we now register tlie degrees of the thermometer. An instrument of this kind was made by me for the British Association, and experiments can'ied on Avith it, at intervals, for some yeai"s. Many of the results were very cm-ious, but the iastrument being placed at the Observatoiy at Kew, the obser- vations were imfoi-tunately discontinued.* It is believed that, with an instiniment properly constnicted, the details of the one employed were capable of much improvement ; many very remarkable altei-ations in the relative chemical power of the solar radiations would be detected. From the indications I have obtained, I believe there exists a constant law of change, and that the coiTect expression of the phenomena is given in the following passages — the concluding simimary of my Report on this subject to the British Association at Edinbiu'gh: — " It T\all be evident that the question which ass\imes the most prominence in our consideration of these remarkable phenomena is that of the identity or othei'wise of light and actinism. " Fresnel has s-tated that the chemical effects produced by the influence of light are owing to a mechanical action exerted by the molecules of pether on the atoms of bodies, so as to cause them to assvmie new states of eqiiilibrivmi dependent on the natm'e and on the velocity of the vibrations to which they ai-e subjected, " Ai-ago says, it is by no means proved that the photogenic modifications of sensitive siu-fi^ces result from the action of solar light itself. These modifications are perhaps engendered by invisible radiations mixed with light propei'ly so called, proceed- ing with it, and being similarly refracted. " These views fau-ly represent the condition in which the argu- ment stands, and a yet more extensive set of expeiiments seems to be necessary before we can decide the question. It appears, however, important that we should dismiss, as completely as possible, from our minds, all preconceived hypotheses. The l)henomena were all imkno^Ti when the theories of emission and of undulation were framed and accepted in explanation of luminous effects ; and it will only retard the discovery of the truth, if we prosecute om* researches over this new groimd, with a determination to bend all our new facts to a theory which was fmmed to explain totally dissimilar phenomena." * A new instrument has been constructed, and a regular series of observations are now in progress. THE PHOTOGRAPHOMETER, 143 Section II. — Ixstkuments for Measuring Actinic Variations, &c. the photographometer. M. Claiidet has deyised the Photograpliometer and the Dynactinometer for measiu-mg the intensity of the actinic radiations. These are both most ingenious instruments, the operations of which will be rendered inteUigible by the follo^vinc description : — The accompanying figure (18) shows the photographometer complete. The sensitive plate or paper is placed in a dark box, which is placed in an independent frame, as shown lq Figs. 20 and 21, and as placed in its position at F in the adjoining cut. A black silk webbing being fixed to the moveable plate seen at 19. the head of the instrument, and strained over two rollers, R, r, it will be evident that the sensitive plate is screened from light 144 SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. until the moveable sHde falling down the inclined plane passes over it. The openings in this moveable plate are parallel to each other. Tliey are seven in nimiber, each opening being one-half of the folio-wing one, and double that of the preceding one. Thus, after the operation of the light, we have seven separate images, the different intensities of which represent the * J- pHa= action of light during the intervals of time in the geometric progression of — 1 : 2: 4 : 8 : 16 : 32 : 64 : The box in which the plate or paper is placed for experiment, is pierced with holes, and these correspond with the slits in a b. (fig. 22). By inclining the instrument, which can be very THE FOCIMETER. 145 readily done to any degree by means of the curved arms c D E, any velocity can be given to the falling screen, and thus the plate be exposed to the action of the chemical i-ays for any period of time we please. Fig. 20 shows the result obtained on a plate by this instrument ; the letters corresponding with the holes in the other woodcuts. In fig. 21 the screen with the vertical slits is shown at the moment it is supposed to be passing over the holes A B c D. In this example the plate had been exposed to the vapour of iodine, in such a manner that one zone had attained the first coating of yellow colom- ; a second zone had reached the red ; a third the blue and green ; and a fourth having passed thi'ough all these tints, had obtained the second yellow coating. The number of white circular spots on each vertical zone indicates the degree of sensitiveness of the various coatings ; the less sensitive being the first coating of yellow, D, and the most sensitive the second yeUow coating, A. This is shown by the deposit of mercury on the plate represented by the increased whiteness of the spots corresponding with the holes, each four vertical spots having been exposed for the same time to solar influence. THE FOCIMETER. p^T^y^;r-^pW^'fr")p[ 22. 23. M. Claudet has also devised a very ingenious instrument for focusing, which he calls his Focimeter. (Fig. 22.) This it will be seen from the accompanying woodcvit consists merely of segments of a cux-le, numbered and placed at fixed distances apart, upon a movable axis. This is copied by the camera on a plate or paper, and the result is shown in the annexed figure (23), in which it will be seen difi'erent degrees of efi'ect are sup- posed to have been produced. These determine the best focal 146 SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. point for any lens veiy readily, and it is really a most useful piece of apparatus in the hands of the photogi"apher. THE DYNACTINOMETER. The Dynactinometer is thus described by the inventor : — It consists of a thin metallic disc, perfectly black, having a slit ex- teudinu from its centi-e to the cii'cumference, fixed on an axis revolving through a permanent metallic disc perfectly white. The white disc has also a slit from its centre of the exact length of the radius of the black disc ; and by means of these two slits, which ai-e so adjusted that the black disc can intei'sect the white disc, and by revolving, gi-adually cover the whole white area, the space of the white sm-face on which the black disc can be superposed foi-ms itself a sort of dial, which is divided into any number of equal segments. aU nimibered. The inventor has adopted the number of twenty segments for a lai'ge circle in- scribed on the dial, and of eight segments for a smaller circle, after the manner of the diAT.sions of the Focimeter, but on the same plane. These eight segments are numbered in geometrical progi-ession, 1, 2, 4, 8, 16, 32, 64. /f^^^ /l*^^"^. r \^n K^q/ \. ^^^^^^^ y^pB^H V'"'' 'n^^^^v ^^P<@|^^^ ~ t .^r \"^''-»H-?y^F' ^^ The black disc may be made to revolve in such a manner that it shall cover a new segment of the lai'ge circle duiiug each second, or any other equal fi-action of time. By that means the last segment will have received eight times moi-e light than the first, the black disc having moved over the whole in eight seconds. The difierences of photogenic intensities are hardly observable when they follow the arithmetical progression : the instrument THE DYNACTINOMETER. 147 is so constmcted tliat it may indicate the intensities in the geometrical progi-ession. The first segment remains always covered, in order to be represented black on the daguerreotype plate and mark the zero of intensity : the second is exposed to light dm-ing 1', the third dming 2", the fourth during i", the fifth diu-ing 8", the sixth dui-ing 16", the seventh diu'ing 32", and the eighth dimng 64". This series, which could be extended by dividing the circle into a greater number of segments, is quite sufficient for all observations intended for practically measuring the intensity of the photogenic light, and for comparing the power of object-glasses. The instrument is made to move by applying the hand on a handle fixed on the back at the extremity of the axis on which the disc revolves. An operator accustomed to coimt seconds by memory, or by following a seconds' beater, can perform the experiment with sufficient regularity ; but in order to render the insti-ument more exact and more complete, it can be made to revolve by clock-work, which gives it, at ^\ill, either the arith- metical or the geometrical progi-ession. This last movement presented some difficulty ; but the inventor has been able to obtain it without much complication in the machinery, and the apparatus is -svithin the reach of the greater niunber of operatoi'S having establishments on a complete footing. For the instrviment moving by hand, it is necessaiy that a second person should open and shut the object-glass at a given signal. But in adapting before the object-glass a flap connected with a cord and pulley, the operator, holding the cord in the left hand, can open the flap at the moment that with the right hand he makes the disc revolve, and shut the apparatus when the revolution is complete. When the instrument acts by clock-work, the object-glass may be opened and shut by the same means, at the signal given by a bell wliich strikes at the commencement and at the end of the revolution. If a daguerreotype plate receive the image of the dynactino- meter during its revolution, it is obvious that each segment in- dicates an effect in proportion to the intensity of light and to the time that it has remained uncovered ; also that the niunber of seconds marked on the fii'st segment visible is the measiu-e of the intensity of light at the moment of the experiment ; the effect of each segment being in reality the degree of intensity which can be obtained during the con-esponding time. When we want to compare two object-glasses, they are adapted to two camerte obscui-ae placed before the dynactinometer. After having set the focus of the two apparatus, they are 14S SCIENTIFIC INVESTIGATIONS OX PHOTOGRAPHY. charged each with a dagueiTeot}i)e plate or a photogenic paper. When all is ready, the flaps are opened at the moment that the dynactinometer commences its revolution, and they are shut ■when it is completed. The plates are removed and the images brought out. In compai-ing the result produced on each, it is easy to see which object-glass is the most rapid, and in what pro- portion. For instance, if the ai-ithmetical progi-ession has been followed, and on one of the plates or papers the number i of the gi-eat cii-cle is the fii'st visible, the conclusion is that it has been necessary for the intensity of the light at that moment to opei-ate dui'ing foiu* seconds in order to produce an efiect in the camera obscui*aj and if, on the other plate or paper, the fii'st seven segments have remained black, and the eighth segment is the fii-st upon which the Hght has operated, the conclusion will be that the object-glass which has produced the effect on the first plate or paper has double the photogenic power of the other. But if the geometrical progi-ession has been followed, the same experiment wUl show the image of the segment No. 3, re- presented on one plate, and that of the segment No. 4 on the other, as having each the first degree of intensity : and we have to draw the same conclusion as regai'ds the power of each object- glass. However, this conclusion would be exact only on the supposi- tion that the two plates were endowed with the same degree of sensitiveness : for if they had not been jjrepared identically in the same manner, we could not have the exact measure of the compai-ative power of the two object-glasses. The difference might be due, not to any difference in the power of the object- glasses, but to the inequality in the sensitiveness of the two plates ; although, in i-epeating the experiment several times, the mean result might be sufliciently conclusive. But this difficidty has not escaped the inventor, and he ha-s tried to avoid it. Being able, by means of the photogi-aphometer, to compare the sensitiveness of two plates under the action of the same in- tensity of light, and during the same sj^ace of time, he availed himself of this instrument to determine befoi-ehand the compi- rative sensitiveness of the plates which are to be used in the exijeriment \\ath the dynactinometer. By this means we can tiy beforehand several couples of plates, and keep them as it were stamped "vvith their degi'ee of sensitiveness imtil we want to apply them to test the power of two lenses. The impression is made on one-half of the plate, leaving the other half for the image of the dynactinometer. After having opex-ated in the two camerse obscuia?, each sup- THE DTNACTENOMETER. 149 plied with the lenses the power of which we wish to compare, we siihroit the two jJates, each impressed with both the photo- gi'aphometer and dynactinometer, to the vapoui- of mei'ciuy, which developes the two images on each plate. The number of sjjots given by the photographometer, Fig. 20, will uidicate the sensitiveness of the plate; and in comparing the two images given by the dynactinometer, Fig. 24, 25, accounting for the difference of sensitiveness of each plate, if there is any, we are able at once to determine the comparative power of the two lenses. For the practical investigation of this veiy important photo- gi'aphic qnestion, Mr. Knight has devised an apparatus that will be most valuable as affording the means of adjusting readily to the best focal distance. Mr. Knight's apparatus consists in a frame having two grooves ; one vertical, in which he places the ground glass, and the other forming an angle with the first destined to receive the plate : the planes of the grooves intersect each other in the middle. After having set the focus upon the ground glass, this last is removed, and the plate is placed in the inclined groove. Now, if a newspaper, or any large printed sheet, is put before the camera, the image wiU l)e re^jresented on the inclined plate ; and it is obvious in its inclination the various points of the jilate will meet a different focus. The centre of the plate will coincide with the visual focus; by its inclination it will in one direction meet the photogenic focus at a point more or less distant fi-om the centre, if the photogenic focus is shorter than the visual focus, and in the other du-ection if it is longer. The frame is frunished with a scale of division, having the zero in the centre. When the image is represented on the dagaierreo- tyjie, by applying against it another movable scale of division similar to the other, the operator can find what is the division 150 SCIENTIFIC mVESTIGATIOKS ON PHOTOGRAPHY. above or under zero, at whicli the image seems best defined ; and after having removed from the camera the expeiiment fi-ame, and set the focus as usual on the ground glass, he has only to move the tube of the object-glass by means of the rack and pinion, and to push it in or out ; a space con-esponding with the division of the scale indicating the deviation of the true photo- genic focus: the tube of the object-glass is for that purpose marked with the same scale of division. CHAPTER Y. THERMOGRAPHY. Since the curious nature of tlie results obtained, as I believe, by heat radiations, have been supposed by some to belong to the same class of phenomena as those we have particularly imder con- sideration, I am induced to introduce the subject in this treatise on photography, merely reprinting my original commimication on the subject, as the investigations have not been continued. The Journal of the Academy of Sciences of Paris, for the 18th of July, 1842, contained a communication made by M. Ptegnault from M. Moser, of Konigsberg, " Sm- la Formation des Images Dao-uerriennes;"* in which he annoimced the fact, that "when two bodies are sufficiently near, they impress their images upon each other:' The Journal of the 29th of August contained a second communication from M. Moser, in which the results of his researches are summed up in twenty-six paragx-aphs. From these I select the following, which alone are to be considered on the present occasion : — " 9. All bodies radiate light even in complete darkness. "10. Tills light does not appear to be allied to phospho- rescence, for there is no difference perceived whether the bodies have been long in the dark, or whether they have been just exposed to daylight, or even to direct solai- light. "11. Two bodies constantly impress theii' images on each other, even in complete darkness. " 14. However, for the image to be appreciable, it is neces- sary, because of the divergence of the rays, that the distance of the bodies should not be very considerable. " lo. To render the image visible, the vapom- of water, mer- ciuy, iodine, &c., may be used. "17. There exists latent light as well as latent heat." The announcement at a meeting of the British Association of these discoveries, natiu-ally excited a more than ordinary- degree of interest. A discoveiy of tliis kind, changing, as it did, the features, not only of the theories of light adopted by * Comjptes Jiendus, tome xv., No. 3, folio 119. 1.52 SCIEXTIFIC INVESTIGATIOXS OX PHOTOGRAPHY. philosopliers, but also the commonly received opinions of man- kind, was more calculated to awaken attention than anything which has Ijeen brought before the pubhc since the piiblication of Daguerre's beautifid photogi-aphic process. Having institvited a series of experiments, the results of which appear to prove that these phenomena are not produced by latent light, I am desirous of recording them. I would not be understood as denying the absoi-jition of light by bodies ; of this I think we have abundant proof, and it is a matter well deserving attention. If we pluck a nasturtium when the sun is shining brightly on the flower, and carry it into a dark room, we shall still be enabled to see it by the light which it emits. The human hand will sometimes exhibit the same phenomenon, and many other instances might be adduced in proof of the absorption of light ; and I believe, indeed, of the principle that light is latent in bodies. I have only to show that the conclu- sions of M. IMoser have been formed somewhat hastily, being led, no doubt, by the striking similarity which exists laetween the effects produced on the daguerreotype plates imder the influence of light, and by the juxtaposition of bodies in the dark, to con- sider them as the work of the same element. 1. Dr. Draper, in the Philoso'plncal Magazine for September 1 840, mentions a fact which has been long known, — " That if a piece of veiy cold clear glass, or, what is Ijetter, a cold polished metalKc reflector, has a little object, such as a piece of metal, laid on it, and the surface be breathed over once, the object being then carefully removed, as often as you breath on it again, a spectral image of it may be seen, and this phenomenon may be exhibited for many days after the first trial is made." Several other siixdlar experiments are mentioned, all of them going to show that some mysterious molecular change has taken place on the metallic surface, which occasions it to condense vapoiu'S unequally. 2. On repeating tliis simj^le experiment, I find that it is necessary for the 2)roduction of a good eflfect to use dissimihu- metals; for instance, a piece of gold or platina on a plate of copper or of silver will make a veiy decided image, whereas copper or silver on their respective plates gives but a very faint one, and bodies which are bad conductors of heat, placed on good conductors, make decidedly the strongest impressions when thus treated. 3. I placed upon a Avell-polished copper plate a sovereign, a shilling, a large silver medal, and a penny. The plate was gently warmed by passing a spirit-lamp along its under surface : THERMOGRAPHY. 153 -ttlieu cold, the plate was exposed to tlie vapour of mercury: each piece had made its impression, but those made by the gold and the large medal were more distinct ; not only was the disc marked, but the lettering on each was copied. 4. A bronze medal v.as supported upon slips of Avood, placed on the copper, one-eighth of an inch above the plate. After mercmialization, the space the medal covered was well marked, and, for a considerable distance around, the mercury was un- eqtially deposited, giving a shaded border to the image ; the sjiaces touched by the mercury [1] were thickly covered with the vapour. o. The abo^e coins and medals were all placed on the plate, and it was made too hot to be handled, and allowed to cool without theii- being removed ; impressions were made on the plate in the follo^^dng order of intensity, — gold, silver, bronze, copper. The mass of the metal was found to influence ma- terially the result : a large piece of copper making a better image' tlian a small piece of silver. When this plate was exposed to vapour, the results w-ere as before. On rubbing oif the vapour, it was found that the gold and silver had made per- manent impressions on the copper. G. The above being repeated with a still greater heat, the image of the copper coin was, as well as the others, most feithfully given, but the gold and silver only made permanent impressions. 7. A silvered copper plate was now tried with a moderate warmth. Mercimal vapoiu-s brought out good images of the gold and copper ; the silver marked, but not well defined. 8. Having repeated the above experiments many times with the same results, I was desiroiis of ascei-taining if electricity had any similar efl:ect : powerful discharges were passed through and over the plate and discs, and it was subjected to a long-continued ciuTent Avithout any efiect. The silver had been cleaned oif from the plate ; it was now warmed \ni\\ the coins and medals upon it, and submitted to discharges from a very large Leyden jar : on exposing it to merciuial vapoiu-, the ijnpressions were A-eiy prettily brought out, and, strange to say, spectral images of those which had been received on the plate when it was silvered — thus proving, that the influence, whatever it may be, was exerted to some depth in the metal. 9. I placed upon a plate of copper, blue, red, and orange- coloured glasses, pieces of crown and flint glass, mica, and a square of tracing paper. These were allowed to remain in con- tact half an horn-. The space occupied Ijy the red glass was well marked ; that covered by the orange was less distinct, but the blue glass left no impression ; the shapes of the flint and crown 154 SCIEN'TIFIC rS'VESTIGATIOXS OX PHOTOGRAPHY. glass -vrere well made out, and a remarkably strong impression where tlie croAvn glass rested on the tracing paper, but the mica had not made any impression. 10. The last experiment repeated. After the exposure to mercm-ial vapom-, heat was agaiu applied to dissipate it : the impression still remained. 11. The experiment repeated, but the vapom- of iodine used instead of that of mercury. The impressions of the glasses ap- peared in the same order as before, but also a ven,' beautiful image of the mica was developed, and the paper weU mai-ked out, showing some relation to exist between the substances used and the vapoiu's applied. 1 2. Placed the glasses used above, with a piece of weU-smoked glass, for half an hour, one-twelfth of an inch below a polished plate of copper. The vapour of mercmy brought out the image of smoked glass only. 13. Ail these glasses were placed on the copper, and slightly warmed : red and smoked glasses gave, after vaporisiition, equally distinct images, the orange the next, the othei-s left but taint marks of their forms ; polishing with Tripoli and putty powder would not remove the images of the smoked and red glasses. 14. An etching, made upon a smoked etching ground on glass, the copper and glass being placed in contact. The image of the glass only could be brought out. 15. A design cut out in paper was pressed close to a copper plate by a piece of glass, and then exposed to a gentle heat ; the impression was broiight out by the va]x>m- of mercmy in beauti- ful distinctness. On endeavoming to rub otf the vapoiu*, it was found that all those pai-ts which the paper covei-ed amalgamated with mercury, which was rubbed fi-om the rest of the plates : hence there restilted a perfectly white picture on a poUshed copper plate. 1 6. The coloured glasses before named were placed on a plate of copper, with a thick piece of charcoal, a copper coin, the mica, and the paper, and exposed to fervent stxnshine. Mercurial vapour brought up the images in the following order : — Smoked glass, crown glass, red glass, mica beautifully delineated, oi-ange glass, paper, charcoal, the coin, bhie glass — thus distinctly proving that the only ntys which had any influence on the metal were the calorific rays. This ex]>ei'iment was repeated on different metals, and with various materials, the plate being ex- j>osed to steam, mercury, and iodine : I invariably found that those bodies which absorbed or permitted the permeation of the most heat jrave the best images. The blue and violet i-avs THERMOGRAPHY. 155 could not be detected to leave any evidence of action, and as spectra imprinted on pliotogi-aphic papers by liglit, wliicli had permeated these glasses, gave evidence of the lai-ge quantity of the invisible rays which passed them freely, we may also consider those as entii'ely without the power of effecting any change on compact simple bodies. 17. In a paper which I published in the Philosophical Maga- zine for October, 1840, I mentioned some^ instances in which I had copied printed jDaper and engravings on iodized paper by mere contact and exposiu*e to the influence of calorific rays, or to artificial heat. I then, speculating on the probability of our being enabled, by some such process as the one I then named, to copy pictures and the like, proposed the name of Thermo- graphy, to distinguish it from Photography. 1 8. I now tried the effects of a print in close contact with a well-polished copper plate. When exposed to merciuy, I found that the outline was very faithfidly copied on the metal. 19. A paper ornament was pressed between two plates of glass, and warmed ; the impression was brought out with toler- able distinctness on the luider and wannest glass, but scarcely ti*aceable on the other. 20. Rose leaves were faithfidly copied on a piece of tin plate, exposed to the fidl influence of sunshine ; but a much better impression was obtained by a prolonged exposxu-e in the dark. 21. With a view of ascertaining the distance at which bodies might be copied, I placed upon a plate of polished co2:)per a thick piece of plate-glass, over this a square of metal, and several other things, each being larger than the body beneath. These were all covered by a deal box, which was more than half an inch distant from the plate. Things were left in tliis position for a night. On exposing to the vapour of mercuiy, it was found that each article was copied, the bottom of the deal box more faith- fully than any of the others, the gi'ain of the wood being imaged on the plate. 22. Having found, by a series of experiments, that a black- ened paper made a stronger image than a white one, I very anxiously tried to effect the copying of a printed page or a print. I was partially successfid on several metals ; but it was not until I used copper plates amalgamated on one sui'face, and the mercuiy brought to a very high polish, that I produced any- thing of good promise. By careftdly preparing the amalga- mated siu'face of the copper, I was at length enabled to copy from paper, line-engi-avings, woodcuts, and lithographs, with sui'prising acciu'acy. The first specLtnens produced exhibited a minuteness of detail and sharpness of outline quite equal to loG SCIENTIFIC INVESTIGATIONS OX PHOTOGRAPHY. the early daguerreotriies and the j^hotographic copies prepared ■with the chloride of sUver. The follo\\-ing is the process adopted by me. which I consider far from perfect, but which affords us very delicate images : — A well -polished jilate of cojiper is i-ubljed over "^-ith the niti-ate of mercmy, and then well washed to remove any nitrate of copper which may be fomied ; when quite diy. a little mercmy taken uji on soft leather or linen is well rubbed o^"er it, and the sm-face worked to a perfect miiTor. The sheet to lie copied is placed smoothly over the mercmial surface, and a sheet or two of soft clean i:»aper being placed upon it, is pressed into equal contact with the metal by a piece of glass, or flat board : in this state it is allowed to remain for an hoiu' or two. The time may be considei-ably shortened by applying a very gentle heat for a few minutes to the under sxu-face of the plate. The heat must on no accomit be so gi-eat as to volatilise the mercmy. The next process is to place the plate of metal in a closed box, prepared for generating the vajxiiu- of merciuy. The vapoiu* is to be slowly CAolved, and in a few seconds the pictm-e will liegin to appear ; the vapovu* of mercury attacks those jiarts which con-espond to the white parts of the printed page or engi-aving, and gives a veiy faithfid but some- what indistinct image. The j^late is now removed from the mer- cuiial box, and placed into one containing iodine, to the vapour of which it is exposed for a shoi-t time : it will soon be very evident that the iodine vajwiu- attacks those parts which ai-e free from mercuiial vapoiu-, blackening them. Hence there results a perfectly bkck picture, contrasted with the gi-ay gi-ound fc)rmed by the mercmial vapoiu*. The pictm-e Ijeing formed by the vapom-s of mercmy and iodine, is of com-se in the same state as a dagueiTeotvjie picture, and is readily destroyed by nibbing. From the depth to which I find the impression made in the metal, I confidently hope to be enalded to give to these singular and beautiful productions a considerable degree of permanence, so that they may he used by engi'avei'S for working on. It is a ciu-ious flict that the vapom-s of merciuy and of iodine attack the plate difiei-ently ; and I believe it will be foimd that yapoiu-s liave some distinct relation to the chemical or thermo- electrical state of the bodies upon which they are received. Moser has obseiwed this, and attributes the phenomena to the coloiu-s of the mys, which he supjioses to become latent in the vapoiu" on its passing from the solid into the more subtile foi-m. I do not. however, tliink tliis exi^lanation will agi-ee with the results of experiments. I feel cou-\-inced that we have to do with some thennic influence, and that it will eventually be found THERMOGRAPHY. 157 that some purely calorific excitement produces a molecular chano-e, or that a thermo-electric action is induced wliich effects some°chano-e in the polarities of the ultimate atoms of the solid. These are matters which can only be decided by a series of well-conducted experiments ; and, although the subject will not be laid aside by me, I hope the few ciuious and cei-tainly im- portant facts which I have broxight before you, ^\-ill elicit the attention of those whose leisure and well-knowoi experimental talents qualif)^ them in the highest degi-ee for the interesting research into the action of those secret agents which exert so powei-fiil an influence over the laws of the material creation. Although attention was called to the singular maimer in which vapours disposed themselves on plates of glass and copper, two years since, by Dr. Draper, Professor of Chemistiy at New York, and about the same time to the calorific powers of the solar spectmm, by Sir John Herschel,* and to the influence of heat artificially applied, by myself, yet it is certainly due to M. Moser, of Konigsberg, to acknowledge him to be the first who has forcibly caUed the attention of the scientific world to an inquiiy which promises to be as important in its results as the discovery of the electropile by Volta. As to the practical utility of this discovery, when we reflect on the astonishing progress made in the ai't of Photogi-aphy since Mr. Fox Talbot published his first process, what may we not expect fi-om Thermography, the fii-st mde specimens of which exliibit far greater perfection than the early efforts of the sister art ? As a subject of purely scientific interest, thermography promises to develop some of those secret influences which operate in the mysterious arrangements of the atomic constituents of matter, to show us the road into the yet hidden recesses of natiu-e's works, and enable us to pierce the mists which at present envelope some of the most striking phenomena which the penetration and industiy of a few " chosen minds" have brought before oiu- obscured visions. In connection with photography, it has made us acquainted with sxibtile agencies working slowly but siu-ely, and indicated physical powers beyond those which are abeady known to us, which may possibly belong to a more exalted class of elements, or powers, to which Light, Heat, and Electricity are subsidiary in the gTeat phenomena of Natiu-e, * PIdhsophical Transactions, Part I., 1840, p. 50. CHAPTER VI. ox THE POSSIBILITY OF PRODrCEKCT PHOTOGRAPHS ES" TITEIR XATTRAL COLOURS. Few speculations are more replete viixh. intei-est than that of the pi-obability of our succeeding in the production of photographic images in theii* local coloiu-s. !M. Biot, a gi-eat authority, says, — '• Substances of the same tint may present, in the quantity, or the nature of the radiations which they reflect, as many divei-sities, or diversities of the same oi-der. as substances of a diJIferent tint ; invei-sely, they may be similar in theii* pix^'jierty of reflecting chemiod i-adiations when they ai-e disdjnilai- to the eye ; so that the diflei-ence of tint which they present to the eye may entirely disappear in the chemical picture. These ai'e the diflicidties in- herent in the foiTuation of photogi-aphic pietiu-es, and they show, I think, evidently, the illusion of the expeiimenters who hope to reconcile, not only the intensity, but the tints of the chemical impressions produced by i-adiation, with the coloiu-s of the objects fi-om which these rays emanate." It may be i-ememl>ei"ed that two vears since, Sir John Hei"schel succeeded in procuring upon photographic paper a coloured image of the solar sjiectrum : and that eminent inquirer has communicated to me a recent discovery of great interest, which I have his permission to pxiblish. ** I have got specimens of paper," says Sir John Hei-scheL '' long Tcept, which give a considei*ably better i-epresentation of the spectrum in its natural colours than I had obtained at the date of my paper (Febiiiaiy 1S40), and that light on a dark ground ; but at present I am not prepared to say that this will pi-ove an available process for coloured photogi-aphs. though it brings the hope nearer.'' Here we have the specidations of one philosopher representing the pix">duction of such pictm^es as hopeless, while the experiments of another pi-ove these to be within the range of probabilities, Mv own experiments have, in many instances, given me coloured pictures of the prismatic spectrum, dark ujx>n a light ground, but the most beautifid I have yet obtained has been upon the dagueireotype iodidated tablets, on which the colours NATURALLY-COLOURED PHOTOGRAPHS, 159 have, at the same time, had a peculiar softness and brilliancy. Daguerre himself has remarked, that when lie has been copying any red brick or painted building, the photograph has assumed a tint of that character. I have often observed the same thing in each variety of photographic material, i.e., where a salt of silver has been used. In the Philosophical Magazine for April 1840, will be found a paper, — " Experiments and Observations on Light which has permeated Coloured Media," — in which I describe some ciu-ious results on some of those photographs which are prepared with the hych'iodic salts exposed to luminoiis influence with coloured fluids superimposed ; peiinitting, as distinctly isolated as possible, the permeation of the violet and blue, the green, the yellow, and the red rays, under each of which a complementary colour was induced. "During January of the present year, I prepared some papers with the bichromate of potash and a very weak solution of nitrate of silver : a piece of this paper was exposed behind four coloured glasses, which admitted the passage I'espectively of, 1st, the violet, indigo, and blue rays ; 2d, the blue, the green, and a portion of the yellow rays ; 3d, the green, yellow, and orange rays ; and, 4th, the orange and red rays. The weather being extremely foggy, the arrangement was unattended for two days, being allowed to lie upon a table opposite a window having a southern aspect. On examining it, it had, under the respective colours, become tinted of a blue, a green, and a red : beneath the yello>v glass the change was uncertain, from the peculiar colour of the paper, and this without a single gleam of sunshine. My numerous engage- ments have prevented my repeating the observations I desire on this salt, which has hitherto been considered absolutely insensible to light. The barytic salts have nearly all of them a peculiar calorific eflfect ; the muriate, in pai-ticular, gives rise to some most rich and beautiful crimsons, particularly under the influence of light which has permeated the more delicate green leaves ; and also in copying the more highly-colom-ed flowers, a variety of tintings having been obsei-ved. We may always depend on producing a photographic copy of a leaf of a green colour by the following arrangement: — Having silvered a copper plate, place it in a shallow vessel, and lay thereon the leaf of which a copy is desired, maintaining it in its position by means of a piece of glass ; pour upon it, so that the plate beneath the glass may be covered, a solution of the hydriodate of potash, containing a little free iodine : then expose the whole to sunshine. In about half an hour, one of the most beautiftd photographic designs which can be conceived is produced, of a fine green yellow. The fluid 160 SCIENTIFIC INVESTIGATIOXS OX PHOTOGRAPH V. is yellow, and cuts oft' uearly all the " chemical " i-ays, allowing only of the free pa,s.sage of the less refrangible mys ; the ruost abundant being the yellow. This retards the process of solariza- tion, but it produces its complementary colour on the plate. These tacts will, I tliink, prove that the possibiliti/ of our being enabled to produce coloiu-ed photographs is decided, and that the probabiliti/ of it is brought infinitely nearer, particularly by Sir John Herschel's very im[iortant discovery, than it was supposed to be. M. Edniond Becquerel has recently siicceeded in obtaining bright impi'essions of the s])ectrum in colours, and copying highly coloured drawings on metallic ])lates prejiared with chlorine. The residts of M. Niepce de St.-A^ictor have been of a st\tisfactory character : the main pai-ticulars thereof we select from a memoir entitled " Upon the Relation existing between the Colours of certain coloiu-ed Flames with the Heliographic Images colom-ed by Light." When a plate of silver is plunged into a solution of sulphate of copper and chloride of sodium, at the same time that it is I'endered electro-positive by means of the voltaic battery, the chloriile formed becomes susceptible of coloiiratiou, when, having been withih-awn from the bath, it receives the influence of light. M. Niepce de St. -Victor, from obserA"ing that when chloride of sodiimi (common salt) was employed, the plate became more susceptible of receiving a yellow coloiu" than any other, and knomng that it imparted a yellow colour to flame, was led to believe that a relation existed between the colour commmiicated by a body to flame, and the colour developed iipon a plate of silver, which should have been chloridated with the particular body. To avoid complexity, it may be briefly stated that the bath in which the sensitive sm'face is obtained is jirepared with water, holding free chlorine in solution, to which has been added the salt which is essential to give a predominance to any particular coloiu'. It is well knowni that strontian gives a purple coloiu- to flames in general, and to that of alcohol in particular. If we pre}iare a plate of silver and pass it into water s;itm*ated with chlorine to which is added some chloride of strontian, and when thus pre- pared we place vpon it a coloured design of red and other colours, and then expose it to the sunshine, after six or seven minutes we shall perceive that the colours of the image ai'e reproduced upon the i)late, but the reds much more decidedly than the others. When we would produce successfully the other nxys of XATURALLY-COLOURED PHOTOGRAPHS. 161 the solar spectrum, we operate in the same manner as "we have indicated for the red ray — employing for the orange the chloride of calcium, or that of uranium for the yellow, or the hypochlorite of soda, or the chlorides of sodiimi or potassium. Yery fine yellows have been obtained with a bath composed of water slightly acidulated with miu'iatic acid and a salt of copper. The gi'een rays are obtained with boracic acid or the chloride of nickel ; also with all the salts of copper. The blue and indigo rays are obtained with the double chloride of copper and ammonia. The violet rays are obtained with the chloride of strontian and sulphate of copper. Those substances which give white flames, as the chloride of antimony, the chloride of lead, and the chloride of zinc, yield no colour by luminoiLs action. All the coloiu's of a picture have been produced by preparing a bath composed of the deuto-chloride of copper ; and M. Niepce states that this salt thi'own into bm-ning alcohol produces a variegated flame according to the intensity of the fire, and it is nearly the same ^vith all the salts of copper mixed wdth clilorine. Niejjce says — " If we put a salt of copper in liquid chlorine we obtain a very sensitive surface by a single immersion in the bath ; but the colorific result of this mixture is seldom good. I prefer a mixture of equal parts of chloride of copper and of chloride of iron, with thi-ee or four parts of water ; the chloride of ii-on has, as those of coj)per, the property of being impressed on the plates of silver and of jji'oducuig many colom-s, but they are infinitely more feeble, and the yellow always predominates ; and this agrees with the yellow colour produced in flame by this salt." It should be understood that when the plate of silver, being previously connected with a voltaic battery, is plunged into the bath and the circuit completed, it becomes covered ^vith a dark coating, probably of a sub-chloride of silver mixed ydih the salt, on which the coloiu' to be produced by solar radiation depends. If we form a bath composed of all the substances which separately give a dominant colour, we obtain very lively coloui-s ; but the great difficulty is the mixing of the salts in such propor- tions as to give an equality to the tints, as it commonly happens that some colom-s are excluded by others. We cannot always depend upon obtaining the same results with the same materials, owing principally to the difiiculty of preser^■ing the solution at a uniform strength. Liquid chlorine is necessary — the appHcation of (hy chlorine will not produce the same results, and the volatile chlorine is continually escaping from the water. Niepce de St.-Victor has made many experiments to produce the coloui-s upon salts of silver and copper spread on paper, but without success; the metaUic plate appeal's absolutely necessary, 162 SCIENTIFIC DTVESTIGATIOKS OX PHOTOGRAPHY. and the purer the silver the more perfect and intense is the impression- The following Is recommended as the most effectual mode of manipulating. The silver plate Ls highlv polished with the best tripoli powder and ammonia ; being perfectly cleaned it is connected with the battery, and then plunged into the bath prepared in any of the ways stated. It is allowed to remain in the bath for some minutes, taken from it, washed in a large qviantity of water, and dried over a spirit-lamp. The surfece thus produced is of a duU neutral tint, often almost black ; the sensibility of the plate appears to be increased by the action of heat, and when brought by the spirit-lamp to the cerise red colour it is in its most sensitive state. The sensibility, how- ever, of the plates Ls low. two or three hours being required to produce a decided effect in the camera obscura. The name of Heliochkomes has been given to these naturally coloured photographs, some of which, the personal gift of the inventor to Mr. Malone. I have inspected. These, when I fii-st saw them, were perfectly coloiired in correspondence with the drawings of which they were copies ; but the colours soon faded, and it does not appear as yet that any successful mode of fixing the colours has been discovered. CHAPTER VII. OS LENSES FOE THE PHOTOGRAPHIC CAMERA. It is to the photograpliic artist, a matter of considerable moment that he understands the principles upon which his instraments are constructed. It has, therefore, been thought advisable to add a short chapter which should give a sufficiently popvdar explanation of the dioptrical phenomena with which we have especially to deal. Upon the refi-active power of the media employed, depends the perfection of the residts we obtain ; therefore, some of the phenomena of refraction, or breaking hack, as the term implies, should be clearly understood. A ray of light passing though a vacuum progresses in a perfectly straight line, and we should, if we looked at a brilliantly illuminated point — were it possible — under such conditions, see it in its true position, the numerous rays coming undisturbed directly to the eye. But all matter, however attenuated it may be, has the property 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 atmosphere. The most simple illustration of refraction is to allow a sun- beam, a, passing thi'oiigh a small hole in the window-shutter of a dark room, to fall ujDon the surface of a fluid contained in a glass vessel, b b : instead of proceeding onward to a, it will be found to alter its coui'se at the sur- face of the fluid, and pass along the line to a a. Every substance has difierent refractive powex-s in vii-tue of its physical constitution ; but a ray of Kght incident perpendicularly on a refracting medium, as the ray c, (Fig. 27) sufiers no refraction. If we float, one upon the other fluids, b,c,d, having difierent powers of refraction we shall then see the relative phenomena exhibited by the 164 SCIENTIFIC INTESTIGATIONS ON PHOTOGRAPHY. bending of the ray a a, in passing through them (Fig. 28). It will be evident that no great difficulty exists in measming the refractive powers of ditierent trans- parent bodies : and that hence we are enabled to tabulate those which have the highest and lowest refi-ac- tive indices. A few of the most important ai-e given in the following table :— Air Water Alcohol OU of Cloves Crown glass Plate glass Flint glass Do. containing much lead Diamond 1-000294 1-336 1-372 1-535 1-534 1-542 1-830 2-028 2-439 This knowledge enables us to trace a ray of Light through transparent bodies of any form, provided we can find the incli- nation of the incident ray to the sui-face, where it either enters or quits the body. If parallel rays fall upon a plane svirface G, of glass, they will retain their parallelism after passing through it as the ray a (Fig. 29). The rays diverging from the point a, wiU be refi-acted by the fii-st svu-face into the dii-ections b b, and by con- tinuing a a, and b b, back- wards, we shall find they meet at a point beyond A : so that sujiposing the eye to be placed within the body G, the point A would appear removed to B. But when the rays undergo a second refraction by passing out of the second sui-face, we shall find by continuing the lines back- wards that they meet at c ; therefore a plane glass diminishes the apparent distance of the jioint of the diverging rays. If, instead of a plane glass, we employ a piece equally curved, like a watch-glass, it produces very little change in the form and position of objects. Lenses are glasses gi'ound to different forms, their surfaces being segments of spheres, and it is in obedience to the refi-ac- LENSES FOR THE PHOTOGRAPHIC CAMERA. 165 tory power of the surfaces so produced that their peculiarities belong. The adjoining figures represent the varieties. 2ri sfu A so. 1 is termed a plano-convex lens. 2 is a double convex lens. 3 is formed of parts of two circles of different diameters, and is called a meniscus lens, or concavo-convex. 4 is a plano-concave lens. 5 is a double concave lens. And 6 is a concavo-convex lens, formed of jiarts of the inner sui'- faces of two dissimilar circles. It is not necessary to examine the laws of refraction for all these forms ; the phenomena -wdll be fixUy understood by an examination of a few leading points. Whatever may be the form of a lens, the incident rays parallel to its axis pass through without suffering refi'action, as A A a, a a a, Fig. 31. All other rays must have a certain amount of obliquity, and these all consequently suffer refraction, as the rays a a. jSTow IGG SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY. the rays B B, aud the ray c c, are refracted, and meet at D d' ; the line h h represents the focal image produced of the body from which the light proceeds. In the last figure the image produced by the lens is repre- sented as curved : a little consideration will show that it is not possible that such a cm-ved surface as that represented could produce an image of equal distinctness over every part of a plane surface : the rays cannot meet, as they are refracted from cui'ved sm-faces along any straight line, as F F F ; and supposing we receive on the surface of a lens a bright circidar image, it will be brilliant and well defi^ned around the centre, the light becoming fainter towards the edge, and at length passing into a cloudy halo, exhibiting the prismatic colours. Tliis is called spherical aberration, and to it is due that want of distinctness which commonly is found around the edges of pictiu-es taken m the camera obscura. It is therefore important, in the selection of lenses, that we look for sharjmess of definition over the tvhole of a perfectly flat field. To manufacture a lens which shaU effect this, is a task of some difficulty ; 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 from the farthest of the two foci of that ellipse, as in Fig. 32, produces no aberi'ation, much may be effected. A meniscus lens, therefore, with a convex surface, part of an ellipsoid, the focal distance of which coincides with its fai*- ther focus, and a con- cave sm-face, part of a sphere, whose centre is that focus, will meet all our require- ments. The mecha- nical difficulties of producing such lenses are great, but they may, by cautious manipulation, be to a great extent over- come. There are other methods by which the aberration of sphericity may be corrected, but for a description of these the reader is referred to Sir John Herschel's Treatise on Light, in the Encyclopaedia Metropolitana. If we take such a lens as we have been desci'ibing, and stop its centre with a blackened disc, leaving only a small portion of the edge for the light to pass through, and throw its image on a screen, we shall find it will be l)ordered with fringes of LEN'SES FOR THE PHOTOGRAPHIC CAMERA. .1G7 colour. At one distance red -will prevail, at anotlier violet. This is the result of chromatic aberration, and ai-ises from the unequal re6-angil)ilitj of the dissimilar rays. The red rav is less bent than the "^"iolet ; consequently, supposing the ravs R R to fall on the edge of a lens, they will converge to a point at F, Tvhereas if the rays v v fall along the sixnie cii-cular line, they ■sviU, being more refracted, meet at f. Xow if we place a disc at e, just the size of the cone of light, it will be edged with violet, but if we move it to a, the coloiu-ed border will be red. The indices of refraction for the several rays have been most carefrilly determined by Fi-aimhofer, and for a staudai-d medium, a flint glass prism, they ai-e respectively Red 1-627749 dark Hue B Orange 1-629681 C YeUoV 1-635026 D Green 1-642024 E Blue 1-648260 F Indigo 1-660285 G Violet 1-671062 H Fraunhofer has determined the absolute values from the fixed dark lines which he observed in the spectrum : they represent, however, veiy closely the rays distinguished by their coloiu-s. By refeiiing to the table of the refractive powei's of trans- pai-ent bodies (page 1 64), it will be seen that for a beam of white light, the difierence between the most refractory flint glass and crown glass, in their refracting powei"s, is as 2-028 is to 1.534, and this propoi-tion is maintained nearly, but not exactly, for all the coloui-ed rays : if, therefore, we have a crown 84. glass lens, the refractive power of which will place the focus at a, for the violet rays, and at h. for the red rays, and we grind 168 SCIEXTIFIC Ds-VESTIGATIOXS ON PHOTOGRAPHY. to fit it a flint glass lens, the refi-actory power of which would place the foci of the rays at c, d, it will be seen that the result of such a combination would be the formation of a colourless image, at a mean point between them, by recombining the rays into white hght. Such as is represented in the figure is the achromatic lens of a camera obscura. There is, however, a point to be examined in connection with the lens for photographic piu-poses, which is of the fii^st im- portance, and which has not hithei-to been sufficiently attended to. It is this. The luminous and colom-ed rays of the spectrum, and the chemical rays, are not coiucident at any point of the spectral image, and the relation between the chemical j)ower, and the illuminating power, of a ray, is subject to constant variations. It is often stated that the violet and blue rays are the chemical rays, and hence it is inferred, if the glass of a camera hi corrected so as to make these rays, and the less refrangible red, to coiTespond, all is done which can be desii-ed. It miist be distinctly imderstood that the coloiu' of any par- ticular ray has no dii-ect relation to its chemical character. It is true, if the more refrangible rays are made to correspond with the more luminous rays, we approach the desu-ed point, but we do not necessai'ily reach it. The following remarks from a paper read by the author before the Photogi-aphic Society of London will explain this point. I need not go pai-ticulai'ly into the conditions necessaiy to ensure the recombination of the particular rays produced by refraction. When we look through an ordinaiy single lens, or a bad telescope, we find all objects are fi'inged with coloiu' — we have chromatic dispersion — and this arises from the cii'cumstance that every one of the coloui-ed i-ays has a distinct and separate LENSES FOR THE PHOTOGRAPHIC CAMERA. 169 focal distance. Hence the object of a combination of lenses is to bring the coloured rays to one point, where they are reunited into white Mght. If we bring the face of one prism up against the face of another, we recombine those prismatic rays which wovild be produced by refraction in one direction, and obtain a spot of white light by such recombination. I have endeavoured to show, in the accompanying figure, something like the result that takes place. We start with a coloiu'ed image whose parallel rays fall upon a lens of flint glass, that lens representing vii-tually two prisms placed with two of their faces together. Supposing we use a double convex lens, representing the conditions of two prisms placed edge to edge, we should virtually produce achro- maticity. In this way the lenses have been corrected for coloiu^, but this correction for coloiu' does not include the necessary correction for ensiu'ing the coincidence of the chemical and the luminous rays. Supposing the correction has been made for all the chromatic rays from the dark Une A to the line H in the violet, there stUl remains an outlying set of radiations, nearly equal in length to the space between A and H, and over this space the actinic force is more particularly active. Now, in ordinary achromatic lenses, the focus of these rays of high refrangibility must fall nearer the inner surface of the lens than the true luminous focus. Tliis was first noticed in achromatic lenses by Mr. Claudet. The fact for ordinaiy meniscus lenses, was in the first instance pointed out by Mr. Towsou, who, in a paper published in the Philosophical Magazine, showed, that if, having obtained the best visual image, wdth a non-achi'omatic lens in the camera, we then put the prepared j^late or paper about a quarter of an inch nearer the glass, when the focal distance is about 12 inches, an infinitely better photograph is obtained than that produced by the best visual image. Mr. Claudet's observa- tions on this point were also j^i^blished in the PldlosoiJhical Magazine for 1844, and may be referred to ^\dth advantage, as containing some very important observations on this matter. He showed that even with achromatic lenses the visual focus and the chemical focus were not coincident. He states that with some lenses he found the focus was nearer the glass, and sometimes it was further from the glass, than the visual focus. It is rather difiicult to imderstand why this should be, unless the glasses had in one case been " over-corrected," and in the other that they had been " u^nder-coi-rected." Suppose we have the lens coiTected accurately for chromatic dispersion so as to bring the line H and the line A coincident the one with the other, the result would be that the chemical rays would faU still nearer the inner surface 170 SCIESTIFIC rSA-ESTIGATIOXS OX PHOTOGRAPHY. of the lens. And it -w-ill be foTind by a very careful adjustment of the camei-a, particularly vrhere single achromatic lenses are emijloyed, if -we tiy two exf^eriments, obtaining one picture at the plane giving the finest visual image, and then another at a veiy short distance neai-er the lens, that a finer definition in the detailed part of the pictiu'e will be produced in a shorter time in the last experiment, all the other conditions being the same, than in the fii-st. Let it be cleai-ly undei-stood that we have, and requii-e, the achromatic combination of glasses for producing white light : the coincidence of the rays fix)m the coloiu-ed bodies, as shown along the shghtly ciuwed line, in fig. 3-5. But the chemical radiations fi^-om the same object wo\ild fell upon the line, which cuts the curve of luminous intensity, so that the best chemical efiect would be produced along that line. Though in ordinary cases, this is but a very minute distance neai-er the inner surfece of good achromatic lenses, it ls quite certain that a difference does exist, and to this it is most important that attention should be given. With regai'd to the piinciple, there- fore, that should regulate the construction of the lenses for photographic purposes, we should, to a cei-tain extent, set aside the idea of achromaticity. We should not only correct oui- lenses for coloxu', but we should con-ect them for the peculiar piTuciples with which, combined in action, we have to deal. The chemical radiations do not afiect the eye as the coloured radiations do ; we can detect them only by the phenomena of chemical change. They come to the eye associated with coloui" from the coloured objects external to us or to our camei'a. Whatever they may be, I have ah-eady shown on several occasions that Light acts as a positively retarding agent in all the changes which take place on om- photographic pi-ejiai-ations ; therefore, by throwing the coloui-ed i-ays even out of focus, we may reaUy produce a perfect photogi'aphic picture in less time than when the Ught-rays interfere. It appeal's to me cleai- that we ought to consider the chemical spectrum as distinct and sej^arate in all respects fi'om the Imninous spectrum, but, like that luminous spectnim, as made up of bands of dififerent re- frangil>ility, In this manner M. Melloni distinguishes the calorific spectrum as jxtssessing a set of rays which he calles ther- mochroic rays, or rays coloui-ed for heat ; those heat-rays, which are indicated in Sir John Herschel's experiment, being analogous to those from coloured rays produced from the spectr\l image of a round hole, through which the luminoa? jx-ncil is admitted. The chemical spectnim. on whatever material obtained, exhibits an analogous order of refrangibility, — the same degrees of variation of intensity, and a s imilar arrangement of form. It LENSES FOR THE PHOTOGRAPHIC CAMERA. 171 becomes of covu-se impoi-tant, and it is the only means by whicli pliotogi-aphers can work effectively, that they shoiild obtain lenses which wiU give, at the same time, the most perfect visual image that can be produced (so far achi'omaticity is an object to be desii-ed, and one we always must attain), and be coiTect for the actinic focus. Indeed, in doing this, we must of necessity produce a lens which is not merely achromatic, but really over-achromatic. Now instead, therefore, of correcting for the line H in the violet ray, or any particular line in the ordinaiy spectrum, it becomes, fi-om aU that we know, essential to con-ect for those Hues recently discovered by IMi-. Stokes, beyond the extreme lavender ray of the Newtonian spectmm, or else we leave a considerable portion of the chemical rays out of the sphere of action. Therefore, it appeai-s to me, under considera- tion of the conditions I have endeavoured to explain, that it would be convenient that we should adopt for the chemical principle of the simbeam. Actinism, that which Melloni has done for Heat. We should establish a nomenclatvu-e by which we should get rid of terms that we do not con-ectly express things that we have to deal Tvdth. It was Melloni's proposition, that the body which allows radiant heat to pass through it freely should be distinguished as diathermic, fi'om the Greek words, lih, through (in the same way as we use the teinn dia in diameter), and BepixhQ, warmth or heat ;— that a body which is opaque to heat should be called consequently adiathermic, from a priv. and diadtp^xiKog, transcalescent, destitute of calorific trans- parency. Colotu-ed rays, possessing a different heat-character, are called, upon the same principle, thermochroic, that is coloiu-ed for heat*. Now, adopting a nomenclatiu-e of this order, which may be indicative of oiu- scientific results, we should speak of a piece of yellow glass which does not allow the chemical rays to pass as an adiactinic body, or a body opaque to the actinic or chemical rays ; then we may speak of a piece of blue glass as being diactinic. The correct mode^ of expression would be to say dia-actinic, but it will be more convenient, and possibly allowable, for us to drop one a, and use the expression diactinic. Then we might, on the same principle, use, when speaking of the combined influence of colour and actinism, the term actinochrosis, from cik-iv, a ray, and xpoa, colour, signifjong " coloiu-ed for actinism." In future, therefore, instead of asking for an achi-omatic lens, meaning a lens destitute of colom- transparency, we should ask for a diactinic lens, meaning one which is transparent to the chemical rays.^ I am quite satisfied that until we disassociate from our minds * Scientific Memoirs, vol. iii., p. 535. 172 SCIENTIFIC IXVESTIGATIOXS ON PHOTOGRAPHY. the idea that we are dealing with the luminous principle of the sunshine in the production of oiu- pictui-es, we shall not an-ive at that perfection in Photogi-aphy which it is desii-able we should obtain. We certainly shall not succeed in representing nature as nature presents herself to ovir eye, until we carefully examine all the phenomena which are involved. We desire to produce images equal to those beautiful ones which are imjDressed by the physical radiations upon the human retina, and to do this we must ariive at the same conditions in oiu* dark chamber, as those which obtain in the visual camei-a obscmu of the eye, which is not strictly achromatic. We commonly hear of a lens being slow or quick ; tliis is purely accidental, arising entirely from the uncertainty in which all our optical instiiunent-makers remain as to the relation of the chemical and luminous forces to each other. If the lenticular correction does not extend to the point of bringing the rays beyond the violet, upon the field of \'ision, the lens -will be slow in action, because the light rays interfere, as is explained in a previous page ; but if it is truly diactinic it will be a quick lens. For portraiture, and all purposes requiring great distinctness of outline and rapidity of operation, two achromatic lenses are usually employed. By this arrangement the focal distance is diminished ; the image is much reduced in size, but then it is concentrated in eveiy respect, and hence improved in all the necessary particidai-s. These lenses are, however, still open to the objection that they produce some distortion, which is only to be avoided by greatly reducing the size of the apertiu'e through which the light falls on the lens, and this necessarily involves increased sensibility in the preparations we employ. The distortion is not to the extent which has been represented, but it may, by careful examiaation, be discovered in the finest j)hotographic portraits to a greater or less extent. PART III PEACTICE OF PHOTOGEAPHY. CHAPTER I. SELECTION OF PAPER FOR PHOTOGRAPHIC PURPOSES. It is natural to suppose, that a process wliicli involves the most delicate chemical changes requires more than ordinary care in the selection of the substance upon which preparations of a pho- tographic character are to be spread. This becomes the more evident as we proceed in our experiments to produce increased conditions of sensitiveness. As the material, whatever it may be, is rendered more susceptible of change under solar influence, the greater is the difficulty of producing peifectly uniform surfaces, and with paper this is more particularly experienced than with either metal or glass plates. Paper is, however, so convenient and so economical, that it is of the first impoi-tance to overcome the difficulties which stand in the way of its use, as the tablet on which the photographic picture is to be delineated. The ])rincipal difficulty we have to contend with in using paper is, the different rates of imbibition which we often meet with in different parts of the same sheet, arising from trifling ineqvialities in its texture and imequal sizing. This is, to a certain extent, to be overcome by a very careful examination of each sheet by 176 PRACTICE OF PHOTOGRAPHY. the light of a lamj^ or candle at uight. By extending the paper between the light and the eye, and slowly moving it up and do\vii, and from left to right, the variations in its textm-e will be seen by the different quantities of light which permeate it ; and it is always the safest course to reject every sheet in which any inequalities are detected. By day it is more difficult to do this than at night, owing to the interference of the reflected ^4th the transmitted light. It will, however, often happen that paper which has been carefully selected by the above means ^vill imbibe fluids unequally. In all cases where the paper is to be soaked in saline solutions, we have another method of discovering those soiu'ces of annoyance. Ha^sdng the solution in a broad shallow vessel, extend the papei*, and gradually (h-aw it over the siu'face of the fluid, taking care that it is wetted on one side only. A few trials "will render this perfectly easy. As the fluid is absorbed, any irregularities are detected by the difference of appearance exhibited on the upper part, which will, over well-defined spaces, remain of a dull-white, whilst other portions will be shining ^vith a reflective film of moisture. Where the imj)ortance of the use to which the paper is to be applied, — as, for instance, to copying an elaborate piece of architecture, or for recei^ang the portrait of an individual — will repay a little extra attention, it is recom- mended that the paper be tried by this test with pure water, and dried, before it is submitted to the salting operation. It will be sometimes found that the paper contains minute fibres of thread, arising from the mass of which it is formed not having been reduced to a perfect pulp. Such paper should be rejected, and so also should those kinds which are found to have many brown or black specks, as they materially interfere with some of the processes. Many of the spots in paper are formed by particles of brass wire which have separated from the machinery employed in its manufacture, or they may be fi-agmeuts of buttons derived from the rags, and minutely divided in pulping. Some specimens of paper have an ai'tificial substance given to them by sulphate of lime (plaster of Paris) ; but, as these are generally the cheaper kinds of demy, they are to be avoided by piu'chasing the better sorts. The plaster can be detected by fusing a sheet of the paper and examining the quantity of ash. Pure paper leaves less than | per cent, of ash. If plaster is present the ash will be much more considerable : the increase of weight is, how- ever, sometimes due to kaoliii. No really sensitive photographic paper can be prepared when sulphate of lime is present : and it has the singular property of x'eversing the action of the Iodides on the darkened chloride of silver, producing a negative in the place of a positive photograph. It is the custom for paper-makers SELECTION OF PAPER FOR PHOTOGRAPHIC PURPOSES. 177 to fix tlieii- names and the date on one leaf of the sheet of writing paper. It is wdse to reject this leaf, or to select paper which is not so marked, as in many of the jjhotogi^aphic processes which will be described, these mai'ks are brought out in most annoying distinctness. From the varioiTS kinds of size which the manu- facturers \ise in their jjapers, it will be found that constantly varying eflfects will arise. A well-sized paper is by no means objectionable ; on the contrary, organic combinations exalt the darkening property of the nitrate and chloride of silver. But unless we are careful always to use the same variety of paj^er for the same purpose, we shall be much perplexed by the con- stantly varying results which we shall obtain. No doubt, with the advancing importance of the art, the demand for paper for photographic ptu-poses will increase ; manufacturers will then find it worth the necessary care to prepare paj^er agreeably to the dii'ections of scientific men. Several of our paper-makers are now paying much attention to the preparation of photo- graphic paper, and are considerably impro-vdng it. I have been most obligingly fiu-nished by Mr. Sandford, of Paternoster Row, with specimens of a great variety of Foreign and English papers, and from the care that gentleman is besto^-ing on this subject, the most important advantages may be expected. All who desire to make any progress in photography must take the necessary precautions, or be content to meet with repeated failures. The photographic peculiarities of paper mainly depend upon the sizes employed. The English paper manufacturers very commonly employ gelatine, and this in very different conditions. The French, on the contraiy, use starch, and this, from the strong affinity existing between starch and iodine, appears to be one reason why the French paper is supei'ior for the calotype in some of its modifications. Resin soap is largely employed as a size. The soap is applied to the bibulous paper, and then decomposed by an acid water, lea-ving a fine film of resin spread upon the surface, susceptible of the highest polish. The following tables will exhibit the results of an extensive series of experiments, which were undertaken after the publica- tion of Sir J. Herschel's memoir, O^i the Chemical Action of the Rays of the Solar Spectrum, in which he has given a table of results, obtained with different preparations on various kinds of paper ; but as he has not established the influence of the paper, except in a few instances, independent of the preparation, it be- came desirable to do so ; and the result of several years' ex- perience has proved the correctness of the conclusions then arrived at. 178 PRACTICE OF PHOTOGRAPHY. In pursuing this inquiiy, it was fovmd that the same descrip- tion of paper, from different manufactm-ers, gave rise to widely different effects ; so that the most carefully conducted experi- ments, several times repeated, have only given approximations to the truth. The form of experiment was to select a number of specimens of paper, — prepare them with great care in precisely the same manner, and expose them to the same solar influences. They were partly covered with a piece of colourless glass,- — the object of this being to determine whether under it the action was quicker or slower than when exposed uncovered. Sir John Herschel has shown that there are some peculiar differences in this respect ; and this method offered a very correct mode of determining the relative effects. I. — Papers prepared with Chloride of Sodium and Nitrate of Silver. a. Superfine satin post Considerable exalting effect. b. Thick wove post Depressing influence. c. Superfine demy Slight exalting effect. d. Bath cbawing card Changes slowly. e. Thick post Slight exalting effect. f Common bank post Ditto. g. Thin post Very tardy. h. Tissue paper Considerable exalting effect. II. — Papers prepared with Chloride of Barium and Nitrate of Silver. a. Superfine satin post Slight exalting influence. h. Thick wove post Ditto, but stronger. c. Superfine demy Similar to a. d. Bath drawing card Similar to a. e. Thick post Considerable exalting influence. f Common bank post Similar to a. (J. Thin post Similar to e. h. Tissue paper Results uncertain. III. — Papers prepared with Muriate of Ammonia and Nitrate of Silver. a. Superfine satin post Strong exalting influence. b. Thick wove post Results uncertain — dependent on the size employed. c. Superfine demy Slight exalting eftect. (/. Bath drawing card Results uncertain. SELECTION OF PAPER FOR PHOTOGRAPHIC PURPOSES. 179 e. Thick post Results imcertam. f. Common bank post Very slow. g. Thin post Ditto. h. Tissue paper Strong exalting influence. IV. — Papers prepared with Iodide or Bromide of Potassium and Nitrate of Silver. a. Superfine satin post Darkens slowly. h. Thick wove post Results uncertain. c. Superfine Demy Strong exalting influence. d. Bath Di-awing card Very slowly changes. e. Thick post Depressing influence. f. Common bank post Slight exalting efiect. g. Thin post, Ditto. h. Tissue paper Results uncertain. Unsized paper has been recommended by some, but in no in- stance have I found it to answer so well as paper which has been sized. The principal thing to be attended to in preparing sensi- tive sheets — according to my experience, extended over a period of ten years, although it is opposed to the views of some yoimg but able photographers — is to prevent, as fai* as it is possible, the absorption of the solutions into the body of the paper — the materials should be retained as much as possible upon the very surface. Therefore the superficial roughness of unsized sheets, and the depth of the imbibitions, are serious objections to their use. It must not, however, be forgotten, that these objections apply in their foi'ce only to the silver preparations ; in some modifications of the processes, with the bichromate of potash, the common bibulous paper, used for filtering liquids, has been foimd to answer remarkably well, on account of the facility with which it absorbs any size or varnish. Great annoyance often arises fi^-om the rapid discoloui-ation of the more sensitive kinds of photographic cb-awing paper, inde- pendent of the action of light, which appears to arise from the action of the nitrate of silver on the organic matters of the size. Unsized paper is less liable to this change. If we spread a piu-e chloride of silver over the paper, it may be kept for any length of time without any change of its whiteness taking place in the dark. Wash it over with a solution of nitrate of silver, and, particularly if the paper is much sized, a very rapid change of colour will take place, however carefully we may screen it fi'om the light. From this it is evident that the organic matter of 180 PRACTICE OF PHOTOGRAPHY. the si^e is tlie principal cause of the spontaneous darkening of photographic papers prepared "with the salts of silver. The most cui'ious part of the whole matter, is, that in many cases this change is earned on to such an extent that a revival of metallic silver takes place, to all appeai'auce in opposition to the force of afluiity. This is veiy difficult to deal with. I can only view it in this light — the nitric acid liberates a quantity of carbonaceous matter from the paper, which, acting by a function peculiarly its OAvn, wiH at certain temj^eratiires effect the revival of gold and silver, as proved by Count Rumford"s experiments. HaA^ing been informed that the paper-makers are in the habit of bleaching their papers with sulphvu' and sidphites, I have sub- mitted a considerable quantity of the browned papers to carefid examination. In all cases where the paper, covered with chloride of silver, has suddenly blackened, I have detected the presence of svdphui-. Consequently, when the darkening goes on rapidl}', and terminates in blackness, we may, I think, coiTectly attribute it to the foiTuation of a sulphiu-et of silver. It is, however, certain that the slow action of organic matter is sufficient, under certain cu-cumstances, to set up a chemical change, which, once started, piogi-esses slowly, but certainly, imtil the compound is reduced to its most simjDle form. China clay — kaolin — has of late year's been much used by the paper manufactui-ers, for the double purjiose of giving A\'eight to the paper, and of enabling them to produce a smooth surface upon all the finer vai'ieties of paper ; such as the enamelled satin post. This compovmd of alximina and silica would not, if the finest varieties of clay were employed, be likely to do much mis- chief in the papers used for i^hotography ; but the less pure varieties of the Cornish clay are employed, and this commonly contains the oxides of iron and other metals in a state of veiy fine division; and these, where they come to the sm'face, form little centres of action, from which dark cii-cles spread in rather a curious manner. Thin papei-s ha^•e been tried, and niany varieties would answer exceedingly well, l)ut that neai'ly all kinds are found penetrated with small holes, which, though of minute dimensions, suifer light to pass freely, and consequently l^roduce a spottiness on the resulting picture. Sii" John Hei'schel found that this evil could be remedied by fastening two pieces of such paper together; but this method is troublesome and un- certain. Retm'ning to the consideration of size in the imper, the above- named authority — who employed the lead salts in some of his photograpliic processes — has the following remai'ks : — " The paper with a basis of lead turns yellow by keeping in SELECTION OF PAPER FOR PHOTOGRAPHIC PURPOSES. 181 the dark, and the tint goes on gi-adnally deepening to a dark browTi. But what is very singular, this change is not eqnally rapid upon all kinds of paper — a difference depending, no doubt, on the size employed ; which, it may be observed here once for all, is of the utmost influence in all photographic processes. In one soi-t of paper (known by the name of blue ivove x>ost) it is instan- taneous, taking place the moment the nitrate (if abundant) is applied. And yet I find this paper to resist discolouration, by keeping, better than any other, when the mordant base is silver instead of lead. On the other hand, a paper of that kind called smooth demy, rendered sensitive by a combiaation of lead and silver, was found to acquii-e, by long keeping, a lead or slate colour, which increases to such a degree as might be supposed to render it useless. Yet, in this state, when it is impressed with a photogTaphic image, the process of fixing with hyijosulphite of soda destroys this coloiu' completely, leaving the gi'oimd as white as when first prepai-ed. This fortunate restoration, however, does not take place when the paper has been browned as above described. Some of the muriatic salts also are more apt to induce this discoloui-ation than others, especially those with the earthy bases." It AviU be evident fi-om these remarks that it is of the utmost importance to secm-e a paper which shall be as chemically piu-e as possible. Experience has proved that recently-manufactured paper does not answer equally well with that which has been made for a year or two. It has been thought by many that this was an unfoimded statement, but it is not so ; and the causes opei-ating to the improvement of paper by age are evident. The organic matter of the size is liable to a spontaneous change : this goes on for a considerable time, but at length the process becomes so exceedingly slow that it may, for all practical pui-- poses, be said vii^tually to rest. Paper changes its coloiu- by keeping from this cause, and I have found that such as I have selected fi'om the shoji-ioorn stocks of stationers has been generally superior to that which has been more recently manufactiu-ed. Select, therefore, paper of a imiform texture, fi-ee from spots, and of equal transparency, choosing the oldest rather than the newest varieties. Where the process is highly sensitive for which the paper is desii-ed, it is important to treat it in the following manner : — Having a shallow dish sufficiently large to receive the sheets of paper without in any way cmmpling them, it is to be filled with very clear filtered water, to which a sufficient quantity of nitric acid has been added to make it slightly sour to the taste. Taking a sheet of paper, it should be laid on a porcelain slab, and sponged 182 PRACTICE OF PHOTOGRAPHY. with clean water on both sides, after which it should be placed in the acidulated water, and allowed to remain in it for several hours. Too many sheets should not be placed in the vessel at the same time. After a time they should be removed in mass, placed on the slab, and left for half an hour under gently flowing water, — this removes all the acid, and all those metallic and earthy matters which it has removed fi-om the paper. After this it is to be dried, and it is then fit for photographic use. This chapter has been deemed unnecessarily long; but, upon renewing many of the experiments, I have become so convinced of its importance in all particulars, that I could not induce my- self to curtail it. All who aim at excellence in photography should repeat the experiments and closely obsex-ve the results. CHAPTER II. ON THE APPARATUS NECESSARY FOR THE FIRST PRACTICE OF PHO- TOGRAPHY ON PAPER. The most simple metliod of obtaining sun-pictures, is that of placing the object to be copied on a sheet of prepared paper, pressing it close by a piece of glass, and exposing the arrange- ment to sunshine; all the parts exposed darken, while those covered are protected from change, the resulting picture being vjhite upon a dark ground. It should be here stated, once for all, that such pictiu-es, how- soever obtained, are called negative photographs; and those which have their lights and shadows correct as in natm-e — dark upon a light ground, are positive photographs. The accompanying woodcut. Fig. 36, represents a negative copy of a currant leaf, and Fig. 37, the positive copy obtained from it. If a copy is made by means of the camei-a, of any illuminated object, the picture being produced by the darkening of a white 184 PRACTICE OF PHOTOGRAPHY. or yellow paper, it Avill be evident that the highest lights "svill be represented as dark portions, and the shadows as Kghts. Thus we obtain a negative image. The female figure in the adjoining woodcut, Fig. 38, is copied from a calotype negative porti-ait ; and this negative being used by superposition on another prepared piece of paper, pi'oducesa j^osiVive in which the lights and shades are natiuul, as in the second figure, Fig. 39. Let us commence by supposing the experimentalist to be sup- plied with paper prepared by some one acquainted with the manipulation, and that he is now to observe for the first time the effects produced. For the production of photographic dra^vings, it is necessary to be provided with a copying frame and glass, the most conve- nient size for which, is something huger than a single leaf of quiu'to post Avi'iting paper. The glass must be of such a thick- ness as to resist some considerable pressiu'e, and it should be selected as colourless as possible, great care being taken to avoid APPARATUS NECESSARY FOR PHOTOGRAPHY ON PAPER. 185 such glasses as have a tint of yeUow or red, these colours pre- venting the permeation of a large proportion of the most effi- cient rays. Figiu-es 40 and 41 represent such a frame in its most simple form ; the fii-st showing it in front, as it is employed in taking a copy of leaves, and the other the back, with its piece of stout tinned iron, or board, which presses on a cushion, secur- ing the close contact of the paper with every part of the ob- ject to be copied, and its brass bar, w-hich, when pressed into angular apeii;iu-es in the sides of the frame, gives the required pressure to the paper. To copy leaves we proceed thus : — 40. 41. Ha^^ng placed the frame face downwards, cai'efuUy lay out on the glass, the object to be copied, on which place the photo- graphic paper very smoothly. Then cover this with the cushion, which may be either of flannel or velvet, fix the metal back, and adjust it by the bar, until every j)art of the object and paper are in the closest contact. For all ordinary uses, this frame answers exceedingly well ; but a more convenient pressure frame is constructed in the manner represented by Fig. 42. This ^ contains two bars, one of them movable, and both of them may be fixed in any required posi- tion by binding screws. In arranging botanical specimens, the mider siu-face of the leaves should be next the glass, their vxpper and smooth siu-face in contact "\vith the paper. Although very beautiful copies may be taken of di'ied specimens, they bear no comparison with those from fresh-gathered leaves or recently collected plants, of which, with the most dehcate gradations of shades, the veins of the 186 PRACTICE OF PHOTOGRAPHY. leaves, and the down clothing the stems, are exhibited with in- comparable fidelity. In the event of the plant having any thick roots or buds, it will be best to divide them with a sharp knife, for the purpose of equalizing the thickness in all parts, and in- suring close contact. Engravings are to be placed with thek faces to the prepared side of the photographic paper, laid very smoothly on the glass, and then with the cushion and back pressed into the closest contact possible : the least difiierence in the contact, by permitting dispersion, occasions a cloudiness and want of sharp- ness in the photograph. Of course a copy of anything taken by means of the rays which have passed through it, must present all the defects as well as all the beauties of the article, whatever it may be. Thus, in copying a print, we have, besides the lines of the en- gi-aving, all the imperfections of the paper : This renders it necessary that those engravings should be selected which are on tolerably perfect paper. If the preservation of the engraving is not a matter of much moment, by washing it over the back with a varnish of Canada balsam and spirits of turpentine, it is rendered highly transparent, and the resulting impression is much improved. Care must, however, be taken to use the var- nish very thin, that it may not impaii; any yellow tinge to the paper. An exposure of a few minutes only is sufficient to produce strong and faithful copies during sunshine ; but in dif- fused daylight a longer period is necessary. Some kind of copying frame is an indispensable requisite to the photographer : it is used for copying all objects by trans- mLssion, and for multiplying the original pictures obtained by means of the camera obscura from nature : it is, indeed, the printing-press of the artist. Some prefer two plates of stout plate-glass pressed very closely together with clamps and screws ; but, as the intention is to bring the object to be copied and the sensitive paper into the closest possible contact, numerous me- chanical contrivances will suggest themselves for this purpose to the ingenious. A great niimber of experiments should be made with the copying frame before there is any attempt at using the camera obscura. The Camera Obscui-a, or Dark Chamber, was the invention of Baptista Porta, of Padua. Its jirinciple will be best under- stood 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 figmes of external objects will APPARATUS NECESSAEY FOR PHOTOGRAPHY ON PAPER. 187 be seen delineated upon it ; and, by putting a sxnaU lens over the hole, they are rendered much more e\adent, from the condensa- tion of the rays by the spherical glass. If, instead of a darkened room, we substitute a darkened box (Fig. 43), the same effect will be seen. Sxippose, in the first place, the box to be without the lens, the rays wo\ild pass from the external arrow in nearly right lines through the opening, 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 rays stiU more, and a smaller, but a more perfectly defined pic- tui'e, is the result. As in the phenomena of vision, so in the camera obscura, the image is produced by the radiations proceeding from the external object; and as these radiations progress from various parts, more or less illuminated, so are the high lights, the middle tints and shadows, most beautifully presei-ved in the lenticulai- image. The colours, also, being in the fii'st instance the effect of some physical modification of the primary cause, are repeated under the same influence ; and the defijiition, the colour, and soft gra- dation of light and shadow, are so perfect, that few more beauti- ful optical effects can be exhibited than those of the camera obscura. Now as eveiy ray of light producing the coloured image is accompanied by the chemical principle actinism, and as this is regulated in action by the luminous intensity of the rays, the most luminous (j/ellow) producing the least chemical effect, while this increases wdth the diminishing illuminating power of the coloured rays of the radiating source, we have the impression often opposed, in its relations of light and shade, to the colours of the object we would copy. By referring to the frontispiece to the present volume, the effects produced by copying a coloured image will be seen. The yellows, reds, and those colour's usually regarded as lights, are copied as shadows : hence the importance of attention to the colours of the di-ess, when a portrait is to be taken by any photographic process. 188 PRACTICE OF PHOTOGRAPHY. In the ordinary cameras used by artists for sketching, a mir- ror is introduced, which throws the image on a semitransparent table. Fig. 44 is a section of one form of such an instrument : a a represents the box, in one end of which is fixed the lens h. The lenticidar image falls on the miiTor c, placed at such an angle that it is reflected on the plate of ground-glass d. e is a screen to prevent the overpowering influence of daylight, which would render the pictiu-e almost invisible. This form of the apparatus, though very interestmg as a philosophical toy, and extremely usefid to the artist, is by no means fitted for pho- togi'apliic purposes. The radiations from external obj ect s sufier considerable diminu- tion of chemical power in penetrating the lens, and the reflec- tion from the miiTor so far reduces its in- tensity, that its action on photographic agents is slow. To ob\'iate the objection of the reflected image, it is only necessaiy to place the photographic paper in the place of the mirror, but not in an angular position. A great variety of these instriiments have been introduced to the notice of students of the art, many of them so unnecessarily expensive that they are beyond the reach of the humble amateur. It is conceived that a few examples of mechanical contrivances by which the instrument is rendered portable, and in all respects convenient will not be out of place. Fig. 45 represents one box sliding Avdthin the other for the purpose of adjusting the focus, the lens being fitted into a brass tube, which screws into the front of the camera. The woodcut (Fig. 46) is but one box. APPARATUS NECESSARY FOE PHOTOGRAPHY ON PAPER. 189 the lens being fitted into one brass tnbe sliding in another, like a telescope tube, the movable pai-t being adjusted by a screw and rack. The mouth of the tube is contracted, by which any adventitious radiations are ob- structed, and a brass shade is adjusted to close the opening if requii-ed ; the paper is placed in a case fitted with a glass front, as in Fig. 47, and a shutter, by which it is protected fi.-om the light until the moment it is required to throw the image upon it. In the fii'st edition of this work, a form of camera was described, which possesses the ad- vantages of extreme cheapness, and of being in most respects convenient. It is, therefore, here described in the language I employed in 1841 : — ^7. A pliotographic lens should possess, according to Su- John Herschel, "the three qualities of a flat field, a sharp focus at great inclinations of the visual ray, and a perfect achromaticity^'' There can be no doubt but these qualifications are very essential, — the two fii'st particularly are indispensable, and there is but one objection to the latter. We can only jijroduce perfect achroma- ticity by a combmation of glasses, and experiments prove that by increasing the thickness of the object-glass,*and the number of reflecting and refracting siu-faces, we interinxpt a considerable portion of actinism, and consequently weaken the action on the photogi-aphic material, whatever it may be; but our opticians have succeeded to a great extent in overcoming tliis difiiculty. We may, to a considerable degi'ee, get rid of the defects arising from chi-omatic dispersion, without having recourse to a combi- nation of glasses of different refracting powers. I long used my- \ ^ \ self, and consti-ucted for others, a camei-a obscura which answered well, with a non-achi-omatic lens. Fig. 48 a represents the aper- * The recent experiments of the Rev. Mr. Stokes most fully confirm this view. 190 PRACTICE OF PHOTOGRAPHY. ture of the lens ; i i', a, box sliding into an outer case, h h' ; k k, a tWid division, containing a ground glass at the back, and a door which can be raised or lowered by the screw g, the whole fitting into the fi'ame h h'. Figure 49 is a section of the camera, a is a lens of aperisco- pic fonn, whose radii of curvature are in the proportion of 2 to 1. -^t This meniscTis is placed with its convex surface towai-ds the plane of representation, and with its concavity towards the object. The aperture of the lens itself is made large, but the pencU of rays admitted is limited by a diaphragm, or stop, constructed as in the figure at b, between it and the plane of representation, at about one-tenth of the focal length from the lens. By this arrangement objects are represented -«-ith considerable distinct- ness over every part of the field, but little difference being observable between the edges and the centre, c is the plate of ground glass at the back, which serves to adjust the focus by, and also to lay the photographic paper on, when we desii'e to copy any object; d, a door to shut off the light from the paper or plate until the moment we desire to expose it to luminous agency. Fig. 50 represents this screen or door more perfectly, in the act of falling ; e is a door at the back, through which the picture formed on the opaque glass is examined;^ a pin, keeping the door, d, in its place. The following figm-es (Figs. 51, 52, 53) represent a more per- fect an-angement. Its conveniences are those of folding, and thus packing into a very small compass, for the convenience of ES APPARATUS NECESSARY FOR PHOTOGRAPHY OX PAPER. 191 travellers. It is, however, only adapted for views, and not for portraits. With the camera obscura properly arranged, and the copying frame, the photographic student who confines his attention to the processes on paper has nearly all he re- quires. For the con- venience of adjusting the instrument to dif- ferent heights, and to difierent angles of ele- vation, tripod stands are convenient, but not altogether indis- pensable. They are made in several ways; 52. 53. the two figures, 54 and 55, representing those which appear best adapted to the use of the traveller. The arrangement of compound legs shown in Fig. 54 insures greater steadiness than the other ; but the range of movement in Fig. 55 gives it some advantages. Beyond these things, a few dishes, such as are represented in Fig. 56, A A ; and a frame B, upon which a photogTaph can be placed for the pui'pose of being washed, are the only thing-s required for the practice of photogi-aphy, except those pieces of apparatus which, belonging to special processes, will be found described in the chapters devoted to them. The object has been in this chapter to enumerate those only which are necessary for an amateur to make his rudimentary experiments. My object in describing this camera is to enable the yoimg photographer to pui-sue his earlier studies, without having to in- ciir the cost of a perfect lens. An inferior, and consequently 192 PRACTICE OF PHOTOGRAPHY. low-priced achromatic lens, should ever be avoided, the results with such being far less perfect than those obtained by means of a good j)eriscopic lens. CHAPTER III. ON THE MODES OF MANIPULATION ADOPTED IN THE PREPARATION OF SENSITIVE PAPERS. The only apparatus required by the pliotograpliic artist for tlie preparation of his papers, are — some very soft sponge brushes and large camel hair pencils (no metal should be employed in mounting the brashes, as it decomposes the silver salts), a wide shallow vessel capable of receiving the sheet without folds, a few smooth planed boards, sufficiently large to stretch the paper upon, and a porcelain or glass slab. He must supply himself with a quantity of good tvhite blotting-pajjer, and several pieces of soft linen or cotton cloth ; a box of pins ; a glass rod or two ; some porcelain capsules; and some beaker glasses, graduated measures, scales, and weights. Section I. — Nitrate of Silver. The most simple kind of photographic paper which is pre- pared mth the silver salts is that washed with the nitrate of silver only ; and for many purposes it answers well, pai'ticidarly for copying lace or feathers ; and it has this advantage over every other kind, that it is perfectly fixed by well soaking in warm water, free from chloride of sodium. The best proportions in which this salt can be used are 60 grs. of it dissolved in a fluid ounce of distilled water. Care must be taken to apply it equally, with a quick but steady motion over every part of the paper. It will be found the best practice to pin the sheet by its four cornel's to one of the flat boards above-men- tioned, and then, holding it with the left hand a little inclined, to sweep the brush, from the upper outside corner, over the whole of the ^eet, removing it as seldom as possible. The lines in fig. 57 will represent the manner in which the brush should be moved over the paper, commencing at a and ending at h. On no ac- count must the lines be brushed across, nor must we attempt to 194 PRACTICE OF PHOTOGRAPHY. n u cover a spot wliicli has not been wetted, by the application of fresh solution to the place, as it will, in darkening, become a well defined space of a different shade from the rest of the sheet. The only plan is, when a space has escaped our attention in the fii'st washing, to go over the whole sheet with a more dilute solution. It is, indeed, always the safest coui-se to give the sheet two washings. The nitrated paper not being very sen- sitive to luminous agency, it is desirable to increase its power. This may be done to some extent by simple methods. By soaking the paper in a solution of isinglass or parchment size, or by rubbing it over with the white of egg, and drying it prior to the application of the sensitive wash, it will be found to blacken much more readily, and assume different tones of coloiu-, which may be varied at the taste of the operator. By dissolving the nitrate of silver in rectified sj^ii'its of wine, instead of water, we produce a toleral^ly sensitive nitrated paper, which darkens to a very beautiful chocolate brown; but this wash must not be used on any sheets prepared with isinglass, parchment, or albumen, as these substances are coagvdated by alcohol, and wash iip forming streaks. The nitrate of silver is not sufficiently sensitive to change readily in diffused light ; consequently it is unfit for use in the camera obscura, and it is only in strong sunshine that a copy of an engraving can be taken in any moderate time. Ammonio-Nitrate of Silver.— This is an exceedingly useful preparation for many purposes. It is prepared by adding ammonia to a solution of nitrate of silver : a deep olive preci- pitate of oxide of silver takes place ; more ammonia should then be added, drop by drop, until this precipitate is redissolved, great care being taken that no more ammonia is added than is necessary to effect a perfect solution of the oxide of silver. This solution is more sensitive than the nitrate, and may be used with advantage for copying by superposition; but it is not fitted for the camera obscura. Section II. — Chloride op Silver. This is one of the most important salts employed in photo- graphy ; it therefore demands especial attention. Muriated Papers, as they are termed, are formed by producing CHLORIDE OF SILVER. 195 a chloride of silver on their surface, by washing the paper with the solution of chloride of sodium {rnuriate of soda), or any other chloride, and when the paper is diy, with a solution of nitrate of silver. It is a very instructive practice to prepare small quantities of solutions of common salt and nitrate of silver of difierent strengths, to cover slijjs of paper with them in various ways, and then to expose them altogether to the same radiations. A curious variety in the degrees of sensibility, and in the intensity of colour, will be detected, showing the importance of a very close attention to proportions, and also to the mode of manipulating. A knowledge of these preliminary but important points having been obtained, the preparation of the j^aper should be proceeded with ; and the following method is recommended : — Taking some flat deal boards, perfectly clean, j^in' upon them, by theii" foiu- corners, the paper to be prepared ; observing the two sides of the paper, and selecting that side to receive the pre- paration which presents the hardest and most imiform surface. Then, clipping one of the sponge brushes into the solution of chloride of sodium, a sufficient quantity is taken up by it to moisten the siirface of the paper without any hard rubbing; and this is to be appbed with gTeat regTdarity. The papers being " salted," are allowed to dry. A great number of these may be prepared at a time, and kept in a portfoHo for use. To render these sensitive, the papers being pinned on the boards, or care- fully laid upon folds of wliite blotting paper, are to be washed over with the nitrate of silver, applied by means of a camel-haii- pencil, observing the instructions previously given as to the method of moving the brush upon the paper. After the first wash is applied, the paper is to be (Med, and then subjected to a second application of the silver solution. Thus prepared, it will be sufficiently sensitive for all purposes of copying by application. The second wash is ajDplied for the purpose of insuring an excess of the nitrate of silver in combination, or, more properly speaking, mixed with the chloride. Mr. Cooper, with a view to the production of a uni- form paper, recommends that it be soaked for a con- siderable leng-th of time in the saline wash, and, after ' it is dried, that the sheet ss should be dipped into the sdver solution ; while the operator moves over its surface a glass rod held in two bent pieces of glass. 19G PRACTICE OF PHOTOGRAPHY. as in fig. 58; the object of whicli is to remove the small aii- bubbles forming on the surface of the jDapei', -which protect it fi'om the action of the fluid. This process, however well it may- answer in prepax'ing paper for copying engra-viugs, -will not yield paper svifficiently sensitive for camera purposes; and it is objec- tionable on the score of economy, as a larger quantity of the silver solution is i*equired to decompose the common salt than in the process previously described. The young photogi-apher would find it interesting to study the more striking peculiarities of a few of the preliminaiy washes, such, indeed, as those noticed in the scientific di-vision. It will be fovmd that nearly every variety of paper exposed to the full action of the solar beams will pass through various shades of brown, and become at last of a deep olive coloui' : it must there- fore be understood that the process of darkening is in all cases stojiped shoi-t of this point. Remembering this, it Avill be found that very peculiar and often beautiful tints are produced by the chloride of barium, the hydi'O-chloride of ammonia, and some of the organic acids. Papers prepaied -with the chloride of sodium have, ho-wever, been more extensively used than any othei*s for positive pic- tures, o-wing to the ease ^vith which this material is always to be procured ; and for most j^ui-poses it answers as well as any other, but it does not produce the most sensitive photographic siu'face. The proportions in which this salt has been used ai'e exceed- ingly various ; in general, the solutions have been made too stx'ong ; but several chemists have x'ecommended washes that are as mu.ch too weak. For different uses, solutions of various qualities should be employed. It will be found well in practice to keep papers of three orders of sensitiveness prepared ; the proportions of salt and silver for each being as follows : — A paper may be prepared Avith the chloi-ide as follows : — Chloride of sodium, thirty grains to an ounce of water. Nitrate of silver, one hundi'ed and twenty grains to an ounce of distilled water. The paper is fii'st soaked in the saHne solution, and after being carefully pressed between folds of blottiag paper and dried, it is to be washed twice with the solution of sOver, di-ying it by a warm fij'e between each washing. This papei' is very liable to become brown in the dark. Although images may be obtained in the camera on this paper by about half an hour's exposure, they are never very distiuct., and may be regarded as rather cui'ious than useful. A less sensitive paper for copies of engravings — botanical or entomological specimens, should have the foUowiug proportion : — IODIDE OP SILVER. 197 Chloride of sodium, twenty-five grains to an ounce of water. Nitrate of silver, ninty-nine grains to an ounce of distilled water. And a yet more common sensitive paper, for copying lace- work, feathers, patterns of watch- work, &c., may be thus pre- pared at less expense : — Chloride of sodium, twenty gi-ains to an ounce of water. Nitrate of silver, sixty grains to an oimce of distilled water. Applied as above directed. This paper keeps tolerably well, and, if carefully prepared, may always be depended upon for darkening equally. Section III. — Iodide of Silver. This salt was employed very early by Talbot, Herschel, and others, and it enters as the principal agent into Mr. Talbot's calotype process. Paper is washed with a solution of the iodide of potassium, and then with nitrate of silver. By this means papers may be prepared which are very sensitive to luminous influence, provided the right proportions are hit ; but, at the same time, nothing can be more insensible to the same agency than the piu-e iodide of silver. A singular dif- ference in precipitates to aU appearance the same, led to the belief that more than one definite compound of iodine and silver existed ; but it is now proved that pure iodide of silver will not change colour in the sunshine, and that the quantity of nitrate of silver in excess regulates the degree of sensibility. Experi- ment has shown that the blackening of one variety of iodidated paper, and the preservation of another, depends on the simple admixture of a very minute excess of the nitrate of silver. The papers prepared with the iodide of silver have all the peculiari- ties of those prepared with the chloride, and although, in some instances, they seem to exliibit a much higher order of sensi- tiveness, they cannot be recommended for general jDm-poses with that confidence which experience has given to the chloride. It may, however, be proper to state the best proi^ortions in which the iodidated papers can be prepared, and the most approved method of applying the solutions. The finest kind of paper being chosen, it shovdd be pinned by its four corners to a board, and carefully washed over with a solution of six grains of the nitrate of silver to half an ounce of water : when this is dry, it is to be washed with a solution of iodide of potassium, five grains in the same quantity of water, and dried by, but at some little distance from, the fire j then, 198 PRACTICE OF PHOTOGRAPHY. some short period before the paper is required for use, it must be again washed with the silver solution, and quickly dried, with the same precaution as before. If this paper is warmed too much in drying, it changes from its delicate primrose colour to a bright pink or a rosy brown, which, although still sensitive to solar inflviences, is not so readily changed as when in an unaltered state. The peculiar property of this salt to change thus readily by calorific influence, and some other veiy remarkable effects produced on already darkened paper when washed with a salt of iodine, and exposed to artificial heat, or the jjure calorific rays of the spectrum, appears to promise a process of di-awing of a new and peculiar character. The few simple directions here given will be sufficient to guide the young experimentalist in his earliest essays ; and it is particularly recommended that the first experiments should be confined to the salts named in this chapter. The minute details required for the more highly sensitive processes are described in immediate connection with the process to which they refer. I would advise the amateur to start upon his studies with but three solutions — 1st, Chloride of sodium ; 2d, Nitrate of silver ; 3d, Hyposulphite of soda. "With the first he carefully washes several sheets of good letter paper on one side only, and dries ; with the second he, by another washing of the paper, forms the required chloride of silver, on which he may obtain pictures by simple exposiu-e in the copying fi-ame ; with the tliu'd he gives permanency to the pictmes which he produces. CHAPTER lY. ON FIXING THE PHOTOGRAPHIC PICTURES. The power of destroying the susceptibility of a pliotograj)luc agent to the fiu-ther action of light, M^hen the picture is com- pleted by its influence, is absolutely necessary for the perfection of the art. Various plans have been suggested for accomplishing this, which have been attended with very different i-esults ; few, if any, of the materials used prodiicing the required effect, and, at the same time, leaving the picture unimpaired. The hyposulphite of soda is decidedly superior to every other fixing material ; but it will be interesting to name a few other preparations, which may be iised with advantage in some instances. The pictiu-es formed on papers prepared with the nitrate of silver only, may be rendered permanent by washing them in very pure water. The water must be quite free from any chlorides, as these salts convert the nitrate of silver into a chloride, and attack the picture with considerable energy, and soon destroy it, by converting the darkened silver itself slowly into a chloride. Herschel remarks — " If the paper be prepared with the simple nitrate, the water must be distilled, since the smallest quantity of any muriatic salt pi'esent attacks the j)icture impressed on such paper with singular energy, and speedily obliterates it, unless veiy dark. A solution containing only a thousandth part of its weight of common salt suffices to effect this in a few minutes in a picture of considerable strength." The great point to be aimed at in fixing any of the sun- pictures is the removal of all that portion of the preparation, whatever it may be, which has not undergone change, without disturbing those parts which have been altered in the slightest degree by the chemical radiations. When a picture has been obtained upon paper prepared with the nitrate of silver, or the ammonio-nitrate of silver, the best mode of proceeding is to wash it fu-st with warm rain water, and then with a diluted solution of ammonia : if the ammonia is too strong it dissolves the oxide of silver, which in these processes is formed in the flinter parts of the picture, and thus obliterates the more delicate portions. Photographs on the muriated papers are not, however, so easily fijced. Well soaking these in water dissolves out the 200 PRACTICE OF PHOTOGRAPHri'. excess of nitrate of silver, and thus the sensibilitT is somewhat diminished ; indeed, they may be considered as half fixed, and may in this state be kept for any convenient opportunity of completing the operation. Chloride of saper now contains iodide of lead and proto- nitrate of iron : while still moisst it is rendered sensitive by a solution of nitrate of silver (100 grains to the ounce of water) and placed in the camera. After the ordinary exposure it may be removed to a dark room : if the image is not already deve- loped, it will be found speedily to appear in great sharpness without any further apjplication. It may then be fixed with the hyposulphite of soda in the usual manner. In December 1852 Sir John Herschel communicated to the pages of the Athenceura a letter from his brother-in-law, !Mi-. Stewart, a resident at Pau, in the Pvrenees. In this he states, that, at the suggestion of Professor Pegnault, he was induced to adopt a process of manipulation which gave some charming re- sults, and which he thus describes : — '•' The following observations are confined to negative paper processes divisible into two — the icet and the dr>/. The solu- tions I employ for both these processes are identical, and are as follows : — Solution of iodide of potassium, of the strength of 5 parts of iodide to 100 of pure water. Solution of aceto-nitrate of silver, in the following proportions : — 15 parts of niti-ate of silver, 20 of glacial acetic acid, 150 of distilled water. Solution of gallic acid for developing — a saturated solution- Solution of hyposulphite of soda, of the strength of 1 part of the salt to from 6 to 8 parts of water. For both the wet and dry process I iodize my paper as fol- lows : — In a tray containing the above solution I plunge, one by one, as many sheets of paper (twenty, thirty, fifty, itc.) as are likely to be required for some time. This is done in two or three minutes. I then roU wp loosely the whole bimdle of sheets while in the bath ; and picking up the roU by the ends, drop it into a cylindrical glass vessel with a foot to it ; and pour the solution therein (enough to cover the roU completely) ; in case it should float up above the sui-face of the solution, a little piece of glass may be pxished down to rest across the roll of paper and MR. Stewart's process. 219 prevent its rising. The vessel "v\-itli tlie roll of paper is placed under the receiver of an air-piini^^ and the air exhausted; this is accomplished in a very few minutes, and the paper maj he left five or six minntes in the vacuum. Should the glass be too high (the paper being in lai'ge sheets) to be inserted imder the pneumatic pump-receiver, a stiff" lid lined "with India-rubber, ^yit]l a valve in the centre communicating by a tube with a common direct-action au-pump may be employed A\-ith equal success. After the paper is thus soaked in vacuo it is removed, and the roll di'opped back into the ti-ay "with the solution, and thus sheet by sheet picked off" and hung up to dry, when, as "v\-ith all other iodized paper, it will keep for an indefinite time. "I cannot say that I ftxlly understand the i-ationale of the action of the aii--pum[), but several valuable advantages are obtained hy its use: — 1st, The paper is thoroiighly iodized, and "tt^ith an equa- lity tkroughout that no amoimt of soaking procm-es, for no two sheets of paper are alike, or even one perfect thi'oughout in texture, and au-bulbs are impossible. 2d, The operation is accomplished in a quarter of an hour, which genei-ally occupies one, two, or more hoiu-s. 3d, To this do I chiefly attribute the fact that my paper is never solaiized even in the brightest sun ; and that it will bear whatever amoimt of exposure is necessary for the deepest and most impenetrable shadows in the \"iew without injury to the liright light." '• Wet Process. — To begin "with the icet process. Ha"ving pre- pared the above solution of aceto-nitrate of silver, float a sheet of the iodized paper upon the siu-face of this sensitive bath, leaving it there for about ten minutes. Duiing this interval, ha"ving placed the glass or slate of yoiu' slider quite level, dip a sheet of thick clean white printing (imsized) paper in water, and lay it on the glass or slate as a wet lining to receive the sensitive sheet. An expert manipulator may then, remo"ving the sensi- tive sheet from the bath, extend its sensitive side uppermost on this wet paper lining, "without allo"wing any air-biibbles to inter- vene ; but it is difficult ; and a "^'ery simple and most effectual mode of avoiding aii--globules, pai-ticularly in handling A-ery large sheets, is as follows: — Poiu- a thin layer of water (just sufficient not to flow over the sides) upon the lining paper after you have extended it on your glass or slate, and then lay down youi' sen- sitive paper gently, and by degrees, and floating, as it were, on this layer of water, and when extended take the glass and papers between the finger and thumb by an upper corner, to prevent their slipping : tilt it gently to allow the interposed water to flow off" by the bottom, which will leave the two sheets adhering closely and perfectly, "without the slightest chance of 220 PRACTICE OF PHOTOGRAPHY. air-bubbles ; it may tlien be left for a mi mite or two standing upright in the same position, to allow every drop of water to escape ; so that when laid flat again, or placed in the slider, none may retiu-n back again and stain the paper. Of com-se the sensitive side of the sheet is thus left exposed to the uninter- iTipted action of the lens, no protecting plate of glass being interposed ; and even in this dry and warm climate, I find the humidity and the attendant sensitiveness preserved for a couple of hours. " Dry Process. — Tn pre2:)aring sheets for use when dry for tra- velling, &c., I have discarded the use of previously waxed paper, thus getting rid of a troublesome operation, and proceed as fol- lows : — Taking a sheet of my iodized paper, in place of floating it (as for the wet process) on the sensitive bath, I plunge it fau-ly into the bath, where it is left to soak for five or six minutes ; then removing it, wash it for about twenty minutes in a bath, or even two of distilled water, to remove the excess of nitrate of silver, and then hang it up to dry (in lieu of drying it with blotting-paper.) Paper thus prepared possesses a greater degree of sensitiveness than waxed paper, and preserves its sensitive- ness, not so long as waxed paper, but svifiiciently long for all practical piu'poses, say thirty hours, and even more. The Eng- lish manufactiu-ed paper is far superior for this purpose to the French. To develope these views a few drops of nitrate of sdver are requii-ed in the gallic acid bath, and they are finely fixed and waxed as usual." It will be apparent to the careful reader, that all the processes given, are in all essential particidars the same. To a few simple alterations in the manipvdatory details are due all the variations in sensibility, and in the general efiect of the resulting picture. The main principles are : — 1st. To iodize the paper — that is, to secm-e a uniform coating of iodide of silver over every part of the surface of the paper, and an entu-e absence of either the alkaline or the metallic niti-ate. 2nd. To have an excess of nitrate of silver spread over the iodide a short time previously to using the paper ; and if a high degree of sensibility is requii'ed, the combination of such an organic decomposing agent as gallic acid. In all the photographs obtained by tliis process, the impres- sions from gi-een leaves are very impei-fect. This is only to be obviated l)y adopting the advice of Herschel, and substituting the bromide for the iodide of silver. The following remarks are so much to the point, that I have transferred them from the Journal of the Photoijraj^hic Society : — MR. stewakt's process. 221 " I have read, " says Sir J. F. W. Herschel," mtli considerable interest tlie remarks of Sir W. J. Newton, On Photography in its Artistic view, d-c, communicated to the Photographic Society, and by them printed in the Journal of their Society (No. 1). These remarks are in perfect consonance with my own impres- sions as to the absence, in the very best photograi:)hic landscape I have seen, of a true artistic representation of the relative in- tensities of light and shade, the consequence of which is usually a most painful want of keeping ; — a struggle to come forward of parts which natm-e suppresses, and a want of working out, in features which, to the eye, are palpably distinct. " Sii- W. J. Newton strikes with the true eye of the painter on the more prominent evil of the whole case ; he says (p. 6), ' Wonderful as the powers of the camera are, we have not yet attained that degree of perfection as to represent faithfully the effect of colours, and consequently of light and shade. For in- stance, a bright red or yellow, which woidd act as a light in nature, is always represented as a dark in the camera, and the same with green. Blue, on the contrary, is always lighter. Hence the impossibility of representing the true effect of nature, or of a picture, by means of photography.' " No one can have viewed the exquisite pictures of M. Reg- nault or Mr. Stewai't, without feeling that vegetation is unduly black and wanting in artistic production. No one who has studied colom's, not as an artist, but as a photologist, can for a moment be ignorant of its caiise. The red and yellow rays, and especially the former, ivhich form so large a portion of vegetable greens, are suppressed. They affect not the materials at present used in the photographic art in its highest develoj)ment. " One word suffices for the key of the difficulty — Iodine. It is to the practically exclusive use of this element that the whole evil complained of (most justly) is attributable. I have shown (see my papers, Phil. Trans. 1840, 1842, Articles 129, 217, and ' On the Action of the Rays of the Solar Spectrum on the Da- guerreotype plate,' Lond. Ed. and Dubl. Phil. Journal, 1843, Art. xix.) that iodized silver is insensible, or nearly so, to the red and orange rays — that its range of sensibility begins, with astonishing abruptness, beyond the medium yellow and witliin the blue region — is powerful at the indigo, and extends far into rays which have absolutely no effect in producing vision. No wonder then that iodine produces pictures unsatisfactory to the artistic eye. Iodine then must be thrown overboard or limited in its use, co'ide qui coute (and the sacrifice is a formidable one), if photography shall ever satisfy the desires of the artists. " What then are we to have recourse to 1 Bromine. A new 222 PRACTICE OF PHOTOGRAPHY. photograpliy lias to be created, of which bromine is the basis. This I have proved in my experiments on this substance [Phil. Trans. 1840, Art. 77 ; also Art. xix. Lond. Ed. ears the paper should be removed. For those papers which it is desirable to keep for some time, as dming 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 some distilled water ; you plunge completely both sides of the waxed and iodized paper in the first fluid, and allow it to remain about four or five minutes ; withch-aw it, and plunge it immediately into the bath of distilled water, in which let it soak for not less than four minutes. When 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 prolonged. It will of course be understood by all who have followed the pro- cesses described up to this point, that the papers which are pre- pared for keeping are not those which are the most sensitive ; hence it is necessary to expose such a miich longer time in the camera than those prepared by the stronger solution of silver. The more sensitive vaiiety, under ordinary circumstances of light, will require an exposiu-e in the camera of about 20 seconds, the less sensitive demanding about 10 or 15 minutes, according to the circumstances of light. Fourth Process : The Development of the Image. — The pic- tm-e is developed by the aid of gallic acid dissolved in distilled 230 PRACTICE OF PHOTOGRAPHY. water. Le Gray finds tlie following to be the best propor- tions : — Distilled water 40 flmd ozs. Gallic acid 60 grains. 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 iutensity of the rays incident on the paper when in the camera. The develop- ment of the image is much accelerated by the addition of 15 or 20 ch'ops of the aceto-nitrate of silver. Fifth. Process: Fixing. — It is found convenient often, when on a journey, to give a temporary fixedness to the pictures obtained, and to complete the process with the hyposulpliite at any time on your return home. A wash of 360 gi-ains of bromide of potassium to two quarts of water is the streng-th which should be employed. The process of fixing mth hyposulpliite consists, as in other preparations, simply in soaking the paper imtil the yellow tint of the iodide has disappeared ; the details are parti- cularly given in the chapter on Fixing PhotogTaphs. CHAPTER VI. THE DAGUERREOTYPE. In the first division of this work, all the details of the original processes are given with considerable minuteness, and the vig- nette heading to that section exhibits all the apparatus required for even the improved modern practice. Section I. — Daguerre's Improved Manipulation. The following remarks by M. Daguerre on polishing and pre- paring the plates, from the Comptes Rendus of March 13, 1843, shoidd be carefully attended to, as the preliminary process upon which the success of every subsequent state depends. " Since the publication of my process, I have not been able to occupy myself mvich with it. The investigations to which I devoted myself have been in an entirely new direction, and the experiments which they required were analogous with the pre- ceding ones, only inasmuch as they were made on a metallic plate. However, I have lately been so much stinick with the imequal results which the impressions generally present — even those of persons who are especially occupied with them — that I determined to seek some means of remedying this serious incon- venience, wliich I attribute to two principal cavises. " The first relates to the operation of polishing, which it is physically impossible to effect without leaving on the siu-face of the plate traces of the Kquid and of the other substances used in this operation : the cotton alone which is employed, however clean it may be, is sufiicient to leave a film of dii-t on the silver. This fii-st cause constitutes a very great obstacle to the success of the impression, because it retards the photogenic action by preventing the iodine from coming in direct contact with the silver. " The second consists in the alterations of the temperature of the air with which the plate is in contact, fi-om the fii'st opera- tions to the mercurial operations. It is known that when a cold body is surroimded with warmer air it condenses its moisture. To this effect must be attributed the difficulty which is expe- 232 PEACTICE OF PHOTOGRAPHY. rienced in operating in a liuniid niedinm, especially when we come to tlie mercui-ial oj^eration, which reqnii'es, to raise a suit- able vapour, a temjoeratiu'e of 122° F. " This vajjoui', which first heats the aii' contained in the apparatus, produces on the metal a dew which weakens the image. It is very evident that this humid layer is very injurious ; since if, for example, the plate, on leaving the camera obscura, be breathed on two or three times, the mercui'ial vapour can no longer cause the impression to appear. " The water which is condensed, ev&i at the slightest difference oftemiJerature between the siuface of a body and the suiTounding air, contains in solution, or in suspension, a non-volatile sub- stance, which might be called atmospheric dust ; and as soon as the equilibrivim of temperature is established between the air and the surface of the body, the humid vapour which was con- densed on it is volatiHzed, and depositing on it the dust which it contains, goes on to be re-satm^ated in the air with a 6'esh quantity of this imjixu'e substance. " In order as much as possible to neutralize this effect, the temperature of the plate may be kept higher than that of the siUTOunding au', diiring each of the operations. But it is im- possible to cause this heat to reach to 122° F., in order for it to be of the same temperature as the A'apour of merciuy, since, if the plate be exposed to that degree of heat after the opei-ation of light in the camera obscura, the image will be altered. " I first tried to absorb the humidity of the au- in the mercu- rial box by the usual means, sxxch as lime, &c. ; but these means are insufficient, and only complicate the process, without giving a good result. Another means which has been projiosed con- sists in vapoimzing the mercury under the pneumatic machine ; by this process, truly, the dew on the plate is avoided, but the pressure of the air, which is indispensable to the impression, is suj)pressed. The results thixs obtained, also, are always wanting in piu'ity. " The following is the process at which I have stopped, because it is very simple, and because it obviates the tAvo incon- veniences above mentioned ; that is to say, it frees the silver as much as possible from all dirt or dust, and neutralizes the humidity produced by the elevation of temperatiu-e in the mer- curial box. By the first of these two effects it increases the jiromptitude, and by the second it renders the lights much whiter (especially by the application of M. Fizeau's chloride of gold) : these two effects are always certain. The promptitude given by this process is to that hitherto obtained as 3 to 8 : this proportion is accurate. daguerre's improved ]\ianipulation. 233 " This j)rocess consists in covering the jJate, after having polished it, with a layer of very 2:)ure water, and heating it very strongly with a spirit-lamp, and in afterwards pouring off this layer of water in such a manner that its upper part, where the dust which it has raised floats, does not touch the plate. " It is necessary to have a fx-ame of iron wii-e of the size of the plate, having at one of its angles a handle, and in the mid- dle, on the two ojiposite sides, two small cramp-irons, to retain the plate when it is inclined. After having placed tliis frame on a horizontal plane, the plate is placed on it, which is covered "ndth a layer of very p\u-e water, and putting as much water as the surface 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 disa^ipear ; the heat must be continued to ebullition, and then the water must be pomed off. The operator should commence by placing the lamp under the angle of the fi'ame where the handle is ; but, before removing the fi'ame, this angle mvxst be very powerfully heated, and then, by gradually removing it by means of the handle, the water immediately begins to run off. 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 svifficient for the layer of water, in retiring, not to lose in thickness ; foi', if the water were diied up, there would remain small isolated drojDs, 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 piu'e water does not destroy its polish. " This operation should be j^erformed only 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 submitted to the vapoiu" 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 jDlaced opposite to one another, at a very short distance apart, and carefully enveloped to prevent change of air between the plates. " The plates cannot be too well polished. It is one of the most important points to obtain a fine polish ; but the purity often disappears when substances which adhere to the surface of the silver are used, — such as the peroxide of ii-on, which has been very genei-ally made vise of for giving the last polish. This substance, indeed, seems to biu-nish the silver, and to give it a more perfect polish ; but this polish is factitious, since it does not really exist on the silvei', but in fact on a very fine layer of oxide of ii-on. It is for this reason that there is re- 234 PRACTICE OF PHOTOGRAPHY. quired for polishing them a substance which does not adhere to the silver ; pumice, which I recommended at the commencement, leaves less residue. " As regards the liquid to be employed : in the fii'st operations nitric acid of five degrees must be employed, as I stated in the first instance ; but for the last operations it must be reduced to one degree. " The polishing with oil and the heating may be suppressed. " I take the opportunity afforded by this communication to lay before the Academy the following observations, which I owe to experience : — " The layer produced by the descending vapours of the iodine and of the accelerating substances forms with sUver a more sen- sible compoimd than is obtained with the ascending vapours. I make this obsei'vation only to lay do^vn a fact, for it would be difficult to employ descending vapours, on account of the dust which might fall dm-ing the operation, and from stains. " The resistance which light experiences in passing through a white glass is well 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 tem- perature 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 opex-ating du-ectly with the object-glass, thus cleansed, I still fiu-ther increased the prompti- tude. This means presents too many difficulties to be put in practice ; only care should be taken to clean the object-glass every day.* " The atmospheric dust, which is the scourge of the photo- genic images, is, on the contrary, favom-able to images which are obtained by contact or at a very short distance. To be con- vinced of this, we have only to clean the two bodies which we Avish to put in contact with the boiling water, as T have just in- dicated, and to keep them both at the same temperature as the air ; thei'e wUl then be no impression, wliich e\'idently proves that these images have no relation with the radiation which gives ])hotographic images." * Professor Stokes has recently confirmed the truth of this by some very conclusive experiments. POLISHING THE PLATE. 235 Section II. — Polishing the Plate. Upon this subject but little remains to be added to what is stated in Daguerre's earliest form of manipulation, and the few remarks just quoted. It is of the utmost importance that a very perfect mirror sur- face should be produced, and to ensure the utmost freedom from all organic matter during the polishing, the plate-holder repre- sented in two positions by e e, in Fig. 63, has been devised. The plate-holder is secured to a table by a clamp, and the plate to be polished is fixed upon the horizontal surface of the plate- holder by means of four binding-screws placed at its comers. The j)late having \indergone the preliminary rubbing, which, as being a comparatively coarse operation, need not be further de- tailed than it is in the earlier section, and having been fixed on the holder, the last polish is to be given to it. The hand- bufi", i, in Fig. 63, is to be dusted over with animal charcoal, and moistened with a little spirits of wine : some opei-ators em- ploy tripoK in a state of impalpable powder mixed with essential oil of lavender. If, however, any essential oil is used, it must be ascertained to be quite free from castor oil, — with which it is very commonly adulterated, — by placing a drop on a piece of paper: if it is a pure essential oil, it will, when warmed, entii'ely evaporate, but if not, a greasy spot will remain. In M. Claudet's establishment, where, from long experience, the best modes of manipulation are introduced, the last buffing is efiected in a somewhat difierent manner. In a box on a roller, to which there is a handle, Fig. 59, is ijili':lil{||j.;ll'!i ■'■^!-H-ll!-|l!;Hl :lil^ . -..,, -^ .....^ i:.lii;!llllllillllllllilllllllHlllllllHlllllllll[|lil]iril!lllllllillllll!i placed a long piece of drab-coloured velvet, which can be drawn out and extended, by means of a second roller, upon the per- fectly flat table. The first foot or two, for example, is drawn out : the plate, which has already received its preliminary polishing, is placed face downwards, and being pressed close with the fingers, a rapid circular motion is given to it, and in a few minutes it 236 PRACTICE OF PHOTOGRAPHY. receives its higliest lustre. As the velvet becomes blackened by use it is rolled off, the portion remaining in the box being always perfectly clean, and ready for use. The plate is now ready for receiving its sensitive coating, and, to avoid the chance of the surface touching any other oljject, M. Claudet adojits the simple but most effective mode of pushing it fi-om the buff into a spherical wooden bowl, in which the plate rests by its four corners ia perfect security. As the edges of the metallic plates are generally sharp, they would often cut the buffs, were that accident not prevented by a suitable precaution. Fig. 60 re- presents an appai-atus called a plate- hender. The sui-face a is perfectly horizontal, and has a steel border near the bai* h : upon the bar h runs a press that carries a steel knife edge so rounded as to be able to bend a plate but not to cut it. The silver plate that is to be buffed is placed on this apparatus with an edge close to the back bar, and the press is then run along it from end to end, by which means the edge of the silver plate is bent downwards in a veiy slight degi-ee, but sufficient to prevent any cutting action on the buffs. All the foiu' edges of each plate are bent in the same manner. Section TII. — To Give the Sensitive Surface to the Plate. Various compoimds, called accelei'ating liquors, have been in- troduced, in all of which we have combinations in various pro- portions of either bromine and iodine, or chloi'ine and iodine, and sometimes of the three. These are known by the names of Eau Bromee, or Bromine Water, Bromide of Iodine, Redman's Sensitive Solution, Hungai'ian Liquid, and Woolcott's Accelei'at- ing American Fluid. These accelerating compoimds are em- ployed after the plate has been subjected to the vapoui" of iodine. They all require to be diluted with water tmtil about the colour of pale sheriy. The plate is exposed to the influence of the vapour which is escaping from the solution used in the same manner as Avith the iodine, biit the coloiu' to be attained differs according to the solution employed. An iodizing box is shown at c, Fig. 63 : at the bottom of this some iodine is strewed, and in general it is covered Avith a little sand or a card; — the object of this is to avoid an iiTCgular action on any part of the plate : the box being adjusted with a cover, the iodine is preserved from evaporation and lasts a long time. ^\Tien the plate has assumed its fine TO GIVE THE SENSITIVE SURFACE TO THE PLATE. 237 straw yellow in the iodine box, it is removed to the action of the accelerating agents, liquid or othei-wise, as the case may be. The following rules will guide the experimenter in using the different preparations. If bromide of iodine be used as the accelerating agent, the plate should remain over the iodine xmtil it is of a pui-e yellow tint, and over the bromine till of a deep rose colour. By observing the time of exposiu-e necessaiy to render a plate sensitive, any number of plates may be prepared exactly alike, provided that the same quantity of the solution, always of an uniform strength, be put into the pan. By using a much weaker solution a longer exposnre is then necessary, but the plate be- comes more evenly covered, and there is less danger of having it too much or too Kttle acted upon by the accelerator. The same remark will ap^ily to other accelerating solutions. If Redman's solution, or the Hungarian liquid, a pale yellow and light rose will be found most sensitive. As a general rule, if the yellow colour produced by the iodine be pale, the red should be pale also; if deep, the red must incline to violet. When several plates are to be prepared at one time, the same solution will serve for all ; but it seldom answers to preserve the mixtui-e for any long time ; and its use, after keeping, is one great cause of the failiu-es wliich so annoy amateiu-s. The bromine contained in these sohitions is veiy subtile, and escapes, leaving little else but iodine remaining, which Tvdll, after some time, give a red coloiu" to the plate, without rendering it sensitive, entu^ely dis- appointing the expectations of the operator. Eau bromee, or bromine water, which is very easily prejmred, is extensively used on the Contiuent, and is simple in its xise. If a certain quantity of an uniform solution be placed in the pan, for each plate pre- pared, one observation ^dll suffice to determine the time of ex- posui'e; if not, the coloiu- must guide the operator, varying according to the degree of colour obtained over the iodine : thus, if the fii-st coloiu" obtained be a light yellow, the plate should attaia a full golden tint over the iodine, and may then be retained over the bromine until it acquires a rose coloiir. If iodized of a golden yeUow, then, ia the second operation, it is taken to a j^ale rose, and in the thii-d to a deejD rose. If iu the fii'st of a fi;ll red, in the second to a deep red, and lastly to a grey ; if the first to a deep red, in the second to a light blue, and in the third, to a white, or nearly the absence of all coloiu". Experience, however, must invariably guide the operator, as scarcely any two solutions, though professedly the same in cha- racter, possess the same properties. In a pamphlet pubUshed by M. Fizeau, bromine-water is reconmiended to be prepared as follows: — "To prepare a solution 238 PRACTICE OF PHOTOGRAPHY. of bromiBe, of a fixed proportion and convenient strength to operate with, I, in the first place, make a satiu-ated solution of bromine in water; this is prepared by putting into a bottle of pure water a gTeat excess of bromine, agitating strongly for some minutes, and before using allowing the bromine to sepa- rate. Now, a definite quantity of this satui-ated water is to be mixed with a definite quantity of plain water, which will give a solution of bromine always of the same strength : this mixtui-e is conveniently made in the following manner : — The apparatus necessary is a droj)ping tube, wliich 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 piu-e water to the mark, then add, by means of the drojiping tube, the pro- per quantity of the sattu-ated solution of bromine. " The pui'ity of the water is of some importance : the foregoing projDortions refer to the pure distilled water, and it is well knoA\Ti that the water of rivers and springs is not pure ; but these difierent varieties can be used as if they were absolutely puie water by adding a few drops of nitric acid till they taste slightly acid ; two or thi-ee drops to the pint is generally suflicient. " The liquid produced, which is of a bright yellow colour, ought to be kept in a well-stopped bottle ; it is the normal solution, and I shall call it simply bromine water, to distinguish it from the saturated solution. " Bromine Box. — The box I employ for subjecting the plate to the vaponr of the bromine water is constructed in the follow- ing manner : — It consists of a box lined with a varnish, which is not acted on by bi'omine ; 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, shoi-t 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." Few men have done more for photogi-aphy than M. Fizeau, and in nearly all his suggestions he has been exceedingly happy : the bromine water thus prepared is used with the best effect by our most eminent dagueii-eotype artists. Bromide of iodine is best prepared by the method of INI. de Valicou.rs, which is as follows : — " Into a bottle of the capacity of about two ounces, pour thii-ty or forty di-ops of bromine, the precise quantity not being of importance. Then add, grain by grain, as much iodine as the bromine will dissolve till quite TO GIVE THE SENSITIVE SURFACE TO THE PLATE. 239 saturated. This point is ascertained wlien some grains of the iodine remain undissolved. They may remain in the bottle, as they ^ill not interfere with the success of the preparation. " The bromide of iodine thus prepared, from its occupying so small a space, can veiy easily be carried, but in this state it is much too concentrated to be used. When it is to be employed, poiu' a small quantity, say fifteen drops, by means of a di'op- ping-tube, into a bottle containing about half an ounce of filtered river water. It 'svill easily be understood that the bromide of iodine can be used with a greater or less quantity of water, with- out altering the proportion which exists between the bromine and iodine." Mr. Goddard, on December 12, 1840, published a letter iathe Literary Gazette on the use of bromide of iodine as an acceler- ating agent, but chloride of iodine was fii'st employed by M. Clau- det in 1841, and is prepared by merely placing iodine in an atmosphere of chlorine. Chloride of bromine is made by mixing two drachms of a saturated solution of bromine with fifteen drops of strong mimatic acid and about nine or ten ounces of water. The Himgarian mixture appear^ to be a similar com- pound to this. For the following exceedingly convenient preparations we are indebted to Mr. E. J. Bingham, who has for some time, with much success, devoted his attention to the improvement of photographic processes. The following exti'acts are from the Philoso2)hical Magazine for October, 1846 : — "An Improvement in the Daguerreotyj^e Process by the appli- cation of some new compounds of bromine, chlorine, and iodine, with lime. — All persons who have practised the daguerreotype must have remarked that in wai-m weather a considerable depo- sition of moistiu'e 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 sm-face of the plate diu-ing the time it is exposed to the bromine vapoiu". In fact, I have been informed by a number of profes- sional daguerreotypists (and I have experienced the difficulty myself), that they were unable to obtain perfect pictures during the excessive heat of the late season ; and a veiy clever and enterprising operator, who last year made a tour on the Con- tinent, and brought home some of the finest proofs I have ever seen, entii-ely failed this season in obtaining clear and perfect pic- tures, fi'om the constant appearance of a mist or cloiid over the prepared surface. This appears to be caused by the deposition of moistme uj^on the plate, arising from the water in which the bromine is dissolved. To obviate this, some have recommended 240 PRACTICE OF PHOTOGRAPHY, the pan to be kept at a low temperature iu a freezing mixtiu'e ; and M. Dagnerre, in a communication to the French Academy of Sciences, recommends the plate to be heated : but in practice both these ai-e found to be unsuccessful, (See Lerebours' Traite de Plwtogrcqyhie.) " It appeared to me, that if we could avoid the use of water altogether in the accelerating mixtvu'e, not only would the diffi- culty I have mentioned be avoided, but a much more sensitive sui-face would be obtained on the plate. With this view I endeavoiu'ed to combiue bromine with lime, so as to form a compound analogous to bleaching powder. In this I was suc- cessful, and find that bromine, chloride of iodine, 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 vapoiu' to act upon hych-ate of Ijme 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 cajisule suppoi-ted a little above the lime. As heat is developed diuing the combination, it is better to place the lower part of the flask in water at the temperatiu-e of about 50^ Fah. : the lime gradually assumes a beautiful scarlet coloiu", and acquires an appeai'ance 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 colovu*. Both these compoimds, when the vapoiu" arising from them is not too intense, have an odour analogous to that of bleaching powder, and quite distinguishable from chloi'ine, bromine, or iodine alone. " Those dagu.en'eotypists who use chlorine in combination with bromine, as in Woolcott's American mixture, or M, Gu^rin's Hungarian solution, which is a compound of bi-omine, 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 vapoiu's into a liquid, and then alloAving the vapour of this to act upon lime, a solid may be obtained having all the properties of the American accelerator ; or by combining the chloro-iodide of lime -wdth a little of the bromide, a mixture similar to that of M, Guerin's may be pi'oduced : but I greatly prefer, and would recommend, * " I call this substance bromide of lime, although there is a difficulty as to the composition of bleaching powder, and which would also apply to the com- pounds I describe. Some chemists regard the chloride of lime to be a compound of lime, water, and chlorine. Balard thinks it is a mixture of hypochlorite of lime and chloride of calcium; and the view of ^lillon and Prof, (irahaiu is, tliat it is a peroxide of lime, in which one equivalent of oxygen is replaced by one of chlorine." TO GIVE THE SENSITIVE 'SURFACE TO THE PLATE. 241 the pure bromide of lime, it being, as 1 believe, tbe quickest accelerating substance at present kno^^^l. By slightly coloxiring the jilate with the chloro-iodide, and then exposing it for a pro- per time over the bromide, proofs may be obtained in a fraction of a second, even late in the afternoon. A yellow coloiu* should be given by the use of the fii'st substance ; and the proper time over the bromide is readily obtained by one or two tiials.* 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 pre- paration, 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 unaffected by the ordinary changes of temperatiu'e." The advantages of a dry material are so great, that the bro- m.ide of lime is now commonly iised. By the emplo}Tnent of these agents a sensitive coating is pro- duced, upon which actinic changes are almost instantaneously made. The modes of proceeding to prej^are the plates are similar to those already named. The time necessaiy for the plate to be exposed to the action of the bromine water, if it be used, must be determined by expe- riment, for it will vaiy according to the size of the box and the quantity of liquid used. It is ordinarily between thii'ty and sixty seconds, the time varying "with the temperatm'e of the atmosphere : when once determined, it "vWll be constant with the same box, the same strength of solution, and the same temperature. The method of coating the plate wdtli bromine from the water which is most approved is as follows : — Place a pan in a properly prepared box, fill a pipette with bromine water, and pour it carefully from this into the pan, then close the vessel -svith a glass plate : the liquid must cover evenly the bottom of the pan ; if not level, it inust be adjusted : the level will be easily seen through the glass slide. When ever\'-thing is thus arranged, the plate, previously iodized, is to be j^laced in its frame over the pan, the slide withdrawn, and the necessary time counted j after * " It is better to count time both over the iodine and the bromide of lime : the exposure of the plate to the iodine, after it has received its proportion of bromine, should be one-third of the time it took to give it the first coating of iodine. We have found tliat if less iodine than this be allowed to the plate it will not take up so much mercury, neither will the picture produced be so bold and distinct." 242 PRACTICE OF PHOTOGEAPHY. this lias elapsed, the slide should be shut, and the plate imme- diately placed in the dark box of the camera. For a second operation, this bromine water must be thrown away, and a fresh quantity used. The bottle containing the bromine water should be kept away from the direct light of the sun, and care should be taken that no organic matter fall into the bottle, such as grease, chips of cork, &c. These enter into new combinations with the bromine, and lead to error as to the amount in solution. Daguerre himself introduced some very considerable improve- ments in the process of iodizing. He avoided the use of metal strips, and gave some curious experiments on the action of edges, grooves, &c., in determining the deposition of vapour. M. Daguerre stated that, but for the difficulty of fixing them, the bands might be very much reduced in size ; for it is suffi- cient for them to produce their effect that there be a solution of continuity between them ; and this is proved by the fact that nearly the same resixlt is obtained by engraving at the ^th of an inch from the edge of the plate a line deep enough to reach the copper. The objections to this are, that during the polishing process the engraved line is filled with dust, and it retains water, which sometimes occasions stains. He then proposed, as a very gi'eat simplification of this process, that the plate should be laid flat in a shallow box containing two grooves, one to receive the plate, and the other a board saturated with iodine. Around the plate he places a border of eitlier powdered starch or lime, and the iodine descends from the board to the tablet. The starch or lime absorbs the iodine with avidity, and thus prevents its attacking the edges of the silver, and the vapour is diffused with perfect evenness over it. Another advantage is, that the satu- rated board may be used for several days in succession, without being renovated. M. Seguier somewhat modified even this process. A box of hardwood, varnished internally with gum lac, contains a lump of soft wood, furnished with a card of cotton sprinkled -udth iodine. Upon this is placed a plate covered with card-board on each of its faces. One of these card-boards furnishes, by radia- tion, to the metal the vapour of iodine, while the other returns to the cotton that which it had lost. It suffices to turn the plate from time to time, in order that the operation may go on with equal rapidity. A plate of glass is placed upon the iipper card-l)oard, where it is not operated on. The plate is sustained a little above the charged cotton by frames of hardwood var- nished with gum lac. By increasing the distance between the cotton and the plate, or the contrary, we are enabled to suit the TO DEVELOPE THE IMAGE FORMED ON THE PLATE. 243 arrangement to the temperature of the season, and thus always operate with facility aud promptitude. M. Seguier also states, that a single scouring with tripoli, moistened with acidulated watex', is sufficient to cleanse the plates thoroughly, thus doing away mth the tedious process of scouring with oil, and after- wards the operation of heating the tablet over a spirit lamp. M. Soliel has proposed the use of the chloride of silver to de- termine the time required to produce a good impression on the iodized plate in the camera. His method is to fix at the bottom of a tube, blackened within, a piece of cai"d, on which chloride of silver, mixed with gum or dextrine, is spread. The tu.be thus disposed is tm-ned towards the object of which we wish to take the image, and the time that the chloride of silver takes to be- come of a gx'ayish slate colour, will be the time required for the radiations in the camera to produce a good effect on the iodated silver. These remarks have been introduced as supplementary to the generally approved modes, as' they are suggestive in themselves of still farther improvements. Section IV. — To Develope the Image formed on the Plate. The plate, prepared by one of the methods directed, has been placed in the camera, and the image impressed u}X)n it — atten- tion being given to the points especially alluded to in the chap- ter " General Remai-ks on the use of the Camera Obscura." The image is developed on the dagaierreotype plate, as has been already described, by the use of mercurial vapour. In the ori- ginal process (Fig. 10), one form of a mercurial vapour-box is given ; and Fig. 63, d, represents another. It matters little in what manner the plate is placed in the mercurial bath ; the mercury should be volatilized very slowly, and the image allowed to have its full development before it is removed from the box. Care should be taken that the operator avoids as much as possible contact with the mercurial vapour, since continued exposure to its influence might lead to serious inconvenience. M. Claudet has adopted a most admirable ari-angement in this respect, as is shown in the woodcut on the following page. Fig. 60 represents a small dark chamber fixed outside the apartment in which the operations are carried on, but opening into it by means of sliding glass doors. On either side of the chamber are placed pieces of yellow glass, through which, on 244 PRACTICE OF PHOTOGRAPHY. opening the shutters liy which they are covered, a sntHcipnt quantity of light is admitted to serve any usefid piu'pose, with- out in any way interfering with the sensitive surfaces of the jilates. Within this chamber are placed two mercioy boxes, each containing a small quantity of that metal. One of these is shown in section. -Each box is placed over a water bath, supplied b}- means of a pipe with water from a cistern above, and a small sand bath is placed between the mercvuy box and the water bath. By means of the gas-bm-ner beneath the box, the water is heated, the mercury volatilized slowly and deposited on the plates, which are fixed on the grooves shown on the sides of the box in section. The windows being closed, any mercm-ial vapours which may escape fi-om the box may piiss out into the air through proper ventilators, and the ojiei-ator is thus j3rotected from the injurious effects of the mercury. FIXING THE DAGUERREOTYPE IMAGE. 245 SeCTIOX Y. FiXIXG THE DAGUERREOTYPE ImAGE. It has already been stated tliat the sokition of hyposulphite of soda is the most effective agent for removing all the unchanged iodide of silver, after the application of, and the development of the image by, the mercm-ial vapour. This being effected, greater permanence is given by the appli- cation of a solution of gold. The process as described by M. Fizeau, to whom we are in- debted for its introduction, is as follows : — •' Dissolve eight gi-ains of chloride of gold in sixteen oimces of water, and thii-ty-two grains of hyposulphite of soda in foiu- ounces of water : pom- the solution of gold into that of the soda, a little by little, agitating between each addition. The mixtui-e, at fii'st slightly yellow, becomes afterwards perfectly limpid. This liquid now contains a double hyposulphite of soda and gold. " To use this salt of gold, the siu"face of the plate should be per- fectly free from any foreign substance, especially dust ; conse- quently it ought to be washed with some precautions which might beneglected if it wasto befinishedljy the ordinary mode of washing. '• The following manner generally succeeds the best : the plate being yet iotUzed, and perfectly free from grease on its two sur- faces and sides, shoidd have some di'ops of alcohol pom-ed on the iodized siu-face ; when the alcohol has wetted all the sui-face, plunge the plate into a basin of water, and after that into a solu- tion of hyposulphite of soda. " This solution ought to be changed for each experiment, and to consist of about one jsart of the salt to fifteen of the water : the rest of the wasliing is done in the ordinary way, only taking care that the water shoidd be as free as possible frc>m dust. , "' The use of the alcohol is simply to make the water adhere perfectly all over the siu-face of the l>late, and prevent it fr-om quitting the sides at each sejjarate inimei'sion, which wovdd infallibly pioduce stains. When a picture has been washed, with these precautions, the treatment "^i-th the salt of gold is very simple. It is sufficient to place the plate on a support, fig. 61, or fig. 63, g, and pour upon its siu-face a sufficient quantity of the salt of gold 61. that it may be entii-ely covered, and heat it -svith a strong spuit-lamp ; the jnctvu'e will be seen to brighten, and Ijecome in a minute or two of great force. When this effect is pniduced. the liquid should be pom-ed off and the plate washed and cfried. 246 PRACTICE OF PHOTOGRAPHY. " lu tliis operation the silver is dissolved, and the gold pre- cipitated upon the silver aud mercury, but -svitli very different results : in effect, the silver, which, hy its reflection, 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 mercury, on the contraiy, Avhich, 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." The plates are then washed by means of an arrangement of this order. The apparatus represented in fig. 62 may be employed. a is a vessel sufiiciently large to take the ell plate, and not more than half an inch ==tl ' 2 n wide : this is filled with distilled water, _j; _^ fAj which is heated by means of a spii-it-lamp ; J; i II 6 is a stand supporting the trough, and c y Mm a holder for the plate. After the plate ' i ^^^ been immersed for a few minutes, -M f j it is to be di-a-svn out slowly, and by ""■^^ ^L blowing on it the water is removed, and / am the warm metal rapidly dried. Such are ^ =^=^^ the principal processes which have been g2_ adopted in the daguerreotype manipu- lation. Other modes for gi^dng perma- nency to the daguerrean image have been adopted, but none of them have been so thoroughly sxiccessful as those. It appears advantageous to quote a few of the modified foi-ms of proceeding for fixing these pictures, when obtained, which have fi'om time to time been recommended. M. Preschot, in a letter to M. Arago, remarks — " In one of the sittings of last month you mentioned a process for fixing photogenic images on metal. Knowing, as I do, the interest you take in the beautiful discovery of the daguerreotype, I hope you will excuse the liljerty I take in troubling you with results which I obtained in ex2)eriments made a few months ago. " Photogenic images, obtained by M. Daguerre's jirocess, may be fixed by treating them with a solution of hyth-osulphite of ammonia. For this purpose, a concenti-ated solution of this fluid is mixed with three or fom- volumes of pvu'e water, which is poured into a flat vessel, in sufiicient quantity that the plate may be steeped in it horizontally, and just covered with the fluid. When, by the action of the fluid, the tints of the drawing are sufiiciently changed, which occiu-s in less than a minute, the plate is to be withdrawn, and put into a flat vessel containing FIXING THE DAGUERKEOTYPE IMAGE. 247 ■water : it is afterwards taken out and di'ied. By this process the polished parts of the metal are tinged gray by the sulphnret, and the amalgamated parts are not attacked, or, at least, but very little. The tints may be vai-ied by the concentration of the fluid or the duration of the immersion ; however, too long an action turns the lights yellow. Photographic images, treated in this manner, bear rubbing with the fingei- without losing any of their details." M. Choiselat proposed a plan which has been i-arely acted upon, but which is well deserving of attention. Chloride, and particularly iodide of silver, dissolved in hypo- sulphite of soda, may be advantageously employed for fixing the images of the daguerreotype. Steeped in these solutions, they ai-e, under the electro-chemical inflvience exerted l)y the copper on the dissolved silver, coated with a film of silver, and thixs become inefiaceable. Instead of the hyposulphite, a mixture of iodide or bromide of potassium, holding the sUver salt in solution, may be em- ployed. The iodide of silver best adapted for this operation is said to be that which is obtained by treating, "with the aid of heat, a plate of this metal by the iodide precipitated from alcohol by water, afterwards dissolving the iodide formed and adhering to the plate in the hyposul^^hite. Dr. Berres, of Vienna, assisted by Mr. F. Kratochwila, has succeeded by another process, bearing some analogy to that of M. Fizeau, in fixing the dagueiTeotype designs. He takes the photograph produced in the usual manner by the process of Daguerre, holds it for a few minutes over a moderately warmed nitric acid vapoiu-, and then lays it in nitric acid of 13" or 14" Reaumur (61-j*^ or 63^'^ Fahrenheit), in which a considerable quantity of copper or sUver, or both togethei", has been previously dissolved. Shortly after having been placed therein, a precipi- tate of metal is formed, and can be changed to any degree of intensity. The photographic picture coated with metal is now removed, washed in water, cleaned, and chied ; it is then polished wdth chalk or magnesia, and a dry soft cloth or leather, after which the coating will become clean, clear, and transparent, so that the pictui-e, with all its details, can again be seen. This 23roceeding is of a most imcertain character — since, with every precaution, the acid solution frequently " bites" into the plate, producing an etching. 248 practice of photography. Section YI. — Simplification of the Daguerreotype. The foUowing expei'iments for the siini)lificatioii of the daguer- reotji^e processes, were made by me many years since ; I have therefore z'etaiiied such jioi-tious of the original paper as do not appear to be eutii-ely iininstmctive. Prociu'e a well-plenished copper plate of the required size, and polish it, fii*st ^vith pumice-stone and watei% than with snake- stone, and bring it up to a muTor siuiace "v\"ith either rotten- stone or jewellei"s' rouge. Plates can be purchased in a high state of preparation from the engravei's. Having prepared the copper plate weU, rub it with salt and watei', and then with some silvering powder. No kind answers better than that used by clock-makers to silver dial-plates. It is composed of one part of well-washed chloride of silver, five parts of cream of tartar, and foui- parts of table salt. Tliis powder must be kept in a dai-k vessel, and in a diy place. For a plate six inches by five as much of this composition as can be taken up on a shilling is sufficient. It is to be laid in the centre of the copjjer, and the fingers being wetted, to be quickly rubbed over eveiy part of the plate, adding occasionally a little damp salt. The copper being covered ydih the silvering, it is to be speedily well washed in water, in which a little soda is dissolved, and as soon as the siu'face is of a fine silvery whiteness it is to be di-ied with a very clean AvaiTU cloth. In this state the plates may be kept for use. The fii-st process is to expose the plate to the heat of a spirit flame, until the silvered siu-face becomes of a well-defined golden- yellow coloiu' : then when the plate is cold, take a piece of cotton, dipped in veiy dilute nitric acid, and iiib lightly over it until the white hue is restored, and dry it with very soft clean cloths. The plate is then immersed in a weak solution of the iodide of potassium, in which a small portion of iodine is dissolved. The silver is thus converted, over its sm-face, into an iodide of silver ; and in this state it is exposed to the solar rays, which blacken it. When chy it is to be again poHshed, either with dilute acid or a solution of carbonate of soda, and afterwards ^\"ith diy cotton, and the smallest possible portion of prepared chalk ; by this means a siu-face of the highest polish is produced. The rationale of this process is, in the fii'st place, the heat applied drives oflT any adliering acid, and efiects moi'e perfect imion between the copper and silver, so as to enable it to bear the subsequent processes. The first yellow surface appears to be an oxide of silver, with, possibly, a minute quantity of copper in combination, wliich being removed leaves a surface chemically pure. Copper plates may also be veiy beautifully silvered by SIMPLIFICATION OF THE DAGUERREOTYPE. 249 galvanic agency, by which we ai"e enabled to increase the thick- ness of the silver to any extent, and the' necessity for the heating process is removed, the silver being absolutely pure. The best and simplest mode is to divide an earthenware vessel with a diapln-agm of membrane or paper: one side should be filled Avith a very dilute solution of sulphimc acid, and the other with either a solution of ferropru.ssiate of potash, or chloride of sodium, saturated with chloride of silver. The copper plate, varnished on one side, is united, by meaus of a copper wire, with a plate of zinc. The zinc plate being immersed in the acid, and the copper in the salt, a weak electric cm-rent is generated, which pi'ecipi- tates the silver in a very uniform manner over the entire sirrface. At a very early stage of my mquu'ies I found that the influence of all the rays, excepting the yellow, was to loosen the adhesion of the iodized siu'face, with the under layer of unaffected silver. When this changed film was removed by rubbing, the silver be- neath always exhibited the most perfect lustre, and I have hence invariably adopted tliis mode of polisliing my daguerreotype plates. The reqiured sm-face is thus prodiiced with one-third the labour, and a very great saving of time • besides which, the silver is in a much more susceptible state for receiving the vapour of the iodine. The plate being thus j^i'epared, we proceed in the manner before directed. It is somewhat singular, that on the fii'st notice of Daguerre's pictiu-es, long before the pubKcation of his process, when I learnt that they were on " hard polished tablets," I entei'tained the idea that plates of copper thus silvei-ed were oxidized, and then acted on by iodine. I applied the iodine both in solution and vapour ; but, of course, as the mercury was not used, I failed to effect any perfect pictures. Tt is, however, worthy of remark, that on one occasion, having placed a piece of silvered copper in a trough containing a weak solution of iodine, with some leaves of hemlock superimposed, these being kept close by means of a piece of glass over all the exposed portions, the silver was completely removed, and the copper abraded to a considerable extent, while beneath the leaves the silver was scarcely affected. I thus pi'ocured a very beautiful etching, the figvu-es being in high relief This was freqiiently repeated with success ; but other inquiries having dra"\vn off" my attention, the process has been long neglected, although I am convinced it is capable of being tui-ned to much useful account. In November, 1839, I pursued a series of experiments with bromine, but no very definite advantage was obtained. Some ciu'ious eflTects wliich I noticed at that time are worthy of notice. I copy the remarks made in my memorandum-book at the time. -50 PRACTICE OF PHOTOGRAPHY. 4. Exposed a plate to the vapour of bromine : it assumed a leaden-gray colom-, whicli blackened by light very readily. Ex- posed this to meremy without much improving the effect or altering the lights. Upon immersing this plate in a solution of the miu'iate of soda, the parts imacted on by light became a jet black, whilst the parts on -which light had acted were dissolved off, leaving a clean coating of silver. The effect was most decisive — a black 2yicture on a tvhite ground. 8. Allowed three plates to assume — the first a sti"aw-yellow, the second a steel-blue, and the thu'd a dull blue, and examined theii' sensitiveness ; the plate which had ai-rived at the dvdl blue colour appeared to be the most sensitive. These experiments, which were then pm-sued with a view to produce more permanent pictures — to fix the mercury, or to engrave the plate — were, however, abandoned, and have not yet been resumed, although it is desii-able that some one should tm-n his attention to this point. On one occasion, after having prej^ared a pictui-e according to the process prescribed by Daguerre, T placed it, without remoA-ing the iodine, in a vessel of cldoriue ; the pictvu-e was obliterated, and veiy sjieedily blackened. On exposing' this black plate to light, it almost instantaneously whitened. This is mentioned to show the extent of cui-ious subjects which photography opens out for examination. The apparatus for the daguex-reotype shown in the ^ignette may be enumerated with advantage. a. Is the camera obscuiu, -with the screen upon which the image is seen, and by which the focus is adjiisted, partly raised ; and when this is accui-ately determined a screw is .shown by which it is secured. b. Silver plate and edges for the same. ♦ c c. Are bromide and iodine boxes of walnut, enclosing each a stout porcelain pan : each pan is furnished with an aii*-tight glass cover. On the upper edge of each box is a groove for holding the plate. On withdrawing the glass cover of the iodine pan, the plate is exposed to its action, and the colom- produced is observed by holding a sheet of white paper in such a po.sition that its reflection may be seen on the plate, which enables the operator to judge of the progress of the opemtion. When the plate has obtained the requii-ed coloiir, the glass cover is pushed in, so as to cover the iodine pan, and the cover over the bromine pan is withdrawn. The plate is now removed from the iodine box and jilaced over the liromine box, and the colour observed ;xs before. When the plate has received the jiroper amount of bromine, which is perceptible by the colom*, the cover of the bromine pan is pushed in, and the plate is again placed over the SIMPLIFICATION OF THE DAGUERREOTYPE. 251 iodine pan for a few seconds, until the ultimate colour required is produced, and it is then ready for removal to the camera. d. Improved mercmy box, of walnut, with sliding legs, iron cistern, glass windows for inspecting the development of the picture, mounted with thermometer for ascertaining the tempera- tui'e of the mercury. Are plate holders, with clamp for securing the same. Is a box for holding the daguerreotype plates. A levelling stand, used in the fixing process, see page 245, A flat peculiar dish for washing, see fig. 1, page 13. i. Is a hand-buff". The pictures being completed, they are mounted in morocco or ornamented cases, such as are shown below. e e. /■ 9- h. CHAPTER VII. THE COLLODION PROCESS. With the advance of this beautiful art, there appeal's to be a progressively inci-easing desii-e to produce more artistic results ; and improvements are constantly being introduced. Collodion, as the film upon which to spread the photographic agents, beyond all other preparations, offers, in its exceeding sensibility, beauty of details in the finished pictm-es, and ease of operating, so many decided advantages, that a separate chapter has been devoted to its consideration. Collodion is a jJecvdiar preparation, formed by dissohnng gun- cotton in ether containing a little alcohol. It is a very mucila- ginous solution of a volatile character, the ether evaporating and leaving a film of the utmost transparency behind. It is not all kinds of gun-cotton which dissolve equally well in ether. Ac- cording to my experience the most easily sohible is prepared by soaking good cotton in a satiu'ated solution of nitrate of potash for some time ; it is then, in a moist state, plimged into sulphmic acid with which but a small quantity of nitric acid has been mixed : after remaining in the acid for about a minute, it is well washed with water until no trace of an acid taste is discovered, and then dried at a temjjeratm'e but very slightly elevated above that of the apartment. Mr. Archer, to wliom, with Mr. Fry, we are mainly indebted for the introduction of this preparation as a photographic agent, gives the following as his processes for preparing giui-cotton : — " There are two receipts for making gun-cotton, from either of which a good dissolving cotton may be obtained. Several others have been described, but I should only be confusing the subject to attempt to give the whole ; and it would be foreign to the limited purpose of this woi'k to do so. The results, however, vary so much with the strength and proportion of the acids used, as to render it extremely difficult to name any one in I)articular which would entirely succeed under all cii'cumstances. In all cases it is more easy to prepare a cotton which will explode readily, and yet not be at all sohible, than one wliich will eutii'ely dissolve in rectified sulphmic ether. THE COLLODION PROCESS. 253 Take of cby niti'ate of potash in powder, 40 parts Sulpluu-ic acid 60 ., Cotton 2 „ '•' The niti'e, sulj)hiu'ic acid, and cotton, are weighed in the above proj)ortions, and placed near at hand witliin reach of the operator, to prevent delay in mixing when the operator has commenced. Then poui' the proportion of sulphuric acid into the powdered nitre, stirring them well together for a few seconds with a strong glass rod. Immediately the two are mixed add the cotton, having previously pulled out the fibres, and mix them well together with two glass rods, in order that the whole of the cotton may come in contact with the nitric acid vapour, which is being rapidly generated from the mixtui-e. This action must be continued for about two minutes ; then quickly remove the cotton V-ith the adhering nitre and sulphiunc acid from the basin, "vmh the glass rods, and plunge it into a large quantity of water ; it is to be well washed in repeated changes of water until all the acid and nitre are washed away. The cotton is then collected together, and fii'st pressed between the hands to di-ain off the water, and then still fui-ther di-ied by pressui-e in a cloth ; the fibres of cotton can now be careftJly separated, and h\uig up with pins to the edge of a shelf, or any other convenient place, to diy. There is no necessity to use artificial heat, as the small quantity requisite for a few oimces of solution can easUy be di-ied ^\dthout it. " The next receipt is by cei'tain proportions of nitric and sulphuric acids : — Take 1 oz. by measure of nitric acid, specific gravity 1 "450 1 oz. ,, sulphuric ditto ordinary 80 gx's. by weight of cotton. " The fibres of cotton mvist be well separated, as in the pre- ceding mode. The two acids are first mixed, and the requisite proportion of cotton added as quickly as possible, and well stirred ^\-ith two glass rods for not more than fifteen seconds : the gun-cotton is removed from the acids, and plunged into water to undergo the same wasliings, kc, as in the former receipt. " It will be seen that the cotton is not exposed to the action of the mixed acids, in this last mode, longer than is necessaiy to satui'ate the cotton ; should the action be continued farther, the solubility of the cotton is entirely lost. " Water must not be spared in washing the cotton, for not a trace of acid should be left ; the collodion would be injm'ed by any remaining." 254 PRACTICE OF PHOTOGKAPHT. The substance lignine — which is the time wood of every variety of plant, and has the composition C 38, H 24, 20 — is capable of being converted into a material having an analogous constitu- tion to true gun-cotton. With strong nitiic acid lignine com- bines directly, and forms a substance called xyloidine. This may be prepared by immersing a piece of paper in strong nitric acid, and then washing it well in pure water ; it thus assumes the feel and tougliness of parchment, and is so combustible as to serve for tinder. The composition of xyloidine is expressed by C 12, N 2, H 8, O 18. Starch dissolves by digestion in strong nitric acid, and on adding water xyloidine is precipitated. There are several other materials of which it may be prepared, and nearly all these substances are soluble in ether, forming collodion. Gim cotton is a compound of lignine with nitric acid — 100 parts of cottoD producing 170 parts of gim-cotton. To Prepare the Collodion. — Thii-ty grains of gun-cotton pre- jmred as described should be taken and placed in 1 8 fluid ounces of rectified sulphuric ether, and then 2 oiuices of alcohol should be added ; making thus an imperial pint of the solution. The cotton, if properly made, will dissolve almost entirely ; any small fibres which may be floating about should be allowed to deposit, and the clear solution poured off previously to the process of iodizing it. Mr. Delamotte adds a few droj)s of ammonia to the collodion, which may possibly prevent an acid reaction, which sometimes takes place. To Iodize the Collodion. — Mr. Archer's method is as follows ; and I believe no better course can be piu'sued. Prepare a saturated solution of iodide of potassium in alcohol, say 1 oz., and add to it as much iodide of silver as it will take up. Or to 1 oz. of alcohol add an excess both of iodide of po- tassium and iodide of silver ; after a day or two, and Math re])eated shaking at intervals to facilitate the operation, a saturated solu- tion of the two salts will be obtained, and if this is filtered ofi' into another bottle, it will always be found ready for use. The first bottle can be kept as a stock bottle, to obtain a still further supjjly by replenishing it with alcohol, and adding now and then small additional quantities of the two salts. The iodide of sil- ver can be i*eadily obtained by precipitation. For instance, take 1 oz. of solution of nitrate of silver used in the process, 30 grs. of nitrate of silver to 1 oz. of water, and add to it sufficient of a solution of iodide of potassium in water as will throw down the whole of the nitrate of silver as an iodide. When this precipi- tated iodide of silver has settled, which it very readily does, the liquid al)0ve must be poured off", and fresh water added, repeat- ing this washing several times. The iodide of silver after this THE COLLODION PROCESS. 255 is dried, and tlien put into a bottle T\dth a small quantity of alcohol, just sufficient to keep it moistened. The quantity of the solution of iodide of silver which can be added to 1 oz. of collodion, must depend upon the quantity of alcohol in the col- lodion. Iodized collodion is liable to decomposition, and iodine is liberated. This is prevented by putting a little piece of pure metallic silver in the collodion, which preserves it colourless and of a constant strength. The collodion process now resolves itself into 1st. Cleaning tlie Glass Plate. — One of the most successful general manipulators in the oi-dinary forms of the collodion pro- cess is Mr. Home, to whom I am indebted for much important information on this process. A variety of substances, such as tripoli, nitric acid, spii-its of wine, &c., have been recommended for cleaning the glass : but all these Mr. Home thinks are quite superfluous ; the only articles actually necessary being a clean cloth or two, and a wash leather that has been well and tho- roughly rinsed through several changes of clean water, to deprive it as much as possible of the dressing which a new one contains, and a little liquid ammonia, not strong, but the ordinary liquor ammonice of the shops. If this is not at hand, a little caustic potash or soda will answer as well, the purport of it being to remove any greasy matter attached to the surface, as glass is frequently marked with soap; and although it might appear at first sight that clean water must thoroughly remove this article, the operator will be certain of spoiling many of his pictures if he depend upon water alone. The plan Mr. Home recommends is as follows : — Pour upon the plate a few drops of ammonia, rub it well over both sui'faces, and thoroughly ruise through two waters, allowing the water to flow over the plate either by poui'ing from a vessel or holding under a tap ; now, with a clean cloth wipe perfectly dry, and finally well rab with a leather. Simple as this may appear, there is much more in it than will be at first imagined, for un- less the glass is free from stains it is quite impossible to be suc- cessful. The plate may be washed perfectly clean, but the sur- face not thorou.ghly dried. Then, again, some hands ai'e very warm, and if the plate is allowed to rest too much upon any one part, or held too long in the fingers at any one particidar spot, that will become warmer than the surrounding part, from the glass being a bad conductor of heat. The cloth and leather should therefore be sufliciently large, that the plate may be as it were insulated as much as possible from the hands, that no unnecessary heat shall be applied. At the same time the em- ployment of a warm cloth is very useful, for the heat is then 2oG PRACTICE OF PHOTOGRAPHY. equally diffused over the plate, and, wliat is veiy essential, the surfoce perfectly and quickly dried. Coating the Plate. — It lias ah*eady been pointed out how necessary it is to handle the plate as little as possible in cleaning ; we therefore suppose the operator to have the plate in a clean dry leather, from which it is taken to receive the collodio-iodide of silver. The plate must be held by the left hand j^erfectly hori- zontal, and then with the right a sufficient quantity of iodized collodio 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 opjiosite corner to that by which the plate is held. At this moment the plate should be brought into a vertical position, when the diagonal lines caused by the fluid running to the corner will fall one into the other and give a clear flat siu-face. To do this neatly and effectually, some little practice is necessary, as in most things, but the operator should by no means hurry the operation, but do it systematically and quietly, at the same time not being longer over it than is actually necessary, for collodion being an ethereal compound evaporates very rapidly. Many operators waste theii- collodion by imagining it is necessaiy to perform this operation in great haste; but such is not the case, for an even coating can seldom be obtained if the fluid is poured on and off again too rapidly ; it is better to do it steadily, and submit to a small loss from evaporation. If the collodion becomes too thick, thin it with the addition of a little fresh and good ether. Exciting the Plate. — Previous to the last operation it is neces- sary to have the bath ready, which is made as follows : — Nitrate of silver 30 grains. Distilled water 1 ounce. Dissolve and filter. The quantity of this fluid necessary to be made must depend upon the /br»i of trough to he used, whether horizontal or verti- cal, and also upon the she of plate. The kind used l)y Mr. Home is the vertical, though many still prefer the former, and attach a piece of Indian rubber to the back of the plate as a handle whilst applying the collodion, and to keep the fingers from the solution whilst dip})ing 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. If, however, the glass used is a little larger than is required, this THE COLLODION PROCESS. 257 is not necessary. Having then obtained one or other of these two, and filtered the liquid, previously fi-ee from any particles of diLst, &.C., the plate is to be immersed steadily and without hesitation, for if a pause should be made at any part, a line is sm-e to be formed, which will print in a subsequent part of the process. The plate being immersed in the solution, must be kept there a sufficient time for the liquid to act freely upon the surface, particularly if a negative picture is to be obtained. As a general rule, it loill take about two minutes, hut this loill vary loith the temperature of the air at the time of operating, and the condition of the collodion. In cold weather, or indeed anything below 50° Fahrenlieit, the bath should be placed in a warm situation, or a proj)er decomposition is not obtained under a very long time. Above 60" the plate will be certain to have obtained its maxi- mum of sensibility by two minutes' immersion, but below this temperature it is better to give it a little extra time. To facilitate the action, let the temperatiu-e be what it may, the plate must be hfted out of the liquid two or three times, which also assists in getting rid of the ether fr-om the surface, for without this is thoroughly done a imiform coating cannot be obtained; hut on no account should it he removed imtil tlie plate has heen immersed about half a minute, as marks are apt to be produced if removed sooner. Having obtained the desfred coating, the plate is then ex- tremely sensitive, and, therefore, we presume the opei*ator has taken every precaution to exclude ordinary day-light. The room must be closed against any portion of day-light, and candle alone employed, placed at a distance from the operator to give the requisite Light. Yellow glass, which has been recom- mended for glazing the opei-ating room, does not fru-nish suffi- cient protection from the chemically active rays. The plate thus rendered sensitive must then be Lifted from the solution and held over the trough, that as much liquid as possible may di'ain off previous to its being placed in the fi-ame of the camera, and the more efiectually this is done the better; at the same time it must not be allowed to dry. The qiiestion is often asked, how soon after coating the plate with iodized collodion shoidd it be immersed in the nitrate bath? Now, this is a difficult question to answer. We have said the time of immersion is dependent upon the tempera- ture and quahty of the collodion; so Likewise miist we be governed as to time hefore immersion. To make collodio-iodide or xylo-iodide, for, chemicaUy speaking, there is no difference 258 PRACTICE OF PHOTOGRAPHY. in the two, it is necessary tliat the ether should contain a cei-tain quantity of alcohol, or the tlifiei-ent articles are not soluble : therefore, if we take a fresh bottle, and coat the plate from this, it contains its fidl dose of ether, and with the thermometer ranging between 60° and 70° the evai^oration will be very rajiid, and consequently a tough film soon formed. If, on the other hand, we are using a solution which has been in use some time, and many plates, perhaps, coated, the proportion of alcohol is much greater, and not being of so volatile a nature, it will necessarily take a longer time to acquu^e the requisite firm- ness for immersion. 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 qvdck; but if, on the other hand, we find the film very tender, and upon chying it cracks, then we have reason to know that plates pre- pared from that bottle must not be immersed quite so soon. The larger the proj)ortion of alcohol the more sensitive loill he the ■plates, and the quicker and more even tvill be the action of the bath; but a longer period may be allowed for the sensitive film to harden before immersion. The next question also often asked is, how long must be the exposiu'e in camera? a question more difficult to answer than the last, without knowing something of the character of the lens and the intensity of sunshine. Practice alone can determine, combined with close obsei'vation of those parts which should be the shadows of a picture. If, for instance, in developing we find those pai-ts less exposed to the light than others developing im- mediately the solution is applied, then Ave have reason to suppose the exposm-e has been too long ; but if, on the contrary, they develope very slowly, we have proof the time allowed has not been sufficient to produce the necessary action. In a good pic- ture we should see first the whites of a di-ess appear, then the forehead, after which we shall find, if the light has been j)retty equally diliused, the whole of the face, and then the ch-ess. The following remarks, by the Count de Montizon, are of value — To Iodize CoUodion. — I haA' e tried many methods of iodizing collodion. Those which have given the most successftil results ai'e the following: — 1st. In 1 oz. of collodion put a little iodide of silver and about 3 or 4 gi'ains of iodide of potassium, and then shake it well up. The collodion becomes very turbid, bvit on being left for some hoiu-s it gradually clears up, beginning at the bottom. When it is quite clear, pour off the liquid into another bottle. THE COLLODION PROCESS. 259 2d. To 1 oz. of collodion add 2 grains of iodide of ammonium. This will give very beautiful gradation in the half-tones, but not so vigorous a pictvu-e as the first. 3d. In 8 drachms of pure alcohol dissolve perfectly 8 grains of iodide of ammonium or iodide of potassi\im, and ^ grain of iodide of silver; then add 24 drachms of collodion. The iodide of silver ought to be fi-eshly made, or the resulting negative will be of inferior quality. The iodide of ammonium too ought to be newly made. This collodion is one of the most sensitive, but the half-tones produced by it are inferior. 4th. In 8 drachms of alcohol dissolve 8 grains of iodide of potassium, 4 of iodide of ammonium, and ^ grain of iodide of silver; then add 24 drachms of collodion. This forms a very sensitive medium. 5th. In 2^ oz. of collodion, 5 drachms of alcohol and 5 minims of liquid ammonia, dissolve 14 grains of iodide of ammonium. This forms a very good collodion, very sensitive and colourless. Gth. In 2 drachms of alcohol dissolve 6 grains of iodide of potassium, and add 6 di-achms of collodion. We now come to the Method of Operating. — I employ nothing but water to clean the glass plate with, using plenty of it, and rubbing the glass with the hand till the water flows freely over the surface. It must be well cMed and rubbed clean with a linen cloth which has been well washed without the use of soap. When the col- lodion comes away from the glass, it is almost always in conse- quence of the exi.stence of grease or dirt, or of a little moisture upon the surface. Pour the collodion upon the glass in the usual way, and almost immediately immerse it in the bath of nitrate of silver, 30 grains to the ounce of water, lifting it in and out of the solu- tion to allow the ether to escape. When it assiimes a bluish opal hue, it is ready for use. By adding a little alcohol to the solution, one part of alcohol to ten pai-ts of water, and one part of nitrate of silver, the collodion is more speedily rendered sen- sitive, and the image produced is more vigoroiis. It seems of some importance to immerse the glass in the nitrate bath, and to place it in the slide in the same direction as that in which the collodion was poured off the glass plate. After the appearance of the opal hue, if the bath be an old one, the plate may be left in it for some time without injmy ; but if the bath be new, it must not be left longer than is neces- sary to excite, or the nitrate would attack the iodide of silver. To obviate this, it is well in making a new bath to add 1 grain of iodide of silver to each ounce of the nitrate solution. 260 PRACTICE OF PHOTOGRAPHY. It is unnecessary to filter tlie Imtli, as it is often altered in its nature by passing through paper containing injurious chemical constituents. A little blotting-paper di-a-\\Ti over the sm-face will remove any particles of dust that may be floating upon it. If the' bath contain alcohol, it should, when not in use, be kept in a stoppered bottle. The Development of Image. — To effect this the plate must bo taken again into the room, and with care removed from the slide to the levelling stand. It ■will be well also to caution the operator respecting the re- moval of the plate. Glass, as before observed, is a bad conductor of heat ; therefore, if in taking it out we allow it to rest on the fingers at any one spot too long, tliat portion will be warmed through to the face, and as this is not done luitil the develojiing solution is ready to go over, the action will be more energetic at those parts than at others, and consequently destroy the evenness of the pictiu'e. We should, therefore, handle the plate with care, as if it already possessed too much heat to be com- fortable to the fingers, and that we must therefore get it on the stand as soon as possible. Having then got it there, we must next cover the face with the developing solution. This should be made as follows : — PyrogaUic acid 5 grains. Distilled water 10 oz. Glacial acetic acid .... 40 minims. Dissolve and filter. Mr. Delamotte employs PyrogaUic acid 9 gi'ains. Glacial acetic acid .... 2 diuchms. Distilled water 3 ounces. Now, in developing a plate, the quantity of liquid taken must be in proportion to its size. A plate measuring 5 inches by 4 will 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 perfecthj clean 7)ieasure, and to tills from 8 to 12 drops of a 50 grain solution of nitrate of silver added. Pour this quickly over the surface, taking care not to hold the moasui-e too high, and not to jiour all at one spot, but having taken the measure projicrly in the fingei's, begin at one end, and carry the hand forward ; immediately blow upon the face of the plate, which has the effect not only of diffusing it over the sur- THE COLLODION PROCESS. 261 face, but causes tlie 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 imder the plate, to observe the development of the pictuj.'e ; if the light of the room is adapted for viewing 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 caiTying it too far. As soon as the necessary development has been obtained, the liquor 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 on it, taking care, both in this and a subsequent part of the process, to hold the plate horizontally, and not ver- tically, so as to prevent the coating being torn by the force and weight of the water. Protosulphate of ii'on, which I first introduced as a photogra- phic agent in 1840, may be employed instead of the pyrogallic acid with much advantage. The beautiful collodion portraits obtained by Mr. Tunny of Edinburgh, are all developed by the iron salt. The following are the best proportions : — Protosulphate of ii-on .... 1 oz. Acetic acid 12 minims. Distilled water 1 pint. This is to be iised in the same manner as the former solutions. Fixings of Image. — This is simply the removal of iodine from the sui-face of the plate, and is efiected by pouring over it, after the water, a solution of hyposulphite of soda, made of the strength of 4 oz. to a pint of water. At this point daylight may be admitted into the room; and, indeed, we cannot judge well of its removal without it. "VVe then see, by tilting the plate to and fro, the iodide gradually dissolve away, and the diflerent 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 the hyposulphite of soda, for, should any of the salt be left, it gradually destroys the pictvire. 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 placed upright to dry, or held before a fire. We have now carried the operator careftdly through every stage of the process, from the cleaning of plate to the fixing of 262 PRACTICE OF PHOTOGRAPHY. image • but our remarks have reference to eoUodio-iodide alone ; that is gun-cotton dissolved in ether^ charged with an iodide of silver. We cannot, however, consider our task finished without mentioning the addition of gutta-percha to the collodion. This valuable discovery Avas made by Mr. P. W. Fry, to which gentle- man belongs some of the most important steps made in the art. The sensibility of the j^lates appears to be more materialh' in- creased by the addition of the gutta-percha ; indeed, pictures by superposition may be obtained with absolute instantaneity, and in the camera obscura in less than a second of time. The plan of proceeding to obtain this extreme sensibility, as recommended by Mr. Fry, is to obtain a thick and strongly charged collodio-iodide, and to two parts of this add one of a saturated ethereal solution of gutta-percha, allowing it to stand a day or two to clear itself, jirevious to being used. The plate is then coated in the usual manner. As the ether evaporates a pecvdiar wliite film comes over, at which time it is ready for immersion in the bath. This must be conducted as previously described, and, from its extreme sensibility, with, if possible, greater precaution than before. For the development of negative pictiires, Mr. Fry recom- mends the pyrogallic solution, rather stronger than that pre- viously given, abovit one grain to the ounce, wdth the addition of an extra portion of acetic acid, and the plate re-dii>pe(l in the nitrate bath, in preference to adchng silver solution to the pyro- gallic acid. In fi:xiug the image after development, it is necessar}^ to keep the hyposulphite on longer than with the ordinary collodion, as the iodide is held \vith greater tenacity. In other respects the method of jiroceeding is precisely the same. Mr. Thomas has modified the collodion jn'ocess as follows : — 1st. Topreparethe glass. — Roughen the siirface of the edgeabout one-sixteenth of an inch all round Avith coarse emery jiajjer ; this prevents contraction of the film, and enables 5^ou to pump uj^on it, if necessary, without any fear of coming off. 2d. To clean the glass if new. — Make a mixture of s})irits of wine and liquor ammonia equal parts, render it as thick as cream with tripoli ; with a piece of cotton wool, kept for this purpose, rub a small quantity ovei' that side scratched as described, wash well inider a tap of water, and A\ipe dry with a piece of old linen washed without soap, and kept scru])uloiisly clean f(.)r this puqiose. N".B. To clean a glass aftei- having iised it, when not A'ar- nished, wash off the collodion film A\-ith water, and dry as above. THE COLLODIOX PROCESS. 263 Ahvays ^^-ipe the glass just befoi-e use, and breatlie upon it ; if clean, the moistiu'e evaporates evenly. 3d. Pour into the centre as much collodion as the glass "will hold, and pour off at that comer diagonal to the one by which the glass is held : prevent the formation of lines, by altering quickly the position of the glass before the film dries ; -ndth observation and practice dexterity is easily acquired. 4th. As soon as the collodion ceases to riui, plunge the pre- pared glass, without stopping, into the following bath : — Into a 20-oz. stoppered bottle put Nitrate of silver 1 ounce. Distilled water 16 ounces. Dissolve. Iodide of potassium .... 5 gi'ains. Distilled water 1 clrachm. Dissolve. On mixing these two solutions a precipitate of iodide of silver is formed. Place the bottle containing this mixtivre in a sauce- pan of hot water, keep it on the hob for about twelve hoiu's, shake it occasionally, now and then removing the stopper. The bath is now perfectly saturated with iodide of silver ; when cold, filter thi'ough white filtering paper, and add. Alcohol 2 drachms. Sulphui'ic aether ... 1 di'achm. A convenient way of satiu-ating the nitrate of silver bath with iodide of silver, is to dissolve the 1 oz. of nitrate of sil- ver in 2 oz. of the water, add the solution of iodide of potas- sium to this strong solution; the precipitate thus fonned is by shaking entirely dissolved; now add the remaining 14 oz. of water, when the iodide of silver is again thi-o^vai down, but in such a finely divided state as to render the complete saturation of the bath more perfect, obviating the necessity of frequent shaking. After half an hoiu-, add the alcohol and ether, and filter. 5th. Allow the prepared glass to remain in this bath eight or ten minutes : just before taking it out move it up and down three or four times ; drain it, but not too closely ; when in the frame place upon the back a piece of common blotting-paper to absorb moi.sture ; the sooner it is placed in the camera the better. 6th. The time of exposiu'e can only be ascertained by practice, no lilies can be laid down, and I am unacquainted with any royal road but that of experience, leading to constant success in this most important section of photography. 7th. The plate being taken from the camera and placed upon 264 PRACTICE OF PHOTOGBAPHT. a levelled stand, develope immediately the latent image with the following solution : — Pyrogallic acid 3 gi-ains. Distilled water 1 ounce. Acetic acid (glacial) ... 1 drachm. Mix. Take one part of this solution and two parts of distilled water for use. The pyrogallic solution made with proper acetic acid and of the above strength, may be kept for a month or more in a cool place away from the light. 8th. When the image is sufficiently intense, wash fi-eely with common filtered water; then pour on a saturated solution of hyposulphite of soda, which should immediately remove the iodide of silver, wash again well with water ; allow as miich as the plate will hold to soak in for at least half an hour, to re- move all traces of hyposulphite of soda ; lastly, stand up to tlry, and if required, varnish with amber varnish. 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 photographic means, it is as well, previous to obtaining these, to render the tender film of collodion less liable to injury. This can be accomplished by means of a vaiTiish, of which there are different kinds that may be used. By far the best kind of varnish which can be employed is one for which we are indebted to Dr. Diamond. This is made by powdering some amber and putting it into chloroform ; by the application of a gentle heat tuider pressure, with care, a perfect solution takes place. This varnish flows readily over the plate, and di-ies in a few minutes, leaving a beautifully transparent hard glaze iipon the pictiu-e. It was shown by Mr. Home in the early days of coUodion, that the negative images could be converted into positive ones by mixing with the pyrogallic solution a very small quantity of nitric acid ; but it has since been shoAvn by Mr. Fry, and others, that a better result may be obtained by the use of proto-sulphate and proto-niti-ate of iron. The former salt is readily obtained, and in a very pure form. It should be used as follows : — Proto-sulphate of iron . . . . 10 grains. Distilled water 1 oz. Nitric acid 2 ch'ops. To develope the image pour the above over the plate, taking care not to carry the development too far. THE COLLODION PROCESS. 265 The proto-nitrate may be obtained by double decomposition, as recommended by Dr. Diamond : GOO gi-ains of proto-siilpliate 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 siilphate of baryta are formed by double decomposition ; also by dissolving sulphuret of iron in dilute nitric acid, as recommended by Mr. Ellis, who proceeds as follows : — To one ounce of nitric acid and seven of water, add a small quantity of sulphuret of iron broken into fragments. Place the vessel aside, that the sulphuretted hych-ogen may escape, and the acid become saturated with iron. Pom* off the liquid, and filter. Then boil in a florence flask, to get rid of the sulphm-, and again filter, when a dark green liquid will be obtained, which is the proto-nitrate of iron. This shoidd be kept in well-stopped bottles, and protected from the air as much as possible, to prevent its changing into a pernitrate, in which state it is qviite useless as a photogi-aphic agent. To develope the pictm-e 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 can be obtained. The negative image being developed, a mixtm'e of pyro-gallic and hypo-sulphite of soda, which has undergone partial decom- position, is poured over the plate, and then it is gently warmed. Upon this the darkened parts are rendered brilliantly wliite by the formation of metallic silver. This picture being backed up with black velvet assumes the air of a fijie daguerreotype, without any of the disadvantages arising from the reflection of light from the polished silver surface. For this beautiful result photography is indebted to Dr. Diamond, who is still piu^smng the subject ^vith much zeal. We have also seen similar efiects produced by Mr. Fry and Mr. Berger, by the use of the proto- sidjihate of fron solution and pyi-ogallic acid. The image is fij'st developed by the iron and the solution poiu'ed ofi"; immediately another of pyrogallic acid is poui-ed on, and the efiect is produced. The pictures are fixed with the hyjjosulphite iu the usual method. A peculiar whitening process was introduced by Mr. Archer, which is as follows : — The pictiu'e being thoroughly washed in plenty of water, after fixing with hypo-sulphite of soda, is treated in the follo^ving manner : — Prepare a satm^ated solution of bi-chloride of mercmy in mu- riatic acid. Add one part of this solution to six of water. Poui* a small quantity of it over the picture at one comer, and allow 2QG PRACTICE OF PHOTOGRAPHY. it to iTin evenly over the glass. It will be fouud immediatelv to deepen the tones of the pictiu'e considerably, and the positiA-e image wUl almost disappear ; presently, a peculiar whitening will come over it, and in a short time a beautiftJly delicate white pictui-e will be brought out. The negative character of the drawing wall be entirely de- stroyed, the white positive alone remaining. This picture, after being well washed and dried, can be varnished and preserved as a positive ; but nevertheless, even after this bleaching, it can be changed into a deep-toned negative, many shades darker than it was originally, by immersing it, after a thorough wa.shing, in a weak solution of hyi^o-sulphite of soda, or a weak solution of ammonia. The white picture will vanish, and a black negative will be the residt. It is very singular that the picture can be alternately changed fi'om a white positive to a black negative many times in succes- sion, and very often with improvement. Thus, by the above process, a most perfect white positive or a deep black negative is pi'oduced, quite distinct from each other. In the fii'st part of this after-process, it will be observed that the effect of this bi-chloride of mercmy solution is to deepen the shades of the pictm-e, and this peculiai-ity can be made available to strengthen a faint image, by taking the precaution of using the solution weaker, in order that the first change may be com- pleted before the whitening effect comes on. The progi-ess of the change can be stopped at this point by the simple ajipliciation of water. The author first pointed out the remarkable action of corrosive subUmate, in his paper, published by the Royal Society, on the Daguerreotype process on paper. M. Adolphe Martin has published some remarks on the col- lodion in the Comjytes Rendus of 5th July, 1852. The collodion he employs is made of — 30 grains of cotton. 750 grains of nitrate of potash. 1500 gi-ains of sulphuric acid. This is well washed and dissolved in 10 volumes of ether and 1 volume of alcohol : by this, 15 gi-ains of gun-cotton are di.ssolved in 1860 grains of ether, and 930 grains of alcohol : add then to this coUodion, 15 grains of nitrate of silver transfoiTned into iodide, and dissolved in 20 gi-ains of alcohol by means of an alkaline iodide. ]M. Adolphe Martin prefers iodide of ammonium. The plate is next plunged into a bath of 1 part distilled water, THE COLLODIOX PROCESS. 267 1 xljtli nitrate of silver, and l^^jth nitric acid. The image is developed by proto-sulphate of iron, and he effects tlie change from negative to positive by a bath of double cyanide of silver and potash, consisting of about 2 quarts of water, in "which are dissolved 375 grains of cyanide of potassium, and 60 gi-ains of nitrate of silver. The pictures thus produced are remarkable for theii" intense whiteness. We must allow ]\Ir. Archer to give his own description of the veiy ingeniously constructed camera, which he has devised for the collodion process. The practice of the collodion process in the open air is a matter of some difficidty ; some ingenious cameras have been devised for this purpose; but there are few better conti'ivances than that introduced by Mr. Ai'cher, and modified by Messrs. Griffin & Co. Description of the Camera for the Collodion. — '• I ^vill proceed to give a general description of the camera I have constimcted, premising that it admits of being made as a very Hght folding camei-a, if thought necessaiy. "It is a wooden box, 18 inches long, 12 inches wide, and 12 inches deep, and is capable of taking a ijictvu-e 1 inches square. Externally it may be thvis described : — In front it has a sliding door, with a cii-cidar oj^ening in it, to admit the lens : this sliding door enables the opei'ator to lower, or raise, the lens, and consequently the image formed by it, on the grotmd glass, as the view may require. The two sides of the camera have openings cut in them, into which sleeves of India i-ubber cloth are fixed, to admit the hands of the opei'ator, and are fiuTiished with India rabber bands at the lower ends, which press against the -sv-i'ists, and prevent the admission of light. " 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 at this opening. In the top of the camera, near the front, is inserted a piece of yellow glass, to admit a small quantity of yeUow hght, and is closed with a hinged door, to regulate the quantity of light requii-ed. " The Ulterior of the box is fiu-nished with a sliding frame, to support the ground glass or the bath and the prepared plate ; and it has a stop, by means of which any focus from 3 inches to 15 inches can easdy be obtained. " The bottom of the camei-a is furnished with a gutta percha tray, about 1 inch deep, to hold the washings, &c., when the camera is in operation. " Also, the bottom of the camera at the back has an opening 268 PRACTICE OF PHOTOGRAPHY. cut in it, extending nearly the wliole widtli of tlie camera, and as far in as the edge of the gutta percha ti-ay. " This opening is intended to admit, when the camei-a is in use, a light wooden case containing the glass bath, focusing frame, stock of glass, and paper required in the process. " There are vai-ious other little contrivances which I have not specified ; such as a drawer for the pictui-es, a shelf for bottles, &c. This form of camera will admit of the following manipu- lation : — Having placed it upon a stand pointing to the object to be taken, the huiged door at the back is opened, and the bath is thi-ee parts filled vnth the solution of nitrate of silver ; a plate of glass is then taken from the cell, and cleaned if necessary. "The collodion is poured on in the manner previously de- scribed; when the film has set a little it is immersed in the nitrate of silver bath, and the lid of the bath is closed down upon it. The next steji is to obtain the focus with the grovmd glass : this can be done whilst the collodion is becoming iodized. "After adjusting the sliding frame to the proper focal distance, the camei-a must be closed, and the rest of the process conducted by passing the hands through the sleeves, and placing the eyes close to the aperture in the back of the camera, and drawing the black cloth over the front of the head. '• By the aid of the yellow light admitted from the top, the operator can carry on the rest of the pjrocess. The plate is now ready for the action of light, and is taken from the bath ; or the bath itself, with the plate in it, is placed in the sliding fi-ame The re£i"acted image is at once thi'own upon the sensitive plate. After the requisite exposure, the plate is taken from the bath, and the picture is developed with the solution previously described. The progi-ess of this operation can be seen by aid of the yellow light, keeping the eyes close to the aperture behind. " When, from experience, the picture is sufficiently brought out, a little water is poui-ed on the glass to wash off the deve- loping solution, and the di-awing is partially fixed by the appli- cation of a small quantity of a solution of common salt. " The draAving may now be I'emoved from the eamei'a without fear of being injured by light, and the remainder of the opera- tions can be conducted outside the camera, "If the film is sufficiently strong to bear removal from the glass, the following procedure is adopted : — The plate of gl:i.ss is placed horizontally upon the back lid of the camera, which is hung so as to fonn a temporary table, and the film is loosened from the edge of the glass with a flat strip of glass ; a sheet of THE COLLODION PROCESS. 269 damp paper is then placed flat on tlie di-awiug, and rather within its upper edge ; the film is turned over the edge of the paper, and a glass rod is placed just within the edge. The sheet of paper with the collodion in contact with it is now raised fi-om the glass, and rolled up on the glass rod. When the drawing is entu-ely enclosed in the paper, the rod is removed, and the dehcate film thus encased is put away into its proper receptacle, to be finally fixed and mounted at leisure. ''The drawing thus rolled up can be preseiwed for months without injiuy, pro^dded it is kept slightly damp ; and if each drawing is enclosed in another sheet of paper, its preservation is still fm-ther secured. " The advantages of a camera of this kind may be thus enu- merated. " It allows the preparation on the spot of the most sensitive surfaces ; their immediate use whUst the sensibility is at its maximum ; the ready development of the image, and after fixing. "All these operations being carried on consecutively, the operator can, after the first trial, see what results the progress of his labours is likely to produce. " It gives him the power of shading off any portions of the view during the action of the light, by holding in front of the prepared plate and near the lens a movable screen, or any flat piece of wood, as the case may require ; thereby preventing the too rapid action and consequent solari^ation of the distant por- tions of the scene. The spire of a chiu-ch, for instance, pointing upwards into a bright sky, often requii-es this precaution to prevent its being entii-ely lost. Other instances of this efiect will readily suggest themselves to those at all acquainted with the art. " The camera can be made, with slight modifications, applicable to any other process on paper or glass, and of coui-se obviates the necessity of any kind of portable tent." — Aix-her, F.S., Manual of the Collodion FhotograpMc Process. The following figures represent Mr. Ai-cher's camera, as con- stiiicted and improved by Mr. Griffin : — The figiu-e 67 is a section of the camera, and 68 its external form, which, with a view to portability, is constructed so as to serve as a packing-case for the entire apparatus represented by figs. 67 to 73. a is the sliding door that supports the lens h. c c ai-e the side openings fitted with cloth sleeves to admit the operator's arms, d is a hinged door at the back of the camera, wliich can be supported like a table by the hook e. / is the opening for looking into the camei'a during an operation. This opening is closed, when necessary, by the door g, which can be opened by 270 PRACTICE OF PHOTOGRAPHY. the hand passed into the camera through the sleeves c. The yellow glass window which admits light into the camera during an operation is ujider the door h. i is the sliding frame for holding the focusing glass, or the frame "svitli the jirepared glass, either of which is fastened to the sliding frame by the check Jc. The frame slides along the rod I, I, and can he fixed at the proper focus by means of the step m. n is the gutta percha washing THE COLLODION PROCESS. 271 tray, o is an opening in the bottom of the camera near the door, to admit the well p, and which is closed, when the well is removed, by the door q. The well is divided into two cells, one of which contains the focusing glass, and the other the glass trough, each in a frame adapted to the sliding frame i. On each side of the sliding door that supports the lens a, there is, within the camera, a small hinged table r, supported by a bracket s. These two tables ser\'e to support the bottles that contain the solutions necessary to be apjjlied to the glass plate after its ex- posure to the lens. Figs. 69 and 70 represent two cases, containing the various instiTiments and chemical preparations required for the collodion process, a, fig. 69, is a grooved cell for a series of glass plates. 6 is a receptacle for the lens of the camera, c contains a spirit lamp J d, a paii^ of glass measures; e, a porcelain pestle and mortar. The door /' encloses a space containing a funnel with filter papers, and silks and leather for cleaning the plates, g con- tains a small retort stand, a porcelain capsule, and a box with scales and weights. 272 PRACTICE OF PHOTOGRAPHY. The case, fig. 70, is divided into two compai'tments. One side, a, contains twelve stoppered glass bottles, with the various chemical preparations reqiiii'ed by the operator. The other side, which can be closed by the door h, contains a supply of photo- gi-aphic paper, both for negative and positive pictures. Fig. 71 is the glass trough for holding the nitrate of silver solution. 71. 72. Fig. 72 is a frame for fixing in the camera such plates of glass as do not requii'e to be exposed to the lens while stUl in the glass trough. Fig. 73 is a pressui-e frame for the preparation of positive from negative photographs. Fig. 7i is a section of this frame. Eoth of these frames, figs. 72 and 73, are so contrived as to be sidtable for plates of many different sizes. In the frame represented by fig. 72, the bars a and h are both movable, to permit the fixing of the plate in the camera directly opposite the, centre of the lens. In the frame represented by fig. 73, the bar a alone is movable, and is fastened by screws that move in the slits h, h. The whole of these boxes and frames can be conveniently packed in the camera. The box, fig. QS, is passed in by the side-door ; the well, x>, ^^^ -"^ll the other cases and frames, by the door d; and the camei-a, thus loaded for ti-ansport, is put into a strong leather case. 74. THE COLLODION PROCESS. 273 It has been proposed to use the bromide, instead of iodide of silver, in collodion. The most successful operator with the bromodized collodion appears to have been M. Laborde, who communicated the fol- loAving as the results of his practice to La Luniiere, French photogi'aphic joiu-nal : — " I have studied the action of bromides by themselves and in combination with collodion. My choice naturally fell upon those soluble in alcohol or ether, and I have tried the bromides of ii'on, nickel, cadmium, zinc, and mercury. The bromides of ii-on, nickel, and cadmium yielded the best results, and among these I give the preference to the bromide of cadmium. I have found it to possess so many advantages, that I have been several times tempted to banish all iodides from my preparations. 15 grains of bromide of cadmium, added to 1^ ounce (by weight) of solution of collodion, gives a liquid which may be used at once, and wliich has been kept for about five months, up to the pre- sent time, without perceptible change. Siilphate of iron, or pyrogallic acid, are used for developing ; gallic acid produces but a very middling effect ; almost all the details of the image appear at once, the effect of the weakest radiations becomes sensible; but the extreme tints of the proof are not sufficiently different to allow of being printed from "wdth success. The following pro- cess is made use of to give them an actual value in this respect. " By adding a weak proportion of iodide of potassiiun to the bromide of cadmium the sensibility is increased, and we obtain at the same time a gi-eater difference between the extreme tints of the proof; the negatives are therefore superior. The follow- ing are the proportions usually employed : — Bromide of cadmium . . . . 12 gi-ains. Iodide of potassium . . . . 0'3 grain. Collodion 1^ ounce. " At fii-st the iodide of potassium tinges the collodion -nath yel- lowish-red, but the bromide of cadmium by degi"ees removes this tint, and the solution becomes coloiu'less." Mr. W. Crookes has lately commenced the investigation of these phenomena "vsdth a zeal and acciu'acy from which we may expect some important results. The following commimication, made to the Photographic Society of London, will be read with interest : — " I have for some time past been working with bromized collo- dion, and as, from my experience, it seems likely to become an agent of great value, perhaps the following account of some ex- periments with it may prove of interest to any photogi^apher, s 274 PRACTICE OF PHOTOGRAPHY. who has the time and means at his disposal to investigate the subject more fully in its practical application. "To prepare the collodion I proceed as foUows : — Mix together equal bulks of sulphuric acid, specific gi-avity 1 SO. and nitric acid, specific gravity 1 '50 ; stii' well with a glass-rod. and then. while still wai'm, immerse as many pieces of good Swedish filtering-paper as the vessel wiU conveniently hold. Allow them to remain together for one hoiu- ; then pom* the liquid away, and wash the paper imtil tree from the slightest trace of acid, and allow it to dry in a warm room. " Take S drachms of the purest washed ether and | drachm of spii'its of wine, 60' above proof, and dissolve in this 6 grains of the above-prep-ared paper. This collodion may be bromi^ed in the following manner : — In a small bottle place about 2 grains of crystallized nitrate of silver and about 10 grains of pure bromide of ammonium; pour on this 2 drachms of spirit 60^ above proof, and allow them to remain together for some hours, shaking the mixture several times. One drachm and a half of the supernatant liquid are to be added to every oiince of the pi-eviously prepared collodion. Thiis bromized, it will remain perfectly coloxu-less and good for a long time. '• I excite the plate in a SO-gi-ain silver bath, which has been previously saturated with bromide of silver : aboui two minutes' stay in this bath is generally svifficient, though a little longer time does not injiu^ it. The film of bromide of silver is a pile orange by transmitted and blue by reflected light, and is very transpai"ent. For developing, I prefer protonitrate of iron, being more accustomed to it, but have no doubt that in other hands pvi-ogallic acid would answer equally well. The above pro- portions of paper, alcohol, and bromizing compound may be vai'ied within certain Hmits without much influencing the result. I have given the proportions which I am most in the habit of usiag, but would recommend that the experimentalist should ascei'tain for himself whether a slight depaitvire from the above proportions would give a collodion of the consistency and strength of that with which he is most accustomed to manipulate. " The chief advantages it seems to possess over the ordinary iodized collodion, besides its gi-eat sensitiveness, are the foUow- ing. In a landscape the requii-ed opacity of the more strongly illuminated parts (the sky, for instance) is not lost by over- exposure ; vegetation is also more easily copied. Its superior sensitivene^ to coloured light is, however, most strikingly shown when coloured glass or sulphate of quinine (as suggested by Sir John Herschel) is employed to absorb the strongly acting in- visible rays. To prove this, I airanged several flowei-s and THE COLLODION PROCESS. 275 plants with a view to obtain a great contrast of coloui', light, and shade. The best picture I could obtain of them on iodized collodion was, as I had anticipated, wanting in half-tint, veiy few of the colours prodvicing an adequate impression. When, however, bromized coUodion was u.sed under the same cu^um- stances, but with the interposition of the bath of sulphate of quinine, every part came out with nearly the same gradation and depth of light and shade as existed in natiu'e : this picture on bromized collodion behind the quinine bath requii'ed 40 minutes ; on iodized, without the quinine solution, 4 minutes ; but when I attempted to take a photograph on iodized collodion, with the quinine bath interposed, I found that Avith the light I was working in, the plate woidd not keep a sufficient length of time to enable me to obtain an image. "The advantages of using bromine in the place of iodine, for all objects having a green or yellow colour, have been already pointed out." CHAPTER YIII. THE USE OF ALBU3IEX OX GI^VSS PLATES, &C. Section I. — Albumex ox Glass. Ix the Technologist for 1848, M. Niepce de Saint Victor pub- lished his mode of applying albumen to glass plates. M. Blau- quart Everard followed ; and successively albumen, gelatine, serimi, and other animal substances, have been recommended for application on glass : but few of them have been found to answer so perfectly as albumen appKed according to the direc- tions of M. Le Gray. He recommends that the whites of fresh eggs, equal to about five fluid oimces, be mixed with not more than 100 grams of iodide of potassium, and about twenty gi-ains of the bromide, and half that quantity of common salt. He then du-ects you to beat this mixture in a large dish with a wooden fork, until it forms a thick white fi-oth ; to let it repose all night, and the next day to decant the -viscous Kquid which has deposited, and use it for the preparation of yoiu' glasses. For this purpose take thin glass, oi-, what is much better, ground glass, on which the adherence is more perfect ; cut it the size of your camera frame, and gi'ind the edges. The success of the proof is, in a gi'eat measure, due to the evenness of the coat of albumen. To obtain this, place one of yoiu* glasses horizontally, the TinpoUshed side above (if you use ground glass, which I think prefei*able), and then pom- on it an abundant quantity of the albumen. Take a rule of glass, veiy straight, upon the ends of which have been fastened two bands of stout paper steeped in white wax : hold this with the fingers in such a manner that they ^^^ll overlap the sides of the glass 2:)late about one-eighth of an inch. You then di-aw the rule over the glass -wdth one sweep, so as to take off the excess of albimien. The object of the sHp of paper is to keep the glass rule from the sm-tace of the plate, and insure a thin but even coatiQg of the albuminous mixture. Thus, in making the paper band more or less thick, you vary THE USE OF ALBUHEN OX GLASS PLATES. 277 the tldckness of the coating. Or you may arrive at the same result by pasting t^.vo narrow hands of pajjer on the sides of the plate, and passing simply the iiile do-UTi. I prefer the first mieans, because, with the second, one is almost sure to soil the glass in sticking on the paper. You must never go the second time over the glass with the rule, or you will make aii- bubbles. When thus prepared, per- mit the plate to chy spontaneously, keeping it in a horizontal position and free from dust. "When the coat of albiunen is well dried, submit joxxr glasses to the temperatiu'e of 160° to 180° Fahrenheit ; this you may do either before a quick fire, or by shutting them up in an iron saucepan well tinned, with a cover ; you then jjlace the saucepan in a bath of boihng water ; the action of the heat hardens the albumen ; it becomes perfectly insoluble, and ready to receive the aceto-niti-ate of silver. The glass thus prepai-ed may be kept for any length of time. I prej)are the first coat also by saturating the former mixtiu'e with gallic acid, which gives it more consistency and greater sensitiveness. When you wish to make a proof (by using the preparation moist), you plunge the glass thus prepared in a bath of aceto- nitrate of silver, described in the second operation of the negative paper. This ojDeration is very delicate, because the least stoppage in its immersion in the bath will operate on the sensitive coating, and cause in-egiilarities which nothing can remedy. To obtain this instantaneous and regular immersion, I make a box with glass sides, a trifle larger than the jJate, and about half an inch wide, with wooden gi-ooves, similar to those in the Daguerreotype plate box : into this I poiu* the aceto-nitrate, and let the prepared glass fall into it -ndth a single movement, leaving it to soak foui- or five minutes in the bath ; then remove it, wash well with distiQed water, and expose it in the camera while moist. The time will vary from two to thirty minutes, or nearly double that time if the glass is dry. When you wish to ojDerate "svith the glasses diy instead of moist, it is proper to dip them in a bath of gaUic acid a quarter of an hour after they are taken out of the aceto-nitrate bath ; then well wash them with distilled water, and chy them as directed. When you take the plate out of the camera, you develope the image in the same way as the negative on paper, by putting it into a bath of satui-ated gallic acid : when it is well developed, ti:x it by the same method indicated for the pa^jer. To obtain a positive proof, it is sufficient to apply on the negative proof a sheet of common positive paper, or, better 278 PRACTICE OF PHOTOGRAPHY, still, a slieet of tlie positive albuminized paper, which is pre- viously described. You then put it in the pressure frame, placing above it a piece of black cloth pasted on one side of a thick sheet of glass ; then shut the frame, giving to the proof a slight pressure ; after which, expose it to the light. In order to follow its action you may just raise it by one corner of the glass, to judge of the tint which the image takes : when you think it suffi- ciently exposed, take it out of the frame, and fix it the same as the positive paper. Niepce de Saint Victor has recently published a- process in which he employs starch instead of albvimen on the glass plates. The main featui-es of this process are as follows : — Abo\it 70 gi-ains of starch are rubbed down with the same quantity of distilled water, and then mixed with three or foui' ounces more water ; to this is added 5| grains of iodide of potassium dis- solved in a very small quantity of water, and the whole is boiled until the starch is properly dissolved. With this the glass plates are carefully covered, and then placed to dry on a perfectly horizontal table. When thoroughly cfried, the aceto-nitrate of silver is applied by wetting a piece of paper, placing this on the starch, and over it another piece of paper wetted with distilled water. This mode of preparation fiu-nishes, it is said, tablets of gi-eat sensibility ; but the starch is liable to break off from the glass, and there is much difficulty in spreading it unifoiTuly in the first instance. Section II. — Mr. Malone's Process. Some very ingenious experiments have been made by Mr. Malone, from whose communication the following remai-ks ai-e quoted : — " To the white of an egg its o\ni bulk of water is to be added; the mixtm^e, beaten with a fork, is then strained through a piece of linen cloth, and preserved for use in a glass stoppered bottle ; then a piece of plate glass, cleaned with a solution of caustic potash, or any other alkali, is to be washed with water and dried with a cloth. When the glass is about to be used, breathe on it, and rub its siuface with clean new blotting paper ; then, to remove the dust and fibres which remain, use cotton- wool', or a piece of new linen. Unless this latter, and, indeed, every other precaution, is taken to prevent the presence of dust, the picture will be fuU of spots, produced by a greater absorp- TKE USE OF ALBUMEN ON GLASS PLATES. 279 tion of iodine (in a subsequent process) in those tlian in tlie siUTOimding parts. "On the clear glass pour the albumen, inclining the plate from side to side until it is covered ; allow the excess to run off at one end of the comers, keeping the plate inclined, but nearly Tertical. As soon as the albumen ceases to drop rapidly, breathe on or warm the lower half of the plate ; the warmth and moisture of the breath will soon cause it to part with more of its albimien, which has now become more fluid : of course, care must be taken to warm only the lower half. Wiping the edges constantly hastens the operation. Until this plan was adopted, the coatings were seldom imiform ; the upper half of the plate retained less than the lower. When no more albumen mns down, dry the plate by a lamp, or by a common fire, if the dust that it is inclined to impart be avoided. "The next opei-ation is to iodize the plate. Dilute pure iodine with dry white sand in a mortar, using about equal parts of each ; put this mixtui'e into a square vessel, and place over it the albuminized plate, previously heated to aboiit 100° Fah. As soon as the film has become yellow in colour, resembling beautifully stained glass, remove the plate into a room lighted by a candle, or through any yellow transparent substance, yel- low calico for instance, and plunge it vertically and rapidly into a deep nai-row vessel containing a solution of one humh-ed grains of nitrate of silver to fifty minims of glacial acetic acid, diluted vsdth five otmces of distilled water. Allow it to remain imtil the transparent yellow tint disappears, to be succeeded by a milky-looking film of iodide of silver. Washing with distilled water leaves the plate ready for the camera. " It may be here noted that the plate is heated in iodizing for the purpose of accelerating the absorption of the iodine : an ex- posure to the vapoui- for ten minutes, with a few seconds' im- mersion in the silver solution, has been found to be sufiicient." Hydrochloric acid, chlorine or bromine, may be used with the iodine to give increased sensibility to the plate. The plate is removed from the camera, and we poiu- over it a saturated solution of gallic acid. A negative Calotype image is the residt. At this point previous experimentalists have stopped. We have gone fiu-ther, and find that by pouring upon the surface of the reddish brown negative image, dming its development, a strong solution of nitrate of silver, a remarkable effect is produced. The brown image deejiens in intensity until it becomes black. Another change commences — the image begins to grow lighter ; and finally, by perfectly natural magic, black is converted into white, presenting the curious phenomenon 280 PRACTICE OF PHOTOGRAPHY. of the change of a Talbotype negative into apparently a positive Daguen-eotjiDe, the positive still retaining its negative properties ■when viewed by transmitted light. To iix the picture, a solution of one part of hyposulphite of soda in sixteen parts of -water is poured upon the plate, and left for several minutes, until the iodide of silver has been dissolved. Washing in water completes the process. " The phenomenon of the Daguerreotype," says Mr. Malone, "is in this case produced by very opposite agency, no mercury being present ; metallic silver here producing the lights, while in the DagueiTeotyjie it produces the shadows of the pictiu-e. We at fii'st hesitated about assigning a cause for the dull white granular deposit which forms the image, judging it to be due simply to molecular arrangement. Later experiments, however, have given us continuous films of bright metallic sUver, and we find the dull dej^osit becomes brilliant and metallic when biu-- nished. It should be observed that the positive image we speak of is on glass, sti-ictly analogous to the DagueiTeotyjie. It is positive when viewed at any angle but that which enables it to reflect the Kght of the ray. This is one of its characteristics. It must not be confounded with the continuous fihn image which is seen properly only at one angle ; the angle at which the other ceases to exist. It is also curious to observe the details of the image, absent when the plate is viewed negatively by transmitted light, appear when viewed positively by reflected light." Section III. — M. Martin's Process. Mr. Mayall published a form of process, employed by M. Mar- tin, which difiers in no essential particular from those ah-eady described ; but as invohdng some niceties of manipulation, on which, the wiiter says, depends the pei-fection of his finished pictures, it is thought ad\-isable to quote it. " First. The albumen of a fresh egg must be beaten into a snow-like mass -with a bimch of quills, (^-opping into it ten di-ops of a satm-ated solution of iodide of potassium ; allow it to stand six hom-s in a place free from dust, and moderatelv warm, — say G0°. " Second. A piece of hand-plate glass, eight inches by six, ■with the edges gi'ound smooth, must be cleaned as follows : -with a piece of cotton wool rub over both sides with concenti'ated nitric acid, then rinse well "with water, and dry. Stick a wafer on that side which I wiU now call the back, to mai'k it ; pounce upon THE USE OF ALBUMEN ON GLASS PLATES. 281 the face a moderate quantity of fine tripoli, moistened witli a few di'ops of a concentrated solution of carbonate of potasli ; then witli a piece of cotton wool rub the sui-face briskly in circles for about five minutes ; then with diy tripoli ; then with clean cotton to clear away all the dusty particles. " Thii'd. To the centre of the back stick a gutta percha ball, as a handle : strain the prepared albumen through clean linen ; pour it gently into the centre of the cleaned side of the glass, keep it moving until the surface is entirely covered, run it into the corners, and finally pour ofi" any excess at the four corners ; disengage the gutta percha handle, and place the glass on another slab, that has been levelled by a spiiit level, in a place perfectly free from dust, and moderately warm. I will call this my iodo- alhuminized glass ; it will keep for any length of time, and may be prepared in daylight. " Fourth. To excite (a yellow shaded light only being used), dissolve 50 grains of nitrate of silver in 1 ounce of distilled water and 120 grains of strong acetic acid ; pour the whole of this so- lution into a cuvette, or shallow porcelain dish, a little larger than the glass plate ; place one end of the iodo-albuminized glass in the solution ; with a piece of quill support the upper end of the glass, and let it fall suddenly on to the solution, lifting it up and down for ten seconds ; take it out and place it, face upwards, in another dish, half filled with distilled water ; allow the water to pass over the surface twice ; take out the glass, rear it up to dry ; it is ready for the camera, and will keep in this state ten days, — of course, shut up from daylight, in a moderately Avarm place, but never moist. The solution may be filtered into a black bottle, and will do again by now and then adding a few di'ops of acetic acid, and keeping it in the dark. Expose in the camera from four- to ten minutes, accord- ing to the amount of light and the aperture of the lens. Sup- pose I say a lens of three inches diameter, sixteen in focus for parallel rays, a one inch diaphragm placed three inches in front of the lens (one of Ross's photographic lenses is just the thing), the exposure would be in good light about five minutes. " Fifth. Develope as follows. Place the glass, face upwards, on a stand with adjusting screws to make it level ; pom- a con- centrated solution of gallic acid over the siu'face ; the image will be from half an hour to two houi's in coming out. It is best to apply a gentle heat, not more than 10° above the temperature of the room, it being 60°. Should the image still be feeble, pour off the gallic acid, rinse the proof with water, and pour on to it equal quantities of aceto-nitrate of silver and gallic acid reduced one-half with water. The image will now quickly de- 282 PRACTICE OF PHOTOGRAPHY. velope ; arrest it in four or five minutes, wash, it well in three waters, and fix Math hyposulphite of soda as follows : — " Sixth. Three drachms of hyposulphite of soda to one ounce of water. Allow the proof to remain in this solution until all the yellow iodide disappears, wash it well, rear up to diy, and it is finished. " Success is sui'e to attend any one practising this method, provided the eggs are fresh and the glass is clean : if the glass is not clean, or the eggs are stale, the albimien will spUt ofi" in fixing. " Caution. — Wash aU the vessels, as soon as done with, with nitric acid, and then with water. Every precaution should be used to avoid dust. The albumen of a duck's egg is more sensi- tive than that of a hen's ; and fi-om an experiment of to-day, I am almost certain that of a goose is more sensitive than either." — Atlienoeuvi, No. 1220. Section IY. — Miscellaxeous Modified Processes. Several other preparations have been employed, with variable success, and recommended for procm-ing an absorbent fiJm upon glass plates — amongst others, the senim of milk has been used by M. Blanquart Everard ; others combine with the albumen or gelatine, grape sugar and honey ; the object of these being to qvucken the process, which they appear to do in \Ti'tue of their power of precipitating the metals from their solutions. Blanquart Everard has lately communicated the following to the Paris Academy of Sciences, as an instantaneous process : — " Fluoride of potassium, added to iodide of potassium, in the preparation of the negative proof, produces in.stantaneous images on exposure in the camera. To assure myself of the extreme sensibility of the fluoride, I have made some experiments on the slowest jjreparations employed in photogi^ajihy — that of plates of glass covered with albumen and iodide, requii'ing exposure of at least sixty times longer than the same prepai-ation on paper. On adding the fluoride to the albiunen and iodide, and substi- tuting for the washing of the glass in distilled water after treat- ment with the aceto-nitrate of silver, washing in fluoride of po- tassium the image immediately on exposm-e in the camera ob- scura, I have indeed obtained this residt (but under conditions less powerful in their action) without the addition of the fluoride to the albumen, and by the immei^ion only of the glass plate in a bath of fluoride after its passage through the aceto-niti-ate of silver. This property of the fluorides is calcidated to give Tery valuable results, and will probably cause, in this branch of THE USE OF ALBUMEN ON GLASS PLATES. 283 photographic art, a change equally as radical as that eflFected by the use of bromine on the iodized silver jjlates of DagueiTe." A process published in the authoi-'s Researches on Lvjlit, in 1844, and named the FluorotyiDe, sufficiently establishes my claim to priority in the use of the fluorides. ]Messi-s. Ross and Thompson, of Edinburgh, have been emi- nently successfid operators with the albumen process. Many of theii' pictures, which are of large size, exhibiting more artistic effect than is jjroduced by any other photogi-aphers. Some of the positives jiroduced are very fine. At the meeting of the British Association in that city, these gentlemen exhibited some positive images on glass plates : these were backed iip with plaster of Paris, for the pxirpose of exalting the efiects, which werevexceedingly delicate and beautiful. Messrs. Langenheim, of Philadelphia, have, however, recently introduced into this coimtry specimens, which they tenn Hyalo- tyjjes. These are positive pictiu'es, copied on glass from nega- tives, obtained upon the same material. Their peculiarity is the adaptation of them for magic-lantern sliders. The process by which they are produced is not published, but judging from the effects obtained, the probability is that a very slight variation only from the processes described has been made. The idea is an exceedingly happy one, as by magnifying those images which are of the utmost delicacy and the strictest fidelity, perfect re- flexes of natiire are obtained. There can be no doubt but other means of coating glass with sensitive materials may be employed. Certainly the use of albumen is a ready method, but this medium appears to interfere with the sensibility wliich it is so desirable to obtain. As stated, by xising combinations of iodine and fluorine salts, there is no doubt but the sensibility may be most materially improved, and we find many of the continental photographers using honey and gi'ape sugar with much advantage. I would, however, venture to suggest that films of silver pre- cipitated from the solution of the nitrate by grape sugar, aldehyde, or gun-cotton dissolved in caustic alkali, upon which any change coiild be afterwards produced, appear to promise many important advantages. Section V. — Positive Photographs fbom Etchings on Glass Plates. A very easy method of producing any number of positive photographs from an original design is in the power of eveiy 284 PRACTICE OF PHOTOGRAPHY, one having some slight artistic talent. The merit of having suggested the process I am about to describe has been claimed by Messrs. Havell and Wellmore, and also by Mi-. Talbot ; indeed, there ajjpears no reason to doubt the oi-iginality of either of these gentlemen, Mr. Havell ha\"ing prosecuted his experiment in ignorance of the fact that Mr. Talbot had used the same means to diversify his photographic specimens. Mr. Talbot proposes that a plate of warmed glass be evenly covered "with a common etching gi'oimd, and blackened by the smoke of a candle. The design is then to be made, by carefully removing fi-om the glass all those parts which should represent the lines and shadows, and shading out the middle tints. It will be evident that the light passing through the uncovered parts of the glass, and being obstructed by the covered portions, "wall impress on the white photographic papers a con'ect picture, having the appeai'ance of a spirited ink dra"wing. Ml'. Havell's method was to place a thin plate of glass on the subject to be copied, upon which the high lights were painted ■with a mixtm-e of wliite lead and copal varnish, the proportion of varnish being increased for the darker shading of the picture. The next day Mr. Havell removed, with the point of a pen- knife, the white groimd, to represent the dark etched lines of the original. A sheet of prepared paper having been placed behind the glass, and thvis exposed to light, a tolerable impression was produced ; the half tints had, however, absorbed too much of the violet rays, an imperfection which was remedied by painting the parts over with black on the other side of the glass ; if allowed to remaia too long exposed to the sun's rays, the middle tints became too dark, and destroyed the effect of the sketch. Another method employed by Mr. Havell was to spread a ground composed of white lead, sugar of lead, and copal varnish, over a plate of glass, and having transferred a pencil dra"wing in the usual manner, to work it out with the etching point. Various modifications of these processes have been introduced by different artists, and they evidently admit of many very beautiful applications. When the etching is executed by an engraver, the photogi-a])h has all the finish of a delicate copjDer- jilate engraving. The only thing wliich detracts from this me- thod of photograjDhy is, that the great merit of self-acting power is abandoned. Etchings upon collodion plates are now employed for piinting from ; and several works, to be illustrated in this way, aa-e now in progress for publication in Scotland. CHAPTER IX. ON THE PRODUCTION OF POSITIVE PHOTOGRAPHS BY THE USE OF THE SALTS OF IODINE. A VERY stort time after the publication of Mr. Talbot's processes, "wliicb I anxiously repeated with various modifications, I dis- covered a singular property in the iodide of jDotassium {Jiydrio- date of 2iotasli) of again whitening the paper darkened by ex- posui'e, and also, that the bleaching process was very much accelerated by the influence of light. Early in the year 1839, Lassaigne, Mr. Talbot, Sir John Herschel, and Dr. Eyfe aj^pear to have fallen on the same discovery. As this process, giving by one operation pictures with their lights correct is of much interest, I gave it for a very con- siderable time my undivided attention. The most extraordinary character of these salts is, that a very slight difference in the strength of the solutions, in the comjiosition of the ijhotogi-ajjhic paper, or in the character of the incident light, j^roduces totally opposite effects ; in one case the paper is rapidly whitened, in the other a deep blackness is produced almost as rapidly. Sometimes these opposing actions are in equilibrium, and then the paper continues for a long time perfectly insensible. I am inclined to hope these researches have reduced to cer- tainty their somewhat inconstant effects, and rendered this method of j)roducing photographs one of the most easy, as it is the most bea^^tifld. That the various positions I wish to estab- lish may be completely imderstood, and to insiu'e the same re- sults in other hands, it will be necessary to enter into a somewhat detailed account of the various kinds of paper xised, and to give tolerably full dii-ections for successfully using them, either in the camera, or for drawings by application, — to examine attentively the effects of different organic and inorganic preparations on the paper, and to analyze the influence of the different rays upon it. See also Part L, Chapter YL, Section YII., page %2. 286 PRACTICE OF PHOTOGRAPHY. These particulars will be copied cliiefly from nay paper, "On tlie Use of the Hydi-iodic Salts as Photographic Agents," pub- lished in the London and Edinburgh Fhilosophical Magazine for September and October 184:0, to which will be added the results of my experiments since that time. The variable texture of the finest kinds of paper occasioning irregularities of imbibition, is a constant source of annoyance, deforming the drawings -with dark patches, which are very difficult to remove : consequently my first endeavours were directed to the formation of a sm-face on which the photographic prepara- tions might be spread Avith jjerfect miiformity. A vai'iety of sizes were used with very uncertain results. Nearly all the animal glutens appear to possess a colorific pro- perty, which may render them available in many of the negative processes ; but they all seem to protect the darkened silver from the action of the solutions of the iodides. The gums are acted on by the nitrate of silver, and browned, independent of light, which browning considei'ably mars the efiect of the finished picture. It is a singular fact, that the tragacanth and acacia gums render the pictures produced much less pei-manent. I therefore found it necessary for general practice to abandon the use of all sizes, except such as enter into the composition of the pa]:)er in the manufactiu'e. It occuiTed to me that it might be possible to saturate the paper ■^■ith a metallic solution, which should be of itself enth'ely uninfluenced by light, on which the silver coating might be spread withovit sufiering any material chemical change. The results being curious, and illustrative of some of the pecu- liarities of the pi-ocess, it will be interesting to study a few of them. Sulphate and Muriate of Iron. — These salts, when used in small proportions, appeared to overcome many of the first diffi- culties, but all the drawings on papers thus prepared faded out in the dark. If, after these photographs have faded entu'ely out, they are soaked for a short time in a solution of the ferrocyanate of potash, and then are exposed to the light, the pictiu-e is re- vived, but with reversed lights and shadows. Acetate and Nitrate of Lead. — These salts have been much used by Sir John Ilerschol, both in the negative and positive processes, and, it appears, with considerable success. I found a tolerably good result when I used a saturated solution ; but jiapers thus prepared required a stronger light than other kinds. When I used weaker solutions, the drawings were covered with black patches. On these a little further ex])lanation is requii-ed. When the strong solution has been used, the iodine Avhich has not been expended in forming the iodide of silver — which form ON THE PRODUCTION OF POSITIVE PHOTOGRAPHS. 287 the lights of the picture — goes to form the ioclide of lead. This iodide is soluble in boiHng water, and is easily removed from the paper. When the weaker solution of lead has been used, instead of the formation of an iodide, the hydriodate exerts one of its peculiar fimctions in producing an oxide of the metal. Muriate and Nitrate of Copper. — These salts, in any quantities, render the action of the iodides very quick ; and, when used in moderate proportions, they appeared to promise at first much assistance in quickening the process. I have obtained, with papers into the preparation of which nitrate of copper has entered, perfect camera views in ten minutes ; but experience has proved their inapplicability, the edges of the parts in shadow being destroyed by chemical action. Chlorides of Gold and Platinum act similarly to each other. They remain inactive vintil the pictm-e is formed ; then a rapid oxidation of these metals takes place, and all the bright parts of the pictm-e are darkened. An extensive variety of preparations, metalhc and non-metal- lic, was used with like effects, and I am convinced that the only plan of obtaining a perfectly equal surface, without impairing the sensitiveness of the paper, is careful manipulation with the ordinary muriates and sUver solutions. By attention to the following directions, which are simple in their character, but arrived at by a long series of inquiries, any one may prepare photogTaphic papers on which the bleaching solutions shall act with perfect uniformity. The kind of paper on which the silver is spread is an object of much importance. A paper known to stationers as satin post, double-glazed, bearing the mark of J. Whatman, Tiu-key Mill, is decidedly superior to every other kind I have tried. The dark specks which aboujid in some sorts of paper must be avoided, and the spots made by flies very carefully guarded against. These are of small consequence dimng the darkening process, but when the bleaching wash is applied, they form centres of chemi- cal action, and the bleaching process goes on around them, inde- pendently of light, deforming the drawing with small rings, which are continually extending their diameters. The Solution of Silver. — Take of crystallized nitrate of sUver 120 gi-ains, distilled water 12 fluid di-achms; when the salt is dissolved, add of alcohol 4 fluid drachms, which renders the solution opaque ; after a few hovu-s, a minute quantity of a dark powder, which appears to be an oxide of silver, is deposited, and must be separated by the filter. The addition of the alcohol to the solution was adopted from an observation I made of its in- fluence in retarding the chemical action, which goes on in the 288 PRACTICE OF PHOTOGRAPHY. shade, of the hydrioclates on the salt of silver. Its use is, there- fore, to make the action depend more on lumhious injliieiice, than woidd be the case without it. Nitric Ether. — Sweet spirits of nitre not only checks the bleaching process in the shade, but acts with the iodine salts to exalt the oxidation of the silver, or increase the blackness of it. In copying lace or any fine linear object, it is a veiy valuable agent, but it is useless for any other piu-poses, as all the faintly- lighted parts are of the same tint. Hydrochloric Ether, used as the solvent of the silver, and applied without any saline wash, has a similar property to the nitric ether; but as it is readily acted on by faint light, it is of greater value. However, papers prepared with it must be xised within twenty-four hours, as they quickly lose their sensitive- ness, and soon become nearly useless. To fix with any degree of certainty the strength of the solu- tion of the salts w4iich wdll in all cases produce the best efiects, appears impossible ; every variety of light to which the paper has been exposed to darken, requiiiug a solution of difierent specific gravity. In dai'kening these papers, the directions given at page 83 should be strictly followed. Any of the following preparations may be employed as the bleaching agents. Iodides of Potassium and Sodium. — The former of these salts being more easily procm-cd than any other, is the one generally employed. The streng-th of the solution of these salts best ada^jted for the general kinds of })aper is thii-ty grains to an ounce of water. The following results will exhibit the different energies manifested by these solutions at several strengths, as tried on the same paper by the same light : — 120 grains of the salt to an ounce of water took "I , ^ niinutes to whiten the paper J "^ 100 do. do. to do. 10 do. 80 do. do. to do. 9 do. 60 do. do. to do. 7 do. 40 do. do. to do. 6 do. 30 do. do. to do. 4 do. 20 do. do. to do. 6 do. 10 do. do. to do. 12 do. The other salts correspond nearly \vitli these in their action ; a certain point of dilution being necessary with all. Iodide of Ammonia, il' used on unsized paper, has some ad- OS THE PRODUCTION OF POSITIVE PHOTOGRAPHS. 289 vantage as to quickness over the salts either of potash or of soda. This preparation is, however, so readily decomposed, that the size of the jmper occasions a liberation of iodine, and the conse- quent foi-mation of bro^NTi-spots. Iodide of Iron.— This metallic iodide acts -with rapidity on the darkened paper ; but even in the shade its chemical energy is too gi-eat, destroying the sharpness of outline, and impaii-ing the middle tints of the dra^ving. It also renders the paper very yelloAv. Iodide of Manganese answers remarkably well when it can be procvu-ed absolutely free of iron. When the manganesic solution contains ii'on, even in the smallest quantities, Hght and dark spots are foi-med over the picture, which give it a curious speckled appearance. Iodide of Barium possesses advantages over every other simple iodine solution, both as regards quickness of action and the sharpness of outline. A solution may, however, be made still superior to it, by combining a portion of iron with it. Forty grains of the hydi-iodate of baiyta being dissolved in one ounce of distilled watei', five grains of veiy pvu'e sulphate of iron should be added to it, and allowed to dissolve slowly. Sulphate of baryta is precipitated, which should be separated by filti-ation, when the solution is composed of iodide of barium and iron. By now adcUng a drop or two of diluted sulphiu-ic acid, more baiyta is precij)itated, and a portion of hydi-iodic acid set free. The solution miLst be allowed to stand untU it is clear, and then carefally decanted off from the sediment, as filtering paper de- composes the acid, and free iodine is liberated. By this means we procui'e a photograpliic solution of a very active character. It should be prepared in small quantities, as it suffers decomposi- tion under the influences of the atmosj^here and light. Hydriodic Acid, if used on paper which will not decompose it, acts very readily on the darkened silver. A portion of this acid, free in any of the solutions, most materially quickens the action. From the barytic solution it is always easy to set ii-ee the requii-ed portion, by precipitating the barytes by sid- phm-ic acid. As the iodide of baiium is rarely kept by the retail chemist, it may be useful to give an easy method of preparing the solution of the requii-ed strength. Put into a Florence flask one ounce of iodine, and cover it Avith one fluid oimce and a half of distilled water ; to this add half a di-achm of phosphorus cut into smal pieces ; apply a very gentle heat until they miite, and the liquid becomes coloui'less ; then add another fluid oimce and a half of water. It is now a so- lution of hydi-iodic acid and phosphoric acid. By adding carbon- 290 PRACTICE OF PHOTOGRAPHY. ate of barytes to it, a phosphate of bar^-tes is formed, which, being insoluble, falls to the bottom, whilst the soluble iodide of barium remains dissolved. Make up the quantity of the solu- tions to nine ounces with distilled water, and carefully preserve it in a green glass stoppered bottle. For di"a^\Tngs by application, less care is required than for the camera obscura. With a very soft flat brush apply the solution on both sides of the prepai'ed paper, until it appears equally ab- sorbed; place it in close contact mth the object to be copied, and expose it to sunshine. The exposure should continue until the parts of the paper exposed to unintei'rapted hght, wliich first change to a pale yellow, are seen to brown a little. The obser- vance of this simple rule wUl be found of very great advantage in practice. Immersion for a short time in soft water removes the browTi hue, and renders the bright parts of the picture clearer than they woidd be otherwise. Engravings to be copied by this process — which they are most beautiftdly — shoidd be soaked in water and superimposed on the photograpliic papers, quite wet. If the paper is intended to be used in the camera, it is best to soak it in the bleaching solution until a slight change is apparent, from chemical action on the sUver : it is then to be stretched on a slight frame of wood, which is made to fit the camera, and not allowed to touch in any part but at the edges ; pkced m the dark chamber of the camei"a at the proper focus, and pointed to the object of which a copy is required, which with good svmshine is effected in about twenty minutes, varying of course with the degree of sensibility manifested by the paper. If the wetted paper is placed upon any porous body, it will be found, owing to the capillary com- mmiication established between different points, that the solu- tion is removed from some pai-ts to others, and different states of sensitiveness induced. Another advantage of the frame is, the paper being by the moisture rendered semi-transparent, the light penetrates and acts to a greater depth; thus cuttmg out fine lines which would otherwise be lost. However, if the camera is large, there is an objection to the frame; the solution is apt to gather into drops, and act intensely on small spots, to the injiuy of the general effect. When using a large sheet, the safest course is to spread it out when wetted upon a piece of very clean wet glass, great care being taken that the paper and glass are in close contact. The picture is not formed so quickly when the glass is used, as when the paper is extended on a frame, owing to the evaporation being slightly retarded. The addi- tional time required — about one-sixth longer — is, however, in most cases, of little consequence. ON THE PRODUCTION OF POSITIVE PHOTOGRAPHS. 291 The picture being formed by the influence of sunshine, it is required, to render it imchangeable by any further action of the luminous fliud, not only that the salt of iodine be entirely re- moved from the paper, but that the iodide of silver which is formed be also dissolved out of the drawing. By well washing the di-awing in warm water, the iodide of potassium is removed, and the pictiu-es thus prepared have been stated to be permanent ; and if they are kejjt in a portfolio, and only occasionally exposed, they are really so : for I shall show jjresently, that tuey have the property of being restored in the darh to the state in lohich they loere prior to the destructive action of light. A drawing which I execvited in June, 1839, which has often been exposed for days successively to the action of sunshine, and has altogether been very little cared for, continues to this date (December, 1853) as perfect as at first. These photographs will not, however, bear long-continued exposure without injury — about three months in summer, or six weeks in winter, being sufficient to destroy them. As this gradual decay involves some very ciuious and interesting chemical phenomena, I shall make no excuse for dwelling on the subject a little. The drawing fades first in the dark parts, and as they are per- ceived to lose their definedness, the lights are seen to darken, un- til at last the contrast between light and shadow is very weak. If a dai'k paper is washed with an iodide in solution, and ex- posed to sunshine, it is first bleached, becoming yellow ; then the light again darkens it. If, when quite chy, it is carefiiUy kept fi'om the light, it will be found in a few days to be again restored to its original yellow colour, which may be again darkened by ex|3osure, and the yellow colour be again restored in the dark. The sensitiveness to the influence of light diminishes after each exposiu'e, but I have not been enabled to arrive at the point at which this entirely ceases. If a dai-k paper, bleached by an iodide and light, be again darkened, and then placed in a bottle of water, the yellow is much more quickly restored, and bubbles of gas will escape freely, which will be found to be oxygen. By enclosing pieces of iodized paper in a tube to darken, we discover, as might have been expected, some hych-o- gen is set free. If the paper is then w-ell dried, and carefuUy shut up in a warm dry tube, it remains dark ; moisten the tube or the paper, and the yellowness is speedily restored. Take a photogi-aph thus formed, and place it in a vessel of water: in a few days it will fade out, and bubbles of oxygen will gather around the sides. If the water is examined there will be found no trace of either silver or iodine. Thus it is evident the action has been confined to the paper. 292 PRACTICE OF PHOTOGRAPHY. "We see tliat the iodide of silver has the power of sepai-ating hydi'ogen from its combinations. I cannot regard this singular salt of silver as a definite compound : it appeai-s to me to com- bine Avith iodine in uncertain proportions. In the process of darkening, the liberation of hydrogen is certain; but I have not in any one instance been enabled to detect free iodine : of course it must exist, either in the darkened surface, or in combination with the imafFected under layer : possibly this may be the iodide of sUver, with iocUne in simple mixture, which, when light acts no longer on the preparation, is liberated, combiaes with the hvcfrogen of that portion of moistiu'e which the hygi-ometric nature of the paper is sure to furnish, and as an hydrlodute again attacks the darkened sm-face, restoring thus the iodide of silver. This is strikingly illustrative of the fading of the photogi-aph. The pictm-e is formed of iodide of silver in its light parts, and oxide of silver in its shadows. As the yellow salt dai-kens imder the influence of light, it parts with its iodine, which immediately attacks the dark oxide, and gradually converts it into an iodide. The modus operandi of the restoration which takes j^lace in the dark is not quite so apjjarent. It is possible that the active agent being quiescent, the play of affinities comes tmdistiu-bed into operation; that the dark parts of the picture absorb oxy- gen from the atmosphere, and restore to the lighter portions the iodine it has before robbed them of. A sei-ies of experiments on the iodide of silver in its piu-e state will still more stri kin gly exliibit this very remarkable peculiarity. Precipitate ^\'ith any iodide, silver, from its nitrate in solution, and expose the vessel containing it, li(piid and all, to sunshine ; the exposed surfaces of the iodide "waU blacken : remove the vessel uito the dark, and, after a Jew hours, all the blackness will have disappeared. We may thus continually restore and remove the blackness at pleasure. If we Avash and then well dry the precipitate, it blackens with difficulty, and if kept quite chy it continues dark; but moi.sten it, and the yellow is restored after a little time. In a watch-glass, or any capsule, place a little solution of silver; in another, some solution of any iodine salt; connect the two -with a filament of cotton, and make up an elec- tric circuit with a piece of platina wire : exiwse this little ar- rangement to the light, and it \s-ill be seen, in a very short time, that iodine is liberated in one vessel, and the yeUow iodide of silver formed in the other, which blackens as quickly as it is formed. Place a simikr arrangement in the dark ; iodine is slowly liberatetl. Xo iodide of silver is formed, but around the wire a beautifrd cnstallization of metallic silver. Seal a piece of ON THE PRODUCTION OF POSITIVE PHOTOGRAPHS. 293 platina wire iuto two small glass tubes ; these, when filled, the one with iodide of potassium in solution, and the other with a solution of the nitrate of silver, reverse into two watch-glasses, containing the same solutions ; the glasses being connected with a piece of cotton. An exposu.re during a few hoiu-s to daylight will occasion the solution of the iodine salt in the tube to become qviite brown with liberated iodine : a small portion of the iodide of silver will form along the cotton, and at the end dij^ping in the salt of silver. During the night the liquid will become again coloiu-less 75. and transj)arent, and the dark salt along the cotton will resume its native yellow hue. From this it is evident that absolute permanence will not be given to these photographs until we succeed in removing from the paper all the iodide of silver formed. The hyjiosulphites dissolve iochde of silver ; therefore it might have been expected, a priori, they would have 1 )een successful on these drawings. If they are washed over Avith the hyposu^lphite of soda, and then quickly rinsed in plenty of cold water, the drawing is improved, but no better fixed than with cold water alone. If we persevere in using the hyposulphite, the iodide is darkened by combining with a poi-tion of sulphur, and the lights become of a dingy yellow, which is not at all pleasant. No plan of fixing Avill be foimd more efficacioiis with this variety of photographic drawings, than soaking them for some hours in cold water, and then well washing them in hot water. It often happens that a picture, when taken from the camera, is less distinct than covild be desired : it should not, how^ever, be rejected on that account. All the details exist, although not visible. In many cases the soaking is sufiicient to call them iuto sight ; if they cannot be so evoked, a wash of weak ammonia or muriatic acid seldom fails to bring them up. Care, however, must be taken not to use these preparations too strong, and the pictvire must be washed on the instant, to remove the acid or alkali. One very singular property of these photographs is, that when first prepared, and after the washing, they are not fixed or other- wise; but when exposed to sunshine, they change in their dark parts from a red to a black. Tliis peculiarity will be found by experiment to be entirely dependent on the influence of the red rays, or that portion of the sunbeam which appears to have the greatest heating power : hence regarded as the seat of greatest calorific power. 294 PRACTICE OF PHOTOGRAPHY. I have before mentioned the peculiar state of equilibrium in which the paper is when wetted with the hydriodate, and that a slight difference in the incident light Avill either bleach or blacken the same sheet. If four glasses, or coloured fluids, be prepared, which admit respectively the blue, green, yellow, and red rays, and we place them over a paper washed with some solution of an ioflide having an engraving superposed, it will be bleached under the influence of the blue light, and a perfect picture produced ; while, under the rays transmitted by the green glass, the drawing will be a negative one, the paper having assumed, in the parts which represent the lights, a very defined blackness. The yellow light, if pure, will produce the same efiect, and the red light not only induces a like change, but occasions the dark parts of the engi'a\"ing to be represented in strong lights: this last peculiarity is dependent on the heating rays, and opens a wide field for inquiry. My point now, however, is only to show that the dai'kening of the finished photogi"aph is occasioned by the least refrangible rays of light; whereas its preparation is eflfected by the most refrangible. I know not of any other process which shows, in a way at once so decided and beautiful, the wonderful constitution of every sunbeam which reaches us. Yet this is but one of numerous results of an analogous chai-acter, produced by these opposite powers, necessary to the constitution of that solar beam, which is poiu-ed over the eai-th, and efiects those various changes which give to it diversified beauty, and renders it conducive to the well-l>eing of animated creatures. Before quitting this branch of the art, it will be interesting to examine the modifications which have been introduced by some continental inquirers. M. Lassaigne, who has claimed priority in the use of the iodide of potassium, satiu-ated his paper ■n^ith a sub-chloride of silver, which was allowed to assume a violet-bro^vn colour, and it was then impregnated with the iodidated solution. M. Bayard simply allowed ordinary letter paper, prepared according to Mr. Talbot's method, to blacken by light. He then steeped it for some seconds in a solution of iodide of potassiiim, and laying it on a slate he placed it in the camera. M. Verignon inti-oducod a somewhat more complicated pro- cess. His directions are — White pajier should first be washed with Avater acidulated by hycb-ochloric (muriatic) acid ; then, after being well dried, steeped in the following solution : — Water fourteen parts, with one part of a compound formed of two parts of muriate of ammonia, two parts of bromide of sodium, and one of chloride of strontium. The j^aper dried again is ox THE PRODUCTION OF POSITIVE PHOTOGRAPHS. 295 passed into a very weak solution of niti'ate of silver. There is thus formed, by double decomposition, a chloride and bromide of silver, wliich is made to turn black by exposing the paper to the light for about half an hour. To use this paper, it is steeped in a very weak solution of the iodide of sodium, and placed, quite ■wet, into the camera obscura, at the proper focus. In fine weather, M. Verignon states, the effect is produced in twelve minutes. I have, however, never produ.ced a good picture by this process in less than thirty miniites. A great objection to this mode of preparation is the very rapid deterioration of the paper : every day it will become less and less sensitive to light, and at the end of a fortnight it is useless. The papers recommended for use in the former pages have the advantage of keeping well, provided ordinary care is taken with them. It is necessaiy to exclude them from the light, to keep them very dry, and, as much as possible, they should be pro- tected from the action of the air. I have kept papers, prepared with the muriate of ammonia, baryta, and strontia, for twelve months, and have foimd them but very little impaired. Dr. Schaf haeutl allows paper prepared in the way mentioned at a former page to darken in a bright sun-light. It is then macerated for at least half an hour, in a liquid prepared by mixing one part of the already described acid nitrate of mercury, with nine or ten parts of alcohol. A bi-ight lemon yellow precipitate of basic hyponitrate of the protoxide of quicksilver falls, and the clear liquor is preserved for use. The macerated paper is removed from the alcoholic solution, and quickly di-awn over the surface of diluted miu'iatic acid (one part strong acid to seven or ten of water), then quickly washed in water, and slightly and carefully dried at a heat not exceeding 212° of Fahr. The paper is now ready for being bleached by the rays of the svm ; and in order to fix the drawing, nothing more is required than to steep the paper a few minutes in alcohol, which dissolves the free bichloride of mercury. I must confess, however, that in my hands the process has not been so successful as it is described to have been by the author. It is perhaps necessary to remark, that we cannot multiply designs from an original bleached photogi'aph. The yellow colom- of the paper is of itself fatal to transfers, and independently of this, the wet hydriodic solution would immediately destroy any superposed photograph. We have seen in a former chapter that the white photographic papers are darkened by the blue, indigo, and violet rays. On the dark papers washed with the iodine salts in solution, the bleaching is effected most energetically by the violet rays : it 296 PRACTICE OF PHOTOGRAPHY. proceeds with lessening intensity to the bkie, while all the rays below the yellow have a dai-kening influence on the paper. This effect will be best illustrated by figui'e 76, in which is shown — somewhat exaggerated for the sake of distinctness — the very remarkable action which takes place : clearly establishing the fact first noticed by WoUaston, that the two extremities of the specti'um have different powers. The remarkable manner in which the point of greatest inten- sity is shifted from the blue to the violet, when papers have but a very slight difference in their composition or mode of preparation, is an extremely cimous point of pliilosophical Visible Spectrum. Impressed Spectrum. Violet.. Indigo . Blue.... Green.. Yellow. Orange. Red.... inquiry. It will be evident from what has been said, that it is necessary the focus of the violet rays should be always chosen in using these papers in the camera. CHAPTEK X. GENERAL REMARKS ON THE USE OF THE CAMERA OBSCURA. THE PHOTOGRAPHIC PENTAGRAPH. These remarks will apply with equal force to all the processes by which views of external objects can be obtained; but they have more especial reference to those highly sensitive ones, the Daguen^eotype, the Talbotype, and the Collodion processes. It has already been stated that a single achromatic lens, producing a large image, should be employed for motionless obj ects, where time is not of consequence. For a building, a statvie, or the like, it is not of much consequence whether one minute or ten may be con- siuned in the operation of obtaining its impression, himian figiu-e and animals the case is very different concentration of the solar radiations is therefore required to insure rapidity of action. This is effected by the double combi- nation of lenses, which are visually mounted and adjusted as shown in the above fig- \ire, 77. In fig. 78, the moimting of the single lens arrangement is shown. It is often of the utmost importance, to obtain definition of the objects, that all extraneous rays should be cut off; this is effected by means of a diaphragm of stops, which can be obtained to fit any lens. With this adjustment any sized ajjertiu'e can be obtained. With the the utmost Section I. — Buildings, Statues, Landscapes, and Foliage. The great defect in nearly all the photographic pictures which are obtained is the extreme contrast between the high lights and 298 PRACTICE OF PHOTOGRAPHY. the shadows, and in many an entii-e absence of the middle tones of the picture. In the very beautifid productions of Mr. Buckle, of Peter- borough, which were displayed in the Great Exhibition, there was a veiy remai'kable degree of fine definition, united with a beautiful blending of the respective parts wliich constituted the picture. There was no glaring contrast between the lights. Those parts wliich were the most brilliantly illuminated were softened into the middle tones of the picture, and those again faded gi'adually into the deep shadows. In the works of M. jNIai-tin and M. Flacheron, whose processes I have given, the same har- monizing of lights and shadows was generally foimd to exist. The usual mistake with amateiu's is that of selecting bright sunshine as the period for operating. It is thought, when a cathedral, for example, is brilliantly lighted up by svmshiue. is the time for obtaining a photographic copy of it. A little reflec- tion will convince the operator that this is the case only under j)articular conditions. When the projecting parts of the building are flooded %vith simshine, they cast the deepest possible shadows; consequently, in the photogi-aphic picture the prominent points would appear brilliantly white, and the shadows intensely dark. It will be understood that I refer always to the positive, or completed picture. A clear blue sky, reflecting its light upon a similar stnictiire, pi'oduces less prominent illumination of the bold ornamental parts, and gives more light to those parts on which the shadows are cast. A photograph taken under such conditions of light and shade will be far more beautiful than the spotted productions which oi-dinarily result from the pi-actice of operating when the sun is shining brightly on the object. In the same manner, when the sun shines brightly on the leaves of trees, a very large quantity of light is reflected from their sui-faces, the other parts appearing by contrast in almost absolute shadow. Hence, nearly all photogi-aphic views of foi'est scenery have more the appearance of scenes which have been sprinkled AAdth snow than foliage glowing with sunshine. An artist studies in his productions the most efiective dis- position of the lights and shadows, and it is by the harmonious disposition of these that he succeeds in giving a peculiar charm to his prodi;ctions. Nearly all photographic pictiu-es, although they have the merit of strict truthfulness, appear to want this gi-eat beauty of art. This has mainly arisen from the circumstance that intense illumination has been sought for i;nder the idea of producing the sharpest pietiu'e; and it is true that thus we do PORTRAITS FROM THE LIFE. 299 obtain a very perfect definition of outline. Many productions are remarkable for this, and, indeed, rej^roduce with unnatm-al exactness all the minnte details of the objects copied; whereas the hnman eye never sees this extraordiiiaiy sharpness of out- line in nature ; upon the edges of every object there are fringes of light which soften off their outlines, and subdue the general tone of objects, blending all harmoniously. Perhaps there is more than ordinary difficulty in producing this in a representa- tion of natm-e which is effected by means of a lens. The artist may, however, do much : all times, even of bright illumination, are not fitted for producing a picturesque photogi-aph. Nature should therefore be looked at with an artist's eye, and the happy moment chosen when the arrangements of light and shade give the most pictiu-esque effects, and when these are in a condition to be correctly reijroduced according to the laws by wliich actinic influences are regulated. Section II. — Portraits from the Life. It is important for the production of a correct likeness that as small an apertiu-e as possible should be used. By doing this there is great loss of light, and consequently the necessarily pro- longed time must be compensated for by greatly increased sensibility in the plates. It is also important that arrangements should be made to cut off from the lens all light proceeding from extraneous objects: this is best effected by the modes adopted by M. Claudet. The camera is placed, as shown La section, Fig. 79, within an arrangement of curtains which, as will be seen in the vignette heading to this part, page 175, is capable of adjustment, so as 300 PRACTICE OF PHOTOGRAPHY. to have any required opening in fi-ont of the camera. The whole of this screen being mounted on rollers is easily moved \ there- fore the operator has it in his power to adjust the opening, and to shut off all adventitiuos radiations, thus seciuing the effec- tiveness of the rays proceeding dii'ectly from the sitter, or the object to be copied. The sitter should be placed in the easiest possible position compatible with the arrange- ment of the body as nearly as is possible in a vertical plane. This is necessaiy, as the parts which are nearest the glass suffer a very considerable degree of distortion and enlargement. Of course great steadiness is required on the part of the sitter diu'ing the few seconds he submits to the operation of the photogi-apher. It is usual to support the head by a i*est fastened to the back of the seat, as shown in fig. 80; but where the person can maintain a steady position without tliis, the result is generally the most satisfactory, the "rest " not unfi'equently giving an air of stiffness to the sitter. In a great number of portraits a dark and unnatural shade is thrown under the eyes : this arises from the employment of a "top light." The light falling vertically produces the shadow of the brow over the eye, and gives a sombre character to the face. This is objectionable also, as being annoying to the sitter, who assumes in consequence a somewhat painful expression. Those who have attended to the analyses of the .siiectnim, included in the second division of oiu' subject, have become aware that the radiations from all coloured objects are not alike. A long description would not render this so apparent as a single illustration. The frontispiece represents, therefore, a gi'oup of flowers, incliiding the three primary colours, and a few compoimd tints ; an exact copy of a photograph taken from such a group is placed beneath it, and the result is shown. Hence it is of the utmost importance, particvdarly to ladies, that they should be dii-ected to avoid in their dresses, when about to sit for their portraits, such colours as would produce darks for lights, and the contrary. PHOTOGRAPHIC PEXTAGKAPH. 301 Section III. — Photographic Pentagraph. In a letter to Sir John Herscliel, which was published in the Athenceum, Mr. Stewai-t directed attention to a means by which photographs could be readily enlarged. The plan had been in operation amongst photographic artists for some time, but it was not usually adopted, and Mr. Stewart's letter certainly brought it into general use. The following is Mr. Stewart's description of the required apparatus : — " One of my friends here, Mr. Heilmann, has lighted on an ingenious method of taking from glass negatives positive impres- sions of different dimensions, and with all the delicate minute- ness which the negative may possess. This discovery is likely, I think, to extend the resoiu'ces and the application of photo- graphy, — and with some modifications, which I will explain, to increase the power of reproduction to an almost unliraited amount. The plan is as follows : — The negative to be reproduced is placed in a slider at one end («) of a camera or other bos, constructed to exclude the light throughout. The siu-face pre- pared for the reception of the positive — whether albumen, col- lodion, or paper — is placed in another slider, as usual, at the op- posite extremity (c) of the box, and intermediately between the two extremities (at b) is placed a lens. The negative at a is presented to the light of the sky, care being taken that no rays enter the box but those traversing the partly transparent nega- tive. These rays are received and directed by the lens at b upon the sensitive surface at c, and the impression of the negative is there produced with a rapidity proportioned to the light admit- ted, and the sensibility of the sm-face jiresented. By varying the distances between a and c, and c and b, any dimension re- quired may be given to the positive impression. Thus, from a medium-sized negative, I have obtained negatives foui- times larger than the original, and other impressions re- duced thirty times, capa- ble of figurins: on a watch- glass, brooch, or ring. "a,c. Slides to hold the frames containing the ne- gative and the receiving surface for the positive. '•6. Frame, with the lens. 81. '' e. Dotted lines, indicating the top of the box or frame, '•yjy! Bottom board, or foundation of the same. 302 PRACTICE OF PHOTOGRAPHY. " Undoubtedly one of the most interesting and important ad- vantages gained by this simijle ai-rangement is, the power of varying the dimensions of a picture or portrait. Collodion giving results of almost microscopic minuteness, such negatives bear en- larging considerably without any very perceptible deterioration in that respect. Indeed, as regards portraits, there is a gain in- stead of a loss ; the power of obtaining good and pleasing like- nesses appears to me decidedly increased, the facility of subse- quent enlai'gement permitting them to be taken sufficiently small, at a sufficient distance (and therefore "with greater rapidity and certainty), to avoid all the focal distortion so much com- jilained of j while the due enlargement of a portra.it taken on glass has the effect, moreover, of depriving it of that hai-dness of outline so objectionable in a collodion portrait, giving it more artistic effect, and this without quitting the perfect focal point, as has been suggested. " But there are many other advantages obtained by this process. For copying by engi-aving, tfec, the exact dimension requLred of any pictvu'e may at once be given to be copied from. "A very small photographic ajDpai'atus can thus be employed, when a large one might be inconvenient or impi-acticable, the power of rejDroducing on a larger scale being always in reserve. Independent of this power of varying the size, positives so taken of the same dimension as the negative, reproduce, as will be readily undei-stood, much more completely the finer and more deKcate details of the negatives, than positives taken by any other process that I am acquainted "\\'ith. " The negative also may be reversed in its position at a, so as to produce upon glass a positive to be seen either upon or under the glass. And while the rapidity and facility of printing are the same as in the case of positives taken on paper prepared ^\•ith the iodide of silver, the negatives, those on glass pai-ticulaily, being so easily injm-ed, are much better preserved, all actual con- tact with the positive being avoided. For the same reason, by this process positive impressions can be obtained not only upon "wet paper, kc, but also upon hard inflexible substances, such as jxtrcelain, ivory, glass, »fcc. ; and upon this last, the positives being transpai'ent, ai'e applicable to the stereoscope, magic lantern, ifec. " By adopting the following arrangement, this process may be used largely to increase the power and speed of reproduction with little loss of effect. From a positive thus obtained, .say on collodion, several hundred negatives may be produced either on paper or on albuminized glass. If on the latter, and the dimen- sion of the original negative is preserved, the loss in minuteness PHOTOGRAPHIC PENTAGRAPH. 303 of detail and harmony is almost imperceptible, and even M'lien considerably enlarged, is so trifling as in the majority of cases to prove no objection in comparison with the advantage gained in size, while in not a few cases, as already stated, the pictui-e ac- tually gains by an augmentation of size. Thus, by the simul- taneous action, if necessary, of some hundreds of negatives, many thousand impressions of the same picture may be produced in the coiu'se of a day. " I cannot but think, therefore, that this simple but ingenious discovery will prove a valuable addition to our stock of photo- gTaphic manipulatory processes. It happily turns to account and utilizes one of the chief excellencies of coUocUon — that ex- treme minuteness of detail which, from its excess, becomes almost a defect at times — toning it do^\Ti by increase of size till the hai-shness is much diminished, and landscapes, always more or less un pleasing on collodion fi'om that cause, are rendered some- what less dry and crude. "A very little practice will suffice to show the operator the quality of glass negatives — I mean as to vigour and development — best adapted for reproducing positives by this method. He will also find that a great power of correction is obtained, by which overdone parts in the negative can be reduced and others brought up. Indeed, in consequence of this and other advan- tages, I have little doubt that this process will be very generally adopted in portrait-taking. "Should your old idea of preserving public records in a concen- trated form on microscopic negatives ever be adopted, the imme- diate positive reproduction on an enlarged readable scale, without the possibility of injiuy to the plate, will be of service." CHAPTER XI. THE STEREOSCOPE. Feom tlie interest whicli this veiy interesting optical instru- ment lias excited, and the very intimate relation which exists between it and photography, since it is only practical to produce images suited for the instriunent by the agency of the camera obsciu-a, it is thought advisable to devote a short chapter to some notice of it. It is not intended that any examination of the phenomena of vision, or of the application of the stereoscope to the explanation of single \dsion with a pair of eyes, shall be attempted ; these questions would be somewhat out of place in the present manual, and would occupy too large a space if pro- perly dealt with. The stereoscope is before the world : a simple description, therefore, of the forms under which it may be constructed, and a sufficient explanation of its principles, is all that can here with propriety. find a place. The name is compounded fi'om two Greek words, signifying solid, and / see, and adopted from the fact that two pictiu'es on a plane surface Avlll, when adjusted in the instrument, resolve themselves into one image, and that image will acquire an apparently distinct solidity, being repre- sented as an object having tliree dimensions, — length, breadth, and thickness. "The theory" — of single vision with a pair of eyes — says Mr. Wheatstone, in his valuable Memou- " On some remarkable and hithei-to unobserved Phenomena of Binocular Vision," — " The theory which has obtained the greatest currency is that which assumes that an object is seen single because its pictiu-es fall on corresponding points of the two retinas ; that is, on points which are similarly situated with respect to the two centres, both in distance and position. This theory supposes that the pictures projected on the retinas are exactly similar to each other, corre- sponding points of the two pictures ialling on correspoiuhng points of the two retinjB." Leonardo da Vinci, in liis Treatise on Painting, has some remai-ks on the peculiarity of vision, which bear in a singular manner on the phenomena of the stereoscope. THE STEREOSCOPE. 505 to tlie effect, that a painting, thougli conducted with the greatest art and finish to the last perfection, both with regard to its con- tours, its lights, its shadows, and its colou.rs, can never show a relievo equal to that of natural objects, unless these be viewed at a distance, and with a single eye ; for if an object, as an orange, be \dewed by a single eye, all objects in that sj^ace behind it, wliich we may suppose to be inckided in its shadow, are invisible to that eye ; but open the other eye without moving the head, and a portion of these becomes visible : those only are hid from sight which are included in the space covered by the two shadows formed by two candles siipposed to be placed in the positions of the eyes. The hidden space is so much the shorter according to the smallness of the object, and its proximity to the eyes. Upon this Mr. Wheatstone remarks: — "HadLeonardodaViuci taken, instead of a sphere, a less simple figure for the purpose of his illustrations — a cube for instance — he would not only have per- ceived that the object obsciired from each eye a different jDart of the more distant field of view, but the fact would also have been forced upon his attention, — that the object itself presented a different appearance to each eye." If any of my readers will be at the trouble to look at a simple solid form, keeping the head perfectly steady, with a single eye, and make an outline drawing of the image as seen — say, first with the left eye, and then -with the right eye — it will be foimd that two dissimilar forms will be obtained analogous to those represented in the following diagi-am: — ^\ / By a little effort, it is easy, by squinting, to resolve these two figures into one, when it will be found that an apparently solid image is formed from these dissimilar outliiies of a solid. The stereoscope of Professor Wheatstone is arranged to pro- duce this in a more effective manner. The instrument, fig. 83, consists of two plane mirrors, so adjusted that theii- backs form 30G PRACTICE OF PUOTOGRAPHY. an angle of ninety degrees with each other. Tliese miiTors are fixed by their common edge upon an horizontal board, in such a manner that, iipou biinging it close to the face, each eye sees the image reflected from the two ends of the instrument in a differ- ent mirror ; at each end of the board are panels in which the drawings are placed. The two reflected images coincide at the intersection of the optic axes, and form an image of the same apparent magnitude as each of the component pictures. This in- strument is called the reflecting stereoscope ; and as it will admit of being made of any size, so as to allow of the introduction of large pictures, it offers many advantages. Mr. Wheatstone sug- gested in his memoir, already quoted, the use of an instniment constnicted with pi-isms, which is analogous to the beautiftdly portable lenticular stereoscope of Sir David Brewster, described by him in the Flnlosophical Magazine. This instrument consists of two semi-lenses, ])lactHl at such a distance that each eye views the picture or drawing o])posite to it, through the margin of the semi-lens, or through ])arts of it equidistant from the margin. A lens, a a, being cut in two halves, these are fixed into a frame L and R, and adjusted to siicli distances that the ceutres of the semi-lenses correspond with the pupil of the eyes. The distance of the centre of one pu])il from the other is at an average 2;^ inches, and to this the semi-lenses maybe adjusted; but if the instrument is provided with the means of effecting a little change in this respect, it will often be found to be of considerable advantage. \ THE STEREOSCOPE. 307 " Wheii we thus view," says Sir David Brewster, " two dis- similar drawings of a solid object, as it is seen by each eye separately, we are actually looking through two prisms, which produce a second image of each drawing, and when these second images unite, or coalesce, we see the solid image which they represent. But in order that the two images may coalesce, withoxxt any effort or strain on the part of the eye, it is neces- sary that the distance of the similar parts of the two drawings be equal to twice the separation produced by the prism. For this purpose measiu'e the distance at which the semi-lenses give the most distinct view of the drawings ; and having ascertained, by using one eye, the amount of the refi-action produced at that distance, or the quantity by which 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 qviantity. If this is not correctly done, the eye of the observer will cori'ect the error by making the images coalesce without being sensible that it is making any such effort. When the dissimilar di-awings are thus united, the solid will appear stand- ing, as it were, in relief, between the two plane representations." The lenticular instrument, fitted for use, is shovni in figure 85 ; it consists of a frame of wood or metal ; the two semi-lenses are fixed ia brass tubes, which are capable of being adjusted to ac- 308 PRACTICE OF PHOTOGRAPHY. commodate the differences of sight in different individuals. At the bottom of the box, as seen through the opening, are ph\ced the two stereoscopic pictures, which may consist either of dia- gi-ams, similar to those already represented, or of images taken by the daguerreotype, talbotype, or collodion processes. These I)hotographic processes enable us to obtain such copies of exter- nal natm-e as are required to produce the magical residts with which the stereoscope renders us familiar. It is reqidred to take two pictures of a single object, at such a difference of angle as will produce the solidity which is evident in orcUnaiy binocular vision, as the result of -shewing two dissimilar images, under certain conditions, on a plane surface. The two accompanying figxires represent a bust as viewed by each of the two eyes singly. If the experiment is tried upon a bust or statue, it will be found that one eye will see surfaces which are invisible to the other. Thus in these examples it will be quite apparent, upon examination, that the line of the cheek is moi*e distant from the line of the nose in one than in the other image, and that a similar inequality exists in several other parts. By a little j^ractice, any reader may, by squinting, resolve these two images into one, and thus produce the stereo- scopic effect. Now the object is to place the oimei-a in the position of the eyes, and thus obtain the representation of two images, as viewed by each eye separately. This may be effected with a single camera, by adjusting it at a certain measured dis- tance from the object to be copied, and having obtained one pictm*e, move it rotind about twenty degrees, and take the ■■(be THE STEREOSCOPE. 309 second image, a may represent the object to be copied, b being the distance at which the camera c is placed, which is, say 100 Is feet from the point a ; the pictm-e from this point being taken, the ^^^'^ camera is moved rovmd, '; still preserving the i same distance from the object by means of a cord attached to the camera obsciira, or by measiu'ing the space. 5''' Two cameras with lenses ^''^ of the same focal length may be employed, and are indeed employed, by M. Claud et and others, for the purposes of obtaining stereoscopic portraits, and it is found that with lenses of the same focus, the figui-es are sufficiently exact for all practical purposes, and produce the most perfect stereoscopic pictures. Sir David Brewster con- tends that it is not practicable to obtain sufficient exactness by either of these methods. He therefore proposes the use of a binocular camera, which he thus describes : — "In order to obtain photographic pictures mathematically exact, we must construct a binocidar camera, which will take the pictures simultaneously, and of the same size ; that is, a camera with two lenses of the same apertiu-e and focal length, placed at the same distance as the two eyes. As it is impossible to grind and polish two lenses, whether single or achromatic, of exactly the same focal lengths, even if we had the very same glass for each, I propose to bisect the lenses, and cousti'uct the instru- ment with semi-lenses, which will give us pictures of precisely the same size and definition. These lenses should be placed with their diameters of bisection parallel to one another, and at a distance of 2| inches, which is the average distance of the eyes in man ; and when fixed in a box of sufficient size, will form a binocular camera, which will give us, at the same instant, with the same lights and shadows, and of the same size, such dissimilar pictures of statues, buildings, landscapes, and living objects, as will reproduce them in relief in the stereoscope." RULES FOR TAKING STEREOSCOPIC VIEWS OF LANDSCAPES. If the nearest object be distant 50 feet, arrange the two cameras perfectly horizontally, and parallel to each other, plac- ing them 2 feet apart, measured from the centre of each lens. 310 PRACTICE OF PHOTOGRAPHY. Let tlie distance between tlieni (measured in this "vray), be always dii-ectly proportionate to the distance of the neai'est object, which must be determined by the tape ; thus, when the object is twice the above distance off (100 feet), place the cameras 4 feet apai't; for 150 feet, 6 feet apart, and so on. For trees it does not seem very important that perfect hori- zontaHty of the camei'as should be preserved. If they are an-anged horizontally, it is only possible, in very peculiar situa- tions, to avoid making the foregi'ound disagi-eeably and dispro- portionately large. Mr. Fenton does not keep the cameras parallel in taking landscapes; but, observing Prof Wheatstone's nile, as above, respecting distances, inclines them so that the same object may occupy as nearly as possible the centre of each groiind-glass plate. Extraordinaiy relief of distant objects may be obtained by arranging the cameras with special reference to them. Thus, views taken across the Thames, by placing the camei"as 12 feet apart, produce an astonishing effect. In such views, of coiu-se, no near objects must be admitted. Horizontal jDosition of the camei-as is absolutely necessary when buildings are taken ; otherwise, when viewed in the ste- reoscope 2^lecimens of it produced both in England and France, have naturally felt a >Wsli to practise it themselves. A variety ol new ajijiliaitions of it have been imagintnl, and doubtless many more remain to be discovered. APPEXDIX. 323 I am unable myself to pursue all tliese numerous branclaes of tlie invention in a manner that can even attempt to do justice to them, and moreover, I beKeve it to be no longer necessary, for the art has now taken a firm root both in England and France, and may safely be left to take its natural development. I am as desirous as any one of the lovers of science and art, whose wishes you have kindly undertaken to represent, that our country should continue to take the lead in this newly-discovered branch of the fine arts ; and, after much consideration, I think that the best thing I can do, and the most likely to stimulate to farther improvements in photography, will be to invite the emulation and competition of oiu- artists and amateurs, by re- laxing the patent right which I possess in this invention. I therefore beg to reply to your kind letter by ofiering the patent (with the exception of the single point hereafter mentioned), as a tree present to the public, together with my other patents for improvements in the same art, one of which has been very recently glinted to me, and has still thirteen years unexpired. The exception to which I refer, and which I am desirous of still keeping in the hands of my own licensees, is the application of the invention to taking photographic portraits for sale to the public. This is a bi-anch of the art which must necessarily be in comparatively few hands, because it requires a house to be built or altered on purpose, having an apartment lighted by a skylight, (tc, otherwise the portraits cannot be taken indoors, generally speaking, without great difficidty. With this exception, then, I present my invention to the country, and trust that it may realize our hopes of its future utility. Believe me to remain, my dear Lord Eosse, Your obliged and faithful servant, H. F. TALBOT The Earl of Eosse, Connaught Place, London. 324 APPENDIX. CORRESPONDENCE OF ENGLISH AND FRENCH WEIGHTS AND MEASURES. English "Weights. English Grains. French Grammes. 2 "2055 Pounds Avoirdupois 2-6803 — Troy . - 15438- 1000^ == 1 Kilogramme 1 Pound Avoirdupois 7000- 453-4 1 — Troy . 5760- 373-096 ] Ounce Troy 480- 31-091 1 — Avoirdupois 437-5 28-338 1 Drachm Apothecaries 60- 3-8864 1 — Avoirdupois 27-344 1-7711 1 Imperial grain . 1- 0-065 « 15-438 !• ^1 Gramme 1-5438 0-1 =1 Decigramme •1544 0-01 = 1 Centigramme •0154 0-001= 1 Milligramme English Imperial Mea SUKES. French Litres. 1 Gallon . . 4-5455 1 Pint = 20 fluid ounces . 0-5682 1 Decigallon =16 fluid ounces . . 0-4545 1 Fluid ounce, being the bulk of an ) avoirdupois ounce of water at 62° V 0-2841 Fahr ) 1 Fluid drachm .... 0-0355 1 Septem, being the bulk of 7 grains of water at 62° Fahr. or the tb^jt of ^ 0-000455 a gallon 0-22 Gallon 1-76 Pint y 1-000 2-20 Decigallon 2-2 Septems 15-4 Grains of water at 02° Fahr. 0-001 = 1 Centimetre Cube INDEX. Acetate of lead, photographic use of, 116. Achromaticity, 168. Actinic focus, 137. Actinism, term proposed, 111. Albumen in Talbot's instantaneous process, 31. Albumen processes, 95. on paper, 223. on glass plates, 276. Alcohol extracts, colouring matter of flowers, 62. Alkalies, stimulating effects of, 67. Ammonia-citrate of iron, 53. Ammonia-nitrate of silver, 193. Amphitype, the term, 33. of Sir J. Ilerschel, 59. Apparatus requii-ed, 183. Appendix, 391. Arago on chemical rays, 142. Archer on the collodion process, 252. on whiting collodion image,265. Archer's collodion camera, 268. Asphaltvun used in heliography, 12. Bayard on positive photographs, 295. Becquerel modifies Ponton's process, 7 1 . on rays of spectnun, 133. Becquerel's coloured photographs, 160. Berard on magnetizing power of violet ray, 5. on chemical spectrum, 9. Berres on fixing daguerreotypes, 247. Berzelius on peculiar conditions of salts of gold, 9. — — on precipitates of gold, 55. Bingham on chromatype, 72. ■ on calotj-pe process, 212. Binocular vision, \Mieatstone on, 305. Biot, M., on the calotj-pe, 21. Bitumen of Judea used by Niepce, 12. Bleaching power of iodme salts, 285. Bockman, action of light on phospho- rus, obser\-es, 6. Botanical specimens, to arrange, 185 Brewster on the spectrum, 108. on the stereoscope, 308. Bromide of silver and mercurial vapour, 81. of silver, 1 1 S . of potassium, use of, 119. of iodine, to prepare, 238. Bromine box, 238. Bromidized collodion, 273. Brook's photographic registration, 140. BuflBng daguerreotype plates, 235. Buildings, &c., to copy, 298. Calotype, the, 20. improvements in the, 27. modern improvements in, 206. process on gelatine and albu- men, 222. on wax-paper, 227. Camera obscvira for daguerreotype, 39. varieties of, 186. folding, 191. for collodion, 267. general remarks on, 298. Catalysotjrpe, the, 75. Change on silver salts examined, 116. Cbanning modifies calotype, 213. Charles, M., said to have produced photographs, 5. Chemical spectrum, 110. China clay used in paper, 180. Chloride of silver observed to blacken, 4. of silver, 115. of silver, to form, 194. Chlorine, combination with hydro- gen, 9. Chromatic aberration, 167. Chromatype, the, 71. Chrysotype, the, 54. Claudet and Goddard improve the daguerreotype, 99. 326 IXDEX. Claudet on the daguerreotype. 132. "s mercurial chamber, 243. Collodion process. 252. to prepare. 254. process, to iodize. 254. introduced in photography. 95. Colours destroyed by complementary ray, 65. ' of positire photographs by one process, 84. • . question of producing them natxirally. 15S. , actinic, expl.^ined, I7l. . of plate -when sensitive, 23". Complementaryrays destroy colours 65. Cooper's method of vr.ishing paper, 195. Copper, phted, used by Niepce, 14. CorcJiortis japonica, colouring matter of. 64. Corrosive sublimate, action of on pho- tographs, S7. Cotton, gun. for collodion, 252. Crookes on the use of bromine, 273. Cundell on the calotype, 206. C\-anotype, the, 48. Ds^erre on Niepce's process. 15. , history of his discovery. 34. observer variations in photo- graphic action, 113. improves iodizing process. 242 Daguerreotype, the. 34. -, improvements in. 43. applied to paper, 85. , theory of the. 124. , the improved, 230. simplified, 248. Daw, Sir H., on change in puce-co- loured oxide of lead. 5. , Sir H., on Wedgwoods experi- ments. 7. , Dr.. on change in solution of corrosive sublimate. 8. Delamotte on developing collodion image. 259. Desmortiers on discoloration of Prus- si.an blue, 6. Developing calotvpe picture, 209. — daguerrean image, 243. Diactinic lens explijined. 171. Diamond, Dr., his practice on collo- dion, 264. Dippel. animal oil of. usedby Xiepce, 15. Discoloration of papers, 179. Doxible salts of iron in cyanotype, 53. Draper, Dr., on daguerreot\-pe pro- traits. 96. , Dr.. on radiant images. 152. Draper's experiments with chlorine, 9. experiments on solar spec- tnun, 113. Dynactinometer, the, described, 146. Eggs, white of. photographic use, 225. Energiatype original of ferrotype, 73. Englefield, Sir H., on heating power of solar rays, 5. on phosphorescence. 9. Engraving by M. Xiepce's process, 14. . photographic. 314. Evexard Blanquarts calotvpe, 213. Blanquart's albuminized pa- per. 226. Exciting collodion plate, 256. Experiments on s.xlts of silver, 115. on iodide of silver. 292. Expostire in the camera of calotvpe paper, 209. Ferro-tartrate of silver. 5S. Ferrocyanide of potossium, photo- graphic use of, 79. Ferrotype, the, 73. Fixing the daguerreotype picture, 43. the photographic picture, 19S. the calotype picture. 210. collodion image, 261. Fizeau's bromine water. 237. Fizeau fixes with chloride of gold, 245. Flacheron's calotype process, 215. Flowers, colouring matter of, 61. Fluoride of silver. 120. Fluorot\-pe. the, 80. Focimeter. the. described, 145. Focus of lenses for photography, 137 Forces, antagonistic, in sunbeam. 112. Fresnel on chemical .iction ofravs, 142. Fry on the collodion process, 252. | Fiilminate of silver. 121. I Fyfe, Dr., on phosphate of silver, 121. ' Gallo-nitrate of silver in calotype, 208. Gaudin. M., on d.iguerreotyj^, 134. Gav-Lussac and Thenards investiga- tions of chlorine, 9. Gelatine on paper, 222. Glass plates, cleaning of, 255. . albuminized. 276. Goddard, Wm., first introduces use of bromine, 47. INDEX. 327 Goddard on bromide of iodine, 239. Gold and silver, difference between, according to the alchemists, 4. ■ , employed in chrysotj^^e, 55. , salts of, used as photographic agents, 89. Gray, Le, on fixing photographs, 202. , processes on glass, 276. , lalbumen process on paper, 224. Green glass, use of. 109. Griffin's modification of Archer's camera, 269. Harrup refutes Eumford's experi- ments, 5. Havell's etchings on glass, 284. Heat and chemical action considered, 111. Heating powers of the prismatic rays, 109. Heliochromes of Niepce, 161. Heliograph of Mr. Jordan, 141. Heliography discovered by Niepce, 11. , the process so called, 12. Herschel on fixing photographs, 205. , Sir W., on heating power of solar rays, 5. , Sir J., on the prismatic rays, 108. on the photographic camera, 189. on bromide of silver, 221. Herschel's photographic processes, 48. chrysotype, 54. History of the discoveries in photogra- phy, 3. • of photography, general sum- mary, 100, Horn, silver observed to blacken, 4. Home, Mr., on collodion, 255. Hungarian liquid, 237. Hyalotypes, 283. Hydriodic acid, its bleaching power, 290. Hydrogen and chlorine, 9. Hyposulphite of soda used in washing, 47. of soda, 201. Indices of refraction for chromatic rays, 167. Instantaneous process of Talbot, 31. Instrument, meteorological, registered by photography, 139. Instruments used in daguerreotype, 251. Iodide of iron used by Talbot, 32. of silver, 118. of silver, to form, 197. • of silver, reasons for rejecting it, 221. Iodides, various bleaching powers of, 288. Iodized gelatine paper, 223. Iodizing daguerreotype plate, 37. collodion, 254. Iron, iodide of, used by Dr. Woods , 32. • — sulphate, used by Robert Hunt 32. - , ammonia citrate of, 53. - , protosulphate of, photographic use of, 75. - , syrup of iodide of, used by Dr. Woods, 70. - salts used in collodion, 265. Jordan, Mr., first registers instruments by photography, 139. on iodizing paper, 213. Jugglers of India, statement respect- ing, 4. Knight's dynactinometer, 149. Laborde on bromodized collodion, 273. Landscapes, peculiarity of, on Niepce 's plates, 14. Langenheim's pictures on glass, 283. Lassaigneon positive photographs, 295. Latent light, Moser on, 151. Lavender, oil of, usedby Daguerre, 15. Lemaitre on engraving, 319. Lenses, on, 163. , forms of, 165. Lenticular stereoscope, 308. Light and chemical action considered, 111. , refraction of, 163. Lithographic impressions by photo- graphy, 319. Luminous power of the solar rays, 109. Magnetic power of violet ray, 5. Malone's pictures on porcelain ta- blets, 29. albumen process, 278. Martin, Adolphe, on collodion process, 266. Martin's calotype process, 214. — process on glass plates, 281. 328 INDEX. Materials, fixing, employed, 200. Media, coloured, employed by Melloni, 109. Melloni on separating light and heat, 109. Mercm-ial vapour and bromide of silver, 81. chamber, 243. Mercury applied to daguerreotype, 41. ■ , photographic properties of, 57. Metals impressed with juxtaposed images, 153. Miscellaneous processes, 69. Moigno Abbe on M. Charles' pro- cess, 5. Montizon, Count de, on the collodion process, 258. Morichini on magnetism induced by solar rays, 5. Moser, M., on the formation of the daguerrean images, 151. MuUer's calotype process, 217. Negative photographs, 183. wax-paper, to prepare, 229. Newton, Isaac, Sir, on the spectrum, 108. Niepce and Daguerre, 34. , de St. Victor, applies albumen, 95. , de St. Victor's, coloured photo- graphs 160. Niepce's process of engraving, 318. production of pictures by light, 10. Nitrate of silver, to spread onpaper, 193. of silver, 114. Nomenclatm-e, new, proposed, 171. Operations of preparing daguerreotype plate, 35. Organic salts of silver, 122. Papaverrlieum, colouring matter of, 63. orientale, 65. Paper, Ilerscliel's experiments on, 177. , photogenic, of Fox Talbot, 19. , qualities of, 176. , selection of, 175. , calotype, 206. Pentagraph, photographic, 302. Petit, influence of light on crystal- lization, 4. Philosopher's stone, 4. Phosphate of silver, 120. Photogenic drawings, 18. Photographic lens, conditions of a, 166. processes of Herschel, 48. 57. 177. properties of mercury, pecidiarities of paper, Photographometer of Claudet, 136. , the, described, 143. Photographs, positive, by one process, 82. on glass plates, 92. ■ in natural colours, 159. , positive, by iodine, 285. Photography, practice of, 157. Pictures on porcelain tablets, 28. Plate, daguerreotype, to polish, 235. , to give sensitive surfaceto, 241. Ponton's, Mr., process, 69. Poppy, red, 68. Porcelain tablets, pictures on, 28. Portraits from the life, to take, 300. Portraiture by daguerreotype, 96. Positive photographs from etchings, 283. photographs by one operation. 285. photographs, 183. Potash, bichromate of, 69. Potassium, ferrocyanide of, as a fixing agent, 200. — , bromide of, as a fixing agent, 201. Preparation of gun cotton, 252. Preschot on fixing daguen-eot;ypes, 246. Pressure frames, 185. Processes motlified, 282. Process of daguerreotype, 34. Proto-nitrate of mercuiy used, 57. Prussiate of potash, formation of in cyanotype, 51. Pays, exciting, 133. , continuating, 133. , passage of, through lenses, 165. Reflecting camera obsciira, 99. steresocope, 307. Refractive powers, 164. Registration, photographic, 139. Regnault's calotype process, 219. Reproduction of pictures, spontaneous, 60. Researches, early, on the chemical action of the solar rays, 3. Ritteron the invisible chemical rays, 5. DsTDEX. 329 Eonald's photographic registration, 140. Eoss and Thomson's albmnen pictures, 2 S3. Rules for stereoscopic landscapes, 310. Eumford, Count, on the chemical pro- perties attributed to light, 4. Sage, M. B. G., on change inrealgar, 8. Salt as a fixing agent, 200. Schafhaeutl on positive photographs, 296. Scheele's researches on light, 4. Seebeck experiments on chlorine, 9. produces colour on chloride of silver, 9. Seguier on iodi zin g, 242. Senebier on chemical action of violet rav, 4. Senicio splendens, colouring matter of, 62. photographic use of juice. 6S. Sensibility of daguerreotvpe plate, 133. Sensitive papers, to prepare, 193. coating, to give to a plate, 236. daguerreotype mixtures, 236. Shaw, Mr. G., on daguerreotype, 125. Silver salts on glass plates, 92. , bromide of, 118. , iodide of, 118. Silver-nitrate. 193; Ammonia, nitrate, 194 ; Chloride, 194 : Iodide, 197. Smee on ferrosesquicyanuret of potas- sium, 49. Soda, hyposidphite, 201. Solar agency producing chemical change, 108. Solvent used in heliography, 12. SomerviUe, Mrs., onmagnetizingpower of violet ray, 5. Sparaxis tricolor var, 67. Spectrum, theoretical, 112. divided by Becquerel, 133. bleached by iodine, 297. Stands, levelling, 192. Stereoscope, the, 305. Stewart's calotype process, 218. Studies, photographic, recommendation for, 198. Sublimate, corrosive, as a fixing agent, 205. Sulphocyanate of potash, 52. Sulphuretted hydrogen used to pre- pare paper, S7. Sun-drawing, note on the term, 11. Talbot's, Henry Fox, photogenic draw- ings, 18. description ofthe calotype, 25. instantaneous process, 31. process of photographic en- graving, 314. Theomography, 151. Thomas', Mr., collodion process, 263. Towson, Mr., on portraiture, 96. Transparent bodies, refraction of light by, 167. Tunny, Mr., developes wit"h iron salts, 261. Unsized and sized papers, 179. Valicour's bromide of iodine, 238. Varnished paper for photography, 30. Terignon on positive photographs, 295. Viola odorata, 67. Tiolet ray, magnetic power of, 5. Togel, M., action of light on fat, 8. , Do. on corrosive sublimate, 8. Wax-paper of M. le Grey, 95. process, 227. , to render sensitive, 229. "Wedgwood's method of copying paint- ings on glass, 6. "Wheatstone on the stereoscope, 305. TVoUaston, Dr., on the decomposition of gum-guaiacum, 5. Wood, action of chlorine and iodine on, 90. Wood's, Dr., on catalysotype, 75. Woolcott's American mixture, 240. mirror camera, 99. Yellow glasses, action of, 135. Young, Dr., experiment of, 8. " The greatest and most important literary enterprise of the day." — Cbitic. CABINET EDITION OF THE ENCYCLOPEDIA METROPOLITANA. Thoroughly Eeirised and abundantly lllustratei Publishing in Volumes, each containing a Complete Treatise. CROWN OCTAVO, CLOTH. Volumes novr Ready. Vol. I., price 2s., cloth lettereil, INTRODUCTORY DISSERTATION ON THE SCIENCE OF METHOD. By Samuel Taylor Coleridge. With a Synopsis. Sixth Edition. Vol. II., price 5s., cloth lettered, UNIVERSAL GRAMMAR, or the Pure Science of Language. By Sir Joh.v Stoddart, Knt., LL.D. Third Edition, Revised. " The soundest and njost philosophical treatise of the kind in the English language." — y. Brit' Review. Vol. HI., price 3s., cloth lettered, LOGIC. By the Most Reverend Richard Whately, D.D., Archbishop of Dublin. The Original Edition, with Synopsis and Index by the Editor. Vol. IV., price Ss. 6d., cloth lettered, RHETORIC. By the Most Rev. Richard Whately, D.D., Archbishop of Dublin. The Original Edition, with Synopsis and Index by the Editor. Vol. v., price 6s., cloth lettered, HISTORY OF THE CHRISTIAN CHURCH in the First Century. By the Right Reverend Samuel Hinds, D.D., Bishop of Norwich, and the Rev. J. H. Newman, D.D. Third Edition. •* Erudite research is here combined with independent thoutjht.'* — Scottish Guardian. Vol. VI., price 4s., cloth lettered, POLITICAL ECONOMY. By Nassau William Senior, Esq., late Professor of Political Economy ui the University of Oxford. Third Edition. Vol. VII., price 2s. 6d., cloth lettered, HISTORY OF THE JEWS, from the Time of Alexander the Great to the Destruc- tion of Jerusalem by Titus, a.m. 3595, B.C. 409, to a.d. 70. By the Ven. Arch- deacon Hale, A.M., Master of the Charter House. Fourth Edition. Vol. VIII., price 6s., cloth lettered, SACRED HISTORY AND BIOGRAPHY, from the Antediluvian Period to the Time of the Prophet Malachi. a.m. 1 to am. 3607, B.C. 397. Edited by the Rev. F. A. Cox, D.D., LL.D. •* Pleasing and good, and worthy of general attention." — Vnited Presbyterian Afagazine. Vol. IX., price 7s 6d., cioth lettered, HISTORY OF GREEK LITERATURE. By the Hon. Sir T. N. Talfourd, D.C.L.; the Right Rev. C. J. Blomfield, D.D., Bishop of London; R. Whit- combe, Esq., M.A., Trin. Coll. Carab. ; E. Pococke. Esq.; the Rev. J. B. Ottley, M.A. ; and the Rev. H. Thompson, M.A., St. John's Coll. Camb. *• Full of information, expressed in the choicest lauiimii^e-'^—AChertceum. Vol. X., price 5s., cloth lettered, MORAL AND METAPHYSICAL PHILOSOPHY— ANCIENT PHILOSOPHY. By the Rev. F. D. Maurice, A.M. Third Edition. Re-written. " Complete and satisfactory." — Literary Gazette. Vol. XL, price 5s., 'cloth lettered, INTRODUCTION TO UNIVERSAL HISTORY— On the Uses of History as A Study, and On the Separation of the Early Facts of History from Fable. By Sir John Stoddart, LL.D. Re-wntten. ** We cannot speak too highly in its praise." — Literarif G'tzette. Vol. XII., price 8s. 6i., cloth lettered, ROMAN ANTIQUITIES. By William Ramsay, M.A., Professor of Humanity in the University of Glasgow. Third Edition. With Map, and One hundred and thirty Illustrations. ** Comprises all the results of mod^n improved scholarship within a moderate compass." — AthencBum, Vol. XIII., price 12s. 6d., cloth lettered, BOTANY. By John Hutton Balfour, M.D., F.R.S.E., Professor of Botany in the University of Edinburgh. Second Edition. Numerous Engravings. " Perhaps the most muterly digest of the science which has yet appeared."— IKif/K»«. Cabinet Edition of the Encyclopaedia Metropolitana— Continued. Vol. XIV., price 3s. 6d., cloth lettered, ELECTRO-METALLURGY : Containing an Account of the most improved Methods of depositing Copper, Silver, Gold, and other metals. Second Edition, with nu- merous illustrations. By James Napier, F.C.S. " With this booli at hand, we don't think it possible to fail in obtaining satisfactory KmUs.'* —Art-Journal. Vol. XV., price Os., cloth lettered, HISTORY OF GREECE from the Earliest Times to the Close of the Peloponnesian War. By E. Pococke, Esq. ; Sir T. N. Talfourd, D.C.L. ; Rev. J. B. Ottley, A.M. ; and the late J. T. Rutt, Esq. With upwards of One Hundred Engrav- ings, from the most authentic sources. ** Altogether a gem." — Glasgow Ci-tizen, Vol. XVI., price 6s., cloth lettered, PHOTOGRAPHY. By Robert Hunt, Esq., Professor of Physical Science in tha Museum of Practical Geology, London. Fourth Edition. Engravings. " Must prove of infloite service to those engaged in the pursuit of this entertaining science."—.! rt-Journah Vol. XVII., price 3s., cloth lettered, VETERINARY ART : A Practical Treatise on the Diseases of the Horse. By W. C. Spooner, Esq., with Fifty Engravings. Vol. X\ail., price 8s., cloth lettered, i EARLY ORIENTAL HISTORY, comprising the Historyof the Egyptians, Assyrians, M Phoenicians, Persians, &c. By Rev. Professor Eadie, D.D., LL.D. With au- " merous illustrations. " In all respects a thoroughly good book." — Dr. Eitto. Vol. XIX., price 8s. 6d., cloth lettered, HISTORY OF THE ROMAN REPUBLIC. Bv the Rev. Thos. Arnold, D.D., late Head-Master, Rugby School; Sir Thos. N. Talfourd, D.C.L. ; the Rev. Professor Jerejiie, and others. With numerous illustrations. Vol. XX., price 7s. 6d., cloth lettered, BIBLICAL ANTIQUITIES AND GEOGRAPHY, includinsr the Language, Geo- graphy, and Early History of Palestine. Edited by the Rev. F. A. Cox, D.D., LL.D. With Jlaps and numerous illustrations. " The.most readable book on the subject in our l&n^\xage.*'~BaptUt Magazine. Vol. XXL, price 12s. 6d., cloth lettered, METALLURGY. A Practical Treatise on the Chemistry of the Metals. By John Arthur Phillips, Esq., F.C.S. Second Edition. 2U0 Engravings. " A sine qua non to every metallurgist."— .VintH^ Journal- Vol. XXII., price 4s., cloth lettered, HISTORY OF THE CHRISTIAN CHURCH in the Second and Third Centuries. By Jas. Amiraux Jeremie, D.D., Regius Professor of Divinity, Cambridge. " It is an admirable Text-book." — Evangelical Magazine. Vol. XXIII., price Ss., cloth lettered, HISTORY OF GREECE AND MACEDONIA, from the Age of Xenophon to the Absorption of Greece in the Roman Empire, including the History of Alexander the Great and his Successors. By Dr. Lyall, Dean of Canterbury; Rev. G. C. Renouard, B.D. ; &c., &c. With numerous illustrations. *' The dissertations are full, luminous, and charmingly written." — Eclectic lieidew. Vol. XXIV., price 10s. 6d., cloth lettered, HISTORY OF ROMAN LITERATURE. By Rev. Tiios. Arnold, D.D., late Head-Master, Rugby School ; Rev Henry Thomson, M. A. ; Rev. Dr. Newman ; Rev. J. B. Ottley, M. A. ; and Rev. J. M. Neale, Warden of SackviUe College. Vol. XXV., price 10s. 6d., cloth lettered, HISTORY OF THE ROMAN EMPIRE. By the Rev. Tiios. Arnold, D.D., late Head-Master, Rugby Sciiool. AVith numerous illustrations. Vol. XXVI., price 12s. 6d., cloth lettered, HISTORY OF THE DECLINE AND FALL OP THE ROMAN POWER. By the Right Rev. Bishop Russel, &c. With numerous illustrations. Vol. XXVI I., price 6s., cloth lettered, HISTORY OF GREEK AND ROMAN PHILOSOPHY AND SCIENCE. By the Right Rev. Charles Blomfield, D.D., Bishop of Londou;j Rev. Dr. Whewell ; and other Contributors. Vol. XXVIII., price Ss. 6d., cloth lettered, MORAL AND METAPHYSICAL PHILOSOPHY— THE FIRST SIX CEN- TURIES. Bv the Rev. F. D. Maurice, A.M. MAY, 1854. CATALOGUE PHOTOGEAPHIC APPARATUS SOLD BY JOHN JOSEPH GRIFFIN, F.CS., CHKMIST, MINEKALOGIST, AND OPTICIAN, 10, FINSBURY SQUARE, LONDON. AND BY EICHAED GEirriN AND COMPANY, GLASGOW. Mr. J. J. Griffin begs to call tlie attention of Amateurs, and Photographers in general, to the following Revised Catalogue of Apparatus and Chemicals used in the art of Photography. They will find that numeroiis additions have been made to his already extensive collection, and that all the Articles are quoted at prices extremely moderate for highly-efficient instruments. Mr. J. J. G. has just had an Operating-room fitted up at the Chemical Museum, 10, Finsbury Square, where personal instructions in the various processes will be given gratuitously to purchasers of Apparatus. ( )rders from abroad, which should be accompanied by an order for payment in London, executed with care and despatch. MEKOHAiiTs, Agents, and the Profession Supplied on Liberal Teems. THE ATTENTION OF THE READER IS RESPECTFULLY DIRECTED TO THE FOLLOWING PARTICULARS :— The cameras No. 25, 28, 31, 33, 34, 36, 38, 44, 45, 47, 48, are intended for taking views, ,1 landscapes, copying pictures and other inanimate objects, the lens with which each ia t fitted being mounted, so that a pwrtion of the external rays is cut off by a stop placed in I front of the lens. This corrects the aberration of the rays of light passing through those ' parts of the lens nearest the edge. This stop gives a degree of sharpness to the pictures which cannot be produced by the double combination of lenses, and hence its general adoption for taking inanimate objects. For jwrtraits taken from life, however, where rapidity of action is a great desideratum, the single lens is nearly useless ; as the amount of light admitted by the stop is so limited that a long time is required to take a portrait, and it is difficult to keep a sitter in the same position for the necessary period. Con^e■ quentlv, if a camera for portraits is required, it is necessary to select it from Xos. 19, 21 . 23, 26," 29, 32, 33, 35, 37, 42, 46, 49, 50, 53, or 56 ; or if a camera for both portraits ai, ; views is required, then the choice must be made from Xos. 26, 29, 32, 33, 35, 37, 46, 4'.'. 50, 53, or 56 ; but in the latter case, the double combination of lenses must be altered ff r views as follows : — The posterior cell, or that nearest the ground giass-ijlate of the camera containing two lenses, must be removed from the mounting, and the anterior cell must l^e unscrewed from the mounting, and have the lens taken out of its cell and reversed. ^• ■ that its plane side shall be placed nearest the object that is to be copied. A tube cf'i-- taining a diaphragm with three stops, No. 66, must now be put over the mounting in the same position as that occupied by the brass cap of the double combination, and one of the stops must be brought into action. The use of the diaphragm is easily understood from inspection ; but which of the three stops is best adapted for an object intended to be taken, is more difficult to determine. It may be given as a general rule that the smallest stop is to be used for pictures to be taken from objects in sunshine ; the next during sun- shine, if the object is in the shade ; and the largest, when the Light is limited. When, for the above or any other purpose, the lenses have been removed from the'r cells, it is essential that they be replaced in their original position, and that the sides : not reversed. As a guide, we may mention that, in the double combination of lenst.-. Nos. 63, 64, 6.5, 67, 68, 69, 70, 71, 72, the least convex side of the posterior lens (or that which passes into the camera), the concave side of the second lens, and the plane side of the anterior lens, must be all turned towards the ground glass-plate of the camera, as must also the convex side of the single achromatic Lens, Nos. 59, 60, 61, 62, 73, 73 a, 74, 75, 76, 77. The camera and lenses of the sets of apparatus for the calotype and waxed paper pro- cesses, Nos. 1 to 5, and Nos. 9 to 14, are also adapted for taking pictures on silver, but for that purpose the articles entimerated after the description of the camera in the s€t No. 15 would be required. The same remark applies to the daguerreotype sets, Nos. 15, 16, and 17, which can be used for the calotj-pe and collodion processes, when the articles enu- merated after the camera in the waxed paper set No. 1, or the collodion set No. 6, cire added. It frequently happens that amateurs do not succeed in immediately producing Photo- graphic Pictures equal to those obtained by experienced artists. In such cases, the fault is sometimes hastily and erroneously charged to the lenses. To prevent complaints on this head, a Collodion picture, produced by each set of lenses, wall be supplied with it (without extra charge), to show the purchaser what the lenses can effect, and insure him against the receipt of lenses not proi)erly adjusted. The attention of gentlemen residing in India, or accustomed to travel much, is directed to the note affixed to article 32, in regard to brass-bound cameras. Those who desire to possess lenses of the very first quality, will find information at page 12. In cases where the whole of the apparatus is wished of the l>est quality, it should be so stated in the order ; which should also state the quantity of additional materials required, such as paper, glass plates, silver plates, chemicals, passe partouts, morocco cases, &c. Packing charged extra. SETS OF APPARATUS FOR THE WAXED PAPER PROCESS. 1. Complete Set of Apparatus for the Waxed Paper Process, consisting of an improved sliding camera (No. 24) of Frencli- polished mahogany or walmit, witli two openings to ada])t it to lenses of different foci, two double paper slides, one slide -with tlu-ee frames for the collodion or daguerreotype process, and a shifting front for regulating the proportion of foregro\ind and sky, fitted Avith double combination of achromatic lenses, in brass mount, with rack and pinion adjustment (No. G3), takmg portraits 3;^ inches by 41 inches, and views 7 inches by 6 inches ; three shallow porcelain dishes for preparmg the sensitive paper and fixing the proofs ; two camels'-hair brashes ; one quii-e Canson's photographic paper; one quire bibulous paper; pressui-e frame for producing positive pictiu-es ; balance, with a set of weights and two glass capsules to contain the substances to be weighed ; two pair of horn forceps to use whilst preparing the sensitive paper; a graduated glass measure, and the following chemicals, &c., in stoppered bottles : nitrate of silver, iodide of potassium, acetic acid, gallic acid, hyposidphite of soda, fluoride of potassium, cyanide of potas- sium, chloride of gold, pure animal charcoal, sugar of milk, and white wax; the whole packed in a portable case for travelling, with lock, key, and handles, XI 0, 10s. Tfie camera of this set is eqiialhj suitable for processes unth paper, glass, or silver. 2. A SIMILAR Set of Apparatus, but with Camera of larger size (No. 27), fitted with single achromatic lens in brass mount, with rack and pinion adjustment, for Views 8 inches by 7 inches, £13, 13s. 3. The above, mounted with double combination of achromatic lenses, taking Portraits 4f inches by G^ iuches, and Views 8 iuches by 7 inches, £15. 4. A similar Set of Apparatus, but with Camera (No. 31), and fitted with single achromatic lens in brass mount, for Views 10 inches by 8 inches, £18. 5. The above, mounted with double combination of achromatic lenses, taking Portraits 6i inches by 8^ inches, and Views 10 inches by 8 inches, £22, 14s. 6d. If desired, Folding Cameras can be substituted for the Sliding Cameras in the preceding sets. For increased prices compare Ifos. 26, 28, and 31, with tlie corresponding Cameras, Nos. 44, 47, and 56. SETS OF APPARATUS FOR THE CALOTYPE PROCESS. These sets ai^e exactly similar in price, size, and oontents, to tlie waxed paper sets Nos. 1 to 5, with the exception, that bromide of potassium and an additional quantity of Turner's photographic paper are substituted for the wax, sugar of milk, animal charcoal, and fluoride of potassium, pre- parations which are not required in the calotype process. SETS OF APPARATUS FOR THE COLLODION PROCESS. 6. Complete Set of Apparatus axd Chemicals for the Collodion Process, consisting of an Improved Sliding Camei-a of French-po- lished mahogany or walnut, with two openings to adapt it to lenses of different foci, one glass slide vnth three frames, and a shifting front for regulating the proportion of foregrovmd and sky, fitted with double combination of achromatic lenses, in brass mount, with rack and pinion adjustment, taking Portraits up to the size of 3^ inches by 4^^ inches; three shallow porcelain dishes; two camel's hail' brushes ; 1 quire Canson's photographic paper; 1 quire bibulous paper ; pressure frame ; balance with a set of weights, and two glass capsules to contain the substance to be weighed ; two pair of horn forceps ; a graduated glass measure ; a glass or gutta percha dipping trough with glass dipper; two plate boxes, and the following chemicals, &g., in stoppered bottles : nitrate of silver, protosulphate of iron, glacial acetic acid, nitric acid, pyro- gallic acid, hyposulphite of soda, chloride of gold, chloride of am- monium, nitrate of baryta, ammonia, alcohol, two dozen glass plates, a bottle of collodion with a bottle of iodizing solution, and amber varnish. The whole, packed in a neat deal case, with lock, key, and handles, £10, 10s. 7. A Larger size, equivalent to No. 3, £15. 8. Larger, equivalent to No. 5, £22, 14s. 6d. SETS OF APPARATUS FOR THE WAXED PAPER AND COL- LODION, OR THE CALOTYPE AND COLLODION PROCESSES. The sets, Nos. 1, 3, and 5, can be adapted for the collodion proces.s, by the addition of the following apparatus, chemicals, &c., to those enumerated : nitrate of silver, protosulphate of iron, glacial acetic acid, nitric acid, pyro- gallic acid, alcohol, hyposulphite of soda, amber varnish, plate boxes, glass plates, dipping bath and clipper, a bottle of collodion, and a bottle of iodizing solution. The extra expense will be as follows : — £ s. d. On No. 1, 2 12 6 On No. 3, 3 3 On No. 5. 4 4 Sets of Apparatus of any other size made to order. CHEAP SETS OF APPARATUS. The Cameras belonging to tlie sets Nos. 9 to 14, are inanu/actured in a cheaper style than those already described, and a less quantity of chemicals is siqiplied loith tJiem. Tlie sets, however, are essentially j)ractical, but cannot be recommended for eoCjiortation to hot cottntries. 9. Set of Apparatus for the Waxed Paper Process, the camera similar iu form to figure a, in the vignette, with one slide for paper, and. 3 frames for collodion or daguerreotype, fitted with double combination of achromatic lenses for taking portraits up to 3| inches by 4^ inches, and views 7 inches by 6 inches ; 2 shallow porcelain dishes ; glass spreading rod for applying sensitive solutions; one quire Canson's photographic paper ; one quire bibulous paj)er ; pressiu'e frame; balance, with set of weights, and two glass capsules to contain the substance to be weighed ; graduated glass measure, and the following chemicals, &c., in stopj^ered bottles : nitrate of silver, acetic acid, gallic acid, iodide, fluoride and cyanide of potassium, hyposulphite of soda, piu-e animal charcoal, sugar of milk, white wax, and chloride of gold; the whole, jmcked in a portable case for travelling, Avith lock, key, and handles, £7, 7s. 10. A Similar Set of Apparatus, but of larger size, fitted with single achromatic lens, in brass mount, with rack and pinion adjustment, taking Views 8 inches by 7 inches, £9, 9s. 11. The Above, mounted with double combination of achromatic lenses, taking Portraits 4| inches by 6i inches, and Views 8 inches by 7 inches, £10, 145. 12. A Similar Set of Apparatus, fitted with single achromatic lens, in brass moimt, with rack and pinion adjustment, taking Views 10 inches by 8 inches, £13, 13s. 13. The Above, fitted with double combination of achromatic lenses, taking Portraits 6^ inches by 8^ inches, and Views 10 inches by 8 inches, £18, 7s. Qd. Cheap Sets of Apixiratus, adapted for tlie Calotype process, can also be had at tlie above prices. 14. Cheap Set of Apparatus for the Collodion Process, comprising a sliding camera with focusing-glass, collodion slide and two femes, fitted with compound achromatic lens in bi-ass mount, with rack and pinion adjustment, taking Portraits 3| inches by 4^ inches; dipping bath and dij^per; Canson's photographic paper; bibulous paper; shallow porcelain dish; glass rod for spreading solutions; glass measure; 1 doz. glass plates; pressure frame ; and the following piu'e chemicals in stoj^j^ered bottles : nitrate of silver, protosulphate of iron, acetic acid, nitric acid, pyrogalHc acid, hyposidpliite of soda, and a bottle of iodized collodion, £5, 5s. SETS OF DAGUERREOTYPE APPARATUS. In the following sets, the silvered plates on which tlie 2Jictures are obtained are not included in the price. The quantity of each size required must he ordered separately. See No. 220, page 19. 15. Complete Set op Daguerreotype Apparatus (as shown by the figui-e on page 1), for pictures on plates up to 4^ by 3^; inches, with sliding camera; double combination of achromatic lenses, mounted in brass, with rack and pinion adjustment, No. 63; thi'ee dark frames ; a focusing-glass ; iodine and bromine a2:)paratus ; two plate boxes; two plate holders; polishing buffs; mercury box with thermometer ; washing tray ; spirit lamp ; pliers ; fixing stand ; and iodine, bx-omide of lime, hyposulphite of soda, chloride of gold, tripoh, charcoal, mercmy and naphtha, in stoppered bottles. The whole packed in two boxes, with lock, key, and handles, <£8, 8s. 16. The SAME Apparatus for larger plates, up to 6i inches by 4| inches, complete, in cases, £14, 14s. 17. The SAME Apparatus for larger plates, up to 8| inches by 6^ inches, complete, in cases, £2Q. DAGUERREOTYPE CAMERAS. 18. Improved Sliding Camera, of French-polished mahogany, two open- ings for sliders to suit lenses of different foci, focusing-glass, and dark slide with three frames, for plates up to the size of 3 j inches by 4^ inches, £2, 2s. 19. The Same Camera, fitted with double combination of achromatic lenses, in brass mount, with rack and pinion. No. 63, £4, 2s. 20. Similar to No. 18, but suited for plates up to the size of 6i inches by 4 1 inches, £3, 3s. 21. The Same Camera, fitted with double combination of achromatic lenses, in brass moimt, with i-ack and pinion adjustment, £6, 135. 22. Similar to No. 18, but suited for plates vip to the size of G| inches by 8^ inches, with sliding front, £5, 5s. 23. The Same Camera, fitted with double combination of achromatic lenses, in brass mount, with rack and pinion, No. 65, £13, 13s. The above Cameras can be had Brass-bound, for Hot Climates (see Note, page 7), at the following extra charges: — No. 18, 14s.; No. 20, £1, 4s. ; No. 22, £2, 10s. They are also sometimes constructed ^vitb inclining backs, by means of which two objects, at different dis- tances, are brought to the same focus, as the head and knees of a sitter. The extra expense is as follows: — No. 18, 16s.; No. 20, £1, 4s.; No. 22, £1, 10s. *** ^'^^^* ^ slight modification in the frames, tliese cameras are equally adapted for tfte collodion process. CALOTYPE CAMERAS. 24. Improved Sliding Camera, of Frencli-polislied mahogany or walnut, two openings to suit lenses of diflerent foci, focusing-glass, two double paper slides, one sKde with three fi*ames for the collodion or daguerreotype processes, and a shifting front for regulating the proportion of foreground and sky, for pictures 7 inches by 6 inches, X4, As. 25. The same Camera, with single achromatic lens, mounted in brass, with rack and pinion adjustment (No. 73), £6, 4s. 26. The same Camera, fitted with double combination of achromatic lenses (ISTo. 63), taking Portraits 3| inches by 4^ inches, and YiEWS 7 inches by 6 inches, £6, As. 27. Sliding Camera, similar to No. 24, but suited for Pictures 8 inches by 7 inches, £5, 10s. 28. The same Camera, fitted with single achromatic lens (No. 60), mounted in brass, with r-ack and pinion adjustment, £7, 15s. 29. The same Camera, fitted with doul^le combination of achromatic lenses, taking Portraits 4| inches by 6| inches, and Views 8 inches by 7 inches, £9. 30. Sliding Camera, similar to No. 24, but suited for Pictures 10 inches by 8 inches, £6, 16s. 6d. 31. The same Camera, fitted with single achromatic lens (No. 61), mounted in brass, with rack and pinion adjustment, £10, 10s. 32. The same Camera, ^vith double combination of achromatic lenses (No. 65), taking Portraits 6| inches by 8| inches, and Views 10 inches by 8 inches, £15, 4s. 6d. If ilie preceding Cameras are fitted with double action front, silver comers to collodion fr anus, d:c., the price will he £1, Is. extra. Larger sizes made to order. It is suggested to parties proceeding to, or residing in, India and other hot countries, to have their Cameras clamped with brass. They are then eminently adapted to withstand the injurious efiect of high temperatures, and form, besides, very handsome instruments. The extra expense is as foUows:— No. 24, £1, 5s. ; No. 27, £1, 10s.; No. 30, £2, 10s. PHOTOGRAPHIC CAMERAS OF CHEAPER CONSTRUCTION. 33. Camera, similar to Vignette, a, so constructed as to be capable of being employed for the dagaierreotype, calotype, or collodion pro- cesses. With sliding body to adapt it to lenses of difierent foci ; focusing-glass in frame ; one frame for the prepared calotype 8 CHEAP PHOTOGEAPHIC CAJSIEEAS. paper, and tkree fi^mes for holding the glass plates for use in the collodion process, and for the silvered plates in the dagneiTeotype process, fitted with double combination of achromatic lenses (Ko. 63), in bi-ass mount, with I'ack and pinion adjustment, taking Portraits up to the size of 3^ inches by 4| inches, £3, 6s. 34. Camera fitted with single achromatic lens, 2^ inches diameter, mounted in bi-ass, with rack and pinion adjustment (Xo. 59), for Views up to 7 inches by G inches, £4. 35. The same Camera, with double combination of achromatic lenses (No. 64), for Portraits up to 6| inches to 4| inches, £5, los. 36. Camera fitted with single achromatic lens 3 inches in diameter, in bi-ass mount, with rack and pinion adjustment Qso. 61), for Views 10 inches by 8 inches, £7, Is. 37. The same Camera, with double combination of achromatic lenses (No. 65), for Portraits up to 6^ inches by 8^ inches, £12, 125. 38. Improved Camera for the Collodion Process, as described in Hunt's Manual of Photoyraphj, p. 270, Fig. 67 to 71. — French- polished mahogany Camera, 2^ inch achi-omatic lens, adapted for taking Views, all the necessary apparatus and chemicals, with a a strong leather case and strap, £16, \6s. 39. Stam) suitable for the above Cameifi, £\. STEREOSCOPE CAMERAS. 40. Sltding Camera, focusing-glass. Griffin's improved stereoscope slide, and set of fi-ames for coUodion or daguen-eotype .stereoscopes; Spencer's sliding front, requii-ing one lens only, thus insuring perfect uniformity of size, and fitted with double combination of achi'omatic lenses, in brass mount, with rack and pinion adjust- ment, taking Portraits up to the size of 3^ inches by 4^ inches, £5, 5s. 41. A SIMILAR Camera, but of larger size, taking Portraits up to 6| inches by 4| inches, £7, 17«. dd. Stereoscope Cameras made to any pattern or size. Mr. Spencer's sliding front can he adapted to any of the preceding forms of Pltotographic Cameras. 42. Camera for MrsTATURES or Brooches, polished mahogany, with double achromatic lenses, moimted in brass, and brass slide, for taking two pictures on the same plate, £3, Ss. 43. Microscope Camera, or Combination of Cajiera with Achromatio Microscope, for Copying Views of Microscopic Objects, consisting of a sliding camera of French-polLshed mahogany, focusing-glass, collodion slide, with set of frames, fitted with achromatic lenses, in brass mount, "ndth fine adjustment, stage for objects, parallel mirror, d:c., £8, Ss. PORTABLE FOLDING CAMERAS. This form of Camera is admirably adapted for Tourists, as it is extremely light, and packs up into a very small compass. It consists of a mahogany box, the sides of which are hinged to fold inwards ; two double paper-frames, to hold four pieces of sensitive paper ; a groimd focusing-glass ; a shifting front, to regulate the proportion of foregromid and sky; and is fitted either with a single achromatic lens for taking views, copying statuary, &c., or with a double combination of achromatic lenses for portraits. In the latter case, the Camera is provided with a third dark slide, with frames for Collodion or Daguerreotype, and a second opening to adapt it to the short focus of the portrait lens. The whole is packed in a neat case. 44. FOLDING CAMERA, ^vith one opening for Views only, fitted with single achromatic lens (No. 60), in brass moimt, with rack and pinion adjustment, taking Views 8 inches by 6 inches, £5, 15s. Gd. 45. A Camera of same size, with doul)le action front, £6, Qs. 46. A Camera of same size, with extra opening for Portraits, focusing- glass, two double paper slides, slide and 3 frames, with silver cor- ners, for the collodion process ; dovible action front, mounted with double combination of achromatic lenses (No. 64), taking Por- traits up to 4f inches by 6i inches, and Views 8 inches by 6 inches, all of very superior construction, £10, 10s. 47. PoLDiNG Camera, similar in form to No. 44, with single achromatic lens (No. 61), producing Views 10 inches by 8 inches, .£9, 9s. 48. A Camera of same size, with double action front, £9, 19s. 6d. 49. A Camera of same size, with extra opening for Portraits, focusing- glass, two double paper shdes, collodion slide and 3 frames, with silver comei-s, double action front, morm.ted with double combina- tion of achromatic lenses, taking Portraits 6^ inches by 8^ inches, and Views 10 inches by 8 inches, all of very superior construction, £18. Other sizes made to order. 10 FOLDING AND SLIDING CAMEEAS. 50. IMPROYED SLIDING AND FOLDING CAMEEA, with focusing-giass, two double paper frames, and shifting front, for Views 9 inches by 7 inches, £1, Is. With double action front . . . . • \0s. extra. With extra opening ft* Poetkaits . . 15s. extra. Collodion slide for ditto 20s. extra. 51. Single Achromatic Lens for Views, for the above camera, 2^ inches diameter (No. 74), mounted in brass, with rack and pinion adjust- ment, £3. 52. Double Combination of Achromatic Lenses for ditto, moimted in bra;ss, with rack and pinion adjustment, producing Portraits 6| inches by 4f inches, (No. 64), £3, 10s. 53. Camera Similar to No. 50, but adapted for Views 10 inches by 8 inches, £8, 8s. With double action front, . . . . 10s. extra. With extra opening for Portraits, . 15s. „ Collodion slide for ditto, 20s. „ 54. Single Achromatic Lens for Views, for the above Camera, No. 75, mounted in brass, with rack and pinion adjustment, £4, 4s. 55. Double Combination of Achromatic Lenses, No. 65, mounted in brass, producing Portraits 6| inches by 8,^ inches, £8, 8s. 5Q. Judge's Portable Flexible Camera. — This Camera combines, to an eminent degree, lightness, portability, and facility and range of focal adjustment, with great efficiency and streng-th. It has one opening only, and is adapted for Lenses of from 3^ inches to 18 inches focus. It is fitted ^vith double action front, focusing-glass, and two double paper frames for Views, 10 inches by 8 inches. When folded up, with the focusing-glass secured inside, it measures 11 inches by 12 inches, and 5\ inches thick, and weighs about 8 lbs. Price, without lens, £6, 6s. 57. The Lens for the above camera, suitable to give Views 10 inches by 8 inches, is No. 61 or No. 75 ; but any other lens of shorter focus can be used with this camera, on account of the ease with wliich the focus can be adjusted. 58. Collodion Slide for the above camera, with fi-ames up to the size of 6^ inches by 8^ inches, £1. If fitted with Spencer's Stereoscope sliding front and Griffin's Stereoscope dark frame (vide No. 40), for Collodion or Daguerreo- type pictures, the price will be £1, 5s. extra. 11 LENSES WITHOUT CAMERAS. SINGLE ACHROMATIC LENSES. These lenses are well adapted, for the plate or paper process, where time is no object (as in taking views, inanimate objects, pictures, &c.); but for taking portraits, when a more rapid action is required, the double com- bination of Achromatic Lenses must be employed. 59. Single Achromatic Lens, 2^ inches in diameter, 10-inch focus, mounted in brass, with rack and pinion adjvistment. Price £1, 15s. 60. Single Achromatic Lens, 2^ inches in diameter, 14-inch focus, mounted in brass, with rack and pinion adjustment. Price £2, 5s. 61. Single Achromatic Lens, 3 inches in diameter, 18-inch focus, mounted in brass, wdth rack and pinion adjustment. Price £3, 13s. 6d. 62. Single Achromatic Lens, 4 inches in diameter, 24-inch focus, mounted in brass, with rack and pinion adjustment. Price £6, 6s. DOUBLE COMBINATION OF ACHROMATIC LENSES. The Double Lenses are adapted fortakingportraits, figures, groups, &c., as they admit a great quantity of light, and consequently produce a picture in less time than a single lens. 63. A Double Combination of Achromatic Lenses, 1 -7 inches in diameter, having a combined focus of about 4 inches, mounted in brass, with rack and pinion adjustment, producing a Picture 4^ in. by 3^ inches. Price £2. 64. A Double Combination of Achromatic Lenses, 2 '4 in. in diameter, having a com- bined focus of about 7 inches, moimted in brass, with rack and pinion adjustment, pro- ducing a Picture 6^ inches by 4| inches. Price £.3, 10s. 65. A Double Combination of Achromatic Lenses, 3 '2 inches in diameter, having a combined focus of about 10 inches, mounted in brass, with rack and piaion adjustment, producing a Picture 8^ inches by 6| inches, £8, 8s. 66. A Diaphragm of stops fitted to either of the above sets of Lenses, 15s. The use of this Diaphragm is given in the explanatory note at page 2. 12 PHOTOGRAPHIC LENSES. ACHROMATIC LENSES OF SUPERIOR QUALITY. The sets of apparatus described in the preceding pages commonly contain the lenses from No. 59 to No. 65, which are of good average quality, as is shown by the specimen which accompanies each of them. But persons who desire it may have lenses of superior quality, possessing the power to cover a greater surface more uniformly, to act more rapidly, to prodiice greater definition in all parts of the picture, and to have the visual and chemical foci coincident. The prices of such lenses are as foUow, ail mouiUed in brass, uith rack and pinion adjustment : — Double Lenses for Portraits. Diameter of Lens. Size of Plate for which they serve. 67. Ig inch 2f inches by 3^ inches 68. l| _ 31 — Ai — . . 69. 2i — 4f — Gi- ro. 31 — 61 — 81 — . . 71. 3f — 8 — 10 — 72. 41 —10 _ 12 _ . . Single Lenses for Views. 73 2 inches diameter, 12 inches focus 73a 21 — 14 — 74. 2| — 16 — 75. 3 — 18 — 76. 31 — 20 — 77. 4 _ 24 — Price. £ s. d. 1 11 6 2 12 6 5 5 12 20 31 10 £■ s. d. 2 2 10 3 4 4 5 5 7 MISCELLANEOUS PHOTOGRAPHIC APPARATUS. Improved JNIercury Box f Vignette, dj, of walnut, with sliding legs, ii-on cistern, glass "wdndows for inspecting the development of the picture, mounted with thermometer for ascei'taining the temperature of the mercury, 3 sizes : — 78. With tlu-ee frames for plates, up to 41 inches by 3^ inches, 10s. 6d. 79. With three frames for plates, up to 6i inches by 4| inches, 14s. 80. With three frames for plates, up to 8^ inches by 6| inches, 21s. 81. Mercury Bottle, of box-wood, for holding the mercmy necessary for use with the mercmy box, 2s. each. 82. Daguerreotype Spirit Lamp, with screw cap, japanned tin, for heating the mercmy box, 2s. 83. Thermometer for the Mercury Box, with Scale after Fahrenheit to 212°. Thi'ee sizes, each 3s. Gd. PHOTOGEAPHIC APPAEATUS. 13 84. Iodine and Bromine Boxes, in paii-s (Vignette, c c), of walnut, en- closing each a stout porcelain pan : each pan is furnished with an air-tight glass cover, 3 sizes : — 85. For plates up to \\ inches by 3^ inches, £1, 4s. per pair. 86. For plates up to 6^ inches by 4f inches, £1, 12s. per pair. 87. For plates up to 8i inches by 6^ inches, £2, bs. per pair. The Iodine and Bromine Boxes may he had, the two combined in one, at the same prices as tJie above. Double Box for Iodine and Bromine, best quality, with a pair of glass or porcelain pans, fitted -with air-tight glass covers, -with mirrors, by wliich the progress of the operation can be examined withoiit exposvire, and with an arrangement for changing the plate from the iodine to the bromine, 3 sizes : — 88. For quarter-size plates, 4^ inches by 3^ inches, £2, 7s. Gd. 89. For half-size plates, 6^ inches by 4f inches, £3, 13s. 6d. 90. For full-size plates, 8^ inches by 6^ inches £5, 5s. Square Porcelain Pans, with air-tight glass cover, for either bromine or iodine mixtui'es ; the body and glaze firm, and not liable to be acted on by any photographic compound, 3 sizes : — 91. For plates up to 4| inches by 3^ inches, with three plate-frames for holding the plates, 5s. 92. For plates up to 6^ inches by 4| inches, with three plate-frames for holding the plates, 7s. 6d. 93. For plates up to 8^ inches by 6| inches, with three plate-frames for holding the plates, 10s. Gd. 94. Focusing-Glass (magnifying lens), in sKding mount, obviating the use of a cloth hood, 4s. 6d. Parallel Mirror, moimted in brass, for attaching to the front of the lenses, when portraits, views, &c., are required to be taken in direct instead of reverse positions by DaguerreotyjDC, 2 sizes : — 95. MuTor, 2^ inches by 3 inches, mounted in brass, £2. 96. Mirror, 4 inches by 3 inches, moimted iu brass, £3. SUPEEFINE COLOURS FOR PAINTING DAGUERREOTYPE OR PAPER PORTRAITS. 97. Box containing 10 colours in glass tubes, with a cup of silver, a cup of gold, and a set of brushes, 10s. 6d. 98. Cup of Sdver, 6d. 99. Cup of Gold, Sd. 100. Camels' Hair Brushes, 2s. a-dozen. 101. Do. best Paris, 4s. a-dozen. 102. Sable Do., 4s. a-dozen. u PHOTOGEAPHIC APPAEATUS. 103. Single Colours, in tubes, Is. each. 1. Blue, Dark 2. , Sky 3. Brown, Dark 4. , Light 5. Carmine, 6. Claret, 7. Flesh-tint, 9. 10. 11. 12. 13. Green, Dark , Lisht Plum, Scarlet, White for Clouds, for Solariza- 15. 16. 17. 18. - tion, 19. Yellow for Clouds, 20. for Draperies. Gray, Lavender, Lemon, Lips, 14. Orange, 104. Apparatus for Besilverdhg Daguerreotype Plates by Electro- plating, consisting of a Smee's Battery, glass decomposition cell and connecting wire, with the requisite binding-screws : — for silvering platesof any size up to 4^ inches by 3 ^ inches. Price 12s. 6d. 105. Silver solution, for Electro-plating Daguerreotype plates, per oz. 2s. Two ounces of this solution, diluted tcith 18 ounces of icater, form a fint of solution of the prajper strength for electro-plating. Full instructions for Electro-plating, &c., will be found in Napier's Manual of Electro-Metallurgy, Price 3s. Qd. Plate-Holder, French pattern, for seciiring the plates firmly and conveniently (Vignette, ee), with clamp. 106. 2g inches by 2g inches 107. 2f - - 31 108. H - - 41 109. 5 4 110. 61 - - 4f 111. 6A - - 81 112. Apparatus for bending the edges of Daguerreotjrpe plates, so as to pre- vent the sharp edges cutting the buffers in buffing. Price 7s. 6d. . Is. Gd. . Is. 9d. . 2s. Od. . 2s. 6d. . 2s. 9d. . 3s. Od. ^1^-^ 113. Haxd-buffs, covered Avith leather or velvet, small size ( Vignette, i), per pair, in box, 9s. Ditto superior, 14s. 114. Hand-buffs, full size {Vignette, t), per pair, in box, 12s. Ditto superior, 21s. 115. 116. 117. Glass Tripod Developing Stand, 2s. Fixing Stand, with u-on foot and levelling screws, for supporting the plates while fixing [fg. 1 1 6), for plates up to 4^ inches by 3j inches, 6s. Ditto for plates up to 8^ inches by 6| inches, 7s. Od. ^>' 116. PHOTOGRAPHIC APPARATUS. 15 Apparatus for drying Daguerreotype Plates, consisting of a flat-shaped copper vessel, tinned inside ; a holder for the plate, and a siipport {fig. 118), 3 sizes : — 118. For plates up to 4^ inches by ?>\ inches, 75. 119. For plates up to 6^ inches by 4f inches, 9s. 120. For plates up to 8^ inches by 6^ inches, 10s. Qd. 121. Steel Pliers for holding the plates whilst drying oflT, 2s. 122. CAMERA STANDS, Portable Folding Tripod Stand, French pattern, with hinged legs, ball and socket joint, and table for camera (Jig. 122), 15s. 123. Do., larger size, 18s. 124. Stand, improved foiTQ, for out-door use, of superior make, very light, portable, and ^^^• strong, small size, mahogany, £1, 15s.; large size, £2, 2s. 125. Strong Stand, -w-ith every adjustment, very steady, and weU adapted for the operating-room of the professional or amateur artist, hardwood, £1, Is. 126. Oak Stand, very substantial and well finished, £2, 2s. 127. Head Rest, for keeping the head of the sitter steady whilst a portrait is being taken. The rest is intended to be fixed to the back of a chair {fig. 127), Shallow Porcelain Dishes, with flat bottom, for con- taining the solutions in the preparation of paper for the Calotype Process, &c. {Vig- nette, h). 128. 8 inches by Scinches 1 129. 8f - 6f - - 1 3 130. 8 - 9 - 1 6 131. 10 - 7^ - 1 6 132. 9 - 10 - 2 133. 10 - 11 — 2 134. 11 inches bv 9 inches 2 135. 10 — ' 12 — 4 136. 11 — 1.5 _ 5 137. 14 — 19 — 15 138. 18 — 24 — 24 Deep Porcelain Dishes, for salting and iodizing paper. 16 PHOTOGEAPHIC APPAP^TUS. Plate Glass Dishes for applying sensitive solutions, washing plates, (tc. Made of plate glass, cemented. 139. For plates 31 inclies by 4^ inches, . is. OJ. 140. Do. do. 4 — 5 — . 5s. Od. 141. Do. do. 4| — 6i — . 6s. 6d. 142. Do. do. 6i — 8i - . 8s. Od. 143. Do. do. 10 — 8 — . 10s. 6d. 144. Do. do. 12 — 10 — . 12s. Od. GuTTA Percha "Washin'g Dishes, at about two-thirds of the above prices. DIPPING BATHS, in PLATE GLASS, so cemented together as to resist the action of nitrate of silver, on foot, with glass dipper. s. d. 145. Por plates 3^ inches by 4^ inches 146. Do. do. 5 — 4 — 147. Do. do. 4^ — US. 149. 150. 151. 152. Do. do. H — H 6 7 8 6 10 6 DIPPING BATHS in GUTTA PERCHA, on Supports with a Glass Dipper to each. *. d. For plates 4^^ incbes by 3;^ inches Do. do. 5 — 4 — Do. do. 6i — 4| — Do. do. 8i — 6i — 3 4 5 9 With Separate Supports (for Portability), \s. each extra. DIPPING BATHS, with supports and dippers, in WHITE GLAZED EARTHENWARR 153. For plates 5 inches bv 4 inches 154. Do. do. 61 _ ' 4f — 155. Do. do. U — 61 — .«. d. 4 6 5 6 DIPPING BATHS of the same material, with movable heads, secured by India-rubber and screws, for travelling, with Dippei-s. i. d. For plates 5 inches by 4 inches .... 7 Do. do. 6i — 4f — . . . . 7 6 Do. do. 81 — 61 — S d. 235. 4 — 236. 4i — 237. 5 — 3 4 — 2s. 6(1. — 3s. Od. per doz. 238. 6 inches by 5 inches, 4s. 6d. 239. 6i — 4f — 5s. 240. 61 — 8i — 8s. 24L 10 — 8 — 12s. Larger sizes cut to order. GLASS PLATES, with ground edges for Stereoscope Pictures. 242. 4^ inches by 9 inches, per dozen, 6s. 243. 5 — 91 — _ 7s. 6d 244. 61 _ 111 _ _ Us. 245. 71 — 3| — — 4s. PASSE-PARTOUTS, or Card-board Frames and Glasses, for holding Daguen-eotype or Collodion pic- tui-es (^. 246). I. Mack, Brown, or Tortoise-shell Grounds, with Gold Ornaments. Dome. 246. For plates 2| inches by 2 inches, per doz., 4s. %d. 247. For plates 21 inches by 2| inches, — 4s. Qd. 248. For plates 3^ inches by 2| inches, — 5s. Od. 249. For plates 41 inches by 31 inches, — 5s. 6d. 250. For plates 5 inches by 4 inches, — 10s. Od. 251. For plates 6| inches by 4| inches, — 12s. Od. 252. For plates 8^ inches by 6| inches, — 24s. Od. II. With white grouiids and gold ornaments, at an inert one-half on the above prices. III. A great variety of ornamental Passe-Partouts, with gold grounds and various styles of ornament. EMBOSSED FRAMES for PASSE-PARTOUTS. Adapted for Passe-Partouts that contain Plates of the following dimensions: — s. d. s. d. Oval & Cushion is. Od. 4s. Od. As. 6d. 5s. Sd. 9s. Od. lis. Od. 20s. Od. case of about 253. 2| inches by 2| inches. 254. 2f 255. 31 - 31 - H - 9 .0 10 .1 2oG. 4 inches by 5 inches...! 6 257. 4f — 61 — ...1 9 ORMOLU FRAMES, Louis XIV. style, with gilt mats and glasses. 258. For plates 2i inches by 2 inches. Is. 6d. 259. — 2i n^ 31 — 2s. 6d. 260. — 31 _ 41 — 3s. 6d. 261. — 5 _ 4 — 5s. Od. I PHOTOGRAPHIC APPAEATUS. 21 91 8 — 16s. H — 24s. H — 30s. 4 — 60s. 4f — 90s. H — 130s. MOROCCO LEATHER CASE, lined with silk velvet, fitted with oval, dome, or cushion -shaped gilt mat, and glass. London -made, superior quality : — 262. For plates 2^ inches by 2 inches, 14s. per dozen. 263. For plates 2^ — 264. For plates 2| — 265. For plates 3j — 266. For plates 5 — 267. For plates 6^ — 268. For plates 8^ — PLATE BOXES, deal wood, divided for 50 plates. 269. For plates 4^ inches by 3^ inches, 3s. 6d. 270. For plates 6^ — 4f — 4s. 6cL 271. For plates 81 — 6^ — 6s. 0^?. SHOW FRAMES for professional artists. Elegant French Patterns. 272. Rosewood, large size, 4 apertures, 3os. 273. Rosewood, middle size, 4 apertures, 28s. 274. Passe-Partouts, prostype, 4 apertures, 21s. 275. Passe Partouts, prostype, 9 apertures, 27s. 276. Passe-Partouts, gold ground, 6 apertures, 27s. 277. Gilt German Mats, 13 apertures, 16s. PHOTOGRAPHIC PAPERS :— 278. Turner's Photographic Paper, for Negative Pictures, si^e, l5 by 9 inches, 3s. per quire. 279. Cansok's Photographic Paper, for Negative Pictures, &\ze, 17 by 22 inches, 2s. per quire. 280. Canson's Photograpliic Paper, for Positive Pictures, 3s. per quire. 281. White Wove Filtering Paper, prepared with the greatest care, perfectly free from smalt, chlorine, lime, iron, and other common impurities, filters rapidly, and is highly absorbent. Is. M. per quire. IODIZED PAPER FOR CALOTYPE. 7 in. by 6 in., 3s. per doz. 7 _ 9 — 5s. — 284. 10 in. by 8 in., 8s. per doz. 285. 15 — 12 — 10s. — Waxed Paper, 17 inches by 11 inches, 3s. Qd. per dozen. Waxed Paper, same size. Iodized, 10s. Qd. per dozen. Do. do.. Sensitive, ready for use in the Camera (to keep 14 days), 10 inches by 8 inches, d>s. per dozen. Other sizes to order. Albumenized Paper, for printing from glass or paper negatives, 1 1 inches by 9 inches, 2s. Qd. per dozen. Solution for Iodizing Paper, Is. %d. per oz. 291. Solution for Iodizing Waxed Paper, 5s. per pint. 292. Solution for Rendering Waxed Paper Sensitive, 6o?. per oz. 282. 283. 286. 287. 288. 289. 290. 22 PURE PHOTOGMPHIC CHEMICALS. Avoirdupois Weight. The prices in the followitig List are subject to continiud variation, but at all times t/ie lowest market prices will be charged. Acid, Acetic, crystallisable, %d. per oz. Arsenic, \s. per oz. Aj-senious, 3d per oz. Formic, solvition, 6c/. per oz. Gallic, 3s. per oz. „ nearly pui-e, 2s. per oz. Pyrogallic, 1 6^. per oz., or 60 grains, in bottle, 2s. Qd. Hydrocliloric, ^d. lb. Niti-ic, Is. 6d. per lb., 2d. per oz. Succinic, 4s. per oz. Sulphuric, Is. 6d. per lb., 2d. per oz. Tannic, Is. Gd. per oz. Tartaric, id. per oz. .Mther, Sulphui'ic, pure, sp. gr. -750, 6c?. per oz. „ Sulpbui'ic, pure, anhydrous, sp. gr. -730, 8d. per oz. Alcohol, Absolute, 10s. per lb. „ 60° over-proof, 4s. per imperial piut. Ammonia, Liquid, Is. 3d. per lb. „ Hydrosulphate, 5s. per lb. Ammonium, Bromide, 8s. per oz. „ Chloride, 2d. per oz. „ Fluoride, 4s. per oz. „ Iodide, 5s. per oz. Arsenic, Iodide, 8s. per oz. Barium, Chloride, 2d. per oz. „ Iodide, 7 s. per oz. Barytes, Caustic, Is. per oz. Barytes, Nitrate, nearly pure, 2s. per lb. „ Nitrate, pure, 4s. per lb. Bromine, 3s. per oz. „ ^ lb. in stoppered bottle, soldered in tin cases for ex- port, £1. „ Chloride, 4s. per oz. „ Iodide, 4s. per oz. „ Water, id. per oz. r, i PUEE PHOTOGEAPHIC CHEMICALS, 23 Cadmium, Bromide, 8s. per oz. „ Iodide, 8s. per oz. Calcium, Bromide, 7s. per oz. Charcoal, fine, prepared for buffing, Is. per bottle. Charcoal, animal, 6d. per oz. Chloroform and Amber Varnish, Is. per oz. Collodion, Bromized, 9d. per oz. „ Iodized, Archer's, 2 oz. in bottle, 2s. „ „ Griffin's, 9d. per oz. „ „ Thomas's, Is. 6d. per oz. * „ not Iodized (for Exportation), 8d. per oz. * „ Iodizing Solution for do., 9d. per oz. Copper, Sulphate, cryst., 2d. per oz. Cotton wool, freed from Grease, and finely carded, 3d. per oz., 3s. per lb. Gold, Chloride, cryst., 3s. per 15 grains in bottle. „ „ and Sodium, 2s. 6d. jjer 15 grains in bottle. „ „ Solution for darkening negatives, 6d. per oz. „ Salt of — (Sel d'Or), 4s. per 15 grains in bottle. Iodine, re-sublimed, 2s. per oz. „ Tincture, Is. per oz. Iodine, Bromide, 4s. per oz. „ Chloi'ide, 4s. Gd. per oz. Iron, Ammonia-Citrate, 9d. per oz. „ Bromide, 4s. per oz. „ Iodide, 2s. 6d. per oz. „ Persulphate, 3d. per oz. „ Protosulphate, Is. per lb. „ „ prepared by alcohol, not subject to oxida- tion. Is. 6d. per lb. Lead, Acetate, 2d. per ox. „ Nitrate, 4c/. per oz. Lime, Acetate, „ Bromide, 2s. per oz. Mercury, 4s. per lb. „ Bichloride, Gd. per oz. Naphtha for burning in the lamp, 2s. per pint. Oil of Lavender, Is. Gd. per oz. Potash, Bicarbonate, Ad. per oz. „ Carbonate, 8d. per oz. „ „ nearly pure, 2c?. per oz. „ Nitrate, 2s. per lb. * Collodion required by photographers living in the country, or for exportation, can be had with the iodizing solution separate. It wiU then keep for any length of time. For use, add 1 part by measui-e of iodizing solution to 8 parts of collodion. 24 PURE PHOTOGEAPHIC CHEMICALS. Potassium, Bromide, 2s. 6d. per oz. „ Chloride, 3d. per oz. „ Cyanide, 6d. per oz. „ Iodide, 2s. 6cl. per oz. „ Ferrocyanide, 3d. per oz. „ Fluoride, Is. per oz. Rotten-Stone, finely prepared, 6d. per oz. Rouge, finely prepared, Is. per oz. Silver Solution, for Electro-plating tlie worn-out Daguerreotype Plates, 2s. per oz. Silver, in sheet or wire, pure, 9s. per oz. Acetate, 10s. per oz. Ammonia-Nitrate, solution. Is. per oz. Chloride, 10s. 6d. per oz. Iodide, 10s. per oz. Nitrate, in crystals, 5s. per oz. Oxide, 9s. per oz. Soda, Hyposulphite, Is. 4:d. per lb., 2d. per oz., 7 lb. for 7s. „ Acetate, 2s. per lb. „ Bicarbonate, 2d. per oz. „ Carbonate, crj^stallised, 2d. per oz. Sodium, Bromide, 2s. 6d. per oz. i „ Chloride, 3d. per oz. „ Fluoride, Is. per oz. Sugar, grape, 4s. per lb. „ of milk, 4s. lb. Syrup of Iodide of Iron, 3s. per lb., 3d. per oz. Test-papers, Red and Blue Litmus, l^d. per book. TrijDoli, finely prepai'ed, 6d. per oz. White Wax, 3d. per oz. Zinc, Nitrate, Is. per oz. STOPPERED BOTTLES, for chemical solutions, best white Ger- man glass, round shoulders : — Narrow Mouth. Wide Mouth. 1 oimce, per dozen, 3s. 5s. 2 — 4s. es. 4 — 58. Ss. 8 — 7s. 10s. 16 — . 10s. 12s. 18 — . 12s. 16s. Amber Varnish, for protecting Negative Pictures on glass, Is. per oz. Judge's Jet Varnish, for backing up Positive Pictures on glass, Is. per bottle. 25 JOHN JOSEPH GEIFFIN, RCS., CHEMICAL AND PHILOSOPHICAL INSTRUMENT MAKER, 10, FINSBURY SQUARE, MANUFACTORY, 119, 120 BUNHILL ROW, REMOVED FEOM 53, BAKER STREET, LONDON. Mr. griffin begs to announce that he supplies all the APPARATUS and PREPARATIONS requii-ed in the Study of CHEMISTRY and EXPERIMENTAL SCIENCE. In his estabhshments at the above adcb-esses the Apparatus may be seen, and information obtained on any subject relating to the study or practice of these sciences. Parties at a distance from London are respectfully refeiTed to liis ILLUSTRATED DESCRIPTIVE CATALOGUE of Chemical and Philosophical Appa- ratus, 200 pages 8vo, with 1200 figures, price 2s., or, post free to any part of Great Britain, 2s. 6d. CHEMICAL LABORATORIES IN PORTABLE CABINETS : con- taining Apparatus and Preparations for a course of Elementary Experiments, arranged by John J. Griffin, F.C.S. No. 0. Containing a Lamp Fm-nace and some of the most essential Instruments, in a deal bos, 10^. 6d. No. 1. Apparatus and Tests, in a mahogany box, 16s. No. 2. Ditto, in a mahogany box, with lock. Sis. 6d. No. 3. In a deal box, with lock. This set contains a lamp furnace, with apparatus and preparations for quaUtive analysis, 42s. No. 4. In a mahogany box, with lock. This is a very comprehensive set of apparatus and tests, adapted for an extensive eoui'se of experiments on a small scale, 52s. 6d. No. 5. In a deal box, with lock. A set of larger apparatus suitable for a school, with means for performing the chief exj^eriments proper to illustrate elementary lessons in Agricultural Chemistry, £5, 5s. No. 6. In a mahogany case, mth lock. A set particularly adapted for Analytical researches, £6, Qs. No. 7. In a mahogany case, with lock. A more complete Analytical set, for travelling Engineers, Metallurgists, &c., £8, 8s. 2 6 3 3 3 26 GHADUATED GLASS IXSTEUMEXTS FOB CHE31ICAL TESTING IX THE ARTS. ALCAIil^IETERS. :?, varioTis fonns and stan- dards of measare, a~ •.>*. «kA : — Forms: — 1. Binks's-; i. G j; 3. Faraday's. CosTESTS of each: — 1. 1'. . ^._:.— -s> or 700 grains of ■water; 2. 1000 grains of -water; 3. 50 Centimeter Cubes; 4. One AToirdopois Ounce; -5. Two Axoirdopois Ounces. Alealimeierg made to order , to a»^ other size orjorm,. Clark's PorKET. used for his Wateb T^t, 100 Dirisions, Ba. GEADrATED PIPETTES. BuxB PiPETixSy Graduated to deliver a fixed quantity, — such as 10, 50, or 100 septem^ 1 ounce, 50 centimeter enbes^ &C.J eaeh Ctlisbiir Pipettes^ graduated into from 20 to 40 septem% Ditto, drfided into spaces of 10 grains of water ... Ditto, dirided into centimeter oibes Decigallox Bottle, which, when filled to a mark on the neck, contains the tenth of a gaQon, or 1 lb., of water 3 6 Ded^illon bottle, about 13 inches high, on foot, contents 1-lOth gallon, divided into 100 parts ... 10 TestOIixeb, Contents about 30 to 32 ounces, diyided into 100 parts, for preparing Test Acid and other Liquoxs for Testing Processes ... ... ... 12 GBrFFDTS TIXEGAB TEST, for determining the strength of Ticegar, and how much of it is due to l^phuzic add. In a Cabinet- with psinted instnu*tion& — In preparation. THEEMO:MErERS for CHE^HCAL TSE, the Scales endosed in GkisL The lyia^, point on the Scales of these Thermometers is generally about 30^ or 40'^ Fahrenheit. The kighegt point to which eadli ranges, as cited below, is apjpmtximate. It may range 50^ above or tmflkr the quotation. Thennometeis with Tw-o Sealetj cost 2s. esetra. £ •. 4L ... 3 ... 4 ... 6 ... 4 6 ... 5 6 ... 7 6 ... 7 6 ... 9 ... 7 6 ... 9 Koe. 7 to 10 consist of tc^ solid tube% about \ inch diameter. No. 1. Kange to 213° FafazenlKit, widipqMTsale 2. — 350 do. do. 3. 600 do. do. 4. — 212 do. widi Bflk.^l*® scale 5. — 350 do. do. 6. — 600 dou do. 7. — 350 dOL eognTcd sale ... 8. — 600 doL do. 9. — 150 Ccntignde, do. 10. — 320 do. do. 27 HYDROMETERS. TWADDELL'S HYDEOMETER, Griffin's impro\-ed comcal form. s. d. Specific Gravity 1-000 to 1120 — 1-120— 1-240 No. 1 0' to 24 2 24 — 48 3 48 — 74 4 74 — 102 5 102 — 138 6 138 — 170 1-240 — 1-370 1-370 — 1-510 1-510—1-690 1-690 — 1-850 Set of Six Spindles, complete, 16*. Set of Six Spindles in a Mahogany Box, 23.?. Strong Pasteboard Boxes, for single spindles, each Ad. Twaddell's HYDROiiETER, adju.sted at 84^ Fahrenheit, for use in the West Indies, at the same price as those adjusted at 60^ Fah. HYDROMETER SPINDLES, single, or in sets, to show directly the Specific Gravity of Liquors, water being = 1 -000 : — From 0-700^ to 1-900'', one spindle with a so- lution tube, in a pasteboard box, 8s. — 1-000= to 2 -000=, one spindle bs. — 1-000 to 2 •000,more closely divided 6.?. 0-800 to 0-875, for Strong Spirits, 5.?. 0-875 to 1-000, for Weak Spirits, 5a. From 0-70° — 1-00 to 1-00° to 1 -50 1-50 to 2-00 0-700° to 1-000' 1-000 to 1-300 1-300 to 1-600 1-600 to 1-900 1-300 to 1-900 1-000 to 1 small size, the set, Is. 6rf. ■ each spindle 5s. 0-720 to 1-000, 5s. — 1-000 to 1-300, finely divided, in a 1-000 to 1-400, 5.9. mahogany box 12s. 1-400 to 1-900, 5.S. — 1-000 to 1-300, with thermometer, do. 18s. Pasteboard Cases for Hydrometers, price Qd. each, ALCOHOLOMETERS. SiKEs's Hydrometer, in Glass, one spindle, range from about 60"^ Ovei'-proof to about 40° Under-proof ... 050 Foreign Alcoholometers, showing the Per-centage of Alcohol : — 1. French, Gay-Lussac's 2. Ditto, with Thennometer 3. Prussian, Tralles's, now adapted by the United States of America ... 4. Ditto, -wdth Thermometer HYDROMETERS FOR SPECIAL PURPOSES :-^ Saccharometer No. 1, Sho^ving pounds of Malt per barrel Saccharometer No. 2, Showing per-centage of Sugar Beaume's Hydrometer, for Sp-ups, Cane-juice, &c. Ditto adjusted at 84'', for the West Indies Oil Guage, or Hydrometer for estimating the pui-ity of, Oils with thermometer enclosed Griffin's AMMO^^A-METER, for Testing Liquid Ammonia Urinometer, for determining the Sp. Gr. of Urine . . . Ditto, with a solution tube, fitted into a Morocco case 4 6 4 6 4 5 2 6 2 6 7 5 3 7 6 28 COLLECTIONS OF PHILOSOPHICAL APPARATUS. CABINETS of Electrical Apparatus at £2, and £5, 5s. Cabinets of Pneumatic Apparatus at £4, 4*., £7, 7s., and £10, 10s. Cabinet of Hydraulic Apparatus at 52s. Qd. Cabinet of Mechanical Powers and Elementary Machines at 44s. MINERALOGY AND GEOLOGY.— Systematic Collections of Minerals, Rocks, and Fossils, from 100 to 1000 Specimens, either with or without Cabinets. MAGIC LANTERNS, Phantasmagorias, and Dissolving Views, Avith Sliders, in gi-eat variety. CHEMICAL TESTING IN THE ARTS.— Graduated Glass Ap- pratus and Pure Tests. ACHROMATIC MICROSCOPES at 5, 10, 12, IG and 20 guineas, of both English and French patterns. SMALL COMPOUND MICROSCOPES at 9s., 12s. 6d., 24s., 31s. Gd. Sliders and aU kinds of Materials and Preparations for experiments with the Microscope. ELECTRICAL, GALVANIC, AND MAGNETIC APPARATUS. BLOWPIPE APPARATUS, Instraments and Tests for ASSAYING MINERALS in the "Wet Way, and all other requisites for jMetallurgic Researches. HYDROMETERS, Thermometers, Alcalimeters, Gradiiated Measures, Balances and Weights. APPARATUS suitable for Experimentsat CHEMICAL LECTURES, adapted to the operations described in all Class Books, English and Foreign. APPARATUS and PURE TESTS for Analytical Researches : sets to suit the Experiments desci'ibed in Chemical Recreations, prepared fur Schools at moderate prices. TO SCHOOLMASTEPvS. Apparatus for Use in Elementary Schools, containing a Selection of Instruments and Preparations for Teaching the most important facts in Experimental Science — namely, in Chemistry (mth especial regai'd to Agricidtiu-e), Hydrostatics, Pneumatics, Electricity, Galvanism, Magnet- ism, and Optics, including the Microscope and the Magic Lantern, -wath astronomical slidei-s. This Apparatus is arranged in three sets, at the following prices : — No. 1 - - - - price £21, 13s. 5d. No. 2 - - - - „ £12, 14s. 3d. No. 3 - - - - „ £10, 12s. \0d. Other larger sets of Apparatus have also been prepared for use in Training Schools and Polytechnic Institutions, at the prices of £100, £130, and £150. 29 FIRST LESSONS IN PRACTICAL CHEMISTRY. Ill Croion Octavo, Illustrated hy 100 Wood-Ctits, Pnce 2s. Cloth, CHEMICAL RECREATIONS, A POPULAE MANUAL OF EXPEPcBIENTAL CHEMISTRY. By JOHN JOSEPH GRIFFIN, LLOW OF THE CHEinCAL SOCIETY, HONORABT MEMBER OF THE PHILOSOPHICAL SOCIETY OF GLASGOW. TEXTH EDITION. FIEST DIYISIOX. The -work -nill be published in Three Divisions : — I. Elementary Experiments. II. The Metalloids and theii- Combinations with one another ; Ail' ; "Water ; The Gases ; The Acids. III. The Metals and their Compounds. CONTENTS OF THE PIRST DIVISION. INTRODUCTION :— Nature, Objects, and Use of Chemistry.— leasons why Chemistry should be a branch of general education. — lethods of Chemical Research. — Different Classes of Experiments. —Micro -Chemical Eperiments. — Different sorts of Chemical Sub- tances. — Chemical Elements. — The Elements that occur in plants and nimals. — Elements peculiai- to mineral substances. — The Cause of Che- lical Combination. — Varieties of Compounds, — Acids, Bases, Salts, (kc. THE ATOMIC THEORY :— ATOMIC WEIGHTS. ELEMENTARY EXPERIMENTS. EXA^IPLES OF CHEMICAL OPERATIONS :— Solution.— evaporation. — Precipitation. — Testing. — Dissolving Powers of different liquids. — CiystaUisation. — Efflorescence. — DeKquescence. — Effervescence. —Filtration. — Discrimination of Vegetable, Animal, and Mineral Bodies. QUALITIVE ANALYSIS OF SALTS :— Substances to be sought or. — Salts adapted for Analysis. — Apparatus requii-ed for the experi- aents. — Preparation of a Solution of the Salt. — Classification of Tests. ON THE PERFORMANCE OF ANALYTICAL EXPERIMENTS 5Y MEANS OF EQUIVALENT TEST LIQUORS.— Appai-atus re- uii-ed for Centigrade Testing. — Centigrade Test Tubes. — Test Mixers. —Pipettes. — Tables of Decimal Measures. — Standaixl Solutions.-^ limits of the Solubility of Acids and Alkalies. — Table of the Solubihty f Acids. — Table of the Solubihty of Alkahes. — Atomic Measure of Test liquors. — Test Liquoi-s of 100°. — Test Liquoi"s of oO\ — General Obser- 'ations on the process for Testing the strength of Acids and Alkalies. — Cable of Test Equivalents. — Chemical Testing in the Aits. — Testing of Carbonate of Soda, Vinegar, Limestones and Marls. — Miscellaneous isperiments with Equivalent Test Liquoi-s. — Experiments with Test l-iquors of 50". 30 PROSPECTUS. Nearly Ready, in Octavo, Illustrated by Numerous Wood-Cuts, POPULAR LECTUEES ON CHEMISTRY, DETAILING TME PRINCIPLES OF THE SCIENCE, Am) TRACING ITS APPLICATIONS TO AETS, MANUFACTURES, AGRICULTURE, DOMESTIC ECONOMY, AND PHYSIOLOGY. FROM THE FRENCH OF ADOLPHE BOBIERRE, WITH NTJMEROirS CORRECTIONS AND ADDITIONS. ACCOMPANIED BY NOTES, CONTAINING PRACTICAL INSTRUCTIONS FOR PREPARING AND PERFORMING THI EXPERIMENTS NECESSARY TO ILLUSTRATE THE LECTURES. SYNOPSIS, L History of Chemistry. 2. General Laws of Chemistry, 3. Atmospheric Air, 4. Carbonic Acid, 5. Water, 6. Carbon. 7. Gases that contain Carbon. 8. Nitrogen. 9. Sulphur, 10. Chlorine, Iodine, Bromine. 11, Phosphorus. 12, Arsenic, Boron, Silicon. 13, Metals and their compounds. 14, Potassium, Sodium. 15, Calcium, Magnesium, 16, Aluminum, Potteiy, Glass 17, Iron, Cobalt, Nickel, 18, Zinc, Cadmium, Chromium, Tin, Antimony, 19, Copper, Bismuth, Lead, 20, Mcrcmy, Silver, 21, Gold, Platinum, (fee. PUBLISHED BY JOHN J. GRIFFIN, CHEMICAL AND PHILOSOPHICAL INSTRUMENT MAEEB, 10, FiNSBURY Square; 119, 120, Buniiill Row, London. 31 lAEGE COLOTJRED SCIENTIFIC DIAGRAMS FOR SCHOOLS. Specimens of a New Series of LARGE COLOURED DIAGRAMS FOR USE IN SCHOOLS. They are to be prepared in sets, and adapted to illustrate Natm-al History, General and Physical Geograj)hy, the Principles of Natural Philosophy, and the Applications of the Sciences to Arts and Manufactures. These Diagrams will place it in the Teacher's power, at a moderate expense, to illustrate School Lessons on Natural and Experimental Science, much more thoroughly than it is possible for him to do without pictorial AIDS, which carry infoi-mation to the pupil's eye rapidly, effectively, and agreeably. Subscribers for the entire Series of Diagrams loill he supplied at a re- duced price. 1. The MANUFACTURE and USE OF IRON. No. 1, Blast I Furnace for Smelting Iron Ore. Section of a Fu^rnace in Work, on a scale of half-an-inch to 1 foot. Size 33 inches by 21 inches ; price, on paper, \s. Ad. ; mounted on cloth, 2s. 2. THE MANUFACTURE OF GLASS. No. 1, Interior of a Glass-House, with Glass- Blowers at Work. Size 35 inches by 52 inches; price, on paper, two sheets, 2s. 8d. ; mounted on cloth, 4s. 3. GAS MAKING. View of a Gas-Work, with Sections of the Principal Apparatus ; showing the Progress of the Gas, from the Retorts in which it is made, through the Condensers, Purifying Vessels, Meter, and Governor, into the Main. Size 33 inches by 63 inches. Price, on paper, three sheets, 4^. ; movinted on cloth, 6s. 4. BOTANICAL ILLUSTRATIONS. No. 1, containing five figures of difierent classes of Plants. Size 28 inches by 21 inches. Price, on paper, 6cZ. ; moimted on cloth, \s. 5. CHIEF CHEMICAL INGREDIENTS IN DIFFERENT VARIETIES OF FOOD ; average results of numerous analyses. Size, 35 inches by 78 inches. 6. ELEVEN EXAMPLES OF DIETARIES, showing the chief chemical ingredients of the food, expressed in ounces per week. Size, 35 inches by 26 uiches. Cost of a Roller for packing these Diagrams, Zd. 32 NEW SCIENTIFIC PUBLICATIONS. A MANUAL of PHOTOGRAPHY, or Practical Treatise on tlie Pro- duction of Pictui'es fi-om Natnre by Solar Radiation, including an account of all the pubKslied Photogi-apMc Processes. By Robert Hunt, Esq., Professor of Physical Science in tlie Metrojiolitan School of Science. Fourth Edition, revised, Crown Octavo, with numerous Wood-cuts. Price Gs. Cloth. PHOTOGRAPHIC CHEMISTRY. By Johx J. Griffix, F.C.S. Crown Octavo, with Tables and Figui'es of Apparatus. Nearly Ready. The existing Treatises on Photography relate almost entirely to Mechanical and Op- tical details. The present Work will treat of chemical processes, such as the preparation of photographic agents, the estimation of their purity, the reduction of receipts for photo- graphic processes to a uniform decimal standard, the systematic graduation of solutions, the economy of waste liquors, &c., &c., &c. A SYSTEM of CRYSTALLOGRAPHY, with its APPLICATIONS to MINERALOGY. By John J. Gkiffin, F.C.S. One large Volume Octavo. Price 9s. This Work contains a very comprehensive Catalogue of all the observed varieties of each mineral that occurs crystallized. A Set o/" 120 Models of Crystals nuiy he had, to illustrate this Work, Price £2, 12s. M. ILLUSTRATED CATALOGUE of CHEMICAL and PHILOSO- PHICAL APPARATUS, manufactured by John J. Griffin. In Octavo, 200 pages of text, with about 1200 Wood-cuts. Price 2s. Mr. Griffin will shortly publish a NEW SERIES of ILLUSTRATED CATA- LOGUES of SCIENTIFIC APPARATUS, in which the articles will be classified accord- ing to their uses. Of this Series, the present list of PHOTOGRAniic Apparatus affords a specimen. The Second Part will relate to Apparatus for Assateks and Analytical Chemists. A Third Part will comprehend Scientific Apparatus for Use in Schools. The CYCLOPEDIA of CHEMISTRY, with its Applications to Mineralogy, Physiology, and the Arts. By R. D. Thomsox, M.D., F.R.S., F.R.S.E., F.C.S., Profes.sor of Chemistiy in St. Thomas's Hospital College. Crown Octavo. Price 12s. Q)d. Cloth. A MANUAL of METALLURGY : being an Account of Assaying, Mining, Smelting, &c. By J. A. Phillips, F.C.S., late Professor of Metallui'gy at the CoUege of Civil Engineei's. Second Edition. With nearly 200 Engravings. Cro^^^l 8vo, 12s. Gd. Cloth. A MANUAL of ELECTRO-]METALLURGY ; containing an Ac- count of the most Impi-ovcd INIethods of Depositing Coi^per, Silver, Gold, and other Metals. With numerous lUustrdtions. By Jas. Napier., F.C.S. Second Edition, revised and enlarged. Crown 8vo, 3s. 6c?. Cloth. GLASGOW: W. G. BI.ACKIE, AND CO., PrjNTEKS, VILLAFIELD. Cabinet Edition of the Encyclopaedia Melropolitana — eontluned. Vol. XXV.. price Khj. Od.. cloth lettered. HISTORY OF THE ROMAN EMPIRE. By the Rev, Thus. Arxold, D.D., hue Head Master. Rugby School, aud Others. With Xuraerous Illustrations. Vol. XXVI.. price lOs. 6d.. cloth lettered, HISTORY OF THE DECLINE AND FALL OF THE ROMAN POWER By the Right Rev. Bishop Rcssel, Ac. With Xumeroiw Illustrations. Vol. XXVTI., price 6s.. cloth lettered, HISTORY OF GREEK AND ROMAN PHILOSOPHY AND SCIENCE. By the Right Rev. Charles Bloitfilld, D.D., Bishop of London; Rev. Dr. Whewell, And other Contributors. ■• A more interesting and Instructire volume than iliis lis* not lx«ii O'.Tered to the public for a long time." — Critic. Vol. XXVIII., price 3s. 6d.. cloth lettered, MORAL AND ^lETAPHYSICAL PHILOSOPHY— THE PHILOSOPHY OF THE FIRST SIX CENTLP.IES. By the Rev F. D. Haluice, M..*.. VoL XXIX, price 7s. tkL, cioth lettered, HISTORY OF THE OTTOMAN EMPIRE; including a Snne\- of tlie Gkeek EitPlEB and the Cecsades. By Colonel Pboctfr, Rev. J. E. Riddle, and Jakes M'Con- ECHT, Esq. Vol. XXX.. price . cloth lettered. TRIGONOMETRY. By George B. Amv, F.K.S,, Astronomer RoyaL Edited hy Hugh BtACKBras, M.A., Professor of Mathematics in tlie University of Glasgow. Vol. XXXI., price , cloth lettered, HISTORY OF THE OCCULT SCIENCES. Dy the Rev. Edwart> Smedley. M.A., E. Rich, Esq.. and other Contributors. ' (la March, i Vol. XXXIl.. price 12s. Bd.. cloth lettered. GEOLOGY — Practical axd Theoretical. By John Phillips, M.A„ F.R.S.. F.G.S., Dcpnt;- Reader in Geology in the University of Osfor 1. Wi:li NiiTueroas Xlinstration.-. {In Mat! ' Totantrs ia Active Fr«>|BarR:ieii. I. SCULPTURE. By Richakd Westmacott, F.R.S., A.R.A.. with Xumeroiis Illustrations, revistd. II. THE STEAM E.VGINE : its History and Apjilicaticns to Locomotion, Naviga- tion, Mining', and Manufactures. liy Wiluam Feegcso*, F.C.S. With Xnoierous Illnstra- tiiin.% in. ECCLESIASTICAL HISTORY, from t!ie Fourth to the Tuelfth C«ntury. By Rev. J. M. GoLDisc. rv'. ECCLESIASTICAL HISTORY, from the Tliirteenth Century to the Present Day. By Rev. Dr. IIampdes, Bishop of Hereford; Rev. J. E, Riddle, and Others. V. GLOSSOLOGY: or, The Historical Rehuions of Languages. By SiR Joii.v Stodoaet, LL.D. VI. MORAL AXD MET.U'HYSICAL PHILOSOPHY — THE MIDDLE AGES. By Rev. F. I). Malkice, 5LA., Chaplain of Lincoln's Inn. vn. MORAL AND METAPHYSICAL PHILOSOPHY— MODERN PHILOSOPHY. By Rev. F. D. Maceice, M.A., Ch-iplain of Lincoln's Inn. VIII. PRLNCIPLES AND PR.4CTICE OF 3IEDICINE. By R. Williams, M.D., Physici.in to SL Thomas's Hospital, London, and W. .\rrKES. M.D." Demonstrator of Anatomv in the Universitv of Glasgow. IX. ARITHMETIC. By Rev Dr. Peacock, Dean of Ek. Revised GRIFFIN'S PORTABLE CYCLOPEDIAS, ^ Snits of ^eftmuc §ool»s, ADAPTED TO THE WANTS OF THE PRESENT AGE, EMBRACING BIOGRAPHY, GEOGRAPHY, HISTORY, RELIGION, THE NATURAL AND PHYSJCAS. SCIENCES, &c. Handsomely printed in 8vo, and profusely Illustrated. BIBLICAL CYCLOPEDIA ; or, Complete Dictionary of Eastern Antiquities, Geography, Natural History, Sacred Annals and Biography, Theology, and Bihlical Litera- ture. By the Rev. John Eadir, D.D., LL.D., Professor of Biblical Literature to the United Presbyterian Churcli. With Numerous Illustrations. Fifth Edition, revised, 7s. 6d. . *,* AVhatever could be regarded as sectarian by any denomination of evangelical Christians (whether Episcopalian, Presbyterian, or Congregational) is scrupulously excluded, especially in all that relates to ritual 'and goveniment. The volume is thus in accordance with the spirit and principles of the " Evangelical Alliance." CYCLOPEDIA OF CHEMISTRY : including tlie Application of the Science tn the Arts, Miseualogt, and Phtsiologt. By Robert Dumdas Thomson, M.D., F.R.S., F.K.S E., F.C.S., &c.. Professor of Chemistry at St. Thomas's Hospital College, London. With Niimeious Illustrations, Pis. (jd. " Its limited compass— its completeness and corrcctncs-s, recommend the Cyclopedia of Che- mistry to all who feel an interest in the science." — Atlieixeuin. ■' In every respect worthy of praise. It is within a limited space by far the best compendium of Chemistry which we have yet sevn."— Lancet. " A practical publication in the highest degree valuable "—Mining Journal. " Contains a comprehensive summary of Chemical science and arts in a form most useful for reference and suitable for study." — Literary Gazette. CYCLOPEDIA OF UNIVERSAL BIOGRAPHY ; containing^ a Series of Origi- nal Meiiiolrs of the most remarkable Individuals of ali Times and Nations. Edited by E. Rich, Esq., with the assistance of numerous Contributors. With 150 Illustrations of Birth- Placea, ifcc. &c. !2s. 6d, NAMES OF THE CONTRIBUTORS. Katiiral aud Physical Sciences. Uistcry. SIK AKCL'IBALD ALISON, D.C.L. JOmC niLL BUKTOS, ESQ. PEOFESSOR CBEAST, M.A. PROFESSOR FriSGCaON, A.M. E. RICH, ESQ. Theology aud Lilcrature. THOJIAS DAVIBSOS, ESQ. PBOFESSOR EADIE, D.D., LL.D. JA3IE9 EEDDERWICK, ESQ. ROBERT JAMIESON, D.D. CHARLES KNIGHT, ESQ. W. BAISD, M.D.. F.I-.S. Sir. DAVID BREWSTER, F.R.S. JAMES BRTCE, ESQ., F.C.S. PROFESSOU OORDOS, F.K.S. PROFESSOR NICHOL, LL.D. R. D. THOMSON, ILD., F.R.S. JAMES M'CONECHT. Fine Arts. JOHN A. HERAUD, ESQ. JAMES MANSON, ESQ. BAl,r:i K. WOSNU5I, ESQ. ss, completeness, and excellence.*— O'rti'c. ■ volumes of Biography in several remarkable features;— the .-^ contains, the variety and indeed celebrity of the writers i ,^ • imparted to the larger notices. The first, and for purposes , is the number of persons noticed : this is managed by very reat numbers of cases by little more than lists with the date • tance, action, or work, which prociu'es the subject a place. los are r.umerous and celebrated, as may be seen from the writer takes that class of lives with which his studies have • "^-. lul Creasy, for example, undertake naval and military men. id novel peculiarity to the lives of prominent men, however filiation. The writers take a whole view of the life and cha- a judgment on both, instead of a bare recital of facts with an imonpiace. The scale is well preserved." — Spectator. an stand a comparison with the present ov.i."— Manchester ha^•e turned in order to test the book we arc highh satis- 1 dictionaries." — Glasgow Herald. HY: a Complete Series of Chronological Tables, Id to the Present Time, on a New Plan, comprehending an s and an Alphabetical arrangement. 10s. 3d. « i^..o ,,„,,. ,..„ u^ .„„,.„ ,.„ „e the "iprv wajTOM of i/fttor)/," and to contain avast amount of infonnation interesting to eveiy one (and who is not?) interested in the progress of the human race. From the peculiarity of its aiTangemcnt, the events which have taken place at any par- ticular time may be seen at a glance; while, by means of a most extensive Inde.x, speedy information can be obtained as to any particular fact. THE GETTY CENTER LtnpARY