~j2- 
 
 iNSTBUCTifoNS IN 
 
 THE'AET of PEODUCING PHDTOGEXfHIC PICTUEES 
 IN ANY COLOB, AND ON ANY MATEEIAL, 
 
 / 
 
 FOR THE USE (|l^ BEGINNERS ; ^ /"Tj yj 
 
 AND ALSO OF PERSONS WHO HAVE ALREADY ATTAINED SOME PROFIcfENCY 
 IN THE ^ 
 
 ^ AND OF ENGRAVERS ON COPPMls[|TO'SfE,- WOOD,. ETC. 
 
 By Dr. G. C. HEEMANN HALLEUE, 
 
 Late Director of the Royal Technical School at Bochum. 
 
 WITH PRACTICAL HINTS 
 
 ON THE LOCALE BEST SUITED FOR PHOTOGRAPHIC OPERATIONS, AND ON THE 
 PROPER POSTURE, ATTITUDE, AND DRESS, FOR PORTRAITURE. 
 
 By E. SCHTJBEET, Painter. 
 
 AND AN APPENDIX 
 
 CONTAINING BRIEF EXPLANATIONS OP SOME OF THE CHEMICAL TEEMS WHICH 
 OCCASIONALLY OCCUR IN THE WORK. 
 
 TRANSLATED FROM THE GERMAN 
 
 By G. L. STEAUSS, Ph. Dr. 
 
 LONDON : 
 
 JOHN WEALE, 59, HIGH HOLBOEN. 
 
 1854. 
 
PEEFACE. 
 
 I HAVE been engaged for several years in experiments and 
 researches on the chemical alterations and modifications produced 
 in various bodies by the action of light. The object which I had 
 more immediately in view was to ascertain whether other 
 metallic compounds, besides those of silver, might be used in 
 photography. 
 
 In addition to this, I had also proposed to myself to try 
 whether the purely conjectural and random way of mixing 
 together the salts used in photographic processes, might not 
 be reduced to something like a law of definite mixing proportions. 
 It affords me sincere gratification to be able to state that I have 
 attained both objects. 
 
 The results of the experiments which I made to ascertain 
 whether other metals besides silver might not be employed 
 in photography, fully established the fact that all metallic com- 
 pounds suffer alteration under the influence of light. In many 
 of them this alteration takes place in a very short time, as in the 
 ease of iron for instance ; others require a more protracted 
 exposure to the action of the light. By combinations of different 
 metallic salts the most interesting variations may be produced. 
 Next to silver, the salts of iron, and the compounds of chromium 
 appear to me the most important. Thus, for instance, the blue 
 or green images produced with a salt of iron and ferricyanide of 
 potassium (commonly termed red prussiate of potash or potassa), 
 look remarkably fine, and are well adapted for light-screens and 
 lithophanies ; to protect them effectually from injury, they need 
 simply be enclosed between two glass-plates set in a frame. 
 The alteration suffered by many metallic salts under the influence 
 
VI 
 
 PllEFACE. 
 
 of light is ia most cases not immediately visible, but it speedily 
 makes its appearance upon the application of the proper re-agent. 
 
 For the benefit of those who may wish to engage in photo- 
 graphic experiments, but do not possess the requisite chemical 
 knowledge, I have added to the present work a Table (III), giving 
 the deportment of the metallic salts with the most important 
 re-agents. Guided by the information contained in that table, it 
 will always be easy to select the proper reagent, and in many 
 cases also to obtain divers variations in the tints of the pictures. 
 This table will serve, moreover, to enable persons unskilled in 
 chemistry to test the substances, which they are about to use, 
 and thus to make sure of their identity and purity. 
 
 In reference to the proper mixing proportions of the substances 
 employed, I think I have found a definite rule in the laws of 
 equivalents or combining proportions ; I have therefore added 
 Tables I and II. An example will show the way in which these 
 tables are to be used. 
 
 Suppose you want to prepare iodised paper (silver iodide 
 paper) for the taking of negative images, and you wish to know 
 in what proportions you ought to mix the iodide of potassium and 
 the nitrate of silver, to obtain a highly sensitive prepai*ation ; you 
 need simply look out in the first column of Table II., iodide of 
 potassium, and there you will find in the third column, the 
 number 166, which is the combining or mixing weight of the 
 iodide ; then look out nitrate of silver, where you will find the 
 number 170, the combining weight of the nitrate of silver. You 
 will accordingly have to mix the two salts in the respective propor- 
 tions of 166 of the one (the iodide), and 170 of the other (the 
 nitrate). It does not matter what denomination of weight you 
 use, whether grains, or grammes, or any other kind ; but of 
 course the weights must correspond for the several substances. 
 Thus, for instance, if you have weighed off 166 grains of the 
 iodide of potassium, you must weigh off, on the other hand, 
 170 grains of the nitrate of silver. You may also use a less 
 number of grains or grammes, &c., the one-half, or the one-third, 
 for instance, of the number given in the table ; but you must keep 
 
PREFACE. 
 
 vii 
 
 rigorously to the proportions indicated. Thus, for instance, to 
 83 of iodide of potassium you would have to use 85 of nitrate of 
 silver. Now, supposing you have weighed off 166 grains of the 
 iodide, and 170 grains of the nitrate, dissolve the two salts 
 separately, each in an equal volume of water, viz., 8 ounces; 
 then imbue the paper which you want to iodise with the two 
 solutions in the usual way (see Talbotype). 
 
 When the two solutions come in contact on the paper, there 
 ensues a double decomposition as follows : — 
 
 f Iodide of potassium. ') 
 
 Iodide of silver. 
 
 I / '• I 
 
 J Iodine. /Potassium. I 
 
 1 Silver. Oxygen./ Nitric acid. | 
 
 Nitrate of potassa. 
 
 Nitrate of silver. J 
 
 Iodide of silver has accordingly been formed on the paper ; but, 
 besides this, also nitrate of potassa or nitre, which must be 
 removed from it. This is effected most readily by laying the 
 prepared side of the paper on water, in which the nitre will 
 speedily dissolve, and, from it greater specific gravity, subside to 
 the bottom, whilst the iodide of silver, being insoluble in water, 
 will firmly adhere to the paper. The paper so prepared is very 
 insensible, and may, if carefully kept, be preserved a long time 
 (for years even), without losing its properties. When you want 
 to make use of it for photographic purposes, you must imbue it 
 once more with the silver solution, or with one of equal strength, 
 but in which a portion of the water is replaced by acetic acid. 
 Your paper will thus receive the requisite e.\cess of silver, and be 
 rendered thereby highly sensitive. 
 
 If you wish to add bromine to your preparation, you need 
 simply calculate from the table the amount of bromide of potassium 
 to be added, and take a corresponding weight of iodide of potas- 
 sium less. Thus, for instance, if you wish to add one-tenth of 
 bromine, you will have to take 11 '92 grains of bromide of 
 potassium, and, to make room for this, 16‘6 grains less of 
 iodide of potassium. 
 
 
vm 
 
 PREFACE. 
 
 These examples will suffice, I hope, to point out the proper way 
 of proceeding in all other cases. 
 
 The substances enumerated in the table, have all been used in 
 my own experiments. I have added the chemical formulce, because 
 I know from personal experience that chemists and druggists will 
 often serve you with a very diiferent article from what you want. 
 To adduce an example, I got at a druggist’s, instead of iodide 
 o/ammomwm {NH4I), iodate of ammonia (NH 40 ,I 05 ) — a pre- 
 paration altogether useless for the purpose for which I intended 
 it, viz., for the preparation of iodised collodion. This is one of the 
 most fertile sources of failure in photographic experiments. Now, 
 if you simply demand the article by name, mistakes of the kind 
 may occur without any great blame being imputable on that 
 account to the druggist ; but if you add the chemical formula 
 of the substance demanded, the substitution of another article 
 would be quite inexcusable. 
 
 I am now on the point of completing another work on the art 
 and science of photography, which embraces all my experiments 
 and researches in the domain of that most interesting of modern 
 inventions. This work which I hope will appear next spring, 
 under the title “ Manual of Photogenetic Chemistry and 
 Photography will contain plain instructions on the easiest 
 and safest way of preparing all the materials required in 
 photography. 
 
 If this little work should contribute to impart a little more 
 certainty and regularity into the various manipulations of the 
 photographic art, I shall deem myself amply rewarded for my 
 labors in that interesting branch of the natural sciences. 
 
 THE AUTHOR. 
 
 Berlin, May , 1853. 
 
X 
 
 CONTENTS. 
 
 
 DaGUEEREOTTPE — 
 
 Brass plates 33 
 
 German silver plates ib. 
 
 Ivory plates . . , 34 
 
 Wood plates. 35 
 
 Talbotype .......... .37 
 
 Oxide of silver 
 
 Nitrate of silver if). 
 
 Prismatic analysis ib. 
 
 Photographic application ...... . . 38 
 
 Chloride of silver ib. 
 
 Prismatic analysis . . 39 
 
 Photographic application . , 40 
 
 Preparation of the paper ......... ib. 
 
 Fixing the picture , .43 
 
 Iodide of silver 44 
 
 Prismatic analysis 45 
 
 Photographic application ,. . . . .. , , . ib. 
 
 Calotype . . . , . . ... . ib. 
 
 Preparation of the paper ib. 
 
 Developing the picture 46 
 
 Fixing the picture ......... 47 
 
 Iodide of silver and ferrocyanide of potassium . .. . .49 
 
 Preparation of the paper ........ 
 
 Fixing the picture ......... 
 
 Production of positive pictures in the camera, by means of 
 
 hydriodates . . , . 50 
 
 Bromide of silver . . . 51 
 
 Preparation of the paper . . ib. 
 
 Developing and fixing the picture ...... 52 
 
 Fluoride of silver . . . . ib. 
 
 Phosphate of silver ......... 53 
 
 Tartrate of silver .... ib. 
 
 Chromide, benzoate, formiate, &c. of silver . . . . ib. 
 
 Chloride of gold ..... ..... 54 
 
 „ and oxalate of ammonia ib. 
 
 „ and acetate of lead 55 
 
 „ and cyanide of potassium ib. 
 
CONTENTS. 
 
 XI 
 
 Talboxype — 
 
 Chloride of gold and nitrate of silver 
 Compounds of platinum .... 
 
 „ iron ..... 
 
 Pi-eparation of the paper 
 Developing the picture .... 
 Compounds of copper .... 
 Sulphate of copper and bichromate of potassa 
 „ chromate of potassa 
 
 Compounds of manganese .... 
 Iodide of lead and nitrate of silver 
 Nitrate of lead and protiodide of iron 
 Iodide of lead and starch paste . . . 
 
 Compounds of nickel ..... 
 Compounds of cobalt, &c 
 
 55 
 ih. 
 
 56 
 ib. 
 
 57 
 60 
 ib. 
 61 
 62 
 ib. 
 63 
 ib. 
 ib. 
 ib. 
 
 VlTROTYPE 
 
 Coating the glass with albtrmen . 
 
 „ joiner’s glue . 
 
 „ starch paste 
 
 Coating the glass with caseine 
 
 „ collodium 
 
 Preparation of silver-iodised collodium 
 Developing and fixing the picture . 
 Collodium and gutta percha . . 
 
 64 
 
 65 
 
 66 
 ib. 
 
 7 
 
 ib. 
 
 68 
 
 70 
 
 ib. 
 
 Akthotype, (photography with vegetable juices) . . . .71 
 
 Guaiacum and chlorine ib. 
 
 Juice of young plants ib. 
 
 „ the rose and violet 72 
 
 Sawdust and shavings of mahogany ib. 
 
 Photo-Lithogbaphy (photography on stone) 
 
 ib. 
 
 Theory oe the Photographic Phenomena 74 
 
 Practical hints on the proper selection and arrangement of the 
 
 LOCALE IN which PHOTOGRAPHIC OPERATIONS MAY BEST BE PER- 
 FORMED, AND ON THE PROPER POSTURE, ATTITUDE, AND DRESS, OF 
 PERSONS WHO WISH TO HAVE THEIR PORTRAITS TAKEN WITH THE 
 PHOTOGRAPHIC APPARATUS 
 
 78 
 
Xll 
 
 CONTENTS. 
 
 PAGE 
 
 Table I. — The most important chemical elements, or simple bodies, 
 with their respective sj^mbols and combining pro- 
 portions 80 
 
 Table II. — The most important chemical compounds (in a photo- 
 graphic point of view), with their formulte and com- 
 
 bining proportions 81 
 
 Table III. — Brief abstract of the principal reactions of metallic salts 
 
 with the most important reagents . ‘ . . .87 
 
 Metallic oxides ^ 5 , 
 
 Metallic acids 101 
 
 Appendix I04 
 
THE 
 
 ART OF PHOTOGRAPHY. 
 
 INTRODUCTION. 
 
 Light, — that essential condition to the existence of the whole 
 vegetable kingdom, with a few rare exceptions, and which, in so many 
 classes of animals, exercises also so great and beneficent an influence over 
 animal life, — is likewise one of the most energetic causes of chemical 
 action ; and there are many chemical combinations and decompositions 
 which can only take place under the influence of light. 
 
 Photography presents us, in this respect, with a number of the most 
 interesting phenomena, which even now have acquired considerable 
 practical value, but promise still greater and more important results 
 for the future. The discoveries made in this new field of science, 
 have naturally called the attention of chemists to the problem of the 
 true nature and essence of light, and have engaged them to make 
 researches with a view to a possible solution of that problem. As 
 the domains of optics and of chemistry may be said to touch and 
 combine in photography, every successful attempt in that direction 
 may reasonably be expected to lead also to some new progress or 
 discovery in optics, which, on its part again, may serve to bring the 
 philosopher neai’er the elucidation of the phenomena of light. 
 
 The action w'hich light exercises upon fused chloride of silver 
 (hornsilver), viz., that it imparts a black tint to the originally white 
 salt, was known as early as the sixteenth century (to the alchymists) ; 
 still it w'as only in the eighteenth century that this phenomenon was 
 closely examined. It w’ould appeal’, also, that about the same 
 
 n 
 
 more 
 
2 
 
 THE AllT OF PHOTOGRAPHY. 
 
 period the influence of light upon the crystallisation of various salts 
 was first observed. Petit published his observations on this latter 
 subject in 1722, and Chaptat and Dieze theirs about sixty-six years 
 after : the former in 1788, the latter in 1789. 
 
 Scheele studied the phenomenon of the nigrescence of chloride of silver 
 under the influence of light ; he occupied himself more particularly 
 with those alterations which the chloride of silver suffers under the 
 influence of the prismatic rays. In 1777, he published the results of 
 his observations. He had discovered that chloride of silver, minutely 
 divided and spread on paper, turned black much sooner under the 
 influence of the violet ray than under that of any of the other colors. 
 Sennebier found, in 1790, that fifteen minutes’ exposure to the violet 
 ray sufficed to impart to chloride of silver the same black tint which it 
 was seen to acquire in the red ray only after twenty minutes’ exposure. 
 In 1801, Ritter discovered that the chemical action of light extends 
 beyond the colored rays of the spectrum, manifesting itself still 
 through invisible rays. About the same time, Wollaston was engaged 
 in similar researches. The results of these investigations led Wedge- 
 wood to further experiments ; and to him unquestionably is due the 
 honor of having been the first photographer ; the allegation that the 
 Indian jugglers had known the art for centuries, and had thereby 
 maintained their influence, being more than doubtful. 
 
 We find in the “Journal of the Royal Institution,” of 1803, a paper 
 by Wedge wood, with observations by Sir Humphrey Davy. The paper 
 is entitled “ An Account of a Method of Copying Paintings upon 
 Glass, and of making Profiles by the Agency of Light upon Nitrate of 
 Silver.” 
 
 White paper, or white leather, saturated with a solution of nitrate 
 of silver, served as the impressionable surface. Wedgewood says inhi.s 
 article, “ The alteration of the colors commences the more speedily 
 in proportion to the degree of intensity of the light. In bright sun- 
 shine, from two to three minutes suffice to produce the full effect, 
 whereas, in the shade, several hours are required to arrive at the same 
 end. Through differently-colored glasses the light acts with different 
 degrees of intensity. When the shadow of a figure is thrown upon the 
 prepared surface, the parts covered by the shadow remain wdiite, whilst 
 the other parts speedily turn black. To copy paintings on glass, the 
 
INTRODUCTION. 
 
 8 
 
 negative images should be taken on leather, because the action is more 
 rapid with this material than if paper were used, 
 
 “ When the color is once fixed on paper or leather, it proves fast to 
 a degree ; water, and even soap-water, failing to remove it. Besides the 
 method of copying just given, there are several others ; it will be 
 useful to make copies of all such objects as are partly transparent and 
 partly opaque. The woody fibres of the leaves of plants, and the 
 wings of insects, may be very accurately copied in this manner ; all 
 that is needed to this end is, to transmit the direct light through the 
 object to be portrayed, and to receive the shadow on prepared paper, 
 or prepared leather.” To this statement, Davy adds: “It has been 
 observed that the image of the camera obscura is too feeble to make an 
 impression upon the nitrate of silver within a reasonable space of time. 
 To copy these images, was Wedgewood’s chief object. I followed up his 
 experiments, and found that the images of small objects, produced by 
 I the solar microscope, may be copied without difficulty on prepared 
 
 I paper. A comparison of the effects produced by the action of light 
 
 i upon chloride of silver, with those produced on nitrate of silver, fully 
 
 I and clearly showed that the chloride is the more sensitive compound 
 
 ; of the two. All that is required now to render these experiments 
 
 as useful as they are interesting is, to find a way of preventing 
 the subsequent coloring of the white parts upon exposure to 
 daylight.” 
 
 It would appear that no further experiments were made for several 
 years. Wedgewood and Davy’s failure was owing solely to the circum- 
 stance that at that time those agents were unknown which are now 
 used with such success to fix the images. Hyposulphite of soda, its 
 properties and its deportment with salts of silver, were only dis- 
 covered in 1819, by Sir John Herschel ; iodine also was unknown in 
 1812 ; and without these agents photography could not advance beyond 
 the point where Wedgewood and Davy had left it. 
 
 In the year 1814, Niepce directed his attention to the chemical 
 effects of light ; his object was, to fix the images of the camera- 
 obscura. He discovered the peculiar property of the solar rays to alter 
 the solubility of various resinous substances. He spread a thin layer 
 of asphalte on a glass or metal-plate, and placed this in the camera- 
 ! obscura ; after waiting from five to six hours, he found on the plate a 
 
 B 2 
 
4 
 
 THE ART OF PHOTOGRAPHY. 
 
 latent image, which became visible npon treating the surface of the 
 plate with a solvent. The development of the invisible image was 
 afterwards made by Mr, Fox Talbot the subject of an English patent 
 for a new invention, although the process had been known and applied 
 twenty years before. 
 
 In the year 1827, Niepce made photographic experiments at Kew. 
 His friends preserve still some of the pictures obtained by him in these 
 experiments. These pictures bear some resemblance to the Daguerreo- 
 types, although they are greatly inferior to them. Daguerre commenced 
 his experiments in the year 1824, and employed, as Wedge wood had 
 done, both nitrate and chloride of silver. In 1826, Daguerre and Niepce 
 became acquainted, and from that time forward, they pursued their 
 experiments jointly. In 1829, Niepce communicated his method to 
 Daguerre in a letter, in which he says : 
 
 “ The discovery which I have made, and to wdiich I have given the 
 name Heliography, consists in this, that I produce instantaneously, 
 by the action of light, the image of the camera-obscura, in all gradations 
 from white to black.” He then goes on to describe his method, and 
 continues : “ The plate so prepared can be exposed to the action of the 
 light in the camera-obscura; however, when it is withdrawn from the 
 camera, after sufficient exposure, no alteration is perceptible in it ; 
 the lines of the image remain still invisible. The next operation is to 
 develope the latent image, which is effected by means of a solvent.” 
 
 In 1829, Daguerre and Niepce employed, for the first time, iodine 
 ‘‘ to blacken the plate which contained the heliographic impression.” 
 However, Daguerre would seem to have observed some peculiarities in 
 the action of light upon silver plates treated in this manner, for in one 
 of his letters to Daguerre, Niepce speaks of a decoction of cassweed 
 (Phlaspi arvense), of phosphor fumes (phosphorous acid), and more 
 especially of sulphur, as acting on silver in the same manner as iodine; 
 and he observes also, that heat produces the same effect by the 
 oxidation of the metal, and maintains that it is from this cause (the 
 oxidation) that proceeds in all these cases the extraordinary sensitive- 
 ness to light. 
 
 Niepce died in 1833, and in January 1839, Daguerre announced his 
 great invention. In the month of July following, the Chamber of 
 Deputies voted an annual pension of 6000 francs to Daguerre, and one 
 
INTRODUCTION. 
 
 o 
 
 of 4000 francs to Isidore Niepce, the son of the late photographer (as 
 purchase-money for the secret of the daguerreotype), for the honor of 
 “ having presented the scientific and artistic world with one of the 
 most surprising discoveries that adorns their country.” France has 
 adopted this discovery, and is proud to present it — “ as a gift to the 
 whole world.” These are Arago’s words, and Duchatel adds : ‘ This 
 discovery cannot he secured by patents ; when it is made known, 
 everybody may profit by it.” Although these expressions were 
 undoubtedly meant most sincerely, yet, notwithstanding, we find 
 Daguerre soon after in the English patent market ; and on the 
 15th July, 1839, Mr. Miles Berry obtained— “ for a foreigner residing 
 in France” — a patent for this invention, which had been so munifi- 
 cently rewarded in France, and had been declared in that country 
 not to admit of being secured by patent. 
 
 On the 31st January, 1839, Fox Talbot published Some remarks on 
 the art of Photographic Painting.” On the 21st February of the same 
 ; year, he gave the methods of preparing the paper used in his 
 photographic processes. Among these methods we find also the one to 
 cover the paper with a thin layer of chloride of silver, made sensitive 
 for exposure in the camera-obscura, by repeated washing. Here we 
 see the same substances employed which Davy recommended 
 ' Wedgewood to use in his experiments, and with nearly the same 
 j manipulations which he himself employed. Mr. Talbot recommended 
 ! to fix the images obtained in a brine bath (solution of chloride of 
 
 ! sodium, or common salt), which process, however, succeeded only very 
 
 I indifferently, since the light parts turned bluish the moment they were 
 I exposed to daylight. 
 
 The next communication of importance was that of Sir .Tohn 
 ^ Herschel to the Royal Society, on the 14th March, 1839, followed on 
 the 20th February, 1840, by a paper on ‘‘ the chemical effects of light 
 in the solar spectrum.” In the former of these tw’o papers, Herschel 
 i recommended the use of hyposulphite of soda as a fixing agent, and 
 in the latter he recommended to use the solution of the hyposulphite 
 hot in the case of iodide of silver, as this latter salt is less readily 
 soluble iir the cold solution of the hyposulphite than is the case with 
 chloride of silver. Herschel recommended also the employment of 
 iodide of potassium, to convert the nitrate of silver on the paper into 
 
6 
 
 THE AET OE PIIOTOGllAPHY. 
 
 iodide of silver, and gave moreover the peculiar properties of the 
 “iodised paper.” He says: “The papers so prepared (with iodide of 
 potassium and nitrate of silver) vary considerably in sensitiveness, 
 according to the strength of the solutions used. A concentrated 
 solution of iodide of potassium gives a paper nearly or altogether 
 insensible j with a weak solution the result is the reverse.” 
 
 At the meeting of the British Association at Plymouth, in July 
 1841, Mr. Robert Hunt read a paper “On the influence of the yellow 
 ferrocyanide of potassium (a compound of equivalents of cyanide of 
 potassium with one of protocyanide of iron, and three of water) upon iodide 
 of silver, and on the high sensitiveness of the same as a photographic 
 preparation. He gave also instructions how to prepare the “ iodised 
 paper, viz., as follows: “Select good smooth letter paper, wash it 
 on one side with a solution of one drachm of nitrate of silver in one 
 ounce of distilled water ; let it dry quickly, and then wash it once 
 more with the same solution. As soon as it is dry again, saturate it 
 with a solution of two drachms of iodide of potassium in six ounces 
 of distilled water ; wash it afterwards cautiously in distilled water, 
 and then let it dry in the dark, at the common temperature.” 
 
 Iodised paper was used likewise by Ryan, Lassaigne, and others ; 
 and it seems moreover pretty certain that this paper, as prepared 
 according to the instructions given by Herschel, Hunt, and others, was 
 an article of commerce, before the patent for the CaXotype had been 
 obtained. 
 
 In Sir John Herschel’s paper above alluded to, we find also mentioned 
 already the use of “ gallic acid” as an accelerative agent. In that paper. 
 Sir John Herschel states, that he “ failed to obtain satisfactory results 
 (in the way of accelerating the process) by any of the agents tried, 
 with the somewhat problematical exception of gallic acid and its 
 compounds.” 
 
 The direct production in the camera-obscura of positive pictures on 
 paper, was the next point which attracted the attention of the friends 
 of the photographic art. Prepared paper blackened by the action of 
 light was saturated with a solution of iodide of potassium, and placed 
 in the camera, where it was bleached by the luminous rays, and an 
 image thereby produced, in which the distribution of light and 
 shade was found to be the same as in nature. The most successful 
 
INTllODUUTION. 
 
 7 
 
 experimenters in this line were, Dr. Fyfe and Robert Hunt. The latter 
 published in September and October 1840, in the “ Philosophical 
 Magazine,” a paper on the use of iodide of potassium as a photographic 
 agent. Several pictures obtained in this manner, and paper prepared 
 for the process, were sold in London, at Ackermann and Co. s. 
 Herschel states also in his communication to the Royal Society, which 
 we have repeatedly mentioned already, that positive paper, prepared 
 after R. Hunt’s method, was manufactured for sale. These tacts prove 
 that iodised paper was in use before the time the calotype patent was 
 obtained. This patent was granted in 1841, and includes the use of the 
 iodised paper, the gallic acid, and, more especially, the development of 
 the latent image. There Can be no question but that Talbot is the 
 inventor of the 'beautiful calotype process ; and every one who takes 
 an interest in the photographic art, must feel grateful to that gentleman 
 for his recent generous abandonment of his patent, whereby he has 
 in a measure presented his process as a free gift to the world. Talbot’s 
 invention appears to be one of those which are usually termed 
 accidental. But in scientific discoveries the term accidental is certainly 
 misapplied, since the observer must in a measure be prepared for the 
 phenomenon observed, in order that it shall not elude his attention, 
 and, still more, that he may improve upon the results of his 
 observations. 
 
 Mr. Talbot, in the course of a series of experiments, tried various 
 chemical preparations, and among others, also gallic acid. He put by 
 in the dark some silver iodide papers which he had treated with this 
 acid, and which showed no alteration ; when he took them out again 
 after some time, he found very distinct impressions on them. 
 
 Fresh experiments confirmed the great importance of gallic acid in 
 the photographic process ; the manipulations of the method of employ- 
 ing gallic acid as an agent in photography are unquestionably Talbot’s 
 own. The first pictures produced in this manner created no incon- 
 siderable sensation in the scientific world, although they did not posse.^s 
 by far the degree of perfection that has since been attained. 
 
 Still this method of Talbot’s, notwithstanding its undoubted excel- 
 lency, could only with ditficulty be employed for the portraying of 
 living objects, as the prepared paper was wanting the requisite degree 
 of sensitiveness, which was imparted to it subsequently by Gundell as 
 
8 
 
 THE ART OF PHOTOGRAPHY. 
 
 stated by that gentleman in the “ Philosophical Magazine,” of May, 
 1844. At the time when Daguerre presented his invention to the 
 hrench government, twenty minutes were required to obtain an 
 impression. It was only subsequently, in 1840, that Dr. Draper, of 
 New York, succeeded in producing the first daguerreotype portrait, by 
 acting upon Towson’s suggestion to employ larger lenses, and to place 
 the prepared plate or paper in the rightly-adjusted focus. 
 
 In the same year the art of photography was essentially advanced by 
 Goddart and Claudet’s discovery that chlorine and bromine, in conjunc- 
 tion with iodine, considerably increase the sensitiveness of the prepared 
 surface. The employment of accelerative agents, such as chlorine and 
 bromine, may be looked upon as a consequence necessarily resulting 
 from the introduction of the scientific element into the study of the 
 photographic art ; since the analogy of iodine, chlorine, and bromine, 
 in their effects and properties was at the time already well known to 
 chemists. The manner of employing these agents underwent numerous 
 modifications, and a variety of mixtures were recommended. 
 
 In 1844, Hunt communicated to the meeting of the British Associ- 
 ation at York, his experiments with sulphate of protoxide of iron, as a 
 liberating or developing agent, to bring to light the latent images on 
 paper. At the same meeting, Dr. Woods made public his method, 
 which he called catalysotype, and in which sesqui-iodide of iron plays 
 an important part. As Talbot was also present at the meeting, the 
 new methods were amply discussed, and Talbot fully acknowledged 
 their importance. Still, notwithstanding these several progresses in the 
 photographic art, the time required to obtain a picture was much 
 too long to admit of the portraying of living objects; and, although 
 some enthusiastic admirers of the art had the rare courage to sit nearly 
 half an hour with open eyes and immovable features (as far as they 
 could command them), in the dazzling sunshine, yet the lineaments 
 impressed on the plates were of a nature that it could not well be 
 expected they should be acknowledged as faithful likenesses. 
 
 It was soon seen that this serious obstacle was in a great measure to 
 be attributed to the camera-obscura, and that this instrument could no 
 longer be retained in its simple construction ; nor did Towson’s improve- 
 ments in it go far enough to remedy the imperfections complained of. 
 A lens had hitherto been used, of three inches aperture, and sixteen or 
 
INlliODUC'i’ION. 
 
 9 
 
 eighteen inches focal distance ; this was covered to one inch aperture, 
 by means of a screen placed before it at a certain distance. Now, this 
 contrivance indeed excluded those rays which, from the form of the 
 lens, could not be brought to converge, and must, therefore, necessarily 
 tend to disturb the distinctness of the image. A pretty uniformly 
 distinct impression w’as thus obtained ; but to achieve this result, an 
 equally great sacrifice was imposed, on the other hand, viz., that of a 
 considerable amount of light, excluded by the smallness of the reduced 
 aperture. All attempts to dispense with the screen, by modifications 
 and improvements in the construction of the lens, failed for a time. 
 Many fruitless experiments were made by practical opticians ; many 
 equally unproductive calculations and computations by theoiists. To 
 a combination of both it was reserved to gain the victory. 
 
 Professor Petzval, of Vienna, at the request of Professor von Ettinghau- 
 sen, who was engaged at the time in a variety of experiments on the new 
 j invention, submitted the question of the construction of an object-glass 
 
 ! that might answer the purpose of photogi’aphy, to a long and searching 
 
 ^ examination, and made extensive calculations and computations on the 
 subject. In 1843 he published the result of his labors,* which then 
 I ultimately led to the combination of glasses in the lens, on which rests 
 the construction of the object-glasses, universally known as Voigt- 
 lander’s. This was indeed a considerable step in advance towards the 
 attainment of the desired end, but it was not yet all that 'v^as required. 
 For, as it was desired to employ photography more especially for the 
 portraying of living objects, and as the slightest movements of the 
 person sitting for the portrait would necessarily tend to efface the clear 
 outlines of the image, the great desideratum was to devise means to 
 heighten the sensitiveness of the prepared surface to such a degree that 
 half a minute’s sitting should suffice to obtain a clear impression. And 
 this problem chemistry has gloriously solved, by a judicious combi- 
 ' nation of the iodine with bromine and chlorine. The opticians, on 
 
 ' their part, continued to devise and apply improvements in the construc- 
 
 tion of the object-glasses ; and it may be affirmed that Breton, Buron, 
 Chevalier, and others, of Paris, Waible, of Vienna, and Busch, of Rathe- 
 
 « « Bericht fiber die Ergebnisse elniger dioptrischer Untersuchungen.” Pcslb, 
 1843. 
 
10 
 
 THE ART OE PHOTOGRAPHY. 
 
 now, supply object-glasses at present, which are in no way inferior to 
 those by Voigtliinder, and may even be said to excel them. This 
 applies more especially to Busch’s, which are from one-third to one-half 
 cheaper than V oigtlander’s glasses, and combine with the greatest accuracy 
 and correctness of delineation, a comparatively high degree of luminousness. 
 I have tried and most carefully examined lenses of every hind and description, 
 procured from a number of different shops, and I can most conscientiously 
 say that the object-glasses made by Busch of Rathenow are positively the 
 best that can be procured at present. 
 
 The apparatus. No. 1, of the annexed price-list (see Appendix) is 
 suited more especially for medallion pictures ; Nos. 2, 3, and 4, are 
 suited principally for daguerreotypes. Nos. 6 and 8 are the very best 
 that can possibly be procured for talbotypes and vitrotypes.* 
 
 The high price of the silver plates, on the one hand, and the 
 circumstance on the other, that the daguerreotypes can only be seen 
 with equal distinctness in all parts in a certain position to the light, 
 and also the unequal texture of paper, naturally induced a desire to 
 devise means for remedying these drawbacks; and this led to the 
 application of glass covered with a thin coating of matter sensitive to 
 the action of light. 
 
 The first who made experiments in this direction was Sir John 
 Herschel. As early as 1840, he attempted, by the precipitation of iodide, 
 bromide ancP chloride of silver, to fix a thin coating of these compounds 
 on glass plates, which he then exposed in the camera. In this manner 
 he obtained very distinct negative images, which could be converted, 
 by a simple process, into positive impressions. For this method, 
 which is unquestionably Herschel’s property, a patent has recently been 
 granted to some other person. Herschel describes his process as follows : 
 ‘‘ the glass plates, so prepared, receive in the camera a distinct negative 
 image, which appears either in the natural position, or reversed, as you 
 look at it in front or from behind. If a solution of hyposulphite of soda 
 is spread cautiously over the surface, and the latter is afterwards 
 rinsed with water, the picture vanishes, but as soon as the plate is 
 dry it comes again to light, when it looks very similar in appearance 
 
 * These apparatus may be had of the publisher, Mr. John Weale, 59, High 
 Holborn. 
 
INTRODUCTION. 
 
 11 
 
 to a daguerreotype, more especially if it is placed on a dark ground, or 
 blackened over the lamp, whereby, indeed, the negative image is made 
 positive.” 
 
 The next improvement, which was made hy Niepce de Saint Victor, 
 and published hy him in the “ Technologist,” of 1848, consisted 
 materially in this, that he covered glass plates with a thin coating 
 of albumen (white of egg), containing iodine. This coating, although 
 the pictures taken on it are truly beautiful, is too little sensitive to 
 serve for the taking of portraits. 
 
 Talbot used various other substances to take photographic pictures 
 on, and took out patents for the whole of them. Among these, 
 porcelain plates are mentioned as giving most gratifying results ; 
 however, the difficulties of preparing porcelain plates suitable for the 
 purpose are so great, that there appears little chance of their ever 
 being much used in photography. The same remark applies equally 
 to the other substances recommended by Talbot. 
 
 Talbot’s latest patent includes the use of sulphate of protoxide of iron, 
 and of sesqui -iodide of iron. Talbot published his method of employing 
 these salts in a letter to the “Athenseum,” bearing date the 6th 
 December, 1851, and in which he states that he has determined the 
 right proportions in which these two compounds may be used most 
 advantageously. 
 
 Talbot’s eagerness to secure for himself by patent every new process 
 and every trifling improvement in photography, served to discourage 
 further attempts at improvements on the part of the best English 
 experimenters — a result which is deeply to be regretted. However, 
 Talbot has now relinquished his patents, and has thereby removed 
 the bar which he had opposed to further researches on the part of his 
 countrymen. 
 
 Le Gray was the first to suggest the saturation of the paper intended 
 for the reception of negative images with white wax. This process 
 gives highly gratifying results, and is excelled only by the collodion 
 method. # 
 
 As, from the unequal texture of paper, the positive impressions 
 obtained are always defective, the original defect of the negative 
 image being transferred also to the positive ; and as it would be 
 difficult to procure a paper less open to this objection, I attempted to 
 
12 
 
 THE ART OE RHOTOGRARHY. 
 
 dissolve paper, and to spread it in a thin coating on glass ; however, 
 after many troublesome experiments, which led to no satisfactory 
 results, I desisted. I then tried some other substances, but also with 
 very indifferent success, until the spring of 1850, when M. Simon, 
 apothecary, of Berlin, called my attention to collodion and its 
 properties.* I immediately made experiments with this substance, 
 but with no great success at first. It was only in the spring of 1851, 
 that I succeeded in producing pictures which, though still imperfect, 
 would bear inspection. 
 
 Messrs. Archer, Fry, and Diamond, of London, had, about the same 
 time, also made experiments with collodion ; and the method of 
 this substance in photographic processes is so greatly 
 improved now that it leaves little to be desired. 
 
 True, that little is of the vastest importance, concerning no less a 
 point than the natural colors of the objects portrayed. Whether this 
 highest aim of the photographer’s aspirations will ever be attained, is a 
 question which time alone can solve. This much is certain, however, 
 that the achievements in this direction accomplished up to this time 
 by Niepce de Saint Victor, and others (with the exception of the North- 
 American Hill), warrant a hope that the photographic art may 
 ultimately reach even this highest goal of perfection. 
 
 Not only with a view to this final glorious achievement, but also 
 on account of certain beautiful changes of color produced by them, 
 various metallic salts have been employed by difiFerent experimenters, 
 and with brilliant results, as will be shown hereafter. 
 
 The entire domain of the photographic art may properly be divided 
 into the following chief provinces or sections. 
 
 I. Daguerreotype, or Photography on metallic plates. 
 
 II. Talbotype, ox Photography on paper , 
 
 III-. ViTROTYPB, or Photography on glass. 
 
 IV. Anthotype, or Photography with vegetable guices. 
 
 V . Photo-Lithography, or Photography on stone. 
 
 W e will now pass on to the description of the photographic apparatus, 
 commencing with the most important of them, the Camera-oiscura. 
 
 * I had at the time been several years absent from Europe, and had therefore 
 not yet heard of collodion. 
 
THE APPARATUS. 
 
 13 
 
 THE APPARATUS. 
 
 The simple camera- obscura, invented by Porta in the year 1650, 
 served for photographic experiments as long as the art remained in its 
 infancy ; but as the art progressed, it was soon found that this instru- 
 ment was too imperfect to satisfy the increasing demands made 
 upon it. We have already seen in the Introduction, how a most 
 material improvement was made in the camera by the combined 
 exertions of Petzval and V oigtlander. But even this improved camera 
 is by no means everything that could be desired. The demands that 
 may be justly made upon an apparatus truly deserving the epithet 
 perfect, are as follows : it must give a large-sized picture, correctly 
 drawn, and equally distinct in all parts ; it must command a most 
 intense light ; and it must be adapted equally for portraying, and for 
 taking views of architectural objects. Now, up to the present time, 
 the problem of fulfilling all these conditions equally, has not yet found 
 its solution ; indeed, one excludes the other. If the picture is to be 
 large, of equal clearness and distinctness in all parts, even to the 
 border, and equally so for near objects as for those farther off, the 
 focal distance must be proportionately longer, and the aperture, 
 through which the luminous rays enter, must be smaller ; the 
 necessary consequence of this mode of construction is, that the 
 apparatus does not command a sufficiently intense light to answer 
 the purpose of taking portraits with it. On the other hand, if the 
 focal distance is lessened, and the aperture enlarged (with a lens 
 suited to the purpose), the apparatus will indeed command a greater 
 amount of light, and will accordingly be better adapted for the taking 
 of portraits — but it will be found that this has been achieved only at 
 the expense of the size of the picture, and of the desired correct 
 delineation, and equal clearness and distinctness in all parts. 
 
 An apparatus so constructed is, therefore, but imperfectly adapted 
 for taking views of landscapes and of architectural objects ; and 
 although small views may, if need be, be taken with it, by placing 
 screens before it to reduce the aperture, the productions so obtained 
 are very inferior to the views taken with an apparatus of greater focal 
 distance and smaller aperture. This applies more especially to pictures 
 
14 
 
 THE ART OP PHOTOGRAPHY. 
 
 taken on paper ; since, from the unequal texture of that material, the 
 minute details of an object delineated on it will necessarily grow 
 indistinct and confused, or even vanish altogether, if the surface acted 
 upon is too restricted to reflect these details on a sufficiently large 
 scale. 
 
 The task of the optician consequently is, to construct and combine 
 the apparatus in a manner to produce the best total effect in every 
 individual case ; which, of course, requires, in the first place, due 
 attention to the choice of suitable curvatures in the lenses, as it is 
 principally upon this that depends the accuracy of the impression. 
 A proper achromatisation of the glasses will obviate the occurrence of 
 colored edges in the images taken. The glass for the lens ought to 
 be as white as possible, and pure and even throughout — requirements 
 which it is not always easy to fulfil. Perfect whiteness, however, 
 is not absolutely necessary ; on the contrary, a violet tint of the glass 
 is rather desirable than otherwise — provided always the coloration be 
 not too intense, since this would tend to lessen the luminousness of 
 the apparatus, more particularly with larger lenses, on account of the 
 greater thickness of the glass. There are not unfrequently little 
 bubbles and small black spots in the vitreous mass ; however, if there 
 are not too many of them, nor over large ones, their presence matters 
 little, as may be readily proved by a simple experiment : cut out a 
 small round of paper, and paste it with gum on the object-glass in the 
 centre ; a picture taken with this glass will show no difference from 
 another taken with a clean glass ; at the most, the time of exposure 
 may require to be prolonged a little, that is, if the piece of paper 
 pasted on the object-glass is of rather large size in proportion to the 
 aperture. But the glass must be free from tears ; and indeed no 
 conscientious optician will make use of glass having tears, which, 
 however, it requires a practised eye to detect. Still, even with glasses 
 of the kind, an apparatus, otherwise properly constructed, is preferable 
 to one with faultless glasses but with a defective combination of the 
 lenses ; the defect caused by tears being, after all, imperceptible in the 
 miniature picture of the camera, or, at all events, scarcely visible to 
 the naked eye. To be enabled to pronounce a correct opinion on the 
 quality of a photographic apparatus, the one thing needful is, to take a 
 picture with it ; of two apparatus of the same construction, that one is 
 
THE APPAEATUS. 
 
 15 
 
 the best which produces the larger pictures of the two, of equal or 
 superior distinctness, and in the shortest time. 
 
 Besides the quality of the object-glass, and the proper fixing of the 
 chemical focus, of which we shall treat in the next section, the accurate 
 adjustment of the apparatus also forms an essential condition for the 
 I good success of photographic operations. The prepared side of the 
 plate or paper, on which the image is to be produced, must be placed 
 exactly in the spot previously occupied by the roughened side of the 
 ground glass plate, or focussing glass (the side turned towards the 
 object-glass). If it is not made to occupy that exact position, the 
 clearness of the impression produced will suffer in proportion to the 
 extent of the deviation from it. 
 
 The construction that has been given to the camera-obscura, and to 
 the frame for the reception of the plate or paper, varies greatly; 
 j however, all the modifications introduced have essentially 'one and 
 I the same object in view, viz., the facilitation of certain manipulations. 
 
 ! In Voigtlander’s apparatus the camera consists of a large cylindrical 
 j brass tube ; in others it is a square wooden box ; the latter again 
 
 varies greatly in size and in the arrangement of the details of con- 
 struction. But they all agree in this point, that they have the object- 
 glass set in the anterior part, the roughened or depolished glass plate, 
 or focussing glass (for which is substituted the frame carrying the plate 
 or paper), being placed in the posterior part. 
 
 Fig. 1. Fig. 2. 
 
 Figs. 1 and 2 may serve to illustrate the construction of Voigtlander’s 
 apparatus. Fig. 1 presents a full, fig. 2 a sectional view of it. 
 
16 
 
 THE AllT OF PHOTOGllAPlJY. 
 
 A is the camera-obscura ; a h. the object-glass^ which may be moved 
 forwards and backw'ards towards the focussing glass e, by means of the 
 rack-work adjustment c. The compound lens consists of two achro- 
 matic glasses; the one nearest the object having an available aperture of 
 eighteen lines, the other, an available aperture of nineteen lines ; the 
 focal length of the tw'o is five-and-a-half inches. The size and the 
 focal length of the glasses differ of course with the size of the apparatus. 
 
 /is a tube screwed on before the object-glass, to exclude the lateral 
 j 9) plate cover to it, which serves to close the aperture of the 
 object-glass. 
 
 h is the conical tube with the focussing glass ; this tube screws into 
 the camera. 
 
 i is the peep-glass in the tube k, which tube is movable, for the 
 better adjustment of the focus. 
 
 B is the pedestal or stand of the camera, consisting of the supporters 
 e e ; the two sliding tubes, m and n, which serve to raise or lower the 
 camera ; the thumb-screw o, which serves to fix the tubes at the proper 
 height; and the plate p, with the three adjusting-screws q, which 
 serve to place the camera in the proper horizontal position. 
 
 C is a frame intended to receive the prepared plate r ; this plate is 
 placed in the ring s s, which screws on to the frame ; < i is the cover of 
 the frame, to screen the iodized plate from the light. 
 
 The camera-obscura, together with the stand and all the accessories, 
 is made of metal. The stand B screws on to the plate p, and may 
 accordingly be unscrewed, to make it more convenient for transport. 
 
 When it is intended to use this apparatus, the plate p is put on a 
 table, the stand B is screw'ed in, and the camera laid on the supporter 
 c, in such a manner that the projecting ring u lies close to the smaller 
 bracket of the supporter ; which will ensure the same position of the 
 camera in every operation. 
 
 One of the great advantages of this apparatus of Voigtlander is, that 
 when taken to pieces and packed in a box, it occupies only a small 
 space, and may therefore be readily carried about, which makes it very 
 convenient for travelling. Moreover, the material of the apparatus being 
 metal, there is no fear of absorption of iodine and bromine, or of 
 aqueous vapors. On the other hand, this apparatus has also its draw- 
 backs ; the plates at present in use being square, the edges of them 
 
THE APPARATUS. 
 
 17 
 
 must be cut off to fit them for the round frame j moreover, the 
 apparatus requires repeated moving in the course of every operation ; 
 and the naturally low temperature of the metal demands a longer 
 exposure of the plate. 
 
 The old construction of the camera, and which is even at present 
 most generally used, differs from the preceding principally in this, 
 that the large brass cylinder 
 is replaced by a square 
 wooden box. See fig. 3, 
 representing a so-called ex- 
 panding camera. 
 
 The tube B, carrying the 
 object-glass, is fastened to 
 the front side of the camera, 
 by means of the annular 
 
 E D 
 
 plate a, and by screws. The 
 
 outer box. A, the size of which is regulated by the size of 
 the plates, encloses a smaller sliding box, C C C, which is open 
 at both ends, and may be moved backwards and forwards on the 
 lengthened ground-board, E D, by means of the rack-work, F. 
 A piece is cut out at G, to admit into the grooves formed inside the 
 box on both sides by the ledges cc, cc, the frame with the focussing 
 glass, or the sliding board which holds the frame, carrying the plate. 
 
 The sliding box C serves to lengthen the camera, which is 
 necessary, more particularly when it is intended to take very small 
 pictures, or to make reduced copies of larger landscapes or portraits ; 
 
 
 
 
 
 
 
 the rack-work F is not sufficient for this purpose. 
 
 This power of lengthening, or expanding the camera is an advantage 
 which Voigtltinder’s apparatus does not possess ; if it is intended to take 
 very small pictures with the latter, the camera must be removed to a 
 great distance from the object to be portrayed ; and this is in many 
 cases difficult, and in others even altogether impracticable. 
 
 Fig. 4 represents a camera of a different construction, which combines 
 
 all the advantages of the two preceding ones. 
 
 The principal advantage of this camera consists in the stretching 
 bag of cloth or caoutchouc, and in the simple way in which the paper or 
 the plate may be adjusted to any angle, which may be thought adapted 
 
18 
 
 THE ART OE PHOTOGRAPHY. 
 
 5 
 
 I 
 
 to obtain a good focus. Another advantage is the vertical mobility of [ 
 
 the object-glass, whereby the object to be portrayed may readily be | 
 
 brought into the centre of the field of vision. The posterior part of i 
 
 the apparatus is fastened to a movable plate, which may be screwed 
 fast on the ground-board, at a longer or shorter distance from the 
 object-glass ; by which means the operator is enabled to employ, if need 
 be, object-glasses of different focal lengths. The whole apparatus is 
 so arranged, that it may be readily folded and packed. It weighs only 
 half as much as a common camera, and when packed up, occupies only 
 about half the space taken up by the latter. 
 
 Instead of, and even in preference to, the cloth or caoutchouc-bag 
 camera, one of pasteboard may also be used, made in the same shape as 
 the bellows of an accordion. See Fig. 5. 
 
 As this camera may be lengthened, without the intervention of a 
 sliding box, it is particularly suited for copying pictures in enlarged or 
 reduced sizes. To do the former, and more especially to copy enlarged 
 
THE APPARATUS. 
 
 19 
 
 positive pictures from small negative pictures on glass or paper, another 
 camera of the same size and construction is required, which is fastened 
 light-tight to the object-glass of the first camera, so as to place the 
 object-glass between the two. The negative picture to be copied is put 
 into the frame in the back of the second camera, which is then so 
 placed that the direct light falls through the negative picture ; in the 
 frame of the first camera is placed the plate or paper intended to receive 
 the positive impression. Of course, the length of both cameras must 
 be adjusted to the desired size of the picture. In this way small, but 
 accurate and perfect portraits may be copied life-size. This apparatus 
 is admirably suited for travellers, to take views of landscapes and 
 architectural objects; negative impressions of small size, and fitting 
 accordingly in a limited compass, may be taken on the journey, and 
 may then at leisure be transferred in larger size to positive plates or 
 positive paper. The operation of copying is conducted exactly the 
 same way as the original taking of the negative impression ; the 
 development of the positive picture is effected in the usual way. 
 
 There is still another camera of different construction, used more 
 particularly in England and France, for taking views of landscapes, and 
 to which the name '‘^traversing camera^^ has been given. The peculiar 
 feature of this camera consists essentially in this, that with a compara- 
 tively small and indifferent object-glass, it produces pictures of 
 considerable size, accuracy, and clearness. Thus, with an object-glass 
 of common quality, views are obtained, fourteen inches long, by four- 
 and-a-half inches wide, and which are perfectly clear and distinct 
 throughout, and embrace a field of vision (horizon), of more than 150 
 degrees. 
 
 The arrangement, by means of which this result is obtained, consists 
 in the main : — first, in an horizontal motion imparted to the object-glass 
 by rack-work, and which causes it to traverse successively all the points 
 of the horizon ; — secondly, in the cylindrical incurvation which the 
 paper or plate is made to assume by means of a groove in the camera ; 
 as the paper by itself would not retain the curved position given to 
 it, it is placed moist on a metal plate, to which it readily adheres, 
 and its incurvation is thus ensured during the operation ; by this 
 contrivance objects at however unequal distances from each other 
 are transferred to the plate or paper, at the same focal distance, and 
 
20 
 
 THE ART OE PHOTOGRAPHY. 
 
 without displacing the camera ; — thirdly, in a small vertical aperture in 
 the bottom of a kind of box, which accompanies the object-glass in its 
 motion. This aperture, which supplies the place of a diaphragm that 
 would occupy a position in the rear, brings to bear upon the excitable 
 surface only the rays in the centre, i. e,, those rays only which have 
 no sensible aberration. This tends, of course, materially to increase 
 the distinctness and accuracy of the impression. 
 
 The position of the turning axis of the object-glass must be fixed 
 with the greatest precision, otherwise the images of the objects 
 towards which the apparatus is successively turned, would, ere they 
 become extinct and give place to the succeeding ones, move on the 
 depolished glass, and accordingly also on the plate or paper, which of 
 course would destroy the clearness of the image. 
 
 To hit the proper position of the axis to the object-glass, the tube of 
 the latter need simply be pushed in more or less, until perfect immo- 
 bility of the images is attained. 
 
 The next apparatus in importance is the Iodine apparatiLs. 
 
 This consists of a wooden box lined with glass ; or of a porcelain or 
 glass* dish ; or cup about two inches deep, and of a size corresponding 
 to that of the plates to be acted on ; the rim of the dish or cup is 
 ground perfectly even ; the cover consists of a strong yellow glass plate, 
 also ground perfectly even. 
 
 Fig, 6 represents an apparatus in which the iodine dish, and the 
 - bromine dish are in the same 
 
 Fjg. 6. 
 
 box. This apparatus, which 
 is much used by English pho- 
 tographers, affords this advan- 
 tage, that the progressive 
 coloring of the plate may be 
 watched in the two mirrors 
 in front ; and that the frame carrying the plate may be readily shifted 
 from the iodine to the bromine. 
 
 
 The Mercurial apparatus (fig 7) consists of a square box, resting on 
 four legs, and for the sake of greater convenience, with the top slanting 
 
 * Yellow glass dishes are preferable to all others ; the porcelain dishes arc 
 strongly affected by the iodine, and after a time the glazing comes off. Phials 
 of yellow glass arc also suited best to keep photographic preparations in. Solutions 
 of silver, for instance, never turn black in them. 
 
THE APPAllATUS. 
 
 21 
 
 at an angle of 45 degrees; at the bottom of the box there is a small iron 
 cup for the mercury. 
 
 In front, and at one side, there are two apertures, closed with panes 
 of yellow window-glass, through which the image may safely be 
 examined by daylight, to note its progress. If panes of ivUte glass are 
 used, the image can be examined without injury only by the light of a 
 small taper. 
 
 Fig. 8. 
 
 Fig. 8 shows a mercurial apparatus of a different construction, which 
 is used in North America. 
 
 This apparatus affords the advantage of a saving of mercury, as in 
 the first place less of that substance is required with it ; and in the 
 second place, the fumes evolved condense on the sloping 'sides of the 
 hopper-shaped box, and roll back into the iron cup at the bottom. 
 Moreover, this apparatus does not require so high a temperature as 
 others of different construction. 
 
 Besides these apparatus, the operator requires also a small stand to 
 lay the silver plates on, in the process of gilding ; and some porcelain 
 or glass cups and dishes to hold distilled water, solution of hypo- 
 sulphite of soda, of nitrate of silver, of iodide of potassium, &c.&c. 
 
 There are several other little contrivances and implements, serving 
 to facilitate certain manipulations, but which every one may devise 
 and construct for himself, as they may seem best suited to the purpose 
 for w^hich they are intended. 
 
22 
 
 THE ART OP PHOTOGRAPHY. 
 
 THE FOCUS. 
 
 It is a remarkable fact, and one which must never be lost sight of 
 in photographic operations, that the rays which possess the greatest 
 luminousness, do not Wcewise exercise the greatest chemical action. 
 Theiefore, even with an adjustment of the apparatus giving a perfectly 
 clear and distinct image of the object, and with the most rigorously 
 exact placing of the photographic plate or paper, there are still certain 
 accessory conditions required to obtain a correct impression. 
 
 The rainbow colors of the white ray refracted through the prisma, 
 are seen side by side on the surface on which they are thrown ; now in 
 the camera-obscura, these colors or rays lie, properly speaking, behind 
 one another, and cover each other, so that they appear to the eye as 
 one coinciding all of them in the yellow ray as the most intense of them; 
 it is accordingly to this ray that the optical focus of the camera-ohscura 
 is adjusted. But the yellow ray is not the one possessed of the most 
 energetic chemical action ; it is the violet ray in which the chemical force 
 and influence of light chiefly resides ; the plate or paper intended for 
 the reception of the image, must accordingly be placed in the focus of 
 this latter ray. Now, as the length of each ray depends partly on the 
 radius of the curvature of the lenses, partly on the refractive power of 
 the vitreous mass, and partly also on the distance of the object from 
 the object-glass, it follows that every object-glass must be specifically 
 tried and tested, to determine the difference between the oj)tical and 
 chemical focus. 
 
 In non-achromatic lenses, the point of convergence of the violet rays, 
 and accordingly the chemical focus, lies usually nearer to the object 
 than the optical focus, which difference decreases, however, in proportion 
 to the distance of the object from the apparatus. In this case, therefore, 
 the camera must be shortened, which is effected most simply by 
 moving the object-glass backwards. 
 
 But the case is different with achromatic lenses ; here no general 
 rule can be laid down, but every object-glass must be submitted to a 
 separate, careful trial. Various apparatus and contrivances have been 
 devised to determine the chemical focus of an object-glass, but the 
 
THE FOCUS. 
 
 23 
 
 simplest and easiest way of all is the following, recommended by 
 Professor Dr. Varrentrap. 
 
 Place nine books, with printed title on the hack, perpendicularly 
 side by side at a certain distance from the object-glass, in such a 
 manner that the second stands an inch further back than the first, the 
 third than the second, the fourth than the third, and so on for the rest. 
 
 Place and ailjust the apparatus so that you see the titles on the backs 
 of the books reflected in the glass plate, with the printing on the back 
 of the in the row appearing the most distinct of the nine, which 
 may be readily and accurately discerned. Now, take a picture with the 
 apparatus so adjusted, and without displacing it. The degree of accuracy 
 and distinctness possessed by the picture will enable you to fix upon 
 the proper adjustment of the apparatus. 
 
 Opticians have indeed endeavored to supply object-glasses, through 
 i which all the rays should converge in one point : in this they have, 
 however, succeeded only for certain distances. 
 
 There is another way of arranging the matter, viz., by employing 
 glasses that intercept those rays of which the chemical action is hut little 
 energetic, or, in other terms, those rays which counteract the chemical 
 effects of the violet ray ; the principal among these rays is the yellow. True, 
 this means involves a certain loss of light, which, however, is amply 
 ' compensated by the increased energy of the chemical action, and the 
 ! greater certainty in the performance of the process. 
 
 As it is, however, rather difficult to procure glasses of the kind, 
 another way still may be recommended, viz., 
 to place before the object-glass a very thin violet- 
 colored glass, ground to exactly the same curva- 
 I lure as the object-glass, as may be seen in 
 ! Fig. 9, where a denotes the violet-colored 
 glass. 
 
 This contrivance, which fully answers the 
 purpose, maj" be readily applied to object-glasses of all kinds. 
 
 Fig. 9. 
 
24 
 
 THE AllT OF PHOTOGRAPHY. 
 
 I.~ DAGUERllEOTYPE ; 
 
 OR, 
 
 PHOTOGRAPHY’- ON METALLIC PLATES, WOOD, AND IVORYL 
 
 Strongly-silvered copper plates are now almost exclusively employed 
 in Daguerre’s method of producing pictures on metallic plates by the 
 influence of light. However, the light does not affect the compounds of 
 silver alone, but almost all metallic oxides, though in very different 
 degrees and spaces of time, as will be seen hereafter. 
 
 The so-called ‘^silver plates” used for photographic purposes are 
 manufactured in two different ways, of which one, however, is greatly 
 preferable to the other. The silvered copper plates generally sold in 
 the early days of photography, had a thin coating of silver hammered 
 or rolled down on them ; the same method is still pursued at the 
 present time in England and France. Now, these plates have their 
 good points, which are outweighed, however, by certain defects inherent 
 in the mode of their manufacture, as will be shown immediately. The 
 other, and better method of plating the copper, is by the galvanic 
 2>rocess. The great advantage of this latter process is this, that the 
 silver spread over the surface of the copper is purer, and more uniformly 
 and evenly distributed, than is the case with the plates prepared by 
 the hammering or rolling process ; and, what is of greater importance 
 still, that the silver coating is of equal density throughout, which cannot 
 well be the case with the hammered or rolled plates. Now a disparity 
 in the density of the silver of the coating is a serious drawback; since 
 not only are the softer and looser parts more strongly affected and 
 wasted in the processes of cleaning and polishing than the harder and 
 denser parts, but the formation of iodide of silver, in the process of 
 iodising, extends also more deeply into the softer parts, which, of 
 course, cannot but impair the beauty of the picture subsequently taken 
 on the plate. 
 
 Another defect which the French plates more particularly labor 
 under must not be passed over here : it is this, that the silver coating 
 
POLISHING THE PLATE. 
 
 25 
 
 on them is so extremely thin (which explains their cheapness), that 
 they can hardly bear one cleaning with pumice powder or Venetian 
 tripoli and oil, and can accordingly, in most cases, be used only once ; 
 which is a serious consideration for beginners, who are so liable to 
 failure in their experiments. Whereas the galvanic-plated article, 
 with its thicker coating of silver, wdll bear cleaning repeatedly, and 
 may, therefore, be used several times. The best plates as yet offered 
 to the trade are those manufactured by F. Schneider, 9, Link’s 
 Strasse, Berlin. 
 
 To render a silvered copper plate sensitive to light, it must be 
 subjected, in the first place, to the processes of cleaning and polishing. 
 
 CLEANING THE PLATE. 
 
 The plates sold in the shops are seldom so free from scratches, &c., 
 that the operation of cleaning can be dispensed with ; however, they 
 need not be rubbed so long as plates that have already been used. 
 
 To clean the plate properly, it should be fixed on a small board or 
 block. The best cleaning material is Venetian tripoli, ground to an 
 impalpable powder upon a porphyry slab, with water, and dried. 
 This powder is dusted over the plate out of a muslin bag, and the 
 surface so dusted over is then rubbed with cotton fleece,* imbued 
 with a little olive oil, or, better still, with ethereal oil, which does not 
 waste the plate so much as olive oil. The hand of the operator should 
 be moved round in circles of various dimensions, until all superficial 
 scratches, spots, or cracks are rubbed out, and the plate presents a 
 uniform white lustre. 
 
 POLISHING THE PLATE. 
 
 The plate cleaned by the preceding operation is then polished. 
 To this end, the particles of fat which may still adhere to it are 
 removed, which is effected in the most simple way by the appli- 
 cation of some polishing agent, and best of most finely levigated and 
 elutriated colcothar (rouge, or jeweller’s red rouge), which is dusted over 
 the surface, and moistened with a few drops of slightly acidulated distilled 
 
 * The cotton fleece had always better be washed first in spirits of wine, and 
 dried again before using it. 
 
 0 
 
26 
 
 THE ART OF PHOTOGRAPHY. 
 
 water {one drop of sulphuric acid, and two drops of nitric acid, to an 
 ounce of water) ; a dossil of clean cotton is then rubbed about on the 
 surface in circles of various dimensions, until the plate is perfectly dry, 
 presents a clean polish, and shows no colored spots or streaks when 
 breathed upon. If it happens to show spots or streaks, the operation 
 must be repeated to get rid of them. The final deep-black lustre is 
 usually given by means of a polishing lathe, mounted with circular 
 velvet buffs. The plate, still attached to the board or block, is 
 dusted over with most finely pulverised colcothar or bone-dust, and 
 is then gently pressed against the huffs, the wheel being kept rapidly 
 revolving, until the desired deep-black lustre is given to the plate. It is 
 by no means a matter of indifference in which direction the polishing 
 stroke or touch is carried ; for it is upon this that depends in a great 
 measure the distinctness of the picture subsequently taken on the 
 plate. The touch must be carried so that it intersects at a right angle 
 the perpendicular lines of the object to be portrayed. In default of a 
 polishing-lathe, buffs to work with the hand may be used instead, in 
 which case the operation will, however, consume more time ; the 
 buffs consist simply of narrow slips of board, covered with prepared 
 velvet or doe-skin leather. 
 
 The polishing of the plate is an operation which requires par- 
 ticular care, as upon its proper execution depends the distinctness 
 of the picture. The polishing material has a great deal to do with 
 the proper success of the operation. An astonishing variety of 
 substances and mixtures have accordingly been suggested for the 
 purpose. One of the best of these is the so-called American plate 
 powder, which is composed of two parts (by weight) of colcothar ; one 
 part of ivory-black, two of graphites, and one of binoxide of tin ; these 
 substances are most finely levigated and elutriated, and most intimately 
 mixed together. 
 
 The plate being thus prepared for the subsequent processes, the 
 operator has now to impart to it the requisite sensitiveness to light. 
 Various agents are employed to effect this. Almost every photographic 
 artist has some pet mixture of his own. 
 
 Among the agents employed in photography, the compounds of silver 
 with iodine, bromine, and chlorine, used either separately or jointly, are 
 the most highly valued, on account of their ready decomposition by light. 
 
IODISING THE PLATE. 
 
 27 
 
 The compounds of fluorine, cyanogen, sulphur, selenium, phosphorus, 
 play likewise an important part, and in many cases also ammonia. Iodine 
 is unquestionably the most important body used in photography, as its 
 compounds with the metals are so very readily decomposed by light. 
 The sensitiveness to light of a plate prepared with iodine, is still 
 heightened by the additional application of chlorine and of bromine, or of 
 both united. 
 
 IODISING THE PLATE. 
 
 As iodine has a tendency, even at the common temperature of the 
 air, to assume the gaseous state, and as it combines in that state with 
 the metals, upon simple contact with them, it is an easy task to generate 
 on the polished silver plate the coat of iodide of silver, requisite for the 
 production of a picture on it. For this purpose we use the so-called 
 I iodine-box. 
 
 i Dry iodine, in a state of minute division, is uniformly spread over the 
 j bottom of the box, which is then covered with the yellow glass plate. 
 
 ! The simplest way of reducing the iodine to a state of minute division, 
 
 1 is to dissolve it in alcohol, precipitate it again with water (a menstruum 
 
 j in which it is only very sparingly soluble), filter off the fluid, and dry 
 
 I the pulverulent precipitate. 
 
 The polished plate is now put into the iodising frame, the glass plate 
 lifted off the box, and the frame carrying the plate substituted for it. 
 The iodine fumes in the box combine forthwith with the silver on the 
 plate, whereupon the surface of the latter acquires first a straw-colored 
 hue, then a golden tint, which changes to rose, then to violet, and finally 
 to blue. Each of these different degrees of iodation is possessed also 
 of a different degree of sensitiveness to light. For the taking of 
 inanimate objects, w'here the time of exposure is a matter of secondary 
 importance, the blue coloration answers the purpose best ; but the 
 case is different in reference to living objects, as we shall see hereafter. 
 If the blue-colored plate is still left exposed to the iodine fumes, it 
 ' commences to turn green, in which state it is almost entirely insensible ; 
 upon a further continuation of the process, the color of the plate 
 changes again to yellow, and then passes once more through the 
 various shades, until the surface ultimately presents again the blue 
 tint, which it exhibited at the end of the first iodation ; this repetition 
 
 c 2 
 
28 
 
 THE ART OF PHOTOGRAPHY. 
 
 of the process seems to heighten the sensitiveness of the plate. Upon 
 a further continuation of the process, the colors change again, passing 
 through all the various shades indicated, from yellow to blue ; but the 
 plate loses thereby in sensitiveness, and is finally rendered quite 
 insensible. One of the principal points to be attended to, is uniformity 
 of coloration, as stains on the plate always necessitate a fresh polish. 
 An unequal distribution of the iodine powder over the bottom of the box 
 is a frequent cause of stains on the plate ; but this defect is often 
 occasioned also by the use of plates that have been kept ready-polished 
 a long time before their iodation is proceeded with. This is a 
 practice to be disapproved of altogether, since the impressions taken 
 on such plates are never quite clear and distinct ; which may be owing 
 to the condensation of atmospheric air or other gaseous bodies on 
 the surface of the plate, where they subsequently tend to impede the 
 combination of the iodine fumes with the silver. 
 
 The plate so prepared may now be exposed to the light in the 
 camera obscura ; the time of exposure varies according to the 
 luminousness of the apparatus, and to the illumination of the object to 
 be portrayed ; from one to two minutes are, however, generally 
 sufficient to produce a clear impression, unless the luminousness of 
 the apparatus is too feeble, and the object not properly illumined. 
 
 By the joint application of bromine or chlorine, or of both together, 
 with the iodine, the time of exposure is shortened to a few seconds. 
 The proper proportions in which these substances ought to be mixed, 
 must be left to personal experience and practice ; this much may be 
 said, however, that the success of the process is greatly dependent 
 upon the proportions used. There are numbers of recipes for the 
 preparation of such mixtures, many of them rather complex, but not 
 the better for that than others that are more simple. The easiest way 
 (if you operate with fluid substances) is to use brome water. One part 
 of bromine requiring thirty-eight parts of water for its solution, all that 
 is necessary to prepare a solution of bromine of accurately known and 
 constant strength, is to pour over a given quantity of bromine, in a glass 
 phial, an amount of w'ater sufficient only to dissolve the greater part of 
 the bromine, so that some undissolved bromine is left at the bottom of 
 the phial. 
 
 This brome water is poured out into a glass or porcelain dish 
 
IODISING THE PLATE. 
 
 29 
 
 covered with an air-tight fitting glass plate, and the silver plate, 
 iodised to the violet tint, is then exposed to the action of the brome 
 vapor rising from the solution, until it has acquired a blue color. 
 To keep the solution of bromine of constant strength, it is advisable to 
 pour the brome-water back into the phial each time after using it, 
 taking care, of course, that there shall always remain some bromine 
 undissolved in the flask. 
 
 Or the plate, iodised to the rose tint, is placed over chloride of lime, 
 until it reaches the violet hue ; it is then exposed to the bromine vapor 
 until it changes to blue. 
 
 Easy and simple though this method unquestionably is, yet the 
 brome water has this great disadvantage, that aqueous vapors will 
 often, and more particularly at a somewhat high temperature, escape 
 along with the bromine, and condensing again on the cold plate, 
 diminish or even altogether destroy the sensitiveness of the latter. 
 Moreover the impressions on plates that have had a touch of aqueous 
 vapor, are always defective, and often look as if a veil or film were 
 spread over them. It may therefore be preferable to substitute for 
 the brome water, lime impregnated with bromine, which may be 
 readily procured by putting bromine into a small vessel, placing this 
 in a larger vessel, containing recently burned lime, slacked in the air, 
 and inverting a glass-bell over the whole. The volatilising bromine is 
 at once absorbed by the lime, until the latter is completely saturated 
 with it, which may be known by the cinnamon color which it exhibits. 
 
 Equal sensitiveness, together with a finer tint, is given to the plate 
 by a combination of chlorine vdth iodine, usually called chloriodine 
 (chloride of iodine), and which is most probably a compound of the 
 protochloride and terchloride of iodine. With this compound, there 
 is no need of a previous iodation of the plate ; the latter may at 
 once be exposed to the fumes of the chloride of iodine, until the blue 
 color appears. A little bromine may be added to the chloriodine ; this 
 addition would seem to impart greater sensitiveness to the plate. 
 
 In default of chloride of iodine, the plate may first be exposed in the 
 iodine-box until it show's the violet tint, and then placed over chloride of 
 lime, until the blue color appears. The result is the same. Bromide 
 of iodine and iodide of bromine are also frequently used in the 
 
 same way. 
 
30 
 
 THE ART OE PHOTOGRAPHY. 
 
 Of all the mixtures hitherto used, that recommended by Graff, of 
 Berlin has been found to answer best. This consists of — 
 
 1 ounce oi protochloride of iodine. 
 
 1 ,, brome water. 
 
 f „ tincture of iodine. 
 
 10 ounces of distilled water. 
 
 Mix the iodine tincture with the water, add the protochloride of 
 iodine to the mixture, and then as much water as will impart to the 
 whole fluid the color of Madeira wine. Add the brome water, and 
 shake the mixture. Upon the addition of the water to the mixture of 
 iodine tincture and protochloride of iodine, the fluid turns turbid, owing 
 to the, separation of iodine ; however, this turbidity disappears again, 
 upon the addition of the brome water. 
 
 The mixture must be allowed to stand at rest for several days before 
 using it. 
 
 The American photographers, whose productions enjoy such universal 
 reputation, use almost exclusively dry substances, to render the plates 
 sensitive to light. The one most generally used is sold in the shops 
 as Thompson’s Dry-quick ; this is prepared as follows : — 
 
 A large lump of quick lime is soaked two hours in spirits of wine, 
 and then let slake in the open air to a fine powder. To one pound of 
 this powder are added one and a half ounce of bromine, and one and a 
 half ounce of pulverised alum. The process of iodation is first con- 
 ducted over the dry iodine in the box, and afterwards over the powder. 
 When this powder has lost some of its strength, the addition of a few 
 drops of bromine suiiices to restore it to the proper standard. 
 
 The American photographers use also a fluid composition, sold in the 
 shops under the name of Thompson's Accelerator. This is prepared 
 in the following manner : — 
 
 Make a strong solution of lime in a quart of water, add to this half 
 an ounce of chloriodine, and then drop bromine into the mixture, until 
 the chloriodine is dissolved.* Then add one drachm of nitrate of 
 silver, shake the mixture well, and add thirty drops of aqua regia 
 (nitrohydrochloric acid). When you want to use this mixture, put first 
 
 * Some recommend as an improvement to add at once a drachm of bromine, 
 and then every day a few drops of that substance, until the desired end is attained. 
 The great point, however, is to avoid the addition of an excess of bromine. 
 
DEVELOPING THE PICTURE. 
 
 31 
 
 a table spoonful of pulverised alum into the dish, and then one part of 
 the mixture, diluted with six parts of wat^r. Expose the plate tiist in 
 the iodine-box, until it has acquired a lemon color, then place it over 
 the mixture in the dish, until a dark orange tint is produced, and 
 ultimately expose it again to the dry iodine fumes one fourth of the 
 time which it took to impart the orange tint to the plate. 
 
 The following method may be resorted to to prevent tbe unequal 
 distribution of iodine fumes over the surface of the plate. Spread the 
 iodine as evenly as can be over the bottom of the box, cover it over 
 with two or three pieces of flannel of the size of the box, lay over the 
 last piece a leaf of very smooth paper, and over this a small board 
 fitting closely into the box. This little board will absorb the iodine 
 fumes equally all over its surface 5 upon this board is subsequently 
 laid the frame carrying the plate, and left there until the required tint 
 is imparted to the latter. 
 
 Besides the “ accelerating agents,” which we have described here, 
 there are, as has already been stated, various other compositions recom- 
 mended for the same purpose ; but they all of them contain the same sub- 
 stances as those mentioned here, and diifer from them only in reference 
 to the respective mixing proportions of the several ingredients. The time 
 of exposure in the camera, required to produce a correct impression on a 
 propei'ly prepared plate, depends on various circumstances, and cannot 
 be accurately fixed therefore. As a general rule, it may be assumed 
 that, with a good apparatus and a properly prepared plate, from thirty 
 seconds to one minute’s exposure to sun light, will always suffice to 
 obtain a clear and vigorous impression. 
 
 The plate removed from the camera, after adequate exposure to the 
 luminous rays, must present no trace as yet of the picture. If the latter 
 can be discerned on it, the exposure has been too long ; in which case 
 the best way is to clean and polish the plate again, as the picture may 
 be looked upon as irremediably spoiled. 
 
 To develope the latent image on tbe plate, the latter is exposed in 
 the mercurial apparatus to the fumes of mercury, which, condensing on 
 the parts acted on by the luminous rays, render the tracings of the 
 image visible. The plate is attentively watched through tbe yellow 
 peep-glass in front of the box, and the exposure to the mercurial fumes 
 is stopped the moment the picture has become distinctly visible in all 
 
82 
 
 THE ART OF PHOTOGRAPHY. 
 
 parts. Persons unskilled in photographic operations,, should watch the 
 thermometer of the apparatus j when this indicates a temperature of 
 from 122 to 140 degrees Fahrenheit, the spirit or oil lamp should be 
 removed to let the mercury cool again. In no case should the heat be 
 permitted to exceed 167°. An eye, practised by experience is, however, 
 always the safest guide in this operation. 
 
 The picture is now indeed finished, but it has still to undergo an 
 additional process before it can be safely exposed to the light of day ; 
 this process concerns the removal of the iodide of silver from the 
 plate. The best and most reliable agent for this purpose is, a solution 
 of one ounce of hyposulphite of soda (NaO,S 2 O 2 +5HO), in a 
 quart of distilled water ; in this solution the plate is immersed, until the 
 whole of the iodide of silver is dissolved, which is clearly indicated 
 by the change of color (the removal of the yellow tint of the iodine). 
 With this solution of hyposulphite of soda, the desired end is readily and 
 expeditiously achieved. A hot concentrated solution of common salt 
 (chloride of sodium) may also be used as a fixing agent, but it does not 
 answer the purpose half so well as solution of hyposulphite of soda. 
 Iodide of potassium and bromide of potassium, might indeed also be 
 used to remove the iodide of silver from the plate ; however, as their 
 action in this respect is by no means superior to that of the hypo- 
 sulphite of soda, whilst, on the other hand, they are much more 
 expensive than that salt, their substitution for it would offer no 
 advantage. 
 
 As soon as the whole of the iodide of silver has been removed, the 
 plate must be washed, first in common water, then in distilled water, 
 and afterwards quickly dried over a spirit lamp. In this latter 
 operation the plate should be held in a very inclined position, and the 
 action of the flame let proceed from the upper to the lower edge, taking 
 care to move the plate incessantly to and fro all the while, and to take 
 away the lamp as soon as the surface is fairly drying. The last few 
 drops of water, which remain adhering, to the lower edge of the plate, 
 may be readily removed with some blotting paper. The operation of 
 washing requires great care and attention, to guard against staining the 
 image, an accident to which the plate is but too liable, more especially 
 if the distilled water used for the last washing is not absolutely pure, 
 since in that case the matters which it holds in solution, are, upon 
 
PICTURES ON COPPER, IRON, STEEL, &C. 33 
 
 its evaporation, left on the plate, and it is difficult to remove 
 them again. 
 
 It is only now that it can be fairly ascertained to what extent the 
 process has been successful, as it is only now that the imperfections 
 and blemishes of the picture are brought fully to light. 
 
 As the latent image produced on the plate by the action of light, 
 has only been developed by the condensed mercurial fumes, and as 
 the mercury has not entered into chemical combination with the 
 silver, but simply adheres to it mechanically, it is evident that the 
 image must be exceedingly liable to be effaced, unless protected from 
 contact ; this protection is best afforded by a thin coating of gold, 
 which is put on by pouring solution of chloride of gold over the surface of 
 the plate, and applying the flame of the spirit-lamp to the bottom. This 
 puts the finishing touch to the picture, which is only now seen to full 
 advantage. After gilding, the plate is washed once more in distilled 
 i water, and quickly dried. 
 
 ! As has already been intimated, pictures may be produced also on other 
 i metallic plates besides silver ; however, the process must be modified in 
 ! certain points, according to the nature of the metal used. Copper plates 
 are cleaned and polished in the same way as silvered plates ; but the 
 surface on which the impression is to be taken, must not on any 
 account be touched with the fingers, before it has been thoroughly 
 cleaned, since that would produce stains upon it, which it would be 
 found impossible to remove afterwards, even by heating the plate to 
 redness. 
 
 The cleaned and polished copper plate is then iodised, and the 
 impression taken on it in the camera, in the same way as in the case of 
 silvered plates ; but, instead of employing mercurial fumes to develop 
 the latent image, the impression is exposed to the vapor of sulphuretted 
 hydrogen, which speedily renders it visible, the several parts of the 
 I image appearing differently colored, according to the intensity of the 
 i illumination of the obj ect. Unfortunately, copper plates are not sensitive 
 
 enough to serve for the portraying of living objects, but they answer 
 very well indeed for landscapes. 
 
 Iron, steel, brass, and German silver may also be used : I have 
 employed these different metallic substances, preparing them in the 
 same way as silver and copper plates, and have obtained very promising 
 
 c 3 
 
34 
 
 THE ART OF PHOTOGRAPHY. 
 
 results with them ; still not yet of so positive and definite a kind as 
 would justify my recommending their general application in the 
 Daguerreotype process. The ultimate decision as to their fitness or 
 unfitness for the purpose, must be left to a series of systematic 
 experiments ; I hope I may at some future tinie have something more 
 to say upon this point. 
 
 The method recommended by Talbot and Malone to produce 
 photographic pictures on steel, should more appropriately be termed a 
 method to produce images on iodised albumen, the steel serving 
 simply as the material over which the layer of the latter substance is 
 spread. This method is said to be applied advantageously in steel 
 engraving, to get the drawing on the plate. However, I cannot say 
 that I have been successful in it. 
 
 But there are two non-raetallic substances which, impregnated with 
 silver, give truly beautiful results, viz., wood and ivory. To prepare 
 the former of these materials for photographic purposes, I select a piece 
 of veneer of hard and fine-grained wood, and which is susceptible of 
 a high polish, and endeavour to make it as even and smooth as 
 possible, by rubbing with pumice-stone and water. I proceed in the 
 same manner with an ivory plate. When the wood or ivory plate is 
 perfectly dry again, I rub it once more vigorously with a clean piece of 
 strong leather. I then immerse the plate in a solution of nitrate of 
 silver (one drachm of silver to an ounce of water), in order to 
 impregnate it with that salt. The ivory plate is left in the solution 
 until it has acquired a yellow color; the coloration of the wood plate, 
 which marks the proper degree of metallic impregnation, depends upon 
 the nature of the wood ; however a little practice will suffice to enable 
 the operator to hit upon the right point in this respect. As soon as the 
 plates are properly impregnated with silver, I expose them under water 
 to the direct light of the sun, until they have acquired a black tint ; 
 I then take them out of the water, and let them dry. The dry plates 
 I clean, polish and iodise, and treat in every other respect exactly 
 as the silvered copper plates. 
 
 The so-called artificial ivory also is well suited for photographic 
 purposes, as it is susceptible of a high polish. This material may, 
 moreover, after it has been prepared for the process, be kept a long 
 time, without suffering alteration. 
 
PICTURES ON IVORY AND "WOOD. 
 
 35 
 
 To prepare a plate of artificial ivory for photographic impressions, 
 it must in the first place he cleaned with finely-ground pumicestone,to 
 remove any trace of fatty matter, and to facilitate thus its impregnation 
 with fluids. It is then polished in the usual way, with Venetian 
 tripoli, but without using oil. The polished plate is immersed for 
 about a minute in a solution of twenty parts by weight of sal-ammoniac 
 (chloride of ammonium), in two hundred parts by weight of water. 
 After its removal from this solution, it is suspended by one of the 
 corners, to let the liquid drip otf ; when no more fluid remains on the 
 surface, the plate is immersed in the dark, in a solution of forty parts 
 by weight of nitrate of silver in two hundred parts by weight of distilled 
 w'ater ; this immersion also should last about a minute. The plate is 
 left in the camera until a more vigorous impression is obtained than is 
 ultimately desired. The plate is then removed, washed in water, and 
 the image fixed on it, with either a cold or hot solution of twenty parts by 
 weight of hyposulphite of soda in one hundred parts by weight of water. 
 As soon as the image has acquired the proper tone, the plate is taken 
 out of the fluid, and washed copiously with water, to remove every 
 trace of the soda salt ; it is then suspended to let the greater portion 
 of the water evaporate, but, before it is quite dry, it is pressed 
 betw'een two plates of soft wood, by which means not only the last 
 traces of moisture are removed, but the warping of the plate also 
 is effectively guarded against. 
 
 If it is intended to take impressions on wood for technical purposes, 
 e.g. to obtain the tracing for an engraving, the process must be con- 
 ducted in a different manner from the one given above. In my own 
 practice, I either produce the impression on the wood directly in the 
 camera, or I transfer the impression to it from another plate ; in the 
 former case I obtain a negative, in the latter, a positive image. Both 
 w’ays answer equally well ; still, upon the whole, I prefer the latter, 
 though the process is a little more tedious. 
 
 In the first method, a piece of boxwood is selected, since this is 
 found to answer better than other sorts, and fitted accurately into the 
 frame which usually carries the plate in the common Daguerreotype 
 process ; the piece must be fitted so that the larger surface, and which 
 is intended to receive the impression, is endwood or graimoood. This 
 surface must previously have been rough-polished with pumicestone , 
 
36 
 
 THE ART OP PHOTOGRAPHY. 
 
 since, were this operation postponed till the wood has been fitted to the 
 frame, it might be difficult to obtain an even surface. The wood so pre- 
 pared and fitted, is once more polished with pumicestone and water, and 
 subsequently washed and dried; when dry, it is again polished, but 
 this time with dry pumicestone. It is then carefully cleaned, and the 
 polished surface is imbued w'ith a solution of one equivalent of iodide of 
 potassium, (K T, see table ii.), in four ounces of water. When it has 
 dried again, it is dipped for about one minute into a solution of one 
 equivalent of nitrate of silver (AgO,NOs), in four ounces of distilled 
 water; the nitrate of potassa (KO,NOs) formed is then cautiously 
 washed away with water, and the plate dried, and laid by in a dark 
 place, until it ^ required for use. Immediately before its exposure in 
 the camera, the prepared surface is imbued once more with a solution 
 of one equivalent of nitrate of silver in four ounces of distilled water, 
 to which are added two equivalents of crystallisable acetic acid (A = 
 CiHaOs-fHO), since this acid promotes the decomposition of the 
 iodide of silver, and keeps the parts not acted upon by the luminous 
 rays, of a beautiful white. The time of exposure varies with the 
 greater or less intensity of the illumination ; however, as a general 
 rule, one or two minutes are sufficient. To develope the latent image, 
 the prepared surface is bathed with a saturated solution of gallic acid 
 (G=C 7 H3O5 -f HO) ; a small addition of nitrate of lead (PbO,NOs) 
 promotes the action of the gallic acid, and imparts a darker tint to the 
 image. Pyrogallic acid, &c., may be substituted for the gallic acid, to 
 develope the image— see the chapter on the Vitrotype. The image is 
 fixed with solution of hyposulphite of soda. 
 
 In the second method, the negative image, taken on a glass plate 
 covered with a layer of iodised collodion (see Vitrotyp^^ is placed 
 right on the wood prepared with iodide or chloride of silver, and is 
 then, in that position, exposed to the solar rays. If the impressionable 
 surface has been prepared with iodide of silver, the latent image must 
 be developed by means of a saturated solution of gallic acid, in the 
 same way as in the first method. The image is ultimately fixed with 
 solution of hyposulphite of soda. 
 
 The negative image may also be transferred to the wood, in an 
 enlarged size, by means of the apparatus illustrated by Fig. 5. 
 
TALBOTYPE. 
 
 37 
 
 IL— TALBOTYPE; 
 
 OB, 
 
 PHOTOGRAPHY ON PAPER. 
 
 COMPOUNDS OF SILVER. 
 
 If Oxide of Silver (Ag,0) precipitated from a solution of the 
 nitrate, is exposed for several hours to the solar rays, the parts exposed 
 to the light acquire a deeper olive tint than the covered parts. If the 
 exposure is continued a week or longer, it is found that the deep 
 olive color turns lighter again, and that the covered parts are much 
 darker than the exposed parts. I have frequently had occasion to 
 observe that oxide of silver spread on paper, acquired a much lighter 
 tint after a few days’ exposure to light.* 
 
 Nitrate of Silver, (AgO,NOs). — This salt, if absolutely pure, is 
 not perceptibly affected by light, neither in the solid state nor in 
 solution ; but in nitrate of silver containing the least admixture of 
 organic matter, the influence of light speedily produces an alteration. 
 This property induced Sir John Herschel, in his first photographic 
 experiments, to put organic substances on the paper which he intended 
 to operate upon, and to imbue it then with solution of nitrate of silver ; 
 however, he did not obtain the desired result. But since that time it 
 has been found that the joint application of organic substances with 
 the silver salt, serves to promote and heighten to an extraordinary 
 degree the alteration which the latter suffers under the influence of 
 light. Count Rumford found that nitrate of silver, mixed with charcoal 
 or with a carbonated earth, suffered reduction to the metallic state 
 under the influence of the solar rays. 
 
 Prismatic Analysis. — The color which the prismatic spectrum 
 produces on paper prepared with nitrate of silver, is first a light brown, 
 which changes slowly to a deeper tint ; the part under the blue ray 
 acquires a bluish brown color, that under the violet ray a peculiar 
 
 This accounts for the fading of the pictures. 
 
38 
 
 THE ART OP PHOTOGRAPHY. 
 
 rose color. The minimum of the chemical action is under the yellow 
 ray, extending to about the middle of it ; the maximum of the chemical 
 action seems to extend to the middle of the blue ray, though up to the 
 edge of the violet ray the effect is only slight — ^beyond this it is very 
 feeble. 
 
 Photographic Application . — Although nitrate of silver by itself 
 is not sufficiently sensitive to light to find application in the 
 photographic process (except in a few cases), still it is the most 
 important salt of silver in a photographic point of view, since all other 
 compounds of silver may be prepared from it. 
 
 If well-sized paper is imbued on one side with a solution of 
 120 grains of nitrate of silver in an ounce of distilled water, and 
 dried in a warm place ; it may very well be used for the copying of 
 feathers, lace, embroidery, and generally such objects as require 
 simply sharp outlines. If the paper, before the application of the 
 nitrate of silver, is first imbued with a solution of isinglass, or parch- 
 ment, or gum arable, or some other similar substance, or is coated over 
 with albumen, the nigrescence under the influence of light proceeds 
 with much greater speed, and it acquires ultimately a tolerably dark 
 tint. The ground of the images taken on such paper may be agreeably 
 varied, by the application of divers organic substances to the paper ; 
 experiments of this kind succeed all the better if the organic substances 
 are thrown down on the paper from their solutions by solution of lead ; 
 the precipitate on the paper must be allowed to dry before the 
 application of the nitrate of silver solution is proceeded with. Some 
 remarks on the property of lead to accelerate the decomposition of the 
 salts of silver, under the influence of light, will be found in the section 
 on lead and its compounds. The pictures produced on the paper so 
 prepared may be fixed by immersion, first in cold then in warm 
 water, and a final careful ablution. 
 
 Chloride of Silver (AgCl). — This salt, no matter whether pre- 
 cipitated from solutions, or existing in the form of hornsilver, speedily 
 changes color under the influence of the solar rays ; indeed, diffused 
 light suffices to produce this effect, nay, even in a totally dark place, 
 the white color of chloride of silver changes to a darker tint, and after 
 some time, turns bluish black. Upon exposure to the solar rays, the 
 color changes first to a reddish hue, then to violet, afterwards to 
 
COMPOUNDS OF SILVER. 
 
 39 
 
 bluish grey, and ultimately to dark blue. A trifling excess of the 
 nitrate greatly promotes the nigrescence, the chloride turning first of a 
 dai'k-brown tint, which gradually changes to a fine olive color ; after 
 an exposure of several weeks, the metallic silver is seen to make its 
 appearance. The great variety of tints produced by the combination 
 of silver with different chlorides is very remarkable. However, it is 
 only during the first stages of exposure to light that this variety exists ; 
 after a time all the different compounds acquire the olive tint. 
 
 With chloride of ammonium (sal-ammoniac NHi, Cl), and 
 chloride of sodium (common salt, NaCl), the tint produced is red ; 
 with chloride of strontium (SrCl-(-6HO), brown; with chloride 
 of barium (BaCl-[-2 HO), brownish purple; with chloride of 
 calcium (CaCl + 6HO), brick-colored ; with chloride of potassium 
 (KCl), the tint varies from a fine brown to a bluish steel color ; with 
 sesqui-chloride of iron (Fe2Cl3 -|-6HO), from deep brown to black. 
 With hydrochloric acid (CIH-)- Xaq.), the color is red, changing to 
 black; with chlorwater (Cl -f Xaq.), red; with chloric ether (C*: 
 HsCl), dissolved in alcohol, black. Other combinations will be 
 mentioned in the sequel. As far as my own experience enables me to 
 judge, these differences in the tints obtained seem to proceed from the 
 presence of the alkalies, earths, or metals, and not from that of organic 
 substances ; though the latter, in combination with nitrate of silver, 
 produce similar variations. 
 
 Prismatic Analysis — paper prepared with chloride of silver often 
 acquires beautiful tints in the solar spectrum, which differ, however, 
 according to the chloride used. Paper that had been imbued with a 
 solution of chloride of ammonium (NH 4 , Cl), or chloride of barium 
 (BaCl-f-2HO), dried, and then dipped into a solution of nitrate of 
 silver, gave a series of colors nearly approaching the natural colors 
 of the spectrum. Under favorable circumstances, the middle red ray 
 leaves a red impression, which under the yellow ray changes to green ; 
 above this a lead color is seen, and under the blue ray, in the part 
 where the chemical action was strongest, a brown coloration changing 
 subsequently to black ; a bluish brown tint is seen to extend under the 
 most strongly refracted rays up to the latent rays. The opposite 
 effect is observed at the least refracted end of the spectrum, where the 
 paper remains white. This may be distinctly observed, if the rays are 
 
40 
 
 THE AET OE PHOTOGEAPHY. 
 
 collected through a good achromatic lens, and more distinctly still, if 
 the spectrum is thrown right on the paper. 
 
 Photographic Application . — It has been already mentioned that 
 Wedgewood, Davy, Daguerre, and others employed chloride of silver in 
 their photographic experiments, though with indifferent success. But 
 in the hands of Mr. Fox Talbot, this salt became a very important 
 photographic agent. The following is the way of procedure adopted 
 by that gentleman : — 
 
 He selects glazed paper of equal texture ; he dips this into a weak 
 solution of common salt (chloride of sodium), and dries it afterwards 
 between folds of blotting-paper, by which means he endeavours to 
 ensure the equal distribution of the salt through the substance of 
 the paper. He then lays the paper on one side upon a solution of 
 nitrate of silver, and dries it again near the fire. The solution of 
 nitrate of silver which he uses, is diluted with from six to eight parts of 
 distilled water. The dried paper is ready for use. If properly 
 prepared, Mr. Talbot considers it suited for all photographic purposes. 
 He states that it gave, for instance, beautiful impressions of leaves, 
 flowers, &c., more especially under the rays of a summer sun; the 
 light passes through the leaves, and copies even the most delicate 
 veins. 
 
 Mr. Talbot found by experiments that there exists a certain definite 
 proportion between the quantity of the salt, and that of the nitrate of 
 silver in solution ; and that the chief effect of the operation fails, if this 
 proportion is departed from. The use of an over-large quantity of 
 salt tends to impair the sensitiveness of the paper to a greater or less 
 extent. 
 
 If we wash a paper prepared by this process, in a saturated solution 
 of common salt, and dry it again, we find that it has almost completely 
 lost its sensitiveness to light, more especially, if an interval of several 
 weeks had elapsed between the two processes. But, upon washing it 
 now again with the silver solution, it re-acquires its sensitiveness, and 
 even in a higher degree than after the first process. I have succeeded 
 in this way, by repeated alternate washing with the salt solution, and 
 the silver solution, and drying after each operation, to heighten the 
 sensitiveness of the paper sufficiently to produce a picture on it in 
 the camera. 
 
COMPOUNDS OP SILVER. 
 
 41 
 
 The results obtained in these experiments are influenced by trifling 
 differences in the respective proportions used of the salt and the 
 nitrate of silver. Sometimes the chloride of silver on the paper will 
 turn black even in the dark, which is a sign that an excessive degree of 
 sensitiveness had been imparted to it. The operator must endeavour 
 to hit the proper point, imparting to the paper exactly that degree of 
 sensitiveness which, whilst leaving the color unchanged in the dark, 
 brings about a change in it upon the least exposure even to the dullest 
 daylight. In my own experiments I prepared a number of papers, all 
 of them differing in the chemical proportions of the agent used ; I cut 
 off a small piece of each, putting corresponding numbers on the papers 
 a«d the samples cut off, and placed the latter in a faint diffused light ; 
 I then selected the papers for use the samples of which had suffered 
 the greatest change of color. 
 
 A simple experiment will suffice to explain this different sensitive- 
 ness to light in paper prepared with the same agent, but used in 
 different proportions. Let a thin layer of chloride of silver be 
 precipitated on a piece of clean glass, which may most appropriately 
 be effected in the following manner : lay a piece of clean glass flat on 
 the bottom of a rather deep vessel, fill the latter with a weak solution 
 of common salt, and add a few drops of solution of nitrate of silver, 
 just sufficient to impart a milky appearance to the fluid ; the chloride 
 of silver formed will speedily subside, and settle on the glass plate ; as 
 soon as . this has taken place, remove the supernatant liquid by means 
 of a small glass syphon ; take off the last traces of moisture from the 
 plate with a common spun cotton wick. In this way a thin coating of 
 pure chloride of silver is obtained on the glass. After drying, expose 
 the plate to light in a somewhat slanting position, and let a few drops 
 of solution of nitrate of silver fall upon it at the upper edge ; you will 
 see that the chloride of silver turns black most speedily and most 
 intensely at the borders of the little channels made in the coating by 
 the solution of the nitrate of silver — which clearly shows that a 
 slight excess of silver increases the sensitiveness of the chloride of 
 that metal. 
 
 I would recommend the following proportions of chloride of sodium 
 and nitrate of silver, to prepare a paper suited to receive impressions 
 in the camera. 
 
42 
 
 THE ART OP PHOTOGRAPHY. 
 
 Dissolve fifty grains of chloride of sodium (common salt, Na Cl), in 
 an ounce of water, imbibe the paper with this solution, and then dry it, 
 first between folds of blotting paper, and finally near the fire. 
 
 Brush the paper now on one side with a solution of 120 grains oi 
 nitrate of silver in one ounce of water, and dry it again near the fire ; 
 repeat the application of the nitrate of silver, and dry again near the 
 fire. For the chloride of sodium, you will often have occasion to sub- 
 stitute chloride of ammonium (NH4,C1) or chloride of barium 
 (BaCl-f-2HO) ; in such cases you ought to use of the former salt 
 thirty grains, of the latter forty grains, to one ounce of water. Of 
 course, if you do not require a highly sensitive paper, you may use a 
 less proportion of silver. All photographic operations demand care 
 and attention. Indifference to the purity of the materials used, or 
 inaccuracies in weighing and measuring, will always prove serious 
 obstacles to the attainment of satisfactory results. The selection of the 
 paper also requires the greatest care. Paper intended for photographic 
 purposes should always be of equal and uniform texture throughout, and 
 perfectly free from spots ; it should combine with the highest possible 
 degree of transparency sufficient thickness to intercept the light more 
 or less completely in the dark parts of the picture. The excitable 
 coating, to be properly sensitive, must be on the surface, not in 
 the substance of the paper, as a few experiments will suffice to 
 show. 
 
 Talbot observed, in his earliest photographic experiments, that how- 
 ever carefully he had prepared his paper with the same agents and 
 in the same proportions, still it often proved almost entirely void of 
 sensitiveness in some parts. All other photographers have since made 
 the same observation. Upon exposure to light, a paper of the kind 
 shows sharply-defined white spots, whilst the other parts turn black 
 with the greatest readiness. Occasionally the spots are of a bluish 
 color, with perfectly white borders. The only cause to which this 
 imperfection can be attributed, seems to be the following : the chemical 
 compound used is present in two distinct different proportions in the 
 dark and in the light parts. If we examine the matter more closely, 
 we find that the same paper absorbs the fluid more copiously in some 
 parts than in others ; accordingly, the quantity of the salt absorbed is 
 also greater in some parts than in others. Now, upon brushing subse- 
 
COMPOUNDS OP SILVER. 
 
 43 
 
 quently the solution of nitrate of silver over the paper, some parts of it 
 will get fairly coated with the requisite quantity of chloride of silver, 
 and the proper excess of the nitrate ; whilst other parts receive only a 
 coating of pure chloride of silver, or, worse still, of a double chloride 
 of silver and sodium. These imperfections in the prepared paper may 
 to some extent be guarded against by spreading the solution of salt 
 uniformly over the paper with a sponge, instead of immersing the 
 sheet in the brine. 
 
 Fixing the Picture. 
 
 To make the picture produced by the light permanent, it must be 
 fixed ; otherwise the light parts will also turn dark under the con- 
 tinued influence of light. Various fixing agents have been proposed. 
 Talbot used first, and with tolerable success, a saturated solution of 
 common salt (brine). This combines with the undecomposed chloride 
 of silver on the paper, forming a double chloride of silver and sodium, 
 which is less liable to be acted upon by light than the simple chloride 
 of silver. However, the pictures fixed in this w’ay acquire, after a 
 time, an unpleasant bluish tone, which in a great measure destroys 
 the original beauty and accuracy of the image ; moreover, it would 
 appear that pictures of the kind get bleached in the course of time. 
 Iodide of potassium (K I) has also been recommended ; but this salt 
 acts, under the combined influence of light and moisture, much more 
 strongly upon the dark parts of the picture than the chloride of sodium; 
 besides, it converts the white chloride of silver into yellow iodide of 
 silver, a circumstance which is very adverse to the taking of positive 
 copies from negative pictures so prepared, as the yellow color impedes 
 the action of the rays which blacken the salt of silver. The more 
 desirable way is to remove the unreduced chloride of silver entirely 
 from the paper ; however, this has its difficulties, since most of the 
 agents which dissolve chloride of silver act also strongly upon the 
 oxide. This is the case more particularly with ammonia. Bromide of 
 potassium (K Br), which has also been recommended as a fixing agent, 
 gives indeed very accurate images, but it imparts the same yellow tint 
 to the paper as the iodide of potassium ; moreover, the high price of 
 the iodide and bromide of potassium is a bar to their general applica- 
 tion as fixing agents. Hyposulphite of soda (Na0,S2 0z,-f-5H0), 
 
44 
 
 THE ART OF PHOTOGRAPHY. 
 
 which was first recommended by Sir John Herschel, is unqaes- 
 tionably, of all the salts proposed, the best suited for the purpose. 
 The best and safest way of proceeding is as follows : put the picture 
 first in clean water, to dissolve and remove the free nitrate of silver, as 
 completely as is practicable ; after this, immerse the picture in water, 
 holding in solution a few grains of chloride of sodium, which will serve 
 to convert into chloride the free nitrate of silver that may still remain 
 adhering to the paper ; if you neglect this precaution, the hyposulphite 
 of soda will convert the remaining nitrate into sulphide of silver, which 
 will impair the beauty of the image by its brown color, and will, 
 moreover, in the course of time, tend to destroy it altogether. Now 
 immerse the picture completely in a solution of hyposulphite of soda ; 
 after some time, take it out, and dip it in pure water ; lay it on a glass 
 plate, and float it over with pure water, until the water running oflf 
 tastes no longer sweetish ; which is a safe sign that the chloride has 
 been removed, as the compound formed with it by the hyposulphite 
 of soda has a very sweet taste, by which it may readily be detected. It 
 is a peculiarity of this method of fixing that all the delicate parts of 
 the picture which seem to have suffered in the process, reappear with 
 the most perfect distinctness after drying. 
 
 The picture may be fixed also by washing it with a solution of 
 chloride of mercury (corrosive sublimate, Hg Cl), rinsing it subsequently 
 in water, and letting it dry. This operation renders the picture per- 
 fectly invisible, and leaves, in the case of silver chloride paper, a white, 
 in that of iodide paper, a yellowish surface. But the invisible picture 
 may be brought to light at any time, by washing with a solution of 
 hyposulphite of soda, rinsing in water, and drying. It may be men- 
 tioned here, that there is a vast difference in fixing pictures taken in 
 blight sunlight, and such as have been taken in common daylight : the 
 former lose little or nothing of their beauty and distinctness by the 
 process of fixing, whereas the latter lose considerably. 
 
 Iodide of Silver (Ag I)._Perfectly pure iodide of silver may be 
 exposed a long time to the action of light, without suffering any 
 perceptible alteration, except in some cases, where a slight increase in 
 the intensity of the yellow tint is observed, which is to be attributed, 
 perhaps, to the calorific rays, as the application of heat to the iodide of 
 silver produces the same effect. But in presence of a little free 
 
COMPOUNDS OP SILVER. 
 
 45 
 
 nitrate of silver, the iodide of that metal is much more sensitive to 
 light than the chloride. 
 
 Prismatic Analysis. — The change which the prismatic spectrum 
 produces on paper prepared with a weak solution of iodide of 
 potassium (K 1) and nitrate of silver, presents certain interesting 
 peculiarities. The maximum of intensity is formed at, or a little 
 beyond, the edge of the most refracted ray (the violet ray) ; however, 
 it varies a little with different papers, and also with the quantity of 
 the free nitrate of silver present. The effect begins almost in the 
 middle of the red ray, where the paper assumes a lead or ash-color, 
 whilst under the most refracted rays it acquires a reddish-yellow 
 color; the change produced under the blue ray, or rather towards 
 the end of the blue and beginning of the violet ray, appears rather 
 suddenly ; beyond the border of the violet ray, the effect decreases 
 very rapidly ; still the nigrescence produced by the invisible rays is 
 more strongly marked than in the case of chloride of silver. 
 
 Photographic Application. — Paper prepared with iodide of silver 
 deserves the preference before all others. The best proportions to 
 use the iodide of potassium and nitrate of silver in, are twenty grains 
 of the former, and forty grains of the latter, dissolved each respectively 
 in one ounce of water. The paper is carefully brushed over with the 
 nitrate of silver solution, and dried ; it is then washed over on one 
 side with the iodide of potassium solution, and dried near the fire, 
 taking care, however, not to expose it to a strong heat, since this 
 would change the fine straw color to a rusty tint, and would nearly 
 altogether destroy the sensitiveness of the paper. 
 
 By combination with certain agents, iodide of silver acquires an 
 extraordinary degree of sensitiveness. This is the case more particu- 
 larly as regards the combination with gallic acid (G^C? HsOs -f-HO), 
 or that with the yellow ferrocyanide of potassium (2KCy,FeCy 
 -f-3HO), whereby the most beautiful results may be attained. 
 
 We will now proceed to give a description of the several processes 
 of using the iodide of silver in conjunction with these agents, 
 commencing with the one to which the inventor, Mr. Talbot, has 
 given the name Calotype. 
 
 Preparation of the Paper. — Dissolve 100 grains of crystallized 
 nitrate of silver in six ounces of distilled water, and brush over the 
 
46 
 
 THE ART OF PHOTOGRAPHY. 
 
 paper with this solution on one side only ; mark the side and let the 
 paper dry, either near a fire, or in a dark room. As soon as it is dry, 
 dip it for two or three minutes with the prepared side in a solution 
 of 500 grains of iodide of potassium in sixteen ounces of water, wash 
 it now in distilled water, and dry it either near the fire, or in a dark 
 room. It is always advisable to perform all these operations in a 
 dark room by candle or lamp-light. The paper so prepared has a 
 beautiful straw color (from the iodide of silver), and is scarcely 
 sensitive to light ; it must nevertheless be kept carefully secluded 
 from light until it is required for use ; but in this way it may be kept 
 for a long time without suffering alteration. When the time has 
 come to use it, it is treated as follows : 
 
 Dissolve 100 grains of crystallized nitrate of silver in two ounces 
 of water, and add to the solution a half-ounce of strong acetic 
 acid. 
 
 Make a saturated solution of crystallized gallic acid in distilled 
 water. When you want to make a calotype picture, mix these two 
 solutions in equal proportions, but only so much of them as is needed 
 for the operation, as the mixture speedily undergoes decomposition. 
 With this solution of gallo-nitrate of silver the silver iodide paper is 
 washed over upon the marked side with a soft brush. After half a 
 minute the paper is dipped in water, and dried lightly by pressure 
 between folds of blotting-paper. The operation must be performed by 
 candle-light. 
 
 Although the paper so prepared may be kept several days, nay even 
 several months, without losing its sensitiveness to light, still the better 
 way is to use it at once, as it is apt to acquire a black tint even in 
 perfect darkness. 
 
 Paper prepared in this way is exceedingly sensitive to light ; an 
 exposure of one second’s duration to common daylight, suffices to 
 bring on an incipient change of color. If a piece of this paper is 
 half covered over, leaving the other half exposed to the light of day, 
 the least possible space of time suffices to bring about an alteration in 
 the exposed part ; this alteration, however, is not visible, but 
 If the paper is laid by in the dark, the alteration becomes visible^^H 
 a time ; or it may be brought out at once, by washing the 
 with the gallo-nitrate of silver, and holding it near ^ frr^whereupon 
 
COMPOUNDS OP SILVER. 
 
 47 
 
 the parts acted upon by the light will acquire a dark-brown tint, 
 whilst the other parts will retain their original color. 
 
 If you have taken an impression on the paper so prepared, and have 
 developed it in the manner just now indicated, you must proceed to 
 fix it, which is done by washing it first in water, and then dipping it 
 in a solution of 100 grains of bromide of potassium in ten ounces of 
 water, removing it after a few minutes, washing with water, and 
 drying. In default of bromide of potassium, you may have recourse 
 to common salt, or to hyposulphite of soda, which latter answers the 
 purpose better than salt. 
 
 The discovery of the extraordinary property of gallic acid to 
 heighten the sensitiveness of iodide of silver so greatly, is one of the 
 most beautiful that Mr. Talbot has made in the domain of photography. 
 The calotype process gives pictures of the greatest beauty, which not 
 only most faithfully render the outlines of the object, but copy it 
 even in the minutest details ; leaving in fact nothing to be desired 
 except the natural colors ; and even this defect is in a great measure 
 compensated by the marvellous harmony of the ensemble. 
 
 The picture produced in the camera is negative. When it has been 
 properly fixed, any given numbers of positive copies may be taken 
 from it. The process of reproduction is conducted as follows : — Lay 
 the negative picture upon a leaf of positive paper prepared in the 
 manner indicated, and put under the latter a smooth and even board, 
 with a few sheets of soft paper on it ; place above the negative an 
 even, clean glass plate, so that the prepared paper and the negative lie 
 between the board and the glass ; press them closely together, to secure 
 the contact of the papers. The frame of reproduction, or reversing 
 frame, will be found to answer the purpose best for this operation. 
 The time of exposure depends, of course, upon the transparency of the 
 negative picture, and the intensity of the solar light. I need hardly 
 mention that all the imperfections of the negative are necessarily trans- 
 ferred to the positive picture ; it is therefore always advisable to select 
 for the negative impression an absolutely equal and uniform paper, 
 ransparent mass, such as glass, for instance (see 
 
 oqd if we remember that this acid precipitates the 
 
 which the gallic acid has in the alterations produced will 
 
48 
 
 THE ART OP PHOTOGRAPHY. 
 
 metallic silver from the solutions of the salts of that metal. If the 
 solutions of the gallic acid and the nitrate of silver be mixed in very 
 feeble diffuse light, a precipitate will almost immediately form, although 
 in the dark the same mixture remains clear for hours. Now if this 
 clear mixture is put on a paper prepared with salt of silver, and 
 which is sufficiently sensitive, or has been exposed already to light long 
 enough to produce an alteration, the black precipitate of metallic silver 
 forms almost instantaneously on the parts acted upon by the light, and 
 indeed in exact proportion to the alteration suffered j the parts which 
 have not been touched by the light, remaining white and unaltered. 
 To keep these parts white, it is advisable to promote the decomposition 
 by the application of heat, or by hot aqueous vapor. It requires some 
 practice to obtain satisfactory results ; for if the action of the gallo- 
 nitrate of silver upon the silver salt on the paper, and which has been 
 changed by the agency of light, is not stopped at the proper time, the 
 negative image produced will not answer the purpose of reproducing 
 positive copies from it, the whole surface of the paper being liable to 
 turn black. 
 
 This method may, however, he considerably simplified ; but before 
 we proceed to speak of this, we will here briefly glance at the 
 alterations which gallic acid produces in various compounds of silver 
 that have been exposed to light. — Paper simply imbibed with a solution 
 of nitrate of silver, gave, after two miuutes’ exposure in the camera, 
 only a faint image, upon being washed with gallic acid. Paper prepared 
 with chldride of silver gave under the same circumstances a tolerable 
 picturey but deficient in force and clearness. Bromide of silver gave a 
 very beautiful picture, after one minute’s exposure. Tartrate of silver, 
 after ten minutes’ exposure in the camera, appeared to remain 
 Unaffected by the gallic acid. Oxalate of silver, after ten minutes’ 
 exposure, gave only a very feeble image. With phosphate of silver, 
 the result was not quite satisfactory. Carbonate of silver gave, after 
 five minutes’ exposure, a tolerably good picture. JBenzoate of silver, 
 
 ' and formiate of silver, gave very satisfactory results. Benzo-formiate 
 of ammonia, in combination with nitrate of silver, gave results simiH 
 to those obtained with the iodide ; this preparation is remarkably wel-P 
 suited for taking architectural views. Cyanide of silver, and cyanide 
 of silver and iron, after ten minutes’ exposure in the camera, showed 
 
COMPOUNDS OF SILVER. 
 
 49 
 
 no alteration upon washing with gallic acid, nor with gallo-nitrate of 
 silver. I have also tried several other compounds of silver. The 
 general results of my experiments have shown that gallic acid, though 
 unquestionably a most important photographic agent, is not sufficiently 
 powerful in all cases to bring out the alteration suffered. The action 
 may indeed be considerably strengthened by an addition of nitrate of 
 lead (PbO,NOs) ; still, even with this addition, it falls short of the 
 energetic action of pyrogallic acid (pGr = CeHsOs) ; which ought 
 therefore always to be used in preference. In many preparations of 
 silver, the reaction of the gallic acid becomes manifest only after the 
 paper has lain for some time in the dark, or after the application of 
 heat. Hyposulphite and hyponitrate of protoxide of iron may be 
 employed in photography for -the same purpose as the gallic acid, and 
 with the same success ; the former of these two salts has even a much 
 more energetic action than the acid. 
 
 Iodide of Silver and Ferroctanide of Potassium. If paper pre- 
 pared with iodide of silver in the usual way, is washed with solution of 
 ferrocyanide of potassium (2KCy -f Fe Cy^, it acquires upon exposure to 
 light instantaneously a greenish-black colorj and turns afterwards still 
 darker. This alteration is most speedy with iodide of silver perfectly 
 pure and free from all foreign admixture. "^iSViugh the same effect is 
 produced irrespective of the proportion in which the salts are mixed, 
 still it is better that there should be a minimum of alkali. 
 
 The best results are obtained with paper prepared in the following 
 way : — 
 
 Brush the paper over on one side with a solution of two diae^is of 
 nitrate of silver in an ounce of distilled water, and dry it as q\Mly 
 as possible ; then brush the paper over on the same side with a solutioi^ 
 of a drachm of iodide of potSfesium in an ounce of distilled water, 
 lay it. with the non-prepared^ide on a glass plate, and wash the whole 
 of the soluble salt carefullpaway^by floating the prepared side over 
 with water. The paper mfyaow Either be used at once, or kept for 
 future experiments. When ^u wish to use it, you need simply 
 imbue it with a saturated solution of ferrocyanide of potassium, and 
 place it in the camera. ^ 
 
 The fixing of the pictures produced on paper so prepared is still in 
 some degree uncertain. It often occurs that of several picthr^^ which 
 
 D 
 
60 
 
 THE AET OP PHOTOGEAPHY. 
 
 have been fixed in one and the same way, some will speedily fade, ! 
 whilst others will show no alteration. This fading of the pictures 
 would seem to be owing to part of the protocyanide of iron having 
 remained in the paper, which tends to destroy the image. The fol- 
 lowing is the best way of fixing pictures on paper prepared w'ith iodide 
 of silver and ferrocyanide of potassium : immerse the picture for some 
 time in hot water, which should be repeatedly renewed j dip it after- 
 wards in a weak solution of iodide of potassium, wash it thoroughly in 
 cold water, and dry. 
 
 The high degree of sensitiveness of this paper is evidently owing to 
 a mutual decomposition of the ferrocyanide of potassium and the iodide ; 
 of silver under the influence of light. 
 
 Ferrocyanide of potassium may be used advantageously also with i 
 other compounds of silver, more especially with bromide and chloride i 
 of silver, whose sensitiveness it heightens considerably. 
 
 Production of Positive Pictures in the Camera, hy means of i 
 Hydriodates. I 
 
 When photographic paper, blackened by light, is washed with a i' 
 solution of an hydriodate, the dark parts are bleached again upon 1 ; 
 subsequent exposure to light. I 
 
 This property has been turned to account to effect the production of | 
 positive pictures by direct exposure in the camera. I 
 
 The paper may be prepared with any of the sensitive salts of silver: | 
 however, chloride of silver has been found to answer best. Chloride of | 
 ammonium and chloride of barium are the salts best suited to prepare | 
 the silver chloride paper with, as the light acts most readily upon a |; 
 surface prepared with these salts, producing impressions of great j 
 accuracy and fineness of delineation. The paper is prepared as follows : — I 
 Dip the paper for from five to ten minutes in a solution of forty ' 
 grains of either chloride of ammonium, or chloride of barium, in four 
 ounces of water, and let the paper dry. Make a solution of 120 
 grains of nitrate of silver in twelve ounces of water, and add four 
 ounces of alcohol, which will render the solution slightly turbid ; let 
 the mixture stand a few hours, and then filter off the fluid from the 
 slight precipitate which has subsided in it. Imbue the paper with the ■ 
 filtrate, and expose it still wet to the sunbeams, when it will speedily 
 
COMPOUNDS OF SILVER. 
 
 61 
 
 turn black. The nigrescence is .not uniform, however, owing to 
 unequal absorption of the fluids ; you must, therefore, imbue the paper 
 once more with the solution of nitrate of silver, and expose it again to 
 the light until it has acquired all over a uniform chocolate color, 
 when you may dry it and keep it ready for use. 
 
 It is indispensable to perform this operation in the unclouded light of 
 the sun ; since, strange though it may appear, it is no less true, that 
 the clouds which may happen to obscure that luminary are faithfully, 
 though very faintly, reproduced on the paper, and make their 
 appearance in the next operation. 
 
 When you want to make use of the paper so prepared, you must 
 imbue it with a solution of iodide of potassium, and expose it wet in 
 the camera. The proper proportion in which the iodide of potassium 
 should be used has not yet been definitely settled, though thirty grains 
 of pure salt to an ounce of water would appear to answer best ; this is 
 a question of great nicety, however, as a few grains more or less make 
 a considerable difference in the results. For my own part, I should 
 prefer iodide of barium to iodide of potassium, taking care to remove 
 previously some of the barium by precipitation with one or two drops 
 of diluted sulphuric acid or sulphate of baryta. 
 
 To fix the pictures obtained by this process, they should be washed 
 with cold water, and then treated in the usual way with solution of 
 hyposulphite of soda. 
 
 From the length of the time of exposure required (fifteen to thirty 
 minutes), this method is adapted only for taking impressions of 
 architectural objects. 
 
 Bromide of Silver (Ag Br). — Though light produces no visible effect 
 upon perfectly pure bromide of silver, there can be no doubt but 
 that this salr, even in the pure state, suffers alteration from the 
 influence of that agent, as may indeed be readily demonstrated by the 
 application of the proper reagents. 
 
 But when a trifling proportion of nitrate of silver is admixed to the 
 bromide, nigrescence ensues instantaneously upon exposure to light. 
 
 Bromide of silver is a most important photographic agent. It is 
 often added to the iodide to increase the sensitiveness of the latter. 
 But it may also be used alone, in the following manner : — 
 
 Imbue paper with a solution of 100 grains of nitrate of silver in an 
 
 D 2 
 
52 
 
 THE ART OF PHOTOGRAPHY. 
 
 ounce of distilled water, and let it dry; imbue it now with a solution 
 of twenty grains of bromide of potassium (KBr) in four ounces of 
 water, and place it finally again in the silver bath. The paper so 
 prepared is exceedingly sensitive ; but it cannot be kept long, as it 
 suffers alteration even in the dark. If the paper is intended to be 
 preserved for use at some future time, a less proportion of nitrate of 
 silver must be used. 
 
 To take an impression on the paper so prepared, it is imbued with 
 a solution of 120 grains of nitrate of silver in an ounce of water, and 
 exposed wet in the camera ; after a few seconds’ exposure it is 
 removed from the camera, and let dry in the dark. When dry, it is 
 placed in the mercurial apparatus, and the mercurial fumes are 
 evolved slowly by the application of a gentle heat ; the image developed 
 often looks quite clouded or veiled over with a film ; but in the course 
 of a few hours this goes off, and a very accurate and vigorous impression 
 appears on the paper. The best way to fix this is to wash the paper- 
 in brine, and to treat it afterwards in the usual way with hyposulphite 
 of soda. The image may be developed also by means of an aqueous 
 solution of gallic acid or of pyrogallic acid. 
 
 Fluoridb of Silver (AgF) suffers about as little alteration under 
 the influence of light as nitrate of silver, though it turns much darker 
 in the course of time than the latter. Used in conjunction with 
 bromide of silver, it considerably heightens the sensitiveness of the 
 latter, more especially if fluoride of sodium (NaF) is employed in 
 the operation. Although the proper proportions in which the two 
 salts (the bromide of potassium and the fluoride of sodium) ought 
 to be mixed are not yet quite settled, still I think the following 
 proportions will be found to answer the purpose : twenty grains of 
 bromide of potassium, and five grains of fluoride of sodium, dissolved 
 each in one ounce of water. To save time, the two solutions may be 
 poured together, and the paper imbued with the mixture ; when 
 the paper is dry again, it is imbued with a solution of sixty grains 
 of nitrate of silver in an ounce of water, and subsequently washed 
 carefully in water, to remove the nitrate of potassa formed. Paper 
 so prepared will keep unaltered for several w-eeks, and may be 
 exposed in the camera in the dry state. After its removal from the 
 camera, it is drawn through water, and then floated over with a weak 
 
COMPOUNDS OF SILVER. 
 
 53 
 
 solution of sulphate of protoxide of iron (green vitriol, Fe 0, SO3 + 
 7H0), whereupon the impression will at once make its appearance. 
 As soon as this is deemed sufficiently distinct, the paper is washed in 
 water, and the picture is then finally fixed with hyposulphite of soda. 
 
 Phosphate of Silver (AgO,POs) is only suited to copy posi- 
 tives from negatives, as it is too little sensitive for exposure in the 
 camera. Phosphate of silver paper is prepared as follows : imbue the 
 paper with a solution of phosphate of soda, and let it dry ; imbue it 
 now with a solution of nitrate of silver, let it dry again, and imbue it 
 once more with solution of phosphate of soda. The paper so prepared 
 is well suited for copying positives from negatives, and affords this 
 advantage, that the impressions on it may be easily fixed with a w’eak 
 solution of ammonia, which readily dissolves the undecomposed yellow 
 salt of silver, leaving the decomposed parts quite unaltered. Phos- 
 phate of silver paper, blackened by the influence of light, may be 
 bleached again in the manner described at page 50, and may then be 
 used for the direct production of positive impressions in the camera. 
 
 Tartrate of Silver (AgO, Tr). — To make tartrate of silver 
 paper, imbue the paper with tartaric acid (Tr=H2C4 0s), or with 
 a solution of a tartrate, and treat it then in the usual way with solu- 
 tion of nitrate of silver. Tartrate of silver seems at first only feebly 
 affected by light, but after a time it grows darker under the influence 
 of that agent than any other salt of silver ; for which reason it is 
 admirably adapted for positive pictures. Its want of sensitiveness, 
 on the other hand, is a bar to its use for negative images. The sensi- 
 tiveness may, however, be somewhat increased by an addition of iodide 
 of potassium or of yellow ferrocyanide of potassium. 
 
 To mention all the silver salts which I have tried would lead us too 
 far here, and wmuld, besides, be of but little practical utility, as some of 
 them are too dear for general use, and others of too dangerous a nature, 
 as e.g., arseniate of silver. Still I may remark here, that agreeable 
 variations in the color of the picture may be produced by means of 
 some of them, such as the chromide, benzoate, formiate, and others. 
 
 The combination of nitrate of silver with ammonia is particularly 
 well suited for positive images, to which it imparts a remarkably warm 
 and pleasant tone. The mode of preparing the paper with nitrate of 
 silver and ammonia is very simple. It is well known that upon 
 
54 
 
 THE ART OP PHOTOGRAPHY. 
 
 addition of ammonia to a solution of nitrate of silver, a whitish pre- 
 cipitate forms, which redissolves in an excess of ammonia. Now, 
 paper need simply be imbued with this fluid (solution of nitrate of 
 silver to which ammonia in excess has been added), and dried, to be 
 at once ready for use. The pictui'es on this paper are fixed in the 
 usual way. 
 
 Let it be borne in mind that, wherever hyposulphite of soda is 
 employed as the fixing agent, the greatest care must be taken to wash 
 from the paper every trace of soda ; since, if the least particle of that 
 substance be left behind, the picture will- after a time show spots, or 
 will even be altogether destroyed. Simple immersion in water will 
 not suffice ; the paper must be moved about in the bath, and the water 
 must be repeatedly renewed. 
 
 COMPOUNDS OF GOLD. 
 
 It is a well known fact that an ethereal solution of gold is decom- 
 posed by light, the metallic gold separating at the side of the vessel 
 turned to the light. Most of the salts of gold present a similar 
 deportment under the influence of light ; and they would accordingly 
 find frequent application in photographic processes, if they were not 
 rather too expensive. 
 
 If paper imbued with a solution of neutral chloride of gold (Au 
 Cls -|-6HO), is exposed to the sunbeams, its color changes at first to 
 a lighter hue, but after a time it grows gradually darker, and acquires 
 finally a purple tint. Though the chloride be now removed out of the 
 influence of light and placed in the dark, the decomposition will 
 continue, until the gold is completely reduced to the metallic state. 
 The decomposition is greatly promoted by dipping the chloride in cold 
 water. Employed in conjunction with nitrate of silver, the chloride of 
 gold is acted upon more rapidly, and gives very fine positive pictures. 
 
 A most sensitive gold paper, which very speedily acquires a purple 
 tint in the light of the sun, may be prepared as follows ; — imbue the 
 paper with a solution of thirty grains of oxalate of ammonia (NH 4 O, 
 C2O3 -f-HO) in an ounce of water, dry it, and then imbue it with a 
 saturated solution of chloride of gold. To fix the picture produced 
 on this paper, it is dipped, first in cold water, afterwards in a solution 
 of ferrocyanide of potassium, and finally washed in water. 
 
COMPOUNDS OF PLATINUM. 
 
 55 
 
 Paper prepared with acetate of lead (PbO,A+3HO) and chloride 
 of gold, is less sensitive than the preceding ; it presents, however, 
 certain interesting peculiarities. When this paper is exposed to 
 light, the yellowish brown color turns at first of a paler hue ; 
 subsequently it changes to a light grey, and acquires finally a slate 
 color. If the action of the light is interrupted, ere the coloration 
 has proceeded so far, and the paper is held in hot steam, or dipped in 
 hot water, the parts acted upon by the luminous rays acquire imme- 
 diately a deep purple tint ; cold water produces the same effect, but 
 only very slowly. Dry heat has no perceptible influence. 
 
 The compounds of gold with cyanide of potassium and nitrate of 
 silver, and various other salts, give very satisfactory results ; still the 
 impressions are inferior to those obtained with silver ; moreover, the 
 high price of gold forbids its general application in this branch of 
 photography. It is often used, however, to impart a deeper and more 
 pleasant tone to the positive pictures produced on silver paper ; this is 
 done simply by dipping the picture, after fixing it with hyposulphite of 
 sodj, in a feeble solution of chloride of gold, and washing it afterwards 
 in water. 
 
 COMPOUNDS OF PLATINUM. 
 
 The compounds of platinum also may find application in the 
 photographic art ; however, the pictures produced with them are of 
 little value, as they speedily fade, and are, after a short' time, com- 
 pletely effaced. 
 
 Paper prepared first with cyanide of potassium, then with bichloride 
 of platinum (PtCh -t-8HO), and finally with nitrate of silver, is 
 speedily acted upon by light, giving a very beautiful deep lilac-colored 
 positive picture. If the nitrate of silver is placed on the paper first, 
 or if it is present in excess, the picture produced appears as distinct on 
 the left as on the right side. Iodide of potassium seems to be the best 
 fixing agent for platinum pictures ; however, as has already been 
 intimated, no precaution, not even absolute seclusion from light, can 
 prevent the gradual fading and final eflfacement of the picture ; after a 
 few months nothing is left of it but a piece of white paper. The 
 compounds of platinum with iodine or bromine give the same 
 ephemeral results. 
 
56 
 
 THE AHT OF PHOTOGRAPHY. 
 
 If the paper prepared with cyanide of potassium, bichloride of 
 platinum, and nitrate of silver, is imbued with a solution of chloride 
 of mercury (Hg Cl), and exposed in the camera for about fifteen minutes, 
 there is hardly a perceptible alteration in it ; however, upon applica- | 
 tion of ammonia to the prepared surface, a deep black positive | 
 picture appears on an iron-grey ground. If this is dipped in 
 a solution of chloride of mercury, a negative picture is produced by 
 the solution of the dark parts. Application of dry heat destroys the 
 whole picture. 
 
 COMPOUNDS OP IRON. 
 
 Almost all the salts of iron suffer a very perceptible alteration 
 under the influence of sunlight ; some of them sooner, others later. 
 
 The change is most easily observable in the salts of the sesquioxide 
 with organic acids. Some of these salts, and more especially the 
 double salts which they form with ammonia or with potassa, are so 
 readily decomposed by light, that they may be used for the pro- 
 duction of negative pictures in the camera ; still, they are better suited 
 for positive pictures. 
 
 But what imparts to the salts of iron a peculiar value in a photo- 
 graphic point of view, is the property which they possess to produce 
 with different reagents a variety of colors. 
 
 This property , and the facility with which they are decomposed by 
 light, make them, under circumstances, fit substitutes for the salts of 
 silver, to which they are even preferred in certain cases. ' 
 
 The most important of these salts are, — the oxalate of sesquioxide 
 of iron and ammonia, the citrate of sesquioxide of iron and ammonia, 
 and the tartrate of sesquioxide of iron and ammonia. The compounds 
 of the oxalate, citrate, and tartrate of sesquioxide of iron, with 
 potassa or soda, and the double sulphate of sesquioxide of iron and 
 ammonia (NHi.0,S03 -f Fe 2 0s, SSOa -f-24HO) are also very sensitive 
 to light. 
 
 Photographic paper may be prepared with any one of these salts in ^ 
 the following simple manner ; — 
 
 Dissolve one part by weight of the salt in ten parts by weight of 
 distilled water ; brush the solution over the paper on one side, and let 
 it dry in the dark. The paper is now ready for use. It may be kept 
 
 
COMPOUNDS OF lEON. 
 
 57 
 
 for years without the slightest loss or diminution of sensitiveness. 
 The best suited for exposure in the camera is the oxalate of sesqui- 
 oxide of iron and ammonia. The paper prepared with this compound 
 is exposed in the usual way for a longer or shorter space of time, 
 according to the intensity of the light and the illumination of the 
 object ; when removed from the camera, no sign of the picture is 
 perceptible, or, at all events, only a very faint trace of it ; hut it 
 becomes visible at once upon the application of one of the reagents 
 which we shall immediately proceed to name. However, as has been 
 intimated already, these salts are more advantageously used to repro- 
 duce positive from negative pictures ; for this purpose, they may be 
 said to answer each of them almost equally well. The negative 
 picture intended to be reproduced, is applied on one of the iron- 
 papers, and affixed to it at two ends with glue, gum,, or paste ; it is 
 then put in the frame of reproduction, and exposed to light (to the 
 solar rays, if possible). The overlapping parts of the paper speedily 
 show a brown tint ; the frame is examined from time to time, to see 
 whether the picture is done. The time of exposure depends upon the 
 degree of intensity of the light ; in bright sunshine, from three to five 
 minutes are generally sufficient. Though the impression should only 
 be faintly visible, or even nearly invisible, the application of the 
 proper reagent will speedily bring it out. 
 
 The picture is then taken out of the frame and brushed over with a 
 solution of red ferricyanide of potassium (3KCy, Fe2Cy3) in 
 water (no matter the proportion, provided always the solution be not 
 too highly dilute), which will immediately bring the picture out with 
 a very intense blue color ; the solution should be applied with a 
 broad flat brush. Simple washing in water suffices to fix the image. 
 Potassa (KO) destroys the blue color, and with this the picture 
 itself; bisulphate of potassa (KO,2SOs -t-HO), on the contrary, 
 heightens the intensity of the color, and makes it permanent ; sulphate 
 of copper (blue vitriol, Cu0,S03 -t-SHO), changes the blue color to 
 a pale greenish blub tint. 
 
 A green picture is obtained by adding solution of gum-arabic [to 
 the ferricyanide of potassium solution. These pictures require no 
 additional fixing ; washing in water would change the green color to 
 blue. 
 
THE ART OF PHOTOGRAPHY. 
 
 Solntion of nitrate of silver imparts a deep blackish-brown tint to 
 the picture; simple washing in water suffices to fix it. 
 
 Solution of ammonio-nitrate of silver (AgO,NOs -fSNHs) imparts 
 a greyish-black tint to the picture ; simple washing in water 
 suffices to fix it. It is not advisable to use a brush to apply the 
 solution of nitrate or ammonio-nitrate of silver to the picture, as 
 these substances would injuriously affect the material of that imple- 
 ment, The better way is to pour the solution into a glass or 
 porcelain dish, or over a glass plate laid down horizontally, and to 
 apply the paper with the latent image to the liquid, taking care to 
 leave no air-bubbles under it, since this would give rise to spots, which 
 it would afterwards be found impossible to remove. If a brush be 
 used, however, care must be taken to wash it thoroughly in water 
 immediately after ; if this is neglected, the implement is of no 
 further use in operations of the kind, as the silver retained in it would 
 spoil the pictures to which it might, happen to be applied. 
 
 With ammonia (NHs -|-aq.) an ash-colored picture is obtained, which 
 is equally distinct on both sides of the paper. 
 
 Solution of terchloride of gold ( AuCls -f-aq.) gives a purple- 
 colored picture, which continues to deepen as long as there remains 
 a trace of undecomposed chloride in the paper. 
 
 Arseniate of potassa (KO,AsOs -{-HO), gives a yellowish-brown 
 picture, of lighter or darker hue, according to the strength of the 
 solution. Simple washing in water ’ suffices to fix the pictures 
 obtained by the application of this and of the preceding substance. 
 
 The use of the arseniate of potassa requires of course great caution, 
 on account of the poisonous nature of the material. 
 
 Some very interesting results, and such as no other metallic salts 
 afford, may be obtained with the salts of iron before mentioned, and 
 more especially with the citrate of iron and ammonia. 
 
 A paper prepared with the latter salt in the manner indicated, is 
 imbued with a solution of ferricyanide of potassium, and dried in the 
 dark. This paper does not keep long, and should therefore be used 
 soon after its preparation. If a picture has been reproduced on this 
 paper, it need simply be dipped in water, to render it instantaneously 
 visible in blue. If the paper is now imbued with a solution of nitrate 
 of suboxide of mercury (Hg 2 OjNOs -)-2HO), the picture imme- 
 
COMPOUNDS OF IRON. 
 
 59 
 
 diately vanishes. The paper must then be well washed in water, 
 that no free mercurial salt may be left in it. The picture may now 
 be rendered' visible again with brown color, by the simple application 
 of heat (holding it near the fire, or passing a hot smoothing iron over 
 it) ; it disappears again upon cooling, but may always be brought 
 out anew by the same process. In some cases, it will not at once 
 disappear upon cooling, but will remain visible for weeks. 
 
 The following is another interesting experiment. Dissolve one pan 
 by weight of citrate of sesquioxide of iron and ammonia in eleven 
 parts by weight of water, and add an equal volume of a saturated 
 cold solution of chloride of mercury ; imbue the paper with this 
 mixture, before a precipitate has had time to form, and dry the paper. 
 The color should be yellowish, without the least tinge of blue. 
 Expose the paper now in the frame of reproduction, until a faint but 
 clearly visible image is produced on it. Pass over it with one 
 stroke of a broad brush, a saturated solution of cyanide of potassium, 
 mixed with three times its own volume of a solution of gum-arabic of 
 moderate consistence. The picture will immediately make its 
 appearance ; after a few days you may freely expose it to light ; it 
 will even bear the light at once, without any great injury. This 
 picture improves with time, parts which at first were half visible, 
 coming gradually out with the greatest distinctness. Another 
 interesting experiment is the following : If a solution of nitrate of silver 
 is added to a solution of bitartrate of sesquioxide of iron, a preci- 
 pitate is immediately formed, which is almost entirely re-dissolved 
 upon the application of a gentle heat ; a further addition of silver 
 solution leaves the fluid clear. The solution of silver should be 
 added in the proportion of one volume to two. The yellowish 
 mixture is filtered ; the filtrate may be kept unaltered in the dark. 
 If a paper imbued with this filtrate is exposed wet in the camera, no 
 picture appears on it, unless the exposure should have been too long 
 protracted but after a time it makes its appearance spontaneously. 
 The result is different if the paper is employed in the dry state to 
 reproduce positive pictures. For this purpose it suffices to apply the 
 paper on the negative picture, and to expose for from thirty seconds to 
 one minute to the solar rays. The exposure must not be continued 
 until the impression commences to make its appearance, since in that 
 
60 
 
 THE ART OE PHOTOGRAPHY. 
 
 case it would soon come out spontaneously 5 there should be no sign 
 of the picture on the paper. Still the picture is there, and to render 
 it visible, you need simply breathe upon it, or hold it over steam, when 
 it will at once appear with great accuracy and distinctness of 
 delineation. It very often vanishes again as soon as the moisture of 
 the breath or the steam is gone off ; but it may readily be called forth 
 anew in the same way. 
 
 . Considering the facility and safety with which the salts of iron 
 may be employed, and the great variety of colors that may be 
 produced with them, and also the moderate prices at which they may 
 be procured, it would be very desirable indeed that a series of 
 systematic experiments should be made with a view to ascertain in 
 how far these salts may be suited for the purposes of the practical 
 photographer, and whether they might not in some measure supersede 
 the salts of silver. 
 
 COMPOUNDS OF COPPER, 
 
 As has already been stated in the chapter on the Daguerreotype, 
 copper also may find application in photography. 
 
 The salts of copper, though of inferior sensitiveness, give yet very 
 interesting results in conjunction with other metallic compounds. 
 Among the salts which may be advantageously added to the salts of 
 copper, we mention more particularly that of chromium, and 
 especially the neutral chromate of potassa, and the bichromate of 
 potassa. The latter salt gives in conjunction with sulphate of copper 
 a highly sensitive preparation, with which pictures may be produced 
 in a variety of colors. 
 
 A paper imbued with a mixture in equal proportions of a saturated 
 solution of sulphate of copper (copper vitriol, blue vitriol, CuO,SOa 
 +5HO), and of a saturated solution of bichromate of potassa 
 (K0,2Cr03), may be used immediately after drying, or it may be 
 kept in the dark for any length of time, without suffering the least 
 diminution of sensitiveness. This paper will, however, serve only to 
 reproduce positives from positives, negatives from negatives. When 
 it is exposed in the frame of reproduction to solar light, the uncovered 
 parts acquire first a brown tint, if the paper is removed from the 
 frame ; at this period the image is negative ; but if the exposure is 
 
COMPOUNDS OF COPPER. 
 
 61 
 
 continued, the brown color turns to a brighter hue, and a positive 
 picture is produced. If the copy, after its removal from the frame, is 
 treated with solution of nitrate of silver (no matter of what strength), 
 a positive, brick-colored picture is produced in both cases ; however, 
 in the latter case, the picture is of greater beauty and vigor than in 
 the former. To fix these pictures, they need simply be quickly 
 washed in perfectly pure w^ater. If the water contains a chloride, or 
 if chloride of sodium is added to it, even in a small proportion, the 
 picture vanishes on the instant, and completely ; but it may be brought 
 out again by exposing it, still wet, to the solar rays, and letting it 
 dry. The color however, is now changed, varying, according to the 
 greater or less quantity of salt used, between rose and deep violet. A 
 longer exposure to sunlight serves to improve the picture. 
 
 The neutral chromate of potassa may be substituted for the bichromate. 
 If a solution of neutral chromate of potassa (KO, Cr Os) is added to 
 a solution of sulphate of copper, a precipitate is thrown down, which 
 when filtered off and thoroughly washed with water, dissolves in 
 water slightly acidulated with sulphuric acid. Paper imbued with 
 this solution has a pure yellow color, which is completely bleached 
 in sunlight. A picture produced on such paper is developed with a 
 solution of carbonate of potassa (KO, CO2-I-2HO), or carbonate of 
 soda (NaO, CO2 -flOHO), or also with a solution of nitrate of silver. 
 It will occasionally happen, more especially if the light was only 
 feeble, that the nitrate of silver bath will impart a uniform tint 
 to the whole surface of the paper, leaving the picture altogether or 
 nearly invisible ; however, after the paper has lain by for some 
 time, the picture makes its appearance, the lights being gradually 
 bleached by the sulphuric acid in the paper, until they are perfectly 
 white, which brings out the shadows the more boldly, yet without 
 hardness. 
 
 If ammonia is used, instead of either carbonate of potassa or soda, 
 or nitrate of silver, the picture, if it happens to be already visible, 
 vanishes again, but it speedily makes its reappearance, with a faint 
 blue color. 
 
 Very interesting pictures may be produced also with bichromate of 
 potassa unmixed with copper. The mode of proceeding is as follows ; — 
 imbue paper with a weak solution of starch paste and let it dry : 
 
62 
 
 THE AET OF PHOTOGEAPHY. 
 
 imbue it now with a saturated solution of bichromate of pctassa, and 
 let it dry. It is now ready for use ; but it may be kept for any length 
 of time without suffering the least diminution of sensitiveness. To 
 produce a positive copy on this paper, apply a positive original on it, 
 and expose it in the usual way in the frame of reproduction, until you 
 have a vigorous yellow impression on a brownish ground ; wash this 
 in water, which will dissolve the undecomposed salt ; and then coat 
 the right side over with an aqueous solution of iodine, which will 
 impart a deep violet tint to the picture, leaving the brownish 
 ground unaltered ; simple washing in water will suffice to fix the 
 picture. 
 
 Salts of Manganese, Lead, Nickel, &e. Of the salts of manganese 
 the manganate of potassa (KO, Mn Os ), is the best suited for photo- 
 graphic purposes. A solution of this salt imparts to paper a brown 
 tint, which exposure to the sunlight destroys again in the parts 
 touched by the rays, restoring these parts to their original white color. 
 Addition of nitrate of silver to the manganese salt heightens the brown 
 tint of the paper ; but upon subsequent exposure to light, the parts 
 touched by the rays turn intensely black, instead of resuming their 
 original white color. The impressions may be fixed by washing in 
 water, and subsequent treatment wdth hyposulphite of soda. 
 
 The other salts of manganese, although they are also perceptibly*; 
 altered by light, are not so well suited for photographic purposes.'-/ 
 
 The salts of lead are useful as photographic agents . ohly •• 
 
 certain conditions. Papers imbued solely with them change color 
 continually, which leads to the ultimate destruction of the pictures 
 produced on them. Added in small proportion to 'other salts, more 
 especially to those of silver, the compounds of lead tend t(5«diei)^ffen 
 the intensity of the color ; but care must be taken not to add too 
 much of them ; since otherwise the picture is apt after a time to turn 
 black all over. 
 
 The only compounds of lead with which I have obtained satisfactory 
 results, are the iodide (Pbl), used in conjunction with nitrate of silver, 
 or with starch paste ; and the nitrate (PbO, NOs), used in conjunction 
 with protiodide of iron and nitrate of silver. Recently precipitated 
 and thoroughly washed iodide of lead dissolves readily and completely 
 in solution of nitrate of silver. Paper prepared with a solution of 
 
SALTS OF MANGANESE, LEAD, NICKEL, ETC. 
 
 63 
 
 iodide of lead in nitrate of silver is highly sensitive to light. The 
 copies produced on it are fixed by simple washing in water. 
 
 A very sensitive paper, and one well suited for taking pictures in 
 the camera, may be prepared also as follows : — 
 
 Imbue the paper with a solution of fifteen grains of nitrate of lead 
 (PbO, NOs) in an ounce of water ■ dry the paper, and when dry, treat 
 it with an aqueous solution of protiodide of iron (FeH-4aq). The 
 paper so prepared will keep a considerable time, if properly secluded 
 from light. It is made sensitive for exposure in the camera, by a bath 
 of one hundred grains of nitrate of silver dissolved in an ounce of 
 water. Should the picture not yet be visible when the paper is 
 removed from the camera, it will speedily make its appearance, without 
 the application of any developing agent. Simple washing in water 
 suffices to fix it. 
 
 Or the iodide of lead, recently precipitated, may be intimately 
 mixed in the dark with starch paste, and the mixture spread uniformly 
 over paper ; upon exposure to light the paper so prepared will imme- 
 diately acquire a black color ; the pictures produced on it are fixed 
 by dipping in solution of nitrate of silver, and subsequent washing in 
 hyposulphite of soda, and in water. 
 
 ; Of the salts of nickel, the best suited for photographic pui-poses is 
 tte iodide (Nil), which is prepared by mixing solutions of iodide of 
 potassium or iodide of potassium and iron, and nitrate of nickel (NiO, 
 NO5 + 6HO). Iodide of ammonium would not answer the purpose. If 
 iodide of potassium and iron has been used, the light blue color of the 
 compound.,-fi;b^es .to a light green upon exposure to the luminous 
 rays. 
 
 l^re .are still many other metallic salts, which sufi’er alteration 
 under the influence of light, as for instance, nitrate of cobalt, hydro- 
 chlorate of cobalt, bichloride of tin, and tartrate of antimony. With ' 
 these salts pictures may be produced in the usual way. 
 
64 
 
 THE ART OE PHOTOGRAPHY. 
 
 III.-YITEOTYPE; 
 
 OH, 
 
 PHOTOGRAPPIY ON GLASS. 
 
 Properly speaking, the term “ pictures on glass ” is a misnomer, as 
 the glass serves simply as the basis whereon the impressionable 
 material is supported, and takes no part in the production of the 
 image. In fact, were it not that the transparence of the basis forms 
 an essential condition in the subsequent process of reproducing copies 
 from the pictures taken, any other material would answer the purpose 
 equally well as glass. 
 
 When Daguerre and Niepce’s ingenious invention became known, 
 it was very natural that the wish should arise to discover some means 
 of multiplying in a direct way the pictures produced by the action of 
 light. A great many experiments, and of the most varied nature, were 
 accordingly made with a view to achieve the desired end, but with 
 imperfect success only. 
 
 The negative pictures produced on paper, and from which a tolerably 
 large number of copies may be taken, may certainly be looked upon as 
 a considerable step in advance in that direction. 
 
 However, as has already been intimated in the introductory part, 
 paper has the almost unavoidable defect of inequalities in its texture ; 
 and as all the imperfections and blemishes resulting therefrom are 
 necessarily transferred also to the copies of the picture taken on this 
 material, these copies always require retouching, — an operation which, 
 more especially in unskilful hands, tends to impair the likeness of the 
 picture, and, moreover, consumes much time. 
 
 Photographers were therefore naturally led to seek whether some 
 other material, free from the defects inherent in paper, might not be 
 substituted for the latter. Sir John Herschel was the first to try glass 
 for this purpose. 
 
 The first difficulty which presented itself with this new material was 
 
PHOTOGRAPHY ON GLASS. 
 
 65 
 
 the fixing on it of the iodide of silver, or some other excitable substance. 
 Niepce, who occupied himself much with this subject, tried various 
 means to effect the purpose in view, such as albumen, glue, starch 
 paste, &c. ; and, indeed, he obtained very good pictures with these 
 materials, but always at the expense of the sensitiveness of the 
 impressionable surface. These substances, therefore, however so well 
 suited for landscapes, are not well adapted for portraits. In the case 
 of albumen, there is besides some little difficulty in the manipulation 
 which may become a source of defects, and which it requires 
 some practice to overcome ; as the following instructions for albu- 
 menising glass plates will show : — 
 
 Mix the whites of a certain number of eggs with an equal volume 
 of distilled water, and whip the mixture into a froth. When this has 
 become perfectly liquid again, filter the clear portion off, and spread 
 it smoothly and evenly over a well-polished glass plate. When you 
 have succeeded in spreading the albumen evenly over the plate by 
 tilting and inclining the latter in various directions, let the superfluous 
 liquid run off at one of the corners, and put the plate to dry in a place 
 perfectly free from dust, taking care to lay the plate down in an hori- 
 zontal position ; you may promote this process of drying by the 
 application of heat. Although the plates so prepared will keep, yet it 
 is not desirable to albumenise too many at a time, on account of the 
 difficulty of removing the particles of dust which will always somehow 
 settle on them if they are long kept lying by, and which subsequently 
 cause spots in the picture. When you wish to take a photographic 
 picture on one of the plates, expose the plate over dry iodine in the 
 iodine box, until it has acquired a yellow tint ; and then plunge it 
 suddenly, and with all parts simultaneously, into a solution of four 
 drachms of nitrate of silver in ten ounces of distilled water, to which 
 have been added two drachms of crystallisable acetic acid ; wash it 
 now cautiously in water, and expose in the camera. The great point 
 here is to effect the sudden and simultaneous immersion of all parts 
 of the surface of the plate, since upon this depends, in a measure, the 
 success of the operation — for this reason, that the albumen, upon 
 coming into contact with the aceto-nitrate of silver solution, shrinks 
 considerably, which tends to produce cracks in it, and this most in 
 those parts where the immersion has been delayed for however so 
 
66 
 
 THE AET OF PHOTOGRAPHY. 
 
 short an instant. These cracks are subsequently transferred to 
 the copy. 
 
 The picture produced on the plate in the camera is developed with 
 gallic acid, and fixed afterwards with hyposulphite of soda. To 
 save trouble, the albumen may also be iodised previously to its appli- 
 cation on the surface of the plate ; for which purpose you need simply 
 add per each egg fifteen drops of a saturated solution of iodide of 
 potassium, proceeding in all other respects as instructed above, with 
 the exception, of course, of the iodine-box operation, which would 
 now be superfluous. 
 
 Application of steam to the albumenised surface previous to its 
 immersion in the silver bath, may also advantageously be resorted to, 
 as it tends to soften the albuminous coating, and thus to facilitate its 
 impenetration by the silver solution. 
 
 The common, or joiner's glue, which has been recommended as 
 giving remarkably accurate negative pictures, is, nevertheless, unsuited 
 for the purpose, since it dissolves in the aqueous solutions with which 
 the plate has to be treated after the exposure in the camera ; this 
 happens more especially upon treating the plate with the gallic acid, 
 to develope the image ; the latter is indeed brought out most beauti- 
 fully, but in the same instant it melts away again, owing to the ensuing 
 liquefaction of the glue. The same remark applies also to isinglass. 
 
 Pure starch paste, made of wheaten flour, is much better suited for 
 the purpose than glue or isinglass ; but care must be taken to use only 
 the very purest starch ; the article which is sold in the shops being 
 generally adulterated, and altogether useless for photographic purposes. 
 The easiest and simplest way of producing pictures on starch paste is 
 as follows : — 
 
 Blend one ounce of pure wheaten starch most thoroughly and 
 intimately with two ounces of water in a levigating dish ; add sixteen 
 ounces of boiling water, rapidly stirring the mixture all the while, 
 and then in the same way one drachm of iodide of potassium dissolved 
 in an ounce of boiling water. Strain the liquid through silk to 
 remove all remaining impurities, and spread it then evenly and 
 smoothly over a well polished glass plate, in the same way as the 
 albumen ; dry it at a tolerably high temperature, and proceed in all 
 other respects as with the albumenised plate. 
 
PHOTOGRAPHY ON GLASS. 
 
 67 
 
 Caseine, dissolved in ammonia, has also been recommended ; this 
 substance gives a very pure and clear coating. 
 
 But the best and most suitable of all substances recommended for 
 vitrotype purposes, is unquestionably collodion or collodium. Collo- 
 dium is a. solution of gun-cotton in ether, which had always best be 
 procured ready-made from a respectable chemist’s. The collodium of 
 the shops is, however, generally much too thick to spread readily and 
 evenly over the surface of the plate ; it must accordingly be diluted 
 to the requisite point with sulphuric ether, perfectly free from the least 
 admixture of acid ; on the other hand, care should be taken not to add 
 too much ether, since’'© ver-tenuity of the collodium film would tend to 
 impair the sensitiveness of the impressionable surface. 
 
 To the sufficiently dilute collodium is now added either simple 
 tincture of iodine (which proceeding, however, gives a product of inferior 
 sensitiveness), ’or iodide of ammonium ; or, and this is unquestionably 
 the best way, iodide of silver at once. If you elect to use the second 
 of those agents (iodide of ammonium), add to six ounces qf .collodium 
 of the proper degree of dilution, one drachm of iodide of ammonium, 
 and four grains of fluoride of potassium, moistened with from four to 
 six drops of distilled water. There is no need that the iodide of 
 ammonium and fluoride of potassium should be quite dissolved befoie 
 being added to the collodium, as these substances readily dissolve in 
 the latter ; the use of much water, would, moreover, be rather hurtful, 
 as it would tend to impair the adhesion of the collodium to the surface 
 of the plate, and might thus lead to the film becoming subsequently 
 detached again in the silver bath. Shake the bottle two or three times, 
 and let it then stand at rest, until the fluid is quite clear and trans- 
 parent. The color ought tp be a pale yellow. However, should the 
 ether or the collodium have contained the least admixture of an acid, 
 the iodide of ammonium will be decomposed by this, and the liberated 
 iodine will impart a dark red tint to the fluid. Should this be the 
 case, the acid must be neutralised, which is effected best by adding a 
 little pulverised cyanide of potassium, and shaking the bottle, where- 
 upon the liquid will speedily show the proper pale yellow tint. 
 
 It happens also sometimes that the iodised collodium turns acid 
 from being kept too long ; this state, which impairs the sensitiveness 
 of the preparation, is indicated by the rubescence of the color of the 
 
68 
 
 THE ART OP PHOTOGRAPHY. 
 
 liquid. Addition of a little pulverised cyanide of potassium will 
 suffice to restore the fluid to its proper condition. But the best way, 
 as already intimated, is to add at once iodide of silver to the collodium, 
 which is done as follows : — 
 
 Put ten grains of recently precipitated and thoroughly washed 
 iodide of silver into a bottle holding six ounces ; add some cr}^stals of 
 iodide of potassium, moistened with the least possible quantity of 
 water, but no more of them (viz., crystals of iodide of potassium) than 
 will suffice to effect the solution of the iodide of silver ; fill the bottle 
 now w'ith collodium of the proper consistence, shake the mixture 
 vigorously, and let it stand until the fluid is perfectly clear and 
 transparent ; the color ought to be nearly white, it is however 
 generally a little yellowish. 
 
 Iodide of ammonium moistened with alcohol may be advantageously 
 substituted for iodide of potassium, to effect the solution of the iodide 
 of silver ; this substitution wdll tend to heighten the sensitiveness of 
 the preparation. 
 
 The iodised collodium which I now exclusively use, and on which I 
 can obtain impressions of objects in motion, as the time of exposure is 
 less than a second in the open air, is mixed and prepared as follows : — 
 Take an ounce of iodide of potassium, dissolved in the requisite 
 quantity of hot water ; add ten ounces of collodium, eleven ounces of 
 sulphuric ether, eleven ounces of alcohol of ninety degrees, six ounces 
 of absolute alcohol ; mix all these ingredients properly together, shake 
 the mixture, let it stand at rest a day or two, and then filter through 
 feltpaper. Should the preparation be still too thick, dilute it with 
 sulphuric ether, alcohol of ninety degrees, and absolute alcohol mixed 
 in the proportion of eleven of each of the^ two former to six of the 
 latter. With this preparation I use a silver bath of one ounce of 
 nitrate of silver, thirteen ounces of distilled water, and one ounce of 
 crystallisable acetic acid. 
 
 As with the object-glasses at present in use, the several parts of a 
 photographic picture lie in a curve, the so-called catacaustic curve, 
 the image must necessarily appear a little distorted, more especially in 
 the more prominent parts of the object depicted. That this must impair 
 the likeness of the picture is self-evident. Nothing can be done to 
 the object-glasses to remedy this evil ; but there is another means 
 
PHOTOGRAPHY ON GLASS. 
 
 69 
 
 which may be most successfully resorted to in vitrotype operations, 
 viz., the substitution of bowed instead of level glass plates. The 
 English bowed window-glass answers the purpose admirably ; plates of 
 equal curvation are cut out of tables of this glass ; the hollow or 
 concave side is then prepared with the silver iodised collodium in the 
 usual way, and turned in the camera towards the object to be depicted. 
 
 I think it need hardly be observed here, that in the subsequent repro- 
 duction of the positive pictures, the glass must be laid with the convex 
 or rounded side upon the paper or other material on which the copies 
 are taken. 
 
 The plates of glass, used in vitrotypic processes, must be perfectly 
 clear and free from striae, as all the blemishes in them would be 
 faithfully reproduced on the copies. The surface which is to receive 
 the film of collodium must be thoroughly cleaned and polished, which 
 is done best with hydrate of potassa (KO,HO), fine Venetian tripoli, 
 and water ; washing the plate subsequently in clean water, and letting 
 it dry. 
 
 To obtain an even film of collodium hold the plate at one corner 
 between the thumb and index of the left hand, in a perfectly horizontal 
 position, or balance it on the tips of the fingers, and with the other hand 
 pour the silver iodised collodium on the middle of the plate ; tilt- 
 towards one corner (if you hold the plate between the thumb and index, 
 towards the corner you hold by — taking care not to let the collodium 
 touch the thumb), incline towards another corner, then towards the 
 third, and finally pour off at the fourth corner, resting this on the neck 
 of the collodium bottle. Incline the plate now repeatedly first to the 
 right, and then to the left, until the ridges are removed. 
 
 Before the collodium is quite dry, dip it evenly into a bath of nitrate 
 of silver (forty grains of nitrate of silver dissolved in one ounce of 
 distilled water, to which a little acetic acid may be added), lifting up 
 and down to allow the evaporation of the ether, and facilitate the 
 combination of the iodine with the silver. When the greasy appear- 
 ance is gone, and the film presents a uniform bluish-white color, the 
 plate is ready for the camera. 
 
 Some photographers would prescribe a certain fixed time to leave the 
 plate in the silver bath ; this is a mistake : a practised eye alone can 
 determine the right point in every individual case, from the absence of 
 
70 
 
 THE ART OE PHOTOGRAPHY. 
 
 all greasy appearance, and from the bluish-white tint of the film. If 
 the plate looks still greasy, and is exposed in that state in the camera, 
 the picture produced will be spotted and cloudy, and cannot, of course, 
 be expected to give good positive copies. 
 
 The time of exposure depends here also upon the power of the sun, 
 and the nature of the subject, and must accordingly be left to individual 
 judgment. The next step is the development of the latent picture ; 
 gallic acid is not sufficient here to bring the picture properly out ; but 
 pyrogallic acid (Cs Ha Os =pG) gives the desired result. The mode 
 of proceeding is as follows 
 
 Dissolve two grains of pyrogallic acid in one ounce of distilled water, 
 and add to the solution half a drachm of crystallisable acetic acid 
 (A-|-H0=C4H3 03 -fHO). Pour the solution over the horizontally 
 placed plate, whereupon the picture will at once make its appearance. 
 Should there be any delay, owing to insufficient exposure in the 
 camera, the development of the picture may be accelerated by addition 
 of a few drops of solution of nitrate of silver. A positive picture is 
 obtained by the addition of from two to three drops of nitric acid. 
 Instead of pyrogallic acid, hyposulphate or hyponitrate of protoxide of 
 ii’on may be used with the same result ; gallic acid, in conjunction with 
 acetate of lead, may also be used as developing agent, but the results 
 are doubtful. The image is then ultimately fixed by pouring a 
 saturated solution of hyposulphite of soda over it, and washing the 
 plate afterwards in pure water; in these last operations, the plate 
 should never be immersed in the fluids, but simply floated over with 
 them ; otherwise the film of collodium may become detached from the 
 plate, which involves the risk of its being torn. 
 
 As the film of collodium on the plate has lost much of its firmness 
 and solidity by the treatment with the solution of silver, &c., it may 
 be advisable to protect it from damage by a thin coating of a hot 
 solution of colorless gelatine or of isinglass. The solution must be 
 free from all impurities, and must be spread uniformly over the picture 
 and dried at the fire. 
 
 A more durable product is obtained by diluting the silver iodised 
 collodium with an ethereal solution of gutta percha ; or also by 
 dissolving gutta percha in chloroform, adding to the solution one 
 sixth of its volume of acetic ether, letting the fluid stand at rest for 
 
PHOTOGRAPHY WITH VEGETABLP] JUICES. 
 
 71 
 
 some time, and finally mixing together equal volumes of this solution, 
 and of the silver iodised collodium. This preparation is exceedingly 
 sensitive, and very solid, and adheres firmly to the glass, A film of 
 this substance is rendered strongly electric by friction, in which state 
 it is liable to cracks. 
 
 IV.— ANTHOTYPE; 
 
 OE, 
 
 PHOTOGRAPHY WITH VEGETABLE JUICES. 
 
 ♦ 
 
 Besides the metallic substances hitherto enumerated, other bodies 
 of very different nature may also be used in photographic processes : 
 unfortunately the pictures produced with them, though very beautiful, 
 are not ermanent, but fade away after a shorter or longer period 
 of time. 
 
 Among other substances we mention here more particularly the 
 alcoholic solutions of various resins, and the expressed juices of nogl^ 
 young plants and flowers. 
 
 The least fugitive of the resin pictures are those prepared with 
 guaiacum resin. If a paper is imbued with an alcoholic solution of 
 guaiacum resin, and is then dipped in water slightly saturated with 
 chlorine, it acquires a beautiful cerulean tint, which is bleached 
 again in the light. A paper so prepared may be used to copy 
 pictures : unfortunately, they are not permanent, but will soon 
 fade away. 
 
 Exceedingly delicate and beautiful pictures are obtained also with 
 the expressed juice of young plants, or the coloring matter of them, 
 extracted with alcohol ; but they are still less permanent than the 
 resin pictures. 
 
 If paper is imbued with the expressed green juice of the leaves of 
 the young cereals, and used in the same way as chloride of silver 
 paper, to copy pictures on, the uncovered parts are speedily bleached 
 under the influence of the luminous rays, and a most delicate and 
 
72 
 
 THE AK.T OE PHOTOGRAPHY. 
 
 beautiful positive copy is produced from a positive original. These 
 pictures need not be fixed. 
 
 The juice of the rose and of the violet, tincture of turmeric, and 
 many other vegetable coloring-matters may be used in the same 
 way. I 
 
 Saw-dust and shavings of mahogany, when boiled in water, yield { 
 to that fluid their coloring matter ; paper imbibed with this | 
 decoction is highly sensitive to light, and gives very pretty pictures ; j 
 but they are not more permanent than the preceding anthotypes. I 
 
 PHOTO-LITHOGRAPHY ; 
 
 OR, PHOTOGRAPHY ON STONE. 
 
 To produce pictures on lithographic stones by the action of light 
 in the camera, and to multiply them afterwards by the press in the usual 
 way, is a task beset with considerable difficulties ; and I believe that, 
 though a great many photographers have tried their hand at it, no 
 one has succeeded up to this time to solve the problem and to attain the 
 desired end. I have been fortunate enough to find means of producing 
 photographic pictures on stone in the camera, and have even succeeded 
 to take portraits on stone ; as early as two years ago I publicly | 
 exhibited pictures produced on that material. For certain reasons I | 
 cannot give here all the methods which I have found successful ; I | 
 will however describe the two least difficult ones of them. | 
 
 1. Select a stone of moderate weight, and fit it into the frame of | 
 exposure (if the stone is very heavy you will find it difficult to fix it [ 
 properly) ; treat the stone in the usual way, to give it the grain ; 
 required for a fine crayon tracing. Imbue it now repeatedly with a weak | 
 neutral solution of oxalate of sesquioxide of iron, taking care to make j 
 the solution as neutral as possible, and to make it penetrate into the | 
 stone as deep as can be. A stone so prepared may be kept a very 
 long time without losing its sensitiveness, provided, of course, it be 
 
PHOTOGRAPHY ON STONE. 
 
 73 
 
 properly secluded from light. The best way is to expose the stone 
 still moist, hut not wet ; the time of exposure depends upon the 
 power of the sun, and the nature of the object to be depicted. If the 
 exposure has been sufficient, the image may already be seen in all parts 
 in a brownish color. A solution of carbonate of ammonia is now 
 poured over the stone, which will bring out the picture to the greatest 
 advantage, and will at the same time serve to fix it. The stone is 
 then floated over with water to wash away the soluble salts. 
 
 In order to multiply the picture by the press, the stone need 
 simply be made to take the printer’s ink on the drawing only, leaving 
 the other parts perfectly clean ; this is effected by etching with 
 an acid in the usual way, and the acid best suited for the purpose is 
 highly diluted oxalic acid. The remaining operations are conducted 
 in the same way as is generally done in lithography. By means of this 
 method, impressions may be taken of architectural objects, and 
 multiplied by the press. 
 
 2. Prepare the stone in the same way as in No. 1, and coat it over 
 with a solution of asphaltum in ethereal oil ; place on it the object 
 to be copied (a drawing, or a negative photographic picture on paper 
 or glass), and press this closely against the prepared surface by means 
 of a strong glass-plate ; expose now to the light. The resinous 
 coating loses its coherence in the parts corresponding to the lights of 
 the negative picture. Upon blackening the stone now with lithographic 
 ink, the saponaceous ink adheres to the stone in all these denuded 
 parts, but not in those where the resinous coating remains intact; 
 upon treating this surface afterwards with an acid, the decomposed 
 soap leaves a fatty layer on the denuded parts and on the resinous coat- 
 ing ; and on washing the stone now with alcohol or ether, the resinous 
 coat, together with the layer of fatty matter covering it, is removed ; 
 whilst in the parts where the fatty layer adheres directly to the 
 denuded stone, no change takes place. By means of this method, and 
 the common etching with an acid, copies of drawings, &c., may be 
 taken by the lithographic press in the usual way. 
 
 Gummi guaiacum and other resins may be used instead of asphaltum 
 to coat over the stone. 
 
 E 
 
74 
 
 THE ART OE PHOTOGRAPHY. 
 
 THEORY OF THE PHOTOGRAPHIC PHENOMENA. 
 
 If we inquire the nature of the action of light in the production of 
 the photographic phenomena, we find that the effects produced arise 
 from the decomposing action which light exercises upon metallic 
 compounds, tending to reduce them to the metallic state. 
 
 In the case of iodised silver plates, the following appears to me the 
 rational explanation of the phenomena observed. 
 
 The iodide of silver formed on the plate in the iodine box, is reduced 
 by the action of the luminous rays to subiodide, the liberated iodine 
 being again absorbed by the plate ; this reduction is most considerable 
 in the most strongly illuminated parts ; in the less illuminated parts it 
 is much less marked, and in the darkest parts, the iodide of silver is 
 hardly affected at all. Now, upon the subsequent contact of the mer- 
 curial fumes with the surface of the plate, the mercury combines with 
 the iodine of the iodide of silver, forming subiodide of mercury, with 
 a corresponding reduction of silver to the metallic state ; the quantity 
 of the subiodide of mercury so formed, is greatest in the shaded parts 
 where the iodide of silver is left almost intact, less in the parts feebly 
 affected by the luminous rays, and least in the parts where the action 
 of the light, has been strongest. As regards the shaded parts, the 
 chemical action stops here ; but the case is different with the parts 
 previously acted upon by the luminous rays ; in these latter parts, the 
 subiodide of mercury formed coming into contact with the subiodide of 
 silver, a double decomposition ensues : the subiodide of mercury 
 separates into two parts, of which one combines with the iodine of the 
 subiodide of silver, and with the iodine of the other part, forming 
 iodide of mercury ; the reduced silver and the reduced mercury 
 amalgamating and settling on the plate. The picture accordingly makes 
 its appearance first in the lightest parts, since the quantity of mercury 
 absorbed is the greater, the richer the parts are in subiodide of silver. 
 In the most shaded parts, on the other hand, where iodide of silver 
 alone is offered to the mercurial fumes, there can be formed only a more 
 or less dark film of subiodide of mercury, mixed with metallic silver, 
 which latter substance being in a state of most minute division, exhibits 
 a black tint. But between these two extremes of the deepest shadow 
 and the strongest light, are seen the semi-tints of the object depicted ; 
 
THEOEY OF THE PHOTOGEAPHIC PHENOMENA. 
 
 75 
 
 and these semi-tints again are lighter or darker in the different parts 
 of the picture, in proportion to the depth of the film of subiodide of 
 silver respectively covering the several parts, and accordingly in pro- 
 portion as the iodide has been acted upon more or less vigorously by 
 the luminous rays ; and thus we find also after the exposure of the 
 plate to the mercurial fumes, that the shaded parts, being covered with 
 iodide of mercury and metallic silver, look black or greenish, whereas 
 the lightest parts look reddish, from the presence on them of an alloy 
 of silver and mercury in invisible particles, covered with a film of 
 iodide of mercury. Upon washing the plate afterwards with a 
 solution of hyposulphite of soda, the iodide of mercury is dissolved, 
 the suhiodide being decomposed at the same time, into iodide, which 
 is then also dissolved, and metallic mercury, which remains on the 
 plate. 
 
 The white parts of the picture are accordingly constituted by the 
 alloy of mercury and silver deposited on the plate, and are the more 
 vivid, the more copiously this alloy has been deposited ; the dark 
 parts on the other hand are formed by deposits of most minutely 
 divided metallic silver. The production of photographic pictures 
 on paper or glass, is likewise the result of the decomposition by the 
 agency of light, of the metallic compounds forming the impres- 
 sionable surface ; of this fact anybody may convince himself by the 
 following simple experiment : 
 
 Take a piece of paper prepared with chloride of ammonium and 
 nitrate of silver, and put it, together with a little potassium, into a 
 perfectly dry glass tube ; seal this hermetically, and leave it about 
 twenty-four hours in the dark, to give time for the oxygen of the 
 air in the tube to combine with the potassium. Place the tube now 
 in sunlight : after a few hours you will find that the pap^r has 
 acquired a black tint ; though not of the same intensity as another 
 piece of the same paper, which has been exposed for a much shorter 
 time in the open air. V 
 
 If you now open the glass under a solution of ammonia, you will^ 
 not indeed detect any free chloride in it ; however, if you examine th^T 
 potassa salt in the glass, you will find that it is the hydrochlorate, an 
 evident proof that hydrochloric acid must have been liberated from 
 the paper, and have combined with the alkali metal. The several 
 
 £ 2 
 
76 
 
 THE AKT OF PHOTOGRAPHY. 
 
 processes of decomposition and combination which have taken place 
 may be briefly stated as follows : — The paper having been prepared 
 with chloride of ammonium and nitrate of silver, we have in it— 
 
 Hydrocblorate of ammonia. 
 
 (Chloride of ammonium, sal-ammoniac.) Nitrate of silver. 
 
 , * s , * ^ 
 
 Hydrochloric acid. Ammonia. Nitric acid. Oxide of silver. 
 
 Hydrogen. Chlorine. Nitrogen. Hydrogen. Nitrogen. Oxygen. Silver. Oxygen. 
 
 
 
 
 Nitrate of ammonia. 
 
 .. 
 
 
 
 
 
 Chloride of silver. 
 
 Water. 
 
 There are accordingly contained in the paper, nitrate of ammonia, 
 chloride of silver, and water, and besides these substances a little free 
 nitrate of silver, as has been intimated already on a former occasion. 
 Under the influence of the solar rays the chloride of silver is decom- 
 posed, the liberated chlorine probably combining w'ith the hydrogen of 
 the decomposed water, and forming hydrochloric acid with it, w^hilst 
 the potassium combines with a portion of the liberated oxygen of the 
 water, forming potassa, which again combines with the hydrochloric 
 acid to hydrochlorate of potassa ; the liberated silver of the chloride 
 combines wdth the other portion of the oxygen to oxide of silver. 
 
 The liberation of the chlorine may be equally demonstrated by 
 another very simple experiment. Put a little pure chloride of silver 
 into a bent glass tube, closed at one end, 
 and confine the other end under water 
 (see figure 10) ; expose the chloride in 
 the tube to light, taking care to shake 
 the tube occasionally, in order that the 
 whole of the chloride may be brought 
 under the influence of that agent. As 
 soon as the chloride of silver begins to 
 acquire a black tint, the water will be 
 seen to rise in the tube. When the 
 whole of the chloride has become black, 
 add a few drops of solution of nitrate of silver to the water, when 
 
 
THEORY OF THE PHOTOGRAPHIC PHENOMENA. 77 
 
 the formation of a precipitate of chloride of silver will at once demon- 
 strate the presence of chlorine in the water. 
 
 This simple experiment sufficiently shows that the chloride of silver 
 suffers decomposition under the influence of light, chlorine being set 
 free, and the reduced silver combining with oxygen instead. 
 
 The same explanation of the process applies of course equally to 
 the iodide and bromide, and other salts of silver. The use of gallic 
 acid to develope the latent image rests upon the great affinity of that 
 acid for oxygen, by virtue of which it decomposes the salts of silver ; 
 properly speaking, therefore, this acid simply serves to complete 
 what the light has already begun. The action of the light has tended 
 already to loosen the connection between the component elements of 
 the silver-salt, in the parts touched by the luminous rays ; in these 
 parts, therefore, the gallic acid readily succeeds in reducing the silver 
 to the metallic state ; the minutely-divided reduced silver exhibiting 
 a black tint. In the parts that have not been acted upon by the light, 
 on the other hand, the silver salt has remained unaltered, and the 
 gallic acid cannot, therefore, effect the separation of metallic silver 
 here so speedily as in the parts impressed by the light. Now, upon 
 treating these pictures afterwards with hyposulphite of soda, the 
 unaltered salt readily dissolves in this agent, and is thus removed; 
 whereas, the separated silver is but very little affected, and remains 
 in the substance of the paper in a state of minute division ; the 
 picture appears accordingly negative (that is, if produced in the camera 
 in the usual way). Instead of gallic acid, other substances, that have 
 a strong affinity for oxygen, such as hyposulphate, sulphate, and 
 hyponitrate of protoxide of iron, may be used with the same result ; 
 also the alcoholic solution of many ethereal oils, more especially of the 
 oil of cloves (oleum caryophyllorum), and of cinnamon (oleum cinna- 
 raomi) ; these latter, however, act much more slowly than the other 
 substances named. 
 
 In the case of the salts of iron, the impression produced by the 
 decomposing action of the light is brought out most fully and clearly 
 by subsequent treatment with ferricyanide of potassium. 
 
78 
 
 THE ART OE PHOTOGRAPHY. 
 
 A few practical hints on the proper selection and arrangement of the 
 locale in which photographic operations may best he performed, and 
 on the proper posture, attitude, and dress of persons who wish 
 to have their portraits taken with the photographic apparatus. 
 By Francis Schubert, Painter. 
 
 Photographic portraits are, of course, always taken best in the open 
 air j however, as it is not at all times feasible to do so, the photo- 
 graphic artist must select and suitably arrange an appropriate apart- 
 ment for the purpose. It need hardly be remarked here that this 
 apartment must be as light as can be ; in fact, the most suitable is a 
 glass house, standing in an open ground, or erected on the top of a 
 building. But here again, everyone has not the means at his command 
 to have a structure of the kind erected in an appropriate spot. Most 
 photographic artists must content themselves with the choice of a well 
 lighted apartment, if possible, with a sky-light. A room receiving 
 the light from the north-west is preferable to others. 
 
 The walls should be painted of a light blue, which will tend 
 to diffuse a mild, uniform light throughout the apartment ; in the 
 case of a glass house, the light may be regulated in the same manner 
 by means of light-blue curtains. This contrivance has another 
 beneficial effect; viz., it excludes those luminous rays which are 
 least effective in a photographic point of view. 
 
 As regards the proper attitude of the person sitting for the portrait, 
 this must of course be left in a measure to the individual judgment 
 and taste of the artist. However, a few hints on this subject may 
 not prove unwelcome. 
 
 The posture of the person sitting for the portrait should be easy 
 and unconstrained ; the feet and hands neither projecting too much, 
 nor drawn too far back ; the eyes should be directed a little sideways 
 above the camera, and fixed upon some object there, but never upon 
 the apparatus, since this would tend to impart to the face a dolorous, 
 dissatisfied look. Stout persons should be placed at a certain distance 
 from the apparatus, turning towards it a little sideways ; whilst people 
 of slender make should be made to sit full in front, and nearer the 
 apparatus. Long arms and legs require drawing back a little. The 
 hands should rest easy on the lap, neither too high nor too low : or 
 
ATTITUDE, El'C., OF PERSONS SITTING FOR PORTRAIT. 79 
 
 one hand may be placed on the table, the other holding a book or 
 some other object. A thick hand should show the thumb in the 
 foreground, with the fingers bent a little inward 5 a long hand had 
 better show the back ; a hand of handsome shape, neither too long nor 
 too short, should show full two thirds, with the fingers easily and 
 gracefully hanging down. A slight lateral inclination of the body 
 forward will generally produce a good effect. In the case of ladies, a 
 shawl or boa, or similar article of dress, thrown lightly over the 
 shoulders, and arranged in a manner to hide some defect, and to 
 properly distribute light and shadow, will mostly tend to produce a 
 pleasant impression. 
 
 Of a full round face, with large mouth, small eyes, and small nose, 
 the portrait should be taken in half profile, so as to show one side of 
 the face in full, with very little of the other side. 
 
 A moderately full face, with aquiline nose, and handsome mouth 
 and eyes, should be taken in three-fourth profile ; a countenance with 
 strongly-marked features full in front. 
 
 The selection of a proper background for the picture is also a 
 matter of some importance ; in some cases, a landscape will give a 
 most pleasing background, in others a simple wall will answer as well, 
 or even better ; the decision here must be left to the individual 
 judgment and taste of the artist. 
 
 If .two persons are to be portrayed in the same picture, the one 
 should be made to lean lightly on the chair of the other, and the faces 
 of both should be partly turned to each other, as in conversation. 
 Or they may be placed at a table seated opposite each other, the 
 one with the right, the other with the left arm laid on the table, and 
 the bodies of both gently inclined forward and towards each other, as 
 in conversation. 
 
 The arrangement of family groups again must be left entirely to 
 the judgment of the artist ; care should always be taken, however, to 
 place the several persons constituting the group all at the same focal 
 distance. 
 
 With respect to dress, colors and objects of intense illumination 
 should always be avoided ; this applies more particularly to yellow 
 and scarlet. Plain-colored dresses, neither too light nor too dark 
 give always the most pleasing pictures. 
 
80 
 
 THE AET OF PHOTOGKAPHY, 
 
 TABLE I. 
 
 THE MOST IMPORTANT CHEMICAL ELEMENTS, OR SIMPLE BODIES, WITH 
 THEIR RESPECTIVE SYMBOLS AND COMBINING PROPORTIONS.* 
 
 NAME. 
 
 SYMBOL. 
 
 EQUIVALENTS, OR 
 COMBINING PROPORTIONS. 
 
 OXYGEN = 100. 
 
 HTDROGEN = l. 
 
 Aluminium . 
 
 Al. 
 
 170-5 
 
 13-6 
 
 Antimony (Stibium) . 
 
 Sb. 
 
 1612-5 
 
 129-0 
 
 Arsenic 
 
 As. 
 
 937-5 
 
 75-0 
 
 Barium . . . . 
 
 Ba. 
 
 857-5 
 
 68-6 
 
 Bismuth 
 
 Bi. 
 
 2600-0 
 
 208-0 
 
 Boron . . . . 
 
 B. 
 
 136-2 
 
 10-9 
 
 Bromine 
 
 Br. 
 
 1000-0 
 
 800 
 
 Calcium . . . 
 
 Ca. 
 
 250-0 
 
 20-0 
 
 Carbon 
 
 C. 
 
 75-0 
 
 6-0 
 
 Chlorine . . . . 
 
 Cl. 
 
 443-7 
 
 35-5 
 
 Chromium . 
 
 Cr. 
 
 3350 
 
 26-8 
 
 Cobalt . . . . 
 
 Co. 
 
 368-6 
 
 29-5 
 
 Copper (Cuprum) 
 
 Cu. 
 
 396-0 
 
 31-7 
 
 Fluorine . . . . 
 
 F.i 
 
 237-5 
 
 19-0 
 
 Gold (Aurum) 
 
 Au. 
 
 2462-5 
 
 197-0 
 
 Hydrogen . . . 
 
 H. 
 
 12-5 
 
 1-0 
 
 Iodine 
 
 I. 
 
 1585-0 
 
 126-8 
 
 Iron (Ferrum) . . 
 
 Fe. 
 
 350-0 
 
 28-0 
 
 Lead (Plumbum). 
 
 Pb. 
 
 1294-6 
 
 103-6 
 
 Magnesium . . . 
 
 Mg. 
 
 150-2 
 
 12-1 
 
 Manganese . 
 
 Mn. 
 
 344-7 
 
 27-6 
 
 Mercury (Hydrargyrum) 
 
 Hg. 
 
 1250-0 
 
 100.0 
 
 Molybdenum 
 
 Mo. 
 
 575-0 
 
 46 0 
 
 Nickel . . , . 
 
 Ni. 
 
 369-3 
 
 29-6 
 
 Nitrogen 
 
 N. 
 
 175-0 
 
 14-0 
 
 Oxygen . 
 
 0. 
 
 100-0 
 
 8.0 
 
 Phosphorus 
 
 P. 
 
 392-0 
 
 31-4 
 
 Platinum . . . 
 
 Pt. 
 
 1236-7 
 
 98-9 
 
 Potassium (Kalium) . 
 
 K. 
 
 490-0 
 
 39-2 
 
 Selenium . . . 
 
 Se. 
 
 494-0 
 
 39-5 
 
 Silver (Argentum) 
 
 Ag. 
 
 1349.6 
 
 108-0 
 
 Sodium (Natrium) . . 
 
 Na. 
 
 287-5 
 
 23-0 
 
 Strontium . , 
 
 Sr. 
 
 545-9 
 
 43-7 
 
 Sulphur . . , . 
 
 S. 
 
 200-0 
 
 16-0 
 
 Tin (Stannum) 
 
 Sn. 
 
 735-3 
 
 58-8 
 
 Uranium. . . . 
 
 U. 
 
 742-9 
 
 59-5 
 
 Zinc .... 
 
 Zn. 
 
 406 6 
 
 32-5 
 
 See Appendix. 
 
TABLES OE CHEMICAL EQUIVALENTS 
 
 SI 
 
 TABLE II. 
 
 — f — 
 
 THE MOST IMPORTANT CHEMICAL COMPOUNDS (iN A PHOTOGRAPHIC POINT 
 OP view), with THEIR FORMULA AND COMBINING PROPORTIONS. 
 
 NAME. 
 
 FORMULA. 
 
 Acetate of alumina 
 
 AI 2 Os , 3A 
 
 — baryta . . . 
 
 BaO, A + HO 
 
 — copper, neutral 1 
 
 CuO, A-pHO 
 
 crystallised • J 
 
 
 — lead, neutral (sugar 1 
 
 PbO, A + 3HO 
 
 of lead) . . . J 
 
 
 — soda 
 
 NaO, A-H6HO 
 
 Acetic acid 
 
 CiHsOs -fHO=A-lHO 
 
 Alcohol ..... 
 
 C 4 He O 2 -P HO 
 
 r 
 
 NH 4 O, SOs + AI 2 O 3 , 1 
 
 Alum, ammoma- . . < 
 
 3SOs-l24HO / 
 
 r 
 
 KO,SOs +Al2 03,3S0s 1 
 
 — potassa- . . ■! 
 
 + 24HO J 
 
 Ammoniacal gas (spirits of ] 
 
 NHs 
 
 hartshorn) . . J 
 
 
 Ammonia, solution or liquor of 
 
 NH 3 T ajHO 
 
 Amylum, see Starch 
 
 
 Antimoniate of potassa . . 
 
 KO, SbOs 
 
 Arseniate of potassa 
 
 KO, AsOs + 2HO 
 
 Baryta . .... 
 
 Ba 0 
 
 Benzoic acid .... 
 
 Ci4 HsOs -f HO 
 
 Biborate of soda (borax) . . 
 
 NaO, 2BOs + lOHO 
 
 Boracic acid, crystallised . 
 
 BOs + 3HO 
 
 Bromic acid . . . . 
 
 BrOs 
 
 Bromide of potassium 
 
 KBr 
 
 — silver . . . 
 
 AgBr 
 
 — • sodium 
 
 NaBr 
 
 Bromiodine . . . . 
 
 IBi-3 
 
 Camphor, Japan 
 
 Cio HeO 
 
 Carbonate of ammonia . . 
 
 JNH 3 , CO 2 
 
 — — sesqui- > 
 
 2NH4,0 + 3C02 
 
 carbonate . . J 
 
 
 Carbonate of baryta 
 
 BaO, CO 2 
 
 — lime . 
 
 CaO, CO 2 
 
 — magnesia . . 
 
 MgO, CO 2 + 3HO 
 
 — potassa (neutral) 
 
 KO, CO 2 
 
 — (acid or bicar- 1 
 
 KO, 2 CO 2 -f HO 
 
 bonate) . . J 
 
 
 — soda (crystall.) . 
 
 NaO, CO 2 lOHO 
 
 — soda(bicarbonate) 
 
 NaO, 2 CO 2 HO 
 
 MIXING 
 PROPORTION. 
 HYDROGEN = l. 
 
 204-2 
 
 136-6 
 
 99-7 
 
 189-6 
 
 136-0 
 
 60-0 
 
 55-0 
 
 453-2 
 
 474-4 
 
 170 
 
 216-2 
 
 180-2 
 
 76-6 
 
 122-0 
 
 190-8 
 
 61-9 
 
 120-0 
 
 1192 
 
 188-0 
 
 103-0 
 
 366-8 
 
 76-0 
 
 39-0 
 
 118-0 
 
 98-6 
 
 500 
 
 69-1 
 
 69-2 
 
 100-2 
 
 143-0 
 
 84-0 
 
 E 3 
 
 
7 
 
 82 THE ART OE PHOTOGRAPHY. 
 
 NAME. 
 
 FORMULA. 
 
 EQUIVALENT, OR 
 
 m^ino 
 
 PROPORTION. 
 HYDROGEN = l. 
 
 Carbonate of strontia 
 Carbonic acid . . . . 
 
 Caoutchouc . . , . 
 
 Chlorate of ammonia , . . 
 
 — baryta . 
 
 — potassa . . . 
 
 — soda 
 
 Chloric acid . . , , 
 
 Chloride of aluminium {ses-T 
 quichl.) . . J 
 
 — ammonium (sal- T 
 
 ammoniac) . . / 
 
 — arsenic . 
 
 — barium . . . 
 
 — cobalt . 
 
 — copper (subchlo-\ 
 
 ride) . . . j 
 
 — ciystallised 
 
 — cyanogen, gase- \ 
 
 ous (proto-) . J 
 
 — — solid \ 
 
 (sesqui.) . . J 
 
 — gold (terchlor.) 
 
 — gold and sodium . 
 
 — iodine, liquid 1 
 
 (proto-) . . / 
 
 — — solid (ter) . 
 
 — iron, proto- . 
 
 — — sesqui- . . 
 
 — lead, neutral 
 
 — lime (bleaching- "1 
 
 powder) . . J 
 
 — magnesium, crystal. 
 
 — manganese, proto- 
 
 — — sesqui- 
 
 — mercury, (corro- 1 
 sive sublimate) . J 
 
 — nickel . 
 
 — — and ammonia 1 
 
 (ammonio-chloride of 1 
 nickel) . . . J 
 
 — nitrogen (terchl.) . 
 
 — platinum, hy- I 
 drated bichloride . J 
 
 — potassium 
 
 silver , . . 
 
 — sodium (common 1 
 
 salt) . . . f 
 
 SrO, CO 2 
 CO 2 
 Ce H 7 
 
 NH 4 0, CIOs 
 BaO, CIOs -4- HO 
 KO, CIOs 
 NaO, CIOs 
 CIOs 
 
 AI 2 CI 3 -1-12H0 
 
 NH*,C1 
 
 AsCh 
 
 BaCl-H2H0 
 
 CoCl 
 
 CU 2 CI 
 CuCl -4- 4H0 
 CyCl 
 
 Cy2Cl3 
 
 AuCls -4- 6H0 
 NaCl + AuCls -4-6HO 
 
 ICl 
 
 ICI 3 
 
 FeCl + 4H0 
 Fe2Cl3 +6H0 
 PbCl 
 
 CaO.ClO-l-CaCl 
 
 MgCl + 5H0 
 MnCl-i-4H0 
 Mn 2 CI 3 
 
 HgCl 
 
 NiCl + lOHO 
 HiCl-4-2NH3 -fHO 
 NCI 3 
 
 PtCk - 4 - 8H0 
 
 KCl 
 
 AgCl 
 
 NaCl 
 
 73- r 
 22-0 
 65-0 
 
 101-5 
 161-1 
 122-7 
 106 5 
 75-5 
 
 241-7 
 
 53-5 
 
 181-5 
 
 1221 
 
 65-0 
 
 98- 9 
 103-2 
 
 61-5 
 
 158-5 
 
 357-5 
 
 416-0 
 
 162-3 
 
 233-3 
 
 99- 5 
 216-5 
 139-1 
 
 127-0 
 
 92-6 
 
 99-1 
 
 161-7 
 
 135-5 
 
 155-1 
 
 108-1 
 
 120-5 
 
 241-9 
 
 74- 7 
 143-5 
 
 58-5 
 
 
TABLES OP CHEMICAL EQUIVALENTS. 
 
 83 
 
 Chloride of strontium . . 
 
 — sulphur (subchl.) . 
 
 — tin, crystallised 1 
 
 proto- • . • J 
 
 — cryst. bichloride 
 
 Chloroform 
 
 Chromate of lead, neutral 
 
 — potassa, neutral . 
 
 — — acid or \ 
 
 bichromate . . J 
 
 Citrate of sesqui-oxide of iron . 
 
 — sesquioxide of iron \ 
 and ammonia . J 
 
 — sesquioxide of iron 1 
 
 and potassa . • J 
 
 — sesquioxide of iron "I 
 
 and soda . . J 
 
 — mercury . . • 
 
 . — silver 
 
 perature . . . 
 
 — precipitated from' 
 a hot saturated solu- 
 tion, and dried at 
 212 ° . . . . 
 
 Cobalt, oxide of . 
 
 Cotton . . . • 
 
 Cyanate of potassa 
 
 Cyanic acid 
 
 Cyanide of potassium . 
 
 — silver 
 
 Cyanogen .... 
 
 Ether . . • • 
 
 Ferrocyanide of potassi 
 (yellow prussiate 
 potassa) 
 
 Fluoride of ammonium 
 
 — calcium (fluor 
 
 — potassium 
 
 — sodium 
 Formic acid 
 
 Gallic acid, crystallised 
 Gold, oxide (teroxide) of 
 Hydrobromic acid 
 Hydrochloric acid . 
 
 FORMULA. 
 
 EQUIVALENT, OR 
 MIXING 
 PROPORTION. 
 HYDEOGEN^l. 
 
 SrCl + 6HO 
 
 133-2 
 
 S 2 CI 
 
 67-5 
 
 SnCl + HO 
 
 103-3 
 
 SnCH -1- 2HO 
 
 147-8 
 
 C 2 HCI 3 
 
 119-5 
 
 PbO, CrOa 
 
 162-2 
 
 KO, CrOa 
 
 98-0 
 
 KO, 2Cr03 
 
 148-8 
 
 C 12 HsOu +5H0=^ 
 
 210-0 
 
 > C 12 HaOu -f 3H0=-a 
 
 192-0 
 
 CoO 
 
 37-5 
 
 CHO 
 
 15-0 
 
 KO, CyO 
 
 81-2 
 
 CyO-f-HO 
 
 43-0 
 
 KCy 
 
 65-2 
 
 AgCy 
 
 134-0 
 
 C2N = Cy 
 
 26-0 
 
 C 4 H 5 O 
 
 37-0 
 
 h 3 KCy,Fe 2 Cya 
 
 329-6 
 
 ^ 2KCy,FeCy-t3HO 
 
 211-4 
 
 . NH4,F1 
 
 37-0 
 
 CaFl 
 
 39-0 
 
 . KFl 
 
 58-2 
 
 . NaFl 
 
 42-0 
 
 . C2H0a+H0=Fo 
 
 46-0 
 
 . C?H2 04 +H0=Ga 
 
 85-0 
 
 . AuOs 
 
 221-0 
 
 . BrH 
 
 81-0 
 
 . CIH 
 
 36-5 
 
84 
 
 THE ART OF PHOTOGRAPHY, 
 
 NAME, 
 
 FORMULA. 
 
 Hydrochloric acid, most con- \ 
 centrated hydrated J 
 Hydrocyanic acid . 
 
 cm -i- 6HO 
 
 Cyll 
 
 Hydrofluate of ammonia . . 
 Hydrofluoric acid . 
 Hydriodate of ammonia . 
 Hydriodic acid . . . . 
 
 Hydrosulphuric acid (suphu-1 
 
 FIH 
 
 NH3,HI 
 
 HI 
 
 HS 
 
 retted hydrogen) f 
 
 Hyponitrate of protoxide of iron 
 Hyponitric acid 
 Hyposulphate of protoxide \ 
 
 NO* 
 
 of iron . . . j 
 
 
 Hyposulphate of soda 
 
 Na0,S2 02 +5HO 
 
 Hyposulphuric acid . . . 
 
 S2 05 
 
 Hyposulphurous acid 
 
 S 2 O 2 
 
 lodate of ammonia . . . 
 
 NH*0, IO 5 
 
 Iodic acid .... 
 
 IO 5 -f-HO 
 
 Iodide of ammonium . . . 
 
 NH*,! 
 
 — iron (sesqui-) . 
 
 Fe2ls 
 
 — potassium . . . 
 
 KI 
 
 — silver . , 
 
 Agl 
 
 — sodium . . . 
 
 Nal 
 
 Iron, protoxide of . 
 
 FeO 
 
 — sesquioxide of , . . 
 
 Fc 2 O 3 
 
 — hydrated sesquioxide of . 
 
 Fg2 03 + 3HO 
 
 Lime, hydrate of . , , 
 
 CaO -H HO 
 
 Malic acid . .... 
 
 C 4 H 2 O 4 + HO=M 
 
 Manganate of potassa 
 
 KO, Mn03 
 
 — — per- , . 
 
 KO, Mn2 O 7 
 
 Milk sugar .... 
 
 C 24 H 22 O 22 -(- 2HO 
 
 Nickel, oxide of . . . . 
 
 NiO 
 
 Nitrate of ammonia 
 
 NH*0, NO 5 -i-HO 
 
 — baryta . . . 
 
 BaO, NOs 
 
 — sesquioxide of chro- \ 
 mium , . J 
 
 Cr2 03, 3NOs 
 
 — copper . . , 
 
 CuO, NOs 
 
 — sesquioxide of iron . 
 
 Fc2 03,3N0s 
 
 — lead 
 
 PbO, NOs 
 
 — mercury . . . 
 
 2(HgO, NOs) 4 - HO 
 
 — mercuryand ammonia 
 
 (NH 3 , NOs) + 3HgO 
 
 — nickel . , , 
 
 NiO, NOs H- 6HO 
 
 — potassa . 
 
 6 
 
 , 12 ; 
 
 d 
 
 — silver . . . . 
 
 AgO, NOs 
 
 — — and ammonia . 
 
 AgO, NOs q- 2NHs 
 
 — soda 
 
 NaO, NOs 
 
 — strontia . . . 
 
 SrO, NOs 
 
 — zinc 
 
 ZnO, NOs 
 
 equivalent, OB 
 
 MIXING 
 PROPOBTION. 
 HYDROGEN = 1. 
 
 90-5 
 
 27-0 
 
 20-0 
 
 144-8 
 
 127-8 
 
 17-0 
 
 46-0 
 
 124-0 
 
 72-0 
 
 48-0 
 
 192-8 
 
 175-8 
 
 144- 8 
 436.4 
 166-0 
 234-8 
 149-8 
 
 36- 0 
 80-0 
 
 107 0 
 
 37- 0 
 67-0 
 98-8 
 
 158-4 
 
 360-0 
 
 37-6 
 
 89-0 
 
 130-6 
 
 239-6 
 
 93 7 
 242-0 
 165-6 
 333-0 
 395-0 
 
 145- 6 
 101-2 
 170-0 
 204-0 
 
 85-0 
 
 105-7 
 
 94-5 
 
TABLES OF CHEMICAL EQUIVALENTS, 
 
 85 
 
 KAME. 
 
 FORMULA. 
 
 EQUIVALENT, OR 
 MIXING 
 PROPORTION. 
 HYDROGEN = 1. 
 
 Nitric acid, first hydrate . . 
 
 NOs -fHO 
 
 630 
 
 Oxalate of ammonia, neutral . 
 
 NH 4 O, C 2 O 3 -t-HO 
 
 71-0 
 
 — — acid (bin- \ 
 
 NHiO, 2C2 03 -f2H0 
 
 116-0 
 
 oxalate) . . J 
 
 121-6 
 
 — baryta • • 
 
 BaO, C 2 O 3 -f-HO 
 
 — cobalt and -ammo- \ 
 
 I 2 NH 3 -lCaCo3 0x2 \ 
 
 478-5 
 
 nia . . . J 
 
 6HO J 
 
 — copper and soda 
 
 CsNaCuOx +2H0 
 
 116-7 
 
 — sesquioxide of iron . 
 
 Fc2 Os, 3 C 2 O 3 
 
 188-0 
 
 — sesquioxide of iron 1 
 
 and ammonia . j 
 
 Ca (SNHi 0)Fe2 O 12 
 
 266-0 
 
 — sesquioxide of iron 1 
 
 CaBasFesOis + 21HO 
 
 582-8 
 
 and baryta . . J 
 
 
 — sesquioxide of iron 1 
 
 CaKsFeaOis 
 
 305-6 
 
 and potassa . . J 
 
 
 — sesquioxide of iron 1 
 
 CeNasFesOis + lOHO 
 
 347-0 
 
 and soda . . J 
 
 
 — sesquioxide of iron 1 
 
 CaSr3Fe2 0i2 -t- 18HO 
 
 481-1 
 
 and strontia . . J 
 
 147-6 
 
 Oxalate of lead 
 
 PbO, C 2 O 3 
 
 — nickel . . . 
 
 NiO, C 2 O 3 -I2HO 
 
 91-6 
 
 — — and ammonia . 
 
 
 
 — potassa, neutral 
 
 KO, C 2 Os H- HO 
 
 92-2 
 
 — — acid, or bin- 1 
 
 KO, 2 C 2 O 3 - 1 - HO -t- 2aq. 
 
 146-2 
 
 oxalate (sorrel salt) J 
 
 67-0 
 
 — soda, neutral . . 
 
 NaO.CsOs _ 
 
 Oxalic acid .... 
 
 C 2 Os -I HO -1- 2aq.=Ox 
 
 63 0 
 
 Pbospbate of potassa . . • 
 
 KO, POs 
 
 118-6 
 
 — silver . 
 
 AgO, POs 
 
 187-4 
 
 — soda . . • 
 
 NaO, POs 
 
 102-4 
 
 Potassa 
 
 KO 
 
 47-2 
 
 — bydrate of . . . 
 
 KO-t-HO 
 
 56-2 
 
 Prussian blue . . • • 
 
 3FeCy-l-2Pe2Cy3 + 9HO 
 
 511-0 
 
 Pyrop;allic acid . . . • 
 
 CsHs03 = pO 
 
 63-0 . 
 
 Racemic acid, see Uvic acid 
 Sal-ammoniac, see Cbloride of 
 ammonium. 
 
 
 116-0 
 
 Silver, oxide of . . • 
 
 Ago 
 
 Soda 
 
 NaO 
 
 31-0 
 
 — bydrate of . . . 
 
 NaO -f HO 
 
 40-0 
 
 Stannate of potassa . . 
 
 KO, Sn02 + 3HO 
 
 149-0 
 
 Starcb 
 
 C 12 Hio Oio 
 
 162-0 
 
 Succinate of ammonia, acid 
 
 
 
 — sesquioxide of 1 
 
 Fe 2 0s,3Su 
 
 230-0 
 
 iron . . . , 
 
 
 — potassa, acid 
 
 _ 
 
 
 Succinic acid, crystallised . - 
 
 Cl H 2 Os + HO = Su + ) 
 L . HO / 
 
 59-0 
 
86 
 
 THE ART OE PHOTOGRAPHY. 
 
 
 
 EQUIVALENT, OR 
 
 NAME. 
 
 FORMULA. 
 
 MIXING 
 
 
 
 PROPORTION. 
 HYDROGEN = 1. 
 
 Succinic acid, sublimed . 
 
 20* Ha Os -f- HO=Su I 
 -fHO / 
 
 109-0 
 
 Sugar 
 
 Ci 2 Hii On 
 
 171-0 
 
 — of lead, see acetate of lead 
 
 
 Sulphate of ammonia, crys- ] 
 tallised . . . J 
 
 NHs,S03 
 
 57-0 
 
 Sulphate of sesquioxide ofl 
 chromium and am- S 
 monia . . J 
 
 NH 4 O, SOs -t- CraOs,! 
 3S0s -1- 24HO / 
 
 479-6 
 
 Sulphate of sesquioxide of] 
 chromium and po- 
 tassa . . . J 
 
 K0,S0s -f-Cr2 0s,3S03 1 
 -t- 24HO / 
 
 500-8 
 
 Sulphate of cobalt and am-1 
 monia . . . j 
 
 (HH 4 O, SOs) -F (CoO,l 
 S0s)-t-6H0 / 
 
 197-5 
 
 Sulphate of copper (blue 1 
 vitrioll . . J 
 
 CuO, SOs + 5H0 
 
 124-7 
 
 Sulphate of copper and am- 1 
 monia . . . J 
 
 NH4 0,S03-4-Cu0,S03 
 
 145-7 
 
 Sulphate of protoxide of iron 1 
 (green vitriol) . j 
 
 FeO, SO 3 + 7H0 
 
 1390 
 
 Sulphate of sesquioxide ofl 
 
 (NH4 0,S03)-t-(Fe2 0s,1 
 
 482-0 
 
 iron and ammonia . j 
 
 3S03)-f24H0 r 
 
 Sulphate of sesquioxide ofl 
 
 K0,S0s +Fea03,3S03 1 
 
 503-2 
 
 iron and potassa J 
 
 ^24HO / 
 
 Sulphate of nickel . 
 
 NiO, SO 3 + 7H0 
 
 140-6 
 
 — potassa, neutral . 
 
 KO, SO 3 
 
 87-2 
 
 — soda, neutral 
 
 HaO.SOs 
 
 71-0 
 
 Sulphite of potassa, neutral . 
 Sulphuretted hydrogen, (hy-"] 
 
 KO,SOa + 2HO 
 HS 
 
 97-2 
 
 17-0 
 
 drosulphuric acid) . J 
 
 Sulphuric acid, English . 
 
 SOs -f HO 
 
 490 
 
 Sulphurous acid . . . . 
 
 S02- 
 
 32-0 
 
 Tannic acid (Tannin) 
 
 C 18 Hs O 9 + 3H0 
 
 212-0 
 
 Tartrate of ammonia, acid 
 
 NH 4 O, 2T-I-HO 
 
 167-0 
 
 — — neutral . 
 
 OH* 0, T -f HO 
 
 101-0 
 
 Tartrate of sesquioxide of iron 
 
 — bitartrate (or acid ] 
 tartrate) of sesqui- 1 
 oxide of iron . J 
 
 
 
 Tartrate of sesquioxide ofl 
 
 
 
 iron and ammonia . J 
 
 
 
 Tartrate of sesquioxide of 1 
 
 
 
 iron and potassa j 
 
 
 
 Tartrate of sesquioxide of) 
 
 
 
 iron and soda . J 
 
 
 
 Tartrate of potassa, acid or "I 
 bitartrate . , j 
 
 K0,2T-t-H0 
 
 188-2 
 
EE ACTIONS OF SALTS OF METALLIC OXIDES. 
 
 87 
 
 NAME. 
 
 FOBMULA. 
 
 EQUIVALENT, OB 
 MIXING 
 PBOPORTION. 
 HYDROGEN = 1. 
 
 Tartrate of potassa, neutral 
 — soda, neutral . 
 
 Tartaric acid . . . • 
 
 Tin, binoxide of (Stannic acid) . 
 Turpentine, oil of . • • 
 
 Uvic acid . . . • 
 
 Water 
 
 KO,T 
 
 NaO, T + 2HO _ 
 CiHaOs -f HO=T-t-HO 
 SnOa 
 
 Cs H* 
 
 C 4 H 2 O 5 -f-HO-faq.=U 
 HO 
 
 113-2 
 
 115-0 
 
 75-0 
 
 74-8 
 
 34-0 
 
 84-0 
 
 9-0 
 
 TABLE III. 
 
 BRIEF ABSTRACT OF THE PRINCIPAL RE-ACTIONS OF METALLIC SALTS WITH 
 THE MOST IMPORTANT RE-AGENTS. 
 
 I. METALLIC OXIDES. 
 
 1. Salts of Potassa. 
 
 Tartaric acid produces in solutions of salts of potassa a crystalline 
 precipitate, which dissolves in an excess of sulphuric acid, hydro- 
 chloric acid, and nitric acid. 
 
 Bichloride of platinum produces a bright-yellow precipitate, which is 
 not dissolved by free acid. 
 
 Hydrofluosilicic acid produces a gelatinous precipitate. 
 
 Cyanic acid produces in alcoholic solutions of salts of potassa a yellow 
 crystalline precipitate. 
 
 Sulphate of alumina produces in concentrated solutions of salts 
 of potassa a deposit of potassa-alum (sulphate of alumina and 
 potassa.) 
 
 2 . Salts of Soda. 
 
 Hydrofluosilicic acid produces in concentrated solutions of salts of 
 soda a gelatinous precipitate ; the other reagents enumerated sub. 1, 
 fail to produce a precipitate in solutions of salts of soda. 
 
 Antimoniate of potassa produces in neutral solutions of salts of soda 
 a white precipitate of antimoniate of soda. 
 
88 
 
 THE ART OE PHOTOGRAPHY. 
 
 3. Salts of Ammonia. 
 
 Bichloride of platinum produces a yellow precipitate. 
 
 Tartaric acid produces only in very concentrated solutions of salts of 
 ammonia a crystalline precipitate. 
 
 Sulphate of alumina produces a crystal of ammonia-alum (sulphate of 
 alumina and ammonia). 
 
 Cyanic acid produces a precipitate only in the most highly concentrated 
 solutions. 
 
 Hydrofluosilicic acid fails to produce a precipitate in weak solutions of 
 salts of ammonia. 
 
 4. Salts of Baryta. 
 
 Dilute sulphuric acid produces a precipitate insoluble in acids. 
 
 Chromate of potassa produces a yellow precipitate, soluble in nitric 
 acid. 
 
 Hydrofluosilicic acid produces a crystalline precipitate, insoluble in 
 hydrochloric acid and in nitric acid. 
 
 Potassa produces a bulky precipitate, soluble in a copious amount of 
 water. 
 
 Ammonia fails to produce a precipitate. 
 
 Carbonate of potassa (neutral) produces a white precipitate, soluble in 
 acids. 
 
 Carbonate of ammonia, a white precipitate, soluble in acids. 
 
 Phosphate of soda, a white precipitate, soluble in acids. 
 
 Oxalate of ammonia, a white precipitate. 
 
 Hydrosulphate of sulphide of ammonium fails to produce a pre- 
 cipitate. 
 
 Ferrocyanide of potassium produces a crystalline precipitate in concen- 
 trated solutions of salts of baryta. 
 
 5. Salts of Strontia. 
 
 Dilute sulphuric acid produces in solutions of salts of strontia a 
 precipitate, which is almost insoluble in acids. 
 
 Chromate of potassa (neutral) produces after some time, a yellow 
 crystalline precipitate. 
 
 Bichromate of potassa fails to produce a precipitate. 
 
89 
 
 EEACTIONS OP SALTS OP METALLIC OXIDES. 
 
 Hydrofluosilicic acid also fails to produce a precipitate, 
 
 Potassa, ammonia, carbonate of potassa, carbonate of ammonia, and 
 phosphate of soda, present the same deportment with salts of strontia 
 as with salts of baryta. 
 
 Oxalate of ammonia produces a white precipitate. 
 
 Hydrosulphate of sulphide of ammonium fails to produce a pre- 
 cipitate. 
 
 Ferrocyanide of 1 oduce no precipitate. 
 
 Ferricyanide of potassium J 
 
 6. Salts of Lime. 
 
 Dilute sulphuric acid produces only in concentrated solutions of salts 
 of lime a precipitate of gypsum (sulphate of lime). 
 
 Sulphate of potassa fails to produce a precipitate, or produces a pre- 
 cipitate only after long standing. 
 
 Chromate of potassa produces no precipitate. 
 
 Hydrofluosilicic acid produces no precipitate. 
 
 Oxalate of ammonia produces a white precipitate, nearly insoluble in 
 acetic acid. 
 
 Potassa, ammonia, carbonate of potassa, carbonate of ammonia, and 
 phosphate of soda, present the same deportment with salts of lime 
 as with salts of baryta. 
 
 Hydrosulphate of sulphide of ammonium produces no precipitate. 
 
 Ferrocyanide of potassium produces in concentrated solutions a white 
 precipitate, soluble in hydrochloric acid. 
 
 Ferricyanide of potassium produces no precipitate, 
 
 7, Salts of Magnesia. 
 
 Sulphuric acid produces no precipitate in solutions of salts of magnesia. 
 
 Hydrofluosilicic acid produces no precipitate. 
 
 Potassa, ammonia, carbonate of potassa, and carbonate of ammonia 
 produce bulky white precipitates, which are soluble in sal-ammoniac 
 (chloride of ammonium) ; however, the precipitate produced by 
 carbonate of ammonia dissolves in the chloride of ammonium only 
 after boiling the fluid. 
 
 Phosphate of soda produces, more especially if free ammonia is present, 
 a precipitate, which is altogether insoluble in chloride of ammonium 
 
90 
 
 THE ART OE PHOTOGRAPHY, 
 
 Oxalic acid produces in presence of free ammonia, a precipitate, which 
 IS soluble in chloride of ammonium, and other salts of ammonia. 
 Hydrosulphate of sulphide of ammonium produces no precipitate. 
 Ferrocyanide of potassium produces a copious white precipitate. 
 Ferricyanide of potassium produces no precipitate. 
 
 8. Salts of Protoxide of Manganese. 
 
 Potassa produces a white precipitate, which acquires a brown tint in 
 the air, and is soluble in chloride of ammonium, 
 
 Ammonia also produces a white precipitate, which acquires a brown 
 tint in the air, and is soluble in chloride of ammonium. 
 
 Carbonate of potassa and carbonate of ammonia produce white 
 precipitates, which remain unaltered in the cold, and are slightly 
 soluble in chloride of ammonium. 
 
 Phosphate of soda produces a white precipitate, which remains 
 unaltered. 
 
 Oxalic acid produces in concentrated solutions after some time, a 
 white crystalline deposit, which is soluble in sulphuric acid and 
 hydrochloric acid, 
 
 Ferrocyanide of potassium produces a reddish-white precipitate, which 
 is soluble in free acid. 
 
 Ferricyanide of potassium produces a brown precipitate, insoluble in 
 acids. 
 
 Hydrosulphate of sulphide of ammonium produces a flesh-colored 
 precipitate, soluble in an excess of the reagent. 
 
 Sulphuretted hydrogen (Hydrosulphuric acid) produces no precipitate. 
 
 9. Salts of Sesquioxide of Manganese. 
 
 Potassa, ammonia, carbonate of potassa, and carbonate of ammonia, 
 produce dark-brown bulky precipitates, which are insoluble in 
 chloride of ammonium. 
 
 Phosphate of soda produces in an accurately neutralised hydrochloric 
 acid solution of a salt of sesquioxide of manganese a very bulky 
 brown precipitate. 
 
 Oxalic acid produces no precipitate, but after a time a discoloration of 
 the fluid. 
 
REACTIONS OE SALTS OE METALLIC OXIDES. 
 
 91 
 
 Ferrocyanide of potassium produces a grayish-green precipitate. 
 
 Ferricyanide of potassium, a brown precipitate. 
 
 Hydrosulphate of sulphide of ammonium, a flesh-colored precipitate. 
 
 Sulphuretted hydrogen reduces the sesquioxide to protoxide, with 
 separation of sulphur. 
 
 10. Salts of Oxide of Zinc. 
 
 Potassa produces a white gelatinous precipitate, which redissolves in 
 an excess of the precipitant. 
 
 Ammonia, the same. 
 
 Carbonate of potassa produces a white precipitate, soluble in potassa 
 and ammonia. 
 
 Carbonate of ammonia produces a white precipitate, soluble in an 
 excess of the precipitant. 
 
 Phosphate of soda, a white precipitate, soluble in acids, potassa, and 
 ammonia. 
 
 Oxalic acid, a white precipitate, soluble in potassa, ammonia, and 
 acids. 
 
 Ferrocyanide of potassium, a white gelatinous precipitate, insoluble in 
 hydrochloric acid. 
 
 Ferricyanide of potassium, a yellowish-red precipitate, soluble in 
 hydrochloric acid. 
 
 Hydrosulphate of sulphide of ammonium, a white precipitate, 
 insoluble in an excess of the precipitant, and in alkalies. 
 
 Sulphuretted hydrogen produces in neutral solutions of salts of oxide 
 of zinc a white precipitate ; but the precipitation is not complete, 
 
 11. Salts of Protoxide of Cobalt. 
 
 Potassa produces a blue precipitate, which is insoluble in an excess of 
 the precipitant, and acquires a green color in the air. 
 
 Ammonia produces the same blue precipitate j this, however, redis- 
 solves in an excess of the precipitant, the solution presenting a 
 brownish-red tint. 
 
 Carbonate of potassa produces a red precipitate, which, upon boiling, 
 acquires a blue color. 
 
92 
 
 THE AUT OE PHOTOGRAPHY. 
 
 Carbonate of ammonia produces a red precipitate, soluble in an excess 
 of the precipitant, and in chloride of ammonium. 
 
 Phosphate of soda produces a blue precipitate. 
 
 Oxalic acid, after some time, a reddish-white precipitate. 
 
 Ferrocyanide of potassium, a green precipitate, which afterwards turns 
 gray ; this precipitate is insoluble in hydrochloric acid. 
 
 Ferricyanide of potassium, a dark-brownish-red precipitate, insoluble 
 in hydrochloric acid. 
 
 Hydrosulphate of sulphide of ammonium produces a black precipitate, 
 insoluble in an excess of the precipitant, and in alkalies. 
 Sulphuretted hydrogen fails to precipitate cobalt from acid solutions ; 
 it precipitates it imperfectly from neutral, but completely from 
 alkaline solutions. 
 
 12. Salts of Protoxide of Nickel. 
 
 Potassa produces an apple-green precipitate, insoluble in an excess of 
 the precipitant, and unalterable in the air. 
 
 Ammonia produces a slight green precipitate, which redissolves 
 immediately upon further addition of the reagent, imparting a fine 
 blue color to the fluid. Potassa precipitates from this fluid, 
 hydrated protoxide of nickel (NiO-|-HO). 
 
 Carbonate of potassa produces an apple-green precipitate. 
 
 Carbonate of ammonia produces an apple-green precipitate, which 
 redissolves in an excess of the precipitant, imparting a bluish-green 
 color to the solution. 
 
 Phosphate of soda produces a greenish-white precipitate. 
 
 Oxalic acid, after some time, a greenish precipitate. 
 
 Ferrocyanide of potassium, a white precipitate, insoluble in hydro- 
 chloric acid. 
 
 F erricyanide of potassium, a yellowish-green precipitate, insoluble in 
 hydrochloric acid. 
 
 Hydrosulphate of sulphide of ammonium, a black precipitate, not 
 altogether insoluble in an excess of the precipitant, and in 
 alkalies. 
 
 Sulphuretted hydrogen produces no precipitate in acid solutions ; from 
 neutral solutions of salts of protoxide of nickel, with weak acids, 
 it precipitates the nickel only imperfectly. 
 
EEACTIONS OF SALTS OP METALLIC OXIDES. 
 
 93 
 
 13 . Salts of Protoxide of Iron. 
 
 Potassa, ammonia, carbonate of ammonia, and carbonate of potassa, 
 produce whitish precipitates, which speedily acquire a green tint, 
 and, upon exposure to the air, a reddish-brown color. Chloride of 
 ammonium and tartaric acid prevent the precipitation by ammonia 
 absolutely, by potassa partially. 
 
 Phosphate of soda produces a white precipitate, which upon exposure 
 to the air acquires, after a time, a bluish-green color. 
 
 Oxalic acid produces, after some time, a yellow precipitate; oxalates of 
 the alkalies produce the same precipitate immediately. 
 
 Ferrocyanide of potassium produces a white precipitate, which very 
 speedily turns blue upon exposure to the air ; this precipitate is 
 insoluble in hydrochloric acid. 
 
 Ferricyanide of potassium produces a dark-blue precipitate, insoluble 
 in acids. 
 
 Terchloride of gold produces a brown precipitate of metallic gold. 
 
 Nitrate of silver, a grayish-white precipitate of metallic silver. 
 
 Hydrosulphate of sulphide of ammonium, a black precipitate, insoluble 
 in an excess of the precipitant, but very readily soluble in hydro- 
 chloric acid. 
 
 Sulphuretted hydrogen produces a slight precipitate only in solutions 
 of salts of protoxide of iron with w'eak acids. 
 
 14 . Salts of Sesquioxide of Iron. 
 
 Potassa, ammonia, carbonate of potassa, and carbonate of ammonia, 
 produce reddish-brown bulky precipitates, which are partially soluble 
 in an excess of the carbonate of potassa or carbonate of ammonia. 
 
 Phosphate of soda produces a white precipitate, which dissolves, in 
 presence of ammonia, in an excess of the precipitant, imparting a 
 reddish-brown color to the solution. 
 
 Oxalic acid produces a yellow coloration, but no precipitate. 
 
 Ferrocyanide of potassium, a dark-blue precipitate, insoluble in hydro- 
 chloric acid. 
 
 Ferricyanide of potassium produces no precipitate. 
 
 Hydrosulphate of sulphide of ammonium produces a black precipitate ; 
 
94 
 
 THE ART OP PHOTOGRAPHY. 
 
 but if the solution contains only a very trifling quantity of iron, this 
 reagent simply imparts a greenish color to the fluid. 
 
 Sulphuretted hydrogen reduces the sesquioxide to protoxide, with 
 separation of sulphur. 
 
 15, Salts of Oxide of Lead. 
 
 Potassa produces a white precipitate, which re-dissolves, upon the 
 application of heat, in a large excess of the precipitant. 
 
 Ammonia produces a white precipitate, insoluble in an excess of the 
 precipitant. 
 
 Carbonate of potassa, a white precipitate, insoluble in an excess of 
 the precipitant, but soluble in potassa. 
 
 Carbonate of ammonia, the same. 
 
 Phosphate of soda, a white precipitate, soluble in potassa. 
 
 Oxalic acid, in neutral solutions a white precipitate. 
 
 Ferrocyanide of potassium, a white precipitate. 
 
 Ferricyanide of potassium produces no precipitate. 
 
 Hydrosulphate of sulphide of ammonium produces a black precipi- 
 tate, insoluble in an excess of the precipitant. 
 
 Sulphuretted hydrogen, in neutral and acid solutions, a black precipitate. 
 Dilute sulphuric acid, a white precipitate, soluble in potassa. 
 Hydrochloric acid, in concentrated solutions, a white precipitate, 
 soluble in a large quantity of water. 
 
 Chromate of potassa, a yellow precipitate, insoluble in dilute nitric 
 acid, soluble in potassa. 
 
 16. Salts of Teroxide of Bismuth. 
 
 Potassa produces a white precipitate, insoluble in an excess of the 
 precipitant. 
 
 Ammonia, the same. 
 
 Carbonate of potassa and carbonate of ammonia, the same. 
 
 Phosphate of soda, a white precipitate. 
 
 Oxalic acid, after some time, a crystalline precipitate. 
 
 Ferrocyanide of potassium, a white precipitate, insoluble in hydro- 
 chloric acid. 
 
 Ferricyanide of potassium, a pale-yellow precipitate, insoluble in 
 hydrochloric acid. 
 
REACTIONS OE SALTS OF METALLIC OXIDES. 
 
 95 
 
 Hydrosulphate of sulphide of ammonium, a black precipitate, insoluble 
 in an excess of the precipitant. 
 
 Sulphuretted hydrogen, even in acid solutions, a black precipitate. 
 
 Chromate of potassa, a yellow precipitate, soluble in dilute nitric acid. 
 
 17 . Salts of Suboxide of Copper. 
 
 Potassa saturates first the free acid of the solution (subchloride of 
 copper dissolves only in an excess of hydrochloric acid), and then 
 produces a yellowish-brown precipitate, insoluble in an excess of 
 the precipitant. 
 
 Ammonia in excess produces no precipitate, but after some time it 
 imparts a blue color to the fluid. 
 
 Carbonate of potassa produces a yellow precipitate. 
 
 Carbonate of ammonia acts in the same way as ammonia. 
 
 Phosphate of soda produces a white precipitate. 
 
 Oxalic acid, a white precipitate. 
 
 Ferrocyanide of potassium, a white precipitate. 
 
 Ferricyanide of potassium, a reddish-brown precipitate. 
 
 Hydrosulphate of sulphide of ammonium, a black precipitate, insoluble 
 in an excess of the precipitant. 
 
 Sulphuretted hydrogen, a black precipitate. 
 
 ],8. Salts of Oxide of Copper. 
 
 Potassa produces a blue precipitate, which acquires a black color on 
 being boiled with potassa. 
 
 Ammonia, a greenish precipitate, which re-dissolves in an excess of 
 the precipitant, imparting a blue color to the solution. 
 
 Carbonate of potassa, a bright-greenish precipitate. 
 
 Carbonate of ammonia acts in the same way as ammonia. 
 
 Phosphate of soda produces a bluish-white precipitate, soluble in 
 ammonia. 
 
 Oxalic acid, a bluish-white precipitate. 
 
 Ferrocyanide of potassium, a reddish-brown precipitate, insoluble in 
 hydrochloric acid. 
 
 Ferricyanide of potassium, a yellowish-green precipitate, insoluble in 
 hydrochloric acid. 
 
96 
 
 THE AET OP PHOTOGEAPHY. 
 
 Hydrosulphate of sulphide of auimoniuruj a black precipitate, insoluble 
 in an excess of the precipitant, and in ammonia. 
 
 Sulphuretted hydrogen, a black precipitate. 
 
 Chromate of potassa, a reddish-brown precipitate, readily soluble in 
 nitric acid ; this precipitate dissolves also in ammonia, imparting an 
 emerald-green color to the solution. 
 
 19. Salts of Oxide of Silver. 
 
 Potassa produces a light-brown precipitate, insoluble in an excess of 
 the precipitant, but soluble in ammonia. 
 
 Ammonia produces, in neutral solutions, a brown precipitate, readily 
 soluble in an excess of the precipitant ; in presence of free acid, the 
 re-agent produces no precipitate by neutralisation. 
 
 Carbonate of potassa produces a white precipitate, soluble in ammonia. 
 
 Carbonate of ammonia, a white precipitate, soluble in an excess of the 
 precipitant. 
 
 Phosphate of soda, a yellow precipitate, soluble in ammonia. 
 
 Oxalic acid, a white precipitate, soluble in ammonia. 
 
 Ferrocyanide of potassium, a white precipitate. 
 
 Ferricyanide of potassium, a reddish-brown precipitate. 
 
 Hydrosulphate of sulphide of ammonium, a black precipitate, insoluble 
 in an excess of the precipitant, and in ammonia. 
 
 Sulphuretted hydrogen, a black precipitate. 
 
 Hydrochloric acid, a white precipitate, soluble in ammonia. 
 
 Chromate of potassa, a dark reddish-brown precipitate, soluble in 
 dilute nitric acid, in ammonia, and in a large quantity of water. 
 
 Sulphate of protoxide of iron, a grayish- white precipitate of metallic 
 silver. 
 
 Protochloride of tin, acidulated with hydrochloric acid, and added 
 rather largely to the solution of a salt of silver, produces a precipitate 
 of metallic silver. 
 
 20. Salts of Suboxide of Mercury. 
 
 Potassa produces a black precipitate, insoluble in an excess of the 
 precipitant. 
 
 Ammonia, the same. 
 
EEACTIONS OF SALTS OF METALLIC OXIDES. 
 
 97 
 
 Carbonate of potassa produces a dirty-yellow precipitate, which is 
 slightly soluble in an excess of the precipitant, and upon boiling 
 acquires a black tint. 
 
 Carbonate of ammonia, a black precipitate. 
 
 Phosphate of soda, a white precipitate. 
 
 Oxalic acid, a white precipitate. 
 
 Ferrocyanide of potassium, a white gelatinous precipitate. 
 
 Ferricyanide of potassium, a reddish-brown precipitate. 
 
 Hydrosulphate of sulphide of ammonium, a black precipitate, insoluble 
 in an excess of the precipitant, and in ammonia ; potassa dissolves 
 the precipitate, leaving a little metallic mercury behind. 
 
 Sulphuretted hydrogen produces a black precipitate. 
 
 Hydrochloric acid, a white precipitate, insoluble in very dilute 
 simple acids. 
 
 Chromate of potassa, a red precipitate. 
 
 21. Salts of Oxide of Mercury. 
 
 Potassa produces a yellow precipitate, insoluble in an excess of the 
 1 precipitant ; in presence of sal-ammoniac (chloride of ammonium), 
 j the precipitate formed is white ; in highly acid solutions, potassa 
 produces no precipitate, or at all events only a slight one. 
 
 Ammonia produces a white precipitate, insoluble in an excess of the 
 precipitant. 
 
 Carbonate of potassa, a reddish-brown precipitate, insoluble in an 
 excess of the precipitant ; in presence of sal-ammoniac, the 
 precipitate is white. 
 
 Carbonate of ammonia produces a white precipitate. 
 
 Phosphate of soda, a white precipitate ; in solutions of chloride of 
 mercury, however, only a slight turbidity, 
 i Oxalic acid, a white precipitate ; in solutions of chloride of mercury, 
 no precipitate. 
 
 Ferrocyanide of potassium, a white precipitate. 
 
 Ferricyanide of potassium, a yellow precipitate ; in solutions of chloride 
 of mercury, no precipitate. 
 
 Hydrosulphate of sulphide of ammonium, a black precipitate, insoluble 
 in an excess of the precipitant, and in ammonia, but completely 
 soluble in potassa. 
 
 p 
 
98 
 
 THE AUT OE PHOTOGRAPHY. 
 
 Sulphuretted hydrogen, the same as hydrosulphate of sulphide of 
 ammonium. 
 
 Chromate of potassa, a yellowish-red precipitate. 
 
 22. Bichloride of Platinum. 
 
 Potassa produces a yellow precipitate, which re-dissolves in an excess of 
 the precipitant upon heating ; the precipitate is not perceptibly 
 soluble in free acids. 
 
 Ammonia produces a yellow precipitate, insoluble in free acids, but 
 soluble in a copious amount of water. 
 
 Carbonate of soda produces a brownish-yellow precipitate only upon 
 long-continued ebullition. 
 
 Carbonate of ammonia and carbonate of potassa produce a yellow 
 precipitate, insoluble in an excess of the precipitant. 
 
 Phosphate of soda produces no precipitate. 
 
 Oxalic acid produces no precipitate. 
 
 Ferrocyanide of potassium precipitates potassio-bichloride of platinum 
 (bichloride of platinum and chloride of potassium). 
 
 Ferricyanide of potassium, the same. 
 
 Nitrate of suboxide of mercury produces a copious yellowish-red 
 precipitate. 
 
 Sulphate of protoxide of iron produces no precipitate. 
 
 Protochloride of tin produces no precipitate, but imparts a dark 
 brownish-red color to the fluid. 
 
 Hydrosulphate of sulphide of ammonium produces a brownish-black 
 precipitate, soluble in a large excess of the precipitant. 
 
 Sulphuretted hydrogen produces after some time, a brownish-black 
 precipitate. 
 
 23. Terchloride of Gold. 
 
 Potassa produces no precipitate. 
 
 Ammonia, a yellow precipitate (fulminating gold). 
 
 Carbonate of potassa, no precipitate in the cold, but upon ebullition a 
 reddish-yellow precipitate. 
 
 Carbonate of ammonia acts the same way as ammonia. 
 
 Phosphate of soda produces no precipitate. 
 
REACTIONS OF SALTS OF METALLIC OXIDES. 
 
 99 
 
 Oxalic acid separates metallic gold in a state of extremely minute 
 division ; the minute metallic particles impart to the fluid in which 
 they remain suspended, a greenish-black color. 
 
 Ferrocyanide of potassium imparts an emerald-green color to the 
 solution. 
 
 Ferricyanide of potassium produces no precipitate. 
 
 Nitrate of suhoxide of mercury, a black precipitate. 
 
 Sulphate of protoxide of iron, a dark-brown precipitate of metallic 
 gold. 
 
 Protochloride of tin, acidulated with hydrochloric acid, produces a 
 deep-purple-colored precipitate (powder of Cassius), which is 
 insoluble in hydrochloric acid. 
 
 Hydrosulphate of sulphide of ammonium, a dark-brown precipitate, 
 which re-dissolves completely in an excess of the precipitant. 
 
 Sulphuretted hydrogen, a black precipitate. 
 
 24. Salts of Protoxide of Tin. 
 
 Potassa produces a white precipitate, soluble in an excess of the 
 precipitant. 
 
 Ammonia, a white precipitate, insoluble in an excess of the precipitant. 
 
 Carbonate of potassa and carbonate of ammonia, the same as ammonia. 
 
 Phosphate of soda, a white precipitate. 
 
 Oxalic acid, a white precipitate. 
 
 Ferrocyanide of potassium, a white gelatinous precipitate. 
 
 Ferricyanide of potassium, a white precipitate, soluble in free 
 hydrochloric acid. 
 
 Hydrosulphate of sulphide of ammonium, a brown precipitate, soluble 
 in a great excess of the precipitant. 
 
 Sulphuretted hydrogen, a brown precipitate. 
 
 25. Bichloride of Tin. 
 
 Potassa produces a white, bulky precipitate, which in the case of the 
 volatile bichloiide, re -dissolves very readily in an excess of the 
 precipitant, hut with difficulty only in the case of the aqueous 
 solution of the modification of the bichloride, insoluble in 
 hydrochloric acid. 
 
100 
 
 THE ART OF PHOTOGRAPHY. 
 
 Ammonia produces a white precipitate, which in the case of the 
 volatile bichloride, re-dissolves, though not completely, in an excess 
 of the precipitant, but re-dissolves only sparingly in the case of 
 the aqueous solution of the modification of the bichloride, insoluble 
 in hydrochloric acid. 
 
 Carbonate of potassa produces a white precipitate, which in the case 
 of the volatile chloride, re- dissolves in an excess of the precipitant ; 
 but is insoluble in it, in the case of the aqueous solution of the 
 modification of the bichloride, insoluble in hydrochloric acid. 
 Carbonate of ammonia produces in both solutions precipitates, which 
 are not completely re-dissolved by an excess of the precipitant. 
 Phosphate of soda produces a white precipitate. 
 
 Oxalic acid produces no precipitate. 
 
 Ferrocyanide of potassium, after some time, a thick, yellowish jelly, 
 insoluble in hydrochloric acid. 
 
 Ferricyanide of potassium produces no precipitate’ in a solution of 
 the volatile bichloride ; a yellow precipitate in an aqueous solution 
 of the modification of the bichloride, insoluble in hydrochloric 
 acid. 
 
 Hydrosulphate of sulphide of ammonium produces a yellow precipitate, 
 soluble in an excess of the precipitant, in ammonia, potassa, and 
 carbonate of potassa. 
 
 Sulphuretted hydrogen, a yellow precipitate ; in dilute solutions only 
 after long standing. 
 
 26 . Salts of Oxide (Teroxide) of Antimony. 
 
 Potassa produces a w’hite bulky precipitate, which re-dissolves com- 
 pletely in an excess of the precipitant. 
 
 Ammonia, a copious bulky precipitate, insoluble in an excess of the 
 precipitant. 
 
 Carbonate of potassa, a white bulky precipitate, which redissolves 
 completely in an excess of the precipitant, upon heating. 
 
 Carbonate of soda and carbonate of ammonia, the same as ammonia. 
 Phosphate of soda, a copious precipitate ; however, the precipitation 
 is not complete. 
 
 Oxalic acid, a bulky white precipitate , after some standing, the preci- 
 pitation is complete. 
 
UEACTIONS OF METALLIC ACIDS. 
 
 101 
 
 Ferrocyanide of potassium, a white precipitate, insoluble in hydro- 
 chloric acid. 
 
 Ferricyanide of potassium, no precipitate. 
 
 Hydrosulphate of sulphide of ammonium, a red precipitate, soluble in 
 an excess of the precipitant. 
 
 Sulphuretted hydrogen, a red precipitate. 
 
 27. Salts of Sesquioxide of Chromium. 
 
 Potassa produces a bright-green precipitate, which readily redissolves 
 in an excess of the precipitant, but separates again completely upon 
 ebullition. 
 
 Ammonia produces a grayish-blue precipitate, which, however, separates 
 completely upon ebullition. 
 
 Carbonate of potassa produces a bright-green precipitate, which com- 
 pletely redissolves in a veiy considerable excess of the precipitant, 
 and is not thrown down again from this solution upon boiling. 
 
 Carbonate of ammonia produces a bright-green precipitate, soluble in 
 an excess of the precipitant. 
 
 Phosphate of soda, a bright-green precipitate. 
 
 Oxalic acid, no precipitate. 
 
 Ferrocyanide and ferricyanide of potassium, no precipitate. 
 
 Chromate of potassa, in neutral solutions, a dark brownish-yellow preci- 
 pitate, in acid solutions simply a coloration of that hue, the actual 
 separation of the precipitate ensuing only upon addition of ammonia. 
 
 Hydrosulphate of sulphide of ammonium, a greenish precipitate of 
 hydrate of sesquioxide of chromium. 
 
 Sulphuretted hydrogen, no precipitate. 
 
 II. METALLIC ACIDS. 
 
 1. Antimonic Acid. 
 
 Acids, more especially nitric acid, throw down the antimonic acid 
 completely from alkaline solutions ; hydrochloric acid in excess 
 dissolves the precipitate readily in the cold ; nitric acid and 
 sulphuric acid dissolve it only upon heating. 
 
10 £ 
 
 THE ART OF PHOTOGRAPHY. 
 
 Sulphuretted hydrogen produces no precipitate in alkaline solutions ; 
 but in acid solutions, an orange-yellow precipitate, which is soluble 
 in hydrosulpbate of sulphide of ammonium. 
 
 2. Chromic Acid. 
 
 Mineral acids impart a reddish-yellow color to the solution. 
 
 Hydrochloric acid decomposes the chromic acid upon continued ebul- 
 lition ; chlorine escapes, and the dissolving sesquioxide of chromium 
 imparts a green color to the fluid. 
 
 Sulphuretted hydrogen imparts a green color to the solution mixed 
 with hydrochloric acid ; this coloration is caused by the reduction 
 of the chromic acid. 
 
 Salts of baryta produce a pale-yellow precipitate ; 
 
 Salts of oxide of lead and of teroxide of bismuth, a lemon-yellow 
 precipitate ; 
 
 Salts of silver, a purple-red precipitate ; 
 
 Salts of suboxide of mercury, a brick-colored precipitate ; — which 
 precipitates are all of them soluble in nitric acid. 
 
 3. Manganic Acid. 
 
 Acids, and even water, produce a red coloration, and a brown 
 precipitate. 
 
 Hydrochloric acid, besides this, reduces the manganic acid, with 
 evolution of chlorine, and the dissolving sesquichloride of manga- 
 nese imparts a dark-brown color to the fluid, which disappears again 
 upon heating, owing to the formation of protochloride of manganese. 
 
 4. Permanganic Acid. 
 
 Potassa produces a green coloration, owing to the formation of 
 manganic acid. 
 
 Nitric acid and sulphuric acid effect, upon heating, a partial decompo- 
 sition into binoxide of manganese, which falls down as a brown 
 powder, and oxygen, which is liberated. 
 
 Hydrochloric acid acts upon permanganic acid the same as upon man - 
 ganic acid. 
 
EEACTIONS OF METALLIC ACIDS. 
 
 103 
 
 Sulphuretted hydrogen produces a precipitate of sulphide of manganese, 
 mixed with sulphur thrown down along with it, and which makes 
 the precipitate look almost white. 
 
 Hydrosulphate of sulphide of ammonium in excess produces a flesh- 
 colored precipitate of sulphide of manganese. 
 
 5. Arsenic Acid. 
 
 Salts of baryta and of lime produce in solutions of arseniates (but 
 not in solutions of arsenic acid) a white precipitate, which is very 
 readily soluble in hydrochloric acid and nitric acid, and also in 
 sal-ammoniac (chloride of ammonium). 
 
 Nitrate of lead produces a white precipitate. 
 
 Nitrate of silver, a brownish-red precipitate. 
 
 Nitrate of oxide of copper, a pale-green precipitate, soluble in nitric 
 acid, and in free ammonia. 
 
 Sulphuretted hydrogen, in acid solutions, a yellow precipitate, which 
 is soluble in hydrosulphate of sulphide of ammonium, and also in 
 potassa and in ammonia. 
 
 Hydrosulphate of sulphide of ammonium produces no precipitate. 
 
 6. Arsenious Acid. 
 
 Chloride of barium and chloride of calcium produce no precipitate in 
 aqueous solutions of arsenious acid ; in solutions of arsenites, they 
 produce a white precipitate, soluble in sal-ammoniac (chloride of 
 ammonium). 
 
 Salts of lead produce a precipitate in moderately strong solutions of 
 arsenites ; in over-dilute solutions they fail to produce a precipitate. 
 
 Nitrate of silver produces in solutions of arsenites a yolk-colored 
 precipitate, soluble in nitric acid and in ammonia ; in solutions of 
 arsenious acid, nitrate of silver can hardly be said to produce a 
 precipitate. 
 
 Sulphate of oxide of copper produces in solutions of arsenites a green- 
 finch-colored precipitate, soluble in potassa and in ammonia. 
 
 Sulphuretted hydrogen, in the acid solution, a yellow precipitate, 
 soluble in hydrosulphate of sulphide of ammonium, caustic and 
 carbonated alkalies, and in nitric acid. 
 
 Hydrosulphate of sulphide of ammonium, no precipitate. 
 
APPENDIX. 
 
 Brief explanations of some of the chemical terms which occasionally 
 
 occur in the present work; intended for the benefit of persons 
 
 unacquainted with chemistry. 
 
 Chemists divide bodies into simple and compound bodies. The 
 simple bodies are also called elements, or elementary substances. 
 Ihese terms, however, by no means imply that the bodies so called 
 are really simple or elementary, but simply that they appear to us so 
 at the present time, having hitherto resisted all attempts to decompose 
 them. The elementary substances at present known to us amount to 
 sixty-two in number. They are usually divided into two great classes, 
 viz., metals and non-metallic bodies, or metalloids. This division is 
 however entirely arbitrary, as the two classes completely merge into 
 each other. The class of metalloids comprises fifteen elementary 
 bodies; however, in the present work (Table I.) we have given only 
 thirteen of them, viz., arsenic, boron, bromine, carbon, chlorine, fluorine, 
 hydrogen, iodine, nitrogen, oxygen, phosphorus, selenium, and sulphur. 
 The class of metals comprises forty-seven simple bodies, of which we 
 have only given, however, twenty-four in Table I., viz., aluminium, 
 antimony, barium, bismuth, calcium, chromium, cobalt, copper, gold, 
 iron, lead, magnesium, manganese, mercury, molybdenum, nickel, 
 platinum, potassium, silver, sodium, strontium, tin, uranium, and zinc. 
 
 Every elementary substance is designated in chemical notation by 
 the initial of its latin name in capital ; or, where the names of several 
 substances begin alike, by the first letter conjoined with a second small 
 one, the most characteristic in the word. This simple or compound 
 letter-mark is called the symbol of the substance ; it designates not 
 only the substance in the abstract, but represents one equivalent of it. 
 Thus, e.g., Hg (from the Greek hydrargyrum) represents one equivalent 
 
APPENDIX. 
 
 105 
 
 of mercury ; Fe (from the Latin ferrum), one equivalent of iron ; 0, 
 one equivalent of oxygen ; H, one of hydrogen ; Ca, one of calcium, &c. 
 
 The compound bodies result from the union of two or several 
 elementary substances. The combinations of metals with each other 
 are called alloys; or, where mercury is one of the constituent 
 elements, amalgams. The metalloids combine with each other, and 
 with the metals, forming bases, acids, and salts. Thus, for instance, 
 the metalloid chlorine combines with hydrogen, forming the w'ell- 
 known muriatic acid, which is more commonly called by chemists 
 hydrochloric acid ; chlorine combines also with the metal sodium, 
 forming common salt (chloride of sodium) ; oxygen combines with 
 the metal potassium, forming the well-known alkaline base, potassa, &c. 
 The combination of bases with acids gives also rise to the formation 
 of salts ; thus, e.g., sulphuric acid, a compound of sulphur and oxygen, 
 forms with the base potassa a salt, the sulphate of potassa. Two 
 salts frequently combine with each other, forming what chemists call 
 double salts ; thus, for instance, the sulphate of alumina and the 
 sulphate of potassa form a double salt, known as the double sulphate 
 of alumina and potassa. 
 
 The chemical union of bodies is governed and regulated by certain 
 fundamental laws, called the laws of combination, and which may be 
 briefly stated as follows : 
 
 1 . All chemical compounds are definite in their nature, the ratio of 
 the elements being constant ; in other terms, the same chemical 
 compound invariably contains the same elements combined in un- 
 varying proportions. 
 
 2. Where a body is capable of combining with another in several 
 proportions, these proportions bear a simple relation to each other. 
 Thus one equivalent of A w'ill combine with 1, 2, 3, 4, 5, equivalents 
 of B ; or two of A, with 1, 2, 3, 4, 5, 7, of B ; or 3 of A with 5, 7 of 
 B ; and so on. This law, which was first advanced by Dalton in 1807, 
 is called the law of multiple proportions. The most simple propor- 
 tions occur most frequently ; we generally find between the com- 
 ponent elements of compound bodies, the proportions of 1 to 1, of 1 to 
 2, of 1 to 3, of 1 to 4, of 1 to 5 ; or of 2 to 3, of 2 to 5, of 2 to 7, 
 
 3. The quantities in which two bodies unite with a third body, 
 express also the relative proportions in which they unite with each 
 other, presuming always, of course, that they do unite with each other. 
 For instance, hydrogen combines with oxygen in the proportion of 1 
 part by weight of the former to 8 parts by weight of the latter ; 
 chlorine combines with oxygen in the proportion of 35.5 parts by 
 
106 
 
 APPENDIX. 
 
 weight of the former to 8 parts by weight of Lhe latter. Chlorine 
 combines accordingly with hydrogen in the proportion of 35.5 of the | 
 former to 1 of the latter. As oxygen has a most extensive range I 
 of affinity, and very great powers of combination, uniting in fact with j; 
 all the elementary substances, with the single exception of fluorine, | 
 and as its compounds are susceptible of the most rigid and exact 
 analysis, this body has been chosen by chemists as the starting ; 
 substance in the construction of the table of chemical equivalents. 
 The number assigned to the equivalent of the starting substance is 
 entirely arbitrary. Continental chemists usually assign the number 
 100 to the equivalent of oxygen, 12.5 to that of hydrogen, 443.75 to 
 that of chlorine ; but it will be readily seen that the relative ratio 
 remains the same : 100 is to 12.5 as 8 is to 1, to 443.75, as 8 is to 35.5. 
 
 8 has been chosen here as the more convenient figure of the two, and 
 because it is the proportion in which oxygen combines with one part 
 by weight of hydrogen to form water, supplying us thus in the 
 equivalent of the hydrogen, with a unity of which the equivalents of all 
 other simple substances should be integer multiples, according to a 
 theory advanced by a most eminent English chemist (Prout) ; a glance 
 at the table of equivalents of elementary bodies will, however, suffice 
 to show that in the present state of our knowledge, at all events, this 
 hypothesis is not sufficiently supported to justify its admission. 
 
 4. The combining quantity or proportion of a compound is the sum 
 of the combining quantities of its components. Let us take, for 
 instance, chloride of sodium. The equivalent of chlorine is 35.5, that ; 
 of sodium 23 ; the combining proportion or equivalent of the chloride 
 of sodium is therefore 58.5. 
 
 Most of the compounds which the metalloids form with the metals, are 
 now generally designated in chemical nomenclature as ides ; but many 
 of them were formerly, and are still by some chemists designated as 
 wets. The termination ide (or uret) is substituted for the termination | 
 of the name of the metalloid, and the preposition q/" interposed between j 
 this and the unaltered name of the metal. Thus, for instance, the | 
 compound formed by the union of the metalloid chlorine with the I 
 metal sodium, is called chloride of sodium ; the compound formed by ; 
 oxygen with silver, is called oxide of silver, &c., &c. | 
 
 As has already been stated, bodies may combine with each other! 
 in several proportions bearing a definite simple relation to each other, i 
 
 Thus oxygen combines with manganese in six* different proportions,! 
 
 i 
 
 *■ There exists even a seventh oxide of manganese (varvicite), which contains 
 seven equivalents of oxygen to four of manganese. ! 
 
 i 
 
APPENDIX. 
 
 107 
 
 viz., 1 to 1, 3 to 2, 2 to 1 , 4 to 3, 3 to 1, and 7 to 2. The first 
 compound (1 of oxygen to 1 of manganese), is called the protoxide 
 of manganese ; the second (3 of 0 to 2 of Mn), the sesquioxide ; the 
 third (2 of 0 to 1 of Mn), the deutoxide or binoxide ; the fourth 
 being, in reality, a compound of the protoxide with the sesquioxide, 
 is properly called proto-sesquioxide ; the fifth compound of oxygen 
 with manganese (Mn O 3 ), having acid properties, i. e., combining with 
 bases to form salts, is termed manganic acid. The composition of this 
 acid would be indicated by the term teroxide of manganese ; the 
 term oxide, however, is not applied to bodies having acid properties ; 
 thus we do not say, for instance, teroxide of arsenic, or pentoxide of 
 arsenic, but arsenious* acid for the former, and arsenic acid for the 
 latter j and the sixth compound (Mng ) is called hypermanganic 
 or permanganic acid. Compounds containing less than one equivalent 
 of oxygen to one equivalent of metal, are called suboxides ; thus, 
 Cu^ 0 (two equivalents of copper to one of oxygen) is called suboxide 
 of copper. The same rules hold generally good also in the nomen- 
 clature of compounds of oxygen with the metalloids, and in those 
 of sulphur and other metalloids with the metals and with each 
 other. Most of the metalloids form acids with oxygen, as chlorine, 
 iodine, bromine, sulphur, phosphorus, nitrogen, carbon, selenium, 
 boron, silicon, arsenic, tellurium ; some form acids with hydrogen, as 
 chlorine, iodine, bromine, fluorine, sulphur ; these latter acids are 
 called respectively, hydrochloric, hydriodic, hydrobromic, hydrofluoric, 
 hydrosulphuric acids. With regard to the neutral or basic compounds, 
 which the metalloids form among themselves, the termination ide is 
 always given to the oxygen, wherever that body forms one of the con- 
 stituents ; chlorine follows next after oxygen in this respect ; thus we 
 say, chloride of iodine, of sulphur, of nitrogen ; bromine follows next 
 after chlorine (bromide of iodine) ; the next is fluorine (fluoride of 
 
 * Tlie terminations oms and ic, applied to acids, signify different degrees of 
 oxidation, the latter being the higher of the two : the salts formed by acids in (ms 
 are called iteS, as, e. g., sulphite of soda, a compound of sulphuroits acid and soda 
 (oxide of sodium) ; those formed by acids in ic, are called ates, as, e. g., sulphate 
 of soda, a compound of sulphuric acid and soda. When oxygen forms more than 
 two acids with a metal or metalloid, the terms hypo and hyper (from two Greek 
 prepositions, signifying respectively under and over) are prefixed to the name of 
 the acid ; thus we have, for instance, hyposulphurous acid, a compound con- 
 taining less oxygen than the sulphurous add j and hyperchlonc add, a compound 
 containing more oxygen than the chloric add. Instead of hyper, chemists use 
 mostly the simple per, saying, for instance, perchloric add, instead of hyperchlonc, 
 permanganic, instead of hypermanganic. 
 
108 
 
 APPENDIX. 
 
 silicon) ; after this comes sulphur (sulphide of arsenic, sulphide of 
 carbon). The compounds which phosphorus, carbon, arsenic, selenium, 
 form with hydrogen, are called respectively phosphuretted, carburetted, 
 arseniuretted (or arsenietted), seleniuretted hydrogen. 
 
 The Pnce-list of the Apparatus, &c., may he had of the Publisher 
 Me. John Weale, 59, High Holbom. 
 
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