Digitized by the Internet Archive in 2017 with funding from Getty Research Institute https://archive.org/details/instructioninpho00abne_1 / '?• 1 From a negative by Captain Abney, R.E. Printed by the Woodburytype Procesi INSTRUCTION IN . PHOTOGRAPHY. BY CAPTAIN ABNEY, R.E., F.E.S., Etc., Instructor in Chemistry and Photography at the School of Military Engineering , Chatham. THIRD EDITION. LONDON: PIPER & CARTER, GOUGH SQUARE, ELEET STREET, E.C. LONDON: PIPER AND CARTER, PRINTERS, GOUGH SQUARE, FLEET STREET. PREFACE TO THIRD EDITION, -4- At the commencement of this year, when my publishers informed me that ^Instruction in Photography” was “ out of print,” I had not intended to bring out another edition of it under the old designation, as Messrs. Long¬ mans had requested me to write one of their “Text- Books of Science” on the same subject. Circumstances, however, lately arose which showed me the advisability of reconsidering my determination, and I have therefore revised and enlarged my original work, leaving it on the same plan as before, and still find myself able to continue preparing “Photography” for Messrs. Longmans. This latter will enter much more fully into theory than it seemed advisable to do in the present Manual, which is intended rather for practical workers than for an educational series. It has been a matter of self-congratulation that the last large edition has become so quickly exhausted, and I am induced to hope that the present one will be equally successful. W. DE W. ABNEY, Captain R.E. Chatham , October , 1876. PREFACE TO SECOND EDITION. A small edition of this Manual was originally prepared for private circulation amongst the officers and men of the corps of Royal Engineers. Much of it, however, got distributed beyond this circle, with the effect of creating such a large demand upon me for copies, that had I supplied them the numbers printed would long ago have been exhausted. Under these circumstances I determined, with the sanction of the Inspector-General of Fortifications, to bring out an edition for the general public. As the contents have been chiefly compiled from notes, names of persons who may be conne cted with processes are often omitted, not from intention, but from ignorance. As it is a work of a practical character, and not a history of the art, I trust that such omissions will not affect its value. W. DE W. ABNEY, Captain R.E. CONTENTS PAGE Acetic Acid, Determination of the Strength of .190 Albumen Beer Process ... ... 71 Albumen for Substratum, To Prepare ... ... ... 181 Alcohol from Old Collodion, To Recover Ether and ... ... 181 Alcohol from Spirits of Wine, To Obtain. 179 Alcohol, Specific Gravity of Absolute ... 193 Alcohol, Testing for Methylated 179 Alcohol, Testing for the Amount of Water in. ... 179 Alcohol, To Make a Still for Distilling ... ... ... 180 Alkaline Development, Theory of .61 Apparatus, Hints on .165 Appendix . ...172 Autotype Process ... ... 131 Bath, Fixing .127 Baths, New from Old.174 Baths . ... 167 Baths, Purifying Printing ... 183 Bath Solution by Boiling down, To Purify ... ... ... 173 Bath, The Sensitizing ... 14, 114 Bottles, Convenient Dropping ... 185 Boxes, Draining ... ... 170 Boxes, Dry Plate .177 Bromide to a Collodion, Simple Method of Adding Extra ... 184 Buckle’s Process ... ... 87 Buildings, Photographing the Interior of . 94 PAGE Carrying Negatives on Tour, Method of ... .171 Chemical Compounds ... ... 194 Chromic Acid Compounds, Prints Obtained by Aid of.131 Cleaning the Glass Plate ...5, 27 Coating the Plates with Collo¬ dion . 30 Coffee Process. ... 65 Collodio-Albumen Process ... 67 Collodio-Albumen Process, Eng¬ land’s . ... ... 70 Collodio-Chloride Paper ... 125 Collodion . 5 Collodion, Coating the Plates with. ... 30 Collodion, Defects Caused by the 42 Collodion, Simple Method of Adding Extra Bromide to a... 184 Collodion, To Decolourize .. 181 Collodion, To Recover Ether and Alcohol from Old ... 181 Copying Plans, Engravings, &c. 96 Cups, Developing ... ... 168 Dark Slide, Defects Caused by th a 4-Q Dark Tent 167 Defects in Negatives: their Causes and Remedies ... 41 Defects in Prints .124 Developing Cups ... ... 168 Development . 16, 37 Development, Defects Caused by 47 Development, Paper Enlarge¬ ments by . ... 107 Development, Theory of Alkaline 61 VI CONTENTS. PAGE Dippers. 167 Dishes ... ... ... ... 170 Dishes, Evaporating ... ... 169 Distilling Alcohol, To Make a Still for . ... 180 Drying and Varnishing the Nega¬ tive ... ... ... ... 40 Dry-plate Boxes .170 Durable Sensitized Papers ... 117 Enamels, Photographic ... 159 England’s Collodio-Albumen Process ... ... ... 70 Engravings, Copying ... ... 96 Enlargement or Reduction. Table of .' 187 Enlargements by Development, Paper . ... 107 Enlarging, &c., To Pind the Equivalent Focus of a Lens for 187 Emulsion Processes ... ... 74 Ether and Alcohol from Old Collodions, To Recover ... 181 Evaporating Dishes .169 Field, Kit for Work in the ... 196 Filter Paper, to Test for Iron in a 185 Fixing . 24, 40 Fixing Bath . ...127 Fixing, Defects Caused by In- tensifying and ... 48 Fixing the Print ... 121 Fog on Wet-plate Negatives ... 50 Fog, Tracing the Cause of ... 50 Funnels ... . ... 169 Gelatino-Bromide Process ... 84 Glass, Ground ... ... 182 Glass, Non-actinic ... 168 Glass Plate, The ... 4 Glass Plate, Cleaning the ... 527 Glass Plates, Defects Caused by 41 Glass, Substitute for Ground ... 183 Glass Tubing, To Bend ... 184 Gold Tri-chloride, To Make ... 178 Greenlaw’s Process ... 90 Ground Glass ... ... 182 Ground Glass, Substitute for ... 183 Gum - gallic Process ... 63 Gum Process, A ... 157 PAGE G-um, To Mix Solutions Con¬ taining ... ... ... 183 Heliotype Process ... ... 143 Hints on Apparatus .165 Hot Water Process . 70 Instantaneous Pictures .. ... 92 Instruction in Photography ... 1 Intensifying ... ... 21, 38 Intensifying and Fixing, Defects Caused by .48 Intensify a Negative after Var¬ nishing, To. .. 184 Intensify a Negative by the Action of Light, To.184 Interior of Buildings, Photo¬ graphing the Interior of ... 94 Iron in a Filter Paper, To Test fora ... ... 185 Iron Stains, &c., out of Linen, To Take Silver and ... ... 182 Iron Stains, To Clean the Hands from Silver and .182 Kit for Work in the Field ... 196 Lea’s (Carey) Process 7.82 Lenses. ... 166 Lens, To Find the Equivalent Focus of a ... ... ... 187 Light, To Intensify a Negative by the Action of .184 Lithography, To Prepare a Stone for .156 Manipulations after Sensitizing and before Development .. 34 Manipulations in Silver Print¬ ing . 113 Maxims for Printing .125 Measures, Weights and ... 191 Methylated Alcohol, Testing for 179 Mirrors, To Silver G-lass for ... 185 Miscellaneous Applications of Photography 92 Mounting Prints ... ... 127 Negative after Varnishing, To Intensify .184 CONTEXTS. Yll PAGE Negative by the Action of Light, To Intensify a .. ..184 Negative, Drying and Varnishing the ... ... ... ... 40 Negative, To Remove Varnish from a... ... ... ... 185 Negatives on Tour, Method of Carrying ... . ... 170 Negatives, Reproduction of ... 103 Negatives, Reversed ... ... 105 Negatives, To Retouch Var¬ nished. ... 184 Nitric Acid, Determination of the Strength of ... ... 191 Non-actinic Screens .168 Non-actinic G-lass .168 Obernetter’s Formula in Powder Process .139 Ovals, Cutting ... 128 Paper, Collodio-Chloride ... 125 Paper Enlargements by Develop¬ ment .107 Paper Negative Processes ... 86 Paper, Plain Salted ... ... 114 Paper, Washed Sensitive ... 116 Papers, Durable Sensitized ... 117 Papyrotype, To Make a Transfer by.155 Photo-lithography and Zinco¬ graphy ... ... ... 152 Photo-lithography and Zinco¬ graphy, Stores Required for... 195 Photo-Mechanical Printing ... 141 Photo-Mechanical Process, Capt. Waterhouse’s... ... ... 148 Photo-Reliefs ... .. ... 163 Picture, Printing the .117 Picture, Toning the ... ... 117 Plain Salted Paper ... ... 114 Plans, Engravings, &c., Copying 96 Plate-holders, Pneumatic ... 168 Plates for Zincography, to Pre¬ pare .157 Plates, Sensitizing the. 32 Platinum, Tetra-chloride, Pre¬ paration of . ... 180 Pneumatic Plate-holders ... 168 Powder Process.139 Printing Baths, Purifying Printing, Manipulations in Silver Printing, Maxims for ... Printing. Photo-Mechanical ... Printing, Silver... Printing the Picture Print, Fixing the . Prints, Defects in Prints, Mounting Prints Obtained byAid of Chromic Acid Compounds Prints, Single Transfer... Purifying a Bath Solution by Boiling Down Purifying Printing Baths Purifying Water for Photo¬ graphic Purposes Pyroxyline ... ... ...C Reduction, Table on Enlarge¬ ment or Reliefs, Photo. Residues, Utilization of Silver... RetouchVarnished Negatives, To Reversed Negatives . Salted Paper, Plain Screens, Non-actinic ... Sensitive Paper, Washed Sensitized Papers, Durable Sensitizing Bath ... 14, Sensitizing Bath, Defects Caused by the.. Sensitizing the Plates ... Silver and Iron Stains, &c., out of Linen, To take Silver and Iron Stains, To Clean the Hands from Silver Nitrate in a Solution, Easy Tests for the Amount of Silver Nitrate, To Make Silver Oxide, Preparation of Silver Printing ... Silver Printing, Manipulations in Silver Residues, Utilization of . Single Transfer Prints... Southampton Plan for Preparing Transfers . Spirits of Wine, To Obtain Alcohol from. PAGE 189 113 125 141 108 117 121 124 127 131 138 173 183 3.72 >, 75* 187 163 176 184 105 114 168 116 117 114 44 32 182 182 175 175 173 108 113 176 138 152 179 Vlll CONTENTS. Stains,&c., out of Linen, To Take Silver and Iron Stains, To Clean the Hands from Silver and Iron Still for Distilling Alcohol, To Make ... Stills . Stone for Lithography, To Pre¬ pare a... Stone or Zinc, Transferring to... Substratum, To Prepare Albu¬ men for Sulphuric Acid, Dertermination of the Strength of . Symbols and Atomic Weights of Elements Syphon, To Make a . Tannin Process. Tea Process Tent, Dark Testing for Methylated Alcohol Testing for the Amount of Water in Alcohol . Tests for Amount of Silver Nitrate in a Solution... Toning the Picture . Transfer by Papyrotype, T^o Make a Transfer Prints, Single... Transfers, Southampton Plan for Preparing Transferring to Stone or Zinc ... Transparencies, Production of... Tubing, To Bend Glass... PAGE Uranium Dry-plate Process ... 78 Utilization of Silver Residues ... 176 Varnished Negatives, To Re- touch ... ... ... ... 184 Varnish from a Negative, To Remove .188 Varnishes ... ... ... 26 Varnishing, Defects Caused by 48 Varnishing the Negative, Drying, &c.40 Washed Emulsion Process ... 81 Washed Sensitive Paper ... 116 Water in Alcohol, Testing for the Amount of ... ... 179 Waterhouse’s (Capt.) Photo- Mechanical Process ... ... 148 Water for Photographic Pur¬ poses, To Purify .172 Weights and Measures.191 Wet-plate Photography ... 3 Wine, To Obtain Alcohol from Spirits of ... 179 Woodbury’s Formula in Powder Process ... ... ... 140 Woodbury type Process... .. 142 Zincography, Photo-lithogra¬ phy and ... ... ... 152 Zincography, Stores Required for Lithography and ... ... 195 Zincography, To Prepare Zinc Plates for ... 157 Zinc, Transferring to Stone or... 157 PAGE 182 182 180 169 156 157 181 191 ! *. 185 70 74 167 179 179 175 117 155 138 152 157 99 184 INSTRUCTION IN PHOTOGRAPHY. Observation has shown that certain metallic and organic com¬ pounds undergo change in the presence of ordinary light. The change may be visible to the eye (as in the case of the darkening of silver chloride), or may be ascertained by their behaviour when certain chemical agents are brought in contact with them, as in the case of iodide of silver in the wet collodion process. It is none the less true that the latter change is as real as the former, though it be primarily unrecognizable. It is found that rays of certain colours (as well as pure white light), affect these compounds, and that those of certain other colours refuse to do so. Those coloured rays of light which will effect a change (visible or invisible) are termed actinic, or chemical, rays ; all others, non-actinic. When light is decomposed by a prism, it is separated into all the colours of the rainbow, and although they pass imperceptibly from one to the other, yet, for the sake of perspicuity, they have been divided into seven, which are called primary colours. These are red, orange, yellow, green, blue, indigo, and violet. Experiment has shown that light of those colours which are included between the green and the violet are actinic, and that of these, that which produces the most rapid change in a silver salt is situated about half-way between the two. With different salts of silver the range of actinic power varies slightly, inclining more or less to the red end of the spectrum. There are certain silver and iron compounds which have proved to be capable of being acted upon by the red rays to from a developable image, and even by dark rays below them in the spectrum; but as yet the discovery has not been utilized, hence only the ordinary silver compounds used by the photo- o grapher for camera work will be considered. It should be remembered, then, that white light only causes a chemical change in a silver salt, because, of its components, some are actinic; and it is because the red and yellow rays are non- actinic that coloured glass of these hues is used in our deve¬ loping rooms, the light admitted through such glass, if it be of good quality, being incapable of producing any primary change on the ordinarily employed silver salt. It must also be noted that when a ray of light is decomposed by a prism into its primary colours, and these be allowed to fall upon a film con¬ taining a sensitive salt, a change in it is produced beyond the place where the extreme violet ray is seen. These rays (to¬ gether with others below the red) are called dark rays of the spectrum, and are usually denoted as ultra-violet. As these produce a change in the salt, they are likewise actinic rays. The sensitive salts of silver which are usually employed in photography are, the iodide, the bromide, and the chloride of silver. There are others, which are rarely used, and to which we may refer further on. In order to illustrate the theory of the formation of a photographic image, the iodide will be taken as a type, the action of light on the other salts being similar. Silver iodide (Ag-1) can be formed in two or more ways—by the action of a soluble iodide on a soluble salt of silver, or of iodine vapour upon metallic silver. This first method is that employed for its formation in ordinary photography : — The soluble iodide of a metal, or metalloid, such as cadmium, ammo¬ nium, &c., is brought in contact with a solution of silver nitrate ; the iodine, having a strong affinity for the silver, forms silver iodide, setting the nitric anhydride free, which in its turn combines with the metal originally in combination with the iodide. Chemically, it is expressed thus— Cadmium Iodide. Silver Nitrate. Silver Iodide. Cadmium Nitrate. CdL ' + r ~2AgIIo7'=* 2AgI + ^Cd(^6^~" In the above equation, if we were to substitute Br for I, the same would hold good, the decomposition being similar. The chemical change that takes place in the iodide of silver by the light we have very good reason to believe to be the for¬ mation of a silver subiodide. Thus— Silver Iodide. Silver Subiodide. Iodine, 2AgI = ' Ag 3 I + I 3 If no body -which will absorb iodine* be present this change will not take place, for if we thoroughly wash silver iodide, and treat it, after exposure to light, with such a developer as will be presently indicated, no alteration in it will be manifest. It will therefore be evident that in wet plate photography the silver nitrate plays an important part. Multiplying the above equation by 6 we have 61 coming in contact with 6AgN0 3 — Iodine. Silver Nitrate. Water. Silver Iodide, Silver Iodate. Nitric Acid. f6l +"6AgN0 3 + 3E*0 = 5Agf + ^TgI0 3 ~V 6H m 3 It must not be supposed that this chemical change neces¬ sarily takes place in the whole of the silver iodide present. Par from it—the change may take place in an infinitely small proportion of it, perhaps only on the surface of the minute granules exposed to light. In dry plate photography the action of light is precisely the same; but the free nitrate of silver solution is replaced in this case by some body which will combine with iodine. WET-PLATE PHOTOGRAPHY. Having treated of the action produced by light on various silver compounds, it is now proposed to describe in detail the process commonly known as the collodion wet process. The sensitive salts of silver usually employed in this process are the iodide and bromo-iodide, the former being used only for special classes of work, to which attention will be drawn. The follow¬ ing is an outline of the process:—1st. Soluble bromides and iodides are dissolved in collodion. 2nd. A clean glass plate is coated with a thin film of this prepared collodion. 3rd. When set, the plate is immersed in a solution of silver nitrate * This is not the case with silver bromide and chloride. A change is effected in these bodies without the presence of an absorbent. f When bromine and chlorine are liberated from silver bromide and chlo¬ ride respectively in the presence of silver nitrate, the reaction that takes place is somewhat different, hypobromous and hypochlorous acid being formed. The above equation is possible when the iodide is the sensitive salt, but it is doubtful if it is not simplified by oxygen being liberated, no iodate being then formed. 4 (usually called the bath solution), which causes the formation of silver iodide or bromo-iodide. 4th. The plate is then exposed in the camera. 5th. A developing solution is applied to bring out the image. 6th. The image is intensified or strengthened. 7th. It is fixed, and (8th) a coating of varnish is given to the dried film to protect the delicate collodion surface. In this stage the negative is complete for printing purposes. THE GLASS PLATE. A few remarks are necessary on the glass that should be selected for camera work. As a rule, patent plate is recom¬ mended by most authorities on the subject, as being perfectly flat and of a good polish. It must, however, be borne in mind that patent plate is really nothing more than sheet glass which has been ground to a flat surface and then polished. The outer skin of all glass is always the hardest and most compact, and conse¬ quently the patent plate is denuded of much of the original surface, and the inner portions of the sheet glass are conse¬ quently exposed to the action of the chemicals employed. In practice it is found that this glass absorbs impurities, during the photographic operations, which cannot be eliminated; and it is almost useless to expect to use the same plate above three or four times, a serious consideration to the tyro in the art when the high price of the article is remembered. Sheet glass is generally “ true” in one direction, but slightly curved in the other, but its surface is hard and well adapted for small-sized plates, where the curvature may be neglected. A good specimen of this glass is one to be recommended. Crown glass, from the nature of its manufacture, has generally double curvature, and is therefore to be employed for large plates with great caution, as it is liable to snap in the printing- frame, and to throw portions of the picture out of focus. Matted crown is not open to this objection, but if it be really flatted its cost should be nearly that of patent plate. It has a hard surface, and when a true sample of it is to be obtained there is nothing better that can be used. For large plates, say over 15in. by 12in., patent plate is recommended; for the inferior sizes, flatted crown; or, failing this, the best sheet glass. Matted crown has only one surface that is smooth, the process o of flattening (which consists in heating the ordinary crown to a red heat and allowing it to flatten on a plain surface) making the other slightly irregular. CLEANING THE GLASS PLATE. In order to make a plate chemically clean, some body must he found which will free it from mechanical dirt—such as dust— and also from grease. Alcohol has the property of holding most kinds of the latter in solution, hence it generally forms a portion of a plate-cleaning formula. Any alkali will turn grease into soap, rendering it soluble in water; hence this is often recommended as an addition. To free a plate from mecha¬ nical dirt, insoluble powder of an impalpable description is found to answer well when made up in a paste, hence the employment of tripoli powder and rouge. Common whitening has the pro¬ perty of absorbing grease when dry; hence a cream of this made up with water is sometimes applied to a plate, allowed to dry, and rubbed off in that state. The usual formulae for a plate¬ cleaning solution is tripoli powder; spirits of wine sufficient to form a thin cream; liquor ammonia, about ten drops to each ■ounce of the cream. Rouge may be substituted for the tripoli powder, but unless it be of the finest nature, it is liable to cause scratches. It has also the disadvantage of injuring the bath if •any be carried into it by the plate. Plates carrying old varnished negatives, which are to be used for fresh pictures, should be allowed to soak in soda and water (one ounce of washing soda to two pints of water). This will generally secure the film leaving the plate. Should the films be unvarnished, hot water may be employed to remove the collodion. In both cases the plates must be treated with the cleaning solution. It may happen that plates are slightly scratched, and refuse to become clean by ordinary means. Resort may then be had to albumen, &c., as given for dry plates. COLLODION. Collodion is gun-cotton ( i.e. y pyroxyline) dissolved in a mix¬ ture, varying in proportions, of alcohol and sulphuric ether. Its qualities vary with the kind of gun-cotton and with the proportions of the solvents used. 6 Pyroxyline is cotton or fibre (cellulose or lignine) which, has been altered in chemical composition by treatment with a mix¬ ture of nitric and sulphuric acids, or an equivalent of the former. The change that takes place is due to the combination of peroxide of nitrogen with the cellulose or lignine. The chemical action may be symbolized as follows :— Cotton. Nitric Acid. Sulphuric Acid. Pyroxyline. WA 4- 2wm 3 +H&£oT" = wSooSo. Sulphuric Acid. Water. + ""SsoT + 2TLO It will be noticed that the sulphuric acid remains unchanged. Its employment is owing to its affinity for water. Hydrogen from the cotton is abstracted, and combines with the oxygen liberated from the nitric acid. This forms the water which the sulphuric acid absorbs. The formula shows that two equivalents of hydrogen are displaced by two equivalents of nitric peroxide. When three equivalents are displaced we have the true explosive gun-cotton. The difference in the temperature of the acids, &c., determines whether tri-nitro or di-nitro (pyroxyline) cellulose will be formed. The manufacture of pyroxyline is one of considerable diffi¬ culty, though not at all out of the range of ordinary skill. For amateurs the second process will, it is believed, be the most useful. The general directions given are those found in Hard- wich’s Photographic Chemistry. 1st Process.—Sulphuric acid 1*845 at 60° F. 18 fluid ounces.* 4 Hitric acid 1*457 ... ... 6 ,, Water. 4f ,, The water is first poured into a strong glazed porcelain basin, the nitric acid next added, and, lastly, the sulphuric acid. The mixture is well stirred with a glass rod. The temperature will now be found to be somewhere about 190°. It must be allowed to cool to 150°, and this temperature must be maintained on a water-bath. A dozen balls of cotton wool, weighing about thirty * It need scarcely be said that great care must be taken to prevent the acid coming in contact with the skin or dress. An india-rubber apron and pair of gloves are useful to save the one and the other from hurt. grains (which have previously been well washed and dried), should now be immersed separately in the fluid with the aid of a glass spatula. Each ball should be pressed separately against the side of the basin till it is evident that the acids have soaked into the fibre. Care must be taken that each one is immersed at once. Eailing this, a different chemical combination takes place, and nitrous fumes are given off, and the success of the operation will be vitiated. Immersing the dozen balls will take about two minutes. The basin should after this be covered up for about ten minutes.'* 4 At the expiration of this time the whole of the cotton should be taken up between two . glass spatulas, and against the sides of the clean porcelain capsule as much of the acids as possible should be squeezed out. The cotton should then be dashed into a large quantity of water, and washed in running or frequent changes of water for twenty-four hours. Finally, when it shows no acid reaction to blue litmus paper, it is dried in the sun or on a water-bath. 2nd Process.—Sulphuric acid of commerce 6 fluid ounces Dried potassium nitrate ... 3J ounces (Av.) "Water . 1 fluid ounce Pest cotton wool... ... 60 grains Mix the acid and water in a porcelain vessel, then add the nitrate (which has previously been dried on a metal plate to about 250°, and then pulverized) by degrees, stirring with a glass rod until all lumps disappear and a transparent viscous fluid is obtained. This will occupy several minutes. The whole of the cotton wool must now be separated into balls the size of a walnut, and immersed as stated in the first process, care being taken that the temperature is kept up to 150°. The cotton is then left ten minutes, and washed as before. Mr. Hardwich states that the chances of failure in this process “ are very slight, if the sulphuric acid be sufficiently strong, and the sample of nitrate not too much contaminated with chloride of potassium.” If failure occur through the cotton dissolving in either of the mixtures, a drachm less water must be used. In both processes the operation may be conjectured to be successful if the cotton tear easily in the hand, and if the original lumps cannot be easily separated. Should nothing but fragments * This prevents the access of the air to the fluid, and consequent absorption of oxygen. A neglect of this precaution will increase the chance of nitrous fumes being evolved. 8 of the lumps be detected, it is probable (if the acids used have been of the strength given above) that the temperature has been allowed to fall. When dry, the pyroxyline, on pulling by the hand, should break up into little bits, and not resemble the original cotton in texture. The weight of good pyroxyline should be greater than the original cotton by about 25 per cent. If the acids employed be too strong, the pyroxyline will be much heavier than this percentage, and on solution yield a thick glutinous collodion; whereas, if the acids have been too diluted, it will probably weigh less than the original cotton, and yield a collodion adhering firmly to the plate, but giving negatives of an abnormal softness; with this specimen any small particles of dust that may fall on the glass will form transparent marks. The formula given above steers between the two extremes. The following are formulae which experience has shown are good for plain collodion:— fPyroxyline Ho. 1. -< Alcohol *820 55 to 65 grains ounces H „ 55 to 65 grains 5 ounces 5 „ Pyroxyline Ho. 2. •< Alcohol -820 /Ether *725 Ho. 1 is most'suitable for winter; Ho. 2 for summer work. The more alcohol in proportion to the ether that is used the slower will the collodion set. A limit, however, to the pro¬ portions that can be used arises from the fact that if the alcohol be added in excess, the film which contains the sensitive salts of silver becomes streaky and slow in securing the impressions of the photographic image; whilst if the excess be of ether, the film becomes too contractile, and has a tendency to split on drying. In mixing the collodion the alcohol should be added first to the pyroxyline, as by so doing its dissolution is aided. It must also be remembered that the quantity of pyroxyline given above is dependent on its quality, whether it tend to form a gelatinous or limpid collodion. In the former case, less must be used ; whilst in the latter, more may be added. When plain collodion has been prepared, and a copious 9 addition of water made to it, it is found that a portion of the pyroxyline remains in solution in the water, the precipitated portion being of a finer quality than the original. If this he dried and made up into collodion once more, it yields a beauti¬ fully textureless film. Should this method of “refining” the pyroxyline be determined upon, coarser and cheaper quantities of solvents may he employed in the first instance. Dr. Liesegang introduced a form of pyroxyline called papy- roxyline. It is prepared from paper instead of cotton, and its value for giving tough films is great. Dour grains of papyroxy- line are equivalent to five of pyroxyline. A judicious mixture of the two in the solvents gives highly satisfactory results. Iodides and bromides of metals are added to the plain collo¬ dion to render it capable of forming a fine layer of iodide and bromide of silver in the negative bath. If iodides are used alone a dense image is formed with but little detail in the high lights, and a long exposure is necessary in the camera. Bromides used alone give a faint image, but full of detail, and the time required to impress a latent image on the sensitized film is shorter than when iodides alone are employed. It is thus evident that a judicious mixture of the two will give a film which, when sensitized, has the delicacy of the bromide and the density of the iodide, whilst the time of exposure will be somewhat between that required for the two separately. The iodides and bromides of zinc, potassium, ammonium, and cadmium, have all been tried by various makers. The two last are the staple iodizers and bromizers employed. The following is a list of the combining proportions of iodine and bromine in the iodides and bromides of certain of the metals. Dor others they can be calculated from the table in the Appendix:— In 10 grains of potassium iodide 7 - 64 grains iodine ,, bromide 6-64 } > bromine cadmium iodide 6*92 y y iodine ,, bromide 5-88 yy bromine ammonium iodide 9*40 y y iodine ,, bromide 8-16 yy bromine magnesium iodide 9-14 y y iodine ,, bromide 8-59 y y bromine zinc iodide 7*95 y y iodine ,, bromide 7-10 yy bromine 10 A standard iodizing solution haying been arrived at by ex¬ periment with any of the iodizers and bromizers given above,, the value of the others may be determined. The following is a standard that has been found to answer No. 1.—^Cadmium iodide 4^- grains Cadmium bromide ... 2 „ Plain collodion ... 1 ounce On referring to the table the following modifications arise in the formula where alkaline salts are used. "We shall have then for one formula : — No. 2.—Ammonium iodide 3-J- grains Cadmium bromide ... 2 „ Plain collodion ... 1 ounce No. 3.—Cadmium iodide ... ... 2^ grains Ammonium iodide ... If „ Cadmium bromide ... 2 „ Plain collodion 1 ounce No. 4.—Ammonium iodide ... 3 grains Cadmium iodide ... l grain Ammonium bromide ... If grains Plain collodion 1 ounce No. 5.—Ammonium iodide ... 4 grains Cadmium bromide ii ... ±4. ,, Plain collodion 1 ounce No. 1 should be mixed at least six months before use : it gives a delicate image and fine detail. No. 2 should be mixed two months before use, and answers well for landscapes. No. 3 should be prepared four months before use, and is good for portraiture. No. 4 may be used after mixing two or three days, and is a good u general purpose ” collodion. No. 5 is a collodion much to be recommended. It gives fair density with detail, both in the high lights and shadows; it can be used two or three days after making. * Cadmium renders collodion glutinous on first iodizing. When kept, it becomes more limpid. Ammonium fits collodion for more immediate use, as t does not cause it to become glutinous, even on first iodizing. 11 The following’ general rules may be given for modifying the tendencies of collodion:— 1. If a decrease of contrast and more detail be required, add bromide. 2. If violent contrasts are wanted, the iodides should be increased and the bromides diminished. One quarter-grain of bromide to the ounce of collodion is found to be sufficient to secure cleanness in the shadows, and all but this quantity may be left out if necessary. As before stated, for certain classes of work it may be necessary to resort to simply iodized collodion, no bromide being admissible. The following are formulae which have been adopted:— ]S T o. 6.—Ammonium iodide Plain collodion ... No. 7.—Cadmium iodide Plain collodion ... 4 grains 1 ounce 5 grains 1 ounce No. 6 should be iodized almost immediately before use. No. 7 requires keeping, and is a most stable collodion. It should here be noted that it is customary, though not necessary, to leave out half the alcohol from the plain collodion, and dissolve the iodide or bromide in the quantity thus omitted. This procedure has advantages, and may be followed if con¬ sidered convenient. Collodion should be stored in a dry and cool place ; if other¬ wise, the ether is apt to become decomposed, which, in its turn, decomposes the pyroxyline. Collodion made with pure spirit and neutral cotton will be colourless after iodizing, but if made with impure solvents’ it will become first dark, but may after¬ wards return to its colourless condition. Should the pyroxyline be acid (not sufficiently washed after preparation), the collodion will become sherry-coloured almost immediately, but will not keep in good working condition for long. Methylated alcohol and ether are often employed by manufac¬ turers as solvents. Experience teaches that, although apparently harmless at first, they both, particularly the former, contaminate the silver nitrate bath if used for any length of time. It is also noticeable that a collodion made with pure solvents fre¬ quently refuses to work in a bath in which adulterated solvents are found. 12 Collodion should be always labelled and dated after manufac- tu r e and iodizing. This precaution will be found of the greatest us e in selecting a specimen suitable for any particular purpose. The following is a specimen of a label:— Plain Collodion made 15th July, 1876. Pyroxyline (prepared 1st of June, 1870) ... 6 grains Papyroxyline ... ... ... ... 2 ,, Sulphuric ether (pure) ... ... ... ounce Alcohol *820 ... ... ... ... ^ ,, Iodized 4th August, 1876. Ammonium iodide ... ... ... ... 2j grains Cadmium iodide ... ... ... ... 2 ,, Cadmium bromide ... ... ... ... 2 ,, Alcohol ‘820 . \ ounce Any bottle of collodion thus labelled will tell its own tale, and be a guide for future manufacture. "With the collodion of com¬ merce all you can do in labelling is to give its date of iodizing; even this will be found very useful. When the iodized collodion is of a pale straw colour, it is in its most sensitive condition. After it assumes the dark brown sherry colour, from the liberation of iodine,* it becomes less sensitive, and is more apt to give harsh pictures. When plain collodion is prepared, it should be tested before iodizing. A plate should be coated, and it should be observed if it dry with any opalescence. Next, the toughness of the film should be tested to see if it be powdery, or if it come away in strips to the touch of the finger. After it is iodized it should be tried by taking two or three negatives, the behaviour of the films being carefully noted. It is useful to have a sample of good standard collodion at hand with which to compare it. If the two halves of a stereoscopic plate be coated with the two collodions re¬ spectively, and the sensitized films be exposed simultaneously, their relative sensitiveness and densities may be readily deter¬ mined, and the results should be noted for future guidance. Any defect in the collodion should, of course, be corrected. Collodion which yields a thick creamy film gives a “ plucky” image, whilst a limpid collodion gives one thin and transparent. * The whole of iodine must be liberated before any bromine can be found in a free state. 13 This latter can be improved by adding a grain or two of pyroxyliue to each fluid ounce. Should this defect arise from the use of alcohol which is too anhydrous, it may be rectified by the addition of a drop or two of water to each fluid ounce. Collodion that has been iodized a long time often has this defect. It will he found advantageous at times to mix the collodions prepared by different formulae; thus, a collodion yielding great intensity of image should be mixed for general purposes with one which is deficient in this quality. This remark applies not only to home-made, but also to commercially supplied, collodions. When testing the plain collodion, should the film dry matt, the sample must be rejected, as the pyroxyline must be unsuit¬ able. Should the film after sensitizing appear like watered silk, then the collodion is too alcoholic, or else contains too much iodide and bromide. The probable cure for this is the addition of a drachm to the ounce of plain collodion prepared according to formula 1, page 8; Should the defect arise solely from the collodion being too alcoholic, it is probable that if the film be allowed to set more thoroughly before sensitizing, a cure will be effected. When collodion is under-iodized, the developed image will be poor and fiat, though it is necessary to distinguish between this cause for the defect, and that due to impurities that may occur in the negative bath. If the film, on drying, show “ crape markings,” the plain collodion has been prepared with solvents of too great a specific gravity— i.e., with too much water in their composition. To remedy this defect, an iodized collodion formed of absolute ether and alcohol should be added till the markings disappear. Should the collodion, on setting, prove of a horny repellent nature, the defect may be cured by shaking it up with a small quantity of carbonate of soda, and decanting the supernatant liquid from the residue. A drop or two of water to the ounce will frequently answer the same purpose. If collodion be made up with absolute alcohol and ether and the above amount of iodides and bromides, it will be found that the plate has the appearance of being stained with opaque streaks, especially at the corner of the plate from which the collodion was poured off, where, consequently, it was least set. To remedy this it is a good plan to add water to half the amount of collodion, till it appears on the withdrawal of the plate from the bath to 14 have the appearance of crape, then to add the remaining half to that portion which was watered. On trying a plate it will he found that the film has lost the streaks, and is more dense than before. On the quality of the pyroxyline depends a good deal the amount of water that can be added. THE SENSITIZING BATH. The strength of the sensitizing bath is of the utmost import¬ ance in photography, as is also the purity of its constituents. The silver salt employed is invariably the silver nitrate, as it is the form most attainable in commerce, and can generally be procured free from impurity. Silver nitrate is readily soluble in its own weight of cold water, and in a still higher degree in hot water ; but for the purpose to which it is to be put in the pre¬ sent instance, a far weaker solution is preferable. When iodides or bromides are used in the collodion, the utmost strength admissible is 50 grains of silver nitrate to each ounce of water, but for ordinary use the former proportion is too large, for this reason: silver nitrate in solution will dissolve up a certain amount of silver iodide/ 4 the quantity depending upon the strength of the silver solution, and on the temperature. If the solution were not, therefore, saturated with the silver iodide, on the im¬ mersion of a collodion film the silver iodide would be partially or wholly dissolved out, according to the time of immersion. hTow, it is easier to saturate a dilute solution than a stronger, and a variation in temperature causes a less marked difference with the former than with the latter. It is therefore evident that the less silver salt in solution the more likely it is that the solution will not show signs of under or over saturation of iodide. The acidity or alkalinity of the bath is a con dition to which it is necessary to give attention, the sensitiveness of the plate being dependent in a great measure on it. When simply iodized (with no bromide) collodion is used, the solution should be strictly neutral, or slightly acid, whilst with a bromized or bromo-iodized collodion it should be decidedly acid (with the former particu¬ larly it should be strongly acid). The reason of the different state of acidity in the two cases is not very easy to trace, but it is probably due to the different reaction that takes place when * It will dissolve scarcely any silver chloride or bromide, hence it is un¬ necessary to saturate it with these salts. 15 silver bromide and iodide are exposed to light in presence of silver nitrate solution. On the purity of the water employed is the sensitiveness of plate to a great extent dependent. Distilled water is naturally the most free from impurities, though even in it they are to be met with, unless great precautions are taken to eliminate them. "When distilled water is not obtainable, water purified, as given in the Appendix, should be used, though if rain-water, not obtained from the roofs of houses, can be procured, it may be substituted with tolerable safety. The following formula may be used for an ordinary negative bath when bromo-iodized collodion is used:— Recrystallized silver nitrate .40 grains Distilled water ... ... ... ... 1 ounce Potassium iodide * ... ... ... grain Take a quarter of the quantity of water that is to be used, and dissolve the silver nitrate in it; then add the potassium iodide, or other soluble iodide. It will produce an emulsion of silver iodide, which will be partially re-dissolved on agitation. Next add the remaining quantity of water. This will cause a re-precipitation of silver iodide. After filtration the bath solution should be tested for acidity or alkalinity. Blue litmus paper should redden slightly after a minute’s immersion. Should the red colour be produced immediately, a little sodium carbonate should be added till a slight precipitate is produced. This should be filtered out and the bath acidified with a few drops of a solution of nitric acid (1 drop of nitric acid to 12 drops of water). Acetic acid is sometimes recommended for acidifying the bath. If it be used, silver acetate is formed, which is injurious to sensitiveness and cleanliness of work, and cannot be eliminated by any convenient method. Should the test- paper refuse to redden, the nitric acid solution should be added. As a rule, if recrystallized silver nitrate be used the bath will require the addition of neither alkali nor acid. Before taking a bath solution (or lath, as it will be hereafter called, for brevity) into general use it should be tested. This is * Some prefer not to add any iodide to the bath, but to allow it to become saturated by work. If a plate be moved about continuously in a bath made minus the iodide, there need be no fear of pinholes. It should be stated that with a solution of greater strength than that given it is very difficult to avoid them when adopting this method of procedure. 16 best clone by immersing in it a plate coated with collodion. When fully sensitized the plate should be placed in the dark slide, and then, for a second, half the plate exposed to white light. It should then be developed. A trace of fog on the part on which the light had not acted will denote that a slight addition of nitric acid is required, or that an organic or other foreign substance is present. The latter case will be treated of when the defects in negatives are under consideration. DEVELOPMENT. As already pointed out, the reduction of the iodide or bromide to the state of sub-iodide or sub-bromide may be invisible or latent. A developer is that agent which brings the chemical change to the cognizance of our senses. Pyrogallic acid is a body which is well known for its affinity for oxygen, as are the ferrous salts, the latter tending to become ferric salts, that is, to combine with more oxygen. When the oxidation of these bodies takes place in the presence of silver nitrate the metal is deposited. We will take the example of the iron salts when applied to the latent image to see how development is effected. The theory is based on the assumption that the silver sub-iodide or sub-bromide has an attraction for freshly-precipi¬ tated metallic silver, and its consequent deposition by the developer upon those parts acted upon by light. The reaction that takes place is thus:— Silver Silver Ferrous-sulphate, deposited on Ferric-sulphate. Ferric-nitrate. Nitrate. the Subiodide. 3AgH0 3 fl- 3EeS0 4 — 3Ag -f- Ee2(S0 4 ) 3 -J- Ee2(H0 3 ) 3 A little consideration will show that if this action take place the image must be principally on the surface of the film, and not in it. Experience shows that such is the case. In the formulae for developers it will be noticed that the addition of (acetic) acid is invariably included. If to a solution of pure ferrous sulphate (or pyrogallic acid) a solution of silver nitrate be added, it will be found that there is an almost instan¬ taneous deposit of metallic silver. If, therefore, such a solution were flowed over an exposed plate which had free nitrate of silver on it, an immediate precipitation of silver would take place all over the film. The attraction of the sub-iodide of silver would be rendered void, owing to the rapidity of deposit. 1 With an acidified solution, however, the deposition would take place with greater regularity and less rapidity, and when suffi¬ ciently slow the sub-iodide would be able to attract all the particles of metallic silver as they were formed, and thus build up a metallic image. In practice the acid added is just sufficient to cause this gradual reduction of the silver. Heat increasing the rapidity of chemical action, it follows that in decidedly hot weather a larger quantity of acetic acid should be used than in cold. It will also be noticed on the next page that different strengths of iron for the developing solutions are given. The stronger the iron solution the greater chemical power it will have, and the more rapidly it will decompose the silver solution. As a con¬ sequence, with a strong solution, all parts of the picture acted upon by light will immediately become nuclei for the deposition of silver, and the deposit will be of more even density than if a weaker solution had been employed; for with the latter those parts most acted upon by the light—«. Pyroxyline ... 6 grains Cadmium bromide ... ... 8 „ The plate coated with this collodion following— is immersed in a bath of the Silver nitrate 80 grains Water . 1 ounce No iodide need be added. The remaining operations are similar to those described above. Alkaline development, described at page 77, may be employed. With a strong alkaline developer the exposure is shortened to that of a wet plate. ALBUMEN BEER PROCESS. The following process was introduced by the writer for solar photography, and was employed by the English Transit of Yenus Expedition. It is, however, equally adapted for landscape work, and is very certain in its results. The collodion employed can be that described at page following is better :— Alcohol •825... Ether Pyroxyline ... Ammonium iodide Cadmium bromide 55, though for more rapid work the 4-J to 3 drachms to 5 7 grains 2 „ 5 The relative proportions of ether and alcohol are adjusted according to the temperature in which the plates have to be prepared. With the ordinary samples of collodion the usual 40-grain silver nitrate bath can be used, but with the collodion made as above it is advisable to use a bath made up to 60 grains, preparing it as given at page 15. In both cases rapidity is increased by the addition of ten grains of uranium nitrate. It has also been found advantageous to dip the plates in the weaker bath, at first allowing them to remain in it for a couple of minutes, and then to transfer them to the stronger for ten minutes more. This mode of procedure gives very sensi¬ tive and opaque films, the greater part of the actinic rays being thus utilized. The sensitiveness, however, greatly depends upon the porosity of the film, and every effort should be made to attain the maximum of this quality without injuring its texture. The addition of the largest practicable amount of water to the collodion tends to give this quality. After sensitizing, the plate is slightly washed, and then the first preservative applied, which is— Albumen ... ... ... ... 1 fluid ounce* Water ... ... ... ... 1 ounce Ammonia ... ... ... ... 1 drachm This is beaten up into froth (or is mixed by pounding it in a mortar with silica), and when settled the clear liquid is decanted off. This solution is mixed with equal quantities of any ordinary beer or stout immediately before use,f and is floated over the plate. (When bottled beer is used, it is advisable to drive off all the carbonic acid by a gentle heat.) The excess is drained off, and the film thoroughly washed under the tap for a * Dried albumen 25 grains may be substituted for the fluid ounce, t This precaution is necessary, otherwise the tannin of the beer is precipi¬ tated by the albumen. 73 couple of minutes, and is finally covered with a solution of plain "beer, to every ounce of which two grains of pyrogallie acid have heen added. The plate is then dried in the ordinary manner. The exposure with well prepared dense plates is at least as short as that necessary for wet plates, but great latitude is admissible. With twenty times the minimum exposure, a good negative can be obtained. The development need not be effected for a month after exposure. The following solutions are required:— No. 1.—Pyrogallie acid ... \Vater No. 2.—Liquor ammonia ('880) . Water ... No. 3.—Citric acid Acetic acid Water No. 4.—Silver nitrate Water. 12 grains. 1 ounce 1 part 4 parts 60 grains 30 minims 1‘ ounce® 20 grains 1 ounce The washing water before development should be of a temperature no less than 60° Pah. When washed as directed (page 56), the following developer is employed :— To each half ounce of No. 1 are added three drops of No. 2, and after well mixing with a stirring-roc! the solution is flowed over the plate ^ Almost immediately the image begins to appear, and after a few -seconds’ interval the detail can be seen by reflected light to gradually develop. Another two drops of No. 2 arc again added to the solution, which is once more flowed over the plate. Six drops of No. 3 are next dropped into the developing cup, and the solution from the plate poured on to it. Again the plate is rinsed, this time by the acid solution, and intensification is given by the use of it Avith a few drops of No. 4. It is advisable not to allow too much detail to come out with the alkaline solution, but to allow a portion of it to be brought out by the subsequent treatment Avith the pyrogallie acid and silver. The alkaline developer reduces the bromide salt, and leaves the iodide to be attacked by the silver solution. Tt will be remarked, that no rcstrainer such as bromide is employed ; the albumen dissolved by the ammonia plays the part of a retarder, but not as a destroyer, of the latent image. 74 When the image appears sufficiently dense, it is fixed by either sodium hyposulphite or by potassium cyanide. A TEA PKOCESS. Of all dry processes, the tea process is the most charming, when exposure can be given to the plates within two or three days of preparation. They can be developed by the gum-gallic, iron, or alkaline developer. They possess a beauty not obtainable by most processes. The plate is coated with a bromo-iodized collodion, sensitized as usual, a preliminary coating or edging having been given to it. After thorough washing it is immersed in an infusion of tea. This latter is prepared by pouring about ten ounces of boiling water on half an ounce of good black tea. After standing one or two hours it is filtered, and is ready for use. It will not bear the addition of either gum or sugar. The plates require about three times the exposure of wet plates, and should be developed within twenty-four hours afterwards. EMULSION PEOCESSES. The emulsion processes which are now to be described differ from all others previously described, in that the sensitive salts are formed in the collodion itself by direct application of a solution of silver nitrate, and not by immersing a film in the solution. The principal sensitive salt is invariably the bromide, though it is frequently recommended to use with it chloride and iodide. An emulsion is formed readily with the chloride and bromide, but with iodide greater difficulty is experienced. It has been found practically that the formation of a small quantity of the chloride with the bromide emulsion prevents the plates fogging when an excess of silver nitrate is added to the collodion. On the other hand, it is not required if a slight excess of soluble bromide remain unconverted. No doubt greater sensitiveness in an emulsion is attained by forming an emulsion with the silver nitrate in excess, but it is not so stable a compound as if it be in slight defect. When the former is the case, the emulsion becomes thin and limpid unless other precau¬ tions be taken. With the latter it remains fit for use for a 75 longer period. Washed emulsion, which will presently he described, will keep indefinitely, and remain at a standard sensitiveness. The pyroxyline for the collodion to be preferred in these pro¬ cesses is that which is prepared at a high temperature, and with proportions of acids differing to that already given at page 6. The following formula is that published by Mr. L. Warnerke, and due to Col. Stuart Wortley. It has been found by the writer to yield a compound which has all the necessary properties for emulsion—viz., porosity with its consequent sensitiveness, and a capacity for taking intensity at a single application of the alkaline development. One hundred grains of the finest cotton wool are put into a porcelain jar, and thirty grains of gelatine dissolved in the smallest amount of water are added. By pressing it with a wooden stick all the cotton will be uniformly impregnated. It is subsequently very thoroughly dried before the fire. Nitric acid (sp. gr. 1*450)... 4 oz., or sp. gr. 1*42 ... 35j dr. Water .12^ dr. ditto ... 9 dr. Sulphuricacid(sp.gr. 1*840) 6 oz. ditto ... 6 oz. are mixed in the order named, and, by means of a water bath, the temperature is kept up to 158° Fah. The dried gelatinized cotton, weighing about 130 grains, is immersed in the mixed acids for about twenty minutes. Here it should be observed that with some cotton it is impossible to preserve this tempera¬ ture. The slightest tendency to dissolve at once raises the temperature rapidly, and the cotton speedily disappears. With such a sample of cotton the temperature must be lessened to such a degree that this result does not obtain. The pyroxyline is now washed and dried as in the preparation of the other pyroxyline. The addition of the gelatine to the cotton causes the formation of nitro-glucose when in the acids, and most of this is lost in washing. The writer has found that by dissolving one grain of this substance with every five of the pyroxyline an extraordinary degree of density can be given. CANON BEECHEY’S PROCESS. The first process to be described will be Canon Beechey’s, as it is very simple and most efficient. The following is the modus operandi :— Take cadmium bromide (anhydrous) ... 400 grains Alcohol (*805) ... ... ... ... 10 ounces 76 and allow the mixture to stand. Decant carefully, and add eighty minims of strong hydrochloric acid. Take of the above solution ... % ounce Absolute ether (*720) ... ... 9 drachms Pyroxyline (as above) ... 10 to 12 grains To sensitize this, dissolve forty grains of silver nitrate in one ounce of alcohol (-820 sp. gr.) The best method to effect this is to pound up the silver nitrate in an agate mortar, and take only a quarter of the alcohol and boil it in a test tube containing the silver salt. The alcohol will become slightly brown (due, probably, to the formation of a fulminate of silver), and should be decanted off into the bottle containing the collodion. The remaining silver should be dissolved up in a similar manner, the ounce of alcohol being just sufficient to effect solution. Between each addition of the silver nitrate the collodion should be well shaken. When the final addition is made the emulsion should be very smooth and rather thick. When poured upon a strip of glass plate it will appear transparent by transmitted light, but after keeping twenty-four hours (occasionally shaking the bottle containing it in the interval) it ought to be very opaque and creamy. The plate having been coated with a substratum or edged, the collodion (which should have been shaken about half an hour* before it is to be used) is poured on it in the ordinary manner, and, when set, immersed in a dish of distilled or rain water. When all greasiness has disappeared it is flooded with any of the preservatives already mentioned. Canon Beechey recommends the plate to be immersed in a dish containing beer to which one grain per ounce of pyrogallic acid has been added. The drying is conducted in the usual manner. The exposure may be taken to be about the same as that necessary to be given to a gum-gallic film. Between exposure and development the plates will keep fairly for a week, but after that seem to lose detail, and appear under-exposed. Strong alkaline development was introduced by Col. Stuart Wortley, and has placed a wonderful power in the hands of the photographer. It is recommended for this, and applied to various other processes, and subsequent reference will be made to it. 1 (Pyrogallic acid. 96 grains (Methylated alcohol . 1 ounce * Canon Beechey recommends the hottle to he shaken immediately before use, and the emulsion filtered. 77 No. 2.—Potassium bromide 12 grains Water distilled 1 ounce J No. 3.—Ammonium carbonate ... 80 grains Hot distilled water 1 ounce Or, Liquor ammonia ... 25 minims Water 1 ounce To develop the plate, take of— No. 1 . jr drachm No. 2 1 drachm (4 drachm in cold weather.) No. 3 . 2 drachms These are the proportions for a plate 7-J by 4^. Should the preservative on the plate he soluble in alcohol, then that solvent should first be applied to the plate (edged round with india-rubber if necessary), and then be washed till all the alcohol has been removed. It is very convenient to develop these plates on a levelling stand, in which case the india-rubber edging is a great help to keeping the solution on the plate. The above solutions should be mixed immediately before use, and after well stirring with a glass rod be flowed over the plate. When the detail begins to appear the bulk of the solution should be poured back into the developing glass, and the appearance of the image watched. If the detail appears slowly and regularly, the deve¬ loper should be again flowed on the plate, and the image be allowed to gain full intensity. If, however, it appear very slowly, and with apparent difficulty, another drachm of No. 3 should be added to the solution in the glass, and again be applied to the film. If the detail flash out at once, the action must be instantly checked by water, and another half drachm of No. 2 be added to the developing solution, which should be again applied. Should sufficient intensity not be gained by this alkaline method, the ordinary intensifier (page 22) should be applied afterwards. It is not always easy to secure sufficient density with emulsion plates, even by the application of silver and pyro- gallic acid. In this case, after fixing, the image may be converted into iodide of silver by the iodine solution (page 22), be washed, flooded with a weak solution of silver, be exposed momentarily to light, and be then intensified by iron or pyro- gallic acid. The plates are fixed by potassium cyanide, or sodium hyposulphite (page 26) 78 Another mode of developing these plates is one lately proposed hy Mr. J. T. Taylor, who employs a colloidal restrainer intro¬ duced by Mr. Carey Lea. This last is prepared by taking one ounce of Trench glue, and softening in one and a-half ounce of water to which one drachm of sulphuric acid is added. The water is then boiled, to dissolve the gelatinous body, and, after the addition of half an ounce more of distilled water, the boiling is continued a couple of hours. Eighty grains of granulated zinc are next added, and the boiling again continued for one and a-half hour more. The solution is now allowed to settle, and the clear fluid is decanted off. To every three ounces of a fifteen-grain solution of iron one minim of this solution is added. The development must be carried out precisely in a similar manner to that described for the gum-gallic process, substituting the above iron solution for that given. It should be noted that a film to which an albumen preservative has been applied is very difficult to develop by any iron salt, and the writer never attempts this mode of development on plates so prepared. URANIUM DRY PLATE PROCESS. The later modifications of this process are not published; but the original form was so satisfactory in the hands of many that it is given here. Col. Stuart Wortley experimented largely and fully in the emulsion processes, and found that the addition of the uranium nitrate to an emulsion added to the sensitiveness of the plates, and rendered the tendency of the silver bromide, when prepared with an excess of nitrate of silver, to deposit, 4 to be much lessened. The uranium likewise he found to restrain “fog” or veiling of the image. It should be here stated than an excess of nitrate of silver in this emulsion renders the dry plates very rapid, nearly approach¬ ing that of wet. The following is taken from a paper read by Col. Wortley before the Dry Plate Club in April, 1872 :— The plain collodion is made with pyroxyline prepared at a high temperature. The emulsion is made as follows:— Plain collodion ... Anhydrous bromide of cadmium Hitrate of uranium nitrate of silver 1 ounce 7 grains 30 13 79 The nitrate of uranium should he pure, and very slightly acidified with nitric acid. The uranium salt and bromide of cadmium should he dissolved in the collodion, and the nitrate of silver added as directed before. The plate should have a substratum, and he coated as usual; when set, it is washed in distilled water till all greasiness disappears, when any of the usual preservatives may he flowed over it. Preservatives con¬ taining sufficient gum to give a protection to the film tend to cause blisters on development. Col. Wortley recommends the following as giving freedom from this annoyance:— The following stock solutions are prepared:— No. 1.—Salicine, enough to make a saturated solution in distilled water. No. 2.—Tannin ... ... ... ... 60 grains Distilled water ... ... ... 1 ounce No. 3.—Gallic acid ... ... ... 48 grains Alcohol... ... ... ... 1 ounce. To make the preservative, take of— No. 1. No. 2 ... No. 3. Sugar ... Water ... 2 ounces 1 ounce 1 2 40 grains 7 ounces. This preservative may he used over and over again with occa¬ sional filtering. The plates are best immersed in it. Aurine must be introduced into the plain collodion, or else a hacking must he given, to prevent blurring. Por the development of these plates, the following solutions must he prepared:— 1. —Carbonate of ammonia* 4 .. Water 2. —Bromide of potassium .. Water . 3. —Pyrogallic acid ... Alcohol ... 64 grains 1 ounce 4 grains 1 ounce 96 grains ... 1 ounce With any preservative which is soluble in alcohol the plates should he flowed over with spirits of wine diluted with twenty to thirty per cent, of water (which may used over and over * Liquor ammonia twenty drops^ water one ounce, may be substituted if necessary. 80 again). When well soaked into the film, and the aurine removed, a thorough washing must he given/" Then mix the developer in the following proportions :— Ho. 1 Ho. 2 !S T o. 3 Water (distilled) Spirits of wine 60 minims 60 7? 2 drachms ^ drachm The plate is covered with this in the usual manner, and worked about. As the detail appears, more ammonia (Ho. 1) is added with half the quantity of bromide (Ho. 2). The following paragraphs are from Colonel Wortley’s direc¬ tions for development, and are worthy of attention:— “ According to the way in which the plate comes out, you will see whether the exposure and development have been right. If the plate flashes out at once on the application of the deve¬ loper, it is over-exposed, and more bromide should he added at once, to control the development. If, on the contrary, the negative remains for thirty or forty seconds without the picture appearing, it will he a sign of under-exposure, and from ten to twenty drops of Ho. 1 may he added to the developer. “It may be that some pictures taken in a weak light may require -much forcing: if so, remember to add the same pro¬ portion of Ho. 2 with Ho. 1. If the plate is very clear, and devoid of detail, it may he permissible to add a few drops of Ho. 1 without any Ho. 2. Bear this rule ever in mind. If you wish the plates to work more quickly, reduce the bromide in the developer; if there is any tendency to fog, increase the bromide or decrease the exposure. “On any dark spot in the picture, where there is a dark shadow, pour the solution constantly, which will soon bring out the detail. It is frequently very useful to pour the developer off the film, and leave the negative on the developing-stand, with no solution on it, for a minute or two at a time, as that assists to bring both detail and density. In pouring off the developer, rock the plate, so that the former does not run in lines. I may here note, that when a plate has had too short an exposure, or the subject badly lit, it is well, if the first lot of developer appears to have exhausted its action, to make up a * If the plates have “backing,” it should be removed previous to the washing. 81 second quantity by adding to the four drachms of water ten drops of No. 3, thirty drops of No. 1, and twenty drops of No. 2 ; continuing to add No. 1 freely with the same proportion of No 2 till the negative is finished.” It is probable that this development will give insufficient density, unless the plates be prepared with an excess of bromide, or with some organic salt of silver (as in the case with certain new ammonia plates). The ordinary pyrogallic acid intensifier may be employed with a thirty-grain solution of silver. Either sodium hyposulphite or potassium cyanide may be used as fixing agent. Intensification may be carried on after fixing if required. This, perhaps, is a safer plan than doing so before. WASHED EMULSION PROCESS. Whex to a soluble bromide in collodion silver nitrate has been added, and an emulsion of silver bromide formed, there remains as the result of the reaction nitrate held in solution, or perhaps in minute suspension; If the emulsified collodion were applied to a plate, and allowed to dry in this state, there would be a crystallization of these nitrates, and unless they were removed the film would be in an unsatisfactory state for removing the image. Washing the film of course effects this ; but recently it has been proposed by Mr. King to remove the nitrates by dialysis, and also by Mr. Bolton, one of the originators of the colloclio-bromide pro¬ cess, by washing the emulsion previous to coating the plate. This allows the plate to be prepared by the simple application of the collodion. The method of dialysis is very neat and scientific in principle, but it is not likely to be so much employed as Mr. Bolton’s method; the latter will therefore be given in detail. The pyroxyline is prepared at high temperatures, the salts dissolved in the collodion, and the silver nitrate is added in the manner to be immediately described. The collodion containing the emulsion is next poured out into a flat dish, to a depth not exceeding a quarter of an inch, and the ether and alcohol allowed to evaporate till the collodion sets, but not till it dries. This is best attained by continually stirring up the mixture with a glass rod, and the evaporation is materially aided by placing the dish over a water bath. When set, any preservative with which it is desired to impregnate the e 82 emulsion is poured on it, and the gelatinous mass ploughed up •with the rod into flakes. The contents of the dish is now bodily transferred to a jar, and left (with an occasional stir) for fifteen to twenty minutes. The jelly is next drained and washed for two or three hours, and finally dried spontaneously, or very gently oyer the water bath. To re-emulsify, the dried collodion pellicle is covered with the proper amount of ether and alcohol, and shaken at intervals till it is dissolved in them. It should be noted that the absolute dissolution of the dried pyroxyline sometimes will take a couple of days or more to accomplish, though twelve hours is sufficient to give a smooth mechanical mixture. By transmitted light it should be invariably of a red orange colour. The plate can now be simply coated with the emulsion, and when dried is ready for use. The first solvents of the collodion may be methylated, and not so concentrated as those employed finally. There are almost as many modifications of this process as there are preservatives, but the above will indicate the method of procedure in all. CAREY LEA’S PROCESS. As an example of this method, it has been thought that Mr. Carey Lea’s might be taken as a representative one, that dis¬ tinguished photographic chemist having been able to emulsify silver iodide together with the bromide and the chloride. The collodion is made as follows :— Ether *730... . Alcohol -805 Pyroxyline... Cadmium bromide (crystallized) Ammonium bromide Ammonium iodide ... ^Copper chloride Aqua regia ... ounce • i 4 5 > 8 grains 6J „ ix A 2 9) 2 drops The emulsion is formed by adding to the above 20 to 25 grains of silver nitrate dissolved in half an ounce of alcohol. The additions should be made little by little, shaking between each. After the emulsion has been allowed to ripen for twenty-four to thirty- six hours, care being taken to shake the bottle containing it * Cobalt chloride has been substituted for this salt, and is said to give better results. Hydrochloric acid (2 drops) may be substituted for it, and also for the aqua regia. 83 thoroughly at intervals, it will be found to be p erfectly smooth and creamy. It is then poured into the dish, an d allowed to set as before described. The following preservat ive is the one recommended by Mr. Carey Lea :— Thick solution gum-arabic with a little sugar 1 ounce Prepared albumen ... ... ... ... 1 ,, Gallic acid (in 1 ounce of alcohol) ... ... 60 grains Tannin (in 1 ounce of water)... ... ... 60 ,, Water ... ... ... ... ... ... 12 ounces The albumen is prepared by the addition of an equal bulk of water to the white of an egg, clarifying with twelve drops of acetic acid to each ounce. The solution after filtering through sponge is that referred to in the above formula. The ordinary beer preservative, as given for Canon Beechey’s process (page 76), is effective, also the albumen beer as described at page 72.* Exposure .—The exposure is about double that required for a wet plate. The development/recommended by Carey Lea is as follows :— 1.—Pyrogallic acid ... ... 4 grains Water ... • • • ... 1 ounce 2.—Potassium bromide • • • ... 15 grains Water ... • • • ... 1 ounce 3.—Ammonium carbonate ... • • • ... 80 grains Water ... ... 1 ounce To 3 ounces of water add 1 ounce of Ho. 1 and 15 minims of Hos. 2 and 3. The detail will gradually develop. When per¬ fectly apparent, the same quantities of Hos. 2 and 3 again are added, and so on till sufficient density is gained. The development may also be carried out by any of the methods indicated for the particular preservatives. A very useful emulsion process is that made as above, using the following formulae :— Methylated ether ... 1 ounce Methylated alcohol... i Pyroxyline, high temperature 6 to 8 grains Zinc bromide ... 10 Aqua regia ... ... 1 drop * When the larger proportion of silver nitrate is employed, Mr. Carey Lea recommends the addition of one-tenth the hulk of the preservative of dinary acetic acid. 84 To this is added (after solution in half-ounce alcohol -830) fourteen grains of silver nitrate, shaking well as the addition is made. The emulsion is then treated as above, and re-emulsified in equal parts of ether and alcohol -830. There are several firms which supply prepared collodio- bromide and collodion dry plates. The Liverpool Dry Plate Company, St. John’s Hill, Clapham Junction, supply colloclio-bromide plates, and also an emulsion ready for use. The latter is made by the washed collodio- bromide process, and requires no application either of water or preservatives. Messrs. Chambers and Co., 251, Goswell Road, London, E.C., supply the latest form of the uranium dry plates; and Messrs. Rouch likewise supply collodio-bromide plates which give very satisfactory results. Collodio-albumen plates are obtain¬ able from J. Pollitt and Co., Barlow Court, Market Street, Manchester. "With all of these full directions for exposure and development are sent out. The photographer will often find the possibility of the purchase of any of these dry plates a boon when too busy to prepare his own. Mr. L. Warnerke has formed a substitute for glass which promises to be of great use for photography in the field. He coats ordinary stiff paper with thin solutions of india-rubber and collodion (see the heliotype process for the kind of collodion em¬ ployed) alternately till a thickness of the substratum is about that of a thin sheet of paper. This he coats with washed emulsion in collodion, and exposes in the camera. To develop his negatives he turns up the edges of the paper to form a little dish, and applies the solution in the ordinary manner. When fixed, washed, and dried, the india-rubber collodion bearing the image is pulled off the paper, and the negative picture is on a flexible support which can be printed from either side. The picture may also be developed on a glass plate by stripping the paper off before that operation. THE GELATINO-BROMIDE PROCESS. In the gelatino-bromide process the employment of collodion is obviated, gelatine being the vehicle in which the’ bromide emul¬ sion is held in suspension. There seems to be a certain advantage in using gelatine, as the sensitive salts are in a much minuter rate of subdivision than in collodion. It may be taken as an 5 axiom that the smaller the particles the greater effect will light have on them, and the greater the facility for development. The following is .Mr. Kennett’s mode of preparing these plates, and as in his hands the negatives are everything that can he desired, it has been thought that it would be preferable to give his method, rather than any other of the various modifications published. One pound of Nelson’s gelatine is soaked in 100 ounces of distilled water, and after it is completely swelled, the jar containing it is heated and solution effected. While still hot, 8^ ounces of potassium bromide are added to and thoroughly incorporated. Next 11^- ounces of silver are dissolved in the least possible quantity of water, and poured into the jar little by little with constant stirring. In the state in which the emul¬ sion is at this time it is insensitive, owing to there being an excess of potassium bromide ; but in all subsequent operations non-actinic light must be employed. The emulsion is poured out into a dish, as described at page 81, and allowed to set, when it is cut into strips and washed in a large number of changes of water (say for six hours). When thoroughly washed free of all soluble salts, the gelatine may be dried by evaporating out the water by heat till it is of the consistency of paste, when it is allowed to set, and finally dried. In this state it will keep any length of time, and Mr. Kennett has obtained a patent for this part of the process. Take at the rate of forty grains pellicle to each ounce of distilled water, and allow them to stand in a bottle. When faWAed, dissolve by aid S of heat, and shake. The plate is warmed, and the solution poured on it as with collodion, and returned to the bottle, and is then placed on a level shelf or table, and the gelatine allowed to set. It is finally dried in a drying closet, the operation being accomplished in about two to three hours. Exposure .—These plates are very rapid, being equal to wet plates, and the addition of an excess of silver salt, which is soluble in ammonia, has been found by the writer to make them excessively sensitive. A half grain of benzoate of ammonia to each ounce of solution before washing was hence found to give great aid. Tor Kennett’s rapid plates, and for the plates prepared with an excess of silver in the shape of the benzoate, the following mode of development is adopted. 1.—Pyrogallic acid ... ... ... 4 grains Distilled water ... ... ... 1 ounce 86 2.—Bromide of potassium 1 drachm Water . ... 8 ounces 3.—Bromide of potassium ... 20 grains Water ... . ... 10 ounces 4.—Ammonia ... 1 drachm Water . 8 ounces 5.—Gelatine* ... ... 20 grains Water ... 10 ounces (It is better to mix Nos. 2 and 4 together.) The plate is first allowed to soak for five minutes in a dish of Ho. 3. (It is advantageous to keep the temperature up 60°.) To this solution in the dish is next added one ounce of Ho. 5, and after well soaking the plate is drained, and the developing solution applied. To every ounce of Ho. 1, one drachm of the mixed 2 and 4 is added, and flowed over the surface. The detail should appear gradually and quietly. When well out, more of Hos. 2 and 4 may be added till sufficient density is obtained. In case the whites still are too transparent, the ordinary pyrogallic inten- sifier (page 22) may be resorted to. Tor perfectly neutral plates the development is carried out in a similar manner, with the exception of the preliminary soaking in Ho. 3, for which plain distilled water is substituted. The fixing solution is usually sodium hyposulphite (see page 26). The plates and pellicle are supplied by Mr. E. Kennett, 8, Maddox Street, Eegent Street, London, and full particulars are issued with both for development. The colour of the deposit on these plates is very deceptive, being of an olive green tint, and the absolute density is not nearly so great as ordinarily requisite with dry plates. The develop¬ ment must take place in very subdued light, as the emulsion is excessively sensitive even to orange, and slightly to red light. Blisters sometimes make their appearance, through the water used in developing being too cold. The great advantage of the gelatine film seems to'lie in its extreme sensitiveness. PAPEE HEGATIYE PEOCESSES. The following are modifications of the original calotype pro¬ cess, which has yielded excellent results in many hands. They are therefore given in detail. Large pictures may be produced * The gelatine is swelled and dissolved in the usual manner. 87 by it which can very nearly bear comparison with those produced with wet plate negatives. Calotype is convenient, owing to the small weight that it is necessary to carry. buckle’s process. The following process is the best of a variety:— No. 1.—Silver nitrate ... ... 35 grains Distilled or purified water ... ^ ounce No. 2.—Potassium iodide ... ... 35 grains Distilled water ... ... \ ounce Mix these two solutions,* and a precipitate will be formed, and if the above proportions of water be maintained the precipitate will retain a more solid and condensed nature, separating itself more readily from the supernatant fluid than would be the case if deficient quantities were used. The deposit of silver iodide should be washed in small quantities of water (one ounce to each washing being sufficient), as large quantities divide the deposit too finely. The method of washing is as follows. The super¬ natant fluid should be carefully decanted from the iodide, the fresh water should next be added, and the deposit briskly stirred in it with a glass rod. "When well settled the water should be decanted off as before. The operation of washing should be repeated three or four times. The iodide must now be redissolved by a solution of iodide of potassium in two ounces of water. The best way of effecting this is to place the precipitated silver iodide in a two-ounce measure with the two ounces of water and six drachms of potas¬ sium iodide. This will not effect the solution of the silver iodide, but extra crystals of the potassium salt should be added till it is complete—that is, till the liquid is just not clear (i.e., in a semi-transparent state). Should this solution of iodide of silver be too powerful and too thick when coating the paper (which can be known by its deep sulphur colour instead of pale primrose on the paper), two-and-a-lialf ounces of water may be used instead of the two ounces. The paper to be used should be as tough and grainlcss as possible. Turner’s paper was the best suited for the process, * The potassium iodide solution should invariably be poured on the silver nitrate solution. 88 but at present it is not procurable. Good English paper of the consistency of medium Saxe answers as a substitute. Cut the sheet of paper into convenient sizes, and pin it by its corners on to a flat smooth board. Apply the solution with a flat cotton wool brush (or a brush as described for coating plates with a preliminary coating of albumen in the dry plate pro¬ cesses) evenly and plentifully. Let it dry paitially. Next wash the sheet in rain water, taking care to expel all air-bubbles, and, having agitated it, leave it in the water whilst a second sheet is coated. When this second sheet is ready for immersion, with¬ draw the first sheet from the pan and place it in a second dish (likewise containing rain water), and place the second sheet in the first pan, and so on. When well washed in the second pan the paper ought to assume a bright uniform yellow colour, tending to green. The washing will take from one to two hours. Pour off the rain-water and rinse two or three times, drain, and hang them up by one corner to dry. The paper in this state is nearly insensitive to light, and can be kept between leaves of a book or blotting-paper. In a dark room pin the paper to a board, as before described, having previously prepared— No. 1.—Silver nitrate ... ... 50 grains Distilled water ... ... 1 ounce Glacial acetic acid ... ... 80 minims No. 2.—^Saturated solution of gallic acid in distilled water. Take six drops of No. 1, to it add six drachms of distilled water, next add six drops of No. 2, and finally add from one to three drachmsf of distilled water again. The mixture should then be well stirred with a glass rod. Apply this solution lightly, but plentifully, with the cotton (or other brush) to the iodized paper, blot off the sheets in succession, and place two back to back with blotting-paper between them. * A stock bottle of gallic acid may be kept, filling up with water, and shaking well after any of the solution is taken out. If all air be excluded from the bottle, it will not turn brown or discolour. t Heat quickly decomposes a strong solution of Nos. 1 and 2, conse¬ quently the greatei the heat, the larger should be the quantity of water added. This method of mixing also prevents their instantaneous decom¬ position. . 89 In very hofc climates, twelve drops of No. 1 and seven, of No. 2 may be substituted with advantage for the proportions given above. A plate of glass of the size of the inside of the camera slide, and having the thickness of the supporting silver wires, having been selected, the corners should be broken olf. The glass should then be placed in the frame ; the back surface of it will now be on a level with the inside of the silver wires. On this plate place the sensitized paper, and back it with another glass plate. The paper will, when in the camera, coincide with the front of the ground glass. By attaching the corners of the paper by gum to one glass plate the use of the second may be avoided. Tor a fifteen-inch focal distance single landscape lens, full aperture, three minutes in bright light will suffice. This may give some sort of a guide for exposure with other lenses. Take the paper out of the dark slide, and pin it on the board as before. Apply equal parts of Nos. 1 and 2, with equal quantities of water, with the brush, and allow the developing action to proceed until it begins to flag. Next apply the solution of gallic acid; very lightly until the deep shadows begin to dim by transmitted light. The development must then stop, otherwise fog will ensue. This, however, may be arrested by placing the paper face downwards in three or four changes of water, allowing a quarter to half an hour between each change. If, on opening the dark frame, the image on the paper appear perfectly defined, and of a dimly red tint, it is a sign that the exposure has been too long. In this case use one part of No. 1 to two parts of No. 2. Should under-exposure be suspected, two parts No. 1 to one part of No. 2 should be the proportions used. On foliage or dark shadows which do not develop readily, the same proportions of Nos. 1 and 2 should be applied. The brush should then be dipped in the solution con¬ taining the ordinary proportions, and be passed over these, together with the other parts, to equalize the development, and to prevent marks arising from the use of the different proportions. The negative is fixed by immersing the developed picture in Sodium hyposulphite ... ... 2 ounces Water .32 ,, The fixing is complete when all the yellow of the iodide has 90 disappeared. This will usually take about half an hour. The paper negative must he washed for two or three hours in running, or frequent changes of, water, and dried spon¬ taneously. The negative, when dried, is ready for waxing. A flat iron should he warmed, and a small cake of pure white wax he brought in contact on the hack of the negative with its point. The heat melts the wax, and, hy moving the iron, the melted wax can he spread over any desired portion of the picture. Elotting-paper should he then placed over the negative, and the hot iron passed over the surface of the blotting-paper till all superfluous wax he removed. The negative is now fit for printing purposes. It is usual to wax the whole of the negative, with the excep¬ tion of the sky. Unless the sky he very dense, any portion of it that has been waxed will have to be rendered opaque with indian-ink or some equivalent. Sensitized calotype paper will only keep two or three days. The quicker it he employed after sensitizing the better will he the result. The paper which has been coated with iodide, hut not sensitized, will keep for an indefinite period if protected from light. Greenlaw’s process.* Uirst examine and select thin negative paper, and reject all that show any irregularities, holes, patches of unequal density, &c.; that recommended for Euckle’s process will answer. Make a solution of— Potassium iodide ... ... ... 1,000 grains Potassium bromide... ... ... 300 ,, (Por much foliage the latter may he increased to 450 grains.) Distilled water ... ... ... 40 ounces and add enough of pure iodine to give the solution a dark claret colour. Then filter. Into this place as many sheets of paper as you can with ease, being careful that no air-bubbles exist. Allow the paper so immersed to rest for one hour ; then turn the whole upside down, and hang the sheets up to dry, taking off the last drops with white blotting-paper. This may be done in diffused light. * Taken from the Year-Book or Photography for 1870. 91 "When dry, place sheet over sheet evenly in a portfolio in which no other papers, except blotting-paper, are placed. They will then he iodized a dark purple, which will keep any time. They, however, turn a light brown colour. Be sure, iu working, that nothing touches the paper, for the very slightest touch will cause a stain in the development. Silver nitrate... ... ... ... 2^ ounces Glacial acetic acid ... ... ... ,, Distilled water ... ... ... 40 ,, Now float a sheet of your iodized paper on this (smooth side downwards) until the purple shall have turned an uniform yellow, which is silver iodide. Allow it to rest for one minute; after this, remove and immerse in distilled water, where it should remain for two or three minutes; if to he kept for some time, remove to another dish of distilled water. Place now on clean white blotting-paper, face upward, and remove by blotting-paper dll moisture from the surface (these sheets can he again used for ironing out the wax by-and-bye); then place between blotting- paper, or hang up to dry; when quite dry, place in your dark slides. Gallic acid ... ... ... ... 200 grains Spirit of camphor ... ... ... 1 drachm Distilled water ... ... ... 40 ounces This is a saturated solution of gallic acid; unless preserved from the air it decomposes; the spirit of camphor is added to preserve it. When about to develop, filter, and add to every five ounces one drachn^of the following solution :— Silver nitrate ... ... ... ... 30 grains Glacial acetic acid ... ... ... f drachm Distilled water... ... ... ... 1 ounce Pour into your dish quickly, and immediately float the picture side of your paper, which is slightly visible on it, being very careful that there be sufficient liquid to prevent the paper touching the bottom of the dish. Constantly watch until the picture becomes visible on the back, and the paper has a kind of brown, greasy appearance. Continue the development until, in holding up a corner when the sky is before the light, you cannot see your finger when moved about between, the light and the paper. If it be not dark enough before the silver gallate 92 decomposes, you have under-exposed. Decomposed gallate of silver ceases to develop. Do not, when examining your paper, lift more than the corner, as an oxide of gallate of silver forms rapidly on the surface like a crust, and, on replacing your picture, it causes innumerable marble appearances; as also if yon do not place your paper speedily on the solution in the first instance. It may be removed by drawing a sheet of blotting-paper over the surface of the solution. Bemove to a dish of common water, and wash out the brown tinge caused by more or less decomposed gallate of silver. When well washed, yon may fix it by placing it in solution of sodium hyposulphite, one and a-half ounce to one pint of water, till every vestige of the yellow silver iodide be removed, after which wash in eight or ten different changes of water ; you Jiave then a fiae, clear, and dense negative. MISCELLANEOUS APPLICATIONS OE PIIOTOGEAPHY. INSTANTANEOUS PICTURES. The term “ instantaneons ” is merely a comparative term, and must be understood as expressing simply a very short exposure. In photographing street scenes, &c., short exposures are of the greatest use, and there are frequently occasions in art photography in which an accurate knowledge of the conditions for obtaining instantaneons pictures is essential. The plates must be excessively clean, as the shortness of the exposure and the strength of the developer used render the slightest chemical dirt apparent. A collodion containing a large amount of bromide is generally used, and it should be of a straw colour to give the best results. The addition of 1 to \ \ grains of bromide to the ounce of ordinary bromo-iodized collodion is advisable as a rule. It is recom¬ mended that the different samples of iodized collodion in stock should be tested one against the other, by means of the cut stereoscopic plate (as described at page 12), and the most rapid and delicate selected. A newly prepared bath (or nearly so) is an essential; the 40-grain (as described in page 15) will answer; a 50-grain bath will, however, ensure better results. With a higlily-bromized 93 collodion, the addition of a drop of concentrated nitric acid to the ounce of bath will often aid sensitiveness ; with a collodion poor in bromide this addition must not be made. If doubt exist as to the quantity of bromide, the more had better be maintained. neutral condition of the bath The iron developer Ho. 3 (page 18) is suitable. Two other formulae are given, both of which are effective. Ferrous sulphate ... 60 grains Water ... 1 ounce Or, Ferrous sulphate ... 60 grains Formic acid 1^ drachms Alcohol... ... quant, suff. Water. 1 ounce A pyrogaliic acid solution has also been used, viz.: — Pyrogallic acid... Formic acid Alcohol ... Water ... ... 20 grains 1 ounce 6 drachms ... 1 ounce It is of the greatest importance that the plate should he covered with the developer quickly. It matters little in this case if part of the free silver solution he washed away by the developer; in fact, it is advisable, as the lack of silver prevents too great a reduction on the higher lights before the detail is brought out. It generally happens that instantaneous pictures require no intensification. If they should require it, the iron and citric acid formula is recommended, as it brings out detail. Care must be taken that harshness is not given to the negative from trying to force out detail, and only really piling up the silver on the high lights without bringing up the half tones. With bath dry plates instantaneous pictures can be obtained, though with less certainty than by the wet process. The great essential with these is that they should be freshly prepared, and be raised previous to development to a temperature of about 100° Fah. This may be managed by immersing them in water of that degree of heat. The developer should likewise be warmed to the same temperature. England’s collodio-albumen process has answered well with the writer, the above precautions being 94 taken. "With. Col. Wortley’s uranium dry plates the ordinary mode of development may he adopted, using a larger dose of the ammoniacal solution. Rapid gelatine plates (page 84) have been successfully employed. A short-foeus lens, having a good defining power, with a large stop, should be preferred. A single lens has the additional ad¬ vantage of having the smallest number of reflecting surfaces. As examples of doublet lenses which are suited for copying, Tallmeyer’s rapid rectilinear, Ross’s symmetrical, and ordinary doublet may be mentioned. The best subjects for instantaneous photography are those in which there is but little contrast. Sea pieces and clouds form objects most suitable for artistic purposes. Trees are rarely rendered satisfactorily, owing to their non-aetinic colour. PHOTOGRAPHING THE INTERIOR OF BUILDINGS. Interiors are often most interesting subjects for the camera. A few hints on the manipulations, &c., when wet plates are used for photographing such subjects, are given. A collodion which has been iodized long enough to assume a dark straw colour, and to which a grain of bromide of cadmium has been used to each ounce, should be employed. Some photo¬ graphers employ two collodions, one newly-iodized, and the other very old. A first coating is given with the new, and, after setting, a subsequent one is given with the other. The plate should be coated as usual; but on immersion in the bath it should be kept in rather violent motion till all the greasiness has disappeared (which will be in about two minutes). It should then be taken out Very slowly, so as to drain completely. Tamp blotting-paper should be placed at its back, and the droppings absorbed in the slide by a strip placed at the lower edge. The plate may, by this-method, be exposed for a long time (two or three hours.) without staining or drying. The rationale of this is as follows :—The plate is kept in the bath long enough to change the iodizers into iodide of silver, whilst the bromide of silver is only partially formed. The free nitrate of silver left on the plate is absorbed by the bromizers to complete the change. This prevents the crystallization of the nitrate of silver on the film. The nitrates of cadmium, &c., formed, being very deliquescent, retain sufficient moisture to prevent the film drying. 95 The exposure for an interior can rarely he too long. The same rule holds good as in ordinary wet-plate photography, viz., expose for the detail in the shadows. If the sun shines into the windows of the building, the light may advantageously he used, by the use of a looking-glass or tin reflector. Those parts in the deepest shadows are those to he illuminated by reflected light. The reflector should always be kept moving about, otherwise an opaque patch will be produced on the negative. Magnesium wire may he burnt in one of Solomon’s lamps, to take the place of the sunlight, the same method of procedure being adopted. When a window through which white light is pouring has to he included in the picture, a yellow cloth or blind should he placed over it till the exposure is nearly complete. This prevents halation or blurring. Ho. 3. Developer (page 18) should be used, the contrasts between the high lights and deep shadows being usually extremely marked. Intensification is rarely necessary; if it be, the ordinary formulae are recommended. It may happen, no matter what care is taken, that markings like slug tracks and oyster shells show with development. These may be caused by using too strong a bath, and also by the drying of the film. Generally they may be obliterated by brushing a fine tuft of cotton wool over the defective spots, either when the film is damp and kept covered with water, or when dry. The latter condition is the safer. The removal of the markings should, in all cases, precede intensification, as the silver deposited on them by means of the intensifier would be brushed off. This would leave the negative intensified at all parts except on those from which the deposits had been brushed. Another method, that has been suggested by Mr. Jabez Hughes, is to wash the plates after sensitizing, and after expo¬ sure to re-dip them. The plate, after having been fully sensitized, is placed in a dish of distilled water, and washed till all greasiness disappears. It is then drained, and placed in the slide, with blotting-paper at the back. After exposure, the plate is re-dipped in the bath for at least a minute, when it is developed in the usual manner. Another method is to wash the plate thoroughly after sensitizing, and float over it any of the given preservatives for dry processes, and develop by the alkaline or gelatino-iron 96 development. Perhaps the most simple preservative to employ is a wash of beer to which one grain per ounce of pyrogallic acid has been added. COPYING PLANS, ENGRAVINGS, ETC. A most important branch of photography is the copying of plans, sketches, &c. The greatest care should be exercised in the selection of lens and chemicals for the operation, success depending mainly upon them. Uo single lens should be used, owing to the curvature given to the marginal straight lines. This confines the choice to the landscape, doublet, and triplet, and to portrait combinations. Of these the doublets are the most satisfactory. With lenses obtained from first-class makers there is no distortion; the reflecting sur¬ faces are fewer in number than in the triplet combination, and therefore it is to be preferred. The triplet seems to have a flatter field ; in bright weather, therefore, when there is plenty of actinic light, it may be used with advantage. The triplet and doublet mentioned may be considered, par excellence , the copying lenses. Portrait combinations also answer; the general objection to them, however, is that the image is so concave as to be out of focus at the margin, unless one of large diameter - be used. Dallmeyer’s D lenses have less of this objection. "With a large stop they answer for portraits, whilst with a smaller one they answer for copying purposes. USTo. 6 D lens, by the above maker, will answer for copying plans on an 18 by 15 plate. If a lens of this size be not at hand, the above maker’s- rapid rectilinear or triplet (for 18 by 15) may be substituted. If the plan have to be reduced by photography with the aid of a portrait combination, it is preferable to have the front lens next the plan to be copied; if it have to be enlarged, the combi¬ nation should be inverted, and the back lens placed in front. Unless a special camera be employed, the rendering the image- of the plan, &c., to be copied of a particular size entails consi¬ derable labour in shifting the board on which the plan, &c., should be fixed. The following mode of attaining parallelism to the focussing screen answers well. On the centre of the board on which the drawing, &c., is to be fixed, a small mirror may be temporarily fixed. This latter should be strictly parallel to the surface of the board. The point corresponding to the centre of the Ions should be accurately marked on the ground glass. On the lens 97 itself an open cap should be fitted, furnished with two cross threads, intersecting on the prolongation of the axis of the lens. The image of these cross threads will be reflected by. the mirror, and should be focussed. The board should then be tilted or slewed round till the image of their intersection coincides with the point marked on the ground glass. The board will now be parallel to the ground glass ; the mirror being removed, the drawing may be fixed on to it, and focussed as usual. A neat stand for the board will readily suggest itself, by which it may be moved parallel to the position thus fixed, so that the distance necessary to give the exact size required may be attained. The mirror may be let-in flush with the board, thus obvia¬ ting the necessity of its removal for fixing up the drawing. A direct light, coming in an horizontal direction, is generally to be preferred for copying, as the texture of the paper is hidden by it. If a vertical, light be used, the shadows of the irregula¬ rities on the surface of the paper, being copied, may mar the purity of the whites.* 4 Should the plan be shaded in flat tint, it may be necessary to copy it in direct sunlight, as Indian ink and sepia, and some other colours, are of such a non-actinic nature as to make but slight impression on the sensitive film; strong light lightens up the shades, which are only dark by comparison. .For like reasons,' plans or engravings on paper which, through age or other causes, has turned yellow, should be copied, if possible, in a similar light. The light for copying oil pictures should come from the direction in which the light has been _ supposed to come in the picture itself. A painter “ loads ” his canvas in such a manner as to give the best effect to his picture when viewed in that particular light. For copying pictures in plain black and white, a simple iodized collodion is recommended by many skilful photographers. In practice it has been found that a bromo-iodized collodion yielding intense negatives answers well for ordinary work. The addition of a grain or two of pyroxyline (or, better still, papy- roxyline) which has been washed in dilute ammonia will often cause a limpid collodion to become fit for copying purposes. * In copying certain classes of drawings the writer has found that light admitted through a funnel-shaped box, formed of tissue-paper stretched on laths, prevents the irregularities of the paper showing. In copying prints from albumenized paper, &c., the same procedure may be followed. H 98 The alkaline reaction in collodion gives intensity, and this is further increased by the addition of the pyroxyline. If a paint¬ ing, either in monochrome or colours, have to he reproduced, the ordinary bromo-iodized collodion is recommended. The bath should be free from any impurity, and may be of the ordinary strength. Tor plans or line drawings, developers Nos. 1 and 8 (pages 18 and 19) are recommended. The iron may be used even weaker than in No. 1, and may be as follows Terrous sulphate Glacial acetic acid Alcohol ... Water ... 5 grains 10 minims quant, suf. 1 ounce With a simple iodized collodion, pyrogallic acid may be resorted to as a developer. Should this be decided upon, half the acetic acid given (formula, page 17) should be added, other¬ wise the deposit may become too crystalline in form. In winter, or when the light is weak, the iron developer should invariably be employed. Tor ordinary paintings a twenty-grain developer may betaken as a standard solution; a stronger or weaker one may be neces¬ sary, according as great or little contrast is desired. Negatives of plans drawn in lines should never be fully deve¬ loped, and they should be slightly under-exposed. When the reduction on the whites has taken place, the developer should be washed off and the negative fixed. By this method deposit on the lines is avoided. The negatives will require intensification. In rare instances the simple application of the iodine solution (page 22), followed by the pyrogallic intensifier, will suffice. Should this, however, not give sufficient density, either Nos. 6, 7, or 8 (page 22) may be tried in addition. The last three should be again followed (after the negative has been well washed) by 9, 10, or 11. If No. 6 be used, the negative should be placed in the sunlight for two or three days, when it will be found that the whites have become perfectly non-actinic. With No. 7 it is convenient to immerse the negative in the solution contained in a flat dish, and it should be left till the film has acquired a white appearance by transmitted and reflected light. If, after Nos. 9, 10, or 11, shall have been applied, the 99 whites are not sufficiently dense, pyrogallic acid intensifies may he applied, and after intensification proceeded with as before. It requires considerable practice in manipulation to prevent (1st) a deposit forming on the lines from the pyrogallic acid in¬ tensification, or (2nd) the lines from becoming filled up by the deposit of mercury and silver. It is safer, after using a solution of mercury, to let the nega¬ tive dry spontaneously. Rapid drying is apt to cause the film to split. The ordinary procedure of wet-plate intensification should be carried out in copying paintings. For copying, it is useful to know the equivalent focus of a lens, ashy it the distance of a plan, &c., from the lens may be known. To determine it, see Appendix. PRODUCTION OF TRANSPARENCIES. The production of positive transparencies on glass from a negative is necessary, as a rule, for the multiplication of negatives, reversed or otherwise. The following are modes of oduction by the camera or by contact printing. When it is determined to use the camera, if a proper copying camera be not at hand, the following substitute may be employed. A is any ordinary rough box, the top of which is removed. Out of the bottom is cut a rectangular portion, B, just large enough to hold the negative from which the trans¬ parency is to be obtained. Small pieces of wire are placed across the angles to support the face of the negative. When the latter is placed in position, a couple of pins inserted at the top and bottom of the outside of the opening will prevent it from slipping. Placed as shown in the figure, with the light from the 100 sky showing on B, or else reflected through it by a mirror or a perfectly smooth sheet of white paper, a transparency may he obtained merely by treating the negative as if it were a place, &c., to be photographed. It has usually been considered that the box holding the negative and the camera ought to be con¬ nected together, no diffused light having access to the front of negative. In practice this is found unnecessary, and where the negative is dense the diffused light is absolutely an improvement. Should it be very weak, a couple of battens placed across the interval, and a cloth thrown over it, will exclude all extraneous light. Another mode of obtaining transparencies is by using an opening (through an outside wall) in the dark room to hold the negative, and placing a table level with it to hold the camera. A mirror placed at about -45° with the horizon, and covered over with plate glass as a protection from dust and rain, reflects the clear light of the sky through the negative. It need scarcely be said that the focussing should be very carefully attended to; a common pocket magnifier is useful to attain extreme definition on the ground glass. The negative for a brilliant transparency should be slightly less dense, if possible, than for good printing. It is, however, by no means to be inferred that a negative of even great density cannot be copied, but only to be understood that this class will give the finest results. The use of a highly-bromized collodion is to be recommended. For ordinary printing-negatives the addition of one grain of bromide to the ounce will suffice; for a negative of the weak type the bromide may be omitted; whilst for a dense negative the bromide may be added up to three grains per ounce. The bromide should be added five or six hours before the collodion is required. The exposure should be long enough to cause the minuted detail in the negative to be apparent in the transparency. On drying, the points of bare glass should be very few ; if it be not so, it may be taken for granted that the exposure is too short. No fixed rules can be laid down for the length of exposure; the operator must use his judgment. The development is carried on with a very weak developer, the strength varying with the density of the negative to be re¬ produced ; the denser the negative, the stronger the developer 101 should be. For a negative of medium density the following may be used :— Ferrous sulphate Glacial acetic acid ... Alcohol Water 5 grains 5 minims quant, suf. 1 ounce For a very dense negative the ordinary 20-grain iron developer (page 18) may be used. Should there be too much contrast, add more bromide to the collodion, and use a stronger developer; if too little, diminish the quantity of bromide, and use the weak developer. Intensification may be carried on to such a point that on looking through the glass the deepest shadow appears nearly opaque. The transparencies should be fixed with sodium hyposulphite (see page 26), in order that the delicate details may not be eaten away in the slightest degree. The ordinary colour given by silver is not an agreeable one, and it is generally necessary to tone the image. This may be effected by a platinum salt, a gold salt, or iridium salt, or by a mixture of any or all of them. The formulae are as follows:— Ho. 1.—Ten-grain solution of platinum- tetra-chloride ... Nitric acid Water 1 drachm 12 drops 10 ounces Ho. 2.—Gold tri-chloride ... ... ... 1 grain Hydrochloric acid ... ... 6 drops Water ... . ... 10 ounces Ho. 3.—Iridium chloride ... ... ... 1 grain Hydrochloric acid ... ... 12 drops Water ... ... ... ... 10 ounces If a mixture in equal quantities by measure of Hos. 1 and 2 be taken and flowed over the plate, a pleasing tone will be given. When toning with gold a pink deposit is apt to form on the transparent portions, which spoils the effect. Sometimes the platinum solution by itself will give rather an inky colour. Transparencies may also be made by placing dry plates in contact with the negative in any ordinary printing frame. The exposure may be made by opening the windows in the dark room for a very short time (varying from half a second to 102 twenty seconds in dull weather), or it may be given by the light from a strong gas jet. With an Argand burner of 12-candle power, and with the frame six inches from it, an exposure of from six seconds to six minutes will be required, according to the sensitiveness of the plate for the particular light employed. With gum-gallic plates the colour given by development (if double the quantity of gelatine solution be added to the iron) will be generally of a warm black, which needs no toning. The collodio-chloride process may also be adopted. A glass plate should be albumenized round the edges, as for dry pro¬ cesses, and is coated with the collodio-chloride (page 126). When dry, the film is fumed by holding it over the mouth of a bottle containing ammonia, and moving it till the entire surface has received the vapour. The plate is now brought into contact with the negative in a pressure frame. If strips of paper be gummed on to the corners of each plate, it may be examined without danger of loss of register during printing; otherwise a tolerable guess may be made of the progress of exposure by opening half the frame and looking through the two plates. It will be found that the print on the collodio-chloride is not possessed of sufficient vigour. The necessary amount is given by flooding it with— Gallic acid ... Lead acetate Acetic acid ... Water 75 grains 50 „ 2 drachms 20 ounces To this a few drops of a twenty-grain solution of silver nitrate should be added. When the intensity* is sufficient, the plate is washed, and then fixed with weak sodium hyposulphate. The image may be toned as given above. Another method of producing transparencies is by carbon printing. The gelatine is transferred to glass (which has had a slight trace of waxing solution rubbed over it) instead of to the zinc plate. The picture in this case will be reversed,! * The intensity increases on drying, therefore a certain allowance must be ade. »*• f In producing transparencies in the camera, the same reversal may be effected by turning the film-side of the negative away from the lens. The glass must be absolutely free from flaws to give a perfect result. 103 which is an advantage in mounting, as the ground-glass protects the film. In mounting a transparency, some translucent substance must be placed behind it. Ground-glass is usually employed, the rough surface being placed on the outside. Another better method is to dissolve to saturation white wax in ether. Filter, and to each ounce of solution add another ounce of ether. Flow over the silver side, and allow to dry. After twenty-four hours the wax will give a beautiful transparency to the picture. With all except the carbon transparencies, the following may be substituted:— Flake gelatine ... ... ... ... 2 ounces Glycerine ... ... ... ... jounce Water ... ... ... ... ... 6 ounces The gelatine should be allowed to soak in cold water till it is thoroughly swelled, and then dissolved by placing the vessel containing it in hot water. Just previous to use, sufficient of the solution should be taken, and to the above amount two ounces of new milk be added, heated to 90° F.; the whole to be stirred together well with a glass rod, and sufficient of the mixture poured from a measure or jug through fine muslin to cover the plate, which must have been accurately levelled. It should be allowed to set, and then be dried spontaneously in a warm room. If the transparency be reversed the gelatine should be poured on the film side. When thoroughly dried (in the last case) the film may be stripped off, and it will carry the collodion pellicle with it. The picture may be cut out and bent to any form after varnishing; for instance, lamp-shades may be composed of a set of prints thus produced. If two hundred grains of zinc oxide replace the milk, we have Mr. Burgess’s Eburneum process. The solution, with the oxide added, should be kept warm, and allowed to stand six or eight hours before being allowed to solidify. The frothy top- layer, and the bottom layer containing the coarse particles, are removed, and the solution is to be re-melted and poured on the plate as above. About four ounces of solution should cover a 12 by 10 plate. REPRODUCTION OF NEGATIVES. In all cases (excepting when the reproduced negative is to be reversed) a rather thin transparency must first be made. Any 104 of the methods given in the last article may he adopted. The transparency is treated in the same way as the negative. From a carbon transparency, however, a negative cannot be made by contact printing, as, being raised in the high lights, the surface of the dry plate or collodio-chloride film is pre¬ vented from being in contact with the picture. It will be noticed that enlarged negatives can be produced either by making an enlarged transparency, or by enlarging the negative from it in the camera. In all cases of enlargement the camera must be employed for one or the other; but it is strongly recommended that the transparency be enlarged, as then only those defects due to the negative are magnified. The one exceptional case where a negative can be reproduced with¬ out a preliminary transparency is by the collodio-bromide process. The negative should be placed in the carrier in front of the lens, with the film side outwards. If a dry collodio-bromide plate be used, it is exposed and developed by the alkaline method, the development being carried on to such a point that the metallic (or oxide of) silver is apparent, in the deepest shades, by reflected light at the back of thp plate. A trace of fog is not objectionable, if the negative to be copied be very dense. The plate is not fixed , but dilute nitric acid (one of acid to one of water answers) is poured over the film. This dissolves away the reduced silver, and leaves a negative image formed of silver bromide. The plate is well washed, and a very dilute solution of ammonia is floated over the film to neutralize any acid. After washing thoroughly, the plate is taken into the light, and developed with the alkaline developer once more. This reduces the silver bromide to the metallic state, and gives the required negative. If too weak, the image may be intensified with pyrogallic acid and silver, as for a wet plate. The same procedure is taken if wet bromide of silver be used. A plate is treated with collodion containing eight grains to the ounce of cadmium bromide ammonium, or a proportion of each. It is sensitized in an eighty-grain bath for ten minutes, or the forty-grain bath for twenty minutes. After thorough washing, any one of the preservative solutions given for dry plates is flowed over it, and the exposure takes place whilst it is wet. The ordinary alkaline development is then proceeded with, and the remaining operations are as above described. 105 REVERSED NEGATIVES. For photo-mechanical printing, and single transfer carbon printing, reversed negatives are essential. Their production may he divided into three classes :—1st, reversed negatives taken in the camera; 2nd, negatives reversed by reversing the collodion films of the originals; 3rd, reproduction from other negatives. In the first case, the negative should be taken by means of a reflector, from a flat plate or glass silvered externally. The accompanying sketch gives an idea of what is required. E is the camera; L the lens; ACEH is the section of a hood round which is fitted a flange (FF) which can be screwed into the camera. A B is a mirror, as above described, which is placed at an angle of 45° with the axis of the lens, and so placed that the centre of the mirror is its continuation; D is a small door, which can be opened or shut at pleasure. The object to be photographed is reflected from A B to the lens, and a little consideration will show that the image on the focussing screen will give a reversed negative. The mode of silvering the mirrors is given in the Appendix. Another plan of obtaining a reversed image is by using a right- angled prism fitted on to the lens. A A is a flange that fits on the lens, taking the place of the cap; C C is a right-angled glass prism, whose breadth is equal to or greater than the diameter of the front glass of the lens. All the surfaces are enclosed in brass mounting, excepting C C, care being taken that the surface enclosing the right, angle is not in contact with the surface of the glass; E is a shutter for exposure; F F, screws for clamping E. 106 The image undergoes total reflection by the prism, and this gives a reversed negative. There is no particular rule for A. using either the mirror or the prism, excepting that both should be free from dust, and the former from tarnish as well. An ordinary negative may be reversed by transferring the film. The best method is that of coating it, whilst unvarnished, with a solution of india-rubber in benzole, of the consistency of collodion* (india-rubber paste dissolves readily in this men¬ struum). When drained, it is allowed to dry. Transfer collodion, made as follows, should then be flowed over the surface, and allowed to dry thoroughly:— Ether ... Alcohol-805 ... Castor oil Pyroxyline ... 5 ounces ... 10 „ J ounce ... i „ The plate should then be immersed in cold water for a few minutes, or until the film seems to become loose. Should this not take place in reasonable time, one ounce of sulphuric acid may be added to each gallon of water, which will aid the detachment. The film should be cut with a penknife round the edges, and should be stripped off gently whilst in the water. It should then be turned over and laid on a clean plate (or one slightly gelatinized, see page 55) whilst still floating. A soft squeegee, as for carbon printing, may then be used to expel the liquid between the two surfaces, and the plate should be set aside to dry. It may be varnished and used as an ordinary negative. About one grain to two grains to the ounce. 107 Reversed negatives may be produced from other negatives by the processes mentioned in the last article. They may also be produced by placing dry collodio-bromide plates in contact with the negatives, dissolving away the image with nitric acid before fixing, and proceeding as before shown. Also see Powder Process. PAPER ENLARGEMENTS BY DEVELOPMENT. Albumenized paper should be sensitized in the following bath :— Silver nitrate ... ... ... ... 40 grains Glacial acetic acid ... ... ... 30 minims "Water . ... ... ... 1 ounce and developed with gallic acid. The gallic acid solution may be made as follows:— Gallic acid ... ... ... ... 3 grains Acetic acid ... ... ... ... 5 minims "Water ... ... ... ... ... 1 ounce. The paper is immersed in a dish of this fluid, and the develop¬ ment takes place rapidly if properly exposed. Remembering that it is a positive print that is required, the purity of the whites must be preserved, and the development stopped before any deposit takes place on the highest light. When properly developed the print should be taken from the developing dish, and well washed. Any of the ordinary toning baths will give it an agreeable tone. It should be fixed, as usual, with sodium hypo¬ sulphite and water. Plain paper may be salted with— Sodium chloride ... ... ... 100 grains Hydrochloric acid ... ... ... 6 minims Water ... ... ... ... ... 12 ounces The paper is immersed for two or three hours, and then dried. It is then floated for three minutes on a solution of silver:— Silver nitrate ... ... ... ... 1 ounce Citric acid ... ... ... ... 8 grains Water (distilled) ... ... ... 8 ounces When moderately dry, the paper is exposed as before, by pinning it on a board, and placing it, after focussing, in the 108 camera or its substitute. A faint image of the negative should be visible, and then it may be developed by— Pyrogallic acid... ... ... ... 2 grains Citric acid ... ... ... ... 1 grain Water ... ... ... . 1 ounce Sufficient of this must be taken to well cover the paper (which * should previously have been stretched on a glass plate, by turn¬ ing the edges underneath it); in the flow no stoppage must be allowed whilst covering the surface. As soon as the proper contrast is obtained, the paper is well washed, and, if necessary, toned. The prints are finally fixed in— Sodium hyposulphite ... ... ... 1 ounce Water ... ... ... ... ... 16 ounces. They are kept in this till the high lights lose any trace of colour; they are then withdrawn from the solution, and washed in the ordinary manner (page 122). Artistic enlargements are also produced by taking an enlarged transparency of the negative and printing it on ordinary albu- menized or salted paper to a depth beyond that ordinarily necessary for silver printing. (See “ Silver Printing.”) The print is then fixed, washed, dried, and waxed (as described at page SO) for the calotype process. Enlargements on paper may also be effected by the calotype process, and call for no very special remark. A reversed paper positive, enlarged or otherwise, may also be obtained direct in the camera by a process due to Mr. Eox Talbot. Calotype paper is sensitized in the ordinary manner, exposed to light for a short time, then immersed in a solution of potassium iodide, and well washed. It is now exposed in the camera for ten minutes, and developed in the usual way with gallo-nitrate of silver. The resulting picture is a positive, supposing a positive has been copied. The same mode of procedure can be adopted with iodized plates. SILVEE PEIjSTTING. Silver chloride darkens when exposed to the action of sunlight, It assumes a deep violet tint, and, if it be immersed in water, traces of free chlorine will be found to have been liberated. 109 The light then, by its vibratory force, decomposes the molecule of silver chloride into a sub-chloride and chlorine gas. Chemi¬ cally, it is expressed thus— Chloride of Silver. Sub-chloride of Silver. Chlorine. ~2Ag cT~W li. Cl ' + ~cP Silver chloride is formed by double decomposition, similarly to the iodide (see page 2). It is soluble in sodium hyposul¬ phite, potassium cyanide, similarly to the silver iodide (as shown at page 25), and also in ammonia. When silver chloride has been acted upon by light, and the sub-chloride formed, the hyposulphite or other fixing agent re-converts the sub-chloride partially into silver chloride, and partially into metallic silver. Thus— Sub-chloride cf Silver. Chloride of Silver. Silver. “Tgt cT ' =T~Tg"ci '+ aT . The fixing agent dissolves the silver chloride, leaving the metallic silver unaltered. When silver nitrate is brought in contact with an organic substance, the resulting compound is found to be affected by light in a somewhat peculiar way: the compound slowly darkens to a reddish tint; the exact chemical reaction that takes place is very complex to trace, but it may be accepted that an oxide of the organic matter and silver is formed. This oxide is stable, unlike the silver oxide, and is not acted on by fixing agents to any great extent. It has been found that a certain proportion of the chloride in combination with the organic compound aids the rapidity of change of colour of the latter. If a paper be coated with albumen (say) in which has been dissolved a certain quantity of a soluble chloride, and floated on a silver solution, both chloride and albuminate^ of silver are formed. It depends, however, on the strength of the solution as to what proportions of each are present, owing to the fact that the organic compound is much slower in formation than the chloride, and has less affinity for the silver. If the silver solution be not sufficiently strong, the chloride may rob that portion of it with which it is in contact of all the silver before any (or, at all events, sufficient) albumin¬ ate has been formed, the molecule being composed almost entirely of silver chloride. The stronger the silver solution the more “ organate ” will it contain; whilst if it be very weak, 110 very little will be present. Hence it is that with albumenized paper which is weakly salted with a soluble chloride a weak sensitizing bath may be used, whilst if it be rich in the chloride it must be of proportionate strength. One other chemical reaction in printing must be considered— viz., that of the free silver nitrate, which is always present. During printing, as stated, the silver chloride becomes reduced to a sub-chloride, evolving chlorine gas. This chlorine has a stronger affinity for silver than has the nitric acid (with which it is in combination in the silver nitrate), and, consequently, it combines with the silver, forming new silver chloride,* which, in its turn, enters into a combination with the organate, liberating nitric acid. This freshly-formed organo-chloride, in its turn, blackens by the action of light, and adds to the strength of the image formed. If the free silver nitrate were absent, we should have the chlorine attacking the darkened organo-chloride of silver already formed,! and partially bleaching it. The result would be “measly” or mealy prints— i.e., prints in which minute red spots alternate with darker ones in the shadows after fixing. From the first part of this article it would be gathered that, as the silver sub-chloride is much more acted upon by a fixing agent than the product of the organate after it has been considerably affected by light, the molecules formed of the organo-chloride of silver, when only partially acted upon by light, would be much more easily attacked by the fixing agents than when fully acted upon. This is the case: the blacker an image formed by the organo-chloride becomes, the less it is attacked by the fixing- agent. As a consequence, the half-tones of a picture are attacked by it proportionally more than the shadows. The most important of the organic substances used in printing is albumen. It has been used hitherto in preference to any other organic compound, on account of the delicate film it forms on the paper free from all roughness, and also for the beautiful colour the print takes by the production of the albuminate of silver. The albumen should be used fresh, and in a slightly alkaline condition. The principal commercial objection to its employment in such a condition as the foundation of the picture * Probably together with hvpochlorous acid. f Thus, Ag 2 Cl -f Cl = 2Ag Cfileaving the organate of silver coloured, w p 1 ilst the subchloride of the molecule was bleached. Ill arises from the difficulty that is experienced in coating the paper evenly with it. Makers of paper prefer old albumen, which gives a slightly acid re-action. When in this last condition, the paper is easily coated, though the toning is retarded, and inferior pictures are the result. Gelatine is the next important organic substance to he re¬ marked upon. The organic silver compound formed with gelatine gives redder tones than the albuminate. In sizing it is fre¬ quently employed, and for pictures which it is intended should be of a reddish tone when printed, such paper may be used. Starch imparts a more purple tint to the picture than the foregoing. Those papers sized with this substance yield the pictures, on toning, of a blue tint. There are two kinds of paper principally used for albu- meniziag—Rive and Saxe. They both are starch-sized papers. The latter is much more porous, and consequently less glossy, than the former. Rive paper is, however, tender when wet, and tears easily when used in large pieces, such as required for large prints. Saxe, therefore, is preferred for large prints, whilst the Rive is admirably adapted for small pictures where great gloss is requisite. Saxe paper can be rendered nearly as glossy by doubly albumenizing and rolling. Other papers generally give inferior tones to those above specified, though they are constantly employed. Toning a Picture. —If a picture printed on albumenized paper or ordinary salted paper (see pages 113 and 115) were at once immersed in the fixing bath, the resulting colour of the image would be of a disagreeable foxy red. In order to remedy this, it is usual to tone the picture by means of a solution of gold. Supposing a print to be thoroughly washed, and immersed in a dilute solution of gold terchloride, the following phenomena would present themselves: the picture would gradually bleach, and a blue deposit would take the place of the more vigorous red image, and on immersion in the fixing bath it would be of a most feeble character. The reason of these changes is this: the chlorine from the gold would attack the silver subchloride, and while depositing as a metal, would in reality convert the image back to the state of chloride ; owing to one atom of gold com¬ bining with three atoms of chlorine, the deposited metal would 112 - be much, less than if the sub chloride had been split up into metallic silver and chloride by the fixing bath. Thus :— Silver Sub-chloride. Gold Chloride. Silver Chlojide. Gold. 3 Ag 2 Cl Au 01 3 ' = ^6 Ag Cf + aT In the second case we should have— Silver Chloride dissolved. Silver left to form the print. 3 Ag 2 Cl =' 3 Ag Cl ' + ' 3 A~g In order to avoid loss of vigour, it is usual to add some compound to the gold solution, and in certain cases to leave a small quantity of silver nitrate in the paper. "When free silver nitrate is thus present, the compound added to the gold should be a retarder in its action, that when the free nitrate of silver is wholly washed out the compound should be an active absorbent of chlorine. As an example of the first case, suppose the lime bath is used (see page 120), where we have a mixture of calcium hypochlorite and calcium chloride ; the latter acts as a retarder to the deposit of the gold, as the chlorine from each of these is nearly equally attracted to the silver nitrate. Hence the addition of chloride of lime naturally checks the too rapid deposition of the gold, and the consequent attack on the silver sub-chloride. As an example of the last case, where all the free nitrate of silver is washed out: sodium acetate has more affinity for chlorine than has the silver subchloride; hence there is but slight reduction in the depth of the print in fixing. It' has been assumed that the additions to the toning bath cause the formation of an oxy-chloride of gold. This may be the case, though the argument seems somewhat obscure. A simple experiment with stannous chloride added to the gold solution will give proof that the absorption of chlorine alone is necessary. Fixing the Print. —Sodium hyposulphite is almost invariably used as the fixing agent, and a strong solution is necessary to secure permanency of the print. The reason is that there are two silver hyposulphites which can be formed :— Silver Chloride. Sodium Hyposulphite. Double Hyposulphite of Silver and Sodium. Sodium Chloride. ’ Ag Cl and Silver Chloride. V Ha 2 S 2 0 3 Sodium Hyposulphite. — Ag Ha S 2 0 3 + Hyposulphite of Sodium and Silver. Ha Cl Sodium Chloride. ' 2 Ag Cl + 3 Ha 2 S 2 0 8 = Ag 2 Ha 4 3 (S 2 0 3 ) + ~2~Na Cl " 113 The first double hyposulphite is nearly insoluble in water; the last is highly soluble. These two salts may be formed for experiment, in the first case by adding an excess of silver nitrate to the sodium hyposulphite solution, in the other by adding a large excess of the latter to the former. With the first we have a dirty-brown precipitate; with the latter there will be a perfectly clear solution. The student is recommended to try the experiment. MANIPULATIONS IN SILVER PRINTING. Albumenizing Paper .—The following is a useful formula for albumenizing paper:— Ammonium chloride ... ... 100 to 200 grains Spirits of wine ... ... ... -§• ounce Water... ... ... ... ... 4J-ounces When these are thoroughly dissolved, fifteen ounces of albu¬ men* should be added. These ingredients then should be beaten up with a bundle of quills or a swizzle-stick. Constant shaking for half an hour in a bottle (holding about double the quantity of mixture prepared) will answer instead. Having allowed the deposit in the albumen to settle, it is filtered through a sponge placed in a funnel, and from thence poured into a porcelain or other fiat dish. The paper being cut into sheets of convenient size, the opposite comers of a sheet, the smooth side underneath, are then taken up by the manipu¬ lator (one in each hand), and a convex surface is given to it by nearly bringing the two hands together. The middle of the paper first touches the albumen solution, and the corners held by the hand are gradually brought down till the sheet floats on the liquid. The formation of air-bubbles on the surface of the paper is thus prevented, as they are squeezed out. The sheet should remain upon the solution a little over a minute, and should then be raised very gradually off by one corner, and hung up by two corners to dry. Two American clips answer for holding the paper whilst drying. Should bubbles be apparent, the paper must be floated again, till a uniform surface is secured. When dried, the prepared paper should be rolled and put way flat. * The eggs used must be nearly fresh. Each good sized English egg will furnish one ounce, whilst an Indian one will only yield five-eighths of an ounce on an average. I 114 Should the paper he floated much longer than stated ahoye, the albumen, being prepared with an alkaline salt, is apt to dissolve the size and sink into the paper. This would destroy the gloss PLAIN SALTED PAPER. Prints on plain paper are useful in certain instances. The formula for preparation is given :— Ammonium chloride ... ... 60 to 80 grains Sodium citrate ... 100 „ Sodium chloride ... ... 20 to 30 ,, Gelatine ... 10 „ Distilled water ... 10 ounces Or, Ammonium chloride 100 grains Gelatine ... 10 „ Water 10 ounces The gelatine is first dissolved in hot water, and the remaining components of the formulae are added. It is then filtered, and the paper is floated for three minutes, as in directions for Albu- menizing PapeT. If it be required to print on plain paper pi a hurry, a wash of citric acid and water (one grain to the ounce) may be brushed over the back of ordinary albumenized paper, and, when dried, that side of the paper may be sensitized and printed in the ordinary manner. For cold tones the wash of the citric acid may be omitted. Pesinized paper, which can be supplied by various manufacturers, may also be found useful for corners of maps and engravings. If the baths be new, and no injurious vapours be present in the air, sensitized paper will keep from a couple of days in hot weather to a week in cold. THE SENSITIZING BATH. A good standard for a sensitizing bath is as follows :— Silver nitrate ... ..! ... ... 50 grams Distilled water ... ... ... ... 1 ounce This solution is suitable for most albumenized paper of com¬ merce that is in the market when it is required to print from 115 good negatives of a fair density. The paper is floated on the sensitizing solution from about three minutes in hot weather to five in cold. The method of floating is similar to that given above for floating on the albumen solution. Care should also be taken to withdraw the paper slowly, as the capillary attraction will remove nearly all excess of silver solution, and thus prevent a waste by the droppings, and a loss of time in drying. The paper should be hung up from one corner by an American clip, and a small piece of clean blotting-paper should be attached to the bottom corner to collect the excess of solution. This blotting-paper should afterwards be placed with the paper residues. The sensitizing solution will, after a few sheets are floated, be found to be below strength. It should be tested by the argentometer (which indicates the number of grains on its stem), or by the method given in the Appendix. The argentometer is somewhat uncertain, as it also indicates the amount of albumen and salts dissolved in the solution. It is, however, sufficiently correct for ordinary use. The sensitizing solution, after a day or two, will be found to become discoloured, owing to the albumen dissolved in the liquid. The method of freeing the solution from it is given in the Appendix. When the albumenized paper is very nearly dry, but not so much so as to crack on unrolling it when it is removed from the clip, it should be placed in clean blotting-paper between boards, in order to be flattened for printing. Should a negative be found very hard, a slight modification of the sensitizing solution will be found beneficial, supposing the ordinary paper is to be used. Silver nitrate ... ... ... ... 30 grains Water ... ... ... ... ... 1 ounce The negative should in this case be printed in the sun. The more intense the light, the less contrast there will be in the print, as the stronger light more rapidly effects a change in the albumenate than if subjected to weaker diffused light. The reason for the reduction in quantity of the silver nitrate in the solution is given on page 109. To print from a weak negative, the sensitizing solution should be :— Silver nitrate ... ... ... ... 80 grains Water ... ... ... ... ... 1 ounce 116 The printing should take place in the shade ; the weaker the negative, the more diffused the light should he. If a negative he dense, hut all the gradations of light and shade he perfect, the strong hath, and, if possible, a strongly-salted paper, should he used. The printing should take place in sun¬ light. It may happen that with a very weak sensitizing solution the albumen may have a tendency to dissolve from off the paper; the addition of ten to twenty grains of sodium nitrate, or a drachm of alcohol, to the ounce, will prevent the evil recurring. WASHED SENSITIVE PAPER. A method of keeping it for longer periods (say for a week or a fortnight) without discolouring has been introduced. It is more sensitive, tones more rapidly, and gives more uniform results than the ordinary sensitized paper; still the negatives may he more than ordinarily weak, and good prints he obtained. The paper, sensitized as usual, is passed, not soaked, face downwards, through two or three changes of water,*' and hung up to dry. The pads of the pressure frame must he fumed with ammonia previous to using the washed paper, in order to produce a rich print—the reason, apparently, being that an alkaline salt of silver is formed on the surface of the paper, which replaces, as it were, the silver nitrate. The alkaline salt seems to he a better sensitizer than the acid or neutral silver salt. Colonel Stuart Worthy’s plan seems the best method of impregnating them with ammonia. He places all the pads to he used in a large box over¬ night, with a little strong ammonia in a saucer at the bottom of the box; by the morning they are sufficiently fumed. The sensitizing hath should, not he acid. If a small quantity of silver carbonatef remain at the bottom of the bottle holding the stock solution, the acidity is prevented. A little powdered chalk added to the bottle answers equally well. Colonel Stuart Worthy uses the following bath for sensitizing paper that is to be washed :— Silver nitrate ... ... ... ... 35 grains Lead nitrate ... ... ... ... 13 ,, .2 Sugar Water 1 ounce * All the free silver nitrate must not be washed away, otherwise the print will want in depth of tone. f The addition of sodium carbonate will form the carbonate of silver. 117 The washed paper may be stored between clean and dry blotting-paper, and pressed between two flat boards. The less ■air admitted to it the longer it will keep. DURABLE SENSITIZED PAPERS. In the market there are two or three permanent sensitized papers, Durand’s being the best known. They are printed, toned, and fixed in the usual manner. There is sometimes a slight lack of vigour in the resulting prints, however, which is partially overcome by fuming the pads as described above. Mr. Hopkins has adopted a method of preserving sensitive paper. He floats the sheets of albumenized paper on a 40-grain bath, as usual; then dries till nearly all the moisture is gone. He then places them between sheets of blotting-paper previously impregnated with sodium carbonate solution (about thirty grains to the ounce of water) and allowed to desiccate. The pile of paper he places under pressure, and withdraws the sheets as required. Another plan of keeping paper in a sensitive condition is by adding from twenty to forty grains of citric acid to each ounce •of nitrate of silver solution. Many find this to give good results, whilst others find a lack of vigour after toning. PRINTING THE PICTURE. Skill is required for obtaining the most perfect prints from any negative, and it is only by paying attention to trifling details that such happy results can be obtained. It should be remem¬ bered that no blind adherence to any rules will attain the object in view ; printing requires thought to be exercised, as well as clean manipulation. In the foregoing article several hints as to the light that should be used for different qualities of negatives have been given, but a little extra trouble bestowed may add to the beauty of the picture. Should a picture print too black in the shadows— i.e., attain a bronze colour—before the details in the lights have printed in, much improvement will be discerned by shading these dark por¬ tions This shading may be done either by placing temporarily j a paper, whilst printing, or gumming tissue paper, cut to the I proper shape, on the reverse side of the negative. On the deepest I shadows two or more layers of tissue paper may be gummed, till j the desired effect has been attained. In some cases cotton-wool 118 may be placed oyer a defective spot which prints in too quickly ; and, in extreme cases, where high lights are wanted, a skilful touch of the brush (using Indian ink or sepia) on the film side will give a piquancy to the print which would not be otherwise obtained. In landscapes there is frequently a want of atmosphere in the far distance and middle distance. In order to give it, the whole of the back of the negative should be covered over with tissue paper by means of starch, and when dry the shadows in the dis¬ tance should be made less obtrusive by means of a stump and powdered crayon. The foreground may be caused to approach by heightening its high lights. A golden rule to remember is, that the greater the distance of an object, the greyer the high lights, and less heavy the shadows. The sky in some negatives prints in too deeply : a mask, cut to the outline of the landscape, and slightly raised from the sur¬ face of the negative, will give a graduated sky, which, if left too white, may be subsequently improved by “sunning” down. This sunning down is generally carried out by means of a sheet of non-actinic paper or cardboard. This is moved gently over the picture, leaving the upper portion of sky more exposed to the action of the light than the lower portion, the landscape itself being always completely covered up. In many landscapes some secondary object, by the brilliancy of its high lights, may attract the eye. As the object of all artistic photography is to cause the eye primarily to dwell on the most important point, these bright spots, if they interfere with the effect of the picture, should be sunned down by shading all the print except that particular part. This may be secured by using a brown paper mask, cutting out the shape of the object to be toned down. Tor this object the negative should be removed, and a clean piece of glass substituted for it in the printing-frame. Transparent spots in the negative may be touched out on the negative itself. Gum should not be mixed with the paint used, for reasons given at page 41. Opaque spots in the negative print white in the print, and these can only be touched out on the print after it is fixed and dried. In toning operations the print loses depth, varying in a great measure according to the toning bath used. This loss of depth should be allowed for in the printing, the picture when taken out of the frame being considerably darker than when finished* 119 To judge the proper depth of colour to he given is, perhaps, one of the most difficult things in photography. Practice alone can determine when a print should he withdrawn from the frame. After the negative has been placed with the film side towards the back of the frame, a piece of paper the size of the plate should be placed on it. A felt or flannel pad should next cover the paper, and the back be placed over this. The pad is principally used to cause an equal pressure being exerted between the negative and the paper. Should the pressure be unequal, the paper will be found not to be in contact at places, and there will be a fuzzy appearance at those parts of the print. Even when pads are used, it is not unfrequently the case that this want of contact exists. If the paper have been dried in a moister, hotter, drier, or cooler atmosphere than that in which the printing takes place, this defect may ensue. In such cases it is a good plan to let the paper remain in the print¬ ing room half an hour before the printing commences, and to place the sheet of paper on the negative in the frame, with the pad behind it, not pressing down the springs on the back. The negative, of course, should be face downwards on the floor to prevent the passage of light through it. After five minutes or so the paper will become contracted or expanded sufficiently to enable complete contact to be maintained. A great source of defective prints is their examination during printing. The frame should never be opened in bright light, otherwise the whole exposed surface of the print may become discoloured, and the purity of the whites lost. When prints are removed from the frames, they should be stored in a dark box, or between leaves of red blotting-paper in a large book. TONING THE PICTURE. The following toning baths are found to give good results. Ho 1 is found to be very stable, and to give brilliant tones :— Ho. 1.—Gold tri-chloride ... ... ... 2 grains Chlorinetted lime (chloride of lime) 2 ,, Chalk ... ... ... ... 1 teaspoonful Water ... ... ... ... 16 ounces If the water be hot, the bath may be used when cool; if not a day should elapse between mixing and using it. 120 No. 2.—Sodium acetate Gold tri-chloride "Water To be mixed the day before it is used No. 3i—Chloride of lime Gold tri-chloride Chalk Sodium acetate Water 30 grains 1 grain 10 ounces 45 grains 45 „ 45 „ 180 ,, 15 ounces (These to be mixed together, without filtering, from seven to fourteen days before use. When required to use, filter out one ounce of solution, and add to eleven ounces of water.) !No. 4.—Gold tri-chloride ... ... ... 1 grain Sodium carbonate ... ... ... 10 grains Water ... ... ... ... 1 ounce May be used immediately. Other toning baths have been employed, but the foregoing are the principal used with albumcnized paper. Nos. 1, 2, and 3 will keep indefinitely. When the bath becomes inactive from lack of gold, it may be strengthened by a solution containing only one ounce of water to the above quantities of the other ingredients. No. 4 can only be used on the day it is made. According to the minuteness of the grains of gold, so will it assume, by reflected light, colours varying from purple to that of the ordinary yellow. The organo-chloride of silver appears through this layer of gold, and the colours of the two mingling together give the different tones in ordinary prints. When a print is over-toned it becomes blue. This is due to the greater amount of gold deposited over the surface of the silver. The change in colour on the immersion of a print in the fixing bath is due to the solubility of the silver chloride. £. With all the toning baths, excepting No. a little of the free silver nrtratc should be allowed to remain in the print—that is, before being immersed in the toning bath, the prints should not be too thoroughly washed (see page 111); whilst with the acetate bath it can be shown that all the soluble silver salt should be got rid of. In the first case, the prints should be washed in two changes of water, and the last change should show 121 decided milkiness/* The paper is immersed in the water, albu- menized face downwards, to prevent the silver chloride or carbon¬ ate (that may be formed from the chlorides or carbonates in the water with the free silver nitrate) being precipitated on the surface of the print, and the gold being deposited on it. Should there be a deposit on the print, it is dissolved away by the fixing bath, and leaves minute spots untoned. The toning bath should be sufficiently large to contain a couple ■of the largest prints side by side. Ko more should be immersed in it than can be conveniently turned over without risk ; eight or - nine medium-sized prints are generally found sufficient. The bath should be given a continuous and gentle rocking motion, allowing the solution to flow over arid between all the prints immersed. This prevents any two prints sticking together, and the consequent want of tone on those parts which have been in contact. The print must be toned a little further than it is intended to remain ; for black tones a slight blueness must be perceptible. In all cases, however, it should possess a rich colour before fixing. It is a good plan to allow the prints to tone face downwards, all deposit of silver chloride formed from the free silver nitrate being by this means kept from their faces. FIXING THE PRINT. The usual strength of the fixing bath is— Sodium hyposulphite ... ... ... 4 ouncesf Water ... ... ... ... ... 1 pint Between toning and fixing it is well to wash the prints slightly. After taking them out of the toning bath they should be placed in a dish of water, face downwards, till a bath is ready for fixing. It will be noticed that the toning action on the print continues during this washing, presumably by the solution of gold contained in the pores of the paper continuing to deposit. The addition of a small quantity of common salt has been found useful to stop this action. If this precaution be not taken, the prints first toned should be left redder than it is intended they should * The milkiness is only perceptible when the water contains chlorides or carbonates. t One ounce of sodium hyposulphite will fix with safety three sheets of paper. 122 remain. The action can also be arrested by acidifying the water. This is dangerous, as the presence of acid in the fixing bath causes a speedy decomposition of the liyposulphitc. The prints should be immersed in the fixing bath for twelve or fifteen minutes.^ The solution should be kept in motion during the whole time of fixing, as for toning. Care should be taken to brush off all bubbles that may cling to their surfaces, as the cushion of air impedes the access of the liquid to the silver salt. When the prints are fixed they will appear colourless in the whites, and free from red patches in the dark portions. In some establishments it has been found advantageous to add a drachm of ammonia to each pint of fixing solution. The ammonia aids the rapidity of fixing, and neutralizes any acid that inadvertently may find its way into the solution; it also attacks the size of the paper, dissolving it out from the paper in a great measure. This renders the washing more perfect, and is found to prevent u blistering,” which is common with so many albumenized papers. The prints should be withdrawn slowly from the bath—in order that all excess of the hyposulphite solution may be drawn from them by capillary attraction—and placed in a trough of water, where they should soak a quarter of an hour. They should then be removed, as before, and placed in a stream of vanning water for twelve hours. If running water be not attainable, a good plan is to place the prints in a dish, changing the water every half hour for five or six changes, and sponging all the moisture out as far as possible after every second change. By this procedure the hyposulphite is almost totally eliminated. Prints washed in this manner have remained unaltered in colour for the last twelve years in the writer’s experience, having passed through climates dry and moist, and varying in temperature from 20° to 110°. It is useful sometimes to test the water for sodium hypo¬ sulphite soda after the last washing, in order to ascertain if its extraction be complete. The following is a most delicate test. Make the following test solution:— Potassium permanganate ... ... 2 grains Potassium carbonate ... ... 20 ,, Water ... ... ... ... 1 quart * The thicker the paper the longer the time of immersion. 123 The addition of a few drops of this rose-coloured solution to a pint of water will yield a slightly pink tinge. If there be any trace of sodium hyposulphite present, the colour will be of a greenish hue. If the permanganate be not at hand, the following well-known starch iodide test may be adopted :— Take about two drachms of water and a small piece of starch about the size of a small pea, powder and boil the starch in the water till the solution is quite clear; add one drop of a saturated solution of iodine in alcohol to this clear liquid. It will now become dark blue. Of this solution drop two drops into two clean test tubes, and fill up one with distilled water and the other with the water to be tested; a faint blue colour should be perceptible in the first test tube. In the second test tube, should hyposulphite be present, this blue colour will have disappeared,, the iodide of starch becoming colourless in its presence. The best mode of comparing the two waters is by placing a piece of white paper behind the test tubes. It frequently occurs that though sodium hyposulphite cannot be detected in the washing water, it may be present in the paper itself. The paper on which most prints are taken being sized with starch, if a very weak solution of iodine be applied with a brush across the lack of a print, a blue mark will indicate the absence of the hyposulphite. Care must be taken that the iodine solution is very weak, otherwise a part of the iodine will first destroy the trace of the salt, and then the remainder will bring out the blue re-action. The dishes used for toning , sensitizing, and fixing should he used for no other purpose than that to which they are origin¬ ally allotted. A porcelain dish on which the glaze has cracked should be rejected for the sensitizing dish and for the fixing dish. In the first case, the porous porcelain absorbs a vast quantity of silver nitrate; and in the latter, old sodium hypo¬ sulphite, when it is very apt to cause yellow markings on the prints. Tin dishes should be avoided in all cases. The tin corrodes and marks the pictures. Perforated zinc is often used for the bottoms of washing troughs. This also should be avoided, as after a time it becomes fouled, the sodium hyposulphite acting upon it, and the prints get stained where they touch it. 124 DEFECTS IN PRINTS. Small white spots, with a black central pin-point, are often met with in prints. Dust on the paper during sensitizing will cause them, the grit forming a nucleus for a minute bubble. All.paper should be thoroughly dusted before • being floated on the sensitizing bath. Grey, star-like spots arise from small particles of inorganic matter, such as ferric oxide, lime, &c., which are present in the paper. They become more apparent by decomposition during the printing operations. They may generally be dis¬ cernible by examining the paper by transmitted light. Bronzed lines (straight) occur through a stoppage during floating the paper in the sensitizing solution. Should the lines be irregular, forming angles and curves, .it is probable that a scum of silver oxide, &c., may be detected on the surface of the sensitizing solution. A strip of blotting-paper drawn across the bath will remove the cause of the defect. Should the print appear marbled, it may be surmised that the sensitizing solution is weak, or that the paper has not been floated long enough. In some cases it may arise from imperfect albumenizing; but in ordinary commercial samples the cause can be easily traced. Bed marks on the shadows may appear during toning, and arc very conspicuous after fixing. They generally arise from hand¬ ling the paper with hot, moist fingers after sensitizing; grease, being deposited on the surface, prevents the toning bath acting properly on such parts. 'Weak prints are generally caused by weak negatives. Such can be partially remedied by paying attention to the strength of the sensitizing bath (as shown in page 109), and by using washed paper. Harsh prints are due to harsh negatives. They can generally be remedied by paying attention to the mode of printing, also given at page 118. If the negative be under-exposed and wanting in detail, there is, however, no cure for this defect. A red tone is due to insufficient toning; whilst a poor and blue tone is due to an excess of toning. The whites may appear yellow from imperfect washing, imperfect toning, or imperfect fixing. Should prints refuse to tone, either the gold has been ex¬ hausted, or else a trace of sodium hyposulphite has been carried 125 into the toning bath by the fingers or.other means. A trace of hyposulphite is much more injurious to the print than a fair quantity of it. Should the toning bath refuse to tone after the addition of gold, it may be presumed that it is contaminated by a trace of sodium hyposulphite. A. dark mottled appearance in the body of the paper indicates imperfect fixing, combined with the action of the light on the unaltered chloride (luring (ixing. If the fixing bath be acid, the excess of acid combines with the sulphur, and forms hydrosul- phuric acid, which will also cause the defect. Tho cause of mealiness or “ measles ” in the print has been explained in page 111. Maxims for Printing. 1. The print should have the highest lights nearly white, and the shadows verging on a bronzed colour before toning. 2. Place the prints, before toning, in the water, face down¬ wards, and do not wash away too much of the free nitrate of silver (see exception, page 111). 3. The toning solution must be neutral or slightly alkaline, and not colder than 60°. 4. Tone the prints to purple or sepia, according as warm or brown prints arc required. 5. Move the prints, in both the toning and fixing solutions, repeatedly, taking care that no air-bubbles form on the surface. 6. Take care that the fixing bath is not acid. 7. Use fresh sodium hyposulphite solution for each batch of prints to be fixed. 8. Wash thoroughly after and before fixing. 9. Make a sensitizing bath of a strength likely to give the best results with the negatives to be printed. 10. Print in the shade, or direct sunshine, according to the density of the negative. COLLODIO-CIILORIDE PAPER. The collodio-chloride process was introduced by Mr. Gr. "Wharton Simpson, the Editor of the PnoTooBArnic Hews. Pri¬ marily, it was introduced for printing on glass or paper, and for such it is given here. 126 The eolloclio-chloricle is formed as follows :— *No. 1—Silver nitrate... Distilled water No. 2—Strontium chloride Alcohol No. 3—Citric acid Alcohol 1 drachm 64 grains 2 ounces 64 grains 2 ounces To every two ounces of plain collodion add thirty drops of No. 1, previously mixed with one drachm of alcohol; then add one drachm of No. 2, shaking well at the same time; lastly, half a drachm of No. 3 solution. In a quarter of an hour it is fit for use. There is sometimes a difficulty found (especially when applying the collodio-chloride to glass) due to the crystallization of the salts on the surface of the film. The writer has entirely overcome it by using the above proportions, and then washing the emulsion thus formed in a similar manner as directed for the bromide emulsion (see page 82). It is, however, necessary to add a small quantity of silver nitrate, after re-dissolving the collodion pellicle in the proper proportion of solvents; about eight grains to the ounce of emulsion is the amount recommended. The above formula) apply to printing on paper, or on glass, porcelain, &c. The paper best adapted for the reception of the collodio- chloride is arrowroot paper. A paper rather larger than the size of print required is taken, the edges turned up for one- eighth of an inch all round to form a tray, leaving a small spout at one corner. This paper is then pinned on to a hoard by the four corners, and is coated in a dark-room with the collodion as for the collodio-bromide process. When well dried, it may he found to increase the brilliancy of the resulting print by pinning it on the inside of the lid of a large box, and exposing it to the fumes of a drachm of ammonia poured into a saucer. The print is taken in the ordinary manner, and may he toned by any of the ordinary toning baths, the lime hath (No. 1, page 119) being the best, providing it he old. * The formulae are taken from the Year-Book of Photography for 1871. 127 The following toning bath, made in two separate solutions, gives rather inky tones :— No. 1.—Ammonium sulphocyanide Sodium hyposulphite Sodium carbonate Water No. 2.—Gold trichloride Chalk . Water . H ounces 45 grains 15 50 ounces 30 grains 1 teaspoonful 60 ounces Equal quantities of these are taken and mixed, and the toning proceeds as usual. The prints ordinarily take from two to ten minutes to tone. If a longer time he required, add more gold till the desired effect is produced. This toning hath can only he used once. FIXING BATH. The fixing hath is composed as follows :— Sodium hyposulphite ... ... ... 1 ounce Water ... ... ... ... ... 30 ounces The print should he immersed in this about eight minutes. MOUNTING PRINTS. More care than is usually bestowed is necessary to mount prints, whether produced by the silver printing, or the perma¬ nent pigment processes. When silver prints are taken from the drying line they are found to he rolled up, and slightly cockled, it may he, in parts; in this state it is difficult to mount them. The method of stroking prints has been introduced to get rid of these defects. A flat piece of hard wood, about one foot long and one and a-half inch broad, and the thickness of a marquoise scale, has its edges carefully rounded off. The print is seized by one corner in one hand, and unrolled; the face of the print is brought in contact with a piece of plate-glass. The “ stroker,” held by the other hand, is brought with its rounded edge on to the back of the print near the corner held by the first hand. Considerable pressure is brought upon the stroker, and the print is drawn through between it and the plate. The print is then seized by another corner and similarly treated. By this means a gloss is put upon the print, and the creases and cockles are obliterated The print is now ready for cutting out. 128 It is well to have a square of glass with true edges cut to- the size of the pictures generally taken. The prints should he trimmed, upon a sheet of plate glass, a sharp penknife being used to cut them. A rough test for ascertaining if the opposite sides- are equal is to bring them together and see if both corners coincide. It may sometimes be found useful to cut out a print into an oval. The following method for tracing any ellipse may be employedOn a thickish piece of clean paper draw a line AB, making it the extreme width of the oval required. Bisect it at 0, and draw DOC at right angles to AB. Make OC equal to half the smallest diameter of the ellipse. With the centre C and the distance CD draw an arc of a circle, cutting AB in E and E. Place the paper on a flat board, and at E and E fix two drawing pins. Take a piece of thread and double it, knotting it together in such a manner that its length when doubled is equal to AB. Place the thread round the two pins at E and E, and stretch it out to tightness by the point of a lead pencil. Move the pencil guided by the cotton, taking care to keep it upright. The resulting figure will be an ellipse. Modifications of this figure may be made by making a second knot beyond the first knot, and placing the point of the pencil in the loop formed. When the figure has been traced in pencil on the paper, it should be carefully cut out with a sharp penknife, and placed on the print which is to be trimmed into an oval. When so placed, a faint pencil line is run round on the print, and the cutting out proceeds either by scissors or penknife. Ovals, in sheet tin or brass of different sizes, are supplied by the dealers in photo¬ graphic apparatus. The little instrument called the photographic trimmer is excessively handy for cutting out the prints when 129 such have been procured. The cutting-wheel is brought against the edge of the shape, and, being pivotted, follows the curve mechanically. There are a Variety of mounting solutions in common use, the most favourite being starch. This is prepared in the ordinary way, and is laid on the back of the print by a hog’s-bristle brush. Starch is dangerous to use, unless perfectly pure and fresh. It is apt to liberate an acid, which destroys a print in contact with it. To prepare gelatine for mounting, take half a wineglassful of gelatine, and cover it with cold water ; when thoroughly swelled—which will be in about three-quarters of an hour— pour off any water that has not been absorbed, and fill up the wine-glass with boiling water. The gelatine will now be dis¬ solved, and will remain fluid if the wine-glass be kept standing in warm water. This mounting medium is applied in the same way as the starch. Yery thin glue is also occasionally employed, and answers well. In the market, at the present time, there are two or three made-up mounting solutions. “ Marion’s Mounting Medium”*' answers admirably for small pictures, though when prints of 15 by 12 are to be mounted, it is apt to be rather difficult to give the back an even coating before it dries. One great advantage of this solution is that it does not cockle the mount, however thin it may be. Prints may be mounted on foolscap paper with the greatest ease, and they will be as flat as if mounted on the thickest cardboard. A similar solution, suggested by Mr. G. Wharton Simpson, is made as follows:— Take gelatine or fine shreds of glue, and swell them with the least possible quantity of water. Boil them with alcohol, keeping them in agitation with a stirring rod the whole time. Eighty grains of gelatine will take about two ounces of alcohol to render it of a fit consistency for mounting. When cool the solution will become gelatinous. It can be used for mounting by letting it stand in a pot of warm water. Before applying the mounting solution, the places where the corners of the print will come on the card should be marked with fine dots. The back of the print, having then been brushed over with the mounting solution, should be carefully placed on the mount, the corners coinciding with the dots. A piece of white * To be obtained from Messrs. Marion, Soho Square. K 130 blotting-paper should next be placed oyer the print, and the hack of the print should be brought in close contact with the mount by rubbing the clenched hand over the blotting-paper. To obtain great evenness a piece of white cream-laid paper may then be placed over the print, and the edge of all ivory (or other smooth substance) paper-knife be scraped briskly over it. This adds a brilliancy to the print, and prevents cockling in a great measure when starch or gelatine is used, all excess being squeezed out. The print is ready for rolling after the mounting solution is well dried. Finally, the surface of the mounted print may be waxed. There are various formulae for the encaustic, the simplest being :— White wax ... ... ... ... 1 ounce Spirits of turpentine ... ... ... 1 ,, the solution taking plainly by the aid of heat. Mr. Valentine Blanchard uses white wax dissolved in benzole. This, he states, leaves a good coating of wax on the print, the benzole evaporating entirely. 'M. Adam-Salomon’s encaustic paste is made as follows :— Pure virgin wax ... Gum elemi ... Benzole Essence of lavender Oil of spike. 500 10 i grains ounce 3 . 4 1 drachm The waxing solution may be taken up by a tuft of cotton wool, and spread roughly over the surface of the print. A clean pad of cotton wool is then used to rub it well in, till the surface assumes a bright gloss, and is free from all appearance of mark¬ ings. For increasing the depth of shadow and general beauty of a print, waxing is of the greatest utility. Recently burnishers of a very excellent type have been intro¬ duced into the market. Burnishing gives extraordinary bril¬ liancy to a print, and is easily executed with a proper instrument. 131 PRINTS OBTAINED BY THE AID OE CHROMIC ACID COMPOUNDS. If gelatine be mixed with a solution of a dichromatic of an alkali, and dried in non-actinie light, it will be found that it is perfectly soluble in water. If, however, it be exposed to the action of light, it will be found to have become insoluble. On this rests the whole superstructure of permanent pigment printing, photo-lithography, heliotypy, papyrotypy, and such processes akin to them. The chemistry of the process is rather involved in difficulties, on account of the organic changes that may take place in the gelatine. It will suffice to point out the main action that takes place, viz., that u gelatine, aided by light, reduces the chromic acid of the bichromate to a lower state of oxidation, and then enters into combination with a compound of chromic oxide pro¬ duced by the mutual decomposition of the chromic acid and gela¬ tine, the original being the formation of a leather-like sub¬ stance,”* insoluble in hot water. The addition of various substances to the gelatinous compound has been found to aid this decomposition. THE AUTOTYPE PROCESS. The first process that is to be described is known as the ** Autotype.” Prom the Autotype Company can be procured sheets and rolls of coloured gelatinized paper of eveiy tint, and these are the foundation of all their permanent prints. The carbon tissue, as it is termed, is difficult to prepare on a small scale ; hence it is better to procure it direct from the firm above indicated. They supply it ready sensitized, and it can be transmitted by post; otherwise it is necessary to float it on a solution of bichromate of potash and water— Pure potassium dichromate ... ... 1 ounce Water ... ... ... ... ... 20 ounces The potassium dichromate should be nearly neutral, and * From a paper read before the Photographic Society, May 10th, 1870 Mr. Swan. 132 contain no free acid. Should it contain acid, the tissue is liable to become insoluble. Free acid*' may be neutralized by the addition of potash in solution till no extraordinary acid reaction is evident to blue litmus paper. A dish somewhat larger than the paper to be floated is used for floating. The solution should be at least a quarter of an inch in depth in the dish. The piece of pigmented paper is taken, and a quarter of an inch folded back at one end at right angles, and rolled up to a diameter of about two to three inches, gelatine surface outside. The turned-up end remains on the outside of the roll. The angle of the folded end is now dropped upon the solution, and the coil of paper is allowed to unfold itself, driving out all hubbies behind as its surface comes in contact with the solution. The floating should last from two minutes in warm weather to three in cold.f The turned-up end should then be pinned by a couple of pins on a thin lath, and slowly withdrawn from the hath, and hung up to dry. The drying of the tissue should take place in a room perfectly free from vapours, such as sulphuretted hydrogen, or those produced by the combustion of gas. If possible, a current of warm, dry air should be created through the drying room ; in summer a large candle placed in a chimney will create sufficient draught, if the paper be dried near the fireplace. The quicker the paper dries, the better will it work, though the less sensitive it is to light. When quite dry, the paper is exposed under the negative in the ordinary manner, a (< safe edge,” as it is technically termed, being placed round it. The safe edge consists of a mask of brown or other non-actinic paper, externally larger than the negative, and internally slightly smaller, the negative being, as it were, framed by it. The pigmented paper must be slightly larger (say half an inch each way) than the size of the print required. If the print be examined during exposure, there will be no change in its appearance, owing to the pigments used to give it the necessary colour; consequently it is necessary to use an actinometer to time the exposure. The autotype actinometer consists of a slip of albumenized * Potassium dichromate always shows a slightly acid reaction to test- paper. f Should the temperature of the solution exceed 80^ F., it must; be reduced by adding a little pounded ice. 133 paper,* rendered sensicive by a standard silver solution. This becomes tinted or coloured by exposure to the light. The tint thus produced is compared with a standard one, painted on a strip of paper or tin. When about to be used, a small portion of the strip of paper is exposed to the light simultaneously with the print. When the paper has attained the colour of the painted standard, it is said to have had one tint. A fresh piece of paper is then exposed for another tint, and so on. Tor a negative of ordinary density two tints will generally be found sufficient in summer, and probably five in winter, but experience must decide the time required for different negatives. Some five years ago, however, it came to the writer’s notice that the length of exposure to actinic light necessary to produce a print by the autotype carbon process might be dimin¬ ished by three-quarters, or even seven-eighths, by withdrawing the print from beneath the negative, and leaving it in the dark. The printing action started continued gradually, and finally, after a lapse of several hours, on development, the picture was found to be fully printed. In winter this curious continuating printing action was of special value, as it enabled eight times the number of prints to be produced from a negative by giving only an eighth of the right exposure, and then keeping them in a dark room. The writer also experimented with certain non- actinic lights, and found the same action was maintained, but with greater rapidity. Hence hanging a partially-exposed print up in a yellow lighted room was better than leaving it in the dark. When one quarter of the exposure was given, a print hung up in the dark was found to be properly printed in twelve hours; whilst if only one-eighth, it required sixteen hours. The development of the tissue should be conducted in a room in which the light is weak or non-actinic. Close at hand, on a table, should be a dish containing water to a depth of an inch Or more. To the bottom'of this is sunk a finely- mulled flat zinc plate, at least one inch larger each way than the negative; the paper is now drawn, face downwards, under the water, till it nearly rests upon the zinc plate. It will be noticed that the paper at first tends to coil downwards, but gradually unrols till it is perfectly flat, and if left it would coil upwards. At the moment it has become flat, the zinc plate is seized by the * Other forms of actinometer arc employed, which depend more on the principle of that employed for heliotypy (see page 145). 134 hands, and raised horizontally out from the dish, the tissue resting upon it. It is then placed on a small low stool standing in another dish; one end of the paper is next pressed on to the zinc plate by one hand, and with the other the remaining portions are brought into contact with the “ squeegee.”* Thu first portion of the tissue is then brought into contact with the zinc in the same manner. The zinc plates used are termed the “ temporary supports n of the tissue. They are mulled in the ordinary manner with a muller and fine sand; the finer the grain given, the finer in detail will be the resulting pictures. Care should be taken that no scratches are on them, as every scratch is reproduced in the finished print. It was found by Mr. Johnson, who introduced this method of transferring the prints, that it was necessary to coat the plates with a fatty and resinous substance, of sufficient tenacity to keep the prints on them during development, but which should have less adherence to them than the film of gela¬ tine has to the paper with which it is to be backed or mounted. The following is the composition of the fatty body :— Beeswax ... ... ... ... 3 drachms Yellow resinf ... ... ... 3 ,, Oil of turpentine ... ... ... 1 pint These proportions are not absolute, as the composition of the beeswax varies. The resin must be added to the beeswax to such an amount that the gelatine film will remain on the plate without cracking or peeling, even when dried in a hot room, but at the same time will leave the plate readily (when the' applied transfer paper has become dried) without the application of any force. "With a piece of fine flannel, or cotton wool, a small quantity of the above fatty body should be rubbed on to the plate. With another piece the excess of grease must be polished off, leaving but a minute layer of the compound on the surface. The * The squeegee consists of a flat piece of wood about two inches wide and three-sixteenths thick, into one edge of which is let a strip of india-rubber about half an inch wide, and projecting half that distance ; the length of both the lath and india-rubber vary according to the size of the zinc plate. It is used by pressing the india-rubber edge against the paper, and passing it hastily over the surface. f The resin causes the adherence of the film to the plate, whilst the bees¬ wax diminishes that adherence to the limits above stated. 135 zinc plate is tlien ready for the transference to it of the tissue. The zinc plates are cleaned, after being* used, by rubbing With flannel in boiling water. If this be not sufficient, a little turpentine or ammonia will cleanse them thoroughly, and render them fit for a fresh application of the fatty compound. Tor some purposes it may be deemed advisable to give the prints a more highly polished appearance than that furnished by the use of a grained zinc plate. A glass plate prepared as follows answers the purpose :— Beeswax in shreds ... ... ... 60 grains Methylated ether ... ... ... 20 ounces After resting twenty-four hours the solution is decanted. To each part of clear fluid is then added five parts of benzoline. The plate is coated as with collodion, and dried. A coating of collodion is next given, and the surface thus prepared is used as a temporary support for the tissue. Development is best effected by a trough or tin basin con¬ taining water, whose temperature can be maintained at 100° T. by aid of a gas jet or a spirit lamp. After the pigmented paper has been pressed into contact by the squeegee with the zinc plate, it should be laid aside for a couple of minutes, to allow the gelatine to swell. By the swelling of the gelatine a partial vacuum is created between it and the zinc plate, and the pressure of the air outside prevents it from peeling or stripping off. The zinc plate, with the adhering paper, is next placed horizontally in the trough for a minute, when it will be found that the paper can be peeled off, leaving the gelatine pigment on the zinc plate. The plate is now moved vertically in the water, or the water dashed over it with the hand; and gradually those parts of the gelatine which have been "unacted upon by light will dissolve away, leaving the picture beautifully developed, with its half tones and deep shadows in perfect gradation. When the water flows from off the plate quite free of colouring matter it should be withdrawn, and then placed for a few seconds in alum and water (a dessert spoonful to a couple of gallons will suffice). This renders the remaining gelatine perfectly insoluble. Should a picture be only slightly under¬ exposed, plunging the plate into the alum water, at the stage required, will stop development and give a passable print. If a picture be slightly over-exposed, water heated to 130° will often 136 reduce its depth sufficiently. The plate, with the picture on it, should lastly be well washed under the tap to rid it of any traces of alum, and then set up in a rack to dry. It may seem curious to some that the pigmented gelatine should have to be transferred from paper to zinc plates to be developed, or, in other words, that development takes place from the back of the gelatine. A little thought will clear up the mystery. The light acts on the pigment according to the actinisui and time of exposure. A ray of light can only penetrate to do work to depths varying with its intensity (the variation is not a simple proportion, hut much more complicated), and the amount of “work” done by it is in a ratio to the time ofj exposure. The light passing through a negative at different parts varies in intensity. Thus it is evident that the insoluble part is at the surface, whilst the soluble is nearest the paper. Now, supposing it were attempted to develop the picture on the paper itself, it would be found that nearly all the surface of the pig¬ ment had become insoluble, and that, consequently, this leather¬ like substance would prevent the dissolution of the underneath portions, which were still soluble. The best exposure for the paper is evidently when the light has penetrated in the deepest shadows just to the surface of the paper, whilst the densest parts of the negative have not allowed the passage of any light. It will he seen from this that a nega¬ tive should possess similar good qualities as for silver printing. The print on the zinc plate will be found to be reversed. This is as it should be, as in the re-transfer it will be found to be in its proper position. The transfer paper is coated with a prepara¬ tion of insoluble gelatine. The re-transfer on to paper is effected in a similar manner to the transfer of the pigmented paper to the zinc. The paper is plunged into water of a temperature of about 170°, where it remains till it becomes slimy to the touch. The plate bearing the dried picture is now dipped into cold water, and carries as much as possible away with it in a horizontal position on to the stool already mentioned. The transfer paper is then placed, prepared side downwards, upon the cushion of water, and issqueegeed ” into close contact with the picture as before. It is then allowed to dry spontaneously (in the sun, if possible), after which it will be found readily to leave the plate, bearing with it the picture on its surface. If dried by the sun it will coil off the plate of its own accord. If the paper be too hastily dried by the fire it will buckle and become cockled, and can only be flattened with difficulty. If a matt surface be required, the print may be finished by rubbing with cotton-wool holding a little turpentine. A bril¬ liant surface can be given by using an encaustic paste as for silver prints :— White wax ... 1 ounce Benzole ... 1 „ dissolved by the aid of heat; Or— White wax 1 ounce Oil of turpentine ... 1 „ dissolved also by the aid of heat. For printing portraits a glass plate may be used in lieu of the zinc. The surface should be rubbed over with the waxing compound. Great care is requisite that the resulting surface is free from lines, as it should be remembered that every line on the surface of the plate will.be exactly reproduced in the print. The glass may also be coated with a film of plain collodion (which should be perfectly transparent when dry), and after varnishing round the edges the film may be used for the transfer. When re-transferred on to paper the collodion is detached, and the surface of the print is brilliantly glazed. It is advisable sometimes to rub the plate once, before applying the collodion, with a little white wax dissolved in ether. This facilitates the film leaving it. Mr. Johnson likewise coats the glass plate with water varnish, prepared as given for heliotypy. Mr. Baden Pritchard re-transfers the picture before it has dried in the ordinary manner. He dries it after re-transferring by placing the zinc plate on a wide ring over a gas-burner. His observations led him to think that there is no deterioration in the print from this method. The danger to be apprehended is a separation of the film at the junction of the high lights with the shadows. In practice (owing to indifferent gelatine being employed, or through other circumstances) occasional prints with cracks in the film, having an appearance of crape, are met with. These may often be remedied by placing the finished print in water of about 130 p F., and leaving the gelatine to swell up once more. When dried, it will be found that the cracks have disappeared. 138 Mr. Sawyer, of the Autotype Company, has recently patented a flexible support, as a substitute for the zinc plate. It is made with a preparation of gelatine, and certain substances added to cause it to he insoluble and impermeable. The advantage claimed for it is that it expands with the tissue, eliminating the chance of a certain kind of blurring which has often been noticeable in the gelatine prints. The results obtained by its employment demon¬ strate the correctness of the claim. Another point in its favour is that the surface is less granular than with zinc, and the print m therefore more delicate. The following is a description of the manufacture of the flexi¬ ble support, taken from a paper read before the Photographic Society of Great Britain :— “ A solution of gelatine is made of variable strength, according to the quality of surface desired in the finished print. Tor a print to have a dead or matt surface, I employ about a five per cent, solution ; for a more highly glazed surface, about seven and a-half per cent.; and for a surface equal to highly glazed albumenized paper, a ten per cent, solution. Paper wound on a reel, so as to be in a long length, is coated upon a carbon tissue-making machine with these solutions, and, when dry, is cut into sheets, and subjected to many tons’ pressure in a hydraulic press. The solution of lac is made by dissolving one pound of button or bleached lac in five quarts of water in which have been dissolved four ounces of borax and one ounce of soda. This is put in what is called a digester, and heated until the lac is dissolved. The solution is then filtered, and when cold is ready for use. The gelatinized paper is floated on this solu¬ tion in a shallow hath or tray, hung up to dry, and then finally rolled between metal plates in a rolling press. Each sheet is rubbed over with a little of a solution made by dissolving resin in turpentine, and adding thereto a few grains of wax.” SINGLE TRANSFER PRINTS. There is another method of producing carbon prints without transferring them to zinc, viz., by transferring them direct to the paper on which they should finally rest. In order to employ this method it is necessary to obtain a reversed negative. The transfer paper, prepared somewhat similarly to the retransfer paper used in the autotype process, is soaked in very hot water, and, after the carbon tissue has been passed through cold water,. 139 tlie two surfaces are brought together by the squeegee or by pres¬ sure. The two papers are then immersed in warm water of about 100°, and the backing to the pigmented paper stripped off. The development of the positive takes place as usual, and the paper bearing the print is hung up to dry, when it is ready for mount¬ ing and finishing. Single transfer gives more delicate results than the double, no grain being present to mar the half-tones. The drawback to the process is the necessity of having a reversed ne gative. THE POWDER PROCESS. Under the head of printing processes comes what is usually known as the powder process. On the Continent it has been used with very good effect for the production of prints on paper, though in England its more familiar application is the repro¬ duction of negatives or transparencies on glass. The rationale of the process is as follows :— "When a tacky body of an organic nature is brought in contact with potassium dichromate, and is allowed to dry as far as possible, and then exposed to light, it will be found that owing to the oxidation of that body by the chromic acid the tackiness will disappear in exact proportion to the intensity of the light acting on it. If a glass plate be coated with such a preparation, and be placed beneath a half-tone negative, the densities of the different portions of the negative will be repre¬ sented by different stages of tackiness. A fine powder sprinkled over the exposed surface will adhere to the tacky portions in the ratio of the tackiness. Hence a picture will be built up which will be a counterpart of the negative, only reversed. Erom this it will be manifest that in order to obtain a positive picture a reversed positive must be employed; though a line engraving, for instance, may be directly copied by this method by allowing the back of the engraving to be in contact with the sensitive surface. The following are the formulae that have proved, in our hands, most successful:— Obernetter's Formula. Dextrine White sugar Ammonium dichromate Glycerine ... Water . 1 drachm lb drachms b drachm 2 to 8 drops 3 ounces 140 Oiy ( JVoodbury 1 s Formula.') Gum arabic Glucose Glyceriue ... Potassium dichromate Water 1 drachm f- drachm 10 drops 30 grains 2 ounces Whichever formula is employed, the solution should be filtered ■whilst warm, and be kept in a glass-stoppered* bottle. A glass plate is next cleaned, and, if thought desirable, coated with a thin film of porous collodion, allowed to set, and then washed under a stream of water till all greasi¬ ness due to the solvents has disappeared. "When drained, suffi¬ cient of No. 1 or 2 is taken in a clean glass measure, and allowed to flow over the surface two or three times. After pouring off the excess of fluid the plate is dried at about 150° P., or gently over a Bunsen burner, or Argand lamp, &c. Whilst still warm, and before the surface has had time to re-absorb moisture, the plate is placed in contact with the transparency or negative from which it is desired to obtain a reverse copy, and placed in sunlight for two or three minutes, or in bright diffused light ten or fifteen minutes. On removal from the printing-frame a faint image will be apparent, should the printing have proceeded far enough. After exposure to the air in order that moisture may be imbibed, plumbagof is applied with a large flat brush. The lights or shades are now represented by the graphite according as a negative or transparency has been super¬ imposed. When the image has been fully developed, the superfluous powder is gently dusted away, and the film coated with tough collodion, that given at page 150 for transferring films answering well. When well set, the plate is placed in water to allow the soluble gum and dichromate to dissolve out; and, if desired, the film may be detached from it by cutting round the edges with a sharp knife, and treating it as shown at page 150. The film thus detached may be made to adhere to any support * A cork should not be rued, as any extraneous organic matter is fatal to good results. f The plumbago should be of the finest description ; that used by electro¬ typers answers better than any other we have tried. 141 required, such as paper or glass, by giving it a thin preliminary coating of gelatine. By this detachment of the film the print evidently may be now reversed, if so required. The application of this process to paper can be now under¬ stood. In practice it is found advantageous to give it a good smooth sizing of gelatine previous to coating with the above. Ordinary albumenized paper, the albumen of which has been coagulated by heat and afterwards washed, may be substituted^ PHOTO-MECHANICAL PBINTINGL All photo-mechanical printing processes for the production of half-tone hitherto worked out (with the exception of the Woodbury type process, to be described) are based on the same principle as the carbon or autotype process; viz., the in¬ solubility in water (either hot or cold) of gelatine impregnated with a dichromate of an alkali, after exposure in a dry state to the action of light. Not only is insolubility produced, but also an inability to swell through the absorption of water. There is one other method of producing insolubility in gelatine, that does not prevent the absorption of water, viz., the addition to it of chrome alum, tannin, mercurous chloride, and various resins. These render the gelatipe tough, and capable of withstanding a large amount of wear and tpar. Now if a layer of gelatine to which has been added potassium- dichromate and (say) chrome alum be exposed to light under a negative, and subsequently immersed in cold water, a little reflection will show that it is all insoluble in water; that where light has acted, there it will refuse to swell by the absorption of water; that where light has not acted, there it will absorb water. If a roller holding greasy ink be passed over the surface, the ink will be repelled from all the swelled portions, whilst it will adhere only to those parts on which light has acted. If a piece of paper be pressed down on such an inked-in surface, it is manifest that we shall obtain a positive print on its removal. 'With half-tone subjects the ink will only take in exact proportion to the time and intensity with which the light has acted on the gelatine surface. 142 WOODBURYTYPE PROCESS. Mr. "Walter Woodbury has successfully worked out a process of producing prints which may be classed under the head of photo-mechanical processes. For amateurs it would be difficult to undertake, owing to the apparatus that is necessary. The following is an outline of it. A film of sensitive gelatine is placed beneath a negative and exposed to light issuing from a fixed point, such as the electric light or to sunlight, the nega¬ tives being always in the same position to the rays. This may be effected by a mirror, or by constantly moving the negative into position. Sky-light may be used, supposing the light be admitted down a tube, all side light being thus shut off. The gelatine film, when fully exposed, is developed by washing away the soluble portion, and the picture is now in relief, the highest lights being represented by the lowest relief. When dried the gelatine print is placed on a soft metal plate, and driven into it by means of immense pressure, an hydraulic press being employed for the purpose. The metal sheet now becomes a mould, and is placed in a position on a metal table which forms part of the Woodburytype process. Beneath the lid is a perfectly flat glass plate, which is so adjusted by the knife that it makes actual contact with the metal mould. A. solu¬ tion of gelatine in a hot condition, containing pigments or dyes, is run into this last; a piece of homogeneous and specially prepared paper is placed over it, and the lid shut down. The pressure causes all the superfluous gelatine to exude, whilst^that in the mould adheres to the paper. When set, this is lifted off, and a picture appears in relief, the lights and shades being formed by varying thicknesses of gelatine. An immersion in a weak solution of alum causes the gelatine to become insoluble, and the picture, when dried, is ready for trim¬ ming and mounting. It will be noticed that, like the Autotype process, the print is dependent for its shade on the transparency of the pigment. Hence, the more transparent the colour em¬ ployed, the better the half-tones are likely to be. The pictures produced by this process are now well known to most people, illustrations of cheap periodical papers being frequently executed by it. They are beautiful and delicate, and, as far as at present known, permanent. The greatest drawback to Woodburytype is the difficulty experienced in obtaining pure white for any large extent, as in the skies of landscapes. In the matter of skies, the difficulty is got over by manual means. 143 THE HELIOTYPE PROCESS. This process is patented, and belongs to the HeUotype Company, being worked by Messrs. Edwards and Wright, of 61, Elect Street. In the heliotvpc process a film of gelatine is prepared on a glass plate, from which it is stripped when dry, and printed in the ordinary manner under the negative. The proper prepara¬ tion of the film is of the highest importance, and unless properly performed the resulting prints will be imperfect. The glass plate should be perfectly flat, and finely ground* on one side. To prepare it, the ground side is waxed with a waxing solution of white wax dissolved in ether. This is applied plentifully to the plate with a soft rag or cotton wool, and rubbed well in. As much as possible is then removed with a little ether or spirits of wine, till the surface presents an even and almost polished appearance. When required for use, the waxed surface of the plate is levelled by means of a spirit-level. The following formula may be used in the preparation of the 11 skins ” of gelatine for plates 22 by 16 :— No. 1.—Gelatine ... ... ... ounces Glycerine... ... ... 1 drachm Water ... . 12 ounces The gelatine which answers well, and is cheap, is Nelson’s No. 3 Elake. It should be allowed to swell in the water, and, when thoroughly swollen, should be melted over boiling water, and then the glycerine added. The temperature of the gelatine should not rise above 115° E., and the solution should be stirred till a perfectly even fluid is produced. The sensitizing solution is made as follows :— ° For Summer. For Winter. Potassium dicliromate of potash 22 grains 30 to 40 grains Chrome alum ... ... ... 15 ,, 15 to 7 ,, Water ... ... ... ... 12 drachms 12 drachms This quantity, after heating to 100° E., is added to the prepared * The polished surface of the glass may be employed by coating it with plain collodion containing equal parts of ether and alcohol, and about seven grains of pyroxyline, giving a horny film ; or by a solution of india-rubber in benzole. 144 gelatine solution immediately before use; in fact, it should be added in the vessel from which the plate is to be coated, and stirred well, to form a perfect mixture. A piece of muslin is tied over the top of the vessel, and the gelatine allowed to strain through it on to the levelled plate. The surface having been covered, and the gelatine allowed to set, the plate can be placed away from all dust in a drying room through which a current of air of about 75° is passing. The plate gradually dries after twenty-four to forty*eight hours. It will keep sensitive on the plate for a week or more. The drying-room should be glazed with deep orange glass, and be kept nearly dark. Yentilation is a sine qua non. Another formula is appended, which has the advantage of giving an opaque white film :— Ho. 2.—Gelatine ... ... ... 2 ounces Glycerine ... ... ... 3 drachms Water ... ... ... 9 ounces This is prepared as before, but, just before use, and before adding the sensitizer, five ounces of skimmed milk (which has been warmed, to cause the cream to rise) are stirred up with the solution. The sensitizer is then added as before:— For Summer. Potassium dichromate 22 grains Chrome alum ... ... 7-J ,, Water ... ... ... 12 drachms For Winter. 30 grains 5 „ 12 drachms When dry the skins are stripped from the glass plate, the edges being raised by a penknife. It is best to allow them to stay for half an hour in a place where the temperature and moisture are similar to that to which they will be subjected during expo¬ sure. This will prevent any danger to the negative in the printing-frame. The skin is next placed, with the surface which was not in contact with the plate uppermost, on a board on which has been nailed black velvet. Two small strips of the skin are cut from its edge, and placed one over the other in an ordinary printing-frame, with an opaque mask over them, in which is cut a lozenge-shaped hole. This is exposed to the light with the skin. When the image of the hole is seen well defined on the nethermost strip of gelatine, the skin is withdrawn, and its surface which was in contact with the glass placed in contact with a reversed negative in a printing- 145 frame. (It is advisable that all the shin excepting that under the negative should be masked, to prevent the light acting on it.) One of the ordinary ac¬ tinometer s, prepared with yellow oiled-silk, is now brought into requisition. In the figure each number denotes the number of thicknesses of the silk; hence, when on a strip of sensitiye gelatine 6 is seen, the light has penetrated through six thicknesses; when 7, through seven thicknesses, and so on. A half-tone negative of ordinary density requires the number 10 to be read on a piece of the sensitive gelatine placed beneath it; a clear line subject, not more than 6 or 7. Of course the actinometer is exposed in the same light as the skin*. When a negative is weak, it may only be half printed, and the continuating action (seepage 133) allowed to act for twelve or twenty-four hours, when a more brilliant result will follow. In this case the preliminary sunning of the skin should be lessened, for obvious reasons. Preparing the Transfer Plate .—A smooth metal plate of slightly larger dimensions than the skin (by preference pewter or nickelled steel) is coated with a solution of india-rubber in benzole, of the consistency of thick collodion (ordinary rectified lamp benzine answers every purpose); this is allowed to dry. The skin is then placed in water, with the prepared plate beneath, for two to three seconds, and both are withdrawn, leaving a layer of water between the sunned side of skin and the coated surface of the plate. A large squeegee is next brought to bear, and the two surfaces brought into close contact, as in the double transfer carbon process (page 134). If any dust be between the two surfaces, great danger is run of blistering. When squeegeed down, the edges are brushed round with india-rubber solution, to prevent the water penetrating underneath and raising them. When the india-rubber is nearly set, the plate is immersed in water for periods varying from ten minutes to one hour.f When all the dichromate is washed out, the surface of the skin * A small carte-de-visite pressure-frame is convenient for holding the actinometer. t For a skin prepared according to No. 2 formula, ten minutes are sufficient. L ' 3 4 5 6 7 8 9 10 11 12 146 is wiped dry, and is then ready for printing.*' Blisters may now he apparent from dust or bubbles in the film ; these can generally be forced out by applying the flat part of the hand, and squeezing them out to edge. Printing from the Gelatine Picture .—The plate is now laid on the bed of a printing press, and small strips of paper are pasted with india-rubber over the edges of the skifL on to the plate. A piece of bibulous paper is placed on the shin, and a good hard pressure brought to bear; this squeezes out most of the super¬ fluous water, and leaves the plate ready for inking. Best litho¬ graphic chalk inkf should have been prepared with green oil, and be of the consistency of soft wax. The gelatine or india- rubber roller should be coated with this ink by rolling on a stone slab or slate. When coated, the roller is applied, evenly and smoothly, to the plate. Those parts acted^ upon by light will take the ink, whilst all others will repel it. If the picture be a half-tone one, a thinner ink of any colour made up with oil or Bussian tallow may be used on another roller. This roller will not rob the plate of the first, on account of the thinness of the second ink, but will support detail in the high lights. Paper is now placed on skin, and, with a moderate pressure, a proof is pulled. Should white margins be apparent round the blackest shadows, or if the relief of the plate be too great, it is a sign that the surface requires 11 smashing down.” This is done by placing bibulous or enamelled paper on the skin, and bringing down the platen of the press with a great pressure. This gradually diminishes the relief. More ink is applied, and proofs are pulled till satisfactory results are obtained. The surface of the skin between each proof pulled should be slightly damped with a sponge, and the excess of moisture got rid ofj by the squeegee and blotting-paper. This keeps the whites clean as in lithography, and gives pluck to the resulting picture. Should the whole of the picture be too deeply printed, a little dilute ammonia (one part to four of water) may be sponged over the surface till the over-printing is no longer visible. In order to keep clean margins to the prints, a mask is cut of the shape * Should a collodionized or india-rubber surface have*been used, care must be taken that all the collodion or india-rubber is detached before printing. These polished surfaces have great advantage, having no grain. t All inks should he very finely mulled. % This should be done as quickly as possible, as, if not, the film is apt to become unequally damped, and give an unequal print. 147 required. The mask paper is prepared as follows :—Stout bank post is laid flat on a board, and boiled linseed oil is brushed over it. It is hung up by clips to dry, and is then ready for use. The mask, of course, is turned back between each inking-in of the picture. Paper .—Any kind of paper may be used with “ milk ” skins, whilst enamelled paper answers best with the ordinary ones. The enamelled paper is prepared with “mountain snow” and gelatine; it is the subject of a patent, and hence cannot be manufactured excepting by licencees of the Heliotype Company. Of ordinary paper, that answers best which is found most adhesive when the tip of the tongue is applied to its surface. Varnishing Prints .—The prints may be varnished, after pulling, if thought necessary, by a water varnish. This is made by dissolving shellac in boiling water to which a little ammonia has been added. As the shellac dissolves, more is added, stirring the solution the whole time. Trom time to time more ammonia and shellac must be added, till the varnish, on drying, leaves a brilliant surface. The varnish is filtered, and applied to the print with a flat brush. Preparing the Gelatine Rollers .—The rollers are made of a solution of gelatine to which glycerine and castor oil are added. They are moulded in a cylindrical mould, on perforated wooden rods, similarly to the manner of preparing ordinary printing rollers. A roller for a first ink is coated with gold size and the fluff of blotting-paper; a second ink roller remains with the gelatine surface to take up the ink. India-rubber rollers can also be obtained, which answer well. The great secret of producing a good heliotype is to have first-rate rollers at command. Failures .—The usual source of failure is the skins, which are not kept sufficiently free from dust, and in which air-bubbles are to be seen. In winter, blisters will appear from the above causes, as well as from too low a temperature of the water. The washing water should never be below 60°. If a skin be over-sunned, or be kept too long after sunning, a scum of ink will invariably be apparent on the high light. If a picture be over-printed under the negative, it may often be corrected by the judicious application of ammonia, as given above. If it be under-printed, thinner inks may be tried; but it is better to print a fresh skin than to waste time over experiment. Imper- 148 fections in the prints often arise from the imperfect use of the squeegee and blotting-paper, and from an uneven coating of the rollers with ink. captain Waterhouse’s photo-mechanical process. All other kinds of photo-mechanical processes are, it is believed, those by which the gelatine film is printed from with¬ out removal from the glass plate. Captain "Waterhouse’s modus operandi is here given, as it is simple, and has proved most effective. The negative must in all cases be reversed as for the helio¬ type process.* Plate glass three-eighths of an inch in thick¬ ness is used; it is ground on one side. When required for use, it is carefully cleaned and levelled in the ordinary manner. (Small wedges of hard wood answer well for this.) The gelatine solution, made as follows, is poured on the plate :— No. 1.—Gelatine ... ... ... ... 1 ounce Sugar ... ... ... .... 1 drachm Distilled water ... ... ... 6 ounces The gelatine must be allowed to swell, and be then dissolved. No. 2.—Honey soapf Distilled water ... 30 grains ... 1 ounce No. 3.—Tannin Distilled water ... 10 grains 1 ounce The above quantities suffice for two square feet of plate. When No. 1 is ready, Nos. 2 and 3 are mixed together hot, and poured gradually, with constant stirring, in No. 1. The whole is then strained through two thicknesses of coarse cotton cloth, and poured evenly over the plates. (It is as well to let a very little run over the sides, as it secures adhesion of the gelatine to the surface.) Bubbles are broken by the point of a penknife. The plates are then covered over with a light paper cover, to prevent dust falling on them. They will set in * Captain Waterhouse recommends, in some cases, that the film should he separated from the plate. Close contact is secured by this method. t Calvert’s medical carbolic soap answers well, and prevents decomposition of the film. 149 this country in about ten minutes’ time, when they should be turned over and allowed to dry, face downwards, being sup¬ ported on blocks of wood at the corners. Drying may also be carried on as for the heliotype process. When they are dry, they are ready for sensitizing; this is done by immersing them in— Potassium dichromate ... ... ... 1 part Water ... ... ... ... ... 20 parts for about five minutes, when they are re-dried. When dry, any deposit at the back of the plate, and inequalities at the corners, are removed, and the plate is ready for exposure to light. ‘ 1 This operation is performed in a pressure-frame in the same way as for ordinary photographs. It is advisable, however, to secure clean margins by shielding the borders of the negative by means of a mask cut out in yellow or brown paper, which should well overlap the edges of the printing plates. The mask is laid on the glass of the pressure-frame, then the negative in its proper position (should this be a transferred film, it is advisable to place a glass plate between it and the mask, in order to secure the most perfect contact) ; the sensitive plate is then rubbed over with a little powdered soapstone, to prevent its adhesion to the negative, and adjusted in its place over the negative, covered with a sheet of black velvet or brown paper, over which a thick glass plate is laid, and, if necessary, a few sheets of thick paper to give a good strong pressure, when the bars are shut down. The thick plate of glass has been found to give much sharper and more even contact than the usual backboard. “ The amount of exposure to light varies from about ten minutes in the sun for a clear line subject to from twenty-five to fifty minutes for a subject in half-tones, according to the subject and intensity of the light; but, as it is impossible to judge of the progress of the printing by inspection, it is necessary to use an actinometer as a guide to the exposure (see page 145). “ When the exposure to light is considered sufficient, the negative and mask are removed, and the bade of the sensitive plate is then exposed to light for about five or ten. minutes, to thoroughly harden the gelatine, and prevent it from swelling too much in the after processes. It is as well to carry on this second 150 exposure under a piece of ground glass ; otherwise, if there should he any scratches on the back of the sensitive plate, or on the glass of the pressure-frame, they will show as white lines on the print; after this the plate is taken out of the frame ; a little tallow is rubbed round the edges to prevent water getting underneath and stripping the film ; it is then plunged in water and thoroughly washed till all traces of bichromate have been removed, and is ready for printing. 11 The Printing .—The plates may he printed in the litho¬ graphic press, and then require to he fixed on a level stone with plaster of Paris. It has been found, however, more con¬ venient, and in other respects better, to print them with vertical pressure in the ordinary Albion press ; and in order to prevent their being broken, the bed of the press is fitted with two or three thicknesses of kamptulicon, besides a sheet of vulcanized india-rubber on which the plate rests. It is also desirable to place a sheet of white paper over the bedding, in order to enable the state of the plate, when it is being inked up, to be better seen. “ The plate, having been well soaked in water, is laid on the press, and, after having been wiped, to remove the excess of moisture, is inked in, if a line subject, with an ordinary lithogra¬ phic roller charged with an ink composed of lithographic chalk ink thinned with a little olive oil, followed by a rolling with a smooth roller to clean away the superfluous ink; a mask of the required size is laid on the plate, over this comes the printing paper covered with a piece of soft felt to drive the paper well into the hollows of the plate, the tympan is lowered, and the impression pulled in the ordinary way. The plate is then damped, and the work goes on in the same manner without diflic ulty. t “Tor printing in half-tones, however, the process is somewhat different, and to obtain uniformly successful results requires considerable skill and experience. As far as we have gone the following procedure has given the best results. 11 The plate is first inked in by means of a small leather hand-roller charged with stiff ink (rendered stiffer, if necessary, by the addition of a little Canada balsam), which takes only on the deeper shadows; the half-tones are then brought out by rolling in with a smooth lithographic roller charged with a lighter and softer ink. Boilers composed of glue, treacle, soap, and catechu have been found useful in certain cases for inking 151 in the plates, but, on the whole, the lithographic rollers are preferred. The impressions are best when printed on enamelled paper, but a smooth glazed printing paper also seems to answer well. ‘‘Before putting away the plates after printing, they are washed with turpentine, followed by a very weak solution of caustic potash, to remove all traces of the greasy ink ; they may also be treated after this with a mixture of gum and glycerine with advantage. “ Corrections .—A point that seems likely to greatly interfere with the extended use of the process was the difficulty of making corrections on the plates. I am glad to say that some experiments lately tried have shown that it is practicable % both to insert and to take out or clear up details on the gelatine films. “ The insertion of details may be accomplished by two or three methods. The first is by writing in the required additions on the dry plate with a pen or fine brush, using an ink composed of bichromate of potash, used alone, or slightly coloured with Indian ink or indigo. After the additions are completed, the plate is exposed to the light for ten minutes or a quarter of an hour, till the bichromate is thoroughly reduced, and may then be washed and printed as usual. In some cases the same object may conveniently be accomplished by brushing over the part with solution of bichromate of potash, allowing it to dry, and then printing in the required details from another negative. “ Experiments have shown that details may be taken out by the aid of a solution of caustic potash or cyanide of potassium; and should a plate print dirty, it may be cleaned up and greatly improved by the use of a weaker solution of the latter substance. “It often happens that the plates show too much relief in the lights, and that the ink will not take readily on the shadows or lines represented by the deepest hollows. This relief may be reduced by brushing the plate over with dilute nitric acid, one-sixth or weaker. The plate is then washed, and on inking-in the ink will take readily in the lines or hollows.” 152 PHOTO-LITHOGRAPHY AND ZINCOGRAPHY. Photo-lithography is an important branch of photography, where the rapid copying and multiplying of line subjects is in question, and requires much care and dexterity to carry out. It is rarely to be found that the process is worked satisfactorily by a beginner, but that constant attention will render it practicable. "What is required* is to obtain a print* from a negative in greasy ink, which may be laid down upon the ordinary litho¬ graphic stone or zinc plates. The principles of the process are the same as for the Autotype process, previously described at page 131. SOUTHAMPTON PLAN FOR PREPARING TRANSFERS. Make the following mixture :— Potassium dichromate ... 2 ounces Nelson’s fine-cut gelatine ... 3 „ Water ... ... 50 „ The dichromate is dissolved in ten ounces of water, and added to the forty in which the gelatinef has been previously dissolved by the aid of heat. Select some good bank-post paper (very grainless) of a medium thickness. If this cannot be obtained, get ordinary thin paper as a substitute-, and cut it into sheets a little bigger than the negative to be printed from. Strain the solution, and pour it into a dish through flannel, keeping up the temperature. This is best attained by getting a tin dish made, standing on four legs. (The dish holds water, which can be heated up to boiling point by a spirit lamp ; and on the top of this should rest the porcelain dish containing the solution.) The paper is floated about three minutes, and hung up by two corners to dry in a room which is non-actinically lighted, and is perfectly free from dust. When dry, the paper must be floated again as before. The sheets should be hung from the opposite * Called a transfer. f The gelatine should soak in water just sufficient to cover it, and then the remainder of the water should be added in a boiling state. 153 corners to those by which they were hung after the first floata¬ tion. Should it he considered desirable to coat the paper with gelatine first, and then sensitize, the dichromate may be omitted from the foregoing formulae. The sensitizing is then effected by floating the prepared paper for one minute on a cold solution of— Potassium dichromate ... ... ... 1 ounce Water ... ... ... ... ... 15 ounces In both cases it is well to pass the sensitized' paper through a copper-plate or lithographic press, to obtain a fine smooth surface. The sensitized paper will keep from about a week in cold to one day in hot weather. The negative must be perfectly opaque in the whites, and transparent in the lines; no clogging or deposit must be apparent on them. It will be found that great pressure is required in the printing-frame to bring the paper and the negative in close contact throughout. The difficulty is increased considerably if the plates are not perfectly flat; hence, for these negatives, patent plate is recommended. The amount of exposure to be given requires great j udgment. With paper of a most sensitive character, a negative extremely •dense in the whites, and the lines perfectly transparent, from half a minute to two minutes will be found sufficient if exposed in bright light, whilst it may take an hour in dull weather. The surest indication of proper exposure is when the lines appear a dark reddish-brown on a yellow ground. Should a negative be weaker in some parts than in others, the weak parts may be shaded by tissue paper, or paint applied on its film side. The prints have now to be coated with greasy ink. At Southampton the following formula of preparation is used :— Lithographic printing ink Middle varnish ... Burgundy pitch... Palm oil... W T ax . Bitumen... 8 ounces 4 „ 3 „ A ounce 1 The ink and varnish are first ground well together with a muller on a stone slab. The Burgundy pitch is next melted over a clear fire till the water is driven off. The wax is next added to it in small pieces, and finally the palm oil. These are 154 well stirred together. "When properly melted, these should catch fire if a light he applied to them, in which case the- bitumen is added, and it is afterwards ignited again. The ink and varnish are now added little by little, the stirring con¬ tinuing the whole time. The pot is now taken off the fire, and when the contents are cooled they are poured into tins for storage. The condition of the ink is of the greatest importance. It must not be too soft, otherwise the sponge will become clogged on washing off in development. If the ink be too hard, it will be difficult to wash it off from the paper at all; in this- case more palm oil should be added. A small quantity of the ink should be taken, and laid upon a flat stone slab, and melted with turpentine sufficient to give it the consistency of honey. This is well worked with a litho¬ graphic roller on a smooth stone or square plate to a fine even surface. A print is now taken and laid face downwards upon this inked stone, and is passed once or twice through the litho¬ graphic press. On carefully raising it, it will be found to have taken a fine layer of ink, through which the detail will be faintly visible by transmitted light. The coating of ink may also be given by a sponge or hand roller, the paper being pinned firmly on to an even board, face uppermost. The finer the layer of ink, the better will be the developed print. These operations should, of course, be carried on in non-actinic light. The print is now floated, face uppermost, on water of about 90° Fah. It is allowed to remain on this till the lines are seen in bas-relief on a swollen-up ground. It is next transferred to a zinc or glass plate placed on the slope, when warm water of about 150° is poured gently over it, and the soluble gelatine is removed by gentle rubbing with a very soft sponge. Should the inked soluble gelatine not leave the paper entirely at this stage, the prints should be soaked in warmer water for about an hour, ; when, the sponging should be repeated. When the sensitized gelatine is moistened it becomes insensitive, consequently these operations may be performed by ordinary daylight. It should be borne in mind that the utmost care is required in the sponging : if the sponge be roughly handled the fine lines will be removed, and spoil the print for transfer. It should also be re¬ collected that a constant flow of water from the sponge must be kept up to remove the inky gelatine after it is loosened, other¬ wise stains may result. 155 The prints, when freed from the soluble gelatine and ink, should be well washed in dishes of cold water, and hung up to dry. They are now ready to transfer to stone or zinc. It is better to leave them a day, however, before the transfer takes place. TO MAKE A TRANSFER BY PAPYROTYPE. This process is one patented by the writer, and is very simple of operation. Any tough paper is coated with a fine layer of gelatine, and subsequently treated with chrome alum or alum. It then receives another coating of gelatine of the same for¬ mula given for the Southampton method, substituting flake gelatine (for cheapness’ sake) for the fine cut. The printing is not carried on to such an extent as in that method, but the lines must appear of a delicate fawn colour on the yellow background. After withdrawal from the frame the print is drawn through cold water , and is then squeegeed down on to a smooth zinc or pewter plate. If found necessary, the edges may be secured by strips of paper and india-rubber solution, as for the heliotypo process. The superfluous water is then blotted off. A gelatine roller (of not too adhesive a character) is then charged with ink by rolling on a slab as follows:— Best lithographic chalk ink ... ... 4 parts Palm oil... ... ... ... ... 1 part This is now rolled on to the paper. The gelatine has only absorbed water where it has been unacted upon by light; consequently the print alone will take the ink, the “ whites” remaining free. After the paper has been well charged with ink, it may be necessary to pass the roller smartly over the sur¬ face to remove any scum that may be adherent. The finished transfer will be found of the most delicate character, and surpasses in sharpness any one produced by other known methods. It is esssntial that but very little of the bichromate of potash should leave the paper, as the success in transferring mainly de¬ pends upon its presence. The transfer print is hung up to dry, and is then again exposed to light. The whole surface now becomes insoluble, and on re-damping, previous to placing on the stone, it has no tendency to stick, nor will the gelatine be squeezed away by the pressure of the scraper in the press. There will still, however, be sufficient adhesiveness left to retain 156 the paper in position. It will be noticed that this process has the following advantages :— 1st. The ink which forms the lines is not left on ridges of gelatine, as in the Southampton method. 2nd. There is no danger of removing the' ink from the fine lines. 3rd. The ink may be applied till a satisfactory result is •obtained. 4 th. Two inks may be used of different consistencies; the thick ink will give solidity to the thick lines, whilst the fine lines will take a thinner. 5th. The surface of the transfer will have no tendency to slip, -as the whole is partially adhesive. It is not proposed to give a detailed description of the appa¬ ratus for lithography, or zincography, as a respectable manu¬ facturer will supply them of a proper character. A list of the articles necessary to procure is given at the end of the book. Both lithography and zincography depend on the property that a calcareous stone or mulled zinc plate possesses for absorb¬ ing or holding water, and on the fact that the grease is repelled by water; thus, where there is grease on a stone or zinc plate (placed by accident or design) the water is repelled. If a roller now be charged with greasy ink, and passed over the surface while still damp, the greasy ink will “take” in those portions where grease was originally on the surface, whilst the other por¬ tions remained unaffected. (The slightest trace of grease on the plate is sufficient to attract the ink from the roller.) TO PREPARE A STONE FOR LITHOGRAPHY. To prepare a lithographic stone for taking the transfer from a drawing, should the surface be uneven, or if a drawing has previously remained on for a considerable time, it may be necessary to grind it down, either by a stone of great size, or by an iron levigator. In both cases fine silver sand is sprinkled between the two surfaces, moistened with water. When the old work is removed, and the surface level, it is thoroughly washed with clean water, and polished with soft pumice stone. The pumice stone is moved backwards and forwards till all grain is removed. It is again washed with a sponge and water, and finally brightened up with snake stone. After washing it is 157 allowed to dry, when it is ready to receive the transfer. The whole of the polishing with pumice and snake stone will take about a quarter of an hour. TO PREPARE THE ZINC PLATES FOR ZINCOGRAPHY. The zinc plates are supplied by manufacturers, of proper weight, and ready planished. They should he about 10 B W guage. To he prepared for receiving a transfer, they must be grained. .Brass founders’ moulding sand is the best form of sand to use, as others, particularly silver sand, is apt to scratch the plate. Prior to use, it is sifted through a fine sieve of about 160 holes to the linear inch. A zinc muller is used to grind the surface after the sifted sand (moistened to the consistency of a cream with water) has been sprinkled on the surface. It is worked slowly round and round with a spiral motion, till the surface after washing appears of a uniform dull grey tint. Any traces of previous work must be obliterated, and all scratches must be ground out. The mullers should be kept free from all accidental grit, and he carefully washed before use. The zinc plate whilst mulling may be laid on any flat surface. A plate should be mulled immediately before use. TRANSFERRING TO STONE OR ZINC. The stone is slightly warmed either before a fire, or, what is more expeditious, by pouring over the surface a kettleful of boiling water. The heat in this case dries the stone, and leaves it sufficiently warm. The transfer is slightly damped, either by a moist sponge, or by damping a sheet of blotting-paper and placing it at the hack. In any case, the top surface of the transfer should not he sponged or greatly damped. "Whilst this is taking place the stone is placed on the bed of the press, and it should he ascertained that the scraper is perfectly true. Should it not he so, it may be adjusted by placing a piece of sandpaper on a perfectly flat surface, and rubbing it down till it is perfectly level. The stone should now be “pinched” by the lever between the bed and the scraper, a piece of clean paper protecting its surface from the leather tympan. If the same amount of pinch be apparent at all parts of the stone, it is ready for use. If one end have less pinch than the other, the former must be raised up by laying under it a few 158 folds of paper, taking care that the folds gradually taper off as they approach the centre of the stone. When adjusted thus the stone must he passed two or three times through the press, to cause a still more accurate adjustment of the transfer. The transfer is then laid on the stone by two corners, and a couple of sheets of paper are laid over it. The tympan is brought gently down, and the whole is passed through the press two or three times. The amount of pinch given should be light for the first pull, it being increased for each subsequent one. The tympan is now raised, and if the transfer adhere tightly to the stone the scraper may be reversed, and the stone is passed through the press a couple of times more. In order to remove the transfer paper it may be necessary to soak it with water. This done, the surface of the stone is moistened with gum-water, and allowed to dry and coil. This is most important, as if it be used too fresh or whilst warm, the lines may spread, and give coarse and broken work. The stone is fixed on the press, and the gum is washed off with a soft sponge, and the moisture distributed with a damping or cheese cloth. Ordinary litho ink having been worked to the consistency of honey, a little is laid on the roller and worked about on the ink slab till a- fine even layer is spread over its sur¬ face. Whilst the stone is moist the roller is passed over it from time to time, that fresh surface may be brought to bear on the work. By this procedure it will be found that the lines take the ink. If a slight scum appear whilst rolling, it is probable that the stone is not sufficiently damp. A fresh application of the sponge and damping cloth, and a smart roll, will lift it, leaving the surface clean. The stone is next slightly etched, to prevent spreading of the lines. A very dilute solution of nitric acid in water effects this. A sponge moistened with this should be passed over the surface, and, after leaving it for two or three seconds, fresh water should be applied with the damping cloth. A little gum-water is then applied, wiped off, and the inking proceeded with again. It may happen that all portions will not take the ink alike—that portions are weaker than others ; in this case, over those parts should be spread thick gum, and through it -should be rubbed a little palm oil, spread on a small square of cloth. This generally gives the required intensity. Impressions are now pulled, inking-in between each. Bor zincography the process is very similar; the transfer is 159 •clamped and passed through the press as above, the zinc plate being screwed on to a flat block of hard wood, so as to lie evenly and of sufficient height on the bed. When the transfer is removed the plate is well washed, and faDnecl dry. An etching solution is made thus :— Decoction of galls ... ... ... 1 quart Gum-water ... ... ... ... 3 quarts Phosphoric acid... ... ... ... 3 ounces The decoction of galls is prepared by soaking four ounces of bruised Aleppo galls in three quarts of cold water for twenty- four hours; the water and galls are then boiled together and strained. The phosphoric acid is made by placing sticks of phosphorus in a bottle of water, so that the ends of the sticks are exposed to the air. The etching solution is brushed on the plate with a broad brush, and allowed to remain a few seconds ; the excess is then wiped off with a cloth, and the zinc plate is fanned dry. It is then washed and rolled up as before. The first few impressions, either from stone or zinc, are generally feeble, and must be rejected. A GUM PROCESS. Take Dive paper, and brush over it a solution of— Picked gum-arabic ... ... ... 25 grains Potassium dichromate ... ... 85 ,, Water... ... ... ... ... 1 ounce Hang it up to dry. This will be accomplished in about half-an- hour in warm weather. The sheet of paper must be placed under the nagative as usual, and exposed to the light. When every detail is clearly seen, the paper should be withdrawn. Take ordinary printing paper, and soak alternate sheets in water, blotting the excess of moisture off in blotting-paper. Make these in a pile (about six sheets of moist and dry will be sufficient). Place the printed paper on the lithographic stone or sheet of mulled zinc, place a dry sheet of paper on its back, and then on it place the pile of damped paper. Finally, place a sheet of zinc or other flat surface on the top. The stone or zinc plate and its load should next he pressed under an ordinary hook-binding press, and a considerable pressure brought on to it. It should be left under this for half-an-hour. 160 The paper is then removed from the stone. Those parts of the gum which were rendered insoluble will leave the stone with the paper, the remaining portions adhering to it. After thorough drying away from light, a little oil is poured or brushed over the surface. The gum protects the white portions of the print from its action. The stone may be cleaned from the gum with a sponge and tepid water, and the ordinary lithgraphic process may then be proceeded with. The process is simple, the drawback being that the gum penetrates to a considerable depth through the surface of the tone, rendering the preparation for fresh work tedious. PHOTOGRAPHIC EHAMELS. Theee are two methods of producing photographic enamels which have been practised in this country : the one by what is called the dusting process (similar, in fact, to the powder process, described at page 143), metallic powder being employed instead of the plumbago ; whilst the other is dependent on the produc¬ tion of a transparency in collodion, the image being toned by various metallic compounds. The first process will not be described, as it is believed that the second is capable of giving very superior results, and is more within the reach of any one. A muffle for this process is absolutely essential. A form for placing m an ordinary fire is supplied by many dealers; but, when feasible, it is advisable to have one which is heated by gas, as with it there is no danger of discolouration, due to smoke, sulphur, &c., which is sometimes the case when coal or coke is the source of heat. Eletcher, of Warrington, supplies a most excellent gas furnace for the purpose (see diagram on next page). It can be fitted into any ordinary gas supply, and attains sufficient heat in a quarter of an hour to fuze any enamel placed within the muffle. The first step in the production of an enamel is to produce a fully developed transparency of the subject to be copied. This is secured in the camera in the usual way, and when fixed should appear very vigorous, though with half tones of a most delicate character. The next operation is to detach the film from the glass plate. This is effected by placing it in distilled water (to which, if the film be refractory, a little dilute sulphuric acid has been 161 added), and after a thorough soaking it can be removed by a camel’s hair brush, deftly applied at one edge. The sulphuric acid is sometimes an advantage if the collodion be tender, as it toughens it; but great care is requisite to ensure that all traces E is the muffle door closed with fire-brick, as shown in section ; D shows the draught-holes opposite the burners, which are a series of pipes; C is a movable piece to which is attached a chimney. The muffle part can be removed, and an alternative portion is supplied for heating crucibles, &c. of it are eliminated before proceeding further. The writer has in many cases toned the transparency before detaching the film from the glass, but the action is slower, owing to the fact that only one surface is open to the deposit of the metal. There are several toning solutions which are all effective, though the colour of the finished enamel varies according to the metal employed. It may here be remarked that there are two methods of burning a picture on an enamel—one in which the image is absolutely burnt into the plaque ; the other in which a soft flux is melted over the metallic image, giving it merely a glaze. The first plan is real enamelling, the metal forming a compound with the composition employed ; while with the latter the image is merely superficially protected, and is not, therefore, so likely to resist injury. For absolute success with the first method, it is merely essential that all silver should be entirely eliminated from the image; for if a true silver com¬ pound be formed, the image will have a dirty canary colour, on burning, which no subsequent treatment can efface, though by regulating the temperature some operators can burn in just M 162 sufficiently to cause the image to sink into the enamel. The com¬ position of the plaques materially affects the tone, hence there is often a discordance in the results obtained by different operators, unless the same materials be used. With plaques supplied by Atkinson, of Liverpool, the platinum toning bath gives to the writer a rich velvety black colour. The toning bath employed is— Platinum tetra-chloride* ... ... 1 grain Water ... ... ... ... ... 20 ounces to each pint of which 4 drops of concentrated nitric acid are added. This gradually converts the film of the image into silver chloride, and causes a consequent deposition of platinum. As one equivalent of platinum displaces four of silver, the reason why a rather dense transparency is required is apparent. The toning operation can scarcely be continued too long when the transparency is of proper intensity. Another toning bath, suggested by Herr Grune, is to tone first with platinum, and then to remove the film to a solution of uranium ferricyanide. Half a grain of uranium nitrate and half a grain of potassium ferricyanide are dissolved in a pint of water, and this solution is employed. When a slight browning action is observed, the fuzed image will have a sepia brown tint. Iridium chloride of a strength about the same as the platinum chloride is also employed by some enamellers with very good effect, the tint of the picture produced being a delicate grey. After well washing,j* the film should be treated with ammonia solution, half ammonia and half water. This dissolves out the silver chloride, and leaves an image formed of metallic platinum and silver. To eliminate the latter after thorough washing in distilled water, it is treated with nitric acid and water (half acid and half water). This finally frees the image of all traces of silver if it again be thoroughly washed. The picture thus finished is allowed to remain floating in a dish of distilled water, and the plaque is brought beneath it. They are brought out of the water together, the film clinging to the surface of the plaque. A penknife is then brought into requisition, and the film is trimmed by it so as just to cover the edge of the latter, and after a few strokes of a fine camel’s hair * Previously neutralized with sodium carbonate. t The film must be thoroughly well washed, in order to free it of any trace of the platinum solution ; otherwise, by the subsequent treatment, a deposit of the metal may take place on the whites, and spoil the picture. 163 brush, collodion and enamelled surface will be found to adhere together without crease or wrinkle. After drying thoroughly, the plaque is placed on a small sheet of cast iron or a small brick, and placed in the muffle, and the heat applied. The process of burning-in can be readily watched, and the instant that it is •complete may be judged by the appearance of the surface of the enamel. First, the collodion film* disappears, next the whole plaque becomes red hot, and the image seems to disappear; a few seconds after this effect is observed, it should be withdrawn, and on looking, it will be found that the burning- in is finished at this stage. The enamel appears dull and devoid of gloss, and it is consequently necessary to apply a glaze to it. The glaze employed is that known as soft glaze, as supplied by various china manufactories. This can be shaken up with plain collodion, so that on coating the plaque with it the image is completely hidden by the white surface due to the fine powder. When dry, another burning is given, but only to such an extent that the soft glaze becomes liquid, after which it is withdrawn. It frequently happens that two or more glazings are required before the right lustre is obtained. The art of enamelling is practised by very few photographers ; those whose productions are worthy of notice could be named on the fingers of one hand. The method given above is founded on that of Herr Grune, and it is believed that most enamels are produced in a somewhat similar manner. PHOTO-BELIEFS. The production of satisfactory photo-reliefs of etchings, &c., has long been a desideratum in the printing trade, and many attempts have been made to secure such. The following process answers well for their production in zinc. A transfer in hard transfer ink from a negative is made as if for lithography or zincography. A one-eighth of an inch zinc plate is then thoroughly mulled as described at page 152, after which it is rubbed down to a smooth surface with pumice, and then with stick charcoal. The appearance of the plate should be such as to be almost polished, and all visible grain # If the sulphuric acid used in the first soaking to detach the film have been too strong, it often explodes, and carries away the image with it. 164 should be absent, particularly if tbe work to be reproduced be fine. Tbe transfer is tben placed on it, and passed through the lithographic press in the ordinary manner, and a good firm impression left on the prepared surface. The plate is now dusted with fine resin or colophony (the dust being passed through a muslin hag to prevent any lumps adhering to the plate), any not attached to the greasy ink being blown off. A solution of— Hydrochloric, acid ... ... ... 1 part "Water... ... ... ... 500 to 750 parts is next prepared, and placed in a flat dish which is sufficiently large to hold the plate, and which can be rocked mechanically. The solution should be of such a depth that when the dish is fully tilted in one direction the surface of the plate should be a little more than half bare. The surface of the zinc bearing the picture is next flooded with a dilute solution of copper sulphate (10 grains to the ounce), and a fine blade deposit of precipitated copper is left. In this stage we have a zinc-copper couple, the contact between the two metals being' so complete that the voltaic action is able to decompose a variety of liquids hitherto not easily acted upon. The coppered plate is immersed in the acid solution, and an immediate evolution of hydrogen shows that an action is taking place, the zinc gradually being attacked where the copper is opposed to it. It should be remarked that the acid solution is so dilute that it has no susceptible effect on un¬ coated zinc, hence those portions covered by this greasy, resinous transfer ink are not acted upon. The dish containing the acid should be constantly rocked, to cause the bubbles of gas to disap¬ pear, and on this depends the success of the process. After twenty minutes in this solution, the slow evolution of hydrogen will show that the acid is nearly exhausted. The plate should then be withdrawn and washed under the tap. It should next be warmed to soften the ink and the resin, and more ink should be rubbed into the lines, as is done in rubbing up a lithographic impression. The dusting process is again resorted to as before. The copper solution is applied, and after washing, the zinc is again immersed in an acid solution (this time of double the strength of the foregoing), and the same motion given to the dish. These operations are again and again repeated, the warmed ink and resin gradually running down the raised lines, and filling LES TROIS MAMELLES, MAURITIUS. Reproduced from “Sub-Tropical Rambles,” by Permission of the Publishers, Sampson Low, Mabston, & Co. 165 in the close spaces. 'When a sufficient depth is given to the close lines, the large portions of the block which should print white may he sawn out with a fine saw.. The accompanying plate was produced in the manner described above. When printing off large numbers, zinc is liable to damage, and printers seem to Abject to this metal. Electrotypes may be taken from the zinc reliefs, and when faced with steel, leave nothing to be desired. It should be remarked that the employment of copper prevents local electrical action in the zinc when iron or other impurities are present, hence the metal may be that ordinarily to be obtained in commerce. The most successful worker in .zinc, as far as the writer knows, is Gillot, of Paris, whose pro¬ ductions are indistinguishable from the best woodcuts. The economy of this method of producing relief blocks is the fact that two or three square feet of them may be executed at the same time, very little additional labour being required. A very short way of obtaining blocks for relief printing is by treating a lithographic stone in a similar manner (omitting the copper solution), and using a hot iron for melting the ink and the resin. A mould is obtained from this in wax, paraffin, or gutta-percha, and an electrotype taken. Great depth is more easily obtained on a lithographic stone than on zinc if the manipulations are carefully attended to. Constant practice is required in these processes to ensure success. There are other processes practised at Chatham for obtaining direct reliefs in copper, but their publication would be premature. HINTS ON APPARATUS. THE CAMERA. Eon out-door and landscape photography the camera should be of the lightest possible make, as far as is compatible with rigidity. That form which is known as “the bellows,” with parallel sides, when properly made, fulfils these requirements better than any other. In it the lens remains fixed, whilst the ground-glass is made to move to attain proper focus. This will be found of great convenience. Every camera should have n “swing-back;” that is, the ground-glass should be made to hang plumb when required, supposing the camera to be tilted. Eor portraiture the same class of camera may be used, though 166 a heavier kind for this purpose is not objectionable ; the body may be rigid, in which case focus would generally be obtained by movement of the lens. For hot climates and rough usage brass- binding is recommended for the woodwork, and Russia leather for the bellows; cockroaches and white ants will not attack the latter. .For an amateur photographer, 8^ by 6|- is recommended as a suitable size. He can, unaided, conveniently carry this size, together with a dozen dry plates. Care should be taken that the inside of body is coloured of a dead black, otherwise reflec¬ tions on to the plate may occur, giving a hazy appearance on portions of the negative. The mode of testing this instrument will be patent to all; the chief defect to be looked for being a want of coincidence of the rough surface of the ground-glass with the plane of the silver wires which support the sensitized plate in the dark slide. Well seasoned mahogany is the wood most suitable for a camera, and it should be borne in mind that polish gives greater durability to it. The camera legs should be of such a length as will allow the lens to be raised at least five or six feet high. This rather exceeds the average height of the eye. There are various port¬ able folding legs extant for rigidity and convenience; though rather heavy, there are none better than Paget’s pattern, to be got at Meagher’s, 21, Southampton Row, London. The Scenograph is a neat little camera adapted for taking 61 by 4f- pictures. It is very light, and is very rigid considering its small height. The legs form a walking stick by a neat arrangement. To a careful {not a rough) photographer the scenograph is worthy of attention. LENSES. For landscape photography a single lens gives the most brilliant picture. It is more rapid than any other, as the loss of light from reflection by the surfaces is the least possible. For architectural subjects a doublet or triplet lens is necessary, as the first-named lens distorts marginal lines. For a complete outfit it is well to have four lenses:—(1) An ordinary single lens; (2) a wide-angle single lens; (3) a doublet lens; and (4) a wide-angle doublet. If only one lens can be provided, 3 should be chosen in preference to the others. For stereoscopic work the same applies. For portraiture a portrait doublet 167 should invariably be used. Ev consulting a catalogue of some well-known maker, all information necessary for guiding the choice will be found. English made lenses are to be recommended in preference to those of foreign make. They are more expensive, but are better finished, and are always achromatically corrected; that is, the chemical and visual foci are made to coincide. BATHS. Porcelain baths answer well till the glaze gets cracked; they must then be put aside, as contamination of the bath solution may result. Glass baths in a wooden case with water-tight top are to be most recommended, as the solution can be in¬ spected from time to time, also any accumulated dirt on the inside will be immediatedy noticed. One precaution should be observed in selecting glass baths, viz., to ascertain that the wooden case does not fit tightly on to the glass. The bottom of the case and its top should be padded with thick felt, to prevent breakage by any casual jar. Ebonite is too brittle and too much injured by climate, whilst gutta-percha is generally too impure a material to be substituted for glass. DIPPERS. Ebonite dippers answer in a temperate climate, and are not liable to break. A hook at the back to catch the edge of the bath, which just prevents it touching the bottom of the bath, is an advantage. Any deposit thrown down is thus undisturbed. Makeshift dippers may be manufactured from a long strip of glass, cementing a smaller strip on to it. Silver wire dippers, perhaps, are the # best, as they prevent an accumulation of the bath solution at the back of the plate. THE DARK TENT. There are a considerable number of dark tents which are capital for field work. A box tent is handy, as it will carry all the chemicals necessary for a day’s photography. Rouch’s pattern is excellent; that as modified by the writer has a few improvements which add much to the comfort of manipulation. A tent should be of such a size and weight that it can be con¬ veniently carried by a man. For hand carriage it should not weigh more than 25 lbs., including chemicals. Stillman’s 168 manipulating box is handy, and also the knapsack tent, for small pictures. When a tent is erected it should, if possible, be placed in the shade. The window should invariably be turned away from direct sunlight. The tent should be tested by placing in it a sensitized plate for a couple of minutes, whilst the window is darkened. Should the plate remain unaltered by development it may be taken for granted that the tent is fit for use. The window glass should be tested as above. DEVELOPING CUPS. Glass developing cups are far superior to any other, as they can be kept clean, and the amount of solution in them can be accurately seen, which is not the case with ebonite cups. In the field it is useful to have a couple of the latter ready at hand in case of accidents with the former. Tor plates up to 10 by 8, the children’s small tumblers, sold for about a penny, answer every purpose, and they are difficult to break. PNEUMATIC PLATE-HOLDERS, There is no better plate-holder than the india-rubber globe pattern. It is convenient to have the globe enclosed in a cylindrical box open at the lower end. NON-ACTINIC GLASS. The orange or red glass used for the dark room or tent should be tested. If a prism, such as a drop from a chandelier, be at hand, this is easily done. The eye should be brought close to one edge of it, and white light from a window be allowed to pass to it through the glass to be tested; if the violet, blue, and green rays be cut off, the glass is non-actinic. A practical test is to lay a piece of sensitized silver chloride paper beneath the glass and expose it to sunlight for half an hour: if the paper remain very nearly white, the glass will answer for ordinary photography. With bromide plates the glass should be tested by exposing silver bromide beneath it. NON-ACTINIC SCREENS. A useful screen for developing dry plates at night by candle¬ light can be made as follows :—Take a sheet of cardboard of the size of about 2 feet by 1 foot 6 inches. Lay off from the 2 feet side distances of 6 inches from each corner, and with a penknife cut half through the card in a line parallel to the ends. These 169 will form, flaps, which can be folded over to meet in the centre. Prom the centre portion, and six inches from the bottom, mark out a square of 8 inches; cut round three of the sides, but only- half cut through the bottom side, the penknife being applied from the inside of screen. This will allow a square flap to fold downwards towards the outside. On the inside of the opening- may be pasted or hung two or three folds of orange paper; or a sheet of gelatine (made by preparing a skin on a glass plate, as for heliotypy—page Ti3—and dyeing it deeply with aurine or aniline scarlet) may be glued to it. The candle is placed behind the screen, which should stand, supported by the two wings, in front of the operator. "When packed for travelling the flaps are folded up, and it can be placed in the portmanteau with the greatest facility. EVAPORATING DISHES. The best evaporating dish is made of platinum or silver.* 1 A substitute for the latter metal can be made by using one thickly electro-plated. It lasts a long time, and is not a quarter the price. Berlin porcelain is generally used. Dishes made of this material should be at least six inches in diameter to use with comfort. A metal dish enables a solution to be evapo¬ rated to dryness without burning the residue or driving off the water of crystallization. FUNNELS. Bibbed glass funnels will be found better than those made with smooth glass, as the air which is displaced can, with the former, find a ready exit. Gutta-percha funnels should be used with caution, as it is impossible to ascertain if they are clean. STILLS. A still should be of a portable character. It should be ascertained that the worm of the condenser is not made of lead or any lead compound. The top of the still should be of such a shape that any water which may be projected upwards during ebullition shall not be able to travel down to the worm. The following is a makeshift, which is in imitation of a well- known Indian contrivance. A is a saucepan of large size ; B is * When a silver dish is used, no nitric acid must be added. 170 the lid inverted. If a tinsmith he at hand, a spout, S, should he soldered into the lid, that the heated water in B may he changed with cold. A small hole is hored in the side of the same pan at 0, into which is fitted a tobacco pipe as shown in the figure. The surface of the water, W, is helow the pipe. "When the water boils the steam is condensed on B, trickles down to the tobacco pipe, and is collected at the other end of it. The first pint of water distilled should be rejected, lest it be con¬ taminated in any way. DISHES. Porcelain dishes are recommended in preference to any other kind. It is easily seen if they be clean, and they are easily scoured out after use. Ebonite dishes may be used for hypo¬ sulphite. They should be constantly cleaned from a sulphur deposit which forms on the bottom. DRAINING BOXES. A draining box which opens at the top and bottom is handy for outdoor work. For economy of space each pair of grooves should be capable of holding two plates back to back. DRY PLATE BOXES. To store dry plates, resort may be had to the plan of sepa¬ rating each one from the other by two strips of cardboard or thick paper bent zig-zag (as a hem is prepared for stitching), one at each end of the plate. Between each fold is placed a dry plate; the whole bundle should be bound round with twine, and wrapped in non-actinic coloured or opaque paper. It is neces¬ sary, however, when the parcel is broken into, to have some 171 mode of storing the plates. This is best done by using a grooved box with a removable lid. The lid should slide into grooves, and lock; an inner loose lid, with a spring attached to its top, and strips of unvulcanized india-rubber placed across its ends, should rest on the edges of the plates. The spring is pressed down on the upper lid, and this presses on the plates, clamping them tightly together in position; two other strips are placed similarly on the inside of the bottom of the box on which the plates rest. Each pair of grooves should hold two plates back to back. The whole of the inside of the box is usually lined with tinfoil; this allows dust to be got rid of, and prevents moisture permeating. METHOD OF CARRYING NEGATIVES ON TOUR. A tourist often finds the transport of a large quantity of glass in his travels a great source of discomfort, and to enable him to avoid it the following plan has been successfully fol¬ lowed by the writer. The method is that suggested by Mr. Walter Woodbury, who has published it in a “ brochure” on the scenograph. The application thus made refers to emulsion plates, but the writer has found it equally adaptable for all kinds of films. After a negative has been taken, fixed, and dried, a sheet of gelatinized paper (see page 152) is taken and immersed in cold water for a few seconds; the plate is placed beneath it, and the two are brought out of the water together as in the carbon development. The surfaces are brought in contact by a squeegee, and when the gelatine has sufficiently adhered, but is still damp, the film is stripped off. When dry, the reversed negative on paper is placed between the leaves of a blank book, and thus transported. The glass is of course serviceable for the preparation of other plates. To re-transfer the film to glass again, a plate of the proper size is flowed over with a solution of gelatine (1 ounce to 10 of water, to which 3 grains of chrome-alum are added) and dried. The film with the paper is immersed in cold water, and the plate brought beneath it and squeegeed as before. This time they are allowed to dry thoroughly, after which they are immersed in hot water. The gelatine from the paper dissolves away, and leaves the film on the glass, that which has been rendered insoluble by the chrome alum retaining it. The process is simple, and never fails with ordinary care, and the tourist will soon learn to appreciate its advantages. 172 APPENDIX. TO PURIFY WATER FOR PHOTOGRAPHIC PURPOSES. The importance of using chemically fit water in photography is not to he over-rated. When distilled water cannot be obtained, resort must be had to purifying it to the best of our ability. The water should be roughly tested, to see what impurities it contains. Eirst add a drop of nitric acid to (say) one ounce of water; warm, and add a few drops of a solution of potassium sulpho- cyanide. A red colouration will show the presence of iron sufficient to be injurious in making up a silver bath. Next add to a fresh portion a little ammonia and ammonium oxalate: a faint precipitate will show lime present to the extent of about six grains per gallon. This may be neglected. If more than a trace of precipitate be apparent, the water must be purified from the lime. Next boil the water. A precipitate will show that the lime is present as a bicarbonate; if not, it is present as a sulphate. Magnesia is much less common in water than lime, and is present generally as sulphate (Epsom salts)'. Supposing all be present, and it is necessary to render them innocuous, we must proceed as follows:—Eirst the water must be boiled, to get rid of carbonic acid, and to precipitate the carbonate from the bi-carbonate of lime ; this will leave about two grains per gallon of the calcium carbonate in solution. Next add ammonia till the water is slightly alkaline to test-paper. This will precipi¬ tate any iron present (probably present as carbonate), leaving carbonate of ammonia and .a little free ammonia in solution. Toil the water again till all the ammonia is expelled. Next add a grain to the ounce of water of silver nitrate, and place it in a blue or white glass bottle in the sun. This will precipi¬ tate the carbonates and chlorides present, and also the organic matter. Next add a few drops of a solution of barium nitrate to precipitate the sulphuric acid that may be present in the sulphates, and filter. The water thus purified will make an excellent bath water. If water be only required for washing- dry plates, &c., it should be boiled and passed through a char¬ coal filter, when it will be fit for use. Rain-water should be passed twice through a charcoal filter to 173 render it lit for use, that is, supposing it has been collected from the roofs of houses. Water collected from snow is generally quite free from every hurtful impurity. THE PREPARATION OF SILVER OXIDE. If to a solution of silver nitrate a solution of potash be added, a precipitate will be formed. This is the silver oxide. The potash should be added till no further precipitation takes place. The oxide should be allowed to settle, when the super¬ natant fluid should be decanted ofl (a syphon arrangement is very convenient), and fresh distilled water added to it. This, in its turn, after the oxide has been well stirred, should be de¬ canted off. The operation should be repeated five or six times, until a drop of the water evaporated to dryness on a clean piece of platinum foil leaves no residue. The chemical reaction is as follows :— Silver Nitrate. Potash.. Silver Oxide. Potassium Nitrate. Water. r ~2Agib7 + 2KHO = Ag 2 (T OT"+ ^HaT The chief use of silver oxide is to neutralize a bath in which there is an excess of free acid, the nitric acid forming with it a fresh silver nitrate. From this it is apparent that the oxide should be added till there is a slight deposit left. The silver oxide is slightly soluble in water, hence on adding it to a bath solution it may be necessary to add a few drops of a dilute solution of nitric acid (one part of acid to ten of water). TO PURIFY A BATH SOLUTION BY BOILING DOWN. The bath should be placed in an evaporating dish, and be evaporated down to dryness, and fused till all the frothiness that may be apparent has subsided. It will be seen that the organic matter has reduced a portion of the silver nitrate to metallic silver. When sufficiently cool, add enough nitric acid and water, 1 to 10, to redissolve this by the aid of heat. JSTow evaporate to dryness. The nitrate should again be re-dissolved in ten ounces of water, and be once more evaporated to dryness, when it will be found that it is fit for making up to strength, all excess of acid being dissipated. 174 F Boiling down a bath rids it of the alcohol and organic matter, but leaves the nitrates of cadmium, &c., unchanged. When surcharged with these latter, the silver should be precipitated. NEW BATHS FROM OLD. First Method .—Dilute the bath to twice its bulk, and filter out the iodide of silver which will be precipitated. In the filtered bath solution place strips of copper or copper wire, and leave them undisturbed for twenty-four hours. This will throw down the silver in a metallic state, leaving the copper and other nitrates in solution. Take two or three drops of the solution, and test for the absence of silver by adding a little solution of common salt to them. If no white precipitate appear, the conversion into metallic silver is complete. Care¬ fully decant the supernatant fluid, and withdraw all the copper visible; wash the silver in three or four changes of water until the blue colour due to the copper nitrate is absent; all the other salts will be washed away with the copper nitrate. Place the metallic silver in a large porcelain dish, and add gradually one drachm of pure nitric acid (1*36, the strength of the British Pharmacopoeia) to every 150 grains of silver nitrate (this can be estimated by the argentometer) in the original bath solution. The silver will gradually dissolve, but will be much aided by the application of heat. The solution will now have a greenish colour, from small particles of copper which have fallen, coated with silver, from the original wires or strips. These small particles of copper will be dissolved by the nitric acid, and will form copper nitrate. Boil down the solution to small bulk—till it begins to spurt. This will free it of any great excess of nitric acid. Next add distilled water to it till it has a slightly larger bulk than it had before boiling down- Hext add silver oxide, little by little, till the blue or greenish colour has entirely disappeared. This will precipitate the copper oxide from the copper nitrate, setting free the nitric acid, which, in its turn, will combine with the silver oxide. The copper will fall as a black powder mixed with any excess of silver oxide there may be. Take one or two drops of the solution in a measure, and add a drachm of water, and then add ammonia to it till the precipitate first formed is re-dissolved. If no blue colour is apparent, the substitution of the silver for the copper is complete; if not, more silver oxide must be added till the 175 desired end is attained. Distilled water must next be added till the strength of the bath is that required. This can be tested by the argentometer. An emulsion of silver iodide may here appear. If it do, no matter. When the solution is filtered the bath is fit for use, being chemically pure, neutral, and charged to a proper extent with iodide of silver. Second Method .—Dilute and filter the bath as in the first method, and place in the solution strips of zinc. The silver will precipitate, as with the copper; small particles of zinc will also fall with the silver, and must be got rid of. This may be done by two methods—either by dilute hydrochloric acid, or dilute sulphuric acid (one part of acid to twelve parts of water). The silver is collected from the solution either by filtration or decantation, and is well washed. It is then placed in a porcelain dish, and is boiled with the very dilute acid (about one part to one hundred of acid). This dissolves the zinc, and only slightly attacks the silver. The mass is thrown on the filter, and washed well with boiling distilled water. If sul¬ phuric acid have been used, this washing dissolves out any silver sulphate which may have been formed. The silver is dissolved up by nitric acid as in the first method. If hydro¬ chloric acid have been used, there will remain a little silver chloride, which will be filtered out. TO MAKE SILVER NITRATE. Silver coins are mostly alloyed with tin or copper. In both cases the coin should be dissolved in nitric acid diluted with twice its bulk of water. If tin be present there will be an insoluble residue left of stannic oxide. The solution should be evaporated down to dryness, re-dissolved in water, filtered, and again evaporated to dryness. It will then be fit for making up a bath. If copper be present, the solution must be treated as given in the last article, where the oxide silver is substituted for copper oxide. EASY TESTS FOR THE AMOUNT OF SILVER NITRATE IN A SOLUTION. Take half an ounce of the solution to be tested, and precipi¬ tate the silver as chloride by adding a slight excess of hydro¬ chloric acid or common salt. Filter the solution off, and dry the filter paper and the chloride over a water bath. The 176 chloride can then he easily removed from the filter paper, and should he weighed. The weight multiplied by T18 will give the amount of silver nitrate. Another very pretty method is as follows :—Measure with a pipette (or dropping-bottle) one hundred drops of the solution to be tested; rinse the pipette, and drop from it, into the silver solution, a solution of dried salt and water (thirty-five grains to the ounce), till no more precipitate of silver chloride is seen to form. The number of drops added to the silver solution will be the number of grains of nitrate of silver in the ounce of bath. There are two methods of ascertaining when no further pre¬ cipitate is formed:—first, by adding drops of potassium chromate (not bichromate) to the salt solution, and noting when the precipitate finally has a permanent red tinge after stirring; or the solution of salt may be placed in a stoppered bottle, and be shaken between each addition of the silver. The silver chloride agglutinates by shaking, and a fresh precipitate is seen to form at once on adding another drop of silver. When all the sodium chloride is precipitated, the solution remains’ milky. UTILIZATION OF SILVER RESIDUES. All paper or solutions in which there is silver should be saved, as it has been proved by experience that from 50 to 75 per cent, of the whole of the silver used can be recovered by rigid adherence to the careful storing of “ wastes.” 1. All prints should be trimmed, if practicable, before toning and fixing; in all cases these clippings should be collected. "When a good basketful of them is collected, these, together with the bits of blotting-paper attached to the bottom end of sensitized paper during drying, and that Used for the draining of plates, should be burnt in a stove, and the ashes collected.*' These ashes will naturally occupy but a small space in comparison with the paper itself. Care should be taken that the draught from the fire is not strong enough to carry up the ashes. 2. All washings from prints, water used in the preparation of dry plates, old baths, developing solutions (after use), and old toning baths, should be placed in a tub, and common salt added. This will form silver chloride with the nitrate. * In large establishments the films from rejected negatives may be added. 177 3. The old hyposulphite baths used in printing, and the solutions of cyanide of potassium, or sodium hyposulphite, used for fixing the negatives, should be placed in another tub. To this the potassium sulphide of commerce may be added, or else a stream of sulphuretted hydrogen passed through it till no more precipitation takes place. Silver sulphide is thus formed. 4. To No. 1 nitric acid may he added, and the ashes boiled in it till no more silver is extracted by it. The solution of silver nitrate thus produced is filtered off through white muslin, and put aside for further treatment. 5. The ashes may still contain silver chloride. This may be dissolved out by adding a solution of sodium hyposulphite, and adding the filtrate No. 3. 6. The solution from No. 4 may next he evaporated to dryness, and crystals of silver nitrate be produced, as given in page 174 ; or else common salt may he added, and the precipitate added to No. 2. 7. No. 2, after thoroughly drying, may be reduced to metallic silver in a reducing crucible*' by addition of two parts of sodium carbonate and a little borax to one of the silver chloride. These should be well mixed together, and placed in the covered crucible in a coke fire, and gradually heated. (If the operator be in possession of one of Fletcher’s gas furnaces, page 161, he can employ it economically, and with far less trouble than using the fire. It is supplied with an arrangement for holding crucibles, which is useful for the purpose.) After a time, on lifting off the cover, it will be found that the silver is reduced to a metallic state. After all conflagration has finished, the crucible should be heated to a white heat for a quarter of an hour. The molten silver should be turned out into an iron pan (previously rubbed over with plumbago to prevent the molten metal spirting), and immersed in a pail of water. The washing should he repeated till nothing but the pure silver remains. 8. Another method may be adopted, which is to place the chloride of silver in contact with sheet zinc or iron, covering it with water acidulated by oil of vitriol. The zinc or iron is converted into chloride, and the silver is deposited in a spongey mass. * The crucible should he of Stourbridge clay. x 178 9. The chloride may also he dissolved in sodium hyposulphite, and added to 3. The silver hyposulphite, having been reduced to the sulphide by the addition of the potassium sulphide, is placed in a crucible and subjected to a white heat; the sulphur is driven off, and the silver remains behind. 10. A last method is that of treating the whole of the residues as hyposulphite. A sheet of zinc is placed in the tub, and the silver is precipitated in a metallic state. The supernatant liquid is syphoned off, and replenished from the other waste solution. "When the amount of silver deposited is sufficient, it is filtered out through fine calico and collected. After thorough washing it should be heated, to drive off the large amount of sulphur which is collected, and may be treated with nitric acid to form silver nitrate, or else be melted in a crucible with borax to form an ingot. If the plan be adopted of forming silver nitrate, the small amount of gold present will be left behind as a grey powder. This, after being well washed, may be treated with nitro-muriatic acid, as given below, and re-converted into tri¬ chloride. There will always be a certain amount of silver sulphate formed from the action of the nitric acid on the sulphur deposited with the silver. TO MAKE GOLD TRI-CHLORIDE [ATT CL 3 ]. Place a half-sovereign (which may contain silver as well as copper) in a convenient vessel; pour on it half a drachm of nitric acid, and mix with it two-and-a-half drachms of hydrochloric acid; digest at a gentle heat, but do not boil, or probably the chlorine will be driven off. At the expiration of a few hours add a similar quantity of the acids. Probably this will be sufficient to dissolve all the gold. If not, add acid the third time; all will have been dissolved by this addition, excepting, perhaps, a trace of silver, which will have been deposited by the excess of hydrochloric acid as silver chloride. If a precipitate should have been formed, filter it out, and wash the filter paper well with distilled water. Take a filtered solution of ferrous sul¬ phate (eight parts water to one of iron) acidulated with a few drops of hydrochloric acid, and add the gold solution to it; the iron will cause the gold alone to deposit as metallic gold, leaving the copper in solution. By adding the gold solution to the iron the precipitate is not so fine as if added vice versa. Let the gold 179 settle, and pour off the liquid; add water, and drain again, and so on till no acid is left, testing the washings by litmus paper. Take the metallic gold which has been precipitated, re-dissolve in the acids as before, evaporate to dryness on a water bath that is at a heat not exceeding 212° F. The resulting substance is the gold tri-chloride. To be kept in crystals this should be placed in glass tubes hermetically sealed. For non-commercial pm poses it is convenient to dissolve it in water (one drachm fora grain of gold). Ten grains of gold dissolved yield 15*4 grains of the salt. Hence if ten grains have been dissolved, 15*4 drachms of water must be added to give the above strength. TO OBTAIN ALCOHOL FROM SPIRITS OF WINE. Take pure carbonate of lime, and burn it thoroughly in a crucible, expelling all the carbonic acid. This product will be quicklime. Add this to the spirit of wine to be rectified, and leave it in a tightly-corked bottle for three or four days. The quicklime will absorb the water, leaving the alcohol nearly anhydrous ; the alcohol, with the quicklime, may now be trans¬ ferred to a glass flask and be distilled over. This gives absolute alcohol of 0-794= If dry potassium carbonate be used instead of lime (see next article), and the distillization takes place, the resulting strength of alcohol is about -814. TESTING FOR THE AMOUNT OF WATER IN ALCOHOL. Take a small quantity of chloroform and pour it into a gradu¬ ated test tube. Add to it a given quantity of the alcohol to be tested. Shake up both well together. On settling, the water will have combined with the chloroform, and the difference in volume may be read off the test tube. Another method is to add an excess of dry carbonate of potash to a given quantity, and then to read off the amount of fluid left, calculating it as of *814 sp. gr. This obtains on account of the insolubility of the carbonate in alcohol and its affinity for water. TESTING FOR METHYLATED ALCOHOL. If a small quantity of caustic potash be added to alcohol suspected of being methylated, the presence of the impurity will be indicated by a brownish tint being given to the liquid. 180 PREPARATION OF PLATINUM TETRA-CHLORIDE [Pt C1J. Take any old scraps of platinum foil or wire, and having cleaned them with boiling nitric acid, place them in a porcelain dish containing aqua regia (four parts of hydrochloric to one of nitric acid). By the aid of heat this will cause a solution of platinum dichloride to he formed. The solution is evaporated nearly to dryness, or until it becomes viscous. It is then re¬ dissolved in water, and evaporated to the same state once more. Bor photographic purposes, this may be re-dissolved again in dis¬ tilled water of the strength of one grain q| the tetra-chloride to one drachm of water. It should be remembered that every ten grains of platinum yield 17 - 2 grains of the tetra-chloride; hence, with every ten grains of platinum dissolved, 17*2 drachms of water must he added to make it of the above strength. TO MAKE A STILL FOR DISTILLING ALCOHOL. The accompanying diagram shows the method for forming a rough still, hut one which is perfectly adapted for small distilla¬ tion. A and B are two Blorence flasks, supported, as shown, hy two supports; S S earring rings. In the neck of A is fitted a perforated cork, C. A'piece of quarter-inch soft glass tubing is bent in a common gas flame, and fitted into the cork, the long arm sloping slightly downwards. Two tumblers, I) and E, are placed in position as shown. D is filled with water, and from it is carried a length of tow. This is wrapped round and round the tubing, and the other end is allowed to hang over E. Capillary attraction will cause the water to be carried round the tubing by the tow; this will ensure the latter always being cooled. Into the flask A is poured the liquid to be distilled, 181 and a spirit lamp, L, is placed below it. The vapour passes into the tube T, where it is condensed, and passes into B. To prevent the water running down T from the tow, a small india- rubber band should be made to fit tightly round the tube, a small pin inserted at the bottom to take off the drops. It is a more convenient arrangement to have a proper Liebig’s con¬ denser. This may be formed by encasing the glass tube in a water-tight tin tube having a small tube with a funnel attached to it at the bottom end, and an overflow tube at the top. Cold water is poured into the funnel, and forces out the warm water from the top. The tin tube may be fitted with corks at each end, through which holes may be cut to admit the glass tube T. This plan will be found of use for distilling alcohol or collecting the solvents from old collodion. TO RECOVER ETHER AND ALCOHOL FROM OLD COLLODION. Add to the collodion a little potash to neutralize all acidity, and also a small piece of metallic zinc. This will cause the iodine to form zinc iodide. The solution may now be distilled over as given above, taking the precaution to fit a cork (through which a safety tube should pass to the bottom of the flask) into the bottle into which the condensed vapours pass.* The solvents may be used for fresh pyroxyline. TO PREPARE ALBUMEN FOR SUBSTRATUM. Place the albumen in a mortar with a little silica or fine white sand, and grind it till it is perfectly even. Eext add the water required. This method may be substituted for that given previously. TO DECOLOURIZE COLLODION. Add to the collodion small strips of metallic cadmium, zinc, or silver, and shake well. ‘With the first two metals the iodide formed will be dissolved by the collodion solvents. With the last the iodide will remain at the bottom of the bottle, except that part dissolved by the other soluble iodides. * The flask should he heated by hot water, till all the ether is distilled, if hy the naked flame the ether vapour is given off too energetically. 182 TO CLEAN THE HANDS FROM SILVER AND IRON STAINS, Take hydrochloric acid and dilute it to half its strength; or, better still, chloride of lime in strong solution. Pour a quarter of an .ounce of this on the hands, and rub well in till the stains disappear. Iron stains may still remain of a greenish tint. Rinse the hands , and apply a little dilute solution of ammonia or potash. The hands will he found free from stains. This method avoids the use of potassium cyanide or sodium hypo¬ sulphite. Chlorides of the alkalies are sometimes recommended in lieu of the hydrochloric acid. They are not so effective. The hydrochloric acid does not discolour the hands permanently. The alkaline solution in any case restores the tissues to their proper colour. After alkaline development the stains may he got rid of by oxalic acid. In all cases potassium cyanide will be effective. This should only be used with excessive caution, on account of its poisonous character. Its free use is apt to cause paralysis. TO TAKE SILVER AND IRON STAINS, ETC., OUT OF LINEN. The same procedure as above is effective: iron and silver are converted into chloride, and pyrogallic acid is decomposed by the acid. The iron washes out, and the chloride of silver is after¬ wards dissolved by the ammonia. To take stains out of cloth the same method may be tried, but it is rarely completely successful by any method, as the dye will be attacked by the acid. Potassium cyanide applied with soap may be tried, but it often leaves stains caused by the mordant of the dye. GROUND GLASS. When the ground glass of the camera has been broken, circumstances sometimes prevent it being replaced by a pur¬ chased article. The following method will give a substitute for it:— Take a piece of glass of the size to be ground. Lay it flat on a board or table, sprinkle the finest emery over the surface, and moisten it. With another small piece of glass grind it smoothly and evenly till a uniform grain is apparent over the whole surface. The finer the emery the fine! will be the resulting grain. 183 SUBSTITUTE FOR GROUND GLASS. Sensitize a plate as usual, expose and develop till there is a fair deposit on the film (if the developer be acidified with nitric acid in lieu of acetic acid, the silver will be deposited in a white form); use the silver as the ground surface of the glass. TO MIX SOLUTIONS CONTAINING GUM. It is often necessary to mix solutions containing gum at a short notice. The gum should be pounded to powder in a mortar, and warm water added to it. It is easily filtered through “ papier Joseph.” On no occount should a flask con¬ taining undissolved gum be placed over a naked flame, or the gum will then become decomposed. An enamelled glue pot is very useful for preparing gum solutions, the temperature of boiling water being thus never exceeded. Should gum be acid, it may be neutralized with lime-water. Lime-water is formed by placing a piece of burnt lime the size of a nut in a pint of water. PURIFYING PRINTING BATHS. The ordinary method of purifying a printing bath from the albuminate formed is to add a small quantity of pure kaolin, then to shake it up and filter. This method answers perfectly, but is rather wasteful. If the bath be rendered quite neutral to litmus paper, and be placed in the sun, the organic matter is deposited together with the silver oxide, and the solution rendered pure. If a small quantity of sodium chloride (common salt) be added, it will be found, on shaking up the silver chloride formed, that the organic matter is deposited with the chloride, and can be separated by filtration. The addition of a sodium carbonate answers equally well, and may be used with advantage. It is generally advisable to have a small quantity of the carbonate of silver at the bottom of the bottle, as by so doing, the neutral condition of the bath is ensured, and the organic matter is continually being deposited. 184 TO INTENSIFY A NEGATIVE AFTER VARNISHING. A negative may be rendered more intense after varnishing by adding iodine to the varnish till it assumes a light port wine colour, and re-varnishing with this solution in the ordinary manner. A SIMPLE METHOD OF ADDING EXTRA BROMIDE TO A COLLODION. Dissolve eighteen grains of bromide in an ounce of collodion. The addition of a drachm of this to each ounce of the collodion will give (very nearly) an extra two grains of bromide. TO INTENSIFY A NEGATIVE BY THE ACTION OF LIGHT. If, after developing, the negative be well washed, and exposed to sunlight till the unaltered silver salts assume a brownish colour, the intensity of the negative will be found to be materially increased. TO RETOUCH VARNISHED NEGATIVES. To retouch negatives a blacklead pencil is found to give the best results (B answers well). When varnished the negative requires a “tooth” given it to take the pencil. This is best obtained by taking very finely powdered resin, and rubbing it gently over the part required to be retouched. Einely-powdered pumice may be substituted for the resin. If a negative be varnished without heat, a sufficient tooth will also be given ; but great care is required, in re-varnishing it, to preserve the blacklead from running. In this case the second coating of varnish should be applied cold, and the plate be after¬ wards well heated. TO BEND GLASS TUBING. Ordinary glass tubing can be bent by simply placing the part where the curve is required in the flame of a spirit lamp, or in an ordinary gas flame. The tube should be held by the two hands, and turned round between the fingers, so that the whole of the surface to be acted upon gets equally heated. 185 When the glass feels softened, a gentle pressure by the hands -will give the necessary bend. If the heating be too great, the tubing will not remain circular in section at the head, but will be flattened. TO MAKE A SYPHON. Bend a piece of tubing, pierce a cork with two holes, and in one fit tightly one leg of the bent tubing, and in the other fit in a piece of straight tubing. To use the syphon, if the cork fit the bottle, press it tightly into the neck, or if it be larger, press it firmly on to its lip. See that the straight tube is above the level of the liquid, whilst the leg is well in it. Blow down the former till the liquid rise past the bend of the latter, when a constant flow will result, till the level of the inner or outer leg is reached. TO REMOVE THE VARNISH FROM A NEGATIVE. Varnish may be removed from a negative by warming it gently, and applying spirits of wine to its surface gently. The spirit must be poured off, the plate re-heated, and a fresh quantity ' applied as before. This operation must be continued till the varnish appears to be totally dissolved from the surface of the negative. Alcohol vapour made by heating spirits of wine over a spirit lamp in a test tube is very rapid in its solvent action. A final rinse of spirits should, however, always be given. Caustic potash will also remove most varnishes. CONVENIENT DROPPING BOTTLES. A convenient dropping-bottle may be formed with any ordinary four or six-ounce bottle by cutting a slot in the cork from end to end, and fixing it in the bottle in the ordinary manner. If this and an ordinary cork be attached to the neck of the bottle by twine, the two may be interchanged as required. TO TEST FOR IRON IN A FILTER PAPER. kloisten the filter paper with a drop or two of hydrochloric acid. Then add a drop of ferricyanide of potassium to the moistened part. A blue stain will show the presence of sufficient iron to be injurious to a bath solution. 186 TO SILVER GLASS FOR MIRRORS.* Prepare three standard solutions :— No. 1.—-Silver nitrate ... Distilled water No. 2.—Potash {pure) Distilled water No. 3.—Milk sugar Distilled water 90 grains 4 ounces 1 ounce 25 ounces ounce 5 ounces Nos. 1 and 2 will keep indefinitely ; No. 3 should he prepared immediately before use. Pour two ounces of No. 1 into a glass vessel capable of holding 35 fluid ounces ; add drop by drop (stirring all the time) as much liquor ammonia as will just dissolve up the first precipitate caused by it; add four ounces of No. 2. The new precipitate must be dissolved up once more by ammonia. Add distilled water till the bulk reaches 15 ounces, and add drop by drop some of No. 1, until a grey precipitate is just formed which does not dissolve after stirring for three minutes. Add 15 ounces more of distilled water. Set this solution aside to settle, but it must not be filtered. "When all is ready for immersing the mirror, add to the silver¬ ing solution twof ounces of No. 3. No. 3 may be filtered. Melt some soft pitch and run it into water to partially cool it, and take a common pencil and cause sufficient of the pitch to adhere to it to form a good large seal when pressed on to the back of the plate, adhesion to which is caused by a little turpentine (gutta-percha may be melted in hot water, and employed simi¬ larly, omitting the turpentine). The pencil fixed vertically to and in the centre of the plate by means of the pitch, no further step must be taken till the latter is quite cool and hard. The glass plate should be worked, or at the least a good specimen of patent plate. The surface which is to be silvered is next to be cleaned by nitric acid, rubbing it gently with a brush of cotton wool or the 11 Blanchard brush.” It is then washed well with common water, and finally rinsed with distilled * The substance of the article is taken from Browning’s “ Plea of Reflectors.” t The writer has found that 3 ounces sometimes aids the complete depo¬ sition of the silver.” 187 Avater. The glass is placed in distilled water till the silvering fluid is ready. In a dish about three inches deep, and slightly larger than the glass, the solution Ho. 3, and the silvering solutions made of Hos. 1 and 2 and ammonia, should be mixed, and the plate he suspended by a clamp or from a loop tied into the pencil in the fluid just so far that the hack is not co\ r ered. After sixty to ninety minutes the silvering will he complete, and the glass must he removed and immediately washed thoroughly, and finally rinsed with distilled water. It should then he placed on end, on hlotting-paper, and he allowed to dry perfectly. When dry the surface is polished by rubbing circularly with a piece of the softest wash-leather, and finally by the addition of the finest jeweller’s rouge. The pitch is then separated from the glass by a chisel, and any small particles remaining are removed by scraping and by a little turpentine. Success in the operation is greatly dependent on not using an excess of ammonia, and on the purity of the distilled water. TO FIND THE EQUIVALENT FOCUS OF A LENS, AND-ITS DISTANCE FROM AN OBJECT FOR ENLARGING, ETC. The equivalent focus of a lens is a term applied to a compound lens. It is the focus of parallel rays entering the lens. It is termed “equivalent” from being compared with a single lens that would produce the same sized image at the same distance from the object. Measure a distance of (say) one hundred and fifty feet away from some fixed point, and place a rod at one extremity. From this point measure a line exactly at right-angles to the first of some forty feet in length, and place another rod at its other end. How place the front of the camera exactly over the start¬ ing point of the first line and leA r el it, the lens being in the direc¬ tion of the first line. Having marked a central vertical line on 138 the ground glass with a pencil, focus the first rod accurately, so as to fall on the pencil line on the ground glass. Take a picture of the two rods in the ordinary way, and measure hack as accurately as practicable the distance of the centre of the giound glass from the starting point, and also the distance apart of the two images of the rods (at their base) upon the negative. Suppose the first measured line, AB, to he 149'; BB, the second line, to he 35'; AC to he 1' ; and EC, the distance apart of the two images, to be 3", E being the point where BE cuts CB. Then BB-fCE : CB :: CE : CE, which is the equivalent focal distance. Here, CB=150 ft. BD+»U=35-25' ft. CE—25 ft. ’.CF = 150+-25 35*25 1*063 ft. This gives the equivalent focal distance, which is the distance of the ground glass from the optical centre. Having taken the thickness of the ground glass previously, the distance may he set off from its smooth side on to the brass work of the lens by a pair of callipers. This point (the optical centre) having once been obtained, its position should be marked on the bras^ work, and from it all measurements should be calculated. This method is very nearly mathematically accurate. Were the distance taken of shorter length than those given, an appreciable error might be found. At the distance given the rays of light entering the lens from the rod are virtually parallel, and thus fulfil the necessary conditions. It must also be remarked that the distance AB being so great in com¬ parison with AC as that any slight error in the back measure¬ ment will affect the result by an inappreciable quantity, CE should be measured most accurately from the negative. The mean of a series of trials should be taken. Having obtained the equivalent focal distance of the lens, the respective distance of the object and ground glass from the optical centre can be obtained by the following formula:— 1 ) v— - and u—nv n where v is the distance of the focussing screen, u that of object from the optical centre, n being the linear reduction, or enlargement. ? On the following page is a table of enlargement or reduc¬ tion for lenses with certain equivalent focal distances. 189 TABLE OF ENLARGEMENT OR REDUCTION. 3 o . £ ® rt o o Enlargement or Reduction. • CD'S a 2 Remarks. 3 oh3 73 « o tf 1 2 3 4 5 6 pa tt 12 18 24 30 36 42 V v — distance of 0 12 9 8 7 * j 7 — 7 u image on ground glass, and «=dis- tance of the ob¬ 32* j 45* 6 * w 18 19* 26 39 ; V ject from the V 13 9f 8§ sr! 7* 7 iV u centre. u 14 21 28 35 j 42 49 V . V 14 10* 9* 8|i 8f ! 8! u 7| u 15 22* 80 37* i 45 52* V V 15 Hi 10 9| | 9 8f u 8 u 16 24 32 40 j 48 56 V V 16 12 iof 10 Of ! Of u 8* u 17 25* 34 42i ! 51 59* V V 17 12f u! 10! 1 10* j Of* u 9 u 18 27 36 45 ! 54 [ 63 V V 1 18 18* 12 j 11* i 10* 10* u 9-i- u 19 28* 1 38 47 t 1 57 66* V V 19 14* 12§ HI H| HiV u 10 u | 20 30 40 i 50 60 ! 70 V V 20 15 13* 12* 12 Hf u 10* u 21 31* 42 52* 63 73* V 21 15| 14 13* 12* ! 12f u 11 u 22 33 44 55 66 77 V V 22 16* 14| 13* 13* 12* u m u 23 34* 46 57* 69 80* V V 23 17* 15! 143 "o 13* 13A u 12 u 24 36 48 60 72 j 84 V V 24 18 16 15 ! 14* 14 n 190 Applying this table to an example :—Suppose the equivalent focal distance of the lens to be 9^", and that it is desired to find the distance at which the ground glass and the object are to he placed, to give an enlargement of four times linear ( i.e ., sixteen times in area). In the first column find and trace it horizontally till it reaches the column headed 4. Then 47^" will be the distance of the screen from the optical centre of the lens; and Ilf the distance of the object from the same point. Where any lens is used for copying, it is useful to find out the exact equivalent focus, and to make a table similar to this for it. By so doing, if a scale he marked on the base-hoard of the camera, the plan or object to be enlarged or reduced may be placed in proper position at once, as may also the ground glass. DETERMINATION OF THE STRENGTH OF ACETIC ACID. To determine the strength of this acid volumetric ally is some¬ what difficult, owing to the fact that sodium acetate possesses a feeble alkaline re-action. The most direct method is to take a known quantity of finely powdered marble or precipitated chalk (calcium carbonate), and add it to a certain quantity of the acid. After boiling, the calcium carbonate which is undissolved should be dried and weighed after washing in hot water. As an example, one fluid drachm of acetic acid was taken, and to it was added 100 grains of finely powdered marble, after filtering, washing, and drying, the residual marble was detached from the filter paper* and found to weigh 52*2 grains; therefore the amount of calcium carbonate converted into calcium acetate was 47*8 grains. The atomic weight of calcium carbonate CaC0 3 = 100 ,, ,, acetic acid C2H4O2 ... = 60 100 : 60 : : 47*8 grains : x .*. x — 21*68 grains The same quantity of glacial acetic acid at 60 weighs 57*8 grains. The solution under consideration contains 49*5 per cent, acid. 191 DETERMINATION OF THE STRENGTH OF NITRIC ACID. Procure some finely dried powdered chalk or marble, and place in a beaker in which has previously been placed 1 drachm of nitric acid diluted with another drachm of water. When all effervescence has ceased, filter off the residue, wash well in hot water, and deduct the weight formed from the original quantity. This gives the amount of calcium carbonate converted into calcium nitrate. The atonic weight of calcium carbonate CaC0 3 = 100 ,, ,, ,, nitric acid HNO = 63 Then 100 : 63 : : weight of lime dissolved : nitric acid. Note .—At 60° F. nitric acid of 1-457° specific gravity contains 79 per cent, of nitric acid, and at 1*420, 69*20 per cent. These specific gravities are those mentioned in the work. DETERMINATION OF THE STRENGTH OF SULPHURIC ACID. This cannot he determined by calcium carbonate, as the calcium sulphate is sparingly soluble in water; in this case, recourse may be had to taking a fixed quantity of the acid as before, and precipitating it with barium chloride, forming- insoluble barium sulphate, which, after washing, is weighed. Taking the atomic weight as before— 230 : 98 : : weight of precipitate : sulphuric acid (HS0 4 ) Note .-—At 60° Fah. sulphuric acid of 1*840 contains 97 per eent. of H,S0 4 . WEIGHTS AND MEASURES. 1 Sovereign weighs ... ... 123-274 grains 1 Shilling „ . 87-273 „ 48 Pence ,, ... ... 1 lb. avoirdupois 1 Half-penny = 1 inch in diameter Avoirdupois Weight. 16 Drachms ... ... 1 ounce (=437*5 grains) 16 Ounces ... ... 1 lb. (=7,000 grains) Trot Weight. 24 Grains ... 1 pennyweight 20 Pennyweights 1 ounce 12 Ounces 1 pound Apothecaries’ Weight, Solid Measure. 20 Grains 1 scruple 3 Scruples ... 1 drachm 8 Drachms 1 ounce 12 Ounces ... 1 pound Apothecaries’ Fluid Measure. 60 Minims 1 drachm 8 Drachms 1 ounce 16 Ounces 1 pound 20 Ounces 1 pint 8 Pints ... 1 gallon French Weights. 1 Gramme ... 15-432 grains Kilogramme ... 1000 grammes ( =2*2 lbs. Avoir, nearly) French Fluid Measure. 1 Litre ... 35-216 ounces (fluid) 1 Centimetre ... 17 minims nearly 50 Centimetres 1 ounce 6 drachms 5 minims French Linear Measure. 1 Metre 39-37 inches Silver nitrate is sold by avoirdupois weight. All formulae the book are to be made up by apothecaries’ weight. THE SPECIFIC GRAVITY OF ABSOLUTE COMBINED WITH VARYING QUANTITIES TABLE SHOWING ALCOHOL WHEN OF WATER AT 60° FAH. Alcohol Specific per cent. Gravity 50 •9228 55 •9068 60 •8956 65 •8840 68 •8769 70 •8721 72 •8672 74 •8625 76 •8581 78 •8533 79 •8508 80 •8483 81 •8459 82 •8434 83 •8408 84 •8382 Alcohol Specific per cent. Gravity. 85 •8357 86 •8331 87 •8305 88 •8279 89 •3254 90 •8228 91 •8199 92 •8172 93 •8145 94 •8118 95 •8089 96 •8061 97 •8031 98 •8001 99 •7969 100 •7938 TABLE OF Name. Aluminium A1 Antimony Arsenic Barium Bismuth Boron Bromine Cadmium Calcium Carbon C 12 6 Chlorine Cl 35-5 35*5 Chromium Cr 52-2 26-3 Cobalt Co 59 29-5 Copper Cu 63*5 31-75 Fluorine F 19 19 Gold Au 197 197 Hydrogen H 1 1 Iodine I 127 127 Iridium Ir 198 99 Iron Fe 56 28 New Old Name. Notation. Notation. Lead Pb 207 103-5 Lithium Li 7 7 MagnesiumMg 24 12 Manganese Mn 55 27-5 Mercury Hg 200 100 Nickel Ni 58-7 29-35 Nitrogen N 14 14 Oxygen O 16 8 Palladium Pa 106*6 53*3 Phosphorus P 31 31 Platinum Pt 98-7 98*4 Potassium K 39-1 39-0 Silicon Si 28 14-0 Silver Ag 108 108*0 Sodium Na 23 23-0 Strontium Sr 87-5 43*8 Sulphur S 32 16-0 Tin Sn 118 59-0 Uranium U 120 60-0 Zinc Zn 65-2 326 THE SYMBOLS AND ATOMIC WEIGHTS OF THE MOST COMMON ELEMENTS. New Old Notation. Notation. 27-4 13*7 Sb 122-0 122 As 75 75 Ba 137 68 - Bi 210 210 B 11 11 Bi- 80 80 Cd 112 56 Ca 40 20 o 194 CHEMICAL COMPOUNDS TO WHICH REFERENCE IS MADE IN THE BOOK. New Notation. New Nomenclature. Ammonium bromide HH 4 Br ,, chloride UH 4 Cl Old Old Nomenclature. Notation. . Bromide of annnoniumUH 4 Br . Chloride of ammoniumUH 4 Cl , Iodide of ammonium UH 4 I . ISTitrate of baryta BaO H0 5 . Sulphate of baryta BaO S0 3 . Bromide of cadmiumCd Br . Chloride of cadmiumCd Cl . Iodide of cadmium Cd 1 . Chloride of calcium Ca Cl . Chloride of copper Cu Cl . Pernitrate of iron Pe 2 0 3 3H0 5 . Persulphate of iron Pe 2 0 3 3S0 3 . Proto-nitrate of ironPeO U0 5 . Protosulphate of ironPeO S0 3 . Terchloride of gold Au Cl 3 . Sulphuretted hydrogen H S . Chloride of iridium Ir 2 Cl 3 . Bichlorideof mercuryHg Cl 2 . Bichloride of platinum Pt Cl 2 . Bromide of potassiumK Br . Chloride of potassiumK Cl . Iodide of potassium K I dichromateK 2 Cr 2 0 7 ... Bichromate of potashKO 2Cr0 3 permanganate KMn Permanganate of potash KO, Mn 2 0 7 ,, iodide hh 4 i Barium nitrate Ba(n0 3 ) 2 ,, sulphate Ba S0 4 Cadmium bromide Cd Br, ,, chloride Cd Cl, „ iodide Cd I, Calcium chloride Ca Cl, Copper chloride Ca Cl, Perric nitrate Pe (H0 3 ) 3 ,, sulphate Pe 2 (S0 4 ) 3 Perrous nitrate Fe (U0 3 ) 2 „ sulphate Pe S0 4 Gold trichloride Au Cl 3 Hydrogen sulphide H, S Iridium chloride Ir Cl 3 Mercuric dichloride Hg Cl 2 , Platinum tetrachloride Pt Cl 4 Potassium bromide K Br chloride K Cl ,, iodide KI 0 , Silver bromide Ag Br ... Bromide of silver Ag Br ,, chloride Ag Cl ... Chloride of silver Ag Cl „ iodide Ag I ... Iodide of silver Agl ,, oxide Ag 2 0 ... Oxide of silver Ag 0 ,, nitrate Ag U0 3 ... nitrate of silver AgonOj ,, sulphate Ago S0 4 ... nitrate of uranium Ur, 0 S0 4 Sulphuric acid H, S0 4 ... Sulphate of silver Ag 0 S0 2 Uranium nitrate U S0 4 ... Sulphuric acid HO S0 3 Zinc iodide Zn I 2 ... Iodide of zinc Zn I „ bromide Zn Br, ... Bromide of zinc Zn Br ,, chloride Zn Cl/ ... Chloride of zinc Zn Cl 195 ABSTRACT OF STORES REQUIRED FOR PHOTO-LITHOGRAPHY AND ZINCOGRAPHY. Acid, hydrochloric) in stop-) ,, nitric >• pered> ,, snlph. ) bottles.) Cloths, cheese ... ... ... Cotton waste ... . Eraser, metal, with box-wood handle... ,, with sheath . Galls, brnised ... Gum-arabic . . Handles, leather, for rollers ... Ink, black, in tin Knives, palette... Millboards (thickest). Mullers, zinc ... Oil, olive „ green . ... 1 lb. ... 1 „ ... 1 „ ... 2 1 pair 1 lb. 2 10 lbs. 2 £ pint Plates, zinc (according to size of press), Ko Press, lithographic Holler, ordinary ,, smooth ... Sand moulders ... Scrapers, box-wood, for press. Sieve, 120 hole. Sponges Stone, pumice ... ,, snake Stone, litho., fine and free from chalk Glaze boards ... Paper, glass Phosphorus 10 gnage. 1 1 i bsh. 2 1 2 4 lbs. 2 6 shts. 1 oz. 196 KIT THAT MAY BE NECESSARY FOR ONE DAY’S WORK IN THE FIELD. Camera. Dark Slides. Camera Legs. Lenses. Focussing Cloth. Do. Glass. Glazier’s Diamond. Circular Spirit Level. Tent. Water Bag and Clip. Tent Legs. Yellow Silk Handkerchief. Bath. Dipper. Glass Plates. Plate Boxes. Funnel. Filter Paper. 4-oz. Measure. Cotton Wool. Chamois Leather. Diaper Dusters. Dusting Brush. Developing Cups. Plate Holder. Emery Powder. Tripoli Powder. Spirits of Wine. Bath Solution. Collodion. Developer, 10 grs. Do., 50 ,, Intensifies Iron Do., Pyrogallic Silver Nitrate Solution, 20 grains. Potassium Cyanide. Iodine Solution. Tannin and Glycerine Solution. Glacial Acetic Acid. Golden Syrup Solution. Spirit Lamp. Bottle of Spirit. Tarnish. Piper & Carter, Printers, Gough. Square, Fleet Street, E.C. s ■ > > -