gi Ls Beas THEGETTY CENTERLIBRARY te PROSPECT STREET, RYE By T. K. GRANT, F.R.P.S. A photograph in natural colours, taken on the Autochrome plate, and reproduced by the four-colour process. = CASSELL’S CYCLOPAEDIA OF PHOTOGRAPHY EDITED BY BERNARD E. JONES ILLUSTRATED BY TWENTY-FOUR FULL-PAGE PLATES IN COLOUR AND HALF-TONE, AND BY HUNDREDS OF LINE DRAWINGS IN THE TEXT VOLUME I CASSELL AND COMPANY, LTD. 43-45 East 19th Street New York 1912 | Ob LIST OF CHIEF T. THORNE BAKER, F.C3S. HENRY W. BENNETT, F.R.P.S. A. H. BLAKE, M.A. GEORGE E. Brown, F.I.C. THEODORE BROWN J. C. Burrow, F.R.P.S. CHARLES P. BUTLER, A.R.C.Sc. (Lond.), F.R.P.S., F.R.A.S. DRINKWATER BUTT, F.R.P.S. EDGAR CLIFTON, F.R.P.S. . F. MARTIN F.R.P.S. WILLIAM GAMBLE ARTHUR D. GODBOLD . WALTER KILBEY, F.R.P.S.. ARTHUR LOCKETT, Honours Silver Medallist in Photography, City and Guilds. DUNCAN, THOMAS MANLY, F.R.P.S. . J. I. Picc, F.R.M.S., F.R.PS. . Percy R. SALMON, F.R.P.S. Py, WALL, F.R.PSS. . W. L. F. WASTELL, F.R.P.S. . CONTRIBUTORS Isochromatic Photography, Photo- telegraphy Architectural Photography, Carbon Process, Lantern Slides, etc. Night Photography Copyright Stereoscopic Photography, Kine- matography Mine Photography Astronomical Photography Studio Design and Construction Lenses Natural History Photography Photo-mechanical Processes Studio Work Focal-plane Shutter Work Cameras, Apparatus, Special Pro- cesses, etc. Ozobrome, Ozotype Photomicrography, X-ray Photo- graphy Historic and General Processes, Developers and Miscellaneous Chemistry, Colour Photography, Special Processes Pictorial Photography and Special Processes eae ' eS | Wht “ es Spf Wa ts PREFACE ANY years ago, while assisting in the production of a small photographic manual, the difficulty experienced in finding room for everything that ought to have been included brought to my mind a suggestion for an encyclo- peedic work covering all the phases of photography. It was not until this suggestion had been discussed, seven years later, with Mr. Percy R. Salmon that it became crys- tallised into something concrete and workable. To Mr. Salmon, more than anyone else, is due the credit for the particular form which this work has assumed. ‘Together we planned it, and together decided the majority of the multitudinous questions of detail that arose. Of photographic dictionaries and cyclopedias printed in the English language there have been as many as could be counted on the fingers of one’s hands; but the present volume is essentially different from any of them, and is undoubtedly the most ambitious work of its kind yet projected. With possible exceptions, its predecessors were written or compiled from cover to cover by one hand; whereas this work is the result of the co-operation of many men, each having special knowledge of his own particular branch. Modern photography has so many ramifications, each calling for the application of special knowledge, that I felt that the only proper course, in attempt- ing to produce a photographic cyclopedia at once authoritative and complete, was to enlist the services of as many specialists as possible. About a score of the best- known and most authoritative expert photographic writers extended their co-operation, and their contributions constitute the bulk of this work. While it must be confessed that complete accuracy is almost too much to hope for in the first edition of a work of reference, I have taken care to do all that could be done to check and verify the statements made. My especial thanks in this connec- tion are due to Messrs. Percy R. Salmon, E. J. Wall, Arthur Lockett and William Gamble, for the trouble they have taken in reading the proofs. I shall appreciate and acknowledge any minor corrections that readers may send me, and shall hope to be able to incorporate them in later editions, in the happy event of such being called for. The scope of the work demands some words of explanation. The object has been to include every accepted photographic term and to survey the whole field of photo- graphic knowledge, whilst giving particular attention to the requirements of the working photographer, both amateur and professional. This cyclopzedia is intended essentially as a simple guide to photographic practice, whatever else it may be. In all cases where the process described is commonly used, or is likely to be worked nowadays, working directions and definite formule are given. This work is intended not only for the practical photographer, but also for the scientific student, who will find in all those articles that have been written especially for him valuable, because authoritative, summaries of what has already been attained in the many branches of photographic science. he manufacturer, too, especially the manufacturer of materials, will find in this volume a mass of information relating to what others have done before him, and by profiting by it he will be prevented from wasting time and money in useless trials in some directions and possibly be given ideas as to commercially remunerative lines of experiment in others. vi PREFACE There are two matters, in particular, upon which I think it desirable to address a word to the critical reader. It will be noticed that a few biographies are given, and the question as to why such and such men are included and others omitted is sure to arise. ‘The biography of no living photographer will be found in these pages } and with regard to the dead worthies, I have done my best to include only those who, when viewed historically, have real claims to distinction. And in such a matter much must be left to personal opinion. The other matter is the omission, with a few exceptions, of trade names. ‘Their inclusion, a highly debatable point, would have meant the addition of more than thirteen hundred headings, the informa- tion given under which might rapidly have gone out of date. The exceptions, as in the case of a certain camera which it would be superfluous to mention, have now become part of the language, and are associated in the public mind quite as much with broad types of apparatus or certain classes of materials as with any particular brands of manufacture. The illustrations call for a word of explanation. The monochrome plates have been selected as representing separate phases of photographic art, and are offered as being good examples of their kind. On the other hand, three of the coloured plates are intended to represent merely the capabilities of the screen plates with which the original pictures were made; while, of the remaining two, one plate shows the steps in the production of a four-colour print and the other the composition of six of the best-known screen plates. The line drawings throughout the book (almost all of which have been drawn by E. S. W. Cunnington from the contributors’ sketches) have the sole object of elucidating the text ; much thought was given to the advisability or otherwise of using photographic illustrations in the text, but it was decided that drawings would be far more instructive. In many cases the drawings have been based upon illustrations appearing in trade catalogues, and in this connection my thanks are due to a large number of firms, including the following: Adams & Co. ; A. H. Baird; Bausch and Lomb Optical Co.; R. and J. Beck, Ltd.; W. Butcher and Sons, Ltd.; J. J. Griffin and Sons, Itd.; J. Fallowfield; J. Halden and Co.; Houghtons, Ltd.; Infallible Exposure Meter Co.; Kodak, Ltd.; J. Lancaster and Son, Ltd.: Marion and Co., Ltd.; G. Mason and Son; Newman and Guardia, Ltd.; A. W, Penrose and Co., Itd.; Ross Ltd.; Sanger Shepherd and Co., Ltd.; O. Sichel and Co.; Thornton-Pickard Mfg. Co., Ltd.; W. Tyler; A. G. Voigtlander and Sohn ; Watkins Meter Co. ; W. Watson and Sons, Ltd.; Westminster Engineering Co., Ltd. ; Westminster Photographic Exchange, Ltd.; and C. Zimmermann and Co. For the principal information given in the article ‘‘ Ceramic Process ” I am indebted to Mr. W. Ethelbert Henry’s standard work, “‘ Photo-Ceramics.”’ With regard to the formule, in practically all cases the parts are given in both British and Metric measures ; by whichever system a solution is made up, the relative proportions of the ingredients will be almost exactly the same, although the actual quantities nearly always differ. B. EB J. LIST OF COLOURED PLATES a Prospect Street, Rye.” A Photograph on the Autochrome Plate. By T. K. GRANT, F.R.P.S. . ° . ° ‘ ° - Frontispiece , ; FACING PAGE Still Life «4 Photograph on the Dufay Dioptichrome Plate ° . ° ° , 07 A Four-colour Print and the Consecutive Steps in its Production . 103 Portrait. 4 Photograph on the Thames Plate By H. ESSENHIGH CORKE, F.R.P.S. . é 5 - : : - : fs : ; Sec yy Screen Plates for Photography in Natural Colours . : : - Ags LIST OF MONOCHROME PLATES FACING PAGE Studio Portraiture—‘ Portrait of A. Haddon.” By FurRLEY Lewis, F.R.P.S.. f ; . : ; ; . : : : ; 16 Architectural Photography (Interior)—‘‘In Westminster Abbey.” By HENRY W. BENNETT, F.R.P.S. _ . ; . ; . : - 49 Zoological ey Head of eed Ram.” By W. L. F, WASTELL, F.R.P.S. . ; ; m1 Oe Various Renderings of Daffodils in Blue Vase _. : ° : + S252 Landscape Photography—‘*‘On Wisley Common.” By J. B. B. WELLINGTON, F.R.P.S. . : f : : ; : #146 Night Photography. By A. H. BLAKE, M.A. ; ; : P SouOd Architectural Photography (Exterior)—‘‘Church of Notre Dame, Caudebec-en-Caux.” By H. W. BENNETT, F.R.P.S. . ° - 208 Seascape and Skyscape Photography—‘“‘ After a Storm” 241 Combination Printing—‘‘ Dawn and Sunset.” By (the late) H. P. ROBINSON . ; : ; , ‘ ‘ ; . 256 289 Home Portraiture. By PERCY R. SALMON, F.R.P.S. - ; ; viii LIST OF MONOCHROME PLATES FACING PAGE Kinematograph Films _. ; . : . . : ° : - 304 Celestial PO Oy ee Moon.” Abgiaraohed at the Paris Observatory : ; : : eee Photomicrography — ‘‘Group of Insects’ Eggs.” By J. I. PiGG, F.R.M.S., F.R.P.S. : . : . . : ee Influence of the Lens on Perspective. By P. R. SALMON, F.R.P.S. 400 Radiography, or X-ray ee ee —‘*A Head.” By J. I. PiGc, F.R.M.S., F.R.P.S. ; . . 448 Firelight Effect. By H. ESSENHIGH CorKR, F.R.P.S. : : Mae fe Focal Plane Shutter Work. By WALTER KILBEY, F.R.P:S. . - 496 Snow and Hoar Frost Photography. By (the late) Col. J. GALE . 529 Telephotography—*‘ North Doorway, Rheims Cathedral.” By ERNEST MARRIAGE, F.R.P.S. ; : : ; ; - 544 CASSELL’S Cyclopedia of Photography ABAT-JOUR (Fr.) (Ger., Schrige Fenster, Oberiicht) A skylight or aperture for admitting light to a studio, or an arrangement for securing the same end by reflection. In the days when studios for portraiture were generally found at the tops of buildings not originally erected for that purpose, and perhaps in narrow thoroughfares or with a high obstruction adjacent, it became necessary to obtain all the available top light. This alone, however, is not well suited for artistic lighting, a side light being usually preferable. The abat- jour, therefore, was so designed as to give what was ptactically a side light, although coming ptincipally from above. A style much used formerly, and still occasionally met with, is Two Styles of Abat-jour shown at A. Into a bevelled opening cut in the wall, the roof, or both, is let a slanting glazed frame. Another form (B) is an inclined box- like structure open at the top and furnished with a mirror, or painted white inside, to reflect light downward through the window or glazing. The teflector used in daylight enlarging is really an application of the latter kind of abat-jour, by which the light, falling vertically from the sky, is reflected in a horizontal direction on the nega- tive in the enlarging camera. ABAXIAL Away from the axis. A term applied to the oblique or marginal rays passing through a lens. ABBE CONDENSER One of the most popular types of substage condensers for the microscope and used in photo- 1 micrographic work. It is made in two forms. The first consists of two lenses, and is of low numerical aperture. The second, used for high- power objectives, has three lenses, and is of higher numerical aperture (N.A.). ABBE, ERNST Professor Abbe died at Jena on January 14, 1905, aged 65 years. He was associated with the optical firm of Carl Zeiss, and paid particular attention to microscope objectives, with which his name is now generally connected. In 1881 he took an interest in the smelting of new optical glasses which was being made by Dr. Schott, and this was the beginning of the Jena glass factory of Schott and Genossen, the products of which have been used by lens makers as the raw materials of the large-apertured lenses known as anastigmats. Professor Abbe was the first to apply these glasses in a practical way to photo- gtaphic lenses. On the death of Carl Zeiss in 1888 Professor Abbe became sole proprietor, and in 1896 he introduced an arrangement by which the employees became practically the owners of the business. ABERRATION (Fr., Aberration; Ger., Abir- vung) A term used in photographic optics to express afaultinalens. (See ‘“‘ Chromatic Aberration,” ‘Spherical Aberration,” ‘“‘Curvilinear Distor- tion,” ‘‘ Astigmatism,” etc.) ABRADING POWDER Rubbed on the smooth surface of dried nega- tives and bromide enlargements in order to give a “‘ tooth ’’ for subsequent pencilling. Such abra- sives as pumice, cuttle-fish bone, etc., are gener- ally used, and these must be very finely ground and be free from grit. On negatives the powder is rubbed on lightly with the finger-tip, but on bromide prints it is applied with a leather stump. An excellent abrading powder for negatives con- sists of 1 part of powdered resin and 2 parts of cuttle-fish bone, the whole being sifted through silk. Cigar or tobacco ash also serves the pur- pose. Negatives may be reduced by means of a moist abrading mixture as described under the heading ‘‘ Baskett’s Reducer.’’ Various grades of emery powder and carborundum are used in lens and sereen grinding, etc. Abrasion Marks In process work, pumice and emery powders are used with water for cleaning or polishing zinc or copper. Fine emery powder is employed for graining the thick glass plates used for collotype printing. Pumice powder is used for removing gloss from prints that have to be retouched. ABRASION MARKS Black or pencil-like markings upon bromide and gaslight papers, chiefly occurring on glossy surfaces. They are seen only upon the finished print, and are due to pressure upon the gelatine film, and particularly to scratching against the printing frame or edges or corners of the packet when withdrawing the sheets. Handling the paper carefully will prevent them, and the use of a special developer, such as the following, will generally be of assistance :— Metol 34 gts. 3-4 g. Hydroquinone . Rye 68 eee a Sodium sulphite . He ta ypaet Baty Sodium carbonate CaO Aa0>; Potass. iodide . ba ld oye Potass. bromide (10 %) 36 drops 4 drops. Water to 20 OZ. 1,000 ccs. Any other metol-hydroquinone developer may be used if 1 grain of potassium iodide is added to each ounce of developer used. The addition of potassium cyanide is also resorted to, the proportion being 3 or 4 drops of a 10 per cent. solution to 1 oz. of developer. But the use of a special developer does not answer for all papers. Abrasion marks may often be removed from the finished print by rubbing lightly with a pad of cotton wool soaked in water, weak ammonia (5 drops per ounce of water), or methyl- ated spirit. An _ effective—although rather troublesome—plan is to immerse the finished print for one minute in the following solution :— Potass. iodide . 20 gts. 2 g. Iodine : s Spe MENS O'2 ,, Water . 20 02. 1,000 ccs, When the white parts of the print turn blue, transfer to a fresh “‘hypo”’ fixing bath for five minutes, and then wash thoroughly. If the iodide bath is allowed to act too long, it acts as a reducer. ABSORPTION (Fr., Absorption; Ger., Absorp- tion) This term is used both in a chemical and an optical sense. In the former sense it is used to designate the taking up of one substance by another, just as a sponge absorbs or sucks up water. As a rule, this is not accompanied by any chemical, but merely a physical change. Optically, absorption is applied to the sup- pression of light, and to it are due all colour effects (see ‘‘ Colour’). It is of great import- ance from a photographic point of view, as on Draper’s law, according to which only those rays which are absorbed by a substance act chemically on it, is based the whole of the photo- chemical action of light. Light, when absorbed, is not lost but is converted into some other form of energy, either heat or chemical action. The absorption spectra of dyes are of great interest, as by their aid it is possible to prepare colour filters of any given tint. Many substances and Absorption dyes have simple absorption spectra—that is to say, more or less well defined continuous por- tions of the spectrum are absorbed; other sub- stances, on the other hand, such as chlorophyll, have complicated absorption spectra, which change in character according to the concen- tration of the solution, or the depth of the solu tion, which is practically the same thing. The position and shape of the absorption bands of a substance are in many cases so characteristic that they serve as a means of identification. Obviously, the most opaque substances are the metals, but even these are translucent in thin films; silver, for instance, appears blue, whilst gold in thin films is green. Even such trans- parent and colourless substances as water, alcohol, glycerine, etc., possess characteristic absorption spectra, and therefore appear coloured when in sufficiently thick films. In studying the absorption spectra of coloured solutions, either the visual or the photographic method may be used, and the latter will be found not only more reliable, but considerably quicker. The visual method can obviously be applied only to the visible portion of the spectrum, whilst by the aid of photography the ultra-violet and infra- red regions can also be mapped out. Dr. Kenneth Mees and S. H. Wratten, who have made a special study of dye absorption spectra by photographic means, give the following outline of the methods which may be adopted : ‘“*(1) One may take a series of photographs with increasing dilution of the dye; (2) one may take a series of photographs with a constant concentration of the dye, but an increasing thickness of the cell; (3) one may take a series of photographs with a constant con- centration and constant cell thickness, but with a varying exposure. These three methods will all produce results differing slightly, though (1) and (z) are nearly equivalent to one another. (1) is a very slow method, and it would be probably quicker to use a spectro-photometer. (2) and (3), though quicker, are still slow if carried out as described. But if in method (2) instead of varying thicknesses of cell there is used a cell of which the thickness varies through- out the length—that is to say, a wedge-shaped cell placed in front of the slit so that the thick- ness of the layer of dye solution in front of the slit varies from end to end of the slit—the method resolves itself into taking one or possibly two photographs of each dye. Method (3) is inferior to the two other methods, as it involves the inter- pretation of the photograph of the plate curve. It is, however, a convenient way of examining the absorptions of coloured films and filters,” This method is most conveniently carried out by placing directly in front of the slit a small wedge of black glass so that the intensity of the light varies from end to end of the slit. This black wedge consists of a narrow prism of neutral tinted glass cemented to a similar prism of white glass, which of course destroys the prismatic effect by forming a parallel plate. With this the intensity of the light varies from 1 to 10,000. For visual measurement of absorption spectra a spectro-photometer is used. This consists of a spectroscope and some means of comparing the brightness of two spectra of one light source. This can be effected in several ways, as, for Accelerator instance, by two slits, which can be independently opened or closed, or by polarising prisms. The disadvantage of the variable slit system is that the two spectra are of unequal purity, and therefore accurate readings are impossible. In the polarising spectro-photometers the slit is usually divided across the middle by a small bar of metal, and the two light beams are polarised and dispersed, or dispersed and polarised, equality being obtained by rotation of a Nicol prism. The two spectra are brought into juxtaposition at the eyepiece, and equality of illumination obtained throughout its length. As one spectrum is con- tinuous and the other darkened Ly the absorption band, the former is reduced in brightness till the two are equal and the necessary readings obtained from the varied width of the slit or the angle through which the Nicols are turned. The transmitted light, divided by the incident light, which is always taken as unity, equals the extinction coefficient. ACCELERATOR (Fr., Beschleuniger) A substance added to developing solutions to shorten the duration of development and bring out the image more quickly. Usually it is an alkali which hastens the development owing to its power of absorbing the bromine set free from the silver salt during development, thus forming an alkaline bromide which acts as a restrainer, and as this increases with continued or repeated use of a developer, due allowance should be made. Common accelerators are sodium carbonate, washing soda, ammonia, potassium carbonate, sodium hydrate (caustic soda), and potassium hydrate (caustic potash). “‘ Hypo’’ (sodium hypo- sulphite) has been recommended when develop- ing with a mixture of ferrous-oxalate, but not infrequently it causes a partial reversal of the image; merely adding a few drops of a weak solution of “‘hypo” to the normal developer has a wonderful accelerating effect in some cases. Attempts have been made to introduce substi- tutes for alkaline accelerators in the form of acetone with sodium sulphite, tribasic sodium phosphate, and other chemicals, but only the two named have met with any success. Some *“one solution’? developers—such as rodinal, azol, etc.—include an accelerator; but in “ two solution ’’ developers, the developer proper is generally included in bottle “A” or “No. 1,” and the accelerator in-bottle “‘B” or ‘‘ No. 2.” It was long thought that an increase of the accelerator in cases of under-exposure brought out more detail, but photographers are now growing out of the idea. It is never advisable to add much alkali, because this invariably tends to produce fog. Accelerators cannot be used as the fancy dictates, some being more suitable for certain developers than others. Ammonia and sodium carbonate, for example, are found to give their best results in conjunction with pyro. Some of the newer developers—amidol, for example—do not require an alkali accelerator, and they will work with sodium sulphite, which is a preservative rather than an accelerator. In regard to the comparative strengths of the numerous alkalis used for accelerating develop- ment, a table will be found under the heading ** Alkalis, Chemical Equivalence of.” Accélévateur ; Ger., Acetic Acid ACCOMMODATION OF THE EYE (See ** Axial Accommodation.’’) ACCUMULATOR (Fr. Accumulateur; Ger., Akkumulator) Accumulators or storage batteries are used in X-ray work when the electric current cannot be obtained from mains. An accumulator consists of a series of lead grids filled in with lead oxide and immersed in dilute sulphuric acid. The potential of an accumulator when fully charged is 2 volts, and recharging is necessary when it falls to 1°8. Current is always leaking from accumulators even when not in use, and they should therefore be recharged at least once a month, or the plates will be ruined. The posi- tive terminal of a cell is painted red, the nega- tive black. In coupling up two or more cells the positive terminals are connected up with the negative terminals, the free terminals being then connected with the induction coil. A coil giving a 10-in. spark requires from six to eight accumu- lators, supplying a current of 5 to 10 ampetes. ACETALDEHYDE ACETATES Salts formed by acting upon metals or their oxides with acetic acid. Examples are lead acetate, sodium acetate, etc., etc., which are described under their own headings. ACETIC ACID (Fr., Essigsadure) Also known as purified pyroligneous acid. HC,H;0,. Molecular weight, 60. There are three kinds of acetic acid :—(1) glacial, con- taining about 99 per cent. of acid and 1 per cent. of water (sp.g., 1:°065); glacial acetic acid is the most widely used for photographic purposes, and receives its name from the fact that it solidifies and freezes into long ice-like crystals at com- paratively low temperatures; (2) commercial ‘** strong,’’ about one-third the strength of the glacial variety, and containing about 33 per cent. of acid, sometimes known as Beaufoy’s acetic acid (sp.g., 17044); (3) dilute acetic acid, made by mixing 1 part of the “strong” acid with 7 parts of water (44 per cent.), and sold as ‘* distilled white vinegar ’’ (sp.g., 17006). Acetic is the oldest of acids, and is given in old diction- aries as “‘ acetous acid.’”’ Its impurities may be hydrochloric, sulphuric and sulphurous acids, but most samples sold by chemists are quite pure enough for photographic purposes. Acetic acid readily dissolves in water, alcohol, and ether; it is a strong escharotic, causing painful blisters if allowed to remain on the skin, but the application of a solution of soda or any other alkali will at once neutralise it. It is extremely volatile, and should be kept in a glass-stoppered bottle and in a cool place. It has many uses in photography, and in the early days, when it cost as much as 8d. per ounce, was largely used as a constituent of the developer for wet plates. Nowadays, it is used for clearing the iron out of bromide prints after development with ferrous oxalate, to assist uranium toning, and, on rare occasions, as a restrainer when developing with hydroquinone. Acetic acid is a solvent for cellwoid, gelatine, and pyroxyline. (See ‘* Aldehyde.’’) Acide acetique; Ger., Acetic Ether € In process work, acetic acid is used in the iron developer for wet plates. The amount required increases as the working temperature increases ; at 60° F. 4 oz. of glacial acetic acid to 20 oz. of developer is a suitable proportion. The acid retards the action of the ferrous sulphate. A mixture of acetic acid and salt is used for clean- ing up the copper plates during half-tone etching to enable the etcher to see the image better when proceeding to re-etch. It is also used for remov- ing the magnesia that is rubbed into the etched plate to make the image visible. ACETIC ETHER (Fr., Ether acétique, Acétate ad éthyle ; Ger., Essigaether) Synonym, ethyl acetate. CH 3 CO O(CeH;). Molecular weight, 89. Solubilities, 1 in 17 water, miscible in all proportions with alcohol and ether. It should be kept in well-stoppered bottles away from fire, as the vapour is very inflammable. A light, volatile, colourless liquid, with pleasant acetous smell, obtained by dis- tillation from alcohol, acetic acid, or sodium acetate with strong sulphuric acid. Sometimes used in making collodion. ACETOL (Fr., Acétol; Ger., Acetol) A gelatine with an acetic acid substratum, used for collodion emulsion, It is said by its advocates to give a beautiful surface and spotless negatives. ACETOMETER (Fr., Acétométre ; Ger., Aceto- meter ) A hydrometer specially graduated to show the sttength of acetic acid. ACETONE (Fr., Acétone; Ger., Aceton) A colourless volatile liquid of peculiar and characteristic odour, having the formula C3; H, O or CH; CO CH;. It is met with commercially in various qualities. It is miscible in all propor- tions with water, alcohol, and ether. As the vapour is highly inflammable, the liquid should be kept in a bottle with a close-fitting cork or glass stopper. Acetone has two separate and distinct uses in photography, as an addition to developers and in varnish making. It acts as a solvent for resins, camphor, celluloid, etc., and should therefore never be used for films or in a celluloid dish. As a constituent of a developer acetone works best perhaps with pyro in the following one- solution form :— Pyro : 4 ; . 180 gts, 18g Sodium sulphite (crystals) 1,120 ,, bb i Acetone . : : 24 mins. 2°4 ccs, Water to 20 0z. 1,000 ,, It may, however, be used with other developers. When mixed with sulphite it forms acetone sulphite, and the soda of the sulphite combines with the developing agent to form a pheno- late, so that it may be used in place of an alkali when sulphite is present. It gives a very clean-working developer, moderately free from stain, and hardens the gelatine, or at any rate does not soften it as alkalies do. As a developer for paper prints it is best when combined with metol-hydroquinone in the following form :— Acetylene Generator Metol a : 27 gts. 2°72. Sodium sulphite 54 0z. 20 E Hydroquinone . 88 gts, aS Potass. bromide (10 %) 22 mins. 22s Acetone. ‘ . 40 drms, 25 ccs Water to . 2002, 1,000 ,, This is a one-solution developer which, as above compounded, is ready for use for both plates and papers. ACETONE SULPHITE (Fr., Acétone sulfite; Ger., Acetonsulphit) A compound of acetone with acid sodium sul- phite, introduced as a substitute for sodium sul- phite and the metabisulphites for development. It has the form of a white powder, and its formula is NaHSO, CO(CH3), H,O. It is soluble in water (up to 50 per cent.), but less so in alcohol, and it is used for making concentrated forms of developers, also for fixing baths and to blacken negatives after being bleached with mercury. Unlike acetone itself, it does not make the developer active, and consequently an alkali or a carbonate must be used. Ten parts of acetone sulphite are equivalent to 7 parts of potassium metabisulphite or 20 parts of anhydrous sul- phite of soda (40 of soda sulphite crystals) in a developer. As a preservative for pyro, 4 oz. of acetone sulphite should be added for each ounce of dry pyro used. ACETOUS ACID The old, and now obsolete, name for acetic acid (which see). ACETYLENE (Fr., Acétyléne; Ger., Acetylen) A hydrocarbon gas (C,H,) having, when pure, a sweet odour, the well known unpleasant smell associated with this gas being due to the pre- sence of impurities. It burns in air with a very bright flame, and is largely used by photographers for studio lighting, copying, etc., and as an illuminant in enlarging and projection lanterns. It is produced by the action of water upon calcium carbide (which see), 1 lb. of which will yield about 5 ft. of gas. It was first described and demonstrated in the year 1836 at a meeting of the Royal Dublin Society under the auspices. of Edmund Davy, a professor of chemistry, and was brought into commercial use about half a century later by the discovery of the modern method of manufacturing calcium carbide in the electric furnace. Acetylene forms, like other combustible gases, an explosive mixture with ordinary air, the presence of as little as 4 per cent. of the gas being sufficient to constitute a dangerous combination. It was in the early part of 1895 that photographers began to turn their attention to the photographic value of acetylene, and photometric tests prove that acetylene has eight times the actinic power of the average incandescent gas mantle. As an illuminant in optical lanterns, acetylene is better than the incandescent gas mantle, but not so good as limelight. (See “ Optical Lantern Illu- minants.’’) ACETYLENE GENERATOR (Fr., Générateur d’acétyléne; Ger., Acetylengasentwickler) An apparatus for generating acetylene by the action of water on calcium carbide. Of the two Acetylene Generator types of generators, that is probably the better in which the carbide is immersed in or dropped into the water, as when water is permitted to fall on the carbide great heat is created, tending to the production of inferior gas, and the evolu- tion of oily products which are liable to accu- mulate in the pipes. However, many generators in which the water drips very slowly on the Wi} iit i | \ | Vey in “MNT A. Bucket-type Acetylene Generator B. Hopper and Valve- type Acetylene Generator carbide, as in the majority of acetylene lamps for cycle use, have a high reputation. Carbide to water generators are illustrated herewith. In the apparatus shown at A the water is contained in the tank E, in which slides the gas bell or reservoir F. The receptacle G, filled with lump carbide, is suspended from the top of the reservoir, which falls by its own weight, acetylene beginning to generate directly the carbide comes in contact with the water. The gas, filling the reservoir, causes it to rise and lifts the carbide receptacle, thus stopping further generation until by the consumption of the gas the reservoir again falls. The carbide receptacle is introduced or removed by extracting the tightly-fitting plug H. In the generator shown at B granulated carbide is contained in the hopper G, in which is a small opening or valve closed by the conical plug J. The plug is attached to a rod having a weight K asitslowerend. ‘The reservoir falls when empty, until the weight strikes the bottom of the water tank, this causing the rod to push up the plug J, allowing a small quantity of carbide to fall through the opening. The ascent of the reservoir as gas is generated raises the weight, which pulls down the plug and again closes the aperture. B is better in principle than A, as the carbide is acted upon in smaller quantities at a time. In all the earlier generators the carbide re- ceptacle was attached to the reservoir, causing an unnecessary pressure, and one also that varied as the carbide was consumed. Another dis- advantage was the fact that the waterseal was furnished from the same water as that used for generation. In the devices shown at C and D these objections are obviated. In the former of these the plug J is weighted to keep it normally Acetylene Generator closed, and its rod is connected at its upper end to a T-piece, this being in turn pivoted at each side to angle irons, which carry wheels at their outer ends. The reservoir F, in falling, depresses the angle irons, and these raise the plug rod by means of the T-piece, thus liberating a small charge of carbide. The plug is re-closed by the weight as the gas-laden reservoir rises. In the device shown at D the hopper ¢c containing the carbide has an upward-closing plug j fixed to a rod. The reservoir F in falling presses on the top of the rod and opens the plug, while the spring I, serves to return the rod and close the opening when the reservoir rises. Except when the carbide is dropped in small quantities into a sufficient excess of water, a washing apparatus of some kind is called for. If any quantity of acetylene is made, it is better also to remove the remaining impurities by passing the gas through calcium chloride with which is mixed a little unslaked lime, the mixture being contained in muslin bags arranged on perforated shelves, one over the other, in the purifier. A similar mixture is sold ready-pre- pared, and with this no bags or shelves are required, the lumps being merely packed in the receptacle. The pressure should not rise above two or three inches of water in the generator, and the pipes should not be less than % in. diameter. All taps must be well ground in, and should be lubricated with vaseline to prevent the corrosive action exerted by acetylene on brasswork. Since the gas leaks more easily than ordinary house gas, greater care must be taken with all joints. Tar and paint are quickly affected, es iS oe regia: % 1 : Tihtty, ' ! ‘rtty ‘ary 7 hh, ist ee ee ed D. “ Dreadnought ” Acetylene Generator C. “Ever Ready” Acetylene Generator and should not be used for this purpose; red- lead or white-lead, applied sparingly, is best. To detect a leak, a solution of soap and water may be applied, noticing if bubbles appear. In starting, the first gas coming off should be allowed to escape, as it contains an admixture of air. ‘The generator should be kept at least 8 ft. or 10 ft. distant from any light, and no light should be at hand when emptying it after use. Copper should not be employed in acetylene Acetylide Emulsion generators, as under certain conditions a deton- ating explosive compound is formed. The best material for the body is tinned or galvanised sheet-iron, brass being used only for taps. Special burners are required for acetylene. The best are of steatite, on the air-injector principle. For photographic use, Bray’s 00000 (acetylene) burners are perhaps most suitable. Fifteen of these, mounted in a white reflector, can be employed for studio portraiture, but a slightly larger number is better. Two-, three-, and four-burner jets are made for optical lantern and enlarging purposes. The soot that soon collects on the burners may be removed with a toothbrush or anything similar, while the holes may be cleared with a fine needle or wire. ACETYLIDE EMULSION Wratten and Mees prepared a silver acetylide emulsion by passing acetylene into ammoniacal solution of silver nitrate and emulsifying the precipitate, which is very explosive, in gelatine. They found that it blackened in daylight about ten times faster than silver chloride paper, but could obtain no evidence of the formation of a latent image with short exposures. ACHROMATIC (Fr, A chromatisch) A photographic lens is said to be achromatic when the visual image as focused upon the ground glass falls upon the same plane as the actinic image which forms the impression upon the sensitive surface. In telescopes and micro- scopes, achromatism means that the visual images are free from colour fringes, but it is quite possible for a photographic lens to show these fringes upon the focusing screen and yet to be capable of giving a sharply defined image upon the plate. ‘‘ Actinic” is a better term to use in connection with photographic instruments than achromatic. (Sce also ‘“* Chromatic Aberra- tion.’’) ACHROMATISM The condition of being achromatic. ACID BLAST The name given to an etching machine for process work, invented by Louis E. Levy, of Philadelphia. The working principle is that the acid is blown up to the plate, by means of air under compression, from a series of atomisers or sprays projecting upwards; a partial vacuum is maintained in the etching chamber above them, and the plate is held face downwards, and slowly moved to and fro horizontally to equalise the etching. ACID CHROMATE OF POTASH ** Potassium Chromate.’’) ACID DEVELOPERS A term usually applied to ferrous sulphate and other wet-plate developers in an acid condition. ACID FIXING BATH The “hypo” (hyposulphite of soda) fixing bath made acid. Ordinary ‘‘hypo”’ fixing baths are neutral, not acid; but acid fixing baths may be used for negatives and bromide and gas- Achromabique; Ger., (See Acid Resist Varnish light prints, although not for prints on print- out papers. Their advantages are that they immediately stop the action of the developer, prevent stains, and keep quite clear in use. It does not do simply to add any acid—say sul- phuric or hydrochloric—to an ordinary “hypo”’ bath, inasmuch as this causes a yellow pre- cipitation with the accompanying evolution of sulphuretted hydrogen, which militates against the permanency of the prints. Sulphurous acid, however, may be added to an ordinary hypo fixing bath in the proportion of 2 drms. to I pint. The best acid fixer is made by adding a little potassium metabisulphite to the ordinary solution of “‘hypo”’; the exact proportions are of no importance, $ oz. to 1 pint being, however, a good average. The following is a precise formula suitable for prints :— Sodium hyposulphite . 3 02. Potass. metabisulphite. $5, ry a Water * . 2055 1,000 cCs. This is suitable for negatives if the “hypo” is increased to 40z, A cheaper form of acid fixer is the following :— 150 g. “Hypo” solution (1 in 5) 25 oz. 1,000 ccs. To which add a mixture of :— Tartaric acid solution (1 in 2). : 2 OZ. 30 ccs. Sodium sulphite solu- tion (I in 4) . iz ” 79 5 There is a danger of overworking acid baths and consequently of not fixing properly, as the clearness of the solution is apt to lead to the belief that it is still in a good working condition, although really it may be partly exhausted. ACID OXALATE OF POTASH “* Potassium Oxalate.”’) ACID RESIST A term applied in process work to all sub- stances used to form the image or protecting coating which prevents portions of the metal from being attacked. Practically all resinous bodies—bitumen, pitch, waxes, lacs, indiarubber, guttapercha—and fatty bodies form acid resists. Talc, graphite, silica, sulphur, carbon, and other inert bodies also form acid resists when dusted on to an image of atacky nature. Non-corrosive metals form another class of resists, as the image may be formed by a metal that is not attacked by the acid, which, however, attacks the base plate. Colloid bodies—such as gelatine, glue, gums, and albumen—also form acid resists, as in the so-called ‘‘ enamel process ” (which see). Acid resists are applied as varnishes for protect- ing the back and margins of the plate, as etching grounds, for scratching or engraving through with needle points and gravers, as etching inks, paints, dusting powders, light-sensitive films, electro- lytic deposits, fused metals. They are used for relief and intaglio etching, for lithography on stone, zinc, and aluminium, for protecting vessels and other articles used for etching, and for elec- trolytic etching or deposition. ACID RESIST VARNISH Shellac is probably the best and most used of the gum resins as a resist varnish. Cover (See Acid Stain Removers the shellac with wood alcohol, and leave for a few hours to dissolve. For 4 oz. of shellac about 8 oz. of methylated spirit will be required, and, for colouring, about 2 drms. of methyl violet dye. To prevent the varnish setting too hard, add to every pint about 4 oz. of linseed oil. Shellac varnish is said to contain impurities which, when exposed to light, become insoluble, so that the varnish is difficult to remove; the remedy is to add 60 drops of oil of lavender to each pint of varnish, and use the varnish a little thinner. ACID STAIN REMOVERS Acid solutions used for clearing away stains caused by developers. Their use is open to objection, as fully explained under the heading “Stain Removers.” ACID SULPHITE (See ‘‘ Sodium Bisulphite.’’) ACIDS (Fr., Acides ; Ger., Sduren) Hydrogen compounds, which have a sharp taste and redden blue litmus paper. Acids may be solid, liquid, or gaseous, and are divided into strong and weak, organic and inorganic. Organic acids are usually such as contain carbon, whilst inorganic are those containing a metal. A further subdivision is made as to hydrogen or oxy-hydrogen acids ; of the former, hydrochloric acid HCl is an example, and of the latter, sul- phutic acid H,SO‘, as this contains oxygen as well as hydrogen. Acids are further differen- tiated into mono-, di-, tri-, etc., basic acids, and this refers to the number of molecules of hydrogen which are replaceable by a metal. For instance, nitric acid HNO; is monobasic, and forms salts of the typical formula XNO, (X here being a metal), Dibasie acids can be exemplified by oxalic acid, H,C,0,, which would form a salt having the composition of X,C,0,—e.g. KeC,0,, oxalate of potash. An example of a tribasic acid is boric acid H3;BO;, which forms borates X;BOs. In process work, acids play an important part. ‘Nitric acid is almost exclusively the mordant used for etching zinc. Acetic, chromic, citric, fluoric, formic, gallic, hydrochloric, nitrous, phosphoric, picric, and tannic acids are all used in photo-mechanical processes. ACIDS, TESTS FOR Whilst strictly belonging to the domain of chemistry, it may be useful to give the usual tests for the acidity or otherwise of a solution. Blue litmus paper is reddened by acids. Phenol- phthalein solution (30 grs. in 10 oz. alcohol), a colourless solution, is reddened by alkalis, and the colour discharged by acids. Methyl orange (4 gts. in 10 oz, of water), an orange solution, turns pink with acids. ACLASTIC (Fr., tisch) Not capable of refracting, or bending, light. ACRIDINE YELLOW AND ACRIDINE ORANGE NO (Fr., jaune d’acridine, Orangé d’acridine NO; Ger., Akridingelb, Akridinorange NO) Two complex basic aniline dyes which have been suggested as sensitisers for emulsion work. Aclasiique; Ger., Aclas- Actinic They ate two of the most powerful sensitisers for green, but have found no practical application, as they stain gelatine very deeply, alcohol alone removing the stain. ACROGRAPH (Fr., Acrographe; Ger., Akro- graph) An engraving machine invented by N. S. Amstutz, an American engineer. Its essential features are a revolving cylinder and an engrav- ing tool—a V-shaped graver—carried along parallel to its axis; a phonograph, or a screw- cutting lathe, gives the idea. A photographic gelatine relief, such as a carbon transfer on cellu- loid with the image in perceptible relief, is wrapped round the cylinder, and over this relief is stretched a sheet of thin celluloid. As the cylinder revolves, a spiral thread is cut on the celluloid, this having the effect of making cuts in straight lines across the picture, but as the tool passes over the relief it cuts more or less deeply, according to the light and shade of the picture. Thus it reproduces the photograph as a kind of half-tone. The celluloid cutting can be printed from direct, or it can be made to serve as a matrix for electrotyping and stereotyping. By filling in the lines with transfer ink it can be used as a lithographic transfer, or by filling them with any opaque substance it can be used. as a negative for printing an image on to metal. The elaborations from the simple principle outlined above are in the form of micrometer adjustments for the tool, a microscope and electric lamp for watching the progress of the cutting and for setting the tool, and dividing wheels for varying the pitch of the lines. ACROMETER (Fr., Oléométre ; Ger., Oelwage) A kind of hydrometer specially graduated for testing the specific gravity of oils; known also as an oleometer or oil tester. An instru- ment of this description is sometimes useful for verifying the purity of the oils used in certain photographic and photo-mechanical processes. ACTINIC (Fr., Actinique; Ger., Aktinisch) A term applied to light that is rich in actinism, this being the property of light that causes chemicals to combine and decompose. In the early days of photography it was assumed that only the ultra-violet, violet, and blue rays were chemically active or actinic, hence these regions of the spectrum were so termed. Later researches have proved that it is practically merely a ques- tion of length of exposure which determines the photo-chemical action of light; in other words, that all the rays of the spectrum or all colours will act on sensitive emulsions if sufficient expos- ure be given. The expression most usual now is the ‘‘more refrangible”’ or ‘‘less refrangible’”’ rays. In process work, where the electric arc light is almost entirely used, the actinic value of the light is ‘of great importance. It is found that the enclosed arc is very rich in actinic rays, and these are increased by operating the lamps with a comparatively high voltage, resulting in a long flowing arc emitting a violet light. This is photographically very active, and exposures are greatly reduced compared with those neces- sary with the open arc. Actinic Doublet ACTINIC DOUBLET ACTINIC FOCUS A term generally used to express the focus for the blue end of the spectrum, to which the sensitiveness of the earlier photographic plates was almost entirely limited. The focus of the yellow or strongly luminous region of the spec- trum did not always coincide with that of the blue and violet rays, so that an image sharply focused, as far as visual observation went, gave a blurred image on the sensitive plate. A lens giving such a result was said to have the visual and ‘“ chemical’ or actinic foci non-coincident. This is very rare in modern lenses, even of the cheaper class. (See also ‘‘ Lens.’’) ACTINOGRAPH An instrument for estimating the exposure necessary for a photographic plate, invented by Hurter and Driffield. It embraces no new principle, but is simply a kind of slide-rule for atriving at a result without calculation in a manner precisely similar to that which was adopted in the exposure tables that were pub- lished by W. K. Burton and other pioneers of modern photography. It consists of two parts, a light scale and a scale of subjects, plate speeds, and lens apertures. The light scale is based on the fact published by Dr. Scott about 1880 that in clear weather the actinic value of the light varies in direct proportion to the height of the sun above the horizon. For example, the altitude of the sun is nearly four times as great in mid-summer as in mid-winter, and little more than one-fourth of the exposure is neces- sary in the middle of June when compared with that of December. In practice its use is less satisfactory to the ordinary worker than the exposure meter. ACTINOMETER An instrument for gauging the depth of print- ing in those processes in which little or no visible image is produced by exposure to light; known (See ‘ Lens.’’) A. Actinometer with Paper Scale also as a print meter. There are two types of actinometers, differing both in character and in method of using. The essential feature in each, however, is that a piece of silver ptinting-out paper is exposed to light until a certain effect is produced, and by this the correct printing of the invisible image can be estimated. The older Actinometer and simpler pattern consists of a small box with an opaque cap or lid, in which is a small opening. At one side of this opening is a small square painted in a medium dark colour to resemble as closely as possible the colour that silver paper assumes and passes during printing. It is essen- B. Johnson’s Actinometer tial that this tint should be a medium tint in silver printing, and that the paper should pass the colour by continuing the exposure; other- wise it would be difficult to determine when the correct matching of the colour, or the correct time of printing, had been reached. A square or a strip of silver printing-out paper is placed under the lid and kept in fair contact by a pad. The actinometer is put out to print with the frames containing the carbon prints, and the small portion of the silver paper visible through the opening gradually darkens until it matches the printed tint at the side of the opening. The time necessary for this is called “one tint.’ As soon as one tint is printed the silver paper is moved forward and a second tint printed, and so on until the prints are completed. Experience alone can determine how many tints will corre- spond with the correct exposure for any print; as negatives and actinometers vary considerably. With this form of actinometer each succeeding tint need not always be exposed immediately the preceding one is printed if the light is uniform. The time of matching the tint may be noted, and three or four succeeding tints timed from that. The second form of actinometer is more simple in use, and more suitable for the amateur worker, It consists of a series of squares of varying density —practically a test negative—and is used exactly as an ordinary negative. These Squares range from one very thin up to a density equal to that of the sky in a very strong negative, and they are numbered consecutively to facilitate reference in printing. If a piece of silver paper is exposed to light under this test plate, Ba Hit exposure will show a faint image of the first two or three Squares, and with a longer exposure more of the Squares will be visible on the silver paper. The Squares are surrounded by an opaque margin to render the image more plainly visible. The actinometer is put out to print at the same time as the frames containing the carbon prints, and each is brought in when the number con- sidered correct for that negative is reached on the actinometer. The actinometer is examined oc- casionally, and the “‘number ”’ that is considered printed is the square bearing the highest number that can be seen. Of course, a very faint image of that square is all that will be visible, the lower numbers, that have been fully printed for some Actinometric time, being seen as darker squares. These darker Squares assist in determining the highest number visible—the faintest square that can be seen. One actinometer will serve for several frames, provided that all are put out at the same time. In process work, various forms of actinometers are used for timing the printing of the image on the plate when exposed to daylight. The sim- plest form is that shown at A, consisting of a series of thicknesses of tracing paper bearing a number corresponding to the layers underneath. Another form has a glass scale bearing a Woodbury film, the pigmented gelatine graduat- ing in thickness from transparency to opacity. Burton’s actinometer consists of a series of six tiny negatives made by the carbon process. The negative to be printed can be compared with these, and a corresponding exposure given. This form of actinometer is very useful for collo- type and photogravure work. Johnson’s acti- nometer B is chiefly used for carbon printing. It only registers one tint, which is compared with a suitably coloured mask. If more than one tint is required to complete an exposure, the sensitive paper is shifted to a fresh position. The Sanger-Shepherd fraction tint actinometer consists of a scale of densities on a quarter-plate glass which is put into a printing frame and a piece of sensitised paper exposed behind it. It is very useful for timing the bichromated films in colour transparency work and for carbon printing, but it can be applied to any other snag in which the exposure has to be accurately timed. ACTINOMETRIC (Fr., Actinométrique ; Ger. A ktinometrisch) Pertaining to actinometers, or to the measure- ment of the chemical, or actinic, power of light. Actinometry is the branch of science that deals with the numerous methods of testing the chemical activity of light, and which makes a study of the variations in its intensity in differ- ent quarters of the globe, or at different seasons and hours. ACTINO-POLYCHROME (Fr., Actino-Poly- chrome; Ger., Farbenphotograph) An early name for a photograph in natural colours. ACTION More often than not, action is rendered in an unsatisfactory manner by photography, although this does not apply to cinematograph renderings. A person’s mental impression of a man walking, a horse running, and so on, is the result of a blending of all the different positions assumed during the action. A single photograph natur- ally records but one position, and inadequately suggests the idea of action (see ‘‘ Chromo-photo- graphy *’). What is known as an “ instantaneous ” picture of a railway train or other object in rapid motion will not convey the impression of speed if it shows, for example, the spokes of the wheels sharply defined; rather would it suggest sus- pended motion. O. G. Rejlander once well ex- emplified this in a couple of photographs of a lady at a spinning wheel. In one, the foot and Adurol spokes were of microscopic sharpness; in the other, the foot and wheel were slightly blurred by intentional movement. Yet it was the second that gave the better impression of an “instantaneous ” picture and the more complete suggestion of action. ADAMANTEAN An old form of ferrotype plate, largely used for the wet collodion process. ADAMANTINE PROCESS A secret process of half-tone etching on copper invented by A. C. Austin in the United States. It produced an extremely hard black enamel resist image for etching. Probably it was a modification of the fish-glue process, but no details have been published. ADAPTERS (See “Plate Adapters” and “Lens Adapters.’’) ADHESIVE TISSUES Thin sheets of paper prepared, generally by the use of shellac, for use in the dry-mounting process, ADIACTINIC actintsch) Non-actinic; a term sometimes applied to the red or orange glass and fabric used to screen the light in a dark-room, No light, however, is absolutely non-actinic, since any light, what- ever its colour may be, will affect a photographic plate if sufficient time is allowed. Photographs have, in fact, been taken by the light obtained from a ruby lamp, although the exposure was, necessarily, very prolonged. For this reason, the plate should not be unduly exposed to the light of the lamp when developing, however ‘*‘safe’’ it is believed to be. The “safety” of any so-called non-actinic glass or fabric is merely relative, and much depends on the nature of the plate or paper and its particular colour- sensitiveness. Thus, a yellow fabric or material that is quite safe for developing bromide papers will instantly fog a rapid dry plate; while even a deep ruby light will have a marked effect on a panchromatic plate. ADIAPHOROUS A diaphor) Neutral ; a chemical term, sometimes applied to substances that are neither acid nor alkaline. ADON A low-power telephoto lens, especially suit- able for hand-camera use. The positive lens is placed in front of the ordinary lens of a camera, in this way producing an enlarged image without abnormal extension of the camera or substantial reduction of the working aperture of the lens. (Fr., Inactinique; Ger., Un- (Br.,. Adtiaphore; . Ger, > ADUROL (Fr. and Ger., Adurol) A developer intermediate in character between the short factor developers, such as pyro and hydroquinone, and the longer factor developers such as metol, rodinal, amidol, etc. ; introduced in 1899. It is a mono-chlor (or mono-brom) hydroquinone. Adurol-Hauff has the formula C,H, Cl(OH),, and Adurol-Schering C;H, Br(OH), Adurol —their actions being similar. The developer as purchased is in the form of a white or greyish- white crystalline powder, readily soluble in water and alkalis. In its action and results it resembles hydroquinone, but it is more soluble, keeps better, and the negatives are slightly softer. The addition of potassium bromide as a restrainer has not much effect, and the developing action is not much slower when the solution is cold. Since its introduction many formule have been published for one-solution, two-solution, and three-solution developers. The following are those in most general use :— Sodium sulphite 8 oz. 400 g Potass. carbonate oF) 300 ,, Water ‘ n 20, 1,000 ccs, Shake till dissolved, then add— Adurol I Oz, 100 g. For negatives and gaslight paper dilute with 3 to 5 parts of water; and for bromide prints with from 7 to 10 parts of water. The above is a one-solution developer, and may be used over and over again. The formula for the two-solution developer is :— No. 1. Adurol , . 85 gers. 17 g. Sodium sulphite . 13 oz. Bey. Water to OO sis 500 ccs, No. 2. Potass. carbonate. 1} ,, 125 g. Water to 100 ge 500 ccs. For use with plates and gaslight paper mix 3 parts of No. 1 with 2 parts of No. 2: for bromide prints add an equal quantity of water. A three-solution adurol developer is as follows :— No. 1. Sodium sulphite . 650 grs, 130g Adurol , . BOL. 16.5 Water to IO OZ 500 ccs No. 2, Sodium carbonate. 100 grs. 20 g. Water to 1OZ, 50 ccs No. 3. Potass. bromide 48 grs, IO g. Water to ee a a 50 ccs, For soft negatives mix 1 oz, of No. I, 310 minims of No. 2, and 20 minims of No. 3. For more brilliant negatives use 10 drms, of No. I, $ Oz. of No. 2, and $ drm. of No. 3. The three-solution formula is best for time-exposed plates, and when over-exposure is suspected. Adurol combines well with metol and gives a developer which acts like metol-hydroquinone. One formula is :— . Metol . - 130 grs. 13 g. Adurol ; . of) 4.2 OZ, 50,, Water to . ee eos 1,000 ccs, Dissolve and add gradually— Sodium sulphite 7 OZ. 350 g. Potass. carbonate 43,, 225.4, For negatives and gaslight papers, dilute with 10 times the quantity of water ; for bromide prints, with 15 times the quantity of water, or take of the stock adurol-metol developer as above 1 drm. and sufficient water to make 2 oz., and add a little bromide. Adurol is the best developer for obtaining warm tones on bromide paper by direct develop- ment. The concentrated one-solution developer 5