4 A DICTIONARY OF PHOTOGRAPHY TOR THE Amateur mb ^xofmimid yfyrtqpayfyer. E. J. WALL, F.R.P.S., AUTHOR OF "CARBON PRINTING." CONTAINING CONCISE AND EXPLANATORY ARTICLES, ILLUSTRATED BY MANY SPECIALLY PREPARED DIAGRAMS. SIXTH EDITION. MOSTLY RE- WRITTEN AND GREATLY ENLARGED. NEW YORK: GEORGE I). HURST PUBLISHER. DICTIONARY OF PHOTOGRAPHY. Aberration. Unfortunately, the optician, from the nature of his material and other circumstances, cannot construct lenses absolutely perfect and free from error or aberration. Aberration is used " to designate the unequal deviation of rays of light when refracted by a lens, by which they are prevented from uniting to a point " ; it is generally defined as meaning errors or faults which are more or less inseparable from an otherwise perfect instrument. The aberrations to which photographic lenses are subject arefive — viz., Astigmatism, Chromatic Aberration, Spherical Aberration, the aberration of form or Curvature of the Field (q.v.), and the aberration of thickness or distortion (q.v.y, which will be treated of under their respective headings. Absolute Alcohol. See Alcohol. Accelerator. A term applied to any substance which is used to shorten the duration of development and to obtain the impres- sion of the slightest impact of actinic light. Thus, in alkaline pyro development the alkali is the accelerator, and with ferrous oxalate, hyposulphite of soda, common salt, and perchloride of mercury have been recommended. A few drops of a weak solution of hypo have a wonderful effect in bringing up detail in an instantaneous negative. Common salt has also a beneficial effect, especially with positive bromide papers, bringing up the detail evenly and gradually before the shadows can become blocked. The addition of hypo and chloride of soda to ferrous oxalate developer is stated to materially shorten the time of exposure, but it is doubtful whether the action is not rather limited to producing a visible image of every ray of light, which may not be the case with ordinary development. See also Development, and Developers. i li Acc] DICTIONARY OF PHOTOGRAPHY. Accessories. See Portraiture. Acetate of Amyl. See Amyl Acetate. Acetate of Copper. See Copper Acetate. Acetate of Lead. See Lead Acetate. Acetate of Silver. See Silver Acetate. Acetate of Soda. See Sodium Acetate. Acetates are salts formed by the combination of metals with acetic acid. Acetic Acid (Ger., Essigsiiure ; Fr., Acide Acetique ; Ital. Acido Aceticd). Formula, HC 2 H 3 0 2 ; molecular weight, 60 ; synonym, Purified Pyroligneous Acid. Prepared from wood by destructive distillation and subsequent purification. There are three commercial strengths. Glacial Acetic Acid contains 99 per cent, of acid and 1 per cent, of water. Its specific gravity varies from 1-065 to I- °66. When cooled to 34° F. it solidifies into a mass of crystals, and remains solid till the temperature is raised to 48 0 . From this property is derived the term glacial. Care should be exercised in handling this, as it is a powerful escharotic; if any should by chance be spilt upon the naked skin, an alkali should be immediately applied. It is, of course, a poison, by reason of its escharotic properties — the obvious antidote is chalk, lime, or other alkalies. It is miscible with water and alcohol in all proportions. It is a solvent of pyroxyline. Acetic Acid. This is one-third the strength of the glacial acid, containing about 33 per cent, of real acid. It can be conveniently prepared from the stronger acid by mixing with it twice its own quantity of distilled water. It is sometimes known as " Beaufoy's Acetic Acid." Specific gravity, 1*044. Dilute Acetic Acid. Made by mixing 1 part of acetic acid and 7 parts of distilled water. Specific gravity, 1 -006. It contains but 3-63 per cer.t. of acid. The impurities in the acetic acids may be either sulphurous acid or tarry matter, both of which may be detected by the addition of a few drops of solution of nitrate of silver. A white precipitate denotes sulphurous acid, -and the darkening of the solution in light indicates tarry matter. 2 DICTIONARY OF PHOTOGRAPHY. [Act Their uses in photography are limited to a clearing bath for Bromide Papers (g.v.), and for the formation of salts known as acetates. Achromatic, when applied to a lens, signifies that it has been corrected for chromatic aberration, and that the imager projected by it are unaccompanied by fringes of various colours. The correction is usually effected by combining two glasses having differing refractive powers, as, for instance, a convex crown-glass lens with a concave flint glass, or by enclosing a flint meniscus between two concavo-convex. There are several methods, but the latter is the usual method employed for the rapid class of lenses now so much in vogue (see Lens). (For the theory involved in rendering lenses achromatic, see Decompo- sition of Light.) Acids may be defined as compounds of hydrogen whose atom or atoms of hydrogen are replaceable by metals, or by radicals having metallic characteristics, and the compound resulting from such substitution is termed a salt. Actinic applies to that portion of light which effects chemical change, in distinction to those portions which furnish light and heat. The actinic portion of the spectrum may be said to be confined to the ultra-violet, violet, indigo, blue, and green ; not, as might be supposed, to that portion which appears to us to be the most powerful — viz., the yellow. But the division is entirely arbitrary, as it depends solely upon the substance exposed as to which rays are actinic or non-actinic. Actinic Focus of Lens. See Focus. Actinograph — Actinometer. Any instrument which mea- sures the actinism of the sun's rays. It usually consists of sensitive paper, which can be exposed to the light in small portions at a time ; and the time which it takes to darken to a standard tint will be found to bear a distinct relation to the necessary exposure required for a sensitive film, whether upon glass or paper, due allowance being made for the presence of any object of importance near the foreground of picture. An actinometer can be made by any amateur by soaking a strip of gelatino-bromide paper in a 2 per cent, solution of nitrite of 3 Ada] DICTIONARY OF PHOTOGRAPHY. potash, drying the same in the dark. When dry it should be rolled up small and placed in the inside of a box which is light- tight, and from which the paper can be drawn in small pieces to allow of its exposure to light and comparison with a standard tint, which can be obtained by exposing a plate on a subject the exposure of which is known, and at the same time exposing the actinometer and noting the time of the darkening of the paper to a certain tint. Supposing the correct exposure of the plate to be 3 sees., and it is found that the paper takes 30 sees, to darken, it is obvious that dividing the actinometer time by 10 will give the correct exposure, with a certain stop and class of picture, from which the others can be calculated. Ordinary albumenised paper, which owes its darkening properties to chloride of silver, is sometimes used, and, although the results, with certain modifi- cations, are some guide, it is obviously unfair to calculate the exposure of bromide of silver from the action of chloride. The term Photometer (q.v.) is sometimes, but erroneously, applied to such an instrument. Under the title of Actinograph Messrs. Hurter and Driffield have devised a series of slide rules based on their researches on the actinic value of daylight, which is recommended for determining exposures in conjunction with their system of plate speeds. Adapter. When using two or more lenses of different sizes it is necessary either to have a separate camera front for each lens or else, by the aid of smaller supplementary flanges, to screw the lens into the largest flange. These supplementary flanges are called adapters ; the term has also been applied to a supplementary bellows, which, affixed to the back of a small camera, allows a larger plate to be used. Aerial Perspective. An artistic term used to denote the idea of distance in a landscape or photograph of the same, which depends upon the fact, that the more remote the object the less forcibly the visual rays are perceived by the retina of the human eye. This feature, which lends so much beauty to photographs, can only be obtained by the use of long-focus lenses, or by the use of as large a diaphragm as possible. (See Focus and Diaphragm.) Agar-Agar (Ger. and Fr., Agar-Agar; ltal., Alga di Giava). 4 DICTIONARY OF PHOTOGRAPHY. [Air This is practically vegetable gelatine obtained from species of white seaweeds {Fucus spznosus, or Gelidium come?tm), common on the coasts of Singapore and Straits Settlements. It has been suggested as a substitute for gelatine, but is liable to give emulsions which are full of transparent nodules. Rebikow has suggested a method of eliminating these nodules, but there are no advantages which warrant its recommendation as a sub- stitute for gelatine. Agate Burnisher. A now obsolete device for burnishing silver prints. In shape an agate burnisher was somewhat similar to a shorthanded spade or household meat-chopper. Agent. That which has the power of acting, or producing effects, upon anything else — e.g., light is the agent which impresses the image upon a sensitive plate, and the developer the agent which makes such image apparent. Air Bells, or Air Bubbles. These annoying defects are liable to make their appearances in all sorts of out of the way places ; generally, too, where they are not wanted. They may occur in the glass support, and if of not large size, and in the face or other prominent part of the picture, may be ignored or touched out on the prints. Air bubbles in the emulsion itself sometimes occur, and give rise to small spots of bare glass, which may be touched out with a brush or pencil before printing from the negative. Air bells in the developer frequently adhere with great tenacity to the gelatine film, and give rise to places of less density than the surrounding parts, or even clear glass. It is always advisable to pass the fingers over the plate when first covered with the developer, or a flat, soft camel's-hair brush may be kept for this purpose. If a brush be used care must be taken that it is well washed after use and does not come into contact with any chemical or foreign matter, which would cause streaks on the finished negative. Air Brush. This is an American invention, by means of which liquid colours can be applied to enlargements and prints Air is pumped by means of a foot-blower through a chamber terminating in a fine orifice, the liquid colour being led to the opening by a movable needle or fine tube. 5 Ala] DICTIONARY OF PHOTOGRAPHY. Alabastrine Process. An old wet-plate process for im- proving the colour of glass positives. It can be applied to gelatine negatives in the following manner (absolute freedom from stains and hypo being a sine qua non) : — Soak the negative in clean water till thoroughly moist, and then in following solution : perchloride of mercury, 40 grs., dissolved in pure hydrochloric acid, 1 drm. ; chloride of sodium, 20 grs. ; sulphate of iron, 20 grs. ; distilled water, 2 ozs. Allow it to soak till thoroughly bleached; wash, dry, and varnish with matt black varnish, or back with black velvet. Albertype. See Collotype. Album. Literally, anything white. Now used in the sense of a blank book, either with openings for the reception of photo- graphs, or blank pages to which they may be affixed. Albumen. An organic principle found in both the animal and vegetable kingdoms. The purest form in which it can be obtained, and the one in which it is used photographically, is the white of egg, its chief use being the preparation of albumenised paper. It may be obtained commercially in a dry form, which is the most convenient for such purposes as the albumen substratum or albumen process. Albumenised Paper. Paper coated with albumen and salt This has now become so necessary an article that it is prepared commercially so cheaply and in such perfection that the ordinary amateur had much better buy it already prepared. The following short directions will give some idea of the method of proce- dure: — Absolutely fresh eggs must be used. Crack each egg into a separate cup or measure before mixing with the bulk, so that in case of the yolk breaking the whole of the albumen may not be spoilt. Take out the germ of each egg. Every fair-sized egg will yield about 7 drms. of albumen. Albumen ... ... ... 6 ozs. or 500 c. cm. Chloride of ammonium ... 60 grs. ,, n grms. Rectified spirit ... ... 96 mins. „ 17 „ Distilled water ... ... 14 drms. „ 160 c.cm. Dissolve the salt in the spirit and water, add to the albumen and beat with an egg-whisk for fifteen minutes ; allow it to settle 6 DICTIONARY OF PHOTOGRAPHY. [Alb and filter it through a tuft of cotton-wool, previously well washed with distilled water. This is sufficient for a quire. The paper should be either Saxe or Rive. Put the albumen into a large flat dish ; take the paper by two opposite corners, and bring the hands close together, so as to make the paper bow out in the middle ; lay the middle of the paper on the surface of the albumen, gradually lowering the ends till it rests on the albumen. When the paper has floated for a few seconds, bubbles will be shown by the numerous puckers ; lift the paper, and wet the bubbles with a camel's-hair brush ; allow the paper to float for eighty seconds — not longer, or the albumen will sink into the body of paper — then gradually raise by one corner, and suspend from two corners to dry ; when thorougly dry, roll between steel rollers, and keep flat. Double albumenised paper is made by coagulating the first layer of albumen by steam, and treating in the same way again. Albumen Process. The finest, but most difficult, of all processes that are used for lantern-slide making. The plates are slower even than gelatino-chloride plates, and are therefore only suitable for contact printing ; but the delicacy of results, the fineness of the deposit and the transparency of the shadows places it facile princeps. Glass plates are first thoroughly cleaned by brushing with nitric acid and water, rinsed in distilled water, and allowed to dry spontaneously ; they are then edged with solution of indiarubber (See Edging), and coated with an old " sherry-coloured " collodion. As soon as the film has set immerse in distilled water till all greasiness has disappeared ; it is then ready for albumenising. Take 10 ozs. of the whites of new-laid eggs, from which the germs have been removed, and add gradually, with constant stirring, I oz. of distilled water, to which 30 mins. of glacial acetic acid have been added. Cover with a piece of muslin, or soft linen, and set aside for twenty- four hours in a cool place. At the expiration of this time remove the coagulated scum, and filter the albumen, when it is ready for the iodiser. Ammonium iodide ... ... 50 grs., or 10 grms. „ bromide Liquor ammonia *88o Distilled water 5 ,1 35 mins. 1 oz. 1 > 1 grm. 6 c.cm. 85 c.cm. 7 Alb] DICTIONARY OF PHOTOGRAPHY. Add this to the albumen and filter. The plate is coated with the iodised albumen and drained, and a second coating of albumen applied. The plate is then allowed to dry spontaneously, or by a gentle heat, the latter being preferable. The plate is now ready for sensitising, and as in this condition it will keep indefinitely a stock may be prepared. The plates are sensitised in a dipping- bath as in wet collodion, the following being the sensitiser : — Nitrate of silver 480 grs., or 10 grms. Distilled water ... ... 10 ozs. „ 100 c.cm. Glacial acetic acid ... ... 1 oz. ,, 10 c.cm. Dissolve and add — Potassium iodide 2 grs. or 0*25 grms. Shake well, allow to stand for half an hour, and filter. The plates must be sensitised in yellow or orange light, and should remain in the bath for about half a minute in summer to one minute in winter. After sensitising, place in a dish of distilled water for five minutes, wash under the tap, and dry. Plates thus prepared will keep, under proper conditions, for several weeks. The exposure, which should always be to daylight, will be about 30 to 40 seconds under a negative of average density. The developer is as follows : — No. 1. 40 grs. or 2*5 grms. 35 mins. ,, 2 c.cm. 10 ozs. ,, 300 c.cm. 12 grs. ,, 0.6 grms. No. 2. Silver nitrate ... ... 12 grs. or -6 grms. Citric acid 12 ,, .6 ,, Distilled water ... ... 2 ozs. ,, 56 c.cm. For use add two or three drops of No. 2 to No. 1. Before development give the film an edging of rubber solution, and place in a dish of hot distilled water for one or two minutes. Place the developer in a porcelain dish, and heat gently by the aid of a spirit lamp to ioo° F. ; place the exposed plate in the 8 Pyrogallol Acetic acid . . . Distilled water Citric acid ... DICTIONARY OF PHOTOGRAPHY. [Alk hot developer, and the image will gradually appear and gain density, this being accelerated, if desired, by the addition of more No. 2. The developer must be maintained at the above temperature, although errors in exposure may be compensated for by using a developer of higher or lower temperature. When sufficiently dense it may be fixed in — Hyposulphite of soda ... I oz. or 10 grms. Water ... ... ... 6 ozs. ,, 60 c.cm. or a 20-grain solution of cyanide of potassium. These slides may be reduced or intensified by any of the ordinary methods ; though, for the latter process, mercuric chloride, followed by ammonia, gives the most satisfactory tones. The image may be toned with the old sel d'or — Sat. sol. of hyposulphite of soda 2-£ ozs. or 1200 c.cm. Chloride of gold ... ... 1 gr. „ 1 grm. After washing and drying, the slides will be ready for binding. Alcohol (Ger., IVeingeist, Alkohol ; Fr., Alcool ; Ital., Alcool). CH 5 HO = 46. Synonyms: Rectified Spirit, Ethylic Alcohol, Hydrate of Ethyl, Spirits of Wine. It is prepared by distillation from fermented saccharine solutions, or any vinous fluid. There are three strengths : — Absolute Alcohol. Contains but 1 or 2 per cent, of water. Specific gravity, *8oo. Rectified Spirit. Contains 16 per cent, of water, and is what is termed 56 degs. over-proof. Specific gravity, '838. Proof Spirit. Made by diluting five parts of rectified spirit with three of water. Alkali. This is the antithesis of an acid. Alkalies turn litmus paper blue which has been reddened by an acid. They precipitate metals from acid solutions, as oxides or hydrates. Their chief characteristic, however, is their readiness to unite with acids to form salts. The three true alkalies are potassium, sodium, and ammonium. Or Bichloride of platinum Water 1 gr. or 1 oz. „ 1 grm. 500 c.cm. 9 Alk] DICTIONARY OF PHOTOGRAPHY. Alkaline Development. See Development. Alpha Paper is paper coated with a chlorobromide emulsion, and was first suggested by Eder in 1883. It is intended for development, and not printing out ; and from the ease with which warm or cold tones can be obtained at will, and from its being possible to obtain prints by its aid at night which are equal to ordinary printed-out papers, has received a good deal of atten- tion. Several formulae have been given for this emulsion-paper. Wellington suggests the following :— Solution A. Silver nitrate... Citric acid ... Distilled water 10 parts. 10 „ 144 .» Solution B. Sodium chloride Potassium bromide Citric acid Gelatine Distilled water 2 parts. 4 » 10 „ 4 n 144 r, Heat both solutions to 66° C, and add A to B, shaking violently ; then add 20 parts gelatine previously swollen in water and melted ; shake the whole well, and pour out into a dish to set ; allow it to remain for twenty-four hours, break it up, wash, re-melt, and coat the paper or other support. One of the ad- vantages of alpha papers is that it is possible to obtain prints of great beauty, rivalling albumen in tone, and superior to them in surface, without the trouble of having to print out ; it is a develop- ment printing process. A fault often found with it, however, is that it is difficult to obtain a certain number of prints from one negative all of one colour ; but this is due to faulty manipulation, and not to the paper. The best method of working it is as follows : — Gas or some artificial light must be used : daylight is too variable. Assuming that we are using a No. 5 Bray burner, which is turned up as full as possible without flaring. At a distance of 9 ins. from this burner on the table, shelf, or wall, draw a straight line. This is the mark on which the edge of the printing frame should always rest. Having chosen your negative 10 DICTIONARY OF PHOTOGRAPHY. [Alu which we will assume to be one of the ordinary character, place your paper in contact with it, and set the frame to the mark. Turn up the gas, and give the paper four different exposures of 90, 100, no, and 120 sees., covering part of the frame up with a piece of black or nonactinic paper at each exposure ; develop the paper as described below, and you will at once have a guide to the correct exposure for any particular colour for that par- ticular negative. It must be remembered that alpha prints can be toned ; but for a photographic purple the developed print should be a pinkish violet after development, and this is the best colour to aim at for all other tones. Having found the correct exposure for the particular negative, expose as many pieces of paper as prints are required, taking care to give exactly the same exposure from a metronome or watch, and then pro- ceed to develop them. Either ferrous oxalate, hydroquinone, eikonogen, or glycin can be used, but for warm tones hydro- quinone is preferable ; and the formulae for these developers suggested for bromide paper may be used if dilated with two or three parts of water and some bromide of potassium added. The final tone depends to a great extent on to the exposure, long exposures tending to give warmer tones. If the iron developer is used the prints must be placed in an alum and citric acid clearing-bath for two minutes, well washed, and then fixed. Alpha prints may be toned in a combined bath, when of course fixing need not be done, or preferably in the following : — Chloride of gold ... ... ... ... 1 gr. Calcium choride (crystal) 10 ,, Water 10 ozs. Place the prints in this after well washing out the fixing solution, and tone till the desired colour is reached. The prints only want well washing and drying to be ready for mounting. Alpha prints can be rolled and burnished, provided too great a heat be not used. Over-exposure gives flat prints without any depth in the shadows and without pure whites, whilst under-exposure gives harsh prints with greenish tones. Alum. Under this name a series of important double salts are classed. These salts are characterised as being double sulphates of monatomic and triatomic metals crystallising in 1 1 Alu] DICTIONARY OF PHOTOGRAPHY. cubes or octahedra, and containing 24 molecules of water of crystallisation, and have therefore the common formula ofM 2 'S0 4 , M 2 "'3S0 4 , 24H2O. The principal alums are ammonia alum, chrome alum, and potash alum. Ammonia Alum (Ger., Ammoniakalaun ; Fr., Alun Ammoni- acal; Ital., Allume di Ammoniacd). (NH 4 ) 2 S0 4 A1 2 3S0 4 24H 2 0 = 560. This is manufactured in a similar manner to potash alum, with the exception that ammonium sulphate is utilised instead of potassium chloride. Solubility : 1 in 7 of cold water, I in o*2 of boiling water, 1 in 2 of alcohol. Chrome Alum (Ger., Chromalaun; Fr. Alun de Chrome ; Ital., Allume di Cromo) . K 2 S0 4 Cr 3S0 4 24H 2 0 = 951. A deep purple crystalline salt, soluble 1 part in 10 of cold water, insoluble in alcohol. Its solution is purple by reflected, and reddish by transmitted, light. It is used for clearing negatives, etc. It is also used in the preparation of emulsions for dry plates to prevent frilling. Potash Alum (Ger., Alaun ; Fr., Alun; Ital., Allume comtme), K 2 S0 4 A1 2 3S0 4 , 24^0 = 948. Is found native in some places, but is usually made from aluminous clay. It is used for render- ing the films of gelatine less liable to mechanical injury, by hardening them, and also clears them from stains (see Clearing Bath). It has also been recommended as a Hypo-eliminator (q.v.), but its action and benefit is doubtful. Solubility : 9-5 in 100 of cold water, 10 in 8 of boiling water ; insoluble in alcohol and ether. Aluminium (Ger. and Fr., Aluminium; Ital. Alluminio). Al = 27. A silvery white metal, obtained principally from the chloride. It has been used to replace brass for lens mounts, and camera fittings on account of its lightness, its weight, bulk for bulk, being less than half that of brass. It has also been used as a substitute for magnesium, for flash light, and has been suggested by Lainer as a means of precipitating silver from residues. Aluminium Chloride (Ger., Aluminiumchlorid ; Fr., Chlorure d'aluminium ; Ital., Clorure di alumin). A1 2 C1 6 is formed by heating alumina and charcoal and passing over it a stream of chlorine gas. It occurs in white tabular crystals which are hygroscopic. It is soluble in water, alcohol, and ether. It has been suggested as a toning agent for gelatino-chloride prints. 12 DICTIONARY OF PHOTOGRAPHY. [Ami Aluminium Sulphate (Ger., Alumininmsulfat y Fr., Sulfate d 'aluminium ; Ital., Solfato di alumin). A1 2 3(S0 4 ), i8H 2 6 is formed by dissolving aluminium hydroxide Al 2 (OH) 6 in sulphuric acid. It has been suggested as a substitute for the ordinary and chrome alums, for hardening gelatino-chloride prints, and in emulsion making. Aluminium Sulphocyanide (Ger., Aluminium sulphocyanid Rhodanaluminium ; Fr., Sulfocyanure d 'aluminium; Ital., Sol- focianuro d'aluminio). Can be formed by double decomposition of barium sulphocyanide with aluminium sulphate. It is volatile, decomposing below 21 2° F., and forms a dark violet red crystalline compound ; but is very difficult to obtain in a crystalline form as it is very deliquescent. Amber (Ger., Grauer Amber, Bernstein; Fr., Ambre ; Ital., Ambra). A fossil resin from an extinct species of pine. It is used for preparing a Varnish {g.V.). Ambrotype. An American synonym for Ferrotype (q.v.). Amidol (Ger., Fr., Ital., Amidol). C G H 3 OH(NH,) : , = 124. Synonym : Diamidophenol. The peculiar characteristic of this substance is that it will develop without the addition of alkali. It is a white crystalline powder readily soluble in water. The aqueous solution does not keep well, not even with sulphite, but soon loses its developing power ; it is preferable therefore to keep it dry and dissolve as required. It is advisable to keep a stock solution of Sodium sulphite 5 ozs. or 250 grins. Distilled water ... 20 ,, 1000 For ordinary negative work take Amidol dry i\ grs. or -5 grms. Sol. sod. sulphite \ oz. 5 cc. Sol. bromide of potash 10% ... 10 drops -5 „ Distilled water 1 oz. 100 ,, To accelerate the development the strong solution of sodium sulphite may be added by degrees. Another form of developer has been proposed which, however, one can only assume to be l 3 Ami] DICTIONARY OF PHOTOGRAPHY. based on the desire of being the author of a new formula, which in our hands possesses no advantages. It is the following : — Solution A. Water 20 ozs. or 100 c.cm. Potassium metabisulphite ... 2 ,, 10 grms. Amidol 1 ,, ,, 5 „ This solution will keep for a very long time if well corked. Solution B. Water 20 ozs. or 100 c.cm. Soda crystals 2 ,, „ 10 grms. Solution C. Water . ... ... ... 20 ozs. or 100 c.cm. Sodium sulphite, cryst., pure 4 ,, 10 grms. Results similar to pyro may be obtained with Solution A ... ... ... ... ... 10 parts. B ... 6—10 „ Water 70 ,, Bromide (1 : 10) ... ... ... ... 3 „ But this formula may, be considerably modified, according to requirements; it is not, however, advisable to increase the quantity of alkali, for fear of inducing fog. For over-exposed plates, add the solution B in the above formula little by little, until the desired effect is obtained, never exceeding the amount above prescribed. Images of a softer character are obtained as follows : Solution A 10 parts. B 20—40 „ Water 70 „ Bromide (1 : 10) \ — J „ Solution D. Water ... ... ... ... ... 20 ozs. Sodium sulphite, pure cryst. ... ... £ oz. Amidol ... 2 ozs. DICTIONARY OF PHOTOGRAPHY. [Ami This solution keeps colourless for a long time in full and air- tight vessels. When opened it goes from yellow to red, which, however, does not affect the developing power, or coloration of plates. For use take — Solution D 5 parts. Water 50—70 Solution C 20 — 30 ,, Bromide (1 : 10) ll ,, This formula also has the advantage, by gradually adding solution C, of controlling development up to the point desired, which is specially important for over-exposed plates. As the image loses on fixing, it is recommended to develop more strongly. For Bromide Paper. Both for prints and enlargements either of the above formulae may be used, and the freedom from stains will prove of great advantage. With diluted solutions clear grey tones are obtained. For Chloride Plates and Lantern Slides. Transparencies of the blackest tones are developed with : — Water 20 ozs. Sodium sulphite, cryst., pure ... ... 1 oz. Amidol 4° grs. Warmer tones are obtained through longer exposure and the liberal addition of bromide, even up to one ounce in the four- ounce developer. Practically the ordinary methods of develop- ment may be followed with amidol — namely, for over-exposure, dilution of the developer with water, increase of bromide, or decrease of the accelerator ; for under-exposure the contrary directions of course hold good. Amidol is likely to prove of great value especially in instantaneous work : it gives fine steely blue or grey-black images, and there is no tendency to stain. The author has found that for subjects with great contrasts, under- exposed plates, and portraiture, this developer will place a great power in the hands of the intelligent worker, because the images *5 Amm] DICTIONARY OF PHOTOGRAPHY. given are soft and harmonious, and one is thus enabled to intensify, to gain the requisite density, without getting harshness. Ammonia (Ger., Wasseriges Ammonia, Salimakgeist ; Fr., Ammoniaque ; Ital., Ammoniacd). NH 3 =i7. Is an extremely volatile, pungent gas, but is only known to photographers as a solution in water, termed liquor ammoniae fortissimus. Specific gravity, *88o, containing about 35 per cent, of NH 3 . It should be kept in stoppered bottles, as the gas is freely evolved at ordinary temperatures, carbonic acid being absorbed from the air, forming carbonate of ammonia. It is used in alkaline development as an accelerator for pyrogallol. The fumes are extremely suffocating, causing sudden contraction of the glottis and consequent death. Its use in ill-ventilated dark-rooms is said to cause permanent irritation of the mucous membranes of the throat, nose, and eyes. There is a weaker strength, known as liquor ammoniae (specific gravity, '936), only one-third the strength of the liq. ammon. fort. Ammonium Bichromate (Ger., Dichromsdures Ammoniak; Fr., Bichromate d'ammoniaque ; Ital., Bicromato d' ammoniacd). (NH 4 ) 2 Cr 2 0 7 =253. Made by neutralising chromic acid with ammonia. It is used occasionally instead of the potash salt in photo-mechanical printing, Ammonium Bromide (Ger., Bromammonium ; Fr., Bromure d' ammonium; Ital., Bromuro d'ammonio). NH 4 Br = 98. Made by neutralising hydrobromic acid with ammonia, or by double decomposition from bromide of calcium. Its chief use is as a Restrainer (q.v.), but it is sometimes used in the preparation of gelatino-bromide emulsion. Solubility : 1 in i£ of cold water, 1 in 13 of alcohol. Ammonium Carbonate (Ger., Ammoniumcarbonat, or, Kohlensaures ammoniak ; Fr., Carbonate d 'ammoniaque ; Ital., Carbonato d ammoniacd). 2(NH 4 HC0 3 )NH 4 C0 2 NH.j= 342. Made by sublimation from chalk and sal-ammoniac. It is used occasionally for development, but is not so suitable as liquor ammoniae. Solubility : 1 in 4 of cold water, sparingly in alcohol. 16 DICTIONARY OF PHOTOGRAPHY. [Anim Ammonium Chloride (Ger., Chlorammonium, Salmiak; Ft., Chlorure d'ammoniwn ; ItaL, Cloridrato d'ammoniaca). NH 4 C1 = 53*5. Synonym : Muriate of Ammonia, Hydrochlorate of Ammonia, Sal-ammoniac. Is prepared by neutralising ammoniacal gas liquor with hydrochloric acid and subsequent purification. It is principally used for salting albumenised paper, and for preparing chloride emulsion. Solubility : 1 in 3 of cold water, 1 in 55 of alcohol. Ammonium Citrate (Ger., A?nmo?iiumcit?'at ; Fr., Citrate d , a?n?noniaque ; ItaL, Citrato d , a?7imoniaca). (NH 4 ) 3 C 6 H-0 7 = 124. This is usually met with in the form of solution, the salt itself being so deliquescent, that it is an extremely difficult matter to keep it. It may be conveniently prepared by exactly neutralising citric acid with solution of ammonia or carbonate of ammonia, the following being the method adopted by the British Pharmacopoeia. Citric Acid ... 12 parts. Strong solution of ammonia ... ... 11 „ Neutralise the acid with the ammonia, and add sufficient dis- tilled water to make 24 parts. This can be preserved as a stock solution for use in alkaline development (see Development). It has been employed in the preparation of gelatino-chloride emulsions, but its principal use is as a restrainer in development of chloride emulsions. Ammonium Iodide (Ger., Jodammonium ; Fr., Iodnre d'ammonintn ; lta\., foduro d' ammonia). NH 4 I = 145. Made by neutralising hydriodic acid with ammonia. It is much used for making Iodised Collodion (q.v.). Solubility : 4 in 3 of water, 1 in 4 of alcohol, I in 20 of ether, and 1 in 20 of alcohol and ether. Ammonium Oxalate (Ger., Ammoniuthoxalat; Fr., Oxalate d'ammo?thi?Ji, or, Oxalate neutre ; Ital., Ossalato di ammoniacd). (NH 4 ).,C 2 0 4 = 124. Made by neutralising oxalic acid with ammonia. It has been recommended lately for preparing the paper for platinotype printing. Solubility: 1 in 3 of water; insoluble in alcohol. 17 c Amm] DICTIONARY OF PHOTOGRAPHY. Ammonium Sulphide (Ger., Ammoniumsuljid, or, Schwef el- ammonium ; Fr., Sulf hydrate d 'ammoniaque ; Ital., Solfidrato d' ammoniacd). (NHJ 2 S = 68. Synonym: Sulphuret of ammonia. Prepared by passing sulphuretted hydrogen through ammonia solution until the gas ceases to be absorbed and the adding an equal volume of ammonia to that originally used. It is used in Intensification (q.v.) to blacken the white image obtained by bleaching the negative with mercuric chloride. A caution is necessary as to the use and storage of this in any room where sensitive surfaces of any kind are kept, as liable to blacken the same without exposure to light. Ammonium Sulphocyanate (Ger., Rhodanammonium ; Fr., Sulfocyanure d' ammonium; Ital., Rodanuro, or, Solfocianuro d'ammonio). NH 4 CnS = 76. A compound of sulphocyanic acid and ammonia. Also prepared commercially by boiling powdered sulphur with ammonium cyanide which is obtained as a refuse from coal tar. It is used for toning gelatino-chloride printing- out papers. It has also been recommended as a fixing agent instead of hypo, but from its comparatively high price, without any increased advantages, it is hardly likely to come into general use. It is a very deliquescent salt, soluble also in alcohol. Amphitype. A curious process which was discovered by Sir John Herschel, who thus describes his method of pro- cedure : — "Paper proper for producing an amphitype picture may be prepared either with the ferro-tartrate or the ferro-citrate of the protoxide or the peroxide of mercury, or of the protoxide of lead, by using creams of these salts, or by successive application of the nitrates of the respective oxides, singly or in mixture, to the paper, alternating with solutions of the ammonio-tartrate or ammonio-citrate of iron; the latter solution being last applied, and in more or less excess. Paper so prepared and dried takes a negative picture in time varying from half-an-hour to five or six hours, according to the intensity of the light ; and the im- pression produced varies in apparent force, from a faint and hardly perceptible picture to one of the highest conceivable fulness and richness both of tint and detail, the colour in this case being a superb velvety brown. This extreme richness of effect is not produced except lead be present, either in the 18 DICTIONARY OF PHOTOGRAPHY. [Amy ingredients used or in the paper itself. It is not, as I originally supposed, due to the presence of free tartaric acid. The pictures in this state are not permanent. They fade in the dark, though with very different degrees of rapidity, some (especially if free tartaric or citric acid be present) in a few days ; while others remain for weeks unimpaired, and require whole years for their total obliteration. But though entirely faded out in appearance, the picture is only rendered dormant, and may be restored, changing its character from negative to positive, and its colour from brown to black (in the shadow), by the following process : — A bath being prepared by pouring a small quantity of solution of pernitrate of mercury into a large quantity of water, and letting the subnitrated precipitate subside, the picture must be immersed in it (carefully and repeatedly clearing off the air-bubbles), and allowed to remain till the picture (if anywhere visible) is entirely destroyed, or, if faded, till it is judged sufficient from previous experience ; a term which is often marked by the appearance of a feeble positive picture of a bright yellow hue on the pale yellow ground of the paper. A long time (several weeks) is often required for this, but heat accelerates the action, and it is often complete in a few hours. In this state the picture is to be very thoroughly rinsed and soaked in pure warm water, and then dried. It is then to be well ironed with a smooth iron, heated so as barely not to injure the paper, placing it, for better security against scorching, between smooth clean papers. If, then, the process has been successful, a perfectly black positive picture is at once developed. At first it most commonly happens that the whole picture is sooty or dingy to such a degree that it is condemned as spoiled, but on keeping it between the leaves of a book, especially in a moist atmosphere, by extremely slow degrees this dinginess disappears ; and the picture disengages itself with continually increasing sharpness and clearness, and acquires the exact effect of copperplate engraving on a paper more or less tinted with pale yellow." Amy! Acetate (Ger., Amylacctat; Fr., Acetate d amyle ; Ital., Acetato d'amilc). C 5 H n C 3 H30 2 = 130. Synonym: Essence of Jargonelle pears. Prepared by distilling 1 part of sulphuric acid, 1 part of amylic alcohol, and 2 parts acetate of potash. The distillate is purified by washing with water, dried with calcium 19 Amy] DICTIONARY OF PHOTOGRAPHY. chloride, and then redistilled from a mixture of massicot (oxide of lead), which absorbs any free acetic acid. It is a colourless liquid with, at first, a fruity smell, but which soon becomes in- tensely nauseous, and gives rise to vertigo and headache. It is insoluble in water, but soluble in all proportions in alcohol and ether. It boils at 137 0 F., and burns with, brilliant flame, which is, however, richer in the more refrangible rays than the violet. It is used in the amyl acetate lamp {q.v.). Amyl-Acetate Lamp. This instrument was devised in 1884 by Hefner-Altenek, and was adopted by the International Congress of Photography in Paris in 1889 as a convenient standard light for photographic purposes. Amyl acetate is burnt in it with a cotton wick, the internal diameter of the wick tube should be 5 mm., and the height of the flame 25 mm. 1 cm. from the axis of the flame is placed a thin metal chimney, in which is a small aperture 4 mm. broad and 30 mm. long, and this can be shifted up and down so as to bring it opposite the brightest part of the flame. The amyl acetate should have a constant boiling point of 138 0 C, and be free from acetic acid and water. The spectral composition of the flame is similar to that of a candle, and compared to the English standard candle, setting the amyl-acetate lamp as =1, the candle = 1-140. All metallic parts of the lamp should be made of fine silver, as the fluid so corrodes brass and other metals as to render them useless. Angle, Mid. This is a term applied to a certain class of lens which has a focal length intermediate between the ordinary rapid rectilinear and the so-called wide-angle. Angle of View, or Width of Angle. It is sometimes essential to know the angle inclosed by a lens, and for this purpose it is only necessary to divide the diameter of its field by the focus, when reference to the following tables will at once give the result. A good deal of discussion has arisen as to the meaning of the term, " angle of view," but notwithstanding what has been said to the contrary, the simplest way out of the difficulty is to limit the term to the definition given above, and to explain the angle included by the lens on a given-sized plate as the picture angle. If this is adhered to we avoid several difficulties. Mr. W. Rice suggests the following simple formula : — 20 DICTIONARY OF PHOTOGRAPHY. [Ang Let P = length of plate. F = focus of lens. Then Angle 63 P Or, exp .ssed in words : — Multiply the base line of plate by 63 and di ide the product by the length of focus, added to \ of the diagonal of the plate. Example: — What is the angle given by a 10-in. lens on a 12-in. plate ? This formula will only apply when the angles included are less than 90 0 . When the angle is greater than 90 0 the following should be used : — Or, expressed in words : — Subtract from 180 the quotient obtained by dividing 126 times the focus of the lens by \ the base line of the plate, added to twice the focus divided by 5. Example : — What is the angle included by a 4-in. lens on a 12-in. plate? 126 x 4 = 504. 12 -~- 2 = 6. (4 x 2) -f- 5 = |. 6 + f 7 ■ 5°4 -r 1% = 61. 180 — 61 = 1 i9°approximateangle included.* One of the most usual methods is by means of the following plan. Draw a straight line a b equal in length to the longer base 12 x 63 10 + V 756 -f I2| = 756. = I2f = 6i° practically. Angle = 180 0 — 126 F P 2F 2 + 5 For Steinheil's tables of angles see Appendix. 21 Ang"] DICTIONARY OF PHOTOGRAPHY. of i the plate used, bisect this accurately at c, from c draw a per- D Fig. 2. A d b, which may be measured by laying a protractor on it and reading off the degrees included. For those who may not have 22 DICTIONARY OF PHOTOGRAPHY. [Ang a protractor handy, the diagram, fig. 2, is given, which may be copied on a lantern plate, and the developed, fixed, and varnished negative used as a protractor. Angle, Wide. Applied to certain forms of lenses which embrace a larger amount of view than the usual run of lenses. Wide-angle lenses exaggerate perspective most painfully, in increasing the apparent size of near objects entirely out of all proportion with those more distant. As the angle of view of the human eye does not exceed about 50° no lens for general work should be employed which would include a greater angle than 50 0 . Practically a lens includes a wide angle, or a large amount of subject, only when its focus is short as compared to the plate with which it is used. The diagram (fig. 3) may make this clear. Let us assume that l is the optical centre of a lens, which will cover a half-plate, cc'. The same lens will also cover a quarter-plate, dd' ; it will also cover a whole plate, bb' ; and a 10 by 8 ; and a 12 by 10. Therefore with the quarter-plate it would be a narrow angle or long focus, with the half-plate an ordinary angle, on a whole-plate a mid-angle, on a 10 by 8 a wide-angle, on a 12 by 10 a wider angle. J3' A Fig- 3- Ang] DICTIONARY OF PHOTOGRAPHY. Aliglol. Under this name was introduced an English manu- factured Eikonogen (g.v.'). Angular Aperture is the relation borne by the working diameter of a lens to its focal length. The wider the angular aperture the less the depth of focus and covering power of the lens. This is well seen in a portrait lens. Aniline (Ger., Anilin; Fr., Aniline; Ital., Anilina). C 6 H 5 NH = 93. Synonym : Phenylamine, Amidobenzine. It is prepared commercially by the reduction of nitrobenzine by heat, steam, iron filings, and hydrochloric acid. Solubility : 3 in 100 of cold water ; very soluble in alcohol, ether, and benzine. It is used in the aniline process (g.v.), and also as a base from which numerous colouring matters used in orthochromatic photography are derived. Aniline Process. In 1865 Willis patented this process which consists of impregnating paper with ammonium bichromate and phosphoric acid, drying, and then exposing under a negative to the action of light, and subjecting it to the fumes of aniline, by which means aniline colours were formed. Reynolds, Dawson, Wild, and others, experimented with this process which has found but little use in practice. H. W. Vogel suggests the following method of procedure : — Sensitising Solution. Potassium bichromate 1 parts. Phosphoric acid, Sp. Gr. 1*124 ... ... 10 „ Water ... ... ... ... ... 10 „ Good paper, such as Rives or Saxe, is allowed to float on this for one minute, and then quickly dried. It is then exposed under negative or line drawing, and developed by placing in the bottom of a box, to the lid of which is affixed a sheet of blotting paper impregnated with commercial aniline 1 part, benzine 16 parts. The image appears fairly quickly (in a few minutes), and of a greenish-blue black, which turns to blue when the prints are soaked in water. If the fuming is carried on for some time the tones become blacker. With over-exposure the ground becomes tinged, and this may be removed by alternately bathing in dilute sulphuric acid i-ioo, or in hydrochloric acid 5*100, and 24 DICTIONARY OF PHOTOGRAPHY. [Ape washing and then bathing in dilute ammonia. Philippe suggested, in 1884, floating gelatinised paper on 10 per cent, solution of bichromate of potash and ammonia. After exposure the print is laid in 1 per cent, solution of potassium cyanide till the whites are clear, then rinsed and developed in Anilin ... ... ... 10 parts. Oxalic acid ... ... ... ... ... 10 ,, Water ... ... ... 100 In 1866 Endemann suggested the use of vanadic acid. Well- sized paper is sensitised with Salt 480 grains, or 5 grms. Potassium bichromate ... 480 5 ,, Sodium vanadiate 320 ,, 3-3 Water ... 20 ozs. „ 100 c.cm. When dissolved add the following mixture after it has become cold — Sulphuric acid ... ... 2 ozs. or 10 c.cm. Water 10 „ „ 50 „ When the paper is dried it is exposed under a negative or drawing for about 7 minutes, and then exposed to the vapour from a heated mixture of 1 part of aniline and 50 parts of water. The image then appears brown, and the print is left in a room full of steam for two hours, or till the image turns black, and finally washed in 1 : 6 ammonia water. Allthotype. A process yielding exceedingly fugitive prints, depending for its principle upon the bleaching action of light upon chlorophyll and other vegetable juices, when the same are spread upon paper and exposed under a negative. Antiplanat. A term applied to a particular type of lens constructed by Steinheil. Aperture of a Lens, Working. By this term is meant such part of the surface of the lens which is actually utilised in impressing the image of the plate. Many amateurs suppose that the working aperture of the lens is the diameter of the 25 Apl] DICTIONARY OF PHOTOGRAPHY. diaphragm, others that the whole surface of the lens is always utilised ; but this is not so. The following method will prove the working aperture of any doublet lens, which varies with each separate diaphragm: — Rack the camera out to the true equivalent focus of the lens ; replace the focussing screen by a sheet of cardboard, in the exact centre of which is a minute hole (a pinhole will do) ; behind this, exactly level, place a strong light, such as a paraffin lamp, and it will be found on looking at the lens that when a diaphragm is inserted in the slot a central portion only of the lens is illuminated. This can be easily seen by breathing upon the lens surface. It should be accurately measured, and this area will be the true working aperture of the lens with the diaphragm used. This area of illumination will be found to differ in geometrical proportion with each separate diaphragm. Aplanatic. A term applied to a lens to denote that spherical and chromatic aberration have been totally eliminated so far as is practicable; it is impossible to do it theoretically. Rays of light diverging from a point parallel to the axis of an aplanatic lens passing through it, though suffering refraction, are brought to a definite focus at a point which is the true focus of a lens. Practically it means that a lens will give reasonably sharp definition with its full aperture. Apparatus. The materials used in producing photographs, such as lens, camera, stand, slides, etc., which will be severally described under their various headings. Aqua Fortis. See Nitric Acid. Aqua Regia. See Nitro-Hydrochloric Acid. Arabic Gum. See Gum Arabic. Architectural Photography. Specialisation in photographic work will often repay an amateur far more than the mere taking of anything and everything that he may come across, and which looks pretty. Architectural photography, if taken up as a special study, will well repay any one ; but it is first necessary, to do this intelligently, that he should have some knowledge of the various styles of architecture. The best books of moderate price upon 26 DICTIONARY OF PHOTOGRAPHY. [ArC this subject are "An Introduction to Gothic Architecture," by J. H. Parker, price 5s., and "A Concise Glossary of Architecture," price Js. 6d. For this particular branch of our art a square bellows camera is required. This form is preferable to the conical as being somewhat more rigid, and there being no chance of the bellows cutting off any portion of the subject. The size of the camera will of course depend entirely upon individual tastes. The lenses must be doublets, and at least three should be obtained — a short-focus, embracing an angle of at least 75 0 ; a medium-angle, about the same focal length as the base of the plate, and a longer focus, which should be half as long again as the base line of plate. All should fit the same flange, or adapters should be obtained. Possibly the most convenient sets of lenses will be found in the so-called M Casket Lenses," which consist of various combinations of varying foci, which screw into a tube forming doublets of the ordinary type varying in foci from very short to long. A plumb and level must be attached to the camera, and the camera back must swing from the centre. The stand should be firm and solid, and the tips of the legs should be provided with cork bungs or indiarubber pads to prevent slipping on stone or marble floors. Equipped as above it will be possible to tackle almost every branch of architectural work, and by using one only of the combinations of above lenses we may obtain lenses of still greater focus. It is true that these will be single lenses, and therefore liable to give marginal distortion, but really this may be ignored as only the centre of the field is used ; in fact, when a single lens is the sole instrument which a worker has, let him not hesitate to boldly attack architectural studies, and no one will be the wiser, if the lens is not strained by raising the front, or the swing back abnormally used. Finally, we may dismiss all further reference to lenses, with the parting advice to use as long a focus one as the situation of the object will allow. Obviously, we cannot think for one moment of including directions as to the best time of day, position, etc., of taking buildings, churches, etc., but a few hints may be acceptable. Never take a church or house full face, nor with the sun dead behind the camera nor dead in front ; try to get a side or corner view and side lighting. In all church or cathedral exteriors, where fine delicate carving or tracery exists, a somewhat long exposure 27 Are] DICTIONARY OF PHOTOGRAPHY. should be given in order not to lose the same. For interior work there is one absolute essential, and that is that thickly coated plates, backed, should be used. No plate that is not backed will give perfect results ; for not only is halation more troublesome, but also the negatives as a rule are less brilliant. When unbacked plates are used, the rapidity of the plate is really of no moment provided one can give long exposures ; but if from any cause this is impossible, then the most rapid plates attainable should be employed. We may add here that colour- sensitive plates are decidedly to be preferred, and that the new multiple-film plate introduced by R. W. Thomas & Co., will be found of great value for all architectural work, especially interiors. The aperture of the lens should always be the largest that will give satisfactory definition over the whole of the screen. Never place the camera exactly in the centre, rather a little to one side, of a church or cathedral. The question of exposure is always an extremely difficult one, and, whilst experience is invaluable, some such guide as an actinometer or exposure meter, which actually gauges the chemical activity of the light, will be of immense advantage. To correctly judge the exposure for interiors, especially if there is much coloured glass about, without some such guide is an utter impossibility. By far the best light to choose for exposure is, for the east end, the afternoon, for the west end the morning, and never in sunshine : diffused light is far superior and less likely to give rise to halation. With regard to development, thin delicate negatives are the most suitable, and the newer developing agents, amidol and metol, will be found of great value, and far superior to pyro. If records and not pictures of architectural subjects are desired, then it is wise to include in the view a two-foot rule which shall show the scale on which the object is taken ; and the plane of the plate should be parallel to the plane of the wall or surface of the building. Area System of marking Lenses and Diaphragms. This was proposed by Mr. George Smith to replace the existing methods of marking stops. It is not so simple and has never come into general use. The actual method, as described by the inventor, is to measure the aperture of stop in sixty-fourths of an inch. This number is squared ; the product is the exact area of 28 DICTIONARY OF PHOTOGRAPHY. [Art the aperture in circles, each one sixty-fourth of an inch in diameter. Thus, supposing a stop aperture measured 20 sixty- fourths, 20 x 20 = 400, the last figure is struck off and the stop called No. 40, no matter what focus lens was used. Any lens is measured for its actual focus by measuring the distance of its burning point from the back of the lens in complete quarter- inches neglecting fractions. Suppose a lens was found to measure 20 quarter-inches ; 20 x 20 = 400, striking off the last figure, its area number would be 40. Any other lens would be measured in the same way in quarter-inches. Thus it will be seen that every stop has its own number, and that whatever relation that number has to that of the lens it is used with gives at a glance the exposure required. It need hardly be pointed out that this method is full of grave inaccuracies. Argentometer. An instrument constructed on the principle of a Hydrometer (q.v.), and marked with a scale to show the number of grains per oz. of nitrate of silver in a silver bath. This is, of course, only applicable when the solution is pure. Argentotype. A name applied to one particular make of gelatino-bromide paper. Aristogen. Under this name Liesegang has introduced a concentrated hydroquinone developer, specially designed for developing gelatino-chloride prints. Its formula is said to be Hydroquinone (10% alcoholic sol.) ... 10 parts. Sodium sulphite cone. sol. ... ... 10 ,, ,, acetate 20% sol. ... ... ... 5 ,, Citric acid, 20% sol. ... ... ... 5 ,, Water 100 „ Aristotype. A name applied to one particular make of gelatino-chloride paper. Arrowroot (Ger., Pfcihvarzclmchl ; Fr., andjltal., Arrowroot). The starch obtained from the tubers of Maranta Arundinacea. It is a fine, white, tasteless, odourless powder which has a parti- cular crepitating feel in bulk. It is used for sizing papers in the platinotype and plain-paper processes. Artotype. See Collotype. 29 Asp] DICTIONARY OF PHOTOGRAPHY. Asphalt (Ger„ Asphalt, Judenpech ; Fr.,t Bitume de Judec, Asphalte; Ital., Bitume di Giudea, Asfaltd). Synonym : Bitumen, Jews' pitch. It is met with in commerce in black or brown lumps of peculiar gassy and tarry odour, and is obtained from Judea Syria, Trinidad, and other places. Syrian bitumen is the one most generally used in photography as it contains 52 per cent, of the light-sensitive preparation. It is prepared for photographic purposes by three different methods : (1) Solution of the asphalt in chloroform and precipitation with from three to five times the quantity of ether. (2) Kayser's method of washing powdered raw asphalt with ether, and using the dried marc for the prepara- tion of the light-sensitive varnish. (3) Husnik's method of dissolving raw asphalt in the smallest quantity possible of German turpentine and precipitating with several times the quantity of ether. Kayser proved that the light-sensitiveness of asphalt increased with the proportion of sulphur, and Valenta based the following processes of increasing the sensitiveness on this statement. To prepare the light-sensitive preparation 7 to 10 parts of sulphur should be dissolved in a sufficient quantity of bisulphide of carbon, and added to 100 parts of powdered Syrian asphalt. The solution is then freed from the bisulphide of carbon as described, and best heated for about an hour in a mortar to iio°C, with constant attrition with the pestle; then in a roomy air-bath slowly heated till sulphuretted hydrogen escapes, and be kept at a temperature of about 180 0 to 200 0 C. for 5 to 6 hours. The formation of burnt products, which prove a decomposition of the asphalt, are caused by too high a temperature, and is to be avoided. The asphalt thus prepared, which now only smells faintly of sulphuretted hydrogen, should be kept in a well-closed bottle in the dark. For working in diffused daylight, and especially if high sensitiveness is desired, it is advisable to free this asphalt from any existent resin, and from traces of burnt products, which may be effected by powder- ing and treating the powder with ether, and with agitation in a wide-mouthed bottle fitted with a cork. After sufficient action, 2 to 3 hours, the ether is poured off and the insoluble portion dried by spreading it out in thin layers on several thicknesses of blotting paper. For use, four parts of sulphurised asphalt, treated as above, are to be dissolved in 100 parts of benzol (not benzine), the solution filtered, and [finally diluted till the film which is 39 DICTIONARY OF PHOTOGRAPHY. [Ast formed by pouring it on the zinc plate appears a golden-yellow colour. (An exposure of from half-an-hour to one hour of the solution of asphalt in an open flask to direct sunlight is advis- able.) To develop the asphalt pictures rectified oil of turpentine free from acid, the most suitable French or Austrian turpentine, should be used. As accelerator of development with strong over- exposure, an addition of so-called^Russian or Hungarian turpentine may be made, which oils, when used alone, would attack the image. As restrainer in developing, an addition of ligroin, benzine (petroleum benzine), or wood oil may be used. The development is best effected by merely rocking in a dish without the help of any pad of cotton wool ; and soon, when the image is developed clear, it should be well washed in a stream of water and allowed to drain and dry. (In order to avoid the unpleasant action of ad- hering drops of water, the plate may be washed with petroleum benzine before washing with water.) It is advantageous before gumming the plate to expose it, as the image adheres better. Valenta also suggests the following simplified method of preparing light-sensitive sulphurised asphalt or bitumen : — 100 grammes of raw Syrian asphalt are to be boiled with an equal quantity of commercial pseudo-cymene in which 12 grammes of sulphur flowers have been dissolved. When, after about three or four hours, the formation of sulphuretted hydrogen has ceased, the cymene is distilled off, andthe product is the light-sensitive asphalt from which the film is prepared in the usual way by solution in benzol. The new preparation is soluble in benzol, toluol, cymene, xylol, and turpentine ; it is said to be even more sensitive than that prepared by Valenta's other method. Bitumen is used in several photomechanical processes for making a light-sensitive film, and raw bitumen for laying the ground in photogravure. Astigmatism. A defect in lenses from which vertical and horizontal lines near the margin of the field cannot be both accurately focussed at the same time. It is particularly notice- able with lenses of large aperture, and is cured to some extent by the use of small diaphragms or by special selection of the glass and calculation of the curves. This should not be con- founded with curvature of the field, as in this case the alteration of the focus will improve the same, though destroying the focus in the centre. To explain this we must have recourse to a figure. 3i Ast] DICTIONARY OF PHOTOGRAPHY. If we assume / o m n to be a convex lens, and a b its axis, and r,r,r,r,r, rays proceeding from a point at some distance from the axis, and from this point draw a line R P, cutting the axis at c, and draw through this point, and the principal axis of the lens, a plane, the lens will be cut by the line / m. At right angles to this we draw the plane o n, through which the plane of rays, r",r,r", jP Fig. 4. shall pass. We shall mow see that the rays passing through 0 c n will meet at the point p, but the rays, r', r', passing through / m will cut the axis R p at 0. If we assume that we have two straight lines as in fig. 5 to reproduce at the margins of the focus- sing screen, we shall find that we can at the point p obtain an image of b b every point of which is slightly lengthened, and can be represented as in fig. 5 d, whilst the upright line a a will be repre- 32 DICTIONARY OF PHOTOGRAPHY. [Ast sented by c\ we shall see a violet image surrounded by rings of blue, green, orange, yellow and red. And by placing the screen at Y> we shall get a red image surrounded by orange, yellow, green, blue and violet rings, and this will be the case at each point where the different coloured rays cross the axis, though for the sake of clearness these are not shown. Now the brightest part of the spectrum to the human eye is in the yellow, whilst the rays which act most on the plate are in the blue and violet, so that if 31 £ ; » \ x 1 X B X Fig. 7 . we obtain an image by the yellow rays, the plate would be affected by the blue and violet, and we should get no sharp picture, because at Y the blue rays would be a circle instead of a point. This is termed non-coincidence of the visual and chemical foci, or the lenses are said to be uncorrected or non- achromatic. Now it is a fact that crown and flint glass have different dispersive powers, that is, they produce spectra which differ in the position of the Fraunhofer lines. With the crown glass the distances between a b and B c, in the red and orange, is greater than with the flint, whereas with the flint the distances between f g and g h are greater than with the crown. Therefore 76 DICTIONARY OF PHOTOGRAPHY. [Chr we may assert that, with the crown glass, the red end or less refrangible rays are extended at" the expense of the violet or more refrangible rays, whilst with the flint glass the opposite holds good. We have seen that we have a lens which is Fig. 8. practically a collection of prisms; we have also seen that the visual and chemical rays do not have the same focus, and it is essential they should possess this in common. Light is always refracted towards the base of a prism, and we have just pointed >- > Fig. 9- out that flint and crown glass act differently on the spectrum, the one extends the blue, the other the red end more, so that it is not difficult to see from fig. 8, that what we want to do is to make /fall upon /'. This represents, exaggerated of course, the action of a convex crown-glass lens. Now, suppose we examine the action of a concave flint-glass lens. In this case, 77 Chr] DICTIONARY OF PHOTOGRAPHY. fig. 9, it is seen that the blue rays are bent out more than the yellow, so that, if we combine a flint concave with a crown convex, we shall get the blue rays extended more, and thus neutralise the effect of the crown to some extent. I endeavour to show this in fig. 10. The focus of the crown lens is shown at 2 for the yellow rays and at I for the blue ; but by adding Fig. 10. a concave flint, the focus of both is lengthened to f. Now, there are more rays than the blue and yellow in the spectrum, and it naturally occurs to ask about the others ; these are left outstanding, and at / form coloured rings round the central spot or sharp focus f, and form what is called the secondary spectrum. In the last figure we only used two lenses, but Fig. ii. if we use three, three rays are combined and the lens is said to be apochromatic, and the faint outstanding rays of colour are called the residuary tertiary spectrum. The advantage of the more perfect achromatism of lenses at the present time is shown from the following statement. The ordinary gelatino- bromide plate is sensitive, not only to those particular portions of the spectrum designated by d and f, but also between d and f. 78 DICTIONARY OF PHOTOGRAPHY. [Cle and f and h; and if we use colour-sensitive plates, we find considerable increase of sensitiveness to the yellowish green about E, so that those rays for which the lens is not perfectly achromatised may act, and as these rays do not form an exact image at that point where d and f meet, they may affect the silver in such a manner as to enable the developer to reduce the same ; and although such reduction would be hardly visible to the naked eye, yet, in enlarging, the points of confusion thus caused might become visible, and give indistinctness or fuzziness. Chrome Alum. See Alum. Chrysotype. An obsolete process. Circle of Least Confusion. An optical term to denote the nearest approach to an absolute focus of an oblique pencil of light after refraction. Citric Acid (Ger., Citronensdure ; Fr., Acide citriqicc ; Ital., Acido Citrico). HQH 5 0 7 , H 2 0 = 208. Occurs naturally in the juice of many fruits, and is obtained chiefly from the lime and lemon juice by heating and adding chalk, collecting the precipitate and decomposing with sulphuric acid, and evaporating the solution till crystals are obtained. Solubility: 133 per cent, in cold, 200 per cent, in hot water, soluble in alcohol and ether. It is used to make citrates, as an ingredient of clearing solutions, and as a preservative for sensitised paper. Clearing Bath. Any solution used to clear or cleanse a negative or positive from the stains of development is thus termed. The following are those in most common use : — Alum 2 ozs. or 50 grms. Citric acid 1 oz. ,, 25 ,, Water 20 ozs. ,, 500 c.cm. The latter is the author's favourite, the chrome alum having a special tanning action on the film much superior to ordinary alum. The addition of a little ferrous sulphate has been recommended, Or Chrome alum Citric acid . Water 1 oz. or 25 grms. 1 » m 25 „ 20 ozs. ,, 500 c.cm. 79 Cli] DICTIONARY OF PHOTOGRAPHY. but without any increased benefit. When plates are developed by pyrogallol and soda, a very non-actinic yellow colour is given to the film, which protracts the operation of printing most in- ordinately. By use of the chrome alum bath this colour is changed to fine olive green, which does not protract printing. In the case of ferrous-oxalate development the same bath is useful for clearing off the deposit of oxalate of lime due to the use of hard water, whether on negatives, positives, opals, or paper. Mr. B. J. Edwards has suggested the following, which, as it possesses one or two features distinct from the others, is here given : — I. Alum I oz. or 28 grms. Citric acid 1 ,, 28 „ Water 15 „ M 400 c. cm. II. Saturated solution of sulphate of iron ... 5 ozs. or 145 c.cm. For ordinary use one part No. II. is mixed with three parts of No. I. If the negative is a little too dense, the use of No. I. solution alone will reduce the same. If not quite dense enough, the use of No. II. alone will often give the slight snap required to pro- duce a perfect negative. Mr. Edwards recommends the use of this clearing bath immediately after fixing, the plate being only just rinsed after being taken out of the fixing bath. The following solution has been specially recommended for removing pyro stains and is very effectual : — Thiocarbamid 30 grs. Citric acid ... ... ... ... ... 10 Water 5 ozs. Cliche. A term applied to the negatives and moulds used in photo-mechanical printing. Cloud Negatives. There are few landscapes or seascapes taken by amateurs which would not be improved by the addition of clouds — in fact, in many instances an otherwise poor print may be made a picture by the judicious use of the same. It must, however, be borne in mind that clouds which are unsuit- 80 DICTIONARY OF PHOTOGRAPHY. [ClO able to the landscape, or which are differently lighted, are worse than a blank sky. For taking cloud negatives it will be found that slow or medium plates, rich in silver and preferably coated with a bromo-iodide emulsion, will answer well ; but the finest effects will be obtained by the use of isochromatic or orthochro- matic plates, with a yellow screen interposed between the lens and plate. The majority of landscape photographs have the horizons from one-third to two-thirds up the plate ; therefore it would not be advisable to point the lens to the zenith to obtain cloud negatives, as the lighting, as a rule, is different to that ob- tained nearer the horizon. It will be found that good cloud scenes may be obtained without much difficulty from any open space near London or any other city or town ; and the author has obtained very fine negatives from the upper windows of an ordinary dwelling house, and in practice he makes it a rule, if possible, to include some of the housetops or distant landscape in the field of view, though this is totally disregarded in exposure and development. The lens used may be, of course, that usually employed, and it should be racked out to its equivalent focus, and a comparatively small diaphragm used — though this will depend upon the character of the clouds, as heavy, dark thunder- clouds will require a larger aperture than the fleecy clouds of bright weather. For dark masses, as a rule,//22 will be large enough ; whilst for bright sunlit masses on a blue sky as small as //64 will be found ample. In any case, however, a shutter exposure will be required ; generally from £ to ^ sec. will be sufficient. For development of such plates it is advisable to keep down pyro, so as to obtain soft and delicate negatives rather than bold or vigorous contrasts, and the development should not be pushed too far. For sunrise and sunset effects isochromatic plates are a sine qua non ; these alone will in any way do but tardy justice to the sometimes beautiful effects to be obtained at these times ; but in every case it must not be forgotten that colour must be disregarded, shape and the relative massing of the clouds alone being of any use to the photographers. To print clouds into a negative it is advisable first to take a print on ordinary albumenised paper, and then the outline of the sky should be carefully cut with a sharp pair of fine-pointed scissors, and this mask, as it is termed, should be adjusted on the negative, and the sky printed in on the print after the landscape or sea- 8l G Col] DICTIONARY OF PHOTOGRAPHY. scape has been printed. For printing clouds in enlargements and lantern slides the same plan may be adopted, or with the latter the clouds may be printed on another plate, and the same, when developed, fixed, and washed, used as a covering glass. In the finished print clouds should, in almost every case, be subordinate to the landscape, and therefore they should not be so heavily printed — in fact, in some cases the merest suspicion of clouds is quite sufficient to produce an artistic effect. Collodio-Chloride Printing-out Paper. This was first proposed by Wharton Simpson in 1865, and for some consider- able time it was a very favourite printing process. It gradually fell into disuse, but has lately been revived. Numerous formulae have been suggested, but the three following will be found to yield good results. Monckhoveris Formula. A. Plain Collodion. Pyroxyline 1 part. Ether 10 parts. Alcohol 10 ,, B. Magnesium chloride (cryst.) 1 part. Alcohol ... 10 parts. Filter. C Silver nitrate 2 parts. Boiling dist. water 3 ,, Alcohol 7 m Dissolve the silver, previously powdered in the water, then add the alcohol. D. Citric acid 2 parts. Boiling dist. water 2 „ Alcohol 16 ~ 82 DICTIONARY OF PHOTOGRAPHY. To make the emulsion, take of Solution A and add gradually, with constant shaking Solution B Then in the same manner Solution C and finally Solution D. ... [Col 60 parts, 5 parts. 6 parts, 4 parts. The emulsion should be allowed to stand at least eight days, and it works, if anything, better in six months. Licscgangs Formula. A. Silver nitrate Alcohol 2 parts 100 .. Strontium chloride Alcohol 2 parts. 100 .. Citric acid Alcohol D. Pyroxylin Ether Alcohol To make the emulsion take of Solution D „ C ... B Mix well and add gradually, with constant shaking, Solution A 83 2 parts. 100 ,, 4 parts. 100 „ 100 .. 100 parts. 10 10 5 parts. Col] DICTIONARY OF PHOTOGRAPHY. The emulsion should be allowed to stand three days. The following is the one which has given us the best results. Geldmache^s Formula {modified). A. Schering's Celloidin 20 parts. Ether ... 400 , , Alcohol 400 Castor oil 4 „ B. Silver nitrate 20 parts. Distilled water 20 „ Alcohol 50 „ C. Citric acid 5 parts. Alcohol 70 ,, D. Lithium Chloride 25 parts. Strontium Chloride 2.5 „ Alcohol 70 i t Mix solutions C and D and add gradually to the collodion, and then add B very gradually with constant shaking, and finally 5 parts of pure glycerine. The emulsion should now be allowed to stand for six hours. Baryta or Kreide paper is always used as the support, and the edges of a sheet are turned up, the paper laid on a sheet of plate glass, and coated with the collodion just the same as though it were the glass itself. It is then allowed to set and dry. It is printed in just the same way as any ordinary gelatino-chloride paper, and may be treated and toned in the same way ; but it will be found that the paper is very apt to curl up in the solutions. This may be avoided by laying the print on the bottom of an empty dry dish, and pouring very hot water on to the collodion film, allowing it to soak for a minute and then washing thoroughly, either in plain water or salt water, as suggested for gelatino-chloride paper. The best results are obtained with the simple sulphocyanide bath. The only precaution to be 84 DICTIONARY OF PHOTOGRAPHY. [Col observed in the use of this paper is that, if bent sharply across, it will crack. Collodion. The vehicle used in wet-plate processes for holding the haloid salts necessary for the formation of the sensitive salts of silver. It is prepared by dissolving Pyroxyline {q.v.) in a mixture of equal parts of alcohol and ether. It is a transparent glutinous liquid, which, when poured upon any sur- face, leaves, by the evaporation of the solvents, an attenuated film of pyroxyline absolutely transparent and structureless, well adapted for the purpose for which it is required. The usual strength is as follows : — Pyroxyline 5 grs. or -3 grm. Alcohol, 820 sp. gr. ... \ oz. „ 12-5 c.cm. Ether, 725 sp.gr | „ „ 12-5 „ Methylated alcohol and methylated ether may be, and are, chiefly used on account of their cheapness. A special kind of collodion, called enamel or leather collodion, is used for enamelling Prints {q.v.). Collotype. Synonyms : Albertype, Artotype, Phototype. Col- lotype is a photomechanical process by which prints in greasy ink are obtained by means of a film of gelatine in relief. Briefly the process is summed up as follows : a film of gelatine containing a bichromate salt is exposed to light under a negative, washed, dried off, and inked with greasy ink, which adheres only to those places.which have been affected by light. By using a suitable press innumerable proofs can be obtained. Negatives for preparing the collotype plates, as they are called, must be reversed (see Reversed Negatives), and should be of a rather soft, delicate character, free from yellow stain. They should also be provided with a safe edge which is usually made of tin foil. It is customary to prepare several negatives of one subject when a large number of pulls or prints is required ; as many as two, four, six, or eight, bring prepared at once, on sheets of plate glass, which should be about fths inch thick ; the edges and corners should be ground off. This glass is grained, and it is usual to grain two at once by placing some emery flour moistened with water on one, which should be laid absolutely flat on a table, and placing another plate on top, and working this about till both surfaces 85 Col] DICTIONARY OF PHOTOGRAPHY. are evenly grained ; care being exercised to keep the emery moist. As soon as the surfaces are ground, the emery is washed off and finer emery flour used in the same way till the surfaces look perfectly homogeneous and free from deep pits or scratches. The plates are then thoroughly washed, rinsed in distilled water, and set up to drain. To ensure adherence of the gelatine to the glass during the hard usage to which it is subjected in printing a substratum is used. This is usually a mixture of beer and silicate of soda or potash. The beer to be used is that known as " four ale," which should be allowed to stand twenty-four hours to get perfectly flat. The mixture is Four ale 200 parts. Silicate of soda (sirupy) 10 „ This mixture is well stirred, allowed to stand for some time, and then filtered through nainsook, well washed previously, and it is ready for use. The plates are heated gently in a collotype drying oven, and then rinsed with a little weak ammonia water, and allowed to dry ; or else, after being dusted, they are flowed over with the silicate mixture, the excess being allowed to run off into the sink, drained for a minute, and a second coating given them, when they are placed in the oven in which they very soon dry. Another substratum, lately recommended by Holzhausen and Wetherman, is No. 1. Dextrine 40 parts. Sugar .. 5 ,, Alcohol 5 „ Water 40 „ No. 2. Silicate of potash (liquid) 1200 parts. Tannin ... ... ... ... ... 2*5 „ Dissolve the dextrine and sugar in the water, and add the alcohol. Dissolve the tannin in a small quantity of water, mix with the silicate, allow to stand for twenty-four hours. Both solutions will keep some time separate. For use take No. 1 ... 1 part. No. 2 2 parts. Water ' 7 „ 86 DICTIONARY OF PHOTOGRAPHY. [Col Filter through cloth. This must be used at once as it will not keep. The plate should be placed on a levelling stand, and after brushing, plenty of the solution should be poured on and spread evenly over, ii necessary using a small piece of paper, then drain oft and place in a rack to dry ; when dry the plates should be well rinsed to get rid of the free silicate, and again dried, and the plates are then ready for coating. The plates may also be dried in the oven, being placed on edge, and leaving the door open, and regulating the heat to about ioo° F. The sensitive coating is bichromated gelatine prepared as fol- lows : — Special collotype gelatine, 80 parts are allowed to soak in water for a quarter of an hour, the water poured off and as much as possible squeezed out ; the gelatine is then placed in a graduated measure, and water added to 1000 parts. The gelatine is melted by the aid of a waterbath, and then 16 parts of bichromate of potash finely powdered are added and dissolved by careful stirring. The mixture is then filtered, and 8 parts of ammonia added, drop by drop, till the solution turns a yellowish orange. The glass is now carefully levelled in the oven and heated, and the plate carefully and evenly coated, from 100 to 120 minims being allowed for about 4 ins. square of glass. The plate or plates having been coated, the oven is closed and the temperature allowed to attain about 115 0 F., and this temperature must be kept even during the whole time the plates are drying ; and the oven should not be opened till the plates are quite dry, which at the above temperature will be in two or three hours. At the end of this time the gas under the oven should be turned out and the plates allowed to cool. The plates when cool are ready for exposure, and this is effected in one of the heavy printing frames with plate-glass front, and with screw-bars to obtain pressure. The duration of exposure is sometimes judged by examining the plates from the back, but the safest way is to use an actinometer» using, as the sensitive paper for the same, a piece of paper coated with the same mixture as used for the plates. A little experience soon determines the number of tints required for the particular class of negative. After exposure the plate is removed, placed face downwards on a sheet of black cloth or paper, and the back exposed to the light ; the reason for this being to cause perfect adherence to the glass, and to lessen the relief, which takes but a short time and may be determined by the photometer 87 Col] DICTIONARY OF PHOTOGRAPHY. or by the plate assuming a brown colour. The plate is then washed for some hours in running water, or till, on placing on a sheet of white paper, it has quite lost its yellow colour, and is then dried and ready for printing, or may be kept in this condition for a long time. For printing, the plate is placed absolutely horizontal, and covered with a solution, which is called the etching solution. Water 300 parts. Glycerine ... ... ... ... ... 600 ,, Ammonia 30 „ Salt ... 30 „ This is allowed to act till, on passing the finger gently over the surface of the plate, the high relief has disappeared. The solution is then poured off, and the excess removed with a soft sponge, and the plate is then rather sharply dabbed with a cloth or fine blotting paper. The plate is now ready for fixing on the machine, which may be either the hand or steam press. A mask of stout waxed paper is cut and mounted, so as to cover the margins, and the plate is then inked and printed from. The inking is usually effected with two rollers — the one of leather which is used with a thick ink and heavy pressure to ink the shadows, and the other a gelatine roller with a thinner ink and lighter pressure for the half-tones. The paper on which the proofs are pulled may be of various kinds. It may be glazed or unglazed, rough or smooth surface, India, China, or Whatman's, according to the result desired, and the proofs may be allowed to dry without further treatment, or they may be glazed, which is usually effected by floating the prints on an aqueous solution of white lac, or by coating them with a brush with label varnish, and drying by the heat of a gas stove, when they present the appear- ance of ordinary albumen prints. The lac varnish is made by mixing 60 parts of white lac with 500 parts of water ; 60 parts of borax are dissolved in 700 parts of water, and the two solutions brought to the boiling point. The borax is added gradually to the other, and the mixture boiled for some minutes, and 2 parts of Marseilles soap dissolved in 12 parts of alcohol with one or two drops of olive oil added, with 800 parts of water ; the whole is well mixed, allowed to settle, and cooled. The prints are DICTIONARY OF PHOTOGRAPHY. [Com floated on this in exactly the same way as for sensitising albumen paper for some seconds, and then allowed to dry. The label varnish is a commercial article, or may be prepared with Mastic ... ... ... 30 parts. Oil of Lavender ... ... ... ... 5 ,, Alcohol ... 150 ,, Benzine ... ... ... ... ... 40 ,, this is allowed to stand for eight days with occasional agitation, and then decanted. This should only be applied to collotypes on chromo or baryta paper, and should be applied with a broad brush, and the prints dried in an oven or drying box of particular construction. Grained copper, zinc and lead plates have also been used instead of glass for the support, but have not found much application commercially. Flexible supports have also been used, and the necessary materials and apparatus may be obtained commercially. Colour, Effect of, in Photography. See Isochromatic Photography. Colouring Photographs. An operation that requires con- siderable artistic skill and ability. The subject is much too comprehensive to be treated fully here. Water colours have a decided objection to adhere to the glossy surface of an albu- menised print, but they may be made to do so by applying a weak solution of inspissated and purified ox-gall. Colour of the Film. This exercises a great effect upon the subsequent operation of printing. The yellow-stained film is the most non-actinic and slowest, the olive-greenish black being the quickest and giving the most brilliant prints. Combination Printing. See Printing. Composition. An artistic term denoting the grouping of the materials of a picture so as to form a pleasing and harmonious whole. It can be well said of the majority of photographs taken by amateurs that there is but little composition in them ; most are but a faithful portrayal of subjects as they are found naturally. But, whilst the photographer does not possess that 89 Con] DICTIONARY OF PHOTOGRAPHY. power of composition which is the backbone of the artist's work, he x:an at least modify to some extent the scenes, etc., ready found to his hand. The amateur who desires rather to produce pictures than faithful photographs is recommended to obtain Robinson's " Pictorial Effect in Photography," and " Picture Making by Photography," in which the subject is most ably treated at great length. These two books should form part of the library of every one practising photography. Concave. A term applied to lenses when the surfaces are hollowed out like the inside curve of an arch. Concave, Concavo-Concave, Concavo-Convex Lens. See Lens. Condensers. These are combinations of lenses of various forms, which have for their purpose the condensing or collecting of rays of light which would otherwise be scattered or lost. They form a necessary part of every lantern, and take various forms. The action of a condenser is well shown in the following diagrams. Let R be the light emitting rays which pass through Fig. 12. the negative on slide p, and let o be the objective or projecting lens. It will be seen from this that practically very little light passing through the slide reaches the objective ; but by placing a condenser between the radiant and slide it will be seen that it refracts light which would otherwise be lost, as shown by the dotted lines, and condenses it, so that it is utilised by the pro- jecting lens. Simple lenses could be used for condensers, but on 90 DICTIONARY OF PHOTOGRAPHY. [Con account of their great thickness and the spherical aberration they would be liable to crack, and would give but confused images. It has been the custom, therefore, to split the single lenses, and mount the two lenses with their convex surfaces nearly touching, Fig. 13- as in fig. 14. A further improvement, suggested by Mr. Traill Taylor, was the form shown in fig. 1 5, which consists of a meniscus lens and a double convex, preferably a crossed lens. It is essential with a lantern — very essential — that as much light as Fig. 14. Fig. 15. possible should be utilised, and assuming the dotted lines a and b to represent an angle of illumination of 90 0 , it is seen that unless the condenser is placed very close to the light, and is of short focus, it cannot grasp more than c d ; therefore, by placing a small lens nearer the radiant, as in fig. 16, it is evident that 9i Con] DICTIONARY OF PHOTOGRAPHY. more light will be collected, provided the third lens is thin and of long focus, when the light is brought to within two inches Fig. 16. of the small lens, and, passing through it, diverges, and then is rendered parallel by the second lens and condensed by the third Fig. 17. lens. Further than that, by using three lenses the spherical aberration is reduced to one-ninth of that of a single lens. Fig. 18. Mr. Traill Taylor suggested many years ago the condenser shown in fig. 17, which consists of three plano-convex lenses, the centre 92 DICTIONARY OF PHOTOGRAPHY. [Con being achromatised. This, however, is expensive. Grubb sug- gested the form shown in fig. 18, in which A is a piece of plain glass to absorb the heat, b a plano-convex lens which acts as a condenser, c a plano-convex, and d an over-corrected combina- tion. From c to D the rays are practically parallel, and thence diverge, and are condensed by the large lens E. The best form of condenser, when only two lenses are used, is that|shown in fig. 19, according to Mr. Traill Taylor, whose notes on this subject I have Fig. 19. condensed, and consists ol a plano-convex lens with its flat side to the radiant, the second lens being a crossed lens. Most con- densers are made of crown glass, and have a slightly greenish tinge. Colourless optical flint would be better, but the price would be higher. All condensers shouid be so loosely mounted in thin cells that they can be turned round, otherwise the expan- sion by the heat may cause them to crack. Clock glasses filled with liquid have been suggested as condensers for enlarging, but these are so long in focus as to be practically useless. Conjugate Foci. See Focus. Contact, Optical. Any two substances brought into mechanical union one with the other, so as to absolutely join, and made to present but two instead of four surfaces, are said to be in optical contact. A familiar example is the common mirror, where the amalgam and glass are in absolute optical contact. Contrast. The placing of the light and shade and objects in a photograph that they may give due value the one to the other. Convex. The opposite to concave — i.e., shaped on the exterior into a spherical or round form. 93 Cop] DICTIONARY OF PHOTOGRAPHY. Copal (Ger., Copalharz ; Fr., Copal; Ital., Gomma copale). A resinous substance obtained from certain leguminous trees, from Madagascar, China, Africa, and America. It is also found as a fossil. It occurs in pale yellowish tears, which are insoluble in water, slightly soluble in alcohol, more so in alcohol and camphor, freely soluble in chloroform, ether, and turpentine. It is used for making varnishes. Copper, Bromide of (Ger., Kupferbromid ; Fr., Bromure de cuivre ; Ital., Bromuro di rame). CuBr 2 = 223*3. Synonym: Cupric Bromide. It occurs as a blackish powder, or in light-blue needle-like crystals, and is formed by dissolving cupric oxide in hydrobromic acid, evaporating and crystallising, and by mixing solutions of cupric sulphate and bromide of potash, evaporating, and separating the sulphate of potash. It is a deliquescent salt, and slightly soluble in alcohol. It is used as an intensifier. Copper, Chloride of (Ger., Kupferchlorid ; Fr., Chlorure de cuivre; Ital., Cloruro di rame). CuCl 2 = 134*3. Synonym : Cupric Chloride. Formed in a similar manner to the bromide, with hydrochloric acid, or by mixing a solution of cupric sulphate and calcium chloride, filtering from the precipitate of calcium sulphate, evaporating, and drying. It forms brilliant emerald- green needles, which are very deliquescent and easily soluble in alcohol. It is used as a reducer, and in Obernetter's copper process. There is also a lower chloride, cuprous chloride CuCl or Cu 2 Cl;,, which is only used as a convenient absorbent of chlorine in the preparation of chloroplatinite of potash. Copper, Sulphate of (Ger., Kupfersulfat, or Kupfervitriol ; Fr., Sulfate de cuivre, or Vitriol bleu ; Ital., Sulfato di rame). CuS0 4 ,5H 2 0=249'3. Synonyms: Cupric Sulphate, Blue Cop- peras, Blue Vitriol. This is made by roasting copper pyrites with free access of air, lixiviation of the mass with water, evaporating, and crystallising. It occurs in beautiful blue crystals, some of very large size, which effloresce on exposure to air, lose all their water of crystallisation, and form a white powder, which is extremely hygroscopic. Cupric sulphate has been used as an addition to the ferrous oxalate developer, its action being stated to be merely a retarding of oxidation of the ferrous sulphate. 94 DICTIONARY OF PHOTOGRAPHY. [Cop Copying. This is an operation which is frequently necessary, and may be divided into three heads for convenience : (a) copy- ing black-and-white objects ; (b) copying photographs ; (c) copy- ing coloured objects, like oil-paintings, missals, etc. (a) Copying Black-a?id-White Work, such as Engravings, Line-Drawings, etc. For the professional worker wet collodion undoubtedly still holds its own in this branch ; but for the amateur, or when only one or two subjects have to be copied, dry plates may be used with perfect results. In copying a black- Fif. 20. and-white object we want no gradation, no half-tones, no shadows; merely black and white. Should the paper show a grain it is necessary to light the subject in such a manner that no sign of this grain is visible, which can usually be effected by a full front lighting, and by even, all-round illumination as is obtained out of doors. Frequently it is necessary to use some support to retain the page of a book or print flat ; this support may be either a piece of stout wood placed behind the leaf or print, which can then be held in position by a couple of stout india-rubber rings, if the print to be copied cannot be pinned flat by the aid of 95 Cop] DICTIONARY OF PHOTOGRAPHY. drawing-pins. A capital copying-stand, suggested by the " Ker- nel," the author of " Photography in a Nutshell," is shown in fig. 20. This is so obvious that we need hardly explain its action. The most suitable plates are those commercial brands, which are specially made for this work, and which are called '* photo-mechanical " ; but, failing these, any ordinary slow lantern plate designed for giving black tones can be used. The lens should be a rapid rectilinear or doublet of not too long a focus, because it must be remembered that when copying at close quarters the focus is lengthened, and therefore a lens of such a focus must be chosen that the increased focus is not too long for the bellows of the camera. This increase in focus must be taken into account when estimating the factor of stop aperture for cal- culating exposure. The exposure of course will vary enormously with the subject ; but, as some guide, I may say that copying a black-and-white line-drawing, such as one of the diagrams in this book, the same size, using // '22 diaphragm and a photo- mechanical plate at noon in an ordinary room, facing a north- light window on a bright, but not sunny day, the exposure given was 40 sees., and found to be correct. For development ferrous oxalate, eikonogen, amidol, and metol are useless, and the best results will be obtained by using either hydroquinone or pyro ; glycin also being of value, though for this work I have not obtained such successful results as with pyro. Reference to the Appendix will give the formulae of the different makers, that of Mawson and Swan's being the one I have succeeded best with. The main point in developing is to obtain clear glass in the lines representing the blacks of the print ; density of the part represent- ing the paper is of secondary consideration because it may be obtained afterwards by intensification, though with correct ex- posure good density combined with clear glass can be easily obtained. Continue development as far and as long as possible, but on the slightest sign of any deposit on the lines instantly drop the plate in an acid fixing-bath. After fixation wash thoroughly, and then examine the negative ; should there be any deposit in the lines reduce by the aid of Belitzski's reducer, thoroughly wash, soak for 10 mins. in a hypo eliminator, again wash, and intensify with the potassio-silver cyanide intensifier. {b) Copying Photographs. In copying photographs, photo- gravures, collotypes, or any prints in which there is half-tone, it 96 DICTIONARY OF PHOTOGRAPHY. [Cry is advisable to use a medium rapidity or ordinary plate, and with prints with a considerable amount of heavy shadow it is advisable even to use a more rapid plate. The developer should be the one usually recommended for the plates, or that which the operator is in the habit of using, and soft, full-of-detail negatives should be aimed at. (c) Copying Coloured Objects, Oil-Painti?igs, etc. With all coloured objects there is only one particular kind to use, and that is the colour-sensitive plate. When the object contains much red, then one sensitised for this colour must be used ■ if there is much blue or violet, then must also a yellow screen or filter be employed. In fact, it may be taken for granted that with all oil-paintings a yellow screen is advisable, as it prevents the reflections from the cracks and inequalities of the surface. The best light in which to copy all coloured objects is sunlight : the colours are more correctly rendered. Next to sunlight would, of course, come the electric light, and then magnesium ribbon.' In copying oil-paintings the question of lighting is an important one, as the thicknesses of the coats of paint will show with strong light from one particular direction ; at the same time, it must be borne in mind that artists frequently desire to see these inequalities or brush marks, whilst for ordinary purposes the brush marks are objectionable. For the correct reproduction of colours it is necessary to use light filters, which will cut off the action of the blue and violet rays, whilst the red and yellow act. The composition of these screens for this purpose is given under Heliochromy (q.v.). Further information will also be found under Screens and Isochromatic Photography. Crystal Varnish. This is specially designed for varnishing lantern-slides and transparencies, and is made by dissolving- Gum dammar ... ... 25 grs. in Benzole ... ... ... ... 1 oz. another formula being Canada balsam ... ... 5 parts Shellac (yellow) !6o Sandarac Alcohol 170 , 1000 , 97 h Cur] DICTIONARY OF PHOTOGRAPHY. rr Fig. 22. photographer, be formed on a plane or flat surface ; but, taking a single lens (fig. 21), we shall find that the focus for b is at e, whilst the focus for a is at g, for c at f, h i represents the 98 DICTIONARY OF PHOTOGRAPHY. [Cya plane ot the sensitive plate, from which it is obvious that, theoretically, only the point e would be in focus. A concave or negative lens has, as is well known (see also Chromatic Aberration), no real focus, and the marginal rays are more refracted than the central, so that by combining a concave with a convex lens we lengthen the focus of the marginal rays, and thus flatten the field. The use of a stop also still further increases the flatness of field, as shown in fig. 22. a b c is a plane object, and / a lens ; the rays from b — the point situated on the axis — will come to a focus at F ; but, the rays from «, (1., II., III., iv., v.) are refracted to a, b, c, d, e, and from c (l, 2, 3, 4, 5 ) are refracted to a', b', c\ d', e' . From this figure it is evident that only a iv., a v., c 5 and c 4 have their focus anywhere near F, so that by placing a diaphragm, Op, so as to intercept all but these rays we shall practically have a flat field. Cutting Prints. This is trimming off the unnecessary part of the print till of the desired size. It should always be done prior to toning, to save the waste of gold in toning unnecessary matter. It should always be done whilst the print is dry. Plate-glass cut, with polished edges, to certain sizes can be obtained commercially, but any old negative glass or flat ruler will do. Numerous shaped knives are sold for this purpose but the author has found a leather-cutter's knife, termed a dicker's knife, the most convenient, and the price is but a few pence. Too many amateurs consider that the finished print should be exactly the full size, when much more pleasing pictures can be produced by trimming off certain portions of the print. Cyanine (Ger„ Cyanin, or Chinolinbleu; Fr., Cyanine, or Bleude quinoleine ; Ital., Cianind). Synonyms: Cyanine, Cyanin Iodide, Quinolin, or Chinolin Blue. C.^I-^NJ = 525. This is prepared by the action of iodide of amyl on quinolin ; it occurs as a dark blue powder or prismatic crystal, with metallic lustre; it is not very soluble in water, but more so in alcohol. As cyanine is sensitive to light it must be kept in the dark. It is one of the best sensitisers for red, and for this purpose is used in orthochromatic work, the disadvantage being that the plates are very liable to fog, and therefore Dr. Eder suggests the use of 99 Cya] DICTIONARY OF PHOTOGRAPHY. chloro-cyanin, which has not this action, and gives the following directions for making the same : — Powder the ordinary com- mercial iodo-cyanin'; place in a porcelain or platinum dish, and cover with some water and hydrochloric acid ; evaporate to dryness with constant stirring ; the mass thus obtained is again wetted with hydrochloric acid, and again evaporated, when hydriodic acid is given off and chloro-cyanin is left behind. By weighing the capsule containing the cyanin before and after this treatment one may dissolve the mass at once in ale ihol and keep in the dark for use. Cyanotype. Synonyms: Negative Cyanotype, Ferroprussiate, or Blue Process. A process discovered in 1842 by Sir John Herschel. It is called negative cyanotype, because it produces copies of engineers' or architects' plans with white lines on a blue ground, the action being the reduction of a ferric salt by light to the ferrous state, and the precipitation of Prussian blue by the action of ferridcyanide of potassium. Herschel's formula was A. Potassium ferridcyanide 8 parts. Water 50 ,, B. Ammonio-citrate of iron ... ... ... 10 parts. Water 50 „ The solutions are mixed in equal parts, filtered, and kept in the dark, and 'will- keep'jfor some little time. The ferridcyanide should (be just rinsed [with water to clean it from any adherent powder, T and the solution should be of a yellowish or orange-red colour, and'not greenish blue ; if the latter colour, it should be thrown away and fresh mixed up, or heated and a few drops of bromine water added. Latimer Clark suggested the following improved formula : — A. Ammonio-citrate of iron 90 parts. Water , 3°° •> 100 DICTIONARY OF PHOTOGRAPHY. B. Potassium ferridcyanide ... ... ... 80 parts. Liquor Ammonia ... ... ... ... 7 „ Water 300 ,, Sat. Sol. oxalic acid ... ... ... ... 60 ,, This is more sensitive. Ehrmann and Fries suggested the addition of bichromate of potash, the former stating that this addition kept the papers unchanged for from three to five months. Ehrmann's formula is A. Ammouio-citrate of iron ... ... ... 60 parts. Water 256 „ B. Potassium ferridcyanide ... ... ... 40 parts. Water 256 Mix in equal parts, and to every 960 parts of the mixture add 1 part of bichromate of potash. Watt suggested the addition of boric acid for the same purpose. A. Ammonio-citrate of iron ... ... ... 96 parts. Boric acid ... ... ... ... ... 1 part. Water ... ... ... ... ... 190 parts. B. Potassium ferridcyanide ... ... ... 96 parts. Water 196 „ Mix in equal parts. Rockvvood suggested the addition of gum Arabic, or dextrin, as a preventative of the solution sinking into the paper. A. Potassium ferridcyanide ... ... ... 1 pait. Water 10 parts. j 01 Cya] DICTIONARY OF PHOTOGRAPHY. B. Ammonio-citrate of iron ... ... ... 3 parts. Water 10 „ Gum Arabic, or dextrin \ part. The sensitising solution is spread over well-sized paper with a pad or brush, working in one direction, and then across to even the marks out. The paper is then hung up to dry, and appears of a greenish-yellow colour ; and where the light acts on it it turns blue. After exposure it is merely washed in water, when the image becomes bright blue, and the ground, or unexposed portion, should remain quite white. Over-printed proofs may be reduced, after thoroughly washing, by being dipped into a weak solution of ammonia or a 2 per cent, solution of sodium carbonate, well washing, and then dipping into weak hydrochloric or acetic acid and well washing. Under-printed proofs may be intensified by immersion in a solution of ferric chloride, or nitrate or sulphate of iron, 3*5 parts to 1000 parts of water, till the image appears darker in colour, and then well washing. Corrections, or taking out spots, etc., can be effected by touching the dry prints with a 4 per cent, solution of oxalate of potash, with which also titles may be written ; and if red aniline ink be added to the above, or 4 parts of oxalate be dissolved in 100 parts of the red ink, the title will appear red on the blue ground. The blue images thus obtained can be con- verted into ink images, or blackish images, by soaking first in 5 per cent, carbonate of potash solution, washing, and then immersing in a similar strength of tannin solution ; a good brownish-black colour is obtained by immersing them direct in a saturated solution of carbonate of soda, mixed with an equal quantity of water, to which has been added as much tannin as it will dissolve. It has also been suggested immersing the prints in weak hydrochloric acid to clear the whites, then in weak ammonia 1 : 15,000, and finally in a bath of Alum ... ... ... ... ... ... 10 parts. Tannin ... ... ... ... ... 1 part. Water 130 parts. exposing the prints to sunshine for ten minutes, and then bathing in dilute ammonia. Cyanotype, or Ferroprussiate prints, may 102 DICTIONARY OF PHOTOGRAPHY. [Cya also be converted into silver prints by immersing the prints in a 2 per cent, solution of silver nitrate, washing well, and de- veloping the pale yellow image with ferrous oxalate developer. Instead of using a mixture of ferridcyanide and ammonio-citrate as the sensitive mixture, the latter solution alone may be used for sensitising the paper, and the ferridcyanide solution used as a developer. Positive Cyanotype, or Pellet's Process. This process is the opposite to the last — that is, it gives blue lines on a white ground from a plan, or, in other words, where the light acts no image is formed ; only on those parts where the light does not act is a precipitate of Berlin blue formed by the action of the ferro- cyanide of potassium with a ferrous salt. This process was also suggested by Herschel, but no satisfactory progress was made till Pellet patented in 1877 his process of adding a viscous substance to the sensitising liquid. Pellet used Oxalic acid 5 parts. Ferric chloride ... ... ... ... 10 ,, Water 100 ,, Gum Arabic... ... ... ... ... 9-5 ,, In 1880 Collache patented a similar process, and used Gum Arabic ... 7-10 parts. Citric acid ... ... ... ... 2-3 ,, Ferric chloride solution 45°B. ... ... 4-6 ,, Pizzighelli in 1881 gave good working formula: for this pro- Water ... 81-87 cess : — 1. Gum Arabic . . . Water 20 parts. 100 ,, II. Ammonio-citrate of iron Water 50 parts. 100 111. Ferric chloride Water 50 parts. 100 Cya] DICTIONARY OF PHOTOGRAPHY. The two latter solutions will keep several weeks. The solutions are mixed in the following proportions and order : — Solution No. I. , ... 20 parts. No. II ... 8 „ No. Ill 5 „ As soon as mixed this solution is thin, then becomes thick and cloudy, and then clear and liquid again, when it is ready for use. Well-sized paper is evenly coated with this solution with a broad brush, and the coating evened out with another brush. It must be quickly dried in a warm room, and protected from damp and light. In printing, the image appears as yellow on a darker ground. The developer is Potassium ferrocyanide 20 parts. Water 100 ,, which should be spread over the proof with a broad brush, care being taken that no solution touches the back of the paper or stains will be produced. As soon as the image appears of a deep blue colour, the print should be well washed, and then laid in dilute hydrochloric acid 1 : 10 till the ground appears white ; and the print should then be well washed and dried. Waterhouse has suggested another process. I Gum Arabic 170 parts. Water 650 ,, II. Tartaric Acid ... 40 parts. Water 150 III. Sol. ferric chloride 45 0 B 1 50-1 20 parts. Mix solutions 1 and 2, and add gradually, with constant stirring, No. 3 ; allow the mixture to stand for twenty-four hours, and then dilute with water till the specific gravity is rioo. The solution, and the paper sensitised with it, will keep for some considerable time. The exposure in direct sunlight is from 15 to 40 seconds, in diffused light from 10 to 30 minutes. As the 104 DICTIONARY OF PHOTOGRAPHY. [Dag image formed by light is only very faintly visible, it is advisable to use a strip of paper, either exposed under one corner of the plan or drawing, or under a similar and smaller one at the same time ; and when test slips from this develop a blue image on a yellow ground the exposure is sufficient. The developer is a 20 per cent, solution of ferridcyanide of potassium. The edges of the print are turned back so as to form a sort of dish, or protecting shield, so that no developer gets on the back of the paper. The print is then carefully floated on to the developer and left for about thirty minutes, and then examined at one corner till blue spots begin to appear, when the print should be immediately removed, floated carefully again on a dish of clean water and left for some minutes, and then immersed in dilute hydrochloric acid 1 : 100, and any blue spots removed by carefully brushing ; and, finally, the print should be laid at the bottom of an empty dish and a vigorous stream of water from a rose or tap allowed to play on it. Corrections are made by the same solution previously mentioned, the spots being touched with a fine pencil and blotted off with clean blotting-paper. Daguerreotype. The oldest process for obtaining any per- manent picture ; discovered by Daguerre. A sensitive surface of silver iodide and bromide was formed by exposing a silvered copper plate to the direct action of the metalloids. After ex- posure, which was inordinately prolonged, the development was effected by exposing the plate to the vapour of metallic mercury i which was deposited on the plate as an amalgam of silver and mercury. The unacted-upon iodide and bromide were then dissolved by cyanide of potassium or hyposulphite of soda, and the image toned by sel d'or. (See Gold Hyposulphite.) Daguerreotype, To Clean and Copy. Carefully remove the daguerreotype from its frame and separate from its covering glass, and place face upwards in a dish of cold water. Be extremely careful not to touch the front of the plate, as the slightest touch will leave a permanent mark. Lift the plate by the corners, and remove the paper from the back when suffi- ciently soaked ; rinse the plate thoroughly, and, should the water be repelled as though the plate were greasy, flow over a little methylated spirit. If the tarnish on the edges be blue in colour, immersion in an ordinary fixing bath will remove the same ; but io5 Dal] DICTIONARY OF PHOTOGRAPHY. if any bronzing is visible, make a solution of cyanide of potas- sium, ten grains to the ounce, and keep pouring this on and off till all tarnish is removed. Wash the plate thoroughly to free from cyanide, and rinse well with distilled water ; then take hold of one corner of the plate with a pair of pliers, and dry evenly from a top corner downwards over a spirit lamp or Bunsen burner. If any stain or deposit is left by unequal drying, the plate must again be rinsed with distilled water, and dried in the same way. The chief point is not to touch the plate with any- thing but the liquids,' or a mark will be made which nothing will eradicate. To copy a daguerreotype the best plan will be to place it inside a deep box, lined with velvet or black cloth, with a hole in the lid for the lens to peep through, and a piece cut out of one side only to illuminate the plate by — sunshine is best, though the light from an enlarging lantern is equally as effective. In most daguerreotypes the marks of the buffer are seen as fine horizontal lines. In copying, these should be placed vertical, and when in that position are barely visible. Dallastint. A secret process of photo-mechanical printing, famous for its rendering of half-tone. Dammar. A tasteless, odourless, whitish resin obtained from the Amboyna pine, whose habitat is the Malay Archipelago. It is used in varnish-making, for which purpose it is usually dissolved in turpentine, or benzole. Dark-Room. The room in which all operations requiring actual handling of the sensitive plate must be conducted It is usually lighted by daylight filtered through some non-actinic glass or medium. It was the custom but a year or two back to utilise none but the deep ruby glass for this purpose, but now some equally non-actinic colours giving much more general illumination are used. A good, safe light can be obtained by using what is termed cathedral green glass, with one thickness of canary medium. The author invariably uses artificial light from a paraffin lamp, as by this light, which is constant, a much better idea of the progress of development can be obtained than by such a variable quantity as daylight. Whatever light is used it should always be tested by placing a sensitive plate upon the developing table with some opaque substance, such as a piece 106 DICTIONARY OF PHOTOGRAPHY, [Den of black cardboard, upon it, and left for three or four minutes and then the plate carefully developed should show no image of the card. The general arrangements of the dark-room must be left entirely to the amateur, but the following may be considered to be some of the principal features : — A shelf or table on which to develop. This should be of a convenient height, to allow the operator to sit at his ease whilst developing. It should be covered with some non-absorbent material, such as sheet lead or zinc, and the edge of this should be turned up about a quarter of an inch to prevent any solution which might be spilt from running over. There should also be a sink, with a tap and a good supply of water. Shelves should be placed at convenient heights for th£ storing of bottles, printing frames, boxes, etc. The room and developing table should be kept scrupulously clean, and after operations all solutions spilt and the trays, measures, etc., should be cleaned and put away. Dark-Tent. A portable dark-room, little used now, but ot absolutely necessity in the old days of the wet process. Decomposition of Light. White light on passing through a prism is decomposed or separated into its constituent rays. All lenses being formed on the principle of a prism, it is evident that light passing through a lens would be decomposed and give rise to chromatic aberration, but this is obviated by combining a lens of different shape and glass, so as to recombine the scattered rays. (See Spectrum and Lens.) Definition is the accurate concentration by the lens of the light from a point in an object to the corresponding point in its image without spreading to adjacent parts. Perfection of defini- tion depends chiefly on the rapidity of the lens, on the com- position of the glass employed, the relative positions and forms of the surfaces and their proper grinding, the centreing of the elements of a combination, and, in a doublet, the centreing and due separation of the combinations. Deflection. An optical term used to denote the swerving from its straight course of a ray of light when passing very near an opaque object, the ray being deflected towards that body. Density — literally opacity ; and in this sense correct density is an attribute of a good negative. It should be just sufficient to 107 Dep] DICTIONARY OF PHOTOGRAPHY. give due relation to the shadows, and yet allow the detail in the high-lights to print. Almost all plates differ in the value of the deposit of metallic silver, of which density or opacity is formed ; and the correctness of the judgment necessary in this particular is one of the best tests of a good worker — it can only be obtained by experiment with every brand of plate used. With some the development must be pushed till the high-lights just show on the back of the film, and the whole surface of the plate is becoming blackened ; whilst with others, especially those containing iodide or those having a film rich in silver, the test of the blackening of the surface of the plate will usually be sufficient. The colour of the deposit of silver affects the result in a great measure. If, when the negative has been fixed, the amateur finds that his judgment has not been correct, he has, fortunately, methods of increasing or decreasing the density, as described in the operations of Intensification and Reduction (q.v.). Depth of Focus. See Focus. Detail. The definition of each minute part or parts of the material of a picture, whether in the negative or print therefrom. Detective Or Hand Cameras. These are cameras of par- ticular designs, so constructed as to be portable and unlikely to attract attention. Their name is legion ; their makes diversity itself ; and to attempt to include even a brief description of them would be beyond the limits of space at my command. Practi- cally, however, hand cameras may be divided into two main classes: (a) those with automatic plate or film-changing appa- ratus ; (b) those with dark slides. I do not intend to attempt in any way to describe these. Each operator must decide for him- self which pattern meets most nearly his requirements ; but we can consider the individual parts of the camera. The Lens. As one of the chief features of detective work is the portrayal of objects situated at varying distances from the camera, it is obvious that lenses with great depth of Focus {q.v.) are required; and as this property decreases with increase of focal length and aperture, we are limited in our choice to certain forms and apertures of lenses, although the great advance made lately in practical photographic optics has given us instruments which are of valuable assistance in this work. It will be found 108 DICTIONARY OF PHOTOGRAPHY. [Det that, generally, lenses of short focus — i.e., which have a focus about equal to the longer base of the plate which they are intended to cover, thus for a quarter-plate a 4-in., 4o-in., or 5-in. focus lens — should be used. The rectilinear, or doublet form of lens, will be found the best, though single or landscape lenses, working at a large aperture, fjZ or f/10, will often serve equally as well. The Diaphragms or Stops. The question of aperture is governed by two considerations — the first, that of depth of focus ; and the second, the actinic power of the light. As the first increases with diminution of aperture, the smaller the diaphragm the greater the depth of focus ; but as this is also governed by the second consideration, it is obvious that, except for brightly lit scenes, such as seascapes and river views, and work on the sea- shore in brilliant sunshine, it would be injudicious to use too small an aperture, as loss of detail in the heavy shadows would result- For ordinary work //8 or f\\o will be found quite small enough, while for sea and river views //16 will be found large enough. The form of diaphragm, whether Iris or Waterhouse, is not a vital question, as, unless the former is controlled from the out- side of the case, there is no advantage in its use. The Shutter. This should be capable of accurate adjustment for various speeds, from very rapid to slow. From j^th to T ^ sec. will be found quite range enough. The speed at which the shutter will be required to work is governed, of course, by the rapidity of movement and nearness of moving object to the camera. Reference must be made to the tables and rules given under Instantaneous Photography, p. 246, for information upon this point ; but as it would be impossible to make any calculation at the time of exposure, the operator must depend upon experi- ence alone to teach him all that is required on this point, although the application of these rules in the formation of a set table of distances, rapidity of movement, and speed of shutter, would be useful. For example, supposing a 4-in. focus lens is used, by a little calculation we shall find that a shutter must work at the x^th of a second to take a man, walking at the rate of four miles an hour, twenty yards off; and a horse at thirty yards' distance, going about twelve miles an hour, will require about / th of a second speed. Plate Arrangement For those who use films, roller slides, of course, will be required ; but for the general run the question as 109 Det] DICTIONARY OF PHOTOGRAPHY. to which is the better, dark slides or automatic changing methods, will be an all-important one. Focussing. In many hand cameras this is altogether dis- pensed with, the use of a so-called fixed-focus lens obviating the necessity of the same ; but this we again object to on the same principle as the automatic changing arrangement is objected to — namely, the limitation of the use of the camera. The table- of distances beyond which everything is in focus (p. 193) will be useful on this point, and the question of fixed- focus Lenses (q.v.) will be treated of separately. Finders. Many very successful workers in this branch of our art utterly pooh-pooh the necessity of finders ; but, speaking from personal experience, these are an absolute necessity; nothing is more annoying than to find on development that only the half of a desired object is included on the plate. There is, however, one evil which is usually seen with most finders of the camera obscura model, the one usually employed, and that is, if the ground glass is not deeply sunk in the camera case, any bright light shining on the same effectually prevents the miniature image from being seen. This should be noted in the choice of a camera, or disappointment may ensue. Of the working of a detective or hand camera but little need be said ; but still it is just as well for the following points to be con- sidered. In most cases comparatively wide-angle lenses are used, and these tend to dwarf the distance and give exaggerated perspective. Do not be disappointed, therefore, if instantaneous pictures of distant mountains or other objects appear as insigni- ficant in size ; plates exposed indiscriminately on all sorts of subjects do not, as a rule, yield pictures, though they may produce perfect negatives. Subjects with very great contrasts of light and shade, such as street views, one side of which is generally in shadow, do not yield perfect results ; and rapidly moving objects, such as horses or men, may be taken in too brief a period of time, and the results, though perhaps scientifically accurate, are not truthful as we see them, because the eye receives an impression of several movements combined in one. Of the plates to be used any good brand is suitable. There are several points in connection with hand-camera work which should be noted. First as to holding the camera. Some workers ad- here to the method of holding the camera under the arm pressed T TO DICTIONARY OF PHOTOGRAPHY. [Det close against the body, and use the small finder to judge of the position of the object ; others hold the camera under the chin and sight along the top. The best position depends upon the position of the object to some extent. Suppose we wish to get a shot at a person or group about ten feet off, placing the camera under the chin will probably cut off his feet, whereas holding it under the arm may include all the figure. Then, again, suppos- ing the object to be a distant scene, such as would be taken from a steamer going down the Thames ; in this case holding the camera under the arm will include far too much foreground. A method for which I am indebted to a well-known optician has proved in my hands exceedingly useful. It is : — When the object is within about ten or fifteen feet, hold the camera close to the body, with both arms at full length ; this places the camera low, includes a lot of foreground, and obviates any chance of cutting off any one's feet. Supposing the object to be taken is about twenty feet distant, then the camera may be held against the chest ; if the object is about thirty feet off the camera may be held up to the chin ; but, supposing we are working from the deck of a steamer or from such a position that there is a lot of unnecessary foreground, then by raising the camera level with the eye and the arms at full length we cut off a lot of foreground, and there is not the slightest difficulty in seeing whether the camera is level and whether we include the desired object. If there is any difficulty on this point we may use one or two sights, like the back and fore sights of a rifle. I beg leave to enter a protest here against the craze for working shutters at unneces- sarily high speeds. The idea with many workers seems to be how quickly the shutter may be driven, whereas how slowly it can be used should be the real aim, in order that full exposure to the shadows and darker portions of the picture may be given. A brief word of remonstrance may not be out of place at the absurd requirements of some workers. They expect for a few shillings to obtain a hand camera which will enable them to turn out the very finest work, to compete with that done by cameras costing as many guineas. I do not wish to decry cheapness, for I have myself done work with a twelve-shilling camera quite equal to anything done by a twelve-guinea one ; but then it was only by recognising the capabilities of the camera, and not by expecting it to do impossible things, by recognising that the lens I T r Dev] DICTIONARY OF PHOTOGRAPHY. was working at a small aperture, that the shutter would not be suitable for the finish of a race or an express train at full speed, etc. Ignorance of the capabilities of the instrument is in many cases the cause of disappointment. For judging distances, always a difficult matter for a beginner, the simplest plan is to learn distances from his ordinary surroundings : for instance, take the street he lives in ; find the width of it from his door, or window to the opposite pavement, to the centre of the road ; measure the distances down the street ; and by constantly counting these over in his mind whilst looking at them he soon learns to judge all distances by them. Finally, it should be remembered that a hand camera is not an instrument devised for the purpose of taking photographs in positions which are likely to cause derision of, or annoyance to, anybody ; they are merely portable cameras which should be used to obtain mementos of rapidly moving scenes and persons, and for universal picture-making. Development. As the developer is the agent which renders the latent image visible, so the operation of using the developer is termed development. Development may be divided into two distinct classes — physical and chemical. If we have a wet collodion plate which has been exposed on a subject, we shall have practically a film of silver salt, part of which has been affected by light and which is covered with adherent solution of nitrate of silver. On adding a solution of ferrous sulphate to nitrate of silver we get a precipitate of metallic silver, this precipitation, however, being delayed by the presence of organic acid such as acetic or citric. If a piece of clean silver wire be placed in the acidified ferrous-sulphate and silver solution, the silver is slowly deposited from the solution on to the silver. In the case of the wet plate the sensitive salt of silver which has been affected by light acts precisely in the same way, and the nascent silver from the adherent nitrate solution is deposited on the light-affected places forming the image. At present there is no proof that the sensitive salt is itself reduced. This is called physical development. At the present time when dry gelatino- bromide plates are so much in use we have practically another state of things. In this case the sensitive salt affected by light is itself reduced to the metallic state by certain chemicals. In this case we have no silver nitrate slowly depositing silver, but 112 DICTIONARY OF PHOTOGRAPHY. [DeX the sensitive silver salt itself is reduced, hence this is called chemical development. In a developer there are four essential ingredients: (i) the developer proper ; (2) the accelerator, which hastens the action of the developer ; (3) the restrainer ; and (4) the solvent or water. The developing agent may be pyrogallol, hydroquinone, eikonogen, amidol, metol, etc. The accelerator is usually an alkali, ammonia, or the hydrates or carbonates of potassium or sodium. The restrainers are the bromides of potassium or sodium citrates, etc. If a developer of normal strength is applied to a plate which has never been exposed to light and allowed] to act for a long time, it will be found that there is a general reduction of the silver salt ; this general re- ducing action is, however, less, if some soluble bromide be added to it. Frequently a sulphite is added to a developer, and this is useful in that it prevents the too rapid oxidation and consequent discoloration of the developing agent, and thus prevents stain- ing of the hands and gelatine of the film. Having thus far considered the main points of development we may consider the chemical theory of the same to be as follows : — The latent image, which we will assume to be sub-bromide of silver, Ag.,Br, is split up into metallic silver and bromine ; the bromine is at once absorbed to form bromide of the alkali or some more complex compound, the reducing agent or developer proper being oxidised ; but if the action were to cease at this point, the image would be very faint ; the metallic silver and the unacted - on bromide of silver react and form more sub-bromide, which is again reduced by the developer to the metallic state. For convenience sake the particular modifications of the various developers is arranged for different cases likely to occur in practice under the heads of the different developers. Deviation. An optical term to denote the alteration of the course of a ray of light when it is refracted or reflected from the surface of, or when passing through, anything. Dextrine (Ger., Stiirkegnmmi ; Fr„ Dextrine ; Ital., Destruia). Synonym : British Gum. C 12 H 10 O, 0 . Is made by heating starch until it loses its gelatinous property, or by heating it in the presence of a dilute acid, when it becomes soluble in hot and cold water. It is usually a pale buff powder, and is used as a substitute for gum. (See MOUNTANTS.) 113 1 Dia] DICTIONARY OF PHOTOGRAPHY. Diactinic. A term applied to any medium through which the actinic rays of light can pass. Substances which allow only non-actinic rays to pass are termed adiactinic. Dialyser. This is sometimes used in the washing of emul- sions, and can be prepared as follows : — Take a tin with a tightly fitting lid, knock out the bottom and top, stretch over one end of the tin a piece of parchment paper, and fit the rim of the lid over it, so as to clasp it tightly down. It is used by floating it in a vessel of distilled water, and the materials to be dialysed are placed in the tin. All bodies which will crystallise will pass through the septum of parchment paper, leaving those which will not crystallise in the dialyser. In the case of emulsions the unnecessary salts, such as nitrate of potash, etc., pass through the septum, leaving the colloid gelatine holding the sensitive silver salt. Diameter. Any straight line passing through the centre of a circle and touching the circumference at opposite points is thus termed. If the diameter of a circle is known, multiplying that by 3-14159 will give the circumference, and vice versa; and the diameter squared and multiplied by 7854 will give the area of the circle, and the cube of the diameter multiplied by "5236 will give the solid contents of a sphere. Diaphragms are either loose plates of metal, or a rotating metal screen, both having apertures of certain diameters ; or another form is of tongues of metal actuated by an external pin or ring, which can be closed and opened out to any desired size. The Iris diaphragm consists of thin flat tongues of metal fastened to a ring in the lens mount, by means of which the aperture of the diaphragm may be enlarged or diminished by turning the ring backwards or forwards, causing the tongues to contract or enlarge the opening, the use of which obviates all chance of losing or misplacing the diaphragms. The diaphragms of the ordinary or Waterhouse pattern can be pinned together by a brass rivet just by the tongue, on which the numbers are stamped, thus lessening the chance of losing them. The influence of the diaphragm on the picture is great and of con- siderable practical importance, not only on the character of the picture, but also on the duration of exposure, as we shall see when treating of that subject. The influence of the diaphragm on the character of the image transmitted by the lens is seen 114 DICTIONARY OF PHOTOGRAPHY. [Dia first in a reduction of the amount of light admitted by the lens secondly, by increase of the marginal definition ; and, thirdly, by increase of the depth of Focus (q.v.). Diaphragms are very often termed stops ; but this is not quite correct, as a stop is placed in contact with the lens, and a diaphragm some distance from it. For single lenses the diaphragm is usually placed from \ to A of the focal length in front of the lens, in which position it limits the diameter of the pencils of light, and causes them to cross the axis at the aperture of the diaphragm, before refraction. (See Distortion.) The distance of the diaphragm is in many instances, when placed in front of the lens, the cause of Flare (q.v.). This can be obviated by altering the position, one-eighth of an inch either way being generally sufficient to obliterate it. In all symmetrical doublet lenses, the proper position of the diaphragm is equidistant between the two combinations ; in unsymmetrical combinations, the position is proportionate to the foci of the combinations. For general use the following maxims should be remembered : — A large diaphragm gives a bolder picture than a small one ; focus with the largest apertiu r, then insert the smaller diaphragms till sharpness is obtained over the whole screen. The smaller the itop the Ion go the ex- posure, also the flatter the field of the lens, and the greater the depth of focus. It is customary to give the apertures of diaphragms definite diameters; that is to say, the diameter of the diaphragm apertures should be a definite fraction of the focal length of the lens. There are several methods adopted, the one in general use being the ratio aperture, or ffx system. To find this number divide the focal length of the lens by the diameter of diaphragm — e.g., focal length of lens, 8^ ins. ; diameter of diaphragm, | in.; 8J-rJ=ir3; number of diaphragm, //1 1-3. The Photographic Society of Great Britain number the dia- phragms, however, in rather a different way, taking f\\ as the standard, which they call No. I. This system is termed the " Uniform Standard," or U. S. No., and the U. S. number for any diaphragm marked on the f/.v system may be found by the following rule : — Divide the focal length of lens by diameter of diaphragm to find fx, square the result, divide by sixteen, and the result will be the U. S. No. Ex. : Find U. S. No. of diaphragm marked //iT3. 113X 11*3 = 127-69 ; 127-69-7- 16 = 7*98, or practically 8, U. S. No. (See also Appendix.) "5 Dia] DICTIONARY OF PHOTOGRAPHY. In 1882 Dr. Stolze suggested a system of diaphragm numbering which was found by squaring the focal length and dividing this by the diameter of the diaphragm squared ; thus, taking as an example, a lens of 81-in. focus and diaphragm apertures of j tV> £ x H m -f we should find the numbers as follows : — (8^x8^(1^x1-^)= 64. (8*x8*)-H t* *) = I28. (8**8i)-M ttx «) = 256. In 1886 Dr. Stolze suggested, as an improvement on this, the marking of the stops with numbers, obtained by dividing the square of the focal length by one hundred times the square of the aperture, e.g. : — (81 x 81) -f- (i T V x i T V) 100 = -64 (8£x8£)-f( fx i) 100 =1.28 (8lx81) + ( l|x ft) 100 = 2.56 This practically means taking //io as the unit, which aperture was also adopted by the International Congress on Photography, held at Paris in 1889. Mr - T. R. Dallmeyer recommended the marking of the diaphragms on a system which takes as its unit 1 I • •' • \ —7= = tttz - . The diaphragms, numbered on this system, would v'io 3 1D then be as follows : — 8£-t-i x V= 8 x 8 =64 -~io= 6.4. 81 -r |= 113 x n «3 == 127-69-7- 10 = 12769. 81 -f- i ^ = 16 x 16 =256 -^10 = 25-6. It will be seen from this that the system is practically a modifi- cation of Stolze's. Zeiss, the famous Jena optician, has adopted yet another system, which takes as its unit fj 100, as suggested by Dr. Rudolph, and the actual working aperture of the lenses is taken as the diaphragm aperture. The following table gives, therefore, the connexion between the relative or ratio aperture and the stops : — No. of Stop. Relative Aperture. No. of Stop. Relative Aperture. 1/100 32 I/I8 2 I/7I 64 r/12'5 4 I/50 128 1/8 8 1/36 256 1/6-3 16 1/25 512 i/4'5 116 DICTIONARY OF PHOTOGRAPHY. [Dia The photographic exposure corresponding, cater is paribus, to the different stops, is, therefore, in the inverse ratio of those numbers. Goerz, the optician of Berlin-Schoneberg, has adopted yet another system of marking the diaphragms ; this is the relative time of exposure (/) calculated from the formula /= ^{^j .when / = the focus, d — effective aperture. This is i really Dallmeyer's system of — == ( but the diaphragms are num -•/io bered differently. The following table shows the fjx number for each diaphragm, as marked by Goerz : — 4 = //6-3 6 = f/7'7 12 = //II 24 = //i5'5 48 = //2i- 9 96 = 7/31 192 = //43-S 384 = //62. We have stated above that to determine the value of the diaphragms it is necessary to find the focal length and divide this by the aperture of the diaphragm. Burton gives a very convenient table in his useful little handbook, " Modern Photo- graphy," which gives the diameter of the stop aperture for lenses of any focus from 6 to 1 1 in., and the diameter of any aperture for lenses of less or longer focus may be found by multiplying or dividing, as the case may be. I here insert this useful table : — Focal Length. Stan- fjx OR dard 6 in. 6i in. 7 in. 7$ in. 8 in. 8} in. 9 in. 9* in. 10 in. 11 in. Ratio No. No. •25 3'° 3"25 3'5 3'75 4-0 4*25 4'5 4'75 5'o 5"5 A* 7/4 •5 2 - I2 2'3 2-47 2*65 2-82 3*oi 3-x8 3-36 3'53 3-89 V £ 1*62 i"75 1-87 2'0 2'12 225 2'37 2-5 2*75 2 I'OO 1-23 1-32 1-41 I*50 * "59 i-68 1-77 1 -94 y/s-6 5 6 4 •75 •81 •87 •62 •93 I'O i*o6 I'I2 x-i8 1-25 i*37 m 8 •53 •57 •06 •71 '75 •80 •84 •88 •97 .//"•si 16 •37 •40 *44 •47 •5 "53 •56 •59 •62 •69 he 32 •26 •28 '31 '33 •35 •38 •40 '42 •44 '49 7/22*62 64 •188 •20 •22 •23 •25 •26 •28 •29 •31 '34 y/32 128 •132 •144 ■iS5 •168 •177 •188 •20 •21 •22 •24 y/45'25 256 •094 •101 •109 •117 •125 •i33 •141 •148 •i S 6 •172 y/64 Now for an example or two how to use this table. We have a lens of 5-in. focus, and want to cut our diaphragms for //8, 117 DICTIONARY OF PHOTOGRAPHY. // II '3> f/ 1 ^ fl 22 > aR d //3 2 - Turning to the table, we find no 5-in. lens included, but we find a 10-in. ; therefore we have the diameters there given. Carrying the eye down the column under 10-in., we find opposite //8, 1-25, then -88, '62, -44, -31, so that we must cut our apertures to 1-25 — 2 == -625 in., -88 -f- 2 = -44 in., •62 ~ 2 = -31 in., and so on. Where the focus of the lens is given in the table we merely take 4 the apertures there given. To some it may be difficult to accurately measure the diameters of apertures, and to facilitate this I include a diagram (fig. 81) taken from the " American Annual of Photography." Each cross line varies in length from the adjacent one by i^th of an inch. To use, lay the stop flat on this scale, and select a cross line which is of the same length as the greatest diameter of the opening ; read this off by means of the figures, which will be the measure- ments in y^ths of an inch. The equivalent focal lengthof lens, divided by this measure- ment of the stop opening, will give the fraction expressing relative rapidity of lens — //4, or whatever it may be. Personally, I have had a piece of thin brass cut exactly to measurement, and thus ruled and con- tinued till at its widest part it measures four inches. By inserting this in a stop, one is able at once to read off the diameter, and, dividing the focal length by it, to obtain the f/x number. The following convenient diagram and table were given some years back in the " British Journal of Photography Almanack ": — The Photographic Society s Standard Diaphragms, — The annexed diagram and table are intended to facilitate the calcu- 118 DICTIONARY OF PHOTOGRAPHY. [Dia lation of the proper number with which to mark the diaphragms according to the Photographic Society of Great Britain's Uniform System, which will be found described on another page. This number it is proposed to call the '' U. S." (or uniform system number). The numbered circles in the diagram represent the sizes of stops. The photographer, knowing the equivalent focus Fig. 24. of his lens, Jooks along the line opposite the number which represents the circle nearest inside to his diaphragm, and when he gets to the column headed by that equivalent focus the number there found is the U. S. number to be marked on the diaphragm. For example, a lens of eight inches equivalent focus has a dia- phragm in size about No. 5 on the diaphragm. Running the eye along the line opposite No. $, we find in the column under T19 Dia] DICTIONARY OF PHOTOGRAPHY. " focus eight inches " the number II, which is the U. S. number required. "si ■j) 0 3 w 3 uj 3 Cfl 3 n 3 V) 3 to 3 n 3 No. Circ .0 SJ in w . w <2 CO 1 0* 0 a 0 0 u <2 >* I II 25 39 5 6 1 1 1 1 2 11 17 25 34 44 *6 j 68 1 ■2 3 1 1 10 14 19 25 31 ^ w 56 | A 1 1 A t 64: 9 12 16 20 2? 36 48 c J | 2f 4 1 4i 1 61 8* 1 11 id. 17 25 1 34 6 | 2 1 3^ 1 4$ 6* 1 8 IO 1 1^ 18 | 25 7 1 1 2^ 3i 4-2 6 8 IO 14 I 19 8 | ii 1 2 1 2| 1 3f 1 5 1 61 1 v '4 1 8 1 II 1 15 9 1 1 1 I I" 1 2| 3 1 4 1 5 1 6i 1 9 1 m 10 1 I 1 i.i 2| 3* 4* 6 \ n 1 1 ! 1 1 r ¥ m 2 a* 1 3l 5 1 6 12 1 1 1 "3" 1 I* 2 21 3h 1 41 "3 II 1 1 ^ 1 if 1 if 1 21 1 4 14 II 1 I 1. ** 1 H 1 2£ 1 3 15 II 1 1 1 1 1 1 S 1 l| I 2| 16 il 1 1 1 I 1 H 1 2 17 ll 1 1 1 ii 1 ll 18 ll 1 1 1 1* 1 Ii 19 II 1 1 1 1 1 l| 20 ll 1 1 1 Ii 21 II 1 1 1 I I 1 I 1 1 It has been stated above that the ratio aperture of diaphragms could be found by dividing the focal length by the diameter of the aperture. This is practically accurate, but not scientifically so. Where the diameter of either or both of the lens combina- tions is less than the fixed stop, the diameter of the combination is the actual aperture ; where there is a fixed stop or a ring of metal in the interior of the lens mount, the diameter of this is the actual maximum aperture. These ratio apertures are strictly accurate when the lens is a single landscape lens ; but with all doublet lenses the condensation of the light by the front com- binations must be taken into account — especially when comparing, either for scientific or lens-testing purposes, the actual ratio 120 DICTIONARY OF PHOTOGRAPHY [Dia apertures, practically we are testing the effective or working apertures of the lens. This is by no means a difficult operation, and one of two plans may be adopted. The first is to rack the lens out to its equivalent focus, and to replace the ground-glass or focussing-screen by a piece of cardboard or thin metal plate, in the centre of which, and central with the axis of the lens, is punctured a minute pinhole. The camera should now be taken into a dark room, and a lighted candle placed close to the pin- hole in the cardboard. On examining the front lens, a circle of light will be faintly visible, or may be rendered still plainer by breathing on the lens or dusting it with a little French chalk or plain powder. A pair of dividers may be used for taking the diameter, and this may be at once read off on applying the same to a foot rule, and the focal length divided by this will give at once the true aperture of the stop. The second plan is by the aid of a simple mathematical calculation as follows : — Let D = the true aperture value. d — actual diameter of diaphragm aperture. /= the focus of front combination. / == the distance between the plane of diaphragm and the centre of the front combination, which centre is situate midway between the front and back surfaces of such lens. Then (I.) D = d x J- t (II.) d= D To many doubtless this is all Greek. An example may make it plainer. Let us suppose we have a Euryscope lens of n-in. focus, the focus of the front combination is 21 in., the distance between the centre of combination and plane of diaphragm is 1^ in. ; we want to calculate the value of a diaphragm 1 in. in diameter ; then, substituting the above values for the letters, we find ~ 21 21 . /) = 1 x = 1 x — = 1-0632 =11 in. nearly. Therefore our stop of i-in. actual diameter has a true aperture value of i x V in. ; not much difference, it is true, but still sufficient 121 DiaJ DICTIONARY OF PHOTOGRAPHY. to render accurate scientific work an impossibility. It may happen that, by this calculation, we find this true aperture value greater than the diameter of the front lens ; if this is the case, the diameter of the lens is the true value. Now suppose we have a lens of 16-in. focus, and wish to cut our diaphragms to have a value of //8, f/iv$i, f/16, etc. We know that //8 should be 2 in. if we disregard the condensing power of the front lens ; the focus of front lens being 30, and the distance from the centre of this lens to diaphragm plane 1 in., we get then d = 2 x 1 — 2 x ?2 = it4 actual diameter of //8. 30 30 lo ' Jl Then for // 1 1 -3 1 we shall get 7 , , x 30—1 29 : d = (16 — 1 1*31) x = 1*41 x - = 1-363 = ll in. It is true these measurements show but little difference to the actual diameter of stop, but in portrait lenses the difference is greater, and even in small diameter lenses the difference is sufficiently large to be taken into account when testing lenses. In practice it will be necessary to calculate out the true diameter of diaphragms for the first two only, the smaller diameters being obtained by dividing by 2, 4, etc. Another method of making the necessary allowance of the condensation of the light by the front lens is to cut the stops in fractions of a focus less than the true focus of the lens, and this may be found in the following manner : — Let F — the equivalent focus. / = the focus of front combination. / = the distance between centre of front lens and plane of diaphragm. A = the assumed focus. Then k = fJ-=±. Or to take the example given above, viz., a lens of 16-in. focus, front lens focus 30 in., the distance from lens to diaphragm plane being 1 in., we get a t 30—I r 21 A = 16 x £ = 16 x - = 14-13. 3° $6 T2'2 DICTIONARY OF PHOTOGRAPHY. [Dia We therefore cut our apertures for a I4*i3-in. focus instead of 16-in. focus. There is one point in connection with diaphragms which it is essential to note, and that is, the ratio aperture is calculated from the equivalent focus, but that in photographing near objects, such as portraits or line subjects, we have to rack out the camera considerably, and that therefore the ratio aperture of any given diaphragms decreases in proportion to the racking out. An example will make this plainer, perhaps — for reproducing a diagram full size with an 8^-in. focus lens. The distance between the lens and focussing screen must be 17 in. We have found that a diaphragm marked //16 will give the requisite sharpness, but this aperture is calculated from the equivalent focus. Therefore, as the diameter of the aperture of the dia- phragm remains constant, it is obvious that it cannot now be fj\6 ; we must therefore calculate out afresh the ratio aperture: — The stop is marked fj\6 and is ^ of the focal length = 8.1 in. .*. Diameter = 8^-7-16= H. The focus when copying diagram is 17 in. .'• l 7 + Ih ~ 3 2 » tne new rat i° aperture of stop. Diazotype or Primulirie Process. This is a process patented in 1 89 1 by Messrs. Green, Cross, and Bevan, and is based upon the property which certain diazotised dyes possess of being so altered by light that they will not form colouring matters with certain anilines and phenols. As various colours can be obtained, and the process is applicable to paper, material or gelatine on glass, it affords a ready means of obtaining decorative material, although the colours are not very brilliant, nor is the ground pure white. The solution of primuline is prepared as follows : — Primuline ... ... ... ... ... 10 parts. Distilled water 1,000 ,, The water should be heated to near boiling-point, and kept at this temperature by means of a spirit lamp or Bunsen burner, and the primuline added, with constant stirring till dissolved. In this hot solution the linen, silk, plush, or velvet — the two former being deprived of their dressing by washing — should be immersed, and care taken that the dye is evenly distributed through the material by pressing with glass rods, etc., and stirring about. The material after about five minutes' immersion should be allowed 123 Dia] DICTIONARY OF PHOTOGRAPHY. to drain, rinsed once in cold water, and dried. In this stage it is not sensitive to light, and the dipping and drying may be effected in daylight. It will also keep well in this condition. The drying should be rather rapid, and therefore blotting off between blotting paper, or a free current of air, should be resorted to. The sen- sitising solution is composed of Sodium nitrite ... ... ... ... 4 parts. Oxalic acid 6 ,, Distilled water 1,000 „ In this the material should be immersed and well saturated, then drained, rinsed, and superflous moisture removed by pressing between thick blotting paper. The material need not be bone dry, and should be exposed at once, as it will not keep. The sensitising and drying must be done in a dark room or by weak gaslight. As this process is what is called a negative printing process — that is, it yields a negative from a negative — we require a positive to obtain a positive. The material is then exposed under a positive for about thirty seconds in sunlight, to ten minutes or more in diffused light. The process of printing can be gauged to some extent by examining the material in the ordinary way, the action of light bleaching the material, which assumes a dingy colour. It is advisable till practice is secured to use small test pieces of material, exposing them side by side with the printing frame till they no longer give colour with the developer. The developers are as follows : — /3-napthol 6 parts. Sodium hydrate ... ... ... ... 8 ,, Distilled water ... ... ... ... 1,000 ,, For Yellow Tones. Carbolic acid (crystal) 10 parts. Distilled water 1,000 „ For Red Tones. For Orange Tones. Resorcin Sodium hydrate Distilled water 6 parts. 9 M ... 1,000 124 DICTIONARY OF PHOTOGRAPHY. [Diff For Purple Tones. a-Napthylamin Oxalic acid ... Distilled water ,000 12 parts. i'2 ,, For Blue Tones. Eikonogen Distilled water ... 1,000 12 parts. For Brown Tones. Pyrogallol 12 parts. Distilled water 1,000 „ As soon as the colour is sufficiently developed, the material should be well washed in water, and dried. Napthylamin has an intensely disagreeable smell, which may be removed from the hands and dishes by using the nitrite sensitising solution. For purple pictures the material should be rinsed in dilute solution of tartaric acid and dried without further washing. For obtaining prints on paper it is advisable to size the paper well first with a 2 per cent, solution of gelatine with a little chrome alum, and allow this to thoroughly dry, and then sensitise by floating on the hot nitrite solution, care being taken that none gets on the back. The after-treatment is the same as for materials. Transparencies and opals can be made by coating glass with Primuline ... ... ... ... ... 80 parts. Gelatine 480 „ Chrome alum ... ... ... ... 2 ,, Distilled water ... ... ... ...9,600 allowing to set and dry, and then sensitising by immersion in the nitrite solution. Prints produced by this process are permanent, unless exposed to brilliant sunshine. Designs in different colours can be made by thickening the developers with boiled starch and applying with a brush. Wool and silk require longer exposures than cotton or linen, and the blue and purple developers are not so suitable for the former, and for these two instead of primuline dehydro-thiotoluidine-sulphonic acid is recommended as giving a purer ground. Diffraction or Inflection. An optical term used to denote 125 DICTIONARY OF PHOTOGRAPHY. the bending of the rays of light when such rays pass by the edges of an opaque body. The effect of diffraction on the waves of light is exactly the same as that peculiar property of running water of curving round behind an obstacle. Diffused Light. Generally, in opposition to direct light. It is the only light which should be used for Portraiture (q.v.). Diffused light in the camera is generally taken to mean any actinic light other than that passing direct on the plate from the lens. It is a certain producer of fog. Dish. One of the most necessary articles of an amateur's outfit. It is made of various materials : glass, earthenware, vulcanite, metal, and wood are the most useful. It is only necessary to say it should be kept scrupulously clean, being occasionally scrubbed with a stiff brush and some strong acid. One dish should be kept specially for each operation, and used for that only. Dispersion. An optical term used to denote the separation of a ray of heterogeneous light by refraction into its component rays of different refrangibility. Different transparent media have different dispersing powers, or different powers of widening the angle between the red and violet rays, and it is owing to this difference of dispersive power in different kinds of glass that chromatic aberration is eliminated. Dissolving Views. See Magic-Lantern. Distance. The objects in a landscape farthest from the eye, forming a background to the scene ; and, in an artistic sense, the representation of objects rendering an idea of remoteness, obtained by the due observance of the rules of perspective, etc. (See Aerial Perspective.) Distilled Water. H 2 0=i8. Absolutely pure water obtained by vaporisation in a still or retort, and subsequent condensation of the vapour. It should be used in all operations of photo- graphy, especially in the manufacture of emulsions and ferrous oxalate development. Distortion. All images may suffer from no less than three kinds ot distortion, (a) distortion of perspective, {b) distortion of 126 DICTIONARY OF PHOTOGRAPHY. [Dis parallel lines, and (c) distortion of marginal lines or the aberration of thickness of the lens. (a) Distortion of perspective. This is frequently noticeable in ordinary work, particularly in architectual studies where lenses of short focus, compared to the size of the plate have been used. In such a case near objects look exaggerated in dimension compared to others more distant, when the prints are examined at the distance of normal vision, whereas if the pictures are viewed from a distance equal to the focus of the lens this is not seen. (b) Distortion of parallel lines. Whilst this is strictly speaking a distortion of perspective, it is better to consider it as a separate subject, because it is solely due to a misuse of the camera. When a lofty object has to be taken and the camera is tilted up, unless the swing back be used, what should be parallel lines in the print will appear to converge as in fig. 25. (c) Distortion of marginal lines or aberration of the thickness of lenses. If a square ruled on paper be examined with an ordinary reading glass it will be found that the lines instead of being straight will be curved. When a landscape or single lens is used with a stop in front of it, lines falling near the margins will be curved outwards, as with the stop in this position the low er part of the lens forms the image of the upper part of the object ; with the stop behind the lens, the reverse is the case, and the distortion is pincushion shape. From this it is obvious that by placing a lens on either side of a diaphragm we get the two distortions curing one another, and hence the rectilinear or doublet lenses. 127 Div] DICTIONARY OF PHOTOGRAPHY. Divergent Rays in optics are those which continually recede farther and farther from one another, being the opposite to con- vergent. All concave lenses are divergent. (See Lens.) Dodging Negatives. There are few negatives which will not be improved by some after treatment. Under the heads of Intensification and Reduction will be found instructions for these processes which have for their general purpose the increase of, or reduction of, density respectively, but in many cases it is found that one portion of a negative is so dense in proportion to the rest that it will not print : to improve such a negative we may use the method of harmonising Harsh Negatives {q.v.), or we may locally reduce it or intensify it. To locally intensify a negative it should be thoroughly well washed free from hypo, or, if dried, soaked in water for an hour, then intensified by the use of the uranium intensifier (see Intensification), then rinsed once or twice, and an alkaline solution such as i : 20 solution of carbonate of soda may be applied with a camel's hair brush to the dense parts of the negative ; and this has the effect of dissolving the uranium intensification and leaving the dense parts, therefore, in their original condition, so that the result will be a negative intensified in the shadows but not touched in the high lights. If necessary the negative may now be dried, and the high lights still further reduced by the local application of Farmer's ferridcyanide and hypo reducer. Vidal has suggested for local intensification or as we call it dodging, painting over the dense parts of a negative with asphalt dissolved in benzine, allowing this to dry, and then dipping the plate into a solution ol some aniline dye, like aurantia, chrysoidine extra, Bordeaux red, etc, the strength of the solution and the stay of the negative in the same being of course adapted to the degree of intensification required ; the gelatine absorbs the colouring matter, and thus the thin parts are locally intensified. If afraid to treat the film in any way for fear of losing it, one may paste the back of the negative with starch paste, and lay it down on a flat sheet of tissue paper with slight pressure, allow to dry and trim the paper down. We have now a surface on which we may work with a crayon and stump, with retouching pencils or water colour. Another method is to coat the back of the negative with matt varnish which has been stained deep red by the addition of some aniline dye, or yellow by dis- 128 DICTIONARY OF PHOTOGRAPHY. [Dry solving gamboge in it. When the varnish is quite dry, we may scrape it off with a sharp penknife over those parts we wish to print through more and thus get better results. Local reduction may of course be carried out by exactly reversing the directions for some of the above processes, but enough has been said to point out the method of procedure to any intelligent operator. Doublet. This term is applied to lenses which have a glass or combination at each end of the lens tube. Various names have been given to these lenses, or to slight modifications, and as far as possible I include a list of them : Antiplanatic Orthoscopic Rapid doublet Aplanat Panorthoscopic Rapid paragon Aplanatic Pantographic Rapid symmetrical Autographic Portable symme- Rectigraphic Euryscope trical True view Hemispheric Rapid rectilinear, Universal Orthographic or R.R. Orthopanactinic Drachm or Dram. See Weights and Measures. Drop Shutter. See Shutter. Drying Box. A light-tight box used for drying plates, etc., coated with a sensitive film. There are many different kinds, but the following will answer well : — Make a box of half-inch deal, 2 ft. long by I ft. wide and I ft. deep, with a door opening at one side, with a deep fillet to prevent the ingress of light ; at the bottom pierce about twelve holes, and have a second bottom made, but with openings at the side. In the centre of the top have a two-inch gas or zinc pipe fixed with an elbow joint, and in the bend of the joint insert a small gas burner, so as to cause a draught of air when lit. Anhydrous chloride of calcium may also be placed upon the bottom of the box. The interior may be fitted with stout wire, or glass shelves, about three inches apart. Drying Marks. These are generally irregular wavy marks seen near the margins of dry plates or sometimes as fairly regular patches which are of different density to other portions of the negative, and are caused by unequal drying of the coated plates, 129 K Dry] DICTIONARY OF PHOTOGRAPHY. those portions remaining moist longest being more sensitive and therefore appearing as over-exposed. Drying marks are also caused in an otherwise perfect negative if the same be allowed to dry unequally or at different temperatures. For instance, if a \ot of plates are placed in a drying-rack close together and left for some time the centres will not dry so quickly as the edges, and unequal density is caused; or if part of the negative be allowed to dry spontaneously and the other part be dried by the heat of the fire, or by the aid of spirit, marks will be caused. Dry Plates. Glass of particular size coated with a film of gelatine in which a sensitive salt of silver is emulsified. These are to be bought, commercially, so perfect in preparation that but few amateurs will be tempted to coat their own, but the formulae given under Emulsion will be found all that can be desired, and the manufacture of emulsion is an education which all operators if time and circumstances permit, should undertake. It is advis- able for all workers to examine the plates that they intend to use, especially when starting on a tour, to determine one or two points. Plates should be examined as to whether they are cut to size correctly or not, whether they are evenly coated, this being done by holding the plate or one or two plates in turn, before the dark-room light, and seeing whether one part lets through more light than another. Freedom from fog is another essential, and the best way to test this is to take out a plate from a freshly opened packet in a very dim red light, and place in a dish, and develop with freshly mixed ferrous oxalate or pyro-soda developers of normal strength for the normal time, and then see whether it be free from fog or not. With regard to the sensitive- ness of the emulsion this is usually determined and marked by the maker. Dusting-on Process. See Powder Process. Eau de Javelle is used for eliminating the last traces of hypo from the film, and also for reducing over-dense negatives, its action being due to the free chlorine evolved. It can be made as follows : — Chloride of lime 2 ozs. or 50 grms. Carbonate of potash ... 4 „ „ 100 ,, Water 40 ,, 1,000 c.cm. j 30 DICTIONARY OF PHOTOGRAPHY. [Eff Mix the lime with 30 ozs. of water, dissolve the potash in the remainder, boil, and filter. Ebonite. A modification of indiarubber made by heating it with sulphur under pressure. It is used for making dishes, instantaneous shutters, etc., and, though brittle and affected by heat, answers well, from its great lightness and hardness. Edging. See Safe Edge. Effective Aperture. The effective or working aperture of the lens is that portion which actually comes into use with the various diaphragms, and the size of the working aperture is dependent A J Fig. 26. not only on the size of the diaphragm, but also on the distance ol the object ; but for comparison of lenses, and in the ordinary course of testing a lens, parallel rays only are considered in estimating the effective aperture. According to Dr. Stolze, " with any but parallel rays of light, such as those proceeding from near objects under otherwise equal conditions : (1 ) with single lenses, P A P Fig. 27. with diaphragm in front, the effective aperture increases if the distance of a luminous point decreases ; (2) with doublets, with diaphragm between the lenses, the effective aperture increases as the distance of a luminous point increases." The above diagrams show very clearly how the working aperture of single and doublet lenses is respectively equal to and greater than the 131 Elk] DICTIONARY OF PHOTOGRAPHY diameter of the diaphragm aperture. In both figures f is the focus of parallel rays, r ; p the lens ; and the diameter, cd ) in fig. 26 is equal to ad, the diaphragm aperture, but in fig. 27 cd is greater than a b. Directions for finding the correct working aperture have been given under Diaphragm. Eikonogen, introduced by Dr. Andresen of Berlin in 1889, is the sodium salt of amido-/3-naphthol-/3-sulphonic acid, and has the formula C, 0 H 15 SO 3 NaOHNH 2 . It was first discovered by Professor Meldola in 1881. No. 1. For Portraits and Landscapes. Solution A. Sodium sulphite 4 parts. Distilled water 60 „ To this solution add Eikonogen 1 part, which has been previously finely powdered by means of a mortar, and dissolve by shaking. Should a mortar be wanting, the solution can also be prepared by placing the salts into boiling water, and shaking till dissolved. Solution B. Washing soda 3 parts. Distilled water 20 Immediately before developing mix the developer as follows: — Solution A 3 parts. Solution B 1 part. No. 2. For instantaneous work (about ^th-sec. exposure). For this purpose formula No. 1 is to be used, with the exception that the crystallised carbonate of soda is substituted by the same quantity of carbonate of potash. No. 3. For very short instantaneous exposure (r^tii of a second), or or increasing the power of Nos. 1 and 2 for under-exposed plates. 132 DICTIONARY OF PHOTOGRAPHY. [Eik Sodium sulphite 5 parts. Carbonate of potassium 2 ,, Eikonogen ... 1 part. Boiling distilled water 30 parts. The following is the formula for the fixing baths recom- mended : — Hyposulphite of soda 4 parts. Bisulphite 1 part. Distilled water 20 parts. Or Hyposulphite of soda ... ... ... 20 parts. Sulphite of soda (neutral) 5 Distilled water 100 parts. Sulphuric acid (sp. gr. 1*845) 1 part. For bromide paper it is advised to soak the paper after exposure in 40 parts of water, and when limp add 10 parts of No. 3 solution ; if the image hangs fire add more of the solution. For over-exposure reduce the quantity of Solution 3. Bromide of potassium should not be used. After developing wash well, and place in an alum bath for several minutes, whereupon it is^again fixed and washed. The author has used the following with good results : — No. 1. Eikonogen 40 grs. or 2*6 grms. Sodium sulphite ... ... 40 „ 26 „ Distilled water ... ... 10 ozs „ 250 c. cm. No, 2. Soda carbonate 400 grs. or 26 grms. Caustic potash ... ... 50 ,, ,, 3-25 Distilled water 10 ozs. ,, 250 c.cm. For use mix equal parts ; for instantaneous work add 5 grs. or •3 grm. hypo to No. 2. Eikonogen is not easy to preserve in solution, or to get in solution, its solubility being low, only about seven grains per ounce of water ; and, further, its avidity for oxygen is so great that it readily oxidises and turns brown, even in solution with a sulphite. The best preservative is acid 133 Eik] DICTIONARY OF PHOTOGRAPHY. sulphite of sodium or an acidulated solution of soda. A good formula for stock solution is Voight's, as follows : — Acid Sulphite. Sodium sulphite 170 grs. Distilled water to make 1 oz. Hydrochloric acid ... ... ... ... 40 minims. Dissolve in the above order. Stock Solution. Eikonogen 125 gr. Sodium sulphite ... ... ... ... 625 ,, Distilled water ... ... to make 25 ozs. Acid sulphite as above 1 oz. Dissolve in the above order. Another convenient formula is : — Eikonogen ... ... ... ... ... 125 grs. Acid sulphite of sodium ... ^ oz. Distilled water to make 25 ozs. For accelerators we may use either caustic alkalies or the car- bonates ; and having this choice gives us far more control over our negatives than would otherwise be the case. For ordinary work it is not advisable to use the caustic alkalies, and carbonate of soda may be used where soft results are desired, whilst potash gives us a little more contrast and density. One of the most important points when using eikonogen as a developer is the temperature of the solutions. At 32 0 F. its developing power is practically none, and its power increases with the rise of tem- perature : the temperature ol the developer should be about 65 0 F. to obtain the best results. Briefly formulating a method of development with eikonogen, we arrive at the following conclu- sions : — Under-exposure and instantaneous shots : Use either of the caustic alkalies ; or with extreme under-exposure or very sharp snap-shots use a one-solution developer compounded on Warnerke's formula, which is as follows : — Eikonogen 1 oz. Caustic potash ... ... 1 „ Sodium sulphite ... ... ... ... 2 ozs. Distilled water (boiling) 10 „ l 34 DICTIONARY OF PHOTOGRAPHY. [Eik We have deprecated the use of one-solution developers, but as the addition of caustic alkali enables us to obtain a much greater concentration of solution, it is useful for instantaneous work. The above solution should be diluted with from three to ten parts of water as required, more water giving softer results. Where only slight under-exposure exists the use of a mixed accelerator of caustic and carbonate will be found useful, and the caustic may be increased as desired or found necessary. Normal ex- posure : For portraiture, carbonate of soda should be used, as in all cases where softer effects are desired ; for outdoor or land- scape work, carbonate of potash should be used, and with a small addition of bromide of potash. Over-exposure : in cases where over-exposure is known to exist, practically the same method of development may be adopted as with pyro — viz., increase of bromide and reduction of accelerator, which should be carbonate of potash. We have given some formulae for stock solutions of eikonogen ; we now come to stock accelerators. Carbonate of Soda Accelerator. Carbonate of soda 300 grs. Distilled water, to ... ... ... ... 10 ozs. Carbonate of Potash Accelerator. Carbonate of potash 1 50 grs. Distilled water, to ... ... 10 ozs. One part of these may be mixed with an equal quantity of eikonogen stock solution and applied to the plate. The caustic alkalies should only be used in cases where such are indicated as above, and stock solutions may be prepared either in 10 per cent, or 20 per cent, as desired, and they should be added, drop by drop, so as to avoid frilling and fogging of the film. A good all-round accelerator, which gives excellent results, and which can be modified with extreme ease, is the following : — Carbonate of soda ... ... 400 grs. Caustic potash ... ... 50 ,, Distilled water, to 20 ozs. One part of this may be mixed with an equal quantity of stock T 35 Ele] DICTIONARY OF PHOTOGRAPHY. eikonogen. If development hangs fire at all, or the plate shows signs of under-exposure, add gradually, or drop by chop, watching the action after each addition — Caustic potash 120 grs. Distilled water, to ... ... ... ... 1 oz. Of the application of eikonogen to lantern and bromide work we cannot speak at present, but in our opinion it is far superior to ferrous oxalate or hydroquinone for this purpose. It is advisable when using eikonogen to employ the acid fixing bath, as obviating all stains, and hardening the film and preventing frills and blisters, which are liable to occur when forcing plates with caustic alkalies. The superiority of eikonogen over pyro and hydro- quinone is manifest, particularly in developing snap-shot and portrait work, as, no matter how dense the high lights and how weak the shadows, the resulting prints are far softer and more harmonious than would be the case with the other' two reducing agents. It gives an image of a bluish black or grey colour, free from any brown tinge, as is the case with pyro, and development has, therefore, to be carried rather farther than old pyro workers are accustomed to. Elemi. A concrete resinous exudation from Canwium com- mune, a native of Malay. It is sometimes used in the preparation of Varnish (q.v.). Eliminator, Hypo-. Any salt or solution of salt used to get rid of the last traces of hypo from the films or prints. Many so-called eliminators have been recommended, as peroxide of hydrogen, eau de javelle, alum, acetate of lead, hypochlorite of zinc; but opinions seem to be about equally divided as to the benefit of their action. Emulsion. Photographically, a mechanical mixture of any sensitive salt of silver in extremely minute division, held in suspension in any viscous vehicle, such as gelatine or collodion, which, when spread upon any transparent medium, shall present a perfectly homogeneous appearance when viewed by transmitted light. It would be unnecessary and impossible to write a thoroughly comprehensive account of the emulsion processes ; for such a work the amateur must consult Eder's " Handbook to 136 DICTIONARY OF PHOTOGRAPHY. [EmU Emulsion Photography," but a few well-proved formulae will be given. The material upon which the emulsion may be spread may be either glass, paper, or any special substance desired. The emulsion may be either for the production of negatives, transparencies, positives, or lantern slides, for development or printing out. In this article that intended for negative work alone will be treated of. To summarise all the methods which have been suggested for emulsion making would be almost im- possible, at least, within reasonable limits. Practically, however, we may consider that there are three methods in general practice, viz. — (a) The ammonio-nitrate process. (d) The acid-boiling process. (c) The cold process. The ammonio-nitrate process, which may be briefly described as the conversion of the nitrate of silver into the double salt by means of ammonia, and the addition of this to a bromised gelatine solution, and digestion of the emulsion at a moderate temperature for a given period, is simple and easy to carry out, and the one specially suitable for amateur emulsion makers. The acid-boiling process requires more apparatus than the previous one, and though clean working plates are obtained, the sensitive- ness is not quite so great as with ammonia. The cold process i is simple and easy, requires no heating, but it is far more difficult to obtain regular results. (a) The Ammonio- Nitrate Process. Eder was the first to suggest this process, and the following is his latest formula. Two solutions are required. A. Potassium bromide ... 24 parts. Solution of potassium iodide (10 percent.) 3-8 ,, Hard gelatine (Winterthur) 20 ., Distilled water ... 250 ,, Allow the gelatine to soak for from 30 to 60 minutes in the water in a closed vessel, then place the vessel in a water bath and allow the gelatine to dissolve, and add the haloid salts. Now place the thermometer in the gelatine solution, and make the 137 Emu] DICTIONARY OF PHOTOGRAPHY. same register 40 0 C. (— 104 0 F.). Should the emulsion be too cool, raise the temperature of the water bath ; if too hot, place the vessel in cold water for a little time till the emulsion reaches the desired temperature. B. Silver nitrate. . . ... ... 30 parts. Distilled water 250 „ When dissolved, add cautiously liq. ammonia, -88o, till the brown precipitate first formed is redissolved. So far these operations may be performed in daylight, but it is now necessary to enter the dark-room, and the silver solution should be added to the bromised gelatine in small quantities at a time, vigorously shaking between each addition. The total time of mixing must not be long, as otherwise the temperature sinks too low. Eder states that the silver solution should be used at the ordinary temperature and not heated ; but I have obtained equally good results by using hot water for dissolving the silver, and thus using the solution warm. As soon as the emulsion is mixed it should be placed in the water bath, the temperature of which should be 45 0 C. (= 1 1 3 0 F.). Eder now recommends wrapping the vessel in blankets, flannels, etc., to retain as far as possible an even temperature. By using a very faint spirit flame or gas flame, however, it is quite possible to keep the temperature the whole time at 45° or just above. It will be noted in the above formula that the quantity of iodide solution is not definite — viz., 3 to 8 parts. According to Eder, increase of the iodide up to 8 parts gives rather more sensitive emulsions which are less liable to halation in landscape work. Many operators prefer to use, for portraiture, an emulsion which contains little or no iodide, and, therefore, the amateur plate-maker can take his choice. The duration of the digestion of the emulsion in the water bath has the most important influence on the final sensitiveness of the emulsion. When the above emulsion is digested for about 15 minutes, a slow landscape emulsion registering about 15 0 W. and working with great clearness and vigour "will be obtained; with 30 minutes' digestion the sensitiveness will be about 17 to 19 0 W. ; with 45 minutes' digestion about 22 to 24 0 W. During the digestion the flask must be shaken two or three times so as to prevent any undue separation of the sensitive silver salts. 138 DICTIONARY OF PHOTOGRAPHY. [Emu When commencing to make the emulsion, take of hard gelatine 15 to 20 parts. Allow this to swell in distilled water, and as soon as the emulsion has been digested pour off the water from the gelatine, allowing it to drain slightly, and carefully let it melt in the water bath, which it should readily do, as in the course of an hour or so, which has passed in the above operations, it will have absorbed enough water to melt. This melted gelatine should then be added to the emulsion and the whole well shaken, then the froth should be allowed to subside a little, and the emulsion poured out into a flat glass or porcelain dish to set. The emulsion should be about three-quarters of an inch thick in the dish, and should be placed in absolute darkness to set, which takes, as a rule, about five to eight hours, according to the temperature. In the height of summer a little ice placed in the same box as the emulsion will be of assistance ; in cold weather this is not necessary. The above process is suitable for plates of medium sensitiveness, and it is just as well to state here that very rapid plates are extremely difficult to make, and fog and all such incidental and minor troubles, such as frilling, blisters, spots, etc., are more likely to make their appearance when trying to make rapid plates. The simplest formula which the writer has tried, and the one in which success is more likely to attend a novice's efforts, is the following of Eder's, which gives a very good, clean working plate of about 1 5 0 W. : — A. Ammonium bromide ... 20 parts. Solution of potassium iodide (10 percent.) 3 ,, Hard gelatine ... 45 M Distilled water ... 300 ,, Allow the gelatine to soak in the water for one hour ; dissolve by the aid of a gentle heat ; add the salts. B. Silver nitrate 30 parts. Distilled water ... 300 ,, Dissolve the silver, and convert into the ammonia-nitrate by the addition of ammonia as previously directed. Heat solution A t° 35° C. (= 94 0 F.), and add solution B ; digest for 30 *39 EmuJ DICTIONARY OF PHOTOGRAPHY. minutes, and pour out to set. By digesting 10 minutes only a very fine-grain emulsion is obtained, which gives good lantern slides. The proportion of iodide solution may be increased from 3 to 8 parts with advantage when the plates are intended for landscape work ; but in-this, as in every formula where the iodide is increased, the bromide must be correspondingly reduced, which may easily be done by referring to the tables given at the end of this work. Very rapid plates are not easy to make, but in order to complete this note we may briefly indicate how to prepare the same. The formula for the emulsion may be precisely the same as that given on p. 137 ; but the iodide should be the full quantity of 8 parts, and the bromised gelatine be heated to 6o° F. (= I40°.F.), and the silver solution added to it, and after about 40 to 50 minutes' digestion, in the water bath, at a tem- perature of 40 0 C. (= 104° F.), a sensitiveness equal to about 23 0 W. will be easily obtained. When making such an emulsion, it is advisable to cool rapidly and wash rather quickly, as the digestion at such high temperatures has a tendency to give rise to frilling and blisters. Some manufacturers use chrome alum to prevent this frilling, and it is possibly due to this that some commercial plates require so long to develop and fix — not always a desirable feature. Chrome alum too is always faintly acid, and tends, therefore, to the lowering of the sensitiveness ; this, however, may be avoided, I think, by neutralising it by the cautious addition of liq. ammonia, and, so far as I have been able to determine, this in no way affects the hardening action of the alum on the gelatine. On the other hand, if the chrome alum solution be rendered more than very faintly alkaline, there seems to be a greater tendency to fog. Practically, an addition of 20 parts of a 2 per cent, solution of chrome alum to every 1000 parts of emulsion will not be amiss, and it is advisable, if it is desired that the plates should keep long, to make an addition of 15 to 20 parts of a 1 per cent, solution of potassium bromide to every 1000 parts of emulsion ; these additions must be made immediately before coating. The Acid-Boiling Process. The disadvantage of not being able to obtain such a high sensitiveness, nor such great regularity as with the ammonia process, rather places this hors de combat, one well-known writer even going so far as to say that it is impossible to obtain good plates by this process. Possibly the 140 DICTIONARY OF PHOTOGRAPHY. [Emu best answer to that is, that it is used by a well-known firm of plate makers to prepare excellent plates. The following is the process, devised by Mr. Wilson, which won a prize offered by Mr. Paget in 1880. To make a pint of emulsion select a 20-ounce, narrow-mouthed stoppered bottle, with a well-fitting stopper and thin bottom. Make it perfectly clean. Make a stock solution of Hydrochloric acid (pure) 1 fl. drm. Distilled water 1 2A ozs. Put into the 20-ounce bottle 20 minims of the above dilute acid. 3 fluid ounces distilled water. 210 grains ammonium bromide. 80 grains Nelson's No. 1 photo, gelatine. Leave the gelatine to swell for, say, fifteen minutes or longer. In a clean glass vessel (beaker, measure, or flask) dissolve 330 grs. of nitrate of silver (re-crystallised) in 3 ozs. of distilled water. Pour out about 2 fluid drms. of this silver solution into another small vessel (say test tube), and dilute it to half strength with an equal quantity of distilled water. Take the 20-ounce bottle and the two lots of silver solution into the dark-room. Mr. Wilson prefers to use a large paraffin lamp, protected by one thickness of ruby and one of dark orange glass to two thicknesses of dark orange paper without any ruby. In the dark-room have a gas- boiling stove, and on it a tin pot or saucepan deep enough to contain the bottle when the lid is on. It should have a tin, perforated, false bottom to prevent the bottle resting immediately on the true bottom ; or a piece of wire gauze will answer. Let the pot contain some 3 or 4 ins. in depth of boiling water. Turn out the gas of the stove, if alight, and plunge the bottle into the water two or three times, so as to avoid cracking it by too sudden heating ; then leave it in for a few minutes until the gelatine is completely dissolved. Do not leave it in longer than necessary for complete solution. Take it out, shake up, remove the stopper, and set bottle down on the table near your lamp, so that you Can see what you are doing. Pour in, all at once, the 4 drms. of dilute silver solution. Put in the stopper, and shake up thoroughly, but not too violently, for about half a minute. Now pour in the 141 DICTIONARY OF PHOTOGRAPHY. strong silver solution in quantities of about half an ounce at. a time, shaking as before after each addition, and, when all is added, give a final, thorough shaking for, say, a couple of minutes. Now put the bottle into the pot of hot water, see that the stopper is not jammed in, and put on the lid. Light the gas, and boil up as quickly as possible. If the water was previously boiling, and the gas only turned out for the mixing operations, it should boil up in less than 5 mins. ; then keep boiling for 59 mins. At the end of this time turn out the gas, take off the lid, take out the bottle, and remove the stopper at once, or you will not get it out afterwards. The bottle must now be cooled down as quickly as is consistent with safety to the glass. In very cold weather it may stand on the table for 10 mins. or so, and then be cooled with water ; or, in any weather, place it in a pan of nearly boiling water, and cool gradually by allowing cold water to trickle slowly in, shaking the bottle occasionally. Whatever method is adopted, it should be down to 90 0 F., or lower, in J 5 or 20 mins. at the most. It cannot easily be made too cold, as the gelatine has lost its power of setting. In a glass beaker (about 12 or 14 ozs. size) put l oz. of Nelson's No. 1 Photographic or " X opaque "gelatine, and pour over it 10 ozs. of clean ordinary water. Leave it to soak until the gelatine has absorbed 4 ozs. of water, pour off the surplus 6 ozs., melt the swelled gelatine by immersing the beaker in hot water, and pour it into the 20-ounce bottle containing the cooled emulsion. Shake up well, and pour all back into the beaker, draining out the bottle thoroughly. Leave it to set in a cool place for 24 hrs. It has next to be washed. The addition of the gelatine after boiling should be made when the boiled emulsion and dissolved gelatine are both at as low a temperature as possible, and between the time of this addition and that of washing the emulsion it should be kept as cold as possible. For the washing clean ordinary water at a temperature cooled down to below 40 degs. by melting ice in it, should be used. In a glazed earthenware pan or other suitable vessel put about 3 pints of cold water, and add 3 ozs. of saturated solution of potassium bichromate (made by saturating clean ordinary water with the bichromate). Before squeezing the set emulsion through the canvas it should be cooled down so as to be as firm as possible. The water into which it is squeezed will then remain almost clear, or but slightly milky. If the emul- 142 DICTIONARY OF PHOTOGRAPHY. [EmU sion be soft, even though the water be ice cold, the water will be more milky, and the emulsion take up too much. Too much excess of acidi bromide, too high a temperature at the time of adding the gelatine, or keeping at too high a temperature between adding and washing, will produce the same result. Having cooled the beaker of set emulsion down to 40 0 F., run a bone spatula or paper-knife round, and turn out the emulsion, or cut it out in lumps. If cold, it will come out almost quite clean from the glass. Place it on a piece of coarse " straining cloth " or canvas, and squeeze through the meshes into the water, the operation being performed under the surface of the water. Leave it so for an hour. Lay the straining cloth over the mouth of another pan or large jar, and pour the mixture of emulsion threads and liquid on to it so as to let the latter run through. Squeeze the emulsion a second time through the cloth into clean cold water, and immediately repeat the operation for a third time, leaving the emulsion in the last water for half an hour. When strained for the last time, place cloth and all in a large beaker, and put the latter into hot water until the emulsion is completely melted and warmed to about 115° F. — i.e., not warmer than is pleasant to the hand. With a clea?i hand take out the cloth and squeeze it ; very little will be lost. The emulsion should now measure about 16 or 17 ozs. Add 2 ozs. of alcohol, and mix thoroughly. The alcohol may be either pure ethylic alcohol, sp. gr. about "830, or good colourless methylated spirit. If the emulsion now measures less than 20 ozs., make it up to that by adding clean water. The emulsion is now ready for use. It should be filtered into the coating-cup through cotton-wool to free from bubbles, and plates coated in the usual way, dried and used as usual for rapid gelatine plates, using about an ounce of emulsion for a dozen quarter-plates. Cold Emulsijication. — This process is not very reliable, be- cause the degree of sensitiveness depends solely, or to a great extent, upon the temperature of the air. Henderson's original process is as follows : — Allow 2 to 3 parts of gelatine to swell in 75 parts of distilled water, and then dissolve at a temperature of 50 0 C. (=112° F.), and add 3 parts of pure carbonate of ammonia, then add 22 parts of bromide of ammonia and 3 parts of 10 per cent, solution of iodide of potassium. Finally add 200 parts of alcohol (92 per cent.) and 9 parts of solution of ammonia 143 DICTIONARY OF PHOTOGRAPHY. (sp. gr. =0-91). Dissolve 30 parts of nitrate of silver in 150 parts of water, and now, in the dark-room, add the silver solution in small portions and with frequent shaking to the alcoholic bromide solution. The mixture should now be shaken frequently for two hours, the flask being closed by means of a cork, and the whole allowed to stand ten hours, or if made in the evening, till the next morning. Forty parts of Winterthur gelatine must now be covered with distilled water, allowed to soak for half an hour, and then, after pouring off the surplus water, it should be melted and added to the emulsion, which should be heated to 35 0 C. (= 95 0 F.). The whole must now be well shaken and poured out into a flat dish to set (and this should take place in an hour or two), and then broken up and washed. In the winter it will be difficult by this process, to obtain a sensitiveness greater than about 15 0 W. after the emulsion has stood ten hours. In the summer, however, as high as 22° W. may be obtained, but there is a danger, if the emulsion is allowed to stand more than eight hours, of fog setting in, or of obtaining thin emulsions of no value in practical work. Henderson's original method was to pour the liquid emulsion into three or four times its quantity of alcohol, and stir with a glass rod ; when the emulsion adhered to the rod, it was removed, cut up, and well washed. Henderson has since suggested another process of making emulsion, which is some- what similar to one proposed by Obernetter in 1882. I give the report of the lecture as printed in the British Journal of Photo- graphy, as some of the preliminary remarks are well worth reading : — " Mr. Henderson then proceeded to give his promised demon- stration of a perfect emulsion by a new method; but, before doing so, briefly dealt with some of the principal points in emulsion-making. It was important, he said, to have pure water ; he always experimented with distilled water, and recom- mended its use. A great many failures were due to impure water, and he read a list of the common impurities generally found in it, and pointed out that by employing ordinary water in emulsion-making certain silver salts are liable to be formed in the emulsion, which are not amenable to some developers, and that, therefore, unequal results are produced. There were various way of making emulsion, and he enumerated and de- 144 DICTIONARY OF PHOTOGRAPHY. [ElMl scribed some of them, among them the boiling processes, which, he considered, produced decomposition of the gelatine, and consequently fog in the image. Incidentally, on the question of the gelatine employed, he remarked that this substance often contained sulphurous acid, which would have an injurious action on the silver bromide. Then there was the precipitation pro- cess, in which no washing was required, as well as his own plan of emulsifying with ammonia, for which the late Dr. Van Monckhoven had often been given credit. He (Mr. Henderson) was the first to publish the method. The method he proposed to show them that evening consisted of the conversion of th<* silver nitrate into carbonate, and the introduction of the latter into a solution of bromised gelatine, or vice versd. Thus the silver nitrate at no time came into contact with the gelatine. He then proceeded to convert a solution of silver nitrate into carbon- ate by means of a solution of carbonate of potassium, and, having dissolved the gelatine in a small quantity of water, added the bromide to it, and mixed the two solutions. The iodide, said Mr. Henderson, should be added after the bromide, as iodide of silver was formed quicker than the bromide. The emulsion was washed by being forced into shreds through a large mesh into a sieve placed in a jar of water, soluble salts being carried off by a metal pipe. He condemned the use of canvas, and said less washing was required by his method. Many failures were caused by impure rubber piping. He recommended the black kind ; the red and grey varieties contain sulphur, which causes spots in the emulsion. He exhibited a small filter for water which he had found useful and effective ; it was a tube about six inches long, with a piece of sponge at each end, and the centre filled with charcoal. By reversing the filter on the top it was self-cleansing. Mr. Hender- son filtered his finished emulsion through wash-leather, hastening the process by pneumatic pressure. He then showed a coating mug, the emulsion passing through a piece of muslin ; he usually had a piece of fine silver gauze. By this means he avoided bubbles. The action of the centrifrugal separator in removing the soluble salts was then shown. Concluding, Mr. Henderson said that, if he wanted an emulsion giving clear shadows and great density, he would convert the silver nitrate into acetate or citrate, instead of carbonate, and such an emulsion would do for 145 L Em ] DICTIONARY OF PHOTOGRAPHY. line or lantern slide work. He strongly recommended that, in ripening by heat, uniform temperature and bulk of water be employed. He further said that impurities in chemicals must be guarded against, and mentioned the instance of a pupil of his whose bromide, when tested, was found to contain one-third of another substance, which the manufacturer subsequently ad- mitted. Another pupil got spotty pictures, which he (Mr. Henderson) found to be due to the deliquescent iodide contain- ing some sulphates. The formula he now recommended as a good base: — Silver nitrate 120 grs. Water 3 ozs. Potassium carbonate 60 to 90 grs. Water 3 ozs. Gelatine 240 grs. Potassium bromide,... ... ... ... 90 ,, Potassium iodide ... ... ... ... 1 gr. The gelatine to be dissolved in sufficient water, and the emulsion to be made up to fifteen ounces. He preferred to do without alcohol. A washed emulsion of this description, if treated with a solution containing two grains of potassium nitrate, one grain of potassium bromide, and half a grain of chrome alum in ten or fifteen ounces of emulsion, and allowed to stand at a temperature of from 80 to 90 0 for some hours, increased in rapidity, and also gave more density. If the salts are to be removed by the centrifugal separator, it would be necessary to have the bromide dissolved in a small quantity of gelatine, say fifteen grains, and then, when separation had taken place, the bulk of gelatine added ; a still finer precipitate will ensue by the addition of gelatine to the formed carbonate of silver. In emulsions required for subjects of great contrast, more iodide and gelatine will be found advantageous." There are several methods of washing emulsions but to the amateur emulsion-maker the simplest is to place the set emulsion in the piece of canvas netting previously mentioned, to gather up the ends, and then twist the same and force the emulsion through the meshes, thus breaking it up into little nodules, or shreds, which, presenting a greater surface to the washing water, allow of 146 DICTIONARY OF PHOTOGRAPHY. [EmU a quicker extraction of the inert salts. The squeezing of the emulsion should always be done in distilled water, care being taken to wash both the hands and canvas well first, and rinsing the same in distilled water. In breaking up the emulsion in this way there is always some lost by adherence to the canvas, but not much ; and where experimental batches of, say, 4 or 5 ounces only are made, the simplest plan is to cut the emulsion up, with a silver fruit-knife, into little dice, and then place these in a beaker of distilled water, stirring frequently during the course of an hour. If, however, it is inconvenient to give so much time to it, the simpler way is to collect all the dice on a piece of well- washed calico, gather up the loose ends and tie them together, and suspend the little bag thus made by the aid of a piece of string on to a glass rod ; place this across the mouth of a decent- sized beaker or jar, fill the jar sufficiently full with distilled water to cover the bag, and leave it for an hour or two. The water filling the bag extracts the useless nitrates and excess of bromides, and being heavier than the pure water sinks to the bottom of the vessel, so that there is always a current of water less heavily charged, and the washing is mechanically performed. After about two hours of this soaking, the water should be changed, the bag being allowed to drain well before the vessel is refilled. Washing may thus be effected very thoroughly in from six to eight hours, or comfortably in a day. Twenty-four hours is not actually too much — in fact, very strongly recommended by Eder and other authorities. If a good supply of water is to be had,. the washing may be performed by fixing the vessel under a tap, and allowing the same to run on it all night, but personally I think it is better to use distilled water even for washing the emulsion. There is one method of washing the emulsion which is, I believe, rarely used by commercial makers, and that is by the aid of alcohol, as was noted in speaking of Henderson's emulsion process. As soon as the cooking is finished, the still warm and liquid emulsion is poured into three or four times its quantity of alcohol, and well stirred round. The extraction of the unneces- sary salts is not so complete and is more costly than when washing is effected with water, but it is of advantage in saving time and there is less chance of frilling in the subsequent operations of developing, etc. After washing by this method, it is essential to allow the emulsion to soak in water for an hour, in order that it 147 Emu] DICTIONARY OF PHOTOGRAPHY. may absorb the necessary amount of water. When the emulsion has been sufficiently washed, it should be collected on a piece of clean and well-washed linen, allowed to drain, and gently squeezed so as to press out the superfluous water, then collected and melted by placing it in a beaker or other convenient vessel, which should be placed in a water bath. Care should be taken not to heat the emulsion too much, or else it will become fogged, and useless, and the more rapid the emulsion the less heat it will bear in this second melting. However careful has been one's method of preparation and washing, one is never certain that the emulsion is free from mechanical impurities, such as little bits of fibre, hair, etc., and it is therefore advisable to filter the emulsion before use. For this purpose, flannel, felt, or wash-leather may be used, and whilst the flannel is the quickest to allow the emulsion to pass, leather is the most effectual. Personally, I always use a felt filtering bag, such as may be obtained from any chemist to order, z bout 2s. for a pint size, which will be too large for most amateur workers, as the bag absorbs too much emulsion, but the bag may easily be cut down to half its size. If wash- leather be used, it is necessary to wash it well in weak soda solution first, about I in 20, to free it from the natural grease, and then wash thoroughly to free from the soda. When the emulsion is perfectly fluid, it should be poured into the bag, presuming the felt bag be used, or into the wash-leather or flannel stretched on a filter. When the felt bag is used, it is only necessary to suspend it by its ring from a retort stand, or any convenient makeshift, and thus less emulsion is lost, and it does not get cold quite so quickly. Gentle pressure on the top of the bag soon forces the emulsion through. With wash-leather it is almost necessary to have some pumping arrangement, and this may be either the ordinary indiarubber balls as used for spray diffusers, or the more powerful brass force pump used for filling pneumatic cycle tyres or footballs. When leather or flannel is used, the most convenient filtering apparatus I have found to be a small glass percolator, a utensil known to every chemist, and this fitted with a cork to the upper part or body allows one to affix the forcing arrangement. It is advisable before using the emulsion for coating, to add some bromide, and a little chrome alum to the emulsion, the latter especially when the process adopted has been the ammonia boiling process, as this addition 148 DICTIONARY OF PHOTOGRAPHY. [EmU prevents fog and frilling. A I per cent, solution of bromide of ammonium, and a 2 per cent, solution of chrome alum should be made, and 1 oz. of each should be added to every pint of emul- sion. The addition of chrome alum lowers the sensitiveness slightly ; at least, so it is said, and certainly I think it does, but there are no ill effects if the chrome alum be rendered neutral by the cautious drop by drop addition of solution of ammonia. The addition of the chrome-alum solution should be made to the emulsion very gradually, with shaking between each addition, and this addition may be made either before or after filtration, preferably after. Many workers add a little alcohol to the emul- sion, to make it flow over the plates ; and it is, I think, to be recommended when coating is to be done by hand. One part of pure rectified spirit of wine to every twenty parts of emulsion is the right proportion. The necessary utensils for coating plates may be either very simple, or more or less elaborate, according to the operator's ideas. The one absolute essential is a levelling stand, and if we are going to coat any quantity of plates, a good- sized sheet of plate glass and a level. All these may be bought from any photographic dealer, or the glass alone obtained from any glass warehouse. Sheets of glass of the necessary size, we need not say, are also essential. The glass on which the emul- sion is to be spread should be well cleaned, and for this purpose tripoli made into a paste with methylated spirit may be used, or prepared chalk made into a thin cream with water. After rub- bing the glass well with either, it should be rinsed in tepid water, then well rinsed again in hotter water, and given a final rinse in hot water, when it may be placed in a rack to drain, and, if thought necessary, polished with a soft wash-leather, which has been freed from grease by washing in soda. When the glass is cleaned, each piece should he taken up by means of a pneumatic holder, which may be obtained from any photographic warehouse, and examined for flaws and large bubbles ; all defective pieces being rejected. The glass should be piled together and heated by being placed in an oven or before the fire for a little time. It must not, however, be made too hot, only just pleasantly warm, so as not to chill the emulsion when it is poured on. A measure may also be used by the amateur in his first trials to measure out the quantity of emulsion, but with a little practice one is soon accustomed to pouring out about the right quantity. The method 149 Emu] DICTIONARY OF PHOTOGRAPHY. of coating depends upon the size of plate ; with small plates — for instance, half and quarter plates — it may be poured into the middle of the plate, which is supported by the pneumatic holder, and then the emulsion made to run to the four corners by tilting the plate as when coating a plate with collodion. This, however is not a very easy matter, and it is far simpler to pour the emul- sion in a line right across the plate, and spread by means of the simple little distributor shown in fig. 29, which is a piece of glass rod, not tubing, bent to the above shape in a Bunsen flame ; this is placed in hot water till quite hot, wiped dry, and then the emulsion is spread with it, the plate being on the plate of glass on the levelling stand. Mr. W. K. Burton, in his well-known and excellent little handbook 11 Modern Photography," describes a different method of coating, which I have used with success, and as I have also one of the drying boxes he describes, I give the extract from the book entire. " There are several methods of coating plates in common use. The best for those who have the skill is the method used for coating with collodion, and which we describe ; but we imagine most of those who have not worked the wet process will find the plan which has been used for some time by the writer, and which is also described, the most convenient. For the ordinary method the apparatus necessary is as follows : — " A small teapot. A large flat dish of the nature of a porcelain flat bath to catch spillings. A pneumatic holder. This is an india-rubber ball with sucker attached, the whole forming an apparatus whereby it is possible to pick up a plate. " In coating by the ordinary method, it is advisable to have two ruby lamps, one placed at the back of the operating table f the other in front of the operator, and above the level of his head. He can thus see the emulsion on the plate, both by re- flected and by transmitted light. The flat dish is placed between the lower light and the operator ; the teapot full of emulsion, melted, and at a temperature of 120 0 F., or thereby, may be placed on this dish, and the plates, polished side downwards, are placed to the right of the flat dish. "The pneumatic holder is taken in the left hand, which is stretched across the flat dish, to take hold of a plate. The plate is held level, and a pool of emulsion is poured on to it, and guided over it exactly as was described for varnishing a plate. 150 DICTIONARY OF PHOTOGRAPHY. [Emu The only difference is that more than half the plate is at first covered with emulsion, and that, instead of the plate being drained, it is only slightly tipped up, so as to let a little of the emulsion return to the teapot. After this is done, the plate is gently rocked for a few seconds, till we see by looking through it that the coating has spread evenly. To tell whether the plate has had enough emulsion left on it, we look through it. Fig. 28. after it has set, at one of the ruby lights. If we can see the form of the light through the film, there is not enough emulsion on the plate. "The plates, as they are coated, are placed on the levelling slab to set. Some emulsion is sure to be spilled into the flat dish. It is allowed to set, is then scraped up with a strip of glass, and remelted. For the method of coating which we Fig. 29. recommend to those not skilled in the wet process the pneumatic holder is not required. It is necessary, however, to make a small tripod. This is done by gluing three somewhat large-sized shot on to a quarter-plate in the form of a triangle, (see fig. 28). " There is also needed a glass rod about two inches longer than the width of the plate to be coated, and a jam pot or glass measure in which to stand the rod. The dark-room lamp is placed within a few inches of the left-hand end of the levelling 151 EmuJ DICTIONARY OF PHOTOGRAPHY. shelf, and to the back of it. There is to the left of the lamp room only for the pile of plates, which in this case have the polished side upwards. The rod standing in the jam-pot is to the right of the lamp. The teapot with emulsion in it, as before, is in front of the lamp, and farther forward still, near the front edge of the slab, is the small tripod mentioned. A plate is taken from the pile, and placed on the tripod. " A pool of emulsion, about half covering the plate, is poured from the teapot. The glass rod is taken between the fingers and the thumb of each hand, and dipped into the pool of emulsion right across the plate. The emulsion will run between the rod and the plate to each edge of the latter. By a motion of the Fig. 30. finger and thumb of each hand, the rod is lifted the smallest possible distance from the plate, and is rapidly moved first to one end, then to the other, the tips of the finger and thumb resting on the level table as a guide. This, if properly done, will cover the whole plate with emulsion ; and if the plate be small — half-plate or under — it is sufficient to send it to the far end of the table to set. If the plate be large, the coating will not be evenly spread unless it is lifted, balanced on the tips of the fingers of the left hand, and rocked gently for a few seconds. By this method the plates may, after a little practice be coated with great rapidity. There is no need to wipe the rod each time it is used. "As no excess is poured off the plate nor spilled in this method, it is possible, by using a very small teapot, to keep a I5 2 DICTIONARY OF PHOTOGRAPHY. [Emu constant check on the quantity of emulsion going on to the plates. The covering power of the slow emulsion will be found somewhat greater than that of the rapid. With each ounce of the slow emulsion, eight quarters or four half-plates may be coated ; with the rapid, only seven quarters or three halves. "The plates will 'set' in a few minutes — that is to say, the emulsion will stiffen like a jelly, and will not run off the glass, whatever position it is placed in. They are now transferred to the drying box. When dry, they are ready for use. "The drying box calls for some description. There are various forms in use. They all have in view the inducing of a current of air among the plates generally by the burning of a gas jet in a tube or chimney. The fault of most is that the air passages are far too contracted. In many, heat is applied to the incoming air. This is quite un- necessary if the air passages are sufficiently large and well arranged, and if the box can be placed in a fairly dry place. It is, moreover, the greatest mistake to use artificial heat in drying plates, if it can possibly be avoided, as they are rendered distinctly slower thereby. " We illustrate (fig. 3 1 ) a form . 0 of box which has been in use by the writer for several years, and has given complete satis- faction. It will be seen that the air enters at the top of the box. It is drawn into an air chamber at its lower portions, and hence passes up the large tube with a gas flame burning in it. This tube must be carried either into the open air or into a chimney. The plates are placed in racks, which were first designed by Mr. G. F. Williams. A sketch of one of these is given (fig. 30). Two plates may be placed back to back in each pair of notches if desired. The racks may be placed on the cross rods shown 153 Ena] djictionary op photography. in the box, the height of which may be adjusted to suit various- sized plates. Boxes and racks as described are made by Messrs. D. Gordon Laing & Son, 2, Duke Street, Adelphi, London, W.C." As an alternative method of drying plates, the following may be adopted, and it is one which personally I prefer to that suggested by Mr. Burton. All that is required is an air-tight box and some anhydrous calcium chloride. The plates to be dried should be merely placed in racks in the box, and a porcelain dish, as large as the box will hold, in the bottom. In the dish place the anhydrous chloride of calcium, put the dish in the box, the racks containing the plates, and shut the door, or lid, and leave for three days, by which time the plates should be perfectly dry. In no case should the box be opened till a reasonable time has elapsed, or else peculiar markings will be caused, due to unequal drying. When the calcium choride has once been used, it should be heated in an oven till it fuses and melts, when it will lose all the water it has absorbed. The disadvantage of drying by air alone is that the rate of drying is proportionate to the amount of moisture in the air, and that the unequal drying caused by a fall in temperature may give rise to marks which are absolutely irremovable and always show in the finished negative. Enamels are photographic images burnt into porcelain and coated with a porcelain glaze, which makes them absolutely per- manent. They are usually prepared on small copper plaques, which are coated with a special porcelain or material, which may practically be considered to be glass. Metal plaques already pre- pared can be obtained commercially. On these an image is laid and fired. There are several processes — (a) the substitution process, (b) the powder process, (c) the pigment or carbon pro- cess, (d) the collotype process. For the substitution process a collodio-chloride printed-out positive is prepared, toned, and fixed. The image is toned with platinum, gold, palladium, iridium, manganese, and uranium. The positive is then stripped, transferred to the plaque, and carefully smoothed out, and then fired, coated with glaze, and refired. The powder process is the preparation of a positive by the powder or dusting-on process on a sheet of glass, coating it with collodion, stripping, and transfer- ring to the plaque, and firing. The pigment process is merely a 154 DICTIONARY OF PHOTOGRAPHY. [EllC modification of the carbon process, gum arabic instead of gelatine being used as the material; it is transferred and fired. The collotype process is used for preparing the image, a special ink being used and the print being on litho-transfer paper, from which it is transferred to the plaque. It is impossible to enter fully into the subject, and the process is one very little used at the present day. Enamelling Prints. This consists of coating the finished print with a film of collodion to give it a brilliant surface, which gives greater protection and more softness and depth. The following is the method of procedure : — Clean a glass plate — an old negative glass or a cutting shape will do — with French chalk, and polish thoroughly ; now coat the plate with enamel collodion (see Collodion), and, having made a solution of gelatine, 10 grs. to the ounce of distilled water, slip the collodionised plate and the print carefully into the solution of gelatine, avoiding air bubbles ; bring the print face downwards into contact with the coated plate, remove from the solution, and squeeze into optical contact, and allow to dry. When thoroughly dry, raise one corner with a knife, and the print will strip from the glass, bearing the collodion film with it. Encaustic Paste. A paste used to give a brilliant surface to the finished print without the use of hot rollers or of collodion. There are several formulae ; but the following, proposed by Salomons, is decidedly the best : — Pure white wax 500 grs. or 32 grms. Gum elemi 10 -6 grm. Benzole 4 drms. ,, 14 c.cm. Essence of lavender 6 ,, ,, 21 ,, Oil of spike 1 drm. ,, 3-5 ,, Melt the. wax and elemi, add the benzole and other ingredients, and allow to cool, stirring frequently. Smear a little of the paste over the face of the print with a tuft of cotton-wool, and polish with a clean piece till the surface is clean from markings. It increases the depth of shadow and general beauty to a large extent. A more simple paste can be made as follows : — 155 End] DICTIONARY OF PHOTOGRAPHY. Dr. Eder's Cerate Paste. Pure white wax Dammar varnish Pure oil of turpentine ... 100 grs. or 6-5 grms. ... 40 mins. „ 2*5 can. ... 100 „ „ 6 „ Prepared and used as above described. Endemann's Process. See Aniline Process. Enlarging is the operation of obtaining a larger image of a negative or positive upon some sensitive surface. There are several methods of doing this, either by the use of daylight or artificial light, which will be severally described. But it is first necessary to make a few remarks upon the negative used for this purpose. Absolute sharpness of focus is a sine qua non ; for, supposing a quarter-plate negative taken in the ordinary way is to be enlarged — it may be considered that the discs of confusion appear as points of less than T i„ of an inch in diameter, a point inappreciable to the human eye ; but if these said discs of con- fusion are enlarged, they will become of appreciable size — viz., enlarge a quarter-plate to 12 by 10, or three times, and these discs of confusion will be enlarged in the same ratio ; therefore they will be about T f of an inch in diameter, and will be easily seen. Again, the negative should be plucky, and with good, but not too great, contrasts, and of accurate density ; in fact, a good silver printing negative will give a good enlargement. For con- venience sake we may divide our apparatus into two classes ; first, that required for daylight enlarging ; and, secondly, that required for artificial light. We may again subdivide our two classes into minor sub-classes : thus, daylight enlarging may in- clude (1) Solar work, (2) Diffused light; and artificial light includes (1) Lantern work, including the use of condensers; (2) Work without condensers. Then, again, we may use petro- leum, gas, enriched gas, limelight, or magnesium these, however, will be described as we go on. (1) Solar Work. By this term we understand the use of the solar rays themselves, and not their light reflected from any card or white surface. Although this was one of the first processes employed before bromide paper was invented, and was used for Daylight Enlarging. 156 DICTIONARY OF PHOTOGRAPHY. [Enl printing on ordinary silver paper, carbon tissue, etc., we shall dismiss this in a few words, because the apparatus is costly, and sunlight, unfortunately, not always to be turned on and off at will. For this work Woodward invented his solar camera, and Monckhoven improved upon this with his dialytic apparatus, other instruments also being made for the same purpose. Large condensers are absolutely necessary, not less than nine inches in diameter, and the solar rays have either to be kept motionless by means of a heliostat, or mirror mounted equatorially and driven by clockwork, or else by careful and attentive work of an operator. As, however, equally good results can be obtained by using the apparatus described hereafter, no further description will be given ; but, for the information of those desirous of spending their money, full and complete instructions will be found in Monckhoven's " Optics." (2) Enlarging by Diffused Daylight. By many this will be found the most convenient and cheapest method of making enlargements ; but as to whether it is the best is altogether another question, which we shall consider later on at the end of the instructions for both methods of illumination. We have here also what may be practically considered as two distinct methods of working, the one using the actual light of the sky itself, and the. other using reflected skylight. Before entering into particulars of either method, however, there are one or two details which it is advisable to elucidate. We may decide to use a darkened room or a special camera for the purpose of obtaining the enlargement, and the necessary arrangements will now be described. If we desire to use a darkened room, such as an ordinary sitting-room, it is obviously necessary that the light shall be prevented from having access to it by some means or other ; therefore we will suppose that the room has one window, which, if possible, should face the north, and it is desired to block out this window temporarily, so that the room may be afterwards used in the ordinary way. It is obvious that pasting brown or non-actinic paper on the panes of glass is not admissible ; therefore we must have recourse to some other arrangement which can be temporarily applied and bodily re- moved when done with. A convenient contrivance, which can be very cheaply put together by any one possessing a little knowledge of carpentering, may be made, or any working carpenter *57 Enl] DICTIONARY OF PHOTOGRAPHY. will knock it up in a few hours at a trifling charge. To make it still plainer we will take an actual example made for our own use. The window which it was requisite to block up measured six feet by four feet, and, like most windows, was divided across the middle by a double sash. The sashes of the window measured at the sides one inch in breadth ; at the top and Fig. S2. bottom, two inches. Two frames were therefore made, one to fit into the upper part of the window, and one into the lower ; the upper frame is shown in fig. 32, the lower in fig. 33. The frames were made of deal half an inch thick and two inches wide : the upper one, fig. 32, had a crosspiece to strengthen it, which was also convenient to lift it up by ; the lower one, fig. 33, had two crossbars to strengthen it, and which were also used, as described hereafter, for the reception of the negative. We have 158 DICTIONARY OF PHOTOGRAPHY. [Enl now the skeleton, and it is only necessary to clothe it to make it a complete and useful piece of apparatus. For this purpose stout, dark-brown American cloth, which is a kind of coarse canvas covered with some coloured water-proof substance, was chosen, and this was tacked on to the upper frame, and the edges brought round to the back of the frame so as to exclude Fig. 33- any stray ray of light which might otherwise creep in ; the shiny side of the cloth was at the back, the woolly side being towards the window. To make absolutely certain that no light penetrated the cloth, ruby paper was pasted on the woolly side of the cloth. At the edges of the frame, where it touched the sashes of the window, a double thickness of woollen list was tacked ; so that, when the frame was inserted in place and secured at the top by a turn button and at the bottom by the catch of the window, iS9 Enl] DICTIONARY OF PHOTOGRAPHY. there was sufficient pressure on the frame to make it fit up close to the sash and exclude all light. The lower frame was treated in the same way, with this exception, that an aperture was cut in the cloth, and the edges then nailed to the little crosspieces, where the negative is afterwards placed ; when these two frames are fitted into the window and the aperture blocked up, there should be no stray streaks of light anywhere. Brown paper, of course, may be used instead of American cloth, but the latter is much more durable, and less likely to suffer accidental damage by the fingers being put through it. Now, let us see as to using a special camera, so that we may not need to darken the room. To make a camera which shall answer this purpose is evidently not very difficult, and we will give an idea on the subject and leave ou readers to work out the details themselves. The operator's own camera and lens may be used, and a makeshift arrange- ment con- sisting of black silesia running on iron rods, and fitting on to the lens at one end, and bearing a focussing screen and a dark slide to hold the sensitive surface at the other. We have seen earlier that we may use the actual light of the sky itself, and this is shown also in fig. 34, where the camera is presented to the sky. If we are using a darkened room, then the camera must be tilted in the same manner; this may have some advantages, which in our opinion are outweighed by the extremely awkward manner in which the camera has to be sloped, the sensitive surface, of course, having to be parallel with the negative. We come back, 160 DICTIONARY OF PHOTOGRAPHY. Enl] DICTIONARY OF PHOTOGRAPHY. therefore, to the method of using the reflected skylight, and fig. 35 will show us how to arrange the whole apparatus. We have described the method of blocking-out the window. The method of placing the negative in position, if more than one size is to be enlarged from, is by the use of carriers as used in dark slides, which should be provided with little buttons for fastening in place, and springs for holding the negative, these said carriers fitting into the aperture in the window. Or the negative may be placed in the dark slide of the camera, and the slide inserted in the groove in the ordinary way, and the shutters of the slide pulled out so as to allow of the free passage of the light through the negative. The camera must be pushed close up to the negative, or a cloth so arranged that no light enters the room but that transmitted through the negative. It is not, of course, absolutely necessary that the camera should be used actually. All that is necessary is a board to support the lens, the focussing cloth or a black sleeve to prevent all light but that transmitted through the negative from having access to the sensitive surface. It will be found convenient if the camera or the lens and easel or board for the support of the sensitive surface be on the same level, so that a board or table may be used, as seen in fig. 35, to obtain this end. The table or board should have two parallel pieces of wood nailed to it, so as to enable the camera and sensitive surface to be kept exactly parallel. The next question is the reflector (see fig. 35) outside the window. Many operators use a mirror for this purpose, but the objection to this is that a dark and a white cloud passing simultaneously over it, or actually the image of the clouds, will cause unequal illumination of the negative, and consequently unequal illumination of the enlargement. Certainly a mirror gives the greatest illumination. In place of the mirror, a sheet of white cardboard, enamelled iron, or opal glass may be used. The operator will make his own choice in this matter. The reflector must be fitted at an angle of 45° outside the window ; and a cord fastened to the top of it, and passing through the sash at the middle of the window, will keep it in position, and enable it to be raised or lowered at will. We use a sheet of opal glass mounted in an old picture frame, which is hinged at the lower end to the bottom of the window sash, and fastened by a cord at the top to the middle of the sash ; a gimlet 16? DICTIONARY OF PHOTOGRAPHY. [Elil was used to make a hole in the sash, and the cord run through and rendered taut by a turn or two round a stout nail. The reflector, no matter what material it is made of, must be suffi- ciently large that, when the eye is placed at the position of the lens, and the negative removed, nothing but the reflector can be seen through the aperture in the shutter. The only point now needing a little elucidation is that of the easel or other support for the sensitive surface. This may actually be an easel, as offered by some commercial firms. We use an arrangement of a large printing frame measuring 24 by 20, which carries a sheet of plate-glass puttied into the rebate. Behind this is placed the ground-glass focussing screen, the centre of which is ruled in small squares of half an inch with lead pencil, and then varnished with crystal varnish for a space of about the size of a quarter-plate ; this is used with a compound focusser for obtaining microscopically sharp enlargements. The ground side of the glass is next to the plate-glass, and consequently facing the lens, just as in an ordinary camera ; the ground-glass is held at the sides by two small studs, as used for the interior of dark slides. The printing frame fits into a specially made stand, which runs on a couple of parallel pieces of wood on the table, and is instantly clamped at about the right distance from the lens by lever cams, fine focussing being adjusted by means of a short rack and pinion. The above arrangement is, of course, a little more elaborate than actually required, as a printing frame supported in any way so as to be absolutely steady when placed upright, and also parallel with the negative, is sufficient. What is the best lens for enlarging ? is a question we often see asked. Well, the answer is very easy — viz., that lens which took the negative. But this answer requires a little modification. If the negative to be enlarged is a portrait, then a portrait lens may be used ; but the back lens of the combination must be placed next to the negative. The most useful lens is undoubtedly the doublet of the rapid rectilinear type, as it gives, as a rule, excellent marginal definition. A single or landscape lens may also be used, but from the necessity of using a smaller diaphragm it is obviously slow ; in this case the convex side must be pre- sented to the negative, the plane or concave surface being towards the sensitive surface. The diaphragm should be about the diameter of the lens in front of the concave surface — that is, 163 Enl] DICTIONARY OF PHOTOGRAPHY. between the lens and sensitive paper. There is, of course, some residuum of distortion which may prove troublesome when enlarging architectural subjects. In the case of the rectilinear doublets, it is immaterial which lens of the combination is pre- sented to the negative. Apparatus for Enlarging by Artificial Light. To most amateurs, especially those engaged in business during the hours of daylight, artificial light is the only one they can employ for enlarging ; hence considerable attention will be paid to this. We, first of all, as already suggested, divide our lights into petroleum, or mineral oil, gas, enriched gas, limelight, mag- nesium, and the electric light ; and we shall endeavour to describe the arrangements for all, but must premise that the first essentials for successful work are that the light, no matter what kind it is, must be, first, small in dimensions, and, secondly, actinic in quality ; the first gives greater sharpness, the latter short exposures. Mineral Oil Lamps. Opinions differ as to the best form of lamp for enlarging, most, if not all, commercial apparatus being provided with lamps having flat wicks turned endwise to the condensers. Here again we find a divergence of opinion, some preferring two-wick, some three-wick, others four-wick lamps ; generally, however, three-wick lamps are used. We have used, with good results, however, a round-wick lamp, or so-called Argand burner, this being actually a Defries lamp of forty-candle power. The burner of this lamp is circular, with an air passage up the centre, and has a chimney of glass contracted just above the burner, and above the contraction the flame appears intensely luminous and solid ; it is at this point that the flame should be used. For this purpose it is necessary to provide the lamp with an outer case of brass or tin, which may be fitted in position and slid up and down, without in any way touching the glass chimney. The tinned sheet-iron is carried up above the glass chimney for some distance so as to lengthen the chimney, thus creating more draught, therefore more perfect combustion of the oil and a more actinic light. The outer sheet-iron case is provided with an aperture, circular, of half an inch diameter ; and, on looking into this, nothing but an intensely luminous circle of white flame is seen. No matter what lamp is used, the circle of illumination 164 DICTIONARY OF PHOTOGRAPHY. [Enl thrown by the objective should show no lines of variable illumina- tion. The most important thing in all illumination is to have the radiant a point, otherwise we are troubled with parallax, varying illumination, and want of sharpness ; but, provided the degree of amplification be not too great, this trouble will not arise. Gas and Enriched Gases. Ordinary gas, unless of good quality, is not so suitable as gas enriched by the vapour of some hydro- carbon. The commercial form of albo-carbon will be found very suitable. Mr. TraillTaylorhassuggestedaveryconvenient arrange- ment, " which consists of two fish-tail burners separated from each other by the extent of an inch, both flames having their flat sides towards the condensers, there being an opaque disc, with a circular aperture in it of a little over half an inch in diameter, placed as close as possible up against the foremost flame so as to reduce its effective area. The position of this aperture must be such as to be opposite to the most luminous part of the flame. The second flame behind the anteVior one serves to confer in- tensity, and is of great utility ; but nothing seems to be gained by a third burner. The gas flame, when thus enriched by the vapours of the albo-carbon, become very intense. An Argand flame from gas thus enriched ought to yield a light of great excellence, provided it has a smaller flame ascending through its centre, and that provision is made to condense it by diminish- ing its diameter, either by a brass solar cap to cause a strong current of air to impinge upon the flame a little above the burner, or by a contraction in the glass chimney. Whiteness and intensity in such a case are increased by a judicious lengthen- ing of the chimney to increase the draught. The area of the flame must, however, be reduced by the expedient already pointed out." The Welsbach or Incandescent gas burner is one par- ticularly adapted for enlarging, as the light emitted is exception- ally rich in actinic rays, and the exposure thereby considerably shortened. In some experiments in connection with this light we found that with the ordinary household gas supply the exposure was cut down to one-quarter of that with an ordinary three-wick lamp. Limelight. This is, of course, one of the most convenient of all sources of light, and is so well known as to need but little description. Magnesium. So far as we know there is no commercial 165 Enl] DICTIONARY OF PHOTOGRAPHY. apparatus for utilising magnesium as an illuminant with con- densers, though of course it would be quite possible to utilise any ordinary enlarging lantern with a clockwork arrangement for feeding the magnesium to a small spirit flame, so as to keep the radiant point at one particular distance from the condensers. The Electric Light. Few amateurs, or even professionals, can afford the necessary outlay for this light, the cost of even a primary battery or accumulators being considerable. In many parts of London, however, the wires for electric lighting are now laid along the principal thoroughfares, and it would therefore be easy to connect, and the cost of installation is about thirty shillings per lamp. A portable battery, the Schanchieff, has been used for lantern work, and would also answer well for enlarging. The apparatus for enlarging by artificial light bears some resemblance to the ordinary or so-called magic-lantern. It is immaterial of what nature or substance the body of the lantern is, provided it be light-tight and strong. Russian or sheet-iron, copper, or wood with metal lining — all are used by commercial firms. The enlarging apparatus practically consists of a camera attached to an optical lantern, focussing being effected by rack and pinion. We need make no further mention of these, except that we shall later give a sketch showing how an ordinary magic-lantern may be adapted for enlarging. The Condensers. The function of the condenser is to collect the rays of light and refract them through the negative. The usual form of condenser employed is two plano-convex lenses placed side by side, with the convex surfaces nearly touching. The first question to decide in purchasing an enlarging lantern is, What size condensers are required ? as the size of the con- densers governs the price. It is a question which has often been asked by beginners as to what size condenser will cover a certain-sized plate. This is by no means difficult to decide. All that it is requisite to do is to measure the diagonal of the negative in question, and this diagonal will be the diameter of the required condenser. In practice it is always advisable to allow an extra quarter or half an inch where this does not add too much to the cost. Mr. Hughes has introduced a rectangular condenser. In selecting condensers, the most important points to note are, first, to see that they are as free as possible from colour ; secondly, that the one next the negative is free from 166 DICTIONARY OF PHOTOGRAPHY. [Enl air-bubbles and striae ; thirdly, that they are not set too tightly in their mountings, or when heated from the light they will crack. Enlarging by Artificial Light without Condensers. This is a procedure which will commend itself to many an operator, because the necessary apparatus may, in many cases, be knocked up from odds and ends in odds and ends of spare time. Thus we utilised an old square sugar case which cost 4^., and the sheet-tin to line it gd., the lamp 15^., odds and ends, such as screws, ground-flashed opal glass, another 2s. ; so that for i8.y. an enlarging apparatus was obtained, which worked well for over two years. As condensers are usually rather costly, the follow- ing ingenious arrangement, which dispenses with them altogether may be utilised ; it is suggested by Major Barrington Baker, in Fig. 3 6 - the British Journal of Photography tor 1888. Fig. 37 on next page is a rough reproduction of Major Baker's diagram, and the following precis is given of his directions. The case is made of £-in. deal, with a hole, n, 6\ by 4% for negative, or made the size desired. l, a Beige lamp of 42-candle power, is placed in the case through the door d, half a dozen holes (a a) being bored in the bottom of the box for ventilation. An opal globe is used to diffuse the light ; the negative is placed film side outwards in a rebate at n, and held in its place by two small turn-buckles ; the camera may be used, or a specially made pair of bellows. The exposure is, of course, prolonged with rapid papers, being from 10 to 15 mins. The author would suggest as an improvement upon this that the case be lined throughout with tin, and a sheet of ground glass or opal be placed before the negative, and that a parabolic reflector be used. Some of the modern cameras will 167 Enl] DICTIONARY OF PHOTOGRAPHY. be found utterly useless for enlarging, the pull of the bellows, or the greatest distance they will stretch, being very short ; then the following arrangement, now always used by the author, will take their place : — Obtain some black twill, I yard in width and length, and cut it into four pieces in the following manner (it is better to cut paper pattern first, in case of error) : — Fold the cloth in half, and again in half, so as to give four pieces 9 ins. wide and 36 ins. long ; now cut two slanting strips from each, commencing at 2 ins. wide, and narrowing down to the other end ; this will give four pieces of cloth 36 ins. long — 9 ins. wide at one f L C j 3 Fig. 37- end, and narrowing to 5 ins. at the other. Have these sewn together by the edges, so as to form a conical sleeve, which will take the place of bellows 36 ins. long. At the wide end nail a frame of wood large enough to take the negative, and at the narrow end a piece of wood to take the lens, or the camera front may be utilised for this purpose. It will not be necessary to pleat it like bellows, but it can be finely pleated at intervals, and safety pins used to hold the pleats together when required to shorten the distance, so the pleats can easily be let out when required, or pieces of elastic can be run along the edges to serve the same purpose. The possessor of a magic-lantern can easily 168 DICTIONARY OF PHOTOGRAPHY. [Elll utilise that, no matter what size the condenser, if a sleeve of black cloth is made to fasten at one end round the lantern objective and at the other to the camera, the negative being placed in the position of the focussing glass of the camera. Where the operator can utilise gas or several oil-lamps it is only necessary to place between them and the negative a sheet of flashed opal glass ground on the flashed side, or a piece of ground glass coated on the ground side with an emulsion of sulphate of baryta in gelatine or of finely sifted carbonate of lead. When using an ordinary lantern it is absolutely necessary that no stray light should find its way out of the same ; therefore it is nearly always necessary to enclose it in an outer box. This is a point which requires careful attention, or foggy, degraded whites will ensue in the resulting enlargement. Focussing. It may be taken as an accepted axiom that the nearer the light is to the condensers and the nearer the condensers to the negative the greater will be the illumination, and the greater the distance between the lens and sensitive surface the less the illumination ; or, in other words, the larger one enlarges, the longer one must expose, everything else being constant. There is one precaution necessary when using condensers, or even artificial light of any kind with condensers, and that is, to see that everything is gradually warmed. Don't turn your light on full power at once, and place it close up to the condenser, and then be surprised if your condenser cracks. Warm everything gradually by having your light low and some distance from the condenser, and gradually reduce the distance and increase the light. It will be obvious to the merest tyro in enlarging that the farther the lens is from the sensitive paper the larger the image, and vice versa ; and also that there are certain distances which bear a certain relation one to the other, so that when enlarging, the distance between the negative and lens and lens and sensitive surface bear a strict relation to one another. The approximate distance between the negative and lens and lens and paper may be found from the following formula : — (1) d=f+S. (2) D=(»+ l)f. 169 Enl] DICTIONARY OF PHOTOGRAPHY. Wherein d = the distance between the negative and lens. D = the distance between the lens and sensitive surface. / = the equivalent focus of the lens. n = the number of times of enlargement. Or to the non-mathematic mind we will put it in another way. To find the distance between the lens and sensitive surface, add one to the number of times (linear measurement) the negative is to be enlarged, and multiply by the focus of the lens. To find the distance between the lens and negative, divide the product of the above calculation, or the distance between the lens and sensitive surface, by the number of times of enlargement, and the quotient will be the distance between negative and lens. For example, it is required to enlarge a quarter-plate negative to 16x12 with a 6-inch lens. 4^x3! enlarged to 16 x 12 —4. times (linear). The distance will be then approximately (4+ 1) x 6 = 30 inches, between lens and sensitive surface. To find the distance between lens and negative 30-r4 = 7-£. To save trouble, however, there are well-known tables which have been calculated for enlargements with lenses of varying foci, and one will be found in the Appendix. The distances given in the tables will be found to be approximately correct ; but in all cases accurate focussing should be obtained by adjustment of the screen or lens by rack and pinion. Whilst many operators are content to use merely a white piece of paper, and to focus from the front, it will be found far pre- ferable to use the ground-glass screen and compound focusser above described. In all cases where marginal- definition is defective, stops or diaphragms must be used, exactly as in field work. Having obtained a sharp focus, the next operation is placing the sensitive paper in position. The methods adopted for this are slightly different, some operators preferring to use a cap in which a piece of yellow or ruby fabric or glass is placed, so as to illuminate the surface focussed on. Others, again, cap the lens as usual, and use a ruby lantern to place the paper in position ; we prefer the former plan, because, when orange glass is used in the cap, it enables one to ascertain whether any alteration in focal sharpness of the image takes place, as this may sometimes occur from the sensitive paper buckling. Another point is the method of fastening the sensitive surface to the easel board if this be used. Of course, if the dictionary of photography. [Enl large printing frame be used, as we have suggested, there will be no difficulty about this point ; but when the paper has to be affixed to a board there is a slight difficulty. One plan we have tried with success has been to have a quarter-inch groove cut in the face of the easel board along one side or the top, and in the groove a piece of stout steel or copper wire, preferably the former, is placed, and the ends of the wire are turned over the sides of the board, and passed through stout brass eyelets, and then provided with a screw thread, on which fits a milled nut. The action of this wire is merely to clip the paper in the groove, and if such a groove is placed at top and bottom of easel board, it is possible to clip the paper firmly under one groove, and then to pass it under the other, and stretch it taut, and then screw up the milled nuts. Another method is to use large-headed drawing pins at the four corners, or to use broad indiarubber bands. The advantage of using some broad surface like the head of a drawing pin is that it enables one to accurately determine whether the whites of the enlargement are pure or fogged. Surgeon-General J. L. Ranking suggested in the Amateur Photographer of November 28th, 1890, curving the paper, and gives the following directions : — " I have applied this principle to my easel in the following manner : The ce?itre of a sheet of paper, 16x12 in., my usual size for enlarging from a quarter-plate negative, being pinned to the easel top and bottom, a wedge- shaped piece of wood was passed beneath one end of the paper till the margin of the picture was equally sharp with the centre. The distance to which the margin was advanced towards the lens was found to be 1 in. Two pieces of wood were then prepared, 12 ins. long and 6 ins. wide. They were then planed down so as to form two wedge-shaped pieces 1 in. deep at outer and ^ in. at inner edge. These were then screwed down upon the easel, and to them a thin piece of cardboard fixed, thus forming the required curved surface. Upon the picture being sharply focussed the sheet of sensitised paper is pinned. With Ilford rapid paper and the artificial light I use, which I shall presently describe, and using an R.R. lens, 8-in. focus, at full aperture, an exposure of from 8 to 10 seconds suffices to enlarge from a quarter-plate up to 16x12. If a longer exposure be necessary, as it is in enlarging from landscape negatives, into which skies have to be introduced, the lens can be stopped i 7 l Enl] DICTIONARY OF PHOTOGRAPHY. down to any extent, the exposure being calculated upon the well-known ratios of the squares of the diameters of the stops, or a slow paper can be used. The artificial light I use is the Welsbach incandescent gaslight, said to be 16-candle power, and I find it most convenient. It is attached to the nearest gas- bracket by a flexible tube, and it can be lighted and extinguished in a moment." Exposure. Having obtained a critically sharp image, the next point to decide is what exposure is required ; and the determination is perhaps quite as difficult and equally as important as in negative making. Various methods have been suggested, but before entering upon these it would be advisable to consider the factors which govern the duration of exposure : — (i) The actinic power of the light ; (2) The density of the negative ; (3) The intensity ratio of the stop ; (4) The number of times of enlargement, or the distance between the lens and sensitive surface ; (5) The sensitiveness of the material on which the enlargement is made. (1) The Actinic Power of the Light. The only satisfactory method of determining this is by the aid of an actinometer ; and the most satisfactory, and, in fact, the only ones to use are those based upon the action of light upon bromide of silver paper impregnated with solution of nitrite of potassium. There are two such actinometers in the market, Stanley's and Watkins', in which the actinic power of the light is gauged by the time a bromide of silver paper prepared as above takes to match a standard tint. In connection with this we would point out that it is said to be extremely difficult to match the standard tint ; but the following quotation from the instructions issued by the maker of the latter actinometer is worth consideration : — " In testing the light no notice should be taken of the exact colour of the sensitive paper, which may vary slightly with the humidity of the air ; the depth of tint is the important point. The paper darkens rapidly in light ; up to a certain point it is lighter than the standard tint, after this point it is darker. The point when it is neither lighter nor darker is that to be timed." To prepare a somewhat similar actinometer it is only necessary to soak ordinary bromide paper in a 10 per cent, solution of nitrite of potassium, and then to dry it in the dark. A small piece is 172 DICTIONARY OF PHOTOGRAPHY. [Enl allowed to darken in daylight, and the time that it takes to deepen to a tint which may be arbitrarily chosen accurately counted, or timed by a watch. This tint should then be matched in water-colours, and painted on a strip of paper. It must be noted, however, that the tint of the paint when dry must agree with the tint of the darkened paper. Now, to use this actinometer, paste the strip of painted paper on the top of a cardboard match- box, place inside the box the sensitive paper soaked in the nitrite solution, and draw a small piece out and allow it to darken at a distance of about 18 ins. from a No. 5 Bray's gas burner turned full on without flaring behind the half-tones of a negative, noting accurately the number of seconds it takes to darken to the standard tint. Now take a sample of some bromide paper, Eastman's, for instance, and expose half-a-dozen sheets of the same paper behind the negative at the same distance, 18 ins., giving various exposures, then on developing these six sheets it will be possible to pick out one print correctly exposed ; and from this we can establish one factor, which will enable us to calculate other exposures under other conditions. Thus if the actinometer paper takes 10 seconds to darken to the standard tint, and we find 8 seconds the correct exposure for the said negative at 18 ins. from the gas burner, it will not be difficult to calculate the exposure for any distance or any more or less actinic light. For example, the exposure required for the same negative at a distance of 36 ins. from the same gas burner is easily calculated by the rule that the exposure alters as the square of the distance between the light and sensitive paper. The exposure required at 18 ins. = 8 sees., .*. the ex- posure required at 36 ins. will be in the ratio of 18'-': 36-, or as 324 : 1296. Now 324 : 1296 are as 1 : 4, .*. if the exposure in the first case = 8 sees., the exposure in the second case = 8x4 =32 sees. This will explain the use of the actinometer, and deter- mine the first factor. (2) The Density of the Negative. It is difficult to accu- rately determine this, as the actual deposit of silver does not alone represent the density of the negative. The colour of the deposit, and the presence or absence of stain in the film, will also influence this factor ; but by using the actino- meter as suggested under the first factor we practically determine the second factor also. *73 Enl] DICTIONARY OF PHOTOGRAPHY. (3) The Intensity Ratio of the Stop. Most workers know the usual definition of this term, which is the ratio the aperture of the stop or diaphragm bears to the equivalent focus of the lens ; when using a lens for enlarging, however, we never use it at its equivalent focus, the focus altering with the degree of enlargement. Therefore we have to calcu- late anew the intensity ratio of our stops for the new focus. Thus, supposing we are using an 8^-in. focus lens for an enlargement of a quarter-plate to 12 by 12, or, in other words, if we are enlarging four times, the focus of our 8J-in. lens becomes io| in. ; therefore all the diaphragms will be pro- portionately reduced in ratio diameter. It will always be found more convenient if diaphragms of definite diameters are used. Thus special diaphragms of i-in. diameter aperture or £-in. diameter aperture can be obtained ; and it is thus easy to cal- culate at once the new intensity ratio, without troubling to measure the diameter every time. (4) The Number of Times of Enlargement, or the Distaiice between the Lens and Sensitive Surface. It is requisite to take into account this factor, because, according to the well-known Fig. 38. rule, the intensity of illumination 011 a given surface is inversely as the square of its distance from the source of light, or, in other words, the greater the distance of the sensitive surface from the lens the longer the exposure. This is very clearly seen from the above diagram. Let l be the source of light, and if we place the bromide paper at 1., 12 ins. from the light, and we find the exposure to be 45 seconds, when we place the paper at n„ nr., 174 DICTIONARY OF PHOTOGRAPHY. iv., respectively— at 24, 36, and 48 ins., the exposure will not be 45, 90, 135, and 180 seconds, but in the proportion of i, 2 2 , 3 2 , 4 2 , or 45, 180, 395, and 720 seconds respectively. (5) The Sensitiveness of the Material on which the Enlarge- ment is made. This has been, to a great extent, a matter of con- jecture hitherto ; but I give a table of relative speeds compiled by Mr. Alf. Watkins for use with his exposure meter, merely noting that the exposures will be in inverse ratio to the P. numbers. P. Numbers. Exposure. Eastman slow 6 6§ ,, rapid ... 40 1 Morgan and Kidd ... ... 15 Anthony rapid ... 50 Ilford slow ... 3 13^ ,, rapid ... ... 30 li Dr. Just 4 10 Mawson ... 6 65 The first column shows the P. number obtained, and the second one the relative exposures required. Before closing this note it would be but fair to give to Mr. Ferrero the honour of having first drawn out a table of exposures for enlarging, which is given in the Appendix. Full directions for developing, clearing, fixing, etc., will be found included under Bromide Paper ( TT)"!! Then 67-4 2 = 33 ft. 8 in. And t*i + 4 = 104 = 8 ft. 8 in. Then 8 ft. 8 in. 2 = 4 ft. 4 in. Taking T ^ of an inch as the permissible error, I have worked out from Mr. Cheyney's rule, the following table, which may be useful : — Point Beyond which All Objects will be in Focus. Apertures. //8. //16. 4 ft. 6 „ 8 „ 10 ,, 13 >i 16 „ 19 » 22 ,, 26 „ 9 in. 6 „ 6 „ 9 .» 3 >l o „ o „ 6 H o ,, 3 4 6 8 9 1 1 15 16 20 6 in. 9 » 3 tf 10 „ 9 r, 9 H o „ 6 H o ,, 2 ft. 3 » 4 t> 5 if 6 „ 8 n 9 M 11 M 13 » 6 in. 3 3 ,f 6 „ 6 „ o 6 3 o 194 DICTIONARY OF PHOTOGRAPHY. [Fix Another rule for finding the same is : — Multiply 27 by the square of the focal length of the lens and by the fraction expressing the diameter of the diaphragm aperture. Example: — Required the nearest point in focus with a lens 4^-in. focus, //io diaphragm. 27 X \\ X 4£ x T V = 27 x 20-25 x -i = 5-46 yards. Fixing. The removal of any sensitive salt unacted upon by light or by the developer, thus rendering the negative or print unalterable by the further action of light. The usual method of effecting this in the case of the silver salts is by the solvent action of Hyposulphite or Thiosulphate of Sodium (q.v.) ; cyanide of potassium, sulphocyanide of potassium or ammonium, and sulphite of sodium have also been recommended. Neither sulphocyanide of potassium or ammonium, nor sulphite of soda are likely to come into general use, as their fixing powers are not so good as those of hypo, and their price is greater. Cyanide of potassium is more powerful than hypo, but its action on the image is so great as to completely destroy the half-tones occa- sionally ; its use should never be countenanced for dry plates or prints. Hypo, then, is our sole resource ; and, whilst it is much abused, there is no doubt of its being at present the best salt for the purpose. The difficulty of completely eliminating, how - ever, is its great drawback, and this will be treated of under Washing Negatives and Prints {q.v.). For lixing negatives the author recommends the use of two fixing baths, the strength being about 4 ozs. to the pint of water in each, the negative being allowed to remain for ten minutes in the first, and for about five minutes in the second ; by this a more thorough fixing of the negative is effected. For fixing prints the strength generally recommended is about half that for negatives — that is, about 2 ozs. to the pint — and sufficient liquor ammonia or carbonate of ammonia should be added to make the solution smell faintly of ammonia. This neutralises any free acid which may be present in the solution, and prevents any loss of tone in fixing. The author always uses, however, the same strength as for negatives, with the addition of ammonia, and uses the bath at a tempera- ture of 70 0 F. ; and, from some lengthened experience, the results prove the increased advantage of doing this, as the fixing is com- 195 Fla] DICTIONARY OF PHOTOGRAPHY. pleted in half the time, and there is less chance of loss of tone. R. E. Liesegang has suggested the use of Thiosinamine {q.v.) as a fixing agent, and it is specially adapted for prints. For plates its action is much slower than hypo, but it is said to possess the advantage of being more quickly removed. The strength sug- gested is i per cent. Flare. A fogged central patch on a developed plate, or seen as a circular patch of light on the focussing screen. It is said to be an image of the aperture of the diaphragm, or in some cases of the lens itself. The surface of the lens reflects the opening of the diaphragm and forms a distinct image of it, and when this coincides with the focus of the lens this image is seen as a flare spot. Again, others, and amongst them Monckhoven, in his " Photographic Optics," states that it is due to too close an adherence to the globular form by the optician who constructed the lens. Others, again, state that it is due to the edges of the diaphragm aperture being worn bright, and this no doubt is a general cause for its sudden appearance in a lens. The Iris diaphragm, but lately introduced for photographic objectives, seems to be particularly liable to this, from the friction of the tongues of metal of which it is formed ; others state that when the lenses are mounted in cells which are not blackened, a flare is almost certain to make its appearance. All lenses should be examined for this most annoying effect, which can rarely be wholly eradicated. It is very often a defect in portrait lenses when such are used for outdoor work where any portion of bright sky is included in the background, and in this instance it is clearly an image of the lens by reflection from the surfaces. The remedies are not by any means satisfactory, as, whatever is done, at its best the flare spot is so distributed over the whole plate instead of being localised. When the diaphragm edges are worn bright they should be blackened, and the cells in which the lenses are mounted should also be attended to. It can be eliminated partially as stated above, by altering the position of the diaphragm slightly ; but as this is used to reduce distortion to a minimum, the remedy may be worse than the disease by introducing this defect. Slightly altering the relative positions of the two lenses will also efface it, but, as said before, only by distributing it. 196 DICTIONARY OF PHOTOGRAPHY. [FOC Flatness. A want of vigour and contrast in the negative and resulting prints, due to over-exposure, or to the use of too strong or too weak a developer. Fluorhydric, or Hydrofluoric Acid. HF=i92. Is obtained by heating fluor-spar with sulphuric acid in a leaden or platinum retort, connected with a receiver of the same metal. It is a colourless gas, very soluble in water, and condensing at 20 ° C. into a mobile fuming liquid, which boils at 59 0 F. It has the peculiar property of dissolving glass and other silicates, and for this reason leaden or platinum vessels are used to prepare it, and the aqueous solution is stored in india-rubber bottles. Extreme care is necessary in handling it, as even when dilute it causes very painful ulcers when applied to the skin, and dissolves the nails. Fluorine. F= 191. A non-metallic element never met with in a free state, and usually obtained from fluor-spar, a fluoride of calcium, CaF 2 . It is of little practical photographic use ; but its compound, hydrofluoric acid, has been recommended for detaching the negative film from glass plates, for preparing a film negative. (See Stripping Film.) Fluorine has only recently been isolated Focal Length, Focus, or Equivalent Focus. A term ap- plied to a compound or doublet lens. It is the focus of parallel rays entering the lens, and is thus called from the fact of an image formed at that point equalling in size that formed by a single lens. It is extremely important that every photo- grapher should know how to find the focal length of his lens, because upon this depends the determination of several factors. Before deciding, however, on the best method of measuring the focal length, it is necessary to know where we are to start measuring from. If we take a single or landscape lens we shall find that there are three or four points which we can measure from. Thus we may measure from the plane of the diaphragm, from the front surface of the lens, or from the centre of the lens, or from the posterior surface of the lens ; and each point will give us a different length. Thus in the case of a rectilinear lens we can measure from several points : from the front lens, from the plane of the diaphragm, from the back surface of the posterior 197 Foe] DICTIONARY OF PHOTOGRAPHY. lens. It is very usual to see in some opticians' catalogues the term " back focus," and this is the distance between the posterior lens and ground-glass ; and is, I believe, inserted for the infor- mation of professional photographers, to enable them to judge whether the lens can be used on their cameras. The correct point to measure the focal length from is one of the " nodal points " of a lens, but, practically, the following methods may be used with the satisfaction of knowing that the focal length of any lens thus measured is sufficiently accurate for all practical pur- poses. For practical purposes it is quite sufficient to set the camera up and focus the sun or the clouds, and in the cases of single lenses measure the distance between the front surface of the lens and ground-glass, and with portrait or doublet lenses the distance between the diaphragm slot and ground-glass. This method is not precise, however ; more accurate measurements may be made by one of the following plans : — (i) GrubUs Method. On the ground-glass of the camera draw two pencil lines about an inch from the margin at each side. Now set up the camera before a window, preferably upon some flat surface, such as a table, upon which is spread a sheet of Fig. 39- white paper, and focus for some distant scene, more than 1 50 or 200 yards off, in which there is some distinct feature, such as a church spire or tall chimney. Make the image of this fall upon one of the pencil marks on the focussing screen, and with a pencil draw a line upon the paper along the side of the camera ; 198 DICTIONARY OF PHOTOGRAPHY. [Foe now bring the image of the chimney or spire upon the other line, when draw another line upon the paper also along the side of the camera ; remove the camera, and with a flat rule continue these lines till they cut one another, so as to form an angle, across which draw a line, so as to form a triangle, which line must be exactly the same length as the distance between the two pencil marks on the focussing screen. Find the centre of this base accurately, and connect the junction or apex of the angular lines with the centre of the base. This line will then be the true equivalent focus of the lens. The lines aa' } bb', are those traced on the paper along the sides of the camera, extended until they meet at c. d e is the base, being the exact distance apart of the two pencil marks ; / its centre, and cf the true equivalent focus of the lens. (2) Method by Focussing a Given Object the Same Size. With long-extension cameras a very common method is to focus on any object till the image is exactly the same size as the object, then measure the distance between the object and ground-glass, and divide by four, when the result will be the equivalent focus, A convenient object to use is a foot rule. Example : — On focus- sing a foot rule, till the image or part of it measures exactly the same, we find the distance between object and ground-glass to be 73£ in. Then 73^-f4=i8f in., the focal length of lens used. (3) Schroeder s Method. This can only be used by possessors of a telescope. First of all take a piece of cardboard — a mount will do — and punch two holes in it some little distance apart ; Fig. 40. place this card flat on the ground side of the focussing screen, and with a lead pencil blacken the ground-glass through the holes. Now go into a darkened room and set up the card, and place behind it a lamp or candle, erect the camera, and rack the 199 Foe] DICTIONARY OF PHOTOGRAPHY. lens in or out till the bright spots of light coming through the holes in the card fall exactly on the black spots on the ground- glass, and mark accurately the position of the ground-glass on the base-board of the camera, as shown in fig. 40, in which a is the card with the two holes, p the lens — here represented by a single double-convex lens — and b the focussing screen, marked by the pencil with the two black dots, on which are focussed the bright spots of light as shown by the dotted lines. A small telescope is now focussed on the moon, and, the focus temporarily fixed, the ground-glass is removed from the frame, and a negative of a strong contrasted subject is placed in the frame, from which the ground-glass has just been removed. A very good negative, if handy, is that of a line-drawing. The eye-piece of the tele- scope is now placed in the same position as the card previously used — i.e., opposite the lens of the camera ; a candle or lamp is placed behind the negative, and the camera racked-in till the t Fig. 42. lines of the negative are seen sharp and clear. Now, as the telescope focus has been fixed for infinity, the negative will only appear sharp when it is at the true focus of the lens, this position is then accurately marked, as shown in fig. 41, in which t is the telescope focussed for infinity, p the lens, and d h the position of the plane of the negative. Fig. 42 is, as will be at once seen, a 200 DICTIONARY OF PHOTOGRAPHY. [Foe combination of the two previous diagrams — figs. 40 and 41 — and the distance between the plane 1 and plane 11 is the true equivalent focus of the lens designated in the diagram by F. (4) Stolze's Method. This, or the following method, No. 5, will be found the most convenient in practice. Dr. Stolze described his method in " Photographische Nachrichten, vol. ii., p. 164, 1890, as follows : — "One first focusses on a very distant object, or, so to speak, on infinity, and marks this position of the focussing screen on the base-board of the camera. Then the camera is directed at a very near upright object of known, or easily measurable, size — best on a foot rule — so that the image falls on the focussing screen ; this is sharply focussed, and this position of the screen again marked on the base-board ; a negative is taken of the object in this position, and after development the size of the image of the photographed object is carefully measured, and one thus determines how much smaller the former is than the latter. If one multiplies the difference between the two foci with this number, the result will be the focal length." Possibly an example will make this a little clearer : We have focussed on a very distant object, and marked the base-board, and have also focussed on a foot rule and taken a negative, and find that the image of the foot rule measures 10 in., the distance between the two marks on the base-board is 19 in., then F = 19 x = 22-8 in. The size of the image should be as large as possible — that is to say, the amount of reduction should be as little as possible, because the greater the reduction the less accurate the result. (5) Proportional Method. This method is extremely con- venient when working with somewhat short-focus cameras and long-focus lenses. The camera is placed upon a table, when convenient, or if such is not handy, on the ordinary tripod. We support on a wall, shelf, or convenient place a foot rule which is plainly marked in inches. On the ground-glass of the camera, a space of two inches is accurately marked as near the centre as possible : it is merely necessary to mark off the two inches, not to divide it out into parts. The camera is now moved backwards or forwards till the image of the foot rule of twelve inches just falls on the two-inch space we have marked out. The coincidence of the image on the lines should be examined with an eye-piece 201 Foe] DICTIONARY OF PHOTOGRAPHY. or compound focusser, to see that they do coincide, then the distance between the foot rule and the focussing should be care- fully measured, and this distance jotted down, as from this we obtain the focal length of the lens. This number is multiplied by the figure which represents the proportion of the image to the original object, and the result is then divided by the square of the proportional number plus one. Taking an example, we find that the distance between the foot rule and its image equals 63 ins. .\ 63 x 6 = 378; 378 -7- 49 = 7f in., the required focal length. It must not be thought that the above proportion between the object and its image is essential ; any convenient proportion may be taken, such as 4, 5, 8, etc., but the rule holds good with all. Parallel rays proceeding from any object and transmitted by a convergent lens are refracted in such a manner that they meet at a point and form an image of that object, this point being called the principal focus. Rays which are not parallel but which diverge from an object are transmitted by a convex lens and united to a point, and the two points thus connected are said to be conjugate foci ; or in other words the distance between any point in any object and the lens, and the distance between the lens and the image of that point, are said to be the conjugate foci of the lens. These foci are of great importance when enlarge- ment or reduction of any print, engraving, or negative is required. The rules for finding the conjugate focal distances are given under Enlargements {q.v.), and a table of same in the Appendix to save any calculation. Actinic Focus. As has been stated under chromatic aberration the actinic focus is not actually coincident with the visual focus, unless the lens be rendered achromatic. (See also Testing Lenses.) Depth of Focus is the power of defining upon a plane surface, with sufficient definition to satisfy the requirements of artistic ideas, the images of objects situated at varying distances. Theoretically this is an impossibility, but practicality when any point is focussed sharply there is a certain distance before and behind that point which is also sharp. To find this distance the 202 DICTIONARY OF PHOTOGRAPHY. [Foe following rule may be used. The use of diaphragms increases it ; the smaller the aperture the greater the depth of focus. Having focussed any point, to find the distance in front of that point which will be in focus (all measurements to be in inches, and the distance of object to be measured from the optical centre of lens) — (i) Multiply the focal length by the diameter of the stop, and the result by the difference between the focal length and the distance of the object. (2) Multiply the focal length by the diameter of the stop, and add T £ 7 part of the distance of the object. (3) Divide the first product by the last, add the focal length, and subtract the result from the distance of the object, when the result will be the distance sought for in front in inches. To find the depth of focus behind a given point— (1) Multiply the focal length by the diameter of the stop, and the result by the difference between the focal length and the distance of the object. (2) Multiply the focal length by the diameter of the stop, and subtract r J 5 part of the distance of the object. (3) Divide the first product by the last, add the focal length, and deduct the distance of the object ; the result is the distance behind in inches. Example : — Find the depth of focus when focussing an object 15 ft. distant with a lens of 7-in. focus, working at //5- //5 = If in. 15 ft. = 180 in. 7 x [{ = 180 - 7 = 173. 49 X H77 5 5 7 x !! = -¥• 49 180^42 9^58 5 100 5 5 s 8477 . 58 8477 . ^-5 = 58 =I46 ' 146 + 7 = 153 180 - 153 = 27 in. (3). The depth of focus in front = 27 in. Example : — To find the depth behind. 7x1$ = -^ 1 80 - 7 = 1 73. 203 Foe] DICTIONARY OF PHOTOGRAPHY. 7 x i = -V-. 49 _ i8o = 49 _ 9 = 4o 5 100 5 5 5 8477^ 40 = 8477 = 2IQ 5 ' 5 4o 210 + 7 = 217 217-180 = 37. The depth of focus behind = 37 in. Focussing Glass, or Compound Focusser. A small telescopic magnifying eye-piece, used to obtain microscopic sharpness of focus upon the ground-glass, and it should be invariably used by every amateur, especially those who desire to enlarge the result- ing negatives. Focussing Screen. The ground-glass upon which the image formed by the lens is seen. The best glass to use for this purpose is patent obscured plate, obtained by grinding patent plate with very fine emery. To make a screen of ground-glass coarse emery powder should be made into a paste with water, and lightly rubbed over a piece of glass, using a small painters' muller, or any other convenient flat surface for grinding, till the surface begins to show signs of abrasion, when the coarse emery should be completely washed off, and the finest emery obtainable used till the glass is obscured enough. Two pieces of glass can be ground at the same time by fixing a small cork, or anything that will serve as a handle, on to one piece of glass, with a piece of cobbler's wax or pitch, and using the one to grind the other. Should the focussing screen be accidentally broken, a piece of plain glass daubed over with putty, or coated with a paste of flour and water, or at a pinch a fine cambric handkerchief, may be used. The following solution spread on glass has been sug- gested as a substitute for the ground-glass : — White wax 120 grs. or 7 grms. Ether 1 ozs. „ 28 c.cm. Or the following matt varnish : — Sandarac ... ... ... 18 grs. or 1 grm. Mastic 4 „ „ -3 „ Ether 200 mins. „ 12 c.cm. Benzole 80 to 100 „ 5 to 6 c.cm. 204 DICTIONARY OF PHOTOGRAPHY. [Fog The more benzole the finer the matt surface obtained. Or an ordinary negative varnish, containing one per. cent, of tartaric acid ; or a very good substitute may be obtained by soaking Gelatine or glue 60 grs. or 4 grms. In water 4 drms. ,, 14 c.cm. and adding Boiled milk ... ... ... 2 drms. or 7 c.cm. melting by the aid of a gentle heat, and flowing over the glass. Aids to Focnssi?ig. Oiling the screen renders the grain of the glass but very little perceptible. Or a better expedient still for use with the compound focusser is a microscopic covering glass cemented to the ground surface of the screen with a drop of Canada balsam ; a small cross should be marked in lead pencil on the ground surface before doing this or else, through the ready accommodation of the focus of the eye, this plan will prove a hindrance rather than a help. Both the cross and image should be in focus together. Fog is one of the commonest of all faults with gelatine nega- tives, and is seen as a veil over the whole negative, and is a deposit of silver upon the shadows more or less dense according to the greatness or slightness of the fog. There are two great divisions of fog — chemical and light fog. The former is caused by errors in the manipulation of the plate manufacture, or in development ; the second by the impact of light, as through some crevice in the camera or dark slide, or through over- exposure. Chemical Fog, from errors in manufacture, may be traced to several causes, the chief being an abnormal excess of silver nitrate in the emulsion, and also by decomposed gelatine, caused by too long stewing, when the emulsion is made by the boiling process. If the fog is very bad, there is no cure for it, but when slight the emulsion may be squeezed through coarse canvas or muslin, as described under Emulsions (c/.v.), into a solution of bichromate of potash, ten grains to the ounce, and allowing it to stand for one hour, then washing for two hours in running water, or the addition of a few grains of cupric chloride or auric chloride 205 For] DICTIONARY OF PHOTOGRAPHY. will generally effect a cure. Chemical fog is often seen as iridescent green stains near the edges of plates, and is likely to make its appearance with an ammonia developer ; it is less likely to ensue with the fixed alkalies, potash and soda, and rarely with ferrous oxalate. The obvious remedy for this evil, with a brand of plate known to be liable to green fog, is the use of potash and soda or ferrous oxalate ; but where it does exist it can be eliminated by treating the plate after fixing and washing with Ferric chloride ... ... 50 grs. or 3.2 grms. Potassium bromide ... ... 30 ,, ,, 1*9 grm. Distilled water 4 ozs. „ 118 c.cm. Soak the plate in this for a minute or two, when it will be found that the fog will disappear, and the plate be reduced in density ; rinse well, and then apply a ferrous-oxalate developer, when the required density can be obtained ; the plate should be then refixed and washed. Light Fog makes its appearance generally all over the plate, and, as has been stated above, may be due to three causes. When the fault is supposed to lie in the camera (and the reason to suspect this is to find the edges of plate covered by rabbet of slide free from fog), cap the lens, remove the focussing screen, cover the head with the focussing cloth, and carefully examine the interior of camera to see if any stray thread of light is admitted. The plate may be fogged in the dark slide, and the effect will be seen on development by certain streaks and bands of fog making their appearance, a very usual place being at the leather hinge which allows the shutter of this slide to be folded back, and this fog seems to be not only due to light, but in many cases is actually induced by the material or something used in making the hinge. It may also make its appearance at the side where the manufacturer places the small slips of card- board to separate the plates, and in this case it is due to some impurity in the paper used. Stray actinic light or an imperfect non-actinic light in the dark-room may also cause general fog, and if this be suspected the light should be tested as described under Dark-Room. Formic Acid. (Ger., Ameisensaure ; Fr., Acide Formique). 206 DICTIONARY OF PHOTOGRAPHY. [Fri HCH0 2 =46. An acid liquid prepared by oxidation from starch, but was originally obtained from ants, whence its name. This has been recommended as preservative of pyro, and the writer has found that half an ounce of dilute formic acid will preserve i oz. of pyrogallol even when exposed to light and air for over two months, but when mixed with the accelerator the developer turns thick and muddy quicker than plain pyro. Frilling. By this is meant the gelatine leaving the plates in folds or wrinkles. It usually begins at the edges, and occurs chiefly when fixing, but often during development or washing. The causes are numerous, but as most of these are but slightly under the control of the operator they will only be enumerated, and the possible cures given at length. The chief cause is the use of a gelatine of ;too horny a nature, and possessing but little tenacity. Again, long-continued boiling of an emulsion especially tends to this evil ; an improperly washed plate, unequal drying, and excessive slowness of the emulsion in setting, due to the use of a soft gelatine or the heat of the weather, or by allowing too forcible a stream of water to impinge upon the edge of a plate, or the use of an exceeding strong developer, or the differing temperatures and densities between the developing, fixing, and washing fluids. The remedy for some causes are obvious ; but with the ordinary run of amateurs, who are not plate-makers, when a batch of plates purchased is found to be subject to frilling, they should, if possible, be kept for two or three months, when the fault will be nearly, if not completely, eradicated ; but where this remedy is impracticable, or, by reason of the number of the plates being but small is hardly desirable, the following immediate steps may be taken. The plate, before development, may be coated with collodion made as follows : — Pyroxyline ... ... ... 6 grs. or -4 grms. Alcohol (-820) A oz. ,, 12-5 c.cm. Ether (735) i » » ^ S „ Castor oil ... 4 drops ,, 3 ,, When this is used, the plate, after being collodionised, must be well washed with clean water till it no longer repels water from the surface of the film. When the plate is collodionised, it is advisable to add about 10 per cent, of methylated alcohol to 207 Gal] DICTIONARY OF PHOTOGRAPHY. developer. Soaking the plates in the following for five minutes is an absolute cure, but it prolongs development : — Chrome alum 2 grs. or -2 grm. Dissolved in Water ... ... 1 oz. or 25 c.cm. Add Methylated spirit 1 oz. or 25 c.cm. But the author has found the following an unfailing remedy, and by its use development is not so much prolonged : — Have by the side of the developing or fixing bath a dish of methylated spirit, and if the slightest sign of frilling or blisters, which are but localised frilling, makes its appearance, immerse the plate immediately in the spirit till the frill disappears, then proceed with development or fixing. Some plates frill at the edges only ; for these an edging of grease or india-rubber solution is the remedy. When plates are found to frill in the fixing, but not in developing, an intermediate soak in the chrome alum Clearing Bath (q.v.) will prevent it. Fuming. The process of subjecting silver albumenised paper to the vapour of ammonia. It is claimed for this that it renders the prints more brilliant, that the paper prints quicker, and that it makes the tones of the finished print purple, without much trouble. Many elaborate boxes have been designed for this purpose, but the simplest and a really efficient plan is to use an old cardboard plate box, and, having cut the paper to the required size, pin it by the four corners face downwards to the lid, and on the bottom inside sprinkle a few drops — about ten or fifteen — of liquor ammonia -88o, put on the lid, anpl leave it for ten minutes in hot and fifteen in cold weather. Paper when once fumed should be used within two or three days, or the good effect will be lost. Fumed paper is more liable to discolour than ordinary. The after-operations of washing, toning, and fixing are precisely the same as usual. Gallic Acid (Ger., Gallussaure ; Fr., Acide gallique ; Ital., Acido gallico). HC 7 H 5 0 5 == 170. Obtained by fermentation from powdered galls. Solubility 1 per cent, in cold, 33 per cent. . 208 DICTIONARY OF PHOTOGRAPHY. [Gel in boiling water, very soluble in alcohol, less so in ether. It was used fordevelopingin the collodion and waxed paper processes, and has been also suggested for developing gelatino-chloride paper. Gallon. See Weights and Measures. Gamboge, or Camboge (Ger. Gummigutti ; Fr. Gomme Gutte ; Ital. Gomma Gutta). An orange-coloured gum resin, from the Garcinia Morella, a native of Siam and Cochin China. The finest is that called " Pipe Gamboge," which is collected in bamboo canes. The inferior is called cake gamboge. It is almost entirely soluble in alcohol, and when rubbed down with water forms a thick emulsion of a brilliant yellow colour. It has but little taste, and no smell. It is used but rarely in photography, being sometimes the colouring matter of varnishes and lacquers. The action upon human beings when taken internally is that of a most drastic and hydragogue cathartic. Gelatine. An animal substance obtained by boiling bones, hoofs, horns, and other animal substances. It contains about 15 to 20 per cent, of water at ordinary temperatures, and in cold water swells up and absorbs from five to ten times its weight. Good samples will absorb sufficient water to dissolve them when the temperature is raised above 90 0 F., the solution setting again to a jelly on cooling. The continued application of heat for some time destroys this setting powder, a new compound called metagelatine being formed. Gelatine will keep indefinitely in the dry state, but in the presence of water it soon putrefies, turning first acid, and then alkaline, and at this stage ammoniacal vapours are given off. Alum, alcohol, carbolic, salicylic, and boracic acids, thymol, and the salts of zinc act as antiseptics. Acetic, hydrochloric, sulphuric, and oxalic acids dissolve gelatine even in the cold — acetic acid the most readily. Carbolic acid and alcohol precipitate it from aqueous solutions when they are in excess. Silver nitrate exposed to sunlight in contact with gelatine produces a red colour, due to a compound of gelatine and suboxide of silver. The alkaline dichromates in solution of gelatine render the latter after exposure to light insoluble and incapable of absorbing water, this action being the basis of the carbon and nearly every photo-mechanical printing process. Chrome alum and tannin render it insoluble, but capable of absorbing water. Ordinary alum raises the melting point, but 209 p Gel] DICTIONARY OF PHOTOGRAPHY. does not render it insoluble. The composition of gelatine varies with the source from which it is obtained, but the following may be taken as the percentage composition : — Carbon 50*1 Hydrogen ... ... ... ... ... 6-6 Nitrogen 18-3 Oxygen 25-0 Sulphur o-i2 The selection of a gelatine suitable for emulsion making is a most important point, but the following leading characteristics of a suitable kind may be of service to the amateur plate manu- facturer : — The weight of the ash left after incineration should never exceed 2 per cent., proving the absence of earthy or mineral matter. The amount of water it will absorb should in no case exceed ten times nor be less than five times its weight. For emulsion making by the boiling process it should give an acid reaction, and its solubility should not be affected at a lower temperature than 70° F., nor higher than no° F. Another most important test is its expansive power, for upon this depends to a great extent its frilling or non-frilling properties. The following table of the chief characteristics of the best com- mercial brands will be of practical use ; but it may be stated that the best film can, as a rule, be obtained by a mixture of one part of hard and two parts of soft gelatine : — Water Ash. Absorbed. Name. Charac- Per Times in ter. Cent. Weight. Coignet's gold label hard I .. n 2. ,, special... >) I 3- Nelson's No. 1 pho- tographic soft 2 .. 6 4- Nelson's opaque ... hard 2 5- ,, amber ... soft I ... 4f 6. Swinborne No. 2 isinglass >» • .. ' I .. 6i 7. Russian isinglass a 8. Simeon's Swiss ... hard I .. 8| 9- Heinrich's ... I ... 8| Nos. 1, 3, 8, and 9 are the best to use, 210 DICTIONARY OF PHOTOGRAPHY. [Gel It is always better to make a small batch of emulsion first, with a sample of gelatine, to test its suitability, rather than have a large batch spoilt by finding the gelatine used totally unsuitable. Gelatine has a great affinity for bromine, chlorine, and iodine, and upon this fact depends to a great extent their increased sensitiveness over collodion plates. Gelatino-Chloride Emulsion Paper. This is an outcome of collodio-chloride emulsion paper, which was known in England as Simpson-type ; just as gelatine took the place of collodion for plates, so gelatine replaced the collodion for this purpose, J. B. Obernetter, of Munich, being the first, we believe, to make the gelatino-chloride emulsion paper. The following formulae will be found all that can be desired for making the same : — No. I. Gelatine ... ... ... 230 grs. or 15 grms. Distilled water ... ... 6 drms. ,, 22 c.cm. Soak for an hour and dissolve by the aid of a gentle heat, and add Nitrate of silver 6 grs. or 4 grms. To this mixture add gradually Lithium chloride ... ... 1 gr. or *o6 grm. Tartaric acid ... 1 ,, „ 06 „ Distilled water 1 drm. ,, 3 c.cm. No. II. Nelson's soft gelatine Heinrich's hard gelatine ... Ammonium chloride Distilled water 139 grs. or 9 grms. 293 - m 19 h 54o tt „ 35 » 100 drms. ,, 360 c.cm. Allow to soak for half an hour, and dissolve by the aid of a water bath, and add gradually, almost drop by drop, with constant stirring, the following at about 90 0 F. : — Nitrate of silver 154 grs. or 10 grms. Distilled water 336 mins. ,, 20 c.cm. Gel] DICTIONARY OF PHOTOGRAPHY. Allow the emulsion to set hard, press through canvas, wash in four changes of water five minutes each, and drain well. Now prepare the following : — Soak for half an hour and dissolve, and add the following at a temperature of 90 0 F., with constant stirring : — Sodium citrate (neutral) ... 30 grs. or 2 grms. Distilled water ... ... 170 mins. ,, 10 c.cm. Dissolve Nitrate of silver ... ... 46 grs. or 3 grms. Citric acid 77 „ „ 5 „ Distilled water ... ... 170 mins. ,, 10 c.cm. Add to the citrate and gelatine very gradually, constantly stirring, set quickly and wash in five changes of water five minutes each, drain well, and add to the chloride emulsion as above, and add Citric acid ... ... ... 15 grs. or 1 grm. Distilled water 119 mins. ,, 7 c.cm. Allow the emulsion to stand in a fluid state for one hour, occasionally stirring. Keep for three days, and then coat the paper. Mr. W. K. Burton gives the following. Two separate emulsions are made as in the last case : — Heinrich's gelatine ... Distilled water 100 grs. or 6*5 grms. 150 mins. ,, 9 c.cm. No III. A. Ammonium chloride Gelatine Distilled water 53 grs. or 3-5 grms. 420 „ „ 63 „ 30 ozs. ,, 500 c.cm. 212 DICTIONARY OF PHOTOGRAPHY. [Gel Allow to soak for an hour, and dissolve by the aid of a water bath ; then add Nitrate of silver ... ... 150 grs. or 10 grms. Distilled water ... ... ^ oz. 12 c.cm. B. .Sodium citrate 30 grs. or 2 grms. Gelatine ... ... ... 100 6*5 Distilled water ... ... 3^ ozs. „ 100 c.cm. Soak for an hour, dissolve by heat, and add Nitrate of silver 45 grs. or 3 grms. Citric acid 80 ,, ,, 5 ,, Distilled water ... ... ^ oz. „ 14 c.cm. Mix both emulsions. Allow to set, and wash as directed for No. II. emulsion. The same authority also suggests the following formulae and method of mixing the same : — Formula No. 1. A. Nitrate of silver ... ... ... ... 400 grs. Water 4 ozs. B. Gelatine, soft ... ... 80 grs. Chloride of ammonium ... ... ... 80 ,, Citric acid ... ... ... 120 ,, Water ... ... ... 8 ozs. Formula No. 2. A. Nitrate of silver 400 grs. Water 4 ozs. B. Gelatine (soft) ... ... ... ... 80 grs. Chloride of ammonium ... ... ... 80 ,, Citric acid ... ... ... 120 ,, Carbonate of soda (dry) 45 ,, Water ... 8 ozs. Gel] DICTIONARY OF PHOTOGRAPHY. Formula No. 3. A. Nitrate of silver ... ... ... ... 400 grs. Water ... ... ... 4 ozs. B. Gelatine (soft) 80 grs. Chloride of ammonium 80 „ Citric acid ... ... ... ... ... 60 ,, Carbonate of soda (dry) ... ... ... 80 ,, Water 8 ozs. The first formula gives an emulsion suitable for preparing paper to be used for printing from dense negatives, the second from medium negatives, and the third from thin negatives. The third formula is, I am afraid, dreadfully unorthodox, for Mr. Burton says : " There is just about enough of ammonium chloride and of sodium citrate formed by the double decomposition of the citric acid, and of part of the soda to decompose the whole of the nitrate of silver. The formula works all right, and the paper that results from the use of it keeps very fairly. The paper resulting from either of the other formula will probably keep as long as any sensitised paper. The following is the method of emulsify- ing. The two solutions are heated to a temperature of 1 io° to 120 0 F. The temperature should not be greater than 120 0 , or there is a great chance that some of the insoluble silver salts produced will be thrown down in the granular orm. A is then added slowly to B with much stirring. The emulsion is filtered through a double thickness of cambric, and is then immediately ready for use. If it is wished to keep the emulsion for any length of time, 10 per cent, of alcohol, in each ounce of which a few grains of thymol have been dissolved, should be added to the emulsion. It is to be observed, however, that, even with this addition, emulsion by formula No. 3 will not keep for very long.'' Mr. Burton recommends floating the paper for three or four minutes to coat it, or by brushing the emulsion over the paper, allowing it to get surface dry and repeating the operation. The temperature of coating room should be 70 0 F. The above quantity of emulsion will coat eight sheets 22 by 17, or ten or twelve by floating. Either gold or platinum may be used for toning, but the prints should be well washed first. The best method of coating the paper is a question of quantity : in small quantity the 214 DICTIONARY OF PHOTOGRAPHY. [Gel paper should be wetted thoroughly in warm water, and squeegeed to a sheet of glass, and the emulsion poured on it ; with larger quantities the sheets should be drawn over the surface of the fluid emulsion. The majority of operators will no doubt prefer to buy their paper ready made, and the following may be considered as the necessary manipulations for producing perfect prints, although this paper undoubtedly gives its best results when used'for rather thin negatives or those wanting in contrasts. The paper, cut to the required size, is placed in contact with the film side of the negative in the ordinary printing frame, and placed in a good printing light. Where the negative is exception- ally thin the frame should be placed in a weak light with opal or green glass over it, where the contrasts are greater use a stronger light ; examine the print during the operation of printing in a very subdued light, and great care must be exercised that the paper does not shift whilst thus examining it, as it is very likely to do from its highly polished surface. As a preventative a pad of felt, or two or three thicknesses of stout blotting paper should be used. On the depth of printing depends to a great extent the tone of the resulting print ; it is our practice when using this paper to carry the printing sufficiently far, so as to give the very highest lights a decided tinge, and, if black tones are required, till the highest lights are deeply coloured. After printing, the pictures should be carefully preserved from damp and light, and thus may be, if necessary, kept till some considerable number are collected, as they deteriorate but little by being kept a week or even longer. For toning, numerous baths have been suggested to give various tones ; most operators get into a particular groove of working special photographic papers, and from some consider- able experience I can recommend the following method of pro- cedure as conducive to good results. The first consideration is the negative ; every negative is not suitable for this paper, though every negative will give a print on it. Those negatives which have very weak shadows and dense high lights give unsatisfactory results because there is a tendency in the paper to give an increased contrast, and for this very reason it is excep- tionally valuable for weak or somewhat thin negatives. For veritable ghosts, then, we can use green or yellow glass in front of the negative, or tissue paper or opal, so as to reduce the light, and print in weak diffused light. For stronger" negatives we can, 215 Gel] DICTIONARY OF PHOTOGRAPHY. of course, print in stronger light. The question how far to carry printing is an important one and a good deal depends upon the toning bath that is used. Practically it may be said that the paper should be exposed till there is a decided tinge on the high lights. Chloride paper may be kept some weeks before toning if actually required, but it is not advisable to keep it too long, or the whites suffer and it is more difficult to tone. We must now enter slightly into the chemical composition of gelatino-chloride emul- sions. All commercial papers, we believe, contain chloride of silver, with some organic salt, usually citrate of silver, with free nitrate of silver, and frequently citric acid. The nitrate and citrate are soluble in water, and cause the milkiness which is apparent when chloride prints are placed in water. These should be got rid of before toning or else they contaminate the toning bath, and in the case of the alkaline baths, such as the acetate or borax, the prints must be free from any acid, or else the bath becomes acid, and tones but slowly or not at all. If the sulpho- cyanide bath be used, free silver salts mean the formation of silver sulphocyanide, the bath will not keep, and toning is rendered more difficult. In the case of the combined bath we have hypo ; and to place a print containing acid in this means decomposition of the hypo and sulphurisation and degradation of the whites. As soon as sufficient prints are obtained, for it is not worth while toning one or two, make a solution of salt, ordinary household salt, 2 oz. to the pint of warm water. When dissolved and cool, place the prints in the solution and keep them on the move for ten minutes, pour away the salt, and wash for ten minutes in plain water. The use of salt renders toning some- what slower, more even, and obviates any free soluble silver salt. If the prints are washed in water first, the salt being omitted, it is necessary to change the waters very quickly, or yellowed whites will be the result, from the silver combining with the paper and gelatine. It is preferable to use salt or carbonate of soda, the latter in the proportion of 1 oz. to the pint — I prefer the salt. Now with regard to the toning bath. When matt- surface papers were introduced, I started a series of experiments, using one print of matt and one of glossy paper, and tried the usual baths, acetate, borax, phosphate, carbonate, and sulpho- cyanide, and found that with all but the last there was a tendency to pinky tones, and this was puzzling for some time, till the con- 216 DICTIONARY OF PHOTOGRAPHY. [Gel elusion was come to that it was due to the action of the gold upon very faint — too faint to be visible — impression of light upon the silver salt. This was confirmed by the curious pinkish tinge on vignettes. An instructive experiment was then made : a letter was cut out of deep ruby paper and placed in close contact with a sheet of paper, and the whole put out in the light and strips covered up every thirty seconds — the strip last covered just showed a very faint sign of light action. The print was washed and toned in strips, and in baths of different strengths, and after fixing three decided strips were visible with increasing pinkiness. This proves that the paper must be exposed as little as possible to white light, or there is an action set up which only becomes visible in gold toning. When the ordinary baths, acetate, borax, etc., were strengthened so as to have the strength of i£ grs. of gold to the 8 oz., instead of i gr., there was less chance of pinki- ness. With the matt papers as well as the glossy, no bath works so well as the plain sulphocyanide, but it is absolutely necessary to get rid of all free nitrate and acid by salt and washing, or else the action was uncertain. Plain paper with uranium and gold toning was a great favourite for black tones, but with the matt- gelatine papers black tones could not be obtained ; from this bath we were led on to the others. Now, as to the making of the bath, I always keep my gold in a slightly acid solution, and before using it requires neutralising. I strongly recommend also that all commercial gold chlorides should be neutralised because one well-known brand is very acid. The simplest way to do it is to place a little precipitated chalk or magnesium carbonate into the gold solution; »it requires very little for one grain of gold, about as much as will lie on a threepenny piece ; shake well, then add the solution to the sulphocyanide. All the sulphocyanides are deliquescent, and when bought should be immediately dissolved in distilled water and kept of a definite strength ; a convenient one is one in four. The quantity of sulphocyanide compared to the gold varies in many formulae, and may vary, provided it is more than four times the weight of the gold and less than sixty times ; sulphocyanides will dissolve gelatine when too strong. A convenient strength is gold chloride i grain, sulphocyanide 30 grains, water 8 ounces. See that your dish is clean. Mix your bath by adding the gold to the sulphocyanide gradually with shaking, not the reverse. Never mind the slight turbidity caused 217 Gel] DICTIONARY OF PHOTOGRAPHY. by the chalk or magnesia. Place your well-washed prints in the bath, not too many at a time ; this is important. Keep them moving, touching them with clean fingers at one corner only. Do not attempt to be economical of gold ; do not tone more than twelve quarter-, six half-, or three whole-plate prints with one grain of gold ; of course, the number depends a good deal on the style of the print. Finally keep your toning bath at about 65 0 F. Carry toning on till on looking through the print you see that all the red has disappeared from the heavy shadows for purple tones, and till the red has gone from the half-tones for browns. When the bath is used throw it away or put it in the residue tank ; don't use it again, and don't try and revive it by adding more gold. After toning place the prints in salt and water, and fix in an alkaline bath, and wash well in running water for from twenty to thirty minutes. Combined toning and fixing baths are a great convenience, so it is said, as by their use the number of solutions and operations requisite for making a print are reduced. I firmly believe, however, that there is far less chance of the prints being permanent when treated with such a bath by the average worker. If a combined bath is properly made and properly used there is no reason why it should not yield as permanent results as any other ; but, as ordinarily used, these baths are fatal to permanency. Hyposulphite of soda is decomposed by acid and alum, and sulphurous acid and free sulphur are set free and sulphur toning caused. Although I give many formulae of combined baths, the only one which I should use myself would be No. IX. For those who must use alum and lead salts the following may be adopted : — Water ... ... ... ... ... 500 parts. Hyposulphite of soda ... ... ... 200 „ Ammonium sulphocyanide ... ... 25 ,, Nitrate of lead 10 ,, Alum 20 ,, Dissolve the hypo in the water first, add the sulphocyanide, then dissolve the alum in a little water, and add to the hypo, with constant shaking. Then add the lead nitrate in the same way, that is, dissolved in water, heat the whole to 50 0 C. for ten minutes, allow to cool and filter, and to every 100 parts of this 218 DICTIONARY OF PHOTOGRAPHY. [Gel concentrated bath add 100 parts of water, and 7 to 8 parts of a 1 per cent, solution of gold. t. Liesegang's Baths. Solution A. Chloride of gold 2 grs. or • 12 grm. Distilled water 2 ozs. „ 560 c.cm. Solution B. Ammonium sulphocyanide 30 grs. or 2 grms. Hyposulphite of soda ... 1 gr. 06 grm. Distilled water 3 ozs. „ 84 c.cm. Mix for use by pouring 1 part of A into an equal quantity of B (never reverse this order). This gives a purplish tone. II. The Phosphate Bath. Solution A. Ammonium sulphocyanide 1 oz. or 30 grms. Sodium phosphate ... ... 1 ,, 30 ,, Distilled water ... ... 25 ozs. M 700 c.cm. Solution B. Chloride of gold ... ... 15 grs. or 1 grm. Bistilled water ... ... 3 ozs. ,, 84 c.cm. Mix for use by pouring 1 part of B into 10 parts of A. This bath gives bluish-black tones. III. Solution A. Chloride of gold 15 grs. or 1 grm. Distilled water 60 ozs. ,, 1,700 c.cm. 219 Gel] DICTIONARY OF PHOTOGRAPHY. Solution B. Ammonium sulphocyanide I oz. or 30 grms. Alum 1 ,, „ 30 ,, Ammonium carbonate ... 4 grs. „ "25 grm. Distilled water ... ... 23 ozs. 500 c.cm. For use, pour 3 parts of A into 4 parts of B, with deep printing. This bath gives deep black tones. For rich chestnut brown with no trace of blue, dilute the mixed bath with three times the quantity of water. IV. A New Combined Toning and Fixing Bath. Dr. Liesegang recommends the following in the International Annual, 1889: — Solution A. Chloride of gold ... ... 15 grs. or 1 grm. Distilled water ... ... 3 ozs. ,, 84 c.cm. Solution B. Ammonium sulphocyanide 60 grs. or 4 grms. Common salt ... ... 240 ,, ,, 16 Alum 120 ,, ,, 8 ,, Hyposulphite of soda ... 2 ozs. 62 ,, Distilled water ... ... 12 ,, ,, 350 c.cm. Allow Solution B to stand for at least eight days and then filter. To make 9 The Toning Bath, Pour Solution A ... ... ... ... 7 parts Into „ B 60 „ and add 40 parts of old used combined toning and fixing bath. This bath gives the prints in ten minutes a red colour, in fifteen minutes it tones to a splendid brown, and in twenty minutes to a brownish violet. The bath acts quicker if the prints are taken out after five minutes and laid on a clean glass slab. As soon 220 DICTIONARY OF PHOTOGRAPHY. [Gel as the desired tone is reached place them in a salt and water bath. V. Obernetter's Baths. Solution A. Chloride of gold 15 grs. or 1 grm. Distilled water 3 ozs. ,, 84 c.cm. Solution B. Phosphate of Soda 12 drms. or 43 grms. Distilled water 30 ozs. „ 840 c.cm. Solution C. Ammonium sulphocyanide 10 drms. or 32 grms. Distilled water ... ... 30 ozs. ,, 840 c.cm. For use mix 10 parts of B with 10 parts of C, and add 1 part of A. This gives warm purplish tones. VI. Solution A. Chloride of gold 15 grs. or 1 grm. Distilled water 4 ozs. 112 c.cm. Solution B. Ammonium sulphocyanide 5 drms. or 20 grms. Distilled water ... ... 32 ozs. 1 litre. For use, pour A into B, and allow to stand for twelve hours. This gives warm brown tones. The addition of 10 to 15 grs. of hyposulphite of soda will give cold tones. VII. Solution A. Chloride of gold 15 grs. or 1 grm. Distilled water ... ... 3 oxs. „ 84 c.cm. 221 Gel] DICTIONARY OF PHOTOGRAPHY. Solution B. Acetate of soda I oz. or 31 grms. Distilled water ... ... 25 ozs. „ 738 c. cm. Solution A 2 „ ,, 56 ,, Solution C. Ammonium sulphocyanide 2 drms. or 7 grms. Distilled water 10 ozs. „ 250 c.cm. Solution A ... ... ... 1 oz. 25 „ For use add 3 parts of Solution C to 10 parts Solution B. This gives fine brown or black tones. Reddish brown tones maybe obtained by adding to Solution C 10 to 15 grs. hypo- sulphite of soda. VIII. The following is a toning bath which Mr. Bruce, of Duns, a famous collodio-chloride printer, recommended : — Solution A. Ammonium sulphocyanide 10 drms. or 40 grms. Hyposulphite of soda ... 9 grs. ,, -6 grm. Distilled water ... ... 60 ozs. „ 1,300 c.cm. Solution B. Chloride of gold 22 grs. or 1.5 grm. Distilled water ... ... 60 ozs. 1,300 c.cm. Add one part of B to an equal quantity of A, and add a good-sized pinch of common chalk, and allow to stand for twenty-four hours. IX. The following is suggested by Mr. Tylar : — Chloride of gold 6 grs. or -4 grm. Tungstate of soda 60 ,, ,, 4 grms. Ammonium sulphocyanide 100 ,, ,, 6-5 . ,, Hyposulphite of soda ... 960 „ ,, 62 Distilled water, to make ... 8 ozs. ,, 200 c.cm. Dissolve the salts in half the water made hot, and make the solution measure 8 ozs. by adding more water. Then add the gold. 222 DICTIONARY OF PHOTOGRAPHY. [Gel X. The following is a simple bath suggested by Mr. W. K. Burton, although the addition of nitrate of lead is due to Mr. J. Chester Jervis : — Chloride of gold 6 grs. or -4 grm. Nitrate of lead 3 ,, *2 ,, Hyposulphite of soda ... 3 ozs. „ 93 grms. Distilled water ... ... 20 ,, 500 c.cm. Put the prints direct into the toning bath without washing. Chloride prints may be easily developed, and by this a great saving of time is effected. The first method of doing this was by means of gallic acid developers, such a developer being Gallic acid ... 4 parts. Citric acid ... 6 ,, Sodium acetate 20 ,, Solution of lead nitrate (10 per cent.) ...15-20 „ Distilled water ... ... 1000 „ Warnerke suggested the use of about two feet of magnesium ribbon burnt quite close to the printing frame, by which a very faint image was rendered visible, and it was then developed to full intensity with Water ... ... ... 1000 parts. Acetic acid ... ... 10 ,, Sodium acetate ... ... 10 „ Gallic acid ... ... ... ... ... 5 ,, When dissolved add Solution of lead acetate (10 per cent.) ... 10 parts. The above solution should be diluted with from 5 to 10 parts of water, and the print, without washing, being placed in this soon gains in intensity, and the development is stopped by placing the print in salt and water, when it should be thoroughly well washed and toned in the following bath : — Water ... ... ... ... ... 1000 parts. Hyposulphite of soda ... ... ... 100 ,, Acetate of lead 10 Solution of chloride of gold (1 per cent.)... 20 ,, 223 Gel] DICTIONARY OF PHOTOGRAPHY. Valenta suggested the use of acid hydroquinone and pyrogallol developers. Hydroquinone Developer. A. Hydroquinone 10 parts. Alcohol ioo „ B. Sodium sulphite ... ... ... ... ioo parts. Distilled water ... ... ... ... 500 Citric acid 5 For use, 50 parts of Solution A should be mixed with 50 parts of Solution B, and 1000 parts of water added. Pyrogallol Developer. Distilled water 1000 parts. Sodium sulphite ... ... ... ... 100 „ Pyrogallol 10 ,, Citric acid 11 ,, The ingredients should be dissolved in the water in the above, and the clear and almost colourless solution used immediately. The hydroquinone developer works clear and slowly ; the violet tone of the printed-out image turns in developing into a yellowish- brown. The prints were toned and fixed in the combined toning and fixing bath composed as follows : — Distilled water 500 parts. Hyposulphite of soda ... ... ... 200 „ Sulphocyanide of ammonia ... ... 25 ,, Alum 30 „ Acetate of lead solution (1 : 10) 40 ,, This solution is to be heated on a water bath to about 6o° C, by which a quick deposition of the precipitate formed is obtained. It should then be filtered, and 100 parts of it mixed with 50 parts of water and 10 parts of 1 per cent, solution of choride of gold. In this combined bath the yellowish-brown developed prints assume a yellow tone, which very soon turns into brownish-red, and into a beautiful deep, purple brown. The toning process should be stopped when the prints have assumed the desired tone, and it should be noted that after washing the tone is rather deeper. Liesegang specially recommends the following for his own paper, but for others it is not suitable : — 224 DICTIONARY OF PHOTOGRAPHY. [Gel A. Pyrogallol Developer. Solution of pyro (7 per cent.) 2 parts. „ „ sodium acetate (20 per cent.) 6 Distilled water 60 „ B. Paramidophenol Developer. Solution of paramidophenol (7 per cent.) 2 parts. if sodium acetate (20 per cent.) 10 „ Citric acid ... ... ... ... 1 Distilled water ... ... 50 „ The greatest advance in this process was made by Mr. Wilson, of the Paget Prize Plate Co., when he suggested the use of a solution of potassium bromide prior to development. The follow- ing is the precise method of working this modification of the process : — The paper should be exposed in the printing frame in the ordinary way, but the insolation is only continued till there is quite a faint image. It is advisable not to print too far, and as a good guide we may suggest that the details should just be visible in the half-tones. After printing, the paper should be taken from the frame, and placed without washing into a 10 per cent, solution of potassium bromide. The action of this bath is to convert the soluble silver salts into silver bromide, and if allowed to act for some time, there is no doubt it would also replace the chlorine in the silver salt forming the image. The time of immersion in the bromide solution is not very material, and we prefer to leave it for fifteen minutes. Great care must be taken that no bubbles adhere to the paper, or else spots will appear in the development. After being in the bromising solu- tion the prints must be washed well for five or ten minutes in running water ; if the washing is not pretty complete and thorough, so much bromide is left in the paper that development is enor- mously protracted, and there is a tendency to stain. The original developer recommended was — I. Hydroquinone h oz. Sulphurous acid 1 4 M Sodium sulphite 1 t II Potassium bromide... 6o grs. Water, to ... 25 „ 225 Q Gel] DICTIONARY OF PHOTOGRAPHY. II. Caustic soda ... ... ... £ oz. Sodium sulphite ... ... ^ ,, Water, to 25 ozs. III. Ammonium bromide ... 1 oz. ,, carbonate ... ... ,,. 1 ,, Distilled water, to ... ... ... ... 25 ozs. Mix in equal parts. The following simpler developer is now suggested : — I. Hydroquinone ... ... ... ... 1 oz. Sodium sulphite ... ... ... ... 1 ,, Sulphurous acid ... ... ... ... ^ ,, Water, to 40 ozs. II. Potassium bromide ... ... ... ... i\ ozs. Liq. ammonia (8-8o) ... ... ... 180 m. or Sodium carbonate ... ... ... ... 2 ozs. Water, to 40 ,, For use, mix one part of each, and add one part of water. For average negatives, use one part No. I., one part No. II., one part water. Whatever variations are made, make up always to bulk three parts, by adding or omitting water. If required to work slower, use less No. II., or make up the stock solution with less ammonia. If harder effect (more contrast) be desired, use less No. I. ; if softer results (less contrast), use more. It may happen that we find that the print when finished is too dark, and has been over-printed. The question is how to reduce it. It is questionable whether it is worth the trouble, whether it is not almost as easy to make a fresh print altogether. The old ferrid- cyanide and hypo reducer has been suggested for gelatino-chloride prints ; and reduce them it will, so energetically, even, in weak solutions that its action is uncontrollable. Whilst talking of this reducer it may not — in fact it does not seem to — be generally 226 DICTIONARY OF PHOTOGRAPHY. [Gla known that it will totally remove even a gold-toned image, and as the image disappears entirely it must be assumed that the gold is also dissolved. Haddon suggested a mixture of sulphocyanide and ferridcyanide, and this certainly acts more slowly and evenly, but the sulphocyanide makes the gelatine very soft. Valenta suggests, however, a mixture of hypo and uranium nitrate, and states that it gives very good results. He suggests a cold satu- rated solution of hypo diluted with four times the quantity of water, and to every 100 parts of this liquid one part of a 10 per cent, solution of uranium nitrate is added. This acts very evenly and slowly, and gives excellent results, as we can testify. Valenta states that prints treated with Thiosinamin 5 parts Water 100 ,, Solution of uranium nitrate (10 per cent) 5-10 assume a brilliant red tone, which gives place in toning to a rich sepia. All chloride papers can be toned with platinum, by ob- serving the directions given under Platinum Toning (r/.v.). Since the introduction of matt-surface chloride papers there has not been so much need for obtaining matt surfaces on glossy papers ; but this can be done either by rubbing down the dry print with powdered pumice stone or squeegeeing to fine ground-glass or celluloid, both of which should be previously smeared with a little oil. To obtain a high glaze or polish, plate-glass, ebonite, metal plates, or wood-pulp slabs can be used, but the first gives the finest surface. Whichever material is used, it should be first rubbed with solution of wax, as used for the carbon tissue, en- caustic paste, or a little oil, and the wet print well squeegeed down to it and allowed to dry, and then stripped. For mounting such prints it is advisable to paste on the back a sheet of the waterproof backing-paper, which can be obtained commercially, whilst the print is damp, and allowing the two to dry together, and then mounting with one of the gelatine mountants, now placed on the market, or a formula for which is given under Mountant (q.v.). Glass. A transparent brittle substance, now of universal occurrence and application. Its origin is uncertain. It was known to the Egyptians 5000 to 6000 years ago. The earliest 227 Gla] DICTIONARY OF PHOTOGRAPHY. specimen known is a small tablet in the British Museum, of about 1445 B.C., of Egyptian make ; it is opaque and coloured. There is also a goblet found in Nineveh, of about 700 B.C., the earliest piece of any size. The manufacture was gradually improved, till, in Italy, 58 B.C., the theatre walls in some towns were ornamented with mirrors, and at Pompeii windows which were glazed have been found intact. About a.d. 674 the art of glass-making was introduced into England, and it is now carried on at Newcastle, Liverpool, Bristol, Birmingham, Leeds, London, Glasgow, and other places. Some of the lens glass is imported from abroad. There are many kinds of glass, but only one or two of any interest to photographers. Crown and flint are the kinds used for lenses, while for the best dry plates an inferior plate is used. Crown glass is composed of a mixture of silicates of potash (K 2 03Si0 2 ), lime (Ca 2 03Si0 2 ), and alumina (Al 2 03Si0 2 ). It has specific gravity 2-487. Flint glass is a mix- ture of silicates of potash, alum, and lead (Pb 2 02Si0 2 ). It has specific gravity 3 - 5- It is much more refractive than crown. Crystal glass is an extremely pure variety of glass, and is the one generally used for the finer lenses. Glass can be coloured by fusing metallic oxides with it. Gold and copper give red, silver or iron green, uranium yellow, cobalt blue colours. When the glass is coloured throughout it is called "pot metal." Another method of colouring is by attaching an extremely thin sheet of pot metal to white glass, when it is known as " flashed glass.'' Opal glass is made by fusing with the metal one of the oxides of tin or zinc. In the manufacture of crown, flint, and crystal glass for optical purposes extreme care is taken to make the resulting glass non- hygroscopic, or non-absorbent of water, to which some glass is particularly liable, also to obtain it absolutely free from bubbles and striae, the latter being lines due to imperfect mixing of the molten metal. (See Lens.) In 1881 Drs. Abbe and Schott instituted a series of experiments at Jena, in Germany, on the improvement of the manufacture of glass for optical purposes, and, after some successful trial smeltings, in 1884 they received a handsome subsidy from the Prussian Bureau of Education, which enabled them to commence operations on a manufacturing scale. The old optical glasses were limited to practically few varieties, which were characterised by the dispersion always being in a certain relation to the mean refractive index, so that 228 DICTIONARY OF PHOTOGRAPHY. [Gol a higher index of refraction was accompanied by a greater dis- persion, and vice versa. This limited the optician considerably in his work, and entailed a certain residuum of errors in correc- tion of chromatic and spherical aberrations, which were unavoid- able. The Jena glass, by the introduction of new elements into its composition, has been obtained, not only with all the charac- teristics of the old glass, but also with quite the opposite characters — that is to say, with high index of refraction and low dispersion, and vice versa. To enter fully into the method of manufacture, and all the theoretical considerations involved, would be beyond the scope of this work ; but the practical out- come of the introduction of these glasses has been considerable improvement in the manufacture of the old type of lenses, and many new and improved lenses, such as the Ross Concentric, the Zeiss anastigmats, and the double anastigmat of Goerz. Glucose (Ger., Glucose, Starkezitcker, Traubenzucker ; Fr., Glucose; Ital., Glucosid). Synonyms: Grape Sugar, Dextrose. C 6 H,.,0 6 =i8o. There are several kinds of glucose, which is preferably to be considered as a generic name. It occurs either in white crystals or a thick, syrupy liquid, and was used as a preservative in the collodion process, and also in some powder processes. Glycerine (Ger., Glycerin; Fr., Glycerine; Ital., Glicerina ; Lat., Glycerinuin). Synonyms: Glycerol, Propenyl Alcohol. C 3 H 8 0 3 =92, or C 3 H 5 (OH) 3 . A peculiar, sweet, viscid liquid obtained from oils and fats by saponification and subsequent purification. Specific gravity, 1-260. It is extremely hygro- scopic, and cannot be dried by heat without decomposition. Its non-drying properties are taken advantage of in photography to prevent the too rapid drying of some substances, and it is also used as a preservative of pyro. It is miscible in all proportions with water and alcohol. It has also been suggested as a re- strainer in developing, its action being purely physical in this sense. Gold (Ger., Gold; Fr., Or; Ital., Oro ; Lat., Auruni). Au. = 196-6. A yellow or yellowish-red metal soluble only in nitro- hydrochloric acid. It occurs native in conjunction with quartz and sand in various parts of the world. It is used for the pre- 229 Gol] DICTIONARY OF PHOTOGRAPHY. paration of chloride i oft gold, a convenient source being current coin, particularly Australian sovereigns and old jewellery. A sovereign should weigh when new 123^ grains, and contain 113 grains of pure gold. Gold, Chloride (Ger., Goldchlorid, Chlorgold; Fr., Chlorure d'oro; Ital, Chloruro d'oro). Synonyms: Auric Chloride, Trichloride or Perchloride of Gold. AuCl 3 =303. A yellowish- brown crystalline mass, made by dissolving gold in aqua regid. Usually commercial chloride is obtained by solution as above and the evaporation of the acid liquid, in which case bright yellow crystals of AuCl 3 HCl are obtained, from which it will be seen that one equivalent of hydrochloric acid is combined with it. Preferably the double neutral salts of gold and potassium, sodium or calcium are used. Gold, Potassio-Chloride (Ger., Chlorgoldkalium ; Fr., Chlorure double d'or et de potassium ; Ital, Chloruro doppio d'oro e di potassio). AuCl 3 KCl +3H 2 0 = 4I3. The usual method of making this is to dissolve one part of pure gold in as small a quantity of aqua regid as possible, by the aid of heat. Evaporate gently, and then add 20 parts of distilled water, in which 0-51 parts of bicarbonate of potassium has been dissolved. Carbonic acid is given off, and the resulting solution should be evaporated to dryness. Lainer of Vienna has also suggested the following method for obtaining a stable and constant salt of gold, which can easily be prepared chemically pure and free from acid, which does not deliquesce or effloresce, and gives toning baths of constant and reliable action. One hundred parts of gold are dissolved in aqua regid, and hydrochloric acid added to the solution. To the solution of pure chloride of gold thus prepared are added 38 parts of chloride of potassium. The mixture thus obtained is carefully evaporated till crystallisation, when the dish or vessel is placed under a bell jar containing concentrated sulphuric acid or quicklime. The mother liquid is poured off, and this again evaporated and treated as above. The crystals thus obtained are dried under a bell jar, and heated to 100 — no° C. to drive off the remaining traces of free hydro- chloric acid. The salt thus procured forms yellow hexagonal needles, easily soluble in water. 230 DICTIONARY OF PHOTOGRAPHY. [Gra Gold, Sodio-Chloride (Ger., Chlorgoldnatrium ; Fr., Chlorure double d'or etde sodium; Ital., Chloruro doppio d'oro e di sodio. AuCl 3 NaCl+2H.,0=397. This is usually the commercial salt, and occurs as yellowish-brown needles, which are very deliquescent, soluble in alcohol and water. It may be prepared by dissolving 5 parts by weight of gold chloride, and I part by weight of sodium chloride in as little water as possible, and allowing the solution to crystallise. Another method is to dissolve I part of gold in 10 parts of aqua regid by the aid of heat, dilute with 100 parts of water, filter through glass wool, precipitate the gold with saturated solution of sulphate of iron, and collect and wash the precipitate, which is pure gold ; add 3 parts of sodium chloride to every 1 of gold ; dissolve the mixture in aqua regid and evaporate. The following table shows the equivalent quantities of the various salts used in photography : — Gold. Gold Gold Gold Chloride. Potassio-Chloride. Sodio-Chloride. 1-5420 2-1048 2-0229 0-6485 I I-3645 I-3II9 0-475I 0*7326 I 0-961 1 o-4943 0-7623 I -0405 I The following calculation will show that home-made chloride is cheaper than commercial. An Australian sovereign contains H3grs. of pure gold, which will make 174^ grs. of pure chloride, 237-9 grs. of potassio-chloride, and 228-6 grs. of sodio-chloride, and, assuming that the latter be the commercial salt, this is equivalent to 15^ tubes. Gold, Hyposulphite (Ger., NatriumaurotJiiosulfat, Unter- schwefligsdures Goldoxydulnatron ; Fr., Hyposuljite double d'or et de sodium; Ital., ipolsolfito d'oro e di sodio). Synonyms: Sel dor, Fordos and Gelis' salt. 3Na 2 S 2 0 3 ,Au,S_X) 3 ,4H a O = io5o. This salt was originally suggested for toning daguerrotypes, and later for albumenised paper, and more recently still for gelatino- chloride paper. It may be formed by gradually adding a neutral 2 per cent, solution of chloride of gold to a 6 per cent, solu- tion of hyposulphite of soda. To obtain it in crystals, mix the solution formed above with alcohol, when the salt will crystallise out in fine white needles. Grain. See Weights and Measures. 231 Gra] DICTIONARY OF PHOTOGRAPHY. Gramme. See Weights and Measures. Green Fog. See Fog. Ground-Glass. See Focus. Gum Arabic (Ger., Gummi arabicum, Arabische Gummi ; Fr., Gomme arabique ; ltal.,Gomma arabicd). A gummy exuda- tion from the stems of various species of acacia. It is of peculiar bland taste, odourless, insoluble in alcohol and ether, but entirely- soluble in water, in which form it is used as a Mountant (q.v.). It is also used in the powder process and photo-lithography. Its adhesiveness is increased by addition of aluminium sulphate, less so by ordinary alum. It is decomposed at a temperature of 300°* and is converted into dextrine by the action of sulphuric acid. Gum Dammar. See Dammar. Gum Dragon. See Tragacanth. Gum Elemi (Ger., Oelbaumharz : Fr., Gomme elemi.) A resinous exudation from Canarium commune, imported from the Philippine Islands, and also obtained from Amyris elemifera in Central America. It is used in varnishes and encaustic paste. It is very soluble in alcohol, insoluble in water, and should have somewhat the colour and consistence of honey, but generally, from exposure to air and impurities, is more yellowish-brown. Gum Guaiacum. A resinous exudation from Guaiacum officinale, a native of San Domingo and Jamaica, soluble to the extent of 90 per cent, in absolute alcohol, and when triturated with water forms a mucilage of pale greenish hue. It is used in some of the old collodion processes. Gun-Cotton. See Pyroxyline. Halation. A blurring of the image and an encroachment of the high-lights upon the surrounding shadows or darker portions. It is but too well known as the defect of photographing an interior in which a brilliantly lighted window appears ; or again, when photographing landscapes in autumn or winter, halation is very likely to make its appearance when the leafless boughs of the trees appear against a bright sky, or in any case where extreme contrasts of light and shade exist. It is caused by reflection from the back of the plate. The rays of light are scattered by the particles of silver salt, and, obeying certain 232 DICTIONARY OF PHOTOGRAPHY. [Har laws of reflection, are reflected from the surface and back of plate. The remedies are Backing the Plate (g.v.), the use of thickly-coated and matt-surfaced plates, and plates containing iodide of silver, the latter being an almost certain preventative of halation, chiefly because the iodide emulsion is more opaque than a bromide ; but if an emulsion could be obtained absolutely transparent, there would be practically no halation. When photographing interiors, it has been recommended to cover the window with some slightly opaque substance, such as pale yellow linen or unbleached calico, so as to reduce the intensity of the light ; and, again, it has been recommended to cut small shapes of black velvet, and hang on wires in front of the camera, so as to exclude the windows themselves from the focussing screen, re- moving them only a short period before the close of exposure. When halation does not exist in a negative, local Reduction (q.v.) may be resorted to, or the process described under Harmonising Harsh Negatives (q.v.) may be used with great success, or the dense deposit may be partially removed by careful rubbing down with wash-leather and methylated alcohol. Half-Plate. The size of dry-plate 6} 2 by 4$ The true half- plate is 6£ by 4|. Halogens. This term has been applied to the group of the four elements, chlorine, bromine, iodine, fluorine, which are closely connected by similarity of their chemical properties, and the term has arisen from their forming salts closely allied to sea salt, and the salts thus formed are called haloids. Harmonising Harsh Negatives. This process is a very valuable one, and should be far more frequently used than it is. It will reduce the dense parts of a harsh negative and intensify weak parts. By means of this process it is possible to obtain a really decent print from a negative of a church interior which is almost a mass of halation, and passable prints may be obtained from harsh under-exposed negatives. It was suggested first by Eder in 1883. The negative, after being fixed and well washed, should be soaked in a solution of Potassium bichromate ... ... ... 1 part. Hydrochloric acid ... ... ... ... 3 parts. Alum ... ... ... 5 Water 100 M 2 33 Har] DICTIONARY OF PHOTOGRAPHY. In this the negative gradually turns white, and care must be exercised that it is thoroughly bleached from the back as well as the front. The negative must now be thoroughly washed in running water for at least two hours, or repeated soaking, film downwards, in frequently changed water for at least four hours. The bleached plate may now be redeveloped, either with an old hydroquinine developer or with ferrous oxalate. This is the important point in this process, for development must only be carried on till the details in the shadows are fully developed, and not till the high lights are developed right through, or in the latter case no improvement will be seen. As soon then as the details in the shadows and half-tones are developed, the plate may be rinsed and refixed. There being still some undeveloped chloride of silver at the back of the dense parts, this is fixed out, and the negative will be found by no means so hard as before. I have stated that this process in- tensifies the shadows, and this is only, strictly speaking, true when the bleached plate is exposed to daylight for some time and then developed, the chloride of silver image then being con- verted into a more nonactinic character than previously. An alternative method due to Mr. J. Mcintosh is the following. Prepare the following solution : — Bichromate of potassium ... ... ... 10 grs. Bromide of potassium ... ... ... 5 ,, Water 1 oz. Bathe the plate and allow the solution to permeate the film. Pour the solution off and add to it five drops of nitric acid. Again flood the plate and the image will be converted into bromide of silver. Allow the action to proceed through the film. Bathe in three changes of alum, a 5 per cent, solution of potassium metabisulphite, to remove the bichromate and harden the film, and wash thoroughly in water. As the opera- tions are carried out in white light, such as that of gas or a lamp, the plate is amply exposed by the time the washing is completed. The following pyro developer was found quite suitable. Any preservative may be used, but as there is nothing on the plate but the image to be affected by the developer, there is no necessity to use a bromide. A small trace may be useful to 234 DICTIONARY OF PHOTOGRAPHY. [Har control development, but if any bichromate of potassium remains in the film it will unite with the bromide, and convert the image back into bromide of silver as fast as it developed. Pyro 2 grs. Ammonia 2 mins. Bromide of potassium (if used at all) ... £ gr. As the shadow detail lies on the surface it will first be developed, the half-tone will follow, and the high lights will remain white when viewed from the back of the plate for some time. As the surface of the film will veil over as soon as the developer begins to act, the progress must be judged entirely from the back of the plate. The only judgment required in the process is in stopping the development at the right time. If stopped too soon, the negative will be flat ; if carried too far, the negative will still be hard. Mr. Mcintosh says : " It will be well to have ready for reference a print from the negative in which the shadows have been printed to their proper depth. When the lightest half- tone which shows in the print is nearly, but not quite, blackened through by the developer, on viewing the plate from the back the action should be stopped, the plate washed and transferred to the hypo, which will speedily dissolve out the undeveloped silver in the high lights, leaving the negative much thinner in the high lights than it originally was. A little practice with waste negatives will give the required power of judgment. A negative which is hard from under-exposure, and one which has been fuHy exposed but is hard from over-development, will not present the same appearance during redevelopment, after rehalogenis- ation. If the former be redeveloped right through, the high lights will appear black at the back of the plate, the high light in the fully exposed negative will never appear black, however far the redevelopment may be pushed, and as the layer of white-coloured silver present in this case will not be dissolved out by the hypo, an allowance for this must be made in re- development, or the negative will still be too dense. There is no theoretical objection to the negative being again treated by the process to obtain the required reduction, but in practice there is an additional risk of stains appearing the second time. It is better to err on the side of under-development and intensify 235 Hea] DICTIONARY OF PHOTOGRAPHY. if necessary. In this process, as in all others, great cleanliness is required, and the plate must have been thoroughly freed from hypo before proceeding to rehalogenise. If hypo or other chemicals be present, thin patches and dark spots will show. If there are grease-spots or finger-marks on the plate, irregular action will take place. It is best to take but one trial print from the negative, and exercise great care in doing so if re- halogenisation be thought needful. When operating on old negatives I wash them gently with dilute ammonia to get rid of, if possible, grease-spots before beginning the process." Head-Rest. An apparatus used for maintaining an exact position and steadiness of a sitter during exposure. Great prejudice exists in the minds of most people against it, due to its use having been abused to such an extent as to become an absolute instrument of torture. In all cases the head-rest should be brought to the sitter's head, and applied fgently, so as to give sufficient support without giving any idea of rigidity. Hectogramme. See Weights and Measures. Hectolitre. See Weights and Measures. Hectometre. See Weights and Measures. Heliochromy. See Photography in Natural Colours. Heliotype Process. See Collotype. High-Lights. The brightest parts of a picture, which are represented by the greatest density or opacity, in the negative, as the face in portraits, the sky and other bright portions in the landscape. History of Photography. See Photography. Hydriodic Acid (Ger., Iodwasserstoffsaure ; Fr., Acide iodhydrique; Ital., Acido iodidrico). HI=I28. Made in a some- what similar method to hydrobromic. It forms salts called iodides. Hydrobromic Acid (Ger., Bromwasserstoffsaure ; Fr., Acide hydrobro?nique ; Ital., Acido idrobromico). HBr=8i. Is made 236 DICTIONARY OF PHOTOGRAPHY. [Hyd either by decomposing potassium bromide with tartaric acid or by passing sulphuretted hydrogen through bromine water. It forms salts termed bromides in which form alone it is used in photography. Hydrochloric Acid (Ger., Chlorwasserstoffsaure ; Fr., Acide chlorhydrique ; Ital., Acido chloridricd). HCl=36 - 5. Synonyms: Muriatic acid, Spirits of salts. Made by roasting salt in furnaces with sulphuric acid. Specific gravity ri6o. Its use is limited to the clearing bath, and combined with nitric acid to make chloride of gold. It combines with alkalies and basylous radicles to form chlorides. Hydrogen. H|= I. A gaseous element of very frequent occurrence in nature in a combined state, especially in the form of water. It is taken as the unit of atomic weights. It is used for the production of the lime-light. Hydrogen Peroxide (Ger., Wasserstoffsuperoxyd ; Fr., Eau oxygenee ; Ital., Aequo, ossigenatd). H 2 (X = 34. Synonyms: Hydroxyl, Hydrogen dioxide. Made by passing carbonic acid gas through water in which barium dioxide (Ba0 2 ) is suspended. Barium carbonate is precipitated, hydroxyl being formed in solution : BaO., + CO* + H 2 0 = BaC0 3 + H.,O a . It is a powerful oxidiser and bleaching agent, and is used to free prints and negatives from the last traces of hypo, which it does by oxidising it into sulphate ; but it must be used very weak (about 2 drms. to 5 ozs.), or the density of the negatives and the tones of the prints will be reduced and sulphur deposited. Hydroquinone (Ger., Hydrochinon ; Fr., Hydroquinone; Ital., Idrochinone). C 6 H 4 (OH L ,) = no. Synonyms: Hydrokinone, Hydrochinone, Ouinol. It is prepared commercially by oxidising aniline sulphate with bichromate of potassium. Solubility : 58 per cent, in water o°C, 10 per cent, in water at 30 0 ; soluble also in alcohol, ether, and glycerine. It is allied to pyrogallol in che- mical composition, pyro being a trihydroxybenzine, C 6 H 4 (OH) 3 ; and quinol, as |it should |be called, being a dihydroxy benzine. It was first suggested as a developer by Captain Abney, and attracted but little attention in consequence of the unsuitable cha- racter of the accelerator, — ammonium hydrate, or liq. ammonia, 237 Hyd] DICTIONARY OF PHOTOGRAPHY. — which was recommended to be used with the same, and also from its prohibitive price ; but, as more experiments were made with it, and better formulae were given for its use, it crept gradually into general favour, and an enormous reduction in price has led to its universal adoption. When used with the carbonates of potassium and sodium its action is somewhat slow, and only since the general use of the hydrates of these alkalies has it given satisfaction. The question as to whether it is better than pyro is one that cannot be decided, so much depending upon the personal bias of the user of the same. Many old opera- tors who have used alkaline pyro since its first introduction still cling to it, and refuse to believe that quinol is as good ; whereas many others state that it is infinitely preferable. For some conditions of work it undoubtedly is far superior to pyro. The number of formulae given is enormous, almost every worker seemingly suggesting some slight modification. The author has made a great number of experiments, and believes that with the following formulae good results can always be obtained. For negative i work : — No. i. Quinol 154 grs. or 10 grms. Sodium sulphite (pure recryst.) 154 ,, 10 ,, Sulphurous acid ... ... 17 mins. ,, 1 c.c.m. Distilled water, to make ... 10 ozs. „ 250 „ Dissolve the sulphite in the water and add the acid, and lastly the quinol. No. 2. Sodium carbonate (pure) ...1,300 grs. or 84 grms. Potassium hydrate (caustic pot- ash in sticks) 154 „ „ 10 „ Distilled water, to make ... 10 ozs. ,, 250 c.cm. For use mix equal parts of each, and dilute with twice or three times the quantity of water. About 4 drms. of each will be ample for a J-plate which has received a normal exposure. The image should make its appearance in about thirty to forty-five seconds, and development be completed in four or five minutes. For under-exposure soak the plate first in the accelerator for one 238 DICTIONARY OF PHOTOGRAPHY. [Hyd minute, and then add the quantity of No. i. For over-exposure add I drm. of a 10 per cent, solution of sodium sulphite, or 5 mins. of bromide of potassium, and reduce the quantity of accelerator No. 2. Dr. Herklots Vos has given the following formulae as being all that can be desired. No. i. Quinol 4 grs. or -25 grm. Sodium sulphite 24 ,, „ 1*5 „ Distilled water ... 1 oz. 25 c.cm. No. 2. Potassium bromide 60 grs. or 4 grms. Distilled water, to make 10 drms. or 37 c.cm. of solution. No. 3. Potassium hydrate 2 ozs. or 60 grms. Distilled water 1 oz. ,, 25 c.cm. For normal exposure add 5 drops of No. 2 and No. 3 solutions to 1 oz. of No. 1, and allow development to continue for some minutes ; then add another portion of No. 3 to obtain the required density. For under-exposure omit No. 2, and gradually increase the accelerator No, 3 ; for over-exposure increase No. 2 to 10 drops to the ounce. The above quantities are for a j-plate. The following is recommended by a well-known firm of plate- makers: — No. 1. Quinol 160 grs. or 10 grms. Sodium sulphite ... ... 2 ozs. ,, 56 ,, Citric acid 60 gr. ,, 3 8 „ Potassium bromide 30 ,, 16 ,, Distilled water to 20 ozs. ,, 500 c.cm. No. 2. Sodium hydrate ... ... 160 grs. or 10 grms. Distilled water to ... ... 20 ozs. ,, 500 c.cm To develop, mix equal parts of each. It is recommended to use the alum bath after development. May be used for negative or 239 Hyd] DICTIONARY OF PHOTOGRAPHY. positive work. For positives, whether on glass or paper, the author recommends the following for black tones : — No. I. Quinol 154 grs. or 10 grms. Sodium sulphite ... ... 437 ,, 28 „ Sulphurous acid 20 mins. „ 1*2 c.cm. Distilled water to make ... 10 ozs. ,, 250 „ No. 2. Sodium carbonate 1,300 grs. or 84 grms. Potassium hydrate ... ... 154 10 „ „ bromide 20 „ ,, 1*2 grm. Distilled water to make ... 10 ozs. ,, 250 c.cm. Mix in equal parts, and dilute with three times the quantity of water. The following will give good purplish tones to trans- parencies on glass, and brownish tones to bromide paper : — Quinol 2 grs. or -12 grm. Ammonium carbonate .. 24 15 ,, bromide ... ... | „ ,, *oi6 Distilled water ... ... ... 1 oz. 25 c.cm. Mix immediately before using. As a convenience for travelling, the following dry powder developer will be found simple and convenient : — I. Quinol 90 grs. or 6 grms. II. Sodium sulphite (granular) ... 2 ozs. 60 III. Carbonate of soda (dried) ... 1 oz. „ 28 „ Wrap each salt in waxed paper and tinfoil. Dissolve these quantities in a quart of water. As a further convenience they may be subdivided into four or eight packets each, so as to make sufficient quantities for 10 or 5 ozs. of developer. Although 240 DICTIONARY OF PHOTOGRAPHY. [Hyd a one-solution developer is not the best form, it may be found con- venient for travelling, and then the following will answer well : — Quinol ... 90 grs. or 6 grms. Sodium sulphite 2 ozs. ,, 60 ,, Carbonate of soda ... ... 2 ,, ,, 60 ,, Distilled water to make ... 10 ,, ,, 250 ,, Eosin ... .. ... ... i^gr. ,, -06 This solution will keep at least two months, and when required for use should be diluted with four times the quantity of water. For over-exposure use old developer, for under-exposure new developer, and for normal half old and half new. In using quinol as a developer several precautions are necessary. Absolutely clean dishes must be used, as any trace of pyro produces a brown stain. For negative work fresh developer should be used for each plate ; but the used developer may be kept and used for bromide paper and transparencies. Both negatives and posi- tives should be well washed after development prior to fixing ; and if either of the caustic hydrates of the alkalies are used, then an alum bath should be used after development to prevent frilling. All plates and papers developed by quinol require clearing and thoroughly washing after being fixed, to dissolve out the slight precipitate of carbonate of lime deposited from the water. Numer- ous researches have been made on the subject of this reducing agent and more numerous still the formulae that have been recom- mended, one of the most complete papers was by Lainer, who summarises his experiments as follows : — A Concentrated Rapid Hydroquinone Developer. A. Water 100 c. cm. Sodium sulphite 2 S~3° grms. Hydroquinone ... ... ... 10 „ Dissolve these by the aid of heat, and add to the solution 25 grms. of potassium ferrocyanide dissolved in 100 c.cm. of water. B. — Dissolve 50 grms. of potassium hydrate in 100 c.cm. of water, or 30 grms. of sodium hydrate in 90 c.cm. of water. For development, take 60 parts of A, 6 to 8 parts of the potash solution, and 40 parts of water ; the potash solution may be replaced by 10 parts of the solution of caustic soda. The two 241 R DICTIONARY OF PHOTOGRAPHY. original solutions may be mixed, and should then be diluted with thrice its bulk of water. Other Formulae. A. Water ... ... ... 600 Hydroquinone ... ... 10 Neutral sodium sulphite 25 Potassium ferrocyancide — B. Potassium hydrate ... 50 Sodium hydrate ... — Water 100 2 3 4 5 900 950 1,000 55o. 10 10 10 10 40 30 35 35 120 90 25 25 50 5° 30 60 IOO 90 55o 55o Developer I. — 60 c.cm. of A and 3 c.cm. of B, brought out a sensitometer image in three-quarters of a minute to 24 0 ; but isiapt to produce fog with some kinds of plates. The addition of about 12 per cent, of potassium ferrocyanide is found to have a very beneficial effect. Developer 2. — 60 c.cm. of A and 6 c.cm. of B permits exposures to be shortened, gives excellent details in the shadows, and allows very rapid development. Developer 3. — 60 c.cm. of A and 12 c.cm. of B gives negatives of a softer character than those given by Developer 2. Developer 4 is a slower developer, 60 c.cm. of A being mixed with from 6 to 9 c.cm. of a 50 per cent, solution of sodium hydrate and diluted with 60 c.cm. of water. Developer 5. — Equal bulks of these solutions are mixed immediately before use. It resembles Developer 4 in its action. Acetic acid and acetates act strongly as restrainers, yellow prussiate of potash acts as an accelerator. The great fault with incautious use of hydroquinone is that one is very liable to obtain negatives with very great contrasts, and since the introduction of the newer developers it has considerably fallen in use. Hydroxylamine Hydrochloride (Ger., Salzsdures Hydro- xylamin ; Fr., Chlorhydrate d 'hydroxylamine ; Ital., Chloridrato d'idrossilimind). NH 3 0HC1 == 69-5. Prepared by the reduction of nitrite and nitrate of ammonia. It is very soluble in water and alcohol; it has been recommended as a new developing agent ; but its price is at present decidedly against it, besides there being few, if any, advantages over hydroquinone and pyro- 242 DICTIONARY OF PHOTOGRAPHY. [Ima gallol, with the great disadvantage that it causes the film to blister, due to the disengagement of nitrogen. The following is the form recommended by Messrs. Egli & Spiller : — I. Hydroxylamine 32 grs. or r8 grm. Citric acid 15 „ 1 Distilled water ... ... 1 oz. ,, 25 c.cm. II. Carbonate of potash ... 480 grs. or 27 grms. Carbonate of soda ... ... 480 „ „ 27 „ Distilled water ... ... 10 ozs. 250 c.cm. Developer. Solution I. ... 30 mins. or 2 c.cm. Solution II 120 ,, 8 ,, Distilled water ... ... 1^ oz. 37 Sufficient for half-plate. It is especially recommended for chloride plates, bromide and Alpha papers. Hypo. An abbreviation of Hyposulphite of Soda (q.v.). Image. An optical term denoting the appearance of any object made by reflection or refraction, and in this sense applied to the reproduction of an object upon the ground-glass. Image, Latent. The action of light upon the sensitive salts of silver has always been a moot-point with scientific photo- graphers, and it would be impossible within reasonable limits to give all the arguments pro and con. For some considerable time past, and even now, a few photographers hold that the action of light upon the sensitive salts is to set up a vibratory motion, which the developer takes advantage of, reducing these vibrating molecules to a metallic state. This theory, however, has been shown, and it is generally considered most conclusively so, by Captain Abney and Dr. Armstrong, and more lately by Carey Lea, of New York, to be erroneous. The latter scientist has written most exhaustive papers upon this point, and has been enabled to prepare, chemically, salts identical in composition and 243 Inc] DICTIONARY OF PHOTOGRAPHY. action with those formed by the action of light ; these he calls photo-salts, and they would seem to be compounds of a lower haloid salt, with the normal haloid in varying proportions. In all cases there seems to be an evolution of the haloid element, and the action has been thus chemically expressed — 2AgBr + light = Ag 2 Br + Br. / Silver \ / Silver \ /Bro-\ It seems unlikely that all the molecules of haloid salt are reduced ; on the contrary, but a very minute portion is. But, as shown in the article oh Development, the action set up by the impact of actinic light is continued by the developer. It has been stated that when the action of reduction by light has once begun, it continues indefinitely in the dark ; but the arguments in favour of this statement are very weak, as it has been shown, on the other hand, that the action of light may be obliterated by keeping. Confirmation of the disassociation of the molecule of bromide of silver by light has been given by the researches of Guntz, who has been able to prepare the sub-haloid salts of silver. Incidence, Angle of. Is the angle made by a ray of light, passing through any point or line of a surface, with the perpen- dicular to that line or surface drawn through the point in ques- tion, or to the tangent of a circle in the case of spherical curves. The angle of incidence and the angle of reflection are always equal. Indian Ink. A black pigment obtained from China. It is an exceedingly fine lampblack, said to be produced by burning oil of sesame, mixing the product with some vegetable gum, and drying till it turns into a solid cake. Indiaruboer Solution. This is used for edging plates or as a substratum for the collodion process, and also for mounting gelatino-chloride prints. It may be dissolved in benzole, chloro- form, or carbon bisulphide, the two former being preferable in the proportion of ten grains to the ounce. Pure masticated rubber should always be used. Ink Process. Under this title several processes may be 244 DICTIONARY OF PHOTOGRAPHY. [Ink included, but Lemling's process is the one usually meant by this term now ; the procedure being as follows : — Bichromate of potash ... ... I part. Distilled water 20 parts. Dissolve and render neutral with ammonia. To every three parts of this add with constant stirring in a mortar Powdered gum-arabic ... ... 1 part. Transfer to a bottle and shake frequently till dissolved, which probably will be in about twenty-four hours ; it should then be filtered and spread evenly over a sheet of albumenised paper with the aid of a Blanchard brush. The paper should then be laid, film up, on a sheet of plate-glass, a good-sized pool of the solution poured on to it and made to cover it evenly, the excess poured off, and the paper hung up to dry. The difficulty in this process is to prevent the albumenised paper from curling ; therefore it is preferable to hold it paper-side down over a jet of steam, so as to partially coagulate the albumen next the paper, and then lay on the glass ; or the glass may be wetted and the paper squeegeed to it with a rubber roller and then coated as described above. The operation may be conducted in daylight as the paper is insensitive whilst wet ; the drying should be conducted in the dark. It is exposed behind a negative in the usual way, then laid face downwards on water and allowed to soak for some time with repeated changing of the water, and then it should be soaked in alum solution and again washed. It is then drawn over the surface of the following solution : — Pyrogallol ... ... ... ... 1 part. Distilled water 50-80 parts. Or it may be floated on the same for two minutes, then thoroughly washed and floated on a solution of Sulphate of iron ... ... 10 parts, Distilled water 100 ,, and again washed. If not dark enough the process may be repeated. Another process sometimes used by artists and others for preparing drawings for reproduction is as follows. A print is 245 Ins] DICTIONARY OF PHOTOGRAPHY. obtained in the usual way either on albumenised, bromide, or plain paper, the latter being preferable ; and failing this an image may be obtained on the back of albumenised paper. As long as the details are there the depth of printing should be very slight, no toning or fixing is required. The image is then traced over with Indian ink, with the aid of a crowquill or fine pen. Allow this image to dry thoroughly and immerse in Saturated solution of iodine ... ... 10 parts. Saturated potassium cyanide 15 „ Distilled water ... ... ... ... 500 ,, when the silver image will disappear and the print may then be washed and dried. The saturated solution of iodine can be prepared by saturating a 10 per cent, aqueous solution of potas- sium iodide. Insensitiveness. When, by reason of faulty chemicals or manipulations, the sensitive surface refuses to record any action of light. Instantaneous Lens. A term incorrectly applied to lenses when intended to convey a particular construction, as all types of lenses would, in a sufficiently powerful light, enable in- stantaneous photographs to be taken. Instantaneous Photography is the obtaining of negatives by exposures of the fractional part of a second. The following tables and rules may be found useful : — A man walking 3 miles per hour moves 4^ft. per second. „ 4 n tt 6 m A vessel travelling 9 knots per hour 15 ,, » 12 „ „ 19 » tt *7 M M 28 „ 20 11 ft 35 A trotting horse „ 39 A galloping horse , 50 ,, An express train at 38 miles per hour „ 59 ,, Flight of a pigeon ,, 61 „ Waves during a storm ... ... ,, 65 „ Express train at 60 miles per hour ,, 88 ,, Flight of the swiftest birds ... „ 264 ,, A cannon ball „ 1,625 » 246 DICTIONARY OF PHOTOGRAPHY. [Ins An object moving I mile per hour moves i^ft. per second. 2 miles ,, 1, 3 >i >> 3 I* 4 „ 4 11 6 )) 5 „ 7^ M >t 6 11 9 11 >i 7 „ IO* „ 8 11 12 11 n 9 n 13 n M IO „ 11 14 1 1 M ii ii n 16 n II 12 „ n I7i ii If 13 „ 19 M „ 14 11 20^ 11 f| 15 11 22 11 II 20 ,, 11 29 11 »» 25 37 11 If 30 11 44 M 35 ,, 51 ii 40 ,, 59 11 II 45 11 66 11 II 50 11 73 ,, II 55 •1 80 60 ,, 88 75 1 10 II 100 147 11 125 i> 183 11 II 150 220 11 To find the distance moved by the image of an object on the ground glass, multiply the focus of the lens in inches by the distance in inches moved by the object in one second, and divide the result by the distance of the object in inches. Example. — Find the displacement of image on ground-glass of an object moving 20 miles an hour, with a lens of 8£-in locus, and the object 1 50 yds. distant. 8£ x 348 -5- 5,400 = %%% = \ in. per sec. practically. To find how quickly a shutter must act to take an object 247 Ins] DICTIONARY OF PHOTOGRAPHY. in motion, that there may be a circle of confusion less than i-iooth inch in diameter, divide the distance of the object by ioo times the focus of the lens, and divide the rapidity of motion of object in inches per second by the result, when you have the longest duration of exposure in fraction of a second. All measurements in inches. Example. — Required the speed of a shutter to take an object moving 20 miles per hour, with a lens of 8^-in. focus, the object being 150 yards distant. The object moves 29 feet = 348 in. per second. 5,400, distance of object in inches, ~ (8£ x 100) 108 = 5»4oo ~ 850 = — O J r , • n IO8 348 X 17 348, speed of object per second, — = iQg — 493 = — = 55 practically. .*. the shutter must work at -fa of a second. Knowing the rapidity of shutter and moving object, required to find the distance to place the camera to give an image with a circle of confusion less than T ^ of an inch in diameter. Multiply 100 times the focus of the lens in inches by the space through which the object would pass during the exposure, and the result is the nearest distance in inches between object and camera. Example — A shutter works at sec, object moves four miles an hour; how near must camera be placed with an 8^-in. lens ? An object moving four miles per hour moves 72 in. per second. .'. an object moving four miles per hour moves i T V in. in ■h sec - 17 X IOO X 12 %\ X IOO X I 2 X II = 927 m " "~ 25 y 248 DICTIONARY OF PHOTOGRAPHY. [InS Dr. Eder gives the following table (" Jahrbuch," 1887): — Sec. Sec. Sec. Laughing children, etc., probably require ... i to 1 Dogs and cats .... ... f „ T V Street scenes, according to size of figures ... „ 3 V Cattle feeding, sheep, etc. ... ... ... fa „ fa Moving ship 500 to 1,000 yards off fa ,, -5V Moving ship nearer fa „ tU Animals which appear on focussing screen from one to two inches high ... ... ... fa ,, T -J-o Trotting and jumping horses, birds, etc. ... T ^ ,, lifartOi^ro Pizzighelli ("Anleitung zur Photographic" p. 83) gives the following useful little table : — B * _B IS !>> ti fl ti B M c £ Lies rott "2L O 111 p lll|) ice. iri O Horse t Horse ga Horse jt Steams dista Train 3 an h Moving a distance in yards per second of 400 1 T it 500 It 1 ti 600 „ II >t 700 11 3 ■3-2 }} 3 sir 11 800 TS tt 1 TT> n 900 „ i 15 ft 1 ITS tt 1,000 ,, II For the sake of convenience, I have carried this table the reverse way, that is to say, giving the distances of the above-named object as less when the height of the image of a man and horse is respectively greater. Man. If in. o 5 tt 2- 7 - ''s n 3tV tt 31- M 4t\ 1, 5 H Horse. ■ I, 1 ■ 2 T V • 2| ■ 3iV • 3h ■ 31 • 4i The Object is distant from the Camera. 40 times the focal length. 30 24 20 18 16 14 250 DICTIONARY OF PHOTOGRAPHY. • [Ins Another table compiled by MM. Henry Hermagis and Rossignol is also convenient : — Approx* Approx. Distance Subject. speed of Approx. height of in yards. shutter Reduction. man in seconds. in inches. -■» X 3? otandmg children or 1 1 1 0 half-length men with heads about \ inch from top to chin 7h See-saw, skipping chil- dren, etc.* & to ff V ri 2\ to 2f 12 to l6\ Horse walking, dan- cers "j" A to C V 4 to l£ 12 to 24 Acrobats, clowns, dan- 1 <-<-» 1 tJTT tO XI7I j ¥7 to -j^ i to I§ cers, etc.f Moving people, but 15 to 20 rfr to C V tO 7Tr 1 to I| not walking about — crowds, bathers i8£ to 30 People walking, sol- ft ^ tJo } to t\ diers quick-march- ingf 22 to 32 People, troops, yachts, 1 TT>0 * to f tramcars % 27 Horse trotting, in- TV tO A 1 115 i fantry charging, run- ners | 33 Calm sea, ships, at rest or moving + 1 1^0 1 2 43 1 f>7> 1 1TH7 I 50 1 T7tf en j J Train (35 miles per hour), tricycle, sledge f ii'&TF 1 4 70 to 75 Express train, balloon, storm waves, grey- hound coursing, skater,, racehorse, dynamite explosion 71 i The exposure to be made at the moment of partial rest or least movement, t Object moving across the field of view. I Object moving across the plate. § Object moving to or from lens or only slightly across. The secret of successful results with instantaneous work is to watch the moving object till it attains that position which the 25 1 Ins] DICTIONARY OF PHOTOGRAPHY. French call le point mort y and which is well seen in the case of a ball thrown perpendicularly up into the air. For some time the ball travels up, and then just for one almost inappreciable period of time it is stationary, and begins its downward course, and an exposure should be made just at the moment of reversal of motion. It will be found that with nearly every moving object some such point mort will occur, and the successful worker seizes this moment to fire off. Too many amateurs allow their very laudable ambition to run away with their sense, and expect the combination of shutter, lens, and plate to do impossibilities. For very quick work, brilliant sunshine is absolutely necessary, and two important points should be taken into consideration — (i) That the nearer a moving object is, the more rapid must be the action of what is called the shutter, which, by way of parenthesis, might with equal force be termed an opener ; (2) The longer the focus of the lens, the quicker the shutter should act. Another point is that when an object is moving across the field of view, or more or less obliquely to the axis of the lens, the shutter must act more quickly, whilst with an object moving parallel to the axis of the lens, or away from or towards the lens, the displacement on the ground glass or the difference between the size of the image at two points is by no means so great as in the first case ; and to improve matters the theoretical impossibility, the depth of focus of the lens, is again of assistance. Many commercial shutters are fitted with an index showing the speed given by the shutter when certain levers, etc., are placed in certain positions, but strict reliance cannot always be placed upon such speeds. Methods of testing instantaneous shutters will be treated of under that heading. Instantaneous Shutters. See Shutters. Intensification means the increasing of the deposit or the printing density of a negative. There are several methods of doing this; but the majority consists in the use of mercuric chloride, and then subsequent darkening. Before intensifying a negative with mercury it is absolutely essential that it should be absolutely free from hyposulphite of soda. It is, therefore, advisable to give the negative a thorough washing, and then immerse for 10 mins. in a 5 per cent, solution of hydrogen peroxide, and again wash. Negatives which have been allowed 252 DICTIONARY OF PHOTOGRAPHY. [Int to dry should be well soaked in water before being bleached, and varnished negatives must of course have the varnish removed by means of methylated spirit, and then soaked. The mercuric solution is prepared as follows : — Perchloride of mercury ... ... ... 2 parts. Hydrochloric acid I part. Water 100 parts. The hydrochloric acid should be placed on the powdered mercuric chloride, and then the water added. The negative to be in- tensified, having been previously treated as above suggested, should be laid in the solution, and the dish gently rocked till on looking at the back of the plate it is seen to be quite white. It should then be thoroughly washed for at least 20 minutes in running water, and then immersed in one of the following solutions : — I. Sodium sulphite ... ... ... .., 1 part. Water 6 parts. II. The ordinary ferrous oxalate developer. III. Hydroquinone developer. IV. Liquid ammonia fort. 1 part. Water 10 parts. V. Silver nitrate ... ... ... ... 20 parts. Distilled water ... 500 „ and add gradually Potassium cyanide 20 parts. Distilled water ... ... ... ... 500 Shake well after each addition, till only a small quantity of white flocculent precipitate remains. It is important that the solution should never be quite free from sediment. 2 53 Int] DICTIONARY OF PHOTOGRAPHY. VI. Potassium cyanide ... iodide i\ parts. 2\ „ Mercuric chloride Distilled water iooo VII. Schlippe's salt 10 parts. Distilled water 400 Ammonia ... ... ... ... ... 5 „ The ordinary method of intensifying is to adhere to the use of one solution as a blackening agent ; but it frequently happens that the same degree of increment is neither desirable nor necessary, then choice may be made from the above solutions. Mr. Chapman Jones has tabulated in convenient form the action of many of these. He says : — " In the following series of opera- tions each change is supposed to be thorough — that is, that the change of colour in every case shall be visible clearly at the back of the plate in the densest part of the negative. (1) Mercuric chloride, followed, after well rinsing, with sodium sulphite, gives the little addition of brilliancy sometimes wanted in a carefully made and successful negative ; (2) mercuric chloride on the original negatives, followed, after thorough washing, by ferrous oxalate, gives about as much increase of density, as compared with No. I., as No. I. gives when compared with the original negative ; (3) a repetition of the application of mercuric chloride and ferrous oxalate — that is, these re-agents applied to the result of No. II. — gives another step in the intensification ; * (4) the result of No. III. may be treated again with mercuric chloride and ferrous oxalate, and so on, as may be necessary ; (5) the fourth or fifth consecutive application of mercuric chloride and ferrous oxalate will probably give a result equal to that of the uranium intensifier acting upon the original negative ; (6) if a still greater effect is desired, the lead intensifier may be used on the original negative." Continuing this series we may say that the action of No. V. is fully equal to, if not slightly greater than, mercuric chloride, followed by ammonia; whilst No. VI. gives * The result of this treatment is about equal to the action of mercuric chloride, followed by ammonia, upon the original negative. 254 DICTIONARY OF PHOTOGRAPHY. [Int as great increase as the lead intensifler if desired. No. VII. about the same as No. V. Instead of hydrochloric acid in the bleaching or mercuric chloride solution, many recommend potas- sium bromide or ammonium chloride ; either may be used, with- out any difference in results being detected. Nos. II. and III. solutions give about the same density ; Nos. V., VI., and VII. are all poisonous, as is also the mercuric chloride solution. The bleached negative should not be allowed to remain too long in No. V., or else the shadows are attacked. When the negative is placed in No. VI. it turns first bright yellow, then much darker brown. At this stage it is very dense, and only extremely thin negatives should be removed now ; for normal work, the negative should be left in still longer till it turns a lighter brown. No. VII. gives a bright reddish-brown negative. Whichever darkening solution is used, it should be allowed to act till the back of the image, as seen through the glass, is dark, and then thoroughly washed. The Uranium Intensifler. This stains the image a bright reddish-brown. It is absolutely necessary that all hypo should be eliminated Potassium ferridcyanide I part. Uranium nitrate ... ... I ,, Acetic acid, glacial 10 parts. Water ... ... ... 100 ,, The plate, after intensification, should be well rinsed and dried ; continuous washing, especially in ordinary tap water, removes the intensification bodily. This very defect makes this process useful, as by means of an alkali any part of a negative intensified with uranium can be bleached by treatment with ammonium carbonate. The Lead Intensijier. This gives a very dense increment, and is, therefore, rarely necessary or used. Potassium ferridcyanide ... 6 parts. Lead nitrate ... ... ... ... ... 4 Acetic acid, glacial ... 10 ,, Distilled water ... ... 100 ,, Soak the negative in this solution till bleached, then wash thoroughly, and flood with 255 Int] DICTIONARY OF PHOTOGRAPHY. Nitric acid ... ... ... ... ... 1 part. Water 7 „ Rinse well, and pour over it ammonium sulphohydrate ; then wash well and dry. Silver Intensifiers. Whilst some operators still hold to this, the relic of old wet- plate days, it has not found its way into general practice. It is difficult to avoid the occurrence of stains, as silver nitrate so readily combines with gelatine. Several formulae have been suggested. A. Pyrogallol 1 part. Citric acid ... ... ... ... ... 2 parts. Distilled water 300 B. Silver nitrate 2 parts. Distilled water ... ... ... ... 100 „ The plate should, first of all, be flowed over once or twice with Solution A, and then to every 50 parts of A 30 to 40 parts of B should be added. Belitzski suggests the following : — A. Gallic acid 1 part. Hot distilled water 100 parts. Dissolve and filter ; when cold, add an equal volume of Silver nitrate ... ... ... ... 1 part. Acetic acid, glacial 1 „ Distilled water 50 parts. The following has also been suggested : — I. Silver nitrate ... ... ... ... 22 parts. Distilled water ... .. 250 „ II. Potassium bromide ... ... ... ... 10 parts. Distilled water ... ... ... ... 25 ,, 256 DICTIONARY OF PHOTOGRAPHY. [Iro Mix, collect the precipitate, wash thoroughly, and dissolve in Sodium hyposulphite ... ... ... 60 parts. Distilled water 170 ,, The mixture is thoroughly stirred, allowed to stand for a few hours, and filtered, sufficient water being added to make the total bulk measure 450 parts. The plate is soaked in this solution for 5 minutes, drained, and a ferrous oxalate developer applied, and then washed and dried. The following intensifier has also been suggested for negatives of line work, but is also applicable to ordinary work : — A. Potassium bromide 1 part. Water 16 parts. B. Copper sulphate ... 1 part. Water 16 parts. Mix in equal proportions, and flow over the plate till the image is bleached, then wash well, and blacken with Silver nitrate 1 part. Water 16 parts. or Ammonium hyposulphite ... ... ... 1 part. Water 4 parts. Then wash and dry. Iodine (Ger., lod; Fr., lode ; Ital., Iodid). I = 127. One of the halogen elements. Is obtained from seaweed, and appears commercially in metallic bluish-grey scales. Solubility : 1 in 7,000 of water, 1 in 12 of alcohol, 1 in 4 of ether ; very soluble in a solution of any alkaline iodide. Thirty grains of iodine and 30 grs. of potassium iodide will dissolve in one drm. of distilled water. The metalloid itself is of little use, but when in combi- nation as iodide is much used for emulsions, etc. Iridescent Stain. See Fog. Iron, Ammonio-Citrate of (Ger., Citroncnsaurcs Eisenoxy- dammon ; Fr., Ammonio-citrate de fer, Citrate ammoniacal dc 257 S Iro] DICTIONARY OF PHOTOGRAPHY. fer; Ital., Citrato diferro ammoniacale). Fe 2 (NH 4 ) 2 (C 6 H 5 0 7 ) 3 . Synonym : Ferric Ammonium Citrate = 293. Is prepared by dissolving ferric hydrate in citric acid, and adding liq. ammonia till neutral. It should be in small transparent scales of a deep reddish-brown colour, and peculiar mousey odour. Solubility : 1 in 0-5 parts of water ; almost entirely soluble in alcohol. Five parts dissolved in 7*5 parts of water make 10 parts of solu- tion. It is used in the ferro-prussiate process. Should be kept in the dark. Iron, Ammonio-Oxalate of (Ger., Oxalsaures Eisenoxydul- ammoniak; Fr., Oxalate ammoniaco-ferrique ; Ital., Ossalato di ferro ammoniacale?) Fe 2 (NH 4 ) 2 (C 2 0 4 ) 4 = 360. Synonym : Ferrous Ammonium Oxalate. Prepared by dissolving ferric hydrate in oxalic acid and adding ammonium oxalate. It occurs in brilliant emerald crystals, which should be kept in the dark, as they are partially reduced by light to a ferrous state. Ninety parts are soluble in 100 parts of cold water, and 126 parts in 100 of boiling water. Used in platinotype and blue-printing processes. Iron, Ammonio-Sulphate of (Ger., Schwefelsaures Eisen- oxydtdammon ; Fr., Sulfate ferreux ammoniacal ; Ital., Solfato di protossido diferro e d'ammoniaca). Fe(NH 4 ) 2 2S0 4 6H 2 0 = 392. A double salt of iron and ammonium, proposed as a sub- stitute for ferrous sulphate ; but its action is much feebler, though the salt and its solution are more stable. One ounce of ferrous sulphate is equal to 1^ ozs of the double salt. The author has found it, however, a good but slow developer for bromide papers. Solubility : .about 1 in 6 of cold water ; liable to decompose in hot water ; insoluble in alcohol. Was fre- quently used for developing wet collodion plates. Iron, Oxalate (Ger., Oxalsaures Eisenoxyd, Ferridoxalat ; Fr., Oxalate ferrique; Ital., Ossalato di perossido di ferro). Fe 2 (C 2 0 4 ) 3 . An olive-brown syrupy liquid, which cannot be crystallised, except with great difficulty. It is prepared by dis- solving ferric hydrate in oxalic acid. A more convenient method is to dissolve 556 grs. of ferrous sulphate in 1 oz. of distilled water, to which \ drm. of strong sulphuric acid has been added, and to add nitric acid, in small quantities at a time, keeping the whole 258 DICTIONARY OF PHOTOGRAPHY. [Iro boiling till ferric sulphate is formed, which can be recognised by the solution not giving a blue precipitate, with potassium ferro- cyanide. Now add ammonia till no further precipitate is formed, collect and wash the precipitate, and mix it with a cold solution of 378 grs. of oxalic acid in 4 ozs. of distilled water, and allow it to stand in the dark for some days. The resulting solution con- tains 376 grs. of ferric oxalate. It may also be made by dis- solving 10 parts of ferric chloride in 10 parts of water, and adding 4 parts of solid oxalic acid and 1 part of water, and allowing to stand in the dark for some days. The resulting solution will contain 119 parts of ferric oxalate. The solution used in platino- type-printing should contain 100 grs. of ferric oxalate per ounce ; therefore the above solutions must be diluted till of that strength. Iron, Oxalate of (Ger., Eisenoxalat ; Fr., Oxalate ferreux ; Ital., Ossalato ferrico). FeC 2 0 4 2H 2 0=i90. Synonym: Ferrous Oxalate. Prepared by decomposition of sulphate of iron and oxalic acid. It is but rarely used dry, being generally prepared as wanted in solution by double decomposition by adding solution of sulphate of iron to solution of oxalate of potash. (See Developer.) It is sparingly soluble in water, more soluble in any solution of alkaline oxalate. It is the develop- ing agent of the ferrous-oxalate developer, which has rather more adherents on the Continent than in England. Iron, Per chloride of (Ger., Ferrichlorid, Eisenchlorid ; Fr., Perchlorure de fer, Chlorure ferrique; Ital., Clornro ferrico). Fe 2 Cl 6 ,6H 2 0=433. Synonym: Ferric Chloride. Prepared by passing chlorine over red-hot iron filings, when the ferric chloride distils over. It can also be made by dissolving iron wire in hydrochloric acid, adding nitric acid, and heating till the ferrous chloride first formed is converted into ferric. It occurs in yellowish-red opaque masses, which are very deliquescent. Solubility: 160 per cent in cold water; soluble also in alcohol and ether. It is used for the reduction of negatives, for cyano- type paper, for etching copper and zinc. Iron, Sulphate of (Ger., Eisenvitriol, Schwefelsaures Eisenoxydul ; Fr., Sulfate ferreux ; Ital., Solfato di ferro). FeS0 4 7H 2 0 = 278. Synonyms: Ferrous Sulphate, Protosulphate 2 59 Isi] DICTIONARY OF PHOTOGRAPHY. of Iron, Copperas, Green Vitriol. Prepared by dissolving iron wire in dilute sulphuric acid, evaporating and crystallising. The crystals should be of a fine bluish-green colour, free from any adherent brownish rusty powder, which is caused by the action of the oxygen of the air, the product being an oxy-sulphate : to this action is also due the deteriorations of solutions of this salt. When this change in colour of a solution is noticed, it should be rejected and fresh solution used. The solution may be preserved for some time by the addition of a crystal of sulphate of copper whilst fresh. Solubility: I in 1*5 of water; insoluble in alcohol and ether. Isinglass. The purest form of gelatine known, obtained from the swimming bladder or sound of the sturgeon. The finest is exported from Russia. Isochromatic, Orthochromatic, or Orthoskiagraph^ Photography. These terms are used to distinguish that branch of photography which attempts to render in correct or more truthful gradations the colours as seen by the human eye. The two words " iso-" and " ortho-chromatic " are derived from Greek roots signifying equal or correct colour tones ; and whilst neither are scientifically accurate in their description, as they are in common use, they are here used. The merest tyro is too soon aware that the sensitive salts of silver are incapable of translating colours into correct monochrome as seen by the human eye. Thus a Dright yellow sunflower or skein of yellow wool is reproduced by photography as black, and many shades of blue are, though visually dark reproduced as nearly white. In the article upon the Spectrum (g.v.) it will be seen that a ray of white light is split up into its various constituent rays of different colours : the brightest of these colours to the human eye is yellow, and then orange, two colours which are reproduced by black. As the question of colour is so closely connected with this subject, a brief consideration of colour will not be out of place. No sub- stance known possesses any colour of itself. Colour is caused solely by the action of the substance on the light which falls upon it. Natural bodies possess the power of absorbing the light which enters them, and they have this power in a selective manner; that is, some objects select and absorb certain of the coloured rays and reflect others. When all the light is wholly absorbed, 260 DICTIONARY OF PHOTOGRAPHY. [ISO the substance appears black ; but when all the rays of light are equally but not entirely absorbed, grey is the resultant tint. Colour, therefore, is due to the absorption or extinction of certain of the coloured rays of white light within the object, and the remaining rays are reflected to the eye, imparting to that object its characteristic colour. It must, however, be borne in mind, that all objects, irrespective of colour, reflect white light when illuminated by white light. An engraver, when translating into monochrome any coloured objects, gives not only a correct form, but also a correct idea of colour, by giving varying depths of deposit of the pigment used, so as to give to the eye, were a gamut of colours engraved, a steadily increasing depth of tint from absolute white to deepest black, so that each tint or colour receives its quantum of deposit that will accord to some extent at least with the colours as they affect the human eye. In the diagram on next page, fig. 43, are shown what are called the primary colours of the spectrum, traversed by numerous dark lines, which are called Fraunhofer's lines, after their discoverer. To give an idea of the relative luminosity of colours to the human eye, the following diagram has been prepared, from which it will be seen that the greatest luminosity is between D and E fig. 44, or in the yellow, shading off rapidly through orange on one side to the red, and through yellowish-green and green to the violet on the other. In fig. 45 is given the curve showing the luminosity of colours to the ordinary photographic dry plate. Thus it will be seen that the most luminous part to the dry plate or photographic retina is between F and H, and practically no luminosity between C and F, where the greatest visual luminosity resides. It is obvious, therefore, that to reproduce colours in correct gradation as seen by the human eye, we must in some way exalt the sensitiveness of the ordinary plate to green, yellow, orange, and orange red, and at the same time reduce the sensitiveness to blue. It has been found that the particles of silver haloid are most sensitive to those colours which they absorb, and numerous experiments have been undertaken to find a substance which would enable the silver sal to absorb the whole of the rays in the same intensity as we see them ; but this has been found so fai impossible, and although means have been discovered to rendei the silver salts more sensitive to the less refrangible rays between C and F, which are most luminous to the eye, yet they still 261 DICTIONARY OF PHOTOGRAPHY. [ISO remain most sensitive to the blue rays about G. These colours are toned down or robbed of some of their actinic value by being filtered through coloured media; but unfortunately the total sensitiveness of the whole plate is lowered in consequence. Colonel Waterhouse was the first to suggest the application of NMLH C PEDCBA Kig. 46. eosin, one of the coal-tar dyes. Numerous other experimental- ists, such as Abney, Carey Lea, Eder, Vogel, and Bothamley, continued the researches in this direction. I do not consider it necessary to enter at great length into the chemical composition the various dyes used. Nor shall I refer to any extent to the chemical theories involved in this question. For information on this point the reader is referred to Professor Meldola's interest- 263 ISO] DICTIONARY OF PHOTOGRAPHY. ing work on " The Chemistry of Photography " (p. 288, et. seq.). Vogel was the first to formulate a workable process for using these dyes in 1873, but his researches were confined to the collodion process only. In 1882, Attout Tailfer, a French chemist, successfully worked a process for the gelatine dry plates, and this process is protected by a patent in England and France, and it is worked commercially by Messrs. B. J. Edwards and Co. Tailfer's process consists of the use of eosin or erythrosin in conjunction with ammonia, and the same may be added to the emulsion at the moment of formation of the sensitive salt, or the previously prepared and coated plate may be bathed in such a solution ; and these plates are thereby rendered more sensitive to yellow and yellowish-green. Dr. Vogel has introduced com- mercially a process in which u azaline " is used, and this is said to be a mixture of quinoline blue (cyanin) and quinoline red, by means of which the sensitiveness is still further increased for the orange, orange-red, and red rays. The chart of curves on p. 136 is taken from Meldola's work mentioned above, and is constructed from results given by Bothamley and Abney, and it shows the relative sensitiveness of the film dyed with various colouring matters. (1) Violet dyes ; (2) green dyes ; (3) iodine green ; (4) cyanin; (5) eosin; (6) ammoniacal rose, Bengal; (7) coerulein ; (8) chrysaniline ; (9) eosin on chloride of silver ; (10) eosin and cyanin mixed; (11) erythrosin on iodide of silver and nitrate of silver; (12) erythrosin on bromide of silver; (15) erythrosin on chloride of silver ; (14) cyanin on chloride of silver. Where the haloid is not specified bromide of silver has been used. It will be seen by an examination of the above chart that, although the sensitiveness of the haloid salts is increased towards the less refrangible rays beyond E in the yellow and red, yet the greatest sensitiveness is still in G and H in the blue ; therefore, to obviate this, a coloured screen is used, usually of glass of a more or less deep tint of yellow, which was first suggested by Professor Crookes when editor of the Photographic News, long before any iso- or ortho-chromatic process was thought of. The glass screens may be used either in front of the lens, between the combinations of a doublet, or behind the lens ; and it should be of absolutely plain glass, with parallel surfaces, so as not to interfere with the definition of the lens ; or a really serviceable makeshift may be made according to the plan proposed by 264 DICTIONARY OF PHOTOGRAPHY. [ISO Engler, in which glass plates are first of all waxed, and then polished and coated with a plain collodion, as free from structure as possible, and when thoroughly dry are coated with gelatine, stained to the desired tint with aurantia or Manchester yellow. For general use a good lemon tint should be made. When thoroughly dry the gelatine film may be stripped from the glass and cut into pieces, and enclosed between small brass plates or cardboard, cut in the form of the ordinary diaphragm, in place of which it is used. In working iso- or ortho-chromatic plates extreme caution should be exercised as to the illumination of the dark-room ; as little light as possible, and that of only a deep ruby, should be used, and the plate should be covered as far as possible during development. No special developers are required as the plates will work with any ordinary developer, whether pyro, quinol, or ferrous oxalate. Their sensitiveness to white light is generally about the same as other plates, and when used with a yellow screen require from three to ten times the ordinary exposures, according to the depth of tint. The value of colour- sensitive plates is seen in the better rendering of foliage, distance clouds, and water, and in portraiture in the suppression to a great extent of freckles, and the truer rendering of light or golden hair. For copying pictures or coloured objects of any kind these plates are now universally used, and are also of great benefit in photomicrography. The following are the formulee for the princi- pal baths for sensitising ready-prepared plates :- Bothamley's Process. Solution of erythrosin (i in 1,000) ... I to 2 parts. Ammonia (10 per cent.) ... ... .. 1 part. Water 8 parts. Dust the plate, and immerse for two or three minutes. Allow to drain on blotting paper, and dry in the dark. The conclusions drawn from a series of experiments, and given by Mr. Bothamley at the Photographic Convention, 1889, were : "(1) Alcohol up to 10 per cent, has no influence whatever, and may be dispensed with where the dye is soluble in water. Alcohol in larger pro- portion produces a distinct decrease in sensitiveness. (2) With a concentration of the dye up to 1 in 5,000, the washing after immersion is totally unnecessary. (3) A preliminary bath may 265 ISO] DICTIONARY OF PHOTOGRAPHY. be omitted." It is as well to point out that the use of eosin or erythrosin in conjunction with ammonia is covered by Tailfer's process, and that permission must be obtained from the English licencees to work the same. Vogel's Formula. Azaline tincture i oz. or 29.5 c.cm. Distilled water 3^ ozs: ,, 103.25 „ Alcohol or methylated spirit ... 4 drms. „ 14.75 » Liquid ammonia ... ... 1 drm. „ 3.6 „ Dust the plates, and immerse for one minute ; rock during immersion. Drain on blotting paper, and dry in the dark. Schumann's Cyanin Bath. Soak the plate in 1 or 2 per cent, of ammonia solution for two or three minutes ; then immerse in — Alcoholic solution of cyanin (1 in 500) 168 mins. or 10 c.cm. Ammonia ... ... ... 68 ,, 4 Alcohol 168 ,, „ 10 Distilled water 7 ozs. 200 „ for not more than 100 seconds, drain and dry. Bothamley's Sensitiser for Pictures. Solution of rose Bengal (1 in 1,000) ... 10 parts. Solution of cyanin (1 in 2,000) 10 Solution of erythrosin ( 1 in 2,000) ... 10 ,, made alkaline with 1 per cent, of ammonia. These are the principal baths, and from these others may be used, which may be made on the above lines. The usual distinction between iso- and ortho-chromatic plates is that the former are prepared by adding the dye to the emulsion when making the same, and that the latter are plates prepared by bathing after being coated and dried. Before closing this article, it is but fair to state that Mr. F. E. Ives, of Philadelphia, U.S., has made numerous ex- periments with collodio-bromide, and finds that the best results are obtained by flowing over the coated plate, as soon as the 266 DICTIONARY OF PHOTOGRAPHY. [Kal collodion has set, a strong alcoholic solution of chlorophyll, obtained by digesting blue myrtle or the periwinkle (vinca major) leaves in alcohol, then immersing the plates in water strongly tinted with blue shade eosin, and drying. This process is said to render the plate sensitive for the whole range of the spectrum. Ivory. The teeth and tusks of the elephant and walrus. Photographs can be obtained on ivory by coating with an emulsion or by transfer as in the carbon process. Ivory Black. Made by calcining ivory in close crucibles ; used as an ingredient for black varnish, etc. Japan Varnish. See Varnish. Kallitype. A printing process invented by Dr. J. Nichol, the principle of which was that ferric salts were reduced by light to ferrous, and in this condition reduced to the metallic state a soluble silver salt. The paper is first sized, then coated with either of the following solutions, which contains Sodio-citrate of iron solution ... 20 per cent. Neutral potassium oxalate ... ... 5 ,, ,, The sodium salt can be replaced by the ammonium or potassium salts, or by the tartrate salt, or by mixtures of these compounds. The paper is printed in the same way as platinotype, and developed for bluish tones on a solution containing Potassium oxalate 20 per cent. Silver nitrate 1*5 ,, ,, to which sufficient ammonia is added to dissolve the precipitate first formed. For neutral black tones a solution containing Potassium oxalate 10 per cent. Silver nitrate ... 1*5 M and ammonia is used. For sepia tones a solution containing Borax 7 per cent. Silver nitrate ... ... 15 ,, ,, Ammonia as above, is used. Good results may also be obtained by sensitising with Ferric oxalate ... 5 per cent. Ferric tartrate 5 ,, Oxalic or tartaric acid 1 „ „ 267 Kal] DICTIONARY OF PHOTOGRAPHY. For developing this either of the two following solutions is used : — I. Potassium citrate 15 per cent. Sodium acetate ... ... ... 10 M „ Silver nitrate ... 1*5 „ Ammonia to dissolve the precipitate first formed. Potassium citrate 15 per cent. Potassium oxalate ... ... ... 10 „ ,, Silver nitrate 1-5 Ammonia as above. After development the prints should be placed in a clearing bath of a 20 per cent, solution of citrate or tartrate of potassium, sodium or ammonium rendered alkaline by liquid ammonia. If greater contrasts are desired, 2 to 10 parts of a 5 per cent, solution of potassium bichromate should be added to every 1000 parts of the developer. A modification of the process was published later, in which the silver was incorporated with the sensitising solution, and applied to the paper, the solu- tion being a mixture of ferric oxalate, ferric tartrate, oxalate and nitrate of silver, and free nitric acid. The prints were deveLoped on the following solutions : — For Black Tones. Rochelle salts 10 parts. Borax 10 „ Water 200 For Purple Tones. Rochelle salts 10 parts. Borax 2-5 ,, Water 100 „ For Sepia Tones. Rochelle salts ... ... ... ... 5 parts. Borax 175 part. Water ... ... ... ... ... 100 parts. Hydrochloric acid a few drops. To the developers a few drops of a dilute solution of potassium 268 DICTIONARY OF PHOTOGRAPHY. [Lea bichromate were added to keep the prints clean, and to increase contrasts ; after development, they were immersed in a solution of Rochelle salts ... ... ... ... 10 parts. Water 100 ,, and then in Water 80 parts. Ammonia ... ... ... 1 part. and subsequently washed and dried. Kaolin. Synonym : China Clay. A very fine hydrous silicate of alumina, containing about 14 per cent, of water. It is a decomposition product from natural decay of felspar. It is used for cleaning plates, and was used in the old wet process as a mechanical purifier of the silver bath. Lac. See Shellac. Lamp. Well known as the source of artificial illumination in the dark-room. All lamps should be fitted with one or more screens of ruby or orange glass, so as to decrease or increase the light as desired. As some amateurs may desire to rig up a temporary lamp whilst on tour, the following suggestions may be useful : — Every amateur should comprise amongst his travel- ling paraphernalia one or two square feet of ruby or golden fabric ; by means of this a lamp may be improvised from an ordinary candle, or night-light, or a Chinese lantern, or the side may be knocked out of a card-board hat-box. The author has before now changed plates when away from home by the aid of this little piece of ruby cloth by placing a candle in the empty fire-grate, and the ruby cloth over the bars. Lampblack. The very light form of carbon produced by burning pitch, resin, or any other smoky substance with limited access of air, and collecting the soot formed. Landscape Lens. See Lens. Lantern, Optical. See Magic-Lantern. Lantern Slides. See Transparencies. Latent Image. See Image, Latent. Lead, Acetate of, (Ger., Essigsdures Blei; Fr., Acetate de 269 Lea] DICTIONARY OF PHOTOGRAPHY. plomb; Ital., Acetato di piombo). Pb(H 3 C 2 0 2 ) 2 ,3H 2 0 = 379. Synonyms : Plumbic Acetate, Sugar of Lead. Made by dissolving litharge in an excess of acetic acid and subsequent purification and crystallisation. It is met with in white crystals usually massed together which have an intensely sweet taste, and smell faintly of acetic acid. It is used as an addition to some combined toning and fixing baths, and has been suggested as a hypo- eliminator but the benefit is doubtful. Solubility ; 60 per cent, in cold and 200 per cent, in hot water ; 12 per cent, in alcohol ; insoluble in ether. Lead, Chr ornate of (Ger. Bleichromat ; Fr., Chr ornate de plomb; Ital., Cromato di piombo). PbCr0 4 = 323*5. Prepared by double decomposition of lead, acetate, and chromate of potassium. It is a yellow insoluble powder, and is only used as colouring matter for certain dark room fabrics. Lead, Nitrate of (Ger., Bleinitrat; Fr., Azotate de plomb; Ital., Azotato di piombo). Pb(N0 3 ) 2 = 331. Synonym : Plumbic Nitrate. Made by dissolving litharge or white lead in nitric acid, evaporating and crystallising. It occurs in hard, white, opaque, octahedral crystals. It is used in intensification (q.v.) as a constituent of some combined toning and fixing baths. Lead, Toning with. A solution of acetate of lead has been proposed as a toning bath for albumenised and gelatino-chloride papers. The following formula has been suggested : — Lead acetate or nitrate ... ^ oz. or 15 grms. Sodium hyposulphite ... 4 ozs. „ 120 „ Distilled water 20 ,, ,, 500 c.cm. The toning action in any bath of this character is entirely due to sulphuration as described under Combined Toning and Fixing (q.v.). Least Circle of Aberration is the smallest possible section of the cone of rays of light emergent from a lens. Practically it is the nearest approach to a perfect focus that parallel rays of light can have. Leimtype. A special process for the production of half-tone blocks invented by Husnik of Prague, the particulars of which have never been published. 270 DICTIONARY OF PHOTOGRAPHY. [Ldl Lens. An optical term given to discs of glass bounded by two spherical surfaces, or by a plane and a spherical surface. A true lens is one which has the form shown in fig. 47, a ; but the name now includes many other shaped glasses or combination of glasses from the analogy of their action upon light. The first mention of the use of a lens which I have been enabled to trace out is by the Chinese moralist Confucius, 748 B.C., who says, " As we use a glass to examine objects, so must we look to the present for futurity." In the Western classics, about a.d. 40, mention is made by Seneca, Aristophanes, and other writers for the first time of globes of water and globes of glass ; but of a true lens absolutely no mention is made, and it is even doubtful whether they were more than conversant with the burning powers of the above globes. There is, however, in the Assyrian Section of the British Museum a piece of rock-crystal of plano-convex form, which Sir David Brewster states was designed for magnifying. It has been shaped oval, evidently by a process of chipping and grinding, and both plane and convex surfaces have been partly polished. It seems more likely, however, that it was used as an ornament. The date of this is about 720 B.C. There are also in the British Section several antique glass bosses, which have been evidently polished and cut to a wonderfully true curve. These, however, it is supposed, were used for ornamenting shields, sword-handles, etc. The first lenses that we can find any really reliable record of are of those of spectacles, and these are mentioned by Giordano da Rivalto in 1305, as having been invented only " twenty years ago." This will fix the date at 1285, when they were invented by Salvino d'Armati, a Florentine. Like some of those who have followed in his footsteps in the present day, he desired to make his fortune by this invention or discovery by keeping the same secret ; but the patent laws, unfortunately for him, were not quite so well developed as at the present time ; and a scientist of Pisa, Alessandro della Spina, having seen some of Armati's spectacles, made some for himself, and published the method of manufacture. The gradual and perhaps accidental deepening of the curves of these lenses produced shorter foci, till, by the accidental placing at some distance apart of a concave and convex lens by some children of a Dutch spectacle maker, the telescope was discovered, and from this origin all lenses of the present day 27 1 Leil] DICTIONARY OF PHOTOGRAPHY. have been evolved. All lenses are made of crown or flint glass, the former being free from, and the latter containing lead, the flint being slightly more refractive than the crown. The sectional forms of the various lenses are here given : — a I c Fig. 47 .— a, double-convex ; b, plano-convex ; c, concavo-convex, or converging meniscus ; d, double-concave ; e, plano-concave ; /, divergent meniscus. The first three, a, &, c, which are thicker at the centre than at the margins, are convergent or positive ; and the second three, d, e,f t are divergent or negative. All lenses are formed by the union of prisms, and therefore have to a great extent the pro- Fig. 4 8. perties of prisms. Fig. 48 will show the way in which the prisms are united to form a biconvex lens, and the concentration of the rays of light by such prisms or lens. Fig. 49 is the representation of the prisms forming a double- concave, and the divergent action of such prisms or lens upon the rays of light. It is obvious that 272 DICTIONARY OF PHOTOGRAPHY. [Len by combining the two lenses the convergent or positive action of the one may be counteracted by the divergent or negative action of the other. It is upon these principles that the whole of the modern lenses are calculated. As soon as it was announced in 1830 by Daguerre and Fox Talbot that they had been enabled to obtain a comparatively permanent image in the camera obscura, Fig. 49. the ability and skill of mathematicians and opticians were brought into play to produce lenses which should be free from the objections common to the double-convex lens, which was the only one used in the camera obscura in those days. The single lens was replaced by the achromatic combination of the telescope. This was eventually reversed, and the plane side presented to Fig. 50. Fig. 51. the object, as in fig. 50- Then Wollaston's meniscus (fig. 5-) came to be recognised as a means of extending the definition ; and in 1840, Chevalier, a Paris optician, still further improved it by a different method of achromatising the lens. But in the following year, through the agency of Voigtlander, a practical optician, a lens designed by Professor Petzval, a mathematician of Vienna, was made and introduced commercially in 1841. This was the 273 X Len] DICTIONARY OF PHOTOGRAPHY. portrait lens ; and it is a remarkable fact that it is the model for the finest portrait lenses of the present day. The following Fig. 52. Fig. 53. (fig. 53) is a sketch of Petzval's original portrait lens : — The dark shaded parts are crown, the light shaded parts are flint glass, and, as will be seen, the front combination exists of a double- Fig. 54. Fi S- 5,5- convex crown cemented to a double-concave flint, and the back of a flint concavo-convex separated from a double -convex lens of crown glass ; the flint concavo-convex having such a negative 274 DICTIONARY OF PHOTOGRAPHY. [Len refractive power as to completely balance the positive aberration of the whole combination. This has been modified by Dallmeyer, by Grubb, and the noted American optician Morrison ; but all Fig. 5 fi. are constructed on the principle of above lens (fig. 53). Professor Petzval calculated at the same time a landscape lens (fig. 54), which was not introduced commercially till 1857 ; and an English Fig. 57- Fig. 58. optician, in 1858, introduced a lens having a concave glass in place of the diaphragm to lengthen the focus and flatten the field, and Dallmeyer introduced his famous triplet (fig. 55), which was much used and admired. Single lenses were firs 275 1 Lenj DICTIONARY OF PHOTOGRAPHY. of all of the kind shown in fig. 51, with which extremely small diaphragms are necessary to reduce spherical aberration and distortion. This was improved on by Grubb, and his lens is shown in fig. 56, in which a crown-glass lens of meniscus form is presented to the object, and is cemented to a flint Fig. 59. Fig. 60. meniscus. This gave a much flatter field, and spherical aber- ration was much reduced, allowing the use of larger dia- phragms. Dallmeyer introduced his single lens (fig. 57), which consists of a negative flint enclosed between two positive crown- glass lenses. 1 This enabled a much larger aperture to be Fi S- 61. Fig. 62. employed, and totally eliminated spherical aberration. Marginal definition and flatness of field were both improved. To obviate distortion, many doublet lenses were introduced, that of Mr. Ross being shown in fig. 58. This instrument possesses a wide angle, giving splendid definition, without any distortion or aberration, In all doublets the diaphragm being placed between the combina- 276 DICTIONARY OF PHOTOGRAPHY. [Len tions, the distortion of the one is cured by the distortion of the other. In i860 Harrison of New York introduced his globe lens (fig. 59), which had an extremely wide angle, but which, from too close an adherence to the globe form, gave a flare. Busch improved upon this with the pflntoscope (fig. 60), and Dallmeyer Fig. 63. introduced his wide-angle rectilinear (fig, 61). Steinheil intro- duced what he called his periscopicjens (fig. 62), which consists of two uncorrected meniscus lenses of crown glass ; and chro- matic aberration not being eliminated, the focussing screen had to be brought nearer to the lens after focussing and before exposing, by ^ of the focal length of lens. Mr. Sutton's panora- mic lens (fig. 63) consisted of two concavo-convex lenses, with spherical curvatures and a hollow space between filled with water. This possessed a wide angle, and gave no, or practically no, spherical or chromatic aberration, but from its peculiar con- struction, and the necessity of using curved plates, has never 277 Len] DICTIONARY OF PHOTOGRAPHY. come into general use. In figs. 64, 65, and 66 are shown lenses by Steinheil, fig. 64 being an aplanatic rapid rectilinear, and figs. 65 and 66 wide-angle aplanats, some of the finest lenses of the day ; and in figs. 67 and 68 are shown two more of Steinheil's lenses, which work at //2*5, No. 67 being for groups, No. 68 for portraits. In fig. 69 I am enabled, by the kindness of Messrs. Fig. 66. Perken, Son, & Rayment, to give a sketch of the Euryscope lens, which is composed of two symmetrical combinations of flint glass, and works at an aperture of //6, a great gain for rapid work. These lenses are perfectly free from spherical and chro- matic aberration and distortion, and for such a large aperture have a wonderful depth of focus, with an extremely flat Fig. 67. Fig. 68. field. Mr. Dallmeyer has introduced a rectilinear or non- distorting single lens, which works at a large aperture, which is absolutely free from distortion, without astigmatism, and a very flat field (fig. 70). Thus far I have endeavoured to give some slight sketch of the leading and fundamental forms of all lenses, and whilst numerous modifications exist which may be considered advantageous by some, they are all made on the principles involved in one of the above. A lens, or rather a 278 DICTIONARY OF PHOTOGRAPHY. [Len doublet lens, is said to be symmetrical when both combinations are precisely alike and possess the same optical properties. In all such combinations the diaphragm is placed midway between the two. Non-symmetrical lenses are those in which one of the Fig. 69. combinations is the more powerful in some way or other, in which case the diaphragm is placed at the exact proper distance as calculated by the optician. To enable the amateur to select a lens for his own use, several considerations are necessary, and Fig. 70. although he may be to some extent guided by the vendor of the lens, the following may be of some assistance : — The lens should be absolutely free from striae ; these can be detected by placing the eye at the focus of a lens before a strong light such as gas or 279 Len] DICTIONARY OF PHOTOGRAPHY. a lamp ; bubbles can also be seen, but too much stress need not be laid on the presence of one or two bubbles, as when not present in very large numbers they may be disregarded. For what purpose is the lens required? For ordinary landscape work, architectural subjects, interiors, or portraits ? For landscape work pure and simple there are few lenses to equal the achromatic single landscape lens, which gives brilliant negatives ; and although distortion is present it may be disregarded, and it is practically unnoticeable in small views except by mathematical measurement. Some of these lenses are now made to work aplanatic with an aperture of //8, and are therefore of nearly the same rapidity as the rapid rectilinear, which is, however, the lens par excellence for amateurs, as its use is practically unlimited, especially as some are now made to work at almost as large an aperture as a portrait lens. Few amateurs will require a portrait lens, as they are not only difficult to use properly, but are exceedingly limited in action, and also expensive. The question of how much view to include on a plate is another important consideration which should not be lost sight of (See Angle, Width of) ; for ordinary work it should never exceed 5o°to 55 0 , and 45 0 is decidedly better, as this is about the angle included by the human eye. If a much greater angle be included, the result* ing' pictures have a distorted appearance, because it is extremely unlikely that the eye will be placed at a focal length of the lens from the picture. The glass of which lenses are made should be absolutely colourless ; this can be tested by laying the lens upon a sheet of white paper and looking down through it. Some of the cheaper lenses are made of glass which is not colourless : and any colour, especially brown or yellow, will make the lens slow. As stated under the article Glass, it is absolutely necessary to obtain it perfectly homogeneous, free from striae, colourless, and transparent ; bubble, lines, and opaque particles in lenses merely obstruct a certain amount of light, but striae prove imperfect and unequal mixture of the substances composing it, and will therefore give different refractions. The glass is made in the following manner : — Crucibles of fire-clay of particular form are raised to a white heat in a furnace, and when the fuel ceases to give off smoke, they are charged with the materials, and the heat is continued for eight or ten hours. The crucible is now raised to a white heat for four hours, and the mixture stirred with a bar 280 DICTIONARY OF PHOTOGRAPHY. [Leu of potter's clay. Six times from hour to hour the mixture is stirred. The heat is then reduced, that the bubbles may rise, and again at the end of two hours the heat is raised to make the glass fluid ; again stirred for two hours, and the crucible and the openings of the furnace closed and left for eight days to cool. The crucible is taken out and broken, and the glass is removed and divided into pieces. The divided glass is examined and sorted, the finest being retained for astronomical purposes, the second quality for photographic lenses, and the third for ordinary magnifying glasses, the rest being waste, which is added to the next melting. The pieces are then softened in a muffle furnace, and formed into plates about two or two and a half inches thick. Sometimes the plates are then cast, after being softened by heat, into rough moulds of clay or iron coated with sand so as to give them a rough form ; but the best opticians prefer grinding, as striae and bubbles are not so liable to be formed, except with condens- ing lenses in which striae and bubbles are not of so much impor- tance. The rough-shaped glasses have now to be made into perfect lenses, for which purpose extreme care is absolutely necessary, approximate forms being given by grinding with emery in concave or convex tools of cast iron. It is in the follow- ing operations that the greatest skill and care of the optician are required : — The roughly shaped lens is now to be ground with emery in spherical tools of brass or iron, which tools are made either by casting, or by rough casting and subsequent work in a lathe. These are given the necessary curves by means of extremely accurate gauges of copper. The roughly fashioned glass or lens is fixed to a plate of brass by means of pitch, and is then worked in the tool with rough emery moistened with water; when the glass is found to touch the tool at all points, finer emery is used, and it is worked a little more, the gauge being now frequently applied to the tool, to see that the radii of curvatures are not altered ; then finer kinds of emery still are used, till at last some degree of polish begins to show ; fine putty powder is then substi- tuted for emery, and the polishing is begun. The operation of polishing is really the test of a good optician, as this process may alter the sphericity or the radii of curvature of the lens to such a degree as to completely alter the character of the lens. The lens is fixed on to a block of wood by means of a pitchy cement, and a tool is coated with a resinous mixture, and fine rouge is sprinkled 281 Len] DICTIONARY OF PHOTOGRAPHY. on the tool when cold, and the polishing finished entirely by hand. When two lenses are required to be cemented together so as to present one common surface, they are slightly warmed, and a drop or two of Canada balsam is applied, and the two lenses pressed forcibly together, so as to squeeze out excess of balsam. When cooled, they present the appearance of one single piece of glass, and cannot be separated without heat. When two lenses have not a common surface, three small pieces of tinfoil are introduced at equal distances apart between their margins, or when the separation is greater, as in most portrait lenses, a ring of brass is used for the same purpose. When the lens is fixed in its brass ring, so that it cannot be taken out without raising the bent edge of the brass, it is said to be set. Under the article Focus will be found numerous rules and tables, which may be of some service. Since the article on lenses was originally written great advances have been made, and new forms of lenses have been introduced, in the majority of which the new optical glass manufactured at Jena is employed. The following are the principal novelties, and in those cases in which diagrams are given I am indebted to the makers or agents for the same. Messrs. Swift & Sons' new lenses are fig. 71, a universal paragon lens working at U.S. No. 2 or y 5*65, and fig. 72, Swifts portrait paragon, a symmetrical lens, working at U.S. No. I, or //4, the combinations of this lens being of the new Jena glass. E. Suter of Basle has a series of aplanatic lenses, which work at U.S. No. 2, Fig. 71. 282 DICTIONARY OF PHOTOGRAPHY. [Len and also a very fine lens of the symmetrical type, manufactured of the new glass, which works at No. 2 U.S., or //$'$. With these Fig. 72. the flatness of field is much increased, the angle of sharpness being about 6o°. He has also introduced a new wide-angle Fig- 73- aplanat, which has an effective aperture of //12 for an angle of 6o°, and //16 and //22 up to 90° a diagram (fig. 73) of which I am enabled to give by the kindness of Mr. Gotz, the 283 Len] DICTIONARY OF PHOTOGRAPHY. English agent. The field of this lens is very flat, and the front lens may be used as a single landscape by unscrewing the same, and screwing into the place of the back lens. The front combi- nation is of Jena flint combined with crown glass, and of great curvature, whilst the back glass is of much less power. Messrs. Taylor, Taylor & Hobson, Wray & Swift have introduced special lenses, which, in the smaller sizes, work at f/$'6 for detective cameras, although any of the above lenses of sufficiently short focus would answer equally as well. Messrs. Perken, Son, & Rayment have issued a new wide-angle euryscope, working at Fig- 74- //c/5 ; and Messrs. Voigtlander & Son have introduced two new wide-angle lenses, the one a landscape, composed of a bi-convex crown cemented to a bi-concave lens. Both glasses, of the new Jena material, are extremely light, and of little dispersive power, in great disproportion to the index of refraction ; thus the bi- concave lens, which is usually a flint, is more like a crown glass lens. It subtends an angle of 76° has an exceedingly flat field, and distortion of the marginal lines is reduced to a minimum ; working aperture, //16. The other lens is a new wide-angle euryscope, which works at f/6 (approx.), and includes 284 DICTIONARY OF PHOTOGRAPHY. [Len an angle of 8o°. This also is constructed of the new glass. From its large aperture and short focus it is eminently suited for group work in confined situations, and for instantaneous or hand cameras. In 1889 Ross & Co. obtained a patent for a new form of lens, which they called the " Concentric," from the fact that the internal and external surfaces of each combination were struck from a common centre, as shown in fig. 74. It will be seen that these lenses are practically what would with the old glasses be negative lenses — that is, they are thinner in the middle than at the margins ; but by the use of particular kinds of Jena glass the manufacture of such combinations with a positive focus was rendered possible. The advantage of these lenses lies in the fact that they are free from chromatic aberration and astigmatism ; and a lens the focus of which is one-third less than the longer base line of the plate covers that plate sharply with //19. Some of the lenses are made to work at //16, and at this aperture they give a general softness of definition, which is exceptionally pleasing. The only disadvantage is that focussing must be done with the aperture which is to be used for exposing with. These lenses possess a flatness of field which is very remarkable. Zeiss of Jena has introduced several new forms of lenses, all constructed of Jena glass, and possessing a freedom from astigmatism and chromatic aberration.quite remarkable. Several opticians have also introduced telephotographic lenses — that is, lenses which, with moderate extension of the camera, give much-enlarged images. The lens is the most important and at the same time the most expensive part of a photographer's outfit. Too much care cannot be taken, therefore, in choosing or in keeping the same. Lenses should always be kept, when not in use, in a leather case, or else in a tin box padded with wool or washleather to prevent the access of light, air, and dust. The inside of the lens-tube and the diaphragms should be occasionally re-blackened to avoid disturbing reflections. If the lenses become dusty or somewhat dim, they should be most carefully and tenderly wiped with a piece of soft silk or washleather, and when it is necessary to clean the internal surfaces of lenses (doublets, portraits, etc.), it is advisable to remove one combination and clean it, and then replace it before unscrewing another combination to clean ; by this means displacement of the combination cannot take place. With some old lenses a peculiar tree-like marking makes its 285 I*en] DICTIONARY OF PHOTOGRAPHY. appearance, which, to uninitiated eyes, appears to be in the middle of the glass. This is due to the balsam, which is used in cementing the glasses of the combination together, becoming old and starring. In such a case it is advisable, if the lens is worth anything at all, to send it to an optician, who will unset the lens and properly re-cement and reset it : if the lens is not of much value, and the owner is desirous of trying his hand at a practical remedy, the lens should be placed in some methylated spirit or turpentine in a water-bath and gradually heated, when the cement will be softened. The two glasses can then be taken apart, well wiped and cleaned, and re-cemented by a drop or two of Canada balsam, and gently warming. If by accident one of the lenses should be scratched, it is preferable to fill the scratch with black varnish, as the loss of light is in this case preferable to the dis- turbing reflections of the scratch. The following notes on choos- ing and testing a lens are written from a practical standpoint, and if an accurate scientific examination is required, it would be advisable to send the lens to the Testing Department at Kew ; but if a lens answers successfully to the tests described below, it may be accepted as practically perfect. The first point to decide in choosing a lens is to determine for what class of work it will be required ; but presuming that my readers are amateurs, and that many of them will be, or have to be, content with one lens, then a doublet or rapid rectilinear should be chosen. Perhaps it would be advisable to state for the benefit of those who are totally ignorant of the different forms of lenses, that there are three main classes in lenses: (i) portrait lenses, specially con- structed for the requirements of portraiture ; (2) doublet or rapid rectilinear lenses, which are constructed for architectural work, groups, copying, and landscapes, and may be termed universal lenses ; (3) landscape or single lenses, which are most suitable for pure landscape work. We have recommended the doublet lens for all-round work for the amateur as the most suitable lens, and which may be used for portraits, groups, architectural work, both exterior and interior, and landscapes. The next point to decide is the focal length of the lens; this is usually fixed by the optician at a certain length, which increases with the size of plate for which the lens is required. The following may be assumed to be the focal length of the majority of commercial lenses for the given-sized plates : — 286 DICTIONARY OF PHOTOGRAPHY. [Len For 4i x 3i or £-plate, the lens is usually 4 to 5-in. focus. For 5 x 4 6 „ For 6£x 4£ or Opiate, 8 „ 9 For 7 X 5 9 ,» 10 „ For *h x 6£ or y-plate, 10 „ 11 For IO x 8 12 „ 14 For 12 X 10 15 M 16 If more than one lens is required, I strongly advise the second lens should be a long-focus single or landscape lens of a focal length equal to i£ times that of the doublet. If a third lens is required, then a doublet of short focus may be chosen, the focus being about two-thirds that of the doublet. Thus, for a half-plate, we have first a rectilinear of 9-in. focus, then a single lens of 13^-in. and lastly a second doublet of 6-in. focus. Such a set of lenses will enable us to obtain pictures of almost every character, and to obtain the images of objects varying in size. See Wide Angle. Many an amateur possessing a single or landscape lens, which he may have purchased at the outset with his outfit, yearns for a doublet, in the hope of improving his pictures, acting under the very general impression that far finer results are given by the latter lens. This, however, is a mistake. The sole superiority of a doublet consists in its working at a larger aperture, and in being free from Distortion {q.v.). It may, perhaps, be of interest to some if I state that on examining my register of exposures for three months, I find that out of 137 exposures a doublet was only used twenty-three times ; of these in nineteen instances it was for copying diagrams, the other four for interiors. There is a good deal of talk about distortion caused by single lenses, but few would be able to detect the same in my prints, many of which have buildings included in the views. Testing a Lens. — The first point to decide in testing a lens is its equivalent focus or focal length ; the second point, the ratio aperture of the diaphragms ; the third, covering power of the lens ; (4) the flatness of the field ; (5) the freedom from spherical and chromatic aberrations ; (6) the freedom from flare and ghosts ; (7) the accurate centreing of the lenses ; (8) the perfect polishing of the surfaces ; (9) the freedom from striae or waves. (1) To Determine the Equivalent Focus. — Several methods are given under this heading. 287 Len] DICTIONARY OF PHOTOGRAPHY. (2) To Determine the Ratio Aperture of the Diaphragms. — This is described under Diaphragms (q.v.). (3) The Covering Power of the Lens. — To determine the covering power of the lens is by no means a difficult object, especially if the lens be used with a given-sized plate, that is for the one for which it is advertised. Many lenses will, with small diaphragms, cover a much larger plate than that for which they are designed, and all lenses will cover a smaller plate. If you wish to test whether a lens will cover a given-sized plate, all that you require to do is to affix the lens to the front of a camera which has a focussing screen of the given size, and then focus till you obtain a sharp image at the centre ; it will be at once seen whether the lens will cover. But it is not only necessary that a lens should cover a given-sized plate, but most photographers require that, besides covering a plate, a lens should give good definition all over a plate, which is a totally different thing. Many a lens will cover a plate and yet give very poor definition at the margins, because either (a) the spherical aberration for oblique pencils is not corrected, or (b) it has a very curved field. For special purposes such as hand-camera and instantaneous work it is now considered absolutely necessary that a lens shall give sharp definition over the entire surface of the plate for which it is intended. It is often suggested that to test for this in a lens the best plan is to set up a sheet of newspaper and, focussing sharply, to examine the definition with a com- pound focusser. Personally I prefer to make a practical test as suggested by Mr. W. E. Debenham, as follows: — In order to arrive at a judgment as to whether a lens defines as sharply as it should do, it is necessary to have something which re- presents the standard of sharpness expected from the particular kind of lens. There is no recognised standard, and, for want of it, such absurd expressions as " as sharp as a needle " have sometimes been used to describe exceptionally fine definition. Perhaps the Congress at Paris may settle upon something in the way of a standard for the defining power of lenses. Meanwhile, however, we will describe the standard which we have employed, and which has served to make the work of various lenses com- parable. W e take a sheet of printed matter that is always to be had of one-sized type (nonpareil), namely, " Births, Deaths, and Marriages " column of the Standard newspaper. This column is 288 DICTIONARY OF PHOTOGRAPHY. [Len placed slantwise, the top of the column being farthest from the plate, but each particular line runs square across it as before directed, in the middle of the column, and at such a distance that, when a printed line is focussed in the centre of the field, the image is one-eighth of the original size. The width of two columns in the focussing screen will be just over five-eighths of an inch. With a good portrait lens having an aperture of one- fourth of the focus, the standard adopted as unity by the Photo- graphic Society ot Great Britain up to, say, a 12-in. lens, at all events, the definition in the centre of the field should be such that the small type will, on examination with an eye-piece, be quite legible. The same test may be employed for all lenses, and those professing to be aplanatic will for the most part be found to pass it, though with different degrees of perfection. Of course, by stopping down, almost any lens may be made to define well, at all events, in the centre of the field ; but we are speaking of lenses worked with the largest apertures with which they are supplied, and which, in most lenses of the Steinheil aplanatic type — rapid rectilinear, rapid symmetrical, Euryscope, etc. — will be found from fjy to f/9. In the newer forms of cemented aplanatic lenses, in which the glass from the Jena factory has been utilised, somewhat larger apertures have been practicable, but whatever the aperture is, it is to be supposed that good definition is obtainable with it, and therefore the test mentioned may be fairly employed. When we come to examining the defining power of the lens at some distance from the centre of the field, we shall find with rapid lenses that there is a very great falling off. Taking again as an example a portrait lens of 12-in. focus and of aperture //4, and slewing round the camera so that the image is rendered at a distance of 2 in. from the centre of the focussing screen, we shall find that the small type of our newspaper column is no longer readable. The larger type used for the heading "Marriages," etc., should still be legible, but nothing more. Now insert diaphragm y/8, No. 4 on the universal system, and the small type again becomes distinguishable. With a Steinheil type lens of//8 aperture the definition at this angle may be expected to be still satisfactory without further stopping down. This then is Mr. Debenham's method ; personally I use a modification of it, only in that I cut out several of such columns as he mentions, and paste them on a piece of stout millboard, 289 U Ldl] DICTIONARY OF PHOTOGRAPHY. which is framed to keep it flat. Diagonally across the centre is pasted an ordinary inch tape. The whole arrangement is then hung up flat against the wall, and the camera set up and the image focussed till reduced to one-eighth in size, as suggested by Mr. Debenham. I may remark here that focussing is not effected in the ordinary way on the ground-glass of the camera, but on a specially prepared sheet of obscured glass inserted in the dark slide, which is slid into the grooves at the back of the camera. The specially prepared sheet of obscured glass was made by me by slightly etching the surface of a perfectly true piece of thin plate-glass by means of hydrofluoric acid, and this sheet, when looked through, shows merely a very thin milky haze, which shows no grain, the centre being marked by a cross in fine Indian ink. Focussing is easily effected by means of a magnifier, and the centre of the screen is made to coincide with the central division of the inch tape. The dark slide is now removed, a slow dry plate inserted in the dark-room, an exposure made, the plate developed, and the resulting nega- tive, when dry, carefully examined by the magnifier. The image of the inch tape at once affords a guide as to the limit of sharp focus, and it is therefore possible to state without trouble the extent of sharp focus expressed in terms of the focal length as suggested by Mr. Debenham. For example, a lens was received for examination which gave the following data : — Equivalent focus ... ... ... in. Working aperture ... ... ... f/7'9- Ratio aperture of largest diaphragm //8. Limit of sharp focus fl'% 2 5 = 9'5 in. This lens would therefore cover any plate sharply the diagonal of which was not more than c,\ in. In the case of small lenses, or lenses of short focus I should say, I prefer a still more practical test, and that is to focus sharply, as described above, on the bricks of the house opposite my first-floor window, throwing the window at which I place the camera open. Now these bricks are just 52 feet (by actual measurement) from the point at which the lens is placed, an exposure is made, and the results examined on the negative. This test more nearly approaches the conditions of practical work. (4) To Determine the Flatness of Meld. The foregoing tests 290 DICTIONARY OF PHOTOGRAPHY. [Len aic quite sufficient to determine this, but it" an actual illustration is required of the amount of the curvature of the field we have only to use the newspaper again, and by marking on the base- board the focus for the centre, and then refocussing for the margins, and again marking, we can easily plot out a curve which shall show us exactly the form of the field of the lens. (5; The Freedom Jrom Spherical and Chromatic Aberratio?is. The tests for spherical aberration are comparatively easy ones. A steady, naked flame, such as a candle or small gas flame, may be focussed sharply at the centre of the screen, and the image examined with an eye-piece ; it is preferable to focus on a piece of plain, not ground, glass. If a halo is seen round the flame, it may be assumed that some spherical aberration is present. The objection to this method is that the fringes may not be due to spherical aberration, but to halation or ghosts. Another test, and the one I usually employ, is to fix to a window two small, dark-coloured wafers, with their edges just in contact ; the camera is set up at least ten times the focus of the lens distant, and then the images sharply focussed as stated above, with full aperture ; on the insertion of a small diaphragm there should be no increase of sharpness. Another method is to proceed as above, and affix to the centre of the front lens of a doublet or the centre of a single lens a piece of black paper three-fourths of the diameter of the lens ; the image which is now formed by the margins of the lenses is sharply focussed. The black paper is removed, and a small diaphragm inserted, and the image ex- amined ; if it requires refocussing by racking in or reducing the distance between lens and screen, the lens suffers from negative spherical aberration ; if the camera requires racking out, positive spherical aberration exists. Chromatic aberration, or practically non-coincidence of the visual and actinic foci, is rarely found in modern lenses. No lens is actually achromatic — i.e., without colour — because the finest lenses corrected as much as is possible (I except here all lenses made with the Jena glass) show fring s of colour, as may be at once practically proved by any one in the following manner : — Arrange a thermometer with a naked bulb, so that a spot of light is reflected from the mercury, and focus this spot of light (the optician's artificial star) on the focussing screen of plain glass by the aid of a magnifier; on racking, the camera in slightly, a faint fringe of gr^en is seen surrounding the 291 DICTIONARY OF PHOTOGRAPHY. spot, and by racking out beyond the focus a fringe of reddish purple comes into view. This is best seen with an eye-piece. To test, however, whether the visual and actinic foci actually coincide, place the newspaper previously described squarely opposite the lens, but leaning away from it ; focus sharply, with full aperture, on one particular line of type — focussing must be effected by placing the screen in the dark slide, or the fact of non-coincidence of the plane of the focussing screen and sensitive plate may cause error ; then on exposing a plate, if the same line of type as focussed does not come out the sharpest, it is proved that the lens possesses a chemical focus, and we at once determine whether this is beyond or within the visual focus. (6) Freedom from Flare and Ghosts. Flare is visible as a central patch of light, and arises from an incorrect position of the . diaphragm in single lenses, and from reflections from the surfaces of the lenses in doublets. To test for the same, I use the plan suggested by Mr. Debenham. A sheet of black velvet or deep red cloth is hung up in a room at night, and in front of it, at some little distance, eighteen to twenty-four inches, is placed a lighted candle. The image of the flame is sharply focussed, and there will be generally seen a halo or ring of diffused light sur- rounding the flame. The camera is now slightly slewed round, and the image watched ; if the ring or halo of diffused light is steady at the centre of the screen, it may be assumed to be "flare"; if, on the other hand, the halo moves with the image of the flame, it is due to a secondary image or ghost very much out of focus. To actually determine this, rack the camera in or out to about half or double the focal length, when a small image of the flame will be seen surrounded by a large disc of light, the small image being the previous flare, and the halo the real image formed at the focus. " Ghosts " are the images of a brightly lit object reflected by the surfaces of the lens on to another portion of the screen. The same may be tested for as described for flare only ; the image of the candle flame should be brought to one side of the screen, and the ghosts looked for on the opposite side. One or more ghosts may make their appearance, and will be easily visible in this way. Practically, " ghosts " are a nuisance when photographing a dark interior which contains a brilliantly lit window, as a ghost of the window may make its appearance 292 DICTIONARY OF PHOTOGRAPHY. on the opposite side of the plate in a dark portion, and also in portraiture a white shirt front may appear duplicated. (7) Accurate Centreing. To test a lens for accurate centreing, it is advisable to mount the lens temporarily in the camera and focus on a naked candle or gas flame placed a little to one side, then turn back the focussing screen, and several images of the flame will be seen on looking into the camera. If the lens is correctly centred, these images remain stationary when the lens is unscrewed ; if they do not, the lens should be returned to the maker. (8) Perfect Polishing of the Surfaces. This is by no means an easy test for an amateur, but it is possible to determine this by examining the surfaces with a very powerful eye-piece. (9) Freedom from Stria, or Waves. The presence or absence of these defects may be observed by holding the lens near a flame, when the waves, or striae, caused by imperfect admixture of the glass material, may be observed. Levelling Slab. A perfectly even piece of glass, slate, or any other material sufficiently thick not to bend when placed upon the levelling stand, which is preferably of a triangular form, having a fine screw at each corner to allow of the height being altered as required. The slab of glass, or slate, is placed upon the stand, and accurately adjusted by means of a spirit-level. Lichtdruck. See Collotype. Light is that principle' which emanates from all luminous bodies, and the luminosity of such bodies is due to intensely rapid molecular vibration, which vibration is propagated in a supremely subtle elastic medium, termed the luminiferous ether, and light waves radiate from a body in all directions and from all points of that body. Light always travels in straight lines* unless deviated from its course by the action of some body through which it passes. All substances are either transparent (not hindering sight), translucent (hindering sight), or opaque : transparent substances allow light to pass through them, but deviate the course of the rays of light ; translucent bodies whilst allowing some rays of light to pass through reflect others ; whilst opaque bodies reflect some rays and absorb others, but the rays passing on each side of the opaque substance still continue their course, and leave behind the body a space which is not iilu- 293 DICTIONARY OF PHOTOGRAPHY. minated, or only partially so. This space is termed shadow. Shadows, however, are not rigidly defined, as the shadow cast by the interception of rays from the top edge are partly illuminated by the rays from the lower edge, and vice versa, and the shadow is always partly illuminated by neighbouring rays. The velocity of light is about 186,830 miles per second. The intensity of the light varies in inverse proportion to the square of the distance from the source of light. If rays of light fall upon a body which is opaque, and the surface of which is unpolished, certain portions of such light will be absorbed or enter to a certain depth, the remaining portion being reflected in all directions ; but certain bodies absorb only certain of the constituent rays of light, and reflect one or more of the others, and thus we arrive at the colours of objects. For example, an object which absorbs all the primary colours but red will appear red ; one that absorbs all colours, black ; and one that absorbs none, white ; and so on. A ray of light is reflected from a polished surface at the same angle with a line drawn perpendicular to the surface of mirror, that the ray striking the mirror makes — i.e., "the angle of incidence is equal to the angle of reflection." When a ray of light strikes a plane reflecting surface, it will, after reflection, so diverge from a point situated similarly behind the mirror — i.e., the image of an object 10 ft. away from the mirror will be reflected from a point seemingly 10 ft. behind the mirror. When light passes from one transparent medium to another transparent medium, unless per- pendicular to the surfaces of both, it is refracted or bent aside to a greater or less degree. This power of refraction differs for every different substance, but remains the same at all times for the same substance. It is only at the surfaces of transparent media that refraction occurs. The power of refraction possessed by each body is termed its " index of refraction." A ray of light refracted through a medium with parallel surfaces will have the same direction after leaving such medium as when entering ; and a ray of light traversing two media having parallel external surfaces, but differing refracting indices, will emerge in a direction parallel to the incident ray. When a ray of light is refracted, it also suffers what is termed dispersion — i.e., it is separated into its con- stituent rays. (See Decomposition of Light and the Spectrum.) Light-Fog. See Fog. 294 DICTIONARY OF PHOTOGRAPHY. [Lin Lime, Chloride of (Ger., Chlorkalk ; Fr., Chlorure de chaux; Ital., Cloruro di calce). Synonyms : Chlorinated Lime, Bleaching Lime, Bleaching Powder, Hypochlorite of Lime. The composition of this is a moot point : it is said to be by some a mixture of calcium hypochlorite Ca(C10) 2 and calcium oxychloride Ca 3 0 2 Cl 2 , according to another view its formula should be CaCl„ CaHClO.,. It is made by passing chlorine over slaked lime. It occurs as a dirty white powder, generally moist if kept some time, and probably contains some undecomposed hydrate and some carbonate. • When mixed with water it forms a solution of calcium hypochlorite Ca(C10) 2 and calcium chloride CaCL, with some hydrate Ca(HO)-> and carbonate which remains to a great extent undissolved ; this solution very readily parts with its chlorine, and may be used for preparing this gas. Good samples of chloride of lime should contain 30 per cent, of chlorine which is evolved on the addition of an acid. It is used as its name implies for bleaching and also for toning and the preparation of a hypo-eliminator. Lime Light. See Oxyhydrogen Light. Lime Water. This is a solution of hydrate of lime made by agitating slaked lime (Ca2HO) with water. It is but a feeble alkali, and contains only \ grain of lime (CaO) to the ounce of water. By heating, this quantity is still further reduced. A more powerful preparation, actually about fourteen times stronger, may be made by triturating one part of lime with twice its weight of pure sugar, manna, or glycerine ; then adding 20 parts of water and decanting the clear solution. Lime water has been suggested as an accelerator for quinol development ; but it is unsuitable, the action being very slow. It is also added to some toning baths, but seems to have but little, if any, beneficial effect. Line Drawings, To Copy. This is a subject about which many difficulties seem to hang, although actually there is do necessity for the same. The chief point is to use a slow plate, one not showing more than 12 on Warnerke's sensitometer ; and this must be considered the limit — one even less sensitive than this should be chosen ; the commercial lantern plates are usually of this class. The following directions will, it is hoped, make this an easy operation for any one. Having decided upon the 295 Lit] DICTIONARY OF PHOTOGRAPHY. size that the resulting negative shall be, the next question is to determine the focus of the lens to be used. If only one lens is possessed, then the size of the image is ruled by this, and the extension of the camera. Supposing we desire to reduce a plan or line drawing from 9X7 in., to 4^ x 3^, the lineal reduction is practically two ; therefore by consulting the table given in the Appendix, we shall find with a 5-in. focus lens that our lens must be 15 in. from the plan and j\ in. from the focussing screen. Supposing our camera does not rack out sufficiently far, we must improvise an extension by means of a 3-in. or 4-in. cone, or else by adapting one of the cardboard cases used for sensitised paper. If we have a choice of lenses, we may pick that one which is of sufficiently short focus to enable us to use the camera without any additional extension. The next point is to place the axis of the lens exactly central with the print, and the focussing absolutely parallel with the plane of the line drawing. It is hardly necessary to dilate upon this, as any tyro can do it. Then comes the question of lighting. This should be as bright as possible ; the author, using sunlight diffused by ground glass, or tissue paper, when sunlight is to be had. The lens should be used with a large aperture, so as to get as great a contrast as possible, as the use of small diaphragms tends to render any picture or scene, and therefore any image of a line drawing, flat and wanting in contrast. A short exposure should be given, if anything under-exposure, because we want to get hardness and contrast. No guide can be given for exposure, as it depends so entirely upon the actinic power of the light. The developer should be either quinol, or Edwards's pyro rede- veloper may be used ; we prefer the former. Development should be continued as far as possible without any blocking of the lines showing; if this shows, immediately stop the development, wash, and fix. After thoroughly washing, the negative should be cleared till the lines show as absolute bare glass, with the ground absolutely opaque. For this purpose we specially recommend Edwards's clearing solution (p. 80), used with the iron. Then, after thoroughly washing, if not dense enough, intensify with intensifier No. V., p. 253). Lithium (Ger., Lithium; Fr., Lithium; Ital., Litio). Li = 7. A comparatively rare metal occurring in lepidolite, lithia-mica, 206 DICTIONARY OF PHOTOGRAPHY. [Lun petalite, and triphane. It can be obtained by decomposing lithium chloride by a galvanic current. It is a soft silvery-white metal decomposed by water, and is remarkable as the lightest solid element (Sp. Gr. 0-59). Lithium Bromide (Ger., Bro?nlithtu?n ) Lithiumbro7nid ; Fr., Bromure de lithine ; Ital., Bromuro di litio?) LiBr = 87. This salt, which occurs in transparent white tablets or colourless needles which are very deliquescent, can be prepared by direct combination between the elements, or by double decomposition of lithium sulphate and barium bromide. Solubility 143 per cent, in cold, 290 per cent, in hot, water. Very soluble in alcohol and ether. Sometimes used in collodion emulsion making. Lithium Chloride (Ger., Chlorlithium, Lithiumchlorid ; Fr., Chlorure de lithine ; Ital., Cloruro di litio). LiCl,2H.,0 = 78-5. This can be prepared in a similar manner to the bromide salt. It occurs in octahedral crystals which are very deliquescent. Solubility 82 per cent, in cold, 146 per cent, in hot water, soluble in alcohol and ether. It is used in the preparation of collodio- chloride emulsions. Lithium Iodide (Ger., Iodlithium, Lithiumiodid ; Fr., Iodurc de lithine ; Ital., Ioduro di litio). Lil = 134. Made in a similar manner to the bromide salt. Occurs in yellowish crystals which are very deliquescent. Solubility, 100 per cent, in cold, 133 per cent, in hot water ; freely soluble in alcohol. Used for iodising collodion. Litmus (Ger., Lackmus ; Fr., Tournesol ; Ital., Tomasole). A blue colouring matter obtained from several weeds and lichens by fermentation with potash and ammonia. It appears com- mercially as small cakes, being made into a mass with chalk. It is used to indicate the presence of an alkali or an acid, the latter turning the solution red, and alkalies restoring the colour; the indications, however, are not very reliable. It is usually met with in the form of small books made by steeping unsized paper in tincture of litmus. Liver of Sulphur. See Potassium Sulphide. Loss of Tone in Fixing. See Toning. IdUnar Caustic. See Silver Nitrate. 297 Lux] DICTIONARY OF PHOTOGRAPHY. Luxograph. A term used to denote certain methods of artificial lighting. Macro -Photography. A term used to denote the enlarge- ment of the negative. Magic-Lantern. An apparatus used to project a magnified image of a positive upon a white screen in a darkened room. Practically it consists of a tin box, in which is placed a lamp in the focus of a silvered reflector, the light being condensed by a pair of plano-convex lenses, the positive being placed close to the condensers, and a special photographic lens being placed at the focus of the condensing lens, which produces a magnified image. Usually a three- or four-wick lamp is employed to give the illumination, the edges of the flames being presented to the condensers, which should be as close as possible to the flame without danger of cracking them. The positive should be placed upside-down, and film-side inwards, as close as possible to the condensers ; the magnifying lens, which is usually provided with a rackwork movement to ensure easy and accurate focus, being placed at the focus of condensers. The following rules and table will be found useful in determining the dimensions of the pictures thrown on the screen with various lenses : — 1. Knowing the length of room and diameter of picture desired, required to find the focus of front objective of lantern. Multiply the distance between the lantern and screen by the size of the opening in slide, and divide by the diameter of disc. Example. Room length 50 feet, diameter of picture 20 feet ; required to know focus of lens to be used. (Three inches is always taken as the size of opening of slide.) 5° x 3_ i5o _ 71-in. focus lens. 20 20 2 2. Having a given focus lens, and given diameter of picture, required to know what distance from screen to place lantern. Multiply the diameter of picture required by the focus of the lens, and divide by the diameter of the slide. Example. Size of picture desired 15 feet; focus of lens 8 ins. 15 * 8 = - 4 o feet, 3 298 DICTIONARY OF PHOTOGRAPHY. [Mag tO N ON o CO CO Ln vO vO CO ON CO CO «* Ln vO CO On O to ^J" Cj vo ON o CO vO ON n <*■ vO . n •a CO CO CO Ln vO CO ON O ft. ins. 2 6 1 ON CI O CO CO CO CO ON CO O Ln CO vO vO h» ON CO o o CO vO N in O c o CO o _ vO O vO o CO CO . N CO CO CO CO vO CO ON o N O in 0 o O O o o O O . VO 45 vO CO Ov N in CO n CI o co to" vO s CO O ON vO CO o ON vO CO o ON vO CO ON ON O Ln CO M CI vO o co CO CO t\ CO HI J) I. a cc/j 3 299 Mag] DICTIONARY OF PHOTOGRAPHY. 3. Having a given focus lens, and given distance between lantern and screen, required to know diameter of picture that will be produced. Multiply the distance between lantern and screen by the opening of the slide, and divide by the focus of the lens. Example, Lens of 9-in. focus, distance between lantern and screen 40 feet, required size of disc. 4 ° X 3 = HP = 13 ft. 4 in. diameter of disc. 9 Magic Pictures. A process discovered by Sir John Herschel, which is more of an ingenious toy than of any practical use. The process is as follows : — Print as usual on albumenised paper, fix without toning, and wash thoroughly ; immerse the prints in a saturated solution of perchloride of mercury until the image is thoroughly bleached and disappears, wash and dry. To make these invisible images appear at the word of command, as if by magic, place over them a wetted sheet of blotting paper, which has been previously soaked in a saturated solution of hyposulphite of soda, and pass the hand over them, when the image will start up with more than its original vigour. Maglip, or Meglip. An artist's material, made by mixing boiled linseed oil with mastic varnish. It is used for thinning oil colours and for glazing on delicate tints on finished oil- paintings. Magnesium (Ger., Magnesium; Fr., Magnesium-; Ital., Magnesid). Mg_24. Occurs in large quantities as dolomite or mountain limestone — an impure carbonate. The metal is silvery white in colour, and is met with commercially in the form of wire, ribbon, and powder. It is now of common use for pro- ducing negatives by night, as the metal burns at a comparatively low temperature, giving an extremely actinic and brilliant light. It has also been suggested as a means of precipitating silver from old fixing baths (see Kesidues). Magnesium Chloride (Ger., Chlormagnesium ; Fr., Chlorure de magnesium ; Ital., Cloruro di magnesid). MgCl 2 ,6H 2 0 = 203. White crystals or needles, very deliquescent, formed by the action of chlorine on magnesium, or by dissolving magnesia or magnesium carbonate in hydrochloric acid. It has been employed 300 DICTIONARY OF PHOTOGRAPHY. Mas] in gelatino-chloride emulsions, and was proposed by Liesegang as a Fixing Agent. Solubility : 160 per cent, in cold, 370 per cent, in boiling water ; 50 per cent, in absolute alcohol ; 500 per cent, in boiling alcohol. Magnesium Sulphate (Ger., Magnesittmsidphat, Schwefel- sdures Magnesium ; Fr., Stdfate de magnesie ; Ital., Solfato di magnesia). Synonyms : Sulphate of Magnesia, Epsom Salts. MgS0 4 7H 2 0. Occurs naturally in certain springs, but is usually made by dissolving dolomite in dilute sulphuric acid, and subse- quent purification and crystallisation. It has been recommended as a preventative of frilling. Solubility : 104 per cent in cold, and 700 per cent in hot water; insoluble in alcohol. Manganese, Bin-oxide of (Ger., Mangandioxyd, Braunstein ; Fr., Peroxyde de manganese ; Ital., Perossido di manganese). Mn0 2 =86. Synonyms: Manganese Dioxide, Black Oxide of Manganese. Occurs native as the ore of manganese as a black crystalline powder, and is used for the home production of oxygen for the limelight. Manipulation. A term used to express the conduct of any photographic operation or process. Masking Skies. See Printing. Masks and Discs. Pieces of opaque paper used in photo- graphic printing, usually with albumenised paper. In the opaque paper shaped openings are cut ; and the piece cut out is termed the disc, the margin being called the mask. The mask is placed between the negative and the paper, when it is obvious a print will result of the form given by the opening of the mask, and the margin where covered by the mask will be white. The print may be finished off at this stage, or the disc may be carefully and accurately placed over the print, and the margins exposed to light till they darken to the required tint. A good effect is sometimes given to portraits with light backgrounds by printing under a mask, then using a disc and blackening the margin, enamelling the print, and giving the centre portion a convexity, as described under Cameo. Mastic, or Mastich. A resinous exudation from the stems of Pistacia lentisctis, grown in the island of Scio. It is usually met with in the form of whitish or yellowish-white drops or 301 Mat] DICTIONARY OF PHOTOGRAPHY. tears, about the size of small peas. Insoluble in water ; almost entirely soluble in alcohol, ether, chloroform, oil of turpentine, and benzole. It is used for preparing certain Varnishes (q.v.). Matt Paper. Popular opinion, amongst photographers at least, has veered round towards printing papers with a dull or non-glossy surface. Several commercial makes of matt-surface gelatino-chloride paper have been placed on the market which require no different treatment to the ordinary glossy paper. Matt Surface. A dull, not glossy or shiny, surface obtained in various ways according to the material — glass, metal, paper, etc. Matt Varnish. See Varnish. Mealiness Of Prints. A peculiar mottled appearance on the surface of prints, due to a weak paper-sensitising bath ; and as this is also the cause of lack of vigour, contrast, and brilliancy, the term is frequently used to denote all these. Measles. A peculiar defect in prints, which shows, when they are held up to the light, as opaque blotches, which are due to imperfect fixation and non-solution of the insoluble hypo-sulphite of silver. On keeping, these spots turn yellow, due to formation of sulphide of silver ; whence the name, from a fancied re- semblance to the human ailment. Measures. See Weights and Measures. Meniscus. See Lens. Mercuric Chloride (Ger., Quecksilberchlorid, Mercurichlorid, Sublimat ; Fr„ Bichlorure de mercure ; Ital., Bicloruro di mer- curid). HgCl 2 = 27i. Synonyms: Perchloride of Mercury, Bi- chloride of Mercury, Corrosive Sublimate, Sublimate, Muriate of Quicksilver. Can be prepared by heating mercury in an excess of chlorine, but it is prepared commercially by sublimation from a mixture of mercuric sulphate and common salt. It is usually met with in commerce in extremely heavy colourless prismatic crystals or as a white powder. Specific gravity : 5*43. Solubility : 1 in 19 of cold, 1 in 3 of hot water, 1 in 5 ol rectified spirit, 1 in 6 of ether. It sublimes without decomposition, and melts at 509 0 F. It is used for Intensification {q.v.). Its solution in water is liable to decomposition ; but any soluble chloride pre- vents this, and nearly all chlorides increase its solubility in cold 302 DICTIONARY OF PHOTOGRAPHY. [Min water, a compound salt being formed. It is a most powerful poison, 3 grs. being the smallest fatal dose known. The antidote is albumen, or white of egg, with which its forms an insoluble compound, followed by emetics. As the salt is readily absorbed by the skin, it is advisable not to dabble unnecessarily in it. Mercury (Ger., Quecksilber ; Fr., Mercure; Ital., Mercurio). Hg = 200. Synonym: Quicksilver. Occurs native, but is chiefly \ obtained by roasting the ore cinnabar, which is an impure sul- phide, obtained from China, Spain, California, and America. Mercury, at ordinary temperatures, is a brilliant silvery white metallic liquid, becoming solid at -40 0 F., and volatilising below the heat of visible redness. Specific gravity: 13-5. It has now but little photographic interest, but was used in the old daguerreo- type days to develop the image. Metallic Spots. These sometimes occur on albumenised paper, and are due to impurities, usually metallic iron, in the substance of the paper itself. Methylated Ether. See Ether. Metric System. See Weights and Measures. Micro-Photography — the antithesis of macro-photography- - consists of the reproduction of positives in a very minute size, which require the use of a simple microscope or magnifying glass to examine. It must not be confounded with photo-micrography, which is the production of photographs of microscopic objects ; yet, curiously enough, in Hardwich's " Photographic Chemistry," ninth edition, Photo-micrography is described under Micro- photography. Micro-photographs are well known to the majority of amateurs, from the minute photographs which are usually sold at seaside places, the photographs being fixed behind a minute magnifying glass in the handle of some little but fancy article. Their production is comparatively easy, but the collodion process is the only one possible to use. It is obvious that it is nothing but the process of reduction carried out to a minute degree ; but as the focussing of so small a point is impossible, some large object must be photographed and the negative put in its place. Minim. See Weights and Measures. 303 Mir] DICTIONARY 0^ PHOTOGRAPHY. Mirror, Reversing. One of the essentials for carbon and all line work, unless film negatives are used (see Reversed Negatives). Mirror Silvering. As an amateur may desire to resilver a mirror or a copper reflector, the following recipes may be found useful : — For glass- No. i. Nitrate of silver Distilled water No. 2. Nitrate of ammonia... Distilled water 175 grs. or 10 grms. 10 ozs. „ 250 c.cm. 262 grs. or 15 grms. 10 ozs. ,, 250 c.cm. No. 3. Pure caustic potash 437 '5 grs. or 25 grms. Distilled water ... ... 10 ozs. 250 c.cm. No. 4. Pure sugar-candy Distilled water 210 grs. or 6 grms. 5 ozs. 125 c.cm. Dissolve and add Tartartic acid 50 grs. or 3 grms. Boil in a flask for ten minutes, and when cool add Alcohol Distilled water to 1 oz. or 25 c.cm. 10 ozs. „ 250 „ For use : Mix Nos. 1 and 2 in equal parts ; mix Nos. 3 and 4 in equal parts ; then mix the two solutions, and suspend the glass in it. To silver copper or any metal it must first of all be cleansed with dilute acid to free from dirt, etc., then well washed, and one of the following applied : — Dissolve 60 grs. of nitrate of silver in 1 oz. of distilled water ; add sufficient liq. ammonia to redissolve the precipitate first formed ; add to this solution ^ drm. of caustic potash solution and ^ drm. of glycerine ; apply to the metal ; add a few drops of ether ; rub with a tuft of cotton-wool ; dry before the fire, and polish ; repeat as often as desired to brighten it. 304 DICTIONARY OF PHOTOGRAPHY. [Mou Or Nitrate of silver Liq. ammonia Hyposulphite of soda Prepared chalk Distilled water 65 grs. or 3-5 grms. 60 mins. „ 7 6 c.cm. 100 grs. 6*4 grms. 100 „ „ 6-4 „ 1,000 „ „ 667 c.cm. Mix, and apply with a flannel. Or Nitrate of silver 60 grs. or 4 grms. Cream of tartar ... ... 120 8 ,, Salt 120 ,, ,, 8 Cyanide of potash 60 „ ,,6 Make into paste with water and chalk, and apply with a flannel. Monocle. Under this term have been introduced uncorrected spectacle lenses, which have been strongly recommended for portraiture and ordinary landscape work where softness of defini- tion is desired. The usual form of lens employed is the peri- scopic of about i^-in. diameter, and may be obtained of any focus from about 2-in. and upwards. These lenses, being un- corrected, necessarily have two foci, a chemical and visual, and it is therefore necessary to make a correction after focussing and before exposing. For ordinary landscape work the necessary correction may be made by means of the formula A/ =: /°'° 2 > which is practically equal to 7 Vth of the focus. But this only applies when the lens is working at its equivalent focus. In the Appendix will be found tables giving the necessary correction for varying foci and sizes of images. Monocular Vision. As the term implies, it is seeing with one eye only. It was formerly supposed by many eminent opticians and physicists that one eye only was employed in vision ; but Wheatsone, to whom the great invention of the principle of the stereoscope was due, proved the fallacy of this. In monocular vision objects on the true optical axis line are distinctly seen, but other objects less so, although they are in the circle of vision, and in this particular the similarity of the lens and the human eye is very evident. Monocular vision can judge the direction, but not the distance of an object. Mountant. The substance used to make the print adhere to its mounts. It is absolutely necessary that the mountant should 305 X DICTIONARY OF PHOTOGRAPHY. be free from acidity, in order to prevent the destruction of the delicate image. There are several kinds in common use — viz., starch paste, arrowroot, gum, dextrine, india-rubber solution, liquid glue, and gelatine. Starch Mountant Starch in powder i oz. ; mix into a cream with I oz. of water, and add to it, constantly stirring, 8^ ozs. of boiling water in which 20 grs. of common alum and 5 drops of carbolic acid have been dissolved. The mixture should be now a clear translucent jelly free from lumps ; if it is not, it should be gently heated in a dish or pan till it clears, constant stirring being an absolute necessity ; then it should be squeezed through fine muslin. Ordinary household flour makes a more adhesive paste, but is more liable to acidity. Both will keep fit for use about a week, after which they should be rejected. Arrowroot Mountant, called Permanent Paste. Dissolve by the aid of gentle heat Arrowroot ... 150 grs. or 10 grms. Gelatine ... ... ... 150 „ ,, 10 ,, Distilled water 3 ozs. ,, 100 c.cm. When cool, add Methylated spirit ... ... 2^ drms. or 9 c.cm. Carbolic acid 3 drops „ 0-3 ,, Gum Solution, or Mucilage. Pale-coloured gum arabic in clean lumps, 4 ozs. ; distilled water, 8 ozs. Wash the gum by placing it in a half-pint cup or measure ; add half-pint of water ; stir briskly round twice or three times, and pour off the water : this carries off any dust or mechanical impurities. Now add the distilled water, and stir frequently at intervals till dissolved. It should be kept in bottles filled as full as possible, and the addition of a little carbolic or salicylic acid will help to preserve it. It will keep only about ten or fourteen days, and when made with hot water about half that time. Powdered gum arabic should never be used. Dextrine Solution. This is one of the nastiest of all mountants, and decidedly unsatisfactory. It can be made as follows : — Pure white dextrine ... 1 oz. or 28 grms. Boiling distilled water ... 3 ozs. ,, 100 c.cm. Methylated spirit ... ... £ oz. ,, 14 „ Stir till dissolved, and strain through calico. 306 DICTIONARY OF PHOTOGRAPHY. [Mou India-rubber Solution Pure masticated rubber ... 80 grs. or 0-5 grm. Chloroform or benzole ... 8 ozs. „ 25 c.cm. Shake till dissolved. Benzole is cheaper than chloroform, but the smell is rather unpleasant. Gelatine. This is the author's favourite mountant. It is less liable to change than any other medium, and if properly made is more convenient and easier of application. The print can be mounted whilst still damp, and it can be shifted about on the mount, or any excess of mountant wiped off, without leaving any trace on the mount, even the highly enamelled ones. The following is the most satisfactory method that the author has found: — Soft gelatine, 200 grs. : soak in distilled water (6 ozs.) for an hour. Dissolve by the aid of a water bath, and add, in small quantities at a time, methylated spirit, 2\ ozs., stirring con- stantly ; allow it to set. Should any spirit separate out, it should be remelted, and a little more water added. The product should be a pure milk-white firm jelly. A little carbolic acid may be added if desired. When required 'for use, melt by the aid of hot water or a water bath. Liquid Glue. This is sometimes used, but as many different preparations are sold under this name, each sample should be tested for acidity, as som£ consist of gelatine dissolved in acetic acid, which would soon cause fading. Another kind which the author has used, but cannot highly recommend, is prepared by dissolving 120 grs. of shellac in 4 drms. of methylated spirit by the aid of heat. Some adhesive mounts have been intro- duced into the market, which are rather convenient, although the author has found them rather liable to stick together at the edges; but if any amateur is desirous of making these, the following directions given by the author in the A??iate7tr Photographer will be ofjservice ; — Mix in a small glass, mortar, or measure, 120 grs. of powder tragacanth with 6 drms. of rectified or methy- lated spirit, and having put 9 ozs. of water into a pint bottle — or an old pyro bottle will do — pour the mixed tragacanth and spirit quickly into the water ; shake for a few minutes, and allow it to stand for twelve hours, shaking it occasionally, and at the end of the time there will be sufficieat mucilage of tragacanth to coat 100 to 200 mounts. All that is necessary to do is to give the 307 DICTIONARY OF PHOTOGRAPHY DICTIONARY OF PHOTOGRAPHY. [Mou mounts a good thick coating with a brush, allow it to dry, and give them a second coat. The mounts will curl up, but they can be easily straightened when dry. Mounting is the operation of causing prints to adhere to some substance, such as card, cloth, wood, or glass, either for ornament or the better protection of the print itself. As the mounting of a print is in many cases the making of it, great attention should be paid by amateurs to this subject. The following points should be chiefly regarded : — The mount should be of a suitable colour and size, and sufficient margin should be allowed, no excessive ornamental lines, and the print should be accurately in the centre of its mount. As the difficulty of placing prints equidistant from the margin is one likely to be met with by every amateur, the following hints may be found useful : — After applying the mountant, lay the print face downwards upon a mount exactly similar to that upon which it is desired to mount the print, shift the print about till it is exactly in the centre ; now lay on top of the print another mount exactly the same size, making the edges of the two mounts coincide: rub the hand gently over the top mount, when it may be lifted up with the print in situ. Another ingenious method, which is recommended by Mr. T. C. Hepworth, is as follows : — Procure a piece of stout carboard — a mount will do — 22 by 15; draw diagonals from corner to corner, AC, bd, in sketch, cutting each other in centre, and on these lines rectangular figures of the usual dimensions of the trimmed prints. For instance, the smallest may be 4 by 3 or 3 by 3, the next 4^ by 3^, 5 by 4, 6 by 4, 6 by 5, 7 by 5^, and so on. When it is desired to mount a print, place it face down- wards upon this gauge, when it will be found that it will coincide with certain of the lines ; note the number of figure, remove the print, apply the mountant, and replace upon the lines it covered before, and place upon it the mount which will be found to coincide with some other set of lines ; proceed as in the above case, and lift the mount and its adhering print ; use further pressure, and roll or burnish. A very convenient little instrument for those who do not possess either a burnishing or rolling machine is an india-rubber roller squeegee, same as used by printers, which will cause absolute contact between the prints and their mounts. For those who possess a copying press, 309 Mur] DICTIONARY OF PHOTOGRAPHY. sheets of zinc or tin may be placed between the mounted prints, and great pressure applied in the ordinary way ; whereas those whose household appurtenances include a clothes-wringing machine with india-rubber rollers, may, if allowed, use these ; or the bevelled edge of the cutting glass drawn carefully over the print with some pressure will do all that is required. For mounting prints in optical contact with glass the following method answers well : — Make a solution of gelatine (Nelson's X opaque), 20 grs. to every ounce of water, and whilst still warm immerse the print face downwards in it ; place the glass in it, and after a few seconds bring them into intimate contact, and withdraw from solution, and squeegee thoroughly, and allow to dry. To mount prints which have an extremely glossy surface, like Aristotype, etc., when it is desired to retain the high gloss which cannot be done by mounting in the usual way, squeegee the print on to an old negative glass, or cutting shape, or ferrotype plate, and when nearly dry coat the back with the mountant, and apply to the mount ; use the squeegee vigorously, and when dry the glass may be stripped off, leaving the print in all its beauty upon the mount. Muriate of Ammonia. See Ammonium Chloride. Muriatic Acid. See Hydrochloric Acid. Naturalistic Photography. Under this title has lately been published one of the most striking works ever written- on photography, by Dr. P. H. Emerson. Naturalistic Photo- graphy is an attempt to render by means of the usual tools and operations of photography the same as given by the so- called " Impressionist" school of painting, of which Whistler is the leader. As perhaps the clearest exposition of the teaching and aim of this school, we cannot do better than refer to Dr. Emerson himself, who says that a picture "should be made just as sharp as the eye sees it, and no sharper ; for it must be remembered the eye does not see things as sharply as the photographic lens, for the eye has the faults due to dispersion, spherical aberration, astigmatism, aerial turbidity, blind spot, and beyond twenty feet it does not adjust perfectly for the different planes. All these slight imperfections make the eye's vision more imperfect than that of the optician's lens, even when objects in one plane only are sharply focussed ; therefore, except 310 DICTIONARY OF PHOTOGRAPHY [Nit in very rare cases, which will be touched upon elsewhere, the chief point of interest should be slightly — very slightly — out of focus, while all things, out of the plane of the principal object, it is perfectly obvious from what has been said, should also be slightly out of focus, not to the extent of producing destruction of structure or fuzziness, but sufficiently to keep them back and in place. . . . The rule in focussing, therefore, should be, focus for the principal object of the picture, but all else must not be sharp ; and even that principal object must not be as perfectly sharp as the optical lens will make it. It will be said, But in Nature the eye wanders up and down the landscape, and so gathers up the impressions, and all the landscape in turn appears sharp. But a picture is not 1 all the landscape ' ; it should be seen at a certain distance — the focal length of the lens used, as a rule ; and the observer, to look at it thoughtfully, if it be a picture, will settle on a principal object, and dwell upon it, and when he tires of this he will want to gather up suggestions of the rest of the picture." Whilst not agreeing with Dr. Emerson in toto, the author refrains from any criticism of a work of which the writer says, "It is always fairer to read an author's writings than to read the stupid constructions put upon them by untrained persons." Negative is the term applied to the image in which the lights and shades are reversed. These can be made by direct action of light in the camera, or by printing in a frame from a positive Negative Storing. To the amateur whose work is frequent and successful the stock of negatives soon becomes considerable, and the question of storage a bugbear. Many use the grooved negative boxes, but while these are convenient their bulk is a great objection. The best plan is to use paper negative bags, on which can be written the subject, date, and duration of exposure, aperture of diaphragm, mode of development, and any other remarks which may be considered necessary. The negatives in the bags can then be packed close together in boxes not grooved, and they will take up about one-fourth of the room of grooved boxes. An index can be kept of them, and a list can be pasted inside the lid of each box for further reference. Nitric Acid (Ger., Salpetersiiure ; Fr., Acidc Nitriquc). HN0 3 = 63. Synonym: Aquafortis. Prepared by distillation 3ii Nit] DICTIONARY OF PHOTOGRAPHY. from Chili saltpetre (nitrate of soda) and sulphuric acid. Specific gravity, 1*45. A heavy colourless liquid fuming in the air. It is extremely poisonous, having a most powerful corrosive action ; 2 drms. is the smallest fatal dose known — the antidote, any alkaline earthy carbonate, as chalk, lime, magnesia. Nitro-Hydrochloric Acid (Ger., Konigswasser ; Fr., Eau regale). Synonym : Aqua regia. A mechanical mixture of 3 parts of hydrochloric acid with 1 part of nitric acid ; the oxygen of the latter combines with the hydrogen of the former, setting free chlorine, and forming water 2HCI + HN0 3 =H 2 0 + Cl 2 + N0 2 It is used to dissolve gold for the preparation of gold perchloride, the principal agent for which purpose being the free chlorine. Non-Actinic Rays. See Spectrum. Obernetter's Process, or Lichtkupferdruck. A mechanical printing process of very ingenious idea and of extremely pleasing and artistic results. The metallic image of silver of a gelatine positive is converted into chloride of silver, and the film is then stripped and applied to the surface of a copper plate, and, under the influence of a voltaic current, the silver chloride is decom- posed, and the chlorine unites with the copper and etches it to a greater or less degree, according to the depth of deposit of silver chloride. The result is a grained intaglio plate of extreme delicacy and beauty, which is inked and printed from the same as any ordinary etching. Objective. A term sometimes applied to the lens. Oil of Lavender. See Lavender, Oil of. Oil of Spike. See Spike, Oil of. Oil Paintings, to Copy. See Copying. Opacity. See Density. Opalotype. A term applied to pictures on opal glass. They can be made by coating opal glass with a plain gelatino-bromide emulsion, or by using a printing-out emulsion. The exposure and development are the same as for bromide paper. Either polished or ground opal glass may be used, the latter giving very pleasing pictures of a matt surface. Another method of 312 DICTIONARY OF PHOTOGRAPHY. [Opa obtaining pictures by the printing-out process is by the use of a collodio-chloride emulsion, which may be made as follows : — No. i. Silver nitrate 31 grs. or 2 grms. Methylated ahohol 28 drms. 100 c.cm. Dissolve by the aid of heat immediately before using. No. 2. Strontium chloride 31 grs. or 2 grms. Methylated alcohol 28 drms. ,, 100 c.cm. No. 3. Citric acid 31 grs. or 2 grms. Methylated alcohol 28 drms. 100 c.cm. No. 4. Pyroxyline or celloidin ... 62 grs. or 4 grms. Methylated alcohol 28 drms. ,, 100 c.cm. „ ether 28 „ ,, 100 To make the emulsion Take of No. 2 150 mins. or 9 c.cm. No. 3 150 „ „ 9 „ „ No. 4 28 drms. 100 ,, Mix, and add gradually, with constant agitation, No. 1 ... ... 75 mins. or 4*5 c.cm. Give the plates an edging of albumen or india-rubber solution a quarter of an inch broad, and, after coating, allow them to dry thoroughly. The prints should be washed, toned, and fixed in the same way as ordinary silver* prints or the sulpho-cyanide toning bath may be used with better effect. (See Toning.) As it is necessary to examine the opal during the operation of printing, it is obvious that some arrangement must be made for replacing it in exactly the same position. Printing frames may be obtained commercially specially adapted for this work, but an ordinary printing frame may be utilised in the following manner : —Replace the hinged back by a solid piece ol wood fa 3 X 3 Opt] DICTIONARY OF PHOTOGRAPHY. of an inch less in thickness ; coat the inside of this back with a composition of gelatine made as follows : — Gelatine (Nelson's X opaque) I oz. or 2 grms. . Water 4 ozs. „ 132 c.cm. Glycerine ... ... ... 2 „ 56 Soak the gelatine in water, and dissolve by the aid of heat ; add the glycerine last. The opals will adhere to this on being damped, or a thick india-rubber solution, with a little castor oil added, may be used : — Pure masticated rubber ... 40 grs. or 2 grms. Castor oil ... ... ... 10 drops ,, 0*6 c.cm. Benzole ... 1 oz. „ 25 „ A small spot of this at each corner will cause the opal to adhere firmly to the wood. To keep the negative in position, a screw may be driven through one end of the printing frame, and the point of the screw cut off ; a groove cut in it in which to fit the negative. To the back affix three or four small tongues of metal pierced with holes, which holes may drop over pins driven into the sides of frame, or the back may be permanently fixed by a hinge to one end of the frame. Optical Centre. In every lens exists a point situated in its principal axis, any incident ray passing through which point Fig. 76. does not suffer deviation ; this is termed the optical centre. None but single lenses have true optical centres, but the optical centre may be approximately found in an achromatic combina- 3H DICTIONARY OF PHOTOGRAPHY. [Oxa tion by considering it as a single lens. To find the optical centre of a lens draw a line to represent the principal axis, a c a' ; then from the centres of curvature draw two radii, ab and a'b', parallel to one another, but oblique to the central axis ; then join their extremities, b, b', and the point c at which the principal axis is cut by this line is the optical centre. To find the optical centre of a meniscus lens prolong b b' till it meets the principal axis ; the optical centre of plano-concave and plano-convex lenses is found by the intersection of the spherical surfaces by the principal axis. Optical Lantern. See Magic Lantern. Optics. That branch of science relating to the nature and laws of vision. The subject is too comprehensive to treat here. For further study the amateur is referred to Glazebrook's " Physical Optics." Orange Light. Actinic light filtered through any medium which absorbs all but the orange rays. It is frequently used for the illumination of the dark-room, and is perfectly safe if not too brilliant. Orthographic and Orthoscopic. Two fanciful titles given to certain classes of lenses. Osmose. The action that takes place when two liquids of differing densities are separated by a permeable medium. (See Dialyser.) Over-Exposure is the undue prolongation of the exposure of the sensitive surface, and, as the author has endeavoured to show, the ill effects can be corrected by careful development. The effect of over-exposure on the sensitive surface is that the image starts up quickly, and the plate shows signs of Fogging (q.v.) before proper density is obtained, the resulting negative being thin, but full of detail. Oxalate Developer. See Developer. Oxalic Acid (Ger., Oxalsdurc ; Fr., Acide Oxalique). H 2 C>0 4 , 2H 2 0=i26. Prepared by oxidation of sugar or sawdust by nitric acid. It is recommended for acidifying the oxalate of potash solution for ferrous oxalate developer, but its chief use is in the preparation of oxalate of potash, ferric oxalate, and other 315 Oxg] DICTIONARY OF PHOTOGRAPHY. stable salts. It is extremely poisonous (60 grs. being sufficient to cause death) ; its antidote, magnesia, chalk, or lime in any form, with which it forms insoluble oxalate of lime. Solubility : 1 in 15-5 of cold water, 1 in 1 of boiling; sparingly soluble in alcohol. Ox-Gall. The fresh gall of the ox purified, and evaporated to a suitable consistency. It is used photographically to make water-colours take to the surface of albumenised prints. It should be obtained from a chemist's, and in this state is a sticky, rather offensive-smelling mass. It is soluble in water and spirit, and can be dissolved in either, or, preferably, a mixture of both, and applied to surface of print with camel's-hair pencil. Oxygen. O = 16. A gaseous element of ordinary tempera- tures, forming | by weight of water, and \\ of the air ; it is about the most abundant element known, entering into the composition of all animal and vegetable tissues, and about half the weight of the solid earth. It is used in the oxy-hydrogen light, and is usually prepared by heating a mixture of chlorate of potash and black oxide of manganese. Oxy-Hydrogen, and Oxy-Calcium or Drummond's Light. Both are so much alike that but one description is required. A cylinder or ball of lime is placed in the focus of a parabolic mirror, and a lighted jet of oxygen and hydrogen or coal gas is directed upon it. The lime burns with an exceedingly intense flame, which can be seen at night in hazy weather a distance of sixty miles, and in clear weather over a hundred miles. The oxy-calcium light differs but slightly, the flame of a spirit-lamp being used instead of hydrogen. Packing Plates. Several methods are employed by commer- cial firms to preserve dry plates from accidental injury and fracture whilst travelling, but the best method is that practised by a well-known London firm, whose method is as follows : — Absolutely pure tissue paper is cut the exact width of the plates, but sufficiently long to enclose five or six plates ; stout card cases, just a shade larger than the plate, and a strip of non-actinic paper, are placed lengthwise in the box, with free ends projecting ; then a sheet, or the commencement of a sheet, of tissue paper ; a plate is laid face downwards, and the tissue paper folded over 316 DICTIONARY OF PHOTOGRAPHY. [Pan the back of it ; then another plate is laid face downwards on the tissue paper, and this is continued till the case is full, when the free ends of the non -actinic paper are folded over; the whole is then wrapped in black paper, slipped into another case, and that into the outer box. By alternating the plates and paper in this manner, any number of plates may be safely carried by road or rail without any fear of fracture. As some amateurs may desire to travel abroad — and the Custom-house officer is their bugbear — the following labels may be useful : — English. — Photographic dry plates. To be opened only in ruby light. Fre?ich. — Plaques seches photographiques. A ouvrir seule- ment avec eclairage couleur rubis. Italian. — Lustra da seccare fotografiche. Da aprire solamente con illuminazione colore di rubino. Getman. — Photographische Trocken Platten. Nur bei dunkel- rother Beleuchtung zu offnen. Spanish. — Planchas secas para fotografia. Abrase el paquete en un cuarto oscuro y a la luz rubi. Dutch. — Photographiche drooze platen. On open gemaakt te worden alleen im roode licht. Swedish. — Ljuskaushga fotografiska platar, blivfa forstorda om de uttsattas forljus. Fas derfore ej oppuas utom i ett absolut morkt rum. Or the two following, in French and German, are a little more explicit : — French.— Plaques photographiques sensibles. Abimees par exposition a la lumiere. Prendre garde de n'ouvrir la boite que dans une chambre parfaitement obscure. Germa?i. — Photographische Trocken Platten, werden verdor- ben in dem Lichte ausgesetzt. Mussen also nur in einem absolut dunkeln Zimmer geoffnet werden. Palladium. Pd= 106. A metallic element sometimes found native in the pure state, and frequently mixed with platinum, which it much resembles. It has been recommended for toning transparencies and enamels in the form of chloride, but its use is limited. ' Panel. The style of a commercial photograph, size about 4 by 8^ ins. 317 Pap] DICTIONARY OF PHOTOGRAPHY. Paper, Albumenised. See Albumenised Paper. Paper, Plain or Matt-surfaced. See Sensitised Paper. Paper, Sensitised. See Sensitised Paper. Papyrotype, or Papyrography. A modification of photo- lithography, in which paper is used as the support, instead of a stone or metal plate. Parabola is the curve described by a moving point, which is always at the same distance from a fixed line, its directrix, that it is from a fixed point, its focus. The chief use in photography .of the parabola is in the construction of mirrors or reflectors for artificial light from the fact that the rays of a light placed in the focus of a parabolic mirror will be reflected in parallel rays. Paste. See Mountant. Paste, Encaustic. See Encaustic Paste. Pearlash. A synonym for impure Potassium Carbonate (g.v.). Pellet's Process. See Cyanotype. Pellicle. Literally a thin skin or film, and in this sense applied to the emulsion when the solvents are evaporated. Pellicular films were introduced many years back, and were one of the first adaptations of gelatine to photography. Pencil of Light. A term applied to the rays of light pro- ceeding from any luminous body. When the object is near, the pencil or rays of light are divergent rays ; when the object is very distant, the pencils may be considered parallel. A pencil, the rays of which lessen as it proceeds, is said to be convergent. Perspective is the art of representing solid bodies on a plane surface. It is divided into two branches — linear perspective, which shows the apparent forms of objects on the prospective outlines ; and aerial perspective, which distinguishes the distance of objects by the relative brilliancy of their colour. The subject is much too comprehensive to treat here. The amateur who desires to learn the rules of perspective must refer to some of the manuals on this subject. ' Phosphorus. P = 31. A non-metallic element widely dis- tributed throughout the animal and vegetable kingdom, but 318 DICTIONARY OF PHOTOGRAPHY. [Pho never occurring in the free state. It is insoluble in water, soluble in ether, chloroform, benzine, turpentine, and other oils, and bisulphide of carbon. It is prepared from bone-ash and other phosphates by treatment with sulphuric acid and sublima- tion with charcoal and sand. It has but little interest photo- graphically, phosphoric acid, a compound, being but rarely used. Photo-Engraving. Numerous processes are in every-day use, in the best of which the action of light upon a bituminous film is taken advantage of. As these processes are hardly within the scope of the general run of amateurs, no further mention will be made. The best handbook on the aubject is W. T. Wilkinson's " Photo-Mechanical Processes." Photography is the art of obtaining the representation of objects by the agency of light upon sensitive substances. The following is a short history of the rise and progress of the art : — In the sixteenth century Baptista Porta, a Neapolitan, invented the Camera Obscura (q.v.), and this was used to obtain sketches by hand of the objects projected by the lens. In 1777 Scheele, the great chemist, discovered the important fact that chloride of silver blackened in sunlight, the chief action lying in the violet end of the spectrum. In 1802, Thomas Wedge wood, son of the famous potter, published in the "Journal of the Royal Institu- tion " an account of a method of copying paintings on glass, and of making profiles by the agency of light upon nitrate of silver. In the experiments which are thus described he was assisted by Sir Humphrey Davy. They managed to obtain images upon paper and white leather by means of the solar microscope, but were unable to fix them; therefore the image was soon obliterated by the darkening of the whole surface. In 1814 Nicephore de Niepce commenced a series of experiments, but although he managed to obtain images upon a bituminous film, the process was impracticable for ordinary purposes, from the inordinate exposure (several hours) which was required. He then, in partnership with Daguerre, carried on his experiments ; but it was not until 1839, s ™ years after Niepce's death, that Daguerre communicated to the Acad6mie des Sciences at Paris the process so well known as Daguerreotype. Early in 1839 Fox Talbot, previous to Daguerre's communications, announced to the Royal Society a method of " photogenic drawing," in which pictures 3*9 Pho] DICTIONARY OF PHOTOGRAPHY. were produced upon paper prepared with chloride of silver. Fox Talbot effected the fixation of these pictures by saturated solutions of chloride of sodium and bromide of potassium. The use of hyposulphite of soda, however, soon became general, Sir Humphrey Davy having, in 1821, published the action of this salt upon the salts of silver. In 1841 Fox Talbot patented his process called Talbotype or Calotype (q.v.). To the Rev. J. B. Reade is due the credit of first recommending a developer, although Fox Talbot was the first to use a restrainer. Up to this point paper negatives alone were in use; but in 1848 a cousin of the original Niepce, M. Niepce de St. Victor, proposed the use of albumen on glass as a vehicle for the sensitive salts of silver. These plates, however, were very insensitive, and numerous substances, such as starch, gelatine, gum, etc., were proposed; none, however, were successful. In 185 1 Le Gray, of Paris, and Scott Archer, of London, proposed the use of collodion, the latter publishing such a complete description of the wet collodion process that but little improvement has ever been effected. A great disadvantage, however, of this process was the necessity of exposing the film whilst wet, necessitating the use of bulky and heavy impedimenta for the landscape photographer, in the shape of dark tent, etc. It was then dis- covered that the application of certain organic substances to the washed film would allow of the plates being used in the dry state. In 1862 Major Russell discovered the use of alkaline pyrogallol as a developer, and his accidental discovery of the restraining power of the soluble bromides gave the first impetus to the manufacture of bromide of silver films, which could be exposed dry. In 1864 Messrs. Sayce and Bolton described the process of collodion emulsion making, which was poured upon glass plates, and then washed to free from inert salts. In 1874 it was discovered that the emulsion might be washed previous to use, and in 1871 Dr. R. L. Maddox published the first notice of a gelatine emulsion, and from that, in 1878, Mr. Charles Bennet discovered the capabilities of the process and power of increasing the sensitiveness by digestion at high temperatures. Since then the process has been most rapid, the ammonia pro- cess becoming known, and rapid films and plates being of every- day occurrence. During the last few years film photography has become quite a standard process, and increased active inventive- 320 DICTIONARY OF PHOTOGRAPHY. [Pho ness upon the part of commercial firms has improved these till but little ; improvement seems necessary. Of the application of photography in every-day life it would be almost impossible to treat ; the various mechanical printing methods, the use of photography for supplying pictures for illustrated papers, cata- logues, price lists, etc., are too well known to need any descrip- tion. Its use in astronomy for making charts of the celestial bodies, in the interests of justice for the detection of criminals, for the purposes of experimental warfare and as an assistant in scientific research, for sounding the depths of the sea and for pathological study in medicine, seems almost unlimited. Photography in Natural Colours. The methods of repro- ducing objects in the colours of nature may practically be divided into three heads: (i) by the use of subchloride of silver; (2) by Lippmann's process, or the production of interference waves ; and (3) by the heliochromic or three-colour sensation process. The first process is that which was experimentally examined by Seebeck, Becquerel, Niepce de St. Victor, Poitevin, Kopp, etc., and practically consists of exposing subchloride of silver to the coloured rays, either of the spectrum or beneath a coloured glass positive, etc. The disadvantage of this process is that there is no means of fixing the colours which are thus obtained, and consequently the results will not bear a prolonged exposure to light. Some of the most successful results can be obtained by using commercial gelatino- or collodio-chloride paper, and treat- ing it as suggested by Kopp. The paper should be exposed to diffused light whilst immersed in the following solution till it turns blue-green : — Chloride of zinc ... ... 015 grms. Sulphuric acid ... ... 2 drops Water ... 150 c.cm. The paper can then be well washed and dried between blotting paper and kept in the dark. It will keep in this state for some time. The following solution should be prepared : — Potassium bichromate (pure) 15 grms. Cupric sulphate (pure) ... 15 „ Water ... ... 100 c.cm. If necessary the ingredients should be dissolved with heat. 321 Y Pho] DICTIONARY 01 PHOTOGRAPHY. Mercurous nitrate, 15 grs., should also be dissolved in as small a quantity of water, acidulated with nitric acid, as possible ; the two solutions mixed, both being at 21 2° F. ; the mixture fil- tered, and the total bulk of the solution brought up to 100 c.cm. The blue-green paper is bathed in this for a minute, well drained, and then immersed in a 3 per cent, solution of zinc chloride or nitrite of soda till it turns blue again, then blotted off between blotting paper, and exposed whilst damp under the coloured Fig. 77. object. After exposure it will be seen that the green and yellow will be visible, but the other colours require developing, and for this the green and yellow must be covered with a varnish, and then the paper immersed in a dilute 2 per cent, solution of sul- phuric acid. In order to fix the print to some extent, it should be immersed in the mercury bath, then into the chloride of zinc ; wash and dry between blotting paper, and then coat with a solution of gum arabic with 5 per cent, of sulphuric acid added. Fig. 78. The explanation of the theory of the formation of these colours is, according to Zenker, precisely the same as that involved in the following process : — 2. The interference method of Lippmann was announced by him in February 1891. This is founded on the theory of stationary waves, propounded by Zenker and Wiener. Let us assume abed, fig. 78, to be a ray of light proceeding in the direction of a d, and the small dots to be the particles of ether vibrating or in rapid motion, and on its reaching d it meets with some reflecting surface which sends the ray back. We shall have the second ray proceeding along the same line but 322 DICTIONARY OF PHOTOGRAPHY. [PllO in the opposite phase, and at b and c the pull or vibratory motion of the ether particle will be equal in both directions, as shown by the small arrows ; so that at these points there will be no light, whilst in the loops in between there will be increased light. Now in fig. 77 we see a ray of light proceeding in the direction A B ; and the arrows represent the vibratory motion of the particles of ether, a d or c b is a complete wave length. Now by referring to fig. 78 it is obvious that the point b is exactly half a wave-length from a and c, and c exactly half a wave-length from b and d\ so that we get no light at points which are exactly half a wave-length apart. If a ray of light thus treated passed through a film of sensitive material, it is obvious that where we get no light we shall have no chemical action, and consequently no deposit of silver ; whilst in between these places we shall get a deposit ; and a film of this character, after development, will only reflect that light which has a wave-length just double the distance between the reflecting particles of silver ; consequently we get a reproduction of the colour which caused this deposit. Lippmann used first of all Taupenot's albumen process, which consists practically of using iodide of silver sus- pended in albumen ; later he used bromide of silver suspended in albumen ; but he met with one great difficulty, and one which every practical photographer meets with in ordinary practice, and that is that the silver salts are more sensitive to the blue and violet than to any other colour, or, to put it more popularly, the photographic plate sees the blue and violet as the brightest part of the spectrum ; therefore he exposed his spectrum in sections, using a deep orange-red screen and giving one hour's exposure to get the red, and then five to ten minutes for green with a yellow screen, and a very pale yellow screen and twenty to thirty seconds' exposure for the blue. After exposure the plates were developed with pyrogallol, and fixed, washed and dried. Natu- rally, when the accounts of Lippmann's experiments were pub- lished, and the results confirmed, many had a good try to do the same thing. Kron6 of Dresden was one of the first, and he used albumen plates, but instead of mercury he used black velvet. Chas. R. Thwing, in 1892, used collodio-bromide plates, and re- duced the exposure to twenty minutes in the sun. M. de St. Florent, in 1892, exposed an ordinary gelatino-bromide plate with an orange screen under a coloured transparency, and then, 323 Pho] DICTIONARY OF PHOTOGRAPHY. without developing, fixed and washed it ; and it was said this plate whilst damp reproduced the colours. In 1892 MM. Auguste and Louis Lumiere showed at a meeting of the Societe des Sciences Industrielles of Lyons some spectra produced by Lippmann's method which were superior in brilliancy. These were made on gelatino-bromide plates. In 1892 Valenta pub- lished some experiments on the preparation of such an emulsion, and a year later Lumiere published their formula. Valenta's process is as follows : — A. B. Gelatine 10 g. Gelatine 1 1 20 g. Water 300 c.cm. Water 300 c.cm. Silver nitrate ... 6 g. Potassium bromide 5 g. The solutions should be cooled to 30°-35° C, and then solution A . gradually added to solution B, with constant stirring, and a faint opalescent or almost transparent liquid is obtained, which is immediately poured into about 1 litre of 90 per cent, alcohol, and well stirred till the gelatine emulsion clings to the glass rod. It is then cut up into small pieces, washed in running water for a short time, and made up to the original bulk (600 c.cm.) with water, melted and filtered, for which purpose Valenta strongly recommends fine Italian hemp, well washed with caustic potash and water or glass wool. After filtration the emulsion is colour- sensitised with some dye and coated. Valenta states that, after the emulsion has set, the plates should be soaked in dilute alcohol, and rocked till the small air bubbles, which adhere very firmly to the film, are no longer visible. They should then be washed under a tap, and dried. To render these plates colour-sensitive alcoholic solution of cyanine 1 : 500 is used, and either 1-2 c.cm. of this is added to every 100 c.cm. of emulsion before coating, or the plates can be bathed after coating in a bath of 1-5 c.cm. of above solution in 100 c.cm. of water. Better results are obtained by mixing cyanine and erythrosin as follows : Cyanine solution (1 : 500) 4 c.cm., erythrosin solution (1 : 500) 2 c.cm. ; and of this mixture 1-2 c.cm. can be added to every 100 c.cm. of emulsion. Vogel's azaline may be used in the same proportion. The silver salts of eosine have been very successful in reproducing mixed colours. Valenta gives the two following chloro-bromide emulsions as also giving good results, particularly 324 DICTIONARY OF PHOTOGRAPHY. [Pho with the less refrangible rays, but cannot state which is the better : — I. A. B. Water 200 c.cm. Water 15 c.cm. Gelatine ... 10 g. Silver nitrate ... 1-5 g. C. Water 15 c.cm. Potassium bromide 0-35 g. Sodium chloride 0-35 A is divided into two parts, one poured into B, the other into C, well mixed, and then B added toC at 35°-4o n C. II. A. Water ... ... 300 c.cm. Gelatine 10 g. Silver nitrate ... ... 6 ,, B. Water ... ... ... ... ... 300 c.cm. Gelatine ... ... ... 20 g. Potassium bromide ... ... 2-4 „ Sodium chloride ... ... 1*5 Mixing temperature, 35 0 C. The exposure for sunlight for the bromide plates with a width of 0-3 to 0*5 mm. slit is one minute, but with a wide open slit and a condensing lens ten to twenty seconds. For developing Valenta used — A. Pyrogallol 4 g. Water ... 400 „ Nitric acid 6 drops. B. Potassium bromide 10 g. Water 400 ,, Ammonium sulphite 12 „ Ammonia (sp. gr. 0*91) 14 c.cm. Pho] DICTIONARY OF PHOTOGRAPHY. For 2-3 parts of B are mixed with 1 part of A and 12-14 parts water. Valenta has also used the following modification of Lumiere s developer : — A. Water ... ... ... ... ... 100 c.cm. Pyrogallol ... ... ... 1 g. B. Water ... ... ... 200 c.cm. Potassium bromide 20 g. Ammonia (sp. gr. 0-96 at 18 0 C.) 67 c.cm. For use mix Solution A ... ... ... 10 c.cm. n B 20 „ Water 70 „ For chloride bromide plates these developers should be diluted to double the volume. For fixing, a 4 or 5 per cent, solution of potassium cyanide is the best. Valenta points out that under- exposed and under-developed photochromes thus prepared can be intensified with mercuric chloride, followed by amidol and sulphite. Lippmann presented to the Academie des Sciences de Paris on October 24th, 1892, some good reproductions of the solar spectrum on bichromated albumen and gelatine ; these only show the colours when wet. The albumen must first be coagulated with mercuric chloride solution, then well washed before treating with bichromate of potash. Lippmann's theory of the formation of these colours is that in the chromated film series of maxima and minima of interference are formed. The maxima alone make the film insoluble, and in treating the plates with water a laminar structure is formed which is partly saturated with water and partly dry. The index of refraction of the laminae varies periodically and thus gives rise to the interference pheno- mena and the colours. St. Florent is stated to have obtained photochromes or colour photographs by treating a plate coated with a thin gelatine film with a solution of — Water 1,000 c.cm. Ferric chloride ... ... ... ... log. Citric acid 5 „ 326 DICTIONARY OF PHOTOGRAPHY. [Pho and then exposing under a coloured glass picture. Valenta writes upon the preparation of emulsions for Lippmann's pro- cess : "The drawback to plates prepared by the Lumiere or Valenta process for colour photographs is that the means taken to secure the grain being sufficiently fine results in the plates being very slow. So slow is this emulsion that a plate exposed in a sensitometer for five minutes to a light of fifty candle power scarcely shows the first number. Valenta finds, however, that the addition of one gramme of sodium sulphite to 300 c.cm. ol emulsion with subsequent heating at 38 0 C. results in five minutes in an emulsion showing the fourth number on the sensitometer, or the eighteenth number in an hour. Krone has formulated the following conditions or rules which must be complied with for the successful working of Lippmann's process. (1) It is essential that the sensitive film be homogeneous, and that a reflecting surface be in contact with the film, the rays from which reflecting surface must interfere with the direct rays and thus produce stagnant or stationary waves in the film. (2) If the thickness of the film exceeds a certain thickness, the colours are not obtained, or not the correct colours. Where the regular film encloses a particle of dust this appears particularly notice- able. (3) The faithful reproduction and appearance of the colours in correct position is not absolute, but depends upon the following without exception : — (a) an absolutely accurate con- currence in the film of the finest divided silver haloid with the colour sensitiser and the correct amount of the latter ; (b) on the temperature in drying the film ; (c) on the duration of exposure ; (d) on the development. It may thus happen that with less favourable- concurrence of the above-mentioned factors, green may appear in the place of blue, and yellow in the place of red. This is also the reason why many appearances of anomalous colour-dispersion appear, and that many colours are wanting, etc. (4) An increased or diminished dampness of the results alters the colours. (5) The altitude of the sun at the time of the exposure has considerable influence on the results, as shortly before sunset or after sunrise, although all the colours may appear vigorous in the spectroscope, yet the more refrangible rays show much less actinic power, so that finally, with prolonged exposure — for instance, shortly before sunset — the violet, blue, and ultra-violet are not reproduced. The ultra-violet first dis- 327 Pho] DICTIONARY OF PHOTOGRAPHY. appears, then the blue, the place of the latter being taken up by a prolongation of the green, or shows a steely-grey colour. (6) With sufficiently long exposure the, to the eye invisible, infra-red (beyond the line A) appears as a dark purple, the ultra-violet (beyond H) sinking into yellowish rose-red lavender. (7) In the ultra-violet (beyond H) there appears, when an electric arc light is used, a very intense light maximum which is separated from the H group by a group of colourless carbon lines, this maximum being visually recognised, and with sufficient exposure, is of a deeper and more intense dark blue than the indigo blue of the solar spectrum. (8) The actinic intensity of the electric arc light, at a distance of 36 cm. from the slit of the spectroscope to the positive pole of the carbons, is to direct sunlight (mid-day, April, clear sky) as 1 : 38 to 1 : 40. (9) Only by using Lippmann's mercury mirror, when the requirements of rule 3 are complied with, is it possible to obtain the photographic colour results corresponding to the visual spectrum and the colours in their correct places. Reflected light acts always more strongly than direct light, and Krone recommended in the first place the use of a metallic mirror in order to avoid the formation of two spectrum images which would give rise to the formation of mixed colours in the pictures. Fig. 79 shows Lippmann's arrangement for obtain- ing a spectrum, l is an electric arc lamp, the rays from which are condensed by a lens upon F which is an opaque screen with a narrow slit in it. a is a convergent lens which renders the rays parallel from whence they strike the prisms p, and are formed into an image by o, the lens of the camera c, on e, the dark slide of particular form. To view these photographs in natural colours it is necessary to cement them to a prism of small angle and back them with black velvet or black varnish. The method of showing them by artificial light being sketched in 328 DICTIONARY OF PHOTOGRAPHY. [Pho Fig. 80. fig. 80, in which A is the lantern, c the condensers, sending a beam of parallel light on to the picture whence it is reflected and taken iup by a projecting lens and thrown on the screen. _ ^ = 7^~ 7 Heliochromy, or Three Colour-sen- sation process. This is based upon / \ the theory of colour sensation first / • promulgated by Young, Helmholtz, and Clerk Maxwell, which assumes that, although we have six or seven spectrum colours, yet our eyes are provided with three nerve fibrils, one conveying the sensation of red, another of blue, and another of green, the other and intermediate colours being excited by a mixture of the red, green, and blue in varying propor- tions. The first suggestion was made by Collen in 1865, and practically tried by Duhauron, Cros, and Ransonnet, and later by Ives, Vogel, Kurtz, and others. The subject may well be divided into two heads, first, the production of lantern slides or transparencies, and, secondly, the production of prints. For the production of lantern slides the process is by no means difficult. We require three negatives, a representing the red sensation, b the green sensation, and c the blue sensation. For the red sensation a red sensitive orthochromatic plate should be used, or an ordinary plate which has been sensitised by a solution of cyanine, one-third of a grain in an ounce of absolute alcohol ; the plate should be flowed over with this, dried in absolute darkness, then immersed in distilled water for two or three minutes, and again dried in the dark. For the coloured screen to cut off the blue rays a piece of orange-red glass should be used. For the green sensation a commercial isochromatic plate should be used, and two thicknesses of chromium green glass. For the blue sensation an ordinary plate with two thick- nesses of cobalt blue glass should be used. From these negatives, lantern slides should be made in the ordinary way, and projected by means of a triple lantern. The transparency representing the red sensation should be projected through the glass used to take it, that of the green sensation through one 329 Pho] DICTIONARY OF PHOTOGRAPHY. thickness of the green glass, and that of the blue sensation through one thickness of the blue -violet glass. If the images are accurately superimposed, the result will be a reproduction of the objects in their colours. For the production of prints a slightly different procedure is required. Three negatives are obtained in somewhat similar fashion, but in this case we use red, yellow, and blue as the three primary colours. As in all photomechanical printing processes, like collotype, which we will take as an example, it is the shadows which print. If a collotype plate is exposed under a negative, it will be found that, after washing, only the shadows or those portions of the film acted upon by light will take the ink, the high lights where the film was protected refusing to take the greasy ink. The result of this is that we use that negative for making the printing plate, in which the particular colour corresponding to the ink has not acted : for instance, the collotype plate made from the red negative, or the negative taken through the red screen, is inked with blue ink ; the plate from the negative taken with the green screen is inked with red ink ; and the plate from the negative taken with the blue-violet screen is inked with yellow. The negatives used for any printing process must represent the action of two colours, and represent the third as transparent : for instance, with the negative taken with the orange-red screen, the red and yellow must be opaque, but the blue transparent ; the negative taken with the green screen must have the yellow and blue opaque, but the red transparent; the negative taken with the blue-violet screen must have the red and blue opaque, but the yellow transparent. The plates suggested for lantern-slide making may be used again, but the same screens will not do. Various screens have been suggested, but at present I am unable to give exact directions for making them. Hruza has suggested the use of cochineal red and aniline yellow, I : 100, for the orange-red screen ; for the green screen a solution of malachite green, I : 200 ; and for the blue a solution of ethyl violet, 1 : 200. The disadvantage of using liquids is that there is far greater loss of light than when using collodion or gelatine dyed. The inks used vary slightly according to the recommendations of autho- rities, but cadmium or chromium yellow, carmine and milori or ultramarine blue may be taken as the usual ones. The yellow is printed first, then the red, and finally the blue. In the pro- 330 DICTIONARY OF PHOTOGRAPHY. [Pho duction of prints by the aid of process blocks, one line screens only are used for each block, the said lines crossing each other at angles of 30 0 . Whilst from the difficulties of obtaining perfect printing inks corresponding exactly to the spectroscopic absorption curves required, it is at present impossible to obtain an absolutely faithful reproduction of an artist's sketch or draw- ing. There is no difficulty in making lantern slides of absolutely faithful accordance with the original, nor is the work beyond the ordinary scope of an amateur. Photogravure. A process of photomechanical printing by means of which, by the aid of various light-sensitive substances, copper plates are obtained, which are inked and printed from, the same as an engraver's copper or steel plate. There are several methods of working it, but the most popular, and the easiest for an amateur, is that known as Klic's. The apparatus necessary for this is, first, a dusting box, which should be at least three times the area on all sides of the largest plate to be coated. This is provided with a narrow door at one side. The box should be mounted on trunnions or side pivots, so as to swing freely. Raw Syrian asphalt, finely powdered, or a mixture of asphalt and resin, is also required. Finely polished copper plates and perchloride of iron ; this latter should be solid, and not the acid solution of the chemist. The perchloride is dissolved in water by adding one- third the quantity of distilled water to it and allowing it to dissolve as much as possible, and then diluting it with distilled water till it marks 45 0 Baume, 40 0 , 38° 35 0 , and 27 0 Baume. These five solutions are carefully prepared of the above strength, or, in the absence of a hydrometer, the solutions may be made up of the percentage strengths which correspond to the above, 47, 41, 38, 35, and 27. These must be the percentage solutions, and can be made as follows, assuming that we require 10 ozs. of solution : — 1. Perchloride of iron, 2,256 grs. Dist. water to make 10 ozs. 2. „ i,9 68 n 3- n 1,824 H 4- n 1,680 „ 5- „ 1,296 „ We require a transparency of the negative to be reproduced. This transparency should be made on an ordinary dry plate, not a lantern plate, and should be soft and delicate, more approaching 33* Pho] DICTIONARY OF PHOTOGRAPHY. the ordinary negative than lantern-slide characters. From this transparency we must prepare a negative in carbon. Either transparency or standard brown may be used. The negative must be thin, and quite free from any deposit in the deepest shadows. The dusting box must be lined with varnished paper, and the asphalt sifted through fine linen. The copper plates should be obtained already bevelled and polished, and merely require cleaning with weak caustic potash solution and then with ammonia, and washing, whitening, rinsing and drying. The plates are now ready for graining. To do this the box, con- taining from one-half to a pound of powder, is rather slowly revolved for about three times, and then brought to a stand with the door at the bottom. It is allowed to rest for one minute, and then the copper plate, placed on a larger piece of plate-glass, is placed on a box or piece of wood on the bottom of the box inside, the door closed, and the dust allowed to settle for about five minutes, and then taken out and examined to see whether enough dust or grain is on it. How much grain to lay is a matter of experience. A dark subject requires not only more grain, but a coarser grain, than a lighter subject. For ordinary subjects the best way is to allow the dust to settle for about one minute, and then to leave the copper plate in for ten minutes. Having grained the plate, the next thing is to fix the grain. This is done by heat, and the best heater is a proper copper plate heater. Failing this, an ordinary gas stove may be used, or merely a sheet of iron placed over a gas stove. The plate is now placed on the hot plate till the grain melts and adheres firmly to the plate. The sign of the grain being fixed is a peculiar bloom or steely colour, which appears, when looking at the plate, at an angle of about 30 0 . When the grain is fixed the plate should be allowed to spontaneously cool ; and in this condition the grain will not rub off, and the plate may be kept some time. The carbon negative is the next thing to be prepared, and this is printed in the usual way, a safe edge being used. As we wish the margins to be white, it is necessary to use some protecting covering ; and the simplest method is to cut a sheet of orange paper the full size of the negative. Out of the middle of this cut a piece the exact size of the desired picture, and from the margin cut another eighth of an inch all round; and, after the real exposure has been given, cover the exposed portion with the 33 2 DICTIONARY OF PHOTOGRAPHY. [Pho central cut-out and the margin with the edge. This is best done by pasting the mask and margin on a piece of glass the exact size of the negative. This ensures an insoluble strip of carbon tissue all round the picture. The carbon negative is now deve- loped on the copper plate in the usual way, and when developed and fixed is rinsed with water, then with a mixture of equal parts of methylated spirit and water, and finally with spirit alone till all the water is out of the film. The plate, both margins and back, is covered with black varnish, allowed to dry, and it is ready for etching. The plate is now placed in No. I bath of perchloride, and left for one minute ; then into No. 2, where it is left for two or three minutes ; then into No. 3 for about three minutes ; then into No. 4 for three minutes ; and, finally, into No. 5 till the highest lights on the copper are just darkened, and half a minute longer. The plate is now dropped into a 5 per cent, solution of caustic potash, the resist or carbon cleared off, and then the varnish, with turpentine and benzole, the plate well washed and polished with whitening, when it is ready for printing from in the copperplate press. Photo-Lithography. One of the most important of all photo-mechanical methods in which a print is obtained from a negative and transferred to lithographic stone, and printed from in the ordinary way. Photometer. Literally a measurer of light. It has lately been much recommended for calculating the exposure for the sensitive plates ; but as the action of these is solely to measure the visual rays, and as the latest image is imprinted on the plate by the chemical and not the visual rays, it is obviously unfair to judge of the exposure to the one by the intensity of the other. Photo-Micrography. The art of obtaining photographic en- largements of microscopic objects by the aid of the microscope. The chief advantage of photo-micrography is that the results obtained are free from much of the personal element which is always present with hand-drawn diagrams. And again, although the successful results are often extremely difficult and tedious to obtain, yet when obtained they are far superior to anything that can be done by hand, and actually, the author thinks, not so tiring as having to pore for some hours over a microscope with pen and pencil, and laboriously trace the minute details of some 333 Pho] DICTIONARY OF PHOTOGRAPHY. pathological or histological subject, which was for many months the author's work : this, unfortunately, before a practical know- ledge of photography was obtained. Only the bare details of this art can be entered upon. For fuller detailed instruction the operator must refer to the special handbooks, such as that of Charters White, Jennings, Dr. Sternberg, Andrew Pringle, Bousfield, the monthly Microscopical Journal, "The Transactions of the Royal Microscopical Society,"- etc. Any good firm micros- cope stand may be employed, and the draw-tube should be lined with black velvet or cloth — not the usual black matt varnish, which soon wears off. Caution must be exercised, however, that the foreign makes with somewhat narrow draw-tubes are not obtained, as these limit the field of view very much. A mechanical stage is almost a necessity. Several lenses will be required, and these should be of low or narrow-angle, and usually a 2-, I-, \-, and |-in. will be found sufficient, and a ^-in. wide-angle also. These should be obtained from English makers who now manufacture lenses specially for photo-micrography, A large bull's-eye condenser and a parabolic reflector are also required. The majority of beginners will most likely confine themselves to small plates, the lantern size 3^ x 3^ being the most usual. Special forms of light cameras are now made for this size for use with the eye-piece, and from practical ex- perience the beginner is recommended to always use the eye- piece till he has become more proficient. The camera, however, must have a sufficient pull of bellows, about 12 or 14 inches. For focussing, the usual ground glass is utterly useless, the only method being to use a piece of patent plate which has lines drawn upon one surface with a diamond; and when these lines and the image are both in focus with a compound focusser, the correct focus is obtained. Or another method consists of moving the head from side to side, and when the image moves with the head the object is not in focus ; when, however, it remains stationary the focus is correct. The method of attachment of the microscope to the camera differs with every operator, — some employ loosely fitting black velvet sleeves ; others employ a brass connection, into which the microscope tube either screws or merely slides. The question as to the best plates to use can only be answered to some extent by asking what is going to be photographed, as the plates must be suited for the subject; preparations of 334 DICTIONARY OF PHOTOGRAPHY. [Pin objects stained with the various dyes usually used require dif- ferent plates. In some cases, especially those in which yellow predominates, isochromatic plates will be found the best. In others, where orange or orange-red is the prevailing colour, then plates specially sensitised for these rays will be found most effectual. If the illuminant used is gas or lamp light, then the exposure may be considerably shortened by always using iso- chromatic plates as these plates are much more sensitive to such light than ordinary plates. The rapidity of the plate is not a subject of much consequence, as equally good results have been obtained by eminent workers on both slow and rapid makes. Phototype. A mechanical printing process in which a gelatine film itself is used to print from. Pinholes. Minute transparent spots making their appear- ance on the plate in the fixing bath. They are chiefly due to air bubbles, or particles of dust adhering to the film whilst in the developer, and thus preventing the action of the developer on the film at these spots. To obviate these the film should be brushed with a soft camel's-hair brush whilst in the developer, but where pinholes are in existence recourse must be had to retouching or painting them out with some non-actinic colour. Pinhole Photography. Of late years the possibility of taking passable negatives without the use of an ordinary camera and lens has become an established fact. For this purpose any rectangular box which is absolutely light-tight will do. In one end make a minute hole with the point of a needle, and at the other end place the sensitive plate, keeping it in its place by means of a clip or other simple arrangement. A prolonged exposure is required, about twenty or thirty times the ordinary one for any given subject. No focussing is required, as the image is always fairly sharp, no matter what distance the plate is from the hole. The larger the plate the wider the angle, and the greater the distance the larger the image. As an experiment, it should be tried by every amateur, as the materials are always at his command in the shape of an empty plate-box. There is with every different aperture a correct position for the sensitive surface which gives the maximum of sharpness, and this can be found by Abney's formula. Mr. Alfred Watkins has calculated 335 Piz] DICTIONARY OF PHOTOGRAPHY. out a table on the above formula, and suggests that, as ordinary sewing needles are made to standard sizes, they should be used to punch the holes in the metal plate or card. No. of Needle. Diameter. Distance to Plate. Ratio. Calculate as ! 2V inch 32 inches 1 7inr fl7o 2 1 1 ■?"3 » 28 „ 1 ^475" fH 3 ■h » 23 M f/60 4 20 „ 1 6 SO 5 1 a 1 » 15 » T5"6~ 6 » 13 » 1 44"0" fM 7 1 liTT M IO „ 1 TJ9IT f/39 8 4V }) 8 „ MS 9 1 4 9 »» 6 „ 1 f!*9 10 1 Si »> 5 r, 1 fl*7 and multiply by 100. Pizzighelli's Printing-out Process. Rives or Saxe paper may be used, either glossy or with matt surface. The following solutions are required : — No. 1 Solution, Gum Arabic. Gum arabic (finest white lumps) 770 grs. or 50 grms. Distilled water 27 drms. ,, 150 c. cm. No. 2 Solution Arrowroot. Arrowroot ... ... ... 30 grs. or 2 grms. Distilled water 27 drms. ,, 150 c. cm. Mix the arrowroot into a paste with a little water, add to the remainder of distilled water whilst boiling, and keep the tempera- ture up for five or ten minutes. No. 1 solution gives the best effects. 336 DICTIONARY OF PHOTOGRAPHY [Piz No. 3 Solution, Ammonia Ferric Oxalate. Ferric oxalate 308 grs. or 20 grms. Oxalic acid ... ... ... 8 „ 0.5 grm. Ammonium oxalate ... 288 or 308 or 18 to 20 grms. Distilled water 27 drms. or 150 c.cm. No. 4 Solution, Sodium Ferric Oxalate. Ferric oxalate ... 308 grs. or 20 grms. Oxalic acid ... 8 ,, ,, 0 5 grm. Sodium oxalate ... ... 230 to 290 ,, or 50 to 60 grs. Distilled water 27 drms. or 150 c.cm. The exact amount of sodium or ammonium oxalate to use is found by the formation of a brilliant emerald green colour, turning slightly darker as more of the salt is added. The addi- tion of the salt must be stopped at this stage. After shaking slightly, filter the solutions, and preserve from actinic light. No. 5, Sensitising Liquid. Solution of chloro-platinite of potash (1 in 6) ... 408 mins. or 50 c.cm. No. I 391 „ „ 49 „ m 3 374 m m 48 m Or No. 6. Solution of chloro-platinite of potash (1 in 6) ... 24 mins. or 50 c.cm. 11 4 39i n 11 49 .1 1 374 n ii 48 11 Or No. 7. Chloro-platinite of potash ... 24 grs. or 1*5 grms. Sodium oxalate ... 24 „ ,, 1*5 Ferric oxalate 31 ,, „ 2 ,, Oxalic acid ... ... ... 3 grs. or 0-3 grm Gum arabic ... 52 ,, ,, 4 c.cm. Distilled water, to make ... 480 mins. „ 25 The mixtures are well stirred, filtered through muslin, and kept from actinic light. No. 5 gives bluish black, No. 6 brownish 337 z Pla] DICTIONARY OF PHOTOGRAPHY. black tones. The coating, drying, and storing of the paper are precisely the same as for the original process patented by Willis. Chlorate of potash may be added in the same way, to increase contrast. About 90 minims of sensitising liquid are required for a sheet 10 by 8. The printing may be carried on until the image has appeared in all its parts, and should be no darker when printed than required. When finished, the print is washed in acidified water, as recommended for the old process) and finished in the ordinary way. A second method of printing is to print till the general details are out, but all the half-tones are wanting. The print is then taken from the frame and put on one side, when the action set up by the light continues, and in from a half to two hours the print is finished, and can be treated as above in acidified water, or the incomplete picture may be developed upon a cold dilute solution of carbonate of soda of the following strength : — Carbonate of soda 38 grs. or 2 grms. Distilled water 27 drms. 150 c.cm. Immerse the print in this till sufficiently developed. A third method of printing is to expose till only the principal details are visible, and develop, as in the old process, upon a hot solution of potassium oxalate. Platinotype. The process was first invented by Mr. W. Willis, and the right for the sale of the paper and materials for making it rests solely in a company formed by him. The basis on which this process is founded is the reduction of ferric oxalate by the action of light into ferrous oxalate, and the reduction of a platinum salt by the ferrous oxalate in the metallic state, when wetted with a suitable agent. The following is stated by Berkely to be the action that takes place : — Fe 2 (C 2 0 4 ) 3 = 2FeCA, + 2C0 2 Ferric oxalate = Ferrous oxalate + Carbonic acid gas 6Fe(C 2 0 4 ) + 3K 2 PtCl 4 = 2Fe(C 2 0 4 ) 3 + Fe 2 C16 Ferrous Chloro-platinite Ferric Ferric 4- = 4- oxalate of potassium oxalate chloride • + 6KC1 + 3 Pt + Potassium + Platinum. chloride 338 DICTIONARY OF PHOTOGRAPHY. [Pla The following are concise directions for the process : — Paper of good strong quality, even in texture and white in colour, should be chosen, and may be sized in one of the following baths : — Soak 150 grs. of Nelson's X opaque gelatine in 30 ozs. of water for half an hour, and heat in a water bath at a temperature of 140 0 F. to dissolve it. Add 45 grs. of powdered alum and 7 ozs. methylated spirit, filter through muslin, and put in large flat dish. Thoroughly immerse the paper bodily in this solution, taking care to break all adherent bubbles ; the paper should be allowed to soak for three minutes, and then hung up by clips to dry. The drying should be as rapid as possible, and a second bath for the same time should be given, and the paper hung up by the opposite corners. A sizing of gelatine tends to a bluish black tone ; arrowroot and starch to a brownish tinge. If arrow- root or starch be used, the following bath may be prepared : — Rub 150 grs. of arrowroot or pure starch powder into a cream with a little water, and then pour gradually and with constant stirring into 30 ozs. of boiling water, and boil for ten minutes ; then add 7 ozs. methylated spirit, and allow to cool. The fol- lowing are Pizzighelli and Hiibl's formulae for sensitising the paper : — Solution of Ferric Oxalate. Ferric oxalate ... ... ... 120 grs. or 8 grms. Distilled water ... 1 oz. „ 25 c.cm. Oxalic acid ... ... ... 8 grs. ,, 0-5 grm. No actinic light must be allowed to gain access to this solution, or the ferric will be reduced to ferrous salt. Solution for Increasing Contrast. Solution of ferric oxalate ... 1 oz. or 25 c.cm. Chlorate of potash ... ... 2 grs. ,,o.igrm. The same care must be exercised in the keeping of this as of the former solution Solution of Chloro-Platinite of Potassium. Chloro-platinite of potassium ... 80 grs. or 5 grms. Distilled water ... 1 oz. ,, 25 c.cm. 339 Pla] DICTIONARY OF PHOTOGRAPHY. Sensitising Solutions. Na i> Sol. chloro-plat. of potassium ... 24 drms. or 75 c.cm. ferric oxalate ... ... 22 „ ,, 69 ,, Distilled water 4 „ 14 „ A normal solution, working well and giving deep blacks. No. 2. Sol. chloro-plat. potass 24 drms. or 75 c.cm. „ ferric oxalate 18 ,,50 „ Sol. chlorate potash (contrast sol.) 4 „ „ 14 ,, Distilled water 4 „ ,, 14 „ This gives brilliant prints. No. 3 Sol. chloro-plat. potass.... ... 24 drms. or 75 c.cm. „ pot. chlor. (contrast sol.) ... 4 ,, „ 12 5 ,, Distilled water 4 I2 '5 » This is a solution for weak negatives. Chloro-platinite of potash when obtained commercially should be tested as follows : — (1) 1 drm. of the salt should be soluble in 6 drms. of distilled water. (2) The solution should not be acid. This solution will keep unaltered by light for an almost indefinite period. Very feeble light must be used for coating the paper. To keep the paper flat whilst coating, the edges should be turned under- neath a plate of glass placed upon a table ; for larger pieces the paper can be easily clipped to glass plate by wooden clips, or it can be pinned at the corners by drawing pins. For coating a sheet of paper 8 by 10 ins., 30 minims of sensitiser are required, which should be poured into the middle of paper and spread over the surface with a uniform circular motion, by means of a pad composed of a tuft of cotton-wool enclosed in a piece of fine washed muslin. The rubbing should be continued gently for at least three or four minutes. As soon as coated, the sheet should be hung up by two corners to dry, and as soon as the surface moisture has disappeared, the paper should be carefully and quickly dried over a gas burner, or before a stove or fire. The whole success of the process lies in this stage — the drying of the 340 DICTIONARY OF PHOTOGRAPHY. [Pla paper ; the paper must be absolutely dry. This point is known from the change in colour from lemon to an orange colour, and by the crackle of the paper. Care should be taken not to scorch the paper, or fog will be the result. Between the coating and drying about five minutes must be allowed to elapse in summer and eight or nine minutes in winter. The exposure required for the paper is about one-third of that required for a silver print from the same negative. Absolute dryness, both in the keeping before, during, and after exposure is a sine qua ?wn ; the slightest trace of moisture immediately renders the paper useless. It should be stored in tubes in which chloride of calcium (anhydrous) is kept to absorb the moisture. The image on the paper is but faintly visible, and requires a developer to bring it out in all its beauty. This is made as follows : — Oxalate of potash 130 grs. or 7-5 grms. Distilled water 1 oz. ,, 25 c.cm. This solution may be kept as a stock solution, and when required for use must be heated to a temperature of 170 0 to 180 0 F. Development is effected by passing the print face downwards over the surface of the solution, and allowing it to remain for two or three seconds; the developed print should be passed at once into a bath of hydrochloric acid 1 oz., water 6oozs., and allowed to remain for ten minutes ; it should be then passed into another bath for the same period, and lastly into a third ; it can be then washed, dried, and mounted in the usual way. The developing solution may be used over and over again. For over-exposed prints solution at ioo° F. can be used; for under-exposed over i8o°F. may be used with advantage. Warm Tones with Platinum Prints. The Platinotype Com- pany issue a paper which gives a sepia tinge, which perhaps owes its colour to mercuric and cupric chlorides. The addition of a few drops of solution of these chlorides to the developer materially alters the colour of the image. Warmer tones may be obtained by the following process. The following solutions are required : — Solution No. 1. Oxalate of potash ... ... 463 grs. or 25 grms. Oxalic acid ... 15 ,, „ 1 grm. Distilled water ... .... ... 27 drms. 100 c.cm. 341 Pla] DICTIONARY OF PHOTOGRAPHY. Dissolve and add Solution No. 2 ... ... ... 3 drms. or 10 c.cm. Shake thoroughly, and leave; if crystals form they are of no consequence. Solution No. 2. A. Chloride of calcium, crystal ... 147 grs. or 10 grms. Distilled water ... 2 ozs. ,, 60 c.cm. Dissolve. B. Sulphate of copper, crystal ... 249 grs. or 15 grms. Distilled water ... ... ... 10 drms. ,, 36 c.cm. Dissolve. Mix A and B, filter, and label "Cupric Chloride Solu- tion, No. 2." Put solution No. 1 into an iron enamelled dish, and heat to 180 0 F., then develop the prints as usual ; wash in acidified water (the tint can be altered by raising or lowering the temperature). Prints that are already developed may be treated in the same way. After washing, the prints are soaked for a short time in a 5 per cent, solution of ferrous sulphate, acidulated with a drop or two of sulphuric acid, then rinsed in acidified water and dried. In 1888 a modification of the above process was suggested by Willis, in which the heating of the developer is entirely done away with, and greater transparency in the shadows and more control over results can be obtained. The paper has to be preserved with the same care from damp, and the image is printed rather deeper than with the old paper. It can be developed upon the solution of the developing salts of the manufacturers, or upon the normal oxalate solution as used for ferrous oxalate developer. The print is floated on this, and as soon as intense enough washed in the acid baths in the usual way. Considerable control over results may be obtained by the use of glycerine in the following manner. Three solutions should be prepared : — No. 1. Solution of oxalate of potash 2 parts. Pure glycerine 2 „ 342 DICTIONARY OF PHOTOGRAPHY. [Pla No. 2. Solution of oxalate of potash I part. Pure glycerine ... 4 parts. No. 3. Pure glycerine. The print should be pinned to a board and a small pool of the pure glycerine poured on to the print and evenly distributed all over it by means of a soft pad of linen. If there are any portions of the print which have a tendency to appear too white, or wanting in detail, a broad mop or flat brush charged with solution No. 2 should be applied to those places, and then gradually over the whole of the print, except in the very deepest shadows, which should be left untouched. As soon as the image begins to develop, the brush should be charged with No. 1 solution, and passed rapidly and evenly over the whole print ; the print will gradually gain in intensity, and by careful use of solutions No. 1 and 3 with brushes, it will be possible to hold back one portion*. and coax another out. As with most other processes, success is not always attained at first, and it may happen that our finished prints are too dark or too light. In the former case there is not much to be done, as platinum is one of those intract- able metals not easily amenable to reagents ; strong chlorine water will reduce the image slightly. Platinotype prints can be far more easily intensified, and several processes have been suggested for this purpose, by means of which also various modifications of tone are possible. Dollond suggests what is practically a gold toning process what he describes as follows. The solutions required are : — 1. Gold chloride ... ... ... ... 15 gr. Distilled water *]\ drachms. Neutralised with chalk, filtered, and one drop of strong hydro- chloric acid added. 2. Glycerine, 3. Sodium sulphite Water to Metol 4. Potassium carbonate Ware to 343 1 oz. 10 „ 5o gr. I oz. 10 ,, Pla] - DICTIONARY OF PHOTOGRAPHY. The following is the method of application : — The platinotype print developed, cleared and dried in the usual way, is soaked for two or three minutes in water, then laid upon a flat surface, preferably a sheet of opal glass, and blotted to remove the excess of water. Next glycerine is gently spread over the whole surface of the print with a soft brush or the finger-tip. When evenly coated, a few minims of the gold solution are dropped on and rapidly mixed with the glycerine with a soft camel-hair brush. Very soon the print will begin to gain in strength and assume the blue-black colour. During the whole time the toning is proceed- ing, the surface of the print should be brushed lightly and quickly, in order to insure even action and to constantly bring fresh gold chloride into contact with the platinum image ; also there seems to be less tendency for a deposit to be formed on the high lights if the solution is kept in motion. The high lights should be watched, and as long as they remain clear the action may be allowed to continue. When the desired effect is obtained or when any coloration is seen in the high lights, the print should be quickly rinsed to remove the adhering glycerine and gold. After this a mixture of equal parts of metol and potash solutions is sponged over both front and back of the print. Washing for half an hour completes the operation. Prints may be kept after development for some weeks, or even months, before toning, but very old prints will not readily tone. If the weather is cold, the water and dishes used will probably require to be slightly warmed or the action will be very slow. Prints are best toned in good daylight, as it is easier to see that the gold is kept evenly distributed over the print, and daylight also assists the action and renders the process more rapid than when performed by gaslight. The general effect of the toning action is to slightly increase the contrasts in the print, as proportion- ately more gold is deposited where there is a large quantity of platinum present than where there is a small quantity. The best results are obtained when the actual increase in intensity required is small only. The method of treatment I have described will, I think, be found to have four distinct uses: (i) To strengthen under-exposed prints ; (2) To convert a rusty or brownish colour in a print into a pure black ; (3) To produce blue-black in the place of black prints when this modification of colour is considered desirable ; (4) To enable brighter prints 344 DICTIONARY OF PHOTOGRAPHY. [Pla to be obtained from flat negatives than is usually possible by the ordinary method." A method of intensifying platinotype with silver has also been suggested. For this either an acid pyro or acid hydroquinone developer could be used, to which a few drops of a 10 per cent, solution of silver nitrate had been added. The solutions required are, i. Pyrogalloi 2 grs. Citric acid 20 grs. Distilled water ... 1 oz. 2. Hydroquinone ... ... 2 grs. Citric acid ... ... 20 grs. Distilled water 1 oz. 3. Silver nitrate 48 grs. Distilled water 1 oz. The prints after clearing must be thoroughly freed from acid and placed in a clean dish. Ten drops of No. 3, should be added to one oz. of either 1 or 2, and the solution, which turns white and cloudy immediately applied to the print and the dish rocked. As soon as the desired degree of intensification is reached the print should be thoroughly washed and then fixed in hypo, and well washed to free it from any soluble silver salt. The intensified print can afterwards be toned with gold or platinum to obtain different tones. Platinotypes may also be toned with uranium by the following process suggested by Hubl : — Uranium nitrate 48 grs. or 10 parts. Glacial acetic acid 48 grs. „ 10 „ Water 1 oz. „ 100 „ B. Potassium ferridcyanide ... 48 grs. or 10 parts. Water ... 1 oz. ,, 100 C. Ammonium sulphocyanide 240 grs. or 50 parts. Water 1 oz. „ 100 „ 345 Pla] DICTIONARY OF PHOTOGRAPHY. For use, add to 1,000 parts of water 10 parts of the above solu- tions one after the other. The well-washed platinum print should be placed in a dish and covered with the solution, and the dish rocked till the desired tone is attained. The toning bath should then be poured away, the prints washed in frequently changed water. The process of toning is complete in about five minutes, and with concentrated baths takes place so quickly that it is impossible to avoid failure. In place of the sulphocyanide, sodium sulphite may be used, but as this acts more energetically the bath must be more dilute. For this should be used 5 parts of A and B and 5 parts of a 10 per cent, solution of sodium sulphite to 100 parts of water. Grape sugar acts very slowly, and thiosinamin very quickly. Platinotypes may be toned in a similar manner to the above, with ferridcyanide of iron, and blue tones be obtained which are suitable for moonlight and night scenes. With this process sodium sulphite is less suitable. The following solutions should be used : A. Ammonium iron alum .. 48 grs. or 10 parts. Hydrochloric acid ... ... 48 grs. or 10 ,, Water .., ... ... 10 oz. ,, 1,000 ,, B. Potassium ferridcyanide ... 10 per cent, solution. C. Ammonium sulphocyanide 50 per cent, solution. For the toning bath, to 1,000 parts of water add first 5 parts of A, then 2 parts of B, and 5 parts of C. The solution should be of a red colour, and is used similar to the above-mentioned uranium bath. The above physical uranium and iron toning is very easily carried out, and the desired tones may be obtained. In preparing the pictures, however, it must be remembered that these baths have an intensifying action. The prints before toning should have soft delicate half-tones, pure whites, and not too deep shadows ; in no case should they be too brilliant, otherwise after toning they will be hard. Soft, harmonious, and somewhat thin negatives on soft-printing platinotype paper are the most suitable. If the toning process is a failure, or the 346 DICTIONARY OF PHOTOGRAPHY. [Pla desired tone is not obtained, the prints may be restored to their original condition by treatment with dilute ammonia. Any slight yellow stain may then be removed by dilute hydrochloric acid. The ferrocyanide compounds of iron and uranium with- stand the action of acids, but are removed by alkalies ; therefore the toning bath must be faintly acid, and the washing of the toned prints must not be done by ordinary water containing lime or alkalies. It is in any case advisable to add a few drops of acetic acid to the washing waters to prevent the removal of the toning. Platino-Uranotype, Mercuro-Uranotype, Palladiotype. Under these names Mr. Alleyne Reynolds has given some account of the result of his experiments, which may possibly be of some use in the future as printing processes. Formula for Platino-Uranotype. Solution A. Saturated solution of uranium chloride. Solution B. Chloro-platinite of potash ... 60 grs. Distilled water i£ ozs. Ninety minims each of A and B are mixed and spread over a well-sized sheet of paper 26 X 20 ins. Potassium chlorate may be added to increase contrast. Expose under a negative until the faintest trace of an image is visible ; then develop upon a cold solution made as follows : — Make a saturated solution of neutral oxalate of potash in cold distilled water, and dissolve dry ferrous oxalate in this to saturation. Wash in water acidified with hydrochloric acid about \\ per cent, till the drawings are colourless. Wash thoroughly and dry. Formula for Mercuro-Ura?wlype. Solution A. Saturated solution of uranium chloride. Solution B. Saturated solution of mercuric chloride. 347 Pla] DICTIONARY OF PHOTOGRAPHY. Sensitising Liquid. Solution A i oz. B i drm. About 170 minims will be required to sensitise a sheet 26 X 20 ins. Expose behind a negative until the image attains full strength, and then float on a dilute solution of chloride of gold or chloro-platinite of potash to tone it. Then wash in water acidified with hydrochloric acid and wash ; or the toning may- be omitted, and the print merely washed in acidified water, and then thoroughly washed and dried. Palladiotyfie. No distinct formulae are given, but the operations are thus described : — " 1st. Coating the paper. This may be done with either uranic chloride, ferric oxalate, or sodic ferric oxalate, or a mixture of any or all of these. " 2nd. Exposure. "3rd. Development. Half a drachm of a 15-grain solution of sodio-chloride of palladium is diluted with about 1 oz. of water, and the print floated thereon face downwards. It is better to add a trace of hydrochloric acid to the developer. "4th. Fixing as in platinotype. The result will be a print like a platinum print, only of a nice warm tone, which may be rendered colder by adding a trace of platinum to the developer. Platinum (Ger., P latin ; Fr., Platine ; Ital., P latino). Pt = 1967. Synonym : Platina. This metal occurs usually in the free state, the chief source of supply being Mexico, Brazil, and Siberia. It is a silvery white metal, having specific gravity 21*5. When in an extremely fine state of division, it is absolutely black, and is one of the most permanent and immutable of all metals. It is tolerably hard, very difficult of fusion, not dissolved by hydrochloric, nitric, or sulphuric acid, and only slightly acted upon by some alkaline substances. Platinum Perchloride (Ger., Platinwasserstoffchlorid ; Fr., Bichlorure di platine; Ital., Bicloruro di platind). PtCl 4 2HCl,6H 2 0 = 489. Synonyms : Bichloride of Platinum, 348 DICTIONARY OF PHOTOGRAPHY. [Pla Platinum Chloride, Platinic Chloride, Muriate of Platina, Chloro- platinic Acid. This salt is prepared by dissolving metallic platinum in aqua regia. It occurs in small brownish-red masses extremely deliquescent, forming a deep orange or brownish- orange solution. Very soluble in alcohol and water. It is used for preparing chloroplatinite of potash, and has been suggested for toning prints and collodion positives. This salt readily combines with the chlorides of potassium, sodium, and ammonium to form double salts — e.g., PtCl 4 2KCl. Platinum Toiling. Either with the desire for greater variation in the tones, or for possible greater permanence of the image, platinum has been applied to the toning of silver images, and whilst rich brown blacks and cool sepias are obtained it does not seem possible to obtain pure blacks as when using platinotype paper. There are several conditions which are essential for successful work. The prints, whether on gelatino- chloride, plain salted, or smooth or rough surface paper, need not be printed any deeper than usual. The platinum salt employed must be the chloro-platinite, the ordinary perchloride being comparatively useless for this purpose. The print must be absolutely freed from soluble silver salts before toning, the toning bath must be acid, and the paper must be free from all acid and soluble platinum salts before fixing, or else the whites become yellowed. To free the print from silver nitrate the best thing to do is to allow it to soak for five minutes in a solution of salt and water 2 ozs. to the pint, and then wash so as to free it from excess of salt, and then place in the toning- bath. Numerous formulae have been suggested for this, but the most suitable are either that of Stieglitz, which is — A. Oxalate of potash ... ... 256 grs. Acid phosphate of potash ... ... ... 128 ,, Distilled water ... .... ... ... 5 ozs. B. Chloroplatinite of potash ... ... ... 60 grs. Distilled water ... 2 ozs. For use take of Solution A 3 parts. Solution B ... 1 ,, Distilled water 2 ,, 349 irnej dictionary of photography. This can be brushed over the well-washed print. A far simpler bath is obtained by using the chloro-platinite with an acid or acid salt, and provided nitric or hydrochloric acid is not used there is not much difference to be detected. If a faintly acid and somewhat weak bath be used, such as is obtained by using a saturated solution of cream of tartar, warm sepia tones are obtained, whereas, by using stronger acids, such as phosphoric or citric and a greater concentration of bath, deeper tones are obtained. No. i for Sepia Tones. Acid tartrate of potash (cream of tartar) ... 60 grs. Potassium chloroplatinite 1 ,, Distilled water ... ... 6 ozs. No. 2 for Blacker Tones. Citric acid ... ... ... ... ... 60 grs. Potassium chloroplatinite ... ... ... 2 ,, Distilled water 2 ozs. Not much guide as to the final tone of the print is to be obtained by examining them by transmitted light. After toning the prints should be well washed, and then passed into solution of carbonate of soda, about 1 oz. to the pint, and thence into the fixing bath. Pneumatic Holder. A convenient little apparatus for holding plates for the purpose of coating them, used chiefly in the old collodion days, the principle relying upon the pressure of the atmosphere to keep the plate in its position on the holder, due to the india-rubber ball being partially exhausted of air. Poisons. Some of the chemicals used in photographic pro- cesses are poisonous when taken internally or when absorbed through the skin. The table on p. 351 will be of some assistance on that point. Fluoric acid when applied to the skin, even in a dilute state, causes painful ulcers, and 1 in 80 can also cause irritation and tenderness. Bichromate of potash and cyanide of potash, when applied to cuts, wounds, and abrasions, are absorbed, and cause, the first painful sores, the latter death. 3SO DICTIONARY OF PHOTOGRAPHY. [Poi 2 2.2 - £ !f - 0) .•a 3 H.2 ^2 * d C »' r £ d 1 &^ £ £ i . a - £ £ £ § •a s ttJ O in ,■ g 2 .2 S ^ m <+-. T3 ° ^d M life's' 1 4< V M SO : as K u :£ o : d *3 d .2 3 W £ £ o C :=2 d t/i 3 I 2 4 4 '6 1 1 8 3 2 7 3 1 2 8 3h 2 8 Sh 1 5 1 1 4 2 1 I 2 18 18 4 3 l\ 428 DICTIONARY OF PHOTOGRAPHY. [Var For photographic purposes special varnishes are required, and the following will be found very good ones : — Negative Varnish (0 Orange shellac i£ oz. or 38 grms. Mastic J 11 11 7 11 Sandarac i| ,, 38 „ Oil of turpentine £ 7 ,, Venice turpentine \ ,, 7 " Camphor 10 grs. o*6 grm. Methylated spirit, 66 over proof . 20 ozs. „ 500 c.cm. Or (2) Orange shellac 2 ozs. or 60 grms. Sandarac ... ... .. ... 2 „ 60 Canada balsam ... ... ... 60 grs. ,, 4 ,, Oil of lavender ... ... ... 1 oz. 25 c.cm. Methylated spirit... ... ... 16 ozs. „ 400 Or (3) White hard varnish ... ... 15 ozs. or 400 c.cm. Methylated spirit 25 ,, 700 The above varnishes must be flowed over the negative, and then dried before a brisk fire. The following may be applied without warming : — (4) Negative varnish ... 5 ozs. or 150 c.cm. Liq. ammonia *88o Add sufficient to cause the cloudiness first formed to disappear. Or White hard varnish ... ... 10 ozs. or 250 c.cm. Liq. ammonia 880 As above. Water 5 ozs. or 125 c.cm. 420 Var] DICTIONARY OF PHOTOGRAPHY. Burton has strongly recommended the following : — Sandarac I lb. Venice turpentine 4 fluid ozs. Oil of turpentine 8 „ ,, Alcohol (sp. gr. -825) 1 gallon. The alcohol should be poured over the gum, which will dissolve in a few hours without heat, if the vessel be occasionally shaken- The Venice turpentine is then added, and the measure rinsed out with the oil of turpentine, which is also added. The varnish is then ready for use. Black Varnish. Benzine 1000 parts. India-rubber ... ... ... 6 „ Asphalt , ... 300 ,, Lamp black Quant, suff. Matt Varnish. This can be prepared from : — (1) Sandarac 100 parts. Mastic (in tears) 20 ,, Ether 1000 „ Benzine 500 (2) Sandarac 60 „ Gum Dammar 60 „ Ether 1000 „ Benzine 350 to 400 parts. The more benzine is added the coarser the grain, and vice versa. Lainer strongly recommends : — Ether 100 c.cm. Sandarac 10 grms. Dissolve by agitation, fllte*, and add — Toluol 35 to 40 c.cm 43° DICTIONARY OF PHOTOGRAPHY. [Vie View Finder. This is a little instrument used for instan- taneous photography to see when the moving object is in the middle of the field of view and in the middle of the plate. One form is a piano or double-concave lens mounted on the front of the camera, the eye being placed at the back of the camera. A good form of this finder is with a concave lens mounted with a mirror at an angle of 45° behind it. Another good method is to utilise the camera obscura, which may be made at a trifling cost out of a spectacle double-convex lens of about 1^ to 2-in. focus mounted in a brass tube, a mirror at an angle of 45 °, and a piece of ground glass on the top with a shade. In the accompanying Fig. 97. diagram showing the arrangement, A B c D is a rectangular box of card or wood, L a lens in the mirror, g the ground glass, s movable shade, which can be raised.or lowered at will. Another method is to use the focussing screen, which, when turned back over the top of the camera, should have lines drawn on it as shown in the diagram ; then, when the eye is placed at A, and looking along ab, the object, when opposite this, will be in the centre of the plate. Or a double-convex lens of exactly the same focus as the photographic lens may be mounted on the front of the camera, and the focussing cloth thrown over the whole so as to form a second or temporary camera. View Meter. An instrument used to gauge the amount of view included by the lens upon the focussing screen without the trouble of setting up the camera. The following, which has 43 1 Vie] DICTIONARY OF PHOTOGRAPHY. now been placed upon the market commercially, is a very good form : — abcd, a brass tube bearing at one end a cap in which is an opening (g h), bearing a proportionate size to the plate used : for instance, for quarter-plates, or 4^ by 3^, the opening may be Fig, 98. H in- by yf ; or for half-plate, f| by This opening frames the view, and limits its extent according to the distance the inner tube is drawn out. e f is a double concave lens of i^-in. focus, and m a double convex lens of 3-in. focus ; when the eye is applied to the convex lens the picture is viewed in miniature, p will show front view of cap. Fig. 99. To use this it must be adjusted to the lenses with which it will be worked. To do this it is only necessary to erect the camera, focus carefully, and, marking two prominent objects on the edges of the screen, adjust the small view-meter till the same objects are exactly on the edges of the field of view in that. Now mark on the inner sliding tube with a knife or file 43 2 DICTIONARY OF PHOTOGRAPHY. [Was the exact point to which it was pulled out or in, and this will always include the amount of view included by that lens. By fastening two fine wires across the cap p, as shown by the dotted lines, it will serve well also as a view-finder, as, when the moving object is at the point of intersection of the crossed wires, it will be in the centre of the plate. It may also be used as some guide to the probable exposure by placing inside the cap a circle of blue glass, so as to cut off all the rays but those chemically active and which affect the plate. Vignetting. This consists of shading off the margins of a picture, so as to cause the figure or subject to gradually fade away. There are numerous methods of effecting this : one is by the use of glass with oval or other shaped openings surrounded by a gradually deepening margin of coloured non-actinic glass. These, however, are not satisfactory. Another method is that employed by the French operators of using graduated thicknesses of tissue paper with serrated edges. Another method is to use wooden covers with openings having the underneath edges bevelled off. But the best of all is to use stout sheet lead or pure tinfoil, and to cut the sized opening required, and either to slightly turn up the edges or serrate them, so as to soften the outline ; and the farther the vignetting shape is placed from the negative the larger the vignette and the softer the outline. When the so-called Russian vignettes or images on a black ground are required, a very good method is to use a vignetter in front of the lens or between the lens and the plate. When used in front of the lens a card or metal plate with the particular shaped opening is supported in front of the lens, and gently moved backwards and forwards an inch or two during exposure. The distance in front of the lens being found by adjustment. When used in the camera the most convenient form is that of an American invention which is practically a large iris diaphragm placed about a third of the focus from the lens. Obviously cards or metal plates may be used in the same way. Washing Negatives and Prints. — Upon the perfection of the washing process practically depends the life of negatives and prints, as the presence of hyposulphite of soda, or silver, tends to fading of negatives and prints, and yellowness of the whites of the latter. There are numerous commercial washing tanks and 433 FF Was] DICTIONARY OF PHOTOGRAPHY. troughs, which answer their purpose admirably. Running water is the most effective means for the elimination of the undesirable faults, but when the water supply is limited, the prints or nega- tives should be allowed to soak in water for ten minutes, and then the water changed ; and this operation repeated six times will usually be sufficient for negatives and prints. Messrs. Grundy & Haddon have proved that ten minutes thorough wash- ing is quite sufficient to eliminate all the hyposulphites that can be eliminated, and it is a recognised fact that prolonged soaking of prints in water is one of the best means of obtaining faded and spoilt prints. Wastes. See Residues. Waxing Negatives. See Oiling. Weights and Measnres. The confusion which reigns in the photographic world with regard to weights and measures is something appalling. Numerous plans have been proposed to remedy this, but at present with little effect ; the confusion arises in great measure from the numerous systems of weights and measures used in different countries. All solid chemicals are sold by avoirdupois weight, whilst many formulae are written in what is called apothecaries' weight. It has been proposed to use the metric system, but at present there seems no likelihood of its coming into general use. The author has endeavoured through- out the Dictionary to give all formulae in standard weights about which there can be no dispute. As a standard for dry substances the grain has been employed, and for liquids the minim, or the ounce of 480 minims, except in some cases where the weights are practically immaterial, where a few grains more or less would make no appreciable difference. The author does not intend to enter into any arguments on the question, but simply gives those tables of weights in general use. Apothecaries' Weight. 20 grains 3 scruples . . . 8 drachms... 1 scruple (3). 1 drachm (5). 1 ounce (5). The above weights are used by chemists for the compounding of prescriptions, 434 DICTIONARY OF PHOTOGRAPHY [Wei i oz. (3j) == 8 drms. (5viij) = 24 scruples (3xxiv) = 480 grs. (The pound in this weight is never used; it contains 12 ozs. == 5,760 grs.) Avoirdupois Weight. 16 drachms ... 16 ounces ... ounce, pound. 1 lb. = 16 ozs. = 256 drms. = 7,000 grs. (This weight is used by all dealers for retailing chemicals, etc. 1 oz. = 437*5 grs.j. Liquid Measure. 60 minims 8 drachms 20 ounces 8 pints 1 drachm (f. 5). 1 ounce (f. 3). 1 pint (O). 1 gallon (C). 1 gal. (Cj) = 8 pts. (Oviij) = 160 ozs. (f. 5, 160) = 1,210 drms. (f. 5» 1,280) = 76,000 minims. The following is the Metric System of weights and measures in use in France and on the Continent generally, and in the United States, and in England amongst scientific chemists. The division in each case is by 10, so that it is extremely easy to calculate the division or multiplies of any weight. Lineal Measure. 1,000 millimetres 100 centimetres 10 decimetres 10 metres 100 „ 1,000 ,, 1 metre. I n I M I decametre. 1 hectometre. 1 kilometre. The metre is the unit, and is equal to 39*37 English inches Liquid Measure. 1,000 millilitres 100 centilitres 10 decilitres 10 litres 100 ,, 1,000 „ 1 litre. I „ I M I decalitre. 1 hectolitre 1 kilolitre, 345 Wei] DICTIONARY OF PHOTOGRAPHY. The litre is the unit, and is equal to 35*216 fluid ozs. Liquid measures are usually expressed, however, as cubic centimetres, or c.cm. ; ='i6*8 minims. Dry Measure. 1,000 milligrammes ... = 1 gramme. 100 centigrammes ... = 1 10 decigrammes ... = 1 10 grammes ... ... = , 1 decagramme. 100 „ ... ... = 1 hectogramme. 1,000 ,, =3 1 kilogramme. The gramme is the unit, and is equal to 15*432 grs. For converting these weights into English, the following tables will be found sufficiently accurate for all purposes : — Conversion of Grammes into Grains. 1 gramme = 13*432 grains. 2 grammes... ... ... == 30-864 ,, 3 h = 46*926 „ 4 = 61-628 „ 5 » = 77'i6o „ 6 „ = 92-592 ,, 7 == 108*024 ,, 8 „ == 123-466 „ 9 rt - = 138*898 „ Conversion of Grains into Grammes. 1 grain = -0648 gramme. 2 grains = -1296 ., 3 >. = '1944 4 = -2592 5 » == -3240 6 „ ... m -3888 „ 7 „ = -4536 8 , = -5184 „ 9 = -5832 Supposing it is desired to convert 506*94 grammes into grains, the table is used as follows : — » 43 6 DICTIONARY OF PHOTOGRAPHY. [Wei 500 grammes = 77160 grains. 6 , = 92592 •90 gramme = 1 3*889 •04 * = *6l7 „ 7823-098 „ The numbers taken from the tables simply require the altering of the position of the decimal point. The following may be useful for those short of weights to obtain an approximate weight : — Weight. 1 sovereign, new .. . ... ... 123-274 grains. 1 shilling ... ... ... ... 87.273 48 pennies ... ... ... ... 1 lb. avoirdupois. 1 halfpenny and 1 threepenny-piece \ ounce. 1 florin and 1 sixpence \ ounce. 3 pennies 1 ,, 4 half-crowns and 1 shilling ... 2 ounces. 4 florins, 1 half-crown, 2 pennies 4 ,, It has become somewhat general lately to give formulae in parts, and this is, though not strictly accurate,, a somewhat con- venient method of translating metric measures into English weight and measures. If in every case the grain is taken as the unit, no confusion can arise. Frequently we find a solution spoken of as " a 48-grain bath,'' " a 60-grain bath," etc. ; and this means that each ounce of the solution contains 48 or 60 grains of the salt. Ten par cent, solutions are, again, somewhat of a trouble to some, and the trouble arises from the fact that we are in the habit of measuring liquids, and that the avoirdupois ounce con- tains only 437'5 grains, whilst a fluid ounce contains 480 minims. To make a 10 per cent, solution of any salt we proceed as follows : — Let us take, for instance, an ounce of pyro., and it is required to make a 10 per cent, solution ; that is to say, we require a solution, every 10 minims of which shall represent 1 grain of pyro. ; then, having 437*5 grains of pyro., the total bulk of the solution will be 437 5 x 10 = 4375 minims = 9 oz. 437 Wet] DICTIONARY OF PHOTOGRAPHY. 55 minims. Any other strength solution may be made in the same way. Wet Collodion Process. This was the first process in which a vehicle for the sensitive silver salt was used. Either negatives or positives can be produced ; and the latter, when taken upon thin enamelled-iron plates, are known as ferrotypes or tintypes. The following is a short resume of the process : — A well-cleaned glass plate is coated with Collodion (q.v.), and as soon as the collodion has set, this coated plate is immersed in a bath made as follows : — Nitrate of silver ... ... ... 119 grs. or 7 grms. Potassium iodide 1 gr. , , *o6 grm. Distilled water ... ... ... 8 ozs. ,, 200 c.cm. Dissolve the silver salt in 2 oz. of water, and the potash in \ oz. Add the latter to the former, and add the remainder of the water. Filter, and test for acidity. If the blue litmus paper is not turned red after an immersion of some short period, a few drops of a dilute nitric acid (1 in 12) should be added till the bath is decidedly acid. The plate is exposed whilst still wet, the exposure being about ten times that for gelatine dry plates of ordinary rapidity under similar circumstances. For development any of the following may be used, but the author prefers Nos. 2, 3, and 4, the last being especially useful, as shorter exposure is required, and more detail is brought out. With No. 5 longer exposure is required, but extreme contrast is obtained : — No. 1. Ferrous sulphate 3°° g^. or 20 grms Glacial acetic acid ... 200 mins. „ 12 c.cm. Methylated spirit i oz. „ 12 „ Distilled water ... 10 ozs. M 250 „ No. 2. Ferrous sulphate 200 grs. or 12 grms. Cupric 100 „ if 6 „ Glacial acetic acid 200 mins. „ 12 c.cm. Methylated spirit ^ oz. » 12 „ Distilled water ... 10 ozs. M 250 ,, 438 DICTIONARY OF PHOTOGRAPHY. [Wet No. 3. Ferrous sulphate Cupric Distilled water .. 240 grs. 30 M 5 oz. or 15 grms. 2 „ 125 c.cm. Nitrate of baryta Glacial acetic acid Methylated spirit Distilled water ... 30 grs. or 2 grms. 2 drms. 6 c.cm. £oz. „ 12 5 „ 5 ozs. ,, 125 Dissolve A and B separately, then mix and filter. No. 4. Ferrous sulphate Glacial acetic acid Formic acid (sp. gr. 1 -060 ) Methylated spirit Distilled water Ferrous sulphate Glacial acetic acid Lump sugar Methylated spirit Distilled water ... No. 5. 300 grs. 200 mins. 100 „ 240 „ 10 ozs. 200 grs. 180 mins. 100 grs. 240 mins. 10 ozs. or 20 grms. „ 12 c.cm. n 6 „ M 1 * It M „ or 12 9 grms. 10 8 c.cm. ,, 6-5 grms. 147 c.cm. M 2957 M No. 6. Ammonio-sulphate of iron Glacial acetic acid Methylated spirit Distilled water ... . 250 grs. or 10 grms. . 250 mins. ,, 15 c.cm. . 240 „ 12 5 „ 10 ozs. ,, 250 ,, To develop the exposed plate is should be fixed upon a pneumatic holder and a little of the developer poured evenly on to the surface, and gently rocked bockwards and forwards till the image is sufficiently developed, when it may be poured off. The image nearly always requires intensification for negative work, and the following may be used : — Ferrous sulphate ... ... 5 grs. or Citric acid 10 „ „ Distilled water 1 oz. „ 25 439 0 3 grm. o-6 „ Wid] DICTIONARY OF PHOTOGRAPHY. Add immediately before using a few drops of Silver nitrate 10 grs. or o*6 grm. Distilled water i oz. „ 25 c.cm. Pour on to the unfixed negative, and rock backwards and for- wards till dense enough. Then fix in Potassium cyanide 120 grs. or 7-5 grms. Distilled water 10 ozs. „ 250 c.cm. Wash thoroughly, dry, and varnish. Wide-Angle Lens. See Lens. Woodburytype. This is a very beautiful photo-mechanical process, and consists of exposing a thick film of bichromated gelatine to light under a negative ; and when fully exposed it is washed to dissolve the unacted-upon soluble portions, and after being soaked in alum is dried. When dry, the gelatine print, which at this period looks like a delicate piece of silk with the ■ image in relief, is placed on to a bed of metal, and a pressure of from four hundred to five hundred tons brought to bear on it. This forces the gelatine into the metal, and makes an impression the same as a seal on hot sealing wax, the film of gelatine itself being unharmed and used over and over again. The metal sheet bearing an impression now becomes a mould, and this is placed in a press, and some special liquid gelatine ink is poured on to it, and a sheet of non-absorbent paper placed over. The press is now closed, and pressure being applied, it is obvious that the ink will leave the high-lights and. collect in the shadows. When the gelatine ink has set, the paper is removed, bearing the image, and is fixed in alum and dried. Siannotype. This is also an invention of Mr. Woodbury, and in this process an image in intaglio is produced by exposure of a bichromated gelatine film under a positive, and this is coated with tinfoil, and used for printing from in almost the same manner as in Woodburytype. Yellow Fog. See Fog. Yellowness of Prints. See Toning. Yellow Stain. See Clearing Bath. Zinc (Ger., Zink ; Ft., Zinc; Ital., Zincd). Zn = 65 exists as 440 DICTIONARY OF PHOTOGRAPHY. [Zin calamine or carbonate, as sulphide in zincblende, as oxide, and occasionally in a pure state. It is used in photography in several photomechanical processes, and its salts, the bromide, iodide, and chloride, which are formed in somewhat similar manner to the cadmium salts, are not much used. Zinc hypochlorite has lately been recommended for making hypo eliminator. The formulae for the salts of zinc are — Bromide, ZnBr, = 225 ; Iodide, ZnL = 319 ; Chloride, ZnCl 2 =136 ; Hypochlorite, ZnCL ZnCl 2 0 2 = 304. Zincography. A photo-mechanical printing process, in which the image is impressed upon a zinc plate by means of a greasy ink, and an etching fluid being applied which eats away the groundwork, leaving the image in relief, so that it can be printed from like ordinary type. 441 APPENDIX. I. PLATE-MAKERS' FORMULA. In this section is included the formulce and working directions for all, or nearly all, of the commercial varieties of plates and papers. Blair's Film. Mix each solution in the order given. Use equal parts of each. Keep the developer cool by using ice. Amidol Developer Formula. Water ... ... ... ... ... 24 ozs. Sulphite Soda (Crys.) 2 „ Amidol 120 grs. Hydrochinone ... ... ... ... 60 Eikonogen ... ... ... ... ... ... 60 „ Bromide of potassium ... ... ... ... 12 „ Mix in order named ; use 3 parts of this solution to 2 parts water. As soon as developed, rinse in clear water to remove the developer and transfer to the fixing bath. Water I qt. Hypo fib. After fixing, wash one hour in running water or by changing the water in tray, and then soak for half an hour in a soaking solution composed of — Alcohol 4 ozs. Water 16 „ Glycerine ... ... ... ... ... ... \. „ Do not rinse the film after removing from the soaking solution. The object of the soaking solution is to prevent the film from curling when dry. To Dry. Pin the film by the corners to a board and, when thoroughly dry, wipe off the back with a soft cloth. It is of the utmost importance to keep the finished film flat, do not roll it up as it causes trouble in printing. Any ordinary pyro-soda de- veloper may also be used with good results for these films. 442 I. PLATE-MAKERS* FORMULAS. "Cadett" Plates. — "Ordinary" " Lightning" and "Snap- Shotr Stock Solution. Pyrogallic acid ... ... ... I oz. av. Ammonium bromide ... ... ... ... ... } „ Potass metabisulphite ... I „ Distilled water to make altogether 7 ozs. 3 drs. fl. Dissolve the metabisulphite and bromide in part of the distilled water before adding the pyrogallic acid. A. Stock solution ... ... 1 oz. Distilled water to make altogether ... ... 20 ozs. = 1 pt. B. Ammonia ('890) ... ... ... ... ... 2I drs. Distilled water to make altogether ... ... 20 ozs. = 1 pt. Mix equal parts of A and B to make developer. Fixing Solution. Hypo 1 lb. Water I qt. We also give another formula for pyro-ammonia development without the metabisulphite of potass. Stock Solution. Pyrogallic acid ... ... ... ... ... I oz. av. Ammonium bromide ... ... ... ... ... 1 „ „ Sulphurous or sulphuric acid or citric acid ... 1 drm. Distilled water to make altogether ... ... 7 ozs. 3 drs. fl. Mix the acid with part of the distilled water before adding the bromide and pyrogallic acid. A. Stock solution ... ... ... ... ... ... I oz. Distilled water to make altogether ... ... 20 ozs. = I pt. B. Liquid ammonia ('890) ... ... ... ... 2 A drs. Distilled water to make altogether ... ... 20 ozs. = 1 pt. Mix equal parts of A and B to make developer. 443 APPENDIX. Fixing Solution. Hypo i lb. Water ... ... ... ... ... ... ... I qt. Clearing Solution. Hydrochloric acid ... ... ... ... ... ^ oz. Saturated solution of alum ... ... ... ... 20 ozs. Pyro-Soda Developer. Stock Solution. Pyrogallic acid ... ... ... ... ... 1 oz. av. Potassium metabisulphite ... ... ... ... 40 grs. or Sulphuric acid ... ... ... ... ... 1 dr. fl. Distilled water to make altogether 10 ozs. fl. A. Stock solution ... ... ... ... ... ... 3 ozs. fl. Distilled water to make altogether ... ... ... 20 „ fl. B. Sodium carbonate (crystals) 1 1 ozs. av. or „ „ (anhydrous) ... ... ... 4 „ „ Sodium sulphite (recryst.) ... ... ... ... 15 „ Distilled water to make altogether ... ... ... 80 „ „ Equal parts of each to make developer. A few drops of a 10 per cent, solution of potassium bromide may be added to the developer when necessary. In very hot weather the hypo bath should not be stronger than 1 lb. of sodium hyposulphite to 2 quarts of water. Photo- Mechanical Plate. Development. A. Pyrogallic acid 60 grs. Potassium metabisulphite ... ... ... ... 60 „ Ammonium bromide ... ... ... ... ... 60 ,, Distilled water to make ... ... 20 ozs. B. Ammonia ('890) 2.\ drs. Distilled water to make ... ... ... ... 20 ozs. Equal parts of each A and B to make developer. 444 I. PLATE-MAKERS' FORMULA. Lantern- Plates. — Developers. Pyro-Ammonia. A. Pyrogallic acid ... ... ... 40 grs. Ammonium bromide ... ... ... ... ... 40 „ Potass, metabisulphite ... ... ... ... 120 ,, Distilled water to make altogether ... ... ... 20 ozs. fl. B. Liquid ammonia ... ... ... ... ... 150 mins. Distilled water to make altogether ... ... ... 20 ozs. fl. Equal parts of A and B to make developer. This formula gives rich warm tones with suitable exposure. For warm black tones the following may be used : — A. Pyrogallic acid ... ... ... ... ... 30 grs. Sodium sulphite ... ... ... ... ... 100 Sulphurous acid (or citric acid 5 grs.) ... ... 5 mins. Ammonium bromide ... ... ... 30 grs. Distilled water to make altogether ... .. ... 20 ozs. B. Liquid ammonia ("890) ... ... 40 mins. Distilled water to make altogether ... ... ... 20 ozs. fl. Equal parts of A and B to make developer. A rich warm black can be obtained with hydroquinone, and we strongly recommend the following formula : — A. Hydroquinone... ... ... ... ... ... 70 grs. Potass metabisulphite ... ... 10 „ or Sulphurous acid ... ... ... ... ... 15 mins. Potassium bromide ... ... ... ... ... 35 grs. Distilled water to make altogether ... 20 ozs. fl. B. Potassium hydrate (sticks) 140 grs. Sodium sulphite 700 „ Distilled water to make altogether ... ... ... 20 ozs. 445 APPENDIX. Equal parts A. and B. to make developer. Cold but brilliant black tones are obtained with ferrous oxalate, adding a sufficient quantity of a 10 per cent, solution of potassium bromide to prevent too rapid development. A. Ferrous sulphate Sulphuric acid ... Distilled water to make altogether .. B. Neutral potass, oxalate ... 10 ozs. av. Distilled water to make altogether 40 ,, fl. Dissolve the potass, oxalate in about £ of the distilled water, made warm, and make up to bulk after the salt is dissolved. The ferrous sulphate should be powdered just before solution in about I of the distilled water, to which the sulphuric acid has been previously added. Make up to bulk after solution. To make developer, add 1 part of A to 4 of B. For over exposure, add a few drops to the mixed developer of a 10 per cent, solution of potassium bromide. Fixing Solution. Hypo 1 lb. Water I qt. Tone or colour considerably depends on exposure, short ex- posures favouring colder tones ; also, the more the developer is restrained with soluble bromides, the warmer the tones will be, and vice versa. Edwards, Austin, " Queen " Negative Films. Instructions. The only variation in working which need be made when using "Queen" Films instead of plates are simple mechanical ones, which readily suggest themselves in handling a flexible film in lieu of a rigid glass plate. The chemical treatment is exactly the same as for plates, any developer which is suitable for the one is equally adapted for the other ; the length of time required for development, and the appearance of the image during and after development, being the same in both. 446 5 ozs. av. 10 mins. 20 ozs. av. I. plate-makers' formulae. To expose " Queen " Films in an ordinary dark slide. Put the film in as you would a glass plate, and then place a piece of black cardboard (12-sheet thickness), of the same size as the film, at the back ; or a film carrier may be used. The slide being filled, draw the shutter, and carefully dust the face of the film with a camel-hair brush or soft piece of wash-leather kept for this purpose. Care should also be taken to have the slides and camera free from dust. Spots on negatives often result from inattention to these precautions. Development. Any good developer may be used, but the following Pyro and Soda formula is specially recommended. It undoubtedly gives the finest possible results with the "Queen Films of either speed . The " Queen " Pyro and Soda Developer. No. 1. Pyrogallic acid ... ... .. I oz. or 30 grms. Nitric acid ... ... ... ... 20 drops ,, I c.cm. Water ... ... ... ... 80 ozs. „ 2 lits. 300 c.cm. Note. — No. 1 may be mixed as a stock solution, if preferred, by using only 8 ozs. of water instead of 80 ozs., and diluting to above proportions as required. No. 2. Sulphite of soda ... ... ... 10 ozs. or 300 grms. Carbonate of soda (crystals) ... 9 „ „ 250 Water 80 „ „ 2 lits. 300 c.cm. No. 3. Bromide of potassium ... ... 4 drms. or 16 grms. Water ... ... 4 ozs. 114 c.cm. For use, mix equal parts of No. 1 and No. 2. Tor landscape work use the same, with two minims or drops of No. 3 added to each ounce of the mixed developer. In case of under-exposure, or for subjects possessing great contrasts of light and shade, dilute the developer and use no No. 3. For over-exposure 447 APPENDIX. restrain by adding more No. 3, or use less No. 2. After develop- ment, rinse and immerse in the following Fixing Bath. Hyposulphite of soda ... ... I lb. or 500 grms. Water 40 ozs. „ 1,250 c.cm. This is most conveniently used in a deep porcelain dish. The precaution should be taken when films are put into the fixing bath of pressing them well under, so that they are perfectly covered by the solution, otherwise stains may be caused.* The negatives should remain in the fixing bath for a few minutes after they are apparently fixed, to ensure perfect fixation.* Washing. The negatives should then be well rinsed and placed in a grooved washing tank, in which they are to be washed for not less than two hours, the water running frequently through the tank, or being frequently changed. Drying. When sufficiently washed, hang the film negative up to dry. Spring clips are most convenient for this purpose, the films being suspended by one corner. Edwards, B. J. & Co.'s Isochromatic and Ordinary Plates and Films. The Dark Room. When using Isochromatic films or plates great care must be taken to work with a deep ruby light only. Three thicknesses of good ruby glass or two of ruby fabric give a fairly safe working window for ordinary daylight. For lamplight the protection required is of course dependent on the strength of the light employed : two thicknesses of ruby glass or one of ruby fabric will generally be found sufficient, but it must not be supposed that the light in either case is sufficiently non-actinic to have no action. Care should be taken not to expose the film or plate more than is necessary even to this light, especially before and during the first part of the development. It is a good plan to cover over the developing dish or otherwise shield it from the light. Development with Pyrogallic. Any of the following developers are suitable for these plates or films : — * Special attention is called to these points because it has been found that nearly all troubles in working films are due to disregard of one or other of them. 448 I. PLATE-MAKERS' FORMULAE. Pyro and Ammonia Developer. No. i. Pyrogallic acid Citric acid ... Water I oz. or 30 grms. 40 grs. or 3 „ *}\ ozs. or 214 c.cm. No. 2. Strong ammonia ( - 88o) Bromide of potassium I oz. or 28 c.cm. 120 grs. or 8 grms. Distilled water 7 ozs. or 200 c.cm. The above will keep good for months if well corked. For use dilute 1 part No. 1 with 19 parts of water, and in another bottle 1 part No. 2 with 19 parts of water. The dilute solutions should be made fresh every day. To develope a correctly exposed plate or film, mix equal parts of these two solutions. In hot weather, when making up the dilute solutions for use, add 4 parts of No. 1 to 3 parts of No. 2, instead of equal parts of Nos. 1 and 2. In no case should the quantity of No. 2 exceed that of No. 1. Pyro and Soda Developer with Metabisulphite. No. 1. Pyrogallic acid ... ... ... 1 oz. or 30 grms. Metabisulphite of soda (Boake's) 1 ,, or 30 ,, Water 80 ozs. or 2 litres 300 c.cm. Dissolve the metabisulphite, and then add the pyro. No. 2. Carbonate of soda (washing soda) 12 ozs. or 360 grms. Water ... ... 80 or 2 litres 300 c.cm. To develop mix equal parts of Nos. 1 and 2. When working in the summer time in a good light, with full exposure, add 5 minims of No. 3 to each ounce of developer (or, to save the trouble of measuring small quantities, \\ ozs. of No. 3 may be No. 3. Bromide of potassium Water I oz. or 30 grms. 9 ozs. or 250 c.cm. 449 APPENDIX. added to the 80 ozs. of No. 2) ; in winter the bromide may generally be omitted, and also for rapid shutter exposures, and portrait work in the studio. This developer gives exceedingly fine and delicate negatives, with full detail in the high lights, and of good colour for printing. Pyro and Soda Developer. No. 1. Pyrogallic acid ... ... ... 1 oz. or 30 grms. Nitric acid ... ... ... ... 20 drops or I c.cm. Water ... ... ... ... 80 ozs. or 2 litres 300 c.cm. No. 2. Sulphite of soda 10 ozs. or 300 grms. Carbonate of soda (crystals) — wash- ing soda 8 ,, or 226 „ Water 80 „ or 2 litres 300 c.cm." No. 3. Bromide of potassium ... ... 1 oz. or 30 grms. Water ... ... ... ... 9 ozs. or 250 c.cm. To develope mix equal parts of Nos. 1 and 2, and add 10 minims of No. 3 to each ounce of the mixed developer, or, instead, 3 ozs. of No. 3 may be added to the 80 ozs. of No. 2. For rapid shutter exposures omit the bromide. This developer gives bold vigorous negatives of a neutral grey colour. In either of the foregoing developers, the No. 1 solution may be mixed as a stock solution, if preferred, by using only 8 ozs. of water instead of 80, and diluting to above proportions, as required. General Notes. Dust the face of the plate just before placing it in the dish for development, and, putting it face upwards, pour the mixed developer steadily over the dry plate, removing any air bubbles by passing a flat camel-hair brush (kept specially for this purpose) over it immediately ; rock the dish gently, taking care to keep the film or plate well covered with the solution. When using pyro developer, where a plate is found to be under- exposed, the normal developer should be at once diluted by the addition of water ; in some cases as much as three or four times 45° - I. Plate-makers' formula. its bulk of water may be added with advantage, the development proceeding proportionately slowly. By this means detail is brought out in the shadows without permitting the high lights to gain too much density. Under-exposure should always be avoided, as with these plates or films a considerable amount of over-exposure can be controlled in development, but if the light has not acted sufficiently on the plate no process of development can possibly make a good negative of it. For interiors and other subjects possessing great contrasts of light and shade, a weak developer should always be used. The best and most efficient method of correcting over-exposure is that introduced by Mr. Edwards in 1888. This consists in using a separate strong but well-restrained developer as a redeveloper, which is substituted for the normal developer, as soon as over-exposure is recognised. When developing this redeveloper is kept ready mixed in a measure, and if the detail of the negative rushes up too quickly, indicating over-exposure, the normal developer is poured off and the redeveloper instantly substituted for it without waiting to wash the plate, by this means very considerable over-exposure can be satisfactorily remedied, the redeveloper giving density without bringing out much more detail. This method of tentative development will be found exceedingly useful when developing a number of various or unknown exposures. The following is the formula for pyro. and ammonia redeveloper ; separate formulae are given for redevelopers to be used with pyro and soda, and hydrokinone or eikonogen : — Pyro and Ammonia Redeveloper. No. 1. Pyro Citric acid ... Distilled water 1 oz. or 30 grms. 2 drs. or 8 ,, 32 ozs. or 1000 c.cm. No. 2. Ammonia ("88o) ... Bromide of ammonia Distilled water 2 ozs. or 60 c.cm. 24 drs. or 96 grms. 32 ozs. or 1000 cc.m. For use mix equal parts of Nos. 1 and 2 451 APPENDIX. Pyro and Soda Redeveloper. No. i. Pyro Metabisulphite of soda (Boake's) Distilled water No. 2. Carbonate of soda (crystals) ... 9 ozs. or 250 grms. Bromide of potassium ... ... 2 „ or 60 „ Distilled water 28 „ or 800 c.cm. For use mix equal parts of Nos. 1 and 2. Development with Hydrokinone and Eikonogen. Hydrokinone Developer. No. 1. Hydrokinone Sulphite of soda ... Bromide of potassium Distilled boiling water to make ... No. 2. Carbonate of potash \ oz. or 15 grms. Distilled water to make 12 ozs. or 340 c.cm. First dissolve the hydrokinone, and then add the sulphite and bromide. For use mix equal parts of Nos. 1 and 2. In cases of slight over-exposure add a few drops or minims of a 10 per cent, solution of bromide of potassium to each ounce of developer more or less according to extent of over-exposure. For con- siderable over-exposure use the redeveloper. For under-exposure pour off the hydrokinone developer and finish development with the eikonogen developer given below. Eikonogen Developer. Eikonogen \ oz. or 14 grms. Carbonate of potash ... ... 1 or 30 „ Sulphite of soda ... ... ... 2 ozs. or 60 grms. Distilled boiling water 20 „ or 600 c.cm. FiTSt dissolve the eikonogen, then the sulphite, and lastly the 45 2 I oz. or 30 grms. 1 „ or 30 „ 28 ozs. or 800 c.cm. \ oz. or 7 grms. 1 „ or 30 „ 7 grs. or £ grm. 12 ozs. or 340 c.cm. I. plate-makers' formula. carbonate of potash. This will be found a very useful developer for snapshot work and portraiture ; for ordinary landscape work a mixture of this and the above-given hydrokinone developer is to be preferred to eikonogen alone. One part of the eikonogen to two parts of the mixed hydrokinone developer will be found to work well, but the proportions may be varied to produce a developer possessing the required characteristics, eikonogen tending to softness and fulness of detail, and hydrokinone to bright shadows and full density. Instead of mixing the developers, the development may be commenced with eikonogen, and when the detail is sufficiently out, hydrokinone substituted for it, without waiting to wash the negative, and the development finished with this, or in case of much over-exposure with the following hydro- kinone redeveloper : — Redeveloper For Hydrokinone or Eikonogen. No. i. Hydrokinone Sulphite of soda Bromide of potassium Distilled boiling water to make ... No. 2. Carbonate of soda (crystals) ... 2 ozs. or 60 grms. Sulphite of soda 2 ,, or 60 ,, Distilled water to make 12 „ or 340 c.cm. For use mix equal parts of Nos. 1 and 2. Fixing. After development well wash the negative under the tap, and immerse in the following : — Fixing Bath. Hyposulphite of soda 6 ozs. or 180 grms. Water I pt. or 600 c.cm. This is most conveniently used in a deep porcelain dish. The precaution should be taken when films are put into the fixing bath, of keeping them well under so that they are perfectly covered by the solution, otherwise stains may be caused. The 453 £ oz. or 7 grms. 2 ozs. or 60 i oz. or 7 „ 12 ozs. or 340 c.cm. APPENDIX. negatives should remain in the fixing bath for 2 or 3 minutes after they are apparently fixed, so as to ensure perfect fixation. If an acid fixing bath is preferred, add 1 oz. of metabisulphite of soda (Boake's) to the 6 ozs. of hyposulphite of soda, the addition of the metabisulphite tends to keep the fixing bath clear, and prevents discoloration of the negative. Clearing. When fixed the negatives should be well rinsed under the tap, and if they have been developed with pyro, put into a dish containing the following clearing solution for about a minute. If developed with a developer other than pyro, the clearing bath is not necessary, and the negatives may be removed direct from the hypo to the washing tank. Clearing Solution. Alum 1 oz. or 30 grms. Citric acid I „ „ 30 or Sulphuric acid \ ,, „ 7 „ Sulphate of iron ... ... ... 3 ozs. „ 90 „ Water 20 „ fl 600 c.cm. Washing. After treating with the clearing solution, the negatives should be again well rinsed, and placed in a grooved washing tank, in which they are to be washed for not less than 2 hours, the water running continuously through the tank or being frequently changed. In placing film negatives in the grooves it is best to put two films back to back in one groove, as they stand up better in this way. When finished washing, hang the film negatives up to dry ; spring clips are most convenient for this purpose, the films being suspended by one corner. Varnishing. The negatives may be printed from as soon as perfectly dry, but if this be done without previously protecting them with a coat of varnish, there is always a danger of the silver from the sensitised paper staining the negatives. Special Transparency Plates for Lantern Slides. — Instructions for Use. They are equally suitable for contact printing 454 I. plate-makers' formulae. or reductions in the camera. For contact printing by gas- light, using the light of a good fish-tail burner at a distance of 12 inches from the flame, any time from 10 to 60 seconds exposure may be required, according to the density of the negative, more exposure being necessary when it is intended to develope with pyro for brown tones, than for black tones with hydrokinone or amidol. Very thin negatives should be exposed at a greater distance from the light and very dense ones nearer to it. Exposure may also be made by diffused daylight in the dull light of an ordinary room ; it is, however, far more difficult to judge the correct time of exposure, therefore it is preferable to use artificial light. It is important that as nearly as possible correct exposure be given ; under-exposed plates when developed appear hard with black shadows, and want of detail in the half tones, while very much over-exposed pictures are usually thin and flat, without sufficient contrast. The colour obtained is also dependent on the length of exposure. The best indications of the correct timing, or otherwise, of the exposure are the time taken before the image begins to appear, and the time necessary to attain the required density. For lantern slides, at least some portion of the highest lights in the picture should be represented by absolutely clear glass, without a trace of fog or deposit of any kind, which would detract from the brilliancy of the image. These plates cannot be satisfactorily developed with any of the usual formulae for negative work, but either of the following formulae will give results perfect in every way. To develop, place the exposed plate in the developing tray, and pour over the developer without previously wetting the film : all danger of air bubbles may be avoided by passing a brush over the surface of the plate immediately after pouring on the developer. Pyro and Ammonia Developer for Warm Tones No. 1. Pyrogallic acid ... I oz. or 30 grins. Sulphite of soda 4 ozs. ,, 120 ,, Citric acid ... | oz. „ 8 „ Water 16 ozs. 460 c.cm. First dissolve the sulphite and citric acid, and then add the pyrogallic. 455 APPENDIX. No. 2. Bromide of ammonium I oz. or 30 grins. Liq. ammonia (880) ... ... 5^ drs. „ 20 c.cm. Water to make ... ,.. ... 16 ozs. ,,460 „ For use mix one part of No. 1 and three parts of No. 2, and dilute with water to double the quantity. The mixed developer may be used over again for several plates. For lantern slides and transparencies from very thin negatives dilute the stock solution with less water. For contact printing under the conditions given above, the exposure for negatives of medium printing densities will be from 20 to 60 seconds. If the correct time has been given the image should begin to appear in from 40 to 50 seconds, and the development be complete in about five minutes. Hydrokinone Developer for Black Tones. Hydrokinone ... ... ... 60 grs. or 3 grms. Sulphite of soda ... 2 ozs. 45 ,, Carbonate of soda (crystals) .... 4 „ ,, 90 ,, Carbonate of potash ... ... 2 ,, „ 45 „ Bromide of potassium ... ... 40 grs. „ 2 „ Hot distilled water ... ... 20 ozs. „ 450 c.cm. For black and white line subjects add 1 drachm of a 60-grain solution of bromide of potassium to each ounce of developer. Dissolve the hydrokinone in the water, and add the other ingredients in the order named. This developer will keep good for at least a month ; it can be used over again for several plates. Exposure for contact printing as above, 10 to 30 seconds. The image should begin to appear in about 40 seconds to a minute, and the development be completed in about 4 minutes. Amidol Developer for Black Tones. Amidol ... ... ... ... 80 grs. or 5 grms. Soda sulphite ... 2 ozs. „ 45 „ Bromide of potassium ... ... £ oz. „ 15 „ Water 12 ozs. „ 360 c.cm. This developer is to be used without dilution, except when working from a very strong negative, when it can be diluted with an equal amount of water. It may be used repeatedly without apparent loss of developing power. With correct 456 I. PLATE-MAKERS' FORMULAE. exposure it yields slides of a very fine black colour. Exposure for contact printing the same as for hydrokinone. Time of development about 8 minutes. These plates may be developed in either yellow or ruby light, the plate should be examined by looking through it from time to time, taking care not to expose it too much to the light. With pyro developer the transparency appears of nearly the same density before fixing as when finished, but when using hydrokinone or amidol the image must be developed to look much denser, as there is considerable reduction in the fixing bath. As soon as the transparency is sufficiently dense in the shadows, place it direct in the fixing bath, without previous washing. Fixing Bath. Hyposulphite of soda ... ... 4 ozs. or 120 grms. Water 20 ,, „ 600 c.cm. Leave in this for at least 5 minntes, and then wash thoroughly for an hour or more. To secure greater brilliancy and dissolve away any deposit caused by impurities in the washing waters, the transparency should be immersed for 2 or 3 minutes in some of the following clearing solution contained in a dish, using fresh for each plate. The transparency is afterwards to be well washed for ten minutes : — Alum ... ... ... ... 1 oz. or 30 grms. Citric acid 1 ,, „ 30 „ Water 20 ozs. „ 600 c.cm. If, from an error in the exposure or want of quality in the original negative, the lantern slide or transparency is still wanting in sparkle, through the high lights being veiled, it may be effectually cleared either at this stage or after being dried, by using Mr. Howard Farmer's reducer, made as follows : — No. 1. Ferridcyanide of potassium ... 60 grs. or 4 grms. Water 20 ozs. „ 600 c.cm. No. 2. Hyposulphite of soda I oz. or 30 grms. Water 20 ozs. „ 600 c.cm. For use Mix No. 1 and No. 2 in equal proportions. Place the transparency in a dish and flood it with the solution ; the dish 457 APPENDIX. must be continually rocked and the transparency carefully watched, and removed instantly the highest lights are cleared, which will not usually take more than I or 2 minutes : it is then to be again well washed before being dried. This reducer is in practice very useful, but requires using with great care, as it is capable of dissolving away the whole of the image, should the transparency be left in too long. When thoroughly washed, the lantern slides or transparencies should be allowed to dry spontaneously, and are then ready for binding or mounting in the usual way. If desired, they may be previously varnished, using either our crystal varnish or protective varnish for films. Gelatino-Chloride Plates. — Instructions for bse. Exposure. These plates are chiefly intended for contact printing under a negative in an ordinary pressure frame ; when used in this way they are extremely sensitive to daylight, the time of exposure varying from 1 second to 15 or 20 seconds, accord- ing to the power of the light and the density of the negative. Full exposure in a dull light usually gives the best results. With thin or weak negatives it is better to cover the printing frame during exposure with a sheet of opal glass or white tissue paper, giving sufficient exposure to compensate for the loss of light. A convenient method of printing by artificial light consists in burning an inch or two of magnesium ribbon at a distance of 12 inches from the printing frame. These plates can also be used for making enlarged or reduced positives from negatives in the camera, but for this purpose a much longer exposure, probably 5 to 10 minutes, in a good light will be found * necessary to ensure success. Development. Make two stock solutions as follows : — No. 1. Neutral oxalate of potash 2 ozs. Chloride of ammonium ... ... ... ... 40 grs. Distilled water ... ... ... 20 ozs. No. 2. Sulphate of iron ... ... ... ... ... 4 drms. Citric acid 2 „ Alum 2 „ Distilled water ... ... ... ... ... 20 ozs. 458 I. PLATE-MAKERS FORMULA. The above solutions will keep indefinitely. When required for use mix equal portions of the above solutions, adding No. 2 to to No. i to form the developer, place the exposed plate film uppermost in a porcelain dish, and pour over rapidly and evenly the mixed developer, rock the dish during the progress of development (which may be examined from time to time by yellow or non-actinic light), when sufficient density is obtained, which will usually be in about 2 minutes, pour off the developer into a measure, and flood the plate with water and wash well under the tap. The above developer with moderate exposure will give positives of a warm black colour, still warmer tone may be easily obtained by simply diluting the mixed solutions with an equal quantity of distilled water, or by adding to each ounce 2 or 3 drops of a 20-grain solution of bromide of potassium, and proportionally increasing the time of exposure. Short exposure and rapid development will give black tones, while full exposure and slow development will give warm brown or red tones to the transparency. It will be found a good plan to make up two separate portions of developer, strong and weak, and commence with latter ; should the plate prove to be under-exposed the developer must be poured off, and the more concentrated solution used to bring out the picture and complete development. This method will allow considerable latitude in the time of exposure. Several plates may be developed in the same solution, but the developer gradually loses its energy and will not keep long after being mixed. Fixing. Hyposulphite of soda ... ... 2 oz-. Water 16 „ Pour sufficient of the above, when dissolved, into a porcelain dish and immerse the developed and washed plate for 2 or 3 minutes, or until fixed, then rinse thoroughly under the tap and apply the following : — Sulphuric acid I oz. Saturated solution of alum ... ... ... ... 20 ozs. Pour a small quantity of the above repeatedly over the plate for about half a minute, or until the slight deposit of oxalate of lime (caused by the washing water) is dissolved away, and the 459 APPENDIX. picture becomes bright and clear. The high lights of the transparency should be perfectly bare glass without a trace of deposit of any kind ; as soon as cleared wash well in repeated changes of water, and allowed to dry spontaneously. Caution. Great care must be taken that not the faintest trace of hyposulphite of soda comes into contact with the developing solution or with the plate before or during development. Separate dishes must be used for each solution. The dishes, as well as the hands of the operator, should be frequently washed and kept scrupulously clean during the various mani- pulations, otherwise the films are liable to become stained and discoloured. When quite dry the transparencies may be varnished with good clear negative varnish applied with heat in the usual way. Bromide Opals. — Instructions for Use. Exposure. Place the opal plate film-side next to the negative in an ordinary printing frame, and expose to the light of a paraffin lamp, or by preference, that of an ordinary fish-tail gasburner, at a distance of 2 feet from the flame, for from 12 to 24 seconds, according to the density of the negative. Development. The following formula will be found to give very satisfactory results. Stock Solutions. No. 1. Oxalate of potash 60 grms. or 2 ozs. Chloride of ammonium ... ... 3 »» »» 4^ &rs. Bromide of potassium ... ... \\ ,, „ 20 „ Distilled water 500 c.cm. „ 16 ozs. No. 2. Sulphate of iron 15 grms. or 4 drms. Citric acid ... 8 „ „ 2 „ Alum 8 „ ,, 2 „ Distilled water 500 c.cm. „ 16 ozs. Having mixed equal parts of the above solutions (adding always No. 2 to No. 1), place the exposed opal film uppermost in a developing dish and pour the mixture evenly over the plate, rock the dish during the development, and watch its progress 460 I. PLATE-MAKERS' FORMULAE. by a ruby or deep yellow light. When the image appears to have acquired the detail and vigour desired in the finished picture, wash the plate well under a tap for 2 minutes and then immerse for 10 minutes in the Fixing Solution. Hyposulphite of soda 120 grms. or 4 ozs Water 500 c.cm. „ 16 „ The plate must now be well washed in running water for 1 hour to remove the hyposulphite of soda, when it will be ready for toning in the sulpho-gold toning bath to a rich velvety black. Stock Solutions for Toning. No. 1. Chloride of gold ... 1 grm. or 15 grs. Distilled water ... 220 c.cm. „ 8 ozs. No. 2. Acetate of soda ... 30 grms. or I oz. Sulphocyanide of ammonium ... 4 „ „ I drm. Distilled water to make ... ... 250 c.cm. 8 ozs. When the desired shade has been obtained, the picture should be well rinsed under the tap, and it may now be cleared of the slight deposit of oxalate of lime (caused by the washing water) by pouring over or immersing it for half a minute in the following Clearing Solution. Sulphuric acid 15 grms. or \ oz. Saturated solution of alum ... 600 c.cm. 20 ozs. After which it should be thoroughly washed to complete the process. When quite dry the opal can be finished in mono- chrome or water colours as may be desired, or may be varnished with crystal varnish. Caution. It is of the greatest importance that not the slightest trace of hyposulphate of soda be allowed to contaminate the dishes or measures employed in developing or toning the opals. Therefore great care should be exercised and the hands well washed between the various operations. 46 1 APPENDIX. Elliott & Son's " Barnet," " Studio," and " Rocket " Plates. Pyro and Ammonia (io per cent. Solution). No. i Solution. Ammonia (-88o) I oz. Water 9 ozs. No. 2 Solution. Bromide of ammonium ... ... ... ... ... I oz. Water to make 10 ozs. No. 3 Solution. Pyro 1 oz. Water to make ... ... ... ... ... ... to ozs. Citric acid (pure) ... ... ... ... ... 30 grs. - For studio use : Take 80 minims No. 1 ; 40 minims No. 2 ; 20 minims No. 3 ; and make up to 2 ozs. with water. For outdoor work : Take 80 minims No. 1 ; 60 minims No. 2 ; 40 minims No. 3 ; and make up to 2 ozs. with water. For specially quick exposures with "Rocket" plates: 120 minims No. 1 ; 20 minims No. 2 ; 20 minims No. 3 ; and make up to 2 ozs. with water. Pyro and Soda Developer. No. 1 Solution. Pyro I oz. . Water 86 ozs. Nitric acid (pure) 20 drops. No. 2 Solution. Pure sulphite soda ... ... ... 10 ozs. Pure carbonate soda (crystals) ... ... ... 9 „ Water ... ... ... 86 „ Use equal parts of No. 1 and No. 2, and dilute with equal bulk of water. To each ounce add 1 or 2 drops of a 10 per cent, solution of bromide of potassium. 462 I. plate-makers' formul/e. Eikonogen Developer. No. i Solution. Eikonogen Sulphite of soda Hot water ... No. 2 Solution. Common washing soda Water Use equal parts of No. i and No. 2. Hydroquinone Developer No. i Solution. Hydroquinone Sulphite soda Citric acid Bromide potassium Distilled water ... No. 2 Solution. Caustic soda Distilled water ... Use equal parts of No. I and No. 2. 4 ozs. 6o ., 12 OZS. 8o ,. [6o grs. 2 ozs. 6o grs. 20 ozs. [60 grs. 20 ozs. Clearing Solution. Chrome alum ... ... ... ... ... ... 2 ozs. Citric acid ... ... ... 1 oz. Water ... ... ... 20 ozs. " Bamef Lantern Transparency Plates. For cold or warm tones (according to exposure and development). Instructio7is for Use. — Contact Printing. For black tones the exposure required is about ten seconds at the distance of a foot from an ordinary gas flame ; the developer to be used is either No. 1 or No. 2. To secure warm tones it is necessary to increase the exposure to two or three minutes and use either No. 3 or No. 4. To obtain still warmer (reddish) tones increase the ex- posure still further to five or six minutes, and develop with No. 5. Reducti07is in the Camera. — For black tones with stop //16 in bright diffused light from a £-plate negative an exposure of about ten seconds is required, using No. 1 or No. 2 for developing. 463 APPENDIX. For warm tones increase the exposure to two or three minutes, and using for developer either No. 3 or No. 4. For still warmer tones further increase the exposure to five or six minutes, and develop with No. 5. Formula for Developers. Note. — In cold weather all solutions should be raised to a temperature of 6o°. No. 1. Cold Black Tones. A. Metol ... ... 400 grs. Soda sulphite ... ... ... ... 8 ozs. Water 80 „ B. Carbonate of potash ... ...1,200 grs. Ammonium bromide ... ... ... 240 „ Potassium bromide 480 „ Water 80 ozs. Take equal parts of A and B. Note. — The ammonium bromide is necessary for the production of absolutely cold black tones ; a larger quantity is not re- commended as it tends to produce a slight veil in the high lights. Length of time in developing about two minutes. No. 2. Warm Black Tones. - A. Hydrokinone 640 grs. Soda sulphite ... ... ... ... ... ... 8 ozs. Potassium bromide ... ... ... ... 120 grs. Water 80 ozs. B. Sodium hydrate 640 grs. Water 80 ozs. Take equal parts of A and B. This produces a very pleasing warm black. Length of time' in developing about two minutes. 464 I. plate-makers' formula No. 3. Warm Brown Tones. A. Pyro 1 oz. Soda sulphite 4 ozs - Water 80 „ B. Carbonate of ammonia ... ... ... ... 900 grs. Potassium hydrate ... ... ... ... ... 75° » Ammonium bromide ... ... ... ... ... 600 „ Water ... ... ... 80 ozs. Take equal parts of A and B. Length of time in developing about two minutes. No. 4. Or the following may be used : — Take equal parts of No. 2 formula and add to each ounce 3 grs. carbonate of ammonia and 3 grs. of ammonium bromide. Length of time in developing about three or four minutes. No. 5. Very Warm (Reddish) Tones. Take equal parts ot No. 2 formula and add to each ounce 6 grs. of carbonate of ammonia and 6 grs. ammonium bromide. Lengtji of time in developing about eight minutes. Fixing Bath. We recommend the bath not to be made stronger than — Hypo 5 02s. Water ... ... ... 20 „ Clearing solutions will not be found necessary with these plates. Hill-Norris Dry Collodion Plate.— Instructions for use. Remarks. These plates being isochromatic, should only be developed in a ruby light; ordinary canary medium alone is unsuitable. Exposure The exposure required is about the same as that of the best gelatine plates on the market. Development : These plates while wet being soft and pappy, like wet collodion, must not be touched or brushed during de- velopment. They may be put straight into the developer, i.e., without previous wetting ; the latter does not recede from the 465 H H APPENDIX. surface as in the case of gelatine, neither do any air-bells attach themselves to the film. Enough developer should be used in a suitable dish to keep the plate always well covered with the developing solution. All the customary reducing agents, e.g., iron, pyrogallol, hydroquinone, eikonogen, can be used, but ammonia is not so good an accelerating agent as the fixed alkalies ; and the latter, inasmuch as they allow less exposure to be given, are therefore to be preferred. These plates can be built up with silver and pyro after fixing, as in the old collodion process. The temperature of the developing room and solutions should not be below 6o° F. As a guide we append several formulae for developing. Hydroquinone — Potash. No. i. Sodium sulphite ... 3,200 grs., or 7 ozs., 137^ grs. av. Potassium bromide ... ... ... ... ... 70 grs. Potassium hydrate ... ... ... ... ... 1 oz. av. Water 26 ozs. « No. 2. Hydroquinone ... 32 grs. Sodium sulphite 160 „ Water 2 ozs. If tentative development is practised, the hydroquinone solution should be withheld in part for a time. For ^-plate, take 3 drms. of No. 1, and \ drm. of No. 2, and fill up with water to 2 ozs. Hydroquinone — Soda. No. 1. Hydroquinone ... ... ... 1 60 grs. Sodium sulphite ... ... ... ... ... 2 ozs. Citric acid ... ... ... ... ... ... 60 grs. . • < Potassium bromide ... ... ... 40 ,, Water 20 ozs. ' - No. 2. Sodium hydrate ... 160 grs. Water ... ... ... ... 20 ozs. Mix equal parts and add an equal quantity of water. 466 I. PLATE-MAKERS' FORMULAE. Pyro-Soda (Carb.). Sodium sulphite 25 grs. Sodium carbonate (not bicarbonate) ... ... 25 ,, Water ... ... ... ... ... I oz. One to 3 grs. of dry pyrogallol to be added to each ounce of developer used. If tentative development is practised, the pyro should be withheld in part in preference to the alkali. Ferrous Oxalate. No. 1. Potassium oxalate ... ... ... ... ... 14 ozs. Water 50 No. 2. Protosulphate of iron ... ... ... ... ... 4.^ ozs. Acid sulphuric ... ... ... ... ... 2 drops. Water ... 8 ozs. For ^-plate take i£ oz. of No. 1 and 3 drms. of No. 2. Fixing Solutions. No. 1. Potassium cyanide ... ... ... ... ... 1 oz. Water ... ... ... 10 ozs. Rinse well under tap. No. 2. Sodium hyposulphite 4 ozs. Water 20 „ If No. 2 is used more washing is required. Lantern Plates. These plates are suitable for reduction in camera or contact printing. Exposure. It is impossible to give any correct directions on this point, as the quality and pressure of gas varies so greatly, while for camera work the light is subject to much more variation. The brilliancy and vigour of the slide is always proportionate to the intensity of the light. As a guide to making test exposures we give the following : — In camera — mid«day, sun shining, to a north light with stop //16 from 30 to 60 sees. Contact printing 467 APPENDIX. requires, with a No. 6 batswing burner and a negative of average density, 10 to 20 sees., at a distance of 2 ft. Development. This should be conducted in a temperature of 6o° to 65 0 F. The process should be continued until sufficient density has been acquired. This may be judged by observing (1) that all veil has disappeared from the surface of the plate ; (2) that the image is clear and of a good black colour ; (3) that the image appears dense and black by the transmitted light of the ruby lamp. Ifi cases of under- or over-exposure the slide will be weak or flat. Over-exposure may be remedied by cutting short the development, fixing, washing, and re-developing with silver and pyro. The plate should be put into the developer without previous wetting, and must not be touched or brushed on its surface. We recommend the following formula : — Developer. No. 1. Hydrokinone ... ... .., ... ... ... 160 grs. Sodium sulphite ... ... ... 2 ozs. Citric acid ... ... ... ... ... ... 60 grs. Potassium bromide 40 „ Water ... ... ... ... ... 20 ozs. No. 2. Sodium hydrate 100 grs. Water ... ... ... ... ... 20 ozs. Take equal parts of each. Should No. 1 solution become yellow it is better to make fresh. Fixing Solutions. No. r. Potassium cyanide 5 oz. Water 10 ozs. Before fixing rinse the plate well under the tap, and after immer- sion bring out into the light and wash at once as soon as all the unaltered silver bromide has disappeared. No. 2. Sodium hyposulphite ... ... I ozs. Water 20 „ If No. 2 is used more washing is required. 468 I. PLATE-MAKERS' FORMULAE. Re-developer. No. i. Pyrogallic acid ... io grs. Citric acid 25 „ Water 2 ozs. No. 2. Silver nitrate ... 20 grs. Distilled water ... ... ... 2 ozs. To £ oz. of No. 1 add 30 drops of No. 2. Ilford Plates— New Developing Formula. Stock Solution. Pyrogallic acid ... ... 1 oz. Water ... ... ... 5.J ozs. Add 20 drops nitric acid before the pyro. This will keep for a considerable time. No. 1. Stock solution ... ... ... I to 2 ozs. Water 18 „ No. 2. Carbonate of soda (crystals) (not bicarbonate) ... 2 ozs. av. Sulphite of soda ... ... 2 ,, ,, Bromide potassium ... ... 20 grs. Water to ... ... ... ... 20 ozs. The smaller quantity of stock solution will develop softness and detail in the shadows of the negative. The larger quantity is conducive to density and contrast of light and shade. For use take equal quantities of Nos. 1 and 2. Pour the developer care- fully over the plate, avoiding air bubbles, rock the dish, carefully keeping the plate well covered with solution ; allow the plate to remain after all detail is out, to obtain proper density. Judge of this by looking through the plate. To compensate for errors of exposure the proportions of Nos. 1 and 2 can be varied thus ; for under-exposure use more of No. 2 than of No. 1, and for over- exposure more of No. 1 than of No. 2. It is a good plan, when there is a doubt as to the exposure being correct, to commence the development with twice the quantity of No. 1 to that of No. 2, and add more of No. 2 if found desirable. 469 APPENDIX. Alum Bath. After developing, wash the plate well under the tap, and immerse for a few minutes in Alum, 3 ozs. ; Water, 20 ozs. Fixing. Wash well again, and fix as usual. Hypo., 1 lb. ; Water, 40 ozs. Allow to remain in this bath for several minutes after fixation is apparently completed. Never omit alum bath, and do not be tempted to add anything either to it or to the fixing bath. N.B. — This developer is suitable for all the Ilford negative plates, and yields undoubtedly the finest possible results. A Universal Developer. The following modifications of the Ilford hydroquinone formula have been worked out : — Or Hydroquinone... Bromide potassium Sulphite soda ... Water, up to ... Soda hydrate Water ... Hydroquinone... Eikonogen Potassium bromide Sodium sulphite Water, up to ... Sodium hydrate Water Solution No. 1. Solution No. 2. Solution No. I. Solution No. 2. [60 grs. 2 ozs. av. 20 „ 100 grs. 20 ozs. 80 grs. 120 „ 30 » 2 ozs. 20 ,, 100 grs. 20 ozs. Use as follows : — For negatives on Ilford Plates — Equal parts Nos. 1 and 2. For Ilford Alpha Lantern Plates (for warm tones) — One part No. I, half part No. 2, two parts water. For Ilford Bromide Papers — One part No. 1, one part No. 2, one part water. For Ilford Special Lantern Plates (for black tones) — One part No. 1, one part No. 2, two parts water. For Ilford Alpha Papers — One part No. 1, half part No. 2, two parts water. Although it must be understood that, in our opinion, hydro 470 I. PLATE-MAKERS FORMUWE. quinone is somewhat inferior to ferrous oxalate for papers, yet we do not hesitate to put forward this universal developer as an alternative method of working for those who desire simplicity. The mixed hydroquinone and eikonogen may be relied on for both plates and papers. Note. — The clearing bath must not be used when developing papers with this developer. Imperial Dry Plate Company's Plates.— Developers. Pyro and Soda. A. No. i. Pyrogallic acid I oz. Potassium bromide ... ... ... ... ... 50 grs. Soda sulphite ... ... ... ... ... ... 5 ozs. Water to , ... 50 No. 2. Soda carbonate (washing soda) ... 5 ozs. Water to ... 50 „ For use take equal quantities of No. 1 and No. 2. For over- exposure use more of No. I. For under-exposure use more of No. 2. Pyro and Metabisulphite. B. Stock Solution. Pyrogallic acid ... ... ... ... ... 1 oz. av. Ammonium bromide » M „ Potassium metabisulphite ... ... ... ... 1 „ _ Water to make 10 ozs. Dissolve the metabisulphite and bromide in part of the distilled water before adding the pyrogallic acid. No. 1. Stock solution l£ ozs. Distilled water to make altogether... ... ... 20 „ No. 2. Ammonia ('890) 2\ drms. Water ... ... 20 ozs. For use take equal quantities of No. 1 and No. 2. For over- exposure use more of No. 1. For under-exposure use more of No. 2. 47 1 APPENDIX. Pyro and Ammonia. C. Stock Solution. Pyrogallic acid ... ... ... ... ... i oz. av. Ammonium bromide ... ... ... I „ Water to make ... ... ... ... ... 10 ozs. fluid. Sulphuric acid, strong ... ... 20 drops. No. I. Stock solution i| ozs Water i8£ „ No. 2. Ammonia ('890) ... ... ... i\ drms. Water ... ... ... ... ... ... ... 20 ozs. For use take equal quantities of No. 1 and No. 2. For over- exposure use more of No. 1. For under-exposure use more of No. 2. Hydroquinone. D. No. 1. Hydroquinone 150 grs. Potassium bromide ... ... ... ... ... 25 „ Soda sulphite ... ... ... ... ... ... 2 ozs. av. Water 20 „ fluid. No. 2. Caustic soda 100 grs. Water 20 ozs. For use take equal quantities of No. 1 and No. 2. For over- exposure use more of No. 1. For under-exposure use more of No. 2. Oxalate and Iron. E. No. 1. Potash oxalate 4 ozs. Water ... 16 „ No. 2. Iron sulphate 4 ozs. Water ... 12 „ Citric acid 50 grs. For developing negatives add 1 oz. of No. 2 to 3 ozs. of No, 1. 472 I. PLATE-MAKERS' FORMULAE. For opals add i oz. of No. 2 to 5 ozs. of No. 1 ; and to every oz. of developer add about 10 drops of a 10 per cent, solution of potassium bromide. No. 2 solution must always be added to No. 1, and not vice versa. Eikonogen Developer. G. No. 1. Eikonogen ... ... ... ... \ oz. Soda sulphite ... ... 1 „ Water ... ... ... ... 20 ozs. No. 2. Caustic potash £ oz. Water 20 ozs. For use take equal parts of No. 1 and No. 2. For over-exposure use more of No. 1. For under-exposure use more of No. 2. Eikonogen Developer. H. In one Solution. Eikonogen \ oz. Caustic potash ... ... ... ... ... h „ Soda sulphite ... ... ... ... ... ... I „ Water ... ... ... ... ... ... ... 20 ozs. Dilute with a similar volume of water. If the picture develops too rapidly, add more water. Metol. I. Metol 75 grs. Soda Sulphite ... ... ... I oz. Soda carbonate (washing sod'i) ... ... ... 2 ozs. Water 10 „ For use dilute with equal measure of water. Metol. J. No. 1. Metol 50 grs. Dissolve in water ... ... ... ... ... 10 ozs. Then add soda sulphite ... ... 1 oz. No. 2. Soda carbonate (washing soda) ... ... ... 2 czs. Water to 10 , 473 APPENDIX. No. 3. Potassium bromide \ oz. Water to ... ... ... ... 10 ozs. The developer for normal exposures to consist of 3 parts of No. 1 to 1 part of No. 2, to each oz. of which may, as a rule, be added 20 mins. of No. 3. For instantaneous exposures omit No. 3, for doubtful or tentative development use 10 mins. of No. 3 to each oz. of developer. Amidol. K. Amidol \ oz. Soda sulphite ... ... 2.\ ozs. Water 12 „ This should be diluted with 3 to 10 times its volume of water before using. N.B. — The mixed developer will not keep. Clearing Bath. L. For Negatives. Alum ... ... ... ... ... ... ... 1 oz. Water ... ... ... 10 ozs. Wash before and after immersing in alum bath. For Opals. M. Alum ... ... ... .. ... 2 ozs. Water 40 „ Citric acid ... ... ... ... \ oz. Or instead of citric acid use \ oz. of sulphuric acid. Do not wash before immersing in clearing bath. Fixing Solutions. For Glass Negatives and Films. N. Hypo ... 1 lb. Water 50 ozs. For Lantern Plates, Opals, and Bromide Paper. O. Hypo ... ... .... ... 4 ozs. Water 20 „ Bromide Opals. — "Rapid" for Enlargement and "Slow" for Contact Printing. The exposure required with "Slow" 474 I. plate-makers' formulae. opal plates, for oxalate developer E, for contact printing with a negative of ordinary density, will be about ten seconds, at a distance of 12 inches from a medium-sized gas burner ; for metol developer I or J, about five seconds. The exposure required with "Rapid" opal plates, for oxalate developer E, for contact printing with a negative of ordinary density will be about ten seconds, at a distance of 24 inches from a medium-sized gas burner; for metol developer I or J about five seconds. For enlargements use the test paper supplied with sizes over 8^ x 6|. Metol developer I is strongly recommended for opal work. It is quicker and cleaner than oxalate developer E, and does not require the clearing bath L. With oxalate and iron E, add 1 oz. of No. 2 to 5 ozs. of No. 1, and to every ounce of developer add about 10 drops of a 10 per cent, solution of potassium bromide. No. 2 solution must always be added to No. 1, and not vice versa. When development is complete, immerse the opal in clearing solution M, for a few minutes before washing. After rinsing ten minutes in a few changes of water fix, in fixing solution O, and wash as usual. Take care to have everything perfectly clean. The slightest trace of impurity con- veyed to the solutions by dirty hands will spoil all results. Observe the following : — Developing solution to be fresh and cold. Clearing solution immediately after development before washing. All dishes to be clean, and one to be used ex- clusively for developing. Intensification of Negatives. No. 1. Potassium bromide ... 10 grs. Mercuric chloride ... ... ... 10 „ Water 1 oz. No. 2. Potassium Cyanide 10 grs. Silver nitrate ... ... ... ... ... ... 10 ,, Water ... I oz. To intensify a negative soak it first in the No. 1 solution until more or less bleached. This depends on the amount of intensi- fication required. After a thorough washing in water place the 475 APPENDIX. negative in No. 2 solution until it becomes sufficiently intense Instead of No. 2 solution a weak solution of ammonia may be used, or a 10 per cent, solution of sulphite of soda. Never intensify a negative unless absolutely necessary, for unless a great amount of care is taken, staining is almost sure to occur. Uranium Intensifier. In one Solution. Ferricyanide of potassium ... 20 grs. Uranium nitrate ... ... ... ... ... 20 Glacial acetic acid I drm. Water ... 1 oz. Bathe the negative in this solution until the desired density is obtained, and afterwards wash well in water. Reducing Negatives. Wash the negative well in water and place in a 5 per cent, solution (say 20 grs. to 1 ounce water) of copper chloride until the surface begins to appear covered with a whitish film. It should then be taken out and well washed in water, and then placed in a dilute solution of ammonia, when the negative will become clear and less intense. Instead of ammonia, hyposulphite of soda fixing bath may be used, when it will require more washing than with ammonia. Another method recommended by Dr. Eder is by using a single solution composed as follows : — Ferricyanide potassium 40 grs. dissolved in 1 oz. of water. (N) Hyposulphite soda 10 ozs. In this solution the negative will gradually become weaker, and when the action has proceeded far enough it can be stopped. Wash thoroughly afterwards in water. Intensifying and Toning Negatives. No. 1. Nitrate of uranium 1 oz. Glacial acetic acid ... ... ... 1 ,, Water 50 „ No. 2. Ferricyanide potassium ... .. ... I oz. Glacial acetic acid ... I ,, Water 50 „ Soak the negative first in solution No. I, then in solution 476 I. PLATE-MAKERS' FORMULAE. No. 2. The result will be a fine brown tone. Wash thoroughly after intensifying. Films. These films are coated with emulsion (of the same rapidity and quality as used for Imperial Plates), on thick transparent celluloid, consequently requiring the same ex- posure. They can be used in ordinary dark slides by supporting the frlm with a thin piece of card, but preferably by using a film carrier. For development, any of the imperial plate developing formulae may be used, but it is not advisable to develop more than one film in a dish, so preventing all risk of scratching the moistened emulsion surface. After fixing and washing, soak the film for five minutes in the following: — Glycerine ... I oz. Water 25 ozs. After ten minutes' washing, in running water, the films should be hung up with clips to dry. " Special" Lantern Plates. For producing transparencies of a black tone. The exposure required for a negative of ordinary density will be about five seconds, at a distance of 24 ins. from a medium-sized gas burner. Developing formula (Hydroquinone) is the same as that used with the ordinary plates. See D. For development, use 2 parts of No. 1 to 1 part of No. 2, adding to the mixed developer an equal quantity of water. Metol Developer I is also excellent. After development, the manipu- lations, washing, etc., will be the same as for negatives, but use Fixing Solution O. " Slow " Lantern Plates. For producing transparencies of a warm tone. The exposure required for a negative of ordinary density will be about fifteen seconds, at a distance of 12 ins. from a medium-sized gas burner. Developing formula (Hydro- quinone) is the same as that used with " Special " Lantern Plates, excepting that equal portions of Nos. 1 and 2 are used adding to the mixed developer an equal quantity of water. Lumiere's Extra Rapid Gelatino-Bromide of Silver Dry- Plates. The dark room should be lit only with a red or a green light. In order to avoid the chances of fog, artificial light should be used in preference to natural light, as the intensity of the latter varies considerably from one hour to another. We advise, there- 477 APPENDIX fore, tor the lighting of the dark-room, the use of either gas or a candle in a lantern having two yellow and two green glasses, with a movable door on one side, arranged in such a way as to enable half of these glasses to be suppressed, leaving one green and one yellow for the purpose of examining the negative by transmitted light. Always remove the dust from the plate with a soft brush before putting it into the developing dish. Developers. Most of the developers usually recommended are suitable for the development of Lumiere's plates. We think it advisable, however, to mention the following on account of the certainty which the operator can obtain with same, provided they are used always at a temperature of 6o° to 65 0 F. Amidol. The following is the composition of the normal developer : — " Water 5 ozs. or 100 parts. Sodium sulphite cryst. pure 72 grs. „ 3 „ Amidol 12 „ „ 0-5 „ This solution should always be used fresh. In order to use the developer in the most economical way, it is recommended to make up a solution of sodium sulphite in water (which will keep for any length of time), and to add at the time of using the necessary amount of amidol, either weighed or measured with a small horn spoon. Pyro-Soda. Make the following solutions for storage and use : — A. Water 15 ozs. Sodium sulphite 3 Nitric acid 30 mins. Pyro ... ... ... ... ... 1 oz. B. Water ... 15 ozs. Carbonate soda cryst. 4 „ Sodium sulphite ... 3 478 t. plate-makers' formula. To develop a half-plate, take : — Water Solution A Solution B I oz. i drm. i-ii drms. Increase the quantity of B drop by drop during development, if the negative has been under-exposed. For portraiture a good pyro- ammonia developer will contain in each ounce of developer :— Pyrogallol, with sulphite as usual I gr, Potassium bromide \ „ Liquor Ammoniae (*88o) ... ... 2\ m!ns. This will allow of short exposures. When the image has attained the desired density, stop development and wash ; then fix in — Water 14 ozs. or 1000 parts. Hyposulphite of soda 2 „ „ 150 ,, In very warm weather or in hot climates, add 25 grs. of alum dis- solved in hot water and filtered. Afterwards wash the negative in running water, then immerse for five to ten minutes in — Water 16 ozs. or 1000 parts. Ordinary Alum I oz. ,, 60 ,, Washing after this for two hours in water changed several times will usually suffice. It is better, however, to continue this wash for ten to twelve hours in order to ensure a negative which will preserve itself. If the plate shows any signs of frilli?ig, soak before fixing in a saturated solution of potash alum, wash well, and then fix as above. Intensifying. If the negative has not been sufficiently developed and the mage is wanting in vigour, it can be intensified in the following bath :— Water ... ; 1000 parts. Bichloride of mercury 6 ,, 479 APPENDIX. The result of this is a whitish negative, which is toned by putting the plate, after having washed same, in the following solution : — Water iooo parts. Ammonia 40 „ Or : — To 1 pint of a saturated solution of mercury bi- chloride add 1 drm. of commercial hydrochloric acid. Bleach well and then wash thoroughly. Then soak in a 3 per cent, solution of sodium sulphite, or in water made to smell strongly with liquor ammonias. Reducing. If the negative is too dense, it can be reduced as follows. Prepare : — A. Water 500 parts. Red prussiate of potash 5 w B. Water 50 parts. Hyposulphite of soda ... ... ... ... 5 » Mix the two solutions at the moment of using them, and immerse all at once the negative in the mixture, the action of which is very regular. Wash the plate again, and if the image is to be retouched, plunge it into a fresh solution of borax at 3 per cent., then dry. MawsOIl & Swan recommend the following developer for use with their " Mawson" and "Castle" Plates. Developer. Stock Solution (10 per cent). Pyrogallic acid 480 grs. Bromide of ammonium 240 „ Metabisulphite of potassium 480 „ Distilled water to make 10 fluid ozs. 480 I. PLATE-MAKERS FORMULAE. Dissolve the metabisulphite in part of the water, then add the other ingredients, and make up to bulk with water. Stock solution ... 300 mins. Distilled water to make ... 10 fluid ozs. B. Liq. Ammonia (*88o) ... ... ... ... ... 70 mins. Distilled water to make ... ... ... ... 10 fluid ozs. Use equal parts of A and B, mix at time of developing. Pyro-Soda Developer. A. Pyrogallic acid ... ... ... . . ... 60 grs. Metabisulphite of potassium... ... ... ... 5 ,, Distilled water to make 10 fluid ozs. B. Washing soda ... ... ... 600 grs. Sulphite of soda ... ... ... ... ... 800 „ Distilled water to make ... ... 10 fluid ozs. Use equal parts of A and B, mixed at time of developing. To correct over-exposure add a few drops of 10 per cent, solution of potassium bromide. For under-exposure, increase B solution. Eikonogen Developer. A. Eikonogen 100 grs. Sulphite of soda (recryst.) 100 „ Distilled water to make ... ... 10 fluid ozs. B. Carbonate of potassium (coml.) ... 1200 grs. Sulphite of soda (recryst.) 500 „ Distilled water to make 10 fluid ozs. c. Caustic potassium (sticks) 400 grs. Sulphite of soda (recryst.) ... ... 900 Distilled water to make ... ... ... ... 10 fluid ozs. 481 II APPENDIX. Three parts of A to one part of B. In cases of under-exposure, or for instantaneous pictures, use C instead of B. To correct over-exposure, add a few drops of 10 per cent, solution potassium bromide. Ferrous Oxalate Developer. The following solutions may be made in quantity and kept separately : — A. Neutral oxalate of potassium ... 1200 grs. Bromide of potassium ... ... ... ... 5 Citric acid ... ... ... ... 15 Distilled water to make 10 fluid ozs. B. Ferrous sulphate 1600 grs. Citric acid 120 M Distilled water to make ... ... ... ... 10 fluid ozs% Distilled water should be used, otherwise the lime in ordinary water will cause turbidity frcm formation of oxalate. A will keep indefinitely, but B should not be used after it turns brown or yellow. When required for use, pour four parts of A rapidly into one part of B. The resulting solution will be of a deep red colour. After development and fixing, the plate frequently ex- hibits an opalescent appearance ; this is a deposit of oxalate of lime that forms in washing : to remove it, immerse the plate, after thorough washing in Hydrochloric acid ... ... ... I oz. Saturated sol. alum ... ... ... ... ... 19 ozs. washing the plate again after the operation. Hydrokinone Developer. A k Hydrokinone 40 grs. Metabisulphite of potassium... ... ... ... 40 „ Distilled water to make 10 fluid ozs. B. Caustic potassium (sticks) ... ... ... ... 80 grs. Distilled water to make 10 fluid ozs. Use equal parts of A and B, mixed at time of developing. 482 1. PLATE-MAKERS FORMULA. Fixing Solution. Hyposulphite of soda iooo grs. Water to make 10 fluid ozs. Developing Solutions recommended for Mawson & Swan's Photo-Mechanical Plate. A Pyrogallic acid Bromide of ammonium Metabisulphite of potassium... Distilled water to make B. Liq. Ammonia (*88o) ... ... ... ... ... 70 mins. Distilled water to make ... ... ... ... 10 fluid ozs. Use equal parts of A and B, mixed at time of developing. If the plate has been correctly exposed, the time required to complete development is usually from four to six minutes. The following developer is recommended for use with these plates, by Mr. Wilkinson, and is known as Payne's Hydroquinone Developer. 1. Hydroquinone... Metabisulphite of potash Bromide of potash Distilled water 2. Potassium hydrate (stick) ... ... ... ... 10 grs. Distilled water ... .. ... ... ... 1 oz. Equal parts of 1 and 2. Morgan and Kidd's Richmond Dry Plates. Pyro and Ammonia Developer. A. Citric acid ... ... ... ... ... ... 1 dr. Sulphite of soda 4 ozs. Distilled water ... ... ... ... ... 60 ,, Pyrogallic acid ... ... ... I oz. Note. Dissolve the citric acid and the sulphite of soda in the 483 30 grs. 30 » 30 » 10 fluid ozs. 4 grs. 4 M ' gr. I oz. APPENDIX. water before adding the pyro ; keep for use in a well-stoppered bottle. B. Liquid ammonia ( 880) I oz. Bromide of ammonium ... ... 2 drs. Water ... ... ... ... ... ... ... 2 ozs. C. Bromide of ammonium ... ... ... ... 2 drs. Water ... ... ... ... 2 ozs. Solutions B and C to be kept in dropping bottles. For use take of A solution 1 oz., water 3 ozs., B solution 8 to 10 drops. Add more of B if development is too slow, or negative is undertimed. For over-exposure add a few drops of C and more A solution. For under-exposure add more of B solution, should image appear to be developing up too dense, dilute developer with water and' continue development until all detail is out. Pyro and Soda Developer. A and C solutions as above. . B. Water 60 ozs. Pure dry carbonate of soda 4 „ For use take equal parts of A and B. If more density is required use a drop or two of C to each ounce of mixed developer. For over-exposure add a few drops of C and more A solution. For under-exposure add more B solution, and dilute with water if negative is developing with too much density. After develop- ment wash and then soak for 5 minutes in a saturated solution of common alum, wash again and fix in hyposulphite of soda, 8 ozs. to a quart of water. The Paget Prize Plate Co. " Phoenix XXX and XXXXX." Instructions for use. — Keeping. Plates should be kept in a cool place, in as pure air as possible, and dry. But damp is not so injurious as excessive heat. They should be stored, if possible, in a room where gas is not burnt. If circumstances necessitate their being kept in an impure atmosphere, each package should 484 I. plate-makers' formula. be wrapped in a double coating of tin or lead foil ; this is an effectual protection. Development. Any developer may be used with these plates, but for quality of result, gradation, and adaptability to varieties of subject and circumstance, there is none equal to pyro and ammonia. The following formula has been carefully adapted to suit these plates, and we strongly recommend its use in pre- ference to any other : — Stock Solutions. P. Pyrogallic acid ... ... ... ... ... i oz. Citric acid ... ... ... ... 60 grs. Sodium sulphite (pure) ... ... 2 \ ozs. Distilled water to make ... ... ... ... 20 ,, A. Liquid ammonia (*88o) ... ... ... ... 1 oz. Ammonium bromide ... ... 80 grs. (For Phoenix Plates, 120 grs.) Distilled water to make 20 ozs. Dissolve the citric acid and sulphite in about half the water, which may be made hot to assist the solution. When cold add the pyro, and make up to 20 ozs. with remainder of water. This solution will keep a long time, if preserved from contact with the air, in well-stoppered bottles. Sulphite of soda (not sulpha or sulphzVfc) varies greatly in quality, and spoils if left long exposed to the air. The best re-crystallised should be used. Studio developer. Dilute 1 part of P with 5 parts of water, and dilute 1 part of A with 5 parts of water. Mix the two dilute solutions in equal quantities for use. (Such developer contains about 2 grs. pyro, 2 mins. ammonia, \ gr. bromide, 5 grs. sulphite, \ gr. citric acid, in each ounce.) If a thinner and softer negative be desired, use less of P. Outdoor work. For groups, street scenes, near views, and other subjects not too distant and with moderate contrasts, the above developer will generally be found suitable ; but the outdoor photographer who wishes to be able to modify his developer to 485 APPENDIX. suit great varieties of subjects will probably prefer three separate stock solutions, each of 10 per cent, strength, as follows : — No. Pyrogallic acid Sodium sulphite Citric acid Distilled water to make No. 2. Ammonia bromide ... ... ... i oz. Distilled water to make 9 ozs. 55 mins. No. 3. Liquid ammonia ('880) ... ... ... ... 1 ox. Distilled water to make 10 ozs. Ten minims of each of these solutions will contain 1 gr. pyro, 1 gr. bromide, and 1 min. of liquid ammonia *88o respectively. To the inexperienced photographer it may be useful to point out that the strength of developer to be used depends greatly on the natural contrasts of light and shade in the subject ; in a distant view, for instance, there is usually very little contrast; in a portrait or near view, with foliage, etc., the contrasts are fre- quently great. As a general rule, the less contrast in the subject the stronger should be the developer. In ordinary cases this will vary from, say, 1 or i| gr. of pyro per ounce for a strongly lighted portrait, to as much as 6 or even 8 grs. per ounce for a distant landscape or marine view. Bromide may vary from one- sixth up to an amount equal to weight of pyro used. The quantity of bromide chiefly influences the time of development ; if much be used a longer time will be required. If the developer be necessarily a strong one, a large proportion of bromide should be used, and plenty of time given. In most cases the quantity of ammonia should not much exceed that of pyro ; it is generally advisable to commence development with only about half or two-thirds of the ammonia, and add the remainder as may be found necessary. Over-exposure. A solution of citrate of soda, 1 oz. in 10 ozs. of water, is a most useful one. If over-exposure be known or suspected, commence with a developer containing less than 486 ... 1 oz. 2\ OZS. 60 grs. 9 ozs. 55 mins. I. PLATE-MAKERS' FORMULAE. usual of ammonia. This will cause the image to come out more slowly, and give more time to observe its character. When nearly all necessary details are just visible, if the appearance of the image be such as to indicate over-exposure, at once add to the developer some of the citrate solution, the quantity required depending on the amount of over-exposure, and varying from a few drops to 2 or 3 drms. This will stop development, but not intensification — i.e., no more detail will be produced, but the image already formed will be allowed to grow stronger. To obtain the requisite density more of either P or A, or both, may be now added, and the action allowed to proceed as usual. If too much citrate has been added, the developer may be poured off, the plate washed, and a fresh less-restrained developer ap- plied. Citrate possesses this great advantage over bromide, which is generally used for the same purpose : that whereas bromide destroys the latent image, citrate does not, but only restrains development so long as itself is present. For Under-exposure, use developer containing P and A in equal quantities, but strong. No plate much under-exposed ever gives a thoroughly satisfactory result ; if at all possible expose another, and for all subjects requiring very brief exposure use the most rapid plates. General Hints. Do not wet the plate before development. Do not drop plate into developer. Do not use pyro developer for a second plate. Lay the dry plate in dry dish and pour developer over it in one sweep, taking care plate is well covered. Rock dish occasionally during development ; this has a great influence on vigour. However "safe" you may consider your light, do not expose plate to it more than is absolutely necessary. Have a cover for dish during development. Do not fix plate directly you see enough detail, but give enough time to acquire density also. Fix thoroughly. Have all your solutions and washing water as nearly at the same temperature as possible, and under 6o° if you can ; differences of temperature tend to produce frilling ; warm developer induces fog and flatness ; very cold developer takes a long time to act, and may be used stronger. Fixing. Wash well after development, and fix in — Hyposulphite of soda ... ... ... ... ... 6 ozs. Water ,,, 1 pt. 487 APPENDIX. The plate should remain in the fixing bath for several minutes after it appears to be cleared. When fixed, it should be placed, after a good washing, in a saturated or nearly saturated solution of common alum, and left for three or four minutes. This greatly assists in extracting the hypo, and in every way improves the plate. It should then be very thoroughly washed with water, and allowed to dry spontaneously. On no account must it be heated to hasten drying. In very hot weather the alum bath may be used before fixing, as an extra precaution against frilling. Do not expose the plate to white light until it has been placed in the alum after fixing. Intensification. With proper exposure and development in- tensification ought never to be necessary. The following intensifier is, however, very effectual : — M. Bichloride of mercury (corrosive sublimate) ... \ oz. Bromide of potassium ... ... \ „ Distilled water ... ... ... ... ... I pt. S. Cyanide of potassium (in crystals or best fused) ... \ oz. Water I pt. Drop a strong solution of nitrate of silver into this (S), stirring round and adding silver until a precipitate is formed which does not re-dissolve. Do not use for twenty-four hours. Soak the plate, after fixing and thorough washing, in the alum bath for at least ten minutes, wash thoroughly for at least half an hour, and lay it in solution M until it becomes white all over and has the ap- pearance of a positive. Then wash thoroughly, say for an hour, and place in solution S until it becomes perfectly black all through. Wash once more, and allow to dry. A plate so treated should be absolutely black, with clear shadows ; and if the soaking in alum and washing after each operation have been thoroughly done, there is little to fear with regard to permanency. The least trace of yellowness indicates that the washing has not been effectually carried out. If the amount of intensification required be not great, a 10 per cent, solution of sulphite of soda may be used instead of solution S. If sulphite be used the washing after M need not be prolonged. 488 I. plate-makers' formulae. Reduction. In cases where, from over-development, the negative has been allowed to become too dense, the following method of reducing (due to Mr. E. Howard Farmer) will be found very convenient and effective : — Prepare a solution of ferricyanide of potassium (red prussiate of potash) by dissolving i oz. in a pint of water, and keep for use when required. To reduce a negative, immerse it in a hypo solution of a strength of about i oz. to the pint of water (a little of the fixing bath diluted answers perfectly), to which has been added a little of the above ferricyanide solution. A gradual uniform reduction will take place, the rapidity depending on the quantity of ferricyanide added. When sufficiently reduced, take out and wash thoroughly. To reduce locally, immerse the plate in water for a few minutes, and apply the mixed solution with a camel's-hair brush or pellet of cotton wool to the parts required. The ferricyanide solution must be added to the hypo when required, as the mixed solution does not keep. Pyro-soda, hydrokinone, or eikonogen may be used, if preferred, with these plates. Pyro-Soda. No. i. Pyrogallic acid ... ... ... \ oz. Sulphuric acid ... 5 drops. Distilled water to make 20 ozs. No. 2. Carbonate of soda (crystals, pure) ... Sulphite of soda (pure) Distilled water to make Equal parts of each. Hydrokinone. No. 1. Hydrokinone ... Methylated spirit Sulphurous acid Potassium bromide Dissolve the hydrokinone in the spirit, and add the acid. In another vessel dissolve the potassium bromide in 3 ozs. of 489 2 ozs. 2 n 20 „ IO ozs. 2 oz. j APPENDIX. distilled water. Mix the two solutions, and make up to 20 ozs. with distilled water. No. 2. Caustic soda (in sticks) Sodium sulphite Distilled water to make 1 part of each to 4 parts of water, hard a negative, use more water. ... 1 oz. 5 ozs - 20 „ If this be found to give too Eikonogen. No. 1. Eikonogen ... ... ... 1 oz. Sodium sulphite ... ... 1^ ozs. Potassium bromide ... ... ... 8 grs. Distilled water to make ... ... ... ... 30 ozs.' 60 grs. hydrokinone added to above is a decided improvement, increasing brilliancy and density. No. 2. Potassium carbonate ... ... ... ... ... 1 oz. Distilled water to make ... ... .., ... 10 ozs. 3 parts of No. 1 to 1 part of No. 2. Lantern Plates. Instructions for Use. Rapid Series. Exposure. These plates, which give only black tones, require about one-sixth of the exposure of the slow series as below. Development. Any of the formulae given for the slow series for black tones are equally suitable for these. Slow Series. The great difference in density and character of negatives renders it impossible to make any definite statements with regard to exposure. The "slow" plates, exposed in contact with a good, clear landscape negative of average density, have been found to require for black tones an exposure of about 30 seconds at a distance of 1 foot from an ordinary fishtail • 490 I. PLATE-MAKERS' FORMULA. gas-flame, or i inch of magnesium wire burnt at a distance of 3 feet. The exposures given under the heading of " warm tones " also refer to the same negative. Denser negatives will, of course, require more. In the case of negatives of different densities, it is better to regulate the exposure by varying the distance from the light than by altering the time. Dense negatives being exposed nearer to, and thin ones farther from, the light. Development. For black tones development should in no case exceed 3 minutes. If longer is required the exposure has been insufficient, and the result will not be so good. Any of the following formulae are suitable : — Hydrokinone ... Sulphurous acid Potassium bromide Water to Hydrokinone. Solution 1. \ oz. * n 60 grs. 20 ozs. Solution 2. Caustic soda ... ... ... ... £ oz. Sodium sulphite ... ... 2\ ozs. Water to 20 „ For use, take ^ oz. of each to 1 oz. of water. Eikonogen Developer. Solution i. Eikonogen ... ... ... ... £ oz. Sodium sulphite ... ' ... ... ... ... \\o/.s. Potassium bromide ... ... ... S grs. • Distilled water to ... ... ... ... ... 30 ozs. Solution 2. Potassium carbonate ... ... ... ... ... 1 oz. Distilled water to ... ... ... ... ... 10 ozs. Take 3 parts of No. 1 to 1 part of No. 2 solution. 491 APPENDIX. Rodinal Developer. Rodinal concentrated solution Water I part. 30 parts. This is a very clean developer, and gives a rich black colour. Ferrous Oxalate Developer. Solution 1. Neutral oxalate of potash Citric acid Hot water 16 ozs. 60 grs. 50 ozs. Proto-sulphate of iron Citric acid Hot water Solution 2. 4 ozs. 15 grs. 8 ozs. Bromide of potassium Water Solution 3. Joz. 10 ozs. For development, take 6 ozs. of No. 1, and add 1 oz. of No. 2 and 24 drops of No. 3. Gives cold black tones. Pyrogallic acid Sodium sulphite Citric acid Distilled water to Pyro-Ammonia. Solution 1. I oz. l£ ozs. i oz. 10 ozs. Liquor ammonia (*88o) Ammonium bromide ... Distilled water to Solution 2. 1 oz. 10 ozs. For use, take 45 minims of each solution and make up with water to 2 ozs. 492 I. plate-makers' FORMULA. Warm Tones Developer. Solution i. Hydroquinone ... ... ... ^ oz. Sulphurous acid ... ... ... £ ,, Potassium bromide ... ... ... ... ... 60 grs. Water to 20 ozs. Solution 2. Caustic soda ... ... ... ... ... ... I oz. Sodium sulphite ... ... ... ... ... 2 A ozs. Water to 20 ., Solution 3. Bromide of ammonia ... ... ... ... ... 1 oz. Carbonate of ammonium ... ... I „ Water to ... ... ... ... ... ... 20 ozs. Carbonate of ammonium should be in clear lumps ; if from exposure to the air it has become coated with the white powdery bicarbonate, the latter should be scraped off. Brown. Exposure, 60 seconds, 1 foot from gas-flame, or 2 inches of magnesium wire burnt at a distance of 3 feet Developer, solution 1, £ oz. ; solution 2, £ oz. ; solution 3, 100 minims; water to 2 ozs. Time required in development, about 5 minutes. Purple brown. Exposure, 90 seconds, 1 foot from gas-tlame, or 3 inches of magnesium wire burnt at a distance of 3 feet. Developer, solution 1, £ oz. ; solution 2, £ oz. ; solution 3, 200 mins ; water to 2 ozs. Time required in development, about 10 minutes. Purple. Exposure, 3 minutes, 1 foot from gas-flame, or 3 inches of magnesium wire burnt at a distance of 2 feet. Developer, solution 1, \ oz. ; solution 2, \ oz. ; solution 3, 250 mins. ; water to 2 ozs. Time required in development, about 12 minutes. Red. Exposure, 5 minutes 1 foot from gas-flame, or 5 inches of magnesium wire burnt at a distance of 2 feet. Developer, solution 1, A oz. ; solution 2, \ oz : solution 3, 300 mins. ; water to 2 ozs. Time required in development, about 15 minutes. 493 APPENDIX. Wash the plate in running water for at least 3 minutes before fixing : otherwise a yellow stain may afterwards appear. Fixing-Bath. The simplest is the following : — Hyposulphite of soda ... ... ... ... 6 ozs. Water 20 „ After fixing, the transparency is well washed for 1 hour in several complete changes of water. Printing-Out Opals. — Instructions for Use. Printing is best done in the special frame, in which the negative is fixed to the frame and the opal to the back in such a way that the opal can be examined during printing and afterwards returned to exact register on negative. If an ordinary frame be used the negative must be firmly secured in its place, say by small wood wedges or other means found convenient. In laying the opal down it should be pushed thoroughly up into one corner of the frame, so that after examination, during printing, it may be replaced in exactly the same position without difficulty. Printing should be carried on to the same extent as when printing paper. Somewhat deeper printing is required when the " combined " bath is used than is necessary for separate toning with sulphocyanide. It should be borne in mind, when toning, that the finished image will be bluer and slightly stronger when dry than in the wet state. Toning. Either of the following well-known baths answers admirably. Combined Toning and Fixing Bath. No. 1 Stock. Hyposulphite of soda ... ... 20 ozs. Alum (potash alum only) ... 5 „ Sodium sulphate (not sulphite) 14 „ Water to I gallon. Dissolve the hypo and alum each in about 1 quart of hot water, mix, and then add sodium sulphate already dissolved, making up to 1 gallon with remainder of water. This mixture should then be left for some hours for the precipitate to settle, when 494 I. plate-makers' formulae. the clear solution may be poured off or filtered and is then ready for use. It will keep indefinitely. No. 2 Stock. Gold chloride 15 grs. Acetate of lead ... ... ... ... ... 64 Distilled water 8 ozs. Dissolve the acetate of lead in the water and add the gold. A heavy precipitate forms in this solution, which should be shaken up when any is to be poured out : it redissolves when added to No. 1 stock solution. For use : mix 8 ozs. of No. 1 with 1 oz. of No. 2. When this bath is used the plates should not be washed before toning. Separate Toning Bath. Sulphocyanide of ammonium .. ... ... 30 grs. Gold chloride ... ... ... 2$ „ Water 16 ozs. Before immersion in this toning bath, the plates should be very thoroughly washed for at least 15 minutes in running water. This is necessary to insure even toning. In hot weather, if necessary, the plates may be soaked in alum (alum 4 ozs., water 20 ozs.) for five minutes before toning in this bath. Another thorough washing is necessary between the alum and toning baths. Fixing Bath. Hyposulphite of soda ... ... 3 ozs. Water I pint. With most negatives the most pleasing result will be obtained by vignetting or masking the edges. If by any accident any part of the edge be printed where not intended, the film may be removed by careful rubbing with a warm damp rag, or (on the polished surface opals only) by scraping with a sharp knife. Clearing Stains. The extreme edges of these plates sometimes become brown, and after very long keeping this stain may extend more or less inwards. In any case the discoloration does no harm whatever, 495 APPENDIX. as, after the picture is finished, it may be easily wiped away with a tuft of cotton-wool dipped in a deep solution of cyanide of potassium oz. in a pint of water). As this solution also reduces the image, it must be carefully used, and water should be kept running over the picture during the operation, so as to avoid a sharp line. The same solution, diluted with five or ten times its bulk of water, and poured all over the picture, forms an admirable clearer or reducer, should such be required. Note. Cyanide of potassium is extremely poisonous. Bromide Opals. — Instructions for use. Exposure. The time required for exposure will, of course, vary with the light and the density of the negative. As a guide, however, it might be stated, that a negative of good silver printing qualities required an exposure of ten seconds at a distance of one foot from an ordinary fish-tail burner, or half an inch of magnesium wire burnt at a distance of four feet from the negative. Development. For black tones the following developer is the one chiefly used : — Ferrous Oxalate Developer. Solution i. Neutral oxalate of potash 16 ozs. Citric acid 60 grs. Hot water 50 ozs. Solution 2. Protosulphate of iron 4 ozs. Citric acid (or acetic acid \ drm.) \ 02. Hot water 8 ozs. Solution 3. Bromide of potassium \ oz. Water 10 ozs. For development, take (when cold) 6 ozs. of No. 1, and add 1 oz. of No. 2, and \ drm. of No. 3. For warm black tones use the hydrokinone developer, made up as follows: — 496 I. plate-makers' FORMULA. Hydrokinone Developer. Solution i. Hydrokinone ... Sulphurous acid ... ... Potassium bromide ... Water to Solution 2. Caustic soda ^ oz. Sodium sulphite ... ... ... ... ... 2 A ozs. Water to ... ... ... 50 ozs. For use take equal parts of the two solutions. By increasing the exposure and using less of No. 1 solution, still browner images can be obtained. Other developers, such as Eikonogen, Pyro, Rodinal, etc., can also be used. Clearmg. — When using the ferrous oxalate developer it is necessary, as soon as development is completed, to at once immerse the opal in either of the following baths : — Water ... ... ... 80 ozs. Alum (powder) ... 2 „ Citric acid ... ... ... ... ... ... 1 oz. or Acetic acid ... ... ... ... I drm. Water 20 ozs. Use just enough to cover the opal, allow it to act for a minute or so, then pour it away and apply a fresh portion. Well rinse in clean water and place in the fixing bath composed of Fixing Bath. Hyposulphite of soda ... ... ... ... ... 4 ozs. Water ... ... ... ... ... 20 „ In this the opal should remain for ten or fifteen minutes, after which they are well washed and dried. Notes. — To insure success the utmost cleanliness should be observed, especially with the Ferrous Oxalate Developer, with 497 K ^ *oz. 1 f tt 60 grs. 50 ozs. APPENDIX. which a dish should be kept for each operation and used for that only. The clearing bath is only necessary with the Ferrous Oxalate Developer ; do not wash before immersing the opal in it. With the Hydrokinone Developer the plate must be thoroughly rinsed before fixing, otherwise yellow stains will appear. Printing-out Lantern Plates. — Instructions for use. Printing may be done in an ordinary frame, half of the back being opened, as is usual with printing paper. The progress of printing is best judged by reflected light, and should be carried on until the densest parts of the negative (which should be clear glass in the finished transparency) begin slightly to print. It must be borne in mind that the density of an image to be seen by transmitted light requires to be much stronger, and therefore more fully printed than in the case of paper. As the slightest want of sharpness in a lantern slide is greatly magnified on the screen, the plate should, under no circumstances, be removed from the negative until completely printed ; unless a frame specially made for the purpose is used. Print by direct sunlight when possible ; and as, in order to ensure the greatest possible sharpness, it is desirable that the light always fall at the same angle on the negative, the frame, after being examined, should be replaced in the same position as before. To prevent mistakes, mark one side of frame " top," and keep it so. When using a frame larger than the negative, it is necessary to adopt some means of preventing extraneous light from reaching the edges of the lantern plate. A mask will answer the purpose ; but it must, of course, be put on the back of the negative (not the film side). Toning. — Either of the following well-known baths answers admirably : — Combined Toning and Fixing Bath. No. 1 Stock. Hyposulphite of soda ... ... ... ... 20 ozs. Alum (potash alum only) 5 oz. Sodium sulphate (not sulphite) 14 ozs. Water to ... ... I gal. Dissolve the hypo and alum each in about a quart of hot water, 498 i. PLATE-MAKERS' FORMULAS. mix, and then add sodium sulphate already dissolved, making up to a gallon with remainder of water. This mixture should then be left for some hours for the precipitate to settle, when the clear solution may be poured off or filtered, and is then ready for use. It will keep indefinitely. No. 2 Stock. Gold chloride ... ... ... ... ... ... 15 grs. Acetate of lead ... ... ... 64 Water (distilled) 8 ozs. Dissolve the acetate of lead in the water and add the gold. A heavy precipitate forms in this solution, which should be shaken up when any is to be poured out ; it redissolves when added to No. 1 stock solution. For use : Mix 8 ozs. of No. 1 with 1 oz. of No. 2. With this bath the plates should be rather more fully printed than when separately toned. They should not be washed before toning. Separate Toning Bath. Sulpho-cyanide of ammonium ... ... ... 30 grs. Gold chloride ... ... ... ... 2\ „ Water ... ... 16 ozs. Before immersion in this toning bath the plates should be very thoroughly washed for at least fifteen minutes in running water. This is necessary to ensure even toning. In hot weather, if necessary, the plate may be soaked in alum (alum 4 ozs., water 20 ozs.) for five minutes before toning in this bath. Another thorough washing is necessary between the alum and toning baths. The image is a transparency, which has to be toned right through, of course takes longer than a paper print, which is toned on the surface only, and the colour should only be judged by transmitted light. Fixing Bath. Hyposulphite of soda ... ... 3 ozs. Water I pint. 499 APPENDIX. Verel & Co.'s " Runaway " and other Plates. Pyro-Soda Developer. Stock Pyro Solution. Pyrogallic acid .. . ... ... i oz. Nitric acid ... ... ... ... ... ... 20 drops. Water ... ... ... 6 ozs. No. I. Stock ... ... ... ... ... 2 ozs. Water 18 „ No. 2. Carbonate soda (crystals) Carbonate potash Sulphite soda ... Bromide Potash Water Use in equal parts. Pyro-Ammonia Developer. No. 1. Pyrogallic acid Sulphite soda ... Citric acid Water No. 2. ... ... oz. 4 dnns. 16 ozs. For half-plate, use 2 drms. each of above in 2 ozs. of water. Should the plate be over-exposed, add a few drops of a solution of bromide of ammonium (equal parts of bromide and water), and use a smaller quantity of No. 1, — say 3 parts of No. 2 to 1 of No 1 . Alum Bath. — One part of alum to 20 parts of water. Leave in this bath for 10 minutes. You should always use the alum bath. Fixing. — Hyposulphite of soda, 1 to 4 parts of water. 500 2 ozs. 1 It 2 „ 80 grs. 20 ozs. I oz. £ drm. 16 ozs. Liquor ammonia Ammonium bromide ... Water t, PLATE-MAKERS' FORMULAS. Eastman's "Permanent" and "Extra Rapid' Bromide Papers. Oxalate Developer. No. i. Oxalate of potash (neutral) lib. Hot water 48 ozs. No. 2. Proto-sulphate of iron ... ... ... ... 1 lb. Citric acid ... ... ... ... ... ... £ oz. Hot water ... ... 32 ozs. No. 3. Bromide potassium ... ... ... ... ... 1 drm^ Water ... ... ... 10 ozs. These solutions keep separately, but must be mixed only for immediate use. To Develop. For Normal Exposures. — Take in a suitable tray No. 1, 6 ozs. ; No. 2, 1 oz. ; No. 3, \ drm. (about 5 drops to the ounce of developer). These solutions should be employed as cool as possible, and mixed in the order named. After exposure, soak the paper in water until limp ; then immerse in the developer. Use fresh developer for each batch of prints. With a glass- bottomed tray, 8 ozs. of developer are sufficient for a 25 X 30 print. The bromide is added to the developer for the purpose of producing vigorous contrasts of light and shade and of pre- serving the clear whites of the prints. When printing from a negative which is thin, or flat, the proportion may be safely increased to twice that named above. No Toning required. — With Eastman's permanent or extra rapid bromide paper the final tones may be varied to almost any extent, depending as they do upon the density of the negative, the quality of light used in printing, and the proportion of iron and bromide employed in the developer. For delicate, grey tones like the India-ink washes of an artist's brush, it is requisite to expose to a well-diffused light, and to develop with a smaller quantity of iron and bromide in the developer. For 5 01 APPENDIX. vigorous prints, with full contrasts, the image should appear slowly and should develop up strong, clear, and brilliant. When the shadows are sufficiently black, pour off the developer and flood the print with the clearing solution : Acetic acid ... i drm. Water ... ... ... ... ... ... ... 32 ozs. Instead of acetic acid, citric acid may be used in the clearing solution, in the proportion of £ ounce to the quart of water. Citric acid has the advantage of being odourless. Purpose of Clearing Solution. — The purpose of the clearing solution is to prevent the precipitation of the iron from the developer into the fibre of the paper. This can only be done by keeping the paper acid while washing out the developer. Do not wash the print after pouring off the developer, and before applying the clearing solution. Use a sufficient quantity to flow over the print, say 2 ozs. for an 8 X 10. Allow it to act for one minute, and then pour it off and apply a fresh portion ; repeat the operation a third time, then rinse in four changes of pure water and immerse for ten minutes in the fixing bath : Hyposulphite of soda ... ... ... ... ... 4 ozs. Water 20 „ After fixing, wash thoroughly in several changes of water for two hours at least, and hang up to dry. Solio Paper (Printing-out Paper). Caution. This paper being more sensitive to light than ordinary albumenised paper, great care must be taken to handle it in a subdued light only. Whilst printing, the prints should be examined in a weak light, otherwise a great risk will be incurred of destroying the high lights and purity of the resulting picture. The paper must also be kept perfectly dry. Printing should be done in a strong light if the negatives are hard; only thin or delicate negatives being printed in the shade. The printing should be carried only a little darker than it is desired the finished print should appear, as this paper loses very little in the subsequent toning and fixing operations. It is advisable to use a piece of waterproof material in the back of the printing frame during damp weather. Toning. Any of the usual formulae may be used for this 502 I. PLATE-MAKERS' FORMULA. paper, but the following are specially recommended as giving by far the best results : — Eastman's Combined Toning and Fixing Bath. Stock Solution A. Hyposulphite of soda... ... ... 8 ozs. Alum (common) ... ... ... ... ... 6 n Water 80 „ When dissolved add borax, 2 ozs. ; dissolved in hot water, 8 ozs. Let it stand overnight and decant the clear liquid. Stock Solution B. Chloride of gold ... 15 grs. Acetate of lead (sugar of lead) 64 „ » Water ... ... 8 ozs. Solution B should be shaken up before using, and not filtered. For use take stock solution A, 8 parts ; stock solution B, 1 part. Place prints, without previous washing, into the above. The combined bath must be cold, not above 40 0 or 50 0 F. This condition can be obtained by placing a piece of ice in the bath when toning. If your bath is too warm you will get yellow prints, with a greenish cast in the half tones. Use a ther- mometer, and keep it in your toning bath all the time. The combined bath is an acid solution, any attempt to neutralise the bath will precipitate the alum. Tone to desired colour, and immerse prints for five minutes in the following salt solution to stop the toning : — Salt 1 oz. Water ... 32 ozs. If the prints tone in less than fifteen minutes it is desirable that the following extra fixing bath be used to ensure thorough fixing. After the salt bath give one change of cold water and fix for ten minutes in the — Extra Fixing Bath. Hyposulphite of soda ... ... ... 1 oz. Sulphite of soda (crystals) ... 60 grs. Borax $ oz. Water ... 20 ozs. 503 APPENDIX. Wash one hour in running cold water, or in sixteen changes of cold water, when prints may be mounted same as albumen prints. Examining prints while toning. Tone to the colour desired in finished prints. Great care must be taken not to tone too many prints with the same bath. Nine ounces of the mixed toning bath, made as above formula, will tone one sheet of paper of the standard size, i\\ by 17 inches, or one is. packet, and more should not be used. Printing from hard negatives. The combined bath makes soft prints, and may be used to advantage with hard or under- timed negatives. Separate Toning Baths — Sulphocyanide Bath. Cold Tones. Owing to the softening action of sulphocyanide on gelatine it is necessary to pass the prints through an alum bath previous to toning. After the prints have been washed in three changes of water they should be immersed in the following bath for ten minutes : — Alum ... ... ... ... ... \ oz. Water ... ... ... 20 ozs. Thoroughly wash after the alum bath for five minutes in running water. Toning Bath. Stock Solution A. Sodium acetate ... ... ... 600 grs. Water ... 20 ozs. Gold chloride 15 grs. Stock solution B. Ammonium sulphocyanide 50 grs. Water ... 20 ozs. For use: Take of A, 2 parts; B, 2 parts; water, 4 parts. Allow to stand an hour before using. The toning may be stopped 5°4 I. PLATE-MAKERS* FORMULAE. at any stage by transferring the prints to the following (the prints must be kept in motion for the first few seconds) : — Short Stop. Common salt ... I oz. Water 32 ozs. The prints should be well washed and then fixed in the following Fixing Bath. Sodium hyposulphite ... 3 ozs. Sodium sulphite ... ... ... U „ Water 20 ,. After the prints are fixed they should be washed for one hour in running water. Alum bath can be used before or after fixing if desirable, care being taken to well wash the prints between each two operations. Warm Tones. Wash the prints from five to ten minutes, then immerse in either of the following baths, examining the prints by transmitted light : — Platinum Toning Bath (for Sepia Tones). Stock Solution. Potassium chloro-platinite ... 5 grs. Citric acid ... ... 40 ,, Sodium chloride (salt) 40 ,, Water ... ... 20 ozs. Tone to a dark brown or chocolate colour (not to a black). Acetate Bath (Brown Tones). Stock Solution. Sodium acetate ... ... ... 150 grs. Gold chloride ... ... ... ... ... ... 5 Water ... ... ... ... 40 ozs. Tone to a chestnut brown only. Short stop and fixing operations are the same as for sulphocyanide bath. 505 APPENDIX. Black Tones. Exquisite black purple, and blue-black tones can be obtained by using the following combinations of toning baths : — Tone the prints in platinum or acetate bath, as per above formulae, until they just begin to assume a chestnut brown ; then transfer at once to the combined toning and fixing bath, and tone to the desired colour. By the above process the acetate bath yields blue-black and purple tones. The platinum bath yields brown-black tones. Note. In all the above operations care must be taken to keep the prints moving in the various solutions. Caution. With the separate toning and fixing baths the greatest care must be taken not to allow any sodium hyposulphite to come in contact with the prints while in the toning. Washing. The prints can be most effectually washed after fixing by removing them from one dish to another, repeatedly changing the water. The process of washing should not exceed one hour. Drying. The prints can be dried by laying them upon blotting paper face upward, but must not be left between blotting paper ; or they may be suspended by one corner and allowed to dry spontaneously. Glazed surface. This may be obtained by squeegeeing the prints as soon as they are taken from the last washing water face downward on to a ferrotype plate, the surface of which has been previously polished with waxing solution as follows : — Spermaceti wax ... ... ... ... ... 120 grs. Benzine ... ... ... ... ... ... 20 ozs. ' Enamelled surface. For a highly enamelled surface a piece of plate glass must be used instead of the ferrotype plate. A little of the solution should be applied to the ferrotype or glass plate by means of a tuft of cotton wool, going over the whole surface and then polishing off thoroughly with a soft cloth. French chalk may be used instead of waxing solution for the glass plate, but it should be used in the same manner. The prints should be taken from the water and laid face downward on to the polished surface — or a better method is to float them on to the glass under water — a piece of American or india-rubber cloth being then placed on the prints. They should be squeegeed 506 t. PLATE-MAKERS FORMULAE. well into contact to expel all water and air bubbles. The plate should then be placed on end, and the print allowed to dry thoroughly, before any attempt is made to strip them. Matt surface. A dead matt surface can be obtained by using in place of the ferrotype or glass plate a piece of finely-ground glass or celluloid. Opalines. When making opalines, the alum bath previously mentioned for hardening the gelatine film should on no account be used, as it will prevent perfect adhesion. The combined bath is unsuitable for making opalines. Note. The hot gelatine bath should not be used for solio paper ; the prints will adhere perfectly if squeegeed on to the glass directly they are taken from the washing water. Burnishing. The temperature of the burnisher should not exceed 170° Should a bar burnisher be used the surface of the prints must be lubricated. This is best done by using a piece of ordinary Castile soap as follows : — The soap should be rubbed with a piece of flannel or cloth until it makes the cloth greasy ; the surface of the print is then rubbed over with the cloth. If, on the other hand, roller burnishers are used, it is not necessary to lubricate the prints. Mounting. The prints may be mounted with starch paste in the ordinary manner, but if it be desired to mount them with an enamelled surface, the prints should first be backed with backing paper, then brushed over with very thin, pure, well-filtered glue and placed in position on the mount. Any chemically pure paper will answer the purpose for backing prints. Note. When mounting a quantity of prints in the ordinary way it is usual to place them in a pile, after being taken from the water, one on the other, for the purpose of pasting the backs. It is not safe to do this with solio paper, unless the prints have been previously passed through an aluin bath before or after fixing. Nikko Paper. Oxalate Developer. No. 1. Oxalate of potash ... ... ... lib. Hot water ... ... 48 ozs. Acetic acid ... ... ... ... 3 drms. 507 APPENDIX. No. 2. Proto-sulphate of iron ... ... ... ... i lb. Hot water ... ... ... ... 32 ozs. Acetic acid (or citric acid, | oz.) \ drm. No. 3. Bromide potassium ... ... ... ... ... 1 oz. Water ... I quart. These solutions keep separately, but must be mixed only for immediate use. To develop, take in a suitable tray : No. Ij 6 ozs. ; No. 2, 1 oz. ; No. 3, \ drm. Mix in the order given ; use cold. After exposure, soak the paper in water until limp ; then immerse in the developer. The image should appear slowly, and should develop up strong, clear, and brilliant. When the shadows are sufficiently black pour off the developer and flood the print with the Clearing Solution. Acetic acid I drm. Water ... ... ... ... ... 32 ozs. Do not wash the print after pouring off the developer and before applying the clearing solution. Use a sufficient quantity to flow over the print, say 2 ozs. for an 8 in. by 10 in. Allow it to act for one minute, and then pour it off and apply a fresh portion ; repeat the operation a third time, then rinse in pure water and immerse for ten minutes in the Fixing Bath. Hyposulphite of soda 3 ozs. Water 16 „ After fixing, wash thoroughly for two hours and hang up to dry. Use fresh developer for each batch of prints. With a glass bottom tray 7 ozs. of developer are sufficient for a 25 in. by 30 in. print. No toning required. W T ith Eastman's Nikko paper the finest tones are obtained entirely by development, and range from a soft grey to a rich velvety black, depending somewhat upon the density of the negative and the quality of the light used in printing. 508 I. PLATE-MAKERS' FORMULAE. Clean dishes. — Clean hands. The faintest trace of hyposulphite of soda or of pyrogallic acid is fatal to good results with Nikko paper, and the operator cannot be too careful to avoid any con- tamination. The tray used for developing with oxalate should never be used for anything else. To avoid yellow prints four things are absolutely necessary. First, the developer must be acid ; second, the clearing solution must be used as directed ; third, fresh hypo solution is required for fixing each batch of prints ; fourth, the washing must be thorough after fixing. Mealy prints are caused by over-exposure, alkaline oxalate, or too little iron ; and are never the fault of the paper. Other developers — Metol, Amidol, Eikonogen, Hydrochinone, and Para-amidophenol — may all be used to develop Eastman's Nikko paper, formulee for the use of which accompany the chemicals. Platino-Bromide Paper. An argentic bromide paper giving platinum effect. Oxalate Developer. No. i. Potassium oxalate (neutral) ... Hot water No. 2. Ferrous sulphate ... ... i lb. Citric acid ... ... | oz. Hot water ... ... 32 ozs. No. 3. Potassium bromide ... ... ... ... ... 1 drm. Water 10 ozs. These solutions must be cooled and kept separately, and should be mixed only for immediate use. To develop. For normal exposures take in a suitable tray No. 1, 6 ozs. ; No. 2, 1 oz. ; No. 3, \ drm. (about 5 drops to the ounce of developer). These solutions should be employed as cool as possible, and mixed in the order named. After exposure, 5°9 1 lb. 48 ozs. APPENDIX. soak the paper in water until limp ; run off the water, and pour the developer rapidly and evenly over the sensitive surface. Use fresh developer for each batch of prints. With a glass-bottomed tray 8 ozs. of developer are sufficient for a 25 in. by 30 in. print. The bromide is added to the developer for the purpose of pro- ducing vigorous contrasts of light and shade, and of preserving the clear whites of the prints. When printing from a negative which is thin or flat, the proportion may be safely increased to twice that named above ; whereas in the case of a hard negative it may be reduced, or entirely omitted. The image should appear slowly, and should develop up strong, clear, and brilliant ; with a fine black tone. For delicate grey tones, like the India-ink washes of an artist's brush, it is requisite to expose to a well- diffused light, and to develop with a smaller quantity of iron and bromide solution in the developer. When the shadows are sufficiently black pour off the developer and flood the print with the Clearing Solution. Acetic acid 1 drm. Water 32 ozs. Instead of acetic, citric acid may be used in the clearing solution, in the proportion of | oz. to the quart of water. Citric acid has the advantage of being odourless. Do not wash the print after pouring off the developer and before applying the clearing solution. Purpose of clearing solution. The purpose of the clearing solution is to prevent the precipitation of the iron from the de- veloper into the fibre of the paper. This can only be done by keeping the paper acid while washing out the developer. Use a sufficient quantity to flow over the print, say 2 ozs. for an 8 in. by 10 in. Allow it to act for one minute, pour it off, and apply a fresh portion ; repeat the operation a third time, then rinse in four changes of pure water and immerse for ten minutes in the Fixing Bath. Sodium hyposulphite ... ... ... 4 ozs. Water 20 „ After fixing, wash thoroughly in several changes of water for two hours at least, and hang up to dry. 510 I. plate-makers' formulae. Alum bath. If it be desired to toughen the gelatine of the fixed print, the latter may be immersed in a saturated alum bath after removal from the fixing bath, care being taken to thoroughly rinse between the two operations. In all cases a thorough washing must complete the process. Blisters. In very warm weather, and in tropical climates generally, blisters sometimes appear in Platino-Bromide paper. These may usually be avoided by adding a little common salt to the first washing water used after fixing. Obstinate cases of blistering may be cured by adding a small quantity of ice to the solution in which they appear. The paper, too, should not be roughly handled, as the abrasion caused thereby induces blistering. Clean dishes. — Clea?i hands. The faintest trace of sodium hyposulphite or of pyrogallic acid is fatal to good results with Platino-Bromide paper, and the operator cannot be too careful to avoid contamination. The tray used for developing with oxalate should never be used for anything else. To avoid yellow prints four things are absolutely necessary. First, the developer must be acid; second, the clearing solution must be used as directed ; third, fresh hypo solution is required for fixing each batch of prints ; fourth, the washing after fixing must be thorough. Mealy prints are caused by over exposure, alkaline oxalate, or too little iron, and are never the fault of the paper. Othe? developers. Metol, Amidol, Eikonogen, Hydrochinone, and Para-amidophenol may all be used to develop Eastman's Platino-Bromide paper. Formulae for the use of these chemicals are provided with them. Of the above developers, Metol is specially recommended, as under : Water 80 ozs. Sodium sulphite ... ... 2 „ Metol 160 grs. Sodium carbonate ... \\ czs. Dissolve in the~order named. Develop in the usual way, but avoid removing the print from the bath until quite developed, as a repeated exposure to the air during development has a tendency to yellow it. No clearing solution is necessary as this de- veloper is used. For soft results new developer is recommended ; 5*i APPENDIX for greater contrasts old developer, or the addition of a few drops of a 10 per cent, potassium bromide solution. Toning. By following the above instructions the finished prints will show delicate grey or rich black tones, which can, if desired, be readily changed into sepia or black brown tones of equal permanence by making the prints somewhat darker and then toning the finished and dried picture in the following Sepia Toning Bath. Sodium hyposulphite... io ozs, Alum ... ... I oz. Boiling water 70 ozs. Dissolve the hypo in the water first, then add the alum slowly. When all is dissolved, the solution should be milk white. This solution should not be filtered, and it works better when it becomes a little old ; it may be strengthened from time to time with a little fresh solution. Never throw the bath away entirely, but replenish in the manner stated. The best results are obtained by keeping the bath hot, or as warm as the emulsion will stand ; say, no° to 120 0 F. In this bath prints will tone in from thirty to forty minutes. A new bath tends to reduce the prints rather more than an old one. When toned, the prints may be placed in a tepid solution of Water 70 ozs. Alum 2 „ Then wash thoroughly. Alum bath. When a toning bath is to be employed, the use of the alum bath after fixing is absolutely essential. Moreover, the prints should, in this case, not be subjected to a prolonged washing, but should only be slightly rinsed before being dried. Ilford Bromide Paper and Opals. The paper is made in four grades : S.S , smooth slow ; S.R., smooth rapid ; R.S., rough slow; R.R., rough rapid. The slow kind is suitable for both contact printing by artificial light and for enlargement for day- light. The rapid for enlargement by artificial light. The question of surface is one of taste only, though the rough is preferable for large work. 5*2 I. plate-makers' formulae. Exposure. For contact work on slow paper place paper in printing frame under negative in dark room. Expose for about twenty seconds at twelve inches from an ordinary fish-tail gas burner with a negative of average density. Rapid bromide is twenty times as sensitive. To obtain uniform results exposure must be made under uniform conditions as to light and distance. Development. Make the following solutions and use when cold : No. i. Neutral oxalate of potash Warm water ... Bromide of ammonium Filler. No- 2. Sulphate of iron ... ... ... I lb. av. Warm water ... ... ... ... ... ... 48 o^s. Sulphuric aeid ... ... ... ... ... ... 1 drm. Kilter. For use, add 1 oz. No. 2 to 6 oz. No. r, not vice versa. As for Alpha, old developer gives brilliancy, especially in cases of over exposure or weak negatives. Development is complete when image appears fully out. After development, and without washing, immerse the prints for about two minutes in clearing solution ; pour off, and repeat. Clearing Solution. Water So ozs. Sulphuric acid... ... ... ... ... ... .1 oz. Wash thoroughly for about ten minutes in several changes of water. All the acid must be removed, or fading of prints will result. Fixing Solution. Water ... 80 o/.s. Hyposulphite of soda ... ... ... ... ... 1 II). av. Allow fifteen minutes for thorough fixation. Use fresh solution for each batch of prints. After fixing wash for two hours in 513 L L I lb. av. 64 ozs. 20 grs. APPENDIX. running water, or in frequent changes. Allow prints to dry naturally. Work with clean hands and clean dishes. Printing-out Paper. Working instructions. — Printing. This should be done in shade, by preference, unless negatives are specially strong in contrast. The image loses very little depth in toning, etc. First washing. For fifteen minutes in several changes. Toning. For simplicity and excellence of results we recom" mend the following : — Water ... 16 ozs. Sulpho-cyanide of ammonium ... 30 grs. Chloride of gold 2 f , The prints tone in this bath in about six minutes, and it should be borne in mind that prints dry somewhat darker and much colder than they appear when wet. The bath should not be used many times ; indeed, it is well to make a stock sulpho-cyanide solution in bulk, and take as much of it as is needed, adding the gold as wanted. A bath with double quantity of water tends to warm tones. Second washing. For five minutes in several changes. Fixing. Use new solution for each batch of prints. The following is best strength : — Hypo, 3 ozs. ; water, 20 ozs. Fixation is complete in about ten minutes. Filial washing. For at least two hours in running water, or many changes. Drying. Lay the prints face upwards on the blotting paper (or hang up by clips) and allow to dry naturally. Mount with starch paste in usual way. Alum bath. If weather is hot, and the surface of prints becomes soft, immerse for ten minutes in alum bath (water, 20 ozs. ; alum, 2 oz.) after the first washing and before toning ; then wash for ten minutes before putting into toning bath. Special notes. Do not use any excess of sulpho-cyanide over quantity mentioned. Use the washing water and all solutions as cold as possible. Keep the prints moving whilst in the various solutions. Above remarks apply to both varieties of P.O.P. 5 T 4 t. plate-makers' formulae. Ilford Alpha Paper. Exposures. Place paper in printing frame under negative in dark room. Expose at six inches from ordinary fish-tail burner for two and a half to three minutes, with a negative of average density. To obtain uniform results exposures must be made under uniform conditions as to light and distance. Development op Alpha Paper. Make the following solutions, and do not use until cold : — No. I. Oxalate of potash (neutral) ... ... I lb. avoir. Bromide ammonium ... ... ... 320 grains. Warm water . . ... 64 oz. Filter. No. 2. Sulphate of iron ... ... ... ... 4^ ounces avoir. Sulphuric acid ... ... ... ... 1 drachm Water ... 80 ounces. Filter. For use add 1 part of No. 2 to 3 parts of No. 1 , not vice versa. It will be noticed that the developer is weak and much restrained, a more vigorous formula is unsuitable. The prints can be soaked in water, if desired, but it is not essential, the only object being to secure an even flow of developer over surface. Development is complete when image appears fully out. At this stage a . correctly exposed print will be of a warm brown colour, with a peach bloom over the whole surface. Over-exposures are indicated by a yellowish red colour, and under-exposures by a greenish black. The paper gives wide latitude, and unless the error in exposure is very great, perfect prints are produced by judicious toning (see special pamphlet, free on application). Old developer, freshened with a proportion of new, just before use, gives the best results. This is best kept in a bottle filled up to the stopper, replenished from time to time as required, with the two solutions freshly mixed. After development, and without washing, immerse for about half-a-minute in clearing solution, pour off, and repeat. 5"5 Appendix. Clearing Solution. Water, 80 oz. Sulphuric Acid, ^ oz. This has a reducing action on Alpha prints, therefore do not allow them to stay in the bath longer than time given, unless it is desired to correct over-development. Wash thoroughly for eight to ten minutes, in several changes of water ; all the acid must be removed, or yellowness of whites will result. Prints are now ready for toning and fixing, which can be done by gas or subdued daylight. Combined Toning and Fixing Bath. Water 10 ounces. Hyposulphite of soda ... ... ... 2^ ounces "j Acetate of soda ... ... ... jounce J- Avoirdupois. Sulphocyanide of ammonium ... ... £ ounce J Chloride of gold ... ... ... 4 grains. This bath should be made forty. eight hours before use and allowed to clear ; it keeps good for months in the dark, and may be used over and over again if replenished from time to time with a few drams of a stock solution made up as above, with 5 of water only and double quantity of gold. The constituents of the bath must be added and dissolved in the order given. When first put into the combined bath, the prints turn yellow and lose all their vigour, but gradually regain both colour and strength, and toning is complete in about a quarter of an hour. Prints dry darker in tone, more vigorous in image, and with more detail than they appear when wet. After toning wash for two hours in running water, or in frequent changes. Allow the prints to dry naturally, or they can be squeegeed down whilst wet on talced glass, matt or polished, or clean ferrotype plates, to produce matt, or enamelled surface, as may be desired. Work with plenty of Yellow Light. Work with clean hands and dishes. Keep prints constantly moving in all the solutions. Ilford P.O.P. Printing. This should be done in shade by preference, unless negatives are specially strong in contrast. The image loses very littl depth in toning, etc. First washing. For fifteen minutes in several changes. 516 I. PLATE-MAKERS FORMULAS. Toning, Any of the recognised formulae for this class of paper may be used, either simple toning or combined toning and fixing; but for simplicity and excellence of results we recommend the following: — Water, 16 oz. ; sulphocyanide of ammonium, 30 grains; chloride of gold, 2 grains. The prints tone in this bath in about six minutes, and should be withdrawn when there is just a trace of warmth in the heaviest shadows on looking through the prints. On the surface they will appear overtoiled, but this will alter in the fixing bath. This toning bath ca?i be used at once, but preferably should stand for twenty- four hours before use. When it becomes dirty or refuses to tone properly, a new one should be made. Second washing. For five minutes in several changes. Fixing. Use new solution for each batch of prints. The following is best strength : — Hypo, 3 oz. ; water, 20 oz. Fixation is complete in about ten minutes. Final washing. For at least two hours in running water, or many changes. Drying. Lay the prints face upwards on the blotting paper (or hang up by clips), and allow to dry naturally. Mount with starch paste in usual way. Prints thus treated and passed through roll give a fine glossy surface, better than albumen. This paper can also give prints of enamelled or matt surface by squeegeeing down on plain or ground glass in the usual way. Alum bath. If weather is hot, and the surface of prints becomes soft, immerse for ten minutes in alum bath (water, 20 oz. ; alum, 2 oz.), after the first washing and before toning, then wash for ten minutes before putting into toning bath. SPECIAL NOTES. — Do not use any excess of sulphocyanide 07/er quantity mentioned. Use the washing water and all solutions as cold as possible. Keep the prints moving whilst in the various solutions. Imperial Bromide Paper. Smooth or rough surface for contact printing or enlargements. The exposure required for Imperial bromide paper will be found to be the same as for slow 517 APPENDIX. opals, and according to the developer used. The developing formulae I and J are recommended for rapidity and cleanliness in working. Negatives with strong contrasts should be printed in a strong light, weak negatives in a subdued one. The treatment of bromide paper in development is very similar to the treat- ment of bromide opals. In drying, however, the prints should be placed face upwards on clean blotting paper, or hung up with paper clips. Imperial " Kloro " Paper. With appropriate treatment " Kloro " paper gives superb definition ; does not curl. Instructions. Prints must be only slightly darker than required when toned and fixed. Hard and fairly dense negatives should be printed from in a strong light ; weak and delicate negatives in the shade and through tissue paper. After printing, wash for ten minutes in running water, and immerse in an alum bath. Alum ... ... ... ... ... \ oz. Water ... ... ... ... ... 20 ozs. Leave for ten minutes, and wash again in running water for five minutes. Toning. Any toning formula may be used, but the finest results are obtained with Sulpho-cyanide of ammonium 15 grs. Chloride of gold I gr. Water 8 ozs. This bath gives beautiful purple tones. Can be used at once, but will not keep. When toned sufficiently place in a bath composed of Common salt 1 oz. Water 20 ozs. to prevent further toning. Well wash the prints in running water and fix in Soda hyposulphite Soda sulphite ... Water N.B. — Do not use the same fixing bath twice. 51S 3 ozs. H „ 20 „ I. plate-makers' formulae. After fixing, wash the prints for one hour in running water. The alum bath must be always used with a sulpho-cyanide toning bath, and also in hot weather with any other bath. Acetate Bath (Brown Tones). 'Soda acetate 150 grs. Chloride of gold 5 „ Water 40 ozs. This bath keeps, and should tone equal to four or five full sheets of paper before it is necessary to strengthen it by the addition of more chloride of gold. The bath is ready for use twenty-four hours after being prepared. Special care must be taken that not the slightest trace of hypo comes into contact with the prints, toning bath, or washing solutions, at any time prior to fixing. Finishing. If a glossy surface is required, dry on glass pre- viously prepared with French chalk. If a matt surface is required, dry on fine ground glass previously prepared with French chalk. If the appearance of a silver print is desired, dry face upwards on blotting paper and mount with starch paste. If to be burnished the alum bath musthz used, and the burnisher is not to be heated to more than 160 0 . Enamelled prints should be backed with waterproof paper before being detached from the glass plate. Lumiere's " Citos " P.O.P. Citrate of Silver Printing-out Paper (mauve). The printing of the positives is the same as with albumenised paper. All the methods of toning may be made use of with these papers, but the following formula? are recommended : — Combined Toning and Fixing. A. Hot water ... ... 17^ ozs. or 1,000 parts. Hyposulphite of soda ... ... 7 ,, ,, 400 ,, Citric acid ... ... ... ... 15 grs. ,, 2 ,, Ordinary alum ... ... ... 155 ,, ,, 20 ,, Acetate of lead 15 „ „ 2 ,, B. Water... ... ... ... .. 3.^ ozs. or 100 parts. Chloride of gold ... ... ... 15 grs. ,, I part. Let solution A remain standing for several hours, then filter 5'9 APPENDIX. carefully. To prepare the normal bath add to 100 parts of A 6 to 8 parts of B. The prints may be immersed directly into this solution, but by previous washing more vigorous tones may be obtained, and the bath will retain its qualities for longer. In the latter case a small quantity of alum (i to 2 per cent.) should be added to the first water. Toning and Fixing Separately. Toning. Hot water, 120 0 to 140 0 F. ... 17^ ozs. or 1,000 parts. Precipitated chalk ... ... ... 35 grs. ,, 5 „ Chloride of gold ( I per cent, solution) if ozs. „ 100 „ This solution should be prepared twenty-four hours beforehand ; it constitutes a "reserve bath," which will keep for a long time. To prepare the final toning, take 100 parts of water and 15 parts of this solution. The prints should be first immersed in an alum bath (1 percent, of ordinary alum), then washed in several waters. It is necessary to use both the alum bath and the ordinary water bath abundantly. The toning is then done as in the case of albumenised paper ; the prints change from red to a brown-purple after twelve to fifteen minutes. This tone obtained, they are fixed in Water Hyposulphite of soda Bisulphite of soda Ordinary alum Nitrate of lead (1 per cent, solution) 17^ ozs. or 1,000 parts. *t „ „ 150 „ 45 g rs - v 6 30 „ „ 4 M 115 m „ 15 »» Dissolve these ingredients successively in the order named. On being put into the fixing bath the prints become a yellowish-red, but they rapidly change to reddish-brown and to blue. The bath is stopped as soon as the desired tone is obtained. The fixing bath should be often renewed. The diluted toning bath can be used for a long time on the condition that it is strengthened with the " reserve solution," and filtered through a little chalk when the toning is finished. 520 I. plate-makers' formula. Platinum Toning. Water ... ... ... ... ... 500 parts or 16 ozs. Sodium chloride (salt) 2 ,, ,,30 g rs - Alum 5 „ 75 „ Potassium Chloro-Platinite I part „ 15 Leave the prints in this toning bath until a black tone is obtained, then wash in several waters, and fix them in the combined fixing and toning bath. Images treated in this way and dried, after washing, on ground glass have the aspect of the most beautiful platinum paper, and a delicacy of tone which the latter process cannot give. General observations. Solutions should always be perfectly clear. During toning the prints should be kept constantly on the move. Great cleanliness is necessary in the handling of this paper. Yellow stains, which might appear during and after toning, are only stains of hyposulphite, produced by contact with the fingers or with uncleaned dishes. Care should be taken to remove air-bubbles in case they form on the surface of the paper ; for, even after the first washing, the little red stains which might appear after the toning, are simply due to these bubbles. Sulphur stains are never produced when the final washing is abundant and not too prolonged ; thus it is advisable to wash the prints for only three or four hours, and in water changed frequently. Hang up till completely dry, when they can be cut to the necessary dimensions. The mounting with starch is done in the same way as for prints on albumenised paper. They can be burnished hot or cold, the same as albu- menised paper. In any case, when burnished hot, it is important that the prints should be completely dry. Brilliant surface. Prints presenting a very brilliant surface may be obtained by transferring on to perfectly clean glass, rubbed with a solution of beeswax in benzine. Matt effects. Fine matt effects may be obtained by transferring on to waxed ground glass, with the customary precautions for these transfers. The papers should be protected from light and from dampness. 5*« APPENDIX. Morgan & Kidd's Argentic G-elatino-Bromide Paper. Developing Solutions. No. I. Oxalate Solution. No. 2. Iron Solution. Potash, neutral oxalate... l6ozs. Iron sulphate (pure) ... 15 ozs. Citric acid I drm. Citric acid I drm. Hot water 50 ozs. Hot water 30 ozs. No. 3. Bromide Solution. Bromide of potassium ... ... I oz. Water ... ... ... 20 ozs. After exposure, soak the exposed paper in the water while mixing the developer. For normal developer take 6 ozs. No. I, add 1 oz. No. 2 and 6 drops No. 3, to be mixed in order given and immediately before using. When fully developed, rinse the print with a clearing solution of 1 oz. of acetic acid to 6 pints of water, immediately the developer is thrown off and before washing with water. The clearing solution may be used over again until it becomes discoloured. After well washing, immerse for about fifteen minutes in the fixing solution : Hyposulphite of soda... ... ... ... ... 6 ozs. Water 40 Wash for several hours in changing water, clip up to laths, and hang to dry. Opal and canvas enlargements. The same formula is used for enlargements on opal or canvas. Paget Prize Collodio -Chloride Printing-out Paper (pink, white, or mauve). Printing should be somewhat darker than the finished print is required ; about the same as for the P.O.P., not quite so dark as for albumen. Was/ring. Before immersion in this toning bath the prints should be very thoroughly washed for at least five minutes in running water, or in three or four changes. If the dry prints are first laid face downward in a dish of hot water, as warm as the hand can bear, for about a minute, and afterwards in two changes of cold water, the washing will be much more effective, will overcome any tendency to curl, and the toning will be more satisfactory. 522 I. plate-makers' formutje. Salting. After washing, it is advisable to place the prints for about one minute in a solution of common salt, strength un- important, say I oz. to a pint of water. This removes any last trace of silver and reddens the print, so that the progress of toning can be more easily judged. After salting, wash for about five minutes before toning. Toning. Any of the ordinary toning baths employed for albumen or gelatine may be used, but no bath gives such rich brilliant tones, either warm or cold, as the sulphocyanide. If a little care be taken to ensure clean dishes and clean fingers, there is no bath more simple or certain. Sulphocyanide of ammonia ... ... 30 grs. Gold chloride 2 „ 1 Water .. ... 16 ozs. Tone to exactly the colour desired, judging the prints as they lie in the dish, but it should be borne in mind that the finished image will be slightly bluer and stronger when dry than in the wet state. Wash and fix in Hyposulphite of soda ... 3 ozs. Water I pint. Allow at least ten minutes for fixing. Wash thoroughly in running water for at least an hour. The prints may then be dried between blotting paper, or quickly in a moderate heat. They may be mounted in the ordinary way with starch, and afterwards rolled, burnished, or enamelled, in fact treated in exactly the same manner as albumenised paper. Paget Prize Printing-out Papers (ordinary, or matt surface). Printing should be somewhat darker than the finished print is required. It should be borne in mind when toning that the finished image will be bluer and slightly stronger when dry than in the wet state. Toning. Either of the following well-known baths answers admirably : Combined Toning and Fixing Bath. No. 1 Stock. Hyposulphite of soda... Alum (potash alum only) Sodium sulphate (not sulphite) Water to 20 ozs. 5 u 14 » I gal. 5 2 3 APPENDIX. Dissolve the hypo and alum each in about one quart of hot water, mix, and then add sodium sulphate already dissolved, making up to one gallon with remainder of water. This mixture should then be left for some hours for the precipitate to settle, when the clear solution may be poured off or filtered, and is then ready for use. It will keep indefinitely. No. 2 Stock. Gold chloride ... .. ... ... ... ... 15 grs. Acetate of lead ... ... ... ... 64 „ Water (distilled) ... 8 ozs. Dissolve the acetate of lead in the water and add the gold. A heavy precipitate forms in this solution, which should be shaken up when any is to be poured out ; it redissolves when added to No. 1 stock solution. For use : Mix 8 ozs. of No. 1 with I oz. of No. 2. When this bath is used the plates should not be washed before toning. Separate Toning Bath. Sulphocyanide of ammonia ... ... ... ... 30 grs. Gold chloride ... ... ... ... i\ ,, Water ... ... ... ... ... ... ... 16 ozs. Before immersion in this toning bath the plates should be very thoroughly washed for at least fifteen minutes in running water. This is necessary to insure even toning. In hot weather, if necessary, the print may be soaked in alum (alum, 4 ozs. ; water, 20 ozs.) for five minutes before toning in this bath. Another thorough washing is necessary between the alum and toning baths. Fixing Bath. Hyposulphite of soda... ... ... ... ... 3 ozs. Water 1 pint. After fixing, wash well. A highly glazed surface can be obtained by squeegeeing a print (on the ordinary paper) when wet on to a sheet of clean glass, previously rubbed over with French chalk ; but care must be taken that the French chalk is well rubbed off. Burnishing may be done in the same manner as with albumen prints, but if a bar burnisher be used the bar should not be much hotter than the hand can bear to touch. t. plate-makers' formula. Rapid Printing on Paget Prize Printing-out Paper by Partial Development. A piece of this paper exposed behind a negative in the ordinary way by daylight need not be fully printed, but may be removed from the frame when only partially printed, developed up to the necessary strength and detail, and then toned and fixed in the usual manner, with exactly the same results as if the picture had been fully printed. Time of exposure. A very slight and feeble image may be developed up to full strength, but it is not advisable to do this, as such extreme forcing may impair the purity of the whites. It is recommended that not less than one-tenth of the full printing time be given, and beyond this it does not matter how much longer the printing be carried on ; it may be stopped at any time short of full printing. Of course the longer the printing the less the development required. Development. Take the partially-printed picture from the frame and immerse, without washing, in a solution of Potassium bromide ... ... I oz. Water ... 10 ozs. and leave it for at least two minutes. The image will become yellow in colour and look weaker in this bath. Now wash the print in running water for at least three minutes, then develop it in a developer composed of equal parts of the three following stock solutions : Solution i . Hydroquinonc Sulphurous acid Sodium sulphite Potassium bromide Water to Solution 2. Solution 3. Caustic soda Jo/.. Bromide of ammonium ... 10/.. Sodium sulphite V „ Carbonate of ammonium 1 ,, Water to 25 ozs. Distilled water to 25 ozs Carbonate of ammonium should be in clear lumps; if from exposure to the air it has become coated with the white powdery 5 2 5 oz. f 1 1 1 •J H 60 grs. 25 ozs. APPENDIX. bicarbonate the latter should be scraped off. If Solution 3 be made with ordinary water, it will be cloudy from precipitation of the lime in the water. This must be filtered out, or left to settle, and the clear solution poured off ; otherwise the lime may cause spots. Solutions 1 and 2 are also improved by filtering or settling ; as undissolved particles of any kind are likely to cause spots. More of No. 2, up to double the quantity, may be used with the effect of quickening development ; but we prefer work- ing more slowly. The time of development will vary somewhat according to exposure given, etc., but for a short exposure it will average from three to five minutes Development must not be carried too far, as the image gains greatly in strength in the toning ; develop until nearly all the picture is visible, but not the very fine or faint details ; these will appear afterwards in the toning. When sufficiently developed wash at once and thoroughly in running water for at least five minutes. If the print be not quickly washed so as to get rid of any developer left in the paper, development may be found to have gone on too far during the washing. The print is now in the same condition as if it had been fully printed out in the ordinary way and washed (except that its colour is different, and it looks much too weak), and it may be at once placed in either the sulphocyanide or the combined toning bath, toned, fixed, and treated as usual. Light. All the above described operations up to toning may be conducted in the ordinary light of a printing-room ; that is to say, in daylight which has passed through yellow glass or a yellow blind, or in gaslight or lamplight. 526 II. TABLES. THE following useful tables lor calculating the time of exposure, according to A. de la Baume Pluvinel, appeared in a recent number of Nenheiten, a monthly periodical issued by Robert Talbot, of Berlin : — For the time of exposure, /, of a photographic plate applies approximately the well-known and easily-proved formula — ( Focus ) ■ t = constant X \ — - . ,. . \ ( Diameter of diaphragm ) in which the constant receives certain values, first empirically determined by Dorval. In this formula are now, however, as one perceives at first sight, several important factors totally dis- regarded, and it may be therefore desirable, on the ground of the laws of mathematical optics, and with the aid of certain necessary assumptions, to submit the problem to a deeper investigation, and to strive to bring its solution into better harmony with the physical facts. In a meritorious brochure ('' Lc Temps de Pose," Paris, 1890, Gauthier Villars), issued recently, the French investigator, De la Baume Pluvinel, made the attempt to determine a formula applicable to any possible case, according to which " the time of exposure " — indeed, any time can be reckoned which will be required to expose a photographic plate, actually an ortho- chromatic — so that a correct printing negative will be finally obtained. If actually La Baume Pluvinel's theory and tables of resultant times of exposure have only an illusory precision — which is to be expected from the impossibility of aa urate 5 2 7 APPENDIX. measurement of the different constants which arise — still I think that it will be welcome to the reader to be made acquainted with the results of this theory, without needing to follow the long mathematical calculations of the author, and therefore I briefly recapitulate the principal results and empirical data of La Baume Pluvinel. However, before the general final formula for the time-exposure is given, the units of the factors appearing in it should be ex- plained, or their mathematical expressions be given. An important factor is the amount — log Ajcos'a, - log A 2 cos' , rt 2 4.0m A 1 cos' , « 1 - A 2 cos 4 « 2 X pv (1 — e~ mi ) This is briefly designated In which e represents the thick- ness of the gelatino-bromide of silver film ; m, its absorptive coefficient ; v, the absorptive coefficient of the film saturated with reduced silver ; a x and a> the angle which the secondary axes of the different illuminated elements of the object form with the principal axis of the objective ; A, and A 2 , the corresponding actinic active quality of light (reckoned for units of time, surface, and distance). One can now actually, for any single case, approximately reckon the value of -~ , with the help of certain assumptions, and on the basis of actinometrical and other measurements. Still, this would be impracticable for practical work ; it is thus better to estimate ~ in a purely experimental way for special requirements, and the different cases which occur in practice, from this to reduce (see the table of the value of -g- below). This also applies to the amount J, which represents the actinic intensity of the illuminating beam of light, and for which one finds a table below. For the desired time of exposure, /, results now, according to La Baume Pluvinel's theory — ■ i JJ J In which F represents the equivalent focus of the objective ; 5^8 II. TABLES. I), the distance of the object from the lens, measured along the principal axis ; d, the working aperture of the lens — with doublets d = p^ry where P is the equivalent focus of the front lens, d' the diameter of the diaphragm, / the distance of the centre of the diaphragm from the optical centre of the front lens ; N, the number of degrees of Warnerke's sensitometer which the plate used shows. N, with the most sensitive plates, = 25, and varies usually between 16 and 23. The co-efficient r ±* with landscape is about 1, because t D I then D is great ; on the other hand, it comes considerably into account in enlargements, since then D is only small. In the 1 above, it must be noticed that the absorption, as well as the reflection of the lenses of the objective, is not calculated. The same has a mean result of loss of light of about 20 per cent. Value of Clouds ... ... ... . . 00005 Sea .. OOOI Snow OOOI Ships on sea .. 0 003 Glaciers with rocks .. 0 003 Open landscape (panorama) .. 0003 Foliage, with water or white houses... .. 0005 Foliage only, and near .. o-oi Living subjects, portraits, still life, etc. .. O'OI Reproduction of black lines on white ground 002 Value of _L According to Eder, Abney, and VOGEL. Direct upright sunlight ; for Paris, June 21st, noon also if the sun stands 66° above the horizon .. I Diffused light, bright weather , 4 ,, „ sky covered , . 4 to 10 Under trees 270 In the studio 12 In a room, 1 metre from window , 7o Well-lighted church ... , 200 5 2 9 M M APPENDIX. Afternoon. ooooooooc ro ro ro ro ro ro ro ro o l>. r^vD VO totort-^rorocvi M *i M ri £ 1 w z o ro to O ro to > — > to rooo vO i^roN m « ro w ro to D > > < ro to . . to to r^vp Tj- co N « « : lu-iNOroNNwwMwJ-ii-M-Hi- to M H en to • • v* t*" w r* j - * ro to 0 0 j 5 O CO to . . . MvO^tMNNn to « u PQ S3 < to . . . to toOO *~^vp ^ rf- fl fl N : : : o tooo \o^«m«m«hmmh ro >-i O to Septe ICH. ro to . . . . op r^vD to >o ^t- ro~ 05 w N < s to mmoo n r-»vo vo to o H o O JARY. LO . . . . . to to 00 00 00 00 : : : : :o^«\0'troNN>-HHM ro w «-> to pi w » Febri to to IO to to ro m w O rO to w > o S3 ARY. rp lO y>y^ t^M M to w n s Janu lO to to : : : : : : : : o to o to ro ro ro « hi ro i to w o u Q Coooooooog 3 rororofOrofOrOfOO ^ ^ to tovD vo t-^ r^.00 00C\6oOhh'^ Morning. 530 II. TABLES. ha w .-OOOOOOOO-'I 5 ro fO ro CO ro rO rO rO g ON N t>.\© O 4 * fi N h n o j 5 CO Nl^fON H N N H M M - n inop v° ^ r 1 lOrON H N H - » H . in r^o w — o CD . . . N ifl 3n -t i/Tt rl N . . . . rO 0<3 vp u~> rf N N : : : : ^Ion h k i- « m n u-100 I-^sO 10 rf N N — — tSfOfON MMHMMMMMM u-)>o r-O ;<-i yo -f- rf -1- n - M N jn go t^vO vp j ^ I ^ ^ flrOM - - - - n h , ^ jr . . . u-> lo Cnqo 1^ JJ 1 ! : . . . .10 in Gs^p M QO r*i ^ i-OOOOOOOOc 9 ro ro f> t*) ro ro ro g (J* m m m m ^ 53 APPENDIX. The formula determined for t can approximately be written as follows : — , T i F 2 For this the values of L, according to Dorval, are : — - Sunlight. Diffused Light. Cloudy Day. Morning'. Day. Morning and Evening. Panorama and sea views ... 5 _ Totf 0 TVS f _ i on tvv Panorama with large masses of foliage ... 1 1 00 2 TVV TVV T^ 0 loo View with bright foreground or white buildings T¥7> TVV Ttfo 4 ToTT View with dark foreground or dark buildings... 1 5 \ o oTf n 1 -iV Tto e 9 1 1) 0 Under trees, shady river banks, ravines, etc. 1 2 TIT IT 2 l ? '3 To Living objects, groups, por- V traits, etc., in the open air 4 1 0 (7 TITO" 1 2 10 0 TJF The same, very near a win- dow or under a roof . . 4 1UTT 8 TVV TifV 24 Reproductions, enlargements of photographs, engrav- ings, etc. ... 3 10U r. nnr c TVV _2_5_ Day," in Summer, from 9 to 4; in Winter, from 11 to 2. Holetschek's Tables calculated for Vienna latitude. Chemical Intensity of the Light from a Blue Sky. Noon. na.m. 10a.m. 9 a.m. 8 a.m. 7 a.m. 6 a m. 5 a.m. 4 a.m. Jan. 21st ... 26-53 25'53 22*30 16*42 7'4i Eeb. 20th ... 32*22 3i-43 28-93 24-14 16-31 5*i3 March 20th . 36-23 35'77 34'io 30-65 24-64 1532 2*78 April 21st ... 38"07 37'9o 37-13 35-12 3o'99 2414 14*18 'i' : 6 4 May 22nd ... 38-30 38-29 38-02 36-85 33 98 28-66 20*62 10*23 June 21st ... 38-27 38-30 38-18 37'27 34*77 30-06 22*75 13*14 2 07 July 21st ... 38-30 38-29 38 02 36-85 33 98 28 66 20*62 10*23 Aug. 21st ... 38-07 37-90 37-13 35*12 3o'99 24*14 14*18 1*64 Sept. 23rd... 36-23 35*77 34*io 30-65 24-64 15*32 2*78 Oct. 21st ... 32*22 3i'43 28-93 24-14 16-31 5*i3 Nov. 21st ... 26-53 25*53 22 30 1642 7-41 Dec. 21st ... 22-63 22*57 19-14 12 90 3-48 1 Noon. 1 p.m. 2 pm. 3 P-m. 4 p.m. 5 p.m. 6 p.m. 7 p.m. 8 p.m. 53 2 I. TABLES Chemical Intensity of Direct Sunlight. Noon. 11 a.m. 10a.m. 9 a.m. 8 a.m. -■ 7 a.m. 6 a.m. 5 a.m. . 10 97 _ o'8o 29-81 20'OQ 827 0*76 ia'a" 57 '64 .... r 9*18 0 47 9329 88-17 73*5* 51-96 27-87 8-27 0*25 ni-77 106-65 9I-85 69-52 43-65 19-24 3'5o O'Ol 1 17*44 1 12*30 97-77 75 '62 49-26 24-11 6-o6 O'l 2 111*77 106*65 91'85 69-52 43-65 19-24 3 '50 O'OI 93 "29 88-17 73-5I 51-96 27-87 8-27 0*25 62-25 57"64 44-45 26-44 9 -i8 0-47 33 '54 29-81 20 - CK) 8-27 0*76 F3'27 10-97 5*44 o*8o 7-40 5-8i 2'24 0*10 Noon. 1 p.m. 2 p.m. 3 p.m. 4 p.m. 5 p.m. 6 p.m. 7 p.m. Jan. 2 1 st . Feb. joth .. March 20th April 21st.. May 22nd . June 22nd July 21st .. AU£. 2ISt ., Sept. 23rd Oct. 21st .. Nov. 2ISt ... Dec. 21st .., Combined Power of Blue Sky and Sunlight. Noon. 11 a.m. 10a.n1 9 a.m. 8 a.m. 7 ajn. 6 a.m. 5 a.m. 4 a.m. Jan. 21st ... 39-80 36*50 27*74 ',-22 7-41 Keb. 20th ... 65-76 61*24 49*02 32*41 17*07 5''3 March 20th . 98-48 93'4i 78*55 57-09 33-82 I5-79 '2*78 April 21st ... i3'\36 126*07 110*64 87-08 56-86 32*41 14*43 ',"•64 May 22nd . . 150*00 144*94 129*87 106 37 77-63 47-90 24*02 19*23 June 21st ... I55-70 150*66 I35-94 112*89 84-03 54-17 28*21 13-26 2*07 July 21st ... 150*07 144*94 129*87 106*37 77-6.3 4790 24*12 10*23 Aup. 21st ... 131-36 126*07 110*64 87*08 56*86 32*41 14*43 i*6 4 Sept. 23rd ... 98*48 93"4i 78 55 57-o9 33-82 15-79 278 Oct. 21st ... 65-76 61*24 49 *02 3241 17*07 5-i3 Nov. 21st ... 39-8o 36*50 27*74 17*22 7'4Ji Dec. 21 st ... 3i'03 28*38 21-38 13*00 3-48 Noon. 1 p.m. 3 p.m. 3 P-m. 4 p.m. 5 p.m. 6 p.m. 7 p.m. 8 p.m. Miethe's Table of Fixed Foci. Distance of nearest object in focus expressed in units Aperture. of the focal length. F/4 87 ... 70 Example F/5 • F/6 . F/7 • F/io F/12 F/15 F/20 F/30 To working at F/lO. ... 58 ... 50 ••• 35 ... 29 ... 23 ... 17*5 ... ii*6 find the nearest point in locus with a 5-111. lens 5 x 35 = 175 ins. = 14 ft. 7 ins. 533 APPENDIX. •«-o 4-. U5 ^50 e»|» o 1 o ; 2J.O 1° S3 3 o O on .£ O 8 8 „ § CO c s y ■3 J ft «J £ a! CO 6 n h>3 5 "2 Oh u O tin O O ! o I? o 0" u o o" 534 II. TABLES. Piatt's Tables. Table I. — Subject and Light. „ .. .. , . . , - o in p i ic el tinci sii^xitly 3.itGrGQ irom Eder's and Burton's Tables. Sun shine. JL/ III UoCU Light. Dull. v DulL Gloom. Sea and Sky j Panoramic View 2 3 4 s Do. with Thick Foliage, or Strong Foreground, or Light Buildings 2 4 6 8 10 Dark Buildings 3 6 9 12 15 Heavy Foliage Foreground ... 4 8 12 16 20 Woods and badly lit River Banks ,. ... IO 20 3° 40 50 Living Objects Outdoors 4 8 12 20 30 Portrait near Window 8 16 24 40 bo Interiors upwards of IOO 12 20 Copying same Size 6 Table II.— Time (Dr. J. A. Scott). Hour of Day. a.m. p.m. June. May. July. April. Aug. March. Sept. Feb. Oct. Jan. Nov. Dec. 12 2 31 4 1 1 1 I* I| 2. j 4 5 IO 2 it IT 3 5 6 9 3 2 4 16 8 4 2 3 10 7 5 2 3 6 6 6 2-J 3 6 Yellow Sunset affects these figui 5 7 5 6 es. 4 S 12 535 APPENDIX. Spitaler's Table of the Chemical Intensity of the Light for every ten degrees of latitude, for the northern hemisphere, and the middle of each month. This may be used for the southern hemisphere by altering the time of year ; thus, January in the place of July, etc. Latitude. o° IO° 20° 30 0 40 0 5o° 6o° 7o 0 8o° 90° January 408 332 2SO 161 80 22 1 February 437 385 315 232 146 68 March 45i 433 391 329 251 166 84 23 April 433 451 445 414 361 288 203 113 3 1 May 396 442 465 464 438 388 3i5 212 195 203 June 373 430 467 481 469 432 367 280 3 I 3 324 July 384 432 465 47i 452 408 34o 222 250 259 August 418 446 45i 43i 388 323 242 150 69 72 September 444 438 408 356 286 204 119 45 5 October 441 399 338 261 176 94 30 2 November 415 348 266 178 96 32 2 December 397 319 231 142 64 14 Mean of the Year ... 416 405 374 327 267 203 1 146 87 ! 72 74 Tables for the Simplification of Emulsion Calculations. {Brit. Joum. Phot. Almanac?) With a view of simplifying the calculations involved in emulsion making, Mr. William Ackland has worked out some useful tables, which will enable even those most ignorant of chemical philo- sophy to calculate with ease and rapidity the proper quantities of silver or haloid salts in any formula. Even those who are able to perform the calculations in the recognised style will find their labours materially lightened by means of these tables, which should be kept in a convenient place for reference in every laboratory. 536 II. TABLES. No. I. Ammonium bromide Potassium Sodium Cadmium com, anh Zinc ,, Ammonium chloride Sodium ,, Ammonium iodide Potassium Sodium ,, Cadmium ,, Weight Weight Weight Weight I Weight of silver of soluble of silver AgN0 3 soluble haloid haloid haloid Equiva- required haloid pro- required pro- lent to con- required duced to pro- duced weights. vert one to con- by one duce one from grain of vert one grain of grain of one soluble grain soluble silver grain haloid. AgN0 3 . haloid. haloid. AgNOa. 98 1*734 •576 1-918 •521 \ 119-1 1-427 ■7OO 1-578 •633 103 1-650 •606 1-825 •548 - 1*106 172 •988 I OI2 1-093 •915 136 i-25 •800 1*382 ■723 j j 1 2 ' 1 1 '509 •663 1*670 *6oo ; 53'S 3**77 •315 2-682 •373 j } -844 58-5 2-906 •344 2*453 •408 j 145 1*172 •»S3 1*620 •617 ! 166-1 1*023 "977 1*415 ■707 | 1 - '150 i*i33 •882 1-566 •638 1 183 •929 1*076 1*284 •778 The principal bromides, chlorides, and iodides which are likely to be used in emulsions of either gelatine or collodion have been included in these tables. Table No. 1 presents to the reader, without any mystification which may be involved in equivalents, the actual weights of haloid or silver, as the case may be, required to convert or combine with one grain of the other. In order to test the utility of this table, let us suppose that it is desired to make (say) ioozs. of emulsion by a new formula, which, for the sake of showing the working of the table, we will write down as follow- : Bromide of potassium 1 50 grains. Chloride of ammonium 10 grains. Iodide of potassium 10 ,, Gelatine ... ... 200 ,, Now, we want to know how much silver nitrate should be em- ployed in sensitising this mixture. For this purpose we use the first column, in which we find against each haloid the exact quantity of silver nitrate required to fully decompose one grain. Taking, then, the figures we find in column No. 1 against the three salts in the above formula, and multiplying them by the number of grains of each used, we have the following sum : — Potassium bromide 150x1427 = 214 j Weight „ iodide 10 X 1*023 = 10*23 > silver nitrate Chloride of ammonium 10x3-177= 31*77 / required; or the total quantity of silver nitrate required for full conversion, 256 grains. 537 APPENDIX. •apipoi umimpe3 •apipoj mnipog •apipoi utnissBjoj •apxpoj uintuouiiuv uimpoc, ro •>*■ *0 ct) ro on 2 * g 5- ? M M M uiniuotumv •aptuicug 3UJZ (•p.Cijuv) •apiuicug uiniuipB3 (•11103) •apiuicug uiniutpB^ 'apimcug umipog •apiuiojg •aptmcug uiruiiouiuiy VO 1- N < 538 1- e ci.5 «- u ;H S § e 2 s If 8*6?* 2 ujx « o).S i>£ §>S 6 ~ 2 -Q jh t w ° .2 £ a 5 c S 8 ° « « S ~ - 2 > o -~ c 3 D E 3 . « t) « y « ° .22 W D a site o £ W>StJ § bC ~G (U^S cn ' II. TABLES. Soret's Tables of Angles included by a Lens. Diagonal of the Angle included Diagonal of the Angle included plate. by lens. plate. by lens. 2/ + if 1 00 It) J + u 50 0 2/ + \J io2 43 J +tV/ en 0 n' 57 37 2 / + sf 9» 50 -f J 53 0 n r . 1 f 2 / + 4/ r»ft° yl /I ' f 1 f J — TV/ /1« 0 -7*7' 45 27 2/ 90 1 f 47 54 / + t/ 82° 22' f » f f — h/ 47 *5 / + #7 1 J — if 46° 24' 7 2 " 1 44' f _ ' 40 I 1 / + |/ 67 0 31' /- 1/ 44° 23' / + 1/ 64 0 /- if 41 0 7' / + \f •6i°55' /" hf 36° 52' f + If 6o° 30' f~ hf 28 0 4' f+tf 59° 28' if 18 0 36' f + if 58 0 42' 1/ 1 4 0 20' Example : What angle is included by a 12-in. lens on a plate the diagonal of which is 10 ins. 12 — 10 or/ + and against this we find 6i° 55'. Table of Indices of Refraction (for D). Phosphorus Carbon disulpl Oil of cassia Aniline ... Nitrobenzine Phenol Cubebine... Pseudocumene Benzine ... Glycerine Turpentine Chloroform Amylic alcohol Ethylic alcohol Ether Acetone ... Methylic alcohol Water ... 1 -075 I*634 1-580 1-570 1-540 I-550 I-5IO 1490 1490 I-470 1-460 1-440 1-400 1-390 I-350 1-350 I'TI 539 APPENDIX. Equations Relating to Foci, etc. {Brit. Journ. Phot. Almanac.} The following simple optical formulae and calculations, worked out by Mr. J. A. C. Branfill, will prove useful in many branches of photography, especially where several lenses of varying foci are in constant use for a variety of purposes : — Let p = Principal focus. F = Greater conjugate do. / = Lesser do. do. D — F + /= distance of image from object. y = Ratio of any dimension in original to the same dimension in copy (in case of reduction), or vice versa (in case of enlargement). a = Effective diameter of diaphragm. U. S. No. = " Uniform System " No. of do. x = Comparative exposure required. Ff F yf Then p — D (y + i)- D y + 1 y t i f = 7) U. S. No. r~ N.B.— For ordinary landscape work, where r is greater than 20, x may be taken as — IOrt" Note.— In case the above may not be clear to some photographers, the following rules may be better understood : — To find the principal focus of a lens (/>), focus a near object in the camera, and measure the distance between it and the ground-glass (D); next find the proportion which any dimension in the object bears to the same dimension on the ground-glass (/-). Thus, if the original dimension be four times as large as its reproduction, we 540 II. TABLES. say that r equals ( = ) 4. Multiply D by r, and divide the product by the square of a number greater by one than r (r + i)\ This rule was lately published by Mr. Debcnham. To find the lesser conjugate focus (/) (if p and r are known) multiply p by the sum of r + 1 and divide the product by r. Or divide D by r + I, To find the greater conjugate focus (F) multiply p by r + 1. Or multiply / by r. To find D (the distance which the ground-glass should be from the object to be copied in order to get a given value for r) multiply p by 1 *:he sum of r + - + 2. r Or To find r divide F — p (the difference between F and p) by p. divide p by/ — p. Or divide F by /. To find .r divide the square of / by 16 times the square of a (the diameter of aperture to lens). For example : focus an object which is five inches high, so that it is one inch high on the ground-glass; thus we know that r = 5. Next measure the distance between the object and the ground-glass (Z)). which is found to be 45 inches. Then p = 45 x (multiplied by) 5 -f- (divided by) 6x6 = 6^ inches, f=6\ x 6 -f- 5 = J\ inches. Or /= 45 -f- 6 = "j\ inches. F — 6} x 6 = 37^ inches. Or F= 7 J x 5 = 37^ inches. D = 6\ x (5 + I + 2) = 6\ x 7i = 45 inches. r = (37i-6*)-S-6* = 5. Or r = 6* + (7* - 6*) = 5. Cadett's Table, showing the relative Rapidities of Plates of varying Sensitometer Numbers. Number of times more sensitive than — 25 24 23 [9 18 17 16 I \\\\ li 1 ?! 3 4 5 7 9 12 — I 2j 3 4 5 7 9 i* ii *i 3 4 5 7 i| 2} 3 4 5 1 M ii 2i 4 1 ii 2| 3 1 Ii I I| ij 2 J I 1 25 24 2 3 22 21 20 19 18 17 16 15 A To use this table to compare the rapidity of two plates, the sensitometer numbers of which are known, run the eye up the 541 15 16 12 9 7 5 4 3 2\ ii 1 1 1 APPENDIX. column A till the sensitometer number is reached, and then along the line of figures till it reaches the column of figures under the sensitometer number of the second plate, when the figure there shown will tell at once the difference in rapidity. Example — A plate has been used of ordinary rapidity showing 18 on sensito- meter, and it is desired to use a plate of sensitometer No. 22 : what will be the reduction in exposure ? Find 22 in column A, and carry the eye along the line of figures opposite to it till it meets the column under 18 in B line — the number 3 will be found ; therefore the 22 plate is three times as sensitive as the No. 18, and will therefore require one-third of the exposure. Table of Exposures for Enlarging. By E. Ferrero. ot&nley s Actinometer. /A6 f/2? //32 //48 //72 //too Seconds. min.sec. min.sec. min.sec. min.sec. min.sec min.sec. min.sec. min.sec. IO 0 9 O 17 O 23 O 36 0 55 I 20 3 0 5 47 15 O 13 0 25 0 34 0 54 1 23 2 O 4 3° 8 40 20 O 18 O 32 O 46 I 12 1 5i 2 40 6 0 " 34 25 O 22 O 42 0 57 I 30 2 18 3 20 7 30 14 27 30 O 27 O 49 1 9 I 48 2 46 4 0 9 0 17 21 40 O 36 ■ 5 1 34 2 24 3 42 5 20 12 0 23 8 50 0 45 1 24 1 54 3 0 4 36 6 40 15 0 28 54 60 0 54 1 38 2 18 3 36 5 32 8 0 18 0 34 42 70 1 3 1 54 2 42 4 12 6 28 9 20 21 0 40 29 80 1 12 2 10 3 7 4 48 7 24 10 40 24 0 46 15 90 1 21 2 29 3 28 5 24 8 18 12 0 27 0 52 0 IOO 1 30 2 48 3 48 6 0 9 12 13 20 30 0 57 48 I20 1 48 3 16 4 36 7 12 n 5 16 0 36 0 69 24 I40 2 6 3 48 5 23 8 24 12 56 18 40 42 0 81 0 l6o 2 24 4 20 6 14 9 36 14 48 21 20 48 0 92 0 180 2 42 4 58 6 56 10 48 16 36 24 0 54 0 104 0 200 3 0 5 36 7 36 12 0 18 25 26 40 60 0 1 16 0 225 3 22 6 18 8 33 13 30 20 45 30 0 67 30 130 0 250 3 45 7 0 9 30 15 0 23 0 33 20 75 0 144 0 275 4 7 7 42 10 27 16 30 25 20 36 40 82 30 159 0 300 4 30 8 24 11 24 18 0 27 40 40 0 90 0 174 0 The table shows the exposures to be given to Eastman's and Britannia slow bromide papers, according to the actual intensity ratio of the lens, and to the actinic power of light as measured by Stanley's actinometer. Britannia rapid bromide paper requires one-fiftieth of the exposure indicated, and gelatino-bromide plates of ordinary rapidity one-fifteenth to one-twentieth. 542 II. TABLES. Holetschek's Table of Drop-shutter Speeds. Distance of the opening of the drop shutter above the aperture of lens. 2 cm. 4 cm. 6 cm. 8 cm. iocm. 15 cm. 20 cm. 25 cm. 30 cm. o U cm. ). ... (NH 4 Br). ... (ZnBr 2 ). ... (CdBr»4H,0). (CdBrJ. " APPENDIX. 187-54 Lithium iodide (Lil3H 2 0). 145-0 Ammonium iodide f NH.jI). 159-5 Zinc iodide (Znl 2 ). 182*5 Cadmium iodide ... ... ... (CdL,). Table of Specific Gravities of Chlorides. Salt, per cent. 1 ■So- PQ U J? n° U S U -V U m M @ 7*1 (/) 4- ca — 0 - U £ u 2 I -0144 1-0183 i "0 1 70 1-0198 I*Ol82 1 *o 1 46 — I "0I05 IOI3 I OlO I A 4 1-0288 1-0367 I •02.06 I -026/1 1 U J U 4 1 0292 1 u 33° I "026 t •n2< : i'> 6 I -0435 IO557 T *OCnC I "0548 I,0 439 I "040 1 *-04° 8 1-0584 I -0754 I-0682 I O795 I '°734 1-0587 1 UO04 I '°54 1-0738 10 I 0734 I-095I I -0869 1 U997 1-0734 1-0859 ro68 1 2 1-0890- 1-1164 i-io-"6 I'I228 i-i 178 1 -0894 I ■ 1 04C 1*082 T • I I 22 T/l 1-1047 I-1378 1 -12/12 I ' 1 460 I* 1/126 I • TOC A I ' 1 22C I "007 1 " I 227 16 1-1207! ri6oo T*I/122 I ' 1 71 1 I -1696 1*1215 I ' 1 404 1*112 1 x ^49 18 1-1820 I-l628 T • T 275^ T • t cni 1 o9 J 1*128 I • T 76n 20 I'l £27 I "206 1 I ' l822 1 ^^45 ri542 1 ' 1 780 T ' T /I A 144 I ' 1 989 22 I ' T 700 T "7 2 T 7 I -2028 T2.X.A 7 I -2501 T* T 1 a(\ 1 I74O T • T r>7& 1 1970 i'i6i I -2225 2/1 ^4 1-1881 1-2574 T '22 2/1 1 -2849 T *277n 1 2/79 I-I950 t "7 i 7 e T * T 77 1 1/7 I -2462 26 1 '2058 1*244 **. i-3o-*8 1 J U J° I *2 1 1*. C T -2278 I '104 1-2708 28 1-2241 1*2662 I "2228 I - 226 C I-2586 1*212 1*2964 0° 1-2422 1*2879 1*2618 1-2568 I "220 t -2220 o z 1-2615 I • 2 TO/I t *2r>Cr> 1 277O T "> AtS 1 o495 •2 A 34 1-2808 t • 1 2 2r» 1 333° 1 4^07 T "?r>88 1 zyoo 1*268 ^6 1-3007 1 35 DI 1 -46 1 5 I '3 I 99 1*288 18 1-321 1 !'3797 1 4949 1-341 1 1*309 4 U i'34i5 I, 4°33 I 5204 1-3622 1 '33 0 42 I 3070 T">ro 1 3^- i 44 "! I -41 18 T '27/1 1 J/4 46 T 'A -iftl 1 43°7 I *207 1 .597 48 1-46 1 7 1 • AO 1 1 4^1 50 1-4867 1-445 52 1 3*3j T '/I 7 T 1 4/ 1 54 ;•• 1-5439 i*497 56 1-5729 1-525 58 1-6023 1-554 60 ::: 1-6317 1-582 62 1*613 64 1-644 66 1-677 68 1*711 70 ::: 1-745 72 ... 1-783 74 1 '82 1 544 II. TABLES. Salt, per cent. | Ammonium Chloride. Potassium Chloride. Sodium Chloride. Potassium Carbonate. Potassium Bichromate. Salt, per cent. Potassium Carbonate. 1 I - 00j2 I 0065 I 007 7 I C09 1 1-007 27 1-20/9 2 I 'OO63 f -n 1 in I "O I A C | 1 UI 4j 1015 28 I -2789 o I OOQ ? I'OIQC I '02 I 7 I "027A 1 "022 I -2900 A 1 I 'OI26 I - 0260 I "02C O I 'O l()7 I '0366 I 029 ^0 I "2 "MO C rOI58 I '012 C I 'OA Z 7 I '0 7 7 1 1 I'l I 26 6 roi88 I '0302 I "OA ifi I -oss I I 'OA 7 32 J 7 1 '02 18 I O458 I '05 I I I 'O645 I 'O5O 33 i • 1 3 cS 1 j3j° 1 -0248 TOC2C 1 'O74O I "056 •2/1 1 j47j i-3s88 Q 1*0278 1 O^O I I 0659 I C834 I 065 ;c JJ IO 1 -0^08 IO658 I '07 2 1 I O928 I 07^ ^6 1 • 1 70S I I I '08 IO I I026 I '080 37 1 • 1828 I 2 T T> ?66 I "0796 1 -0886 I'll 24 I 'O9O ?8 I 7 I 'O sQ<\ I -0865 1 '0962 I " I 222 I 007 jy I 4067 1 A 1 'OA X2 I "OQ^d. 1 ■ 1028 r 1320 1 " IO J AO f c I "0452 1 - 1004 ri 1 15 [-I418 I ' I 10 4 I 16 I O480 1-1075 1-1194 I I52O 42 1-4434 17 IO509 1 • 1 1 46 11270 ri622 43 i'4557 18 I-0537 I-I2I8 I-I352 I-I724 44 1-4681 19 I-0565 1-1289 1-143' 1-I826 45 1 -4804 20 I -0593 1-1361 1-1511 | I 1929 46 14931 21 ; I 062O 11435 II593 1-2034 47 1-5059 22 I-06 4 8 1-1509 11675 12 140 48 1-5180 23 I-0675 1-1583 1-1758 1-2246 49 i-53i3 24 I-0703 1-1657 1 • 1 840 12352 5o 15441 25 PO73O 1-1923 1-2457 5i 1-5573 26 I -Q737 12010 1-2568 52 15705 Table of Specific Gravities of Solutions of Phosphoric Acid at 15° C. Specific Gravity. P0 4 H ? . Per Cent. F2O.V Per Cent. Specific Gravity. P0 4 H 3 . Per Cent. P.O.. Per Cent. 1-476 6404 47lO I 236 3769 27 30 1-442 60-90 4413 1*197 32-IO 23-23 1-418 58-22 42-61 1 162 27-24 1973 I-384 55-40 40- 1 2 1-136 23-41 1695 1-356 52-46 38-00 1109 1830 13-25 1-328 5093 36- 1 5 1 066 I I 9 1 862 1293 45-05 3271 1-031 5-73 415 1-268 4160 • 30-13 roo5 I- IO 079 545 APPENDIX. Table of Specific Gravities and Strengths of Chromic Acid. Specific Gravity at i 7 °i. Per cent. Cr0 3 . Specific Gravity at i7°5- Per cent. Cr0 3 1-037 5 1-258 • 30 1076 10 1-373 40 i'n8 x 5 1-512 50 1162 20 1-665 60 1 208 25 Table of Specific Gravities of various Salts. Salt, per cent. il 11 (f) a X Barium Nitrate. Strontium j Nitrate. 1 Magnesium Nitrate. Lead Nitrate. Potassium Oxalate. Potassium Chromate. Platinic Chloride. Potassium Ferrocyanide. 2 1-0105 I OI 7 I-OI7 1-0078 1-0163 1-0134 * 1 1-0161 IOI8 I. OI 16 4 I 02 1 I 1-034 I 034 1-0158 1-0331 I -0268 1-0325 1-036 1-0234 6 1-0317 I 05O I 049 1-0239 1-0502 1-0401 10492 1-056 1-0356 8 1-0423 1*069 ro68 IO32 1 I 0682 1-0529 1-0663 1-076 1 -0479 10 I O529 1-087 1-085 I -0405 1-0869 1-0656 1-0837 1-097 1-0605 12 1-0639 1-0490 1-1059 1-0784 1-1014 I-II9 1-0734 14 I-075I 1-0577 1-1257 1-0912 1-1196 1*141 1-0866 16 I-0863 1-0663 1-1463 1-1043 1-1380 1-165 1 -0999 18 1-0975 1-0752 1-1677 11175 1-1570 1-188 1-1136 20 I-I087 i-i'Si 1-0843 1-0934 1-1902 1-1306 1-1765 1-214 1-1275 zl I-I204 1-2132 1-1964 1-242 ... 24 I-I322 I-I026! 1-2372 1-2169 1-270 26 II44O I-1I20 1-2620 1-2379 1-300 ;;; 28 I-I558 ri2i6' 1-2876 ... 1-2592 I-330 30 1-1676 1-292 1-1318 1-3140 ... 1-2808 1-362 ... 32 ri8oo 1-1410 1-3416! ... x -3035 1-395 34 1 • 1 924 ... 1-1508 1-3702 ... 1-3268 i-43i 36 1 -2048 11608 1-3996 ... ^oS 1-469 38 1-2172 1-1709 . . . 1- 3746 1-500 40 1-2297 1-422 11811 i- 399 i I-546 42 1-2427 1-1914 i-59i 44 1-2558 1-2019 ... 1-641 46 1-2690 . . . 1-2126 . . . 1-688 48 1-2822 1-2231 1736 50 1-2954 1 -234c ... 1-785 1 546 II. TABLES. *2 Hi s w n *~ &° c r! -* N L- u £ ^ *o . M — . c O* D g 5 <3 *e3 Pi MS* i* 1* - ■ M h *• 0 « Nal per cent, at i9°5. • 51 0 ~ 5 i'°45 I'045 1*037 I -040 — _ — I-0 35 Q I -03b I '040 „ 1*035 10 1 "091 1 009 1 O50O 1 '070 I OoO 1 -072 I O7O 1*082 1*079 l S 1*137 1 - 140 1 - 1 1 6 I ' I 26 1*113 I ' I 20 1*128 I' 124 20 I I OO 1*195 I ' I I 72 1 159 1*174 1-156 I IOO 1*179 1*172 25 1-235 1 "256 I IOl9 1-207 1*226 1 -204 I "> 1 ft I 215 1-234 I *224 3° 1*291 1 321 1*256 tl/ ,(>T I 251 1 254 I "27 1 1-294 I 260 35 1352 1-309 1*344 1-309 i*33i 1*360 i*344 40 1-420 1-472 1-2557 1-366 1-410 1-368 1*396 1*432 1414 45 1-488 1 430 1*483 1-500 1-566 1-656 1*500 1*565 1-580 ^546 i*6oo 1*575 ^5 1-650 ... 60 1-740 1-890 ... 1*734 1810 1*777 Table of Specific Gravities of some Acetates. Per Sodium Calcium Barium Lead Per Lead cent. Acetate. Acetate. Acetate. Acetate. cent. Acetat _ . 2 I*0Il6 1*0132 1*0174 TOI27 32 1*2395 4 IO232 I '0264 IO348 1*0255 34 1-2578 6 I*034I 1*0362 1-0500 1-0336 36 1-2768 8 I*0439 I -0426 I -0628 10520 38 1 -2966 10 I*0539 I 0492 1*0758 1 0654 40 i*3* 6 3 12 I 0644 10562 I 0902 10796 42 1-3376 14 1*0750 I 0632 1 * 1 046 1 0939 44 1*3588 16 10856 10708 II 20 1 1-1054 46 13810 18 1*0910 1*0792 »'I363 1 • 1 234 48 14043 20 1*1074 1 0874 ri522 11384 5o 1-4271 22 1*1194 10976 I * 1 694 1*1544 24 1*1314 1*1078 1*1704 26 1-1440 1*1139 11 869 28 1*1572 1*1307 1 -2040 30 1*1706 II426 I -2402 I '22 1 I Table of Specific Gravities and per cent. Strengths of Formic Acid at 15° C. Specific Gravity. CH,0>. Specific Gravity. CH,0,. Specific Gravity. CH»0 2 . I-025 10 II24 50 I-20I 90 1-053 20 1*142 60 1*223 IOO ro8o 30 I*l6l 70 1*105 40 Il8o 80 547 Appendix. Table showing the Specific Gravities of varying strengths of Alcohol in degrees over and under proof. Over Proof. ' Specific Gravity. Over Proof. Specific Gravity. Under Proof. Specific Gravity. Per cent. Per cent. Per cent. — 67*0 •8156 28-0 •8825 8-o •9295 65-0 •8199 27-0 •8840 9*0 •9306 64-6 •8221 26-0 •8854 io-o •9318 6 3 -I •8238 25-0 •8869 no •9329 62'0 •8259 24*0 •8883 I2'l '9MI 6ri •8277 23-0 •8897 131 '9353 6o-o •8298 21*9 •8912 14-2 •9364 59' 1 •8315 209 •8926 15*3 •9376 58-0 •8336 19-9 •8940 16-0 ■9384 57' 1 •8354 19-1 •8951 17-1 •9396 56-0 •8376 18-0 •8966 18-2 •9407 55"° •8366 16-9 •8981 x 9'3 •9419 54* 1 •8413 159 •8996 •9008 20 -o •9426 S3' 1 •8431 •8448 15-0 21'2 '9437 521 I 3'9 •9023 22'2 •9448 5 1 ' 1 •8465 131 •9034 23*1 '945 6 50-1 •8482 120 •9049 23*9 •9464 49' 1 •8499 in •9060 25-I •9476 48-0 •8516 IO'O •9075 26"3 •9488 47'° •8533 8-9 •9089 27-I •9496 46-0 •8550 8-o •9 IOC 28-0 '95°3 45'° •8566 7-1 •91 1 1 29- 2 '95 l 5 43'9 •8583 5'9 •9126 30-I •9522 43' 1 •8597 5'° •9137 35' 1 '95 6 5 42-0 •8615 3'9 •9152 40*1 •9603 4I-.I •8629 3 -o •9163 •9178 45'o •9638 40-0 •8646 19 5o-3 •9674 39'i •8660 rp •9189 54'8 •9701 38-0 •8678 Proof spirit •9200 60-4 '9734 37'i •8692 653 •9762 35-9 •8709 Under proof 70-1 •9790 35 - o •8723 1*3 •9214 75'4 •9822 34-i •8737 2'2 •9226 80-4 •9854 32-9 •8755 31 •9237 85-2 •9886 32-0 •8769 4-0 •9248 90-2 •9922 310 •8783 5*o •9259 95'4 •9962 300 •8797 60 •9270 1000 10 29-0 •881 1 7-0 •9282 548 II. TABLES. Table for the Reduction of Hydrometer Degrees into Specific Gravities (Gerlach). A. For liquids lighter than water at 12-5° C. Degs. Beaune. Cartier. Beck. Degs. Beaune. Cartier. Beck. O roooo • 31 •8742 : •8707 •8457 I •9941 32 •S690 •S652 ■8415 2 ... •9833 33 •8639 ■8598 •8374 3 ... •9826 34 •8588 •8545 •8333 4 •9770 35 •8538 •8491 •8292 5 ... •97M 36 •8488 •8439 •8252 6 ... ... •9 6 59 37 •8439 •8387 •8212 7 ... •9604 38 •8391 •8336 •8173 8 ... •9550 39 •8343 •8286 •8l33 9 •9497 40 •8295 •8095 10 1 OOOO •9444 41 •8249 •8061 1 1 ■9932 •9392 42 •8202 •8018 12 •9865 •9340 43 •8156 7981 13 •9799 •9764 •9289 44 •81 1 1 7944 14 •9733 •9239 45 •8066 •7907 15 •9669 •9695 •9189 46 •8022 •7871 16 •9605 •9627 •9159 47 7978 ... 7834 •7 •9542 •9560 •9090 48 7935 •7790 18 •9480 •9493 •9042 49 •7892 7763 19 •9420 •9427 •8994 50 •7849 7727 20 •9359 •9363 •8947 5i 7807 •7692 21 •93OO •9299 •8900 52 •7766 7658 22 •924I •9237 53 7725 •7623 23 •9183 •9175 •8808 54 •7684 7589 24 •9125 •9114 •8762 55 7643 755 6 25 •9068 •9054 •8777 56 •7604 7523 26 •9OI2 •8994 •8673 57 7565 7489 27 •8957 •8935 •8627 58 •7526 •7456 28 •8902 •8877 •8585 59 7487 7423 29 •8848 •882O •8542 60 7449 •7391 30 •8795 •8763 •8500 Specific Gravities of Caustic Alkali Solutions. Per Cent. NH 3 . KHO. NaHO. Per Cent. KHO. NaHO. I •9959 1009 I OI 2 36 1-361 i\395 2 •9915 1017 I O24 37 i'374 1-405 3 •9873 1-025 I O35 38 1387 4 •9831 I 033 I -046 39 1-400 1*426 549 APPENDIX. Specific Gravities of Caustic Alkali Solution (Continued). i er Leni, IN ri... 1/ [in Nal IO. Per Cent. KHO. NaH. c j I 'O41 I 058 /IO 4 U <— I '41 2 1 'A 77 1 40/ 6 *Q7AO y/4 w I'OAQ I -070 A T 4 1 I *A2C 1 4^3 T */L/17 1 44/ 7 'Q70Q yi^y 1-058 1*081 A2 . 1 40" I 'AC.7 1 4 j / 8 •q67o I "065 1*092 /t 7 40 1 4j w 1-468 o y T •_07/t T • IA1 1 lUj 44 I '462 T-/I78 1 47O 10 •QCQ7 yjyo i-o8^ t • t t rr 1 1 1 D A C 43 T *A7 C 1 4/ D 1-488 1 1 *CK C.6 I "092 I ' I 26 /16 4 U 1-488 T */l QQ 1 ^yy 1 2 •n C20 I ' IOI T * T 17 A 7 t '/inn 1 4yy i • con 1 D u y '0184. 1*1 10 I*I48 4.8 4° I • C T f I •C. IQ y44y 1 1 iy T • t cn 49 T • CO C i • con 1 b-^9 I c y4"-4 I-I28 1 ■ 1 7© CO I • C 7Q 1 jJy 1 * C/IO A J4 U 16 •0380 y^ou T'l 77 i'i8i C T T ' C C O T • C CO 1 bb u I 7 yj4/ I"I46 I - 1 92 CO t *c6c 1 b u b 1 -560 18 9j a 4 T • T C C I '202 bo 1 b/° T * C70 1 b/ u IQ •Q28^ Il66 1*217 1 _ 1 j C/l T *COO 1 ^ou 20 •Q2C I 1*177 1 1 / / I "22C 1 '604 1 "COT 1 Dyi 21 •9221 ri88 I *2l6 c6 1*618 I *6oi 22 •QTQI yiy 1 1*198 T 2/1 7 C 7 01 t '670 i *6 1 1 o -> -J '9162 1 '209 I*258 c8 I '642 1 '622 24. •Q1 11 1*220 1*269 Co jy i*6ct( 1 Jj 1-677 2< J •9IO6 I "270 60 1*667 T 'f\A 7 26 5 •Q078 I *24I I '290 61 i*68i t *6ca 1 u j4 27 •QOC2 I "252 62 1 *6oc 1 u yj I "664 28 '9026 I "264 I '310 6i u j T *70C I "67A 29 •9OOI 1*276 1321 64 1*718 1-684 30 8976 1*288 1-332 65 1729 1*695 31 •8953 I-300 i'343 66 1-740 I*705 32 •8929 I-3II i'353 67 1754 1715 33 •8907 1-324 1-363 68 1-768 1*726 34 •8885 I-336 1-374 69 1-780 1-737 35 •8864 1-349 1-384 70 1790 1*748 Sulphurous Acid. Quantities of Anhydrous Sulphurous Acid in Solutions of different Densities. F. Authon. Specific Anhydrous Specific Anhydrous Specific Anhydrous Gravity. Acid in 100. Gravity. Acid in iod. Gravity. Acid in 100. 1-046 9-54 1-023 5-72 1036 8-59 IOI3 2*86 1-031 7-63 ro2o 4-77 1*009 I90 1-027 6-68 1*016 3-82 1-005 o-95 55° II. TABLES. Sulphuric Acid. Quantities of Liquid and Anhydrous Acid in Mixtures of Sulphuric Acid and Water at different Densities. Anhy- Anhy- ■2 4 Anhy- •fi 8 Spcci fic •o M 2 Specific Gravity. 'm- • a \ acid Gravity. acid in Gravity. ■0 M m — •' c acid in a* mi J d, CO _ in 100. 100. 100. 18485 IOO 8i-54 I-5503 66 5382 1-2409 33 269 1 1-8475 99 80-72 I-5390 65 5330 1 2334 32 26-09 I -8460 98 79-90 15280 64 52-18 I-226o 3i 25-28 1-8439 97 7909 I-5170 63 5i-37 1-2184 30 2446 1-8410 96 78-28 1-5066 62 5o-55 1 2I08 29 23-65 1-8376 95 77-46 I -4960 61 49 74 1 2032 1-1956 28 22-8 3 I-8336 94 7665 I -4860 60 48-92 27 22-OI 1-8290 93 75-83 1-4760 59 48- 1 1 1-1876 26 2T20 1-8233 92 75-02 I -4660 58 47 29 I-I792 25 2038 1-8179 9 1 74.20 14560 57 46-48 1 • 1 706 24 1957 I-8II5 90 73-39 I -4460 56 45-66 ri626 23 1875 1-8043 89 72.57 1 4360 55 44-85 11549 22 17-94 1-7962 88 7175 1-4265 54 4403 1-1480 21 1712 1-7870 87 70-94 1-4170 53 43-22 I-I4IO 20 163I 1-7774 86 70-12 I-4073 52 4240 1I330 19 15 49 1-7673 85 69-31 68-49 1-3977 5i 41-58 i I I246 18 I468 1-7570 84 1-3884 50 4077 II 165 17 I386 I-7465 83 67-68 1-3788 49 3995 I • 1 090 16 I305 1-7360 82 66-86 1-3697 48 39-14 1-1019 15 1223 I-7245 81 6605 1-3612 47 38-32 1 0953 H lr4I 17 100 80 65-23 1-3530 46 37-51 10887 13 IO-6o 1 6993 79 64-42 1-3440 45 3669 1 0809 12 978 1-6870 78 63-60 1-3345 44 35-88 I-Q743 11 8-97 1-6750 77 62-78 I-3255 43 35o6 1 -0682 10 815 1-6630 76 61-97 1-3165 42 3425 10614 9 7-34 1-6520 75 61-15 13080 41 I 3343 1-0544 8 652 1-6415 74 60-34 1-2999 40 3261 1 0477 7 571 1-6321 73 ! 59-52 12913 39 1 3180 1 -0405 6 489 1-6204 72 i 5871 1-2826 38 : 30-98 1-0336 5 4-08 1-6090 7i | 57-89 1-2740 37 30- 17 1 -0268 4 326 1-5975 70 57-o8 1-2654 36 29-35 1 -0206 i 3 2-45 1-5868 69 5626 1-2572 35 28-54 10140 I 2 163 1-5760 68 55-45 1-2490 34 27-72 10074 •82 1-5648 67 54-63 I 55' APPENDIX. Nitric Acid. Quantities of Liquid and of Anhydrous Acid contained in Mixtures of Nitric Acid and Water at different Densities (Ure — 6o° F.). Specific gravity. Liquid acid, sp.gr. in 100. Anhy- drous acid in ico. ' Specific gravity. Liquid acid, sp.gr. 1*5, in 100. Anhy- drous acid in 1:0. Specific gravity. Liquid acid, sp.gr. 1 '5, in 100. Anhy. drous acid in 100. I • KCO IOO 70'7OO 1 y 1 1^78 *■ j/" 66 52-602 1-189 22 jj 26*301 I '4q8 00 1&Q02 / .7 j i'27 2 65 5l-8o5 j * j 1-183 22 J 2^'KOA i -406 q8 y 78-I06 1-368 64 5 1 -068 ri77 21 J 2A'707 I '404 07 y 1 77*^.00 1 J w J 63 50*21 1 1*171 ^O 2l'QOO I '401 Q6 76**;i2 1-358 62 4Q'4I4 17 ft 1*165 20 ^■y 2TI I 2 j 1 J I-488 QC 7^-7i 1 j 1 1 j I * 2C 2 61 48-6I7 1*1 KQ 28 22*^l6 r48i; 04 74-Q18 I"U8 60 47-820 I ■ I c -3 27 2 I "57Q j J y 1-482 93 yj 74T2I r "343 59 47-023 1*146 26 20*722 I'479 02 y 7V 2.24 / J J r 1 338 JJ 58 46-226 1*14 25 J 10*02-; r476 y 72-527 1*332 JJ 57 45-429 1*134 24 19*128 r473 90 7I-730 1-327 56 44-632 1*129 23 J 18331 jj I-470 8o 7o-q^^ 1*322 55 43*835 Tj J J I' 122 22 17*-; 34 1 / JJT r467 88 87 70 - 1 26 I*3l6 J ^4 JT- 43*038 tJ ^S) 1*117 21 l6'737 I'464 6q"?3q y jj7 I • -2 I I J ^3 JJ 42-241 1*111 20 I 'Q40 r460 86 68-542 I" 306 J 52 J 41'444 1-105 J 10 i -;'i43 r457 85 67-745 1-300 51 40-647 1099 18 14346 l'A^2 84 66-048 I'2Q5 ^0 J 3Q-850 J7 J roQ^ 7J 17 I 3*-;4Q 1 3 jty I-450 83 66-155 I-28o 49 39-053 I*088 16 I2-752 r446 82 65-354 I-283 48 38^56 r082 15 "•955 I 442 8l 6 4-557 1-276 47 37'459 r076 *4 IPI58 80 63-760 1-270 46 36662 I-07I 13 IO361 1 '435 79 62-963 1-264 45 35-865 1-065 12 9'564 i-43i 78 62-I66 I-2 5 8 44 35-068 I-059 1 1 8*767 1-427 77 61-639 I-252 43 34-271 I-054 10 7*970 1-423 76 60'572 1-246 42 33-474 I-0 4 8 9 7-173 1-419 75 59-775 I-240 4i 32-677 I O43 8 6376 i'4i5 74 58-978 1-234 40 31-880 I-037 7 5-579 141 1 73 58-I8I 1-228 39 31-083 IO3 2 6 4782 1406 72 57^84 T22I 38 30-286 I'027 5 3-985 1402 7i 56 587 1-215 37 29-489 I 02 1 4 3-i88 1-398 70 55-790 I-208 36 28-692 IOl6 3 2*391 1-395 69 54-993 1-202 35 27-895 roii 2 1-594 1-388 68 54-I96 1-196 34 27-098 1*005 1 o-797 1-383 67 53'399 552 1 1. TABLES. Hydrochloric Acid. Quantities! oil Liquid and of Anhydrous Acid and of Chlorine in Mix- tures of Hydrochloric Acid and Water at different Densities. I iquid H. CI. 1 Liquid Specific Acid, CI. Spcci fic Acid, j H. CI. CI. ( i ravity. sp.gr. 1 "20 in 100. in 100. in 100. ( iravitv. sp.gr. 1 '20 in 100. in 100. 1 I "2000 100 40-777 39*675 i* 1000 50 1 ' 20*388 19-837 1-1982 99 40-369 39*278 1 "0980 49 19*980 19*440 I '1964 98 39-961 38-882 38-485 1 "0960 48 *9'57 2 19*044 1-1946 97 39'554 1*0939 47 19*165 18*647 1-1928 96 39'46 38-089 1*0919 46 '8*757 18*250 1-1910 95 38*738 37-692 1*0899 45 ' -8*349 17*854 1-1893 94 38 '330 37-296 1*0879 44 17*941 '7'457 fi8 7 s 93 37"9 2 3 36*900 1*0859 43 '7*534 17*060 1-1857 92 37*5*6 36'5 0 3 1 '0838 4 2 17*126 16*664 1-1846 9 1 37-108 36*107 i*o8i8 4' 16*718 16-217 1-1822 90 36*700 35'707 1*0798 40 16*310 15-870 1-1802 89 36*292 35*3*0 1*0778 39 15*902 15-474 1-1782 88 35-884 34*9 X 3 1*0758 38 '5*494 1 5"°77 1-1762 87 35*476 34'5'7 1*0738 37 15*087 14.680 1*1741 86 35-o68 34*121 1*0718 36 14*679 14*284 1-1721 85 34* 660 33*724 1 '0697 35 14*212 13*887 1*1701 84 34*252 33*328 1*0677 34 13*863 i3'49o 1-1681 23 33'845 3 2 *93' 1*0657 33 '3*456 I 3'°94 Ti66i 82 33*437 32-535 1 "0637 32 ' 3*049 12*697 1*1 64 1 81 33'o27 32*136 1*0617 31 12*641 12*300 1 * 1620 80 32*621 3''746 1*0597 30 12*230 1 1 '903 1-1599 79 32-213 3**343 1*0577 29 11*825 1 1*506 1 -1578 78 31*805 30*946 1 *°557 28 1 1 *4 1 8 11*109 i"i557 77 31-398 30*550 ' '0537 27 I I'OIO 10*712 '*'537 76 30*990 30-582 3 0-I 53 1*0517 26 10*602 10*316 75 29*757 1 0497 25 10*194 9*919 1*1494 74 3o-i74 29*361 1*0477 24 9*786 9-522 '"'473 73 29-767 28*964 *' 0 457 23 9*379 9*136 72 29*359 28*567 ''o437 22 8*971 8-729 '*i43' 7i 28-951 28*171 1 -04 1 7 8*563 8*332 1 '1410 70 28-544 27*772 '-°397 20 8 'i55 7*935 1-1389 69 28-136 27*736 '"0377 '9 7*747 7*53? 1-1369 68 27*728 26*979 *'0357 18 7*34° 7*141 '''349 67 27-321 26*583 '"0337 .7 6*932 6*74- 1-1328 65 26-913 26-186 1*0318 .6 6-524 6*343 1-1308 65 26-505 25'789 1*0298 •5 6'n6 5*95« 1-1287 64 26*098 25-392 1 -0279 14 5'709 5*554 1 1267 6 3 25*690 24'996 1*0259 13 5'3°» 5*'58 1 -1247 62 25-282 24*599 1 '0239 12 4-893 4*762 1 '1226 61 24-874 24*202 I *0220 1 1 4*486 4-362 1 'I2C6 60 24*466 23-805 I "02C>0 10 4*078 3-968 1-1185 59 24*058 a ; "4< I *OI 80 9 3-670 3*571 1-1.64 58 23-650 23*012 1*0160 8 3*262 3'74 i'«43 57 23*242 22*615 I 0140 7 2*854 2*778 I'II23 56 22*834 22'2l8 I '0I20 6 2*447 2'?8l 1 *i 102 55 22*426 21-822 i'oioo 5 2-039 1-984 1*1082 54 22*019 21*425 1 *oo8o 4 1 -6 3 1 1-588 i'io6i 53 2l"6ll 2I*028 i "0060 1 1*224 1*191 1 "1041 52 21-203 20*632 1 0040 2 o*8i6 o*795 1 " 1020 5i 20*796 20*236 1*0020 0*408 o*397 553 APPENDIX. Acetic Acid. Quantities of Crystallisable Acid in Mixtures of Acetic Acid and Water of various Densities at 15 0 C. Pa rts of Parts of Parts of 3 arts of Crystal- li sable Acid in Specific Gravity. Crystal- lisable Acid in Specific Gravity. Crystal- lisable Acid in Specific Gravity. Crystal- lisable Acid in Specific Gravity. 100. ICO. ICO. 100. 100 i'°553 75 1*0746 5° 1*0615 25 "4*0350 99 1*0580 74 I-C744 49 1*0607 24 1 '0337 98 1*0604 73 1*0742 48 1*0598 23 1*0324 97 1*0625 72 1*0740 47 1*0589 22 1*0311 96 1*0644 7 1 1*0737 46 1*0580 21 1*0298 95 1*0660 70 I- °733 45 1*0571 20 1*0284 94 1*0674 69 1*0729 44 1 '0562 J 9 1*0270 93 1*0686 68 1*0725 43 1*0552 18 1*0256 92 1 "0696 67 1*0721 42 1 'o543 17 1*0242 9 1 1*0705 66 1*0717 4i i'Q533 16 1*0228 90 1*0713 65 1*0712 40 1*0523 15 1 '0214 89 1*0720 64 1*0707 39 1*0513 I *020I 88 1*0726 63 1 '0702 38 1 0502 13 I OI05 87 1*0731 62 1*0697 37 1*0492 12 I 'OI7I 86 1*0736 61 i'o69i 36 1*0481 I*OI57 85 60 1*0685 1 '0470 10 84 1*0742 59 1*0679 34 1*0459 9 l*OI27 83 I- °744 58 1*0673 33 1 -0447 8 I*OII 3 82 ; 1*0746 57 1*0666 32 1*0436 7 I '0098 81 ; 1 "0747 56 1 *o66o 3 1 1 0424 6 1*0083 80 1*0748 55 1*0653 3° 1*0412 5 1 '0067 79 1*0748 54 1 "0646 29 1 '0400 4 I *0052 78 1*0748 53 1*0638 28 1*0388 3 I*0037 77 1*0748 52 1*0631 27 1 '0375 2 I "0022 76 1*0747 5i 1*0623 26 1*0363 1 I "0007 N.B.— The density of the mixture increases until nearly 25% of water is present, after which it again decreases. Acetic Acid is therefore better tested volumetrically with a standard solution of alkali. Table of Solubilities of various Acids in 100 parts of Water at various Temperatures. Tempera- Benzoic Boric Acid. Oxalic Tartaric Ammonia ture. Acid. Cryst. Anhyd. Acid. Acid. Alum. 0 i*9 ri 5'2 115*0 5'2 IO •21 2*9 i*6 8*o 120*0 9*2 20 4*0 2*3 i3'9 1390 137 30 •42 ... 23*0 1560 19-3 40 •55 7*0 39 35'0 176*0 273 50 51-2 195*0 36-5 60 1*2 1 1"0 6*'i 75° 217 O 51-3 70 1*8 1 1 8*o 244*0 72*0 80 1 6*8 95 205*0 273*0 103*0 90 345-o 307*0 1 88*o IOO 59 290 16*0 i 3430 422*0 1 554 II. TABLES. Thermometer Table showing the comparison of degrees of Centigrade, Reaumur, and Fahrenheit c 1 I r . C. ■ IV. C. R. w r . 1 100 80 212 56 44*8 132-8 12 9-6 53*6 99 79-2 210*2 55 44 131 1 1 8-8 51*8 98 78-4 2o8'4 54 43*2 129-2 10 8 50 97 96 77*6 206-6 53 42-4 127-4 9 7-2 48-2 76-8 204*8 52 41-6 125-6 8 64 46-4 95 76 203 51 40-8 123-8 7 5*6 44*6 94 75'2 20T2 50 40 122 6 4-8 42-8 93 74*4 199*4 49 39*2 I20'2 5 4 41 92 73* 6 I97.6 48 38*4 118-4 4 1 3*2 39*2 9 1 72-8 195*8 47 37*6 n6-6 3 2-4 37*4 90 72 194 46 36-8 114-8 2 16 35* 6 89 71*2 192*2 45 36 113 1 08 33*8 88 70-4 190-4 44 35*2 I I 1*2 0 0 32 87 69-6 188-6 43 34*4 109-4 - 1 - o-8 30-2 86 68-8 186-8 42 33* 6 IO76 — 2 - 16 28-4 85 68 185 4i 32-8 105-8 3 - 2-4 266 84 67-2 1832 40 32 104 - 4 - 3*2 2 4 -S 83 66-4 181-4 39 312 102-2 - 5 - 4 23 82 65-6 179-6 38 3°*4 IOO-4 - 6 - 48 2T2 81 64-8 177-8 37 296 98-6 - 7 - 56 I94 80 64 176 36 28-8 96-8 - 8 - 64 I7.6 79 63-2 174-2 35 28 95 - 9 - 7-2 •5*8 78 62*4 172-4 34 27-2 93*2 -10 - 8 14 77 6r6 170-6 33 26-4 914 - 1 1 - 8-8 I2'2 76 60.8 1688 32 256 896 — 12 - 9*6 IO*4 75 60 167 3 1 24-8 87-8 -13 — 104 8-6 74 59"2 165-2 30 24 86 -14 — 11*2 68 73 58-4 163*4 29 23-2 84-2 -15 -12 5 72 57*6 1616 28 224 82-4 -16 -128 3*2 7 1 568 159*8 27 216 806 -*7 -136 i*4 70 56 158 26 208 78-8 -18 - 144 - 0-4 69 55'2 156-2 25 20 77 - 19 -152 _ 2-2 68 54'4 154*4 24 192 75*2 -20 -16 - 4 67 53*6 1526 23 18-4 73*4 -21 -16-8 - 5*8 66 52-8 150-8 22 176 716 -22 -176 - 7*6 65 52 149 21 168 698 -23 -185 - 9-4 64 51-2 147-2 20 16 68 -24 l -19-2 — I I '2 63 504 145*4 19 15*2 66-2 -25 -20 — 13 62 49*6 143*6 18 144 644 -26 — 20-8 — 14S 61 48-8 1418 17 136 626 -27 — 21-6 -166 60 48 140 16 128 608 -28 — 22-4 — 18*4 59 47-2 138-2 15 12 59 -29 -232 — 20-2 58 46-4 1364 14 I 1-2 57*2 -30 -24 -22 57 45-6 1346 13 104 55*4 1 555 APPENDIX. Table of conversion of Fahrenheit, Centigrade, and Reaumur. F. C. R. F. C. .- - R. F. c. R. + 212 + 100 + 80 170 76-67 6 1 33 128 53-33 42-67 21 1 99-4 79-56 169 76-1 1 60-89 127 52-78 42-22 2IO 98-89 79-11 168 75-55 60*44 126 52-22 41-78 209 9 8 "33 78-67 167 75 60 125 51-67 41-33 '208 97-78 78-22 166 74-44 59-56 124 5111 40-89 207 97-22 77-78 165 73-89 59" 123 50-55 40-44 206 96-67 77-33 164 7333 58-67 122 50 40 205 96 1 1 76-89 163 72-78 58*22 121 49-44 39-56 204 9555 76-44 162 72-22 57-78 120 48-89 39-11 203 95 76 161 71-67 57-33 119 48-33 38-67 202 94*44 75-56 160 7111 56-89 1 18 4778 38-22 201 93 ' 8 9 75" 159 70-55 56-44 117 47-22 37-78 200 93*33 74-67 158 70 56 1 16 46-67 37-33 199 9278 74-22 157 69-44 55*56 "5 46- 1 1 36-89 198 92-22 73-78 156 68-89 114 45-55 36-44 197 91-67 73*33 155 68-33 54-67 113 45 36 196 91*11 72-89 154 67-78 54-22 1 12 44-44 35'56 195 90-55 72-44 153 67-22 53-78 in 43-89 35-n 194 90 72 152 66-67 53-33 no 43'33 34-67 193 89-44 7I-56 151 66-ii 52-89 109 42-78 34-22 192 88-89 71-11 150 65-55 52-44 108 42-22 33-78 191 88'33 70-67 149 65 52 107 41-67 33-33 190 8778 70-22 148 64-44 5 --56 106 41-11 32-89 189 87-22 6978 147 63-89 51-11 105 40-55 32-44 188 86-67 69-33 146 63-33 50-67 104 40 32 187 86-n 68-89 H5 62.78 50-22 103 39-44 31*56 186 85-55 68-44 144 62-22 49-78 102 38-89 3m 185 85 68 H3 61-67 49-33 101 38-33 30-67 184 84-44 67-56 142 6i - ii 4s 09 100 37-78 30-22 183 83-89 67-11 141 60-55 4844 99 37*22 2978 182 83-33 66-67 140 60 48 98 36-67 29-33 181 82-78 66*22 139 59'44 47 56 97 36-11 28*89 180 82-22 6578 138 58-89 47 11 96 35'55 28-44 179 81-67 6c— 2 °5 j3 T -5*7 l 37 c8-->t 95 35 28 I 7 8 8rn 64-89 136 5778 46-22 94 34*44 27-56 177 8o-55 64-44 135 57-22 45-78 93 33;89 27 ' 1 1 176 80 64 134 56-67 45-33 92 33-33 26-67 175 79'44 63 56 133 56-11 44.89 9i 32-78 26-22 i74 78-89 63- 1 1 132 55-55 44-44 90 32-22 2578 173 78-33 62-67 131 55 44 89 31-67 25*33 172 7778 62-22 130 54-44 43-56 88 87 31*11 24-89 171 77-22 6178 129 53-89 43-n 30-55 24-44 556 ii. TABLES. Table of conversion of Fahrenheit, Centigrade, and Reaumur— continued. F . 1 C. ' R. F. c. R 1 1 F. C. ' R. 86 30 24 : 43 61 ] 4-8 9 I | — 17-22 -13-78 84 i 29-44 | 23-56 42 555 4-44 O -1778 — 14-22 28-89 23-11 41 5 4 — 1 -18-33 -14-67 83 1 28-33 i 22-67 40 4-44 356 — 2 — 18-89 -I5-II 82 27-78 22-22 39 5/89 311 1 J — 1944 -«5-56 Si 27 22 2178 38 \ 3'33 2-67 — 4 -20 16 80 26-67 21-33 37 : 2-78 222 5 : -20-55 — 1644 79 26- 1 1 2089 36 2-22 i-78 - 6 — 2 in — 16-89 78 25-55 20-44 35 1-67 . l-33 - 7 — 2167 -17-33 77 25 20 34 111 0-89 — 8 —22-22 -17-78 76 24-44 19-56 33 o-55 0-40 — 9 —22-78 — 18-22 75 ; 23-89 19-11 32 0 0 -10 —23-33 -18-67 74 23-33 18-67 31 ! - 0 55 ! — 0-40 — 1 1 —23J9 — I9-II 73 2278 18-22 30 1 i-n — 089 — 12 — 24-44 - I9-56 72 22-22 1778 29 — 1-67 | — i'33 —13 -25 20 71 21*67 17-33 28 — 2-22 - .78 —14 -25-55 -2044 70 21*1 1 16-89 27 - 2- 7 8 — 2-22 - >5 —26-11 -20-89 69 20-55 16-44 26 - 3 33 — 2-67 -16 -2667 -2133 68 20 16 25 3-89 3 -ii -17 — 27-22 - 21-78 67 19-44 I5-56 24 - 4-44 - 3-56 - 18 - 27 78 22 22 66 18-89 15-11 23 _ 5 - 4 -19 -28-33 — 2-2-67 65 18-33 1467 22 ^ 5-55 — 4'44 —20 -28-89 23-II 64 1778 1422 21 — 611 - 4-89 — 21 29-44 -2356 63 17-22 1378 20 - 6 67 — 5-33 —22 —30 24 62 16-67 1333 19 — 7-22 - 5-78 —23 -30-55 —24-44 61 161 1 1289 18 - 7-78 — 622 —24 -3III -24-89 60 15-55 12-44 17 - 8 33 — 667 -25 —31-67 —2533 59 15 12 16 — 8.89 - 7 II —26 -3222 -257S 58 14-44 1 1-56 15 — 9'44 - 756 -27 -32-78 —26-22 57 13-89 11*11 14 10 - 8 -28 — 3333 --26-67 56 1333 1067 13 — io-55 - 8-44 -29 -3389 —271 1 55 .2-78 1022 12 — ii-ii - 8 89 -30 —34 44 —27-56 54 12*22 9-78 11 — 11-67 -- 9-33 -31 35 -28 53 1 1-67 9-33 10 — 1222 - 978 -32 —35-55 — 28-44 52 1 11 I 8-89 9 —1278 — 1022 — 33 —36-11 -2889 5 1 IQ'55 8-44 8 —i3'3 — IO-67 -34 —36-67 —2933 50 10 8 7 -13-89 — I I II —35 37-22 —29-78 49 9-44 7-56 6 —14-44 — U56 -36 37-78 — 3022 48 8-89 711 5 15 —12 37 38-33 -38-89 -3067 47 8-33 6-67 4 -15-55 —12-44 -38 \-3Vll 46 1 7-78 6-22 3 — 1 6* 1 1 -12-89 39 —39-44 -3'-56 45 7-22 5-78 2 — 1667 — 13-33 40 40 -32 44 6-67 5*33 557 APPENDIX. Table of commercial shutters, showing the speed of each. Where the speed is distinguished by an asterisk, it has been experimentally determined by some observer ; in all other cases the speed is that stated by the makers ; where no speed is given, this depends upon particular circumstances, such as, with the drop shutter, the use of indiarubber bands, etc. Class and Name. Speed. Remarks. Lowest. Highest. I. — Exposing Shutters. Lancaster's Pneumatic ... Newman's Studio Taylor's Exposing Flap ... Thornton-Pickard Studio TxtIht <; ^\#=m f.Pnrfr'n l f Time Time* Time n >» ws sec «* t7 5 sec. * £- 5 sec sky, 2 ^ sec. foreground. II. — Rapid Shutters. a i. Drop. „ „ with india- f sec. j 4 ^ sec. T V sec* a 2. Flap and Drop. Reynolds and Branson's "Leeds" Reynolds and . Branson's "Phcenix" a 3. Double Drop. 1- ih sec*| T V sec* «V sec. sky, -g\ sec. foreground; and y 1 ^ sec. fore ground, T ^ sec. sky. Less for sky, sec* Tylar's Foreground Vevers' Window Blind ... Time ?? aV sec* -At sec* -jy sec* 2 V sec. sky, ^ sec. foreground. A sec. sky, sec foreground. ■h sec. sky, ft sec. foreground. 558 II. TABLES. Class and Name. a 4. Rotating Screens. Cadett's Lightning Lancaster's Instantograph Leisk's Sky Underwood's XL. a 5. Flap and Double Flap. Furnell's Guerry Tylar's Norden Flap a 6. Go and Return. Lancaster's Chronolux Mitchell's Pneumatic Re- turn Pcrken's Plunge Sl'EED. Lowest. Highest. Remarks. it sec -* tV se c-* sec* X sec* A sec* -.h sec/ Screen shaped to give less sky exposure. Less for sky. And time. 1T sec* j Sky ^ sec, fore- ground I sec. ; sky sec, fore- ground sec. a 7. Blind. 4 sec* i s sec' sec* Kershaw Thornton-Pickard's Time .» it In- stantaneous Underwood's Instantolux a 8. Opening from Centre. Gotz Wing Lancaster's '90 Chronolux Thornton-Pickard's Double Blind Sands and Hunter's Ribbon The " Stanley " Stereoscopic Company's... Watson's Double Snap ... a 9. Ever-Set. L'Atitomatique Less for sky. iU sec* Time* sec* : Sec table below. ..V sec* J. sec* & sec* sec* A sec* With two bands, ^ 3 sec. * A sec* TffTT sec. 17 sec* A 'sec* •A scc -* sec* ... 559 APPENDIX. Speed. Class and Name. Remarks. Lowest. Highest.) ■fe sec* „ „ Oval -V sec* T V sec* II. b. — Behind Lens. ... Sec table below. II. c. — Between Lenses. i. Go and Return. sec* I sec* X sec* Varies consider- ably.* Time nj sec* 2. Blind or Drop. Thorn ton-Pickard's Blind > 1 n 2 5 »» 6 102 ,, j> 1 „ 42 »» 7 119 - H 1 n 59 2 drachms 16 8 136 „ j> » 9 153 - >> 2 „ 33 10 170 , 2 ; , 50 » 20 340 • 5 n 40 30 510 .. >> 1 ounce 0 drachm 30 minims. 40 680 ,, >> 1 » 3 drachms 20 „ 50 850 ,, 1 „ 6 10 „ 60 1020 j? 2 ounces 1 0 „ 70 iroo 2 3 50 •• 80 1360 , , 2 „ 6 40 90 1530 3 1 30 „ TOO T700 3 4 20 561 00 APPENDIX. The Conversion of French into English Weights. Although a gramme is equal to 15-4346 grains, the decimal is one which can never be used by photographers; hence in the following table it is assumed to be 1 5^- grains, which is the nearest approach that can be made to practical accuracy : — I gramme I 5l grains. 2 grammes — 30* 3 = 4 _ 6if or I drachm if grain. 5 77 17 grains 6 9 2 i I 3 2 T 7 — io7f 1 47t 8 — I2 3t 2 drachms 9 _ I38f 2 i8f 10 154 2 1 1 _ 1694 2 49t 12 184+ 4t 13 — 2 °°5 20| — 2I 5t 3 35t 1 c j _ 2^1 ■2 0 CI J 16 = 2461 4 17 261* 4 II 2ii 18 2 77l 4 >» 37i »> 19 2925. 4 »> sn >> 20 308 5 n 8 u 30 462 7 w 42 » ,4° 616 10 16 »» 5o 770 12 n 5o tt 60 924 15 24 11 70 1078 17 »» 58 i» 80 1232 20 11 3 2 90 1386 23 11 6 11 100 1540 25 n 40 >» Conversion of Minims, Drachms, Ounces, and Pints to Cubic Centimetres and Litres. Minims to c.cm. Drachms to c.cm. Ounces to c.cm. Pints to Litres. OO5916 3'5495 28-396 0-56792 2 0-11832 7-0990 56-792 IT3584 3 0-17748 106485 85-188 1-70376 4 0-23664 14-1980 II3-584 2-27168 5 0-29580 17-7475 141-980 2-83960 6 0-35496 21-2970 170-376 3-4Q75 2 7 0-41412 24*8465 198-772 3'97544 8 0-47328 28-3960 227*168 4-54336 9 o'53 2 44 31-9455 255*564 5-11128 562 II. TABLES. Conversion of Grains and Ounces into Grammes. Grains to Grammes. Ounces to Grammes. Grains to the Ounce- Grammes to icoc.cm. 1 0*06479 28*3495 O 22817 2 0*12958 56 9660 045635 3 0-19437 850485 06845 2 A 4 0*259 16 1 1 2*^080 A'AT 0 f~in u y 1 zuy 5 0*32395 I4I7475 1*14086 6 0*38874 I7OO97O 1*36904 7 Q'45353 I984465 1*59721 8 0*51832 2267960 1*82538 9 0*58311 255'1455 2-05356 Table showing the Correction for Actinic Foci with Monocles or Spectacle Lenses. Proportion between Image a?id Object. iV A ITT A A 1% '& s T(T ±. f IOO A/ 2 no 2*4 120 29 I30 34 140 39 I50 4'5 l6o 5*1 170 58 l8o 6*8 190 72 200 80 I50 A/ 3 3*6 180 4*3 195 5'i 210 5 9 225 6*8 24O 77 255 87 270 97 "285" io-8 300 120 / 200 A/ 4 220 48 240 5'8 260 6*8 280 7'8 3°o 90 320 10 2 340 116 360 130 380 144 400 16 0 / 250 A/ 5 275 61 300 IL 325 35o 9*8 375 "*3 400 128 425 145 45o 162 475 181 500 200 / 300 A/ 6 330 7'3 360 8*6 390 IOI 420 117 450 135 480 154 5io 173 540 19*4 57o 217 6co 240 / 35o A/ 7 "385" 8-5 420 IOI 455 n*8 490 137 595 15-8 560 179 595 20*2 630 22*7 665 253 700 280 /" 400 A/ 8 440 97 480 "•5 520 13*6 560 157 600 180 640 205 680 23I 720 25*9 760 289 800 320 / 45o A/ 9 495 10*9 340 130 585 152 630 177 675 203 720 230 765 260 8lO 29*2 855 327 900 360 / 5oo A/ IO 55o 12*1 600 14*4 650 16*9 700 196 750 22*5 800 256 85O 289 900 324 950 361 I, coo 400 563 APPENDIX. English Measures. Proportion between Image and Object. A A A 1 0 c To" A 8 1 0 A 1 0 To f 3lt A/tV 41 117 41 jl 8 5* tVo 5* 1 3 Tffo 51 3 TU 64 5 1 2 4 0 ft* 2 9 i^¥ 7* if 3 TS 71 * / 5* A/ \ 3 2 0 7i 4 3 ?40 71 5 1 2~i^) 8* 5 9 "5 4¥ 75 o 9s 77 34 0 I°A Air 1 of 9 S ? 9 "So" "if 4 f n A/i ~8f 1 ioi l 7 TO" II 1 3 0 0 ii! 3 8 12* 5 1 ■42IT I3f 2 9 T.TT Hi u 15 3 % 15! I / 9*3 A/ A IO| 4" TIT it 13! 4 9 l^-o" l*ir 38 11 i6f II 17! SI TUO- 18! 1 S 1 2 4U 19** I /"it A/i 13 14* 43 T2 "0" i5l 10 1 2 4TT » i7! tt iA 20^ 173 -2--4-0 21* 97 tto 22A 23I / I3tt A/,ir, ISA 1 7 4 4 1D T<7 10 1 240 i7t§ 1 I9 t. 20H T¥XT 22 A 17 9 24 0 23 A 101 T5T7 24! 2 3 7 24 0 26ft 2 27A 1 o / i5! A/ i I7A I9H ttt IX 3 0 22 23l I 2 5A 4 I TS 26| If 17 8 0 30 1 A 3>2 ii / 17! A/§ 10 0 241T 2 23 A 3TT 2411 3 4 26| 6 291 2 3 "24 3°8 iA 3^ 33A if 354 1* / 19! A/ i 5 . 21 T.T 1 3. 251 1 7 f"4 27^ 5 29§ 1 5 TB" 311 I t S 334 1* 351 1 A 37 A 39A 1 In the above tables f = the solar focus. A f— the correction for actinic rays. Preparing Percentage Solutions. [Anthony s Annual.) By C. C. Sherrard, Ph. C. The first table gives percentage solutions ; the second gives parts in 1,000 or less. The use of the first is as follows : Run down column one until the correct percentage wanted is found, then move to the right along the line until the column is found giving the amount of fluid measure to be made up ; at the intersection will be found the weight of salt required. It must be remembered that this is the amount of water to take, and not q.s. water to make the volume ; also that these tables are true only for water, and not for alcohol or othcr fluids. 564 ». TABLES. For Making any Quantity of Percentage Solutions. 1 fluid water ne salt i fluid water le salt 3 fluid water le salt ♦ fluid water le salt 5 fluid water le salt 0 fluid ' water le salt 6 fluid water le salt For each ounce of take of tl For each : ounces ot take of tl For each ounces ot take of tl For each . ounces ot take of tl For each ounces of take of tl For each 1 ounces of take of tl ! For each j ounces of take of tl To make Grains. Grains. T, rains. Grains. Grains. Grains. . Grains. 1 per cent 2 per cent 3 per cent 4 per cent 5 per cent io per cent IS per cent 20 per cent 25 per cent 40 per cent 4*557 9-114 13-671 18-228 22-785 45*57 68-355 91-14 113-925 182-28 9-114 18-228 27-352 36*456 45*57 91-14 136-71. 182-28 227-85 364*56 13-671 27*342 41*013 54-684 68-355 136-71 205*065 273*42 341*775 546*84 18-228 36*456 54*684 72*912 91*14 182-28 273*42 364*56 455'7o 729*12 22-785 45'57o 6d*355 91-14 113-925 227-85 341-775 455 - 7o 569-625 9x1*4 45*57 91-14 136-71 182-28 227-85 455-7 68-355 911-4 •i39 - 25 1822-8 72-912 145*824 218-416 291-648 364-56 729- 1 2 109368 1458-24 1822 8o 2916-48 For Making any Quantity of Solution when stated in Parts per 1,003, 100, etc. ■ For each 1 fluid ounce of water take of the salt For each 2 fluid ounces of water take of the salt For each 3 fluid ounces of water take of the salt For each 4 fluid ounces of water take of the salt For each 5 fluid ounces of water take of the salt For each 10 fluid ounces of water take of the salt For each 16 fluid ounces of water take of the salt i To make solution of Grains. Grains. Grains. Grains. Grains. Grains. Grains. 1 in 1,000 1 in 500 1 in 400 1 in 300 1 in 200 i in 100 1 in 50 1 in 25 1 in 10 1 in 5 •4557 •9114 1-139 1*519 2*2785 4*5£7 9*114 18*228 45*570 91*14 •9114 1-8228 2*278 3*035 4*557 9-114 18*228 36-456 91*140 182-28 1*3671 2*7342 3*4»77 4*557 6-8355 13*671 27-342 54*684 136*710 273'42 1-8228 3*6456 4*557 6*076 9*114 18-228 36-456 72*912 182*280 364-56 2 278 4*557 5-695 7*59 u*39 22-785 45 57 91*14 227-85 455*7 4*557 9*114 11*392 15*19 22*785 45*57 91*14 182*28 455-70 yii'4 7-291 14-582 18*228 24304 36-456 72*912 145824 2yi*648 7 29- 120 ■458*24 We may say that, in giving the above figures, the resulting solution is correct as regards percentage composition, though it may measure slightly more than the water taken, owing to the increase in volume which always takes place in some degree when a solid passes into a solution in a given amount of liquid. This expansion is not appreciable for small amounts of the solid, say up to 5 per cent., but .it 25 per cent, or more, it may be noticeable. 565 APPENDIX. Relative Exposures for Varying Proportions of Image to the Original. By W. E. Debenham. Proportion of image to original (linear). Distance of image from lens Proportionate Exposures proportioned to in terms of exposures.* that required for principal focus. copying same size. i so" T 1 1 30 I -07 •27 1 , 1 IIO •28 lTF 1 lV I "21 '3 H 1-27 jl I 6 136 '34 l 4 I -56 '39 .1 I* 2-25 •56 I If 3-06 76 I 2 4 I (same size) 2 3 9 2 '25 3 4 16 4 4 5 25 6-25 5 6 36 9 6 7 49 12-25 7 8 64 16 8 9 81 20*25 9 10 100 25 IO 1 1 121 30-25 1 1 12 144 36 12 13 169 42-25 13 H I96 49 14 15 225 56-25 15 16 256 64 16 17 289 72-25 17 18 324 81 18 19 36i 90-25 19 20 400 100 20 21 441 110-25 21 22 484 121 22 23 529 132-25 23 24 576 144 24 25 625 156*25 25 26 676 169 26 27 729 182-25 27 28 784 196 28 29 841 210-25 29 30 900 225 30 3i 1 961 240-25 566 II. TABLES. Table of Enlargement or Reduction. Focus c o Enlarge- ment. of Lens in ts 3 1. 2. 3. 4. 5. 6. 7. Inches 73 Inches Inches Inches Inches Inches es. Inche DC ies. Inches Inches 2 J A i\ 4 8 ' 1 0 1 2 16 l8 g 1 V 15 4 3 2 i 2 a -72 -71 A 2h /■ / A /V 5 7l IO 1Z 2 J 5 17$ 20 22* g i I 13 3? 1 I 31 it 3 ->1 1 *rs 2 7 2 ld A /\ 3 r J A /\ 9 12 1 c l D iX 2 1 -7 yf 24 2 7 g g 6 /l 1 4$ 4 3f 3a 3? 31 A 3J ( A 7 1 0 H 4| I 7 1 ' ? 2 1 -7/1 > 2 42 9X 3 1 1 3*3 g 1 li ? 7 5 4i 4s 4 •3 1 5 3ro A 4 J 1 /v y o 1 2 1 a 1 0 20 24 oX 3 2 3° 4a g 1 V B 5 r 1 5? c A * 4.-, 4f 4r A f A 9 *3 2 iX I 0 0^ 1 27 7 1 1 0 X 2 3° 4° 2 g 1 g 9 f. 0 C •? 5s rl 5t 57 r 1 5ic A 5 t \ A I o 20 2C 3° 7 r 35 40 45 D g I o 71 161 °f 0 1 0 5£ r 1 5r 5ff A i A 1 I 33 3° 2 44 49 2 13 K. g Xi «* 7 8 6""' fi2 fi •' 5, A 6 { A 2 iX 24 3° 42 48 45 54 g VJ D 1 2 9 0 0 72 »rl 7 da 6; A *3 1 n 1 26 32 i 39 452 5 2 cX> 5°2 7iG u I> 1 I. D J 3 91 8 1 Its i T 7 f A '4 2 1 28 1 c 35, 42 49 5° °3 g \ V g J 4 1 a! IO ? 9£ 82 0 jj- XI Off X 7 7 7i f J A I c *5 22. 2 77 1 37 3 45 52* fin °72 g \ r> 13 l S IO 9§ 9 y 04 8 7 A 8 f\ 1 j A 16 "7/1 3* 1 of /in 4 U 40 5° 04 7 Z g i i g 16 1 2 IO 9f 9ff 9 7 9 A 8| f\ J A I 7 ■? c 1 2 5a 34 All 4 2 $ 5 1 59 2 _ 6X 76I 7°? g 1 V. ( g I 7 l 7 I2f 10^ 9o 9s 9 iV A 9 18 2 7 "7.6 45 C A 54 61 °j in 1 7 2 81 g B 18 I 3 1 '3-2 ?X' I 0 1 z 1 't 1 472 IO} in2 io 7 io s A f A -jX 3° 57., 00 2 7° Xc 1 °^2 B \ g 12;, 1 14 ill "if in' 1 A 10 f A 20 J° 40 en " j Xn' 90 B I g 20 111 ! 33 I2« 1 2 1 1 1 XI 7 I 1 1 A r A 3 T "2 42 5 2 63 7jj 84 94i B \ B A 21 i5i 14 3<>i \2'l 66 I2| 12 r ill 1 1 tt A 11 f 22 JO 44 77 88 99 B \ B 22 i6« Hi 30^ 13:1 12^ 124 12% I A 11.1 j A 23 34* 46 57^ 69 8o£ I3A 92 B { B 23 15:'. I4k j »3t5 131 i 2 !i A 12 f A 24 36 48 60 72 145 «4 96 '3? 108 B \ B l 24 18 * 15 I3a A 567 T3 « ,2 ,H .S fl o c m- 2 ..5 r-rCO MOrnOtni) ■fc >t3 d ^c„- S rt JE- SS'S §:2t3 gi«8f ^-§,g iSgSgsaS-s.s.aSs.s c'S u g3 S "' H g ~ c« 3 •3pmd|nstQ S o « o S CO tfl ■iuaojoao[q3 1 Ml* •[oqoDiv .2 bj £ I I £11 l l > "8 w .5 a - o o > 2-o ° 0 S E £ 8 15a J 1 .J- 2 o CO co co M rf- y> o co m io O co co N (X) in A ro ft O, O O O co O « b >-h ro t 0\ O O CO co rt- co in N N O O r-<. tJ- CTi O 0\ N b b b b ~ b ~ b b b b b tS u' K O S" S 1 O O s s 5 * s § £ s s y y s g ^'g K « ^ f| fj N N ilin ve. u •~ J* 1 A 3 r/ 0 Ho gl ts 0 isso 5 if • > parts c vater di 100 par Icohol d 10 parts disso Remarks. 0 n Acetone m. m. m. m. Acid, Acetic m. m. m. ,, Boracic 4 29 25 boiling ,, Carbolic ,, Citric 140 200 ,, Formic s. s. DI. „ Gallic 1 33 I2"5 ,, Hydrobromic ... dec. dec. ,, Hydrochloric ... m. m. ,, Hydrofluoric ... m. m. ,. Lactic m. m. m. m. ,, Nitric m. m. dec. dec. ,, Picric s. s. 5 s. s. ,, Pyrogallic 5° 100 90 V. s. ,, Salicylic 023 8 dec. 28-57 ,, Sulphuric m. m. dec. ,, Sulphurous s. dec. s. ,, Tannic •8 '5 120 ,, Tartaric 25 100 20 Alum (ammonia) „ (potash) 13 358 insol. insol. ,, (chrome) 9"5 50 insol. insol. Amidol 42 Ammonium Bichromate 9 422 s. s. ,, Bromide v. s. o'n o-8 % in ,, Carbonate ... 25 dec. s. s. alcohol-ether. ,, Chloride ... 30 100 ,, Citrate 200 40J s. ,, Iodide 165 V. s. 25 05 5% in alcohol-ether. Nitrate 200 43 cold, 80 boiling „ Oxalate 33 50 s. ,, Sulphocyanide 160 V. s. v. s. ,, Sulphite 100 dec. s. s. s. s. Amyl Acetate insol. insol. m. m. Aniline 3 V. s. v. s. Barium Bromide 100 168 s. V. s. in benzine. 57' APPENDIX. Table of Solubilities of Various Chemicals {Continued), Barium Chloride ,, Iodide ,, Nitrate ,, Hydroxide (baryta) Benzine Borax Bromine Cadmium Bromide „ & Amm. Brom ,, Chloride... ,, Iodide ... Calcium Bromide ,, Chloride ,, Carbonate Hydrate ,, Iodide Cobalt Bromide „ Chloride ,, Iodide „ Nitrate ,, Sulphate Copper Bromide ,, Chloride ,, Nitrate ,, Sulphate Cyan in Dextrine Eo*in Erythrosin Eikonogen Ether Acetic ,, Sulphuric ... Glycerine Glycin Gold Chloride Hydroquinone ... Hydroxylamine Hydro- chloride Iodine Iridium Chloride Iron Chloride (ferric) 2 ° C O T> 36 200 4*7 insol. 6 •06 130 400 100 400 insol. 100 33 40 42 9 8 100 5' [60 o ? 3co 35 insol. 200 dec. v. s. v. s. 650 i35 166 650 insol. 135 i33 0'26 dec. dec. m. 0 o §1 "c3 133 10 at 30 0 c. v. s. s. s. o-i cold, 5.5 boiling insol. •9 boiling 13 cold, 70 boiling 102 13 cold, 70 boiling insol. insol. v. s. sol. s. s. s. s. insol. sol. s. insol. m. m. insol. c'4 0-4 insol. insol. insol. insol. m. s. s. Remark-' 10 % in glycerine. jl-eiher. 6'2 alcohol 4% in alcohol-ether. 50% in alcohol-ether. insol. in abso- lute, s. s. in dilute alcohol. s. in glycerine. II. TABLES. Table of Solubilities of Various Chemicals {Continued), Iron Chloride (ferrous) ,, ,, Iodide ,, ,, Oxalate (ic) „ (ous) ., Sulphate ., Nitrate ., Ammonio-citrate ,, -oxalate .. Sodio ,, ,, Ammonio Sulphate Bromide Lead Acetate ,, Chromate ,. Nitrate Lithium Bromide ., Carbonate ... Chloride ... ,, Iodide Magnesium Bromide ,, Chloride ., Iodide ... Sulphate Mercury Herchloride Metol l'aiamidophenol Palladium Chloride ... M atinum Bichloride .. Potassium Acetate ... ,, Aceto-tungstate ,, Bicarbonate ... Bichromate .. Bromide Carbonate ,. Chlorate ,, Chloride ,, Chloroplatinite ,, Chromate Citrate Cyanide „ Ferricyanide... ,, Ferrocyanide ,, Hydrate ... . Iodide ... . 2°j3 o : > <=°iO<« Sic 140 V. s. V. s. 0-05 60 50 25 90 66 insol. 50 143 0-77 82 100 100 160 s. I '2 S. IOO J 90 s. 33 12 50 149 6-5 32 17 50 166 I coo 40 28 200 2? dec. 0*03 insol. 140 290 0-78 146 i33 i33 37o 133 700 200 800 V. s. 50 94 305 50 57 V. s. 60 232 part. dec. 776 50 400 200 2 v> 8/3 Remarks. insol. insol. s. in dilute s. insol. s. s. s. insol. 12 insol. insol. insol. insol. v. s. insol. s. ; s. S ::: 50 cold, sco I boiling s. in&ol. 33 cold, 93 25 with hyHro- s. in an alkaline oxalate. boiling s. 4"5 S. V. s. 30 cold, 50 boiling s. insol. dec. o"i 5 cold. 7 boiling insol. insol. s. s. insol. insol. insol. 1 '2 insol. insol. s. s. chloracid 5*5 I. s. insol. insol. insol. dec. 0"2 insol. insol. insol. insol. insol. v. r. in caustic alkalies. 005 % in alcohol-ether o-8 % in alcohol-ether. 573 APPENDIX. Table of Solubilities of Various Chemicals {Continued). ioo parts of cold water at 15° C, or 59 0 F., dissolve. 100 parts of boiling water dissolve. 100 parts of alcohol dissolve. 100 parts of ether , dissolve. Remarks. Potassium Metabisul- phite ... 33 v. s. insol. insol. ,, Nitrate 3° 335 insol. in cold, 2 in „ Nitrite boiling 100 200 Oxalate 33 5° • "1 insol. • "" insol. ., Permanganate 0 5 10 insol. ,, Silicate 33 IOO dec. dec. Sulphocyanide 217 V. s. sol. Sulphide „ (bi) Tartrate ... Potassium Tungstate o'4 . ••• . inso . 7 insol. S. inso . s. insol. Pyrocatretim v. s. V. s. v. s. v. s. s. in alcohol- Pyrogallol . 40 V. s. V. s. v. s. ether. Pyroxylin insol. in 0 . insol. insol. Resorcin 86"4 _ s. insol. Silver Albuminate ... insol. 'nsol insol. insol. Acetate „ Bromide ' 1 . '*' , ' 1 * " 1 insol. „ Carbonate insol insol' in^ol insol. ,, Chloride insol. insol. insol! insol. „ Citrate ,, Cyanide . ••• , . "• , . ••• . ,, Iodide ,j insol. inso . ins .°. insol. Nitrate 100 200 15 cold, 25 s. boiling „ Nitrite dec insol „ Oxalate 3 0-4 s. insol. „ Oxide insol. insol. insol. insol. ,, Sulphate Sodium Acetate 92 204 45 insol. „ Aceto-Tungstate s. v. s. s. insol. ,, Bicarbonate ... 10 dec. insol. insol. Bichromate ... V. s. V. s. dec. dec. ,, Bisulphite v. s. V. s. insol. insol. ,, Bromide 85-5 154 6 0-08 20 % in ,, Carbonate 93 445 insol. insol. glycerine. ,, Chloride 35 39 '6 insol. „ Citrate 28 204 45 insol. ,, Hydrate 60 127 s. insol. ,, Hyposulphite... IOO V. s. insol. insol. ,, Iodide 180 310 8-4 027 „ Nitrate 88 IOO 3 ,, Nitrite ., Oxalate 3*5 7 insol. insol. „ Phosphate 15 260 insol. insol. ,, Silicate 40 s. s. dec. dec. „ Stannate 61 s. s. insol. insol. 574 II. TABLES. Table of Solubilities of Various Chemicals (Continued). V B o • > — of c s°c ssol ts 0 isso 5 % « V 100 parts 0 water di 100 par alcohol d 100 parts ( dissol Remarks. Sodium Sulphate 5° 200 s. ,, Sulphite... ... 2 5 100 insol. insol „ Tartrate 5° v. s. insol. insol. ,, Tungstate ... 55 124 insol. insol. Strontium Bromide ... IOO 133 s. s. ,, Chloride ... 55 IOO s. s. ,, Iodide 200 400 s. s. ,, Nitrate Sulphocarbonide 9 v. s. V. s. insol. Thiosinamine s. s. s. s. s. Uranium Bromide IOO 200 s. ., Chloride ... V. s. V. s. v. s. ,, Citrate s. s. insol. insol. ,, Iodide ,, Nitrate 200 V. s. 33'3 25 Zinc Acetate ,, Bromide 320 V. s. s'oi. sol. ,, Chloride 300 V. s. V. s. ,, Iodide 300 v. s. V. s. ., Sulphate 142 200 insol. Table Showing at a Glance the U. S. No. for All Diaphragms. F. U. S. No. 1-'. U. S. No 1 4-25 ... 112 \\ -097 4-5 1-26 1-414 ••• 475 ••• 1-41 1-5 -140 5 156 175 ••• 'I9 1 525 ... 172 2 55 1-89 2-25 ::: - 3 i6 5656 ... 20 2-5 -390 575 ••• 206 2-828 ... 6 2*25 2 75 - -472 6-25 ... 2-44 3 562 6-5 264 3-25 -66o 675 284 3'5 765 7 306 375 -878 7-25 ... 3-28 4 ro 7*5 351 575 APPENDIX. F. U. S. No. F. I ... "2*7 C J 10 45 d'O ... ... -J. V 8-2; /l •'T'C ! 4^ 8-5 A-cr /17 H-l 875 40 9 5 -06 AO ... 3 CO 7 .1 • • • ... ... j U4 r t j * y 1 J • • • IO 6-2; JJ II T c6 C A 1 1 I 1 1 j 1 ••• r r 3 3 12 9° 50 ... ... ■it-' j"*-" 57 IA 12*25 5° I C j ... 14-06 16 i6*o 60 17 18-06 61 18 20*25 62 IO 1 J 22*56 u 3 20 6a 21 z/ 3"-" 6; 22 • • • ... J^ J 66 22-62 32'0 67 J "2 ^-06 JJ ^ 68 24 36*0 6o j • • « 70 26 4^ ^5 7 I 27 /l c • c6 ... 45 5 U 7"? I z 28 ... 4V u 73 20 y . . .• C2'C6 j j 7A J « • • c6*9 C 7 C 2 I 6o - o6 76 ^2 f\AT\ ... ... "4 77 78 JJ • • • 68-o6 34 72'2C ... ... / ^ ^ j 7Q 03 ... 76'c;6 ... / *-" 0" 80 36 80-0 8l 37 0 j 3 W 82 38 00*2 C 8^ 39 q*;-o6 84 40 ioo-o 85 4i 105-06 86 42 110-25 87 43 115-56 88 44 1 2 TO 89 U. S. No. ... 126*56 ... 128-0 ... 132-25 ... 138-06 ... 144-0 ,.. 150-06 ... 156-25 .. 162-56 .. 169*0 .. I75-56 182*25 .. 189-06 .. 196-0 .. 203-06 .. 210-25 .. 217-56 .. 225-0 .. 232*56 .. 240-25 .. 248-06 .. 256-0 264*06 .. 272*25 .. 280-06 .. 289*0 .. 297*56 .. 306-25 .. 315*06 324'o .. 333-o6 .. 342-25 .. 351-56 .. 301.0 .. 37o-56 .. 380*25 ,. 390 06 .. 400-0 ,. 410*06 .. 420-25 .. 430 56 440'0 ,.' 45I-56 ,. 462*25 . 473-06 484-00 '. 495*o6 576 II. TABLES. 90 9050 91 92 93 94 U. S. No. ... 506-5 ... 5120 ... 517-56 ... 5290 ... 54056 ... 552-25 95 96 97 98 99 100 U. S. No. . 564-06 . 576-0 . 58806 . COj'2 5 . 612 56 . 625-0 Inverse values of and of n (lOQ 1 ^) (US6C * in P notometrv) - n x n (— — V n 1 n / n y n 1 n / \ V IOO — n/ \ I ' » —11/ \ 100 — 1 / I I* 34 0294 •245 67 0149 4-08 2 •5 35 •0286 •289 68 0147 451 3 •333 36 0278 ■316 69 ■0145 495 4 •25 37 •0270 •344 70 •0143 5'44 5 •20 38 0263 •377 7i 0141 609 6 •167 39 0256 •408 72 •0139 6- 60 7 •143 40 •0250 • ■445 73 0137 7-29 8 •125 4i •0244 •483 74 •OI35 8- 10 9 II I 42 0238 ■524 75 0133 9- 10 •IO 43 •0233 •568 76 0132 1002 11 •09I 44 •0227 •618 77 •0130 11*21 12 •083 45 0222 •669 78 •0128 1257 13 •077 46 Zll •724 79 0127 I4-15 14 •0714 47 0213 ■7S7 80 •0125 16- •5 •0667 •03 1 1 48 0208 •852 81 0123 181 16 '0625 •02(11 4y "0204 82 '0 1 22 20 - 8 17 •0588 •0419 50 020 r 83 •0120 23-8 18 0556 •0482 51 0196 108 84 •01 19 27-4 19 •0526 •0550 52 0192 116 85 0118 321 20 '° 5 ^ •0625 53 •0189 127 86 01 16 365 21 •0476 •0706 54 •0185 136 87 01 15 44'7 22 •0454 •0795 55 0182 1 -48 88 01 14 23 •0435 •0892 56 0179 163 89 01 12 24 •0417 •0992 57 ■OI75 176 90 01 1 1 25 •040 III 58 •0172 rc,o 91 01 10 26 0385 •123 59 •0169 207 92 0109 27 •0370 •137 60 0167 225 93 •0108 28 •0357 •151 61 0164 241 94 •0106 29 •0345 166 62 •Ol6l 2-66 95 0105 30 •0333 183 63 •0159 298 96 0104 3i 0323 •202 64 •0156 3'i5 97 0103 32 •0312 •221 65 •OI54 3-46 98 0102 33 •0303 •242 66 0151 376 99 OIOI 577 p p APPENDIX. uiiu'ssbioj uinipos uiniuouiuiv mmss^oj umipog •bjuoxxiuiv S2 S N •apiuiojg uint'ss-B^oj •apiuiojg raniuouiuiv •So l>nio3 CQUUJQQWW 73 "U d tfl -.2.2 = WW WW W 3 u H c So o >, WW ;7« II. TABLES. M % in m b 00 'O ^ o . o b b £ o 000" 0 o £ g < o p 0 O V u 0) O 0 r>» ui ; ; ; 10 0 !£? 9, 10 -J- b b g : ** : : o o >o O 11S 0 mo^o u-ico « N, ;p\:tmflNOH ; ; ; ; 0 • M N • - • £ M O c OQ 0 ' b m b ' " ** ** m 0 b b 0 0 ' r ' ' 0 '« « m V. "0 0 b mo 0 + « 00 JLO M 0 0 0 g 10 00 00 PI 0\ m J PI pi pi pi *pi M n « M PI N P) - ' ' ° m pi ' O N B '« tl O '» N '» H M '« H N fl KM 0 Wi N :::::: i: : :6 : jz : e< : : : : : : :::::::::::: jg £>3 a : o r ;ooo . _ .35 .« . . . q.^cq .3 d „, S ,, il ™,- 1j =|::::.: = = : = ::::: .£|-J ' ' ' ' ' J iffll i| S M :| : • • i • : : • ! JgU*! a i2c nn« ^^^^ ~ - _ C u - trt : :: : iooo o o (/) iu :: .2 579 APPENDIX. .5 £ n ^ * R 9 CO u Hi a © « «8a 00 o -a td o o Hill Sortie cd cS .C o T3 o (A -a . 6 287,496 8-124 4-041 67 210*49 3525'65 4,489 300,763 8-185 4-061 68 213-63 3631-68 4,624 314,4^2 8-246 4-081 69 216-77 3730*28 4,761 328,509 8-306 4-101 70 210*01 "7 y 3848-45 4,900 343,000 8 366 4-121 71 233-05 3959*19 5,041 357,911 8-426 4-140 72 226-19 4071*50 5,184 373,248 8-485 4* 1 60 73 229-34 418539 5,329 389,017 8-544 4*179 74 232*48 4300-84 5,476 405,224 8-002 4-198 75 235-62 4417*86 5,625 421,875 8-660 4-217 76 238-76 4536*46 5776 438,976 8-717 4-235 77 241-90 4656*62 5,929 456,533 8774 4-254 78 245-04 4778-36 6,084 474,552 8-831 4-272 79 248*19 4901*67 6,241 493,039 8-888 4-290 80 25I-33 5026-55 6,400 512,000 8-944 4-308 582 II. TABLES. Table of Circumferences, Circles, Squares, Cubes, Square Roots, and Cube Roots. n. Circum- ference of diameter n. Surface of circle of diameter n. Squares n". Cubes n • Square roo's Cube roots 81 25447 5I53-00 6,561 53M41 9-OCO 4-326 82 257-61 528102 6,724 551,368 9055 4*344 83 26075 5410-61 6,889 571,787 o-i 10 4-362 84 263-89 5541-77 7,056 592,704 9.165 4-379 85 267-03 5674-50 7,225 614,125 9-219 4-396 86 270-18 5808-80 7,396 636,056 9-273 4-414 87 273-32 5944-68 7,569 656,503 9327 4-43I 88 276*46 6082*12 7,744 681,472 9386 4-447 89 279-60 6221-14 7,921 704,969 9'433 4'464 90 28274 6361-72 8, 100 729,000 9-486 4481 9i 235*88 6503-88 8,281 753,371 9 539 4-497 92 289-03 6647-61 8,464 778,688 9 591 4-5I4 93 292- 1 7 6792-91 8,649 8o4,357 9'643 4-530 94 2953I 6939-78 8,836 830,584 9695 4-546 95 29845 7088-22 9,025 857.375 9746 4-562 96 301*59 7238-23 9,216 884,736 9797 4-578 97 304-73 738981 9,409 912,673 9-848 4-594 98 307-88 7542-96 9,604 941,192 9899 4-610 99 3 1 ro2 769769 9,801 970,229 9949 4 626 100 314-16 7853-98 10,000 1,000,000 1 0000 4-642 Properties of the Circle. Diameter x 3- 141 59 = circumference. ,, x 8862 = side of an equal square. ,, x 7071 = ,, ,, inscribed square. ,, squared x 7854 = area of circle. Radius X 6-28318 = circumference. Circumference ^ 3-14159 = diameter. ,, = 3-54 V area ot circle. Diameter = 1128 Varea of circle. Length of arc = number of degrees x -017453 radius. Arc of i° to radius 1 = 0 01 745329. ,, 1/ ,, 1 — 00002908S. ,, 1" ,, 1=0-000004848. Volume of prism and cylinder = base x height. ,, triangle and cone = £ ,, x ,, 583 APPENDIX. Multipliers to facilitate Rapid Calculation. Area of circle =■ diameter squared x 7854. „ X -6366 =side of inscribed square. Avoirdupois pounds x x x x x x ,, inches x Circumference of circle Cubic inches feet Diameter of circle French tonnes metres „ litres hectolitres „ grammes ,, kilogrammes Feet per second Gallons Grains Miles per hour Pounds avoirdupois troy avoirdupois on sq. inch foot Square root of area of diam. of sphere x •009 = cwts. •000455 == tons. •00058 = cubic feet. •01638 = litres. •03705 — cubic yards. 6-232 = imperial gallons. •003607 = = diameter x 3'i4i6. •2251 — side of inscribed square. •2821 = „ equal square. •3 1 83 1 = diameter. 3-1416 = circumference. •7071 = side of inscribed square. •8862 = „ equal square. •984 = English tons. 3- 281 = „ feet. •2202 = imperial gallons. 2-7512 = English bushels. •002205 = lb s - avoidupois. 2- 205 = „ •682 = miles per hour. 4- 541 = French litres. •001429 = lbs. avoirdupois. •1467 = feet per second. 7000 = grains, •82286 = lbs. troy. 1*2153 == lbs. avoirdupois. •009 = cwts. •00045 — tons. 144 = lbs. per sq. foot. •007 = ,, inch. 1*12837 == diameter of equal circle. 3- 1416 = convex surface. 584 II. TABLES. Logarithms. N. 0 1 2 1 3 4 5 6 7 8 9 D. 10 0 ooo 043 086 128 170 212 253 294 334 374 40 i 414 453 492 53i 569 607 645 682 7'9 755 37 2 79 1 828 864 899 934 969 004 038 072 106 33 1 J 206 271 101 3QQ 420 4 461 492 523 553 584 614 644 673 703 732 29 5 76l 79O 818 847 875 9°3 93 1 959 987 014 27 6 2 04I O68 122 I48 17c ID 201 227 J j 279 2? 7 J 1 JO JJJ 380 40; 430 480 504 529 24 8 j j j S77 601 62; 648 672 6ck 718 742 765 21 9 788 8lO 833 856 878 900 923 945 967 989 21 20 3 010 032 °54 075 O96 ll8 *39 160 l8l 20I 21 i 222 243 263 284 304 324 345 365 385 404 20 2 424 444 464 483 502 522 54i 560 579 598 19 3 617 636 655 674 692 711 729 747 766 784 18 4 802 820 838 856 874 892 909 927 945 962 17 5 979 997 014 0? O48 O65 082 099 u6 133 17 6 4 150 166 183 200 2l6 232 249 265 281 298 16 7 3 l 4 330 346 362 378 393 409 425 440 45 6 16 8 472 487 502 518 533 548 564 579 594 609 15 9 624 639 654 669 683 698 713 728 742 757 14 30 771 786 800 814 829 843 857 5Z. 1 886 900 M i 914 9?8 942 955 969 983 997 on 024 038 13 2 5051 065 079 092 105 119 132 145 159 172 '3 3 185 198 21 1 224 237 250 263 276 289 302 »3 4 3i5 328 340 353 366 378 39 » 403 416 42S »3 5 441 453 465 478 490 502 514 527 539 55i 12 6 563 575 587 599 611 623 635 647 658 670 12 7 682 694 705 717 729 740 752 763 775 786 12 8 798 809 821 832 843 855 866 877 888 8_9? 12 9 911 922 933 944 955 966 977 988 999 010 1 1 N. 0 1 2 3 4 5 6 7 9 585 APPENDIX. tn M u a 6 u With excess of salt, although very in- tense, still less so than with excess of silver. Scarcely more in- tense with fuming than without. Fuming scarcely in- creases the inten- LesJintense thanNo. i, the normal paper : scarcely more in- tense with fuming. Paper prepared ac- cording to Abnej-'s process. The papers attain nearly the very B. With Ammonia fuming. Colour and Intensity. violet, v. i. bluish grey, n. i. yellowish grey, n. i. SS3U3AI5lSU3g § §,Ki i I A. Without Ammonia fuming. Colour and Intensity. violet, v. i. bluish grey, n. i. yellowish grey, n. i. •ooi = d3vjo ss3u3ai1isu3c} §> £ % 1 i I B. With monia fuming. Colour and Intensity. blue black, more intense than without fuming b si) grey, n. i. reddish grey, n. i. violet, with a red tinge, v. i. Intense, equal to normal No. i. violet, v. i. Am •°°i = ID3vJO SS3U3ApiSU9C; o o o o o o O 0 lO O CO o ■ M Os H H M A. Without Ammonia fuming. Colour and Intensity. blue black, v. i. bluish grey, n. i. greenish grey, n. i. violet, with red tinge, v. i. Intense, very nearly equal to the normal, No. i. violet, v. i. •o°i = ID2v J° ssouoai;tsu3S 2 a • 1 ' ' 3 £ § Name. Chemical Formula (Solubility). 1. Silver Chloride : AgCl (insol.) 2. Silver Bromide : AgBr (insol.) 3. Silver Iodide : Agl (insol.) 4. Silver Chloride : AgCl; excess of silver nitrate removed by washing. 5. Silver Chloride : AgCl treated as in 4, and then floated on KN0 2 solution. 6. Silver Chloride : AgCl, prepared as No. 5, but Sodium Sul- phite used. 586 II. TABLES. 9 i? 91 >, V «j 4) g «'i C "O 1,1 rt Xe"S §S5'c -eg K ,2 o rt 0-b/c w Xi P ST""* 2 1 - 4; hew: fij 2 «i2 s §*s:«§rse s -a cS u = £ .2 <« -n F <" ii 2 a) *■ « 2 ? „, c/3 H « r o a.? <« • ^ rt o C 3.M ' s Ba. i/i r— Cu u. C 4) u o 2ir (0 J2 S." 5 s rt c o p._- JO » 3 B T3 MM Ifi •a •a 3 "5 O . 'I «j s * E ■a 00 o £ 1 1 8 o N M 00 xT •own, own, E be a > ellow, i red, own, reddii n. i. 1- V} ja — > "a pie bi v. i. — lowisr s. i. red bro s. i. X" A £ .2 lowisl n. i. )let br m. i ind a yell red( "o >> > VO m 0 m R 1 1 o CO 00 fi 53 iT-d S3 fi o » - ka O fi 18 « dS. 1 » t& »R :* « 3 m « h -T.x fiU~ fiU~ £ 5 i) T3 a. ®"P "5 »;* -~ 55 SI'S SI* b| fell : S1 II IS go la n e£c fie f|« WOT . . '<.<.< ,U .tt CO O M II M HIM>- ~ M l_ ~ 587 APPENDIX. IS S.3 u Is •ooi=i33v jo SS3U3AUtSU3g CO -O 3 O < 588 II. TABLES. o o •z: c o 3" c fa £ 2 o 3 5 "O'O > a 2 9 13 *J U, u o " s I a, «i r: « — ■Si** 0 * ■SSI-S-Slsi (/> to p ish, h u be in red, red, yellow n. i, greenish s. i brown 6. i, yellow t. i. 2. ** 13 >i in VO o t S c/yj b/5 o o u a OS O 3 .-Si <• o O y o s . ..or t* w ^5 O O ..u «E go zx JSCJ Is s - o I SOS «^ 3J* 2oj , o MX fitf 2Ue bX 1$ X u 589 APPENDIX. Table of the Formulae of Chemicals used in Photography. Formula. Molecular Weight. Acid, Acetic HC„H 3 0 2 60 ,, Boracic or Boric h;bo 3 " 62 Carbolic... HC 6 H e O 94 ,, Citric H 3 C 6 H 5 0 7 , H,0 210 Formic ... HCHO, 46 Gallic ... HC 7 H 5 0 3 170 „ Hydrobromic HBr 81 Hydrochloric HC1 36-5 ,, Nitric HN0 3 63 , , Oxalic H 2 C 2 0 4 , 2H 2 0 126 Pyrogallic H 3 C 6 H 3 0 3 126 Salicylic HC 7 H 5 0 3 138 ,, Sulphuric H 2 S0 4 98 Sulphurous H 2 S0 3 82 Tannic ... H 4 CtfHi 8 O l7 618 ,, Tartaric H 4 C 4 H 2 0 6 1 5o Alcohol C 2 H 5 HO 46 „ Methyl CH 3 HO 32 Alum A1 2 (S0 4 ) 3 , K,S0 4 2 4 H 2 0 948 , , Chrome Cr,(S0 4 ) 3 K 2 S0 4 . 24H;o 999 Ammonia ... NH 3 17 Ammonium Bichromate (NH 4 ) 2 Cr 2 0 7 253 ,, Bromide ... NH 4 Br 98 , , Carbonate NH 4 HC0 3 , NH 4 C0,NH, 175 ,, Chloride NH 4 Ce 535 , , Iodide NH 4 I 145 ,, Nitrate NH 4 N0 3 80 „ Oxalate (NH 4 ) 2 C 2 0 4 124 ,, Sulphide... NH 4 HS 5i ,, Sulphocyanide ... NH 4 CNS 76 Barium Bromide BaBr 2 297 „ Chloride BaCl,, 2H,0 244 Iodide Bal, 39i Nitrate Cadmium Bromide Ba(NO" 3 ) 2 261 CdBi^Hp 344 ,, Chloride ... CdCL, 183 Iodide Cdl," 366 Calcium Bromide CaBr 2 4H,0 272 Carbonate ... CaCO s 100 „ Chloride CaCl 2 in Iodide Cal, 294 Calcium Hypochlorite, or Chloride of Lime .. CaCl 2 0,CaCl, 254 590 II. TABLES. Formula. Molecular Weight. Copper Acetate Cu(C 3 H 3 0.,) H 0 200 „ Bromide CuBr., 223-4 „ Chloride CuCLH 2 0 171 Sulphate CuS0 4 *5H,0 249 and Ammonium Sul- phate CuS0 4 4NH 3 245-5 Glycerine C 3 H.,(HO) 3 92 Gold Perchloride AuCl, 3025 Ilydroquinone C 6 H 4 2HO no Hydroxylamine Chloride NH 3 OHCl — Iron Chloride (ferrous) FeCl, 127 ,, „ (ferric) Fe 2 Cf 6 325 ., Citrate .. Fe 2 (C 6 H,0 7 ) 3 598 „ Iodide Fel, 3IO „ Nitrate Fe(N0 3 ).,6II 2 0 288 ,, Oxalate (ferrous) FeC 2 0 4 ' I44 „ (ferric) Fe 2 (C,0 4 ) 3 370 ,, Sulphate (ferrous) FeS0 4 , 7ll,0 278 (ferric) Fe,(S0 4 ) 3 4OO ,, Ammonia Sulphate FeS0 4 , (NH 4 ) 2 S0 4 6ILO 392 Lead Acetate ... Pb(C,H 3 0 2 3),H,0 379 ,, Carbonate Pb(C0 3 , Pb(HO), 774 Iodide Pbl 2 460 ,, Nitrate P1)(N0 3 ), 33i ,, Oxide ... PbO 223 Lithium Bromide LiBr 87 ,, Chloride LiCl 42'5 ,, Iodide Li I 134 Magnesium Bromide ... MgBr 1X4 Chloride ... MgCL 95 Iodide Mgl 2 278 ,, Sulphate ... MgSOjILO 246 Mercury Chloride (mercuric) HgCL 271 ,, (mercurous) Cyanide HgCl 235-5 HeCy, 252 ,, Iodide (mercuric) ... Hgl, 454 ,, ,, (mercurous) ... Hgl 327 Platinum Chloride PtCL 339 Potassium Bicarbonate KHCO3 100 Bichromate K.,Cr.,0 7 294-6 I >1 1 |i u ... ... l\ 1 )1 1 191 ,, Carbonate K,C0 3 138-2 Potassium Chlorate KC10 3 1224 ,, Chloride KC1 745 ,, Chloro-platinite ... 488-4 , , Citrate K 3 C f( IL,0 7 H 2 0 324 3 Cyanide KCN 65 59i APPENDIX. Potassium Ferricyanide , , Ferrocyanide , , Hydrate . . . Iodide ' Nitrate , , Permanganate ,, Sulphocyanide Silver Acetate Bromide , , Carbonate Chloride Citrate Fluoride Iodide ... ,, Nitrate ,, Nitrite Oxalate Oxide ... , , Sulphide Sodium Acetate „ Biborate (Borax) Bromide ,, Bicarbonate ... ,, Carbonate „ Chloride Citrate Hydrate ,, Hyposulphite „ Iodide Nitrate „ Sulphantimonite Sulphate Sulphide „ Sulphite Strontium Bromide ... ,, Chloride ... Nitrate Tin Chloride (Stannic) ,, „ (Stannous) Uranium Bromide „ Nitrate „ Sulphate Zinc Bromide Chloride ... „ Iodide ,, Nitrate ,, Sulphate Formula. K 4 FeC 6 N e3 H s O KHO KI KN0 3 K 2 M 2 0 3 KCNS AgC,,H 3 0 2 AgBr Ag 2 C0 3 AgCl Ag 3 C 6 H 5 0 7 AgFl Agl AgN0 3 AgNO, Ag 2 C 2 0 4 Ag 2 0 Ag 2 S NaC,H 3 0.„ 6H,0 Na,B 4 0 7 ioH,6 ' NaBr NaHC0 3 Na 9 C0 3 ioHX> " NaCl NagC fl H 5 0 7 NaHO Na,S.,0 3 5H 2 0 * Nal NaN0 3 NaSbS 3 Na 2 S0 4 ioH 2 0 Na 2 S9H,0 Na 2 S0 3 7H 2 0 SrBr 2 6H,0 SrCl 2 6H;0 Sr(N0 3 ), SnCU SnCl 2 2H 2 0 UBr^HaO UO,(N0 3 ) 2 6H,0 Ua(S0 4 )3H,b ZnBr., ZnClJ Znl 2 Zn(N0 3 ) 2 6H,0 ZnS0 4 , 7H,6 592 II. TABLES. Usual Sizes of French and Italian Dry Plates. French. Inches. 64 bv 9 Centimetres ... ... 2-; by 37 9 »l 12 , ... ••• ... 37 ,, 47 T C xj n ... ... ... 47 „ 5 '9 l 1 18 ... 31 , , / ** 12 , 20 ... 47 „ 7-8 I c 21 ,, ... ... j y 1 » 8-2 22 11 • ■ • J y i) 8-6 18 9/1 7 - 0 21 „ 27 „ ... 8-2 „ 106 24 II 3° • •• 9'4 n T I -8 27 M 33 ■> ... io-6 12-9 27 M 35 m ... io*6 137 30 M 40 ... ir8 157 40 1, 50 ... 157 „ 19-6 60 ... 19*6 „ 23-6 Italian. Inches. 9 by 12 Centimetres ... 37 by 47 12 „ 16 , • 47 6-3 12 ,, 18 „ ••• 47 11 13 M 18 „ ... 5'i » 7-0 12 „ 20 47 m 7*8 18 „ 24 ... 70 M 9-4 21 „ 27 „ ... 8-2 „ io*6 24 » 30 ••• 9'4 ,. 1 1-8 27 33 ... io-6 129 30 „ 36 ... 1 1 S „ 141 40 11 5o ... 157 - 19^) 50 „ 60 ... i9'6 „ 236 Sizes of Glass, Mounts, Paper, Etc. Petite cards 1' by One-ninth plate ... ... ... 2 „ 2.\ One-sixth plate ... 3| ,, 3] One-fourth plate ... ... ... 3] „ 4] Half plate 4} Jay 6$ and 4] 5 1 593 QQ APPENDIX. Sizes of Glass, Mounts, Paper, Etc. {continued). Half plate (English) 4f „ 6£ Whole plate (4-4) 6£ U Extra 4-4 ... 8 ,, io Other sizes are expressed by inches. Sizes of Mounts. Stereoscopic 3| by 7, 4 by 7, 4^ by 7, 4^ by7, 5 by 8 Victoria 3i by 5 Imperial 7| „ 9* Boudoir Si H »i Panel ... 4 M Minette I! M 2| Card 4 „ 4* Cabinet 4i M 6i Promenade 4i „ 74 Sizes of Albumen Paper. 18 by 22f, 2o| by 24^, 22 by 36, 26 by 40, 27 by 42 Sizes of blotting paper 19 by 24 Freezing Mixtures. Reducing the Temperature From To parts. Degrees C Degrees C. 3 Nitrate of sodium + 4 water ... +13-2 — 5-3 9 Phosphate of sodium + 4 dilute nitric acid +10 — 9 3 Sulphate of sodium + 2 dilute nitric acid + 10 — 10 1 Nitrate of sodium + 4 water — io-6 1 Chloride of potassium + 4 water — 11 -8 5 Sal-ammoniac + 5 saltpetre 8 Sulphate of sodium + 5 cone, sul- phuric acid +10 — 17 1 Sulphocyanate of potass. + 1 water + 18 — 21 1 Chloride of sodium + 3 snow — 2 1 1 Sal-ammoniac + 1 saltpetre + 1 water ... ... ... ... +8 — 24 3 Crystal, chloride of calcium + 1 snow —36 1 Snow 4- 1 dilute sulphuric acid ... — 5 — 41 594 II. TABLES. Table of Elements Name. Atomic weight. /\tuminiurii ... Antimony T OCX Arsenic ... 75 oarium ••• l 37 43 "R " cm n tVi JDlcjiHUUl ... 208 "9 Boron 1 1 Rrnminp Ul KJHHLIKZ ... 1 £1 H TT1 1 11TTI « it ammon. Ger. Ammonio-citrate of iron. „ ,, Silber. Ger. Silver c itrate. Clair de lune. Fr. Moonlight effect. Cliche. Fr. Negative. Cliches poses. Fr. Time exposure. Cliquet. Fr. Spring catch for dark slide. Collage. Fr. Mounting. 605 APPENDIX. Colle d'amidon. Fr. Starch paste. „ liquide. Fr. Liquid glue. „ marine. Fr. Marine glue. „ de poisson. Fr. Fish glue. Collodionage. Fr. \ ' . . . Collodioniren. Ger.) Collodionising. Collodion ricine. Fr. Enamel collodion. „ sensibilise. Fr. Sensitive collodion. Collodium. Ger. Collodion. „ verfahren, trockenes. Ger. Collodio-bromide process. „ „ nasses. Ger. Wet collodion process. Collodiumwolle. Ger.\ p Colloxylin. Ger. J * J Colophane. Fr j Resin Colophonmm. Ger. J Combinationsdruck. Ger. Combination printing. Compensateur. Fr. Yellow screen. Compositbild. Ger. Composite portrait. Concentrirt. Ger. Saturated (solution). Condensateur. Fr. Condenser. Contactdruck. Ger. Contact print. Contretype. Fr. Reversed negative. Controlluhr. Ger. Indicator, register. Copie. Ger. Print. Copirautomat. Ger. Automatic printing machine. „ camera. Ger. Copying camera. Copiren. Ger. Printing. Copirrahmen. Ger. Printing frame. Corallin gelbes. Ger A . ,,. . ^ r Aunne. Corellme jaune. Fr. J Corindon. Fr. Emery. Corps de la monture. Fr. Lens tube. Coton azotique. Fr.\ „ .. ^ I Pyroxylin. „ poudre. Fr. J Couche sensible. Fr. Sensitive film. Coupe ovale. Fr. Print trimmer. Courbure de champ. Fr. Curvature of field. Coussin de feutre. Fr. Felt pads. Couvercle de l'objectiv. Fr. Lens cap. Crayeuse epreuve. Fr. Chalky print. Cremaillere. Fr. Rack and pinion. Creuset. Fr. Crucible. Cristalline. Fr. Aniline. 606 IV. SYNONYMS. Crochet. Fr. Dipper. Crocus. Gey. Oxide of iron. Cyankalium. Gey. Potassium cyanide. Cyanofer. Fr j Cyanotype. Cyanotypverfahren. Ger) Cyanure. Fr. Cyanide. Cyanwasserstoffseife. Ger. Potassium cyanide soap. D Daguerrotypie. Fy. Daguerrotype. Dammar harz. Gey. Gum Dammar. Dauerpapier. Gey. Ready sensitised paper. Deckung. Gey. Density. Definition sur les bords. Fy. Marginal definition. Degradateur. Fy. Vignette. Deltapapier. Gey. Gelatino-chloride paper. Demiteintes. Fy. Half-tones. Depot pulverulent blanc. Fy. White powdery deposit (lime). Destilliren. Gey. To distil. Deutoxyde de mercure. Fy. Mercuric oxide. Dialyse. Fy. Dialysis. Diaphanaskop. Gey. Diaphanoscope, lanternoscope. Diaphragme centrale. Fy. Central diaphragm. „ etoile. Fy. Star stop. , Iris. Fr. Iris diaphragm. „ qui reduit l'lntensite* lumineuse du ciel. Fr, Cloud stop. „ tournant. Fy. Wheel diaphragm. Diapositiv. Gey. Transparency. Diazodruck. Gey. Diazotypc printing. Dichtigkeit. Ger. Density. Distance focale. Fy. Focus. Doigtier. Fr. Plate lifter. Doppelcassette. Gey. Double dark slide. Doppelgangerbild. Ger. Double photograph, one person in two positions on one plate. Doppeljodid. Gey. Solution of silver iodide in potassium iodide. Doppelobjectiv. Gey. Doublet lens. Doppeltchromsiiures Ammoniak. Ger. Ammonium bichromate. „ Kali. Gey. Potassium bichromate. Doppeltkohlensaures Natron. Gey. Sodium bicarbonate. Doppeltransportverfahren. Ger. Double-transfer carbon pro© ss, Dosenlibelle. Gey. A level. Double tirage. Fr. Combination printing. 607 APP.ENp.IX. Draussenaufnahme. Ger. Outdoor photography. Drehblende. Ger. Revolving or wheel diaphragm. Dreibeinstativ. Ger. Tripod stand. Drillingscassette. Ger. Multiple dark slide. Druck. Ger. Print. Drucken. Ger. Printing. Dunkelzelt. Ger. Dark tent. „ zimmer. Ger. Dark room. ,, „ larape. Ger. Dark room lamp. Durcir. Fr. To harden. Dynaktinometer. Ger. \ . „ Y Actinometer. „ metre. Fr. J E. Eau brom.ee. Fr. Bromine water. „ chloree. Fr. Chlorine water. „ de Javelle. Fr. Eau de Javelle. „ mere. Fr. Mother liquor, regale. Fr. Aqua regia. Ebenheit des Feldes. Ger. Flatness of field. Ebonit. Ger. Ebonite. Eburneumverfahren. Ger. Eburneum process. Eclair magnesique. Fr. Magnesium flash light. Eclairage. Fr. Lighting. „ a la Rembrandt. Fr. Rembrandt lighting. , , inoffensif. Fr. Non-actinic light. Ecran d'eclairage. Fr. Reflector, jaune. Fr. Yellow screen. „ strie. Fr. Cross-line screen. Ecrou du pied. Fr. Tripod head. Effets du jour et du nuit. Fr. Dissolving views. Einfaches objectiv. Ger. Single landscape lens. Einfachtransportverfahren. Ger. Single-transfer carbon process. Einfallswinkel. Ger. Angle of incidence. Eingebrannte Photographien. Ger. Ceramic photographs. Einlage. Ger. Printing-frame pad. Einlagen. Ger. Carriers for dark slides. Einstaubverfahren. Ger. Powder process. Einstellen. Ger. To focus. Einstell-loupe. Ger. Focussing magnifier. Einstellschraube. Ger. Focussing screw. Einstelltuch. Ger. Focussing cloth. Eintaucher. Ger. Dipper. 608 IV. SYNONYMS. Eisenblaudruck. Ger. Cyanotype process. Eisenchlorid. Ger. Ferric chloride. Eisenflecken. Ger. Particles of iron. Eisenoxalat. Ger. Ferric oxalate. „ oxyde. Ger. Ferric oxide. „ ,, schwefelsaures. Ger. Ferric sulphate. „ vitriol. Ger. Ferrous sulphate. Eisessig. Ger. Glacial acetic acid. Eiweiss. Ger. Albumen. Elemente. Ger. Elements. Elfenbeinschwarz. Ger. Ivory black. Emailfarbe. Ger. Enamel colours. Emailler. Fr. To enamel. Emailphotographien. Ger. \ _ . _ , ? ~ ]■ Ceramic enamels. Emaux photographiques. Fr. J Emeri. Fr. Emery. Empfindlichkeit. Ger. Sensitiveness. Emulsion a collodion iodo-bromuree. Fr. Collodion iodo-bromide emulsion. „ a l'ebullition. Fr. Boiled emulsion. Encre de Chine. Fr. Chinese ink. Englisch Roth. Ger. Oxide of iron. Entfarben. Ger. To clear, decolorise. Entwickelung. Ger. Development. „ sdruck. Ger. A print by development, e^g. bro.nitle. Entwickler. Ger. Developer. Eosin-blaustich. Ger. Erythro.sin. Epreuve. Fr. Proof, print. Epreuves bombees. Fr. Cameo prints. ,, sans eclat. Fr. Flat prints. Escamoter les plaques. Fr. To change plat( 5. Esprit de bois. Fr. Wood spirit, methylated spirit. Essence de goudron. Fr. Coal-tar oil. „ huile terebinthine. Fr. Spirit of turpentin< „ de poires. Fr. Amyl acetate. Essigsaure. Ger. Acetic acid. Essigsaureamylester. Ger. Amyl acetate. Essigsaures Blei. Ger. Lead acetate ,, Eisenoxydul. Ger. Ferrous acetate. „ Natron. Ger. Sodium acetate. Essoreuse. Fr. Centrifugal machine. Etendage. Fr. Coating (plates). Etoffe jaune. Fr. Canary medium. 609 R K I APPENDIX. Euryskop. Gcr. Euryscopc. Exposition. Ger. Exposure. „ messer. Ger. Exposure meter. F. Faiblisseur. Fr. Reducer. Fallverschluss. Gcr. Drop shutter. Farbenempfindlich. Ger. Colour sensitive. Farbschleier. Ger. Green fog. Farrine fossile. Fr. Infusorial earth. Fecule. Fr. Starch. Federharz. Ger. India-rubber. Fernobjectiv. Ger. Telephotographic lens. Ferreux, sels ferreux. Fr. Ferrous salts. Ferricyanure de potassium. Fr. Ferricyanide of potassium. Ferridcyankalium. Ger. Ferridcyanide of potassium. Ferrioxalat. Ger. Ferric oxalate. Ferriques, sels ferriques. Ferric salts. Ferroacetat. Ger. Ferric acetate. Ferrotypie. Fr., Ger. Ferrotype. Ferrotyplack. Ger. Benzole or crystal varnish. Fiel de boeuf. Fr. Ox-gall. Firniss. Ger. Varnish. Fischleim. Ger. Isindass. Fixage. Fr. Fixation. Fixirbad. Ger. Fixing bath. „ saures. Ger. Acid fixing bath. Fixirnatron. Ger. Hyposulphite of soda. Flacon comptes gouttes. Fr. Drop glass. Fleurs de zink. Fr. Oxide of zinc. Floue, image floue. Fr. Flat image. Fluorwasserstoffsaure. Ger. Hydrofluoric acid. Flussaure. Ger. Hydrofluoric acid. Flussmittel. Ger. Flux.- Focale, distance focale. Fr. Focus, focal length. Focimetre. Fr. Focimeter. Focus-differenz. Ger. Non-coincidence of foci. „ messer. Ger. Focimeter. „ tiefe. Ger. Depth of focus. „ weite. Ger. Focus, focal length. Folien. Ger. Films. Fond. Fr. Background. Foyer Fr. Focus. 610 IV. SYNONYMS. Freilichtaufnahmen. Ger. Outdoor photography. Fulmi-coton. Fr. Pyroxylin. Fumigation. Fr. Fuming. G. Gaiacol. Ger. Guaiacol. Gallussaure. Ger. Gallic acid. Ganze Platte. Ger. Wholeplate, 8.V x 61 inches. Gasgluhlicht. Ger. Incandescent gas light. Gaze azote. Fr. Nitrogen. „ nitreux. Fr. Nitrous oxide. Geheimcamera. Ger. Detective camera. Gelatine bichromatee. Fr. Bichromated gelatine. Gelatinobromure. Fr. Gelatino-bromide. Gelatinochlorure. Fr. Gelatino-chloride. Gelatinotypie. Fr. Leimtype. Gelbfarbung. Ger. Yellow stain. ,, scheibe. Ger. Yellow screen. „ schleier. Ger. Yellow stain. „ wurzel. Ger. Turmeric. Gerben. Ger. To harden. Gerbsaure. Ger. Tannic acid. Gesicbtsfeld. Ger. \ . Gesichts-winkel. Ger.) An & lc of v,ew ' angle mcluded by lenb ' Giessen. Ger. To coat. Gla^age. Far. Enamelling. Glaserkitt. Ger. Putty. Glashaus. Ger. Studio. Glimmer. Ger. Mica. Glu marine. Fr. Marine glue. Goldbad. Ger. Gold bath, toning bath. Goldchloridkalium. Ger. Chloride of gold and potassium. Goldgelber Stoff. Ger. Canary medium. Goldsalz. Ger. Gold salt. Goldsaures Ammoniak. Ger. Fulminating gold. Gomme. Fr. Gum. „ elastique. Fr. India-rubber. „ laque. Fr. Shellac. Gommeline. Fr. Dextrin. Gravimcter. Fr. Hydrometer. Gravure heliographique sur zinc. Fr. Zinc etching. „ „ en taille douce. Fr. Photogravure. Gnines Plattenputzpulver. Ger. Infusorial earth. 6n APPENDIX. Griinschleier. Ger. Green fog. Guajakharz. Ger. Guaiacum resin. Guillotineverschluss. Ger. Drop shutter. Gummi. Ger. Gum. „ elasticum. Ger. India-rubber. „ lack. Ger. Shellac. „ Quetschwalze. Ger. Roller squeegee. ' H. Halo. Fr. Halation. Harten. Ger. To harden. Harzseife. Ger. Resin soap. Hausenblaes. Ger. Isinglass. Haute. Ger. Films. Heiss-satinir maschine. Ger. Burnisher. Heliogravure. Ger. Photogravure. Hermetischer Verschluss. Ger. Hermetically sealing. Hervorrufung. Ger. Development. Hintergrund. Ger. Background. Hinterkleiden. Ger. Backing. Hirschhornsalz. Ger. Ammonium carbonate. Hof. Ger. Halation. Hone lichter. Ger. High lights. Hbllenstein. Ger. Silver nitrate. Holzalkohol. Ger. Methylated spirit. Holzessig — Holzessigsaure. Ger. Pyroligneous acid. Holzgeist. Ger. Methylated alcohol. Honig. Ger. Honey. Hornsilber. Ger. Silver chloride. Huile de lavande. Fr. Oil of lavender. „ lin. Fr. Linseed oil. Hydrogene. Fr. Hydrogen. „ sulfure. Fr. Sulphuretted hydrogen. Hydrooxygenlicht. Ger. Oxy-hydrogen light. Hydrothionsaure. Ger. Sulphuretted hydrogen. Hydrure de phenyle. Fr. Benzine. Hyposulfite de soude. Fr. Hyposulphite of soda I. Iconogene. Fr. Eikonogen. Iconometre. Fr. \ , 7 . _ } View meter. Ikonometer. Ger.) Image confuse. Fr. Flat image. 612 IV. SYNONYMS. Image double. Fr. Double image. Impression par contact. Fr. Contact printing. Infusorienerde. Ger. Infusorial earth. Innenaufnahmen. Ger. Interiors. Instantanes. Fr. Instantaneous shots. Intensite. Fr. Intensity, density. Interieurs. Fr. Interiors. Inter mediaires. Fr. Carriers, lode. Fr. Iodine. Iodure. Fr. Iodide. Irisblende. Ger. Iris diaphragm . Islandisches Moos. Ger. Iceland Moss. Ivoire vegetal. Fr. Vegetable ivory. J. Jalousiecassette. Ger. Roller-blind dark slide Jalousieverschluss. Ger. Blind shutter. Javelle'sche Lauge. Ger. Eau de Javellc. Jenenser Glas. Ger. Jena glass. Jod. Ger. Iodine. Jodammonium. Ger. Ammonium iodide. Jodbromsilber-Collodium emulsion. Ger. Iodo-bromide collodion emulsion. Jodbromsilber-Gelatine emulsion. Ger. Iodo-bromide gelatine emulsion. Jodcadmium. Ger. Cadmium iodide. calcium. Ger. Calcium iodide. „ collodium. Ger. Iodised collodion. „ eosin. Ger. Erythrosin. „ kalium. Ger. Potassium iodide. „ lithium. Ger. Lithium iodide. natrium. Ger. Sodium iodide. papier. Ger. Iodised paper. „ quecksilber. Ger. Mercuric iodide. „ tinctur. Ger. Iodine tincture. wasserstoff. Ger. Hydriodic acid. „ zink. Ger. Zinc iodide. K. Kali Blausaures. Ger. Potassium cyanide. Kaliumchromalaun. Ger. Chrome alum. „ eisencyanid. Ger. Ferridcyanide of potassium. „ „ cyanur. Ger. Ferrocyanide of potassium. 6x3 APPENDIX. Kaliumnatriumtartrat. Ger. Rochelle salts. „ platinchlortir. Ger. Chloroplatinite of potassium. ,, wasserglas. Ger. Silicate of potassium. Kalk. Ger. Chalk. „ gebrannter. Ger. Quick-lime. „ geloschter. Ger. Slaked lime. Kalklicht. Ger. Limelight. Kalkschleier. Ger. White powdery deposit (lime). Kaltemischungen. Ger. Freezing mixtures. Kappenrohr. Ger. Flange, lens hood. Kasein. Ger. Casein. Kautschuk. Ger. India-rubber. Keragyre. Fr. Silver chloride. Kienruss. Ger. Lampblack. Kieselguhr, geschlammter. Ger. Infusorial earth. Kieselsauresalze. Ger. Silicates. Kieselsaures Kali. Ger. Silicate of potash. Kippschalen. Ger. Well dish. Kitt. Ger. Putty. Klammern. Ger. Clips. Klappenverschluss. Ger. Flap shutter, sky shade shutter. Klarbad. Ger. Clearing bath. Klarheit. Ger. Clearness. Kleben. Ger. Mounting. Kleesaure. Ger. Oxalic acid. Kleister. Ger. Starch paste. Knallgas. Ger. Hydrogen. Kochemulsion. Ger. Boiled emulsion. Kochsalz. Ger. Common salt. Koliledruck. Ger. Carbon printing. Kohlendisulfid. Ger. Carbon bisulphide. Kohlensaure. Ger. Carbonate. Konigswasser. Ger. Aqua regia. Kopf halter. Ger. Head rest. Kopfscbirm. Ger. Reflector. Korn. Ger. Grain. Kraft. Ger. Density. Kraftigung. Ger. Intensification. Krauseln. Ger. Frilling. Kreidiges Bild. Ger. Chalky print. Kreosot. Ger. Creasote. Kronglas. Ger. Crown glass. Krummung. Ger. Curvature. 614 IV. SYNONYMS. Kugelobjectiv. Ger. Globe lens. Kupfer. Ger. Copper. „ vitriol. Ger. Sulphate of copper. L. Laboratoire noire. Fr. Dark room. Lack. Ger. Varnish. Lackmus. Ger. Litmus. Lampe de laboratoire. Fr. Dark room lamp. Lampenruss. Ger. Lampblack. landschaftslinse. Ger. Landscape lens. Lanterne americaine. Fr. Sciopticon lantern. „ magique. Fr. Magic lantern. Lapis. Ger. Silver nitrate. Laque. Fr. Shellac. Latentes Bild. Ger. Latent image. Laterna magica. Ger. Magic lantern. Laternbilder. Ger. Lantern slide. Laufbrett. Ger. Baseboard. Lavendelbl. Ger. Oil oflavender. Ledercollodium. Ger. Enamel collodion. Leimtypie. Ger. Leimtype. Leinol. Ger. Linseed oil. Lentille. Fr. Lens. Leucbtfarbe. Ger. Luminous paint. Leveur des plaques. Fr. Plate lifter. Libelle. Ger. Level. Lichen d'Islande. Fr. Iceland moss. Lichtbildmesskunst. Ger. Photogrammetrv. Lichtdruck. Ger. Collotype. Lichtempfindlichkeit. Ger. Sensitiveness. Lichter, hone. Ger. High lights. Lichtfleck, centraler. Ger. Flare spot. Lichthof. Ger. Halation. Lichtkraft eines objectiv. Ger. Rapidity of a lens. Lichtkupferdruck. Ger. Photogravure. Lichtpapier. Ger. Waxed tissue paper. Lichtpausverfahren. Ger. Cyanotypc. Lichtschleier. Ger. Light fog. Lignin. Ger. Cellulose. Lineaturen. Ger. Screen plates. Linotypie. Ger. Enlargements on canvas. Linse. Ger. Lens. 61.S APPENDIX. Locale Verstarkung. Ger. Local intensification. Lochcamera. Ger. Pinhole camera. Longuer de foyer. Fr. Focal length. Losung. Ger. Solution. Loupe de mis au point. Fr. Focussing magnifier. „ redressante. Fr. Erecting eyepiece. Lourde, epreuves lourdes. Fr. Flat prints. Luftblasen. Ger. Air bells. Luftperspektiv. Ger. Aerial perspective. Lumiere diffuse. Fr. Diffused light. „ de Drummond. Fr. Limelight. „ eclair. Fr. Flashlight. Lumieres, grandes lumieres. Fr. Lights, high lights. Lut de vitrifier. Fr. Putty. M. Macgilp. Ger. Maglip. Magazin. Ger. Magazine. Magnesie noire. Fr. Black oxide of manganese. Magnesiumblitzlicht. Ger A _„ . „ putzlicht. Ger.) Ma g nes >" m flashlight. Magnium. Ger. Magnesium. Makrophotographie. Ger. Macrophotography, enlarging. Mangane. Fr. Black oxide of manganese. Mangansuperoxyde. Ger. Black oxide of manganese. Marienbad. Ger. Hot-water bath. Marienglas. Ger. Mica. Marineleim. Ger. Marine glue. Marquer automatique. Fr. Automatic indicator. Marques. Fr. Spots. Masken. Ger. Masks. Masquer. Fr. To back (plates). Mastix. Ger. Mastic. Matrize. Ger. Negative. Mattlack. Ger. Matt varnish. Mattolein. Ger. Matt varnish (Dammar I part, turpentine 5 parts). Mattscheibe. Ger. Ground glass, focussing screen. Maturation. Fr. Ripening. Megilp. Ger\ Megilpe. Fr.) Mehlig. Ger. Mealy. Menisque. Fr. Meniscus. Mennige. Ger. Minium, red lead. 616 IV. SYNONYMS. Mensur. Ger. Graduated measure. Mercure. Fr. Mercury. Mercurographie. Ger. Merc urography. Mere lessive. Fr. Mother liquor. Messbildverfahren. Ger. Photogrammetry. Metadiphenol. Fr. Resorcin. Metallflecken. Ger. Metallic spots. Methylalkohol. Ger. Methylated spirit. Miel. Fr. Honey. Mikrophotographie. Ger. Microphotography. Milch. Ger. Milk. Milchglas. Ger. Opal glass. Milchsaure. Ger. Lactic acid. Milchsaures Silber. Ger. Lactate of silver. Minium. Fr. Red lead. Mise au point. Fr. Focussing. Modell. Ger. Sitter. Molken. Ger. Whey. Momentaufnahmen. Ger. Instantaneous exposures. „ verschluss. Ger. Instantaneous shutter. Mondscheineffect. Ger. Moonlight effect. Monochrom. Ger. Monochrome. Monosulfure de potassium. Fr. Liver of sulphur. Mortier. Fr. Mortar. Moscouade. Fr. Cane sugar. Muscovit. Ger. Mica. Mutterlauge. Ger. Mother liquor. N. Nadelstiche. Ger. Pinholes. Natrium. Ger. Sodium. weinstein. Ger. Tartrate of soda and potash. Naturalphotographie. Ger. Naturalistic photography. Nebelbild. Ger. Dissolving view. Negatif de dessins au trait. Fr. Line negative. „ sur papier. Fr. Paper negative. Negativ. Ger. Negative. bad. Ger. Negative bath. „ lack. Ger. Negative varnish. ft papier. Ger. Negative paper. retoucbe. Ger. Negative retouching. „ stander. Ger. Drying rack. „ waschkasten. Ger. Plate washer. 6i 7 APPENDIX. Peinture de Balmain. Fr. Luminous paint. Pellicules. Fr. Films. „ a celluloides. Fr. Celluloid films. „ d'huilage. Fr. Negative paper. Perdre de l'intensite. Fr. To lose depth, intensity, vigour. Perlsalz. Ger. Sodium phosphate. Petrole. Fr. Naphtha. Phenylamin. Ger.\ AnUine Phenylamine. Fr.) Phenylsaure. Ger. Carbolic acid. Phosphin. Ger. Chrysanilin. Phosphor. GerA ph horus . Phosphore. Fr.) Phosphorographie. Ger. Phosphorography. Phosphorsaures Natron. Ger. Sodium phosphate. „ Silber. Ger. Silver phosphate. Photochemigraphie. Ger. Zinc etching in line. Photochromie. Ger. Crystoleum painting. Photocopie. Fr. Positive, print. Photogalvanographie. Ger. Photo-galvanography. Photoglyptie. Ger. Woodbury-type printing. Photogrammetrie. Ger. Surveying by photography. Photographie ohne Objectiv. Ger. Pinhole photography. „ stereoscopique. Fr. Stereoscopic photography. ,, sur bois. Fr. Photography on wood. „ vitrifiees. Fr. Enamels. Photogravure directe. Fr. Line and half-tone block-making. „ du mercure. Fr. Mercurography. ,, sur zinc. Fr. Zincography. Photolithophane. Ger. Photography on porcelain. Photo livre. Fr. Book camera. Photomecanique. Fr. Photo-mechanical. Photomechanische verfahren. Ger. Photo-mechanical process. Photometre. Ft. Photometer. Photominiatiir. Ger. Crystoleum painting. Photoplastigraphie. Ger. Photo-sculpture. Photorelief. Ger. Woodbury-type. Photosculptur. Ger. Photo-sculpture. Phototel. Ger. ~\ A process of transmitting photos along a Phototelegraphie. Fr. j wire by electricity. Phototopographie. Ger. Photographic surveying. Phototype. Fr. Negative. Phototypogravure. Fr. Line and half-tone block-making. 6i8 IV. SYNONYMS. Orthoskopisches Objectiv. Ger. Orthoscopic lens. Optische Brennpunkt. Ger. Visual focus. „ Sensibilisatoren. Gey. Optical sensitisers. Ouverture de l'objectif. Fr. Lens aperture. Oxalsaure. Ger. Oxalic acid. Oxalsaures Eisenoxyd. Ger. Ferric oxalate. „ Ammon. Ger. Ammonio-ferric oxalate. „ Natron. Ger. Sodio-ferric oxalate. „ Eisenoxydul. Ger. Ferrous oxalate. Oxalsaures Kali neutrales. Ger. Neutral oxalate of potash. „ Natron. Ger. Sodium oxalate. „ Silber. Ger. Silver oxalate. Oxaniline. Fr. Paramidophenol. Oxyammoniaque. Fr. Hydroxylamin hydrochlorate. Oxydes. Fr. Oxides. Oxygene. Fr. Oxygen. Oxyphenol. Fr. Pyrocatechin. Ozon. Ger. Ozone. P. Panier laveur. Fr. Plate washer. Panoramalinse. Ger. Panoramic lens. Papier albumine. Fr. Albumenised paper. „ „ brillant. Fr. Double albumenised paper. „ couche. Fr. Baryta paper. dioptique. Fr. Waxed tissue paper. „ au gelatino-chlorure. Fr. Gclatino-chloride paper. „ bromure. Fr. Gelatino-bromide paper. „ iodnree. Fr. Iodised paper. „ n^gatif. Fr. \ „ negativ. Ger.) Negatlve paper - „ nitroglucose. Fr. Nitro-glucose paper. photographique. Fr. Photographic plain paper. „ positif pelliculaire. Fr. Transferotype paper. reactif. Fr. Test paper. ,, sale. Fr. Plain salted paper. de Saxe. Fr. Saxe paper. „ sensible albumine. Fr. Ready sensitised paper. „ similiplatine. Fr. Simili-platine paper. Papyrographie. Ger., Fr. Papyrography. Parasoleil. Fr. Lens hood. Patronen. Ger. Cartridge. 619 APPENDIX. Neige, battre en neige. Fr. Snow, to beat to snow. Nettete. Fr. Sharpness (of image). Netznegativ. Ger. Line screen. Nicol'sches Prisma. Ger. Nicol's prism. Nitramidin. Ger. Xyloidine. Nitrirterzucker. Ger. Nitro-glucose. Nitroglucosepapier. Ger. Nitro-glucose paper. Nitrostarke. Ger. Xyloidine. Niveau d'air, niveau a bulles d'air. Fr. Level. Nivellirgestell. Ger. Level. Noir animal. Fr. Ivory black. „ de fumee. Fr. Lampblack. „ d'ivoire. Fr. Ivory black. ;, de platine. Fr. Platinum black. O. Objectif. Fr. Objective, lens. „ achromatique. Fr. Achromatic lens. „ double. Fr. Doublet lens. „ a portraits. Fr. Portrait lens. rectilineare grand angle. Fr. Wide-angle rectilinear. „ simple. Fr. Single lens. „ symetrique. Fr. Symmetrical lens. „ telephotographique. Fr. Telephotographic lens. Objectiv. Ger. Objective, lens. „ brett. Ger. Lens board. „ deckel. Ger. Lens cap. „ satz. Ger. Casket lens. „ verschluss. Ger. Instantaneous shutter. Obturateur. Fr. Shutter. Oeffnung der linse or des Objectivs. Ger. Lens aperture. Oel. Ger. Oil. Opalplatten. Ger. Opal plates. Oppositions. Fr. Contrasts. Ochsengalle. Ger. Ox-gall. a clapet. Fr. Flap shutter, a guillotine. Fr. Drop shutter, a rideau. Fr. Blind shutter, a secteurs. Fr. Sector shutter. 620 IV. SYNONYMS. Randscharfe. Ger. Marginal definition. Rasterplatte. Ger. Ruled or line screen. Rauchern. Ger. To fume. Reagenspapier. Ger. Test paper. Recolte des residus. Fr. Recovery of residues. Rectilinearlinse. Ger. Rectilinear lens. Reducteur. Fr. Reducer. Reductionsmittel. Ger. Reducers. Reflecteur. Fr. Reflector. Reflectorschirm. Ger. Reflector. Reibschale. Ger. Mortar. Reifen. Ger. To ripen. Reisecamera. Ger. Tourist camera. Reisestativ. Ger. Tourist stand. Reliefdruck. Ger. Woodbury-type printing. Rembrandtbeleuchtung. Ger. Rembrandt lighting. Renforcateur. Fr. Intensifier. a l'azotate de plomb. Fr. Lead intensifier. a l'azotate d'urane. Fr. Uranium intensifier. au mercure. Fr. Mercury intensifier. Residus. Fr. Residues. Resine de dammar. Fr. Gum Dammar. „ ga'iac. Fr. Gum Guaiacum. Retardateur. Fr. Restrainer. Retouche. Fr. Retouching. Retouchirlack. Ger. Retouching medium. Retouchirpult. Ger. Retouching desk. Revelateur. Fr. Developer. Revolveblende. Ger. Wheel diaphragms. Rhodanammonium. Ger. Ammonium sulphocyariide. Rhodankalium. Ger. Potassium sulphocyanidc. Rochellesalz. Ger. Rochelle salts. Rohcollodium. Ger. Plain collodion. Rohpapier. Ger. Plain paper. Rbhrenlibelle. Ger. Level. Rohrzucker. Ger. Cane sugar. Rollcassette. Ger. Roll holder. Rosolsaure. Ger. Aurine. Rotationsapparat. Ger. Panoramic camera, Rotheisenstein. Ger. V _ . . Renforcement. Fr. Intensification. Rdthel. Ger. / ^ xme Rothschleier. Ger. Red log. 621 APPENDIX. Rouge de quinoleine. Fr. Chinoline red. Rouleau a collage. Fr. Roller squeegee. Riickstande. Ger. Residues. Russische bilder. Ger. Vignettes on black ground. Sac a escamoter. Fr. Changing bag. Safran des Indes. Fr. Turmeric. Salmiak. Gen Sal-ammoniac. Salon de pose. Fr. Studio. Saloncamera. Ger. Studio camera. Salpeter. Ger.\ e . a. 7- r Potassium nitrate. Salpetre. Fr. J Salpetergas. Ger. Nitrogen. Salpetersalzsaure. Ger. Aqua regia. Salpetersaure. Ger. Nitric acid. Salpetersaures Ammoniak. Ger. Ammonium nitrate. „ Blei. Ger. Lead nitrate. „ Eisenoxydul. Ger. Ferrous nitrate. Uranoxyd. Ger. Ferric nitrate. „ Uranoxydul. Ger. Uranium nitrate. Salpetrigesaure. Ger. Nitrous acid. Salpetrigsaures Kali. Ger. Potassium nitrite. Salzpapier. Ger. Plain salted paper. Salzsaure. Ger. Hydrochloric acid. Salzs'aures Blei. Ger. Lead chloride. Hydroxylamin. Ger. Hydroxylamin hydrochloride. Sammellinse. Ger. Convergent or positive lens. Sandarak. Ger. \ _ , „ v Sandarac. Sandaraque. Fr. f Sandbad. Ger. Sand bath. Saponite. Fr. Talc, French chalk. Satinage. Fr. Burnishing. Satiniren. Ger. To burnish. Sauerstoff. Ger. Oxygen. Sauren. Ger. Acids. Saures scbwefligsaures Kali. Ger. Potassium metabisulphite. „ „ Natron. Ger. Acid sulphite of soda, i weinsaures Kali. Ger. Cream of tartar. Savon a l'acide cyanhydrique. Fr. Cyanide soap. Schalen. Ger. Dishes. Scharfe. Ger. Definition, sharpness. Schatten. Ger. Shadows. 622 IV. SYNONYMS. Pkotoxylographie. Ger. Photography on wood blocks. Photozinkographie. Ger. Photozincography. Physikalische Entwickelung. Ger. Physical development. Pied. Fr. Stand. „ d'atelier. Fr. Studio stand. „ canne. Fr. Walking-stick stand. ,, parapluie. Fr. Umbrella stand. " table. Fr. Studio or table stand. Pierre infernale. Fr. Silver nitrate. „ ponce. Fr. Pumice stone. Pince a cliches. Fr. Plate lifter. Pinces americaines. Fr. American wooden clips. Planchette d'objectif. Fr. Lens board. „ se deplacant dans les deux sens. Fr. Shifting lens board. Planitude des champs. Fr. Flatness of field. Plaque entiere. Fr. Whole plate. „ souple. Fr. Films. Platindruck. Ger. Platinotype process. Platine. Fr. Platinum. Platinkaliumchlonir. Ger. Chloroplatinite of potash. Platinmohr. Ger. Platinum black. Platinpapier. Ger. Platinotype paper. Platinschwarz. Ger. Platinum black. Platten. Ger. Plates. Plattentrockenstander. Ger. Drying rack. Plattenformate. Ger. Plate sizes. Plattenhalter pneumatischer. Ger. Pneumatic holder. Plattenheber. Ger. Plate lifter. Plattenwaschkasten. Ger. Plate-washing tank. Plattenwechselvorrichtung. Ger. Plate-changing arrangement. Plattenzahler. Ger. Indicator. Plein air. Fr. Open air. Plissement. Fr. Frilling. Point de rosee. Fr. Dew point. Porcelaine transparente. Fr. Opal glass. Porte-objectiv. Fr. Lens board. „ plaques. Fr. Plate sheaths. Portrait a l'interieur. Fr. Indoor portraiture. „ en plein air. Fr. Outdoor portraiture. Portrataufnabme. Ger. Portraiture. Portratbust. Ger. Bust portrait. Portratobjectiv. Ger. Portrait lens. 623 APPENDIX. Pose. Fr. \ „ _ , „ Y Exposure. Pose, temps de. Fr. J ,, insuffisante. Fr. Insufficient, under-exposure. Positif. Fr. Positive. „ pour projection. Fr. Lantern slide. „ sur verre. Fr. Transparency. Positiv. Ger. Positive. Positivlack. Ger. Positive varnish, crystal varnish. Positivpapier. Ger. Raw paper. Positivretouche. Ger. Retouching prints. Potasche, * Ger. Potassium carbonate. Poudrage, procede par. Fr. Powder process. Poudre-coton. Fr. Pyroxylin. Poudre d'email. Fr. Enamel powder. Praservativ. Ger. 1 ~ _ , > Preservative. Preservateur. Fr. J Pressbausch. Ger. Felt printing-frame pad. Presse a satiner. Fr. Rolling machine. „ „ a chaud. Fr. Burnishing machine. Primulinverfahren. Ger. Primuline process. Prisma. Ger. Prism. Procede au charbon. Fr. Carbon process. ,, du double transfert. Fr. Double-transfer carbon Profondeur de foyer. Fr. Depth of focus. Projectionsapparat. Ger. Optical lantern. Pupitre a retoucher. Fr. Retouching desk. Pyrogall. Fr. \ Pyrogallol. Ger. I Pyrogallic acid. Pyrogallussaure. Ger. ) Pyrophotographie. Ger. Enamels. Pyroxyle. Fr. Pyroxylin. Q. Quart de plaque. Fr. Quarter plate. Quecksilber. Ger. Mercury. Quecksilberchlorid. Ger. Mercuric chloride. Quecksilberchloriir. Ger. Mercurous chloride. Quecksilberjodid. Ger. Mercuric iodide. Quecksilberverstarker. Ger. Mercury intensifier. Quetscher. Ger. Squeegee. R. Raclette. Fr. Squeegee. 624 IV. SYNONYMS. Schaukelcuvette. Ger. Automatic rocker. Scheidewasser. Ger. Nitric acid. Schellack. Ger. Shellac. Schichtseite. Ger. Film side. Schiessbaumwolle. Ger. Pyroxylin. Schirmstativ. Ger. Umbrella stand. Schlammkreide. Ger. Whitening. Schleier. Ger. Fog. Schlippe'sches Salz. Ger. Schlippe's salt. Schlitten. Ger. Baseboard. Schmelzfarben. Ger. Enamel colours. Schmelzfarbenbilder. Ger. Enamels. Schmelztiegel. Ger. Crucible. Schnee. Ger. Snow. Schnellphotographie Amerikanische. Gcr. Ferrotype. Schraffurplatten. Ger. Line screen. Schwarzen tiefste. Ger. Deepest shadows. Schwefel. Ger. Sulphur. Schwefelammonium. Ger. Ammonium sulphydrate. Schwefelantimon. Ger. Antimony sulphide. Schwefelantimon-Schwefelnatron. Ger. Schlippe's salt. Schwefelather. Ger. Sulphuric ether. Schwefelcyanammonium. Ger. Ammonium sulphocyanide. Scbwefelcyankalium. Ger. Potassium sulphocyanide. Schwefelkohlenstoff. Ger. Carbon disulphide. Schwefelleber. Gcr. Liver of sulphur. Schwefelmilch. Ger. Milk of sulphur. Schwefelsaure. Ger. Sulphuric acid. Schwefelsaures Eisenoxydul. Ger. Ferrous sulphate. »> ii ammon. Ger. Ammonio-sulphate of iron. Schwefelsaures Kupfer. Ger. \ ,, oxyd. Gcr. f Co PP er sul Phate. Schwefelsilber. Ger. Silver sulphide. Schwefeltonung. Ger. Sulphur toning. Schwefelwasserstoff. Gcr. Sulphuretted hydrogen. Schwefelwasserstoff-Ammoniak. Gcr. Ammonium sulphydrate. Schweflige Saure. Gcr. Sulphurous acid. Schwefligsaures Natron. Gcr. Sodium sulphite. Schwimmwaage. Ger. Hydrometer. Sectorenverschluss. Ger. Sector shutter. Seignettesalz. Ger. Rochelle salts. Sel. Fr. Salt. „ Ammonia . Fr. Sal-ammoniac. 625 S S APPENDIX. Sel de cuisine. Fr. Common salt. „ Saturne. Fr. Sugar of lead. „ Schlippe. Fr. Schlippe's salt. „ „ Seignette. Fr. Rochelle salts. Selen. Ger. Selenium. Selle's Uranverstarker. Ger. Selle's uranium intensifier. Sensibilisatoren, chemischer. Ger. Chemical sensitisers. Sensibilisiren. Ger. To sensitise. Sensibilite. Fr. Sensitiveness. Sensitocolorimeter. Ger. Colour sensitometer. Sicherheitsrand. Ger. Safe edge. Silber. Ger. Silver. Silberalbuminat. Ger. Silver albuminate. Silberbad. Ger. Silver bath. Silberbromid. Ger. Silver bromide. Silberchlorid. Ger. Silver chloride. Silberchlorur. Ger. Silver subchloride. Silberdruck. Ger. Silver print. Silberglanz. Ger. Silver sulphide (native). Silberjodid. Ger. Silver iodide. Silbermesser. Ger. Argentometer. Silbernitrat. Ger. Silver nitrate. Silbernitrit. Ger. Silver nitrite. Silberoxalat. Ger. Silver oxalate. Silberoxyd. Ger. Silver oxide. Silbersalpeter. Ger. Silver nitrate. Silbersulfid. Ger. Silver sulphide. Silbersulphat. Ger. Silver sulphate. Silicate. Fr. Silicate. Similiplatinpapier. Ger. Simile-platine paper. Smirgel. Ger. Emery. Soda. Ger. Sodium carbonate. Solution qui se conserve. Fr. Stock solution. Soufflet. Fr. Bellows. Soufre. Fr. Sulphur. Soulevements. Fr. Blisters. Sousexposition. Fr. Over-exposure. Speckstein. Ger. Talc, French chalk. Spektralanalyse. Ger. Spectrum analysis. Spektrum. Ger. Spectrum. Support a vis calantes. Fr. Levelling stand. Surexposition. Fr. Over-exposure. 626 IV. SYNONYMS. T. Taches. Fr. Spots, stains. „ metalliqu.es. Fr. Metallic spots. Tafelglas. Ger. Ordinary sheet glass. Tamis en crin. Fr. Hair sieve. Tanninverfahren. Ger. Tannin process. Tassen. Ger. Dishes. Tauchcuvette. Ger. Dipping bath or trough. Taucher. Ger. Dipper. Teinte. Fr. Tint. jaune. Fr. Yellow stain. Teinteur pour positifs. Fr. The cut-out part of a mask, disc. Tele-objectiv. Ger. Telephotographic lens. Temps de pose. Fr. Exposure. Tente. Fr. Dark tent. Terpentinbl. Ger. Spirits of turpentine. Tetrabromfluorescein. Ger. Eosin. Thaupunkt. Ger. Dew point. Thierische substanzen. Ger. Animal substances. Thierkohle. Ger. Animal charcoal. Tiefe des focus. Ger. Depth of focus. Tintencopirverfahren. Ger. Ink process. Tirage. Fr. Printing. Tischstativ. Ger. Studio or table stand. Tonen. Ger. Toning. Tonfixirbad. Ger. Combined toning and fixing bath. patronen. Ger. Combined toning and fixing cartridges. Topophotographie. Ger. Photographic surveying. Tournesol. Fr. Litmus. Trame artificielle. Fr. Screen plate, line screen. Transfert. Fr. Transfer. Transparentbild. Ger. Transparency. Traubenzucker. Ger. Glucose. Traumaticin. Ger. Solution of india-rubber in chloroform. Triebrohr. Ger. Lens tube. Trockenplatten. Ger. Dry plates. Trockenplattenlack. Ger. Dry-plate varnish. Trockenschrank. Ger. Drying cupboard. Trockenstander. Ger. Drying rack. Tropfglas. Ger. Drop glass. kalium. Ger. Erythrosin. Tragacanth. APPENDIX. Trous d'epingle. Fr. Pinholes. „ d'objectif. Fr. Casket lenses. Tusche. Ger. Indian ink. Tuyau mouture de l'objectif. Fr. Lens tube. Typogravure. Fr. Process-block making. U. Ueberbelichtung. Ger A Over-exposure. Ueberexposition. Ger. J Ueberfangglas. Ger. Flashed glass. Uebermangansaures Kali. Ger. Potassium permanganate. Unschadlicb.es Licht. Ger. Safe light. Unterbelichtung. Ger. Under-exposure. Unterchlorigsaures Calcium. Ger. Chloride of lime. Unterexposition. Ger. Under-exposure. Unterschwefligsaures Goldoxydulnatron. Ger. Sel d'or. „ Natron. Ger. Sodium hyposulphite. Unze. Ger. Ounce. Uraneopirverfahren Ger. Uranium printing process. Uranglas. Ger. Uranium glass. Urannitrat. Ger, ) Uranium nitrate . Uranylnitrat. Ger J Uranverstarker. Ger. Uranium intensifier. V. Ventouse pneumatique. Fr. Pneumatic ho Verbleichen. Ger. To bleach. Verbranntes Bild. Ger. Burnt out, over-exposed picture. Vergilben. Ger. To yellow, to turn yellow. Vergrbssern. Ger. To enlarge. Vergrosserungsapparat. Ger. Enlarging apparatus. Vernis. Fr. Varnish. ,, depoli. Fr. Matt varnish. ,, a negatifs. Fr. Negative varnish. „ siccatif. Fr. Meglip. Verre. Fr. Glass. „ depoli. Fr. Ground glass. „ de Muscovie. Fr. Mica. ,, d'urane. Fr. Uranium glass. Verschluss. Ger. Shutter (instantaneous). Verschwommenes Bild. Ger. Fuzzy image. Verstarker. Ger. Intensifier. Verstarkung. Ger. Intensification. 628 IV. SYNONYMS. Verzeichnung. Ger. Distortion. Verzogerer. Ger. Restrainer. Viertelplatte. Ger. Quarter plate. Vignetten. Ger. Vignettes. Vignettirdeckel. Ger. Vignetting board. Vinaigre de bois. Fr. Pyroligneous acid. glacial. Fr. Glacial acetic acid. Virage. Fr. Toning. Vis de rappel. Fr. Focussing screw. Viseur. Fr. Finder. Visirscheibe. Ger. Focussing screen. Visitkarte. Ger. Carte-de-visite. Vitriolsaure. Ger. Sulphuric acid. Voile. Fr. Fog. „ jaune. Fr. Yellow fog. „ noir. Fr. Black fog. „ rouge. Fr. Red fog. „ vert. Fr. Green fog. Volet a coulisses du chassis. Fr. Shutter of dark slide. Vorbad. Ger. Preliminary bath. Vorderblende. Ger. Diaphragm in front of lens. Vorrathslbsung. Ger. Stock solution. W. Wachs. Ger. Waschkasten. (*< or print washer. Wasser. Ger. Wau Wasserfirniss. Ger. Water varnish. Wasserfrei. Ger. Anhydrous. Wasserglas. Ger. Potassium silicate. Wasserstoff. Ger. Hydrogen. Wasserstoffsuperoxyd. Ger. Hydrogen peroxide. Wasserwaage. Ger. Water level, spirit level. Wechselkasten. Ger. Changing box. Wechseln der Platten. Ger. Changing plates. Wechselsack. Ger. Changing back. Weinsaure. Ger. \ Weinsteinsaure. Ger J Tartaric acid. Weinstein. Ger. Potassium bitartrate. Weitwinkelobjectiv. Ger. Wide-angle lens. Wiedergewinnung des gebrauchten Silbers. Ger. Recovery of silver residues. Wblbung des Bildes. Ger. Curvature of the field. 629 APPENDIX. Wolframsaures Natron. Ger. Sodium tungstate. Wolkenblende. Ger. Cloud stop. Woodburydruck. Ger, Woodbury-type printing. X. Xylo'idine. Ger., Fr. Xyloidine. Xylophotographie. Ger. Photography on wood. Z. Zahlvorrichtung. Ger. Indicator, register. Zahnstangentrieb. Ger. Rack and pinion. Zaponlack. Ger. Varnish of pyroxylin and amyl acetate. Zauberphotographien. Ger. • Magic photographs. Zeitaufnahmen. Ger. Time exposure. Zelt. Ger. Tent. Zerstreutes Licht. Ger. Diffused light. Zerstreuunglinse. Ger. Negative or divergent lens. Zimmeraufnahmen. Ger. Indoor portraiture. Zink. Ger. Zinc. Zuckerkalk-entwickler. Ger. Calcium saccharate developer. Zuckersaure. Ger. Oxalic acid. Zu Schnee schlagen. Ger. To beat to a froth. Zweifach chromsaures Kali. Ger. Potassium bichromate. 630 £5 GETTY RESEARCH INSTITUTE 3 3125 01409 2809