r'v**^^ olin.anx (^mmll Wimvmiii» J itoijg BOUGHT WITH THE INCOME | FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henrg W. Sage XS91 A.71G2.Q /6l7J9^. r '^-^-^'^ T / 1 Cornell University Library The original of tliis bool< is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031278470 PHOTOGEAPHY WITH EMULSIONS. PHOTOGBAPHY flTH EMOLSMS. A TEEATISE ON THE THEOEY AOT) PRACTICAL WORKING COLLODION AND GELATINE EMULSION PROCESSES. Capt. W. de W. ABNEY, R.E , F.R.S. TEIED EDITION. L02SID0N : PIPER & CAKTEE, 5, CASTLE STREET, HOLBORN, E.G. 1885. LONDON : PlPEll AND CAUTEK, CASTLE STREET, HOLEOKN, E.G. PREFACE, Another Edition of this work has been called for by the Publishers, and, in preparing it, the Author has endeavoured so to re-arrange and prune the older matter, and to insert new, as to make it useful to those whose knowledge of chemistry may be limited, as well as to those who are experts in that far-reaching science. Again, there are many who at present care nothing about theory, and who regard practical results as their sole aim. An endeavour has been made to meet their views as well, by, as far as possible, confining all theoretical considerations to those chapters which are marked with double asterisks in the table of Contents. These chapters may be omitted without in any VI PREFACE. way interfering with the practical part of the subject. Those readers who prefer to buy their dry plates in the market to preparing them them- selves, may omit the chapters marked with a single asterisk. The Author feels that there must be many short- comings in the book, although he has tried to keep it up to date. One thing, however, he may add, that there is no process stated in it which he has not thoroughly tried, and no theory which is given which he has not endeavoured to confirm or refute experimentally. W. DE W. Abney. South Kensington, September, 1885. CONTENTS. **I. —Preliminary Considerations ... i **II. —Alkaline Development ... .. ... ... ,,, 14 **III.— The Cause and Care of Fog in Emulsions 21 IV. — Dark Room and its Fittings 30 V. — Illumination of the Dark Room ... ... ... ... 41 **VI. — Introductory Remarks on Gelatine Emulsions ... ... 49* **VII. — Silver Iodide and Chloride in Emulsions .58* **VIII.— Gelatine 62* IS. — Gelatino-Bromo-Iodide Emulsion 69* X. — Bennett's Gelatine-Bromide Process 8L* XI. — Paget Prize Emulsion 81* XII. — Burton's Process 91* XIII. — Dr. Eder's Emulsions ' 93* XIV. — Cold Emulsifioation Process 101* XV. — Mr. Cotesworth's Cold Emulsifioation Process ... .. , 101* XVI. — A Process for Gelatine Emulsion Making in Hot Weather 105* XVII. — Gelatino-Bromide Emulsion by Precipitation 107* XVIII. — Dr. Van Monokhoven's Processes Ill* XIX. — Preparation of the Plates (Gelatine) 114* XX.— Testing Plates 122 XXL— Exposure of the Plates [ 127 XXII. — Development of .Gelatine Plates with Alkaline Developers 134 XXIII. — Development of Gelatine Plates with Ferrous Oxalate.,. 149 CONTENTS. CHAPTER TAGE XXIV. — Fixing, Intensifying, and Varnishing Gelatine Negatives 154 XXV.— Gelatino-Chloride Emulsions 163* XXVI. — Aceto- Gelatine Emulsions 169* XXVII. — Gelatino-Bromide and Gelatino-Chloride Papers ... 173* XXVIII.— Exposure of the Negative Paper 179 XXIX. — Development of Gelatino-Bromide Paper for Negatives 183 XXX. — Development of Positive Paper ... ... ... ... 192 XXXI.— Defects in Gelatine Plates ... , 197 **XXXII.— Collodion Emulsions— Introductory 208 XXXIU.— PyroxyUtt 211 XXXIV. — Preparation of a Collodion Emulsion 219 XXXV. — Canon Beechey's Process — M. Chardon's Process ... 229 XXXVI. — Collodion Emulsions to which Preservatives are Added 233 XXXVII.— Cooper's CoUodio -Bromide Reliable Dry Plate Process... 237 XXXVIII. — Collodio-Bromide Emulsion Prepared in the Alkaline State and with Excess of Bromide 2i2 XXXIX. — CoUodio-Albumen Emulsion 245 XL. — Preparation of the Plate 247 XXJ. — Preservatives used with Emulsions 255 XLII. — Development of the Plate 261 XLIII. — Collodio- Chloride Emulsion for Development 270 XLIV. — Defects in Collodion Emulsion Plates 274 XLV. — Emulsion Processes for Printing 277 XLVI. — Packing Plates 284 PHOTOGMPHY WITH EMULSIONS. CHAPTEK I. PRELIMINARY CONSIDERATIONS. The term emtdsion is derived from the Latin word " emulgere," to milk out, and the definition of it as found in the dictionary is, " any milk-like mixture prepared by uniting oil and water by means of another substance." For our photographic technology this is hardly a correct definition, for by it we mean a sensitive salt of silver in very minute division, held in suspension in some viscous body, such as gelatine, or, very often, collodion. An emulsion in its most elementary form may be con- sidered to be simply a pure silver haloid held in suspen- sion in collodion or gelatine, and so well prepared that when a plate is coated with it, a homogeneous film re- sults ; a film which, in fact, is at least equal in sensi- tiveness and in physical qualities to any which can be prepared by any other process. Emulsion processes are divided into two classes : one in which the emulsion is made up and used without any preliminary extraction of the soluble salts which are necessarily present in their manufacture, owing to the 2 PRELIMINARY CONSIDERATIONS. double decomposition of the salts employed, and the silver nitrate ; and the other where these soluble salts are extracted. In the first process the plates are washed after coating, and is usually confined to collodion emul- sions ; whilst in the second they are coated, and generally left to dry spontaneously. All emulsions at present in vogue for making negatives may be considered to be simply bromide of silver, since it is the basis on which all alterations by the addition of iodide or chloride are to be made. It will be seen in the con- text that these additions are not unimportant as regards the range of sensitiveness. The almost universal mode of producing an emulsion is to dissolve certain soluble bromides (such as potassium bromide) in the collodion or in a gelatine solution, and then to gradually pour a solution of silver nitrate dissolved in alcohol and water in the first case, or in water alone in the second, into the viscous fluid, by which means solid bromide of silver is formed, together with a soluble nitrate (sucli as potassium nitrate). It is this latter solu- ble product which in washed emulsions is removed, since, if a film be left to dry without eliminating it, crystalliza- tion sets up, and the surface of the coated plate is spoilt. Silver chloride is readily emulsified in the same way, substituting a soluble chloride (such as of sodium) for the soluble bromide. Silver iodide is also easily formed into an emulsion in gelatine, but it is formed with much more difficulty in collodion. We give the chemical equa- tion for the formation of silver bromide. Potassium Bromide and Silver Nitrate give Silver Bromide and Potassium Nitrate KBr + AgNOs = AgBr ■+■ KNO3 Bromide of silver may be produced in several molecular states, all of which have different degrees of sensitiveness. When we say different molecular states, we mean that the silver bromide has precisely the same chemical com- position, but that it is altered physically, the molecules PRELIMINARY COXSIDERATIOXS. 3 being larger in some cases than others ; the particles are built Tip of a greater or less nnmber of primary molecules, according to the rapidity of the formation of the solid, and its subsequent treatment by heat, ammonia, &c. Thus, it is known that white light, when transmitted through a film composed of gelatine, in which these parti- cles are suspended, may appear of a ruby, orange, green, purple, or grey colour ; and of these, three seem to be different states of molecular aggregation- — viz., ruby, green, and grey ; the others are probably mixtures of one or more of the three. We must assume that the reader is aware what a spectrum is. By exposing any of these modifications to its action, we find that the range of sen- sitiveness to the different coloured rays is varied. Thus PEISMATIO SPECTRUM. H C F E D B A L UUIIK — UOLET Via.ET BUIE CREEN YELIOV BED INFRA-RED Fig. 1. the rtiby and orange modification is sensitive to the ultra violet, the violet, and blue rays, and a little to the green ; the grey blue is sensitive to the same rays, but more strongly in the green, whilst it is able to be impressed by the yellow and by the red rays ; the green modification, when in collodion, is sensitive to the ultra-violet, the blue, very slightly to the green, and much more so to the red, and infra-red regions — that is, those dark ra3^s which are miscalled the heat rays. In fig. 2 the range of sensitiveness of two of these modifications (Nos. 3 and 4) is shown, as well as that of some other salts of silver. The comparative sensitiveness to different parts of the spectrum is shown by the height of the curves. In collodion emulsion the ruby and orange form of bromide is that most sought after, whilst in gelatine emul- PEELIMINAEY CONSIDERATIONS. slon the form whict is supposed to give the most sensi- tive films is the blue grey form ; though for our own part we consider that a tinge of yellow is essential to get the highest sensitiveness. The reason for selecting these forms we shall touch upon by-and-Tbye. PKELIMmARY CONSIDEPaTIONS. 5 Iodide of silver in its pure state is sensitive only to the ultra-violet, the violet, and the blue rays, and it may well be supposed that by adding iodide to the bromide, some modification of the range of spectral sensitiveness must be found. Such is the case, and it is more marked in gelatine emulsion, in which, were no iodide added, the emulsion would take the blue grey state (see fig. 2). The addition of chloride of silver to the bromide modi- fies the photographic qualities of the latter but little, and since it is b\it rarely used in any quantity, we need not consider it. When white light is allowed to act on chloride of silver for a sufficient time to blacken it, in the presence of moisture, or moist air, as is all air unless chemically purified, chlorine is given off. That this is the case is never disputed, its proof being as old as 1780, when Scheele made his classical experiments. We think also it will be allowed that when bromide of silver is acted upon similarly, bromine is given off ; a bromide plate when darkened absolutely smells of bromine, or some compound analogous to it. Let us take chloride of silver as the example on which to found an argument, for any reason- ing which may apply to the one will equally apply to the ■other principal haloid salts of silver — viz., the bromide and iodide. Homogeneous matter is made up of mole- cules, all having a similar composition, and such mole- cules are themselves made up of atoms. In the case of bromide of silver, for instance, the atoms are bromine and silver. Now we are told in most text-books that silver is a monad,* and that it requires only one atom of bromine to combine with one atom of silver ; confining ourselves to pure chemistry, without any reference to photographic action, the evidence of this is based on the behaviour of silver when combined with certain other elements. * The opinion, however, that silver is a monad is not absolutely allowed "by some chemists. b PRELIMINAEY CONSIDEEATIONS. The molecule of chloride of silver is, however, we are constrained to believe, made up of at least two atoms of silver and two of chlorine, and the question arises as to what substance is left behind after the chlorine has been dissociated from it by the action of light. Does such a body as a sub-bromide or sub-chloride exist ? Now we wiU not go into photographic evidence, but confine our- selves at first to chemical evidence simply. In 1839, the year when Daguerreotype was discovered, Wohler found that if hydrogen was passed over argentic-oxalate, mellitate, or citrate, when heated to the boiling point of water, half the acid was set free, and a dark brown argentous salt remained. The acid could be removed by washing, only a small portion of the argentous salt being removed, the solution of the latter forming a port-wine coloured liquid. Further, Wohler obtained argentous oxide (Ag^O) by means of repeatedly boiling soda-ley with argentic arsenite,* and Geuther found that argentous oxide is formed by precipitating silver nitrate with cuprous hydrate. Again, argentous oxide is produced by the action of hydrogen peroxide on metallic silver. A bright silver plate immersed in a neutral solution of hydrogen dioxide becomes covered with bubbles of oxygen, and coated with a greyish white film, while part of the silver is converted into hydrated argentous oxide, according to 'the equation — 2Ag2+H202=2HAg20. Argentous salts are also produced by passing hydrogen into ammoniacal solutions of silver salts. Such is an outline of the chemical evidence of the existence of argentous oxide, and it would appear that such evidence is very strong — in fact, as strong as required under any circumstances. That this is not the work of only one chemist adds more weight to the existence of such a compound. • Argentous oxide is, of course, the base o£ argentous citrate, oxalate, or mellitate. PEELIMINARY CONSIDERATIONS. < Such being granted, the admission of the possibility of the existence of sub-chloride or sub-bromide of silver is at once apparent. Wohler describes a method of prepar- ing it by adding to the argentous oxide a solution of hydrochloric acid, or of common salt. In this case we have : — AgiO+2HCl=2Ag201-t-H2O and Ag40-t-2NaCl=2Ag2Cl+Na.O Argentous chloride is also said to be formed by bringing silver in contact with a solution of sal-ammoniac, as is also the case by the first action of ferric chloride or cupric chloride. The argentous bromide (sub-bromide) can be formed in the same way. By chemical analogy, if there is such a substance as the sub-oxide or argentous oxide, there is the same reason for believing in the existence of the sub-chloride and sub-bromide. Now comes the question as to whether the same compound is produced by the action of light. When sUver chloride is exposed to the action of light, we know well that a violet- coloured substance is pro- duced, and that such a colouration is also found wheu exposure takes place in the presence of nitric acid. We also know that the metallic silver dissolves in dilute nitric acid. Now, since chlorine is evolved, one of two things must occur : either the total Hberation of the chlorine from the silver salt, or else its partial liberation. Which does it do ? Under any ordinary circumstances it would be said that it was not metallic silver which was left, since it was unacted upon by nitric acid ; however, there are those who will accept a conclusion derived from one isolated fact. Some thirty years ago or more, Guthrie experimented on this subject, and ho put it down that metallic silver was formed, but that it was in a passive state, similar to that state which iron takes. The connection between the two is not, however, very apparent. He found that the substance he got in every case of the darkened chloride was insoluble in nitric acid, but that O PBELIMINART CONSIDERATIONS. after treatment with ammonia the residue was soltiLle- This is exactly the hehaviour of chemically produced argentous chloride, and is a striking proof that the light- produced compound and this are identical. It is usually said, if silver bromide he exposed to light in nitric acid, that no change takes place in it — i. e., that it remains as silver bromide. Now, to test this, silver bromide was exposed to light in strong nitric acid, and subsequently the acid was treated with silver nitrate. A faint precipitate of bromide of silver immediately showed. If dilute nitric acid be used, the silver is dissolved from the sub-bromide almost at once. Now we have an exceedingly interesting proof that the salt formed by light and the argentous chloride are the same, independently of chemical proof. If a collo- dion film containing silver chloride be exposed to light till it is lavender, and be then exposed to the action of the spectrum, we get a coloured representation of that spectrum. Further, if a similar film be exposed to light, and the silver be reduced to the metallic state by a deve- loper, and it is then immersed till it assumes a grey colour in ferric chloride or cupric chloride, the same colourific action takes place ; or, again, if a metallic silver plate be treated in the same way, we have a coloured spectrum. It would be curious that such should be the case if the compounds are different. The amount of the chloride converted into the coloured salt, compared with the total amount to which a prolonged exposure to light is given to produce it, is small, perhaps not more than five per cent. ; but it must be recollected that chlorine as it is liberated from the chloride by light has always sub-chloride besides it, and it is always more probable that a larger percentage will combine with the sub-chloride and form chloride (AgjCl+Cl^Ag^Clj) rather than escape. For this reason there is no difficulty in reconciling fact with theory. PEEL13IINARY CONSIDERATIONS. 9 We may mention that Dr. Hodgkinson, by exposing a large quantity of chloride to light, has been able to isolate the sub-chloride by treating the mass with sodium chloride solutions, which are able to dissolve the chloride without destroying the sub-chloride, which remains insoluble. We may now assume that the prolonged action of light is to reduce the haloid to a simpler type, which we may call the sub-haloid. Thus — Silver Bromide gives Silver Sub-Bromide and Bromine. AgjBr^ = AgjBr + Br. It is a pertinent question to put as to whether the visible a,nd the invisible (or developable) image are of the same nature ; which may be answered by another question : Can the line be drawn where the image is invisible ? If so, what is the boundary between the two ? If we admit the theory of the formation of the visible image, it seems hardly logical to deny a similar formation for the invisible or photographic image. It is quite possible that beings with more acute sight than ourselves might be able to see the image which we cannot. As we know, certain insects can hear sounds which do not affect our auditory nerves. Coloured particles are visible when put together en masse ; but if only a few coloured particles are present in a mass of colourless particle, it is quite certain they may remain undetected. If we take a couple of plates, and coat them with emulsion, and place them in som^e conducting solu- tion, connect the films with a very sensitive galvanometer, and allow light for a second to fall on one plate, there will be a deflection of the needle, showing that chemical action is taking place on it ; expose for a time sufficiently long to discolour the film, and the same result occurs. There is chemical action, then, in both cases : what is the difference between the two ? The chemical theory of the photographic image is based upon the fact that where light of a proper kind acts on a molecule the atoms are 10 PRELIMINARY CONSIDERATIONS. made to swing, however short be that exposure. If it he- for a second, the average number of vibrations which light of a mean wave length makes is somewhere about 700 million millions, a goodly number, and which, if the blows from the ether be well timed, is sufficient to make an atom of chlorine or bromine fly off from the molecule, or, in other words, sufficient to make it swing out of the sphere of molecular attraction, particularly if some other molecule is near which is ready to abstract it and incorporate it with its atoms, and so to form a new body. Let us stop and see whether su.ch is the practical, and not theoretical, action. Take bromide of silver emulsion, in collodion, which latter, when pure, is almost an abso- lutely neutral substance, and what occurs when it is used dry V It is sensitive to a certain extent ; but add some bromine-loving preservative to the film, and the increase of sensitiveness is much increased. If the condition of the bromide under the action of light were merely change in the arrangement of the atoms, but not a chemical change, there would be no use in the bromide absorbent, and it ought to be positively detrimental. Let ITS take another example still of this. If a washed iodide of silver emulsion is prepared with excess of iodide, and a plate be prepared and exposed, no image is developable. Dip half of such a plate into a solution of tannic acid or beer, and develop ; the half that has an iodine absorbent will develop after exposure to light, the other half will not. The chemical theory of the photo- graphic image which assumes the liberation of an atom of bromine from the bromide, explains it imme- diately. One of the most remarkable proofs of the truth of this theory is found in the explanation of some experiments made by the author on the effect of the spectrum on mix- tures of the haloid salts of silver, an account of which is published in the " Proceedings of the Royal Society," and PEELIMINAEY CONSIDEEATIONS. 11 a diagram of wliicli is seen on page 4. It is there shown, if you have a mixture of pure and dry iodide and bromide of silver, and expose it to the spectrum, that at the place where the iodide alone would show the greatest action on development, the image on the iodide has been destroyed by liberation of bromine from the bromide, which is in contact with it, and which is also acted upon by rays of the same refrangibility. Now no mere physical theory of the photographic image would account for this. If a mere change in the arrangement of the atoms took place, instead of the developed image being almost nil at this particular part of the spectrum, it would be increased in intensity, and such increased intensity is to be found if a lialogen absorbent is in contact with them. We will merely mention that one form of the physical theory of the formation of tlie photographic image is that the light sets up vibrations, and that whilst no chemical change is wrought, yet that it is the increased vibrations which give the developing power, and that when the vibrations cease the image is non-existent. This is one of those pretty ideas which have to be relegated to the same limbo as perpetual motion. We hear of a gelatine plate being exposed and developed with unimpaired vigour after a lapse of twelve or twenty months. We ourselves have kept gelatine plates a year, and developed some of them every three months. These plates were ex- posed behind a sensitometer, and kept to ascertain if there were any fading of the image. Plates which gave 22 on the sensitometer at first, after the lapse of a year gave an image showing 21. Hence, to accept this theory, we should have to conclude that the vibrations commenced at a certain time, kept of the same amplitude, or nearly so, for the space of a year. If a collodion plate is treated in the same way, the image will die out much more rapidly. A couple of months is sufficient in most cases to obliterate nearly every trace of an image, and yet it is the same material acted upon in both cases. ^Vhy should it act 12 PRELIMINARY CONSIDERATIONS. -differently in the two cases ? The answer is somewhat hard on the vihration hypothesis, hut it is perfectly easy on the chemical theory of the photographic image. Ex- posure to the atmosphere, or to a substance which can oxidize the image, we have shown destroys the developing capacity of the image, and the difference of the enclo- sures of the bromide when in the gelatine and collodion fully explains the reason why the destruction is more rapid in the one case than the other. Again, we can absolutely show that if increased ampli- tude of vibration be given to the atoms of a bromide plate, such vibrations subside rapidly. If we take a hot iron and press it to the back of a gelatine plate, and ex- ,pose the latter to light whilst hot, and then, after cooling, develop the plate, we get an image of tlie iron shown by increased blackening of those parts which were in contact with the glass heated by the ffon. If, however, the hot iron be applied to the back of the plate, which is then allowed to cool, and if, after such cooling, it be exposed to light, no trace of the iron shape is visible ; the silver salt has returned to its normal condition. In the one case, we have the amplitude of the vibra- tions of the atoms of the molecules (which, when at any temperature presumably above the absolute zero, are ■always vibrating) increased by the application of the hot iron, but not sufficiently to make them separate entirely. Where light of proper colour impinges on these atoms, which are already swinging ^viih increased amplitude, they are more readily swung off than when it has the whole of the work to perform upon them, and as a re- sult we have the image of the flat iron shown by the in- • creased number of molecules which have been de-atomized. In the other case the plate is heated, and the increased amplitude of vibration must stiU be there, and, according to the vibration theory, should continue ; but the fact is, that it does nothing of the kind. The atoms resume their normal swing when the plate is cold. It is for those PKELI3IIKAEY CONSIDERATIONS. 13 who liold the physical theory of the formation of the photographic image to explain why the increased ampli- tude, due to the heating, dies away, whilst that due to light does not. The chemical theory, then, fully accounts for these experiments, which, as far as we are aware, no other theory can do. CHAPTEE II. ALKALINE DEVELOPMENT. It will be noticed that all emulsion plates are developed •either by alkaline development, or by ferrous oxalate development, and we propose to consider these two deve- lopers from their theoretical point of view. It may be said, first of all, that iodide is not readily amenable to alkaline development, and we therefore do not consider it ; the bromide and chloride are the salts which are chiefly employed, and it is their part in it we shall consider. An alkaline developer consists of a strong absorbent of ■oxygen, an alkali, and a soluble bromide or chloride. The two first are the only essentials for the reduction of a salt of silver to the metallic state. Thus, if we take precipi- tated bromide of silver,* and add to it a solution of pyro gallic acid and ammonia, we shall find that it is rapidly reduced to the metallic state. If, however, we precipitate the silver bromide in the dark, and add to the developing solutions a little bromide of potassium, we find that the mass is redaced more slowly, the soluble bromide acting as a retarder to the rediiction. If we have a film which has been exposed to a camera image, and develop by the * Precipitated by dissolving a little bromide of potassium in water, and adding to it silver nitrate, and then Trashing. ALKALINE DEVELOrJMENT. 1,5 unrestvained solution, we shall find, as a rule with gela- tine films, and always with collodion films, a reduction all over the surface ; whereas, if we use one containing the restrainer, we shall find that the image develops properly. Whenever there is a reduction of the silver salt there is ■an alteration in the developing solution, due to a chemical change in it. Now what does this reducing action depend on? In the alkaline developer, we repeat, we have three effectives (putting on one side the water, Avhich enters into all three), viz., the pyrogallic acid, the alkali, and the restraining "bromide. When pyrogallic acid is mixed with an alkali, it is in an unstable state, and greedily absorbs oxygen from whence it can get it. During the process of develop- ment it is in contact with water, and with haloid salts of silver — viz., the bromide and the sub-bromide. Take the former into consideration first, leaving out the action of the restrainer, viz., the soluble bromide. We then iave a vigorous oxygen absorbent, and a haloid salt of silver and water. Now, all bodies when mixed together have a tendency to enter into new combinations, which take the most stable form they can. This is what the three substances do. The oxygen absorbent will take up oxygen from the water, which, at the moment of libera- tion, reduces the silver bromide to the metallic state, and the liberated bromine forms, with the hydrogen, hydro- bromic acid. This, in its turn, forms bromide ot the alkali and water again. Roughly, it may be expressed thus — Alkali Pyro Water and Silver Bromide give Oxidized Pyro Silver 2NHj,HO + Pyro+ H^O + Ag^Br^ . = Pyro + 2Ag + Alkaline Bromide and Water. 2NHiBr + 2H2O So far, we have treated merely of the reduction ot bromide of silver (AgBr,), and not the sub-bromide (Agi). Now the action of light on the bromide (AgaBrj) is to cause one atom of bromine to swing off, and in doing this a certain amount of work has been performed by the 16 ALKALIXE DEVELOPMENT. light itself ; and that being the case the reduction of the sub-biomide ought to be more easily effected than the bromide. In other words, light has partially effected on the silver bromide what the chemical action of develop- ment has to do when light has not acted. Suppose, then, we have an amount of work to be done on the bromide in order to reduce it to metallic silver of (say) 100 units, and that light does 20 of these units, evidently chemical action of developing has only to do 80 units. So if we have bromide and sub-bromide of silver together, and arrange that the chemical energy ot the developer shall be (say) 95 units, the developer would be able to reduce the sub-bromide and not the bromide ; and in case the energy of the developer was more than 100 units, it would attack the sub-bromide in preference to bro- mide. With a very weak developer this is the case, and it may be used without any (what is termed a) restrainer. Now what is the action of the restrainer ? This is a point which is more difficult to answer. We were now talking of a chemical restrainer, viz., the soluble bromide. Silver salts are known to form double salts very readily. For instance, there are double chlorides of silver and sodium, and they can be obtained in definite crystals, as can the double bromides, and it seems more than probable that the restraining action is due to this affinity. When we have double salts formed, the energy of their com- bination is shown by the heat which is given out during the combination. Mow, in order to dissociate them from each other, work would have to be done on the double molecules ; in other words, the work that the two do in combining, which is shown by a rise in temperature, the same amount of work would have to be done on them to separate them. The double salt is, therefore, more stable than the bromide salt per se. The energy existing in the developer has not only to do the work of separating the bromine, but also of separating the double salt. It may be said in objection to this that the bromide is in solution, ALKALINE DEVELOPMENT. 17 and therefore cannot form a double salt. Tliat would be valid if we could say that no double salt was formed. We know, for instance, that two salts when in solution will form a double salt, and that two solids form a double salt. The question as to whether a salt in solution, such as potassium bromide, can form a double salt with a solid, such as silver bromide, is not quite so easily answered ; but the evidence, as far as it goes, is in its favour. In some electro-chemical experiments which we are undertaking, the formation of a double salt seems to be confirmed, and, as we have said, the temperature test certainly favours such an idea. It must be quite under- stood that this is not put forward except as a good work- ing hypothesis, which, so far, is uncontradicted by known facts. It may be found to be due to some other cause, though we believe not. We thus lay the action of the restrainer to the forma- tion of a double salt during development, and a conse- quent increase in work that the developer has to perform to reduce it. A body like the sub-bromide does not appear to form double salts ; its composition is not allied to the soluble bromide. Now it may be taken that solubility of the one body in the other is indicative of the possibility of the formation of the double salts. Dr. Hodgkinson finds that whilst the chloride of silver is soluble in sodium chloride, the sub-chloride is not, and thus he arrives at a method of separating the two. This points to a similar action of the bromide and sub-bromide in soluble bromide, or it must not be forgotten that bromide of silver is soluble in bromide of potassium to a limited extent. We have so far treated of the action of pyrogallic acid alkali restrainer, or the bromide or sub-bromide of silver ; but there is a further action in development that has to be considered. The quantity of sub-bromide to be re- duced is infinitesimally small when the brief exposure to light alone produces it. The first act of the developer is to reduce the sub-bromide, but at the same instant that 18 ALKALINE DEVELOPMENT. the metallic silver is formed this metal combines with the silver bromide in contact mth it, and fresh sub-bromide is formed, which is then acted upon, and a visible image is produced. The mere fact of a chemical restrainer being- used, however, retards development, since the metallic silver first deposited by the development of the sub- bromide has, before it can combine with the adjacent bromide, to undo the double salt, and as this is work to be performed, the development is of necessity slower. Thus, silver and silver bromide yield silver sub-bromide ; or, AgBr+Ag=Ag2Br There are two kinds of restrainers : one chemical, and the other physical. We have treated of the former ; no\v as to the latter. A physical restrainer is one by Avhich the developer is deprived ot rapid access to the exposed sensitive salt, and this is particularly the case when an emulsion is prepared in gelatine. In this state the colloidal nature of the gela- tine permits only a very slow access of the developer to the embedded salt. In other words, the small portion of developer which attacks the particle is obliged to attack that portion of it which is more readily reduced, and in the case of gelatino-bromide films, that is the sub- bromide. Albumen acts in the same way, and a physical restrainer is used when with the developer are mixed solutions of gelatine or albumen. It is thus evident that if an absorbent of oxygen, which by itself is capable of reducing the sub-bromide at the first shock without reducing the bromide, must be a better agent to use than pyrogallic acid, which requires a re- strainer. Such an oxygen absorbent has been found by the writer in hydrokinone, which, under ordinary circum- stances, has no tendency to reduce the silver bromide, and it has a greater affinity for oxygen than any known organic substance. From chemical analogy it may be assumed that tlie ALIOiilNE DEVELOPMENT. 19 molecular attraction of the metallic silver is strongest at the instant of its reduction. With the weak alkaline deve- loper the silver is reduced but slowly from the hromide, and hence it hecomes less " nascent," if we may use the term, than it is when it is rapidly reduced. It is found from chemical analysis of the developer after it has been used, that a weakly alkaline solution is only capable of reducing a small amount of the bromide compared with a concentrated solution ; in other words, whilst the same amount of ingredients possess the same amount of total energy, yet when diluted the time taken to use up the energy is longer than with more concentrated solutions, and thus the energy applicable at each small interval of time is less in the former than in the latter case. If we strike a moderately rigidly fixed target with a hundred Ibullets fired at intervals of a minute, we should not ex- pect to overthrow it, but if the 100 bullets were fired all together, and with the same velocity, the united energy of the bullets might probably cause the target to be laid low. In both cases the total energies applied are the same, but the effects are difiierent. In a rough way we may apply this simile to the weak and strong developers when acting on the silver salt. It will be observed, that various formulas are given for alkaline development ; in one ferro-cyanide of potassium is mixed with the pyrogallic acid, and in another sulphite of soda. The value of these appears to be either that they form a new compound, or that they absorb oxygen. In any case, the longer the pyrogallic acid remains unoxi- dized, the more effectual should be the development. The hydi'osulphite developer may be classed amongst the alkaline developers. We next have to consider the ferrous-oxalate developer, and it matters but little, as regards theoretical considera- tions, as to which way it is formed. It will be seen by the formula given later that the ferrous-oxalate developer is in reality a solution of ferrous-oxalate in neutral 20 ALKALINE DEVELOPMENT. potassium oxalate. The latter salt exercises no develop- ing action, but is rather a retarder to development than otherwise. We have therefore only to consider the action of ferrous-oxalate on silver sub-hromide, and it may be expressed as follows : — Ferrous Oxalate and Silver Sub-bromide give 3(Fe,GA) + 2Ag2Br Ferric Oxalate and Ferrous Bromide and Silver re.,(CA)3 + FeBr^ + 4Ag By which it will be seen that a metallic bromide is formed, together with ferric oxalate. This is subject again to a change with the potassium oxalate, ferrous-oxalate and potassium bromide being formed. Experience has shown the writer that the addition of a small quantity of hyposulphite makes development much more rapid, and that a gelatine plate requires less exposure with it. Let us trace what happens to the ferric salt formed : — Sodium Hyposulpliite and Ferric Oxalate give Na^SA + Fe2(C!A)3 = Hyposulpliite of Iron Fe,S203 and Ferrou^-Oxaiate Sodium Oxalate + ■P8(CA) + Na,(CA)3 We thus find that the ferrous hyposulphite and oxalate are formed, and also a sodium oxalate. It seems likely that the destruction of the ferric salt immediately On its forma- tion is one cause of the increased activity of the 'deve- loper. The ferrous citrate, ferrous citro-oxalate, and ferrous tartrate act, chemically, in the same waj- as the ferrous oxalate. CHAPTER III. THE Cause and cure of fog in emulsions. Every student in emulsion work has found, and will find, that the chief obstacle that he has to overcome to obtain success is the tendency for the plates prepared with an emulsion to fog, or veil over on development, and it has taken a great deal of experimental work to enable it to be overcome. The writer ventures to think that the re- searches he has made on the subject have explained in a ^reat measure, if not entirely, its rdison d'etre. Setting aside the collodion or gelatine from the question, and merely taking into consideration the sensitive salts ■employed, we may arrive at very definite results. It has been asserted that a neutral combination between two substances can never take place ; for example, if we mix potassium chloride with silver nitrate we shall never be able to get pure silver chloride, however much we may wash it — that either the soluble potassium or silver salt will always be in excess, though probably in the minutest quantities. This certainly is the case theoretically, because do what you will, and wash as long as you like, there still must be some infinitely small part of the soluble salt left behind. Now, in ordinary chemical analysis, where products have to be weighed, the re- sidual impurity may be inappreciable, being so infini- 22 CAUSE AND CUKE OE FOG. tesimal that no balance yet constructed can show them. Though a halance may he inoperative, yet, as is well known, light is able to show us impurities in a substance which may not be one-millionth part of a grain in weight. By passing the light emitted from heated vapours of the substance and its impurity through a prism, and noting its spectrum, we may be able to detect the latter. The spectroscope will not tell us at present, however, whether the silver or potassium is present as nitrate, chloride, bromide, oxide, &c. Where we are dealing with silver salts which are sensi- tive to light, and which are amenable to development, it is possible to ascertain whether certain compounds of silver are present. Impurities in the bromides, with which the silver bromide, for instance, is to be formed, can, in some cases, be shown by weighing. For, in a paper read before the Photographic ISociety of Great Britain on the 8th of February, 1876, Mr. Warnerke stated that on testing the different bromides, he foimd that considerable variation from the theoretical quantities necessary to combine with silver nitrate was observable. Potassium bromide is one of the most usual salts with which to form silver bromide. Let us see how it may be contaminated in its preparation. We find that the mother liquor from the sea water brine is treated with chlorine, and that this takes the place of the bromine which in sea water is in combination with magnesium ; the yellow liquid is agitated with ether, which takes up the bromine, and this etherial solution is treated with potash in solution. The bromine forms the bromate and bromide of the alkali, and when the alkali is nearly saturated, it is decanted off and further treated. Now, from what we have said be- fore, it is more than probable that the bromide is con- taminated with the alkali, however well it may be separated : the traces of alkali may even be so small as to be undetected by litmus paper. CAUSE AND CURE OF FOG. 23 Again, the bromides of tlie alkaline metals are prepared by acting on the alkalies with an excess of bromine, a similar reaction to that above taking place. The bromate is decomposed by ignition, and this heating alone tends to decompose the bromide, in which case we should have the oxide of the alkali left behind. In good preparations it would be excessiyely small, but still sufficient for the purpose we shall indicate presently. The bromides of the metals may be similarly contami- nated. Take zinc as an example ; the metal is easily oxidized, and the zinc oxide is soluble in zinc bromide, as it is in the chloride. In all these cases, then, it is possible we may have traces of oxide with the bromide. Again, there are some metals which form two bromides", as that of copper ; and experience shows that it is very hard to get all compounds fully saturated with bromine, a part of it being generally in the less saturated state. If such bromides, contaminated with the oxide, or con- taining the lower combination of bromine, be brought in contact with silver nitrate, we shall have two separate reactions to consider. In the case of the oxide contamina- tion, when silver nitrate is in excess, we shall have — Potassium Bromide, Potassium Oxide, and Silver Witi-ate xKBt + ' K2O + («-|-2)AgN03 give Silver Bromide, Silver Oxide, and Potassium Nitrate »AgBr + AgjO -I- (a;+2) KNO3 Or, besides the silver bromide, we shall have silver oxide formed. We have seen that we may have oxides and sub- bromides contaminating the bromides, and in a similar way we may have oxides and sub-chlorides contaminating the chloride. The writer has shown that it was possible to develop an image on a film never exposed to light, but which was in contact with a film (during the operation of development) on which an invisible image had been impressed. The explanation offered seems in every way to meet the requirements of the case, which is, that where 24 CAUSE AND CURE OF FOG. a nucleus, if it may he so termed, exists, there the silver from the adjacent bromide during development will be de- posited in preference to any other part of the film. Such a nucleus is found in the silver sub-bromide or sub-chloride when the one film is exposed to light. If it be chemically produced, we may assume it will act in a similar manner. The case of the oxide is not so clear ; but a little experiment will throw light on it. Prepare silver oxide as an emulsion in collodion ; dissolve (say) 6 grains of silver nitrate in an ounce of plain collodion, and add to it two grains of potash in alcohol. This will give an emulsion of oxide of silver. Now wash it, and add a drachm of it to an ounce of a washed collodion emulsion which works perfectly free from fog; coat a plate, and develop it. It will be found that a veiled image is pro- duced. In this case the silver oxide (presumably partially reduced to the metallic state, since the oxide is an un- stable compound) acts as the nucleus on which the silver bromide is reduced to the metallic state by the alkaline developer. It must be borne in mind that the invisible image must necessarily be composed of very minute particles of the altered silver salt. If, then, such a smaU number of such particles distributed over a film are sufficiently powerful to form nuclei for the development of the image, the same minute quantity of oxide, or chemically-produced sub- haloid of silver, might be capable of producing the same results. The above, then, seems to be the explanation of fog in emulsion plates. Now as to the remedies. It is well known that when we have an excess of soluble haloid, freedom from fog is secured. In some experiments we carried out, we found that silver bromide is formed before any other silver compound, except the iodide, when the sensitive salt is formed from haloid salts, and not from the halogens themselves. Thus, if potas- siiun bromide be contaminated with potash, we shall have both silver bromide and silver oxide formed, if an excess CAUSE AND CURE OF FOG. 20 of silver nitrate be added ; but if there be a defect of the nitrate, there will not be a trace of silver oxide, but only- silver bromide. Again, if we take bromide of copper, "which is usually contaminated with the sub-bromide, as .already stated, it will be found that the bromide is all utilized before the sub-bromide is attacked at all ; and if, in addition to the bromide, we have a metallic chloride present, which may be contaminated with sub-chloride, the order in which they will combine with the silver nitrate is : bromide, chloride, sub-bromide, sub-chloride. Thus, if there be only sufficient silver nitrate added to an emulsion to combine with the two first on the list, the other two will be left in the emulsion as harmless com- pounds. The method of eliminating fog from the finished emulsion in which there is at first an excess of silver nitrate is thus easy to guess, and we have the theoretical •explanation of a statement made some years ago by Major Russell, that a little soluble bromide ought to be left in the film when silver bromide is formed by the bath in the usual way. It may be remarked, parenthetically, that whether the image be developed by the alkaline or acid method, the same result must hold good. Supposing we have a washed emulsion which contains bromide, sub- bromide, and oxide of silver, and also a very slight excess of silver nitrate. The addition of certain metallic chlorides or of hydrochloric acid will at once convert the sub- bromide and oxide into the chloride of silver, leaving harm- less compounds behind. The metallic chlorides which are of use are those which readily part with chlorine, and which, therefore, preferably form more than one chloride, such as gold, copper, platinum, &c. 'When other chlorides, such as of the alkalies, are employed, the needful sub- stitution may not take place, because the affinity of the alkali for the chlorine is greater than for the sub-bromide ; -and therefore the elimination of the sub-bromide is not effected. Thus, if all the silver nitrate in original excess be converted into silver chloride, we have the silver sub- 20 CAUSE AND CUEE OK FOG. bromide to get rid of. Noiv, supposing Ave are using sodium chloride as a corrective, then we should have Silver Sub-bromide and Sodium Cbloride AgoBr + NaCl, which can form no new saturated silver compound, since an atom of metallic silver, sodium, bromine, or chlorine, cannot be left in a free state ; but if we use (say) copper chloride, we have — Silver Sub-bromide and Cupric Chloride L'Ag^Br + CuCl„ which can form — silver Bromide and Silver Chloride and Cuprous Chloride. AgBr + AgCi + CuCl. The CuCl, or sub-chloride of copper, is harmless, and can be left out of consideration. It will, therefore, be seen how it is that addition of these chlorides to a washed emulsion will give freedom from fog. Secondly, if an excess of silver nitrate be used, it is evident that something else besides a mere chloride will be required, since the sub-salts and oxides would be formed. This we find in the employment of an acid, or of a halo- gen itself, or both together, added to the emulsion, to be most rapidly effective. Whatever is used is best added to the soluble salts before the silver nitrate is added. Suppose nitric acid alone be employed, then any oxide or carbonate will immediately be attacked, as also any of the sub-bromides — such as of copper. Again, if aqua- regia be employed, wc know that chlorine is evolved in an extremely nascent state, and that this would attack either oxide or sub-bromide, fully saturating the unsatis- fied atom in the latter. If, now, silver nitrate be added, silver bromide and chloride would result with some com- pounds (perhaps such as the chlorate), which would be as inert as producers of fog as the silver nitrate itself. If a halogen be employed without any acid, the same result would occur. Thus, suppose we had as impurities. CAUSK AND CUBE OF FOG. 27' an oxide and a sub-bromide, and that we added a solution of bromine to it, we should get the oxide changed to a bromide and bromate (the latter salt of which is experi- mentally proved to be inert), and sub-bromide changed to a bromide. If the halogen be added last, when there is an excess of silver, it is probable that until all the latter is converted it will exert no unfogging action ; but if an acid, such as nitric acid, be added, it will exert its proper influence, though slowly ; for it will convert any oxide or compounds of the oxide into nitrate, and froin the silver sub-bromide dissolve away the loose atom of silver, converting the sub- bromide into bromide and nitrate. Thus — Silver , Nitric „• Silver , Silver . Nitrous „„;, -ar^^^^ Sub-tromide """i Acid S'^" Bromide ^""^ Nitrate ™"i Oxide ""^ ^^^"^ 4AgBr + 6HNO3 = 4AgBr -|- 4AgN03 + N2O3 + SHjO. (3r, at all events, a fresh combination will be made, which is unacted upon by the developer. There is also a method of eliminating fog from collo- dion dry plates when coated, without doctoring the emul- sion at all. This need not apply only to Avashed emul- sions, but it can be effected during the washing of the plates prepared by the unwashed emulsion. In addition to the elimination by the acids, and by the metals forming two bromides or chlorides, we can further effect it by using a solution of potassium bichromate,*' permanganate of potash, or peroxide of hydrogen, and other oxidizing agents, such as ferric-sulphate and ferric-oxalate. The reason of this seems to be due to oxidation, or to the direct formation of a new product ; the writer is still engaged in experiments on the subject. It may be, in the first case, that a minute quantity of silver bichromate is formed by the oxide, or that the free silver atom of the sub-bromide is oxidized, and then formed into silver bichromate ; with the second, it may be that the man- * This can be used with gelatine emulsions. 2S CAUSE AN'D CUKE OP FOG. ganese salt is substituted for the silver salt, and is inert ; and in the next two cases it may Tbe that the silver salt is per-oxidized, and forms an oxy-bromide, which is un- affected by the developer. This seems probable, since ozone has the same effect on the fog. It may not be uninteresting to note an experiment which throws some light upon this point, though it is not con- clusive. If a plate be coated with collodion emulsion, and be allowed to thoroughly darken in the daylight, and then drops of the above oxidizing agent be placed on different parts of the iilm, and allowed to act for a few minutes, it will be found, after washing, that on these spots the colour and appearance of the film will remain unaltered. (Where the manganese has been, the film is slightly brown.) Now, if the film be treated with sodium hyposulphite, the parts where all have been will become transparent, show- ing that everything except the collodion has been dis- solved away, whilst on the rest of the plate there will remain a delicate layer of metallic silver. This shows that the loose atom of metallic silver attached to the sub- bromide has been converted into a salt soluble in hypo- sulphite of sodium. Ee the theory what it may, the treatment holds good. Perhaps with collodion plates the application of nitric acid is the safest, where possible, but to that we shall refer later on. Dr. Eder has also shown tliat potassium ferri-cyanide and potassium bromide will cause the same result. The ferri-cyanide acts as follows : — Silver . Ferri-cyanide - Ferro-cyanide . Ferrocyanide , Silver .Sub-bromide^'"' of Potassium Si'« of Potassium *"" of Silver """^ Biomide, iAg.,BT + aK^FeCy,, = 3KiFeCy„ + Ag^FeCye + 4AgBr The potassium bromide converts the ferro-cyanide of :silver into bromide, and ferro-cyanide of potassium is formed. Thus — Ferrocvanide „„;, Potassium - Ferrocyanide „_. Silver of Silver ™'' Bromide ""'' of Potassium """ Bromide. Ag^FeCyc + KBr = K.FeCye + AgBr CAUSE AND CUEE OF FOG. 29~ From tlic foregoing it will be seen that fog may be produced by inorganic matter present with the silver salt ; and further on it will be seen that it may be produced during development and in emulsification. Regarding this last point there is more to be said in regard to gela- tine emulsion, and which Avill be found more fully treated of later on. Suffice it to say that gelatine itself, when decomposed to any extent, has an alkaline reaction, ammonia being one of the products, and that this will reduce the silver bromide held in suspension in it, un- less means be taken to overcome the effect of the alka- linity, or to neutralize the alkalinity. In other words, decomposing gelatine is a feeble developer (or reducer of the silver salt), and may cause fog. The fog caused by the reduction of the bromide to the metallic state is much more difficult to treat than any other, for the mere con- version ot the metallic silver into oxide is useless (see page 24). More vigorous treatment is required. This shows that a collodion emulsion is much more readily un- fogged than a gelatine one, since in the former the reduc- tion of the silver salt to the metallic state rarely, if ever, occurs. With collodion the danger is minimized, and acidity rather than alkalinity is to be apprehended. With gelatine plates it is inadmissible to use any sub- stance which may attack the gelatine ; thus the applica- tion of acids is not to be thought of, nor hydroxyl, nor permanganate of potash. Chloride of copper may be employed, but the safest plan is to use either bichromate of potash or the ferri-cyanide of potassium with the bro- mide of potassium. CHAPTER IV. DARK-ROOM AND ITS FITTINGS. It is of coiirse convenient to have a special dark-room adapted for all photographic work, but in some cases it is impossible, we are well aware. If, however, the amateur will work after dark, there is no reason why a dressing room, a bath room, or any spare room should not answer the purpose without permanently disarranging them. For the preparation of emulsion and plates the requirements are of course greater than when merely development is to be carried on. For the latter, a wash-hand stand andbasin, five or six dishes, a drying rack, and a piece of mackintosh (to prevent spoiling the furniture or carpet by any splash from the developer), are sufficient for any purpose, always provided, the light used in illuminating is made subservient to the purpose for which it is to be employed. In making collodion emulsions, any ordinary room will answer ; and plates may be prepared if a drying cupboard of some description or other is provided. For the manu- facture of gelatine emulsions, much may also be done, only in this case it is necessary to have some convenient gas- stove for heating them, and hot water as well. One of Fletcher's numerous burners may be employed with every satisfaction in the majority of cases, and it need not be a permanence in the room, since it can be attached to any DARK ROOM AND ITS FITTINGS. 31 gas jet. "Tlie following description of a dark-room istaken from " Instruction in Pliotography." The size of the dark-room may, ol course, vary, but it may he remarked that a place six feet square is the least space in which to work. A sample of an arrangement for such a size of room is given in the figure. B is the sink : AA are the two work- e FEET. u Fig. 3. ing tables. On the left, over A, may be placed a glass shelf, running along the left wall towards tue drying cup- board, D. The right hand table, A, may be used for the developing bottles and apparatus. The door of the dark- Toom should open outwards, if possible, and be covered by a curtain, which depends on to the ground, thus shutting out all light which would otherwise get through the chink between the door and the floor. Too many precautions to exclude white light cannot be taken, since gelatino- bromide, if it is to take the place of collodion, should be extremely sensitive to it, however feeble it may be. Water Arrangements. — It is always useful to have water laid on to a dark room, but in many cases it is impossible ; in that case we recommend that a two-gallon jar be placed some three feet about A (fig.) on the right hand, a hole 32 DARK EOOM AND ITS FITTINGS. Ibeing bored about two inclies from the bottom. A cork "vritli a pierced hole, in which is passed a small piece oF glass tubing, should fill up this orifice, and on the glass tube should be drawn a piece of black india-rubber tubing of a convenient length, to which an American clip should be attached. If a hole be bored slantingly- through the clip, so that the india-rubber tube, when passed through it, comes to the termination of the jaws of the clip, this arrangement, which was first described to us by Mr. England, M'ill answer better than more elaborate contrivances. When water is laid on from the main, a rose is a very desirable adjunct to the tap, since it gives a jet which has no force, and which is like a shower or spray. _ Drying- Cupboards. — The principles on which a drying- box should be made should be apparent, though in many forms they are neglected. The first principle which should be carried out is that the air passing through it should be capable of taking up moisture. It very often happens that the air which, in some contrivances, is passed through the drying-box is nearly saturated with moisture, hence it can take up but very little more, and plates dry slowly. Air, of course, may be dried by causing it to bubble through sulphuric acid, or by passing it over dry chloride of calcium ; but in order for this to be effective, the drying-box must not only be light-tight, but also fairly air-tight, since the air would find its way im- mediately through any small chink or cranny sooner than force its way through these obstructions. A better mode is to warm the air entering the box, so as to cause a draught, and at the same time this slightly warmed air will hold more moisture than cooler air. On this principle sound efficient drying-boxes are constructed. An excellent type is that due to Mr. England. If con- structed as in fig. 4 it will dry plates up to 12 by 10. A box is made of the dimensions given, and one side is hinged, and opens as shown. This side has a fillet DARK ROOM AND ITS FITTINGS. 33 placed round it, so that on shutting up no light can enter the interior of the box. Through the centre of the box runs a gas pipe, at the bottom of which is inserted a I" CAS PIPE-' Mg i. small tube closed at the end, and on one side of which is pierced a small hole. To this hole gas is led, and a very small jet is lighted in the gas pipe. At the bottom of the box, and at the top, are two holes of about three to four inches diameter ; and above, two tin tubes, some twelve inches long, are fitted into these tubes as shown in the diagram. It will be noticed that the gas piping passes through the centre of these two tubes. Round the gas pipes are fitted two discs of blackened card or tin, one of which is placed two inches above the bottom hole, and]the 34 DARK ROOM AND ITS FITTINGS. Other the same distance from the top hole. These pre- vent light striking down the tin tuhe into the box. The plates, when set, are laid on pairs of wires stretched across the hox, as shown in the diagram, and a box of the above dimensions may take from half to one dozen plates on each side of the central pipe. Plates dried in such a drying-box are ready for use in about twelve hours after coating. A small thermometer should be hung on the cupboard door, to enable the temperature to be noted. The rationale of this fairly rapid drying is that the gas piping gets heated, warms the air in contact with it, which ascends through the top tin tube, and a current of fresh air comes up through the bottom one. A constant change Fig. 5. of air, more than a very dry or hot air, is the object to be attained. We are in duty bound not only to give its excellencies, but also to point out any defects. In hot weather we found that the parts of the plates dried close to the central pipe DARK ROOM AND ITS FITTINGS. 35 are apt to run; the heat is communicated to the iron wires, and the glass takes it up, and the gelatine is apt to melt when the plate touches the wires. This is evidently- due to conduction, and we helieve that it is hetter to have a non-conducting medium in contact with the glass. Small loose cylinders, about half-an-inch long, of pipe-clay, can be readily baked and slipped over the iron bars, and each end of the plate supported by them. For summer weather, when the air is, as a rule, dry, it is a good plan to have a small gas jet placed just above the box in the iron gas tube. This heats the air in the zinc tube, and a draught is created through the box ; by this means the air is not above the summer temperature, and is not so quick drying. For our own part, when drying gelatine plates, we use racks similar to that shown in fig. 5. A cupboard will dry nearly double as many plates on these racks as when they are laid to dry horizontally. Collodion plates may also be dried in these racks. ^IL c- -^ e e ^1 Fig. 6. The plan recommended by Dr. Van Monckhoven is one 36 DARK ROOM AND ITS FITTINGS. which has long been in use in England, hut he has de- scribed it as follows : — " The drying-hox (fig. 6) is easily made, and consists of a box of thick wood, on the top of which is a zinc pipe to connect it with a chimney. At the bottom is another pipe, but with an elboAv to prevent light from entering. Horizontal shelves are placed in the interior, so that the current of air obtained by the draught in the chimney goes over each, one after the other. This box ought to be placed in a warm and very dark room. As to the necessity of warmth in the room, we demur. Tt is not necessary if arrangements be made for burning a gas jet in the top tube, so as to create a draught." Mr. A. Cowan has also described in the Photographic Almanac a drying box for dry plates which is essentially correct in principle, and no doubt answers well. He says : '' It often happens in very damp weather that gelatine negatives refuse to dry for hours, and even when flooded with spirit take a considerable time. " To those who do not possess a good drying cupboard the following is offered as a thoroughly efficient substi- tute, which anyone can make for himself with a little help from the blacksmith. " The annexed diagram (fig. 7) will explain itself. The box may be of any form most convenient, but the more shallow the better. The one in actual use stands on an ordinary work-bench, and the gas-burner, and iron cone, &c., on the floor, enclosed with a few bricks piled up to keep in the heat and protect any woodwork. A very good proportion for the cupboard is thirty inches high, thirty inches wide, and ten inches deep from back to front. The front is closed up at the lower part about six inches, and a sliding door running in grooves closes the upper part all but about half an inch from the top, a balance weight over a pulley supporting it in any position re- quired. This is found a much better way than having doors opening on hinges, for various reasons. " The current of warm air is conveyed in at the bottonr DARK EOOM AND ITS FITTINGS. 37 through a three-inch circular opening, the iron stove -pipe arrangement being screwed on underneath. Ahove the opening, at a little distance, is supported a thin shelf of wood about an inch smaller all round than the inside of the Fig. 7.; box, which acts as a diffuser, and stops the current of hot air from rushing up in one spot. Above this, at any- convenient height, two bars are fixed to carry the feet of the drying rack containing the plates. It will be found that plates will dry without running at a very considerably- higher temperature than that at which gelatine melts if the heated air be kept in continual motion." Another excellent drying box, due to Mr. Rogers, is sho-wn in fig. 8. The section of the box shows the general principles adopted ; the exit pipe for the warmed air is at the top of thebox. The drying-box may be of any dimensions. Pis a one-inch piece of gas-piping standing on the box G, and through it a small pipe, carrying a minute gas-nipple, 38 DARK EOOM ANT> ITS FITTINGS. passes ; it is soldered in air-tight at the bottom of C, and is connected hy an india-ruhber tube, I, with the gas ; Z is a three-inch stove-pipe, soldered up at one end, and open at the other, through which P passes ; a small leather washer, W, makes the zinc-tube air-tight at the top ; D is an outlet tube passing into the top of the box, over the opening of which may be stretched muslin in order to arrest the entrance of all dirt into the interior. At K is a light-trap, to exclude all light which might be reflected from G, the gas jet ; a current of warmed air thus per- petually circulates in the box B. The gas is lighted by raising the pipe P from off C, which is then replaced. In summer the tube D may be closed, and an inlet pipe, coming from the top of the box, be substituted for it, thus causing only a current of air at the ordinary tem- perature of the room to pass through it. We may mention that the plates dry more rapidly at the top of this box DARK EOOIM AND ITS FITTINGS. 39 than at tlie bottom. This is due to the warmer air having a tendency to remain at the top. Another excellent plan for a drying cupboard is the following, which has been devised by the writer. B is a zinc boiler, from which are taken two pipes, D and H, leading to the coil of pipes, C C C C. A supply tank, T, is fastened against the side of the cupboard, and a supply pipe joins the coil pipe at H. From D another pipe. A, is led, terminated with a tap, which allows any air to be got rid of, which would otherwise stop the flow *«tr £3 ^1_ Sfl lig. 9. into CO. At H is a tap, which allows the whole appa- ratus to be emptied at pleasure. K is a hot-air shaft, being some four feet above the box. It is terminated by a bend in two directions, and can be fitted with a cap, if required, in which are pierced orifices. Beneath are a couple of ventilating inlet pipes, likewise bent in two directions. L L L is a false bottom, pierced with holes, on which the drying racks are placed. F is a gas jet, which heats the water. (The cupboard is shown with only one door.) Each door is made light-tight by means of fillets, which need not be described. The hinges are 40 DARK ROOM AND ITS FITTINGS. pianoforte hinges. The piping is made of composition gas-pipe, though perhaps iron would be better ; still, as they are, they answer perfectly. In this cupboard it is well to have the plates on hori- zontal racks, so that the warm air may pass rapidly over them. CHAPTER V. ILLUMINATION OF THE DARK ROOM. In all emulsion processes, whether collodion or gelatine, ;great precautions have to be taken as to the light in which the plates are prepared, since they are necessarily exposed to its action for some considerable time. There are many persons who attempt to prepare emulsions who fail, and the failure may often be traced to the improper lighting of the dark-room. For development, a light which would slightly fog a plate during preparation may be used, since it is not necessary that it should be exposed to its action more than a second or two, which would not be sufficient exposure to cause any percepti- ble fog. When once development begins, the ingress of more actinic light has but little effect, since there is sufficient bromide used in the development, with the alkaline development, to render the silver salt insensitive or, if ferrous-oxalate be employed, the solution itself is of a colour which effectually cuts off all light that would rapidly harm the image. We have made these remarks, not to discourage the idea that a perfectly safe light should be used, but to show that when such cannot be procured, as on tour, it is possible to develop plates without any danger. It is necessary, first of all, to know what kind of plates are to be prepared, 42 ILLUMINATION OF THE DAEK ROOM. and worked, tefore deciding what light to admit to the dark room. For instance, with collodio-hromide, an orange or yellow light will suffice ; hut with gelatine plates containing pm-e hromide, a ruddy light in which there is hut little green is the safest. It is safe, however, in all cases, to have a red light of the right kind, and we recommend it for general adoption, since every kind of plate can be worked in it. If the quality of the light can he got by which the salt of silver is unaffected, the quantity may he unlimited. To make this more clear, a diagram from another work* is reproduced, from which, together with a reference to figure 2, page 4, a notion can he obtained as to the light to which different plates are sensitive, and the media which may be accepted to cut off that light. No. 1 may be omitted from consideration, since it is sensitive to all rays, and no filtered daylight is admissible where it is employed ; but Nos. 2, 3, and 4 should be studied. When a streak of white light is passed through a prism it is spread out into its component colours, and in 14 they are represented as white. The black portions in 2, 3, and 4 of the diagram show the rays of light in every case which do not appreciably affect a sensitive plate. The white and half-tints represent, as approxi- mately as can be shown in a wood-cut, the relative sensi- tiveness of the plates, the different rays forming white light ; the degree of sensitiveness being indicated by the degree of whiteness. It will be noticed that the gelatino- bromide and coUodio-bromide plates are sensitive to the confines of the red, and some specimens of the former are also sensitive well into the red, whilst the bromo-iodide here shown is only sensitive to the confines of the yellow. Next we need only turn our attention to Nos. 5, 6, 7, 8, 9, 10, and 12. In these are shown the rays of light which pass through different coloured glasses and dyes. * " Instruction in Photography " (Piper and Carter), 6th edition. ILLUMINATION OF THE DARK KOOM. 43 2 3 4 5 1. Special collodio-bromide, 2. Gelatino-bromide. 3. Collodio-bromide. 4. Bromo-iodide. 5. Cobalt glass. 6. Ruby glass. 7- Chrysoidine. 8. Magenta. 9. Flashed orange. 10. Stained red glass. 11. Bottle-green glass. 12. Aurine. 13. Quinine. 44 ILLUMINATION OF THE DARK ROOM. Buby glass would be as near peiiection as possible for every plate were it not that a certain amount of blue light passes through one thickness of it. When two thick- nesses are used the blue is imperceptible. By the use of a combination, orange glass and ruby, or stained red glass and ruby, the light allowed to pass through is such as will not affect most plates unless the exposure to it be pro- longed, since the orange or stained red entirely cuts off the blue which may permeate the ruby glass. The writer has been told that somepeople prepai-e plates so sensitive to^ the red that the light passing through any number of thick- nesses of ruby glass proves an ineffectual protection. Un- less rubyglass were added till total darkness supervened, there is nothing to surprise us in this statement, as the red light which filters through three or four thicknesses of ruby glass has the same quality as that which filters through two thicknesses. What they really express is that they pre- pare plates which are in reality sensitive to red light. When this is the case the development and preparation of such an emulsion become a nuisance, and are probably more of a scientific than of a practical value, since the same sensitiveness can be produced without any liability to veiling of the image through the impact of light of such low refrangibility on the plate. For an ordinary dark room we recommend that, if a north light be obtainable for the window, one thickness of ruby and one of stained red or orange glass be employed. As to dyes, it will be seen that if glass be coated with aurine on one side, and magenta on the other, the same spectral quality will be obtained. At the same time it must be remembered that every aniline dye fades gradually in white light, the fading being caused by those rays which they absorb. Under these circumstances, if orange glass be placed out- side the paper dyed with the foregoing, the means of obtaining a room permanently lighted with a safe light is increased. If plafes very sensitive to the red be pre- j)ared, one thickness of cobalt glass and one of stained red ILLUiXINATIpX OF THE DAUK ROOM. 45- will be tlie best combination to use ; but, as we said before, plates requiring such a light by which to develop should not find a place in a photographer's hands. If the sun shine on the window during any part of the day it is well to have a screen, which can be placed against the window- frame (it can be hinged from the top, and pulled up as a flap by a small pulley arrangement), covered with orange- coloured paper.* This diffuses the light, and renders any chemically active rays which can possibly filter through it less hurtful. It is not always practicable, however, to work by day, and then it becomes necessary to resort t» artificial light, and that must be of the same character as the filtered daylight. Now, candle and gas-light have not the same amount of blue in them as the light from the sun, hence the screen used for shielding such sources need not be quite so perfect. In our practice we have a lantern made like a large sized stable lantern. Holes are pierced at the bottom of it for the indraught of air, and holes at the top of the sides for the outdraught. To pre- vent any light striking the ceiling, we have had a tin cover fitting round the lanternf at the top, and sloping 45° downwards, by which means any light glancing through the holes strikes the shade and is reflected downwards. The sides are covered with two thicknesses of orange paper, and a candle placed inside gives a very fan- work- ing light for coating plates or for development. As may be inferred from our previous remarks, the light must be much more subdued lor the former than for the latter pur- pose. There is a medium called canary medium which has lately been revived for use in the developing and coating room. It is a paper which is impregnated with chromate of lead, and we have tested its capacity for cutting off hurtful light. For most plates it ,answers well when two thicknesses are employed, but it is inferior in illumination * Common orange packing paper answers admirably, t Some lanterns are made with this arrangement. 46 ILLUMINATION OF THE DAKIC ROOM. to the orange paper. It is a pleasant light, however, to work in, and it is to he recommended. Before packing plates, it is always necessary to examine them lor dull spots and imperfections. As a rule, the diffused light coming through paper or other fabric is unsuited for this examination. It is better for this purpose to have a lan- tern with a transparent side, by which means the flame of the light is reflected from the plate to be examined, and this immediately throws in view any imperfections. As the examination can be made in a couple of seconds, this exposure does not injure the plate. ^ Some dry-plate men we know have gas burning close outside a red glazed window which opens into an ad- joining room, but it is not every one who can have such an arrangement. For developing plates at night, whilst on totir, we have Fig, 11. found that a useful piece of apparatus can be easily made. Take a sheet of cardboard of the size of about 2 feet by ILLUMINATION OF THE DARK ROOM. 47 1 foot 6 inches. Lay off from the 2 feet side distances of 8 inches from each corner, and with a penknife cut half through the card in a line parallel to the ends. These will form flaps, which can be folded over to meet in the «entre. From the centre portion mark out a rectangle of ahout 6 inches by 12 ; cut round three of the sides, but only half cut through one side, the penknife being applied from inside of screen. This will allow a square flap to open outwards. On the inside of the opening may be pasted or hung a sheet of orange paper ; or a sheet of paper dyed deeply with a mixture ^f aurine and aniline scarlet may be glued to it. The candle is placed behind the screen, which should stand, supported by the two wings, in front of the operator. A piece of board, or a piece of tin, may rest on the screen, and thus cut off diffused light from the ceiling. We have deve- loped many plates with such a light, and lost none by veil- ing of the image. When packed for travelling, the flaps are folded up, and it can be placed in the portmanteau. Fig. 12. A useful portable lantern is made from a Chinese lan- tern. We first saw it adapted in Mr. Galton's hand ; but 48 ILLUMINATION OF THE DARK ROOM. Dr. Hermann Fol has given a practical method of its con- struction in the Photographic News. He describes it as follows : — " The most portable lantern I make by painting over common white paper Chinese lanterns with collodion containing castor oil and fuchsine. The top and bottom of the lantern are made each of two thin metal plates fastened together by three small chains. Each plate is pierced with holes, and each pair is fastened to the chains so that the holes do not correspond, and half-an-inch remains between the two plates. No white light can then find its way out. The upper pair is, of course, unfixed, and may be lifted out to get access to the candle. This lantern folds up into the smallest possi- ble compass, and when in use perfectly excludes all actinic light without getting hot." Dealers supply lanterns more or less efficient, but we confess to liking home-made apparatus, since, if made by oneself, they can generally be readily repaired. CHAPTER VI. INTRODUCTORY REMARKS ON GELATINE EMULSIONS. Histoi'ieal Outline of the Process. — ^A gelatine emulsion, as it is somewhat crudely called, as first made by Dr. Maddox in 1871, is in reality silver bromide, &c., emulsified in a gelatine solution, with which plates are coated. We have already (page 3) stated that there are various modifications of the molecular state of the bromide, which are brought about in a variety of ways. Mr. C. Bennett first showed how extremely sensi- tive plates CO aid be prepared by keeping the gelatine solution liquid at a temperature of about 90'' for six or seven days. What he accomplished was in reality to bring about a modification which was very easily acted upon by light. It need scarcely be said that in certain states of the weather this long emulsification was attended with enormous risks of decomposing the gelatine, and when gelatine decomposes, the products are apt to reduce the silver bromide to the metallic state, and hence to cause fog. Besides this, there is the danger, even if fog is not produced, of the gelatine refusing to set. Col. Wortley stated that he got the same rapidity in his plates by rais- ing the temperature of the emulsion for a few hours to 160° F., and Mr. Mansfield first recommended the gelatine 50 EEMAEKS ON GELATINE EMULSIONS. emulsion to be brouglit to the boiling point ; but then a very short boiling is liable to destroy the setting qualities of the gelatine. ■ ilr. W. B. Bolton, in an article in the British Journal of Photography ^ first indicated the true method of preparing emulsions by boiling. He emulsified in a small quantity of gelatine, boiled, and then added to the emulsion the proper quantity of gelatine to give it a firm consistency when setting. We may say that the publication of this article opened out a ne"w era in gelatine emulsions. We need not further explain the rationale of the process here. Dr. Van Monckhoven called attention to the fact that by adding ammonia to the silver bromide, a modification was obtained which gave great rapidity ; and Dr. Eder carried the principle further, and gave a really workable, though in some states of weather a dangerous, process. The great desideratum^ according to these authorities, was to obtain a grey emulsion by trans- mitted light, and green by reflected ; but, as will be seen from our remarks on page 3, this state is not what we con- sider the most sensitive, and certainly we have never ob- tained plates so rapid by the ammonia process as we have by the boiling process. We have endeavoured in the following pages to give an accurate description of the way to carry out all these processes. But we here make a dis- tinct record of our opinion, which is, that for rapidity and good quality, the boiling or hot digestion processes are the best and safest. We have also given processes for precipitating silver bromide in water or glycerine and water, and then adding it to gelatine. The processes are effective, but they are not so easily employed where iodide is used, as the iodide is apt to settle down in large particles. We here give one piece of advice, which is, that if the reader has a process with which he is thoroughly satisfied, he should keep to it, and not waste his time or energy in following out more elaborate, but perhaps less successful, processes. REMARKS ON GELATINE EMULSIONS. 51 A pertinent question for everyone to ask himself is, as to whether a very rapid process is always a desideraium. For our own part we unhesitatingly say it is not. For transient effects in a landscape, for instantaneous views, or for portraiture in dull weather, rapid plates are iiseful ad- juncts, but should be nothing more. We believe that finer pictures, more mellow and truthful, are usually produced by the slower plates, be they collodion or gelatine. On the Causes of Sensitiveness in Gelatine Emulsion. — It may be said that in a gelatinp emulsion it is almost neces- sary that the soluble bromide be in excess over the silver nitrate ; that is, that when aU the nitrate is converted into bromide, there should still be soluble bromide left in the solution. It must be recollected that gelatine is a most unstable body, and we believe we are correct in saying that from the first time it is heated its decomposition commences. This decomposition at first gives rise to an acid reaction, and eventually to an alkaline one. In the first stage no harm will ensue to silver bromide suspended in it ; but when the latter stage is arrived at, there is a great tendency for the silver salt to be reduced to the metallic state, unless some body be present which hinders it. Such bodies are found in acids and soluble bromide. The addition of acid must be made cautiously, since acids cause gelatine to lose its setting properties, and there is, consequently, a greater safety in using excess of bromide. Again, if there were any excess of silver nitrate, this ex- cess would combine with the gelatine, and we should have a product formed not particularly sensitive to light, but acted upon by a developer at once, and have in conse- quence a production of red fog. We may, therefore, take it that in the production of gelatine emulsion an excess of soluble bromide is essential. In the first chapter we have already referred to the differences in molecular structure that silver bromide may assume ; and we repeat that the molecular structure 52 SENSITIVENESS IN GELATINE EMULSION. is purely due to physical causes, and not to diiFerent chemical composition ; in other words, hromide, chloride, and iodide of silver emulsions have always the same pro- portions of hromlne, chlorine, and iodine to silver present. When silver hromide is produced with proper precau- tions as an emulsion, or in the film at once, as in the wet collodion process, we have the film transmitting red rays, and ahsorhing the blue rays ; showing that the work per- formed in the film is really done by the blue rays. If a gelatine emulsion, however, be boiled, the bromide, unless great care be taken in mixing, becomes a cold grey colour by transmitted light, and yellowish-green by reflected light, and this shows that some of the yellow and red rays are absorbed, whilst some of the blue rays are transmitted; and yet it is found that this silver bromide is more sensitive to the blue rays than the redder form. Can any explanation be given of this ? We think it can. It is not owing ta the fact that the silver salt is slightly sensitive to the yellow rays, for this woxild only increase the sensitive- ness by about one-twentieth, as photographing the spectrum shows us. It must be recollected that the apparent colour of the bromide may be produced in two ways — or rather, that it may be due to two causes : it may be due to the colour of the silver bromide itself, which is what we may call its molecular colour, or a variation in colour may be due to the scattering of light by the diiFerent sizes of the particles, each particle being pro- bably composed of thousands of molecules. When an emulsion is boiled, an inspection of the films after different lengths of boiling wiU convince us that the longer an emulsion is boiled, the larger the size of the particles which are embedded in the gelatine. Hence boiling pro- duces large particles. The cause is, probably, that silver bromide is slightly soluble in water, and much more so in water containing soluble bromide. Without doubt, during boiling some portions of the silver bromide are dissolved and re-precipitated on the coarser particles, other per- SENSITIVENESS IN GELATINE EMULSION. 53 tions of tlie finer bromide being taken up, and they in their turn deposited, and so on. Mr. Wilson, in his description of his gelatine process (which won the Paget prize), and which statement we overlooked when we subsequently experimented in the same direction, says : — " The proportions of soluble promide and silver nitrate are very important. Contrary to usual statements, the larger the excess of silver bromide, the more quickly is the AgBr converted ; if there be but little excess, a very long cook- ing will be required ; and if exactly the equivalent quantities could be used, the writerbelieves thatnoamount of cooking would give the sensitive condition. Too large an excess, on the contrary, tends to form fog, which is not to be afterwards got rid of by the use of bichromate, but which is more liable to occur with alkaline pyrogallic No. IV ... 1st day 5 No. Ill ... 1st day ... 5 No. VI ... 1st day f) No. V ... 1st day ... 5 No. I ... 2nd day ... ... u No. II ... 2nd day ... ... 4" No. I ... 1st day ... 3^ No. II ... 1st dav ... 3 It may be convenient to remember that the odd numbers contain bromide alone, and the even ones iodide with the bromide. It will be seen, when boiling with a small quantity of gelatine (Nos. V, VI, VII, and VIII), that on the second day the plates containing iodide (VI and VIII) have a little advantage over those which contain bromide alone, and that the digestion with ammonia (VIII) gives no in- crease in sensitiveness.* The same is apparent with VII and V ; the digestion with ammonia does not increase the sensitiveness with pure bromide. The tirst day's plates (VI and VIII) with the iodide are in every way behind the :second day's plates with the bromide alone ; but evidently digestion with ammonia answers partly the same end as * It should be said that Mr. W. K. Burton, who is a most careful expe- rimeter, states, in a more recent communication to the Photographic Society, Hiat increased sensitiveness is given. ICUIDE AND CHLOEIDE IN EMULSIONS. 61 keeping the emiilsion. The same applies also to Nos. I and II. Boiling with a small amount of gelatine, then, in every case, is better than boiling with a full quantity of gelatine, and then digesting with ammonia ; but this plan is far better than digesting with ammonia alone. These formulse are comparative ones, since they all contain eventually the same amount of bromide of silver, and the same amount of gelatine. As regards development, the plates containing the iodide were a little slower in coming out ; but, on the other hand, they were certainly much brighter and cleaner. To test the value of the iodide ftirther, the same formula as Nos. Ill and IV were used, and the emulsions brought to the boiling-point Avlien the ammonia was present. No. Ill fogged ; No. IV remained quite bright. The ammonia undoubtedly makes plates mu.ch more rapid than when no boiling is attempted ; the sensitiveness in which case might, perhaps, be represented as 1 on the same scale as that given before ; but it by no means gives the most rapid kind of plate. We think for comparatively slow plates, where good density is required, Formiila No. II is excellent in every way ; and if any one has a prejudice against iodide, let him use No. I. It will thus be seen that we hold to introduction of iodide into an emulsion ; except for experimental pur- poses, we never omit it, believing it to be a sheet-anchor for obtaining good and unfogged pictures. We are aware that several commercial makers of plates which have a great name in the market use the iodide, and if those who condemn it would but give it a fair and unprejudiced trial, we should have no fear of making converts of them to its introduction. CHAPTEE VIII. GELATINE. In gelatine emulsions one of tlie most prominent features is the gelatine, and it is by no means iinimportant what kind is selected. Dr. Eder has made long and exhaustive researches on various qualities of gelatine, and Mr. T. F. Elsden has also thrown light upon its variability in an article in the Yeae-Book for 1881, and we cannot do better than quote some of their conclusions. Gelatine is compound of glutin and chondrin. The latter is dis- tinguished from the former by its precipitation from an aqueous solution by acetic acid, and its insolubility in an excess of this reagent. Acetate of lead, alum, and sul- phates of iron, aluminium, and copper also precipitate it ; but not glutin. Mr. Elsden also remarks that a con- venient test for the presence of much chondrin in gelatine is to add a concentrated solution of chrome alum to a .solution of 50 grains of gelatine in 1 ounce of water. If chondrin be present in excess, the gelatine will set while hot. Mr. Elsden further says : — Remembering that gela- tine is a mixture of two substances of different composition and properties, it must be expected to find great variation in the behaviour of commercial samples. Most photo- graphic gelatines, however, consist chiefly of glutin, and their general character is not, therefore, affected to so GELATINE. ()3 great an extent by the small quantity of cliondrin usually present in addition. Gelatine is extremely hygroscopic, and contains, at ordinary temperatures, from fifteen to twenty per cent, of water. In cold water it swells up, and absorbs from five to ten times its weight of water ; good gelatine will absorb enough cold water to dissolve it, if the temperature is raised above 90'^ F. Very weak solutions of gelatine will solidify to a jelly when cold, sometimes when only one per cent, is present ; but long boiling destroys, to a great extent, this power of setting. Gelatine will keep indefinitely in a dry state ; but in contact with water it soon putrefies, becoming first acid, and then strongly alkaline, and giving off ammonia ; at a temperature of 90° F., decomposition will often begin in twenty-four hours. Hence it is evident that long boiling, besides destroying its power of setting, also tends to pro- duce decomposition of gelatine. Alum, alcohol, carbolic acid, salicylic acid, glycerine, fuchsin, hydrate of chloral, thymol, and salts of zinc act as antiseptics, preventing the decomposition of gelatine, even in small quantities. If glycerine be used, however, it must be added in rather large quantities. Alcohol and carbolic acid, in large quantities, precipitate gelatine from solution in water. Acetic acid, hydrochloric acid, sulphuric acid, and oxalic acid dissolve gelatine even in the cold. Acetic acid dissolves gelatine with great facility, whilst ammonia acts as a weak solvent. Sugar promotes the solubihty of gelatine, whilst gum, in the presence of acetic acid, renders gelatine less solu- ble, owing to the formation of a compound of glutin with arable acid. Silver nitrate, exposed to sunlight in contact with gela- tine, causes a red discolouration, due to the combination of organic matter Avith a sub-oxide of silver. Chrome alum renders gelatine insoluble ; but long boil- (54 GELATINE. ing and hot dilute acids, potash, potassium permanganatey are able to dissolve the mixture. Alum raises the melt- ing point, but does not render it insoluble. The quality of gelatine may be tested in several ways. Dr. Eder, among other tests, recommends that the gela- tine be incinerated, and the ash weighed, and he says that this varies from ^ per cent, in good samples to 5 per cent. in inferior kinds of gelatine, and to 10 per cent, if adulte- rated with alum. Our own researches in this matter give a greater margin for good gelatines, 2 '5 per cent, being the ash of a certain gelatine which is excellent. We detail some results in the table below. Another test which should be applied is the amount of water it can absorb. Good gelatine should absorb five to ten times its weight of water. A very simple way of testing is to measure out (say) 2 ounces of water, and soak 50 grains of gelatine in it for some hours until it is thoroughly swelled. The water not taken up should then be poured oif into a measure, the gelatine being very gently pressed against the side of the vessel in which it was allowed to swell. The amount taken up is, of course, the difference between the 2 ounces, and the amount returned to the measure. A more scientific method is to allow the gelatine to take up as much water as it can at a fixed temperature, drain it, and surface dry it on blotting-paper, and then weigh it. This is a more tedious method than that given above. Name of Gelatine Coignet's gold label gelatine ,, special gelatine Nelson's No. 1 photographic „ opaque „ amber Ordinary French (not branded) 2 Swinburne's No. 2 patent ising- glass Cox's gelatine in packets Ash, Water absorbed ler cent. by 50 grains. '.. nearly , ... 7 drachms 1 „ . ... 7 )) 2 „ ... 5* )> 2 „ ... 8' ;? 1— 1 ... 4 » 2 „ ... 6 » 1 » ... 5f )? 1 ,, ... 4| )? GELATINE. t)D Name of Ash, Water absorbed Gelatine. per cent. by 50 grains. Eiissian isinglass ... ... 1 )j ... u )) Gelatine supplied tliroiigh Jlr. Henderson ... ... 2 ;j ... 8 J) Simeon's " Winterthur " gela- tine Heinrich's gelatine ... ... 1 j; ... 8 )) Batty' s gelatine 2 » ... 5 )> The next test is that of solubility. A gelatine which by itself is soluble at a low temperature is unfitted for gela- tine emulsions, particularly if the temperature at which it is prepared is at all high, since then it would not set. Take, as an example of this, Nelson's No. 1 gelatine. In warm weather it will dissolve in the water at the tempera- ture of the room in which it is soaked. Take Coignet's gold label as the other extreme, and it will be found not to melt till the vessel has been plunged into water about 110°. As might be expected, as regards setting, these two gelatines are the most opposite. At a temperature of about 75°, No. 1 will scarcely set at all, whereas Coignet's will set in a short time. A further most prac- tical test is by noting the expansion of films of gelatine which have been spread on plates. The greater the lateral expansion in such films, the greater probability there is of such films " frilling," i.e., wrinkling and leaving the plate. The writer has carried out many tests in re- gard to this point, and the results show that any gelatine can be tested as to its capability of resisting trilling in a very easy manner. Twelve grains of the following gelatines were swelled in half an ounce of water and melted. Quarter plates were coated with exactly half of the bulk of each solution, and allowed to dry under the same conditions as that in which plates are dried in the drying box. The films were then stripped from oif the plates, and different portions cut away and accurately measured whilst dry. The films were then allowed to 66 GELATINE. swell in water, ammoniacal water, or a solution of mono- cartonates of soda and potasli, and again measured. The following are tlie results : — CJ Water Garb. Soda and and Gelatine. Dry. Water. Ammonia. "Water. Nelson's No. 1 ... .. 1 . . 1-2 . .. 1-39 .. 1-29 Autotype ... .. 1 .. . 1-09 . .. 1-28 .. 1-21 Heinricli's .. 1 . . 1-08 . .. 1-22 ... 1-15 Simeon's ... .. 1 . . 1-05 . .. 1-14 .. 1-09 Batty's .. 1 . . 1-32 . .. — .. — Nelson's X opaque ... 1 . . 1-19 . .. — .. — Crosse and Blackwell's ... -L . . 1-09 . .. — .. — Nelson's amber . . . ... 1 . . 1-43 . — — An important test is for acidity or alkalinity. For our own part we strongly recommend a gelatine which is slightly acid where an emalsion is to be boiled, and if not in this state, we acidify the gelatine solution. When the ammonia process is used, the condition of the gelatine does not matter so much. In some gelatines, the acidity (due to the hydrochloric acid used in its manufacture) can be tasted by applying a piece to the tongue. A hard gelatine can be at once identified when it is set after dis- solving in the water, which it will absorb. Any exact determination by applying weight to see where crushing begins is misleading, unless the temperature is uniform during all experiments. We would here remark that gelatine has an affinity for iodine, bromine, and chlorine, with each of which it com- bines ; hence it is a preservative in the true sense of the word. The less fatty matter present the better, since it gives rise to opaque spots on development, or else to scum- markings on the plate. Where there is fatty matter present, it may be got rid of by precipitating it in a fine stream in alcohol, or by dissolving it in the quantity of •water which has to be used, and skimming it; or by GELATINE. 67 making it set, and, with a clean ivory knife, cutting off a thin layer from the top. To select suitable gelatine for an emulsion, we recom- mend that a small batch of emulsion be made with the specimens proposed to use, and that a few plates not smaller than 7 by 5 be coated and tested before taking it into use for larger quantities. In our own practice we like to use a mixture of two kinds of gelatine — one hard and one soft, and the propor- tions of these we vary according to the weather. As a rule, we like 1 part of hard to 2 parts of soft, as it will then set with ease at a moderate temperature, and be hard enough to resist the tendency to frill, and is at the same time readily permeable by the developing solutions. One fact must also be recollected, that frequent re- heating of gelatine speedily detracts from its setting powers, and that if too little water be added to it in mixing, the film has a great tendency to become leathery, more particularly if a little chrome alum has been added to it to prevent frilling. A judicious mixture of alcohol to a gelatine solution increases permeability, and should not be neglected. The tise of a sufficient quantity of water is, however, the great desideratum, and should be carefully attended to, the quantity, of course, depending on the temperature at which the plates have to be prepared ; thus, in winter, more water should be used than in summer. A very horny, glassy, film is objectionable in many ways, and a moderately matt surface for the plates should be aimed at. This depends almost entirely on the gelatine -that is used, and at what temperature it is added, unless it Ibe modified by additions such as glycerine, to which we may at once say we object, on account of its affinity for water. It will be noticed that ammonia causes much greater expansion than the carbonate of soda (the carbonate of potassium gives almost identically the same results), and the soda more than plain water. It is easy at once to see 68 GELATINE. which gelatines would be most likely to cause frilling in plates. The absorption of water does not coincide in all cases with the expansion, but this we lay to the different stress put on the different layers of gelatine during the drying. CHAPTER IX. GELATINO-BROMO-IODIDK EMULSION. We propose to give a detailed account of making an emulsion at ordinary temperatures, say up to 65° Fahr., which may he taken as a pattern on which to form others fey any other formula. It will he found to he exquisitely sensitive to the hlue rays, and very slightly to the yellow, which latter quality means that the development and pre- paration of the plates can he conducted in a room fairly illuminated with orange light. To prepare the windows for this, the window maybe glazed with'stained-red glass, or with one thickness of orange and one of ruby glass. If this he undesirable, two thicknesses of common orange packing paper may he employed. The reader should con- sult Chapter V., on the Illumination of the Dark-room, for further information on this subject ; but the reader must remember that tricks cannot be played with the light of the dark-room, such as are admissible when the comparatively slow wet process is used. Thus he should see that no light of the wrong colour penetrates at any place ; he should pay particular attention, for instance, to the chinks under the door, and in the sashes of the window frame. When he has come to the conclusion that no daylight is entering his room, he may think about preparing the emulsion. First of all, he must make a few 70 GELATINO-BROMO-IODIDE EMULSION. preparations. The jar or bottle in whicli the emulsioni has to be mixed must be scrupulously clean. There should be no patches of old emulsion left on it. If a glazed jar be used, it should be seen that the glaze is not cracked in any way, since fog may be expected if it be. For dissolving the gelatine, &c., we like to use glass beakers with a lip, since they are handy for pouring. These also must be scrupulously clean and dry. The scales in which the weighing has to take place should be examined for dirt (chemical or otherwise), and a few circular filter papers on which to weigh the materials should be at hand. Weighing should never be done* without a filter paper of equal size and weight being placed in each pan of the scale. A saucepan of hot water should be ready in which to place the beakers, &c., in which the difierent materials have to be dissolved, and care should be taken that it is not too full. It need scarcely be said that all weighing can be done in ordinary light. To commence operations, the following may be weighed out separately and placed on cleanf paper after weighing, it being supposed that a dozen or a few more whole-plates are required. 1. — Potassium iodide ... ... ... 5 grains 2. — Potassium bromide 135 „ 3. — Nelson's No. 1 photographic gela- tine 30 „ 4. — Silver nitrate 175 „ 5. — AutotypeJ gelatine 240 „ Nos. 3 and 5 are rapidly covered with water, shaken or * Especially on trass scale pans. t Any contamination by dirt of any description, and pardcalarly that to be found in a photographer's work room, is almost sure to spoil the emulsion, or at all events its sensitiveness, and to cause endless evils. Hence clean paper should be used, and the chemicals should not be left on the benches or table in contact with the wood. X In case this cannot be procured, mix 3 parts of Nelson's No. 1 gelatine with 1 part of some hard kind, such as Heinrich's or Simeon's Swiss. GELATINO-BEOMO-IODIDE EMULSION. 71 stirred in it a few seconds, and the water poured off as quickly as possible. This gets rid of any adherent dust on them. Nos. 1 and 2 are then dissolved in 1 drachm and 1^ ounces of water, respectively. To the solution of bromide (No. 2) 1 minim of strong hydrochloric acid is added, together with sufficient of an iodine in alcohol solution to make it a deep sherry colour. No. 3 is swelled for ten minu.tes in 1 ounce of water, and then dissolved by heat ; No. 4 is dissolved in ^ ounce of water, and heated to about 120° Fahr. In the dark-room. No. 3 is added to No. 4, and shaken up in a bottle till a perfect mixture is secured. Three- quarters of the solution containing No. 2 is then dropped in little by little, and shaken iip after each addition ; and then the solution of No. 1 is added to the remaining ^ of the solution of No. 2. The mixture is then added as before. The emulsion should appear of a ruby colour when a thin film of the liquid emulsion is examined by a gas light. This bromide maybe placed in a spray apparatus, which is made as follows : — Bend two thin glass tubes in a common fish-tail burner of the shapes A and B (fig. 13). The tube A should first of all be drawn out so that the 72 GELATINO-BKOMO-IODIDE EMULSION. end is perfectly closed ; this may be done by the heat of a Bunsen burner, by holding the straight tube over it at about an inch from the end, in one hand, and at any con- venient distance in the other, and, when thoroughly softened by the heat at one point, by simply pulling the tube outwards. The glass collapses, and the short bit is pulled off. A flat file is then applied to the point, and the glass filed away till a very small orifice is left. The two tubes are then inserted in a cork, which is fitted into a test-tube as shown. The bromide is placed in the bottom ot the tube, and a very fine spray of liquid can be forced through the orifice of A. The solution of gelatine and silver nitrate should be placed in a glass beaker or a jam-pot, and in the dark- room the spray is blown on to it, and the liquid stirred, at the same time, with a clean glass rod. This gives a very fine emulsion indeed, and, if correctly carried out, a drop of it, when poured on a strip of glass, should show an orange-yellow colour by transmitted daylight, or a deep ruby when a gas or candle flame is examined through it. The possible sensitiveness of an emulsion depends almost entirely on the fineness of grain of the bromide when first formed. With a grey or blue-tinted emulsion extreme rapidity can never be hoped to be attained. The emul- sion should be transferred to a 20-ounce bottle,* and well shaken for a couple of minutes, after which it is ready for the next operation. The method of mixing the silver with the gelatine which we have given above is not practised by most emulsion makers, we believe, though for our own part we have no doubt that it is the best plan of getting the best emulsification with the least trouble. In case the method of mixing the bromide with the gelatine is preferred, the following modification in mixing may be made : — Nos, 1 * Some recommend the use of an earthenware bottle, such as an old ink- bottle. There seems to be no advantage in it, if ordinary precautions be taken for keeping out the light. GELATIN0-BR0310-I0DIDE EMULSION. 73 and 2 are dissolved in 1 drachm and 1^ ounces of water Tespectively, and No. 3 is added to the sohition of tro- mide, allowed to swell, and then dissolved. The silver nitrate, No. 4, is dissolved in 1^ ounces of water, and by means of the spray apparatus, or by caretul dropping, is -added to the bromized gelatine. When half the silver nitrate has been emulsified, the iodide, dissolved in 1 dr. of water, is carefully dropped in, and then the remainder of the silver nitrate is added. Other Methods of Mixing. — There are other methods of emulsifying which are given here. Mr. England finds that if two 1-drachm measures be filled, one with the bromide solution, and the other with the silver nitrate solution, and then be poured into a bottle together and well shaken, and this operation be repeated again and again till the two solutions are exhausted, he gets a perfect emulsion with- out grain, and very smooth, It will be noticed that in this plan the silver and the bromide solutions are in equal quantities. Another plan, adopted by Mr. Warnerke (whether it is original with him is not of great consequence) is to draw out two funnels to fine jjoints, and support them on funnel-holders over a jar. These are filled with the two solutions, which are allowed to run into the jar, a stirrer being used to aid emulsification ; other workers use the scent-diiFuser, by which to secure fineness of grain. Any of these artifices may be employed. A later plan which the writer has adopted, and which is very efi'ective, is to shake the gelatine containing the bro- mide into a froth, and then to add the silver nitrate little by little. This makes a beautifully fine emulsion, and seems to be equivalent to immersing a delicate film of gela- tine into a silver bath, when we know that splendid films are to be obtained, having the very finest grain. A good Stirriiig-rod may be made by taking a glass rod, and tying across it with clean string a strip of glass about a couple of inches long and half an inch wide. This •cross-piece eifectually stirs up the emulsion during its 74 GELATINO-BEOMO-IODIDE EMULSION. formation by a motion of the rod between tlie first finger and thumb. We recommend its use. Boiling the Emulsion. — A saucepan of sufficient size to hold the bottle must be procured, and filled with water to a conyenient height, and a flame, such as a gas-burner, placed beneath it.* After the water has been brought to boiling point, the emulsion is kept boiling for 45 minutes ; it being shaken at intervals (say once every ten minutes) for half a minute or so. A thick cloth tied round the hand prevents any scalding. The boiling, by-the-bye, should take place without the cork being left in the bottle, for if it remain in, it would be blown out by the force of the steam. A cork with a slot cut in it is, however, not open to objection. Coolmg and Washing the Emulsion. — After the proper time of boiling, the saucepan is removed. The gelatine No. 5 should, as already stated, be rapidly rinsed in several changes of water to get rid of any adherent dust. It should then be placed in a pot with 2 ounces of cold water,, and allowed to swell. After this it is melted at a tempera- ture of about 100°, by immersing the pot or flask in hot water, and added to the solution in the bottle. Both the emulsion^ and also the dissolved gelatine, should be cooled to about 70° to 80° F. by allowing water from the tap to run over the jars before the addition is made. After a good mixing by shaking, the froth is left to sub- side, and the emulsion is poured out into a flat porcelain dishjt and allowed to rest. The time which it will take will vary according to the temperature| of the surrounding * To prevent bumping and breaking the bottle, we place half a dozen folds of blotting-paper at the bottom of the saucepan. t There is no " fetish " in a dish. When the emulsion is to be squeezed, . if it is set in a beaker, it turns out in a more convenient shape. In a dish, however, it sets more rapidly, since a greater surface is exposed to the cool air. J In very hot weather, if the dish or jar be stood in iced water, no difficulty in setting will be found. See subsequent chapter for particulars of preparing emulsion at high temperatures. GELATINO-BROMO-IOBIDE EMULSION. 75 air, but a couple of hours is generally amply sufficient, and often a mucli less time will suffice. After a proper consistency is obtained (such consistency being that the gelatine should not tear with a moderate pressure of the finger), the emulsion is carefully scraped off the bottom of the dish with a strip of clean glass, and transferred to a piece of very coarse canvas, or mosquito netting, which has been previously boiled in hot water to get rid of any grease or dirt. The character of the canvas and netting- can be judged of by the accompanying figures, which are Fiff. 14. of their natural sizes. The emulsion is then twisted up in this, and, by a gentle pressure, squeezed through the interstices, the ball of emulsion being absolutely below the surface of the water into which it is forced. The water causes the threads of gelatine to remain tolerably separate, and, as it passes through the liquid, most of the soluble salts are at once extracted. Some emulsion- makers use a thick ebonite cylinder, over one end of which is stretched silver wire gauze, and into the other Is fitted a piston. By placing this piece of apparatus in a screw-press the emulsion is forced through the meshes, and acts like the canvas or netting. For large bulks of emulsion this is certainly the most convenient plan. When all is squeezed through, the particles of gelatine may again be transferred to canvas, stretched loosely over the mouth of a jar or sieve, and be doused with water from the tap or from a water jug. After a coiiple of gallons have been thus passed over it, the emulsion should 76 GELATINO-BKOJIO-IODIDE E31ULSI0N. again be squeezed through the canvas, and the same -operation repeated, thus exposing fresh surfaces oi gela- tine to the action ot water. After another skiicing with water the emulsion may be considered as washed, though, to make assurance doubly sure, the gelatine may be left at the bottom of the iar, and the water changed two or three times. We have ourselves found that there is a great gain in using distilled water as the wash water. The gain is not in sensitiveness, but in brightness of the resulting plates. There being no lime in the water,_the grease or saponified matter cannot form an oleate of lime, to which we have traced some kinds of spots. To show the importance of thorough washing, the following ex- periment may be noted. An emulsion was made as above, and after once squeezing through the canvas, a part was immediately used for making plates. A second part of the same was washed under the tap for five minutes ; a third part was squeezed and washed a second time ; and a fourth part was allowed to soak and squeezed a third time. The relative sensitiveness of the four parts was as follows : 1 li 91 '^1 J. J., ^2 -2 The first washing increased the sensitiveness to 1-|, and the second squeezing to 2^, whilst the third squeezing and washing had no perceptible effect. The writer considers this method of washing superior to that given below. Two squeezes, it is believed, are equal to twenty-four hours' such washing. Grelatine is hard to permeate, and, being a colloidal body, the crystal- line salt has hard work to get throiigh when the emul- sion is not finely broken up. Other Modes of Washinij the Emvlsion. — -There are several modes of extracting the soluble salts from the emulsion. Putting on one side dialysis as introduced by Mr. King, owing to its tediousness, we pass on to the most ordinary method. The emulsion when prepared is poured out into a flat dish in a very thin layer (say) of about ^ of an inch GELATINO-BEOMO-IODIDE EMULSION. 77 thick. When set, it is scraped off the dish with a piece of glass, and transferred to a jar or Tbottle in strips. Mr. England first scores it over with the prongs of a silver fork so hreaking it up into fine strips. Cold water is then poured on to it, and a stream of running water kept flow- ing over it for twelve hoxirs, more or less. The writer has converted a tin canister into an effective washing apparatus, as shown in the figure. In the lid of (P:tH--3-i: Fig. 15. a common canister a hole is perforated so as just to admit of the insertion of a glass tube a, a ; a piece of india- rubber tubing connects tJiis with the water tap, and covers any small chink between the glass and the lid, as shown. A spout is soldered on to the canister, as shown. A bottle containing the emulsion to be washed is placed in the canister, the tube being inserted in it. The ^v&te,x: flows over the top of the bottle, and rises in the canister to the level of the spout, where it trickles over into the sink ; the heavy water containing the soluble nitrate is thus perpetually stirred up and caused to flow over the neck of the bottle. This answers admirably, and can be used in the daylight if necessary, but is more applicable 78 GELATINO-BROMO-IODIDE EMULSIOX. to emulsion that has been cut into strips than to that which has been squeezed twice, as the small particles are apt to be carried over the top of the bottle and choke the exit tube. A combination of this method with that given on page 143 can, however, be made by only once squeez- ing the emulsion through the napless canvas. Dr. Eder, to whose careful researches photographers are much indebted, finds by absolute analysis that emulsions passed through fine canvas are sufficiently washed in about thirty-five minutes in running water, and nearly in the same time in standing water ; through coarse meshed canvas in one and a-quarter hours in running water, and in a much longer time in standing water. When cut in strips, it is probable that twelve to twenty-four hours may be necessary to free it sufficiently from the soluble salts, in order to obtain a maximum sensitiveness. Precipitation of the Emulsion hy Spirits of I'i'ine. — Another method is also due to Messrs. Wratten and Wain- wright, and is as follows : — After the emulsion has been allowed to rest for two or three hours, two ounces of alcohol to each ounce of water used are poured into the bottle containing it, and well shaken up. The gelatine rapidly assumes a pasty appearance, and subsides to the bottom. The bottle is then inverted, and the fluid, which contains the soluble nitrates and excess of water, is poured off, and may be preserved for distillation. The explanation of the efficacy of this method is, that the alcohol has a greater affinity for water than has the gela- tine, and that in extracting the water the soluble salts are extracted with it. Methylated spirit not containing gum may be used, and the lower the specific gravity the more effectual it is. Draining the Emulsion. — When the emulsion is con- sidered to be properly washed, it has to be drained. This the writer generally does over the canvas or net used for the squeezing operations, though some recommend a hair seive, but it does not appear that there is much advantage QELATINO-BROMO-IODIDir EMULSION. 79 to be derived from its use. The great point in either case is to drain long enough. A couple of hours is sufficient time, and then the emulsion is ready for melting. It will sometimes happen that no amount of draining over a hair seive or canvas will render the emulsion suffi- ciently free from water to set well when dissolved up. We have found that by pouring a couple of ounces of alcohol through the emulsion when draining, that the excess of water is taken up, and it becomes firm. It should be noted that before re-dissolving the gelatine it should be firm and free from all sloppiness (if such an expression may be used) ; one dose of alcohol generally effects this, and, if not one, two will. The alcohol may be saved if required. In case this artifice be resorted to, only half the quantity of alcohol given before should be added to the emulsion, when it is re-dissolved for filtering and coating the plates. Emulsion that is cut up into shreds is much more easily drained than that which is squeezed through canvas. It is not that the gelatine takes up more water, but that the water clings mechanically to the small particles forming it. Dissolving the Emulsion. — After draining, the emulsion should be transferred to a clean jar or jam-pot, and then placed in boiling water till all the gelatine is thoroughly dissolved. A temperature of 120" or more may be given it vdth advantage. The emulsion, when all additions are made, will be about 10 ounces. The addition of -J- grain of chrome alum is to be recommended. This should be dissolved in 1 drachm of water, and added with stirring; 6 drachms of absolute alcohol are next to be added in the same way, and the emulsion is then ready for filtering. This operation may be carried out in various ways. The writer now uses wet chamois leather, or two thicknesses of swansdown calico which has previously been well boiled and washed. This is allowed to rest loosely in a funnel, and the emulsion filters slowly through it, all coarse particles being left behind. It is preferable to filter into t)0 GELATINO-BEOMO-IODTDE EMULSION. a Florence flask, as it will bear Iieat, though an ordinaiy medicine bottle will answer if the flask be not at hand. The bottle or flask is again placed in water at a tempera- ture of 120?, and the next operation is to coat the plates. There is one very remarkable feature about emulsions, which is, the great variation in their covering powers. If a plate be coated and found to gi^e great opacity when the ordinary amount of emulsion is poured on and set, no harm will be done by adding another 60 or even 120 grains of gelatine (which have been swollen in a couple of ounces of water and melted) to it. This of course increases the bulk of the emulsion, and at the same time is economical. As a rule, it will be found that the emulsions which remain of an orange tint by transmitted light after boiling are those which possess most covering power. The reason of this is not far to seek, as the orange emul- sion is in finer particles than the blue or violet. This addition should of course be made before filtering. CHAPTER X. BENNETT'S GELATINO-BROMIDE PROCESS. The next process we shall describe is that brought out by Mr. C. Bennett, and was the first process published (1878) which gives extreme rapidity. His description of it is extracted from the British Journal of Photography. Sen- sitiveness is attained by slow digestion at a low tempera- ture instead of by boiling. Mr. Bennett, after describing the light required for the preparation of the plates, on which we have already written (Chapter IV.), says : — " To make ' assurance doubly sure,' use a ruby-coloured hock bottle, and with two eight-ounce decanter-shaped bottles made of test-tube glass to stand heat, weigh out for a ten ounce solution — Ammonium bromide ... Best silver nitrate ^Gelatine Distilled water... Use Nelson's ' No. 1 photographic gelatine,' for with the opaque sixpenny packets you have irregularity, red fog, * It will be noted that the gelatine and the silver nitrate have the pro- portion of twenty to eleven, or nearly two to one. In the bromo-iodide emulsion of Chapter IX. the proportion is four to three, snpposing the gelatine in which the emulsion is boiled ia destroyed. In developing, it is evident the former wiU require less restraining than the latter. a 70 grains 110 ,j 200 ■II 6 ounces 82 Bennett's gelatino-beomide process. and frilling. Place aside four ounces of water for the bromide, and two ounces for the silver ; dissolve the bro- mide with heat in one of the flasks in 1 or H ounces of water ; pour into the hock bottle ; swUl out the test-tube with the remainder of the four ounces set aside for the bromide, and also pour in. I do it by heat to ensure all being dissolved, as it does so very slowly after the gelatine is inserted. The four ounces of solution being now almost cold, add the gelatine, shake up well, and place in two or three gallons of water at 90°. I use a fish-kettle with lid. [A good-sized saucepan with a lid answered perfectly with the writer.] In two hours the bromized gelatine will, after well shaking, be quite liquid, and also nearly at 90". Now dissolve the silver in the other flask in one ounce of water, cool to 90°, and pour in ; use the remainder of the two ounces set aside for the silver to rinse out the flask, heat to 90°, and pour in. By being so particular we get regularity, and are able to mix different batches of emulsion, which is a great boon. Shake the emulsion very briskly, and replace in the kettle for two, four, or seven days, according to rapidity required. The temperature should never be over 90° ; if you do not let it exceed that, you will not have red fog. ' Cosy ' it up with flannel, and it will not lower many degrees during the night. I, however, use a stove two feet across, and place it on that ; a faint gas jet below keeps it always at 90°. I shake up every twelve hours. If washed in two days, the emulsion is rapid and dense ; in four days, more rapid and less dense — quick enough for any drop-shutter known, when developed as below. With some that I kept for seven days, with drop-shutter, on a dull February morning, pebbles close to the camera were perfectly exposed. The negative was thin under ammonia, but bore intensifying to any extent. " Cool the emulsion in a bottle not smaller than a Win- chester quart, and wrap it up in brown paper to exclude ounces. Gelatine dissolved in alcohol, ammonia, and water, will not set so firmly as the same amount of gelatine in water ; yet, if the salts and ammonia are removed by precipita- ting with excess of alcohol, the gelatine recovers its setting powers." ^Ye have tried this plan of emulsion making at various times, and can say that it yields an excellent plate, and very sensitive. At the same time we are not prepared to give it such excellent qualities as is obtained by the boiling process. The drawback to it is the large amount of alcohol required to precipitate the emulsion, and its consequent cost. CHAPTER XV. MR. GOTESWORTH'S COLD EMULSIFICATION ■WITHOUT AMMONIA. Mr. CoTESWOETH described a plan of gaining sensitive- ness by allowing an emulsion to gain sensitiveness by remaining liquid at ordinary temperatures. We recollect that a somewhat similar proposal was made of emulsify- ing at a low temperature in gum-arabic. Following out Mr. Cotesworth's general directions, we have arrived at fairly satisfactory results. An emulsion is prepared, as far as the boiling operations, according to Chap. IX., the mode of mixing given at page 72 being preferred. An emulsion which has a beautiful ruby colour, if kept liquid, will, in twenty-tour hours, have attained a grey-blue colour. A comparison with Bennett's process (Chapter X.) will show that the difference between the two processes is, that Mr. Cotesworth uses very little gelatine for emulsifi- cation to begin with, whilst Mr. Bennett uses the full quantity. ^ The consequence is that the latter gentleman was obliged to have recourse to prolonged emulsification at about db", in order to overcome the viscosity of the gelatine, whilst the former can get sensitiveness in twenty- four hours at (say) 60'' F. In cold weather we have found it necessary to add a couple of ounces of water to the sensitizing emulsion, in order to prevent setting. In this case the extra gelatine required is added dry, and, after soaking, the emulsion is warmed, and the gelatine melts. There is nothing different in the preparation or develop- ment of the plates to call for any special remark. CHAPTER XVI. A PROCESS FOR GELATINE EMULSION "MAKING IN HOT WEATHER. The formula adopted is precisely that given in Chap. IX., €xcept that, before washing, 120 grains of autotjpe, or other hard gelatine, are kept back. After boiling, if this plan be adopted, or after using Cowan's cold emulsifica- tion (see Chap. XIV.), and adding 120 grains of gelatine in 1 oz. of water, the emulsion is poured out into a jam- pot, which is immediately placed in iced water with a few lumps of ice floating in it. In half-an-hour the gelatine will be firmly set. The gelatine is loosened from the sides of the jam-pot, and the lump of emulsion is trans- ferred into moist canvas, and squeezed through into a jar of iced water (the water having been run through filter-paper to get rid of all floating matter) in which a few small lumps of washed ice are floating. After ten minutes the water is changed, and after another ten minutes is changed again, when it is again collected in the canvas, and squeezed through into water. One more change of water should be sufficient to free it from all except traces of soluble salts. It is then transferred to the canvas, and allowed to drain over a jar for half- an-hour to three-quarters. It is again transferred to the jam-pot and melted, and the remaining 120 grains of gelatine, which have been allowed to swell in about 106 GELATINE MAKING IN HOT WEATHER. three-quarters of an ounce of water, is added, together with two or three drops of carbolic acid (or other anti- antiseptic), and then once more placed in iced Avater, In half-an-hour it is set, when it is covered with alcohol and allowed to ripen for a day ; and if the jar be placed in water containing a lump of ice, so much the better. When plates have to be coated, the slab on which the plates have to be set is covered Avith small lumps of ice for half-an-hour, and if the slab be thick it is only- very gradually cooled ; but, on the other hand, it also but very gradually gets warmed again. During this time the emulsion is melted, six drachms of alcohol, one grain of chrome alum in one drachm of water, added, and filtered. When the plates are coated (alter the slab has been dried from all water), it will be found that the film of emiilsion will set in a couple of minutes, and that the slab remains cool enough to enable five or six batches of plates, each batch filling the slab, to be prepared; that is, supposing your slab to hold eight plates, yoix can coat forty to forty-eight without re-cooling the slab. The gas of the drying-box may be lighted immediately, and the drying of the plates wiU proceed rapidly, and they will not re-melt. If gelatine be once loell set, it requires a high temperature to re-melt it ; and the more the water is evaporated, the higher the tem- perature required. As the current of Avarmed air passes over the plates, the moisture is rapidly absorbed, and hence the drying can be effected Avith safety. CHAPTEE XVII. GKLATINO-BROMIDE EMULSION MADE BY PRE- CIPITATION ■WITHOUT THE PRESENCE OF GELA- TINE. The next emulsion is one described in the Pliotograpliic JVeu's by the writer. It is a method of prej)aring an emulsion by adding washed silver bromide to gelatine. Let us suppose we are going to make up about 7 ounces ol gelatine emulsion. Weigh out ammonium bromide, 140 grains (or its equivalent in zinc, potassium, or any other bromide), and dissolve in 20 ounces of water (not necessarily distilled water). Next weigh out 250 grains of silver nitrate, and dissolve in 6 ounces of water, and add 6 drachms of glycerine to it, and stir thoroughly with a glass rod. We prefer to put this mixture in a glass jar holding about 40 ounces (an empty French prune bottle would answer every purpose). The bromide solution should now be added very cau- tioasly. Take a 10-ounce measure, and fill it up to six ounces, or thereabouts, so that it is not too full, and gradually drop, little by little, the solution into the silver solution, stirring very thoroughly the whole time. A milky emulsion forms, and gets thicker and thicker till the whole bromide in the 20 ounces is added, though, of course, the fluid is per se thinner ; a quarter of an 108 EMULSION MADE WITH GLYCERINE. 'Ounce of nitric acid is next added, and well stirred up. This addition is made to save any chance of fog, which anight be caused by the excess of silver present. The reason of this has already been described in Chapter III. This emulsification is better carried on in a dark room, though it is not absolutely necessary. The bromide solu- tion must he poured into the silver solution, andnotvice versa, ■or a failure loill be most probable. The glass jar and its contents may now be placed away into a cupboard, and left for as long a time as is convenient, but not for less than a quarter of an hour. By the latter time the silver bromide will have fallen to the bottom of the jar, with the exception of a very slicjlit milkiness, which will subside in a couple of hours. The silver bromide, however, left in suspension at the end of the quarter of an hour is so small that it may be decanted off without detriment to the emul- rsion. The jar may be tilted, and the liquid poured off, or a syphon may be introduced (and this is a neater way), and the liquid syphoned off close to the precipitate. About 20 ounces of water are again poured into the jar, the precipitate well stirred up, and again allowed to sub- side. As soon as ever the subsidence takes place, the water is again decanted or syphoned off. This operation is repeated four or five times, after which the decanted water may be tested for acidity, and for silver nitrate. To try for the former, moistened litmus paper is held over an open ammonia bottle till it is thoroughly blue, then well washed in distilled water ; this is thrown into the -decanted water. The faintest trace of acid will redden it. If it does turn red, the washing must be repeated. To test for free silver nitrate, add to the wash water 1 drop of potassium chromate. A red colouration indicates the presence of. silver nitrate. In case of the presence ol * It should be remembered that the wider the diameter of the jar, and the shallower the water, the greater will the precipitate collect at the bottom. EMULSION MADE WITH GLYCERINE. 10f> eitlicr one or the other, as is. shown by the litmus paper and the chromate, the washing' must be continued. The original plan we adopted, and of wliich the above is a modiiication, consisted in precipitating silver bromide in pure water, and without the help of glycerine. This is still one of the best methods we have tried, and we give a re'. — Potassium bromide . . . Water No. 4. — ^Silver nitrate Citric acid ... Water Nos. 2, 3, and 4 will keep infinitely. The film should then be well washed under the tap. If there be every reason to suppose that proper exposure has been given, make a developing mixture in the fol- lowing proportion : — • 1 part 12 parts 1 grain 1 ounce 20 grains 20 „ 1 ounce No. 1 No. 2 No. 3 1 drachm 1 drop Sufficient should be taken to well cover the plate. Nos. 268 DEVELOPMENT OF THE PLATE. 2 and 3 should be first dropped into the developing cup, and finally No. 1 is added. (The necessity of stirring is prevented by this procedure.) Flood this over the plate. The image, if everything be eii regie, should appear quickly, and the developer should be worked over the plate till all detail appears by reflected light. When this happens, .another drop of No. 2 to each drachm should be dropped into the measure, and the soltition poured back on to it as before, and the intensification with the stronger ammoni- acal solution proceeded with. The intensity will gradually be increased, and it may happen that the requisite density will be obtained. Should the density not be sufficient, one drop of No. 4, with a drachm of No. 1, may be mixed, and intensification takes place in the ordinary manner. In the writer's experience, the colour and printing quali- ties of all negatives by this process are improved by even a slight application of the intensifier. Should the negative flash out at once on the application of the first developer, it is a sign of over-exposure of the plate. The developer should immediately be returned to the cup, and the plate washed. Two drops extra of No. 3 must be added to the developer, and the development pro- ceeded with as before. The potassium bromide keeps the shadows bright, and acts as a retarder ; so much has it the latter qualification, that if a large quantity be added, the plate will refuse to develop at all. It is better to fix an over-exposed j)icture immediately the detail is all -out, and intensify with pyrogallic acid and silver after- wards. If traces of the picture refuse to appear in three or four seconds after an application of the primary developer, a fresh developer should be made up similar to the above, omitting the bromide of potassium. If the picture refuse to appear satisfactorily when this course is adopted, the plate is hopelessly under-exposed. When the detail is well out, the intensification should be carried on as given at page 263. DEVELOPMENT OF THE PLATE. 269 Fixing Solution. — -The negative should be fixed with potassium cyanide or sodium hyposulphite. Potassium cyanide ... 25 grains Water 1 ounce . ^^■' Sodium hyposulphite ... Water 1 ounce 6 ounces The first may be flowed over the plate, but a dipping bath for the latter will be found advantageous for studio work. There are some images which will not stand the cyanide, and in rare instances some will not stand pro- longed immersion in the hyposulphite ; it may be because the metallic silver is in a very fine state of division. This seems all the more probable since we know that in this state it is attacked by the cyanide. When all the bromide is dissolved from out of the film, the plate should be well washed back and front. It is not amiss to give a dip in a solution of alum, as used for gelatine plates, if hypo- sulphite has been used, since it eifectually decomposes it. The plate should be allowed to dry spontaneously, away from dust, and it should then be varnished. Varnish such as is used for wet plates should be procured and applied, as given at page 161. CHAPTER XLIIL COLLODIO- CHLORIDE EMV'i.SION FOR DEVELOPMENT. Tn the previous processes it will be seen that silver bro- mide forms the staple sensitive salt, though both iodide and chloride have been introduced into the emulsion, but in small quantities. The use of chloride by itself has, till quite recently, been Inadmissible, on account of the diffi- culty of producing a chemical developer suitable for it. Dr. Eder and Captain Pizzighelli found that for gelatino- chloridc plates, ferrous citrate in a weak form gave good development. The developer was very weak, however, in the form they gave, and the writer introduced the ferrous- citro-oxalate form, which has proved suitable for collodio- chloride plates. There are two formula for collodio-chloride emulsions, one with excess of silver, and the other with an excess of chloride. For most purposes the latter is the one we pre- fer, since it can be made and used in a quarter of an hour when required. What is usually calli^d roUodio-chloride is totally unfit for chemical development, and it is mis- leading to class it under this denomination, since it has a large proportion of citrate in its composition. To make the collodio-chloride we proceed as follows : — 10 grains 5 5J 20 )) 50 n COLLODIO-CHLOKIDE EMULSION. 271 Weigh out the following — Pyroxyline (any easily soluble sort) J5 _ ;.' 3) ); j; Calcium chloride ... Silver nitrate Dissolve the calcium chloride in i ounce of alcohol 'SOo, "by warming over a spirit lamp. Place the 5 grains of pyroxyline in 2-ounce bottle, and pour on it the alcohol containing the calcium. After a couple of minutes add ■| ounce of ether, -when the cotton will dissolve. Dissolve the 50 grains of silver nitrnte in a test-tube in the smallest quantity of water, and add to it 1 ounce of boiling alcohol '805, and mix. Previous to this the 10 grains of pyroxyline should have been placed in a four- ounce bottle, and the alcohol containing the silver should be poured on. Next add 1 ounce of ether, little by little, with continuous shaking. The silver nitrate may very probably partially crystallize out, but that is of very little ■consequence. Take the two bottles into the dark-room (a room glazed for wet-plate work will answer perfectly), and pour gradually the calcium chloride collodion into the silver nitrate collodion — on no account vice versa. The resulting emulsion, of course, is silver chloride in an extremely fine state of division. A plate coated with it should show a canary colour by transmitted skylight, and a thickish iilm should make a gas flame appear ruby-coloured. The emulsion may be washed in the usual way, if required (see page 51) ; but, when washed, and used simply dried after washing, it is, like other collodion emulsion prejiared with an excess of haloid, rather insensitive. Before doing anything with the emulsion, however, a plate should be coated, washed under a tap, and placed in the dark slide. The slide should be taken into white light, and half the front pulled up for a second, and then closed. Ferrous- citro-oxalate developer, as given at page 165, should then be applied, and the result noted. A blackening of 272 COLLODIO-CHLOKIDE EMULSION. the film may ensue. If correct on the application of the developer, the film should not show any reduction of the chloride, except on the exposed half of the plate. Should blackening take place, nitric acid may be added ; but that rather rots the film if kept too long in contact with the emulsion, which would be the case if it is to remain un- washed . A simpler plan is to add a soluble chloride which would form a double chloride. Three or four drops of a 20-grain solution of cupric chloride (chloride of copper) in alcohol should be added to the emulsion, and shaken up, and immediately the fog disappears. Two or three drops of gold tri-chloride, or of cobaltic chloride of a similar strength as the copper chloride, would answer equally as well. So far as regards the making of the emulsion. The next point is the preparation of the plates. As was said before, it can be washed, but we really see no advantage in so doing. Polished and edged plates (see page 77) may be coated, washed, and then simply flooded once over with — Beer ... ... .. ... 5 ounces Sugar (white) ... 1 moderate sized lump Pyrogallic acid ... ... ... 5 grains These, when dry, will be very sensitive, and put to shame many a coUodio-bromide emulsion. Any of the preserva- tives given in Chap. XLI. may also be used. To develop, rinse, and then simply immerse them in a dish containing the ferrous-citro-oxalate. In a short time the image will begin to appear, and gradually gain strength. The colour of the image is a beautiful ivory black, and admir- ably suited for collodion transfers. If a warmer tint is required, tone in a dish with — Uranium nitrate... ... ... 10 grains Ferricyanide of potassium ... 10 „ Water ... ... ... ... 10 ounces COLLODIO-CHLOEIDE EMULSION. 273 The colour will rapidly warm, and would eventually become a pretty chocolate colour.' It will be noted that an emulsion prepared in this way may be developed by the ferrous-citro-oxalate ivithout any resfrainer. They will also develop with : — Hydrokinone ... ... ... 10 grains Water ... ... ... ... 1 ounce to every ounce of which are added 3 or 4 drops of a saturated solution of carbonate of ammonia. The emulsion may also be made with an excess of silver nitrate, in which case, in the above formulas, seventy grains of silver nitrate should be used. Fog may be prevented by adding 2 or 3 drops of strong nitric acid to the calcium chloride collodion, or it may be eliminated by the use of bichromate of potash, or by hydrochloric acid, or by cupric, cobaltic, or auric (gold) chlorides, after the excess of silver has been washed away. In fact, the same procedure should be adopted as in the collodio- bromide process. The development of this emulsion is carried on as above. CoUodio-bromo-cJiloride Emulsion. — A very capital emulsion is formed by mixing f part of an unwashed coUodio-bromide emulsion with ^ part of an unwashed coUodio-chloride emulsion. The same proportion of washed emulsions may also be mixed with advantage. The development of this emulsion is most advantageous when an unrestrained developer such as the above is used. CH.\PTEE XLIV. DEFECTS IN COLLODION EMULSION PLATES. It is somevrliat difficult to name the especial detects foimd in tlie emulsion dry plates, but we -n-ill endeavour to point out tlie principal ones. Misters in the film. — ^May be due to a preservative, more particularly if it contain gummy matter. Thiis, with the beer, or the gum-gallic or coftee preservatives, these may make their appearance. The remedy has already been given. Black' spots ondevelopineut are usually due to dust being allowed to settle on the film whilst drying ; decomposing organic matter in fine particles is also a truitful source of these annoyances. Insensitive patches or spots on development have not yet been tracked to an origm ; but if a preservative be em- ployed, they will rarely be met with. They seem to be due to impurities in tlie pyroxylin, since with certain preparations they are altogether absent. Crape markings in the film are usually due to the solvents of the emulsion being too aqueous ; or tliey may be due to the emulsion not having been shaken up shortly before being used, or to the bromide being too coarse. 2hin transparent films with washed emulsion are usuallv due to the last two caiises. DEFECTS IN EMULSION PLATES. 275 Ihe mnulsion refusing to flow properly is due to deficiency of solvents. This is frequently met with if the same emulsion he used for coating many plates. It should be ■dUuted down with 1 part of alcohol (-812) to 2 of ether ■(•720). Wlien the film tends to peel off the plate., the pyroxylin is jjrobahly of too contractile and horny a nature, in which ■case the proper treatment is, to mix it with an emulsion made with one of a more powdery character, or to mix a little gum guiacum dissolved in alcohol with it. Circular insensitive patches in the centre of the plates are •sometimes met with in hot weather, when a pneumatic plate-holder is used. Ihe cause of fog has been pointed out in the first chapter, and need scarcely be alluded to again. To eliminate it in a washed emulsion, the careful addition of ■a few drops of a dilute solution of iodine in alcohol will prove effective. With such an emulsion, when used with a preservative, a dip in a 10 per cent, solution of hydrochloric acid in water wiU eliminate all fog. In an unwashed emulsion the addition of nitric acid will effect a cure. Flates which fog through having been exposed to light may be rendered available for use by washing off any preservative they may have on them, and immersing them in a hock-coloured solution of potassium bichromate, or by water faintly tinged with potassium permanganate, or with a 10 per cejit. solution of hydroxyl or hydrochloric •acid in water. After washing, a preservative may again be applied. Plates which fog under development, when the emulsion is not in fault, must owe this defect to one of two causes : 1st, to the light of the developing room ; or, 2nd, to the ■developer. The first cause is easily tracked, as a plate may be prepared and developed in almost absolute ■darkness without receiving any exposure to ordinary light. If, after a short application of the developer, 276 DEFECTS IN EMULSION PLATES. no fog is found, tlie light used during development is in fault. If the plate fogs, the developer is wrong. _ In this case, try making up fresh solutions, and using more soluble bromide as a restrainer. With the ferrous oxalate developer want of bromide is often the cause of fog. . . , Drying marhings in a film are sometimes met with. They generally form a sort of ripple marking near one edge. They are usually found when impure water is used for the final washing of a plate, and are absent when a final rinsing with distilled water is given. With plain washed emulsion these markings are never met with unless the temperature of the drying oven is high. J hick specks in aplate are usually due to the dried emul- sion from the neck of the bottle mixing with the solution, and finding a resting-place in the film. CHAPTER XLV. EMULSION PROCESSES FOR PRINTING. Collodio-Citro-CMoride. — To prepare a citro- chloride emulsion is not very easy at first sight, since the citrates are very insoluble ia alcohol, and it is necessary to have some such hody present in the collodion to form an organic compound of silver to give vigour to the image. It is very easy to do, however, hy a little artifice which we have thought might be worth describing. Citrate of ammonia is insoluble in alcohol, and therefore rather difficult to introduce into an emulsion in the ordinary manner ; but it can readily be introduced into collodion by the following procedure. Take ten grains of pyroxy- lin, and cover it with half an ounce of alcohol in which 20 grains of citric acid are dissolved, and then add 1 ounce of fether. This forms collodion containing citric acid. In order to get citrate of ammonia into the collodion in a very fine state of emulsion, ammonia (gas) dissolved in alcohol is added to the collodion. This is effected by inserting a bent tube in a cork in a test tube which is a quarter filled with liquor ammonia. Placing this in warm water — in fact, nearly boiling water — the ammonia is given off rapidly, and can be made to pass through al- -cohol in another test tube. The alcohol absorbs the 278 COLLODION PROCESSES FOR PRINTING. ammonia, and takes up a large proportion of gas, as those' who use sal-volatile may be aware. This ammoniacal alcohol is next added to the collodion containing the citric acid, little by little, with shaking and stirring, and sufficient is added till reddened litmus paper shows a very slight trace of alkalinity. A very fine emulsion of citrate of ammonia is thus formed, the grain of which is indistinguishable by the naked eye, and, like other emulsions when first mixed, is orange- coloured when spread upon a glass plate. The emulsion is again rendered slightly acid by the addition of a few drops of a solution of citric acid in alcohol. If an emul- sion of citrate of silver be required, there are two ways of efi'ecting it — one by dissolving (say) 10 grains of silver nitrate in the least possible quantity of water, to which is added one drachm of alcohol, and gradually dropping it into the collodion containing the citrate. It sometimes happens that this gives a granular emulsion. If, how- ever, the silver nitrate be coarsely powdered and added to the emulsion, a very fine emulsion of citrate of silver is produced by shaking. This may be washed in the usual way, or may be precipitated by pouring in a fine stream into water. Another method of forming the citrate of silver is to pour out the emulsion of citrate of ammonia into a flat dish, and, when well set, to cover it with a solution of silver nitrate. It is then drained from the silver, washed, and dried as usual. When re- dissolved, the emulsified citrate of silver should be excessively fine. To prepare a coUodio-citro-chloride emulsion, two Slans may be adopted : either to dissolve 20 grains of ry calcium chloride in a small amount of alcohol, and add it to the citrate of ammonia emulsion, and then to add 80 grains of silver nitrate to it in the usual way. What we prefer, however, is to make a coUodio-chloride emulsion separately, and then to mix the citrate of silver emulsion with it, according to taste. COLLODION PKOCIJSSES FOB PRINTING. 279 To make a pure collodio-chloride emulsion, 1 dissolve 20 grains of calcium chloride in half-ounce of alcohol ; add to it 5 grains of pyroxylin, and then Jounce of ether. To 1 ounce of plain collodion made similarly, I add 60 grains of silver nitrate dissolved in the smallest quantity of water, to which is added one drachm of warm alcohol. This produces an emulsion of silver nitrate in the col- lodion. To this the chlorized collodion is added drop hy drop, with stirring or with shaking in a hottle, and a per- fect emulsion of silver chloride should result. This can be poured out to set in a dish as usual, and washed, dried, and re-dissolved ; or can at once be poured out in a fine stream into a large bulk of water, squeezed, soaked in alcohol twice, wringing out in a cloth all excess of alcohol each time. It can then be re-dissolved in the one ounce of ether and one of alcohol, and should give a good emulsion. The two emulsions may then be mixed together as before stated. It is well to dissolve about 5 grains of silver nitrate in water and alcohol, and add to the emulsion in order to increase the rapidity of printing. Any well-sized paper may be used with this collodion emulsion, but we prefer the enamelled paper, such as is used for collotype printing. The paper is turned up round the edges for about ^ of an inch, to make a shallow tray, and placed on a sheet of glass for steadiness. The collodion emulsion is then poured on to the paper till well covered, and all excess is drained off into the bottle. It is then allowed to dry. It is now ready for printing, which is done to a greater depth than for prints on albumenized paper. After washing it may be toned by the following : — No. 1. — Ammonium sulphocyanate... 1^ ounce Sodium hyposulphite ...45 grains Sodium carbonate ... ... 15 » Water 50 ounces 280 COLLODION PROCESSES EOR FEINTING. No. 2. — Gold tri-chloride 30 grains Chalk 1 teaspoonful Water ... ... ... 50 ounces Equal quantities of these are taken and mixed, and the toning proceeds as usual. The prints ordinarily take from two to ten minutes to tone. If a longer time be required, add more gold till the desired effect is produced. This toning bath can only be used once. We have also found that a good tone may be given by using the lime bath, or by the baths given at page 195. These prints should be permanent, aijd possess a rare beauty. Gelatino-Citro- Chloride. — The writer has introduced a process of printing by means of a citro-chloride in gela- tine, which can be applied to paper and glass. The method of preparation is as follows : — 1. — Sodium chloride *Potassium citrate Water 2. — Silver nitrate ... Water 3. — Hard gelatine ... Soft gelatine ... Glycerine Water Nos. 3 and 2 are mixed together, and then an emulsion formed by adding No. 1 in the usual way when forming a gelatine emulsion. When set, the emulsion is squeezed through canvas into cold water, and after allowing it to remain in the water for ten minutes or a quarter of an hour, dissolved up, with the addition of* about 3 drachms of alcohol and 2 grains of chrome alum dissolved in 2 drachms of water. Plates or paper are then coated with the femulsion, and printing takes place in the usual * Tlje citrate may, be reduced to 20 'grains, and the silver nitrati ^ to 120 grains. 40 grains 40 w 1 ounce 150 grams 1 ounce 160 grams 160 n 1 drachm H ; ounces COLLODION PROCESSES FOK PRINTING. 281 manner. At first the emulsion may appear grainy ; if, however, it be toiled for ten minutes, the grain disappears, for the silver citrate is soluble in warm water. The rapidity of printing by the boiling is certainly increased. Plates, when coated, are rather transparent, and, prima facie, a vigorous print might not be expected from them. The rapidity of printing is very great ; it is more than twice as rapid as ordinary albumenized paper. The image prints of a violet tint by reflected light, and of a rich chocolate colour by transmitted light. If fixed with- out toning, the colour by transmitted and reflected light is that of burnt sienna, and of great vigour and beauty. Prints can be toned by any of the ordinary toning baths. Borax and chloride of gold gives a pleasant tone ; the sulpho-cyanide toning bath gives a black, rather ap- proaching an inky tone. Platinum can be used to tone the fixed print, but it has a great reducing action, and there is a tendency for the whites to become yellowed to a slight extent. No doubt endless variations in the organic salts used might be made, but the citrate answers well. The prints should be well washed. It is believed that they would not fade in the same way that albumen prints are so prone to do, as the organic salt used is a definite compound, and not one which is so complex and uncertain as the albuminate of silver is. The liability to fade is less with the above formula than with one which has an excess of silver present. The potassium citrate is in large excess ; hence no silver will attack the gelatine. Of course this emulsion may be applied to opals or glass, or it may be applied to paper as given in Chap. XXVII. Mr. Ashman says the following gives a good tone : — The following will be found capable of giving any tone to the transparency or positive by reflected light, ranging between warm brown and purple black : — Ammonium sulphocyanate ... ... 1 drachm Water ... ... ... ... 1 pint Gold terchloride 1 grain 282 COLLODION PEOCESSES FOE FEINTING. Upon adding the gold, it is converted into a sulpho- cyanate, which will be seen to have a red colour. The precipitate, however, dissolves in the excess of snlpho- cyanate, and is then ready for use. Washing before toning is dependent on the formulse employed in making the emulsion ; in most cases it will be found advisable. Toning action is first seen at the edges, by the colour changing to a yellowish-brown ; soon the whole print assumes a sepia tint, then purple, and finally blue-black, the usual time occupied in these changes being less than five minutes. The print should then be transferred to another dish containing a plain solution of ammonic sulphocyanate (2 drachms of the salt in 1 pint of water), where it may remain five or ten minates, after which it should be placed in weak hypo 1 — 10 until the soluble chloride is dissolved. Ammonium sulphocyanate alone will be found to fix a plate or paper print made with silver citro-chloride emulsion, but hypa is cheaper and quicker. Should the plates or paper be inclined to frill, place them in saturated chrome alum solution after toning ; this in no way afi'ects the colour or purity of the whites. Washing is the same as other gelatine plates and silver prints. Mr. Warnerke informs us that the paper or glass, when heated, keeps whiter if there be free tartaric acid in the emulsion, which we can well believe. Unwashed Gelatino-Citro- Chloride Emulsion for Printing^ — At a meeting of the London and Provincial Photo- graphic Association, Mr. A.L. Henderson described a modi- fication of the above process : 16 grains of gelatine were swelled in with cold water, and 2^ ounces of distilled water were added. The gelatine was then dissolved by the aid of heat, and 11|^ grains of sodium acetate added. To the 42 grains of silver nitrate, dissolved in 1 ounce of water, was next to be stirred in 5 grains of sodium chloride and 7^ grains of sodium citrate, mixed together in 1 ounce of water. Finally, the 1 ounce of gela- COLLODION PROCESSES FOR PRINTING. 283 tine, swelled in water, was dissolved and added to the emulsion thus formed, and then water added to make up the bulk of 9 ounces. If the emulsion were required to coat paper, he made up the hulk to half as much again, or double. This emulsion would be used without any washing. Slow Collodion Emulsion Process for Transparencies. — The following formula has met with approval for the preparation of a collodion emulsion for transparencies, and was one which we used for producing intense negatives : 50 grains of silver nitrate are dissolved in \ drachm of water, and J ounce of boiling alcohol ('SOS) added. This is poured on 10 grains of pyroxylin, and then 1 ounce of ether added to dissolve the cotton. The silver very probably will precipitate in very fine grains, but this is of no consequence. In another ^ ounce of alcohol, 40 grains of zinc bromide are dissolved, and this solution is gradually added to the above collodion with shaking- Such an emulsion will be found perfectly free from mottling caused by excess of water, and wiU flow smoothly. When a plate is coated it is washed, and any preservative used (preferably beer), to which to every ■J pint a lump of sugar of the size of a large hazel nut is added. Slow Gelatine Emulsion. — Slow gelatine emulsion may be prepared by the formula given in Chap. XXXVII., by reducing the time of boiling to five minutes. If emulsi- fication, as described in Chap. XXXVI., be accepted, it win be found that after twelve hours it wiU be in a con- dition to give a slow plate. Any emulsion may be made slow by adding 10 grains of copper chloride to it after- boiling. These slow plates give wonderful density. CHAPTER XLVI. PACKING PLATES. Packing Gelatine Flates. — The method of packing adopted by some dry-plate makers is an intolerable nuis- ance. They make zig-zags of thick paper, which they stuff between the ends of each plate, or pair of plates ; and when a packet is unclosed and a plate taken out, there is an endless bewilderment of paper and glass, each out of place and hard to put right. Mr. England's plan avoids this, and if the cardboard is smooth, no harm will be done to the plates. He uses little frames of cardboard 7-^ Fig. 17, to place between his plates, and they are just large enough to be flush with their edges. Thus, for our sized plates (Jk t)7 5), we cut strips of card SfV inches wide, 7 J inches and an equal number of strips 5| inches long. long. PACKING PLATES. 285 Tough bank-post paper is gummed over with stiff gum, and allowed to dry, and little squares of about half-inch size cut out. A short piece and a long piece are laid together, on a pair of lines ruled at right angles to one another on a board, and when the square of gummed paper is made to adhere beneath them, and then deftly folded over, two sides of the required frame were made. One more long, and one more short piece, similarly treated, completed the frame. Four-sheet card is what Mr. England recommends. When the strips are cut, we make about thirty of these frames in an hour. The plates are packed alternately back to back and face to face, in the latter case a frame being placed between them. Our plates are packed in half-dozens, enclosed in twa thicknesses of orange paper. The two packets are en- closed in pieces of black varnished paper, and then placed! in boxes. Another plan which we have seen adopted appears tO' be admirable for smallish sized plates, say up to 8^ by 6|. Four small pieces of card about ^ inch by ^ inch are cut for each alternate plate. After moistening one side, they can be made to adhere to the margins of the plate, thus spreading the two plates which are face to face, by an interval of the thickness of the card ; and before placing the plate in the slide, the strips are removed by a pen- knife. For large sized plates, we believe nothing better than to place moderately stout orange packing paper cut to the size of the plate between each pair. The orange paper, as far as we have seen, has no deleterious effect on the plates. Boxes made of stiff millboard, and covered with orange paper, are useful. The cover should cover both the top and sides of the box. They should not be too small, but be 1 inch longer and ^-inch wider, inside measurement, than the plates. A depth of 1^ inches will then take one dozen plates. .286 PACKING PLATES. Packing Collodion Emulsion Plates. — These plates are even more difficult to pack than gelatine plates. Mr. England's masks can be adopted. Dry plate boxes with grooves are, however, what we prefer to all other plans. The drawback to them is that they are rather bulky. Note-Book for Registemig Plates. — In making an expe- dition during Avhich plates cannot be developed, or when only some can, it is advisable to enter in a note-book all details. We give an extract from a note-book, which will show the form we recommend. It must be premised, however, that each plate, besides bearing the number of the batch, should also bear a distinctive number, which, for convenience, may be written on the same label as that indicating the batch, but using a red pencil instead of blue. When the slides are filled before starting, the columns filled up are 4, 5, 6, 7, and the rest are filled up after ex- posure and after development. By adopting this plan a complete record of every plate exposed and developed is obtained, and will be found of use in judging ex- posures. Eemarks. Use of bromide required in de- veloping. Detail in dark trees of island fairly out. - Hypo, used in developer. Detail fair. U3doiaA3(I o o O •p9d0I9A8(I CD~ CO* CO_ so" o" 1 t n River Arun, looking to- wards mill. Lake near Ar- undel, from south. CO ,-t s •amsodxa: 10 sec. Inat. 3 -inch opening o CO •do^g CO CO 1 ( =^ ■suai 1 i JO isqimiH 00 -^ us (o .-< cq •-I w -1 w CO CO 'laqnmii la^atnc^isuag CD CO CD CD OO CO IM C^ !M CI .-1 rH ■nn^a 00 CO 00 00 M cq C5 OS Oi O Q» 00 •8PTIS CC '^ U3 CO t* CO •WSii a Cloudy 1 1 * ■jnoH 2.30 S.IO 1 1 1 ■BJ^a 00 00 ' 18/6/81 Weights and Measures. 1 Sovereign weiglis 1 Shilling ,, ... 48 Pence „ HaK-penny and three-penny piece weigh Florin and sixpence Three pennies 4 half-crowns and 1 shilling 4 Florins, 4 half-crowns, 2 pennies 1 Half-penny = 1 inch in diameter 123-274 grains 87-273_ „ 1 lb. avoirdupois \ ounce h „ 1 „ 2 ounces 4 „ AvoiKDTTPOis "Weight 27ji Grains . . . 16 Drachms 1 6 Ounces . . . 24 grains ... 20 pennyweights 12 ounces... 1 drachm (= 21^ 1 ounce (= 437| 1 pound (= 7000 ;rs.)> „ ) Teot "Weight. ... 1 pennyweight (= 24 grains) ... 1 ounce (^ 480 ,, ... 1 pound (=5760 „ Old A-Poihecaeibs' "WEienx (superseded in 1864). 20 Grains ... 1 scruple (= 20 grains) 3 Scruples 1 drachm (= 60 ,, ) 8 Drachms 1 ounce (= 480 ,, )■ 12 Ounces 1 pound (= 5760 „ } The New Apothecaries' Weight is the same as Avoirdupois. LianiD Measttee. 60 Minims 1 drachm 8 Drachms 1 ounce =1-73 cub. ins. nearly 20 Ounces 1 pint =34-66 ,,, „ 8 Pints 1 gallon=277-25 „ „ The Imp. Gallon is exactly 10 lbs. Avoir, of pure water ; the pint, IJ lbs. Pliiid Measfee. = 1 dessert spoonful = 1 table ,, 1 Minim = 1 drop 2 Drs. 1 Drachm = 1 teaspoonful 4 „ Feench Measuees. 1 Gramme ... 15-432 grains Kilogramme ... 1000 grammes (=2-2 lbs. Avoir, nearly) 1 Litre 35-216 ounces (fluid) 1 Cubic Centimetre (c.c.) ... 17 minims nearly 50 Cubic Centimetres ... 1 ounce 6 drachms 5 minims 1 Metre 39-37 inches INDEX. Aceto-GelatineEmulsioD, 169 Albumen Beer Preservative, 258 Alkaline Development of Gelatine Plates, 134 Alkaline Development, Theory of, 14 Ammonia- Nitrate of Silver in Gela- tine Emulsii 'ns, 93 Architectural Subjects, 129 Argentous Oxide, 6 Backing the Plate, 253 Beechey's Process, 229 Bennett's Gelatino-Bromide Pro- cess, 81 Beer Preservative, 255 Black Spots oa Development, 274 Blisters on Gelatine Plates, 198, 274 Blocks of Sensitive Paper, 179 Boiling Gelatine Emulsions, 74, 97 Burnishing Prints, 195 Burton's Process, 91 Cadett's Shutter, 130 Camera, Exposure in, 180 Canvas for Squeezing Emulsion, 75 Chardon's Process, 229 Chemical Theory of the Photo- graphic Image, 11 Chloride Paper, 194 Coating a Plate with Gelatine Emul- sion, 118, 25ff Coating Paper ■with Gelatine, 175 Coating Machine for Plates, 120 Coffee Preservative, 258 Cold Emulsification, 101 CoUodio-Albumen Emulsion, 245 Collodio-Bromide Emulsion, 242 Ccllodio-Bromo- Chloride Emulsion, 273 Cooper's Collodio-Bromide Process, 237 Collodio-Chloride Emulsion for Development, 270 CoUodio-Citro-Chloride, 277 Collodion Emulsions, 207 Collodion, Preparation of, 218 Colour of Silver Bromide, 3 Cotesworth's Cold Emulsification, 104 Crape Markings in the PUm, 274 Cupboard Shelves, Level, 117 Cupric Chloride a Cure for Fog, 2ft Cyanide of Silver Intensifier, 158 Dark Room and its Fittings, 30 Dark Koom, Illumination of, 41 Defects in Collodion Emulsion Plates, 274 Defects in Gelatine Plates, 196 Density, Correct, of Image, 142 Developer, Alkaline, How Applied, 137 Developer, Wratten and Wain- wright's, 146 Developer, Ferrous Citrate, 165 ccxc Developer, Ferrous Citro Oxalate, 165 Developerj Hydroxylamine, 169 Developer, Nelson's, 146 Developers, Cowan's, for Gelatino- Chloride Plates, 166 Development, Alkaline, 134 Development, Alkaline, Theory of, U Development, CoUodio-Chloride Emulsion for, 270 Development, Ferrous Oxalate, Theory of, 19 Development of the Plate, 261 Deyelopment, Practical, of a Gela* tine Plate, 138 Development, Practical, with Fer- rous Oxalate, 151 Digestion of Gelatine Emulsion with Ammonia, 97 Drop Shutters, 133 Drying Cupboards, 33, 35, 37, 38, 39 Drying Gelatine Plates, 120 Drying Markings, 276 ■ Drying Racks, 34 Dust Causing Pinholes, 206 Dustin'Slides, 126 Eder's Emulsions, 92 Edwards's Intensifier, 159 Emulsiaoation, Cold, 101, 102, 104 Emulsion, Aid to Gelatine, 169 Emulsion, Canvas for. Collodion, 207 Emulsion,. CoUodio- Albumen, 245 Emulsion, CoUodio-Bromide, 242 Emulsion, Cooking and Washing, 73 Emulsion, Dissolving Gelatine, 79 Emulsion, Fog in, 21 Emulsion Draining after Washing, 78 Emulsion, • Gelatino-Bromo-Iodide, Preparation of, 69 Emulsion Mixing, England's Plan, 73 Emulsion Mixing by Spray Appa- ratus, 71 Emulsion, Precipitation of Gela- tine, by Spirit, 78 Emulsion, Preparation by Aqueous Precipitation, 107 Emulsion, Preparation of, 219 Emulsions, Preservatives used with, 255 Examination of Slides, 127 Expansion of Gelatine, 66 Exposure of Gelatine Plates, 127 Ferrocyanide of Potassium in Deve- loper, 145 Ferrous Citrate Developer, 165 Ferrous-Citro-Oxalate Developer, 166 Ferrous Oxalate Developer, 149 Ferrous Oxalate Developer and Hyposulphite ot Soda, 152 Ferrous Oxalate, Eder's Form, 150 Ferrous Oxalate, Simple Form of, 149 ■ Ferrous Oxalate, Strong, 151 Ferrous Oxalate Development, Theory of,. 19 Fixing Baths, 154 Films, Eastman's Negative, 188 Fixing Gelatine Negatives, 1 54 Fixing Solution, 269 Flow Properly, Emulsion Refusing to, 276 Focussing the Picture, 128 Fog, Red, 199 Fog, Green, 199 Fog, General, -200 Fog in Emulsions, 21 Fogging of Plates, 275 Frilling, 19S Gelatine, 62 Gelatine and Absorption of Water, 64 Gelatine Emulsions, 50 Gelatino-Bromide Papers, 173 Gelatino-Chloride Emulsion, 163 Gelatino-Citro-Chloride, 280 General Fog, 200 Geuter on Silver Sub-Chloride, Green Fog, 199 Gum Guiacum Preservative, 260 Henderson's Cold Emulsification, 102 INDEX. CCXCl Holders for Sensitive Paper, 180 Hydrokinone Developer, 148 Hyposulphite m Developer, 20 Hyposulphite of Soda in Ferrous Oxalate, 152 Image Flatness, 201 Image, Too Dense, 801 Insensitive Patches on Develop- riient, 275, 274 Intensifier, Edwards's, 159 Intensifier, The Best, 158 Intensifier, Uranium, 159 Iriteasifiers, Mercury and Gelatine Negatives, 157 Intensification of Eastman's Films, 191 Intensification of Gelatine Nega- tives, 155 Intensification of Silver Gelatine Negatives, 155 Iodide and Chloride in Emulsions, 58 Konarzewski's Emulsion, 172 Lanterns for Dark-Rooms, 46 Lea's, Carey, Preservative, 275 Levelling Shelf, 116 Mercury Intensifier, 158 Mbnckhoven's Gelatine Emulsion Process, 111 Mosquito Netting, 75 Negative Paper, 185 Negative Paper, Double Surface, 187 Negative Tissue, 184 Nelson's Developer, 146 Nitric Acid a Cure for Fog, 27 Note-hook for Registering Plates, "286 Oiling Eastman's Negative Films, 190 Over-ExpoBure and Under- Exposure, 144, 145 Oxidizing Agents Cure for Fog, 27 Packing Collodion Emulsion Plates, 286 Packing Gelatine Plates, 284 Paget Prize Gelatine Emulsion, 84 Paper, Blocks of, 179 Paper, Gelatine -Bromide, 173 Paper, Gelatino-Bromide, Hints on Coating, 177 Paper, Gelatino-Bromide, Develop- ment of, 183 Paper, Gelatine -Chloride, 173 Paper, Holder for, 180 Paper Negatives, 185 Paper Positives, Development of, 192 Paper Positives, Chloride, 194 Papers, Negative, Exposure of, 179 Peeling of the Film off Plate, 275 Photographic Image, Construction of, 5 Photographic Image, Chemical Theory of, 11 Picture, Focussing the, 128 Pinholes, 205 Plate, Backing the, 253 Plate Coating Machine, 120 Plate, Coating the, 250, Plate, Preparation of the, 247 Plates, Cleaning, 114 . Plates, Washing, 118 Plates, Testing, 122 Platiuotye Intensifier, 160 Precipitation Method of Preparing Emulsion, 107 Preservatives in Emulsions, 233, 265 Preliminary Considerations, 1 Printing, Emulsion Processs for, 277 Printing, Unwashed Gelatino-Citro- Chloride for, 282 Pyroxylin, 210, 211 Pyroxylin, Bolton on, 214 Pyroxyliu, Hardwieb, 210 Pyroxylin, Simpson, 212 Pyroxylin,'Stuart Wortley's, 213 Pyroxylin, Warnerke's, 213 Red Fog, 199 Red Gum Preservative, 259 INBBX. Eegistering Plates, Note-Book for, 286 Eetouching on Eastman's Plates, 191 Eeversed Action of Light, 131 EoUer Slide, 180 Scratches, Dark, on Negatives, 206 Shelf, LeveUing, 116 Shatter, Cadett's, ISO Shutters, Drop, 133 SUver Bromide, Colour of, 3 Sensitiveness Hindered by Hard Qelatine, 55 Sensitiveness Increased hy Keeping a Gelatine Emulsion, 54 Sensitiveness in Gelatine Emulsions, 51 Sensitiveness, Eange of, 4 Sensitometer Scale, 123 Seusitometer, "Wamerke's, 122 Silver Sub -Chloride, 7 SUde, Eoller,180 Slides, Examination of, 127 Slow Gelatine Emulsion, 283 Soda, Carbonate of. Developer, 140, 147 Specks in Plate, 276 Spectrum, 8 Spectrum, Sensitiveness to, 4 Spiller's Hydroxylamine Developer, 167 Spots, Opaque, 5!03 Spots, Semi-transparent, 203 Spots, Dull, 204 Spots, Irregularly-shaped, 205 Spray Apparatus, 71 Stain on Gelatine Plates, 202 Starnes' Water Developer, 176 Stops in Focussing, 128 Substrata, 115 Testing Gelatine Plates for Bright- ness, 124 Testing Gelatine Plates for Density, 124 Testing Gelatine Plates for Frilling, 125 Testing Plates, 122 Thin Transparent Films, 274 Tissue, Negative, 184 Transparencies, Slow Collodion Emulsion Process for, 283 Unwashed Gelatino-Citro-Chloride for Printing, 282 Uranium Intensifier, 159 Varnishing the Gelatine Negative, 161 Warnerke's Sensitometer, 122 Washing Emulsions, 77 Waxing Paper, 191 Weighing, 70 Wohler on Silver Sub-Bromide, 6 Wortley's (Col.) Preservative, 269 Wratten and Wainwright's Deve- loper, 146 PHOTOGRAPHY MADE EASY BY THE PLATINOTYPE PROCESS FOR PERMANENT PRINTING This process is equally adapted to either Amateur or Professional use, and -enables the printing to be accomplished in one -third of the time usual with albumenized paper, while the subsequent operations may be completed in a tithe of time ; indeed , a picture may be printed and finished within the space of one liour. The Papers are of various kinds, and may be either " rough " or " smooth," " black " or "sepia," tinted. Platiuotype produced more artistic pictures than any other method of Photo- :graphic Printing. Have been awarded in recognition of the great value of the process, .including the Progress Mbdal of the Photographic Society of Great Britain ; also ■numerous medals for results at various Exhibitions at home and abroad. HIGHEST AWARD AT THE International Inventions Bxliil)ition, THE GOLD MEDAL "FOR EXCELIENCE OF EESULTS IN PHOTOGRAPHIC PRINTING." "Produced bz W. WILLIS' Invention," The Platinotype Process is used by many of the most distinguished Artists and Photographers, both Professional and Amateur ; by many Engineers, and at Works throughout the Country ; also by various Govenmient Departmects. The Prospectus, with List of Papers, SfC, and other necessaries for the process — which are few, simple, and inexpensive {say 24s., in- cluding Paper) — may he had on application ; also INSTRUCTIONS. THE PLATINOTYPE COMPANY, 29, Soutlianipton Eow, Higli Holborn, W-C. Sole Manufacturers of the well-known Sulpho-Pyrogallol, the best Developer ■for Dry Plates. Packed, 2/10. MABION & CO., 22 & 23, Soho Square, London, W. MARION & CO.'S BRITANNIA DRY PLATEST Important Notice. — Although the unpreoedented sale of Britannia Dry- Plates may be said to be a sufficient guarantee and acknowledgement of their superiority over all other Plates before the^Public, the Proprietors are convinced that there are still many Professional and 'Amateur Photographers who have not given due consideration to the advantages obtainable by the use of Britannia Plates, and they beg to submit the annexed Prices for their careful attention, the Plates being now of much superior quality to those of earlier manufacture. Characteristics of the Plates. — Vigour of Image. Evenness of Kim. Great Sensitiveness. Fineness of Texture. Freedom from Fog and FrilUng. Clearness of Shadows and Edges. Cleanness and SimpUcity of Development. Durability, Uniformity, and Cheapness. Sizes. Per Gross. Sizes. Per Gross. Sizes. Per Gross li in. square ... 12 6iX4i ... ... 40 9 X7 ... ... 90 2 „ ... 150 6|X45 ... ... 42. 8iX6i ... 102 3i „ ... 18 7ix4i .., ... 51 10 X8 ... ... 126 4iX3i ... 18 8ix4i ... ... 54 12 XIO... ... 180 5 x4 27 74x5 ... ... 60 13 X8 ... ... 180 6iX3i 38 8iX6i ... ... 72 c 15 X12... ... 318 o. E2CTRJ^ X.,A.Ii<3-B SIZES. Sizes. Per Doz. Sizes. Per Doz. Sizes. Per Boz. Si^es. Per Doz. 17X11 ... 32 18X14 ... 40 20X16 ... 43 24X18 ... 65 O- 17X14 ... 38 18X16 ... 41 23x15 ... 47 o' MARION &- CO.'S NEW SERIES OF BRITANNIA DRY PLATES. EXTRA Rapid. We have prepared the above in accordance with the pressing vrish of number- less customers, who find the emulsion of the Britannia Plates superior to all other, and who desire that the same superior quality may be supplied on a plate specially prepared for Extra Rapid Work. These " Extra Rapid " Plates vrill be found invaluable in the Studio, by enabling the Operator to secure much more natural and pleasant-expressions, whilst; for instantaneous effects out of doors' their utility is practically unsurpassable. Please Note that these Plates are as Quieli as any in the Market. Per Doz. Per Doz. Per Doz. Per Doz 1\ in. sqr. i 6 5 X4 ... 3 9 7-iX5 ... 7 3 10X8 ... IS 2 „ I 10 6iX4i .- 5 3 8 X5 ... 8 8 12x10 ... 22 6 3i „ 23 64X41 •■• S 3 %^-x&^ ... 10 15X12 ... 33 4|x3^ 24 7^X44 ... 6 5 9 X7 ... 12 S GELATINO-CHLOHIDE PLATES. MARION & CO,, Sole Proprietors. The attention of Photographers and Attiateurs is respectfully solicited to these tlates. In our opinion their use is likely to be very extensive, and a source of considerable profit to the Profession. Gelatino-Chloride Plates are printing plates for positives ; a good print can be- obtained in 1 to 5 seconds in diffused daylight, and with gaslight in a proportion- ately longer time. No Transparencies have ever been produced finer in tone or richer in detail than those by Cowan's Chloride Plates. MAKION & CO,, 22 & 23, Sobo SoLuare, London, W. WHAT DO THE PLATES SERVE FOR? 1. Portraiture and landscapes ; most lovely effects visible by transmitted light. 2. Lantern-slides and stereoscopic transparencies ; with full detail, and better tone than by any other process. 3. Transparencies for enlargements ; full of detail, soft, vigorous, and equal in all respects to the finest carbon positives, with this advantage — that they can be produced in any light. 4- For reproduction of negatives, they are invaluable. PerDoz. I PcrDoz. i PerDoz. Per Doz • 3iX3| ... 2 o I 6iX4| ... 56 8^X6^ ... 10 o 12 XlO ... 22 o 4^X3^ ... 2 6 7iX5 ... 76 9 X7 ... 12 o 13 X 8 ... 2?£o 5 X4 ... 40 8JX4i ... Sol lo XS ... 14 6 Any other sizes to order charged in the same proportion. Samples of the Transparencies supplied : C.D.V., Is. ; Cabinet, 2s. ; and Whole-Plate, 3s. each. DEVELOPING SOLUTIONS. Nos. I, 2, and 3, 10 oz. bottles, is. gd. ; 20 oz. bottles, 3s. each. Iron Solution, ,, „ gd.; „ „ is. 3d. each. N.B.— A'series of cheap Metal Gilt Kims, specially adapted 'for .Transparencies, made in all sizes, and low in price. A series of cheap Metal Gilt Rims, specially adapted for Transparencies, made in all sizes, and low in price. MARION'S BRITANNIA ALPHA PAPER. . A very rapid Printing Paper, by which prints can be obtained equal to Silver Prints in the dark days of November by all exposure of ij to 4 seconds, also good Prints obtained by exposure to Gaslight in 25 seconds. 1020 pieces of full Carte-de-visite size, in boxes ready for use 360 „ Cabinet size- 150 „ 81- X6i .. 108 „ 10 X 8 .. 72 „ 121 X 104 •• 48 „ 154x124.. 20 24i., X 19 .. 20, 20 20 20 20 20 20 2 3 Rolls of 10 ft. 8 in. long by 9.i^ in. wide One-third the above qualities can be had price 7/- per box. MARION'S BRITANNIA ARGENTIC BROMIDE PAPER. A New Bromide Paper for Enlargements, &c., giving a superior tone to all other Bromide Papers, and with a perfectly even coated surface fit for fuU printed Prints as well as Vignettes. A Box of 24 Sheets 12^ X lOJ 9 o 16 „ 15J X 12i 9 O 20 „ 24i X 19 27 o A Roll of 10 ft. 8 ins. X 24J wide 9 o MARION & CO., 22 & 23, SOHO SQUARE, LONDON, W, A COMPLETE SYSTEM OF FILM PH0T06RAPHY p CONSISTIKG OF FLEXIBLE NEGATIVE PAPEE in packages of twenty-foup sheets, cut to standard commercial . sizes, for exposure in our Patent PILM CAEEIER (fig. 3) -in any ordinary dark slide. FLEXIBLE NEGATIVE PAPEE, in Spools or EoUs, of 24 expo- sures (fig. 2), for exposure in the EASTMAN-"WALKEE EOLL HOLDEE (fig. 1), adaptable to existing Cameras. Jlig 3. FULL PAETICULAES ON APPLICATION TO— THE EASTMAN DRY PLATE & FILM CO., 13, SOHO SQUARE, LONDON, W. POETEAIT & VIEW LENSES, Unsurpassed for Brilliancy of Definition, Flatness of Field, and Depth of Focus. Used by the leading Photographers throughout the World. PORTRAIT LENSES. IMPRO'fBD. No. 3 for Portraits 6ix 4? „ 3a „ Six 6J 10 X 8 18 X18 22 X18 £17 10 28 15 38 42 10 54 EAPID "CABIlfET." No. 1 for Cabinets, Uft. distance 13 „ 2 „ 18ft. „ 17 10 „ 3 „ 20ft. ,, 19 10 EXTRA KAPID C.D.V. Invaluable for Photographing Children. No. 2a, IJin. focus, dia. 2im- — 13 10 „ 3a, 6 in. „ dia. 3|in. ... 25 QUICK-iCTING C.D.V, No. 1 for Cards, Uft. distance... 5 15 „ 2 „ 16ft. 6 10 „ 3 „ 19ft. „ ... n 10 UNIVERSAL. Por Portraits, Groups, &c. Back No. 1 .. 2 .. 3 .. 4 .. 5 .. View Size. Group Size. fo. 1 3 X3 „ 2 4 X3 " 3 5 X4 .. * nx4i ., 5 8 X5 „ 8 sjxej „ ' 9 x7 >. 8 10x8 „ 9 12x10 „ 10 13x11 ., 11 15X12 >, 12 18X16 5 x4 Sin. £3 7ix4J 4in. 3 5 8 x5 5in. 3 10 84x64 8in. 4 9 x7 7in. 5 10x8 Sin. 6 12x10 9rn. 7 13x11 lOin. 8 15x12 12in. 9 18x16 15in. 10 22x18 ISin. 12 25x21 21in. 15 Focus. 8ix6i ... 7ix4^.... SJin. . 10X8 ... SJXSJ ...lOJin. . 12x10 ... 10x8 ...13Jin. . 15X12 ... 12x10 ...lejin. . 18x16 ... 15X12 ...20 in. . 22x18 ... 18x16 ...24 in. . 25x21 ... 22x18 ...30 in. . Price. 7 10 9 12 10 16 10 23 45 65 VIEW LENSES. SYMMETEICAI..0 For Landscapes and Architecture. 4 x3 5 x4 7ix4i 8 X5 8Jx64 9 X7 10x8 12x10 13x11 15x12 18x16 22x20 RAPID SYMMETRICALS.* For Groups, Views, Interiors, and Copying. The most useful Lens for all Out-door Photography. Size o.£ View. 4x3 5x4 6x5 8x5 Six ei 9 X 7 10 X 8 12 xlO 13 Xll li X12 18 Xl6 22 xlS 25 X22 * Furnished with Diaphragms on the Stan- dard System recommended by the Photo- graphic Society of Great Britain. Size of ] 3quivalen t. Group. Focus. Price ... Stereo.' . . 4iin. . .£4 ... 4x3 . . 6 in. . . 4 5 ... 5x4 . . 7iin. . . 5 5 ... 7iX 4i . . 9 in. . . 5 15 ... 8X6 . . lOiin.. . 6 10 ... Six 6i . . 12in. . . 7 10 ... S.Jx 6i . . 14in. .. 8 10 . 10 X 8 . . 16in. . .. 10 10 ... 11 X 9 . .. 18in. .. 11 10 ... 13 XU . .. 20in. . .. 14 10 ... 15 Xl2 . . 24in. .. 18 10 ... 18 X16 . . 30in. . .. 25 ... 22 *X18 . . 34in. . . 30 Improved Expanding Bellows Cameras for Lenses of Long Focus. AiPrA-RA-TTTS OF EVERY DBSOBIPTION- CATALOeUMS ON APPLICATION. ROSS & CO., Opticians, 112 (REMOVED FROM 164), NEW BOND STREET, LONDON, W. Optical Works— BROOK STREET. lEstaHishedmO.I F. W. VEREL X CO.'S Gelatine Dry Plates. To provide for the ever increasing demand tcr our Plates, we have found it necessary to construct Larger Premises, and, having introduced machinery where practicable, we are now in a position to- greatly increase out out-piit. To facilitate working during the summer months, a Freezing Machine and other appliances have been provided, which will secure uniformity in coating, and thus obviate a difficulty generally experienced in the manufacture. . Those who have not tried these Platea are respectfully requested to do so before ordering for the season. 5 X4 6fX3J 6iX4i 6iX4f 7^X44 7 X5 Terms — Cash with Order only. Special Terms to Dealers and Large Consumers. Our 60-times will be found invaluable for all Instantaneous work. Sample Half-dozen Packet, any speed, J-plate, 12 stamps ; ^-plate, 27 stamps, free. EXCELSiORlNTENSIFIER Above may now be had in Bottles at 1/6 and 2/6 ; per Parcel Post, 1/9 and 3/- safely packed. For general and LOCAL intensification this Preparation is unsurpassed. GIVE IT A. TRIAL. PRICE LIST, PER DOZEN. 10 and 30 times. 60 times. LO and 30 times. 60 times. a. d. s. d. s. d. s. d. .. I 6 . ..20 74X 6 • S • . 6 •• 2 3 • ..30 8iX 6^ .60. . 8 ..32. .. 3 6 9X7 • 76. • 9 ••3 4- ..40 10 X 8 . 10 6 . . 12 6 ..36. .. .4 6 n X 9 . 13 . • IS 6 ••3 9- ••4 9 12 XIO . 15 . . 18 ..40. -SO 15 X12 . 26 6 . . 30 AGENTS- ALBION ALBUMENIZIN8 CO., 96, Bath Street, Glasgow. Messrs. MoGHIB 4 BOLTON, 47, West Nile Street, Glasgow. Messrs. GEO. MASON & CO., 180, Sauchiehall Street, Glasgow. Mr. J. PALLOWMELD, 36, Lower Marsh, Lambeth, London, S.E. Mr. JOHN J. ATKINSON, Manchester Street, Liverpool. Mr. J. M. SMITH, 13, High Ousegate, York. Mr. P. HALL, 118, Grey Street, Newcastle-on-Tyne. Mr. J. M. TUBNBULL, Rose Street, Edinburgh. Mr. W. HUME, 1, Lothian Street, Edinburgh. Mr. B. LOWDON, 65. Reform Street, Dundee. Mr. H. LESTER, Bridge Street, Nuneaton. F. W. VEREL OATHCART, near & CO., GUj ASGhOW, Photographic Apparatus Manufacturer, 26, CALTHORPE STREET, GRAY'S INN ROAD, LonsriDo:^. TBIRTEEN PEIZE MEDALS have been awarded to G and ChaiujilirjSox ^or Excellence of Design and MARE'S Cameras G. HARE'S NEW CAMERA. Invented, and Introduced, June, 1882. The Best and most compact Camera ever Invented. Since its introduction, this Camera has received several important modifi- S) cations in construction. It stands un- rivalled for eleg'ance, lightness, and general utility. It is specially adapted for use with the Eastman-Walker Koll Holder. A 6^x4^ Camera measures ■when closed 8x8x2i in., weighs only 3^1bs., and extends to 17in. The steady and increasing demandf or this Camera is the best proof of its popularity* " Little need be said of Mr. George Harc*s well-known Patent Camera, except that it forms the model upon which nearly all the others in the market are based." — Yide British Journal of Phonography, August 28, 1885. Size of Plate. 5x4 6^X 4i 7^X 5 Square, with Re- versible Holder. £6 7 2 6 7 10 8 15 Brass Binding. £0 16 16 15 16 Size of Plate. lOx 8 12x10 15x12 Square, with Re- versible Holder. £9 16 11 13 5 Brass Binding. £0 18 a 10 10 These prices include one Double Slide. Since this C.imera has been introduced, it has been awarded THREE SILVER MEDALS : at Brussels International Photographic Exhibition, 1883 ; at the Eoyal Cornwall Polytechnic Society, Falmouth; and at the International Inventions Exhibition, 1885. Also Bronze Medal, Bristol International Exhibition, 1883^H1GHEST .AWARD. O. Hare's IMPROVED PORTABLE BELLOWS CAMERA lavented and Introduced 1878. This Camera offers many advantages where a little extra weight and bulk is not objected to. It is very solid and firm in construction, and especially suited for India and other trying climates. IILITSTEATED PRICE LIST on application at the Manufactory— Ill I- < (Da : a +- ■3^2 ;« fc a; 43 E-i .-03^ 9 p4 ; Ph e PI EM 1 .a 111 X h PL, -< a O "3 S ° Ph ■« O .2 P -s ij O 03 S 'ft '^ •^ E: S ao o , J rt •"I ^ o a rt fS ^ .a i-^ri m.-s . o CD ,2 =^5 - ■ no" y :S.£0 >: mBH CO ' t^ g R'^ « !? s ■ - ■ S P fc- XXX -^J!;S OPh 00O3C1 ?* " u ' ft : : : O I I (a* .53 . „-^^ M-3 Eh'3h» s'g XXX S : : s.gs ■ X X X X „ >>■« -W MHr«l 'IJ g P ^ lis CD U3 <; pfLi S Eh ID 0. fc = x~ pq George Houghton & Son, PHOTOGRAPHIC WAREHOUSE, S9, HIGH HOLBOBN, LONDON, MANUFACTURERS OF Cameras & all Kinds of Apparatus, Dry Plates, Chemicals, SENSITIZED PAPEE, MOUNTS, &c., PHOTOGRAPHIC STUDIOS, PORTABLE DARK ROOMS, Xc, DESIGNED, ERECTED, AND PITTED COMPLETE., ALL NECESSARY APPARATUS, DRYING CUPBOARDS, &c., For tlie Manufacture of Grelatine Dry Plates. WETT FEICH LIST ON APPLICATION. PAGET PRIZE PLATE COMPANY. Thle Gelatine Dbt Plates issued by this Company and prepared under the immediate Superintendanoe of Mr. "W. J. "WILSON, F.C.S., Winner of the JPrize of £50 offered hy Joseph Paget, Esq., and awarded ly The FhotograpMc Society of Great Britain, for the best Dry Plate Process, Still maintain the high reputation they have gained, and are in con- stant demand by the leading Landscape and Portrait Photographers in Great Britain and the Colonies. Mk. W. D, Valentine (of Valentine and Sons, Landscape Photographers and Publishers, of Dundee), writes as follows : — "I have just tried the new lot of Extra Eapid Plates, and am much pleased with them. I only ■vvish my operators had had them last year, as the so-called Extra Eapid Plates we were then using were not to be compared to yours." . Mk. G. W. Wilson, (of G. W. Wilson and Co., Landscape Photographers and Publishers, of Aberdeen) writes as follows : — " I am sorry that I bothered this Summer with the plates of other makers, but shall not do it again. "We have been trouile with frilling, fog, thin edges, &o., &c., whilst with yours we are sure of what we are doing." Messrs. West and Son, who have taken the highest awards for their Yacht pictures, write as follows ; — " "We must really compliment you upon the last batch of Plates sent us; they are better than ever." Price Lists of the " Paget Prize Plates," and any information respecting tlteir use, may he obtained by addressing — TUB I/C.A.I>T-A.C3-EI?,, PAGET PRIZE PLATE COMPANY, EALING, LONDON, W. N.B.— All Plates are now sent by the Company carriage free, to Pnoto- graphers, te any Town in the United Kingdom. UIIVEESITT OPTICAL WORKS, 81, TOTTENHAM COURT ROAD, LoasriD03sr. SEVEN GOLD MEDALS AWARDED. In sulamitting the undermentioned list of Camera Lenses to the notice of the Public, J . SWIFT & SON heg to state that they can con- fidently guarantee them to he superior to any yet oSered by the trade, in proof of which they will (on receipt of remittance or London refer- ence) send sample for comparison with any others of English or Foreign manufacture, feeling convinced that they are positively un- equalled. The covering power of these Lenses, together with their great flatness of field, sharpness of detail, combined with delicate softness, is not approached by the Cameras of any other Optician, and the Stops supplied with these Lenses are similar to those recommended by the Photographic Society of Great Britain. Me. JAMES SWIFT having had many years practical experience with the late Mr. Boss (whose reputation as a maker of Camera Lenses is world-wide) is in a position to justify the high character of the above Lenses, which he trusts the scientific public will afford him opportunities of demon- strating. PORTABLE PARAGON CAMERA LENSES, SPECIALLY CONSTRUCTED FOR LANDSCAPES, ARCHITECTURE, AND COPYING. Nos. .. 1 2 3 4 5 6 7 8 9 10 Focus ,. . Sin. 4 in. 5 in. 6 m. 7 in. Sin. 9 in. 10 in. 12 in. 15 in. Plate .., . 3x3 4x3 5x4 7iXih 8x5 Six6i 9x7 10x8 12x10 13x11 Price .. . £2 14/- £2 18/- £3 3/- £3 12/- £4 10/- £5 8/- £6 6/- £7 4- £8 2/. £9 RAPID PARAGON CAMERA LENSES, SPECIALLY CONSTRUCTED FOR PORTRAITS, GROUPS, INTERIORS, AND INSTANTANEOUS WORK. Views ... 3x3 4|x3i 5x4 6x5 8x5 8ix6J 9x7 10x8 12x10 13x11 15x12 Groups ... — Stereo. HxSi 5x4 7Jx44 8x5 84x6$ 9x7 10x8 12x10 13x11 Focus ,„ 3 in. 4i in. 6 in. 7J in. 9 in. lOJ in. 12 in. 14 in. 16 in. 18 in. 20 in. Price ... £3 3/- £5 12/- £3 16/- £4 14/6 £5 3/6 £5 17/6 £6 15/- £7 13/- £? 9/- £10.7/- £13 Off the above prices 10 per cent, is allowed for cash. ^7^^^