Manual of Interfermetric Photography

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Manual of Interfermetric Photography

by A. Berthier, 1895

  • Translated by Colin Kaminski.
  • Note: Colin doesn't speak French so this translation is aproximate. Please see the french version on this site for the original text.



Since the publication of the remarkable experiments of Mr. Lippmann, physicists have sought to reproduce them. Some succeeded, others were less happy and obtained only not very encouraging results. The study of successes as well as that of the vexations is extremely instructive, because it makes it possible to determine rather exactly the conditions of the experiment and, by the fact, the procedure to employ to achieve the desired goal.

There does not exist, until now, of the scientific raity explaining in detail the method to follow in the by interferential reproduction of the colors; the majority of the experimenters who took the route opened by Mr. Lippmann are of a too tested discretion, with regard to the practical details of the process they are useful. In fact, obtaining perfect tests being still at the present time surrounded with difficulties, each one was ingénié in Jes to better overcome of sound, and such artifice which makes an admirable success with one, gives between the hands of another only a poor result. One would not thus know, for the moment, to give a method absolute and final; it is to better show details the various processes employed by the most skilful researchers, to allow each one to make a suitable selection. One could better start only by quoting the creator himself of the interferential method, Mr. Gabriel Lippmann.

Chapter 1

the REPAIR OF the LAYER SENSIBJ, E. 1. - LlppmanlL process Spectrum photographs. - In the month of 1' 1:vrier 1891, Mr.. Lippmann, professor de good Physique it it SOl', announced with the Academy of Science that I! to the solar spectrum had arrived. Reports of the Academy of Science (T exile, p. ' l74 and suiv.) contain this important communication completely. Here is the talk:

"I proposed, said \ Mr. Lippmann, to obtain on a photographic plate the image of the spectrum with!les colors, in such way that this image deIneurât from now on fixed and p11t to remain indefinitely exposed at the great san day!! to deteriorate.

"I could solve this problem while operating with the significant substances, los developers and fixed them current hairs Photographs some, and by modifying sim 1"the ARTIE. - OPERATIONAL PROCESSES. plement physical conditions of the experiment. The essential conditions to obtain the colors Photographs sout two of it: ID continuity of the sensitive layer; 2d presence of a reflective surface leaned with this layer.

"I understand by continuity the absence of, grains: it is necessary that the iodide, the silver bromide, etc, are disseminated inside a blade of albumin, gelatine or another transparent or inert mâtière, a uniform way and without forming grains which are visible even with the microscope; if there are grains, it is necessary that they are of negligible size compared to ID. luminous wavelength.

"the use of the coarse used emulsions ' today is by there excluded, a continuous layer is transparent except usually a light blue opalescence. I employed like support the albu. mine, collodion and the gelatine, like matters

"sensitive ioùure and the silver bromide; all these combinations give good results.

"the plate, dries, is carried by a hollow frame where mercury is poured; this, mercury forms "reflective surface in contact with sible layer SEN. The exposure, the development, the fixation, ', make as if one wanted to obtain a negative black of the spectrum; but the result is different: when the stereotype is finished and dried, the colors appear.

"the stereotype obtained is negative by transparency, it be-with-ùire each color is represented by its complementary. By reflexion, it is positive, and one sees the color itself, which can be obtained very brilliant. To obtain positive thus, rél' is needed 3rd. 1st or sometimes to reinforce the image so that the die. could photographic has a clear color, which is obtained, as one knows, by the use of liquors acidùs..

" One fixes at the soda hyposulphite followed neat C Inva' ges: I have vérifl, 6 that then the colors resisted the light é plus inlens ".

" The theory of the experiment is very simple. Read. incidental mière, who forms the image daus the darkroom, interferes with the light rétléchie by mercury. It is formed, consequently, in the interior of the sensitive layer a system of fringes, i.e. the maximum luminous one and obscure minima. Be maximum only impress the plate; following the photographic operations, these maximum remains marked by more or less reflective money deposits which occupy their grip. The sensitive layers so find divided! by these deposits in a series of blades minees which have for épaisscur

J' interval which separated two maximum, it ost-with-statement a domi-Ionguor of wave of the incidental light. These!times minees has thus precisely I thickness necessary for repl' to oduir

J) Los visible colors on the stereotype are thus of comparable nature that those of soap bubbles. They are only more pure and brilliant plu!l, at least, when the photographic operations gave a quite reflective deposit. That is due with what it is formed dans the thickness of the sensible layer a very great number of superimposed thin blades: approximately 200, if the layer has, for example,tu miIlimèt~e. For the same reasons, ]a considered color is of as much pltJs pure that the number of the reflective layers increases. These layers form, indeed, an in-depth form of network, and for the same reason as dnns the network analysis by reflexion, the purity of the colors is growing with the number of the elementary mirrors, U

In his first experiments, Mr. Lippmann was useful himself of the process to the collodion and the albumin of Taupenot. This process presents the avantages' those at collodion and albumin, in the sense that it perm6& of conser\' gold los ices after their preparation.

An inherent defect with the process on albumin lies in the difficulty in obtaining homogeneous layers (exemptesde bubbles, etc). Mr. Taupenot, by extending albumin on a porous surface of collodion, faH to act porous fibres of this layer on the microscopic bubbles, so as to do them disparaitl:e; One can be useful oneself of sensitized and washed collodion, or collodion mêmo not iodized (Gaumé).

The ice, cleaned well, is covered with ordinary collodion, which one sensitizes and which one washes as for the process,au ()ollodion. L~glace being

drained, after the dèrnièr washing; 011' iarècouvrè('. from albumin, exactemeut as one extends collodion, I and one lets run out excess in a special bottle. 011 employs, for this preliminary albumenizing, least possible of albumin, which is only used to drive out water and which one throws then. When the ice is well drained, one covers it with new albumin. The ices are dried like the ices with tannin. They are preserved inrléfinirrient.

One sensitizes them a few days before making use of it I they conser\' ent this sensitivity during one year. One operates this sensitizing while plunging them san, S downtime in a bath C

  • Eau 100"
  • Nitrate d'argent. . '. .. ... ... .. . . ::. 10"
  • Nitrate de soude 10
  • Acide acétique cristaIUsable . ... , 10

The time of immersion should not exceed twenty seconds. The ice, withdrawn of this bath, is plunged in the distilled water contained in a wood tank, where it remains ten garlic minutes less, then in a tank filled with ordinary water. Withdrawn, it is abandoned Li the desiccation, supported against the wall, and dans the most complete darkness. The exposure to the light is a little shorter than with ordinary albumin (1).

The plates obtained thus are extremely transparent: their grain is very fine, but their SENsibility is relatively low, If one substitutes the bromide ù. '

the money iodide, one makes a success of it slightly exalter this sensitivity. The plates are then prepared in the manner sui praises: 011 begins raI' to cover the ' ice with collodion which one sensitizes in a nitrate bath, then, after lavn:ge, one covers it,

collodion of a layer a]bumineuseformée by an albumin solution containing} ù. ~ for 100 of potassium bromide. The plates "once dry, are subjected during two minutes it a bath of

  • Water. 100 parts.
  • Acetic silver nitrate 10
  • Acid 10

Like all the preparations with silver bromide, this one presents a maximum of sensibilitépOUL' the blue area of the spectrum and a minimum for the yellow and red area: it is thus necessary to employ a bain..sensibilisator (solution of cya-, nine with 1: 25000).

The développeml-MT is carried out either with revealing the addes, or with the reducers alcali~s, or better still with both, by employing them su~cessivement. One starts by revealing the image with a pyrogallic acid solution it. 1 per 100, then one, _ termine' with a pyrogallol solution slightly alkaline, container unpeu of potassium bromide.

The fixation takes place in a soda hyposulphite bath it 15pOl~r 100: the layers being very thin, it - - quickly is finished,

If one does not fear to prolong the exposure time, one can be useful oneself of the process on albumin likely to give good results:

  • Albumin 1.
  • Iodize potassium 10.
  • Iodine 0", 5

The potassium iodide is dissolved in some water drops, then iodine is added there. The whole is then thrown in the albumin, which one beats in snow. After Duit of rest, one elutriates the liquid in a test-tube. Using a pipette, one takes albumin in this test-tube with the average part of the liquid, which is always clearest. The extension of albumin on the ice is extremely difficult. One sel'. transfered oneself of a spinner or a centrifugal apparatus. ~es ices, once albumenized, is preserved indefinitely. One sensitizes them in the following bath:

  • Eau, . ".'. , l00t'C'
  • Azotate d'argent cristalllsablc 6,.
  • Acide acétique cris talUsablc.. .. ... .. . .. 12

The nitrate solution fiItrée is versed in a vertical basin out of glass, in which the ice is plunged without downtime, using a hook also out of glass. The layer of albumin, qui' was originally transparent, becomes slightly tender offer line. Generally, one lets it remain uansle bath of money only ten seconds to one minute (1).

To wash then and dry with, the shelter of the light. To expose to the darkroom, the indications of Mr. Lippmann. The installation is extremely long and can only with difficulty be specified.

Procèdé Lippmann with isochromatic plates. - As of May 189.2, Mr. Lippmann supplemented first stated that it had made his discovery, by the communication suivante':

"In the first communication that I had the honor to make with the Academy on this subject, I said. that the sensitive layers that I employed then lacked sensitivity and of isochromatism, and which these defects were the principal obstacle with the application of the method which I had imagined. Since then, I have réussi to improve the sepsible layer and, although it remains still much to be made, the new results are rather encouraging pour' that I allow myself to make share with the Academy of it.

), On layers of albumino-bromide of money, made isochromatic by the azaline and cyanin, I obtain very brilliant photographs of the sp' êctre.. All the colors come at the same time, even the roug(;1, without interposition of coloured screens, and after an installation comp' small channel between five and thirty seconds.

"On two of these stereotypes, one notices that the colors, seen by transparency, are very definitely complementary among those which one sees by D inflection. The theory indicates that the colors COM -, posed that cover the natural objects would have goes laughed el' Photographs some as well as the simple lights of the spectrum, It was not less necessary to check the fact in experiments. The four stereotypes which I have the honor, to subject àl' Académie represent rather various objects accurately: a stained glass with four colors; a group of flags; a ' orange dish surmounted by a red poppy; a multicoloured pel' "roquet. They show that 10 modelled is returned at the same time as the colors,

"Le~ flags and the bird required from five to ten minùt, are of installation to the electric light or the sun. The other objects were made after many hours of installation to the diffuse light. It remains, therefore to make still much before returning the procédépratique. "

Pl' océdé Lippmann ù the gelatine bichJ' oJJwtée. ~ One knows that a layer dries of albumin or of dichromate gelatine is modified by the light: the organic matter, becomes less hygrometrical.

, the majority of the processes of photomechanical impression employed in industry are founded on this, action of the light '

A layer of albumin (or gelatine) bic.hromatée, run and dried on glass, est' exposed with the darkroom, leaned with a mirror of mel' cure. It is then enough to put it in water for voi; apparaitre colors; this washing it it pure water, by ènlevant bichromate, fixes the test at the same time as it develops it. The image disparait when one dries the plate, to reappear each time that it again is wet,

The colors are very brilliant; one sees them under all the incidences, i.e. apart from the incidence of the regular reflexion. By looking at the plate by transparency, one clearly sees complementary colors seen by reflexion,

The dichromate gelatine is composed in the same way, except that the colors appear in their place, not when the plate is wet into full, but when one, makes it slightly wet into blowing to his surface.

The theory of the experiment is easy to make.

Comme' in the case of the sensitive layers containing a money salt, the mirror of mercury gives place, during the installation, with a series of maxima' and minima of interferences. The maximum ones only impress ln. layer, which takes, pn.r continuation, a In.mellaire structure and is divided into layers alternatively inflatable and ' noninflatable pn.l' the en.u. ' fant that the plate is dry, one n.perçoit pn.s of image; but, as soon as water intervenes, it!! left the layer not impressed soak some; the index of refraction varies consequently periodically, in the thickness of the couc, He, just as the capacity reflectors, and the coloured image becomes visible.

When albumin is employed, it fn.ut to extend a layer of this liquid on glass, ln. to make dry and, moreover, to coagulate it by bichlol' RUE of meroure before plunging it in bichromate of potasse', Without this precaution, not impressed albumin would dissolve at the time of washing it it pure water. One can pass to bichloride mercury either front, or after the plate received the luminous inlpression (!).

These di\' strops experiments of Mr. Lippmann has excited at the most point the interest of the erudite world. Collected initially it it foreign with a skepticism not disguised, they forced the attention by their highly scientific character and the assumptions that they confirm. Also incredulity it made place it fills with enthusiasm it, and one currently sees eminent physicists and skilful experimenters to compete of zeal to improve the obte- results. naked. It would be unjust not to note that, thanks to the contest of these goodwills, in particular of France and Germany, the question notably progressed. We quickly will review the various methods suggested either like alternatives, or like improvement a.u procédéLippma.nn. With the first category are attached all the tests which derive more ' or less directly of the ancians experiments C Becquerel and Poitevin. Their list would be long. It suftlm to quote quelquesuns of it: those C I\:rone, of Saint-Florent, etc. The future does not appear to be reserved to them. With the second category, i.e. it that of the improvements. are attached the processes of MISTERS Lumière, Valenta, ' 1' hwing, etc. C all the eXj)él' imentateul' S which are occupied of this delicate question, ' i\I. Louis Lumière is certainly that which innovated with the most bonheur~ M~I. Valenta and Neuhauss also succeeded in it obtaining good photochromies, as the success of the illustrated conferences of pro attests it, jections which they gave in Vienna and ù. Berlin (1). ,

Krone Procedure

In the current of the year J8D2, Mr. Krone makes a success of ù. to obtain color tests without the use of a reflective mercury surface. To this end. it uti!is' has the reflexion back luminous radiations on the su~face inter~e C the plate glass, to form the necessary fringes ù.la reproduction of the colors. To increase the action of glass, it recouv~ait 13 plate of a tight black velvet against the layer, of albumin. The colours obtained by this process are less beautiful than those that-gives a mercury mirror, but they are perfectly perceptible; The theory of the phenomenon is rather complicated, because diffraction should certainly be fairei~tervenir;:

Since then, read. Krone(2} consigned the result d~ its experiments in a Work where it exposes aùssi work of its precursors. In his opinion, the condions necessary to obtain a correct reproduction of the colors are determined by the following observations:

  • l0 It is essential that the sensitive layer is perfectly homogeneous.
  • 20 When the sensitive layer exceeds a certain thickness, the colors are denatured or disappear completely. Everywhere where a grain of dust is, one observes this phenomenon in all his variations.
  • 30 the formation of the colors corresponding exactly to those of the original depends on the following circumstances: . (has.) Proportion exact and difficult to determine sensitizer compared to salt haloYde of money, this last being in the layer with the ét' At of extreme division;
  • (b) Of the degree of heat to which drying takes place;
  • (c) Of the duration of the installation and I intensity of the lnmière;
  • (d) Of the development. When one or the other of these conditions is not filled exactly, one observes the abnormal production of coulel~r~ false or the disappearance of couleurl! true.
  • 40 the percentage of moisture of the plates moditie D sultat, while varying the colors
  • 50 In the case of the photography solar spectrum, height of the Sun above the horizon intiuo on the value of the colours obtained: IG 1"PART. - OPERATIONAL PROCESSES.
  • 60 actinic intensity of an electric arc lamp whose positive charhon is placed at 36

has, - Process of Saint-Florent ('),

An ordinary plate with money gélatinobromure having been exposed under glass coloured with the rays di-. rects of the sun during fifteen to sixty minutes, then fixed without development and washed after fixation, reproduced the colors of the original if one placed SUl' it will tra -. jet of the pencil of light an orange screen-fillre, the colors are visihles by reflexion when HT layer is wet.

Here the talk of the procedure followed by Mr. of S~int-Florent, such as it gave it in a communication made to the meeting of the French Company of "Photography of December 2, 1892:

"a plate with gélatinobromure is exposed to the sun behind a yerre colored (glass of magic lantern) during a time which can vary fifteen minutes It one hour. With leaving the frame, the plate is not pas dé\' eloppée, but Ilxée immediately in a concentrated hyposulphite bath and washed with the greatest care

"In front of colored glass, one had care to place a screen out of orange glass. Qn can also make use of the successive screens indicated by Mr. Berget (red, green etbleu).

"At leaving the last bath of washing, the test has by réllexion the colors of the model. These colors, which are very low, but nevertheless distinct, disappear almost completely when the ice is dry

"Lcs colors are more sharp and the larger speed if, before the exposure, one plunges the ice to gélatinobromure in a silver nitrate solution to iD for approximately 100, ' added with alcohol in a strong proportion. These plates, without any washing, preserve their sensitivity long enough.

  • This sensitivity increases pal' the addition with the bath of one or two mercury nitrate drops by 100cc of solution.
  • This last bath Sc does not preserve.
  • U The colors by transmission are generally complementary colors seen by reflexion.
  • Please notice that I do not develop the tests, and that there is no mercury mirror in the experiment which I have just described. The reflexion incidental rays is done about normally on a reflective surface, which is most probably the posterior trauche of the significant substance and not that of the ice.

D Principal conditions of the so remarkable experiment of Mr. Lippmann trouvent.donc with louse close realized, and the phenomena of interference pro' are duisent in about similar circonstances'.

D All handling is done, without any in convénient, with a weak diffuse light. D The orthochromatic plates of Mr. Lumière give good results, but I could not encoro pass to me from screen.

D If, garlic place of plate to gélatinobromure, one employs plates with the gélatinochlorure (Perron mark), one often obtains tests whose eouleÙrs are (Pa!, reflexion) complementary of those of the model. I could not, until now, to return to me account of this anomaly "In the meeting of the 7 aoQt 1891 (Bltllcti1~, of September), I made known the tests that I had made by means of the dichromate gelatine appliquée.sur polished metal plate.

D I come from the r.épéter with albumin. D The results obtained are encouraging, but still quite incomplete. The colors have a great glare, a true metallic lustre; they my Trent only when the plate is dry, contrary result with that which has just obtained ~f. Lippmann in CUAI'.

1. - PRI::PARATIOll RE I.A COUCIIE SE"Slnl.E. IV brilliant experiments exél:utées by means of the dichromate albumin applied to glass "It is as extremely singular as the tests with gélatinobromure that I have obtenuos are visible (I speak about the colors) only when the wet ice ost, whereas 1\

1. Perhaps Berget, in its Works and dllns its conferences, expressly known as that the colors se' show only when the ice is completely dry "That is due with the suppression of the révéllltour in the process of which I have the honor to return account to you, suppression with which I was brought in répétllnt the famous experiment of Yung." I have fllit some essllis by means of the black chllmbl'

E; one obtains many épl' euves stained glasses and landscapes, m~is it is very long, and the visible colors son' tà sorrow. One thus needs still well DCS experiments before arriving to the complete solution of the major problem by the method mentioned above "to preserve the color tests, I imagined a kind of vertical basin whose former face is out of glass. This basin is full of slightly carbolic water, and one places the test there on black bottom J the face glass is framed and presents the aspect of a genuine framework of photography.

"By finishing this long letter, I believe duty to announce you a rather singular fact:

"Hunt, about 1845, managed to print the solar spectrum with its couleurd, but the colors disappeared with the fur and measurement which the sheet dried 20

1"PART. - PROCESSES OPÉRÂTOIRE. of paper on which it operated. You will find, in all its details, this experiment in the Roret Handbook, 18G2, tom~ II, page 297. D What proves that there u' is nothing again under the sun

".' . . Another curious fact, also announced by Mr. de Saint-Florent is as follows:

"I arrived, written ~r. of Saint-Florent, fi to produce color tests by means of iron salts to the maximum.

"I employ the bath indicated quite simply, a long ago, by Poitevin:

  • Water. 100"
  • Perchloride of fcr 10
  • tartaric Acid 5

"As I did not have a plaqnes with the simple gelatine. I took the pl!\ques ones with the gélatinobromure of which I removed salt haloid of money to average C hyposulphite

"Aprè.s of the lavag' are neat and a complete drying, the plate, whose gelatine became insoluble, is exposed behind glass colored pendant\.un rather long time. After the exposure, one washes it it tepid water; the insolated parts became more or _ less soluble, and a épl' euve is obtained that devnnt should be dried quickly fire.

"When the image is dry, it presents neck their light, among which the red, yellow and breadth ert. The purple ones and the blue ones are it pains visible.

"These colors are not seen under all the incidences; they should be observed under the same conditions as in the first experiments of Mr. Lippmann.

"I also obtained turns dichromate color with Ia.gélatine applied to glass. One develops with the cau cha.ude. The colors are shown as in the experiment above.

"It appears certain to to me that with a mercury mirror the results must be infinitely better (1)".

In another communication at the French Company of Photography, Mr. de Saint-Florent thus summarizes the results of his experiments:

1. One takes a paper with the chlorl1l' E of built-in money daus a vehicle like collodion, the albu~ mine, the gelatine, etc. Papers with the celloïdiJ1c are excellent

"One exposes this paper to the diffuse light until the moment oil it starts to show traces of metallization: One then applies it, without no preparation, in a positive frame, behind glass colored "At the end of several hours of exposure in full sun, one obtains a positive image which presents at little p1' ès, on a a little dark bottom, all the colors of the model. D 20 a paper sheet to the gélatinochlorure (money excess) are exposed during several hours Photo-gazette (t), 1893, p; 55. behind glass of magic lantern and place to a negative test presenting gives some traces of colors. The image changes, it is -âdire that it becomes positive, if, to leaving the châssi~, one exposes it to sunlight. The colors already a ' little appa.rgraft become more sharp and those which were latent. show souventa.près a duration more or less prolonged. The greens and especially the ja.unes come very with difficulty

"These. tests have a certa.ine stability, they are not fixed ".

With papers with collodion-chlorùre.. (celloYdine, etc), the speed is larger, and the ve1' ts and the yellows come better, if one applies to the test, av' ant its exposure on the ground have, a little varnish to terpentine (very diluted). "

4. Process CH R. ThwJng

Mr. CH R. ' the hwing, with an aim of increasing SEN. sibility of the plates, A. proposed into 1892 of sq;bstituer money collodiobromure to albuminiodure. . formulate indicated is the suiva.nte: \.

  • Cadmium Bromuro,; . 25"
  • Alcohol Acid 250"
  • chlorhydl' Ique... . . . . . . . ... . . . . . . . ... ... . . 5

One mixes Sec this solutionà, 40cc of ether and one adds 2sr pyroxylin' E, then, drop by drop, une' alcoholic solution C nitrate d~argent to 10 per 100. It is necessary to extend. the mixture on the plates before it was transformed into emulsion: the sensitive layer is blue pale, slightly opalescent.

6. -:Procédé Kltz (').

Mr. Kitz announced this fact that certain positive papers, Obernotter paper with money gélatinochlorure (of Emile Buhar, in Mannheim) for example, are likely to reproduce the colors, when one isolates them under coloured glass. The polychrome images obtained cannot be fixed. It is necessary to bring closer this fact coux published by Mr. de Saint-Florent. This experiment is attached rather to old ~é thodes of Becquerel and Poitevin. The colors are né.anmoins due probably to a phenomenon of interference.

6. -:Procédé Lumlére.

As soon as the experiments of Mr. Lippmann had been. published, ' MISTERS Auguste and Louis Light, of Lyon, undertook to repeat them. Of all the experimenters who la.ncèrent themselves in this way, they were more ' happy;! because they not only succeeded to reproduce the colors of the spectrum, but they were able to improve the process and to make it practical in a cèrtaine measurement. Btant given the importance of the results to which they arrived, - as the splendid polychrome stereotypes testify it which one could see in various exposures or conferences, -- we will completely quote their first communication made it it French Company of Photography on Celt question, on May 5, 1893.

"As of the début' of our experiments on the Photography of the colors according to the method, if remarkable, imagined by 1\1. professor Lippmann, we had proposed to make c:onnaitre the process which had led us it it obtaining, of the tests which we had presented at the French Company of Photography, but the irregularities quç we note then retained us and we have préféréattendre a(ln to give indications pr6cises allowing to surely arrive it of good results.

) That us re\' endiquer is allowed, very of A., edge, priority on process which Mr. Valenta made known, of Vienna, and who consists it mélangér, to obtain emulsion, if as well is as one pJisse to thus call the preparation obtained, deux' gelatinous solutions, one containing ùn soluble bromide, -, the other of silver nitrate. NoÙs, indeed, made connaltre, in one, communication on March 23, 1892, it it Company of industrial Sciences.

, of Lyon, the method which we follow then. and which, CllAI'. 1. - the nÉI' AnATlO~ Of COUCllE SENSIULE. 25 as you will see it, differs very little from that in diquée by this expérimentateur' (1).

"the following formulas were established empirically, that goes without saying, but we offorcés ourselves, in the very many experiments which we made, to proceed with method, never not changing, at the same time, which only one of the constituent elements, as well with regard to the emulsion as in what looks at the revealing one. From where the quantity of tests required and the extremely long duration of time that we have dCl to devote to it

"to obtain the sensitive emulsion, the following solutions are prepared:

With. - distll\ée Water.... "........ 400" GéIMino ' 20

"One adds to the solution C half of solution A, then other half of the latter is addi, tionnée i1 D. One mixes then these two solutions ' 1 ';' (')"Vno solution of 5 pOUl' iOOde gélatino ost addiUonnéo of it. 2 pOUl' 100 C bromuro, chloride, Iodide solublo. Of auiro Pa T, tlno soiutlonsemblable C gelatine is addHlonnce of 2 à3 for 100 C nltrato of argont. It sufllt Llo méiangOl' cos two soluLions for rOl' l1101' I' émulsiou, if it or pout appelol' thus 10 result of the mé~ ' lange, then C dyalisol', to obtain to the preparation of which us uous sommos sorvis." (Accounts I end custom of Socic!te! ielles backs Soioncos ine/usll' of Lvon.)

gelatinous by pouring the liquid containing silver nitrate in that containing potassium bromide. One adds then with a suitable coloured sensitizer: cyanin, purple of, methyl, érythrosine, etc, pui~ the emulsion is filtered and couché.e on plates. This operation must be done. with the spinner, the temperature. solution not exceeding 400. "One makes take the layer in frost, then the plates are immersed in alcohol, during a very short time, treatment which allows the complete damping of surface, and finally one washes in a current of cau. The layer being very mean, washing does not require that very little time "This method present, on that indicated by 1\1. Valenta, the advantage of avoiding the enlargement of the silver bromide grain, enlargement resulting from the washing of the mass and the heating required for the recasting, and of allowing the obtentiQn plates of a complete transparency. Moreover, one must avoid, for the same reason, the use of a too great soluble bromide excess, "the plates having been washed suffisammen\.sont put to dry, then, before employment, treated, during two minutes, by the following solution:

Distilled water 200"Nilrato of argont il' acetic Aclde.. ... ............... . . ....... ... . 1

"This last treatment makes it possible to obtain images much more brilliant. It increases, moreover, the sensitivity, but rather quickly brings the deterioration of the sensitive layer. One dries again, then the plate is exposed, in accordance with the indications given by Mr. professor Lippmann.))

7. - Prooédé Va.lenta.

At the same time as Mr. Louis Lumière continued in France his remarkable experiments, Mr. E.Valenta.obtenait in Germany of the similar results by not very different means. It is right to note however that the priority belongs incontestably to the young French scientist whose photochromies had been presented at the Company industrial Sciences of Lyon since 1892. Mr. Valenta exposed làrésultat his research in a certain number of German periodicals (Photographische Çorrespondenz; Photographisches Wochenblatt), and in particular in a Work which it published on this question: Die Photogl' aphy in natiirlichen Farben CHalle. a. S., KnapPi -1894).

. To obtain the continuity and the homogeneity of the layer, - essential conditions of success indiquées' by Mr. Lippmann, - Mr. Valenta observes that all the efforts must tend towards this goal: to prevent the emulsion from mùrir. Ammonia, heat make mflrir the emulsion and increase its sensitivity, but also the particle sizes: they will thus have to be avoided. One will prepare two solutions with also low moderated

ture that possible (300 to approximately 350), one being composed of the quantity necessary of silver nitrate, the other of the gelatine and bromide, then one will pour the first in the second: no precipitate is formed, the solution tt' ouble not, but becomes slightly opalescent; it should be employed earlier ~e possible, tout' delay supporting the production of a coarse grain. Here a' elsewhere the exact formula, fruit of patients research. on behalf of the author:

A. Gélatine 10" Eau. .. .. .. . .. .. ... ... .. 300" Azotato d'argenl., . ... , .. . .. . 0 G' B. Gélatine 20" Eau .. . ... .. . . .. .. .. .. .. .. .. .. ... . .. . ... 300" Bromure de potassium .. 5.,

These solutions are cooled it 350 C; then, in the obscure laboratory, solution A is slowly versed in the solution B, while stirring up constantly.

When the mass is quite homogeneous, one plunges it in approximately was of alcohol with 90 per 100, then one stirs up it with a rod of glass until all the bromurée gelatine is adherent for him. One carries out then washing as for an emulsion ordinkiro, i.e. one divides it into menus fragments which one places a few minutes in running water. 3rd: - well washed milking is then molten at as low temperature as possible in a bell jar; one adds the quantity of water necessary to reform the primitive volume of 600", then one filters and, if there is place, one incorporates with the mass the dyes necessary to obtaining orthochromatism. If one wants to avoid this last operation of fusion of the mixture, one can adopt the artifice indicated by Mr. Lumière. The emulsion is not precipitated, but one proceeds with spreading immediately after the mixture of the two solutions A and B. The plates are placed on a quite horizontal marble support until. what the sensitive layer is taken. One then washes quickly approximately fifteen minutes with running water, Co which is enough perfectly to remove all soluble salts. Da.ns all the cases, the emulsion must be filtered before being wide. To this end, one will be useful oneself with a\' of a funnel whose bottom is furnished with a glass wool plug or better still of hemp ita.lien than one will have beforehand made boil 3.Yec a solution of very wide potash, then washed with large water.

N is necessary of prendr.e guard, when one proceeds with the spreading of the emulsion, quela sensitive layer does not exceed a certain thickness. Mr. Valenta noted that the best results are obtained with leseouches thinnest. If there is not the practice of this kind of operations, one could be useful oneself of a tOllrnant plate on which one will place the ices: grace it ]0. centrifugal force, the emulsion will be distributed amusement in all the directions,

One will observe moreover than, lol' S of the preparation of the plates, it is essential to subject them to an alcohol bath diluted before final washing I if one omitted this precaution, one would notice that the sensitive layer is covered small bubbles of air.

who adhere to the emulsion and prevent consequently water from producing its action. When the sensitive layer is dry, one will thus immerse the plates in a cuv.ette containing wide alcohol and one will agitate the liquid until the whole surface is well wet and which all the bubbles disappeared. One will finish by an energetic washing under an apple of watering-can, then in running water (twelve to fifteen minutes) and one will obtain perfectly transparent ices thus, presenting by reflexion a light opalescent colouring. The plaSlue is then ready to receive the impression}umineuse one, If one had suddenly exposed it to the ammoniacal vapors, the sensitive layer would bleach quickly in consequence of the enlargement of the grain of the emulsion. One could not think any more it of obtaining the reproduction of the colors.

Mr. Valenta noticed that the emulsions with the money chlorobromide gave results more brilliant than those to bromide, It indicated, for this purpose, the following formulas like most practical:

A. Water.............. ... ....................... G 61allne..... . ..... ..... ... ... ....... ....... D, Water..... Lunar caustic.. . . ... ...... C, Water.. . . . . . . . . ... ... . . . . . . . . . . . ..... . . . . ... Bromide ùo potassium...................... Chloride ùe sodium..................

\' 200 " 10.' 15" 1 GI',5. A. Eau.. .. .. .. .. .. .. . .. . .. .. .. .. .. .. .. .. .. .. .. . G 61allne .. .. . . .. .. . .. .. . .. . .. . .. .. .. . .. .. ... D, Eau ..... Azotate d'argent .. . . . .. . ... ... C, Eau.. . . . . . . . , . . .. . .. . . . . . . . . . . . . .. .. . . . . . .. . Bromure ùo potassIum...................... Chlorure ùe sodium... ............... 15" 081',35 0",35

One divides A in two equal parts, one that one pour in B with 3: 0 or 400, the other in G One mix well and one pours B in C.

A. Water 300"GélaLine 10. Silver nitrate... G N Eau 300"Gelatine..... 20. Bromide of potasRlum 2, -, 4 Chloride of sodium..... L,5