PIIOTfMJll.MMIV. IlKCENT PROGRESS IN. 



m 



of the most sensational announcements 



..f recent time- was that made by I'rof. Lipi- 

 111:11111 t' the I 'aria Academy of Sciences in Feb- 

 ruary, IV.M. concerning photography in culm-. 



The Hliniilllieelllellt, as communicated by some 



of the n'\vsjiii|icr corres|Kiiiilents, would have 

 made the world believe tliat I'rof. Lippmanu had 

 secured a photograph in Colon "as vivid as any 

 oliject ill nature." But, speaking of the col- 

 ors in " Le Moniteur de la Photographic," .M. 

 Leon Vidal >a\s: "We only saw them rendered 



\ery imperfectly, and certainly we should never 

 have suspected, if we had not been told of it, 

 that it was a reproduction of the solar spectrum 

 with the colors." The experiment represented 

 by I'rof. Lippmann's plate is based on the wave 

 theory of lignt. Sincethe length of these waves 

 determines the color sensation, Prof. Lippmann 

 seeks, liy tin- action of "crossed" light and 

 interference," to secure a deposit of silver in 

 la\crs of a thickness influenced by the wave 

 lengths of the light. The theory of the experi- 

 ment is thus explained: "The conditions said to 

 lie e-sciitial to photography in colors arc: (1) 

 a -eii-itive film showing "no grain; (2) a reflect- 

 ing surface at the back of this film. Albumen, 

 collodion, and gelatin films, sensitized with 

 iodide or bromide of silver and devoid of grain 

 when microscopically examined, have been em- 

 ployed. Films so prepared have been placed in 

 a hollow dark slide containing mercury. The 

 mercury thus forms a reflecting layer in contact 

 with the sensitive film. The exposure, develop- 

 ment, and fixing of the film are done in Hie 

 ordinary manner; but when the operations are 

 completed the colors of the spectrum become 

 visible. The theory of the experiment is that 

 the incident light interferes with the light re- 

 flected by the mercury ; consequently, a series of 

 fringes is' formed in the sensitive film, and silver 

 is deposited at places of maximum luminosity 

 of those fringes. The thickness of the film is 

 deposited according to the deposits of silver into 

 lamina- whose thicknesses are equal to the interval 

 separating two maxima of light in the fringes 

 that is, half of the wave length of the incident 

 light. The lamina? of metallic silver, formed at 

 regular distances from the surface of the film, 

 give rise to the colors seen when the plate is de- 

 veloped and dried. Evidence of this is found in 

 the fact that the proofs obtained are positive 

 when viewed by reflected and negative when 

 viewed by transmitted light that is, each color 

 is represented by its complementary color." 

 Lippmann's theory has been severely criticised 

 by Stolze and others, but it is very generally ad- 

 mitted that Lippmann. without having produced 

 a satisfactory image in color, or one in itself ma- 

 terially superior to the image, produced by 

 Becquerel, nas entered a path that may lead to 

 important discoveries. 



Developers.' Theories of the latent image 

 and of the nature of the action that takes place 

 in development have received little modification 

 or enhanced clearness from recent discussion, 

 but new developing agents succeed each other 

 with great rapiditv. Ilydrochinon and cikono- 

 gen were followed by pyrocatechin. which met 

 with little favor. German operators recommended 

 formaldehyde as an addition to the emulsion and 

 to the developer. Oil of turpentine was sug- 



gested for the same HUP. Cryrtallon was a) no 

 advised. The moot recent developer, pnra-atui- 

 dophenol, in a powerful agent, of which n. 

 xpei ted ; but it in too early to say much of iu 

 practical availability. 



Printing Processes. Recent movements in 

 printing processes show a marked desire t<. break 

 away from the familiar albumen print. Objec- 

 tions to the albumen print are Im-i-d u|xni it-, 

 color, its surface, ami the limitations of the 

 toning system. A large number of new pro- 

 oesses present ungla/i-d surfaces. The platmo- 

 type process has been widely followed. This 

 process combines with a variety of j,.i.- ible tones 

 a delicacy in detail not frequently gi\cn in 

 processes based on an unglazed surface. A pro- 

 ce>s using metallic silver in place of metallic 

 platinum appears with the nam "kallitype." 

 This process, in which Dr. Nicol has acted 

 upon the suggest ji. us of Merscbcl and of Hunt, 

 is thus described: Paper is coated with a solu- 

 tion of ferric citrate, ferric tartrate, or ferric 

 oxalate, or mixtures of all or any of them, and is 

 dried. It is then exposed behind a negative until 

 a faint image is formed, as in plat inotype, and 

 the image is developed by treating it with a solu- 

 tion containing 10 per cent, of sodium citrate, 1 

 per cent, of silver nitrate, and sufficient ammonia 

 to keep the silver" in solution. After develop- 

 ment the print is immersed in a 20-per-cent. 

 solution of alkaline tartrate or citrate, made 

 strongly alkaline with ammonia, and afterward 

 in two successive baths of a dilute solution of 

 sodium citrate containing free ammonia. The 

 alkaline tartrate or citrate removes the iron 

 compounds, while the ammonia removes the 

 silver compounds, and finally the print is washed 

 in water. A new kallitype process published by 

 Dr. Nicol, and called Kallitype No. 2, coats 

 the paper with a solution containing ferric oxa- 

 late, ferric nitrate, silver oxalate, silver nitrate, 

 and oxalic and nitric acids. The paper is ex- 

 posed until the densest parts of the negative are 

 very faintly indicated, the appearance of the 

 image being very much the same as in the pla- 

 tinotype. For black prints the exposed paper is 

 immersed in a solution containing 10 per cent, 

 of Rochelle salt and 10 per cent, of borax ; for 

 purple prints, in 10 per cent, of Rochelle salt 

 and 2 to 5 per cent, of borax ; for sepia prints. 5 

 per cent, of Rochelle salt. I'^fl per cent, of borax, 

 and a small quantity of hydrochloric acid. In 

 each case a small quantity of a dilute solution 

 of potassium dichromate must be added. 



Dr. Adolph Frcer's "freer type" is based on 

 the fact that diazo compounds in contact with 

 acid sulphites form diaxo-sulphonic compounds. 

 and these form no coloring matter. If, there- 

 fore, a diazo-sul phonic compound is mixed with 

 an equivalent quantity of a phenol or an amine, 

 no coloring matter is formed. But if the mixt- 

 ure is exposed to light, the diazo-sulphonic 

 compound is decomposed, the diazo compound is 

 set free, and, since a phenol or amine is already 

 present, a coloring matter is formed as fast as 

 the diazo compound is lilverated. A few seconds 

 produces a print in daylight, and gaslight may 

 be used. 



A recent KuglMi patent gives the "primulino 

 process." Primuline is descried as a yellow 

 coloring matter containing sulphur. This pro- 



