Development of photographic film

Other Borohydrides. Potassium borohydride was formerly used in color reversal development of photographic film and was preferred over sodium borohydride because of its much lower hygroscopicity. Because other borohydrides are made from sodium borohydride, they are correspondingly more expensive. Generally their reducing properties are not sufficiently different to warrant the added cost. Zinc borohydride [17611-70-0] Zn(BH 2> however, has found many appHcations in stereoselective reductions. It is less basic than NaBH, but is not commercially available owing to poor thermal stabihty. It is usually prepared on site in an ether solvent. Zinc borohydride was initially appHed to stereoselective ketone reductions, especially in prostaglandin syntheses (36), and later to aldehydes, acid haHdes, and esters (37). 

Data obtained by Shiberstoff (63) on the development of photographic film in solutions of conventional developers offer further evidence in confirmation of the latter point. Shiberstoff obtained a general increase in selectivity with decreasing temperature of development for all agents tested. He calculated selectivity in terms of the ratio of the rate of image development to fog formation, using as the rate of the former the reciprocal of the time required to attain a density of 1.5 for a fixed... 

The Ag ion forms strong complexes with thiourea (log K = 12.7 for the Ag(thiourea)J complex and with thiosulphate (log K 13). The strong binding of Ag to thiosulphate is exploited in the use of Na2S20s solution to remove excess Ag during the developing of photographic films. For this reason, Ag can... 

SAMPLE SOLUTION (a) Like the dihydroxybenzenes, the isomeric trihydroxy-benzenes have unique names. Pyrogallol, used as a developer of photographic film, is 1,2,3-benzenetriol. The three hydroxyl groups occupy adjacent positions on a benzene ring. 

The structures of the sulfate and thiosulfate ions are compared in FIGURE 22.21. Thiosulfate salts are used industrially in the paper-making and textile industries and are the fixer solutions in the development of photographic film. 

Any antidote for cyanide poisoning must be administered quickly. One antidote is sodium thiosulfate (the hypo used in the developing of photographic film). This substance converts the cyanide ion to a thiocyanate ion that does not bind to the iron of cytochrome oxidase. 

Dilute solutions of acetic acids are also used as a stop bath during the development of photographic films, and in descaling agents to remove limescale from taps and kettles. In the clinical laboratory dilute acetic acid lyse red blood cells in order to facilitate microscopic examination. 

The nonquantitative detection of radioactive emission often is required for special experimental conditions. Autoradiography, which is the exposure of photographic film to radioactive emissions, is a commonly used technique for locating radiotracers on thin-layer chromatographs, electrophoresis gels, tissue mounted on sHdes, whole-body animal sHces, and specialized membranes (13). After exposure to the radiolabeled emitters, dark or black spots or bands appear as the film develops. This technique is especially useful for tritium detection but is also widely used for P, P, and 1. 

A chemistry based on the conversion of synthesis gas has been developed and appHed extensively in South Africa to the production of Hquid fuels and many other products. A small-scale production is used in the manufacture of photographic film materials from coal-derived synthesis gas in the Eastman Kodak plant in Kingsport, Tennessee. However, the principal production of chemicals from coal involves the by-products of coke manufacturing. 

The most significant development in Japan is the entry of photographic film companies (Fuji and Konishuroku) into the manufacture of magnetic media. They are having a large impact because the heart of the manufacturing process... 

Figure 5.8 A Debye-Scherrer powder camera for X-ray diffraction. The camera (a) consists of a long strip of photographic film fitted inside a disk. The sample (usually contained within a quartz capillary tube) is mounted vertically at the center of the camera and rotated slowly around its vertical axis. X-rays enter from the left, are scattered by the sample, and the undeflected part of the beam exits at the right. After about 24 hours the film is removed (b), and, following development, shows the diffraction pattern as a series of pairs of dark lines, symmetric about the exit slit. The diffraction angle (20) is measured from the film, and used to calculate the d spacings of the crystal from Bragg s law.

Nuclear Emulsions The process involved here is a chemical one. Ionizing radiation from a sample interacts with the silver halide grains in a photographic emulsion to cause a chemical reaction. Subsequent development of the film produces an image and so permits a semiquantitative estimate of the radiation coming from the sample. 

We have seen that full color perception can be achieved by subtraction methods using dyes in suitable combinations. We now have to consider how such dyes are formed on exposure and development of color film. First though, you should recognize that a photographic emulsion, whether for color or black-and-white film, is light-sensitive primarily because of the presence of silver halide. You will recall from previous discussions (Section 26-2C) that the sequence from exposure to development involves the following ... 

Autoradiography is a technique for detecting radioactively labelled species in a gel, paper or thin layer by sandwiching a sheet of photographic film next to the support medium and allowing the radioactive emissions to expose the film. After developing the film, the positions and intensities of the radioactive sources are shown by areas of blackening on the film. 

Although polyester film, introduced by Du Pont under the trade name Mylar in the 1960s, has been added to the traditional supports like paper and cellulose acetate, the principle of photographic film preparation has remained unchanged since daguerreotype was developed. The sensitive surface always contains a silver halide crystal emulsion with a gelatin binder. Despite all the efforts to replace them, silver salts remain the basis of these emulsions, and film manufacturers still require gelatin, which they consume at the rate of 20,000 tons a year. The suppliers are few, and they are carefully selected. The world leader in this area is Rousselot, now a subsidiary of Sanofi Elf Aquitaine, with four units in Europe and one in the United States. 

In addition, a very simple and low cost method can be used to detect surface flaws. This is the use of penetrants that are typically fluorescent dyes. Usually, a three-step procedure is used. The ceramic part is first soaked in a fluorescent dye. Then the part is dried and cleaned in a very controlled manner to remove the dye from smooth surfaces but not from the surface defects. When the part is examined under ultraviolet li t, the surface defects such as cracks and porosity retain the dye and show up brilliantly. This method is used widely for surface inspection of ceramics and is frequently included as part of a quality assurance certification. Penetrants are effective for nonporous ceramics. With open porosity, the penetrant will enter all the pores of the ceramic, giving fluorescence to the whole ceramic piece, thus preventing detection of surface flaws. Not all penetrants are fluorescent dyes. Radioactive krypton can be used as a penetrant. It is retained in cracks or other defects and can be detected by either a Geiger counter or by carefully wrapping the ceramic piece in photographic film. After development of the film, the location of cracks emd pores can be detected. 

This greatly increases the solubility of the silver bromide (Fig. 16.14). The formation of this complex ion is an important step in the development of photographic images thiosulfate ion is a component of the fixer that brings silver bromide into solution from the unexposed portion of the film. 

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