Behaviour of Thiosulphate in Electrodialysis in the Presence of Photographic Gelatin

Electrodialysis of a 10 per cent solution of gelatin containing 30 /M of thiosulphate labelled 3,S in the outer sulphur atom was carried out with a brentzinger apparatus. Forty-five per cent of the radioactivity appeared in the anodic liquid, thirty per cent in the cathodic and the remaining twenty-five per cent in the gelatin solution. The validity of these results is discussed also in relation to other experiments carried out with ,SS labelled sulphate and :aP labelled phosphate.     

The Role of Thiosulphate in the Formation of Sulphide Stains during Bleaching

Image-wise silver sulphide stains were produced on pure, silver bromide emulsions during reversal processing with a dichromate bleach when the first developer contained a small quantity of sodium thiosulphate. The role of the thiosulphate in promoting the stain was investigated. The thiosulphate was found to be strongly adsorbed to the negative-image silver and could not be removed even by strong alkaline hydrogen peroxide. The adsorbed thiosulphate was decomposed in the bleach bath and silver sulphide was formed. Sulphite ion would inhibit the stain only in the presence of silver bromide. Iodide ion acted as a stain inhibitor with or without residual silver bromide and probably competed with thiosulphate in the adsorbed layer.     

The Adsorption of Thiosulphate Ions to Emulsion Grains,and the Role of these Adsorption Ions in Silver Sulphide Formation

The adsorption of thiosulphate to the grains of a silver halide emulsion has been studied with the aid of radioactive thiosulphate. The adsorption has been shown to follow a Langmuir isotherm. The amount of thiosulphate adsorbed falls with increasing emulsion pAg, but is not greatly affected by emulsion pH or temperature. In the digestion process, adsorption is necessary before silver sulphide formation can take place, and this breakdown reaction is a first order one with respect to the amount of thiosulphate adsorbed.     

The Determination of Thiosulphate in Photographic Gelatin

Thiosulphate is determined by direct polarographic analysis of a tryptic hydrolysate of gelatin. Precautions against interfering substances, including sulphite, chloride and surface active materials are described. Higher sensitivity may be obtained by concentrating the thiosulphate with anion-exchange resin but at some sacrifice of reliability. Periodic purification of the resin is necessary. The ultimate drawback of the ion-exchange method is that it concentrates other polarographically-active, anionic materials along with the thiosulphate, and these limit the sensitivity and reliability.     

Thiosulphate In Gelatin Determination By Extraction And Polarography

A proportion of the thiosulphate in gelatin may be bound to the gelatin by cations so that all thiosulphate is not removed by aqueous extraction. After exchange of cations for sodium, a quantitative extraction of thiosulphate can be obtained. This conclusion rests on the following evidence:

(1) all thiosulphate added to deionized gelatin was extracted;

(2) exchange of cations in gelatin for sodium increased the yield of thiosulphate on extraction by an amount that varied between different gelatin samples;

(3) when anions (including thiosulphate) in gelatin were exchanged for chloride, a proportion of any further thiosulphate added remained bound to the gelatin apparently by the residual cations.

It was found that 200 p.p.m. of aluminium ion added to deionized gelatins reduced the fraction of added thiosulphate that could be extracted.

The amount of tetrathionate found was considerably less than the amount of thiosulphate and appears to have been formed during the extraction procedure.     

Characteristics of ZnS films pulse plated using non-aqueous electrolytes

Thin films of ZnS were deposited by the pulse electrodeposition technique employing zinc sulphate and sodium thiosulphate in diethylene glycol solution at 80°C and at different duty cycles in the range 6–50%. The films were polycrystalline exhibiting cubic structure. The intensity of the peaks increased with duty cycle. Transmission measurements indicated interference fringes from which the refractive index fo the films were calculated to be in the range of 2.30–2.70. The band gap of the films was in the range of 3.66–3.62 eV with increase of duty cycle. The films exhibited resistivities in the range of 400–50 ohm cm with increase of duty cycle. The films exhibited higher Photoelectrochemical cell output compared to earlier reports.     

Some Aspects of Developer and Fixing Bath Concentrates Based on Potassium and Ammonium Salts Respectively

The limited solubility of some potassium salts in comparison to corresponding sodium salts is known from analytical chemistry; the analytical behaviour of ammonium salts is similar to that of potassium salts.

On the other hand, potash and potassium sulphite which are of interest for photographic developers ore several times as soluble as soda and sodium sulphite. Most developer concentrates, therefore, contain potassium salts. However, certain processing conditions may lead to turbidity or precipitation in the developers, due to the formation of sparingly soluble potassium hydroquinone disulphonate.

Commercial fixing bath concentrates contain ammonium thiosulphate which is much more soluble than sodium thiosulphate. Potassium thiosulphate is only slightly more soluble than sodium thiosulphate and, moreover, proves useless as a fixing agent. Fixing baths on the basis of ammonium thiosulphate are superior to those based on the corresponding sodium compound in the processing of films containing silver iodide.

In practical use the formation of crystalline deposits containing ammonium, silver, iodide and thiosulphate ions may occur.     

Competitive Adsorption of Chemical Sensitizers and Retarders on Photographic Silver Halide Grains

A working hypothesis, based on evidence reported in literature, concerning the stabilizing action of 7-hydroxy-5-methyl-s-triazolo (I, 5-a) pyrimidine (MTP) and I-phenyl-tetrazoline-5-thione (PTT) on emulsion ripened with sodium thiosulphate is presented. It is suggested that the sodium thiosulphate, which has not reacted during digestion, is displaced by MTP or PTT from the most active sites on the silver halide surface and thus prevented from reacting into fog nuclei (Ag₂S). This is confirmed by adsorption measurements, proving that both MTP and PTT can displace sodium thiosulphate. To investigate further that these products really retard Ag₂S-format ion, experiments were carried out with radioactive sodium thiosulphate. It was shown that MTP effectively inhibits Ag₂S-formation, while PTT acts as a catalyst for Ag₂S-formation although at the same time it retards chemical sensitization. Further it was shown, as already known, that PTT inhibits development, while MTP has almost no influence on development. These experiments confirm the proposed hypothesis for MTP On the other hand, only a small part of the retarding action of PTT on sulphur sensitization can be ascribed to development inhibition. Since Ag₂S-formation is catalyzed by PTT, some other, still unknown interaction, between PTT and sodium thiosulphate must account for the greater part of the inhibiting action of PTT.     

Thiosulphate Reactions at the Surface of Developed Silver

The detection of silver sulphide in processed photographic images has been attributed to the silver adsorbing a monomolecular layer of thiosulphate ions, which react to form silver sulphide when the silver image is bleached in acid dichromate solution. By studying adsorption with thiosulphate having the inner sulphur atom labelled, it has now been shown that most of the thiosulphate ions believed to be adsorbed by the silver image had already suffered rupture at the sulphur-sulphur bond, even before the bleaching step. Treatment of the silver image with a cyanide solution was relatively ineffective in removing the adsorbed sulphur, and it is thus doubtful whether it can be considered to be present in the form of silver sulphide.     

A New Colorin1etric Method for Analysis of Thiosulphate in Gelatin

A new adoption of the methylene blue test has been applied to the analysis of gelatin for its thiosulphate content. Sulphide is produced by borohydride reduction of thiosulphate in alkaline solution. In the presence of p-dimelhylaminooniline and ferric ion in acid solution, the sulphide forms methylene blue. The method is simple. specific. and sensitive. An undesirable side reaction which consumes about one-third of the sulphide in formation of a red by-product is eliminated by iodide ion.     

Ammonium thiosulphate enhanced phytoextraction from mercury contaminated soil--results from a greenhouse study

According to the 'hard and soft' acid-base principle, mercury is a 'soft metal' and will preferentially form soluble chemical complexes with sulphur-containing ligands. In this work mercury uptake by Chenopodium glaucum L. growing on mercury-contaminated soil was promoted using ammonium thiosulphate. The relative geochemical fractionation of mercury in the soil was subsequently investigated as a function of plant growth with and without thiosulphate amendment. The results indicate that the solubility of mercury is significantly increased through the application of thiosulphate to the soil. Substantially higher mercury levels were found in C. glaucum L. treated with 2 g kg(-1) thiosulphate of soil when compared to the non-treated plants. Compared with initial soil, soluble and exchangeable fractions were increased both in planted and planted treated plants. However, no significant difference was observed between the soils of the planted and planted treated plants. The oxide-bound mercury concentration was significantly decreased for the planted soil (treated and non-treated) at the end of the experiment. Moreover, this fraction was highly correlated with the plant tissue mercury concentration. Taken together, thiosulphate assisted phytoextraction could be used to reduce environmental risk apparent for mercury-contaminated soil through reducing the oxide bound fractions, while managing the bioavailable fractions (compared with no treated plant).     

Notes on the Sulphiding of Silver Halide Images

The sulphiding of a silver-bromide image by sodium sulphide is strongly affected by the presence of thiosulphate to the extent that the formation of silver sulphide can be prevented entirely within the emulsion layer even though complete precipitation of sulphide takes place as a loose deposit on the outer face of the emulsion. Toning by alkaline thiourea appears to follow a different course and is affected by thiosulphate to an extent somewhat less than might be expected on the basis of direct competition between fixation and toning.     

Pulse plated zinc sulphide films and their characteristics

Zinc sulphide thin films were deposited by the pulse plating technique using AR grade Zinc sulphate and sodium thiosulphate precursors. The pH of the deposition bath was adjusted to 2. The duty cycle was varied in the range of 20–60%. Total deposition time was kept constant as 60 min in all the cases. X-ray diffraction studies indicated the formation of single phase cubic zinc sulphide films. After heat treatment the crystal structure transformed to hexagonal structure. Optical absorption measurements indicated a band gap values in the range of 3.6–4.0 eV as the duty cycle decreased. EDAX studies yielded a composition of the films deposited at 50% duty cycle is Zn = 48%, S = 52%. XPS studies indicated the formation of ZnS. The Zn 2p and S 3p peaks are observed. AFM studies indicated a rms value of surface roughness of 55 nm for the films deposited at a duty cycle of 60%.     

The Determination of Photographic Sensitizers in Gelatin

Polarographic methods have been used to confirm the presence of thiosulphate and tetrathionate in extracts from 52 photographic gelatins of various types, from seven manufacturers. The quantities of these sensitizers found are, in general, in good agreement with the photographic properties of the gelatins. The method is suitable for the routine examination of gelatins.     

Stabilizer—Sulphur Sensitizer Interactions

Radiotracer studies of the decomposition of thiosulphate during chemical sensitization show that only a minor proportion of the sensitizer has decomposed at optimum sensitivity, and yet more than this minimum quantity of sensitizer is required to be present in order to obtain the highest sensitivity. Moreover, the presence of stabilizers during the decomposition does not radically change the kinetics. Evidence for the displacement of thiosulphate from grains by addition of stabilizers is given.     

Photoelectrochemical behaviour of pulse plated CdS films

Cadmium sulphide (CdS) films were deposited by the pulse plating technique at room temperature and at different duty cycles in the range of 6–50% using AR grade 0.25 M cadmium sulphate and 0.30 M sodium thiosulphate at a deposition potential of −0.75 V (SCE). The total deposition time was kept constant at 1 h. The thickness of the films were around 2.0 μm. X-ray diffraction (XRD) studies indicate the formation of polycrystalline films with the cubic structure. The crystallite size increased from 23.0 to 27.5 nm as the duty cycle increased from 10 to 50%. Optical absorption studies indicated a direct band gap in the range of 2.40–2.80 eV as the duty cycle is decreased. XPS studies indicated the formation of CdS. Photoelectrochemical (PEC) cell measurements made with the photoelectrodes deposited at 50% duty cycle have exhibited higher conversion efficiency compared to earlier reports.     

Book Review

By tracer methods it was demonstrated that thiosulphate is most tenaciously adsorbed to developed silver or silver foil. A limiting amount was held by any surface: one thiosulphate ion being estimated for every three silver atoms in the surface. On bleaching developed silver with acid dichromate, no decrease in radioactivity occurred, demonstrating quantitative formation of silver sulphide from adsorbed thiosulphate. On the basis of these observations, the silver sulphide content of bleached photographic images can be used to estimate the specific surface of the silver. Reasonable estimates were obtained of the particle size of a Carey-Lea silver sol. In agreement with earlier X-ray determinations, the mean filament diameters of developed silver from a series of emulsions did not increase much with increased undeveloped grain size.     

Sulphur Sensitization: Measurement of the Activation Energy

The activation energies of sulphur sensitization have been measured, using a number of sensitometric parameters and four ensitizers: sodium thiosulphate, allylthiourea, thiourea and sodium sulphide. or any sensitizer. the activation energy is the same for all sensitometric parameters. For all four sensitizcrs, the activation energies are surprisingly similar: sodium thiosulphate 32.2, allylthiourea 37.4, thiourea 34.1 and sodium sulphide 35.1 k cal/g mol.     

New Equipment,Materials And Techniques

Potentiometric measurements lead to the conclusion that, when ripening silver bromide suspensions with gold thiosulphate, considerably greater amounts of S² ions are built into the grain than in the case of ripening with equivalent amounts of sodium thiosulphate. The elimination of high intensity reciprocity failure by gold sensitization must be due to the greater number of Ag₂S specks distributed on the surface of the grain.     

聚乙烯亚胺对硫代硫酸盐镀银的影响

以往就聚乙烯亚胺用作光亮剂对硫代硫酸盐镀银的影响研究不够。为此,在硫代硫酸盐体系加入聚乙烯亚胺制备了银镀层,采用SEM、XRD及阴极极化等技术研究了聚乙烯亚胺对镀层表面形貌、晶粒结构、硬度及镀液阴极极化的影响。结果表明:聚乙烯亚胺的加入可以增大镀液的阴极极化,显著细化晶粒,使银镀层的硬度增大、防变色能力得到提高,当加入0.06～0.08 g/L聚乙烯亚胺时银镀层性能最佳。