US 3047393 A
Description (OCR text may contain errors)
3,047,393 ESTERS F THIGSULFONIC ACIDS AS ANTIFOGGANTS Arthur H. Herz and Frank 1). Allen, Rochester, N.Y., as-
signors to Eastman Kodak Company, Rochester, N.Y.,
a corporation of New Jersey N0 Drawing. Filed Jan. 11, 1960, Ser. No. 1,408 13 Claims. (Cl. 96-409) This invention relates to the stabilization of photographic silver halide emulsions, and more particularly, to a method of inhibiting development of spontaneous fog without adversely affecting the sensitivity of the photographic silver halide emulsions.
It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog, and sometimes called chemical fog where it is necessary to distinguish between it and the effects of accidental exposure to radiation; in this invention, we are not concerned with the latter.
Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases With the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is, of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggants and stabilizers may protect, to some extent, against such effects, it is normally understood that antifoggants protect against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both. It is known that photographic silver halide emulsions can be stabilized against'the harmful effects noted above by the addition of sulfinic or seleninic acids, or their watersoluble salts, as disclosed in Brunken US. Patent 2,057,- 764, issued October 20, 1936. It is further known that the stabilizing effect of sulfinic or seleninic acids, or their water-soluble salts, can be improved by the addition of minute amounts of salts or esters of organic thiosulfonic acids. (Mueller US. Patent 2,394,198, issued February 5. 1946.)
We have now found that certain esters of organic thiosulfonicacids have a marked stabilizing effect if substantial amounts thereof are incorporated in photographic silver halide emulsions. Contrasted with this effect of the esters of organic thiosulfonic acids, the salts of organic thiosulfonic acids have some stabilizing action, although they are strong desensitizers for photographic silver halide emulsions when employed at concentrations approaching those at which the esters of our invention are employed. We have further found that when esters of thiosulfonic acids are employed according to our invention, the addition of a sulfonate, such as sodium p-toluenesulfonate, does not improve the stabilization effect obtained, and in fact, frequently interferes with the antifoggant properties of the esters of thiosulfonic acids.
The esters of organic thiosulfonic acids which can be 3,047,393 Patented July 31, 1962 used in our invention include those represented by the following general formula:
wherein R represents an alkyl group, such as methyl, ethyl, propyl, butyl, etc. (e.g., an alkyl group containing from 1 to 4 carbon atoms), or an aryl group, such as phenyl, tolyl, etc. (e.g., a monocyclic aryl group of the benzene series containing from 6 to 7 carbon atoms) and R represents an alkyl group, such as methyl, ethyl, propyl, butyl, etc. (e.g., an alkyl group containing from 1 to 4 carbon atoms), an aryl group, such as phenyl, tolyl, etc. (e.g., a monocyclic aryl group of the benzene series containing from 6 to 7 carbon atoms) or an aralkyl group, such as benzyl, B-phenethyl, etc. (e.g., an aralkyl group containing from 7 to 8 carbon atoms). The esters represented by Formula 1 above have sometimes been named as disulfoxides, in which case they can be written as conforming to the following general formula:
wherein R and R each have the values given above, although recent work by Cymerman and Willis (J. Chem. Soc., 1951, p. 1332) indicates that the disulfoxide assignment is incorrect. I
Our invention also contemplates bis-esters of the type represented by the following general formula:
wherein R has the values given above and R represents an alkylene group, such as ethylene, trimethylene (propylene), tetramethylene (butylene), methyl-substituted propylene, pentamethylene, hexylene, heptamethylene, decamethylene, etc. (e.g., an alkylene group containing from about 2 to 10 carbon atoms). As in the case of the esters represented by Formula I above, the esters of Formula II can also be designated as sulfoxide derivatives, in which case they can be written as conforming to the following general formula (see above comment under Formula Ia):
wherein R and R each have the values given above.
The radicals represented by R and R above can be further substituted by functional groups containing sulfur, oxygen, or nitrogen atoms, such as by hydroxyl, mercapto, amino, methylamino, anilino, methoxyl, ethoxyl, etc., as well as by halogen atoms, such as chlorine, bromine, etc.
Typical esters of organic thiosulfonic acids which can be used in our invention include, for example, the following:
(1) Ethane-1,2-bis(p-toluenethiosulfonate), R. Otto, Rossing, Ber., vol. 20, p. 2088 (1887); ibid., vol. 25, p. 1478. (2) Propane 1,3 bis(p-toluenethiosulfonate), I.C.A. Chivers, S. Smiles, Jour. Chem. Soc., 1928, p. 697. (3) Decane-1,10-bis(p-toluenethiosulfonate) (4) Pentane-1,5-bis (p-toluenethiosulfonate) (5 Benzyl p-toluenethiosulfonate. (6) p-Tolyl p-toluenethiosulfonate. (7) Benzyl, ethanethiosulfonate. (8) Methyl methanethiosulfonate. (9) Methyl ethanethiosulfonate. (10) Ethyl methanethiosulfonate. 1 1 Butyl ethanethiosulfonate.
For the purposes of inhibiting fog formation, the thiosulfonic esters of our invention can be added to the emulsion during the process of manufacture, either during mixing, ripening, of after-ripening, in order to avoid loss of sensitivity and to inhibit the growth of fog with the 3 passage of time under non-ideal conditions of storage.
The thiosulfonic esters can be added to the emulsions in the form of their solutions in a suitable innocuous solvent, such as ethanol, pyridine, dioxane, etc. While the concentration of a given thiosulfonic ester will vary to some extent, depending upon the chemical nature of the thiosulfonic ester, its purity, type of silver halide emulsion, concentration of silver halide, etc., we have found that the concentration of the thiosulfonic esters should be at least 0.05 g. per mole of silver halide. The maximum amount of thiosulfonic ester will also vary, although we have found, in general, that it can be as high as about g. per mole of silver halide. These thiosulfonic esters can be added to unsensitized, chemically sensitized or optically sensitized photographic emulsions and while the effects are not substantial when sensitivity and fog measurements are made soon after coating (except with prolonged or forced development where fog is strongly diminished), the efiect of these compounds becomes quite apparent after an appreciable interval of time upon storage at elevated temperatures and dry or somewhat humid conditions.
The preparation of silver halide emulsions involves three separate operations: (1) the emulsification and digestion or ripening of the silver halide, (2) the freeing of the emulsion from excess soluble salts, usually by washing, and (3) the second digestion or after-ripening to obtain increased sensitivity. (Mees, The Theory of the Photographic Process (1952).) We prefer to add the fog-inhibiting agents after the final digestion or afterripening, although they can advantageously be added prior to digestion.
If desired, the thiosulfonic esters of our invention can be incorporated in the emulsions without adverse efiects by the bathing techniques known to those skilled in the art.
The photographic emulsions used in practicing our invention are of the developing-out type.
The emulsions can be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, Sheppard et al. U.S. Patent 1,623,499, issued April 5, 1927, and Sheppard et al. U.S. Patent 2,410,689, issued November 5, 1946.
The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium, and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U.S. Patent 2,448,060, issued August 31, 1948.
The emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Patent 2,399,- 083, issued April 23, 1946, or stabilized with gold salts as described in 'Damschroder U.S. Patent 2,597,856, issued May 27, 1952, and Yutzy and Leermakers U.S. Patent 2,597,915, issued May 27, 1952. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfo benzothiazole methochloride.
The emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll U.S. Patent 2,487,850, issued November 15, 1949), polyamines, such as diethylene triamine (Lowe and Jones U.S. Patent 2,- 518,698, issued August 15, 1950), polyamines, such as spermine (Lowe and Allen U.S. Patent 2,521,925, issued September 12, 1950), or bis(fl-aminoethyl) sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,- 926, issued September 12, 1950).
The emulsions can also be optically sensitized with cyanine and merocyanine dyes, such as those described in Brooker U.S. Patents 1,846,301, issued February 23, 1932; 1,846,302, issued February 23, 1932; and 1,942,854,
issued January 9, 1934; White U.S. Patent 1,990,507, issued February 12, 1935; Brooker and White U.S. Patents 2,112,140, issued March 22, 1938; 2,165,338, issued July 11, 1939; 2,493,747, issued January 10, 1950 and 2,739,- 964, issued March 27, 1956; Brooker and Keyes U.S. Patent 2,493,748, issued January 10, 1950; Sprague U.S. Patents 2,503,776, issued April 11, 1950, and 2,519,001, issued August 15, 1950; Heseltine and Brooker U.S. Patent 2,666,761, issued January 19, 1954; Heseltine U.S. Patent 2,734,900, issued February 14, 1956; Van Lare U.S. Patent 2,739,149, issued March 20, 1956; and Kodak Limited British Patent 450,958, accepted July 15, 1936.
The emulsions may also contain speed increasing compounds of the quaternary ammonium type of Carroll U.S. Patent 2,271,623, issued February 3, 1942; Carroll and Allen U.S. Patent 2,288,226, issued June 30, 1942; and Carroll and Spence U.S. Patent 2,334,864, issued November 23, 1943; and the polyethylene glycol type of Carroll and Beach U.S. Patent 2,708,162, issued May 10, 1955; or the thiopolymers of Graham and Sagal U.S. application Serial No. 799,839, filed December 12, 8, or Dann and Chechak U.S. application Serial No. 779,874, filed December 12, 1958, or the quaternary ammonium salts and polyethylene glycols of Piper U.S. Patent 2,886,437, issued May 12, 1959.
The emulsions may contain a suitable gelatin plasticizer such as glycerin; a dihydroxy alkane such as 1,5-pentane diol as described in Milton and Murray U.S. application Serial No. 588,951, filed June 4, 1956 (now U.S. Patent No. 2,960,404, issued November 15, 1960); an ester of an ethylene bis-glycolic acid such as ethylene bis(methyl glycolate) as described in Milton U.S. application Serial No. 662,564, filed May 31, 1957 (now U.S. Patent No. 2,904,434, issued September 15, 1959); bis-(ethoxy diethylene glycol) succinate as described in Gray U.S. application Serial No. 604,333, filed August 16, 1956 (now U.S. Patent No. 2,940,854, issued June 14, 1960), or a polymeric hydrosol as results from the emulsion poly merization of a mixture of an amide of an acid of the acrylic acid series, an acrylic acid ester and a styrenetype compound as described in Tong U.S. Patent 2,852,- 386, issued September 16, 1958. The plasticizer may be added to the emulsion before or after the addition of a sensitizing dye, if used The emulsions may be hardened with any suitable hardener for gelatin such as formaldehyde; a halogensubstituted aliphatic acid such as mucobromic acid as described in White U.S. Patent 2,080,019, issued May 11, 1937; a compound having a plurality of acid anhydride groups such as 7,8-diphenylbicyclo (2,2,'2)-7-octene- 2,3,5,6-.tetra-car-boxylic dianhydride, or a dicarboxylic or a disulfonic acid chloride such as terephthaloyl chloride or naphthalene-1,S-disulfonyl chloride as described in Allen and Carroll U.S. Patents 2,725,294, and 2,725,295, both issued November 29, 1955; a cyclic 1,2-diketone such as cyclopentane-1,2-dione as described in Allen and Byers U.S. Patent 2,725,305, issued November 29, 1955; a bisester of methane-sulfonic acid such as 1,2-di-(methanesulfionoxy)-ethane as described in Allen and Laakso U.S. Patent 2,726,162, issued December 6, 1955; 1,3-dihydroxymethylbenzirnidazol-2-one as described in July, K-nott and Pollak U.S. Patent 2,732,316, issued January 24, 1956; a dialdehyde or a sodium bisulfite derivative thereof, the aldehyde groups of which are separated by 23 carbon atoms, such as B-methyl glutaraldehyde bissodium bisulfite as described in Allen and Bur-ness U.S. patent application Serial No. 556,031, filed December 29, 1955 (now abandoned); a bis-aziridine carboxamide such as trimethylene bis(1-aziridine carboxarnide) as described in Allen and Webster U.S. patent application Serial No. 599,891, filed July 25, 1956 (now U.S. Patent 2,950,197, issued August 23, 1960); or 2,3-dihydroxy dioxane as described in Jeffreys U.S. Patent 2,870,013, issued January 20, 1959.
The emulsions may contain a coating aid such as saponin; a lauryl or oleyl monoether of polyethylene glycol as described in Knox and Davis US. Patent 2,831,766, issued April 22, 1958; a salt of a sulfiated and alkylated polyethylene glycol ether as described in Knox and Davis U.S. Patent 2,719,087, issued September 27, 1955; an acylated alkyl taur-ine such as the sodium salt of N-oleoyl- N-methyl taurine as described in Knox, T wardokus and Davis U.S. Patent 2,739,891, issued March 27, 1956; the reaction product of a dianhydride of tetracarboxybut-ane with an alcohol or an aliphatic amine containing from 8 to 18 carbon atoms which is treated with a base, for example, the sodium salt of the monoester of tetracarboxybutane as described in Knox, Stenberg and Wilson U.S. Patent 2,843,487, issued July 15, 1958; a watersoluble maleopimarate or a mixture of a water-soluble maleopimarate and a substituted glutamate salt as described in Knox and Fowler U.S. Patent 2,823,123, issued February 11, 1958; an alkali metal salt of a substituted amino acid such as disodium N-(carbop-tert. octylphenoxypentaethoxy)glutamate as described in Knox and Wilson U.S. patent application Serial No. 600,679, filed July 30, 195 6; or a sulfosuccinamate such as tetrasodium N-(1,2-d-icarboxyethyl)-N-octadecyl sulfosuccin-amate or N lauryl disodium sulfosuccinamate as described in Knox and Stenberg U.S. patent application Serial No. 691,125, filed October 21, 1957 (now U.S. Patent 2,992,108, issued July 11,1961).
The addenda which we have described may be used in various kinds of photographic emulsions. being useful in X-ray and other nonoptically sensitized emulsions they may also be used in orthochromatic, panchromatic, and infrared sensitive emulsions. They may be added to the emulsion before or after any sensitizing dyes which are used. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlo-robromide or silver bromoiodide. The agents may be used in emulsions intended for color photography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials, emulsions of the mixed-packet type, such as described in Godowsky U.S. Patent 2,698,794, issued January 4, 1955; or emulsions of the mixed-grain type, such as described in Carroll and Hanson U.S. Patent 2,592,243, issued April 8, 1952. These agents can also be used in emulsions which form latent images predominantly on the surface of the silver halide crystal or in emulsions which form latent images predominantly inside the silver halide crystal, such as those described in Davey and Kno-tt U.S. Patent 2,592,250, issued April 8, 1952.
These may also be used in emulsions intended for use in diffusion transfer processes which utilize the undeveloped silver halide in the nonimage areas of the negative to form a positive by dissolving the undeveloped silver halide and precipitating it on a receiving layer in close proximity to the original silver halide emulsion layer. Such processes are described in Rott U.S. Patent 2,352,014, issued June 20, 1944, and Land U.S. Patents 2,584,029, issued January 29, 1952; 2,698,236, issued December 28, 1954, and 2,543,181, issued February 27, 1951; and Yackel et a1. U.S. patent application Serial No. 586,705, filed May 23, 1956 (now U.S. Patent 3,020,155, issued February 6, 1962). They may also be used in color transfer processes which utilize the diffusion transfer of an image-wise distribution of developer, coupler or dye, from a light-sensitive layer to a second layer, while the two layers are in close proximity to one another. Color processes of this type are described in Land U.S. Patents 2,559,643, issued July 10, 1951, and 2,698,798, issued January 4, .1955; Land and Rogers Belgian Patents 554,933 and 554,934, granted August 12, 1957; International Polaroid Belgian Patents 554,212, granted July 16, 1957, and 554,935, granted August 12, 1957; Yutzy U.S. Patent 2,756,142, granted July 24, 1956,
6 and Whitrnore and Mader U.S. patent application Serial No. 734,141, filed May 9, 1958.
In the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there may be employed as the dispersing agent for the silver halide in its preparation, gelatin or some other colloidal material such as colloidal alburnin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in Lowe U.S. Patent 2,286,215, issued June 16, 1942; a far hydrolyzed cellulose ester such as cellulose acetate hydrolyzed to an acetyl content of 1926% as described in U.S. Patent 2,327,808 of Lowe and Clark, issued August 24, 1943; a water-soluble ethanolamine cellulose acetate as described in Yutzy U.S. Patent 2,322,085, issued June 15, 1943; a polyacrylamide having a combined acrylimide content of 1520% and a specific viscosity of 0.09- 0.225 or an imidized polyacrylamide having a combined acrylimide content of 60%, a combined acrylic acid content of 412% and a specific viscosity of .251.5 as described in Lowe, Minsk and Kenyon U.S. Patent 2,541,474, issued February 13, 1951; zein as described in Lowe U.S. Patent 2,563,791, issued August 7, 1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith U.S. Patent 2,768,154, issued October 23, 1956; or containing cyano-acetyl groups such as the vinyl alcohol- In addition to vinyl cyanoacetate copolymer as described in Unruh, Smith and Priest U.S. Patent 2,808,311, issued October 1, 195 7; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in U.S.
Patent 2,852,382, of Illingsworth, Dann and Gates, issued September 16, 1958.
If desired, compatible mixtures of two or more of these colloids may be employed for dispersing the silver halide in its preparation. Combinations of these antifoggants, sensitizers, hardeners, etc., may be used.
The following examples will serve to illustrate more fully the useful stabilizing effects of many of the thiosulfonic esters useful in practicing our invention. A series of coatings were made on an ordinary photographic film support, such as cellulose acetate, of an ordinary photographic negative speed bromiodide emulsion, both with and without the addition of one of the esters of thiosulfonic acids at the concentration shown in the following table. The esters were added from substantially neutral solutions. The coatings were then dried and exposed on an intensity scale sensitometer (Kodak Type Ib) and developed for 4 minutes at 68 F. in Kodak D-19 Developer or for 5 minutes in Kodak DK-50 Developer. A separate set of coatings was incubated for one week at F., constant relative humidity at about 50%, and in some cases for two weeks under the same conditions. These incubated coatings were then exposed and processed in the same manner as the fresh coatings described above. The relative speeds and fogs for each of the coatings were then measured. The relative speed is inversely proportional to the exposure to produce a density of 0.3 above fog.
In the following table the compound numbers correspond to the numbers used above for the specific thiosulfonic esters. In each coating series, the same emulsion batch was used, although different emulsion batches were used for certain of the coating series. Wherever a different emulsion batch was used, a new control series was run for that batch to show the degree of improvement obtained. Kodak Developer D-19 has the following composition:
Water, about F. (50 C.) ccs 500 Elon developing agent grams 2.0 Sodium sulfite, desiccated do 90.0
V 1 N -methyl-p-aminopheuol sulfate.
.7 Hydroquinone "do..-" 8.0 Sodium carbonate,monohydrated do 52.5 Potassium bromide do 5.0
Cold water to make 1 liter.
Kodak Developer DK-50 has the following composition:
Cold Water to make 1 liter.
The results of these coating series are given in the following table:
alcohol was added dropwise, with good stirring, to the hot solution. The reaction mixture was refluxed for 4 hours (after the addition had been completed) and filtered while still hot. Ethyl acetate (50 ml.) was added to the hot solution which was then cooled, and the solid product removed by filtration. The material was recrystallized by dissolving in the minimum amount of hot absolute alcohol, and adding one-half volume of ethyl acetate. The material may also be recrystallized from methanol. The yield was 7.5 g., M.-P. 8889 C.
Analysis.-Calcd. for CHI-1340484: C, H, S, 24.9. Found: C, 56.1; H, 6.5; S, 24.7.
In like manner, other thiosulfonic esters can be prepared by using other halogenated alkanes in the above examples,
" or by using sulfinic acids as the starting material as described by Here and Smiles, J. Chem. Soc. 125, page 2359, 1924.
T ABLE Incubation- Incuba- Com- Fresh Coating 1 Week tion-2 Coating Develpound gjmole Weeks N 0. oper No. .AgX
Speed Fog Speed Fog Fog Control 100 12 76 25 1 0. 75 74 10 71 09 2 0. 75 95 10 81 10 3 0. 3 89 11 107 16 3 3. 98 .11 102 .16 Control 100 08 196 17 46 0. 45 89 .06 215 08 25 Control 100 13 64 33 79 6 0.15 80 .12 86 .12 .30 0.15 86 12 78 16 .40 Control 100 .08 135 23 65 8 0.09 94 07 155 09 18 9 0.38 89 07 115 09 .13 0. 38 89 .07 118 .10 .14
The thiosulfonic esters useful in practicing our invention can be prepared according to methods which have been previously described in the prior art. For example, the monoesters of Formula I above can advantageously be prepared by condensing an alkali metal thiosulfonate with a halogen-substituted alkane. The bis-esters of Formula II can be prepared according to the same general method by condensing an alkali metal thiosulfonate with a dihalogenated alkane. This general method of preparation is illustrated in the following examples:
Example 1 .Ethane-l ,2-Bis (p-Toluenethiosulfonate) 1,2-dibromoethane (9 g., 0.048 mole) and sodium-(ptoluenethiosulfonate) g., 0.095 mole) in 70 ml. of alcohol were refluxed for 5 hours. The hot reaction mixture was filtered and cooled. The solid product was removed by filtration and recrystallized from absolute alcohol. The yield was 5 g., M.P. 73-75 C.
Analysis.Calcd. for C H O S C, 47.7; H, 4.8; S, 31.8. Found: C, 48.0; H, 4.7; S, 31.8.
Example 2.Pr0pmze-],3-Bis (p-Toluenethiosulfonate) Sodium(p-toluenethiosulfonate) (21 g., 0.1 mole) was dissolved in 100 ml. of alcohol and heated to reflux. 1,3- dibromopropane (10 g., 0.05 mole) was added dropwisc, with good stirring, to the hot solution. The reaction mixture was refluxed for 5 hours after addition had been completed. The hot reaction mixture was filtered and cooled. The solid product was removed by filtration. The mother liquors were concentrated to dryness for second-crop material. The product was recrystallized by dissolving in the minimum amount of hot absolute alcohol, and adding one-half volume of ethyl acetate. The solid product was removed by filtration and dried. The yield was 10 g., M.P. 6567 C.
Example 3.Decane-1,10-Di- (p-Toluenethiosulfonate) Sodium(p-toluenethiosulfonate) (14 g., 0.066 mole) was dissolved in 80 ml. of alcohol and heated to reflux. 1,10-dibromodecane (10 g., 0.033 mole) in 20 ml. of
wherein R represents a member selected from the class consisting of an alkyl group and an aryl group and R represents a member selected from the class consisting of an alkyl group, an aryl group and an aralkyl group.
2. A photographic silver halide emulsion as defined in claim 1 wherein said photographic silver halide emulsion is a gelatino-silver-bromiodide emulsion.
3. A photographic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of an ester selected from those represented by the following general formula:
wherein R represents a member selected from the class consisting of an alkyl group and an aryl group and R represents an alkylene group.
4. A photographic silver halide emulsion as defined in claim 3 wherein said photographic silver halide emulsion is a gelatino-silver-brorniodide emulsion.
5. A photographic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of an ester selected from those represented by the following general formula:
RSO S--R wherein R and R each represents an aryl group.
9 6. A photographic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of an ester selected from those represented by the following general formula:
wherein R and R each represents an alkyl group containing from l to 4 carbon atoms.
7. A photographic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of an ester selected from those represented by the following general formula:
10 the addition there-to of from 0.05 to 10 g. per mole of silver halide of methyl methanethiosulfonate.
10. A photographic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of methyl ethanethiosulfonate.
11. A photographic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of decane-l,lO-bis(p-toluenethiosulfonate).
12. A photognaphic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of ethyl methanethiosulfonate.
13. A photographic silver halide emulsion stabilized by the addition thereto of from 0.05 to 10 g. per mole of silver halide of propane-l,3-bis(p-toluenethiosulfonate).
OTHER REFERENCES Glafkides Photographic Chemistry, vol. 1., pages 379-380, Fountain Press (1958). Copy in Div. 60.