US3330658A - Photographic silver halide diffusion transfer process - Google Patents

Description

United States Patent Ofifice 3,330,658 Patented July 11, 19 67 3,330,658 PHOTOGRAPHIC SILVER HALIDE DIFFUSION TRANSFER PROCESS Paul B. Gilman, Jean E. Jones, and Arthur A.

Rochester, N.Y., assignors to Eastman Kodak pally, Rochester, N.Y., a corporation of No Drawing. Filed Dec. 20, 1963, Ser.

Claims. (CI. 96-29) Rasch, Com- New Jersey ABSTRACT OF THE DISCLOSURE Q s- 1- 2Q1 wherein R R and R each represent alkylene groups and Q and Q each represent a qua-rternary ammonium salt group selected from the class consisting of 1) trialkyl ammonium salt groups having the formula in which the R groups are lower alkyl and X is an anion and (2) a salt group having the formula in which Z represents the atoms necessary to complete a N-heterocyclic ring selected from the class consisting of pyridyl, piperidly and morpholinyl, X is an anion and R is selected from the class consisting of hydrogen and lower alkyl.

This application is a continuation-in-part of US. application Ser. No. 141,036, filed Sept. 27, 1961.

This invention relates to photography and more particularly to a photographic diffusion transfer process in which silver images of improved tone are obtained.

In the well-known silver halide diffusion transfer process of photograph, an exposed emulsion layer is developed in the presence of a silver halide solvent, the emulsion layer being for at least a portion, or for the whole of the development period in effective contact with a receiving sheet, the surface of which generally carries a quantity of a silver precipitant which may comprise either physical development nuclei such as colloidal silver or silver sulfide or a chemical precipitant for silver ions, such as zinc sulfide. Development of the emulsion layer proceeds, and concurrently the residual unexposed silver halide is dissolved by a silver halide solvent also present in the developer composition, followed by imagewise diffusion of the resulting silver complex to the receiving sheet where the silver precipitant catalizes physical development and causes the formation of an argental image.

In this process the argental image has a characteristic yellow, brownish or other unacceptable color whereas a neutral toned image is desired.

It is known to use toning agents to obtain a neutral tone. The toning agent is customarily added to the devel-oper or to the receiving sheet so that when the silver image is formed, the silver grains are of sufficient size to provide a neutral or black image. However, many of the toning agents which are known for toning in the conventional chemical developing process, when used in the diffusion transfer process, result in positive images which do not have satisfactory gradation in contrast. For instance, these images would not be suitable for continuous tone reproduction, but only for ofiice copying or similar uses where extreme contrast is desired.

In the Tregillus et al. U.S. Patent 3,017,270, for example, various tone modifying components are used in conjunction with quaternary ammonium salts with a linear chain of at least 7 atoms attached directly to a quaternary nitrogen atom. However, this combination acts on the silver halide emulsion to increase the development in the negative so that the resulting positive print, while it is of a neutral tone, may lack satisfactory gradation in contrast.

It has been desirable, therefore, to find an acceptable toner which would not only result in the neutral tone, but which would also provide the desirable gradation in contrast to provide suitable pictorial quality in the positive print. Suitable toners must also be compatible with a silver halide emulsion, must not have a detrimental effect on the speed of the system and must not be deleterious to the ease of processing.

Inasmuch as the toner must be present during the formation of the silver grains in the receiving sheet and is preferably incorporated in the developer solution, the tonermust also :be compatible with the components in the developer. The amount of toner incorporated in the silver halide emulsion must be sufiicient so that an adequate quantity leaches out during the silver halide transfer to affect the silver grain size. Therefore, finding suitable toners has been considered unpredictable in the diffusion transfer field.

We have discovered that if this process is carried out in the presence of dithiabisquaternary ammonium salts the image has the desired neutral tone. The salts are useful when incorporated into either or both the developer solution and the nucleated receiving layer of the process. The salts are particularly effective to produce neutral toned images when used in conjunction with sulfur compounds such as described belo The dithiabisquaternary ammonium salts have the gen eral formula Q- 3- 1 2 Q1 wherein Q and Q represent a quaternary ammonium salt group such as 1) a trialkyl ammonium salt group having the formula in which the R groups are the same or different alkyl groups e.g. methyl, ethyl, propyl, butyl etc. and X is an anion or acid radical, or (2) a salt group having the formula in which Z represents the atoms necessary to complete a pyridyl ring e.g. pyridyl, a-picolyl etc., a piperidyl ring or a morpholinyl ring, and X is as above; R R and R each represent alkylene groups such as ethylene, propylene, 'butylene, pentylene, tetradecylene etc.

The following are examples of the salts useful in our invention and having the above general formula:

3,10 dithiadodecane 1,12-bis-(N-methylpiperidinium-ptoluene sulfonate) (M.P. 180182 C.)

P TS- ITS- CH C H;

CH CH:

1,4 bis (3 thia 8 aza 7 0x0 6 oxa d0decyl)- 1,4-dimethyl piperazinium di-p-toluene sulfonate.-To a cold solution of 9.2 g. of sodium in 500 ml. of methanol was added 41.2 g. 1,4-bis(fl-mercaptoethyl) piperazine. To the cooled reaction mixture there was added with stirring 71.8 g. of B-chloroethyl-N-butylcarbamate. The reaction mixture was allowed to remain at room temperature overnight, after which time the methanol was removed at reduced pressure. The residue was mixed with 250 cc. water and the whole extracted with chloroform. The chloroform was distilled and the residue collected.

Analysis.Calcd.: C, 52.7; H, 7.4; N, 6.5; S, 14.8. Found: C, 53.0; H, 6.0; N, 6.1; S, 15.0.

B-Chloroethyl-N-butyl carbamate.-To 800 g. 2-chloroethanol, 991 g. n-butyl isocyanate was added dropwise. After addition was complete the reaction mixture was heated on a steam bath for 2 hours then distilled under vacuum. Product distilled at 850/62 mm. to give 1700 g. carbamate (95 percent of theory).

7,13 dithianonadecane-I,19-bis-(pyridinium-p-toluene sulfonate).-To a stirred solution of 23 g. (1 g. atom) of sodium in 500 ml. of methanol, there was added with cooling 68 g. (0.5 mole) of 1,5 pentanedithiol. After the addition of 136.5 g. (1.0 mole) of hexamethylene chlorohydrin with cooling and stirring, the reaction mixture was allowed to remain at room temperature overnight. The residue was mixed with one liter of water and the whole extracted with chloroform. The chloroform extract was dried over magnesium sulfate and then the chloroform was removed under reduced pressure. The residue was recrystallized from acetone. Yield 130 g. (72 percent of theory, M.P. 675).

PTS PTS PROCEDURE A PROCEDURE B Ho(oHi).s(CHi)yS(CH, ,oH 20111180201 A mixture of 30.2 g. (0.1 mole) of the above 7,13

dithia-1,19-bis nonadecanediol and 100 ml. pyridine was treated with 39.4 g. (0.23 mole) of p-toluene sulfonyl chloride. After one hour below 20 6., there was added 150 ml. concentrated hydrochloric acid in one liter of water. The oil was extracted with chloroform, washed with dilute acid, separated and dried over magnesium sulfate. Removal of the solvent at reduced pressure gave a light yellow viscous oil.

A solution of the oil was dissolved in excess pyridine, heated at the boiling point for 15 minutes, cooled and poured into cold ether. The solid was filtered, washed with ether, and dried.

It has been mentioned that the dithiabisquaternary ammonium salts are particularly effective to tone the silver images when used with mercaptan compounds. These compounds are characterized in some instances by having a beneficial effect upon tone, but do not give the best image tone (neutral) in the present process except in combination with the mentioned quaternary salts. As will be seen in the following examples one or more dithiabisquaternary ammonium salts can be used alone, or with one or more of the organic sulfur containing compounds such as the following:

5-amino-2-mercapto-1,3,4-thiadiazole 1-methyl-2-mercaptoimidazole 4-aminomethyl-Z-mercaptoimidazole 4-cyano-2, 3-dioxo-5 -thionopyrrolidine 1,10-bis-(morpholino)-1,10-dioxo-2,5,6,9-tetrathiadecane 1,4-bis- (Z-mercaptoethyl) -piperazine 3-mercaptopyridine-N-oxide 5-bromo-6-methyl-1,3,3a,7-tetrazaindene-4-thiol 6-phenyl-l,3,3a,7-tetrazaindene-4-thiol 2-mercaptobenzoxazole 2-mercaptobenzimidazole 7 2,4-dithiolpyrimidine 4-amino-6-hydroxypyrimidine-2-thiol 2-mercapto-4,5,6-triamin-o-pyrimidine 4,5 -diamino-6-hydroxy-2-mercaptopyrimidine Thiouracil S-methylthiouracil 2-thio-barbitu1'ic acid 4,5-dian1in0-2-mercaptopyrimidine 4,6-dimethyl-2-thio-2,3-dihydropyrimidine 4,6-diamino-pyrimidine-2-thiol 2,6-diamino-4-mercapto-pyrimidine S-aminomethylene-I-ethyI-Z-thiobarbituric acid 4-amino-5-carbethoxy-2-mercapto-pyrimidine 3,4,5 ,6-tetrahydro-3-methyl-4-oxopyrimidine-Z-thiol 2-amino-4-mercapto-6-methylpyrimidine 1,4-bis- (2-rnercaptoethyl) -piperazine Bis- [2-(Nmethyl-3-azapentamethylenecarb amyloxy ethyl] -disulfide 1-methylpiperazine-4-ethanethiol Methyl-S-thioctate 1-[pyridinium(chloride)acetyl1-4- phenylthiosemicarbazide -3-rnercaptopropyl-N-rnethylpyridinium-ptoluenesulfonate 1: 1 pentarnethylene-3-pyrid-2-yl-thiourea Z-mercaptopyridine-N-oxide N SH 1,6-bis- [methyl- Z-y-pyridlethyl) -dithiocarb amato] hexane-dimetho perchlorate 2-mercapt0methyl-5 -hydroxy-4-pyrone 6-hydroxy-3 -mercapto-5-methyl- 1,2,3 a,4,7-pentazaindene 7-hydroxy-5-mercapto-1,2,3 ,4,6-p entazaindene 6-hydroxy-3 -mercapto-4-methyl-1,2,3 a,7-tetrazaindene 4-hydroxy-6-methyl-1,2,3a,7-tetrazaindene-3-thiol 4-hydroxy-2-mercaptomethyl-6-methyl-1,3 ,3 a,7-tetr azaindene Z-carboxymethylmercapto-Loxo-5-methyl-6-thiono- 4,5 ,6,7-tetrahydro-1-thia-3 ,5,7-triazaindene 4-mercapto-1-thia-3,5 ,7-triazaindene 6-ethoxy-2- (B-c arboxy-fi-thiolpropionamido) benzothiazole 6-ethoxy-2-( f3-carboxy-a-thiolpropionamido) benzothiazole 4-hydroxy-6-mercapto-1,2,5,7-tetrazaindene 6-rnercaptopurine 7-methyl-6-thiopurine l t l 4-amino-6-mercapto-1-methyl-2-methylmercapto- 1,3,5 ,7-tetrazaindene 4,7dihydroxy-2-mercapto-l-phenyl-1,3 ,,5 ,6-tetrazaindene 4,7 -dihydroxy-2-mercapto- 1 ,3,5,6-tetrazaindene 1-mercapto-3-iminoisoindole 1-methyl-4-thioquinazoline 4-carbethoxy-1,5-dithia-3 -oxospiro [5.5] -hendacane 3-mercapto-1,2,3 a,8-tetrazacyclopenta] -indene 3-mercapto- 1,2,3a-triaza-benz [e] -indene 1-mercapto-5-methyl-2,3,9b-triazabenzol- [e] -indene 2-mercapto-5- (3 -pyridyl) -1,3,4-thiadiazole 5- 3-oxindolyidene -rhodanine til:

3,6-di-(1,2-dihydro-1-methyl-quinolin-Z-yl-idene)- 1,2,4,S-tetrathia-cyclohexane CH3 C The use of the mentioned quaternary ammonium salts in the diflusion transfer processes of the invention is illustrated by the following examples:

Example 1 A silver halide emulsion layer was exposed to a subject in a conventional manner then treated with the following developing solution:

The emulsion layer was then squeegeed into contact with the receiving sheet described below, with a layer of the solution between, and allowed to remain in contact until the exposed silver halide had developed to a silver image and the residual undeveloped silver halide had transferred as a complex with the hypo to the receiving sheet, where positive silver containing image was formed. The emulsion layer was then stripped away from the sheet to reveal the silver image which has a neutral tone. In carrying out the process, the exposed emulsion layer may be wetted with the developer solution, and by passage over and between a series of rollers, brought into contact with the receiving sheet, and the resulting laminated sheet rolled up upon a roller until the transfer step is complete, after which the sheets are separated. Apparatus suitable for this procedure is described in the Vincent US. patent application Ser. No. 132,687, filed Aug. 21, 1961. Alternatively, both of the sheets may be wetted before lamination is effected.

RECEIVING SHEET Part I.To one liter of water at 40 500 ml. of 1% sodium sulfide.

Part 2.To one liter of water at 40 C. were added 7 ml. of 0.4 molar nickelous nitrate. Part 2 was added to Part 1 dropwise with stirring for 2 minutes and the remainder of Part 2 added over a period of about 2 minutes. 45 grams of dry gelatin were added followed by stirring at 40 C. for about 15 minutes to obtain a dispersion of nickel sulfide in gelatin. The above-mentioned dithiabisquaternary ammonium salts were each added to portions of the melted dispersion in amounts of the order of 0.7 gram per liter of the dispersion. Next, 0.1 gram per liter of B-mercapto-1,2,4-triazole and 0.05 gram per liter of S-methyl oxazoline-Z-thiol were added to each batch, after which the compositions Were coated upon separate paper bases.

When each receiving sheet was employed in the process described, a neutral toned image was obtained whereas when a similar nickel sulfide receiving sheet not containing the mentioned salt was used, a brownish toned image was obtained.

The use of the dithiabisquaternary ammonium salts alone as toning agents is illustrated by the following examples:

C. were added gelatin solution and 9.5 ml. of 0.2 molar Example 2 A silver halide emulsion No. 895 was exposed and developed in the following developer solution in contact with a nickel sulfide sheet similar to that of Example 1.

H O m1 700 Z-amhroethanol-sulfur dioxide ml 180 1-phenyl-4,4-dimethyl-3-pyrazolidone g 0.50 Hydroquinone g 5.50

Sodium sulfite, anyhdrous 144 Water to 2000 ml.

To this developer solution were added varying amounts of the compound No. 624-987 [7,13-dithianonadecane- 1,19-bis-(pyri-dinium-o-toluene-sulfonate)] of from to 0.8 gram per liter. As a result, when about 0.4 to 0.8 gram per liter was present the best image tone was obtained on the sulfide sheet, whereas in absence of compound 624 987 a yellow image was obtained on the sheet.

Example 3 A sensitive element similar to that described in Example 1 of the Yackel et al. US. patent application Ser. No. 586,705, filed May 23, 1956, now US. Patent 3,020,155, comprising a cellulose ether phthalate-silver halide emulsion coated upon a zinc sulfide nucleated receiving layer on a support, was exposed then developed at 80 F. in

Water to 3200 g.

After this the element was immersed in 68 F. water to remove the emulsion layer containing a negative image, leaving a neutral toned silver image in the nucleated layer, whereas When the same developer solution free of compound 624-987 was used the image was yellow toned.

Example 4 In the manner of Example 1 an exposed silver halide emulsion was developed in contact with a nickel sulfide coated receiving sheet containing about 20 mg. per square with each of foot of compound 624987 using the following developer solution:

Sodium sulfite g 60 Hypo g 12 Sodium carbonate g 50 Hydroquinone g 4.6 Elon g 4.0 0.5% carboxymethyl cellulose Inl.. 1000 to cc. of which had been added 1.0 cc. 1% methanol solution of 3-mercapto-1,2,4-triazole and 0.5 cc. of a 1% methanol solution of l-methyl-1,2,3,6-tetrahydro-l,3,5- triazine-4-thiol, with the result that the silver image ob tained on the nucleated receiversheet was neutral colored. It was found that varying amounts of 624987 in the sheet gave neutral images.

When the dithiabisquaternary ammonium salts e.g. compound 624987 are used in the nucleated reception layers as described above, good image tone is obtained with from about 0.5 to 25 mg. per square foot; the mercapto compound, when present, such as 3-mercapt0-l,2,4-triazole, is useful in a range of about 0.05 to 20 mg. per square foot, and with l-methyl-1,2,3,6-tetrahydro-1,3,5-triazine- 4-thiol, about 0.0520 mg. per square foot.

Example 5 A silver halide emulsion layer was exposed and processed in contact with a nickel sulfide layer as described in Example 1 using the following developer:

to which 70 cc. of a 1% aqueous solution of compound 624-988 and 10 cc. of 1% 3-mercapto-1,2,4-triazole had been added. The resulting print on the sulfide layer was neutral toned.

Example 6 3,6,9,l2,l5,18, 21,24 octoxahexacosane-l,26-bis-(5-ethyl-2-methylpyrid1nium) methane-sulfonate was added at 0.4 g./l. to a melted dispersion in place of the dithiabismanner. When the positive images using the quaternary salt and S-methyl oxazoline-Z-thiol were Another comparison was made with 3,8-dithiadecane- 1,10-bis-(N-methylpiperidinium-p-toluene-sulfonate) and ot-dimethyldithiocarbamatomethyl-N-methyl pyridinium-p-toluene-sulfonate and 4,4,10,10-tetraoxy-4,

I 1 dithiatridecane-l,13-bis-pyridinium perchlorate with the following results:

uniquely effective in prorequired for formation of as well as neu- The dithia bis compounds were viding the type of environment positive prints with a full tone gradation, tral image tones.

The development nuclei used in the reception elements of the invention are those physical development nuclei for dissolved silver salts well known in the art including colloidal heavy metals, e.g. colloidal silver and gold, colloidal metal sulfides, selenides and tellurides, e.g. lead sulfide, nickel sulfide, cadmium sulfide, silver sulfide, copper sulfide, zinc sulfide, mercury sulfide; metal proteinates, e.g. silver proteinates; compounds forming physical development nuclei with dissolved silver salts, e.g. sodium sulfide, colloidal sulfur, organic sulfur compounds such as thiourea, mercaptans and xanthates.

Reception layers containing development nuclei suitable for use in the invention can be prepared by the reduction of metal salts in the presence of a hydrophilic organic colloid such as gelatin. In a preferred method, a soluble salt of a noble metal such as silver nitrate, gold, platinum, or rhodium chloride, is dissolved in a solution containing O.5-2.0 percent concentration of gelatin or other hydrophilic colloids such as cellulose ether phthalate, or methyl methacrylate-methacrylic acid copolymer. To this solution is added an excess of an alkali hydroxide, carbonate, borate, or phosphate to form a suspension of hydrous metal oxide in a solution having a pH preferably in the range of 9-11. Next a solution of a reducing agent is added in concentration sufficient to at least partially reduce the metal oxide. Reducing agents commonly known to the photographic art may be used such as hydroquinone, monomethyl-p-aminophenol, hydrazines, etc. However, a preferred preparation employs formaldehyde, which serves .both to reduce the metal oxide and harden the coating made from this solution. In a typical proceduce a dispersion of silver resulting from reaction of silver nitrate, sodium hydroxide and a dilute formaldehyde solution was added to a 10% gelatin solution and coated upon a white pigmented cellulose acetatae butyrate support. If desired, the coating can also contain the mentioned quaternary ammonium salts of the invention such as compound 624-987 above.

Nuclei, which may be present in combination with the quaternary salts and the organic sulfur-containing compounds, can be applied in a solution of a colloid vehicle such as gelatin to a suitable support such as paper or 21 subbed cellulose ester or synthetic polymer support as described in the examples.

The silver halide emulsions used in the process to provide the silver halide image transfer to the reception layers, is not especially critical and for example silver bromide, silver chloride, and silver bromoiodide emulsions can be used. Naturally some variation in tone of the final silver image can be expected with different emulsions but in general the quaternary ammonium salts, particularly in combination with one or more of the organic, sulfur containing compounds, are effective to improve image tone.

Variations can be made in the composition of the developing solution. For example, the developing agent particularly non-diffusing ones can be contained all or in part in the emulsion layer. The silver halide solvent such as ammonium and alkali metal thiosulfates amines e.g. 2-amino ethanol N-diethyl amino ethanol etc. may be present in the developing solution or in the receiving layer it only being necessary that the solvent be present to dissolve the undeveloped silver halide forming a complex that will diffuse to the nucleated receiving layer.

Quaternary salts are known to be used as sensitizers when incorporated in the silver halide emulsion. Their action is considered to be that of acceleration in both chemical and physical development. In a diffusion transfer system, physical development in the negative is undesirable. Therefore, the use of quaternary salts would be expected to have a detrimental effect on the positive image due to the physical development occurring in the negative. In the physical development, which occurs in the diffusion transfer process, silver is obtained from the unexposed silver halide emulsion to form the image in the receiving sheet by depositing silver on the nuclei. However, the presence of a quaternary salt tends to promote physical development in the silver halide emulsion and cause the developed silver in the emulsion to act as nuclei for deposition of silver from the unexposed silver halide. This, therefore, reduces the amount of silver available from the unexposed silver halide and markedly reduces the effectiveness of the silver halide transfer to the receiving sheet.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A process for preparing a silver image of improved tone in a silver halide diffusion transfer process which comprises developing an exposed silver halide emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer imagewise by diffusion to an image receiving layer containing physical development nuclei for dissolved silver salts, the transferring being effected with the emulsion layer and the image receiving layer in contact with a silver halide solvent and a dithiabisquaternary ammonium salt having the general formula wherein R R and R each represent alkylene groups and Q and Q each represent a quaternary ammonium salt group selected from the class consisting of (1) trialkyl ammonium salt groups having the formula 1 wherein the salt has the genwherein Q and Q are trialkylammonium salt groups and R R and R each represent alkylene groups.

3. The process of claim 1 wherein the quaternary ammonium salt has the general formula wherein R R and R each represent alkylene groups and Q and Q are pyridiniurn salt groups having the formula 1 I 2-mercapto-5- (3 -pyridyl)-1,3,4-thiadiazole 5-(3-oxindolyidene) -rhodanine 3,6-di-(1,2-dihydro-1-methyl-quinolin-2-yl-idene)- 1,2,4, S-tetrathia-cyclohexane kl i H l is. CH CH QR -SR S-R Q wherein R R and R each represent alkylene groups, and Q having Q each represents a quaternary ammonium salt group selected from the class consisting of (l) trialkyl ammonium salt groups having the formula.

in which the R groups are lower alkyl, X is an anion, and (2) a salt group having the formula in which Z represents the atoms necessary to complete a N-heterocyclic ring selected from the class consisting of pyridyl, piperidyl and morpholinyl, X is an anion, and R is selected from the class consisting of hydrogen and lower alkyl.

8. An alkaline photographic silver halide developing solution comprises a silver halide developing agent and a compound having the general formula wherein R R and R each represent alkylene groups, and Q and Q each represents a quaternary ammonium salt group selected from the class consisting of (1) trialkyl ammonium salt groups having the formula in which the R groups are lower alkyl and X is an anion, and 2) a salt group having the formula in which Z represents the atoms necessary to complete a N-heterocyclic ring selected from the class consisting of pyridyl, piperidyl and morpholinyl, X is an anion, and R is selected from the class consisting of hydrogen and lower alkyl.

9. The process of claim 1 wherein the physical development nuclei comprise nickel sulfide.

10. The element of claim 5 wherein the physical development nuclei comprise nickel sulfide.

References Cited UNITED STATES PATENTS 5/1942 Carroll et al. 96-107 X 1/1962 Tregillus et al. 9666.3 X NORMAN G. TORCHIN, Primary Examiner. R. E. MARTIN, Assistant Examiner.

Claims (1)

1. A PROCESS FOR PREPARING A SILVER IMAGE OF IMPROVED TONE IN A SILVER HALIDE DIFFUSION TRANSFER PROCESS WHICH COMPRISES DEVELOPING AN EXPOSED SILVER HALIDE EMULSION LAYER, TRANSFERRING THE SILVER HALIDE FROM THE UNDEVELOPED AREAS OF THE EMULSION LAYER IMAGEWISE BY DIFFUSION TO AN IMAGE RECEIVING LAYER CONTAINING PHYSICAL DEVELOPMENT NUCLEI FOR DISSOLVED SILVER SALTS, THE TRANFERRING BEING EFFECTED WITH THE EMULSION LAYER AND THE IMAGE RECEIVING LAYER IN CONTACT WITH A SILVER HALIDE SOLVENT AND A DITHIABISQUATERNARY AMMONIUM SALT HAVING THE GENERAL FORMULA