Stable liquid suspensions of sulphur dyes and method for analyzing same

Abstract: Stable, pourable aqueous suspensions of sulphur dyes are provided, especially suspensions which are characterized by a very low content of inorganic sulphides and inorganic polysulphides. The suspensions are produced using certain suspension stabilizing agents consisting mainly of water-soluble polysaccharide gums, such as xanthan gum, whose solutions in water are pseudoplastic. The suspensions may further comprise a non-sulphide reducing agent and/or a dispersing agent. An improved method is also provided for determining the the potential for such suspensions to release hydrogen sulphide upon being acidified at a given temperature, which method comprises acidifying a sample of the suspension to pH 2.9-3.7, capturing all of the hydrogen sulphide released during acidification in aqueous alkali and measuring the sulphide ion content of the aqueous alkali.

Description: The invention relates to stable flowable suspensions of finely divided particulate sulphur dyes and to a method useful for determining their capacity to emit hydrogen sulphide. It is often preferred in the textile dyeing art to use products which are in the form of flowable (liquid) compositions. Such liquid compositions have certain advantages over powdered or granular compositions. They are dust-free and they are better suited for use in automated equipment wherein they are pumped in metered quantities from a storage or holding container to a dyeing apparatus. It is usually desired that the successive charges be uniform. For this it is important that each charge of a given flowable dye composition be of the same strength, so that consistent dyeings can be achieved over a given period of time during which several successive charges will be delivered from a given container to given dyeing apparatus. It is in particular desirable, therefore, that the flowable dye composition remain pumpable and easily stirrable, so that uniformity can be restored, if necessary, when a charge is to be delivered from a container to a dyeing apparatus, e.g. textile dyeing apparatus. It is also desirable that the flowable composition be sufficiently stable so that it will remain uniform throughout the period of its residence in a container. In the field of sulphur dyes the switch from dry powders or granules to flowable compositions in the form of liquids, in particular for the dyeing of textile materials, was made several years ago with the advent of (pre)reduced sulphur dye liquids, i.e. aqueous solutions of sulphur dyes which are in the (pre)reduced (i.e. leuco) form. Such liquids are usually produced by heating a sulphur dye in an aqueous alkaline medium and invariably they involve the presence of one or more inorganic sulphides, such as sodium sulphide, and/or one or more inorganic polysulphides. Such a compound may be carried over from a thionation reaction by which a sulphur dye is produced, or it may be generated in situ during the solubilization of such a dye as a result of the action of alkali on unreacted sulphur from the thionation reaction which is present with the dye, or it may have been added to the aqueous alkaline medium as a reducing agent during the solubilization of the dye or, in small amounts, for the purpose of preventing premature reoxidation of the leuco sulphur dye during shipment or storage, or its presence may result from a combination of these factors. Aqueous suspensions of sulphur dyes in solid particulate form can be produced which are sulphide-free or of such low sulphide content as to pose little or no sulphide-related hazard to humans or their environment. However, such compositions may destabilize and/or the suspended dye may settle out upon prolonged standing. It has been proposed to combine insoluble dyes with substantial amounts of high molecular polymers, in particular in US-A-4 297 100 polycarboxylates and in US-A-4 436 523 aminoplast precondensates and non-ionic copolymers of 2 65 % ethylene oxide with a further olefin oxide, optionally together with a minor proportion of xanthan gum, in order to produce stable aqueous dye suspensions. It has now been found that aqueous suspensions of sulphur dyes that do not contain major amounts of the synthetic polymers of the kind described in US-A-4 297 100 and US-A-4 436 523 or preferably do not contain at all any such synthetic polymers, but containing only a small proportion of a suspension stabilizing agent (A) of pseudoplastic rheology consisting mainly of a water-soluble polysaccharide gum or mixture thereof as defined below, have surprisingly good properties of stability and flowability. It has further been found that the inorganic sulphide content of such suspensions can be monitored to a highly accurate extent, so that it is possible to produce practically sulphide-free sulphur dye suspensions as described below, while the risk of an over-acidification or over-oxidation - for the purpose of eliminating sulphide ions as H 2 S or by oxidation or both - is reduced to a minimum. The invention relates to the defined stabilized sulphur dye suspensions, their production and their use, as well as to the analytical method for measuring the capacity for a sulphur dye composition to release hydrogen sulphide upon being acidified. The invention thus provides a pourable suspension (S) of a sulphur dye or mixture of sulphur dyes in an aqueous liquid that contains a suspension stabilizing agent (A), aqueous solutions of which display a pseudoplastic behaviour and which suspension stabilizing agent (A) consists mainly of a water-soluble polysaccharide gum, in a concentration of 0.01 to 10 % by weight referred to the weight of the suspension. By "pourable" is meant that the suspension (S) is flowable, i.e. it has a viscosity which will enable it to flow freely from a container, preferably a viscosity no higher than 10,000 centipoise (cP), more preferably no higher than 5000 cP, most preferably no higher than 4000 cP, especially no higher than 3000 cP. Advantageously a suspension (S) according to the invention will have a viscosity of at least 30 cP, preferably at least 100 cP, more preferably at least 250 cP, most preferably at least 300 cP, especially at least 400 cP. Sulphur dye suspensions (S) according to the invention having viscosities in the range 250 to 2000 cP, especially 350 to 2000 cP, are particularly preferred, The viscosities stated above are those determined in known manner at 25°C and 60 rpm using a Brookfield rotational Viscometer, model LVT, with a# 3 spindle for viscosities up to 2000 cP and a # 4 spindle for viscosities above 2000 cP. Preferably, a suspension (S) according to the invention is one in which the distribution of the solid sulphur dye particles throughout the liquid is substantially uniform. By this is meant that any two equal volumetric portions of the suspension which are removed therefrom at the same time will contain substantially equal amounts, by weight, of said solid particles. By "substantially equal amounts, by weight" is meant that the amounts, by weight, of said sulphur dye in the respective portions are sufficiently identical that the two volumetric portions, when used separately for their intended purpose under identical conditions, will produce substantially identical results. For example, the two equal volumetric portions, when used in two separate but identical dyeing procedures, in particular textile dyeing procedures, will produce dyeings of substantially equal tinctorial strength, i.e. within ± 5 %, preferably ± 3 %, of one another as measured in known manner using a spectrophotometer, such as the Model CS-5 which, together with appropriate computer software, is available from Applied Colour Systems, Incorporated. More preferably, the weights of the solid particulate material in each portion are, themselves, within ± 5 % of one another. Preferably, the above-described uniformity applies also to the distribution of the suspension stabilizing agent (A), which is described more fully hereinafter. The concentration of the solid particulate sulphur dye in the suspension may vary within fairly wide limits, depending e.g. also on the intended use. For example its concentration may be dictated in part by the desired tinctorial strength of the suspension. In general, concentrations of 5 % or more, based on the total weight of the composition, are contemplated, with concentrations of 20 % or more being preferred. Concentrations of the solid sulphur dye particles may be as high as 60 %, with concentrations as high as 50 % being preferred. Concentrations in the range 10 to 45 %, by weight, are especially suitable. The size of the solid particles may vary, depending on other characteristics of the suspension. They should not be so large as to have too great a tendency to settle out of the suspension. While such a tendency can be overcome to a significant extent by the use of the suspension stabilizing agent (A) as described hereinafter, the particles should not be so large that they require the presence of a suspension stabilizing agent in such a large amount as will increase the viscosity of the suspension to a point where it is no longer pourable. Also, the solid sulphur dye particles should be small enough to be readily dissolved during a dyeing procedure. Suitable particle sizes can be determined and produced by a person of ordinary skill in the art without undue experimentation. Preferably, at least 99 %. ideally all of the particles are smaller than 400 µm (diameter), more preferably smaller than 200 µm, with particles less than 120 µm being most preferred, mean particle diameters (of volume distribution) ≤ 50 µm being especially suitable. The particle size can be measured using a Microtrac II particle size distribution analyzer Model # 7997-10 or # 7997-20 or by using a "Malvern Mastersizer" Model MS1002 from Malvern Instruments, Malvern, England. For many sulphur dyes a suitable particle size is usually obtained directly from the thionation reaction or, if necessary, from a subsequent treatment whereby the dye is precipitated from the thionation reaction mixture, as described below, with little or no mechanical size reduction treatment. In other cases conventional mechanical size reduction, such as milling, can be carried out where necessary. Preferably, a composition (i.e. suspension) (S) according to the invention is stable to the extent that it will retain its above-described uniformity for a period of at least 24 hours, more preferably for at least two weeks, most preferably for at least two months, even for 6 months or more, on standing at temperatures in the range 2 to 35°C. Preferably, a composition (S) according to the invention is also stable against an irreversible change in viscosity for the times and under the conditions specified in the preceding paragraph. By "change in viscosity" is meant such an increase as will render the suspension unpourable or such a decrease as will adversely affect the stable uniformity described above. More preferably, it means a change of more than 50% measured in cP as described above. By "irreversible" is meant a change which cannot be reversed by stirring, pumping or otherwise agitating the suspension. More preferably, the suspension (S) of the invention is stable against any change in viscosity, reversible or irreversible, which will render it unpourable or substantially modify its flow rate or speed e.g. by more than 50 % or even, preferably, by more than 20 %. The aqueous liquid component of the suspension (S) is water or a mixture of water and an organic solvent, in which the material comprising the solid particulate material is insoluble or soluble to an extent of no more than about 20 %, preferably no more than 10 %, more preferably no more than 5 %, most preferably no more than 1 %, by weight of the material, at 22°C at the concentrations at which it is to be present in the suspension. The liquid component is also one in which the suspension stabilizing agent (A) is soluble in the amounts employed, in particular at temperatures in the range 5 to 80°C, especially 10 to 50°C. Preferably, it is water or a mixture of water and no more than about 60 %, more preferably no more than 20 %, in particular no more than 10 % by weight of such mixture, of a suitable water-miscible organic liquid, such as acetone or an aliphatic C 2-4 alcohol, in particular isopropanol, ethylene glycol, propylene glycol, diethylene glycol or glycerol. More preferably, the liquid component consists of water alone. Advantageously, the sulphur dye is sufficiently free of inorganic sulphides and polysulphides that an aqueous mixture of said dye, upon being acidified to pH 3 with phosphoric acid at 22°C, will generate no more hydrogen sulphide than can produce a maximum of 1000 parts per million by weight of sulphide ion (S -- ) in aqueous alkali, based on the weight of the dye, preferably no more hydrogen sulphide than can produce a maximum of 500 ppm, more preferably a maximum of 250, most preferably of 100, especially of 50 ppm by weight of sulphide ion, based on the weight of the dye. Preferably, the sulphur dye is in the oxidized form. The term "sulphur dye", as used herein, is intended to include those dyes which are known as "Sulphur Dyes" or "Sulphurized Vat Dyes" from VENKATARAMAN "The Chemistry of Synthetic Dyes" Vol. II, Chapters XXXV and XXXVI (1952) and Vol. VII (1974) or defined in the Colour Index as "Sulphur Dyes" or as "Vat Dyes" with an indication of sulphurization in the method for their synthesis. Representative dyes are C.I. Sulphur Black 1, C.I. Sulphur Blues 7 and 13, C.I. Sulphur Reds 10 and 14, C.I. Sulphur Greens 2 and 16, C.I. Sulphur Browns 3, 37 and 96 and C.I. Vat Blue 43. Of highest interest are those dyes which are known as "Sulphur Dyes" from the aforementioned references, particularly C.I. Sulphur Black 1. The solid sulphur dye particles can be obtained from a thionation reaction mass which, in turn, can be obtained by a conventional thionation reaction. Such reactions are well known in the art for making sulphur dyes, as disclosed in the aforementioned references. The particular thionation reaction employed is not critical to this invention, but, rather, is dictated by the particular sulphur dye which it is desired to produce. Sulphur dyes which are characterized by the above-discussed degree of freedom from inorganic sulphides and polysulphides may be produced in various ways. Preferably, the thionation reaction mass is oxidized. This has the effect of causing dissolved sulphur dye which may be present in its (partially) reduced (i.e. leuco) form in the thionation reaction mass to precipitate by converting such dye to its water-insoluble oxidized form and converting inorganic sulphide and/or polysulphide salts present in said mass to thiosulphate salts. Oxidation may be effected using various known electron-accepting substances or sources of oxygen, e.g. sodium nitrite, sodium sulphite, a peroxide (e.g. H 2 O 2 or sodium peroxide), gaseous oxygen, air or oxygen blended with air. Strong oxidizing agents (such as peroxides) can cause depolymerization of some suspension stabilizers, such as xanthan gum. This can be avoided by either not using an excess of such an oxidizing agent or by separating any such excess from the dye before combining dye with such a suspension stabilizer or by not using such a strong oxidizing agent. Oxidation is preferably effected with milder oxidizing agents (e.g. with sodium nitrite, sodium sulphite or air) more preferably by aeration of an aqueous mixture of the crude thionation reaction product, e.g. by bubbling air into the aqueous mixture while it is being agitated. The rate of aeration is not critical, but is preferably such as to produce particles of the above-disclosed particle size or close enough to such particle size that extensive mechanical size reduction will not be required. It is well within the skill of the art to determine a suitable rate without undue experimentation. Satisfactory results may be obtained at an aeration rate of about 0.01 to 0.02 m 3 of air (in particular normal air) per minute per kilogram of total mass being aerated. During aeration the temperature of the reaction mixture is usually maintained in the range 50 to 90, preferably 60 to 85°C. The pH may range from 7 to 14, preferably 9 to 12. Oxidation is preferably continued until all of the sulphur dye has precipitated. A convenient method of ascertaining when this point has been reached is to carry out a spot test. According to this test a representative sample of the resulting slurry is spotted on P8 Crepe filter paper at 40°C. The higher the proportion of dye which has precipitated, the greater will be the amount of dye solids in the center of the spot and the less will be the amount of colour in the run out (spread) of the spot. When all of the dye has precipitated, the center of the spot will contain dye solids and the run out will be clear (preferably water clear). The aeration time can vary considerably, depending on the particular dye, the aeration rate and the amount of thionation reaction product being aerated. For some dyes, such as C.I. Sulphur Black 1, a significant proportion of the dye is already out of solution at the end of the thionation reaction and aeration times of about 0.5 to 4 hours may be sufficient to precipitate the remainder, while aeration times up to 48 hours may be required for other dyes which are more completely dissolved in the thionation reaction mixture. The aqueous slurry of water-insoluble sulphur dye particles prepared as described above may be used as such for producing a stable suspension (S) according to the invention. On the other hand, one may separate the solid dye from the original aqueous medium by conventional methods, e.g. filtration and optionally washing, and then make a new slurry by mixing the filter cake with a fresh quantity of water or a mixture of water and a water-miscible organic liquid as described above. This latter technique is preferred for C.I. Sulphur Black 1 and for any other sulphur dyes where it is desired to lower the salt content of the thionation product, i.e. where the initial aqueous slurry may have a higher salt content than is desired. It may also be used in instances where the initial slurry still contains some dissolved sulphur dye. Another method of obtaining the sulphur dye in a suitable state (preferably in particulate solid form) from the thionation reaction mixture is to add sufficient acid to said reaction mixture to cause dissolved dye to be converted to a water-insoluble form and to convert inorganic sulphides and polysulphides which may be present to hydrogen sulphide which can be separated from the dye via a suitable scrubbing apparatus. Acidification is preferably carried out to pH 5-6 using a strong acid, e.g. sulphuric or hydrochloric acid. The extent to which the dye has precipitated can be checked using the spot test described above. The acidification may be carried out until the desired amount of dissolved dye has been converted to a water-insoluble form and the inorganic sulphide content of the resulting mixture has been sufficiently lowered and the resulting mixture may directly be used in forming the final suspension or the acidified mixture may first be filtered and optionally washed, to separate the precipitated dye from any dye which has not precipitated and from inorganic sulphides and/or polysulphides which may remain dissolved in the mixture, and the resulting filter cake may then be mixed with a fresh supply of a suitable aqueous medium which will comprise the liquid component of the final suspension (S). If the sulphur dye is produced largely in solid particulate form by the thionation reaction, the reaction mixture can be filtered as is and the filter cake then mixed with fresh aqueous liquid and oxidized or acidified to pH 5 to 6, as necessary, to convert inorganic sulphide and/or polysulphide salts which may be present to hydrogen sulphide, which can be removed by known methods. The two methods (i.e. oxidation - in particular aeration - and acidification) may also be combined. Regardless of which of the foregoing methods of treating the thionation reaction mass is carried out, sufficient oxidation or acidification should be carried out, optionally with sufficient removal of still unconverted inorganic sulphides and/or inorganic polysulphides by filtration or decantation, that the solid particles of sulphur dye to be present in the final suspension are free from such sulphides and polysulphides to the extent described above. This can be determined by testing an aliquot portion of the solid dye-containing liquid by acidifying it e.g. to pH 3 with phosphoric acid at 22°C, reacting all of the hydrogen sulphide produced thereby in aqueous sodium hydroxide and measuring the sulphide ion concentration of the resulting solution by ion chromatography, as described more fully hereinafter. If the sulphide ion concentration is greater than 1000 ppm by weight, based on the weight of the dye, preferably if it is greater than 500 ppm, more preferably if it is greater than 250 or even 100 ppm, further oxidation and/or acidification is preferably carried out and/or more of the inorganic sulphide and/or polysulphide-containing liquid is preferably separated from the solid dye particles. The pH of the suspensions (S) may range in a broad scope. It is preferred that the pH of the sulphur dye suspensions (S) of the invention be in the weakly acidic to weakly basic range, in particular in the pH range of 6 to 9. In this pH-range the products are also less corrosive and less hazardous than in the stronger acidic or basic ranges. The pH can be adjusted, as necessary, by controlled addition of an effective amount of a suitable acid, such as acetic, phosphoric or, preferably, sulphuric acid to the sulphur dye-containing liquid. This may be done before or after the addition of a suspension stabilizing agent (A), but is preferably done beforehand. When the dye has been precipitated and the content of inorganic sulphides and polysulphides is suitably low, water may be removed from the aqueous dye mixture (e.g. if the mixture is not filtered) or added to the aqueous dye mixture (e.g. if the mixture has been filtered and optionally washed and is in the form of a filter cake, e.g. presscake), as necessary, to adjust its dyeing strength to a predetermined standard. This may be done before or after adding the suspension stabilizing agent (A). The suspension stabilizing agent (A) is characterized by its pseudoplastic behaviour in aqueous solution and consists mainly of a water-soluble polysaccharide gum, which has in particular the function of preventing a solid particulate sulphur dye, as described above, from settling out of suspension in an aqueous liquid, as described above, for a period of time as described above without irreversibly increasing the viscosity of the suspension to a point where it is not pourable. Preferably it is a polysaccharide gum which is effective for stabilizing the substantially uniform distribution, as described above, of the solid particulate sulphur dye(s) in the liquid without increasing the viscosity of the suspension, irreversibly or reversibly, to a point where it is not pourable. More preferably, it is a water-soluble polysaccharide gum which is effective for stabilizing the uniformity of the distribution of the solid sulphur dye particles in the aqueous liquid. The suspension stabilizing agent (A) may, if desired, also contain a minor amount of a further substance which is effective for preventing a solid particulate material, as described above, from settling out of suspension in an aqueous liquid, as described above, for a period of time as described above without irreversibly increasing the viscosity of the suspension to a point where it is not pourable. Preferably it is a substance other than a polysaccharide gum, which also contributes to the stabilizing of the substantially uniform distribution, as described above, of the solid particulate sulphur dye(s) in the liquid without increasing the viscosity of the suspension, irreversibly or reversibly, to a point where it is not pourable. More preferably, it is a water-soluble substance which is effective for stabilizing the uniformity of the distribution of the solid sulphur dye particles in the aqueous liquid. That (A) consists mainly of a water-soluble polysaccharide gum means that the water-soluble polysaccharide gum represents a major proportion, i.e. > 50 % by weight, preferably > 80 %, more preferably 100 % by weight of (A). Preferred suspension stabilizing agents (A) are those substances which are effective to stabilize the uniformity of a suspension of a solid particulate material in an aqueous liquid, as described above, when present in an amount less than 10 %, preferably less than 5 %, more preferably less than 1 % and most preferably less than 0.5 %, by weight of the suspension. More preferably, the suspension stabilizing properties of (A) are related to their ability to increase the viscosity of an aqueous liquid in which they are dissolved and, more particularly, the solutions of the polysaccharide gums (A) in water are of pseudoplastic rheology, or - more briefly - are pseudoplastic. By "pseudoplastic" is meant that the apparent viscosity of the solution progressively decreases as the solution is subjected to increased shear stress and in particular that the aqueous solution is substantially non-thixotropic. The viscosity almost instantaneously begins to return to its full magnitude as the shear stress is reduced to zero. The more preferred suspension stabilizing agents, such as xanthan gum, are also non-thixotropic under most conditions of use. By "non-thixotropic" is meant that an aqueous solution of such an agent does not decrease in viscosity under constant shear stress over a period of time. Another preferred typical characteristic of the stabilizing polysaccharide gums (A) is that their solutions in an aqueous liquid be viscoelastic. Preferably the polysaccharides (A) are heteropolysaccharides, Among the preferred stabilizing polysaccharide gums (A) are microbial polysaccharides, such as dextran, gellan gum, rhamsan gum, welan gum and xanthan gum, of which the latter two are more preferred. Xanthan gum is disclosed in the literature as having the following structural formula: wherein M is Na, K or 1/2Ca and n is approximately 2000. Xanthan gum is an exocellular heteropolysaccharide, which occurs naturally on plants belonging to the cabbage family and is produced commercially by aerobic submerged fermentation using the bacterium Xanthomonas campestris in a fermentation medium containing a carbohydrate (such as sugar) and nitrogen. A method for its production is disclosed in U.S. Patent 3,427,226, the disclosure of which is incorporated herein by reference. It is on the TSCA inventory of the United States Environmental Protection Agency (CAS # 11138-66-2). Additional information about this product, including the above formula, is contained in the booklet entitled "XANTHAN GUM Natural biogum for scientific water control", Fifth Edition (1994), distributed by Kelco (formerly a division of Merck & Co., Inc. and now a unit of Monsanto Company), the disclosure of which is incorporated herein by reference. A stable suspension (S) according to the invention can be prepared by mixing the suspension stabilizing agent (A), the solid particulate sulphur dye or dyes and the aqueous liquid. The solid particulate material and the aqueous liquid may be combined first and the stabilizing agent added thereto or the stabilizing agent and the aqueous liquid may be combined first and the solid particulate material added thereto or the stabilizing agent and the solid particulate material may be added to separate portions of the aqueous liquid and the two aqueous mixtures then combined. The suspension stabilizing agent (A) may be added to an aqueous slurry of water-insoluble or sparingly soluble sulphur dye particles which has been produced as described above or such a slurry or a filter cake of the sulphur dye particles may be added to a solution of the stabilizing agent The aforementioned components of the suspension may be combined over a wide range of temperatures, e.g. 10 to 70°C, with excellent results being obtainable at about room temperature. The suspension stabilizing agent (A) is preferably added to the aqueous slurry with agitation and at a rate such that the formation of lumps is avoided. This can be done by slowly introducing the stabilizing agent at the upper portion of a vortex created by stirring of the aqueous slurry. A particularly suitable method for mixing the stabilizing agent with the aqueous slurry comprises employing an apparatus of the type described on page 20 of the aforementioned booklet on xanthan gum. This apparatus comprises a mixing tank equipped with a stirrer and situated below a liquid supply line to which are attached a mixing eductor and a funnel. Before introducing the stabilizing agent (A), the mixing tank is filled with enough aqueous sulphur dye slurry to cover the mixing blades of the stirrer when a vortex is developed. The stirrer is then turned on and flow of aqueous liquid is then started from the supply line into the eductor at a pressure of 50 to 100 psi and dry stabilizing agent (A) is poured into the funnel, which is attached to the top of the eductor. A mixture of aqueous liquid and stabilizing agent (A) is thereby introduced via the eductor into the aqueous slurry which is already in the mixing tank. The resulting fluid is stirred continuously until the stabilizing agent (A) is dissolved and a suspension (S) is formed. The amount of suspension stabilizing agent (A) will vary, depending on the specific natures of the solid particulate sulphur dye, the aqueous liquid and the stabilizing agent, and also on the concentration of the suspension. It is well within the skill of the art to determine a suitable amount for each situation. As indicated above, it should be such an amount as will stabilize the uniformity of the suspension without permanently (i.e. irreversibly) increasing its viscosity to a point where it is not readily pourable at 25°C, preferably without rendering it even temporarlly (i.e. reversibly) unpoorable at 25°C. More preferably, it should be such an amount as will cause the suspension to have a viscosity within the limits specified above in centipoise. This amount is preferably less than 5 % (i.e. 0.01 to 5 %), e.g. 0.05 to 5 %, more preferably less than 1 %, by weight of the suspension, most preferably less than 0.5 %, e.g. 0.1 to 0.4 %. In order to ensure against the the development of molds or bacteria over an extended period, it is often advantageous to add an effective amount of a biocide or preservative. The particular compound used will depend on the particular microorganisms against the action of which the composition (S) is to be protected, the particular components of the suspension and the pH. Technical Bulletin DB-31 entitled "Preservatives for Kelco Polymers Used in Industrial Applications" from Kelco (1986), the disclosure of which is incorporated herein by reference, lists thirty-five representative preservatives which have been used successfully with xanthan gum and from among which a person skilled in the art can make an appropriate selection without undue experimentation. Among these are sodium dimethyldithiocarbamate (AQUATREAT DNM-30); sodium o-phenylphenate (DOWICIDE-A); formaldehyde; 6-aceto-2,4-m-dioxane (GIV-GUARD DXN); dichlorophene (GIVAUDAN G-4); 2-hydroxypropyl methanethiol-sulphonate (HPMTS-10); tributyl tin oxide (INTERCIDE 340A); 5-chloro-2-methyl-4-isothiazolin-3-one plus 2-methyl-4-isothiazolin-3-one (KATHON WT); benzyl bromoacetate (MERBAC 35); potassium trichlorophenate (METASOL CP); N-[-(1-nitroethyl) benzyl] ethylenediamine (METASOL J-26); methyl-p-hydroxybenzoate (METHYL PARASEPT); 2-bromo-2-nitropropane-1,3-diol (MYACIDE AS); hexachlorodimethylsulphone (STAUFFER N-1386); 1,2-dibromo-2,4-dicyanobutane (TEKTAMER 38); and 2-[(hydroxymethyl)amino] ethanol (TROYSAN-174). Advantageously there may be used about 0.05 to 0.40 %, particularly 0.15 to 0.35 %, and especially 0.25 to 0.35 %, based on the total weight of the stabilized suspension, of PROXEL GXL Liquid from ICI Americas, Specialty Chemicals Div., a preservative comprising 19 % 1,2-benzisothiazolin-3-one, 5-8 % sodium hydroxide, 40-60 % dipropylene glycol and 10-40 % water. Other preservatives, e.g. those listed above, may be employed in equivalent amounts. A suspension (S) according to the invention may also contain a dispersing agent, preferably an anionic dispersing agent. For these suspensions (S) which do contain a dispersing agent, amounts in the range 0.5 to 15 %, especially 1 to 5 %, by weight of the suspension, are preferred. A preferred anionic dispersing agent is a reaction product of lignin with disodium sulphite and formaldehyde (CAS # 05859-97-0) available as REAX 83A. For some dyes, such as C.I. Sulphur Blue 7, C.I. Vat Blue 43, C.I. Sulphur Red 10, C.I. Sulphur Brown 96 and particularly C.I. Sulphur Black 1, stable suspensions according to the invention may be produced which contain no dispersing agent. It is within the skill of the art to determine whether a suspension of a particular sulphur dye can benefit from the presence of such a dispersing agent. According to a further embodiment of the invention, there is provided a sulphur dye suspension (S) as described above which further contains a non-sulphide reducing agent (R) for the sulphur dye. By "non-sulphide reducing agent" is meant a reducing agent which is neither a sulphide nor a polysulphide. The particular non-sulphide reducing agent (R) may vary, depending on the particular sulphur dye with which it is employed. Essentially, it should be one which does not have a reducing effect on the sulphur dye under the conditions at which the suspension is kept prior to being used, but which is effective to reduce the same dye in an aqueous medium under conditions which are more favorable for such reduction. More particularly, the reducing agent (R) should be one which will not cause reduction of the dye at the temperature and pH at which it is kept prior to being used in a dyeing process, e.g. at a pH of 9 or less, especially in the range 5 to 8, more especially 6 to 7, and a temperature below 60°C, especially below 45°C, but which does cause reduction of the dye at a pH above 9.5, especially above 10, and a temperature above 60°C, especially above 70°C. A preferred reducing agent (R) is one which has the aforementioned properties and is a carbonyl compound, especially an aliphatic carbonyl compound which contains, in the alpha-position to the carbonyl group, an amino group which may be acetylated or, preferably, a hydroxy group or etherified hydroxy, e.g. methoxy, group. Of special interest are aliphatic compounds with 3 to 6 carbon atoms, such as 1-hydroxy acetone, 1,3-dihydroxy acetone, 3-hydroxy-2-butanone, carbohydrates with 3 to 6 carbon atoms and their derivatives in which one or more of the present hydroxy groups are etherified with methyl or replaced with an amino or acetylamino group, in particular reducing sugars, viz. aldo sugars and keto sugars and their oligomers and/or desoxy-derivatives and further their uronic acids. Preferred carbonyl compounds may be represented by the following formulae wherein one of R 1 and R 2 is hydrogen and the other is -OH, -OCH 3 or -NH 2 , R 3 is -CH 3 , -CH 2 OH, -CHO or -COOM 1 , M 1 is hydrogen or a cation and m is an integer from 1 to 5. M 1 is advantageously a colourless cation, preferably an alkali metal cation, more preferably sodium. If, in the formula (I), m is an integer from 2 to 5, the m symbols R 1 may have, independently, the same significance or different significances and the m symbols R 2 may have, independently, the same significance or different significances. In formula (I), one of R 1 and R 2 is hydrogen and the other preferably is hydroxy, R 3 preferably signifies -CH 2 OH or, if m signifies 2 to 5, also a carboxy group and m preferably signifies 3 or, more preferably, 4. If, in formula (II), m signifies 3, 4 or 5, the (m - 1) symbols R 1 may, independently, have the same significance or different significances and the (m 1) symbols R 2 may, independently, have the same significance or different significances. In formula (II) one of the two symbols R 1 and R 2 signifies hydrogen and the other preferably signifies hydroxy. If, in formula (II), m signifies 1, R 3 preferably signifies -CH 3 or -CH 2 OH; if, in formula (II), m signifies 2, 3, 4 or 5, R 3 preferably signifies -CH 2 OH. Of the compounds of formula (II), those in which m signifies 1, 3 or 4 are preferred. The monosaccharides of formula (I) and of formula (II) may also be in the pyranoside or furanoside form and the uronic acids of formula (I) and of formula (II) may also be in the lactone form. Representative reducing sugars are, in particular, aldopentoses, especially arabinose, ribose and xylose, and hexoses, especially glucose, fructose, mannose and galactose, and their desoxy, disdesoxy and aminodesoxy derivatives. As the reducing agent (R) there may also be employed oligosaccharides, in particular disaccharides, especially sucrose, lactose, maltose, melibiose and cellobiose, and tri-, tetra- and pentasaccharides, especially melezitose and raffinose, and syrups, such as corn syrup, malt syrup and molasses, which contain reducing sugars. The most preferred reducing agents (R) are those which reduce Fehling's solution, particularly reducing sugars, e.g. d-glucose. The reducing agent (R) may interact to a certain extent with the suspension stabilizing agent (A) as for its stabilizing effectiveness; if such an interaction leads to a lowered stabilizing effectiveness, it may be compensated by increasing correspondingly the amount of (A). Preferably, the reducing agent (R) is one which does not interact with the suspension stabilizing agent (A) in such a way as to excessively diminish its stabilizing effectiveness. By this is meant that the reducing agent (R) is one whose presence in the suspension (S) does not necessitate an increase of more than about 50 % in the amount of the stabilizing agent (A) required, on the basis of the weight ratio of stabilizing agent (A) to total undissolved solids in the suspension (S), to provide the same stability that the unincreased amount of the same stabilizing agent provides to an otherwise identical suspension which contains the same total weight of undissolved solids in the form of sulphur dye alone and does not contain a reducing agent (R). More preferably, the reducing agent (R) is one which does not diminish the stabilizing effectiveness of the suspension stabilizing agent (A) e.g. is one of the above aldosugars or oligosaccharides, It is within the ordinary skill of the art to make this optimization without undue experimentation by comparing samples with and without the respective reducing agent. The amount of the reducing agent (R) in the suspension (S) may vary, depending on the particular combination of reducing agent and sulphur dye, the amount of sulphur dye and the purpose for which the reducing agent is added. An amount of reducing agent (R) may be used which is effective to reduce all of the sulphur dye with which it is combined in the suspension (S) to the corresponding leuco sulphur dye, when such combination is subjected to conditions effective for such reduction, as discussed above, particularly in a dyebath. This option offers the advantage that the correct required amount of reducing agent is already present together with the dye, so that the ultimate user does not need to calculate, weigh and separately add the reducing agent. On the other hand, the reducing agent (R) may also be present in a lesser amount, which provides the advantage of lessening the amount of reducing agent which must be added separately to a dyebath by the ultimate user to effect reduction of all of the sulphur dye. Preferably, the amount of reducing agent (R) is in the range 1 to 60 %, more preferably 15 to 50 %, most preferably 20 to 40 %, by weight of the suspension (S). Preferably, the reducing agent (R) is completely dissolved in the suspension (S) at 25°C at the concentration at which it is present. However, a reducing agent (R) may be employed which is soluble under the conditions at which reduction is to be effected but is undissolved or only partially dissolved in the suspension (S) under the conditions at which the suspension is kept prior to being used in a dyeing process. In the latter situation the reducing agent (R) should be one whose undissolved amount can also be kept uniformly distributed throughout the suspension (S) by the suspension stabilizing agent (A) which, if desired, may be employed in an increased amount, provided that this does not cause the viscosity of the suspension (S) to vary from the parameters described above. The reducing agent (R) may be mixed with the sulphur dye before, during or after addition of the suspension stabilizing agent (A). More particularly, the reducing agent (R) may be added to a stabilizer-containing sulphur dye suspension produced as described above, or a mixture of the reducing agent (R) and the stabilizing agent (A) may be mixed with the sulphur dye, or the reducing agent (R) may be mixed with an aqueous slurry of sulphur dye particles produced as described above and the suspension stabilizing agent (A) then added to the resulting mixture. Conveniently, the reducing agent (R) is premixed with part of the water which is to constitute the aqueous phase of the suspension (S). It is believed that the use of the preferred reducing agents described above, particularly a reducing sugar, such as glucose, can provide the further advantage of decreasing the need which may exist in certain situations for the above-discussed addition of a biocide or preservative. For example, the use of a reducing sugar in an amount of about 30 %, by weight of the suspension, could lower the required amount of biocide or preservative by about 50 % or more, while amounts of about 50 % or more reducing sugar, by weight of the suspension, could, in some instances, eliminate the need for a biocide or preservative where such a compound might otherwise be necessary. It will be appreciated that results will vary, depending on the particular suspension stabilizing agent (A), the particular reducing agent (R) and the particular microorganisms against the action of which the suspension (S) is to be protected. The stable sulphur dye suspensions (S) of the invention are distinguished by an outstanding stability and flowability, even with small proportions of (A), such as ≤ 1 % of (A) referred to the total weight of (S). Further very low contents of inorganic sulphides and inorganic polysulphides are achievable by the above described production method, in particular with the aid of the below described analytical monitoring of sulphide ions. They meet the same criteria for sulphides as set forth above for the aqueous mixtures of solid sulphur dye particles from which they are produced, when tested in the same manner, as described more fully below. Suspensions (S) which produce less than 50 ppm sulphide ion, based on the weight of the dye, may be obtained as a result of the oxidation or acidification of the dye prior to addition of the suspension stabilizer, as discussed above, and/or as a result of further oxidation which may take place during or after the addition of the stabilizer (A). Suspensions (S) according to the invention are particularly well suited for use where a pourable, flowable, pumpable composition is desired, particularly such a composition wherein uniform distribution of the suspended solid particulate sulphur dye is desired. The sulphur dye suspensions (S) can be used to dye substrates dyeable with sulphur dyes, especially textile material, in particular cellulosic textile material such as cotton, using dyeing methods conventional per se for the dyeing of said substrates with sulphur dyes, in particular continuous or exhaust dyeing methods. More particularly, the dye is rendered substantive to the textile material by treatment with a suitable reducing agent in aqueous alkali and then oxidized back to its water-insoluble form once it has been uniformly applied to the textile material. Just as their very low sulphide content and the use of (A) - especially where (A) consists essentially only of a water-soluble polysaccharide gum of pseudoplastic rheology - make the suspensions (S) of the invention advantageous from the standpoint of the environment, the use of these suspensions in a dyeing process in which only non-sulphide reducing agents are employed in an aqueous alkaline medium is also advantageous for the environment. Such a process is disclosed in U.S. Patent 5,234,465, the disclosure of which is incorporated herein by reference. Another suitable method comprises carrying out the dyeing using only non-sulphide reducing agents in an atmosphere of decreased oxygen content, preferably one in which the oxygen content is no more than 12 % by volume, more preferably no more than 10 % by volume, most preferably no more than 7 % by volume. In addition to the non-sulphide reducing agents described above, other such reducing agents are thiourea dioxide, sodium hydrosulphite and thioglycolic acid. When a reducing sugar is used as the reducing agent, generally amounts in the range 1 to 10 grams per liter are employed at temperatures in the range 70 to 130°C and an alkaline pH. The decreased oxygen content of the atmosphere can be achieved by flushing the dyeing apparatus with an inert gas, such as nitrogen. The dyeing apparatus is preferably a jet dyeing machine or a winch-beck dyeing machine. A vacuum pump may be connected to the dyeing apparatus to remove oxygen and establish a constant flow of the inert gas from an inert gas supply. Another aspect of the process of the invention is a method for determining the potential for a sulphur dye composition to liberate hydrogen sulphide upon being acidified. More particularly, it is a method for monitoring the (poly)sulphide content during acidification and/or oxidation of the thionation mass by determining the amount of hydrogen sulphide which a sulphur dye composition comprising material which forms hydrogen sulphide upon reacting with an acid, especially a composition comprising inorganic sulphides and/or inorganic polysulphides, has the potential to release upon being acidified. The purpose of this method, which is essentially a test method, is to enable a person skilled in the art to predict what is the maximum amount of hydrogen sulphide which would be released from a composition, particularly a sulphur dye composition containing inorganic sulphide and/or polysulphide, at a given temperature, if it were acidified. According to this method, an aliquot quantity of the composition to be tested, in particular in the form of a solution or a dispersion or suspension of sulphur dye particles in a liquid at a preset temperature, is acidified to such an extent as to cause hydrogen sulphide gas to be generated, an inert gas is introduced into the liquid in an amount effective to remove the hydrogen sulphide gas from the liquid and carry it into an aqueous solution of a known concentration of an alkaline compound which is reactive with hydrogen sulphide to form a water-soluble sulphide salt, the reaction of the alkaline compound with the hydrogen sulphide takes place and the sulphide ion content of the resulting solution is measured. The composition to be tested may be any such thionation mass, which also contains other material and in which the inorganic sulphide and/or inorganic polysulphide is present as an essential component or as a contaminant. The "other material", itself, may also be capable of forming hydrogen sulphide upon acidification, but, preferably, this will not be the case. When the composition contains solid particles, any such particles in which sulphide or polysulphide could be trapped should preferably be no larger than they would be in normal usage, i.e. no larger than they would normally be at a time when they would (e.g. intentionally or accidently) be brought into contact with an acid in a situation other than during the test method of the invention, so that the test will give a reliable indication of how much hydrogen sulphide gas could be released as a result of acidification in such other situation. More preferably, any solid particles are in finely divided form. Most preferably, and particularly when the composition is a sulphur dye composition, the particle size is as specified above for sulphur dye suspensions which constitute another aspect of the invention. The method of the invention is especially suited for determining the amount of hydrogen sulphide that could potentially be released as a result of the acidification of a sulphur dye composition which contains inorganic sulphides and/or inorganic polysulphides. Such a composition can be one in which the sulphur dye is essentially in solid particulate form, as in the slurries and the stable, pourable suspensions described above, or it can be a liquid composition of a water-soluble (pre)reduced sulphur dye, i.e. leuco sulphur dye. By "inorganic sulphides and/or inorganic polysulphides" is meant water-soluble salts, especially alkali metal salts, such as sodium sulphide and sodium polysulphide. Henceforth, for the sake of brevity, the term "inorganic (poly)sulphide" will be used to refer to inorganic sulphides and/or inorganic polysulphides, unless it is intended to distinguish between the two. The following description will focus on inorganic (poly)sulphides, but it will be understood that similar considerations apply to situations in which the composition to be tested comprises other material which can generate hydrogen sulphide upon acidification. The liquid in which the acidification takes place may be any liquid in which the inorganic (poly)sulphide and the acid can react to form hydrogen sulphide. Preferably, it is an aqueous liquid, i.e. water or a mixture of water with an amount of a water-miscible liquid which will not interfere with the reaction, e.g. as listed above. More preferably, it is water alone. The amount of the liquid in which the acidification takes place should preferably be such that all of the accessible inorganic (poly)sulphide present in the quantity of the composition being tested can become dissolved therein prior to the beginning of the acidification reaction. This is not essential, since dissolution of additional inorganic (poly)sulphide in the liquid can take place as that which is already in solution is converted to hydrogen sulphide and removed from the liquid. More preferably, the amount of liquid is sufficient to also dissolve any other component of the composition which is soluble in said liquid. For sulphur dye compositions it has been found that dependable results are obtained when the amount of liquid is such that the concentration of the dye is in the range 0.1 to 2.0 %. Preferably, the liquid contains an alkali to provide a buffer for better pH control during the acidification. Addition of enough sodium hydroxide to produce a 0.05N NaOH solution has been found to be satisfactory. The temperature of the liquid at the commencement of the acidification should be the temperature at which it is desired to know how much hydrogen sulphide could be released upon acidification of another quantity of the same composition. The temperature may be any temperature at which it is felt that another quantity of the composition is likely to be when it is acidified, e.g. during storage, handling or actual use. The method of the invention may be carried out at various temperatures, preferably in the range of 15 to 65°C. Temperatures in the range of average room temperatures, e.g. 20 to 25°C, are most significant, because they are the temperatures at which an accidental acidification is most likely to occur. Any acid can be employed which is capable of converting the accessible inorganic sulphide and inorganic polysulphide present to hydrogen sulphide. Preferably, an acid is employed which is strong enough to maintain the acidification reaction mixture at the desired pH discussed below. In those situations where it is known that no inorganic polysulphide is present, a wider range of acids, including acetic acid, hydrochloric acid, methanesulphonic acid, sulphuric acid and phosphoric acid can be employed. Otherwise, it is preferred to use a stronger acid than acetic acid, such as methanesulphonic acid, hydrochloric acid, sulphuric acid or especially phosphoric acid, which, while strong enough to decompose inorganic polysulphide, in the form of its partial alkali metal salts makes pH control easier. The amount of acid employed should be that amount which will convert the greatest amount of inorganic (poly)sulphide to recoverable hydrogen sulphide. Care should be taken to avoid such overacidification as might cause protonation of the hydrogen sulphide, thereby rendering it more soluble in water and more difficult to recover. Preferably, an amount of acid used is such as will cause the liquid medium to have a pH in the range 2.9 to 3.7, more preferably, 3.0 to 3.5 during the acidification. Preferably, the rate of acid addition is controlled to keep the pH from dropping below 2.9. Any inert gas capable of acting as a carrier for hydrogen sulphide gas may be used for the method of the invention. Helium and nitrogen come preferably into consideration, with the latter being more preferred. Preferably, the inert gas contains less than 20 parts per million (ppm) by volume of oxygen, more preferably less than 10 ppm, most preferably less than 5 ppm, especially less than 1 ppm. This may be accomplished by pretreating the gas in a commercially available oxygen removal device, such as a SUPELCO oxygen trap, or by bubbling it through an aqueous solution of oxalic acid. One may start with a commercially available gas which already has a low oxygen content (e.g. about 20 ppm), such as ultra high purity nitrogen, and pretreat it as discussed above. The rate of inert gas feed is preferably such that a positive regular flow is established without splashing. More preferably, it is in the range 750 to 850 milliliters per minute, e.g. in test sample of 235 ml. The flow rate can be monitored with a conventional flow meter. Preferably, the entire system is sparged with the pretreated inert gas prior to commencing the acidification. The inert gas is allowed to flow through the system until the maximum amount of the hydrogen sulphide has been swept from the vessel in which the acidification has been carried out. Usually it suffices to continue the flow for about 30 minutes after the acidification reaction has been completed. The aqueous alkaline solution into which the hydrogen sulphide gas is swept by the inert gas may be a solution of any base which can react with the hydrogen sulphide to form a water-soluble sulphide salt without introducing any ions which would interfere with the subsequent analysis for sulphide ion concentration. Preferably, the base is an alkali metal hydroxide such as potassium hydroxide or, more preferably, sodium hydroxide. This solution must be of a known volume and contain at least a stoichiometric amount of the base with respect to the amount of hydrogen sulphide. The atmosphere above the alkaline solution can be checked for the presence of hydrogen sulphide gas using lead acetate paper. If the test is positive, more base should be added to the solution or a second solution of the base, also having a known volume, should be used to take up any excess hydrogen sulphide which is not captured in the first solution and the entire test method should be repeated with a fresh quantity of the composition to be tested. Preferably the concentration of sodium hydroxide in the first solution is ≥ 2 % by weight; this concentration will usually suffice to capture all of the hydrogen sulphide from the sulphur dye compositions described above. When the hydrogen sulphide that can be captured as described above has been taken up in the aqueous alkali, the resulting solution is analyzed for its sulphide ion content using methods known in the art, such as titration with excess iodine followed by back titration with sodium thiosulphate or, more preferably, ion chromatography. The above method allows to monitor the (poly)sulphide content of a thionation mass before it is processed to (S). The invention thus provides also a process for the production of a suspension (S) as defined above, in which during the acidification and/or oxidation reaction the (poly)sulphide content is monitored by means of the above analytical method. In this way the employed amount of acid or/and oxidizing agent may be optimized to a minimum, so that an undesired overacidification and/or overoxidation may be avoided, while no undesired amounts of (poly)sulphide or H 2 S remain entrapped in (S) or respectively in (A). The following examples illustrate the invention. Unless otherwise indicated, all parts and percentages are by weight and all temperatures are in degrees Celsius. "C.I." stands for "Colour Index". EXAMPLE 1 The reaction mixture obtained by a conventional thionation reaction for producing C.I. Sulphur Black 1 dye is aerated at 65-75°C and pH 9.5 until acidification of a sample of the resulting slurry to pH 3 with phosphoric acid at 22°C generates only enough hydrogen sulphide to produce, upon dissolution in an excess of aqueous sodium hydroxide, less than 50 ppm of sulphide ion, based on the weight of the dye. The rate of aeration is about 15 m 3 per minute per kilogram of thionation reaction mixture. The slurry is filtered and 1918 grams of the resulting presscake, having a solids content of 65.7 %, is mixed with 1082 grams of water with stirring. To this mixture is added 11.3 grams of 98 % sulphuric acid, whereby the pH is lowered from 8.9 to 7.5, and then 6 grams of xanthan gum (KELZAN from Kelco, a unit of Monsanto Company) are added slowly at room temperature to the upper portion of the vortex created by rapid stirring of the mixture. To the resulting suspension are added 750 grams of water to adjust the dyeing strength and an additional 1.5 grams of xanthan gum. The resulting product has a viscosity of 800 cP and, when acidified to pH 3 with phosphoric acid at 22°C, generates less hydrogen sulphide than can produce 50 ppm of sulphide ion in aqueous sodium hydroxide, as measured by ion chromatography. EXAMPLE 2 To 300 grams of crude aqueous thionation reaction mixture for the sulphurized vat dye C.I. Vat Blue 43, produced in conventional manner, is added 300 grams of water and 15 grams of sodium nitrite. The resulting mixture is heated to reflux for about two hours until a spot test shows a clear runout. The pH of the resulting slurry is adjusted to 7.5 with sulphuric acid and it is diluted with an additional 600 grams of water to adjust the dyeing strength. To the diluted product is added, at ambient temperature and with stirring, 0.37 % KELZAN xanthan gum, based on the total weight. Analysis of the resulting suspension as described above, shows less than 10 ppm of sulphide ion based on the weight of the dye. It is stable with respect to the uniform distribution of the dye particles for more than two months. EXAMPLE 3 Into 6475 grams of water are stirred 8725 grams of a C.I. Sulphur Black 1 dye presscake produced as in Example 1 but having a solids content of 66.2 %. After stirring for 10 minutes the pH is adjusted to 7.25 with 130.5 grams of 98 % sulphuric acid and then 33.4 grams of KELZAN xanthan gum are added with rapid stirring at room temperature over a period of 10 minutes. Stirring is continued for about one hour and then 2255 grams of water are added with further stirring to adjust the dye strength. The resulting suspension has a viscosity of 482 cP and produces less than 50 ppm of sulphide ion, based on the weight of the dye, when tested as described above. For protection against degradation due to microorganisms, a preservative may be added, as described above. EXAMPLE 4 Twelve grams of the product of Example 1 and 205 grams of water are mixed in a beaker. To this mixture are added 19 grams of 50 % aqueous sodium hydroxide, followed by 20 ml of a 53 % solution of glucose in water and then 2.0 ml of mixed mono- and diphosphate esters of 2-ethylhexanol. This mixture is poured into the trough of a pad dyeing apparatus, heated to 38 to 54°C and stirred for 10 minutes. A length of cotton textile material is padded with the heated dyeing liquor and then steamed for at least 60 seconds in a Greenville/Aztec steamer. The dyed material is immediately washed in water for at least 30 seconds and then oxidized for at least 60 seconds at 60°C in a 2 % aqueous solution of a 50:50 mixture of sodium vanadate-catalyzed sodium bromate (DYETONE) and glacial acetic acid, which solution also contains an effective amount of a sodium salt of an acrylic acid homopolymer (SANDOPURE RSK) as an anti-redeposition aid. It is then rinsed in warm running water for at least 30 seconds and dried on a flat bed press. EXAMPLE 5 A jet dyeing machine is loaded with a cotton textile material to be dyed and enough water to give a liquor:goods ratio of about 10:1 and the contents are heated to 49°C. To the heated bath are added 0.5 g/l of SULPHALOX 100 (aqueous alkaline solution of ethylenediaminetetraacetic acid), 0.5 g/l of SODYECO Defoamer DSV (proprietary mixture of petroleum derivatives), 25 g/l of sodium sulphate, 5 g/l of soda ash, 5 g/l of caustic soda (50 %) and 5 g/l of a mixture of 94.5 % glucose, 5 % reductive dispersing agent and 0.5 % dedusting oil. To the resulting mixture is added gradually over 5 minutes an amount of the product of Example sufficient to provide 16 % dye based on the weight of the textile material and the resulting mixture is heated to 71°C at a rate of 2.75°C/min. while the atmosphere above the liquor in the apparatus is being purged with nitrogen. The resulting dyebath is then heated to 93°C at a rate of 2.75°C/min. and held at that temperature for 45 minutes. The dyebath is then cooled to 71°C and the contents are overflow rinsed with unheated water until the bath water is clear. The liquor:goods ratio is readjusted to 10:1 and the bath is heated to 49°C while the interior of the apparatus is aerated. Two g/l of acetic acid (56 %) and 2 g/l of DYETONE (aqueous 12 % sodium bromate/1 % sodium vanadate solution) are added and the resulting oxidation bath is heated to 65°C and held at that temperature for 10 minutes. The bath is then overflow rinsed and drained and the apparatus is refilled with water to which 1 g/l of soda ash is added. The dyed textile material is then scoured in the resulting liquor for 10 minutes at 88°C. The bath is then cooled to 71°C and the dyed material is removed therefrom. EXAMPLE 6 Into a solution prepared by mixing 176 g of water and 150 g of d-glucose is stirred 174 g of C.I. Sulphur Black 1 presscake prepared as in Example 1 but containing about 70 %, by weight, solids and 30 % water. The pH of the resulting slurry is adjusted to 7-7.5 with 1.1 g of 98 % sulphuric acid and then 2.0 g of KELZAN xanthan gum are added thereto. The resulting slurry has a viscosity of 560 cP as measured with a Brookfield rotational viscometer with a # 3 spindle at 60 rpm. EXAMPLE 7 a) Generation of Hydrogen Sulphide and Isolation of Sulphide Ions A 250 ml three-neck flask with 24/40 joints containing a magnetic stirring bar is clamped above a magnetic stirrer. A pH electrode, which is attached to a calibrated pH meter, is placed (with an adapter) in the center neck and a 60 ml graduated addition funnel with pressure equalizing is placed in one side neck and a sparging tube with a gas inlet/outlet adapter is placed in the other side neck. The outlet from a nitrogen gas regulator attached to a source of ultra high purity nitrogen is connected to a Kings Instrument Inc. Flow Meter (470 to 940 ml/min) with 1/4 inch Tygon tubing and from there to a 250 ml gas washing bottle with fritted glass diffuser to be used as an oxygen trap. Tygon tubing from the oxygen trap is split with a "T" connector, with one branch being connected to the sparging tube of the three-neck flask and the other branch, which is equipped with a clamp for cutting off nitrogen flow, being connected to the graduated addition funnel. The outlet from the adapter with the sparging tube on the three-neck flask is connected via Tygon tubing to the sparging tube of another 250 ml gas washing bottle with fritted glass diffuser, which serves as the hydrogen sulphide trap, and the outlet from said hydrogen sulphide trap is connected to a vent. All connections are made tight with suitable clamps, such as Keck clamps at all 24/40 joints, and strips of moistened lead acetate paper are placed at all joints to detect any hydrogen sulphide leaks. One gram of oxalic acid is dissolved with thorough mixing in 100 grams of deionized water and 100 ml of this solution is placed in the oxygen trap. A small magnetic stirring bar, 50.0 ml of 4 % aqueous sodium hydroxide, which has been produced by mixing 40 grams of sodium hydroxide pellets with 960 grams of deionized water and sparging for 30 minutes with nitrogen, and 50.0 ml deionized water are placed in the bottle serving as the hydrogen sulphide trap, the diffuser tube top is attached, and the bottle is placed on a magnetic stirrer. One half gram (± 0.1 mg) of the product of Example 3 is placed in the three-neck flask. A mixture of 5 ml 4 % aqueous sodium hydroxide and 170 ml nitrogen-sparged deionized water is introduced into the three-neck flask. Sixty ml of an 8.5 % phosphoric acid solution prepared by mixing 100 grams of 85 % phosphoric acid with 900 ml deionized water are added to the graduated addition funnel in the side neck of the three-neck flask and the funnel is then flushed for about 10 seconds with the pretreated nitrogen by opening the clamp of the Tygon tubing connected thereto. The clamp is then tightened, so that the nitrogen with flow only through the sparging tube in the other side neck of the three-neck flask. The magnetic stirrers are activated and nitrogen flow is commenced at a rate such that there is no splashing of the contents of the vessels comprising the apparatus as described above, preferably at about 770 ml per minute. The dropwise addition of the phosphoric acid solution is then commenced at a rate of about 10 ml per minute. When the pH of the acidification reaction mixture has dropped to about 4, the addition is continued at a slower rate until the pH is in the range 2.97 to 3.03. At this point acid addition is discontinued and is resumed only as necessary to return the pH to said range from a higher pH which develops as the acid is reacted. When the pH stabilizes in the range 2.97 to 3.03, acid addition is terminated, but nitrogen flow is continued for an additional 30 minutes, by which time the reaction is complete and all of the hydrogen sulphide generated should have been swept into the bottle serving as the hydrogen sulphide trap and containing the 100 ml of sodium hydroxide solution. The contents of the hydrogen sulphide trap are then subjected to analysis by ion chromatography to determine the sulphide ion content. b) Determination of Sulphide Ion Concentration by Ion Chromatography Instrumentation : Dionex 4500i Chromatograph equipped with a gradient pump, pulsed amperometric detector and an AI450 data station. Instrumentation parameters : Column Dionex IonPac HPIC -AS7 column together with a AG7 guard column; Eluant 100 % 0.5 M sodium acetate, 0.1 M sodium hydroxide (CO 2 free), 0.5 % (v/v) ethylene diamine (99 %) in helium-purged deionized water; Flow rate 1.0 ml per minute; Detector Pulsed Amperometric Detector with silver electrode at zero voltage; Injection loop 50 µl; Temperature ambient. Sample preparation : In a 100 ml volumetric flask 0.01 gram (± 0.01 mg) of the sulphide ion-containing solution from part (a) of this Example is diluted to 10 ml with 0.1 N sodium hydroxide solution prepared by dissolving 8.0 grams of CO 2 free 50 % (w/w) NaOH in 1 liter of helium-purged deionized water. Standard preparation : In a volumetric flask 7.5 mg (± 0.01 mg) of sodium sulphide nonahydrate (98 % A.C.S. grade) is diluted to 100 ml with 1 N helium-purged sodium hydroxide and 0.5 ml of this solution is diluted to 10 ml with 0.1 N sodium hydroxide prepared as described above. Three portions of this standard are analyzed to obtain an average response factor before analyzing the sample. The ion chromatography system is purged with helium for at least one hour to exclude the presence of carbon dioxide. Ion chromatography of the sample is carried out and the amount of sulphide ion is calculated according to the equation: Concentration of S -- (ppm) = Concentration of Sulphide Ion in Sample* x 1,000,000 Concentration of Sample** *weight of sulphide ion in the 100 ml of NaOH solution **weight of dye suspension (i.e. 0.5 g) in the 100 ml of NaOH solution It is determined that the suspension produced according to Example 3 generates an amount of hydrogen sulphide which produces less than 10 ppm sulphide ion according to this test method.

Claims: A pourable suspension (S) of a sulphur dye or mixture of sulphur dyes in an aqueous liquid that contains a suspension stabilizing agent (A), aqueous solutions of which display a pseudoplastic behaviour and which suspension stabilizing agent (A) consists to > 50 % by weight of a water soluble polysaccharide gum, in a concentration of 0.01 to 10 % by weight referred to the weight of the suspension. A suspension (S) according to Claim 1, wherein (A) is present in an amount effective to maintain a uniform distribution of the solid particulate material in the suspension for a period of at least 24 hours. A suspension (S) according to claim 1 wherein the the distribution of the solid particles is uniform for at least two months. A suspension (S) according to claim 1 which has a viscosity no higher than 5000 cP. A suspension (S) according to claim 3 which has a viscosity in the range 300 to 4000 cP. A suspension (S) according to claim 4 or 5 which has a viscosity in the range 350 to 2000 cP. A suspension (S) according to any one of claims 1 to 6 which is stable for at least two months against an irreversible change in viscosity of more than 50 % measured in centipoise. A suspension (S) according to claim 1 wherein the concentration of the suspension stabilizing agent (A) is less than 5 %, by weight of the suspension. A suspension (S) according to claim 7 wherein the concentration of suspension stabilizing agent (A) is less than I %, by weight A suspension (S) according to claim 1 wherein the suspension stabilizing agent (A) is substantially non-thixotropic. A suspension (S) according to any one of claims 1 to 10, wherein the polysaccharide (A) is a heteropolysaccharide. A suspension (S) according to any one of claims 1 to 11, wherein the suspension stabilizing agent (A) is a microbial polysaccharide gum. A suspension (S) according to claim 12 wherein the suspension stabilizing agent (A) is welan gum or xanthan gum. A suspension (S) according to any one of claims 1 to 13, wherein the sulphur dye is C.I. Sulphur Black 1. A suspension (S) according to any one of claims 1 to 14 which, upon being acidified to pH 3 with phosphoric acid at 22°C, will generate no more hydrogen sulphide than can react with aqueous sodium hydroxide to form 500 parts per million of sulphide ion S -- based on the weight of the sulphur dye. A suspension (S) according to claim 15 which, upon being acidified to pH 3 with phosphoric acid at 22°C, will generate no more hydrogen sulphide than can react with aqueous sodium hydroxide to form 50 parts per million of sulphide ion S -- based on the weight of the sulphur dye. A suspension (S) according to any one of claims 1 to 16 Which further comprises a non-sulphide reducing agent (R). A suspension (S) according to any one of claims 1 to 17, further containing a dispersing agent. A suspension (S) according to claim 14 which contains no dispersing agent. A process for the production of a suspension (S) according to any one of claims 1 to 19, which comprises combining an aqueous liquid, a solid particulate sulphur dye or mixture of sulphur dyes which is insoluble or sparingly soluble in the liquid and an effective amount of a suspension stabilizing agent (A) which is soluble in the aqueous liquid and optionally a non-sulphide reducing agent (R) and/or a dispersing agent. A process according to claim 20, wherein the solid particulate sulphur dye or mixture of sulphur dyes is in the form of a thionation mass, which has optionally been subjected to a mechanical particle size reduction and which has optionally been acidified and/or oxidized and/or filtered and optionally washed. A process according to claim 21, wherein the solid particulate sulphur dye or mixture of sulphur dyes is in the form of a thionation mass, which has not been subjected to a mechanical particle size reduction. A process according to any one of claims 20 to 22, wherein the thionation mass is oxidized and/or acidified in order to eliminate disturbing amounts of (poly)sulphide ions. A process according to any one of claims 20 to 23, wherein the sulphur dye is sufficiently free from inorganic sulphides and inorganic polysulphides that an aqueous slurry thereof, when acidified to pH 3 with phosphoric acid at 22°C, will generate no more hydrogen sulphide than can produce, upon reaction with aqueous sodium hydroxide, 100 parts per million of sulphide ion, based on the weight of the dye. A process according to claim 23 for the production of a suspension (S) as defined in any one of claims 1 to 19, in which during the acidification and/or oxidation of the thionation mass the (poly)sulphide content is monitored by measuring the capacity of the mass to generate hydrogen sulphide upon being acidified at a given temperature, which process comprises acidifying an aqueous liquid containing a sample of said mass at said given temperature to a pH in the range 2.9 to 3.7 with an acid which is strong enough to convert substantially all of the accessible inorganic sulphides and inorganic polysulphides present in the sample to hydrogen sulphide, sweeping the acidification reaction mixture with an amount of an inert gas effective to remove substantially all of the hydrogen sulphide therefrom, collecting substantially all of the hydrogen sulphide from said acidification reaction mixture in an aqueous alkaline solution and measuring the amount of sulphide ion in said alkaline solution. A suspension according to any one of claims 1 to 19 which further comprises a biocide or preservative. A process for the dyeing of a substrate dyeable with sulphur dyes, wherein the sulphur dye is employed in the form of a suspension according to any one of claims 1 to 19 or 26. A process according to claim 27 for the dyeing of cellulosic textile material.

Inventors: DANHIEUX GUIDO J, HO CATHERINE S, MERKERT JON W, MYERS DWAYNE R, NISHIOKA MASATO, PERCY LIVIUS T, SZETO MAY N, TRAWALTER MICHEL M, WANG YI LAI, DANHIEUX, GUIDO J., HO, CATHERINE S., MERKERT, JON W., MYERS, DWAYNE R., NISHIOKA, MASATO, PERCY, LIVIUS T., SZETO, MAY N., TRAWALTER, MICHEL M., WANG, YI LAI
Applicants: CLARIANT FINANCE BVI LTD, CLARIANT FINANCE (BVI) LIMITED
Application year: 1996
Main classification: C09B67
IPC codes: C09B67