Molten sulphur

When sulphur is melted viscosity changes occur as the temperature is raised. These changes are due to the formation of long-chain polymers (in very pure sulphur, chains containing about 100 (X)0 atoms may be formed). The polymeric nature of molten sulphur can be recognised if molten sulphur is poured in a thin stream into cold water, when a plastic rubbery mass known as plastic sulphur is obtained. This is only slightly soluble in carbon disulphide, but on standing it loses its plasticity and reverts to the soluble rhombic form. If certain substances, for example iodine or oxides of arsenic, are incorporated into the plastic sulphur, the rubbery character can be preserved. 

Sulphur can be reduced directly to hydrogen sulphide by passing hydrogen through molten sulphur the reversible reaction H2 -I-S H2S occurs. In the laboratory the gas is most conveniently prepared by the action of an acid on a metal sulphide, iron(II) and dilute hydrochloric acid commonly being used ... 

Other chemicals Copper and copper alloys are unsuitable for handling hydrogen peroxide " or molten sulphur . Hydrogen sulphide accelerates corrosion of most copper-base materials. In its presence brasses high in zinc are usually found to behave better than other copper alloys. ... 

Boron reacts with more difficulty. When it is heated to 600°C with molten sulphur it becomes incandescent. 

Freeport Sulphur Company. "Solid Versus Molten Sulphur— Handling, Storage and Processing" Freeport Minerals, Inc. ... 

Molten sulphur can be emulsified into hot liquid AC and this emulsion used in place of regular AC as the binder in the paving mix ). Such a system provides a number of potential advantages ... 

Monoclinic Sulphur. Fill a small porcelain or chamotte crucible with sulphur, and slowly melt it. The melt should occupy at least half of the crucible. Cool the latter until a crystalline crust forms. When the crust almost covers the melt, rapidly pour out the remaining molten sulphur into a beaker of water. Examine the crystals formed with a magnifying glass and draw them. 

Pass a stream of dry chlorine through the molten sulphur during two hours at a rate such that virtually the entire chlorine is absorbed by the molten sulphur. After this, cool the reaction mixture to room... 

The most important deposits of sulphur in the world arc those of Louisiana and Texas, U.S.A., where //. Franck s method of extraction is followed.2 This obviates the formation of sulphur dioxide and at the same time yields a product of such a degree of purity (in some wells as high as 99-9 per cent.) as to be suitable in most cases for direct use. A boring is made in the earth down to the sulphur stratum so that a continuous pipe can pass thence to the surface the pipe consists of throe concentric tubes (see lig. 1). Superheated water, c.g. at 150" is forced down the annular spaces A, A, between the outer tubes, in order to melt the sulphur in the neighbourhood of the cud of the boring. A blast of heated air down the inmost tube, II, then causes the molten sulphur to be carried up between the two inner tubes to the surface, where it is collected.3... 

A full interpretation of the results of the investigations is rendered difficult by the complications introduced by external influences such as those due to certain impurities which it is almost impossible to exclude. It is clearly recognisable, however, that the abnormal behaviour is due mainly to the existence of two distinct modifications of molten sulphur, side by side these are commonly distinguished as A-sulphur and -sulphur, and the equilibrium between them at any temperature may be expressed... 

Tlie position of the equilibrium varies with the temperature, the proportion of/u-sulphur being less at lower temperatures near the melting-point the proportion of //.-sulphur approximates to 4. per cent., and the maximum at higher temperatures generally does not much exceed 40 per cent. It was at one time believed that rapid cooling could effect the separation of molten sulphur into two distinct layers,2 but. careful examination has shown the lack of homogeneity to be due only to temperature differences caused by the viscosity and the poor thermal conductivity of the liquid the two modifications are completely miscible in the liquid state.3... 

By rapidly cooling the fluid mixture it is possible to minimise the readjustment of the equilibrium and to attain a solid condition in which tire original proportions of the mixture are approximately retained in the solid state tire allotropic change is so very slow as to allow careful and fairly prolonged examination of the mixture. It is then found that, the normal mobile liquid constituent (S ) has given rise to crystalline sulphur, soluble in carbon disulphide, whereas the dark-coloured viscous constituent (S ) has produced an amorphous solid, insoluble in this solvent4 (see also p. 10). A rough analysis of molten sulphur in... 

If sulphur is heated to 180° C. and then cooled, it becomes more soluble in carbon disulphide also a saturated solution of sulphur chloride in toluene at the ordinary temperature will, after being heated to the neighbourhood of 180° C. and cooled again, dissolve yet more sulphur. These observations led to the discovery of a third modification in molten sulphur. This form of sulphur, distinguished as n-sulplmr, is formed to some extent when ordinary sulphur is heated to 125° C. The optimum temperature for its formation is near 180° C., when the liquid contains approximately 6-5 per cent, of S with 20-5 per cent, of... 

On account of the variability of the proportions of A-sulphur, p,-sulphur and 77-sulphur in the liquid, the solidifying-point of molten sulphur is not constant, but may range from 114° to 117° C. or even more widely. The freezing-point of pure A-sulphur can be determined by calculation, the result, 119-25° C., almost coinciding with the temperature... 

In spite of these allotropic changes, molten sulphur under certain conditions can be successfully used as a cryoscopic solvent. Soon after having been melted, the freezing-point of the liquid may be as high as 119° ., but after keeping for some hours at a temperature just above... 

As is to be expected the equilibrium between the two above-mentioned forms of liquid sulphur affects other properties in addition to the colour and the viscosity. Thus, the electrical conductivity 5 and the surface tension6 of molten sulphur exhibit abnormal variation with alteration in temperature also the solubility curves for A-sulphur and p-sulphur in high-boiling solvents such as triphenylmethane are quite distinct, the solubility of the former increasing and that of the latter decreasing with rise of temperature the respective coefficients of expansion are also quite independent.7 The reactivities of the two forms towards rubber arc practically equal.8... 

More or less drastic modifications 9 of the above view of the nature of molten sulphur have been suggested, but none appears to be supported by sufficient evidence to deserve acceptance. 

Allotropy in the Solid State.—When molten sulphur is allowed to solidify, the modifications present give rise to corresponding solid forms, the liquid A-sulphur producing crystalline sulphur (rhombic, monoclinic or nacreous, according to the conditions), whilst the deep... 

Crystallisation of sulphur at the ordinary temperature from solution, e.g. from carbon disulphide, yields octahedral crystals which differ from the crystals obtained by the solidification of molten sulphur in that the proportion of y- and 77-sulphur, present in solid solution, is less. Octahedral crystals of sulphur may be prepared at the ordinary temperature also by the gradual atmospheric oxidation of a. solution of... 

Sulphur II. Prismatic, Monoclinic or ft-Sulphur.—This is a variety of monosymmetric crystalline sulphur obtained ordinarily when sulphur crystallises at a temperature near the melting-point from the molten condition. The usual procedure in order to obtain distinct crystals is to allow molten sulphur to cool undisturbed until approximately one-half has crystallised, and then, after breaking the crust, to pour away the remaining liquid.8 Crystallisation by the rapid cooling of hot solutions (see the following) sometimes also yields this modification, although more frequently the variety obtained is S. III.9... 

When prepared from molten sulphur this variety frequently possesses a pale amber colour, which is probably due in part to 7T-sulphur present as impurity, since crystals obtained from solution are of a much paler colour. The density,2 1-957 at 25° C., is lower than that of the octahedral form, whilst the specific heat is higher. As is the case for sulphur I., the presence of variable proportions of rt- and y-sulphur in the crystals affects the constancy of the melting-point, so that whereas as usually prepared the melting-point is 114-5° C., the melting-point of pure monoclinic sulphur should be 119-2° C. (see p. 21). 

These relationships are represented in an exaggerated manner in fig. 2. The lines AO, BC and OD represent the vapour pressures of sulphur I., sulphur II. and molten sulphur, respectively OE and CF show the effect of pressure change on the melting-points of the two crystalline forms, whilst the effect of pressure on the transition temperature is indicated by BF. 

As has already been mentioned, the behaviour of molten sulphur on crystallisation is of a complex nature and dependent largely on the previous temperatures, the rate of cooling and the temperature at which crystallisation begins.6 Occasionally crystallisation occurs in a rhythmic manner, giving rise to an annular appearance in the structure of the solid mass.7 The crystallisation of undercooled molten sulphur is stated... 

The remarkable variations in the viscosity of molten sulphur have already been mentioned. Definite measurements have been made at a series of temperatures by the method of rotating cylinders,5 and it, has been found that exposure of the liquid to air, especially below 160° C., has a marked effect on the viscosity from 160° C. onwards. The viscosity of purified (twice distilled but not gas-free) sulphur lias a value at 123° C. of 0 1094 C.G.S. units this falls to a minimum of 0 0709 at 150° C., rises gradually up to about 159° then rapidly increases above this temperature an exact transition point is not observed, however. The maximum for purified unexposed (gas-frcc) sulphur occurs at about 200° C. and has a value of 215 C.G.S. units. For purified (not gas-free) sulphur after prolonged exposure to the air, the maximum occurs at about 190° C, and may have a value as high as 800 C.G.S. units. Such high viscosity appears to be due to impurities, the chief being sulphuric acid, resulting from exposure to the air sulphur dioxide and ammonia in solution also have an appreciable effect. 

Many metals combine readily with sulphur for example copper in the form of foil or wire and the vapour of boiling sulphur react so vigorously, forming cuprous sulphide, that the metal becomes white-hot 10 sodium burns brilliantly on molten sulphur. The reaction... 

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