S

ULPHUR, a non-metallic element known from very early times, and proved to be an element by Lavoisier, in 1772. It was not definitely admitted to the list of rec-. ognized elements, however, until after the researches of Gay-Lussac and Thénard, in 1809. In the free state, it occurs native in many parts of the earth, usually in volcanic regions or in connection with gypsum and other allied rocks. Until within recent years the commercial supply has been obtained largely from Sicily, though a considerable quantity has been obtained from the Chilean Andes, and from certain parts of Mexico, China, Japan, India and the Philippine Islands. The large deposits of southern Utah are also mined, but the American supply is now obtained almost wholly from the extensive deposits in and near Calcasieu Parish, La. Four general methods have been employed for separating sulphur from the stony and earthy impurities with which it is usually associated in nature. (1) The "ore" containing it may be heated to a temperature high enough to melt the sulphur and permit it to run out at the bottom; or (2) the "ore" may be heated still more strongly, so as to cause the sulphur to volatilize and pass away in the form of vapor; or (3) the ore may be lixiviated with a fluid (such as carbon disulphide) in which the sulphur is soluble, the sulphur being afterward recovered by evaporating the solvent. (4) The Frasch process, specially developed in connection with the Louisiana deposits, is described below. The method by melting is almost exclusively used in extracting sulphur from the inert material with which it is associated in nature, the volatilization and solution methods being reserved for the subsequent purification of the product as first obtained by melting. When the sulphur is extracted from an "ore," the heat required for melting it and isolating it is obtained by various means. In some regions it is obtained by burning a part of the sulphur itself. This method is wasteful in sulphur, but it can be put into practice very simply, and hence its application does not call for skilled labor. In Nevada and California, and, to a more limited extent, in Italy and Sicily, the "ore" is heated by steam under a pressure of 70 pounds or more; the yield by this method being considerably greater, though the expense of treatment is also much greater.

In mining the Louisiana deposits a special method is used, which merits separate description. These vast deposits occur in the form of

subterranean beds, having an average thickness of 125 feet, and covered by about 90 feet of soft rock (mainly gray limestone) and 375 feet of clay, sand and gravel. The deposits were first discovered in 1865, and between 1868 and 1895 many unsuccessful attempts were made to work them commercially by ordinary methods of mining. Herman Frasch, an American petroleum expert, then undertook a careful study of the subject, and worked out a method of mining the sulphur that has proved eminently successful. The entire practicability of the Frasch process was first established in 1903, in which year 35,000 tons of sulphur were brought to the surface by means of it. The essential ideas of the Frasch process are (1) the use of highly heated water to melt the sulphur as it lies in its bed, and (2) the use of compressed air to force the molten sulphur to the surface of the ground. Several concentrically-arranged steel pipes are driven into the ground, and highly superheated water is forced down into the sulphur bed through the outer ones. The sulphur is thereby melted, and as it is considerably heavier than water it collects in a subterranean pool, into which the pipe system dips. Air, compressed to a pressure of about 250 pounds to the square inch, is forced down the central pipe (which is one inch in diameter), and as this air returns to the surface of the ground through the annular space between the inner pipe and the next one to it, the melted sulphur is carried upward at the same time. When the operation is properly conducted the melted sulphur and hot water can be kept separate, so that when the sulphur reaches the surface it is only necessary to run it into bins to cool and solidify. The product that is obtained in this way is remarkably free from impurities. In fact it is not uncommonly 99.9 (and sometimes even 99.98) per cent pure, and hence it does not require further purification for technical use. For a good technical description of the Frasch process, consult Thorpe's 'Dictionary of Applied Chemistry,' article "Sulphur."

Iron pyrites (native yellow sulphide of iron) is utilized quite extensively as a source of sulphur in certain lines of manufacture, but the sulphur of the pyrites is rarely won in the elementary form. Almost invariably the sulphur dioxide that is obtained by roasting the pyrites is used in the preparation of sulphuric acid or other compounds, without being reduced to sulphur.

Native crystals of sulphur are common. They belong to the orthorhombic system, and are usually pyramidal in habit, often with truncated ends. They are transparent to translucent, and are usually yellow in color, with a resinous lustre, a hardness of from 1.5 to 2.5, and a specific gravity of about 2.07.

Sulphur occurs abundantly, also, in combination with other elements, mostly as sulphides and sulphates. Many of the compounds of sulphur are valuable as ores of other elements than sulphur. Galena (sulphide of lead) and cinnabar (sulphide of mercury), for example, are valuable ores of lead and mercury, respectively.

It is difficult to give an adequate physical description of sulphur since the element is capable of existing in many allotropic forms. Six of these appear to have been prepared in a state of satisfactory purity, and others, although they have long been known, are not yet universally admitted to be true allotropic modifications of pure sulphur. A brief description of the six best-known forms follows:

1. Ordinary Rhombic Sulphur.- This is the form in which native crystalline sulphur occurs. Crystals of this variety may be prepared by dissolving ordinary sulphur in carbon disulphide, and evaporating the solvent. This variety is also obtained by melting sulphur and allowing it to cool with extreme slowness. Ordinary rhombic sulphur melts at about 240° F., and boils (under a pressure of 760 millimeters of mercury at Paris) at 832.2° F., according to the very careful experiments made by Callendar and Griffiths with the normal constant-pressure air thermometer. In the solid form rhombic sulphur has a specific gravity of from 2.03 to 2.09, and in the liquid form (just above the melting point) its specific gravity is about 1.81. It is practically a non-conductor of electricity at ordinary temperatures, although it conducts to some extent near its boiling point. When rubbed, sulphur becomes negatively electrified, and globes of sulphur were used in the place of glass in some of the earlier forms of static electrical machines. Rhombic sulphur has a coefficient of linear expansion of about 0.0000356 (Fahrenheit scale), and, when at a temperature just above the melting point, it has a specific heat of approximately 0.235. It is easily soluble in carbon disulphide, and, to a lesser extent, in benzene, chloroform, warm concentrated acetic acid and liquid sulphur dioxide.

2. Monoclinic Sulphur.- Sulphur may be obtained in the form of monoclinic crystals by melting a considerable quantity of ordinary sulphur, allowing it to cool until a crust has formed upon the surface and then piercing the crust and pouring out the still molten portion. The walls of the crucible will then be found to be covered with the monoclinic crystals. It may also be prepared in mass by melting ordinary sulphur, cooling it almost to the point of solidification, and then throwing in a single crystal of monoclinic sulphur; the whole mass then solidifying in the monoclinic form. (If a crystal of rhombic sulphur is added under these circumstances, the crystalline structure of the resulting solid mass is rhombic). Monoclinic sulphur has a specific gravity of about 1.97, melts at about 245° F., and is freely solu

ble in carbon disulphide, from which it crystallizes in the rhombic form. It also dissolves in alcohol, chloroform and benzene, the crystals obtained from these solutions being partly monoclinic and partly rhombic. Monoclinic crystals may be obtained by evaporating the solution obtained by dissolving sulphur in an alcoholic solution of ammonium sulphide. Monoclinic sulphur passes slowly into the ordinary rhom bic form, the transformation being facilitated by rubbing the monoclinic crystals with a glass rod. When heated, under atmospheric pressure, to 203° F., monoclinic sulphur passes at once into the ordinary rhombic form, the transformation being accompanied by a small contraction in volume, and the evolution of a certain amount of heat.

3. Soft Soluble Sulphur.-This variety of sulphur may be prepared in various ways,for example, by decomposing sodium hyposulphite (or thiosulphate) by means of a limited quantity of a mineral acid. It is a soft, amorphous substance, nearly white in color, which gradually hardens, and eventually passes (like all the other kinds) into ordinary rhombic sulphur. This form of sulphur is not (as its name indicates) entirely soluble in carbon disulphide; it consists, apparently, of a mixture of two kinds of sulphur, one of which is soluble, while the other is insoluble. When heated, it evolves sensible quantities of sulphuretted hydrogen, showing that it contains hydrogen in some form or other; but it has not been determined whether such hydrogen is essential to the existence of the sulphur in this form, or whether it is to be regarded merely as a non-essential constituent, which could be eliminated (if we knew how to eliminate it) without affecting the continued existence of the sulphur in the "soft soluble" form.

4. Plastic Insoluble Sulphur.-When ordinary sulphur is melted, it first passes into the form of a clear, yellow liquid; but as the temperature is raised, the liquid begins to thicken and darken at about 300° F., and at about 360° F. it is black and quite viscid. If the temperature is still further increased, the liquid gradually loses its viscidity, until, at about 640° F., it becomes quite fluid again, though it remains dark even at its boiling point (832.2° F.). If sulphur which has been heated almost to its boiling point is suddenly cooled by being poured in a thin stream into water, it becomes converted into a plastic mass, which may be readily kneaded with the fingers. Plastic sulphur is commonly dark brown; but Mitscherlich states that the dark color is due to impurities, and that perfectly pure plastic sulphur is citronyellow in color. Plastic sulphur soon becomes hard and yellow, the transformation taking place quickly (and with evolution of heat) at temperatures in the vicinity of 212° F. It is not soluble, as a whole, in carbon disulphide, though that reagent dissolves a portion of it.

5. Amorphous Yellow Insoluble Sulphur. - Plastic sulphur, when treated with warm carbon disulphide until all the soluble part is removed, leaves a yellow, amorphous powder as a residuum. This form appears to be stable at ordinary temperatures, but at about 212° F. it slowly passes into the ordinary rhombic crystalline form.

6. Colloidal Sulphur.-When sulphuretted

hydrogen gas is passed into a cold solution of sulphur dioxide, sulphur is liberated in still another allotropic form. If the current of sulphuretted hydrogen is continued until all the dioxide has been decomposed and the solution (after filtration) is concentrated by evaporation in a vacuum, a yellow solid is finally obtained, which is soluble in water, but which gradually passes into the form of ordinary rhombic sulphur. "Colloidal" sulphur receives its name from the fact that in its aqueous solution it is not diffusible.

Sulphur occurs in commerce in several forms. When cast into cylindrical or slightly conical sticks it is known as "roll sulphur" or "brimstone." It is very brittle under ordinary circumstances, and when reduced to powder by crushing it is sold simply as "sulphur." When sulphur vapor is suddenly cooled, the sulphur condenses in the form of a very finely divided powder, which is commercially known

as

flowers of sulphur," or "sublimed sulphur." "Precipitated sulphur" is the fine powder that is thrown down upon the addition of hydrochloric acid to a solution prepared by heating sublimed sulphur with lime and water.

Chemically, sulphur has the symbol S, and an atomic weight of 32.06 if O=16, or 31.81 if H=1. It combines directly with many of the other elements, producing binary compounds which are known as "sulphides," and which are analogous to the oxides of the corresponding elements. With hydrogen it forms hydrogen sulphide, or "sulphuretted hydrogen," which has the formula H&S, and is gaseous under ordinary conditions of temperature and pressure. (See HYDROGEN). Many of the metallic sulphides occur in nature as minerals, as has been already mentioned. Many of them may also be prepared by passing a current of sulphuretted hydrogen gas through acid or alkaline solutions of various metallic salts, or by adding a soluble sulphate to such solutions. See CHEMICAL ANALYSIS.

Several oxides of sulphur are known, of which two are of great industrial importance. These are the dioxide, SO2, and the trioxide, SO2.

Sulphur dioxide, SO2, is prepared, in the laboratory, by treating sodium acid sulphite (HNASO) with concentrated sulphuric acid (H2SO4); sulphur dioxide and sodium acid sulphate being formed, as indicated by the equation HNASO, H2SO. SO, +HNASO, + H2O. It is also prepared by heating strong sulphuric acid with metallic copper, the reaction in this case being 2H2SO. + Cu SO, + CuSO. + 2H,O.

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Sulphur dioxide is a colorless gas with the familiar suffocating odor of burning sulphur. It is irrespirable in the pure state, or even when largely diluted with air. Mere traces of it, when inhaled for some time, produce inflammation of the mucous surfaces of the respiratory tract and of the stomach, followed by nausea. The gas is about twice as heavy as air under the same conditions of temperature and pressure. Its specific heat at constant pressure (as compared with an equal weight of water) is about 0.154; and the ratio of its specific heat at constant pressure to its specific heat at constant volume is about 1.256. When exposed to a temperature of 18° F. under ordinary atmospheric pressure, sulphur dioxide condenses to a colorless liquid having a specific gravity of

about 1.43. The critical temperature of the gas is probably about 313° F., and the critical pressure about 79 atmospheres. When cooled to about 105° F. below zero, liquid sulphur dioxide freezes to a transparent solid. Liquid sulphur dioxide evaporates rapidly when exposed to the air, the evaporation being attended with the absorption of a very considerable quantity of heat; a temperature as low as 140° F. below zero being attainable in this manner. On account of this property, liquid sulphur dioxide has been employed to a considerable extent in machinery for the manufacture of artificial ice; though at the present time anhydrous liquid ammonia is usually preferred for this purpose. Gaseous sulphur dioxide dissolves freely in water, especially under pressure; the solution being known as sulphurous acid (q.v.).

Sulphur dioxide is prepared in large quantities, in the arts, by the simple process of burning sulphur with a proper supply of air. When obtained in this manner, the gas contains large quantities of atmospheric nitrogen, but for many industrial purposes this is of no importance. The gas is used for bleaching straw, silk and wool, and (in enormous quantities) in the manufacture of sulphuric acid (q.v.). It is likewise employed extensively in the "sulphite process" for the manufacture of paper from wood.

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Sulphur dioxide and sulphuretted hydrogen readily combine with each other to form water and free sulphur, according to the equation SO2+ 2H2S 3S+ 2H2O; and it has been suggested that the deposits of sulphur that occur in volcanic districts have been formed, at least in part, by this reaction. In bleaching by means of chlorine compounds, it is found to be impossible to wash the last traces of chlorine from the bleached fabric, and hence it is customary to treat the fabric, after the bleaching is complete, with some substance (called an "antichlor") with which the free chlorine will combine, to produce compounds that can be more easily washed out. Sulphur dioxide gas is very useful for this purpose, since it combines with chlorine (in the presence of moisture) to form sulphuric and hydrochloric acids, according to the equation SO2 + 2H2O + 2Cİ

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H2SO + 2HCI. The dioxide is also used as an antiseptic and disinfectant; but it is inferior to chlorine in this respect, and although it possesses germicidal powers to some extent, it is seldom used in sufficient quantities to be really effective in this application.

Sulphur trioxide, SO, may be prepared by distilling fuming sulphuric acid, or by passing a mixture of one volume of oxygen with two of sulphur dioxide over red-hot platinized asbestos; the latter method being now used to a considerable extent in the manufacture of sulphuric acid (q.v.) by the so-called "contact process." The trioxide appears to be capable of existing in two different physical states. The white fumes that are first obtained in the course of its preparation condense into long prismatic crystals, which melt at 62° F. to a colorless, mobile liquid, boiling at 112.8° F. Upon standing, these prismatic crystals are said to change into needle-like forms, which, when heated to about 122° F., pass directly into the gaseous state. Weber has shown that this second form is not observed unless the trioxide contains some measurable quantity of sulphuric acid, due to