Sulphur

Sulphur is one of the most important of the non-metallic elements; sym. S, eq. 32, sp. gr. of rolled sulphur 1.98, and of amorphous sulphur 1.957; sp. gr. of vapour 6.617 at 900° (482° C.) and 2.2 at 1904° (1040° C.), atmospheric air being the unit of comparison for the vapour. At ordinary temperatures it exists as a solid, brittle, tasteless, and inodorous body, of a characteristic yellow colour, and insoluble in water. A piece of solid sulphur, heated to a temperature of 239° (115° C.), fuses into a thin yellow liquid; while in closed vessels it may by further heat be distilled, the boiling-point being about 836° (446° C.), and at this temperature it yields a deep yellow vapour of sp. gr. 6.617. When the sulphur-vapour comes in contact with cold air it condenses in the form of a fine yellow powder, known as Flowers of Sulphur. If fused sulphur be rapidly cooled it solidifies into a compact mass, of a granular crystalline texture; and if, in its liquid state, it be allowed to run into cylindrical wooden moulds, we obtain the ordinary roll-sulphur, or common brimstone. If allowed to cool slowly, it crystallises in long, glistening, deep yellow, oblique prisms, with a rhombic base, which, however, soon lose their most characteristic properties. As native sulphur is frequently met with in yellow crystals, whose form is derived from the octahedron with a rhombic base, it is obviously a dimorphous substance. Sulphur exists in several allotropic forms, red, black, or brown. When sulphur is heated it melts and forms a mobile amber-coloured liquid, which, by continued heat, gradually darkens, at the same time becoming more viscous, until a temperature of 356° (180° C.) is reached. Even though the heat be still continued, the temperature remains stationary for a time, but eventually it rises gradually to 500° (260° C.), the melted sulphur becoming less viscous. If at this stage it is poured into cold water it forms a tenacious ductile mass, which can be drawn out into threads having a certain amount of elasticity. In the course of a few hours these become brittle, and are seen to be crystalline in structure and in no way different from the original sulphur.

Sulphur is a bad conductor of heat, and the mere heat of a warm hand often causes it to crackle or even to fall to pieces, from the unequal expansion. It is an insulator of electricity, and becomes negatively electric by friction. It is slightly soluble in alcohol, ether, and the fatty oils; its best solvents being the bisulphide of carbon and chloride of sulphur. When it is heated in the air it takes fire at about 470° (243° C.), burning with a blue flame, and becoming converted into sulphurous acid, whose pungent suffocating fumes are characteristic of sulphur. This element is second only to oxygen in its powerful affinity for other elements, with most of which it unites, and often in several proportions. With most of the metals it combines very readily, and in some cases with a development of light and heat; thus, silver and copper burn in sulphur-vapour just as iron-wire or zinc-foil burns in oxygen. In consequence of its power, with the aid of heat, of forming sulphurous acid with the oxygen of the air, and thus rendering the latter incapable of supporting combustion, burning sulphur may be usefully employed for the extinguishing of fire—as, for example, in chimneys.

Sulphur occurs very widely distributed in the mineral kingdom, partly free and partly combined with other elements. The free sulphur is either found pure in regularly formed crystals, or intimately mixed with earthy matters. Sulphur is usually plentiful in volcanic districts; most of what is used in Europe has been obtained from Sicily (which in 1880–90 exported from 213,000 to 350,000 tons yearly), but of late large quantities are recovered from the waste of soda manufacture, and sulphur has been actually exported from Newcastle to Italy (see SODA, p. 553). Sulphur is found in many parts of the United States, and some Californian deposits have been utilised to a small extent, but have been unable to compete with Sicilian sulphur. In the form of sulphide, sulphur occurs abundantly in combination with iron, copper (iron and copper pyrites), lead (galena), zinc (blende), &c., the bisulphide of iron (or iron pyrites) furnishing most of the sulphur that is employed in the manufacture of sulphuric acid. Many of the metallic sulphides (formerly known as Sulphurets) occur native, and form highly valuable ores. They are all solid at ordinary temperatures, and, with the exception of those of potassium, sodium, calcium, strontium, barium, and magnesium, are insoluble in water; they are, moreover, conductors of electricity. Many of them, especially of those that occur native, exhibit very brilliant and characteristic colours. The same metal may have several sulphides, and in general there is a sulphide for each oxide. The sulphides are, however, sometimes the more numerous. Sulphur is still more extensively distributed in the form of sulphates, as in the sulphates of lime, magnesia, baryta, &c. In the vegetable kingdom sulphur is a constituent of Albumen (q.v.), and of the volatile irritant oils of mustard, garlic, asafœtida, &c.; moreover vegetable juices contain it in the form of certain sulphates. In the animal kingdom it is not only a constituent of the albuminous, fibrinous, and gelatinous tissues, but of the hair, saliva, bile, urine, &c.

The grosser impurities of sulphur are removed by crude processes of fusion and distillation at or near the place from whence it is obtained. What is called refined sulphur is purified by distillation in a large cast-iron still, and condensed in a receiver kept cool. When the vaporised sulphur is condensed in a large chamber it is obtained in the form of sublimed sulphur, or flowers of sulphur; but as the walls get hot it melts and collects on the floor, and is run into cylindrical wooden moulds, from which, when cool, it is taken out as roll or stick sulphur. The residue left in the retort is a mixture of sulphur with various impurities. Under the name of black sulphur, or Sulphur vivum, it is used in veterinary medicine, and for the purpose of dressing mouldy hops. Sulphur is thrown down from certain of its compounds (as from a strong solution of a polysulphide of calcium, sodium, or potassium) by dilute hydrochloric acid; it falls as a grayish-white, very fine, light powder, known in the Materia Medica as milk of sulphur, or precipitated sulphur. The most common impurities met with in ordinary commercial sulphur are selenium and realgar (bisulphide of arsenic). Flowers of sulphur frequently exhibit a slight acid reaction, in consequence of a little sulphurous acid clinging to them. By rinsing them with water this impurity is at once removed.

Sulphur is extensively employed in the arts and manufactures, as in the manufacture of some matches, gunpowder, &c. When converted into sulphurous acid it is employed as a powerful bleaching agent, as also for the destruction of insects, fungi, &c.; but its chief consumption is in the manufacture of sulphuric acid.

The eight compounds of sulphur and oxygen, when combined with water, present the characters of acids. These acids have this composition:

We shall here notice the most important members of this group—the second, third, and fourth; the third, Sulphuric Acid, is discussed in a special article. (The last four derive the essential part of their name from the Greek theion, ‘sulphur.’)

Sulphurous Anhydride (often called Sulphurous Acid), $SO\_2$, occurs under the ordinary relations of temperature and pressure as a colourless gas, possessing the suffocating odour of burning sulphur. In its concentrated form it is quite irrespirable, and in a diluted state it excites cough. It not only is incapable of burning, but it rapidly extinguishes the flame of burning bodies. It is very freely soluble in cold water, which at $32^\backslash circ$ ($0^\backslash circ$ C.) takes up nearly 69 times its volume of the gas, while at $75^\backslash circ$ ($24^\backslash circ$ C.) it only takes up 32 volumes; the solution known as Aqueous Sulphurous Acid having at first the same smell and taste as the gas, but soon absorbing oxygen from the air, and becoming converted into sulphuric acid. By the action of cold sulphurous acid may be condensed to a colourless transparent limpid liquid, which freezes at $-105^\backslash circ$ ($-76^\backslash circ$ C.), forming a transparent crystalline solid. The specific gravity of the gas is 2.247 (atmospheric air being the unit), and that of the liquid is 1.49 (water being the unit), the solid being considerably heavier. Although dry sulphurous acid gas and dry oxygen when mixed exert no action on one another, there are many conditions under which sulphurous acid rapidly absorbs oxygen, and is converted into sulphuric acid—e.g. if the gas be dissolved in water; a similar action takes place under the influence of hydrated nitric acid, iodic acid, and certain metallic oxides. Hence sulphurous acid is a powerful reducing or deoxidising agent. This gas is a common and abundant product of volcanic action, and is occasionally met with in solution in the springs in volcanic regions. It may be prepared artificially by simply burning sulphur in the air or in oxygen gas, or by heating in a flask 4 parts of flowers of sulphur mixed with 5 parts of powdered black manganese, sulphurous acid and sulphide of manganese being the products, as shown by the equation $S\_8\; +\; MnO\_2\; =\; SO\_2\; +\; MnS$. In consequence of its solubility in water this gas should be collected over mercury. In addition to the uses of sulphurous acid as a bleaching agent, it is valuable both as a disinfectant agent and as a powerful antiseptic, and has been used as an application for lumbago, &c. But by far its most important use is in the manufacture of sulphuric acid. In combination with bases this acid forms the sulphites—a class of salts which, excepting the sulphite of soda, are of little importance, except for their power when moist of extracting oxygen, and thus acting as reducing agents. The salts of the sesquioxide of iron are reduced by them to salts of the protoxide.

Thiosulphuric Acid, $H\_2S\_2O\_3$, formerly called Hyposulphurous Acid, is, as yet, only known in a state of combination with bases; for on attempting to separate the acid from the base the former becomes decomposed into sulphur and sulphurous acid. The most important of its salts is the Hyposulphite of Soda, $Na\_2S\_2O\_3\; +\; 5H\_2O$, described in the article SODIUM. This and other soluble hypo- sulphites may be easily recognised by the facility with which they dissolve the haloid salts of silver, forming a solution of an extremely sweet taste, and containing a double hyposulphite of silver and soda, with an admixture of chloride, iodide, or bromide of sodium. It is this power of dissolving those salts of silver which are insoluble in water that renders the hyposulphite of soda useful in photography.

With hydrogen sulphur forms two compounds: (1) Persulphide of Hydrogen, an oily liquid, having the smell and taste of sulphuretted hydrogen; (2) Sulphuretted Hydrogen, $H\_2S$, known also as Hydro-sulphuric Acid and Sulphydric Acid, a natural gaseous constituent of many Mineral Waters (q.v.), as for instance Harrogate and Strathpeffer in Great Britain. It is formed spontaneously wherever organic compounds containing sulphur undergo putrefaction, as in stagnant sewers and cesspools and in waters charged with organic matter and sulphates. By acting on sulphide of iron with dilute sulphuric acid, sulphate of iron is produced and sulphuretted hydrogen liberated.

Sulphuretted hydrogen is a poisonous colourless gas, with the nauseous odour of rotten eggs. By pressure it may be liquefied and solidified. It is soluble in one-third of its volume of water; but the solution does not keep well unless preserved from contact with air. It is readily combustible, burning with a blue flame, and forming water, sulphurous acid, and usually a little sulphur. It has a weak acid reaction, but combines readily with bases forming sulphides. It is very poisonous, birds perishing in air containing $\backslash frac\{1\}\{1000\}$ part, and dogs in air containing $\backslash frac\{1\}\{500\}$ part of the gas. Owing to its presence in illuminating gas silver becomes tarnished in rooms where gas is burned, while librarians find the bindings of their books become corroded by the sulphuric acid eventually produced by the combustion of the gas. From its property of forming insoluble sulphides with most metals, sulphuretted hydrogen is the sheet anchor of the analytical chemist. These insoluble sulphides again are some of them produced in an acid solution, and some only in an alkaline one. It follows that by first acidifying the solution to be analysed and then adding the sulphuretted hydrogen certain metals will be removed as insoluble precipitates, while others will have been unaffected. On now adding an alkali a second portion will be removed, and so a working method of separating the metals can be devised. The simplest test for sulphuretted hydrogen at the mouth of a drain is the use of blotting-paper soaked in solution of acetate of lead. This rapidly turns brown in presence of the gas.

Sulphur combines with carbon to form Bisulphide of Carbon, $CS\_2$, a colourless, inflammable liquid, heavier than water, and having a disagreeable odour and taste. It is soluble in alcohol, but not in water, and it is a powerful solvent of fats, sulphur, phosphorus, and india-rubber. Owing to its high refractive power it is used in the construction of prisms. It may be obtained by heating fragments of charcoal to bright redness in a porcelain tube, and passing sulphur vapour along it. Its vapour when freely inhaled exerts an anaesthetic action similar to that of chloroform and ether. Workmen in caoutchouc or other manufactures in which bisulphide of carbon is used as a solvent suffer from prolonged exposure to its vapour, which produces headache, loss of appetite, impairment of vision and hearing, and causes general derangement of health by its deleterious action on the nervous system.

Sulphur combines with chlorine in several proportions, the most important of these compounds being the Dichloride of Sulphur, $SCl\_2$, and the Chloride of Sulphur, $S\_2Cl\_2$. Both of them are liquids, and are formed by the direct action of the combining elements. The chloride is a yellow liquid which is decomposed by contact with water—sulphur, hydrochloric, and other acids being produced. It is capable of dissolving about 67 per cent. of sulphur at an ordinary temperature, and, like bisulphide of carbon, is extensively employed in vulcanising india-rubber. The dichloride of sulphur is formed by saturating the chloride with chlorine; a deep-red liquid, resembling the previous compound in most of its properties; it is decomposed by the sun's rays into the chloride and free chlorine.

Sulphur seems to have been known from the earliest times, and sulphuric acid was most probably known to the Arabians; the English manufacture of sulphuric acid dates, however, only from the 18th century. Sulphur is used for various purposes in medicine. It is given internally either as sublimed sulphur (flowers of sulphur) or as precipitated sulphur (milk of sulphur), in somewhat large doses, as a mild cathartic—generally combined with jalap and cream of tartar. The Confection of Sulphur of the Pharmacopoeia is composed of sulphur, cream of tartar, and syrup of orange-peel rubbed together—the dose being from half an ounce to an ounce, or from one to two tablespoonfuls. In small doses sulphur is of great value in cases of atonic gout and chronic rheumatism. The external use of sulphur in the form of ointment has been already noticed in the article ITCH. It is also used externally in other cutaneous disorders, particularly in lepra and psoriasis; its application in the form of vapour is often of service.