Sulphur combines with oxygen to form a di oxide (SO,) and a trioxide (SO,), which in turn combine with water to form sulphurous and sul phuric acids and H,SO, respectively).
It also forms a scsquioxide and a heptox ide ; but these arc unimportant. Sulphur dioxide, or sulphurous anhydride, was known to the ancients, and llomer mentions the fact that the fumes from burning sulphur were used for fumigation, while Pliny says that such fumes were employed for purifying cloth. It is readily formed by burning sulphur in the air, and also by the action of certain metals, such as copper, on sulphuric acid. It is a colorless gas with a suffocating odor and is freely soluble in water, forming sulphurous acid. The gas is used as a bleaching agent, as a disinfectant, and as an antiseptic, serving to prevent the putrefaction of meat and to stop fermentation. It is also used in the sulphuring of wine. Its compound with water, known as sulphurous acid com bines with bases to form a series of salts which are known as sulphites. Sulphur trioxide. or sulphuric anhydride, is formed when a mixture of sulphur dioxide and oxygen is passed over plati num sponge, or by the distillation of fuming sulphuric acid. It is a colorless mobile liquid that solidifies in the form of long transparent prismatic crystals which melt at 14.3° C. The liquid boils at 46° C. It is very acrid and chars paper, wood, and organic matter generally. When thrown into water it dissolves with a hissing sound and evolves a large amount of heat, form ing sulphuric acid (q.v.). Under the name of crystallizable sulphuric acid, it is used in the manufacture of coal-tar colors, such as alizarin, and in the purification of ozokerite. With hydro gen and oxygen sulphur forms a series of acids including, besides those already mentioned, the following: thiosuipharic or hyposulphurous acid which is described elsewhere; hydrosul phuraus acid a powerful reducing discovered by Schfitzenberger and prepared by the action of metallic zinc on acid sodium sul phite; pet-sulphuric acid (ESN, obtained in a combined form by the electrolysis of a strong so lution of acid potassium sulphate; pyrosalphur ous acid whose potassium salt is formed when sulphur dioxide gas is passed into a hot aqueous solution of potassium carbonate; pyros-ulph uric acid (H,S,0,), formed by the di rect union of sulphur trioxide and sulphuric acid; dithiovic acid whose manganese salt is formed by the action of sulphur dioxide on man ganese dioxide; trithionic acid (II,5,00, whose potassium salt is formed by the action of flowers of sulphur on a warm solution of acid potassium sulphite: tetrathionic arid whose so dium salt is formed by the action of iodine on sodium hyposulphite; pcntathionic acid formed, along with free sulphur, by the action of sulphur dioxide on aqueous sulphureted hy drogen.
Sulphur combines with hydrogen to form a disulphide (sulphureted hydrogen, q.v.) and a persulphide, of which the former is well known. The persulphide (probably II„S„) is an oily yel low liquid which is prepared by pouring an aqueous solution of an alkaline polysulphide into excess of a solution of about equal parts of con centrated hydrochloric acid and water. It has the property of bleaching organic coloring mat ters, and reduces the oxides of gold and silver with rapidity. With carbon sulphur com bines to form a disulphide (CS,), which is de scribed in a special article. (See CARBON HI SULP IHDE. ) With chlorine sulphur combines to form a a dichloride ( and a tetrachloride (SC1,1, of which the most important is the monoehloride. This is prepared by passing dry chlorine gas over melted sulphur and distilling off the chloride from the excess of sulphur. It is an amber-colored liquid that fumes strongly in the air, and possesses a pene trating odor. A saturated solution of sulphur in the monochloride is used in vulcanizing rub ber goods.