SULPHUB. 683 STJLPHXTRETED HYDROGEN. It also forms a sesquioxide (SjO,) and a heptox- ide (SjO,) ; but these are unimportant. Sulpliur dioxide, or sulphurous anhydride, was known to the ancients, and Homer mentions the faet that the fumes from burning sulpliur were ised for fumigation, while Plin_v says that such fumes were emploj'ed 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 (H,SO.,), com- bines with bases to form a series of salts which are known as sulphites. Suli>hiir 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 14.8° C. The liquid boils at 46° C. It is very acrid and chars paper, woo<l, 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 cri/stallizable snlphuric 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: lliiosulphiiric or hyposulphnrous acid (H^S^O, ). which is described elsewhere; hydrosul- phurous acid (H^SO,), a powerful i-educing agent discovered by Schiitzenberger and prepared by the action of metallic zinc on acid sodium sul- phite; prrsulphuric acid (HSOj), obtained in a combined form by the electrolvsis of a strong so- lution of acid potassium sulphate: pi/roxiilphur- ous acid (HaS.O.), whose potassium salt is formed when sulphur dioxide gas is passed into a hot aqueous solution of potassium carbonate; pyrosulphuric acid {HJijO,) , formed by the di- rect union of sulphur trioxide and sulphuric acid; dithionic acid (HaS„0„), whose manganese salt is formed by the action of sul])hur dioxide on man- ganese dioxide: irithionic acid (II,SjO„), whose potassium salt is formed by the action of flowers of sulphur on a warm solution of acid potassium sulphite: tetrathionic acid (HoSiOs), whose so- dium salt is formed by the action of iodine on sodium hyposulphite: pentathionic acid (H.SjOb), formed, along with free sulphur, by the action of sulphur dioxide on aqueous sulphureted hy- drogen. Sulphur combines with hydrogen to form a disulpliide (sulphureted hydrogen, q.v.) and a persulphido. of which the former is well known. The persulphide (probably H2S;) 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 great rapidity. With carbon sulphur com- bines to form a disulpliide (CS,), which is de- scribed in a special article. (See Cabbon Di- SULPUIUE. ) With chlorine sulphur combines to form a monochloride(S2Cl,), a dichloride (SClj), and a tetrachloride (SCIJ. of which the most important is the monochloride. This is pre])ared by passing dry chlorine gas over melted sulphur and distilling off (he chloride from the excess of sulphur. It is an amber-colored liquid that fumes strongly in the air, and jiossesses a pene- trating odor. A saturated solution of sulphur in the monochloride is used in vulcanizing rub- ber goods. StlLPHXTE, llEiHCAL U.SKS OF. Sulphur is used in meiliciue botli internally and externally. It is prepared from crude sulphur by sublima- tion, washing, and precipitation. Taken by the mouth sulphur is in medicinal doses a mild laxative, producing a soft stool, which slips by strictures of the rectum, piles, and fissures with little discomfort. It is, there- fore, used in these conditions. Suljihur is particularly valuable for chronic rheumatism, either taken in the form of mineral waters containing this element, or externally by means of sulphur baths. The latter are employed in various chronic skin diseases, of obstinate type, such as psoriasis, lichen, and eczema. (See Bath and JIineral Waters.) Calcium sul- phide is of value in all cases where pus is about to form, as when successive crops of boils ap- pear, or in acne pustulosa. The external uses of sulphur are mostly con- fined to affections of the skin and as a parasiti- cide. It is only active when used in the form of an ointment. For the itch (q.v.) sulphur oint- ment is a specific. It is also a favorite remedy for ringworm (tinea, q.v.). SULPHURETED HYDROGEN, Hydrogen Sulphide, or Hydrosulphuric Acid, HjS. A gaseous acid compound of sulphur and hydrogen, knovn since the sixteenth century, but first care- fully investigated by Scheele in 1777. It occurs uncombined in certain mineral waters and is formed in the decomposition of albuminous sub- stances containing sulphur. It also occurs as a product of transformation of gypsum (calcium sulphate) and other metallic sulphates and is a constituent of volcanic exhalations. But what- ever its origin, it does not long remain un- changed in the air, being oxidized with the great- est ease. The usual method of preparing tlie gas consists in causing sulphuric or preferably hy- drochloric acid to act on feri'ous sulphide. The following rule usually holds good: Sulphureted hydrogen is formed by the action of acids on the sulphides of those metals (e.g. iron, zinc, man- ganese, calcium, magnesium, sodium, potassium, etc.) which can directly decompose the acids with liberation of hydrogen. Sulphureted hy- drogen is a colorless gas, somewhat heavier than air, soluble in water and more so in alcohol, the solutions reddening blue litmus paper. Mixed w-ith 1% volumes of oxygen and ignited, it ex- plodes, the products of the reaction being water vapor and sulphur dioxide (SO.). Under the influence of cold and pressure, sulphureted hy- drogen condenses to a colorless mobile liquid. Sulphureted hydrogen is very poisonous, and even small proportions of it in the air are dan- gerous. The presence of free sulphureted hydro- gen may be demonstrated by means of a strip of filter-paper soaked with a solution of lead acetate, the paper turning brown or black, owing to the formation of lead sulphide. Chlorine and
