formed; in other cases the precipitation takes place best in hydrochloric acid solution. HYDROGEN PERSULPHIDE, H2SË. This compound, which is the counterpart of hydrogen dioxide, exists in the form of a yellow oily liquid. It is prepared by boiling together I part of slaked lime, 6 parts of water, and 2 parts of sublimed sulphur, and pouring the clear solution into cold concentrated hydrochloric acid. The heavy, yellowish, oily compound separates and sinks to the bottom. It possesses an odor similar to that of hydrogen sulphide, and an acrid, unpleasant taste. It readily decomposes into hydrogen sulphide and sulphur. The most interesting feature of this compound is its combination with strychnine, forming a beautiful compound, having the formula 2C21H22N2O2 + 3HgSg. SULPHUR AND CHLORINE. These elements combine directly to form three distinct compounds. Sulphur Monochloride, S¿Clą, is formed by passing dry chlorine over dry sulphur. A reddish-yellow liquid is formed, which may be rectified by distillation. It has a specific gravity of 1.705, and boils at 138°. It is a solvent of sulphur to the extent of 66 per cent., forming a thick syrupy liquid which is used in vulcanizing rubber. Sulphur Dichloride, SClą, is formed when dry chlorine is passed into the monochloride at o°. The excess of chlorine is removed by passing carbon dioxide through the liquid. The dichloride is an unstable, darkred liquid, slowly decomposing at ordinary temperatures into the monochloride and chlorine. The same decomposition takes place on the addition of water. Sulphur Tetrachloride, SC14, is prepared by passing chlorine into the dichloride at a temperature of -20° to -22°. This is a mobile, yellowishbrown liquid, which decomposes as the temperature rises from -20°. On the addition of water the decomposition takes place with explosive rapidity. SULPHUR AND BROMINE. Bromine Monosulphide, S2Br2, is the only compound of these two elements known at the present time. It is prepared by the direct union of the elements, the excess of bromine being removed by carbon dioxide. It is a heavy, red liquid, which is stable at ordinary temperatures, but decomposes slowly at the boiling point, 200° to 210°, into sulphur and bromine. SULPHUR AND IOdine. These two elements unite in two proportions. Sulphur Moniodide, SI, is formed when the two elements are heated together under water, or, according to the Pharmacopoeia, without water in a loosely-stoppered flask. They are directed to be first thoroughly mixed and then gently heated until the mass becomes of a uniform, dark color, when the temperature is increased to the point necessary to melt them. After cooling, the grayish-black mass is rubbed to powder. Thus prepared Sulphuris Iodidum, U. S. P., is a grayish-black, crystalline solid, with the characteristic odor of iodine, having a somewhat acrid taste and a slightly acid reaction. It is insoluble in water, soluble in sixty parts of glycerin, and very soluble in carbon disulphide. Alcohol and ether remove the iodine, leaving the sulphur. It is gradually decomposed on exposure to the air with loss of iodine. On the application of heat it melts at 60°, and at a higher temperature sublimes with partial decomposition, without leaving any residue. Prolonged boiling with water removes the iodine, which escapes with the steam, leaving the sulphur. Sulphur Hexiodide, SI, is obtained by evaporating a solution of the two elements in carbon disulphide, when crystals similar to those of iodine separate. SULPHUR AND OXYGEN. The following compounds of these two elements are known: Two of these, SO, and S,O,, are of interest only as chemical compounds, while the others, SO, and SO,, are well known both in medicine and in the arts. They form, by uniting with water, two well-known acids, as follows: There are also the following acids, the oxides corresponding to which have not been discovered: H2SO2, Hyposulphurous acid. H2SO, Thiosulphuric acid. 22 H2SO, Dithionic acid. H2SO, Trithionic acid. H2SO, Tetrathionic acid. H2SO, Pentathionic acid. SULPHUR SESQUIOXIDE, SOg. This compound is formed when sulphur is added, in small quantity at a time, to sulphur trioxide. It separates as a dark-blue liquid, which solidifies into bluish-green, crystalline crusts: HYPOSULPHUROUS ACID, H2SO. This compound was called hydrosulphurous acid by Schützenberger, its discoverer. The above title, however, is more in accordance with its constitution. It should not be confounded with thiosulphuric acid, which is sometimes improperly called hyposulphurous acid. Preparation. When zinc is added to sulphurous acid the following reaction takes place : Properties. This is a yellow liquid with powerful reducing properties. On exposure to air it is rapidly decomposed, as follows: 2H,SOg Hyposulphurous Acid SO + 2H2O + S. Sulphur Water. Sulphur. It is a more powerful bleaching agent than sulphurous acid, and precipitates a number of the metals from solutions of their salts, for example: HgCl2 + H2SO2+ H2O Mercuric Hyposulphurous Water. Chloride. Acid. = Hg + 2HCl + H2SO. This serves to distinguish it from sulphurous acid. Salts of this acid have been formed, which are true hyposulphites. When sodium bisulphite is treated with zinc, the mixture kept cool, and air excluded, the hyposulphite is formed according to the following reaction: NaHSO2+ Na2SO + ZnSOg + H2O. 3NaHSO + Zn The zinc and sodium sulphites crystallize out as a double salt, the solution is mixed with four times its volume of strong alcohol, by which the remainder of this salt is removed, and the solution is set aside, when crystals of the hyposulphite separate. These should be dried in a vacuum. History. Sulphur dioxide, or sulphurous oxide, was readily recognized by the ancients, since it is always formed when sulphur is burned in the air. Occurrence.-It occurs native as a volcanic gas, and is found in small quantity in the air of large cities, on account of the existence of sulphur in coal. Preparation.-(1) When sulphur is burned in air or oxygen, direct union of the elements takes place with the formation of sulphur dioxide: This process of burning is used for nearly all cases where the gas is made on a large scale, as in bleaching and the manufacture of sulphites and sulphuric acid. (2) When three parts of sulphur are mixed with four parts of manganese dioxide, and the mixture is heated, sulphur dioxide is given off: S2 + MnO = MnS + SO.. Manganese Manganous Sulphur (3) On a smaller scale for laboratory purposes, copper turnings in a glass flask are covered with strong sulphuric acid and the mixture heated gradually, so as to maintain a steady effervescence. Mercury and silver give the same result. Some sulphide is formed at the same time, but the reaction is practically as follows: (4) When the copper in the above reaction is replaced by charcoal, the gas is evolved according to the following: This method is not available when the gas is required absolutely pure, on account of the accompanying carbon dioxide, but for making the official Acidum Sulphurosum the small quantity of carbonic acid is no disadvantage. (5) Sulphur and sulphuric acid heated together give the pure gas S+ 2H2SO4 = 2H2O + 3SO2. (6) When warm diluted sulphuric acid is added to a sulphite, the gas is given off freely: Properties. Sulphur dioxide is a colorless gas, having a suffocating odor. One volume of water at o° dissolves 79.8 volumes, and at 20° 39.4 volumes of the gas. When water at o° is saturated with the gas, it deposits crystals having the formula H,SO,. 14H,O. These crystals melt at 1° to 2°, without evolution of the gas. At a temperature of -10°, or under a pressure of three atmospheres, the gas condenses to a colorless, mobile liquid, which boils at -8°, and at -76° becomes a crystalline solid. The liquid sulphur dioxide has a specific gravity of 1.49 at 20.5°. It is manufactured by Pictet, of Geneva, and sent into commerce in copper cylinders. On the large scale, pressure affords the cheapest means of converting the gas into the liquid state, but for laboratory experiments it may be readily obtained in the liquid condition by passing it through a tube surrounded by a freezing mixture of salt and ice. The liquid may also be prepared and preserved by sealing in a strong glass tube one part of sulphur and five parts of sulphur trioxide. The reaction takes place spontaneously according to the following: A low temperature may be produced by the vaporization of liquid sulphur dioxide, and this may be intensified by directing a current of air over its surface. The gas is very stable under high temperatures until 1200° are attained, when decomposition into sulphur trioxide and sulphur takes place : 3SO2 2SO3 + S. Both gaseous and liquid sulphur dioxide, in the presence of water, possess active bleaching properties. The action in this case is a reducing one, the opposite to that by which chlorine accomplishes the same purpose. In the presence of organic matter it appears to have the power of decomposing water, combining with the oxygen, while the hydrogen in the nascent state is free to combine with the oxygen of the coloring matter, forming colorless compounds : SO2+ 2H2O = H2SO4 + Hg. The coloring matter is not destroyed, as in the case of chlorine, but may be restored by neutralizing with an alkali, hence the importance of thorough washing to remove these sulphur compounds in the process of bleaching. It is especially valuable in the bleaching of wool and silk where chlorine would injure the fabric. With solutions of the metallic hydrates and carbonates, sulphur dioxide produces sulphites according to the following reactions: |