iron vessel, and the sulphur vapour thereby When melted sulphur, in that particular evolved is conducted into a large vaulted state of viscidity which will allow it to run stone chamber, on the sides of which it slowly from the vessel, is poured in a thin condenses. As long as the walls of this stream into cold water, it solidifies in a chamber remain below the temperature at very peculiar manner; for instead of formwhich sulphur melts, the vapour condenses ing a hard, brittle, opaque, yellow subon them in the form of minute crystalline stance, like common sulphur, it becomes grains, of a light yellow colour, constituting dark brown, transparent, and so soft and the product called flowers of sulphur; but tenacious, that it may be drawn out into as soon as the temperature rises above the fine threads, and used for taking impresmelting point, the vapour condenses in the sions of medals. This state, however, is form of liquid sulphur, which collects at not permanent; the sulphur soon loses its the bottom of the chamber. It is then softness and transparency, and in a few drawn off from time to time, and run into days becomes hard and brittle like ordiwooden moulds, which are nearly cylin-nary rolled sulphur, though of a somewhat drical, but rather wider at top than at bot- darker colour. tom. The sulphur cast in this form is called rolled sulphur, or sometimes brimstone. To produce flowers of sulphur, the condensing chamber is made large, and the process is interrupted at certain intervals, to allow the walls to cool down; to obtain rolled sulphur, on the contrary, the chamber is made of smaller dimensions, and the process is carried on uninterruptedly. Sulphur is likewise obtained from eertain metallic sulphides, especially from the bisulphide of iron, or iron pyrites. This substance, when heated, gives off half its sulphur in the form of vapour, which may be condensed as just described. Sulphur, at ordinary temperatures, is a yellow brittle solid, about twice as heavy as water. At 234° it melts, forming a brownish yellow liquid, almost as thin as water. Solid sulphur sinks in this liquid, showing that this substance expands and becomes lighter in passing from the solid to the liquid state, contrary to what takes place in the liquefaction of ice. Melted sulphur retains its colour and fluidity unaltered for a few degrees above its melting point; but if the temperature be further raised, the sulphur begins to thicken, and acquires a dark brown colour; and at 480°, or a few degrees above, it is so thick and viscid, that the containing vessel may be inverted without the sulphur running out. When still further heated, becomes thinner, but never regains the perfect fluidity which it possesses at lower temperatures, even if it be heated to the boiling point. When left to cool gradually, it passes through the same stages in the reverse order, again becoming perfectly fluid just above its solidifying point. Per A very different kind of solidification takes place when the liquid sulphur is allowed to cool down gradually. In that case, as it approaches the temperature of 234°, it regains its former fluidity; and when it attains that temperature, passes at once to the solid state in the form of regular crystals. Substances which, like sulphur and water, pass suddenly from the liquid to the solid state, always exhibit the crystalline structure when solidified; whereas those which, like glass and wax, become viscid and pasty before solidifying, exhibit no traces of crystalline structure. fect freedom of motion appears to be necessary to enable the particles to assume that regular arrangement which constitutes crystallization. The crystallization of sulphur may be well observed by melting a quantity of that substance in a glass tube, and leaving it to cool slowly. Larger crystals may be obtained by melting about two pounds of sulphur in an earthen crucible, leaving it to cool till a crust forms on the surface, then making a hole in the crust with a stick, and inverting the crucible, so that the sulphur which still remains liquid in the middle may run out; if you then carefully break the crucible, you will find that the remaining portion of sulphur is most beautifully crystallized, in long prisms or needles, which shoot out from the sides to the middle, and interlace each other in all directions. Sulphur may likewise be obtained in regular crystals by dissolving it in oil of turpentine, or, better, in sulphide of carbon (a liquid to be described hereafter), and leaving the solution to evaporate freely in the air. The crystals thus produced differ, however, in form from those obtained by fusion. They are elongated octohedrons (Fig. 23, a), or modifications of that form, resulting from the replacement of some of its edges and summits by plane surfaces, as shown at b, c, d. The octohedron a is called the primary form; the others are secondary forms derived from it. The distinction between primary and secondary forms, which is of great importance in crystallography, will be more fully considered hereafter; for the present it must suffice to observe, that most crystals may be split in certain directions more easily than in others; and these directions of easy cleavage are parallel to the faces of the primary form; thus, in the crystals immediately under consideration, the directions of easiest cleavage are parallel to the faces of the octohedron (Fig. 23 a), and not to any Fig. 23. of the secondary faces by which the angles of that figure may be replaced. The prismatic crystals obtained from melted sulphur are derived from a different primary form, viz. an oblique rhombic prism (Fig. 24), and cannot be reduced to the octohedral form by cleavage. Fig. 24. A substance which, like sulphur, produces crystals belonging to two distinct primary forms, is said to be dimorphous, or two-shaped (8 and μopon). Many substances exhibit this peculiarity; and in all of them, the particular form assumed appears to be determined chiefly by the temperature at which crystallization takes place. Thus, the crystals produced in the solidification of melted sulphur are prismatic, whereas those which separate from its solutions at ordinary temperatures are octohedral. The latter form is likewise * An excellent method of rendering these modifications familiar to the eye, is to cut some soft substance, such as a piece of soap or a turnip, into the shape of the primary octohedron (a), and then slice off some of the edges and summits with a sharp knife. exhibited by the minute grains of flowers of sulphur formed by condensing the vapour against a cold surface, and by the crystals of native sulphur, which appear to be formed in a similar manner-by the condensation of vapours issuing from fissures in the ground. Moreover, the octohedral crystals retain their characters unaltered at ordinary temperatures; whereas the prismatic crystals, which, when first produced, are transparent and of a brownish-yellow colour, soon begin to change, and in the course of a few days, become perfectly opaque, and assume the strawyellow colour of ordinary sulphur. The outward form remains indeed the same, but the internal arrangement of the particles is completely altered; and the crystals, which were originally made up of small prisms, are gradually converted into collections of minute octohedrons. By keeping them in a warm place, this change may be greatly retarded, and the original colour and transparency preserved for a long time. Transparent crystals of native sulphur, on the contrary, when heated to a temperature somewhat below 234°, become opaque, in consequence of a change of the octohedral arrangement of the particles into the prismatic. Sulphur boils at 788° Fahr., and if contained in a close vessel (it would burn if exposed to the air) is rapidly converted into an orange coloured gas; the vaporization begins, however, at much lower temperatures, even below the melting point. The formation and condensation of sulphur vapour may be well observed by heating sulphur in a small retort with a receiver attached to it, (Fig. 20, p. 235). The vapour will condense in the form of flowers of sulphur as long as the receiver is kept cold; but if you allow it to become heated, the sulphur will condense in the liquid form. In fact, this experiment is an exact imitation, on a small scale, of the process above described for the purification of crude sulphur. The density of sulphur vapour varies with its temperature in a very remarkable manner. Just above the boiling point, it is 6-617, or rather more than 6 times that of atmospheric air of the same temperature and under the same pressure; but at very high temperatures, 1800° and above, its density (still compared with that of air of corresponding pressure and temperature) inside, for the gas will turn the paint quite falls to one-third that amount, that is to black. The gas obtained by this method say, to 2.206, or not much more than twice is seldom pure, being generally contamithat of atmospheric air. The smaller den-nated with free hydrogen; because the sity appears indeed to be that which sul-sulphide of iron is usually mixed with phur vapour possesses when it is perfectly some portion of metallic iron which has gaseous, and has no tendency to pass to escaped the action of the sulphur-and the liquid state. Such accordingly is the this, when acted upon by the dilute acid, density which sulphur may be expected to liberates hydrogen. Pure sulphuretted exhibit in its gaseous compounds-sul- hydrogen may be obtained by heating the phurous acid, sulphuretted hydrogen, &c. | native sulphide of antimony (a very cheap The density of sulphur vapour in this state substance) with strong hydrochloric acid; is twice that of oxygen, and 32 times that this process, however, is less convenient, of hydrogen. inasmuch as it requires the application of heat. The gas obtained by the first method is pure enough for all ordinary purposes. Sulphur, heated in the air to a temperature somewhat short of its boiling point, takes fire, and burns with a faint blue flame, producing sulphurous acid gas, a compound easily recognised by its peculiar and suffocating odour, commonly, but incorrectly, ascribed to sulphur itself. The same compound is of course more quickly formed in pure oxygen gas, the combustion producing a beautiful violet flame, (p. 61.) SULPHUR AND HYDROGEN. Hydrosulphuric Acid or Sulphuretted Hydrogen, HS.-Sulphur and hydrogen do not combine directly, like oxygen and hydrogen; but when certain metallic sulphides the proto-sulphide of iron, for instance-are introduced into dilute hydrochloric or sulphuric acid (HSO4), an interchange takes place between the hydrogen and the metal-sulphuretted hydrogen being evolved in the form of gas, and a chloride or sulphate of the metal remaining in solution. With sulphide of iron and hydrochloric acid, the action may be thus represented: out. FeS + HCl = FeCl + HS. The sulphide of iron used for the preparation of this gas, is obtained by heating 7 parts of iron turnings in a crucible with not less than 5 parts of flowers of sulphur, till the mixture becomes red-hot throughIt is then left to cool, broken up, and the fragments introduced into a bottle fitted up as for the preparation of hydrogen (Fig. 4, p. 26). Dilute sulphuric acid is then poured through the funnel, and the gas, as it escapes, is collected over water contained in an earthen pan or basin. You must not use your pneumatic trough for this purpose, at least if it be painted Hydrosulphuric acid is a transparent and colourless gas, having an extremely disagreeable odour, like that of putrid eggs. It is highly poisonous, even a small quantity of the pure gas producing insensibility when inspired. When largely diluted with air, it may be breathed without actual danger; but even then it is apt to produce head-ache and other unpleasant symptoms. Small birds die in air containing 1-1500th of this gas, and a dog in air containing 1-1000th. It is a frequent product of the decomposition of animal and vegetable matter, and is one of the chief causes of the poisonous character of the exhalations from sewers and other places where matter of this kind is suffered to accumulate. This gas, when subjected at ordinary temperatures to a pressure of 17 atmospheres-that is to say, when compressed by a forcing pump into a strong glass vessel, till the vessel contains 17 times as much of it as it would under ordinary circumstances-condenses into a very thin, transparent, and colourless liquid; and this, when exposed to a cold of 122° Fahr., solidifies and forms a white crystalline solid, which sinks to the bottom of the liquid. The solid, liquid, and gaseous forms of hydrosulphuric acid, are related to each other in the same manner as ice, water, and steam. Water, at ordinary temperatures, dissolves about 2 times its volume of hydrosulphuric acid gas, forming a solution which exhales the odour of the gas, and slightly reddens litmus. A solution of potash absorbs it rapidly and completely, if it be pure, but leaves behind any free hydrogen that may be mixed with it. Hy drosulphuric acid is found in the state of solution in certain mineral waters, called hepatic waters, such as that of Harrowgate in Yorkshire. the completely gaseous state, is 32 times as great as that of hydrogen, it follows also that hydrosulphuric acid contains half its volume of sulphur vapour; or in other words, that 2 volumes of hydrogen gas and volume of sulphur vapour form 2 volumes of hydrosulphuric acid gas. Hydrosulphuric acid gas, in contact with air or pure oxygen, takes fire on the ap-1 plication of a lighted taper, and burns with a blue flame-the products of the combustion being water and sulphurous acid, the same as if the hydrogen and sulphur were burned separately. Chlorine instantly decomposes the gas, combining with the hydrogen, and liberating the sulphur-at least the greater part of it-which is then deposited in a yellow film on the sides of the vessel. Bromine and iodine likewise decompose the gas with great rapidity. The facility with which chlorine decomposes hydrosulphuric acid, is one of the chief sources of its utility in destroying the poisonous matter of animal and vegetable exhalations. The equivalent number of sulphur may also be determined from the constitution of hydrosulphuric acid: for, in the decomposition of this gas by chlorine, hydrochloric acid is produced, so that 35-5 parts (1 eq.) of chlorine take the place of the 16 parts of sulphur, previously combined with 1 part of hydrogen; hence the equivalent of sulphur is 16, and the formula of hydrosulphuric acid is HS. This result is further confirmed by the action of this compound on metallic oxides, &c., which we shall now consider. Hydrosulphuric acid, both in the state of gas and of aqueous solution, decomposes a great number of metallic compounds, oxides, chlorides, &c., the decomposition consisting in the formation of a metallic sulphide on the one hand, and of water, hydrochloric acid, &c. on the other. Thus, if oxide of lead is the substance acted upon, the products are water and sulphide of lead: HSPbO HO + PbS. If a jar standing over water be filled with hydrosulphuric acid gas, and an equal volume of chlorine slowly passed up into it, the hydrochloric acid, as it forms, will be absorbed by the water, and the whole of the gases will disappear. Now chlorine and hydrogen are known to combine in equal volumes; hence this experiment shows that hydrosulphuric acid gas contains its own volume of hydrogen. The same fact may be more accurately demonstrated by In this case, 16 parts of sulphur take the the action of tin and some other metals, place of, or are equivalent to, 8 parts of which, when heated in the gas, take fire, oxygen. Most of these metallic sulphides combine with the sulphur, and liberate a being insoluble in water and acids, it folvolume of hydrogen equal to that of the lows, that when hydrosulphuric acid is original gas. Thus, when tin is heated by added to a solution of a metal, the sulphide a spirit-lamp, in a small bent tube or re- will be separated in the form of a pretort, filled with the gas and standing over cipitate. Moreover, many of the precipimercury, as shown in Fig. 25, it is found, tates thus formed have very characteristic when the combus- colours-arsenic forming a yellow, antition is over, and mony a brick-red, lead a black, and copper the apparatus has a brownish-black precipitate. These proregained its origi-perties render hydrosulphuric acid nal temperature, valuable agent in chemical analysis. Of that the level of many metals it will detect the minutest the mercury within traces; and the solutions of these metals, the tube remains on the other hand, afford extremely delicate the same as before. Now, hydrosulphuric indications of the presence of the gas itself. acid gas is 17 times as heavy as an equal A piece of paper, steeped in a solution of volume of hydrogen; consequently, out of lead, is quickly blackened by the smallest every 17 parts by weight of hydrosulphuric trace of hydrosulphuric acid, either difacid gas, 1 part must be hydrogen, and the fused through the atmosphere, or dissolved remaining 16 parts, sulphur. Moreover, in a liquid. since the density of sulphur vapour, when in Fig. 25. most Bisulphide or Persulphide of Hydrogen, HS-This compound bears the same relation to hydrosulphuric acid, that peroxide of hydrogen (HO) bears to water (HO). It is a yellow oily liquid, which is very prone to decomposition, and gives up its second equivalent of sulphur under circumstances similar to those in which peroxide of hydrogen parts with its second equivalent of oxygen (p. 180), viz., when brought in contact with certain metals and metallic oxides, such as finely divided platinum, oxide of silver, oxide of gold, &c. It likewise produces a white spot on the skin, and destroys vegetable colours. It may be prepared by pouring a solution of sulphide of potassium containing excess of sulphur, into hydrochloric acid diluted with two or three times its bulk of water : HCI KS, = KCl + HS2. The sulphide of potassium is prepared by fusing common pearlash (carbonate of potassium) with half its weight of sulphur. METALLIC SULPHIDES. Sulphur combines with all the metals, and with many of them in several proportions. Some metallic sulphides are found in nature, and form very important ores. Thus, galena, or lead-glance, the most abundant ore of lead, and that from which the metal is always obtained, is a sulphide of lead; the red mineral called cinnabar is a native sulphide of mercury; iron, copper, zinc, arsenic, and antimony, likewise occur abundantly in the form of sulphides. instance of the same kind.—2. By heating a metallic oxide in contact with sulphur; in which case part of the sulphur unites with the oxygen, and part with the metal.— 3. By heating a metal-tin, for examplein hydrosulphuric acid gas.-4. By the action of hydrosulphuric acid on the oxides, chlorides, and other compounds of the metals, either in the dry state or in solution. This and the third method have already been noticed.-5. By adding a soluble metallic sulphide-that of potassium, for instance-to a solution of another metal: thus, sulphide of potassium and chloride of iron yield chloride of potassium and sulphide of iron.-6. By passing the vapour of sulphide of carbon over a metallic oxide at a red heat.-7. By decomposing a metallic sulphate, sulphite, or hyposulphite (see next Lecture), with hydrogen or charcoal: thus, sulphate of potassium (KSO4), when heated to redness with charcoal, is deprived of its oxygen, and reduced to the state of sulphide (KS). All these modes of formation will be more fully illustrated when we come to speak of the individual metals. All metallic sulphides are solid at ordinary temperatures, and most of them are brittle, and exhibit a crystalline structure; the native sulphides of lead, iron, and zinc, often occur in large and regular crystals.* Most sulphides are less volatile than the pure metals. The sulphides of potassium, sodium, barium, calcium, and one or two others, are soluble in water; but the greater number of these compounds are insoluble. Metallic sulphides are variously affected by heat. Sulphide of gold gives up its sulphur at a moderate heat; whereas sulphide of zinc, if kept from contact with the air, is not decomposed at the highest temperatures. Most sulphides which contain more than one equivalent of sulphur, give off the excess at a red heat; such is the case with the bisulphide of iron, (FeS2) which, as already observed, is one of the Metallic sulphides may also be formed artificially in various ways:-1. By direct combination of sulphur with the metal, the action being frequently attended with evolution of light and heat. Thus, when a mixture of copper turnings and flowers of sulphur is gently heated in a flask till the sulphur melts and is converted into vapour, combination takes place, the whole mass becoming intensely heated, and glowing with a beautiful red light. When the action is over, the copper is found to be converted into a black sul*The student should take every opportunity of phide. This is a true case of combustion, making himself acquainted with the external the light and heat resulting from the characters of minerals, by visiting public colleccombination of the copper and sulphur, for himself. Specimens of the more abundant tions, and, as far as possible, making a collection precisely as in the combination of a sub-and therefore more important-minerals may stance with oxygen or chlorine. The formation of protosulphide of iron, by heating sulphur and iron together, is another be obtained at very moderate prices. To those who live in London, the magnificent collection at the British Museum presents invaluable opportunity of study. |