The Boy's Playbook of Science Part 14

[Ill.u.s.tration: Fig. 120. Gurney's jet. A. Pipe with stop-c.o.c.k leading from the gas-holder. B. The little reservoir of water through which the mixed gases bubble. C. The jet where the gases burn. D. Cork, which is blown out if the flame recedes in the pipe, C.]

Mr. Woodward states, that a series of experiments, continued during many years, has proved, that while the bladder containing the mixed gases is under pressure, the flame cannot _be made_ to pa.s.s the safety chambers, and consequently an explosion is impossible; and even if through extreme carelessness or design, as by the removal of pressure or the contact of a spark with the bladder, an explosion occurs, it can produce no other than the momentary effect of the alarm occasioned by the report; [Page 123] whereas, when the gases are used in separate bags under a pressure of two or three half hundredweights, if the pressure on one of the bags be accidentally removed or suspended, the gas from the other will be forced into it, and if not discovered in time, will occasion an explosion of a very dangerous character; or if through carelessness one of the partially emptied bags should be filled up with the wrong gas, effects of an equally perilous nature would ensue.

[Ill.u.s.tration: Fig. 121. A. The bladder of mixed gases, pressed by the board, B B, attached by wire supports to another board, C C, which carries the weights, D D. E E. Pipe to which the bladder, A, is screwed, and when A is emptied, it is re-filled from the other bladder, R. F F F.

Pipe conveying mixed gases to the lantern, G G, where they are burnt from a Gurney's jet, H.]

In the oxy-hydrogen blowpipe usually employed, the gases are kept quite separate, either in gasometers or gas bags, and are conveyed by distinct pipes to a jet of very simple construction, devised by the late Professor Daniell, where they mix in very small volumes, and are burnt at once at the mouth of the jet. (Fig. 122.)

[Ill.u.s.tration: Fig. 122. Daniell's jet. O O. The stop-c.o.c.k and pipe conveying oxygen, and fitting inside the larger tube H H, to which is attached a stop-c.o.c.k, H, connected with the hydrogen receiver. A. The orifice near which the gases mix, and where they are burnt.]

The gases are stored either in copper gasometers or in air-tight bags of Macintosh cloth, capable of containing from four to six cubic feet of gas, and provided with pressure boards. The boards are loaded with two or three fifty-six pound weights to force out the gas with sufficient [Page 4] pressure, and of course must be equally weighted; if any change of weight is made, the stop-c.o.c.ks should be turned off and the light put out, as the most disastrous results have occurred from carelessness in this respect. (Fig. 123.)

[Ill.u.s.tration: Fig. 123. Gas bag and pressure boards.]

The oxy-hydrogen jet is further varied in construction by receiving the gases from separate reservoirs, and allowing them to mix in the upper part of the jet, which is provided with a safety tube filled with circular pieces of wire gauze. (Fig. 124.) With this arrangement a most intense light is produced, called the Drummond or lime light, and coal gas is now usually subst.i.tuted for hydrogen.

[Ill.u.s.tration: Fig. 124. A A. Board to which B B is fixed. O. Oxygen pipe. H. Hydrogen pipe. C C. s.p.a.ce filled with wire gauze. D. Lime cylinder.]

[Page 125]

_Seventeenth Experiment._

There are many circ.u.mstances that will cause the union of oxygen and hydrogen, which, if confined by themselves in a gla.s.s vessel, may be preserved for any length of time without change; but if some powdered gla.s.s, or any other finely-divided substance with sharp points, is introduced into the mixed gases at a temperature not exceeding 660 Fahrenheit, then the gases silently unite and form water.

This curious mode of effecting their combination is shown in a still more interesting manner by perfectly clear platinum foil, which if introduced into the mixed gases gradually begins to glow, and becoming red-hot causes the gases to explode. Or still better, by the method first devised by Dobereiner, in 1824, by which finely prepared spongy platinum--_i.e._, platinum in a porous state, and exposing a large metallic surface--is almost instantaneously heated red-hot by contact with the mixed gases. When this fact became known, it was further applied to the construction of an instantaneous light, in which hydrogen was made to play upon a little ball of spongy platinum, and immediately kindled. These Dobereiner lamps were possessed by a few of the curious, and would no doubt be extensively used if the discovery of phosphorus had not supplied a cheaper and more convenient fire-giving agent. When the spongy platinum is mixed with some fine pipeclay, and made into little pills, they may (after being slightly warmed) be introduced into a mixture of the two gases, and will silently effect their union. The theory of the combination is somewhat obscure, and perhaps the simplest one is that which supposes the platinum sponge to act as a conductor of electric influences between the two sets of gaseous particles; although, again, it is difficult to reconcile this theory with the fact that powdered gla.s.s at 660, a bad conductor of electricity, should effect the same object. The result appears to be due to some effects of surface by which the gases seem to be condensed and brought into a condition that enables them to abandon their gaseous state and a.s.sume that of water.

When Sir H. Davy invented the safety-lamp, he was aware that, in certain explosive conditions of the air in coal mines, the flame of the lamp was extinguished, and in order that the miner should not be left in the dreary darkness and intricacies of the galleries without some means of seeing the way out, he devised an ingenious arrangement with thin platinum wire, which was coiled round the flame of the lamp, and fixed properly, so that it could not be moved from its proper place by any accidental shaking. When the flame of the safety-lamp, having the platinum wire attached, was accidentally extinguished by the explosive atmosphere in which it was burning, the platinum commenced glowing with an intense heat, and continued to emit light as long as it remained in the dangerous part of the mine. Sir H. Davy warned those who might use the platinum to take care that no portion of the thin wire pa.s.sed _outside_ the wire gauze, for the obvious reason that, if ignited outside the wire gauze protector, it would inflame the fire-damp.

[Ill.u.s.tration: Fig. 125. P P. Two platinum plates connected with wires to the cups. The wires are pa.s.sed through holes in the finger-gla.s.s, B B, and are fixed perfectly steady by pouring in cement composed of resin and tallow to the line L L. Two gla.s.s tubes filled with water acidulated with sulphuric acid, and placed over the platinum plates in finger-gla.s.s, which also contains dilute sulphuric acid to improve the conducting power of the water. The wires of the battery are placed in the cups, and the arrows show the direction of the current of electricity.]

[Page 126]

_Eighteenth Experiment._

Water is decomposed by pa.s.sing a current of voltaic electricity through it by means of two platinum plates, which may be connected with a ten-cell Grove's battery. The gases are collected in separate tubes, and the experiment offers one of the most instructive ill.u.s.trations of the composition of water. (Fig. 125.)

There is a current of electricity pa.s.sing from and between two platinum plates decomposing water, offering the converse of the Dobereiner experiment, and highly suggestive of the probability of the theory already advanced in explanation of the singular combination of oxygen and hydrogen in the presence of clean platinum foil, and more especially when we consider the operation of Grove's gas battery, in which a current of electricity is produced by pieces of platinum foil covered with finely-divided platinum, called platinum black; each piece is contained in a separate gla.s.s tube filled alternately with oxygen and hydrogen, and by connecting a great number of these tubes a current of electricity is obtained, whilst the oxygen and hydrogen are slowly absorbed and disappear, having combined and formed water, although placed in separate gla.s.s tubes. (Fig. 126.)

The a.n.a.lysis of water is shown very perfectly on the screen by fitting up some very small tubes and platinum wires in the same manner as shown in fig. 125. The vessel in which the tubes and wires are contained with the dilute sulphuric acid must be small, and arranged so as to pa.s.s nicely into the s.p.a.ce usually filled by the picture in an ordinary magic lantern, or, still better, in one lighted by the oxy-hydrogen or lime light. If the dilute acid is coloured with a little solution of indigo, the gradual displacement of the fluid by the production of the two gases is very perfectly developed on the screen when the small voltaic battery is attached to the apparatus; and of course a large number of persons may watch the experiment at the same time.

With respect to the application of the light produced from a jet of the [Page 127] mixed gases thrown upon a ball of lime, it may be stated that for many years the dissolving view lanterns and other optical effects have been produced with the a.s.sistance of this light; and more lately Major Fitzmaurice has condensed the mixed gases in the old-fashioned oil gas receivers, and projected them on a ball of lime; and it was this light thrown from many similar arrangements that illuminated the British men-of-war when Napoleon III. left her Majesty's yacht at night in the docks at Cherbourg.

[Ill.u.s.tration: Fig. 126. Grove's gas battery consists of tubes containing oxygen and hydrogen alternately, and having a thin piece of platinum foil, P, inserted by the blowpipe in each gla.s.s tube. The foil hangs down the full length of the interior of the gla.s.s. Each pair of tubes is contained in a little gla.s.s tumbler containing some dilute sulphuric acid, and the hydrogen tube, H, of one pair, is connected with the oxygen tube, O, of the next. W W. The terminal wires of the series.]

Mr. Sykes Ward, of Leeds, has also proposed a most simple and excellent application of the oxy-hydrogen light for illumination _under_ the [Page 128] surface of water, and for the convenience of divers, who are frequently obliged to cease their operations in consequence of the want of light. Mr. Ward's submarine lamp consists of a series of very strong copper tubes, which are filled with the mixed gases by means of a force-pump; and in order to prevent the lamp being extinguished, it burns under _double_ gla.s.s shades, which are desirable in order to prevent the gla.s.s immediately next to the light cracking by contact with the cold water.

[Ill.u.s.tration: Fig. 127. Cherbourg.]

The author tried this lamp at Ryde, and although the coast-guards objected to the production of a brilliant light at night, which they stated might be mistaken for a signal and would cause some confusion amongst the war vessels in the immediate neighbourhood, enough experiments were made, to show that the Ward lamp would burn for a considerable time under water, and could be kept charged with the gas by means of a process that was easily workable in the boat. The gases were taken out mixed in gas bags, and pumped into the reservoir when required. With a much larger reservoir greater results could be obtained; and if nautilus diving bells are to be used in modern warfare, they will require a powerful light to show them their prey, so that they may attach the explosives which are to blow great holes in the men-of-war.

[Ill.u.s.tration: Fig. 128. A A. Tube reservoir to hold the mixed gases. B.

The jet and lime ball. D. The first gla.s.s shade, held down by a cap and screw. C. The second gla.s.s shade. E E. The handle by which it is lowered into the water.]

[Ill.u.s.tration: Fig. 129. Submarine lamp.]

[Page 129]

CHAPTER XI.

CHLORINE, IODINE, BROMINE, FLUORINE.

_The four Halogens, or Producers of Substances like Sea Salt._

Chlorine ([Greek: _chloros_], green). Symbol, Cl. Combining proportion, 35.5. Specific gravity, 2.44. Scheele termed it dephlogisticated muriatic acid; Lavoisier, oxymuriatic acid; Davy, chlorine.

The consideration of the nature of this important element introduces to our notice one of the most original chemists of the eighteenth century--viz., the ill.u.s.trious Scheele, who was born at Stralsund, in 1742, and in spite of every obstacle, fighting his "battle of life" with sickness and sorrow, he succeeded in making some of the most valuable discoveries in science, and amongst them that of chlorine gas. It was in the examination of a mineral solid--viz., of manganese--that Scheele made the acquaintance of a new gaseous element; and in a highly original dissertation on manganese, in 1774, he describes the mode of procuring what he termed _dephlogisticated muriatic acid_--a name which is certainly to be regretted, from its absurd length, but a t.i.tle which was strictly in accordance with the then established theory of phlogiston; and if the latter is considered synonymous with hydrogen, quite in accordance with our present views of the nature of this element. Scheele discovered the leading characteristics of chlorine, and especially its power of bleaching, which is alone sufficient to place this gas in a high commercial position, when it is considered that all our linen used formerly to be sent to Holland, where they had acquired great dexterity in the ancient mode of bleaching--viz., by exposure of the fabric to atmospheric air or the action of the damps or dews, a.s.sisted greatly by the agency of light. Some idea may be formed of the present value of chlorine, when it is stated that the linen goods were retained by the Dutch bleachers for nine months; and if the spring and summer happened to be favourable, the operation was well conducted; on the other hand, if cold and wet, the goods might be more or less injured by continual exposure to unfavourable atmospheric changes. At the present time, as much bleaching can be done in nine weeks as might formerly have been conducted in the same number of months; and the whole of the process of chlorine bleaching is carried on independent of external atmospheric caprices, whilst the money paid for the process no longer pa.s.ses to Holland, but remains in the hands of our own diligent bleachers and manufacturers.

_First Experiment._

[Ill.u.s.tration: Fig. 130. A. Flask containing the fuming hydrochloric acid, which is gently boiled by the heat of the spirit lamp. B. Tube pa.s.sing to the Wolfe's bottle, containing pumice-stone or asbestos moistened with sulphuric acid. C. Second tube pa.s.sing into a dry empty bottle, which receives the hydrochloric acid gas.]

As Scheele first indicated, chlorine is obtained by the action of the black oxide of manganese, on "the Spirit of Salt," or hydrochloric acid; and the most elementary and instructive experiment showing its preparation can be made in the following manner:--

[Page 130]

Place in a clear Florence oil-flask, to which a cork and bent tube have been first fitted, some strong fuming hydrochloric acid. Arrange the flask on a ring-stand, and then pa.s.s the bent tube either to a Wolfe's bottle containing some pumice-stone moistened with oil of vitriol, or to a gla.s.s tube containing either pumice or asbestos wetted with the same acid. Another gla.s.s tube, bent at right angles, pa.s.ses away from the Wolfe's bottle into a receiving bottle. (Fig. 130). On the application of heat, the hydrochloric gas is driven off from its solution in water, and any aqueous vapour carried up is retained by the asbestos or pumice stone wetted with oil of vitriol; the application of the latter is called _drying the gas_--i.e., depriving it of all moisture; sometimes the salt called chloride of calcium is used for the same purpose, and it must be understood by the juvenile chemist that gases are not dried like towels, by exposure to heat, or _by putting them in bladders before the fire_, as we once heard was actually recommended, but by causing the gas charged with invisible steam to pa.s.s over some substance having a great affinity for water. The dry hydrochloric gas falls into the bottle, and displaces the air, being about one-fourth heavier than the latter, and gradually overflowing from the mouth of the vessel, produces a white smoke, which is found to be acid by litmus paper, but has no power to bleach, and is not green; it is, in fact, a combination of one combining proportion of chlorine with one of hydrogen, and to detach the latter, and set the chlorine free, it is necessary to convey the hydrochloric gas to some body which has an affinity for hydrogen. Such a substance is provided in the use of the black oxide of manganese, which is placed either in a small flask or in a tube provided with two bulbs, and when heated with the lamp it separates the hydrogen from the hydrochloric gas, and forms water, which partly condenses in the second bulb. And now the gas that escapes is no longer acid and fuming with a white smoke on contact with the air; but is green, has a strong odour, bleaches, and is so powerful in its action on all living tissues, that it must be carefully avoided and not inhaled; if a small quant.i.ty is accidentally inhaled, it produces a violent fit of coughing, which lasts a [Page 131] considerable time, and is only abated by inhaling the diluted vapour of ammonia, or ether, or alcohol, and swallowing milk and other softening drinks. (Fig. 131.)

[Ill.u.s.tration: Fig. 131. A. The flask containing the fuming hydrochloric acid, heated by spirit lamp. B. Tube pa.s.sing to Wolfe's bottle, containing the pumice-stone or asbestos wetted with oil of vitriol. C.

Second tube, which pa.s.ses into a wide-mouthed small flask containing black oxide of manganese, partly in powder and partly in lump; and the third tube conveys the chlorine to any convenient vessel. The double bulb tube, E E, may be subst.i.tuted for the flask, the oxide of manganese being contained in the bulb M.--N.B. Any tube may be joined on to another by a bit of india-rubber tubing, which is tied by string.]

[Ill.u.s.tration: Tube A is joined to tube B by the caoutchouc pipe C, tied with packthread.]

_Second Experiment._

The mode of preparing chlorine, as already given, though very instructive, is troublesome to perform; a more simple process may therefore be described:--

Pour some strong hydrochloric acid upon powdered black oxide of manganese contained in a Florence oil-flask, taking care that the whole of the black powder is wetted with the acid so that none of it clings to the bottom of the flask in the dry state to cause the gla.s.s to crack on the application of heat. A cork and bent gla.s.s tube is now attached, and conveyed to the pneumatic trough; on the application of heat to the mixture in the flask the chlorine is evolved, and may be collected in stoppered bottles, the first portion that escapes, although it contains atmospheric air, should be carefully collected in order to prevent any [Page 132] accident from inhaling the gas, and it will do very well to ill.u.s.trate the bleaching power of the gas, and therefore need not be wasted. The above process may be described in symbols, all of which are easily deciphered by reference to the table of elements, page 86.

MnO_{2} + 2 HCl = MnCl + 2HO + Cl.

_Third Experiment._