362 A POPULAR COURSE OF CHEMISTRY. VII. It is now my intention to introduce to your notice a most remarkable and highly-interesting gaseous element, namely hydrogen. Before, however, you can succeed properly in evolving it, there are several manipulations requisite to be performed, which are as follows: In the first place, you must obtain a pound or two of the metal zinc, and melt this in an iron ladle over a bright fire, just as you would so much lead. When perfectly melted, pour the metal very slowly from a height of three or four feet into a large pailful of cold water; it will hiss and spatter a good deal, but you need not be alarmed at that, for there is no danger. It is best not to hold the ladle so that all the melted zinc falls exactly in the centre of the water, but to carry the ladle round and round, so that the melted metal may be more dispersed in its fall. Now having done this, empty the water from the pail, and you will find at its bottom the zinc in small irregular pieces, of various sizes; collect them together (and be careful how you do this, for some of them are very sharp, and will wound the fingers very severely), and place them on a sieve, or in a large funnel to drain. The process of thus reducing zinc into small particles is called granulation, and the result, granulated zinc; it is a very convenient form of the metal for many operations. You would find it a matter of no small difficulty to break up a mass of zinc by mechanical means,—with a chisel and hammer it would take you a long time; but here, by the chemical agency of heat, you destroy the cohesion of the metal in a few minutes; and by pouring it in the melted state slowly into water, it soli-difies into small masses. This operation of granulation is not confined to zinc alone; many other metals may be similarly treated, as will be fully shown hereafter. The granulated zinc must now be dried by spreading it on the hob of the grate, and whilst this is doing, you may proceed to another operation. Select a soft, sound, and accurately-cut cork, that will tightly fit a narrow-mouthed pint glass bottle, and with a "rat-tail" file or 66 rasp" make a circular hole very neatly through the cork, so as to admit one end of a foot of common " gas-tubing," either of pewter or copper. If this does not happen to fit as accurately as you could wish, melt a little bees'-wax around it; the tube must now be bent into a shape something like the letter S turned thus, ʊ. A little knack is required in thus bending the tube so as to make two regular and handsome bends; for if you do not mind what you are about, you will get a very ugly shape, flat in some parts, and round in others, on account of the unequal strain upon the metal; but if you stop up one end of the tube with a small cork, then fill it full of dry sand, and stop up the other end also with a cork, you render the tube much more manageable, because as you bend it, the enclosed sand resists any unequal pressure, and supports all parts of the metal alike, and thus you obtain a very neatly bent tube; now remove the corks and shake out the sand. Put an ounce or two of granulated zinc into the bottle, and about half fill it with water; and having arranged your pneumatic trough, and all its bottles and jars with cold water, as directed for oxygen, pour into what we will call the gas-bottle, that is, the glass bottle, some strong sulphuric acid (oil of vitriol), until you find a tolerably brisk effervescence ensue; then insert the curved pipe; wait a minute or so before you plunge its extremity under the water of the trough, in order that all the common air may be thoroughly expelled by the hydrogen which is evolving, for the effervescence is due to its liberation. Then proceed to collect it, by causing it to bubble through the water, as for oxygen or chlorine; you will find it come over very readily and very abundantly; but should the action flag after a time, empty out the liquid contents of the "gas-bottle," leaving only the zinc, and insert a fresh charge of water and acid as before, and thus you may go on evolving hydrogen until all the zinc is entirely dissolved. Now you find that the hydrogen gas collected in your pneumatic apparatus is as perfectly invisible as common air or oxygen; but perhaps during the operation of collecting it some has escaped, and you have observed a peculiar smell; this, however, is owing to impurities in the zinc employed in the experiment; perfectly-pure hydrogen is devoid of smell, but it is a most difficult matter to obtain it. However, what you have collected is quite pure enough for all your experiments; and now proceed to examine its properties. Open a bottle of the gas, and immerse a lighted taper,—the hydrogen instantly takes fire, with a very pale flame, so pale, indeed, as scarcely to be visible in broad day-light; it is therefore an inflammable gas; but you will remark that the taper is extinguished, so that hydrogen although inflammable, and highly so, as subsequent experiments will show, yet will not support combustion. You will have a better opportunity of examining the flame of hydrogen if you make a hole through another cork to fit the large end of a long piece of tobacco-pipe, and placing this in the neck of the gas-bottle, after putting in a charge of zinc, water, and acid; allow the effervescence to proceed for about two minutes, and then apply a bit of lighted paper to the other end of the tobacco-pipe, the hydrogen will instantly take fire with a sharp pop, and burn for a very long time with a beautiful pale flame. This arrangement constitutes "Priestley's philosophical candle;" rather an unlucky term by the way, because, although a "philosophical," it is by no means a luminous candle, being the purest and palest form of flame hitherto known. Place it in a dark room, and you will barely be able to distinguish the printed letters of a book even when held very close to it; but although thus non-luminous, it is most intensely hot; it will readily kindle a bit of paper or wood, and heat a bit of iron to a very high temperature, or if you happen to have a bit of thin platinum-wire amongst your "chemicals," hold it in the pale flame and remark how intensely the wire is ignited, not burned, remember, and how much light is now suddenly evolved, by the introduction of this solid, and almost infusible and incombustible metal. The book actually becomes legible now; but remove the platinum-wire and it is no longer so. All these facts regarding the increased light of pale flames by the introduction of solid bodies, will come before you on a future occasion; and therefore I do not enter upon them in detail at present. Now, in the first experiment, with the bottle of hydrogen in the pneumatic trough, and also in the second, with the "philosophical candle," the gas took fire with only a very slight pop, scarcely meriting the title of an explosion, because it was tolerably pure and free from admixture with common air; but supposing this to have been present, what result would have taken place? why, the hydrogen, instead of burning quietly, would have burned with explosion. Let us take the "philosophical candle," to illustrate this point. You find it burning quietly on, because the combustion is supported by the air around, which comes gradually around to answer the demand of the flame for oxygen, which, as I have frequently told you, is one of the constituents of air; but, supposing that we applied a light to the end of the tobacco-pipe, the instant after the acid was poured on the water and zinc, what would have been the consequence? why an explosion,—because the materials only occupying about one half of the bottle, the other half was filled with air; and when the first portions of hydrogen were evolved, mixing with this they had oxygen enough to support their combustion, not slowly, but rapidly, and the whole arrangement would have been blown to pieces by the explosion. Hence, in experimenting with hydrogen, you should always be cautious to let the common air be completely expelled before you attempt either to collect or inflame the gas, otherwise a serious accident may happen to you, by the fragments of the glass apparatus being violently scattered around by the explosion. You can safely make an experiment which will satisfy you regarding this matter, by taking a bladder rather more than half full of air, and then tying it on to the bent-tube of the gas-bottle, or the pipe of the "philosophical candle," until its inflation is completed with hydrogen; then, removing it from the tube, hold a lighted taper to its neck,—the mixture of air and hydrogen will explode with great violence, rending the bladder into threads. Take a tin tube, about two inches in diameter and a foot long, closed at one end; fill it with water in the pneumatic trough, as you would any other vessel; then transfer into it six parts or small glasses full of air, and two of hydrogen,-apply a light to this, you get a loud explosion, and there is no danger of any accident happening. Do not attempt the experiment in a glass tube of similar size. Supposing that you again take this tube and transfer into it one measure or part of oxygen, and two of hydrogen, and put a lighted taper to this mixture, you will obtain a yet more rapid and powerful explosion, because the oxygen being pure, and unmixed with nitrogen, as in atmospheric air, the hydrogen combines with it far more intensely and eagerly. Next to the inflammability of hydrogen, its levity is the most remarkable character, and we will now proceed to examine this. Take two bottles of hydrogen, place one of them on the table, with its mouth upwards, and remove the stopper; hold the other with its mouth downwards, and remove its stopper; let the bottles remain in this position for about a minute, and then apply a lighted taper to the mouths of each; you will find no flame issue from that with its mouth upwards, but a flame and explosion from that with its mouth downwards; both bottles were full of hydrogen at the outset of the experiment, therefore, what has become of it out of the one bottle? Why, the light hydrogen has ascended into the air, or, if you please, the heavy air has pressed it out of the bottle; but the hydrogen remains in the bottle held with its mouth downwards, because, being so much lighter than air, it cannot fall through it, nor can the heavy air force it out; a little mixture of the air and hydrogen certainly does take place, and that causes the explosion when you apply the taper; and ultimately the hydrogen would all escape, in virtue of a singular tendency which all gaseous bodies have to mix, however opposite may be their relative weights or specific gravities, as will appear from the following experiment: Take a glass tube, about eighteen inches long, and an eighth of an inch in the bore, open at both ends; perforate two corks that will fit the necks of two stout narrow-mouthed four ounce bottles, and thrust a cork on to each end of the tube; now fill one bottle with hydrogen, and the other with oxygen, and connect them with the tube and corks, so as to stand like the annexed figure, the lower bottle containing the Oxygen, and the upper the hydrogen; leave them thus at rest for some hours, and then uncork them, and by a lighted taper test them both; you will probably find the contents of each explosive, and certainly so if you leave them connected for a day or two. This proves that the heavy oxygen has ascended, or been attracted upwards by the light hydrogen, and vice versá; or otherwise, how could each bottle contain a mixture of the two gases? This is a very interesting experiment, and well worth making; I should tell you that in corking the bottle, containing the hydrogen, you must hold it with the mouth downwards; and that containing the oxygen with the mouth upwards. The experiments relative to the levity of hydrogen are very numerous, and very beautiful, and it is difficult to make a selection of the most striking. You probably very well know that balloons were generally inflated with hydrogen, previous to the discovery of the levity of coal-gas, or carburetted hydrogen; you may imitate the inflation of a balloon on a miniature scale, by obtaining, from the philosophical instrument makers, a small balloon, made of membrane, about six or eight inches in diameter; these are now very commonly sold at half a crown, and from that to five or six shillings each; they are excessively light, and if you press all the air out of one of them, and then tie it on to the bent-tube of the gasbottle, or the pipe of the philosophical candle, you can easily inflate it with hydrogen, and then upon detaching it from the pipe, it will be found so buoyant as to rise rapidly to the ceiling of the room, where it remains until the hydrogen escapes through the pores of the membrane, and then your miniature balloon falls to the floor. When this experiment was first shown to a party of philosophers, (I believe by Dr. Black,) they, being unacquainted with the extreme levity of hydrogen, could not believe that the thin membrane or bladder rose and remained at the ceiling of its own accord; they suspected that some confederate was in the room above, who, at a given signal from below, drew up the thin bladder, by means of a fine horse-hair or silk thread, attached to it, and passing through a small hole in the ceiling! Balloons of enormous magnitude, inflated with hydrogen or carburetted hydrogen, are now so common, that almost everybody is aware of the cause of their ascending force, and no one suspects that they are pulled upwards by any threads or strings. But, although thus common, a balloon ascent never fails to excite a vast deal of attention and interest ; indeed, I think it a most magnificent sight to see a huge balloon bound away from the earth, and soar away amidst the regions of the air. Hitherto the balloon has not proved a very useful instrument to science, although some curious facts and observations concerning the state of the higher regions of the atmosphere have certainly been contributed to our stock of knowledge through its agency; and we cannot help looking forward with some considerable degree of interest for an authentic and detailed account of the magnificent voyage of 480 miles, lately made by three aëronauts in the stupendous "Vauxhall Balloon.” But to return more immediately to the miniature experiments of the laboratory: there is another way of showing the levity of hydrogen, both beautiful and instructive. Make a basinful of strong soap-lather, just as if you were about to blow common soap-bubbles; (an amusement, by the way, practised by the immortal Newton, and therefore demanding no apology for its apparent simplicity or childishness.) Then fill a large bladder (fitted with a stop-cock) full of hydrogen, from either apparatus already described, and to the stop-cock adjust a short tobacco-pipe; immerse this in the lather, then open the cock, compress the bladder gently, and you will succeed in blowing a soap-bubble with hydrogen; detach it from the bowl, and away it will soar into the air with great rapidity: this is another miniature balloon. But you will very probably say, "Why, any common soap bubble, blown by a child will do the same thing." Yes, it certainly will ascend, but with nothing like the same rapidity; and the reason that it ascends at all is, that the breath from the lungs with which it is blown is warmer, expanded, and therefore lighter than air; it is an imitation, not of the "air-balloon," which ascends on account of its inherent and permanent levity, but of the "fire-balloon,” which ascends because the air within it is temporarily rarefied by exposure to a high temperature. When this cools, the fire-balloon falls,-whereas the "air-balloon," meaning by the term a gas balloon, will go on ascending until it bursts by expansion in the higher regions of the air. A fact this, well known to aëronauts, who, as they rise to a great altitude, are obliged to allow a considerable portion of the gas to escape, or otherwise it would expand in the rare regions of the air, and burst the balloon. I have not space here to enter into more details concerning the art of aërostation, and therefore shall take leave of the subject, and direct your attention to another experiment, illustrative of the levity of hydrogen. Take a wide-mouthed glass bottle or jar, full of common air, and another of the same size filled with hydrogen, hold one in each hand, with the mouths downwards, and in this position let an assistant take out |