I have said that any person would think that your bottles full of gas were all empty bottles, and perhaps might open them, and thus destroy your labour by permitting the gas to escape. To prevent this, as well as to guard against any accidental expansion of the gas forcing out the stopper, it is as well to tie them over with a bit of cloth or calico; and the gas may thus be kept for many months, in a cool situation.

But supposing one of the bottles holds a quart of gas, and you should like to fill a smaller bottle from it, how is this to be done? Certainly not by the common mode of pouring, as with wine or water; at least, it would require more practical skill than you have yet attained; but there is a very simple and easy method of doing it, as follows.

Fill the smaller bottle quite full of water in the trough, and slide it on the shelf as before; now take the large bottle, and plunging its neck quite below the water, withdraw the stopper.

Suppose these lines to represent the trough and the bottles: B is the large, and b the small bottle, the faint line is the level of the water, the dark lines the section of the trough; with one hand slide the small bottle nearly off the shelf, and with the other incline the large bottle into this position, beneath its mouth: the consequence will be, that the gas from B will bubble up through the water, and fill b to any extent that you please,-say quite full,-it is then to be slid on to the shelf, B restored to the perpendicular, with the mouth still under water remember,

B 6

the stopper replaced, and then remove the bottle from the trough. Now you have to attend to b; slide it off the shelf into deep water, and put in its stopper as before; and thus by inverted pouring, if the expression may be permitted, an invisible gas is transferred from one vessel to

another.

It must be obvious to you that as much water enters в as b contained; and therefore a corresponding quantity, or bulk, of gas from B has entered b. In order to gain dexterity in gaseous manipulation, it is a very good plan to practise transferring common air from one bottle to another; for perhaps at first you may waste a good deal of gas.

Bottles and jars unprovided with stoppers may be filled with gas in the way that has been described, and when these are to be taken from the trough, it is easily done by sliding them into deep water, placing a saucer beneath their mouths, and thus removing them, standing in the saucer, the water remaining in which effectually prevents the escape of the gas, and is called a water-lute. If it is desired to transfer the gas from one of these jars at any future time, it must be brought to the trough, sunk a little below the surface, and then, upon removing the saucer, the jar of gas may be operated upon at will.

For the experiments about to be mentioned with oxygen, stoppered bottles are the most convenient.

The first and most remarkable property of oxygen, is its power of supporting combustion in a far more energetic manner than common air. This was hinted at above, when directing you how to test for its presence; but now that a considerable quantity of the gas has been collected, this fact can be shown in a still more remarkable degree.

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Stick a bit of green wax-taper at the short end of a wire bent like this light it, open one of the bottles of oxygen in the usual way, that is to say, as it stands on the table, and quickly plunge the taper into it; the flame is greatly enlarged, and the light is most brilliant; draw it out, puff out the flame, and again dip in the glowing wick; it is rekindled with a sharp pop or explosion. There is no fear of oxygen escaping whilst you do this, for its weight is greater than that of air, and therefore it remains in the bottle when opened, because the lighter air cannot descend and force it out; just the same as water, which is heavier than air, remains in a glass.

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I cannot enter into the details about ascertaining the weight of oxygen; but perhaps the following example will render the matter intelligible. Supposing that I have a glass vessel, exhausted, or devoid of air; that I take the tare of it, and then allow air to rush in and fill it; upon weighing again, I find that it has increased in weight 1000 parts. This, therefore, is the weight of air which the vessel can contain. now remove the air, leaving the vessel as empty as before, and then allow oxygen to rush in and fill it: upon weighing again, I find that it has increased in weight 1111 parts. This, therefore, is the weight of a bulk of oxygen equal to the former bulk of air; the bulks are similar, the weights are different.

1111.

Oxygen is heavier than air, or, as chemists express it, thus: calling air the standard of unity, or 1.000, the specific gravity of oxygen, in comparison with it, is Now this little difference in weight is amply sufficient to cause it to remain in the bottle for some little time after the stopper is removed: it is true that it will escape out of the bottle in time; but this is not on account of the light air descending and forcing it out, but from a singular tendency which gaseous or aëriform bodies have to mix with each other, independent of all reference to their relative weights or specific gravities; a case somewhat analogous to that of the mixture of spirit and water, mentioned in the paper on Chemical Affinity*.

Although air cannot fall through oxygen, yet oxygen can fall through air, as may be proved by inverting a bottle of the gas, and removing the stopper. After the lapse of a minute, if you put a lighted taper into the bottle, it will burn with its usual flame. If the air of the room is very calm, and you take a wide-mouthed bottle of air, and set it on the table, you may perhaps succeed in pouring it full of oxygen from one of the bottles that has been collected. A lighted taper will soon show whether you have succeeded, for it will burn with brilliancy in the bottle that just now contained the air, but with its usual flame in the other from which the oxygen has poured.

I shall hereafter adduce some very remarkable experiments of this nature with other gases.

See Magazine of Popular Science, vol. ii., p. 41.

Oxygen gas is without taste or smell: it has no action on vegetable colours. Put a bit of litmus and a bit of turmeric paper* into the gas; neither of these tests are affected, and therefore oxygen is neither acid nor alkaline; and yet the name would lead you to imagine that it possessed some relation to acids. Let us see how this can be made out.

Take a little bit of phosphorus, about the size of a small peat, wash it in some clean water, and then place it on a bit of litmus-paper, it shows no signs of acidity, now quickly and cautiously wipe it dry, and place it in a small ladle, called a "deflagrating spoon," the wire of which is thrust through a cork, or "shive," large enough to cover, but not to fit the neck of a bottle of oxygen, the part of the cork next the rim of the bottle should have a circular flat disc of tin-plate upon its surface, for this is a combustible experiment, and the flame of the phosphorus would soon set fire to the uprotected cork, and, perchance, break the bottle; the disc of tin acts as a screen, and prevents this taking place.

Having arranged this matter, and by sliding the wire through the cork, adjusted it so that the spoon may hang about half-way into the bottle, which you can guess at by outside measurement; the bottle is to be placed on the table, its stopper loosened with one hand, whilst the other holds the spoon over the flame of a candle, until the phosphorus first burns. The stopper is then to be withdrawn, and the spoon with the burning phosphorus, quickly, yet steadily, plunged into the gas.

A most splendid combustion instantly takes place, intense heat and light are evolved, in consequence of the mutual affinity which the bodies have for each other, and when the combustion is over, you will find the bottle filled with dense white fumes; remove the spoon, pour in a little water, close the bottle lightly with a cork, and leave it at rest for a few minutes. You must not close the bottle with its own stopper, because, during the combustion, the contents of the bottle are rarefied and expanded by the heat, and if the ground stopper was directly put in, as the bottle cooled, the pressure of the atmosphere would fix the stopper so firmly in its place, that it is a chance whether you would ever be able to move it again. This should be remembered in all analogous experiments, for many a valuable bottle is thus rendered useless, or perhaps broken, by attempts at forcing out the stopper.

Now put a bit of litmus paper into the bottle; its blue colour is intensely reddened; here then you have an instance of chemical affinity, producing an acid, viz., the phosphoric acid.

Sulphur, carbon, and several other simple substances, will burn with considerable splendour in oxygen, and produce acid compounds. So general, indeed, was the acid result, that oxygen was at one time adopted as the universal acidifying principle, and hence the derivation of its name. We now, however, know that it is equally active in producing alkalies (which are diametrically opposed to acids), and also bodies, having neither acid nor alkaline properties, viz. metallic oxides; black oxide of manganese, for example.

Place a small globule of potassium in a deflagrating-spoon, heat it

* See Mag. Pop. Science, ii., 47.

It is very combustible, and must be handled with great caution, for the heat

of the fingers will often kindle it; and, therefore, you must keep it under water until the moment that you want it.

over a spirit-lamp, until it begins to burn*, and then plunge it into oxygen, a vivid combustion ensues; wash out the spoon with a little water, dip in a bit of turmeric-paper, the yellow is instantly changed to brown, indicating the formation of the alkali potassa, or the alkaline oxide of potassium.

If you take out the manganese from the retort, insert a fresh charge, and proceed to evolve oxygen again; another experiment can be made, which is highly instructive: take a large bladder, soak it well in water, tie on to its neck a common gas stop-cock that will fit the end of the pewter pipe, and as soon as oxygen comes off, squeeze the bladder, so that no air remains in it, then fix it on to the pipe with the cock open. If the cock does not screw on, you can make it do so, by putting some paper between; but it is much better to fit it with paper so as to slide on, because when the bladder is full of gas you can instantly remove it by sliding the cock off the pipe-screwing it off is not so handy. When the bladder is full of gas, shut the cock, and quickly remove it from the end of the pipe.

Another bladder may be filled in like manner :-to the stop-cock of the first, fix on a plain brass blowpipe (which can be easily procured at the ironmongers'), and make the joints tight with slips of wetted bladder as before directed.

Now take a piece of charcoal, about six inches long and an inch in diameter, make a small cavity in it with the point of a knife, big enough to hold half a pea, put a bit of lighted amadou in this, and by opening the cock, and gently compressing the bladder, force a stream of oxygen slowly from the beak of the blow-pipe upon the tinder, this will soon heat the cavity of the charcoal red-hot; and when this happens, instantly drop in a bit of steel, broken from the end of a file, or a castiron "sparable" will do:-urge on the gas, an intense heat results, the metal melts, and presently burns with the emission of a shower of brilliant sparks, exactly like the celebrated fire-work, called a gerbe; when these cease, shut off the gas, let the globule cool, and then examine it: : you will find it very brittle and easily reduced to powder. Try it with the test-papers. It is neither acid nor alkaline, it is a neutral metallic oxide of iron.

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Now these three experiments are very instructive ones, they show you intense chemical affinity existing between bodies of the most opposite natures, they show you oxygen, forming an acid, an alkali, and an oxide, all again new and distinct substances; they also show you getically oxygen supports combustion, and about the time that oxygen was adopted as the "universal acidifying principle," it was also adopted as the "universal supporter of combustion." This was another grand error, for we now know that there are instances of combustion in which no oxygen, or compound of oxygen, is present, and of others in which its presence so far from inducing, actually prevents combustion; but it takes

* The potassium must be wiped free from the naphtha in which it is usually kept, and when you hold it over the spiritlamp, very likely you will see a flame like coal-gas quickly rise from the globule, this

is the naphtha burning off; and you must not plunge it into the gas until a purple flame appears; that is, the flame of potassium.

place the moment that oxygen is withdrawn. At the time of the discovery of oxygen (1774), philosophers had hardly shaken off the trammels of alchymy, and it was the fashion to draw sweeping and general conclusions from a few experiments; at the present day, our operations and reasonings are conducted with more refinement and precision; hypotheses and theories are carefully examined before they are so generally adopted as heretofore. Philosophers now endeavour to act up to the Baconian precept, which says, "Conclusions are, in all cases, to be drawn after the comparison of a sufficient number of facts, with a due regard to objections."

Oxygen is an elementary substance, permanently gaseous at all known temperatures and pressures: it is most abundantly distributed throughout the three kingdoms of nature, but always in combination with other elementary substances; it has never yet been found in a free or uncombined state.

The black oxide of manganese is the metal manganese saturated with oxygen, and therefore a peroxide, (see vol. i., p. 298,) consisting of manganese 28 + oxygen 16 = 44; when this is heated red-hot, the affinity between the two substances is weakened to some extent. Part of the oxygen escapes in the free gaseous form, leaving a sesquioxide of a brownish colour, consisting of manganese 28+ oxygen 12 = 40 sesquioxide of manganese; and in this compound the affinity between the two substances is so strongly exerted, that heat alone cannot overcome it, therefore no more oxygen can be extracted from the sesquioxide. This, however, must not induce you to throw it away as useless; it should be preserved for some experiments hereafter to be mentioned.

Oxygen supports respiration: Priestley put a mouse into a jar containing it, and he found that the animal lived about thrice as long as when confined in an equal bulk of common air.

You must not conclude from this, that it is eminently fitted for maintaining the functions of vitality, for the contrary is the case; an animal caused to breathe pure oxygen for any length of time, at last falls a sacrifice to its stimulating agency, and upon examination after death, the blood in the veins is found as florid as that in the arteries.

It is well worth notice and recollection here, that although we have many gases that may be breathed for a considerable time without hurting life, yet we have no gas or mixture of gases fit for its perfect support, save atmospheric air, which you will hereafter find to be a mixture of oxygen and nitrogen.