Liquid oxygen

“ It is impossible to obtain in the market absolutely chemically pure oxygen. All the oxygen that we have thus far been able to purchase contains nitrogen and, in some instances, measurable amounts of water-vapor and carbon dioxide. The better grade of oxygen, that prepared from liquid air, is practically free from carbon dioxide and water-vapor, but it still contains [Pg 85] nitrogen, and hence with every liter of oxygen admitted there is a slight amount of nitrogen added. ”

“ Finally, the fourth application of liquid air is for the purpose of getting oxygen from the air. This can be accomplished by chemical means, but the chemical method is somewhat expensive. Oxygen has commercial value, and cheap oxygen would be a decided advantage in a number of branches of industry. It will be observed that it is the liquid oxygen that makes possible the preparation of the explosive described in the last paragraph. Oxygen as such in the form of gas is of value in Deacon's process for the manufacture of chlorine. ”

“ But a use to which liquid air machines have already been put to a large extent is for obtaining oxygen from the atmosphere. Although when air is liquefied the oxygen and nitrogen are condensed simultaneously, yet owing to its greater volatility the latter boils off the more quickly of the two, so that the remaining liquid becomes gradually richer and richer in oxygen. ”

“ Liquefied oxygen is an exceedingly mobile transparent liquid, with a faint blue tint and boiling (tension = 1 atmosphere) about -180°. Oxygen, like all gases, is transparent, and like the majority of gases, colourless. It has no smell or taste, which is evident from the fact of its being a component of air. The weight of one litre of oxygen gas at 0° and 760 mm. pressure is 1·4298 gram; it is therefore slightly denser than air. Its density in respect to air = 1·1056 and in respect to hydrogen = 16. [21]
Fig. 29.—Mode of burning sulphur, phosphorus, sodium, &c., in oxygen. ”

“ It is sixteen times as heavy as the gas hydrogen when measured by volume under the same temperature and pressure. Under all ordinary conditions oxygen remains in a gaseous form, although it turns to a liquid when compressed to 4,400 pounds to the square inch and at a temperature of 220° below zero. ”

“ Some oxygen gas contained in a bladder provided with a proper jet may be squeezed out, and upon, some liquid phosphorus contained in a cup at the bottom of a finger glass full of boiling water, when a most brilliant combustion occurs, proving that so long as the principle is complied with—viz., that of furnishing oxygen to a combustible substance—it will burn under water, provided it is insoluble, and possesses the remarkable affinity for oxygen which belongs to phosphorus. ”

“ In accordance with these results, then, water must be regarded as a compound containing hydrogen and oxygen in the proportion of 1 part by weight of hydrogen to 7.94 parts by weight of oxygen.
Relation between the volume of aqueous vapor and the volumes of the hydrogen and oxygen which combine to form it. When the quantitative synthesis of water is carried out in the eudiometer as described above, the water vapor formed by the union of the hydrogen and oxygen at once condenses. The volume of the resulting liquid is so small that it may be disregarded in making the calculations. ”

“ The combination of oxygen in combustion is always accompanied by a disengagement of light and heat; whilst this circumstance is not a necessary consequence of simple oxygenation.
CAROLINE.
But how can a body absorb oxygen without the combination of the two electricities which produce caloric?
197 MRS. B.
Oxygen does not always present itself in a gaseous state; it is a constituent part of a vast number of bodies, both solid and liquid, in which it exists in a much denser state than in the atmosphere; and from these bodies it may be obtained without much disengagement of caloric. ”

“ Let us assume, for example, that oxygen becomes liquid under a pressure of 200 atmospheres, whilst azote requires a pressure of 250. Then if atmospheric air be condensed to the two hundredth part of its bulk, the oxygen will be found in a liquid state at the bottom of the vessel in which the condensation is effected, and the upper part of the vessel will contain only azote in the state of gas. The oxygen, now liquified, may be drawn off for the supply of the furnace ”

“ If we mix them in a vessel and apply a match, there is instantly a powerful explosion, heat is generated and there is formed—water. The two strange, invisible gases have combined and formed the well-known liquid. Whenever a substance which contains hydrogen, like wood, paper, starch, sugar, &c., burns, it forms water with oxygen of the air. In fact, these two gases are always ready, on the slightest provocation to unite. Rain, or melted snow, approaches nearest to chemically pure water, but all wells, springs, rivers and seas contain dissolved substances, in greater or less degree. ”

“ Now, what I wish to have you understand by that, is this: that the average man requires about 137,200 cubic inches of oxygen in every twenty-four hours. This is the accepted way of putting it; in reality, he needs the ozone contained in that amount of oxygen. I do not desire that you should receive the impression that the oxygen is not needed for the man, but that the ozone only is required for the continuance of life where there is no action. I may surprise you when I say that each of you draws into your lungs, every day, over seven pounds of oxygen gas, but such is the case. ”

“ Now, in different climates the quantity of oxygen introduced into the system by respiration, as has been already shown, varies according to the temperature of the external air; the quantity of inspired oxygen increases with the loss of heat by external cooling, and the quantity of carbon or hydrogen necessary to combine with this oxygen must be increased in the same ratio. ”

“ Each one of us sitting quietly in this room would breathe about 1000 times in an hour, requiring over 100 gallons of air to sustain the proper supply of oxygen for the blood. During this time we have taken from the air a certain amount of oxygen and have returned to it an equal amount of something else, which we call carbon oxide, or carbonic acid gas. ”

“ I need not therefore say oxygen is a colorless gas; and yet I will say it to you by force of habit. All books of chemistry begin in this way. Besides this, it is without smell and without taste. Oxygen is extremely well fitted for combustion. A half-extinguished candle—that is, one whose wick is still burning but without flame—will relight instantly if placed in a globe full of oxygen. Almost all the metals, except the precious metals, such as gold, silver, and platinum, burn, or oxydize more or less rapidly, when they are put in contact with oxygen ”

“ By forcing air through a series of membranous bags prepared by immersing taffeta in ether, sulphide of carbon, or alcohol, and covering with a fine layer of caoutchouc, he has secured an increase of the percentage of oxygen in respect to nitrogen till the fourth bag gives ninety-five per cent of pure oxygen. ”

“ Put a stopper in the neck of the jar, or hold a glass plate against the mouth of it, and you can take it out of the water and so have bottled oxygen. A lighted candle put into a jar of oxygen blazes up directly, and is consumed before you can say Jack Robinson. Charcoal burns away in it as fast, with beautiful bright sparks—phosphorus with a light that dazzles you to look at—and a piece of iron or steel just made red-hot at the end first, is burnt in oxygen quicker than a stick would be in common air. The experiment of burning things in oxygen beats any fire-works. ”

“ The two constituents of the oxygen gas being thus disposed of, what remains under the receiver must be pure nitrogen gas?
MRS. B.
There are some circumstances which prevent the nitrogen gas, thus obtained, from being perfectly pure; but we may easily try whether the 195 oxygen has disappeared, by putting another lighted taper under it.—You see how instantaneously the flame is extinguished, for want of oxygen to supply the negative electricity required for the formation of caloric; and were you to put an animal under the receiver, it would immediately be suffocated. ”

“ There are other solid oxygenized bodies in which the affinities are less powerful, and hence a lower degree of heat suffices to liberate the oxygen gas, and one of the most useful in this respect is the salt termed chlorate of potash. If the substance is heated by itself, the temperature required to expel the oxygen is almost as high as that demanded for the black oxide of manganese ”

“ Oxygen supports animal life; carbonic acid, vegetable life; and the use of the nitrogen, otherwise than as a diluent, is not known.
Very pure air contains 78.98 per cent of nitrogen, 20.99 per cent of oxygen, and .03 per cent of carbonic acid.
Air begins to be very bad when the oxygen is reduced to 20.60 parts in 100. In mines, where candles [Pg 8] go out, oxygen is reduced to 18.50 parts in 100, and, in the worst specimen yet examined by Angus Smith, to 18.27. Air in which the percentage of oxygen has been reduced to 17.20 is very difficult to remain in for many minutes. ”

“ Oxygen gas will ignite a red-hot match, but hydrogen will extinguish an inflamed one, though it will itself burn. You generally think of water as the great antithesis of, the universal antidote for, fire. The truth is here again only of an ex parte character, as I will show you. If I can, by means of a substance having a more intense affinity for oxygen than hydrogen has, rob water of its oxygen, I necessarily set the hydrogen that was combined with that oxygen free. If the heat caused by the chemical struggle, so to say, is great, that hydrogen will be inflamed and burn. ”

“ Water was therefore the product of the combination of hydrogen with oxygen. The following anecdote is told in regard to this combination. A chemist of the last century, who was fond of flattery, was engaged to give some lessons to a young prince of the blood royal. When he came to explain the composition of water, he prepared before his scholar the necessary apparatus for making the combination of hydrogen and oxygen, and, at the moment when he was about to send the electric spark into the retort, he said, bowing his head ”

“ Why, there is a gas, called nitrous gas, which, if you mix it with oxygen, takes all the oxygen into itself, and the mixture of the nitrous gas and oxygen, if you put water with it, goes into the water. Mix nitrous gas and air together in a jar over water, and the nitrous gas takes away the oxygen, and then the water sucks up the mixed oxygen and nitrous gas, and that part of the air which weakens the oxygen is left behind. Burning phosphorus in confined air will also take all the oxygen from it, and there are other ways of doing the same thing. ”

“ It is very useful to terminate the whole series of absorbent vessels with a glass tube dipping into water; the rate at which the gas is seen to bubble, serves as a guide to the supply of oxygen from the gas-holder, the consumption of oxygen varying, of course, with different soils, and at different stages of the combustion. At the close of the combustion, oxygen, or air freed from carbon dioxid, is passed for some time through the apparatus to drive all carbon dioxid into the absorbent vessels. ”

“ While with a sufficient supply of oxygen disintegration leads to the formation of carbon dioxide and water, therefore to end products, which can quickly and easily be removed by diffusion, the want of oxygen produces complex products of incomplete combustion and finally of anoxydative decomposition, such as lactic acid, fatty acids and even more complex substances in constantly increasing quantities. ”

“ Such reversals occur daily and hourly in nature. By the solar waves, the oxygen of water is divorced from its hydrogen in the leaves of plants. As molecular vis viva the waves disappear, but in so doing they re-endow the atoms of oxygen and hydrogen with tension. The atoms are thus enabled to recombine, and when they do so they restore the precise amount of heat consumed in their separation. The same remarks apply to the compound of carbon and oxygen, called carbonic acid, which is exhaled from our lungs, produced by our fires, and found sparingly diffused everywhere throughout the air. ”

“ If we heat chlorate of potash, mixed with binoxide of manganese, in a retort in a furnace, the gas will be given off. There are many other ways of obtaining oxygen, and we illustrate two (figs. 333, 335) .
The red oxide of mercury will very readily evolve oxygen, and if we heat a small quantity of the compound in a retort as per illustration (fig. 333) we shall get the gas. In a basin of water we place a tube test-glass, and the gas from the retort will pass over and collect in the test tube, driving out the water. ”

“ If it is considered for a moment that the admission of gas out of the steel cylinder is made at just such a rate as to compensate for the decrease in volume of the air in the system due to the absorption of oxygen by the subject, it can be seen that if the exact volume of the gas leaving the cylinder were known it would be immaterial whether this gas were pure oxygen, oxygen with some nitrogen, or oxygen with any other inert gas not dangerous to respiration or not absorbed by sulphuric acid or potash-lime. ”