The Progress of Invention in the Nineteenth Century.

by Edward W. Byrn

Evaporation of Nitrous Oxide.

Evaporation of Pure Oxygen.

FIG. 303.—SEPARATION OF LIQUID AIR INTO ITS CONSTITUENTS.

As to the uses of liquid air it may be said that up to the present time it has attained little or no practical application. There are two principal ways in which it may be utilized; one is to employ its enormous expansive force to produce mechanical power, and the other is as a refrigerant. As a means for obtaining motive power it is a fallacy to suppose that any more power can be obtained from its expansion than was originally required to make it. It is like a resilient spring in this respect, that it can give out no more power than was required to compress it. In some special applications, however, as for propelling torpedoes, where its cost is entirely subordinate to effective results, it might prove to be of value. For blasting purposes also it presents the promise of possible utilization. As a refrigerant for commercial purposes, and for supplying a dry, cool temperature to the sick room, and for the preparation of chemicals requiring a low temperature to manufacture, it might find useful application. Inasmuch as the nitrogen of liquid air evaporates first, and leaves nearly pure liquid oxygen, it may also be employed as a means for producing and applying oxygen. Good illustration of this is given in [Fig. 303], in which at 1 is shown a vessel filled with liquid air. The gas first evaporating is nitrogen, and a lighted match applied to the surface of the liquid is quickly extinguished, since nitrogen does not support combustion. As the level of the liquid falls by evaporation, the remaining portions become richer in oxygen and poorer in nitrogen, and nitrous oxide gas is then given off, which supports combustion as seen at 2; and when the last portions of the liquid are being evaporated, as at 3, it is practically pure oxygen, which gives a brilliant combustion of a carbon pencil, or even of a steel spring when the latter is heated red hot. Already Prof. Pictet has formulated a plan for the commercial production and separation of the ingredients of liquid air—the nitrogen, carbonic acid, and oxygen being separated by their different evaporating temperatures with a view to applying them to various industrial uses. All of the commercial applications of liquid air, however, depend upon its cost of production, which seems at present an uncertain factor. According to the claims of some it may be produced at a cost of a few cents a gallon. More conservative physicists say that it costs $5 a gallon.

FIG. 304.—LIQUID AIR EXPERIMENTS.

1. Magnetism of oxygen. 2. Steel burning in liquid oxygen. 3. Frozen sheet iron. 4. Explosion of confined liquid air. 5. Burning paper. 6. Explosion of sponge. 7. Freezing rubber ball. 8. Double walled vacuum bulb. 9. Boiling liquid air.

However this may be, the phenomena which it presents are both interesting and instructive. In [Figs. 304] and [305] are shown some of the experiments. At No. 1 a test tube containing liquid air, from which the nitrogen has escaped, is strongly attracted by an electro-magnet, showing the magnetic quality of oxygen. At No. 2 is shown the combustion of a heated piece of steel in liquid air, which has become rich in oxygen by the evaporation of the nitrogen. At No. 3 a tin dipper, which has been immersed in liquid air, has become so cold and crystalline that it breaks like glass when dropped. At No. 4 liquid air imprisoned in a tube and tightly corked up, blows the stopper out in a few minutes with explosive effect. At No. 5 a piece of paper saturated with liquid air burns with great energy, and at No. 6 a piece of sponge or raw cotton similarly saturated explodes when ignited. At No. 7 a rubber ball floated on liquid air in a tumbler is frozen so hard that when dropped it flies into fragments like a glass ball. The white, snow-like vapor seen falling over the edges of the tumbler is intensely cold and heavier than ordinary air. At No. 8 is illustrated the preservation of liquid air by surrounding it with a vacuum in a Dewar bulb. At No. 9 a flask of liquid air is made to boil by the mere heat of the hand. A more striking experiment still of the same kind is to place a tea kettle containing liquid air on a block of ice. The block of ice is relatively so much hotter than the liquid air that the liquid air in the kettle is made to boil. At No. 10, [Fig. 305], a heavy weight is suspended by a link composed of a bar of mercury frozen solid in liquid air. So hard is the mercury frozen that a hammer made of it will drive a tenpenny nail up to its head in a pine board. In No. 11 a layer of liquid air on water at first floats because it is lighter than water. As the lighter nitrogen evaporates, the heavier oxygen sinks in drops through the water. At No. 12 a tumbler of whiskey is frozen solid by immersing a tube containing liquid air in it. The frozen block of whiskey with the cavity formed by the tube is shown on the left. It is a whiskey tumbler made out of whiskey. A more sensational experiment is to substitute a tapering tin cup for the tube, then fill it with liquid air and immerse it in water. In a few minutes the tapering tin cup has frozen on its outer walls a tumbler of ice. This may be carefully removed, and the ice tumbler is then filled with liquid air rich in oxygen, which, by maintaining the cold of the ice tumbler, keeps it from melting. A carbon pencil or a steel spring heated to redness will now, if dipped in the liquid oxygen in the ice tumbler, burn with vehement brilliancy and beautiful scintillations, involving the anomalous conditions of a white hot heat and active combustion in the center of a tumbler of ice, without melting the tumbler. In experiment 13, [Fig. 305], a jet of carbonic acid gas directed into a dish floating in a glass of liquid air is immediately frozen into minute flakes, producing a miniature snow storm of carbonic acid. In experiment 14 an electric light carbon heated to a red heat at its tip, is plunged vertically into a deep glass of liquid oxygen. A most singular combustion takes place. The heat of the carbon evaporates the oxygen in its immediate vicinity, and the carbon burns with great brilliancy and violence, forming carbonic acid, which is largely frozen in the liquid before it reaches the surface, and falls back to the bottom of the dish, so that the combustion is maintained and its products retained within the dish. A beefsteak may be frozen in liquid air to such brittleness that it is shattered like a china plate when struck a slight blow. The intense cold of liquid air does not destroy the vitality or germinating power of seed, but produces serious so-called burns on the flesh that destroy the tissues and do not heal for many months, and yet for a moment the finger may be dipped in liquid air with impunity because of the gaseous envelope with which the finger is temporarily surrounded.