Popular Science Monthly/Volume 12/March 1878/Liquefaction of the Gases I
|LIQUEFACTION OF GASES.|
EVERY one knows that the matter which constitutes the various natural bodies occurs in three different forms, namely, the solid, the liquid, and the gaseous states. So, too, every one knows that the state of a body is not at all immutable: a solid may be fused and volatilized; a liquid may become a solid, or be transformed into vapor; a gas may be changed into a liquid or a solid—all these changes occurring according to the conditions of temperature or of pressure to which the solids, liquids, or gases, are subjected. Water turns into ice under the action of cold; into steam under the action of heat. Sulphur, phosphorus, the metals, and most solid bodies, may in like manner assume these three states. Chlorine, protoxide of nitrogen, carbonic acid, etc., may be liquefied or solidified. To this end we have only to bring the molecules nearer to one another by compressing them, or subjecting them to the action of cold.
Faraday succeeded in liquefying a certain number of gases by compression and refrigeration, but there still remained a number that proved absolutely refractory to the most powerful agencies; hence these gases were called permanent. They are hydrogen, nitrogen, oxygen, carbonic oxide, bioxide of nitrogen, and formene (marsh-gas). Chemists, it is true, were quite confident that these gases, like all others, were subject to the general laws of bodies; it was held to be certain that the gases just named would, like the others, yield to sufficiently high pressure or refrigeration. But, nevertheless, they still remained bodies sui generis, defying, so to speak, the powers of the chemist, and their change of state presented itself as a weighty problem, the solution of which was all the more alluring in proportion to the difficulties with which it was surrounded. Berthelot, as we know, subjected them to the enormous pressure of 800 atmospheres, and to a refrigeration of more than 100° below zero, Centigrade; but all was in vain, and the permanent gases justified their name.
This is so no longer. A retired manufacturer, who at the same time is a distinguished man of science, M. Cailletet, has subdued the permanent gases, having succeeded in liquefying and solidifying them. This result, which is one of the most interesting achievements of our time, must unquestionably be regarded as a new and a grand conquest of matter by science.
Nearly at the same moment, another ingenious investigator and inventor, M. Raoul Pictet, reached the same result with regard to oxygen gas. We will pass in review successively the experiments of
these two chemists, commencing with those of Cailletet. Our engraving (Fig. 1) shows the great apparatus constructed by M. Cailletet in his shops at Châtillon-sur-Seine. It consists of a hollow cylinder of steel, A, firmly secured on a bed of cast-iron by means of the clamps B B. A cylindrical rod of untempered steel, serving as a plunger-piston, enters this cylinder, which must be filled with water. The opposite extremity of the rod terminates in a square-threaded screw, passing through the bronze nut F attached to the wheel M. According to the direction given to the wheel by means of the pins at its circumference, the plunger-piston may be made to advance or retreat in the axis of the pump-barrel. A packing of leather prevents the compressed liquid from escaping from the cylinder.
In introducing the water, or other liquid designed to be compressed, it is poured into the glass cup G, which communicates with the inside of the apparatus. A steel screw, with conical point, closes the narrow passage through which the liquid enters. This screw terminates in a small wheel with handle-pins, O. By this arrangement we can suddenly release the compressed gases, and see a dense mist form in the capillary glass tube containing them. (This tube is seen in the middle of the cylinder m.) The mist is formed under the influence of the external cold produced by the sudden removal of pressure, and it is an infallible sign of the liquefaction, or even the congelation, of the gases which hitherto have been regarded as permanent.
a is a steel reservoir, capable of bearing a pressure of 900 or even 1,000 atmospheres; it is connected with the compression-apparatus by a capillary tube of metal. The water in the cylinder, under the pressure of the piston, enters this reservoir, and acts on mercury which compresses the gas.
b is the ajutage which receives the glass apparatus designed to hold the gas under experiment; it is connected with the top of the reservoir by a nut. Fig. 2 represents the arrangement of this part, half the actual size.
m is a flint-glass cylinder, inclosing another glass cylinder, in the middle of which is seen the fine tube in which the gas is to be liquefied. Thus this capillary tube can be surrounded with freezing mixtures, or with liquid protoxide of nitrogen. The outer cylinder m, which is concentric with the inner one, and contains substances which have a strong affinity for moisture, prevents the deposit of ice or vapor on the cooled tube, which would hinder observation.
p is a cast-iron stand to hold the reservoir a. Screws d d serve to raise or lower the reservoir for the purpose of spectroscopic examination, or of projecting the experiments on a screen.
An ajutage S connects together the metallic capillary tubes which transmit the pressure to the various portions of the apparatus.
N is a modified Thomasset manometer, verified by means of an open manometer on the flanks of a hill near the laboratory of Châtillon-sur-Seine.
N' is a glass manometer which serves to check the readings of the mercurial apparatus.
This notable apparatus involves no danger, for the glass tube in which the gas is compressed presents a very small surface, and no serious result could follow were it to break.
|Fig. 2.—Glass Tube with Thick walls, in which Gases are liquified. The gas is compressed in the upper part of the tube by a column of mercury forced upward by hydrostatic pressure. The gas condenses into a liquid drop or into a mist, on pressure being removed. This glass tube is inclosed within a glass cylinder holding the freezing mixture.|
A few years ago an English physicist, Thomas Andrews, was led to infer that, for permanent gases, there exists a critical point of pressure and temperature, above which they cannot be brought to the liquid state. This opinion is confirmed by Cailletet's experiments. Each gas requires that a certain pressure be combined with a certain reduction of temperature: either the one or the other of these two conditions might be employed separately without any effect, even supposing them to reach a high intensity.
The first of the permanent gases liquefied by M. Cailletet was bioxide of nitrogen. As we have just said, unless the two conditions of compression and low temperature be united according to the critical points, the gas does not liquefy. Hence it is that bioxide of nitrogen has remained gaseous at a pressure of 270 atmospheres and a temperature of +8° Cent. Formene or marsh-gas liquefies at 180 atmospheres and +7° Cent.
"If," says M. Cailletet, "we inclose oxygen or pure carbonic oxide in the compression-apparatus; if we reduce these gases to a temperature of -29° Cent. by the aid of sulphurous acid at a pressure of about 300 atmospheres, both gases still retain their gaseous state. But if they be released suddenly, so, according to Poisson's formula, producing a temperature of at least 200° below the starting-point, we at once see a heavy mist, caused by the liquefaction or even, perhaps, the solidification of the oxygen or carbonic oxide. The same phenomenon is observed in releasing carbonic acid, and protoxide and bioxide of nitrogen, which have been subjected to strong pressure."
After having obtained these results, at a session of the Academy on December 31st, M. Cailletet announced that he had won a complete victory over the other permanent gases. M. Dumas informed the members present at the session that the able experimenter had succeeded in liquefying nitrogen, atmospheric air, even hydrogen itself, which would seem to have been the most refractory gas of them all.
We take from the Comptes Rendus the following details:
from the walls of the tube toward the middle, at length forming a sort of vertical column in the axis of the tube; this phenomenon persists for more than three seconds. These appearances remove all doubt as to the true character of the phenomenon. M. Cailletet first made this experiment at home with a temperature of 29° Cent.; he repeated it again and again at the laboratory of the Normal School, in the presence of several men of science.
Hydrogen.—Hydrogen has always been regarded as the most refractory of gases, owing to its slight density, and the almost complete conformity of its mechanical properties to those of the perfect gases. Hence it was with very little hopes of a favorable result that M. Cailletet subjected this gas to the same tests which had produced liquefaction of all the others.
"In my early experiments," says he, "I recognized nothing that was peculiar; but, as often happens in the experimental sciences, the habit of observing phenomena at last leads us to recognize peculiarities where before they were quite unnoticed. This was what happened in the case of hydrogen. On repeating my experiments to-day, December 31st, in the presence and with the assistance of Messrs. Berthelot, H. Sainte-Claire-Deville, and Mascart, I succeeded in observing signs of the liquefaction of hydrogen, which to these expert witnesses appeared to be unquestionable.
"The experiment was repeated many times. Hydrogen placed under a pressure of 280 atmospheres, and then released, becomes transformed into an extremely fine and subtile mist, suspended in the tube throughout its entire length, and then suddenly disappearing. The production of this mist, despite its extreme subtilty, appeared to be indisputable to all the scientific men who witnessed this experiment, and who carefully repeated it again and again, under such conditions as to leave no doubt as to the fact."Air.—"Having liquefied nitrogen and oxygen, the liquefaction of atmospheric air was ipso facto demonstrated. Nevertheless, I concluded to make this a matter of direct experiment; and here, as might have been expected, I was perfectly successful. I need not say that the air had been first dried and deprived of every trace of carbonic acid. In this way," adds M. Cailletet, "was demonstrated the correctness of the views held by the founder of modern chemistry, Lavoisier, as to the possibility of reducing air to the state of liquidity, by producing liquids endowed with new and unknown properties."
Plainly, the power of producing liquid air opens to applied science new horizons. There is no need to prove that, from the purely scientific and philosophical point of view, M. Cailletet's experiments are of supreme importance.
We will conclude this article with a description of the little lecture-room or laboratory apparatus, constructed by M. Ducretet, to show how, according to Cailletet's process, gases are liquefied. It is a copy of the essential parts of the apparatus at Châtillon-sur-Seine. The bell-glass is modified. The screw-press, too, is represented here by a more portable pump. The accompanying figure, which
represents the apparatus in section, will enable us to give a more detailed description of the system devised by M. Cailletet.
T T is a glass tube, containing the gas to be compressed; a current of the gas has passed through it, so as to expel all the atmospheric air. For this purpose it is first placed in an horizontal position; then, after it has been rilled with the gas destined for the experiment, the tube is closed at its extremity p at a lamp, while the other extremity is closed by the finger and introduced vertically into the iron apparatus, as shown in the figure. It dips into a cylindrical reservoir of mercury. The upper part of the tube is surrounded with a glass cylinder, M, filled with a freezing mixture, as in the larger apparatus. The whole is then covered over with a bell-glass, G. The tube TU connects with a compression-pump, worked by hand, and provided with a manometer, which shows the degree of pressure. The water compressed by the pump acts on the surface of the mercury as seen in the figure. This mercury is thus forced into the tube T T, diminishes the space a b, occupied by the gas, and soon bears on its top little drops of compressed gas, which unite to form a small quantity of liquid, b.
The principal parts of the apparatus are B, a box of wrought-iron, with very strong walls; E E', nuts which can be screwed off in order to adjust the apparatus before the experiment begins; A, ajutage; P P, two of the three very strong legs supporting the apparatus; S, support of the bell-glass G and the cylinder M; N, supplementary screw used to stop the mouth of the passage R, while the mercury is being poured into the apparatus.
We would remark that the enlarged lower end of the tube T is subject to an equal pressure within and without, and cannot break. It is only the upper portion of the tube that has to withstand the internal pressure, but its walls are very strong.
The experiment may be projected on a screen by the aid of a Drummond light. The apparatus is very simple, and liquefies a great number of gases. One can with the naked eye observe all the phases of liquefaction, and this without any danger. Hence this instrument is destined to render great service in research and in instruction, whether in colleges or in the lecture-room.—La Nature.
- Translated from the French by J. Fitzgerald, A.M.
- Comptes Rendus de l'Academie des Sciences, December 24, 1877.