Popular Science Monthly/Volume 13/May 1878/Liquefaction of the Gases II
|LIQUEFACTION OF THE GASES.|
AT the very moment when Cailletet was subjecting successively to the test of his apparatus the six permanent gases, and was conquering their resistance to compression, M. Raoul Pictet was making his experiments, first on oxygen, then on hydrogen. But what gives a special interest to the labors of Pictet is the fact that he has succeeded in producing a quite appreciable volume of these gases in the liquid or in the solid state. He describes his apparatus as follows:
A and B (Fig. 1) are two compound exhausting and forcing pumps, so coupled as to produce the widest possible difference between the pressures of exhaustion and compression. These pumps act on anhydrous sulphurous acid contained in the tubular receiver C. The pressure in this receiver is such that the sulphurous acid evaporates at the temperature of -65° C. The sulphurous acid pumped out is carried into a condenser D, cooled by a current of cold water; it is there liquefied at a temperature of -25°, and at a pressure of about 24 atmospheres. The sulphurous acid returns to the receiver C by a small tube d as fast as it is liquefied.
E and F are two pumps precisely the same as the preceding, and with the same kind of coupling. They act on carbonic acid contained in a tubular receiver H. The pressure in this receiver is such that the carbonic acid in it evaporates at a temperature of -140°. The carbonic acid drawn out of it by the pumps is passed into the condenser K which is surrounded by the sulphurous acid receiver C, the temperature of which is -65°; it is there liquefied under a pressure of five atmospheres. The carbonic acid returns to the receiver H through the small tube k, in proportion as it assumes the liquid state.
L is a wrought-iron retort of sufficient thickness to withstand a pressure of 500 atmospheres. It contains chlorate of potash, and is heated so as to give off pure oxygen. It communicates by a tube with a sloping tube M, of very thick glass, one metre in length and surrounded by the carbonic-acid receiver H whose temperature is -140°. A screw-stoppel N, situated above the tubulure of the retort, gives to the latter communication with the external air.
After the four pumps have been at work for several hours, driven by a 15-horse-power steam-engine, and when all the oxygen has been liberated from the chlorate of potash, the pressure in the tube is 320 atmospheres, and the temperature -140°.
On suddenly opening the orifice P, the oxygen escapes with violence, producing an expansion and an absorption of heat so great that a portion of it, in the liquid state, is seen in the glass tube, and spurts out of the orifice on the apparatus being inclined.
A sufficiently clear idea of M. Pictet's method can be had from the above diagram and description; but, as yet, the reader can hardly imagine what the apparatus looks like. Fig. 2 (after a photograph)
and Fig. 3 will supply this deficiency. Fig. 2 is a general view of Pictet's grand liquefaction apparatus, as it stands in his establishment at Geneva; and Fig. 3 exhibits the same in section. This apparatus possesses considerable size; for instance, the head of a man standing would be on a level with the manometer seen near the letter H in the engraving.
The perfected apparatus as shown in Fig. 2 differs in sundry respects from the diagram Fig. 1, as will be seen at a glance. One essential difference consists in the arrangement of the liquefaction apparatus proper, Fig. 4. Here D is an iron shell (or retort), with walls 35 millimetres in thickness; it contains 700 grammes of chlorate of potash when oxygen is the gas to be liquefied. Its orifice communicates with an iron tube five metres in length, 214 millimetres internal diameter. This tube, bent as in the figure, is closed at both ends, but one end may be opened by means of the cock E. A Bourdon manometer, graduated to 800 atmospheres, shows the inside pressure. The tube c E, in which the disengaged oxygen is compressed, is completely immersed in liquid carbonic acid, which, by the mechanism of the pumps before described, enters the apparatus at a and passes out as vapor from the orifice b, after volatilization.
With this apparatus, M. Raoul Pictet, on Monday, December 24, 1877, in the presence of members of the Physical Society of Geneva, three different times obtained violent jets of vapor which contained globules of liquefied oxygen. On the following Thursday the experiment was made for the fourth time. The manometer, which had risen to 560 atmospheres, after a few minutes fell to 505, and there stood for
over half an hour, showing by this diminution of pressure the transition of a portion of the gas into the liquid state, under the influence of the -140° temperature to which it was subjected. The cock closing the orifice of the tube was then opened, and a jet of oxygen escaped with extraordinary violence. A beam of electric light, projected on the cone of escapement, enabled the spectators to see that the jet consisted of two distinct parts: the one central, a few centimetres in length, whose white color gave evidence of liquid or even solid elements; the other external, whose blue color showed the return of the compressed and frozen oxygen to the gaseous state.
In later experiments M. Pictet succeeded in collecting a very appreciable volume of liquid oxygen, and in liquefying all the other "permanent" gases.
- Translated, with some abridgment, from La Nature, by J. Fitzgerald, A.M.
- The degrees of temperature here noted are all according to the centigrade scale.