Page:Popular Science Monthly Volume 12.djvu/640

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rent 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.