622 THE POPULAR SCIENCE MONTHLY. 



rent of the gas has passed through it, so as to expel all the atmos- 

 pheric air. For this purpose it is first placed iu 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 ex- 

 tremity 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 TTI 

 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, dimin- 

 ishes the space a #, 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; HJJS', nuts which can be screwed off in 

 order to adjust the apparatus before the experiment begins ; A, aju- 

 tage ; P JP, two of the three very strong legs supporting the appara- 

 tus ; S, support of the bell-glass G and the cylinder M ; N, supple- 

 mentary screw used to stop the mouth of the passage i?, 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 in- 

 ternal 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. 



