16 



solutions of chlorides will pass through the lower reservoirs into 

 the sewers. 



The apparatus once fitted up is always ready for use, and all 

 superfluous gas is completely led away without producing any 

 smell in the room where the apparatus is fixed. 



92. Cailletet's apparatus for the liquefaction of oxygen. 

 Lent by the Chemical Laboratory, Royal College of 



1887. Science. 



The oxygen is contained in a vessel of the same pattern as 

 that exhibited on the floor of the case. 



The body of this vessel is enclosed in a strong steel cylinder, 

 and is surrounded by mercury ; the capillary tube forming the 

 upper portion of the oxygen receiver passes through a packing 

 in this outer cylinder and is then bent at 120, and again, in the 

 same sense, at 60. 



When in position the end of this tube points downwards ; it 

 is in this portion of the tube that the oxygen is liquefied. A 

 narrow-bore copper tube connects the interior of the steel 

 cylinder with a hydraulic pump by means of which very high 

 pressures may be obtained. 



The end portion of the capillary tube is immersed in liquid 

 ethylene contained in a test- tube, which is surrounded by another 

 glass vessel ; the air between the two vessels is dried by strong 

 sulphuric acid, by this means the deposition of hoar frost upon 

 the outer surface of the ethylene bath is prevented. 



The liquid ethylene may be rapidly evaporated by the passage 

 through it of a current of air previously cooled by transmission 

 through the outer copper worm of a methyl chloride bath, 

 placed immediately above the ethylene bath ; by this means the 

 contents of the capillary tube may be cooled to 123 C., i.e., 

 below the critical temperature for oxygen. 



Under the combined effect of the high pressure and low 

 temperature, dry oxygen gas is readily condensed to the liquid 

 utate, and shows, at the surface of separation between the gas 

 and liquid in the capillary tube, a well-defined meniscus. 



The liquid ethylene is delivered from an inverted steel tube 

 through the inner copper worm in the methyl chloride bath into 

 the test-tube previously mentioned. 



The methyl chloride is rapidly evaporated by a current of dry 

 air ; both the liquid ethylene and the dry air for its evaporation 

 are thus cooled to about 70 C. before passing into the lower 

 bath. 



93. Gay-Lussac's apparatus for determining vapour 

 densities. 



1876. Exhibited by J. Orme $ Co. 



This method consists in determining the volume of a given 

 weight of the vapour. 



