NITROGEN. THE ATMOSPHERE 



295 



The most successful apparatus for use on a small or large scale 

 is that devised by Hampson. In this apparatus (Fig. 75), two 

 concentric copper pipes, about 130 meters in length, are coiled 

 closely in a cylindrical form, with non-conducting covering to 

 prevent access of heat from the outside. Air at 130-150 atmos- 



fl 



FIG. 75 



FIG. 76 



pheres pressure is forced through the inner pipe (upper opening 

 Fig. 75). When it reaches the extremity of this pipe, it suddenly 

 escapes into a closed vessel. This expansion lowers its tempera- 

 ture. A spiral partition between the coils produces the outer 

 tube of which we have spoken. The gas in the tube A (Fig. 76) 

 is under a pressure of 130-150 atmospheres. The distance of the 

 nozzle D from the plug C is adjusted so that the pressure of the 

 gas in the chamber and spiral outer tube is reduced to one atmos- 

 phere. The air can now escape only by traveling back through 

 the outer pipe to the final, wider exit near the top. In doing so, 



