COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN 289 



As it is liquefied with comparative ease, and as the cold produced by its 

 vaporisation is very considerable, 72 it (as also liquid carbonic anhy- 

 dride) is often employed in investigations requiring a low temperature. 



iJ''io. 51. Natterer's apparatus for the preparation of liquid nitrous oxide and carbonic anhydride. 

 The gas first passes through the vessel V, for drying, and then into the pump (a section of the 

 upper part of the apparatus is given on the left). The piston t of the force pump is moved by the 

 crank E and fly-wheel turned by hand. The gas is pumped into the iron chamber A, where it is 

 liquefied. The valve S allows the gas to enter A, but not to escape from it. The cliamber and 

 pump are cooled by the jacket B, filled with ice. When the gaa is liquefied the vessel A is uu- 

 scri'\ved from the pump, and the liquid may be poured from it by inverting it and unscrewing the 

 valve v, and the liquid then runs out of the tube x. 



by heating dry ammonium nitrate in a closed bent tube, one arm of which was immersed 

 in a freezing mixture. In this case two layers of liquid are obtained at the cooled end, 

 a lower layer of water and an upper layer of nitrous oxide. This experiment should be 

 conducted with great care, as the pressure of the nitrous oxide in a liquid state is con- 

 siderable, namely (according to Regnault), at +10 = 45 atmospheres, at = 86 atmo- 

 spheres, at -10 = 29 atmospheres, and at -20 = 28 atmospheres. It boils at -92, 

 and the pressure is then therefore = 1 atmosphere. 



72 Liquid nitrous oxide, in vaporising at the same pressure as liquid carbonic 

 -anhydride, gives rise to_almost equal or even slightly lower temperatures. Thus at a 

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