LIQUEFACTION OF THE GASES. 



79 



with the same kind of coupling. They act on carbonic acid contained 

 in a tubular receiver H. The pressure in this receiver is such that 

 the carbonic acid in it evaporates at a temperature of 140. The car- 

 bonic acid drawn out of it by the pumps is passed into the condenser 

 K which is surrounded by the sulphurous acid receiver C, the tempera- 

 ture of which is 65 ; it is there liquefied under a pressure of five at- 

 mospheres. The carbonic acid returns to the receiver II through the 

 small tube k, in proportion as it assumes the liquid state. 



Fig. 1. Diagram of Pictet's Apparatus. 



L is a wrought-iron retort of sufficient thickness to withstand a 

 pressure of 500 atmospheres. It contains chlorate of potash, and is 

 heated so as to give off pure oxygen. It communicates by a tube with 

 a sloping tube 31, of very thick glass, one metre in length and sur- 

 rounded by the carbonic-acid receiver H whose temperature is 140. 

 A screw-stoppel JV, situated above the tubulure of the retort, gives to 

 the latter communication with the external air. 



After the four pumps have been at work for several hours, driven 

 by a 15-horse-power steam-engine, and when all the oxygen has been 

 liberated from the chlorate of potash, the pressure in the tube is 320 

 atmospheres, and the temperature 140. 



On suddenly opening the orifice P, the oxygen escapes with vio- 

 lence, producing an expansion and an absorption of heat so great that 



