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 carbonic acid drawn out of it by the pumps is passed into the condenser K which is surrounded by the sulphurous acid receiver C, the temperature of which is -65°; it is there liquefied under a pressure of five atmospheres. The carbonic acid returns to the receiver H 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 M, of very thick glass, one metre in length and surrounded by the carbonic-acid receiver H whose temperature is -140°. A screw-stoppel N, 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 violence, producing an expansion and an absorption of heat so great that
