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POPULAR SCIENCE REVIEW. 
chlorate of potash and half a pound of chloride of potassium,, 
mixed together, fused, broken up, and placed in the shell per- 
fectly dry. When the double circulation of the sulphurous and 
carbonic acids has sufficiently lowered the temperature of the 
apparatus the shell is heated by a series of gas-burners. The 
disengagement of oxygen takes place at first gradually, and then 
rather suddenly, near the end of the operation. A pressure- 
gauge at the end of the tube gives constant indications of the 
progress of the reaction. The gauge, which is graduated to 800 
atmospheres, was made expressly for M. Pictet by Bourdon, of 
Paris. 
At the termination of the reaction the gauge indicates a 
pressure of 500 atmospheres, which almost immediately sinks 
and remains at 320 atmospheres. On opening the screw-tap 
a jet of liquid oxygen is seen to squirt out with extreme 
violence. 
Pieces of charcoal, feebly incandescent, placed in the way of 
this jet inflame with inconceivable violence. A ray of electric 
light thrown upon the jet shows it to consist of two parts, one 
central, and an inch or so in length, the whiteness of which is 
suggestive of its being the liquid ; the external portion has a 
blue tint indicating that it is probably a congealed mist. 
Hydrogen . — On January 10 of the present year M. Pictet 
succeeded in liquefying, and even solidifying, hydrogen in the 
laboratories of the Society for the Construction of Physical 
Instruments, at Greneva. 
The experiment was performed in the presence of several 
persons with great success. 
The gas was obtained by the process of Berthelot, which yields 
it in a state of the most perfect purity. The reaction employed 
consists in decomposing formiate of potassium with caustic 
potash. At a pressure of 650 atmospheres and a temperature of 
— 140° C. ( — 220° F.) there was emitted from the jet when the 
tap was opened a steel-blue jet, producing a hissing sound like 
that of a red-hot iron being immersed in water. 
The jet suddenly became intermittent, and there succeeded a 
hail of solid particles, like small shot being projected on to the 
ground with violence. Their fall produced a harsh, shrill noise 
or crackling sound. 
The tap was closed, and the pressure fell from 370 to 320 
atmospheres, at which it remained some minutes. It then rose 
to 325 atmospheres. On opening the tap a second time only 
an intermittent jet escaped, rendering it probable that solidifi- 
cation had taken place within the tube. Proof of this was 
afforded by the fact that when the temperature was allowed to 
rise by stopping the pumps the escape of hydrogen in the liquid 
state was resumed. 
