( 142 ) 
[January, 
SC XENTIFIC NOTES. 
The most important scientific achievement we have to record in the present 
number of the “ Quarterly Journal of Science ” is that of the liquefaction of 
oxygen, which was accomplished on the 22nd of December by M. Raoul 
PiCtet. When a gas is compressed to 500 or 600 atmospheres and kept at a 
temperature of — ioo° or — 140°, and it is allowed to expand to the atmo- 
spheric pressure, one of two things takes place — Either the gas, obeying the 
force of cohesion, liquefies and yields its heat of condensation to the portion 
of gas which expands and loses itself in the gaseous form ; or, on the hypo- 
thesis that cohesion is not a general law, the gas must pass to the absolute 
zero and become inert, — that is to say, an impalpable powder. For some 
time past M. PiCtet’s objeCt has been to demonstrate experimentally that 
molecular cohesion is a general property of bodies, to which there is no excep- 
tion. The apparatus he employed in his experiments may be briefly described 
as follows : Two pumps, such as are used in M. PiCtet’s ice-making appa- 
ratus, are coupled in such a way that the exhaustion of one corresponds to 
the compression of the other. The exhaustion of the first commences with 
a tube i’i metre long and 12-5 centimetres in diameter, and filled with liquid 
sulphurous acid. Under the influence cf a good vacuum the temperature of 
this liquid rapidly sinks to —65°, and even to — 73 0 . the extreme limit allowed. 
Through this tube of sulphurous acid passes a second smaller tube, of 6 centi- 
metres diameter and the same length as the envelope. These two tubes are 
terminated by a common base. In the central tube M. PiClet compressed 
carbonic acid produced by the reactions of hydrochloric acid on Carrara 
marble. This gas, being dried, is stored in an oil gasometer of 1 cubic metre 
capacity. At a pressure of from 4 to 6 atmospheres the carbonic acid easily 
liquefies under these circumstances. The resulting liquid is led into a long 
copper tube, 4 metres in length and 4 centimetres in diameter. Two pumps, 
coupled together like the first, exhaust carbonic acid either from the gaso- 
meter or from the long tube full of liquid carbonic acid. The ingress to these 
tubes is governed by a three-way tap. A screw valve cuts off at will the 
ingress of liquid carbonic acid in the long tube : it is situated between the 
condenser of carbonic acid and the long tube. When this screw valve is closed, 
and the two pumps draw the vapour from the liquid carbonic acid contained 
in the tube 4 metres long, the greatest possible lowering of temperature is 
produced, the carbonic acid solidifies, and descends to about — 140°. The 
subtraction of heat is maintained by the working of the pumps, the cylinders 
of which take out 3 litres per stroke, and the speed is 100 revolutions a 
minute. In the interior of the carbonic acid tube passes a fourth tube, 
5 metres long, intended for the compression of oxygen. Being immersed in 
solid carbonic acid, the whole surface is brought to the lowest obtainable 
temperature. These two long tubes are connected by the ends of the carbonic 
acid tube, consequently the small tube extends about 1 metre beyond the 
other. The small central tube screws into the neck of a large wrought-iron 
shell. This shell contains 700 grms. of chlorate of potash and 256 grms. of 
chloride of potassium mixed together, fused, then broken up, and introduced into 
the shell perfectly dry. When the double circulation of the sulphurous and 
carbonic acids has lowered the temperature to the required degree, the shell is 
heated over a series of gas-burners : the decomposition of the chlorate of potash 
takes place at first gradually, then rather suddenly towards the end of the opera- 
tion. When the reaction is terminated the pressure exceeds 500 atmospheres ; 
but it almost immediately sinks a little and stops at 320 atmospheres. If at this 
moment the screw tap which terminates the tube is opened, a jet of liquid is dis- 
tinctly seen to escape with extreme violence. If the tap is closed a second jet can 
