LIQUEFACTION OF GASES. 



619 



open manometer on the flanks of a hill near the laboratory of Chatil- 

 lon-sur-Seine. 



JST' is a glass manometer which serves to check the readings of the 

 mercurial apparatus. 



This notable apparatus involves no danger, for the glass tube in 

 which the gas is compressed presents a very small surface, and no 

 serious result could follow were it to break. 



A few years ago an English phys- 

 icist, Thomas Andrews, was led to 

 infer that, for permanent gases, there 

 exists a critical point of pressure and 

 temperature, above which they cannot 

 be brought to the liquid state. This 

 opinion is confirmed by Cailletet's ex- 

 periments. Each gas requires that a 

 certain pressure be combined with 

 a certain reduction of temperature : 

 either the one or the other of these 

 two conditions might be employed 

 separately without any effect, even 

 supposing them to reach a high inten- 

 sity. 



The first of the permanent gases 

 liquefied by M. Cailletet was bioxide 

 of nitrogen. As we have just said, 

 unless the two conditions of compres- 

 sion and low temperature be united 

 according to the critical points, the 

 gas does not liquefy. Hence it is that 

 bioxide of nitrogen has remained gas- 

 eous at a pressure of 270 atmospheres 

 and a temperature of + 8 Cent. For- 

 mene or marsh-gas liquefies at 180 at- 

 mospheres and + 1 Cent. 



"If," says M. Cailletet, "we in- 

 close oxygen or pure carbonic oxide 

 in the compression-apparatus ; if we 



reduce these gases to a temperature FlG 2 .-Glass Tube with Thick walls, 

 of 29 Cent, by the aid of sulphurous 

 acid at a pressure of about 300 atmos- 

 pheres, both gases still retain their 

 gaseous state. But if tiiey be released 

 suddenly, so, according to Poisson's 

 formula, producing a temperature of at least 200 below the starting- 

 point, we at once see a heavy mist, caused by the liquefaction or even, 

 perhaps, the solidification of the oxygen or carbonic oxide. The 



IN WHICH GASE8 ARE LIQUEFIED. The 



gas is compressed in the upper part of 

 the tube by a column of mercury forced 

 upward by hydrostatic pressure. The 

 gas condenses into a liquid drop or into 

 a mist, on pressure being removed. This 

 glass tube is inclosed within a glass cyl- 

 inder holding the freezing mixture. 



