[ 4G3 ] 



LVI. Intelligence and Miscellaneous Articles, 



ON THE SEPARATION OF LIQUID ATMOSPHERIC AIR INTO TWO 

 DIFFERENT LIQUIDS. BY S. WROBLEWSKI. 

 TN my note of April 13, 1885, I had occasion to remark that the 

 -*- laws of the liquefaction of atmospheric air are not those of 

 the liquefaction of a simple gas, and that air behaves like a mix- 

 ture the components of which are subject to different laws of 

 liquefaction. If at first sight liquid air seems to behave in such 

 fashion that we might speak of the critical point of air, that arises 

 simply from the slight difference there is between the curves of the 

 tension of the vapour of oxygen and of nitrogen. Thus we may 

 designate the pressures between 37 and 41*3 atmospheres and the 

 temperatures between — 140 o, 8 and —143° as defining the critical 

 point of air. The curve of the tensions of air depends, among 

 other circumstances, on the manner in which the quantity of the 

 liquid is used for the experiment. Huch more does this curve 

 cease to have any significance when we obtain temperatures of 

 — 190° C, and especially at still lower temperatures. Thus with 

 air liquefied under high pressures, and then liberated and exposed 

 to the pressure of only one atmosphere, the boiling-point rises 

 gradually from — 191 0, 4 to —187° C, and that owing to a change in 

 the composition of the liquid. As nitrogen evaporates more rapidly 

 than oxygen, the temperature of the boiling liquid tends towards 

 — 181°*5 C, which is the boiling-point of pure oxygen. 



Still more striking are the special features shown by air evapo- 

 rated in oxygen, as seen from the following Table : — 



Tempera- 



Pressure 



Tempera- 



Pressure 



Tempera- 



Pressure 



ture. 



in centim. 



ture. 



in centim. 



ture. 



in centim. 



-19502 





-19665 





-198-6 



38 



1962 





196-65 



12-4 



1982 





1971 





196-65 



11 



197-9 



36 



1975 





196-55 



10 



197-85 





1976 





196-1 





197-85 



3*5 



197-6 





I960 





19805 





1976 



... 



196-95 





198-5 



32 



197-5 



161 



198 



44 



198-75 





197-5 





198-6 





199-28 





197-38 



15-2 



198-65 



41 



199-55 



30 



197*15 





198-8 



4 



199-8 





196-85 



14-6 



19899 





200 



2-8 



While the tension of the vapours of liquids evaporated by the 

 pump diminishes steadily, the temperature, as shown in the Table 

 for equidistant intervals of time, passes through a series of maxima 

 and minima ; under low pressures it ultimately attains values 

 w r hich are scarcely higher than those of pure oxygen at the same 

 pressure. In these conditions the air only contains a very small 

 quantity of nitrogen. 



But this is not all. Air can give two distinct liquids, different 

 in appearance and in composition, forming two separate layers 



