202 Prof. C. Olszewski on the 



the moment of expansion. I performed the experiment as 

 follows : — 



By opening the cock d I let the liquid oxygen, contained in 

 the steel cylinder a, into the vessel e ; a part of the oxygen, 

 which thus returned into the gaseous state, escaped with 

 violence through the tube i ; another was cooled down to its 

 boiling-point ( — 181°*4C.) and collected as a bluish liquid in 

 the tube e, to a height of 6-7 centim., so that the wider part 

 of the tube / was plunged in liquid oxygen. I afterwards 

 closed the cock d and joined the tube i to the pump, by slowly 

 opening a cock, which is not represented in the figure ; the 

 mercury manometer A indicated the pressure of the liquid 

 oxygen in the vessel e. Liquid oxygen behaves very quietly 

 in the vessel e under atmospheric pressure, boiling quickly 

 but uniformly on being pumped : if we do not reach very low 

 pressures, the oxygen, after cooling according to the lowered 

 pressure, boils again quietly. But if the pressure falls below 

 10 millim. (or less), the oxygen boils irregularly, the liquid is 

 thrown up, and shortly disappears. To avoid this I intro- 

 duced Into the vessel e a capillary glass tube o, the lower end 

 of which reaches to the very bottom of the vessel e, the upper 

 end is connected with the iron cylinder k, containing dry 

 hydrogen under a pressure of several atmospheres. During 

 the pumping of the oxygen the cock of the cylinder k is little 

 by little opened, and a slow stream of hydrogen is let through 

 the liquid oxygen ; by this means the liquid oxygen is con- 

 stantly and easily removed, and it boils quietly, even if the 

 pressure falls to 4 millim. 



When the manometer h indicated a pressure of 10-4 millim. 

 I introduced hydrogen into the tube/, by slowly opening the 

 cylinder c, until the pressure became 140 atm., as indicated 

 by the manometer b. When the hydrogen in the tube / has 

 come down to the temperature of the cooling agent, I little by 

 little produced expansion, by opening the screw-cock L The 

 phenomenon of hydrogen ebullition, which was then observed, 

 was much more marked and much longer than during my 

 former investigations in the same direction (3, 4). But even 

 then I could not perceive any meniscus of liquid hydrogen. 



I have remarked in these experiments, that with a slow 

 expansion the phenomenon of sudden ebullition always appears 

 under the same pressure, no matter how great the initial 

 pressure may be, provided that value be not too low. So that 

 by expansions made, beginning with the pressures of 80, 90, 

 100, 110, 120, 130, 140 atm., the phenomenon described con- 

 stantly appeared at 20 atm.; but if the initial pressure was 70, 

 60, and 50 atm., the ebullition appeared at a lower and lower 



