194 



Prof. C. Olszewski on ihe 



to —100° C, the tube n is connected with a smaller double- 

 action pump which at every movement of the piston draws 



out about 1 litre of gas. When the pressure in the condenser 

 g is lowered to 50 millim. Hg, the vessel m is connected, by 

 turning the cock i, with a large vacuum-pump provided with 

 sliding-valves, and at the same time, by slowly turning the 

 cock A, the ethylene, already considerably cooled, is let down 

 into the vessel m. The liquid ethylene, on entering the 

 vessel m, at first evaporates quickly, and the vapour is forced 

 back into a gasometer by means of the large pump alluded to, 

 and may again be employed as a frigorific agent for a sub- 

 sequent experiment. Owing to the very great difference 

 between the temperatures of the steel cylinder and the liquid 

 ethylene, the latter does not at first touch the cylinder directly, 

 but is separated from it by a thin layer of vapour, being in 



