196 Prof. C. Olszewski on the 



The critical temperatures, also according to my reckonings, 

 are: for oxygen — 118 0, 8 C. ; for air — 140° C. ; for nitrogen, 

 — 146° C. The pressure of ethylene must accordingly be 

 lowered to 100 — 40 millim. in order to liquefy oxygen ; to 

 liquefy air, to 20 millim., and to liquefy nitrogen, to 10 millim. 

 The pressure to which ethylene is subjected in the vessel m 

 is indicated by the metallic vacuometer k, for which in more 

 exact experiments a mercury manometer may be substituted. 

 The pressures I have stated above for ethylene are maximum 

 pressures at which it is still possible to bring about the 

 liquefaction of large quantities of the corresponding gases ; 

 but it is generally necessary to take care that the pressure of 

 the liquid ethylene be lowered to the minimum obtainable by 

 the pump serving for the experiment. The more we lower 

 the temperature of the ethylene, the sooner the cylinder a is 

 filled with the liquefied gas, and the more liquid we obtain 

 by pouring out the liquefied gas under the ordinary pressure. 

 To low r er the temperature of a considerable quantity of ethylene 

 to —146° or —150° C, which temperature is absolutely 

 necessary for the liquefaction of large quantities of air and 

 nitrogen, a large air-pump with rapid and powerful action is 

 required. When in 1890 I used a smaller pump, which drew 

 out two litres of gas at each complete double stroke, I could 

 only liquefy oxygen in the described apparatus ; but when in 

 the following year 1 brought from Burckhard's factory, Basle, 

 an excellent sliding valve-pump, six times larger than the 

 preceding one, and working with great speed and perfection, 

 I was enabled in the same apparatus easily to obtain at once 

 200 cub. centim. of liquid air. It is true that I never tried to 

 liquefy nitrogen in large quantities, but I believed it unneces- 

 sary, taking into account my former experiments with nitrogen 

 (6) . I had already examined the properties of liquid and solid 

 nitrogen, and showed that the use of liquid nitrogen as a 

 frigorific agent is of no greater advantage than that of oxygen 

 or air. However, considering that by using both of my 

 pumps the pressure of ethylene in the vessel m is easily 

 lowered to 10 millim. and the temperature to — 150° C, I can 

 decidedly affirm, that all so-called permanent gases, except 

 hydrogen, may be liquefied in my apparatus. When we want 

 to obtain such a considerable rarefaction of ethylene, the 

 compressing tube of the larger pump must be connected with 

 the exhausting tube of the smaller one, whereby the effect of 

 the larger pump is exceedingly increased. 



It need hardly be said that the processes connected with 

 the liquefaction of large quantities of gases, as the liquefaction 

 of ethylene in the cylinder/, the charging of the cylinder c 



