190 Prof. C. Olszewski on the 



verfliissigten Sauerstoffs und Stickstoffs." In this apparatus 

 I liquefied all the gases spoken of, in quantities varying from 

 a few to a good many cubic centimetres of liquid, and 

 determined their critical temperatures and pressures, as well 

 as their boiling-points under atmospheric pressure. I suc- 

 ceeded in solidifying four of these gases, viz., nitrogen (6), 

 carbon monoxide (6), nitric oxide (7), and marsh-gas (7), by 

 lowering the pressure to several millimetres of mercury, and 

 determined their freezing-points and the corresponding pres- 

 sures of solidification. 1 also showed that liquid oxygen and 

 air boiling in vacuo at a pressure of 4 millimetres of mercury 

 do not freeze though their temperatures are lowered to below 



— 211° and —220° C. By diminishing tbe pressure of solid 

 nitrogen to 4 millimetres of mercury, I obtained a temperature 

 reaching — 225° C, the lowest that has ever been obtained and 

 measured (6). 



With the same apparatus I also made a series of experi- 

 ments with reference to the liquefaction of hydrogen, sub- 

 mitting it to a pressure reaching ISO atm., and at the same 

 time cooling it down to —211° and even —220° C, by means 

 of liquid ethylene and liquid air boiling in vacuo (2). I also 

 showed that the critical temperature of hydrogen is below 



— 220° C. In the same apparatus which served for the lique- 

 faction of hydrogen I liquefied a mixture of two volumes 

 hydrogen and one volume oxygen, and thus obtained a liquid 

 which was in thin layers colourless and transparent (8). 1 

 likewise determined the specific gravity of oxygen, nitrogen, 

 and methane at the boiling-points of these gases (15). The 

 same apparatus was also of use for examination of the absorp- 

 tion spectrum of liquid oxygen and air, and showed that liquid 

 oxygen in layers not thicker than 7 millim. absorbs light 

 very strongly ; also that it gives, among others, two strong 

 absorption bands, corresponding in position to two absorptions 

 of the solar rays, which are due to the oxygen in the air (13). 

 Using liquid oxygen as a cooling agent, I obtained pure ozone 

 in the shape of a dark-blue liquid, easily and violently ex- 

 ploding, and of which I determined the boiling-point (12). 



Besides the above-mentioned gases, I have examined another 

 series with regard to their behaviour at low temperatures, 

 especially those which had not yet been examined in this 

 respect, or which had been examined without success. I first 

 solidified the following gases and determined their melting- 

 points : chlorine (10), hydrochloric acid (10), hydrofluoric 

 acid (11), phosphine (11), arsine (10), stibine (11), ethylene 

 (12), [silicon tetrafluoride * (10)]. Moreover, I determined 

 * Does not melt, but evaporates in solid state. 



