RECENT PROGRESS IN CHEMISTRY. 531 



and (1) the refractive power ; (2), the power of rotating a ray of po- 

 larized light ; and (3), the absorption spectra of both inorganic and 

 organic bodies. 



The meeting of the French Academy of Sciences, held tbe day be- 

 fore Christmas, 1877, was rendered memorable by the announcement 

 that oxygen gas had been liquefied by two independent experimenters. 

 Previous to that date, hydrogen, oxygen, nitrogen, nitric oxide, marsh- 

 gas, and carbon-monoxide had resisted all attempts to liquefy them, 

 whether in the hands of the skillful Faraday, the ingenious batterer, 

 or the learned Andrews. Physicists and chemists, while admitting 

 the class of so-called permanent gases, had for many years looked for- 

 ward to their eventual liquefaction, yet the final success came as a sur- 

 prise. This success was the result of the enterprise and ingenuity of 

 a French iron-master, M. Cailletet, and of a Genevan manufacturer of 

 ice-machines, Raoul Pictet, working independently. In each case, the 

 process consisted in simultaneously exposing the gases to a very high 

 pressure and a very low temperature. Pictet obtained the necessary 

 pressure by generating the oxygen in a wrought-iron vessel strong 

 enough to withstand an enormous strain, and the low temperature was 

 secured by the rapid evaporation of liquid carbonic acid ; Cailletet, 

 whose apparatus was marked by extreme simplicity, obtained the 

 great pressure by means of a hydraulic press, and the low temperature 

 by suddenly diminishing the pressure upon the compressed gases. De- 

 scriptions of apparatus without diagrams are seldom intelligible ; in 

 this place they are superfluous, for we deal with results rather than 

 with methods. Being ignorant of the " critical point " for oxygen, both 

 experimenters employed a much greater pressure than necessary. 



Since the initial successes, the problem of liquefying the quondam 

 permanent gases has been successfully attacked by several experi- 

 menters, especially by Wroblewski and Olzewski, whose names indi- 

 cate their nationality. By employing liquid ethylene (which boils in 

 vacuo as low as 150 C.[ 238 F.]) as a means of cooling the gases 

 under pressure, both oxygen and nitrogen, as well as atmospheric air, 

 have been liquefied at very moderate pressures. 



Among the interesting results obtained are the following : at 102 

 C. (152 F.), chlorine forms orange-colored crystals ; at 115 C. 

 (-175 F.), hydrochloric acid is a solid; at -118 C. (-180 F.), 

 arsine forms white crystals ; at 129 C. (200 F.), ether solidifies ; 

 at -130 C. (-202 F.), absolute alcohol solidifies; at -184 C. 

 (-299 F.), oxygen boils; at 191-2 C. (-312 F.), air boils; 

 at 205 C. (337 F.), air boils in vacuo. These extraordinary 

 temperatures were measured by means of a hydrogen thermometer 

 and by a thermopile. The lowest temperature measured (to date) 

 is 225 C. ( 373 F.), which was reached by reducing the pressure 

 of solid nitrogen to 4 mm. mercury (Olzewski). Further noteworthy 

 results are as follows : Xitrogen was obtained in " snow-like crys- 



