( 164 ) 



differeiil methods the two vahies — 210°.4 C. ^) and —2n\0C.') 



For tlie melting point of oxygen Estreichek*'') gives — 227° C. 

 Relying upon these data, therefore, one should be able to determine 

 the critical constants for neon by using a cryostat containing oxygen 

 cooled by means of liquid hydrogen to the neighbouj-hood of its 

 melting point. Indeed, if Rankine's estimates are correct we should 

 be able to attain the desired temperature by means of oxygen boiling 

 under greatly reduced pressure, by means of which temperatures are 

 usually obtained down to about ± — 217° C. 



Experiment has shown that both deductions are incorrect. 



A cryostat ') consisting of a partly silvered vacuum glass and 

 containing not only the piezometer reservoir full of neon but also a 

 platinum resistance thermometer and a valved stiri-er was filled with 

 liquid oxygen and was connected to a Burckhakut vacuum pump of 

 great capacity. To minimise as far as possible heat exchange with 

 the surroundings (his cryostat was surrounded by a vacuum glass 

 containing liquid air. 



When the pressure in the cryostat had been diminished to 1 mm. 

 we noticed that the liquid oxygen was covered with a crust of solid 

 oxygen. A small increase in the pressure caused the solid oxygen to 

 distribute itself throughout the lifpiid in the form of small transparent 

 pieces (crystals?). As long as these pieces were kejjt in continual 

 motion in the liquid by means of the stirrer a constant tem[)erature 

 of — 218°.4 C. was ol)served. Gradual compression of the neon to 

 60 atm. did not give rise to any trace of li(|ui(l in the neon jjiezo- 

 meter nor did a gradual expansion from 60 atm. to atmospheric 

 pressure. From this we may conclude titat the critical temperature 

 of neon lies at least some degrees below — 218°C., and that there- 

 fore the determination of the critical temperature had, in the meantime, 

 better be made from the isotherms below — 200° C. 



The result obtained for the melting point of oxygen is surprising. 

 The diiference between our value ') and that given by Estkekiieh 

 can, however, be simply explained from the description of his experi- 

 ment liiven bv Estreichek in which he himself moreover declares 

 that it is quite possible that his result lies somewhat too low. In 

 his experiment half of the helium thermometer reservoir was in oxygen 



1) A. 0. Rankine, Proc. R. S. A. 84. p. 190. 



2) A. 0. Rankine. Phil. Mag. Jan. 1911. 



3) T. Estreichek. Bull. A. Sc. Gracovie. Dec. 1903. 



4) Proc. Febr. March 1903. Gomm. N'. 83. 



■Ï) Wc hope to shortly communicate the results of a dcterminalion more accurate 

 than lliis preliminary measurement. 



