1895.] The Liquefaction and Solidification of Argon. 



291 



Expt. Temperature. Pressure. 



8 -128 -6 38-0 atmos. 



9 -129-6 35-8 



10 -129-4 35-8 



11 -129-3 35-8 



12 -129-6 35-8 



Determination of the Boiling and Freezing Points. 



A calibrated tube, intended to receive the argon to be liquefied, 

 and the hydrogen thermometer were immersed in boiling oxygen. 

 On admitting argon, and diminishing the temperature of the liquid 

 oxygen below 187, the liquefaction of the argon became manifest. 

 When liquefaction had taken place, I carefully equalised the pressure 

 of the argon with that of the atmosphere, and regulated the tempera- 

 ture, so that the state of balance was maintained for a long time. 

 This process gives the boiling point of argon under atmospheric 

 pressure. Four experiments gave the numbers 186'7, 186*8, 

 -187'0, and 187*3. The mean is 186'9, which I consider to 

 be the boiling point under atmospheric pressure (740*5 mm.). 



The quantity of argon used for these experiments, reduced to 

 normal temperature and pressure, was 99*5 c.c. ; the quantity of 

 liquid corresponding to that volume of gas was approximately 0*114 c.c 

 Hence the density of argon at its boiling point may be taken as 

 approximately 1*5. This proves that the density of liquid argon 

 at its boiling point ( 187) is much higher than that of oxygen, 

 which I have found, under similar conditions, to be 1*124. 



By lowering the temperature of the oxygen to 191 by slow 

 exhaustion, the argon froze to a crystalline mass, resembling ice ; on 

 further lowering temperature it became white and opaque. When the 

 temperature was raised it melted ; four observations which I made to 

 determine its melting point gave the numbers: 189*0, 190'6, 

 -189*6, and 189*4. The mean of these numbers is 189*6; 

 and this may be accepted as the melting point of argon. 



In the following table I have given a comparison of physical con- 

 stants, in which those of argon are compared with those of other 

 so-called permanent gases. The data are from my previous work on 

 the subject. 



As can be seen from the foregoing table, argon belongs to the 

 so-called " permanent " gases, and, as regards difficulty in liquefying 

 it, it occupies the fourth place, viz., between carbon monoxide and 

 oxygen. Its behaviour on liquefaction places it nearest to oxygen, 

 but it differs entirely from oxygen in being solidifiable ; as is well 

 known, oxygen has not yet been made to assume a solid state. 



The high density of argon rendered it probable that its liquefaction 

 would take place at a higher temperature than that at which oxygen 

 liquefies. Its unexpectedly low critical temperature and boiling 

 point seem to have some relation to its simple molecular constitution. 



