Thermodynamic Properties of Air. 311 



basis of Wroblewski's theorem. With the aid of the table of 

 compressibility given in the preceding paragraph, we calculate 

 the following values of the pressures for which the product 

 pv is a minimum : — 



Temperature. Pressure. Min. pv (approx.). 



+ 100 Less than 10 atm. 1'367 

 + 16 79 1-0379 



95 0-9680 



- 35 115 0-8004 



- 78-5 123 0-5519 

 -103-5 106 0-3873 

 -130 66 0-1985 

 -135 57 0-1551 



The points corresponding to these values of p and pv are 

 connected on PL II. by a dotted curve. 



Now, changing units, take the values 132° (abs. crit. 

 temperature) and 39 atm. as new units of temperature and 

 pressure (which will be denoted on this convention by t and 

 7r), then the foregoing table turns into the following : — 

 t=2-82 tt<0-25 



„ 2-19 ,, = 2-03 



„ 2-07 . „ 2-44 



„ 1-80 „ 2-94 



„ 1-48 „ 3-15 



„ 1-29 „ 2-72 



„ 1*08 „ 1-69 



„ 1*05 „ 1-46 



Draw a curve taking the t's and 7r's for abscissas and 

 ordinates, then according to Wroblewski this should be one 

 curve for all gases. Now it will be found that the curve 

 plotted in accordance with the above numbers runs really very 

 near that drawn by Wroblewski*, and based chiefly on experi- 

 ments on carbon dioxide and methane. It is difficult to tell 

 if the remaining differences are real or else depend merely 

 on experimental errors. At all events it may be taken for 

 granted that these coincidences, as they stand' now, are most 

 remarkable. 



I have limited my experiments to the gaseous states of air 

 but at the same time I tried to approach to the limits of lique- 

 faction as near as possible. It is a very difficult . matter to 

 experiment near those limits ; very constant temperatures are 

 of great importance. It happened frequently that, in con- 

 sequence of a slight variation of temperature, the glass bulb 

 of my apparatus was found full of liquid air, instead of com- 

 pressed gas. For the present time I abstained from an ex- 

 * PI. iv, of the paper on Hydrogen, 



