184 



value of k is important because of its entrance into several of the funda- 

 mental equations of thermodynamics, and also because it furnishes an ex 

 cellent criterion for the correctness of the assumptions made in the kinetic 

 gas theory, concerning the distribution of the energy within the molecule. 

 In view of these intimate correlations of the value of k with other funda- 

 mental factors it is important to study its variation under different con- 

 ditions of pressure and teinperature for the same gas. 



For constant pressure Wiillner- found practically a constant value of 

 k between 0° and 100° C, for air. Witkowski' has found evidence of a 

 variation in k with both temperature and pressure, from theoretical con- 

 siderations. Luduc* shows that 7,: should decrease with rising temperature 

 and with falling pressure. Stevens' finds a value of 1.34 for k at 1000°, and 

 Kalahne" shows that k decreases with rising temperature, reaching a value 

 1.39 for 900°. S. R. Cook,', working with liquid air temperatures, finds 

 the value of /.' for air to be 1.35 (nearly), and Valentiner^ in an exhaustive 

 study of the dependence of k in nitrogen upon pressure, at liquid air tem- 

 peratures, finds the value of k to increase, approximatelj? in proportion to 

 the ratio of the pressure to the saturation pressure for the temperature 

 used. 



In this connection it was suggested to the writer by Professor Rontgen, 

 that a study of the value of k should be undertaken for constant pressure 

 and liquid air temperature, and under his direction the present work was 

 carried out during the winter and spring semesters of 1901, in the Physi- 

 cal Institute at Munich. Two series of observations were carried through : 



I. For constant pressure, the ratio of values of k for the tem- 

 peratures of melting ice and boiling water was determined, the gas 

 used being air, free from moisture and CO;. Values under these con- 

 ditions had been determined by Wiillner (loc. cit.), and were here 

 repeated as a means of checking the method. 



II. For constant pressure, the same ratio was determined over 

 a range of temperature from that of the room, about 20° C, to that 



^Anii. der Physik 4, 1878. 



^Sci. Abs. 3, 1900. p. 387. 



*Sci. Abs. 3, 1900, p. 29. 



' Scl. Abs. 4, 1901, p. 847. 



8 Ann. der Physik 11, 1903, p. 225. 



^Phys. Rev. 23, 1906, p. 232. 



8 Ann. der Physik 15, 1904. 



