Determination of Chemical Constants. 11 



Knudsen gives the probable error of the values obtained 

 from his vapour-pressure formula us 0*002 p between 0° C. 

 and 15° C, 007 up to 100° 0. and 0-012 up to 200° C. . The 

 measurement at 0° C. is considered accurate to less than one 

 part in one thousand. The temperature error was less than 

 0°*15 C, and the value obtained is in all probability not 

 subject to any serious constant error. A confirmation 

 of this figure for the vapour pressure at 0° C. by mea- 

 surement with great precision would be valuable, as the 

 chemical constant could fhen be obtained with certainty. 



If the values at low temperatures are correct within 

 ±0002 p, and if the variation in specific heat is allowed 

 for, then the value of the vapour pressure at the melting- 

 point may vary between 2*00 x 10~ G and 1*95 Xl0 _i5 , The 

 latent heat of vaporization (X ) has been shown to be con- 

 sistent within one part in 3000 ; the variations in vapour 

 pressure and specific heat might lead to a result for 

 A = 15530 + 15. 



The value of ftv may vary within one per cent., so that 

 the value of the specific-heat term may be 1*779 + 0*01. 



The melting-point is certainly accurate within 0°*1 0. 



Hence, inserting in the formula the values obtained : 



+ 14 507±0'015 - 5*924±0*002 



+ 1-823+0-01 - 8*586±0*005 



16-330±0'025 - 14-510±0-007 



-14-510±0-007 



i) = 1-820 ±0-032 



Now l-51ogM = 3-453, and if 1-5 logM-C= -C , a 

 universal constant^ then the value of this constant would be 



C = -1'633±0*032. 



The value calculated from the constants h and k becomes 

 C Q = — 1*608 ; so that the value determined is in complete 

 agreement within the error * (see p. 19). 



Now if C =l*608 the chemical constant for cadmium 

 would be 3*076 — 1'608 — 1*468, and that for zinc would be 



* I find a calculation on similar lines to the above has already 

 been published by Nernst, in his book * Die Theoretischen und Experi- 

 mentellen Grundlagen des Xeuen YVarmesatzes' (1918), which leads to 

 a value C = 1-83 +003. 



