14 On the Temperature and the Tension of Vapours. 



The determination of the value of a for the vapour of liquid 

 ammonia led to less concordant results; this would be expected 

 after what Regnault* has stated in the extract from his memoir 

 about the difficulty which attends the accurate determination of 

 the temperature of boiling ammonia. 



I made use of the formula? 



. a = 0-10605 + 0-0002287 T + 0-0000003T 2 

 and 



lo S P=l-0639 3+ log (273 + T) + log(^ + T)-2-43616 . 



The tensions calculated by means of the above equation differ 

 considerably from Regnault's numbers; it will be easily seen, 

 however, by the following Table that these differences are in no 

 case so great as that which corresponds to o, 3 C. in the deter- 

 mination of temperature : — 



mo 



«. 



P. 



R. 



dd. 



- 40 



0-09738 



530-60 



528-61 



+ 1-99 



- 30 



09946 



873-52 



876-58 



- 306 



- 20 



010159 



1387-30 



139774 



-10-44 



- 101 





211810 







- 10 



010379 



2127-20 



2149-52 



-22 32 



- 5 



010491 



2603-26 



2632-25 



-28-99 







0-10605 



3162-87 



3162-87 



00-00 



+ 5 



010720 



3815-00 



3854-47 



-39-47 



51 





3829-08 







10 



010836 



4570-30 



4612-19 



-41-89 



20 



011074 



642840 



6467-00 



-38-60 



30 



0-11318 



8820-20 



8832-20 



- 12-00 



40 



011567 



11825-90 



11776-42 



+49-48 



401 





11859-00 







The foregoing examples may suffice to prove the superiority of 

 the formula 



l + «j 273 + T 

 273 + t 



P = plO 



to the numerous empirical formulae which have hitherto been 

 employed for the calculation of the tensions of vapours. We are 

 not, however, always in a position to directly determine by means 

 of this equation the maximum tension of a vapour at different 

 temperatures. Certain constants must still be determined empi- 

 rically. But these determinations, since they refer to very small 

 differences, are much more easily made after it has been esta- 



Poggendorff' s Annalen, vol. cxi. pp. 405 and 415. 



