some Thermodynamical Relations 



CO 



22. Ammonium Carbamate and Water. 



49 



|NH 2 

 10NH 4 . Tem- 



H 2 



peratures of water taken as correct. c= —'000696. 



Pressures. 



Ratios. 



Absolute temperatures of 

 Ammonium Carbamate. 



From observed 

 temperatures. 



Smoothed. 



Recalculated. 



Observed. 



millim. 



10 



50 

 100 

 150 

 200 

 300 

 400 



0-9529 

 0-9313 

 09221 

 09159 

 0-9122 

 0-9060 

 0-9017 



0-9510 

 0-9321 

 09230 

 0-9170 

 0-9126 

 0-9061 

 0-9011 



270-4 



290-2 



299-7 



305-45 



309 9 



316-15 



320-8 



270-9 

 289-9 

 299-4 

 305-1 

 309-8 

 316-1 

 321-0 



It is thought that these twenty-two examples, including 

 twenty-one different bodies — solid, liquid, stable, and dissoci- 

 able — are sufficient to prove that the equation R' = R-fc(^ — t) 

 is applicable to all classes of bodies, and that by the de- 

 termination of the constant c, which involves only a small 

 amount of experimental work, it becomes possible to calculate 

 the vapour-pressures of any substance, assuming those of water 

 or some other body to be accurately known, within the limits 

 of pressure included in the experimental determinations of the 

 standard substance. 



It should be pointed out that those dissociable substances 

 which have been investigated, are either, as in the case of am- 

 monium carbamate and chloride and the compounds of chloral, 

 wholly or almost wholly dissociated on their passage into the 

 gaseous state at the temperatures of observation, or the 

 amount of dissociation is very small, as with nitric peroxide. 

 Until reliable data are obtained, it is perhaps premature to 

 make any complete statement in reference to the behaviour of 

 dissociable bodies. 



On the Vapour-Pressures of Mercury, 



It will have been observed in the tables in Part I. of this series 

 of papers that mercury appears to differ from all the other 



substances examined, inasmuch as the values of — . t, when 



compared with either water or carbon bisulphide, are not even 

 approximately constant at different pressures, but rise steadily 

 Phil. Mag. S. 5. Yol. 21. No. 128. Jan. 1886. E 



